final immunomodulators & immunosuppressants

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Sumanth Dept of Pharmacology

Immunosuppressants & Immunomodulators

Abnormal Immune Responses

Whereas the normally functioning immune response can successfully neutralize

toxins, inactivate viruses, destroy transformed cells, and eliminate pathogens.

Inappropriate responses can lead to extensive tissue damage (Hypersensitivity)

or reactivity against self-antigens (Autoimmunity); conversely, impaired

reactivity to appropriate targets (Immunodeficiency) may occur and abrogate

essential defense mechanisms.

Autoimmunity

Autoimmune disease arises when the body mounts an immune response against

itself due to failure to distinguish self-tissues and cells from foreign (nonself)

antigens or loss of tolerance to self.

This phenomenon derives from the activation of self-reactive T and B

lymphocytes that generate cell-mediated or humoral immune responses directed

against self-antigens.

The pathologic consequences of this reactivity constitute several types of

autoimmune diseases.

Autoimmune diseases are highly complex due to MHC genetics, environmental

conditions, infectious entities, and dysfunctional immune regulation.

Examples of such diseases include

Rheumatoid arthritis

Systemic lupus erythematosus

Multiple sclerosis

Insulin-dependent diabetes mellitus (type 1 diabetes).

In Rheumatoid arthritis, IgM antibodies (rheumatoid factors) are produced that

react with the Fc portion of IgG and may form immune complexes that activate

the complement cascade, causing chronic inflammation of the joints and kidneys.

In systemic lupus erythematosus, antibodies are made against DNA, histones, red

blood cells, platelets, and other cellular components.

In multiple sclerosis and type 1 diabetes, cell-mediated autoimmune attack

destroys myelin surrounding nerve cells and insulin-producing islet beta cells of

the pancreas, respectively.

In type 1 diabetes, activated CD4 TDTH cells that infiltrate the islets of Langerhans

and recognize self islet beta cell peptides are thought to produce cytokines that

stimulate macrophages to produce lytic enzymes, which destroy islet beta cells.

Autoantibodies directed against the islet beta cell antigens are produced, but do

not contribute significantly to disease.

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A number of mechanisms have been proposed to explain auto-immunity:

Exposure of antigens previously sequestered from the immune system (eg, lens

protein, myelin basic protein) to self-reactive T lymphocytes.

Molecular mimicry by invading pathogens, in which immune responses are

directed at antigenic determinants on pathogens that share identical or similar

epitopes with normal host tissue.

This phenomenon occurs in rheumatic fever following Streptococcus pyogenes

infection, in which heart damage is thought to arise from an immune response

directed against streptococcal antigens shared with heart muscle.

Inappropriate expression of class II MHC molecules on the membranes of cells

that normally do not express class II MHC (eg, islet beta cells).

Increased expression of MHC II may increase presentation of self-peptides to T

helper cells, which in turn induce CTL, TDTH, and B-lymphocyte cells that react

against self-antigens.

Examples of Autoimmune Diseases, Categorised by Type of Tissue Damage

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Pathophysiology

Transplantation

Currently, most organ transplantation occurs between unrelated individuals.

Donor and recipient tissues express different MHC class I molecules, and recipient

immune cells therefore recognize the transplanted tissues as foreign.

This is termed Alloimmunity, and it occurs when the recipients immune system

attacks a transplanted organ.

In the case of a bone marrow or stem cell transplant, Graft-versus-host disease

(GVHD) can result when donor lymphocytes mount an assault on recipient

tissues.

Solid Organ Rejection

Transplant rejection of solid organs can be divided into three major phases

according to the time to onset:

Hyperacute rejection

Acute rejection

Chronic rejection

are caused by different mechanisms and are therefore treated differently.

Hyperacute Rejection

Hyperacute rejection is mediated by preformed recipient antibodies against donor

antigen. Because these antibodies are present at the time of organ implantation,

hyperacute rejection occurs almost immediately after reperfusion of the

transplanted organ.

In fact, the surgeon can observe the changes in the organ minutes after restoration

of blood flow.

The normal, healthy, pink appearance of the transplanted organ rapidly becomes

cyanotic, mottled, and flaccid.

This rapid change is the result of complement activation by antibody binding to

endothelial cells of the transplanted organ, resulting in thrombosis and ischemia.

Most commonly hyperacute rejection is mediated by recipient antibodies that

react with blood group antigens in donor organs (e.g., type AB donor in a type O

recipient).

Matching of blood types between donor and recipient prevent hyperacute

rejection; therefore, drug therapy for hyperacute rejection is typically not

necessary.

Hyperacute rejection also occurs in xenotransplantation (i.e., organ

transplantation between species, such as pig heart transplanted into a human

recipient), due to the presence of preformed human antibodies that react against

antigenic proteins and carbohydrates expressed by the donor species.

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Acute Rejection

Acute rejection has cellular and humoral components.

Acute cellular rejection is mediated by cytotoxic T Cells and causes interstitial as

well as vascular damage.

This cellular response is most commonly seen in the initial months after

transplantation.

Immunosuppression of T cells is highly effective at preventing or limiting

activation of the recipient immune system by the transplanted organ, thereby

preventing acute cellular rejection.

In Acute humoral rejection, recipient B cells become sensitized to donor antigens

in the transplanted organ and produce antibodies against these alloantigens after

a period of 7-10 days.

The antibody response is typically directed against endothelial cells and is thus

also known as acute vascular rejection.

Like acute cellular rejection, acute humoral rejection can usually be prevented by

immunosuppression of the recipient after transplantation.

Even with immunosuppression, however, episodes of acute rejection can occur

months or even years after transplantation.

Chronic Rejection

Chronic rejection is believed to be both humoral and cellular in nature and does

not occur until months or years after transplantation.

Because hyperacute and acute rejection are generally well controlled by

donor/recipient matching and immunosuppressive therapy, chronic rejection is

now the most common life-threatening pathology associated with organ

transplantation.

Chronic rejection is thought to result from chronic inflammation caused by the

response of activated T cells to donor antigen.

Activated T cells release cytokines that recruit macrophages into the graft.

The macrophages induce chronic inflammation that leads to intimal proliferation

of the vasculature and scarring of the graft tissue.

The chronic changes eventually lead to irreversible organ failure.

Other contributing nonimmune factors can include ischemia-reperfusion injury

and infection.

No effective treatment regimens are currently available to eliminate chronic

rejection.

It is believed, however, that several experimental therapies have a reasonable

chance of reducing chronic rejection.

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Graft-Versus-Host Disease (GVHD)

Leukemia, primary immunodeficiency, and other conditions can be treated with

bone marrow or peripheral stem cell transplantation.

In this procedure, hematopoietic and immune function is restored after the

patients bone marrow has been eradicated by aggressive chemotherapy and/or

radiation therapy.

GVHD is a major complication of allogeneic bone marrow or stem cell

transplantation.

GVHD is an alloimmune inflammatory reaction that occurs when transplanted

immune cells attack the cells of the recipient.

The severity of GVHD ranges from mild to life-threatening and typically involves

the skin (rash), gastrointestinal tract (diarrhea), lungs (pneumonitis), and liver

(veno-occlusive disease).

GVHD can often be ameliorated by removing T cells from the donor bone marrow

before transplantation.

Mild-to-moderate GVHD can also be beneficial when donor immune cells attack

recipient tumor cells that have survived the aggressive chemotherapy and

radiation therapy. (In the case of leukemia, this is called the graft-versus-leukemia

effect, or GVL.)

Therefore, although removing donor T cells from the graft reduces the risk of

GVHD, this may not be the best approach for marrow transplants used in

antineoplastic therapy.

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Immunosuppressants

Pharmacologic suppression of the immune system utilizes eight mechanistic approaches

Inhibition of gene expression to modulate inflammatory responses

Depletion of expanding lymphocyte populations with cytotoxic agents

Inhibition of lymphocyte signaling to block activation and expansion of

lymphocytes

Neutralization of cytokines and cytokine receptors essential for mediating the

Immune response

Depletion of specific immune cells, usually via cell-specific antibodies

Blockade of costimulation to induce anergy

Blockade of cell adhesion to prevent migration and homing of inflammatory cells

Inhibition of innate immunity, including complement activation

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1. Inhibition of gene expression

2. Selective attack on clonally expanding lymphocyte populations

3. Inhibition of intracellular signaling

4. Neutralisation of cytokines & cytokine receptors required for T-cell stimulation

5. Selective depletion T cells

6. Inhibition of costimulation by antigen-presenting cells

7. Inhibition of lymphocyte-target cell interactions

Classification

Inhibitors of Gene Expression: Glucocorticoids

Cytotoxic Agents:

Antimetabolites: Azathioprine (AZA), Methotrexate (MTX),

Mycophenolic Acid & Mycophenolate Mofetil (MPA), Leflunomide

Alkylating Agents: Cyclophosphamide

Specific Lymphocyte-Signaling Inhibitors:

Cyclosporine

Tacrolimus

mTOR Inhibitors: Sirolimus, Everolimus, Zotarolimus

Cytokine Inhibition:

TNF- Inhibitors: Etanercept, Infliximab, Certolizumab pegol,

Adalizumab, Golimumab

IL-12/IL-23p40 Inhibitors: Ustekinumab

IL-1 Inhibitors: Anakinra, Rilonacept, Canakinumab

Cytokine Receptor Antagonists: Tocilizumab

Depletion of Specific Immune Cells:

Polyclonal Antibodies: Antithymocyte globulin (ATG)

Monoclonal Antibodies

Anti-CD3: OKT3 (Muromonab-CD3)

Anti-CD20 mAb: Rituximab

Anti-CD25 mAb: Daclizumab, Basiliximab

Anti-CD52 mAb: Alemtuzumab

LFA-3: LFA-3(CD58), Alefacept

Inhibition of Costimulation: Abatacept, Belatacept

Blockade of Cell Adhesion: Natalizumab

Inhibition of Complement Activation: Eculizumab

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Glucocorticoids

Glucocorticoids (corticosteroids) were the first hormonal agents recognized as

having lympholytic properties.

Administration of any glucocorticoid reduces the size and lymphoid content of

the lymph nodes and spleen, although it has no toxic effect on proliferating

myeloid or erythroid stem cells in the bone marrow.

Prednisone, Prednisolone, and other glucocorticoids are used alone and in

combination with other immunosuppressive agents for treatment of transplant

rejection and auto-immune disorders.

Mechanism of Action

Glucocorticoids are steroid hormones that exert their physiologic actions by

binding to the cytosolic glucocorticoid receptor.

The glucocorticoid-glucocorticoid receptor complex translocates to the nucleus

and binds to glucocorticoid response elements (GREs) in the promoter region of

specific genes, either up-regulating or down-regulating gene expression.

Glucocorticoids have important metabolic effects on essentially all cells of the

body and, in pharmacologic doses, suppress the activation and function of innate

and adaptive immune cells.

Glucocorticoids lyse and induce the redistribution of lymphocytes, causing a

rapid transient decrease in peripheral blood lymphocyte counts.

Glucocorticoids down-regulate the expression of many inflammatory mediators,

including key cytokines such as TNF-, interkeukin-1 (IL-1), and IL-4.

Glucocorticoids curtail (Reduce in extent or quantity) activation of NF-B, which

increases apoptosis of activated cells.

Pro-inflammatory cytokines such as IL-1 and IL-6 are downregulated.

T cells are inhibited from making IL-2 and proliferating.

The activation of cytotoxic T lymphocytes is inhibited.

Pharmacokinetics

Prednisone is converted to active prednisolone in the body and has multiple

effects on the immune system.

Prednisone is very well absorbed from the gastrointestinal (GI) tract and has a

long biologic half-life, so it can be dosed once daily.

Dosing and Administration

An intravenous corticosteroid, commonly high-dose methylprednisolone, is given

during the perioperative period.

The dose of methylprednisolone is tapered rapidly and discontinued within days,

and oral prednisone is initiated.

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Prednisone doses are tapered progressively over time, depending on the type of

additional immunosuppression and organ function.

As doses are tapered, it is preferable to administer corticosteroids every other day

and between 7 AM and 8 AM to mimic the bodys diurnal release of cortisol

Adverse Effects

Long-term glucocorticoid administration has important adverse effects.

Diabetes

Osteoporosis

Cataracts

Hirsutism

Bruising

Acne

Hypertension

Bone growth suppression

Ulcerative esophagitis

Reduced resistance to infections

Sodium and water retention

Increased appetite leading to weight gain

Abrupt cessation of glucocorticoid therapy can result in acute adrenal insufficiency because the hypothalamus and pituitary gland require a number of weeks to months to re-establish adequate ACTH production.

Therapeutic Uses

They are combined with other immunosuppressive agents to prevent and treat transplant rejection.

High dose pulses of intravenous Methylprednisolone sodium succinate are used to reverse acute transplant rejection and acute exacerbations of selected autoimmune disorders.

Glucocorticoids also are efficacious for treatment of graft-versus-host disease in bone-marrow transplantation.

Glucocorticoids are used routinely to treat autoimmune disorders such as rheumatoid and other arthritides, systemic lupus erythematosus, systemic dermatomyositis, psoriasis and other skin conditions, asthma and other allergic disorders, inflammatory bowel disease, inflammatory ophthalmic diseases, autoimmune hematologic disorders, and acute exacerbations of multiple sclerosis.

In addition, glucocorticoids limit allergic reactions that occur with other immunosuppressive agents and are used in transplant recipients to block first-dose cytokine storm caused by treatment with muromonab-CD3 and to a lesser extent ATG (Antithymocyte Globulin).

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Cytotoxic Agents

Cytotoxic Agents are used for immunosuppression as well as for antineoplastic chemotherapy. Two classes of cytotoxic agents, Antimetabolites and Alkylating agents are commonly used as Immunosuppressants.

Antimetabolites are structural analogues of natural metabolites that inhibit essential pathways involving these metabolites.

Alkylating agents interfere with DNA replication and gene expression by conjugating alkyl groups to DNA.

The therapeutic goal in both antineoplastic chemotherapy and immunosuppressants is the elimination of undesirable cells.

Antimetabolites

They have powerful suppressive effect on immune cells. Also accompanied by many adverse effects related to their lack of selectivity.

The older antimetabolites such as Azathioprine and Methotrexate, affect all rapidly dividing cells and can have damaging effects on the GI mucosa and Bone marrow.

Newer antimetabolites, such as Mycophenolate mofetil and Leflunomide, cause fewer adverse effects.

Mycophenolate mofetil mat also be more selective for immune cells, further reducing its toxicity.

Antimetabolites typically affect both cell-mediated and humoral immunity, rendering patients more susceptible to infection.

Azathioprine

Azathioprine (AZA) is a prodrug for 6-mercaptopurine and has been used as an immunosuppressant in combination with corticosteroids.

It is an imidazolyl derivative of 6-mercaptopurine. Although mercaptopurine can also be used directly as a cytotoxic agent,

azathioprine has greater oral bioavailability and a longer duration of action and is more immunosuppressive than mercaptopurine.

Azathioprine and mercaptopurine appear to produce immunosuppression by interfering with purine nucleic acid metabolism at steps that are required for the wave of lymphoid cell proliferation that follows antigenic stimulation.

Mechanism of Action

Azathioprine is an inactive compound that is converted rapidly to 6-mercaptopurine (6-MP) in the blood.

Following exposure to nucleophiles such as glutathione, azathioprine is cleaved to 6-mercaptopurine and is subsequently metabolized by three different enzymes.

Xanthine oxidase, found in the liver and GI tract, converts 6-MP to the inactive final end product, 6-thiouric acid.

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Thiopurine S-methyltransferase, found in hematopoietic tissues and red blood cells, methylates 6-MP to an inactive product, 6-methylmercaptopurine.

Finally, hypoxanthine-guanine phosphoribosyltransferase is the first step responsible for converting 6-MP to 6-thioguanine nucleotides (6-TGNs), the active metabolites, which are incorporated into nucleic acids, ultimately disrupting both the salvage and de novo pathways of DNA, RNA, and protein synthesis. This process is toxic to the cell and renders the cell unable to proliferate.

6-TGNs eventually are catabolized by xanthine oxidase and thiopurine S-methyltransferase to inactive products.

Pharmacokinetics

Oral bioavailability of azathioprine is approximately 40%. Metabolism of 6-MP is primarily by xanthine oxidase to inactive metabolites,

which are excreted by the kidneys. The half-life of azathioprine, the parent compound, is very short, approximately

12 minutes. The half-life of 6-MP is longer, ranging from 0.7 to 3 hours.

However, it is the activity of the 6-TGNs that determines the pharmacodynamic half-life of the drug.

The half-life of 6-TGNs has been estimated to be 9 days. Initial doses of azathioprine are 3 to 5 mg/kg per day intravenously or orally.

Adverse Effects

Dose-limiting adverse effects of azathioprine are often hematologic.

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Leukopenia, anaemia, and thrombocytopenia can occur within the first few weeks of therapy and can be managed by dose reduction or discontinuation of azathioprine.

Other common adverse effects include nausea and vomiting, which can be minimized by taking azathioprine with food.

Alopecia, hepatotoxicity and pancreatitis are less-common adverse effects of azathioprine; they generally are reversible on dose reduction or discontinuation.

DrugDrug Interactions

Allopurinol inhibits xanthine oxidase and can increase the bioavailability of azathioprine and 6-MP concentrations by as much as fourfold. Doses of azathioprine should be reduced by 50% to 75% when allopurinol is added.

Therapeutic Uses

Beneficial in maintaining renal allografts and may be of value in transplantation of other tissues.

It is indicated as an adjunct for prevention of organ transplant rejection and in severe rheumatoid arthritis.

Lower initial doses (1 mg/kg per day) are used in treating rheumatoid arthritis. Have been used in the management of acute glomerulonephritis and in the renal

component of systemic lupus erythematosus. Have also proved useful in some cases of Crohns disease, and multiple sclerosis.

Mycophenolate mofetil

Mycophenolate mofetil is the 2-morpholinoethyl ester of Mycophenolic acid (MPA).

Mycophenolate mofetil (MMF) is a semisynthetic derivative of Mycophenolic acid, isolated from the mold Penicillium glaucus.

Mycophenolate mofetil is a prodrug that is rapidly hydrolysed to the active drug, Mycophenolic acid (MPA), a selective, non-competitive, and reversible inhibitor of Inosine monophosphate dehydrogenase (IMPDH), an important enzyme in the de novo pathway of guanine nucleotide synthesis.

Mechanism of Action

The immunosuppressive effect of MPA is exerted through non-competitive binding to Inosine monophosphate dehydrogenase, the key enzyme responsible for guanosine nucleotide synthesis via the de novo pathway.

Inhibition of Inosine monophosphate dehydrogenase results in decreased nucleotide synthesis and diminished DNA polymerase activity, ultimately reducing lymphocyte proliferation.

The actions of MPA are more specific for T and B cells, which use only the de novo pathway for nucleotide synthesis.

Other cells within the body have a salvage pathway by which they can synthesize nucleotides, making them less susceptible to the actions of MPA and thereby

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reducing, but not eliminating, the potential for the hematologic adverse effects seen with azathioprine, which affects both the de novo and salvage pathways.

In addition to the decreasing lymphocyte proliferation, MPA also may downregulate activation of lymphocytes.

Selectivity

Two main factors contribute to this selectivity.

First, lymphocytes are dependent on the de novo pathway of purine synthesis, whereas most other tissues rely heavily on the salvage pathway. Because IMPDH is required for de novo synthesis of guanosine nucleotides but not for the salvage pathway, MPA affects only cells such as lymphocytes that rely on de novo purine synthesis.

Second, IMPDH is expressed in two isoforms, type I and type II. MPA preferentially inhibits type II IMPDH, the isoform expressed mainly in lymphocytes.

Together, these factors confer on MPA and MMF selectivity against T and B cells, with relatively low toxicity to other cells.

Inhibition of IMPDH by MPA reduces intracellular guanosine levels and elevates intracellular adenosine levels, with many downstream effects on lymphocyte activation and activity.

MPA has a cytostatic effect on lymphocytes, but can also induce apoptosis of activated T cells leading to the elimination of reactive clones of proliferative cells.

Because guanosine is required for some glycosylation reactions, the reduction in guanosine nucleotides leads to decreased expression of adhesion molecules that are required for recruitment of several immune cell types to sites of inflammation.

Furthermore, because guanosine is a precursor of tetrahydrobiopterin (BH4), which regulates inducible nitric oxide synthase (iNOS), the reduction in guanosine levels leads to decreased NO production by neutrophils.

Endothelial NOS (eNOS), which controls vascular tone and is regulated by Ca2+ and calmodulin, is not affected by changes in guanosine levels, again demonstrating the considerable selectivity of MPA.

Pharmacokinetics

Because MPA has low oral bioavailability, it is usually administered as a sodium salt or in its prodrug form, Mycophenolate mofetil (MMF), both of which have greater oral bioavailability.

Because MPA is unstable in an acidic environment, Mycophenolate mofetil acts as a prodrug that is readily absorbed from the GI tract, after which it is rapidly and completely converted to MPA by first-pass metabolism.

The enteric coating of Mycophenolate sodium protects MPA from the acidic gastric pH and allows for MPA to be released directly into the small intestine for absorption.

The absolute bioavailability of MPA when delivered from Mycophenolate mofetil and Mycophenolate sodium is 94% and 72%, respectively.

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Peak concentrations of MPA are reached within 1 hour following administration of either preparation.

A total of 97% of MPA is bound to albumin in the blood. MPA is eliminated by the kidney and also undergoes glucuronidation in the liver

to an inactive glucuronide metabolite (MPAG) that is excreted in the bile and urine.

The half-life of MPA is 18 hours. Mycophenolate mofetil is currently available in both oral and intravenous

formulations.

Adverse Effects

The most common side effects are related to the GI tract, including nausea, vomiting, diarrhea, and abdominal pain.

Mycophenolate also has hematologic effects, such as leukopenia and anaemia, particularly with higher doses.

Because peripheral intravenous Mycophenolate administration is associated with local edema and inflammation, central venous administration may be the preferred route.

Therapeutic Uses

Mycophenolate mofetil is indicated for prophylaxis of transplant rejection, and it typically is used in combination with glucocorticoids and a calcineurin inhibitor, but not with azathioprine.

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Its antiproliferative properties make it the first-line drug for preventing or reducing chronic allograft vasculopathy in cardiac transplant recipients.

Mycophenolate mofetil is used as prophylaxis for and treatment of both acute and chronic graft-versus-host disease in hematopoietic stem cell transplant patients.

Newer immunosuppressant applications for MMF include lupus nephritis, rheumatoid arthritis, inflammatory bowel disease, and some dermatologic disorders.

Animal models show that chronic rejection is also reduced more effectively in recipients treated with MMF than in those treated with AZA or cyclosporine. The efficacy of MMF in treating chronic rejection may be related to its inhibition of both the lymphocyte and the smooth muscle cell proliferation characteristic of chronic rejection.

Leflunomide

Activated lymphocytes both proliferate and synthesize large quantities of cytokines and other effector molecules, and these processes require increased DNA and RNA synthesis. Therefore, agents that reduce intracellular nucleotide pools have effects on these activated cells.

Leflunomide is an inhibitor of pyrimidine synthesis, specifically blocking the synthesis of uridylate (UMP) by inhibiting Dihydroorotate dehydrogenase (DHOD).

DHOD is a key enzyme in the synthesis of UMP, which is essential for the synthesis of all pyrimidines.

Experimentally, Leflunomide has been shown to be most effective in reducing B-cell populations, but a significant effect on T cells has also been observed.

Pharmacokinetics

Leflunomide undergoes significant enterohepatic circulation, resulting in a pro-longed pharmacologic effect.

If Leflunomide must be removed quickly from a patients system, Cholestyramine may be administered. By binding to bile acids, Cholestyramine interrupts the enterohepatic circulation and causes a wash-out of Leflunomide.

Adverse Effects

The most significant adverse effects of leflunomide are diarrhea and reversible alopecia.

Therapeutic Uses

Leflunomide is currently approved for use in rheumatoid arthritis, but the drug has also shown significant efficacy in the treatment of other immune diseases, including systemic lupus erythematosus and myasthenia gravis.

Leflunomide prolongs transplant graft survival and limits GVHD in animal models.

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Inhibition of pyrimidine synthesis by

Leflunomide

De novo pyrimidine synthesis

depends on the oxidation of

Dihydroorotate to orotate, a

reaction that is catalysed by

Dihydroorotate dehydrogenase.

Leflunomide inhibits

Dihydroorotate dehydrogenase and

thereby inhibits pyrimidine

synthesis.

Because lymphocytes are

dependent on de novo pyrimidine

synthesis for cell proliferation and

clonal expansion after immune cell

activation, depletion of the

pyrimidine pool inhibits

lymphocyte expansion.

Experimentally, Leflunomide

appears to inhibit preferentially the

proliferation of B cells; the reason

for this preferential action is

unknown.

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Cyclophosphamide

Cyclophosphamide is a highly toxic drug that alkylates DNA.

Cyclophosphamide has a major suppressive effect on B-cell proliferation but can enhance T-cell responses, the use of Cyclophosphamide in immune diseases is limited to disorders of humoral immunity, particularly systemic lupus erythematosus.

Another use under consideration for Cyclophosphamide is the suppression of antibody formation against xenotransplant grafts.

Adverse effects

Adverse effects of Cyclophosphamide are severe and widespread, including leukopenia, cardiotoxicity, alopecia, and an increased risk of cancer because of mutagenicity.

The risk of bladder cancer is especially notable because Cyclophosphamide produces a carcinogenic metabolite, acrolein, which is concentrated in the urine.

When high-dose Cyclophosphamide is administered by intravenous infusion, acrolein can be detoxified by co-administration of Mesna (a sulfhydryl-containing compound that neutralizes the reactive moiety of acrolein).

Specific Lymphocyte-Signaling Inhibitors

Calcineurin Inhibitors (Cyclosporine and Tacrolimus)

They are structurally unrelated and bind to distinct molecular targets, they inhibit normal T-cell signal transduction essentially by the same mechanism.

These drugs bind to an Immunophilin (Cyclophilin for Cyclosporine or FKBP-12 for Tacrolimus), resulting in subsequent interaction with calcineurin to block its phosphatase activity.

Calcineurin-catalyzed dephosphorylation is required for movement of a component of the Nuclear factor of activated T lymphocytes (NFAT) into the nucleus.

NFAT, in turn, is required to induce a number of cytokine genes, including that for interleukin-2 (IL-2), a prototypic T-cell growth and differentiation factor.

Mechanism of Action

Inhibits the production of IL-2 by activated T-cells.

Activated T-cells increase their production of IL-2 via a pathway that begins with dephosphorylation of a cytoplasmic transcription factor, NFAT (Nuclear factor of activated T lymphocytes).

NFAT is dephosphorylated by the cytoplasmic Phosphatase Calcineurin. Upon dephosphorylation, NFAT translocates to the nucleus and enhances

transcription of the IL-2 gene.

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Both Cyclosporine and Tacrolimus bind to Immunophilins (Cyclophilin and FK506-binding protein [FKBP], respectively), forming a complex that binds the phosphatase calcineurin.

Calcineurin phosphatase activity is inhibited after physical interaction with the Drug-Immunophilin complex.

This prevents NFAT dephosphorylation such that NFAT does not enter the nucleus, gene transcription is not activated, and the T lymphocyte fails to respond to specific antigenic stimulation.

Cyclosporine also increases expression of transforming growth factor- (TGF-), a potent inhibitor of IL-2-stimulated T-cell proliferation and generation of cytotoxic T lymphocytes (CTLs).

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Cyclosporine

It is a cyclic decapeptide isolated from a soil fungus, Tolypocladium inflatum.

Pharmacokinetics

Cyclosporine can be administered intravenously or orally. The intravenous preparation is provided as a solution in an ethanol-

polyoxyethylated castor oil vehicle that must be further diluted in 0.9% sodium chloride solution or 5% dextrose solution before injection.

The oral dosage forms include soft gelatin capsules and oral solutions. Cyclosporine supplied in the original soft gelatin capsule absorbed slowly with 20% to 50% bioavailability.

After oral administration of cyclosporine, the time to peak blood concentrations is 1.5 to 2 hours.

Administration with food delays and decreases absorption. Cyclosporine is extensively metabolized in the liver by CYP3A4 and to a lesser

degree by the gastrointestinal tract and kidneys. At least 25 metabolites have been identified in human bile, faeces, blood, and

urine. Only 0.1% of drug is excreted unchanged in urine. Cyclosporine and its metabolites are excreted principally through the bile into the

faeces, with only about 6% being excreted in the urine. In the presence of hepatic dysfunction, dosage adjustments are required.

Adverse Effects

The principal adverse reactions to cyclosporine therapy are Nephrotoxicity Tremor Hirsutism Hypertension Hyperlipidemia

Hyperglycaemia Gum hyperplasia Hyperuricemia Hypercholesterolemia Hepatotoxicity

Nephrotoxicity occurs in the majority of patients treated and is the major indication for cessation or modification of therapy.

Drug Interactions

Substances that inhibit the enzyme CYP3A4 can decrease cyclosporine

metabolism and increase blood concentrations. These include

Ca2+ channel blockers (e.g., Verapamil, Nicardipine)

Antifungal agents (e.g., Fluconazole, Ketoconazole)

Antibiotics (e.g., Erythromycin)

Glucocorticoids (e.g., methylprednisolone)

HIV-protease inhibitors (e.g., Indinavir) and

Other drugs (e.g., Allopurinol, Metoclopramide)

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Drugs that induce CYP3A activity can increase cyclosporine metabolism and

decrease blood concentrations. Such drugs include

Antibiotics (e.g., Nafcillin, Rifampin)

Anticonvulsants (e.g., Phenobarbital, Phenytoin)

Therapeutic Uses

Cyclosporine may be used alone or in combination with other

immunosuppressants, particularly glucocorticoids.

It has been used successfully as the sole immunosuppressant for cadaveric

transplantation of the kidney, pancreas, and liver, and it has proved extremely

useful in cardiac transplantation as well.

In combination with methotrexate, cyclosporine is a standard prophylactic

regimen to prevent graft-versus-host disease after allogeneic stem cell

transplantation.

Cyclosporine has also proved useful in a variety of autoimmune disorders,

including uveitis, rheumatoid arthritis, and psoriasis.

An ophthalmic preparation of Cyclosporine is approved for the treatment of

chronic dry eyes.

Dosing

The usual intravenous dose of cyclosporine is 2 to 5 mg/kg per day, given as a

continuous infusion or, more commonly, as a single or twice-daily injection.

Initial oral cyclosporine doses range from 8 to 18 mg/kg per day divided into two

doses administered every 12 hours.

Tacrolimus

Tacrolimus is a macrocyclic triene isolated from the soil bacterium Streptomyces

tsukubaensis.

Pharmacokinetics

Tacrolimus is available for oral administration as capsules and as a sterile solution

for injection (5 mg/ml).

Gastrointestinal absorption is incomplete and variable.

Food decreases the rate and extent of absorption.

Plasma protein binding of Tacrolimus is 75% to 99%, involving primarily albumin

and 1-acid glycoprotein.

Its half-life is about 12 hours.

Tacrolimus is extensively metabolized in the liver by CYP3A, with a half-life of

~12 hours; at least some of the metabolites are active.

The bulk of excretion of the parent drug and metabolites is in the feces.

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Less than 1% of administered Tacrolimus is excreted unchanged in the urine.

Adverse Effects

Nephrotoxicity

Neurotoxicity (Tremor, Headache, Motor disturbances, Seizures)

GI complaints

Hypertension

Hyperkalaemia

Hyperglycaemia and Diabetes are all associated with Tacrolimus

Drug Interactions Same as Cyclosporine

Therapeutic Uses

Tacrolimus is indicated for the prophylaxis of solid-organ allograft rejection.

A topical formulation is used for the treatment of atopic dermatitis and other

eczematous diseases

Dosing

Starting dose for Tacrolimus injection is 0.03 to 0.05 mg/kg per day as a

continuous infusion.

Recommended initial oral doses are 0.15 to 0.2 mg/kg per day for adult kidney

transplant patients, 0.1 to 0.15 mg/kg per day for adult liver transplant patients,

and 0.15 to 0.2 mg/kg per day for paediatric liver transplant patients in two

divided doses 12 hours apart.

mTOR Inhibitors

(Sirolimus, Everolimus, Zotarolimus)

These are the newest class of immunosuppressive agents which consists of drugs that

target the mammalian target of Rapamycin and are collectively known as mTOR

inhibitors.

Sirolimus

Sirolimus (which is also referred as Rapamycin) is a macrocyclic lactone produced

by Streptomyces hygroscopicus.

Sirolimus is structurally similar to Tacrolimus but have different mechanism of

action.

Both bind to FKBP (FK506-binding protein 12), but the Sirolimus-FKBP complex

does not inhibit calcineurin; instead, it blocks the IL-2 receptor signalling required

for T-cell proliferation.

22


Mechanism of Action

Sirolimus inhibits T-lymphocyte activation and proliferation downstream of the IL-2

and other T-cell growth factor receptors.

IL-2 receptor signal transduction involves a complex set of proteinprotein

interactions that lead to increased translation of selected mRNAs encoding

proteins required for T-cell proliferation.

Specifically, IL-2 receptor activation initiates an intracellular signaling cascade

that leads to phosphorylation of the molecular target of rapamycin (mTOR).

mTOR is a serine-threonine Kinase that phosphorylates and thereby regulates the

activity of PHAS-1 and p70 S6 kinase (P70 S6 kinase and PHAS-1 regulate

translation).

PHAS-1 inhibits the activity of a factor (eIF4E) required for translation, and p70 S6

kinase phosphorylates proteins involved in protein synthesis.

The net effect of mTOR activation is to increase protein synthesis, thereby

promoting the transition from G1 to S phase of the cell cycle.

Sirolimus (also known as rapamycin) crosses the plasma membrane and binds to

intracellular FK-binding protein (FKBP).

(Sirolimus-FKBP-12 complex does not affect calcineurin activity)

The SirolimusFKBP complex inhibits mTOR, thereby inhibiting translation and

causing T cells to arrest in G1.

23


Pharmacokinetics

Bioavailability after oral administration is low, only 15%, with peak

concentrations being reached within 1 to 2hours.

Sirolimus has a high volume of distribution, readily distributing into most tissues

of the body, even though it binds extensively to erythrocytes because of the high

FKBP12 concentration found in red blood cells.

About 40% of sirolimus in plasma is protein bound, especially to albumin.

Metabolism occurs primarily by CYP3A4 both in the gut and in the liver.

The half-life is reported to be 60 hours but can be as long as 110 hours in patients

with liver dysfunction.

Adverse Effects

Associated with a dose-dependent increase in serum cholesterol and triglycerides

(Hyperlipidaemia) [mechanism of this adverse effect is related to an

overproduction of lipoproteins or inhibition of lipoprotein lipase]

Hyperlipidaemia

Myelosupression

Thrombocytopenia

Leukopenia

Anaemia

GI effects

(No Nephrotoxicity)

Drug Interactions

Since sirolimus is a substrate for CYP3A4 and is transported by P-glycoprotein,

close attention to interactions with other drugs that are metabolized or

transported by these proteins is required.

Therapeutic Uses

Sirolimus is indicated for prophylaxis of organ transplant rejection in combination

with a calcineurin inhibitor and glucocorticoids.

It is used as prophylaxis and as therapy for steroid-refractory acute and chronic

graft-versus-host disease in hematopoietic stem cell transplant recipients.

Topical sirolimus is also used in some dermatologic disorders and, in combination

with cyclosporine, in the management of uveoretinitis.

Recently, sirolimus-eluting coronary stents have been shown to reduce restenosis

and other adverse cardiac events in patients with severe coronary artery disease.

Dosing

A fixed sirolimus dosing regimen is approved for concomitant use with cyclosporine

that includes a loading dose of 6- or 15-mg followed by 2 or 5 mg daily.

24


Cytokine Inhibition

Cytokines (Greek cyto-cell; and kinos-movement) are small cell-signaling protein

molecules that are secreted by numerous cells and are a category of signaling

molecules used extensively in intercellular communication.

The term "cytokine" has been used to refer to the immunomodulating agents, such

as interleukins and interferons.

Cytokines are critical signaling mediators in immune function.

Cytokines are also pleiotropic; that is, they exert different effects depending on the

target cell and overall cytokine milieu.

For this reason, pharmacologic uses of cytokines or cytokine inhibitors may have

unpredictable effects.

The first anticytokine agent approved for clinical use was Etanercept, an anti-

TNF- drug developed for rheumatoid arthritis.

During the initial clinical studies, some patients with severe, drug-refractory

rheumatoid arthritis literally got up from their wheelchairs and walked after

receiving Etanercept.

This dramatic efficacy ushered in a new age of biological therapies for

autoimmune disease, and the number of new drugs that inhibit proinflammatory

cytokines continues to grow rapidly.

TNF- Inhibitors

Tumor necrosis factor- (TNF- ) is a cytokine central to many aspects of the

inflammatory response.

Macrophages, mast cells, & activated TH cells (especially TH1 cells) secrete TNF-.

TNF- stimulates macrophages to produce cytotoxic metabolites, thereby

increasing phagocytic killing activity.

TNF- also stimulates production of acute-phase proteins, has pyrogenic effects,

and fosters local containment of the inflammatory response.

Some of these effects are indirect and are mediated by other cytokines induced by

TNF-.

TNF- has been implicated in numerous autoimmune diseases.

Rheumatoid arthritis, psoriasis, and Crohns dis-ease are three disorders in which

inhibition of TNF- has demonstrated therapeutic efficacy.

Proposed roles for Tumor Necrosis Factor in Rheumatoid Arthritis:

Tumor necrosis factor (TNF) is secreted by activated macrophages in an affected

joint, where this cytokine has multiple proinflammatory effects.

First, TNF activates endothelial cells to up-regulate their expression of cell surface

adhesion molecules (shown as projections on endothelial cells) and undergo other

phenotypic changes that promote leukocyte adhesion and diapedesis.

25


Second, TNF has a positive feedback effect on nearby monocytes and

macrophages, promoting their secretion of cytokines such as IL-1. In turn, IL-1

activates T cells (among other functions), and the combination of IL-1 and TNF

stimulates synovial fibroblasts to increase their expression of matrix

metalloproteases, prostaglandins (especially PGE 2), and cytokines (such as IL-6)

that degrade the joint cartilage. Synovial fibroblasts also secrete IL-8, which

promotes neutrophil diapedesis.

Five therapies interfering with TNF- activity have been approved.

Etanercept, Infliximab, Certolizumab pegol, Adalizumab, Golimumab

Although all of these agents target TNF-, Etanercept is somewhat less specific

because it binds to both TNF- and TNF-.

Infliximab, Adalimumab, Certolizumab, and Golimumab are specific for TNF-

and do not bind TNF- .

26


Etanercept soluble TNF receptor dimer that links the extracellular, ligand-binding domain of human TNF receptor type II to the Fc domain of human immunoglobulin G1 (IgG1)

Infliximab partially humanized mouse monoclonal antibody against human TNF-

Adalimumab Fully human IgG1 monoclonal antibody against TNF- Certolizumab pegol

pegylated anti-TNF- monoclonal antibody fragment that lacks the Fc portion of the antibody; as a result, unlike infliximab and Adalimumab, Certolizumab does not cause antibody-dependent cell- mediated cytotoxicity or fix complement in vitro.

Golimumab fully human IgG1 monoclonal antibody against TNF- that has a longer half-life than the other anti-TNF- agents

Etanercept

Etanercept is a fusion protein consisting of two p75-soluble TNF receptors linked

to an Fc fragment of human IgG1.

MOA: The drug binds to TNF, making it biologically inactive and preventing it

from interacting with the cell-surface TNF receptors that would lead to cell

activation.

The drug is given by subcutaneous injection, 50 mg once weekly or 25 mg twice

weekly, usually through self-injections or administration by a caregiver.

Adverse Effects

Aside from local injection-site reactions, adverse effects are rare.

There are case reports of pancytopenia and neurologic demyelinating syndromes

like multiple sclerosis associated with use of Etanercept, but these are rare.

Patients with multiple sclerosis should avoid use of this drug.

Therapeutic Uses

Etanercept is approved for use in


Juvenile idiopathic arthritis

Plaque psoriasis

Psoriatic arthritis

Ankylosing spondylitis

Infliximab

Infliximab is a chimeric antibody combining portions of mouse and human IgG1.

An anti-TNF antibody was created by exposing mice to human TNF.

The binding portion of that antibody was fused to a human constant-region IgG1

to reduce the antigenicity of the foreign protein.

27


This antibody, when injected in humans, binds to TNF and prevents its interaction

with TNF receptors on inflammatory cells. (Mechanism)

Infliximab is given by intravenous infusion at a dose of 3 mg/kg at 0, 2, and 6

weeks and then every 8 weeks.

To prevent the formation of antibodies to this foreign protein, Methotrexate

should be given orally in doses typically used to treat rheumatoid arthritis for as

long as the patient continues on infliximab.

Adverse Effects

An acute infusion reaction with symptoms including fever, chills, pruritus, and

rash may occur during infusion or within 1 to 2 hours after giving the drug.

Treatment includes slowing infusion rates and administering acetaminophen,

diphenhydramine, or corticosteroids, depending on the severity of symptoms.

The drug may increase risk of infection.

Autoantibodies and lupus-like syndrome also have been reported.

Therapeutic Uses

Infliximab is currently approved for use in

Crohns disease

Ulcerative colitis



Plaque psoriasis

Psoriatic arthritis

Adalimumab

Adalimumab is a human IgG1 antibody to TNF.

Because it has no foreign protein components, it is less antigenic than Infliximab.

MOA

Like the other anti-TNF- biologicals, Adalimumab blocks the interaction of TNF-

with TNF receptors on cell surfaces; it does not bind TNF-.

Adalimumab lyses cells expressing TNF- in the presence of complement.

Therapeutic Uses

Adalimumab is approved for use in


Juvenile idiopathic arthritis

Psoriatic arthritis


Plaque psoriasis

Crohns disease

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Certolizumab pegol

Certolizumab pegol is a recombinant humanized Fab fragment that binds to TNF-

. It is coupled to a 40-kDa polyethylene glycol.

It neutralizes the activity of membrane-associated and soluble TNF- without

lysing cells.(Mechanism)

Certolizumab is indicated for patients with

Crohns disease


Golimumab

Golimumab is a human IgG monoclonal antibody that also binds to soluble and

membrane-associated TNF-.

It is an intact human IgG1 and, like certolizumab pegol, it does not lyse cells

expressing membrane-associated TNF-.

It is indicated for patients with



Psoriatic arthritis

It has the advantage of increased half-life such that subcutaneous injections may

be self-administered only once per month.

General considerations for TNF- Inhibitors:

It is important to note that high levels of TNF- are likely mediators of underlying

pathophysiologic processes.

However, although treatment with an anti-TNF- agent often improves disease

symptoms, it may not reverse the underlying pathophysiology.

Etanercept, Infliximab, Adalimumab, Certolizumab, and Golimumab are proteins

and must be administered parenterally.

A number of important adverse effects must be considered when administering

TNF inhibitors.

All patients should undergo screening for tuberculosis before initiating therapy

because of increased risk of reactivating latent tuberculosis.

Any patient developing an infection while taking a TNF- inhibitor should

undergo evaluation and aggressive antibiotic treatment.

Orally active inhibitors of TNF- and inhibitors of TNF- converting Enzyme (TACE)

are under investigation.

29


IL-12/IL-23p40 Inhibitors

New biological therapies for the treatment of T-cell-mediated diseases include

antibodies to IL-12 and IL-23.

IL-12 and IL-23 are cytokines involved in natural killer cell activation and CD4+ T-

cell differentiation and activation.

IL-12, a heterodimer composed of p40 and p35 subunits, directs the differentiation

of nave T cells into TH1 cells, which secrete IL-2, IFN-, and TNF-.

IL-23 is also a heterodimer that has the same p40 subunit covalently linked to a

p19 sub-unit. IL-23 directs the differentiation of nave T cells into TH17 cells, which

secrete IL-17 and IL-22.

Ustekinumab

Ustekinumab is a high-affinity IgG1 human monoclonal antibody that binds to the

p40 subunit shared by IL-12 and IL-23.

MOA

Ustekinumab is a human IgG1 monoclonal antibody that binds to the p40 subunit

of IL-12 and IL-23 cytokines.

It blocks IL-12 and IL-23 from binding to their receptors, therefore inhibiting

receptor-mediated signaling in lymphocytes.

Therapeutic Uses

Ustekinumab is indicated for patients with moderate to severe plaque psoriasis

and is in late-stage clinical trials for the treatment of multiple sclerosis and

Psoriatic arthritis

The advantage of Ustekinumab over anti-TNF-drugs for psoriasis is faster and

longer term improvement in symptoms along with very infrequent dosing.

Adverse effects include an increased risk of infections.

IL-1 Inhibitors

Anakinra, Rilonacept, Canakinumab

Interleukin-1(IL-1) is an ancient cytokine, expressed in both vertebrates and

invertebrates, that serves as a bridge between innate and adaptive immunity.

Two forms of IL-1, IL-1 and IL-1, are encoded on different genes.

In humans, IL-1 has primarily an immune role, while IL-1 may be involved in

maintenance of epithelial cell function.

Most IL-1 is generated by activated mononuclear cells.

IL-1 stimulates IL-6 production, enhances adhesion molecule expression, and

stimulates cell proliferation.

IL-1 is very important in the pathogenesis of rheumatoid arthritis.

30


It stimulates release of chemotactic factors and adhesion molecules, and these

promote migration of inflammatory leukocytes to tissues.

It also causes release of factors known to dilate blood vessels and direct cytotoxins

that produce connective tissue damage.

Modulation of IL-1 activity in vivo is accomplished in part by an endogenous IL-1

receptor antagonist (IL-1RA)

Anakinra

Anakinra, a recombinant, non-glycosylated form of IL-1RA, is approved for use in

Rheumatoid arthritis.

Mechanism of Action

Prevents IL-1 from binding to its receptor.

Anakinra has modest effects on pain and swelling but significantly reduces bony

erosions, possibly because it decreases osteoclast production and blocks IL-1

induced metalloproteinase release from synovial cells.

A number of rare syndromes that are mediated in part by increased levels of IL-1,

including Muckle-Wells syndrome and Hibernian fever, have also been treated

effectively with Anakinra.

Collectively, these syndromes are termed Cryopyrin-associated periodic fever

syndromes (CAPS a group of rare inherited inflammatory diseases associated

with overproduction of IL-1 that includes Familial cold Auto inflammatory and

Muckle-Wells Syndromes).

Adverse Effects

Neutropenia

Increase susceptibility to infections

It can be used alone or in combination with anti-TNF agents for Rheumatoid arthritis.

Most rheumatologists feel Anakinra has a less-robust response than the TNF inhibitors

and reserve it for use in patients who fail these agents.

Rilonacept

Rilonacept is a recombinant, soluble IL-1 receptor Fc fusion protein.

It is a dimeric fusion protein consisting of the ligand-binding domains of the

extracellular portions of the human interleukin-1 receptor component (IL-1RI) and

IL-1 receptor accessory protein (IL-1RAcP) fused to the Fc portion of human IgG1.

Approved for use in CAPS

Rilonacept is now being evaluated in a phase3 study for Gout. (IL-1 is an

inflammatory mediator of joint pain associated with elevated uric acid crystals)

31


Canakinumab

Canakinumab is a human IgG1 monoclonal antibody to IL-1.

It binds to human IL-1 and prevents it from binding to IL-1 receptors.

Approved by the FDA for CAPS.

It is also being evaluated for use in COPD.

Cytokine Receptor Antagonists

An alternate approach to block the action of inflammatory cytokines is to target

the cytokine receptor.

This approach is attempted less frequently in drug development because there

may be an increased risk of adverse effects if the antibody should have even

minimal agonist activity.

Tocilizumab

Tocilizumab is recombinant humanized IgG1.

MOA

Tocilizumab binds to soluble and membrane-associated IL-6 receptors.

It inhibits IL-6-mediated signaling on lymphocytes, suppressing inflammatory

processes.

The drug is administered every 4 weeks as an intravenous infusion.

Therapeutic Uses

It is indicated for treatment of patients with rheumatoid arthritis who are

refractory to other anti-TNF- biologicals.

It may be used alone or in combination with Methotrexate or other disease-

modifying antirheumatic drugs.

Patients taking Tocilizumab have the same increased risk of infection as those taking

anti-TNF- monoclonal antibodies.

Depletion of Specific Immune Cells

Appropriately targeted antibodies deplete the immune system of reactive cells

and thereby provide effective therapy for autoimmune diseases and transplant

rejection.

When the adaptive immune system reacts to an antigen, the resulting

immunologic response includes the clonal expansion of cells specifically reactive

against that antigen.

32


Treatment with exogenous antibodies against cell-surface molecules that are

expressed selectively on reactive immune cells can preferentially deplete the

immune system of these reactive cells.

Polyclonal Antibodies

Antithymocyte Globulin (ATG)

Antithymocyte globulin is a purified gamma globulin from the serum of rabbits or

Horses immunized with human Thymocytes.

The rabbit or horse antibodies are polyclonal and target many antigens on human

T cells.

Because ATG targets essentially all T cells and leads to profound lymphocyte

depletion.

Mechanism of Action

Antithymocyte globulin contains cytotoxic antibodies that bind to CD2, CD3,

CD4, CD8, CD11a, CD18, CD25, CD44, CD45, and HLA class I and II molecules on

the surface of human T lymphocytes.

The antibodies deplete circulating lymphocytes by direct cytotoxicity (both

complement and cell-mediated) and block lymphocyte function by binding to cell

surface molecules involved in the regulation of cell function.

Therapeutic Uses

Antithymocyte globulin also is used for acute rejection of other types of organ

transplants and for prophylaxis of rejection.

ATG is approved for use in prevention or treatment of renal transplant rejection,

and the equine-derived material is also approved for treatment of aplastic anemia.

It is provided as a sterile, freeze-dried product for intravenous administration after

reconstitution with sterile water.

ATG is administered intravenously once daily for upto 28 days.

The recommended dose for acute rejection of renal grafts is 1.5 mg/kg per day.

Adverse Effects

Polyclonal antibodies are xenogeneic proteins that can elicit major side effects,

including fever and chills with the potential for hypotension.

Premedication with corticosteroids, acetaminophen, and/or an antihistamine and

administration of the antiserum by slow infusion (over 4 to 6 hours) into a large-

diameter vessel minimize such reactions.

Serum sickness and glomerulonephritis (Complexes of host antibodies with horse

ALG may precipitate and localize in the glomeruli of the kidneys) can occur.

Anaphylaxis is a rare event.

33


Hematologic complications include Leukopenia and Thrombocytopenia.

There is an increased risk of infection and malignancy, especially when multiple

immunosuppressive agents are combined.

Monoclonal Antibodies

Muromonab (Anti-CD3, OKT3)

OKT3 is a mouse monoclonal antibody against human CD3, one of the cell-surface

signaling molecules important for activation of the T-cell receptor.

CD3 is specifically expressed on T cells (both CD4 and CD8 cells).

Treatment with OKT3 depletes the available pool of T cells via antibody-mediated

activation of complement and clearance of immune complexes

Mechanism of Action

Muromonab binds to the chain of CD3, a monomorphic component of the T-cell

receptor complex involved in antigen recognition, cell signaling, and proliferation.

Antibody treatment induces rapid internalization of the T-cell receptor, thereby

preventing subsequent antigen recognition.

Administration of the antibody is followed rapidly by depletion and extravasation

of a majority of T cells from the bloodstream and peripheral lymphoid organs

such as lymph nodes and spleen.

This absence of detectable T cells from the usual lymphoid regions is secondary

both to cell death following complement activation and activation-induced cell

death and to margination of T cells onto vascular endothelial walls and

redistribution of T cells to nonlymphoid organs such as the lungs.

Muromonab-CD3 also reduces function of the remaining T cells, as defined by

lack of IL-2 production and great reduction in the production of multiple

cytokines, perhaps with the exception of IL-4 and IL-10.

Pharmacokinetics

OKT3 has a volume of distribution of 6.5 L and half-life of about 18 hours.

Concentrations above 0.9 mcg/mL are considered therapeutic.

If CD3 levels begin to rise, this may signify the presence of antimurine antibodies

antagonizing the actions of OKT3.

Administration of Mycophenolate mofetil has been suggested to reduce the

formation of antimurine antibodies during OKT3 administration.

Although T-cell depletion is achieved within minutes of administration,

resolution of rejection takes 3 to 4 days.

34


Therapeutic Uses

Muromonab-CD3 is indicated for treatment of acute organ transplant rejection.

Muromonab-CD3 is approved for the treatment of acute renal allograft rejection

and steroid-resistant acute cardiac and hepatic transplant rejection.

Adverse Effects

OKT3 administration is associated with significant first-dose adverse reactions.

The Cytokine-release syndrome related to OKT3, including fever, chills, rigors,

pruritus, and alterations in blood pressure, may occur with the first several doses.

Methylprednisolone, acetaminophen, diphenhydramine, Indomethacin, and

pentoxifylline have been used as premedications to prevent or minimize the severity of

this syndrome.

Other adverse effects include

Capillary leak syndrome and pulmonary edema, especially in fluid

overloaded patients.

Aseptic meningitis is another potential complication of OKT3

therapy. If encephalitic symptoms develop, OKT3 should be

discontinued and appropriate care initiated.

Other adverse effects include

encephalopathy

nephrotoxicity

infection, and post-transplantation lymphoproliferative disorder

Nausea/vomiting, diarrhea, abdominal pain,

Malaise, Myalgias, Arthralgias, and generalized weakness.

Potentially fatal severe pulmonary edema, acute respiratory distress syndrome,

cardiovascular collapse, cardiac arrest, and arrhythmias have been described.

Other toxicities associated with anti-CD3 therapy include anaphylaxis and the

usual infections and neoplasms associated with immunosuppressive therapy.

"Rebound" rejection has been observed when muromonab-CD3 treatment is

stopped.

Dosing

OKT3 should be filtered with a 0.2-to 0.22-micron filter and then administered as

an intravenous push over 1 minute.

The dose of OKT3 usually is 5 mg/day for 5 to 14 days.

35


Rituximab

Rituximab is a chimeric murine-human monoclonal IgG1 (human Fc) that binds to

the CD20 molecule on normal and malignant B lymphocytes.

CD20 is expressed on the surface of all mature B cells, and administration of

Rituximab causes profound depletion of circulating B cells.

Mechanism of Action

The mechanism of action includes complement-mediated lysis, antibody-

dependent cellular cytotoxicity, and induction of apoptosis in the malignant

lymphoma cells.

Rituximab is a monoclonal chimeric antibody consisting of mostly human protein

with the antigen-binding region derived from a mouse antibody to CD20 protein

found on the cell surface of mature B lymphocytes.

The binding of Rituximab to B cells results in nearly complete depletion of

peripheral B cells, with a gradual recovery over several months.

Therapeutic Uses

It is also approved for the treatment of rheumatoid arthritis in combination with

Methotrexate in patients for whom anti-TNF- therapy has failed.

Approved for the therapy of patients with relapsed or refractory low-grade or

follicular B-cell non-Hodgkins lymphoma and chronic lymphocytic leukemia.

Recent reports indicate that rituximab may also be very useful in auto-immune

diseases such as multiple sclerosis and systemic lupus erythematosus.

Several additional anti-CD20 antibodies are in clinical development:

Ofatumumab

A fully human anti-CD20 monoclonal antibody that recognizes an epitope distinct

from that of Rituximab.

Ofatumumab is approved for use in Chronic lymphocytic leukemia.

Daclizumab and Basiliximab

Daclizumab and Basiliximab are monoclonal antibodies against CD25, the high-

affinity IL-2 receptor.

IL-2 mediates early steps in T-cell activation.

Because CD25 is expressed only on activated T cells, anti-CD25 antibody therapy

selectively targets T cells that have been activated by an MHC-antigen stimulus.

Basiliximab is a chimeric mouse-human IgG1 that binds to CD25, the IL-2 receptor

alpha chain on activated lymphocytes.

Daclizumab is a humanized IgG1 that also binds to the alpha subunit of the IL-2

receptor.

36


MOA: Both agents function as IL-2 antagonists, blocking IL-2 from binding to activated

lymphocytes, and are therefore immunosuppressive.

Therapeutic Uses

Daclizumab is administered prophylactically in renal transplantation to inhibit

acute organ rejection.

It is also used as a component of general immunosuppressive regimens after

organ transplantation.

Daclizumab is typically administered in a five-dose regimen, with the first

administration immediately after transplantation and then four additional doses

at 2-week intervals.

This type of dosing regimen, in which drug is administered for a limited period

immediately after transplantation, is referred to as Induction therapy.

Alemtuzumab

Alemtuzumab is a humanized IgG1 with a kappa chain that binds to CD52 found

on normal and malignant B and T lymphocytes, NK cells, monocytes,

macrophages, and a small population of granulocytes.

Campath-1 (CD52) is an antigen expressed on most mature lymphocytes and on

some lymphocyte precursors.

Its effects on depleting both T and B lymphocytes make it useful in solid-organ

transplants.

Mechanism of Action

Alemtuzumab is a humanized monoclonal antibody directed at cells that express

the CD52 surface antigen, which is found on both T and B lymphocytes, as well as

macrophages, monocytes, eosinophils, and natural killer cells.

When Alemtuzumab binds to the CD52 surface antigen, antibody-dependent lysis

occurs, which removes both T and B lymphocytes from the blood, bone marrow,

and organs, resulting incomplete lymphocyte depletion.

Therapeutic Uses

Alemtuzumab is approved for use in B-cell chronic lymphocytic leukemia.

Adverse Effects

The adverse effects of alemtuzumab include infusion-related reactions, hematologic

effects, and infections.

Infusion-related reactions include rigors, hypotension, fever, shortness of breath,

bronchospasms, and chills. The potential for developing these reactions can be

reduced by administering premedications, including corticosteroids,

37


diphenhydramine, and acetaminophen, or by administering smaller doses and

escalating the dose gradually.

Hematologic effects include pancytopenia, neutropenia, thrombocytopenia, and

lymphopenia.

Dosing

Commonly recommended dosing strategy for Alemtuzumab is 30 mg as a single dose.

LFA-3

LFA-3(also called CD58) is the counter-receptor for CD2, an antigen expressed at

high levels on the surface of memory effector T cells.

Interaction of CD2 on T cells with LFA-3 on antigen-presenting cells promotes

increased T-cell proliferation and enhanced T-cell-dependent cytotoxicity.

Because the memory effector T-cell population is elevated in patients with

psoriasis, a pharmacologic agent (Alefacept) that disrupts the CD2LFA-3

interaction was tested for use in psoriasis.

Alefacept

Alefacept is an LFA-3(leukocyte-function-associated antigen-3)/Fc fusion protein

[Alefacept is an engineered protein consisting of the CD2-binding portion of

leukocyte-function-associated antigen-3 (LFA-3) fused to a human IgG1 Fc

region]that interrupts CD2LFA-3 signaling by binding to T-cell CD2, and thereby

inhibits T-cell activation.

Additionally, the Fc portion of Alefacept may activate NK cells to deplete the

immune system of memory effector T cells.

Clinically, alefacept significantly decreases the severity of chronic plaque

psoriasis.

Because CD2 is expressed on other adaptive immune cells, administration of

alefacept also causes a dose-dependent reduction in CD4 and CD8 T-cell

populations.

Its use is therefore contraindicated in patients with HIV, and patients taking

alefacept may have an increased risk of serious infection.

Alefacept therapy may also be associated with an increased risk of malignancy,

primarily skin cancer.

38


Inhibition of Costimulation

Abatacept, Belatacept

Costimulationthe requirement for multiple simultaneous signals to initiate an immune responseensures that stimulation of a single immune receptor does not

activate a damaging immune reaction. Signal 1 provides specificity, while signal 2 is permissive, ensuring that an

inflammatory response is appropriate.

Regulation of costimulatory molecules is a mechanism whereby the innate

immune system regulates the extent of an immune response.

If antigen is presented with-out a coincident costimulatory signal (i.e., without

innate immune activation), then anergy results, whereby a cell becomes

unreactive and will not respond to further antigenic stimuli.

Drugs that induce anergy could be therapeutically attractive, because such agents could

allow long-term acceptance of an organ graft or limit the extent of an autoimmune

disease.

Abatacept

Abatacept consists of CTLA-4 (Cytotoxic T-Lymphocyte Antigen 4) fused to an IgG1

constant region.

Mechanism of Action

Abatacept complexes with costimulatory B7 molecules on the surface of antigen-

presenting cells.

When the antigen-presenting cell interacts with a T cell, MHC:antigenTCR

interaction (signal 1) occurs, but the complex of B7 with abatacept prevents

delivery of a costimulatory signal (signal 2), and the T cell develops anergy or

undergoes apoptosis.

By this mechanism, Abatacept therapy appears to be effective in down-regulating

specific T-cell populations.

Therapeutic Uses

Abatacept is approved for the treatment of rheumatoid arthritis that is refractory to

methotrexate or TNF- inhibitors.

Adverse Effects

The major adverse effects of Abatacept are

Exacerbations of bronchitis in patients with pre-existing

obstructive lung disease

Increased susceptibility to infection

39


Abatacept should not be administered concurrently with TNF- inhibitors or anakinra

because the combination carries an unacceptably high risk of infection.

Belatacept

Belatacept is a close structural congener of Abatacept that has increased affinity

for B7-1 and B7-2.

In a large clinical trial, Belatacept was as effective as cyclosporine at inhibiting

acute rejection in renal transplant recipients.

Belatacept is currently under further investigation as an immunosuppressant for

organ transplantation.

Blockade of Cell Adhesion

The recruitment and accumulation of inflammatory cells at sites of inflammation

is an essential element of most autoimmune diseases; the only exceptions to this

rule are autoimmune diseases that are purely humoral, such as myasthenia gravis.

Drugs that inhibit cell migration to sites of inflammation may also inhibit antigen

presentation and cytotoxicity, thus providing multiple potential mechanisms of

beneficial action.

Natalizumab

Alpha-4 integrins are critical to immune-cell adhesion and homing.

The 4 1 integrin mediates immune-cell interactions with cells expressing

vascular cell adhesion molecule 1 (VCAM-1), while the 4 7 integrin mediates

immune-cell binding to cells expressing mucosal addressin cell adhesion molecule

1 (MAdCAM-1).

Natalizumab is a monoclonal antibody against 4 integrin that inhibits immune-cell

interactions with cells expressing VCAM-1 or MAdCAM-1.

Natalizumab was approved for the treatment of relapsing multiple sclerosis.

During post marketing surveillance of the drug, however, several patients treated

with Natalizumab developed progressive multifocal leukoencephalopathy (PML),

a rare demyelinating disorder caused by infection with JC virus.

This finding resulted in voluntary withdrawal of the drug.

After further FDA investigation, it was decided to resume testing of Natalizumab

and to add a warning to the product label regarding the possible association.

Natalizumab was subsequently reapproved for use in the treatment of multiple

sclerosis and Crohns disease.

40


Inhibition of Complement Activation

The complement system mediates a number of innate immune responses.

Recognition of foreign proteins or carbohydrates leads to sequential activation of

complement proteins and eventual assembly of the membrane attack complex, a

multiprotein structure that can cause cell lysis.

Patients with paroxysmal nocturnal hemoglobinuria (PNH) have acquired defects

in complement regulatory proteins, leading to inappropriate activation of

complement and complement-mediated lysis of erythrocytes.

Eculizumab

Eculizumab is a humanized monoclonal antibody against C5, a complement

protein that mediates late steps in complement activation and triggers assembly of

the membrane attack complex.

Eculizumab is approved for the treatment of PNH; it significantly decreases

hemoglobinuria and the need for erythrocyte transfusions in patients with this

disorder.

Genetic evidence indicates that complement activation may play an etiologic role

in age-dependent macular degeneration, suggesting that inhibitors of the

complement cascade could be useful local therapies for this disease.

Immunostimulants

In contrast to immunosuppressive agents that inhibit the immune response in transplant

rejection and autoimmunity, a few immunostimulatory drugs have been developed with

applicability to infection, immunodeficiency, and cancer.

Levamisole

Thalidomide

Bacillus Calmette-Guerin (BCG)

Recombinant Cytokines (Interferons)

Interleukin-2

Levamisole

Levamisole was synthesized originally as an anthelmintic but appears to "restore"

depressed immune function of B lymphocytes, T lymphocytes, monocytes, and

macrophages.

In combination with the antimetabolite 5-fluorouracil, this drug is now approved

for use in the treatment of colon cancer.

41


Thalidomide

Thalidomide is best known for the severe, life-threatening birth defects it caused

when administered to pregnant women.

For this reason, it is available only under a restricted distribution program and

can be prescribed only by specially licensed physicians who understand the risk

of teratogenicity if thalidomide is used during pregnancy.

Thalidomide should never be taken by women who are pregnant or who could

become pregnant while taking the drug.

It is indicated for the treatment of patients with erythema nodosum leprosum and

also is used in conditions such as multiple myeloma.

Its mechanism of action is unclear. Thalidomide has been reported to decrease

circulating TNF- in patients with erythema nodosum leprosum.

Alternatively, it has been suggested that the drug affects angiogenesis.

The anti-TNF- effect has led to its evaluation as a treatment for severe, refractory

rheumatoid arthritis.

Bacillus Calmette-Guerin (BCG)

Live bacillus Calmette-Guerin is an attenuated, live culture of the bacillus of

Calmette and Guerin strain of Mycobacterium bovis that induces a granulomatous

reaction at the site of administration.

By unclear mechanisms, this preparation is active against tumors and is indicated

for treatment and prophylaxis of carcinoma in situ of the urinary bladder and for

prophylaxis of primary and recurrent stage Ta and/or T1 papillary tumors after

transurethral resection.

Adverse effects include hypersensitivity, shock, chills, fever, malaise, and immune

complex disease.

Recombinant Cytokines-Interferons

Although interferons (alpha, beta, and gamma) initially were identified by their

antiviral activity, these agents also have important immunomodulatory activities.

The interferons bind to specific cell-surface receptors that initiate a series of

intracellular events:

induction of certain enzymes

inhibition of cell proliferation

enhancement of immune activities, including increased

phagocytosis by macrophages

augmentation of specific cytotoxicity by T lymphocytes.

Recombinant interferon alfa-2b (IFN-alpha 2, INTRON A)

Obtained from Escherichia coli by recombinant expression.

42


It is a member of a family of naturally occurring small proteins with molecular

weights of 15,000 to 27,600 daltons, produced and secreted by cells in response to

viral infections and other inducers.

Therapeutic Uses

Interferon alfa-2b is indicated in the treatment of a variety of tumors, including

hairy cell leukemia, malignant melanoma, follicular lymphoma, and AIDS-related

Kaposi's sarcoma.

It also is indicated for infectious diseases, chronic hepatitis B, and condylomata

acuminata.

In addition, it is supplied in combination with ribavirin (REBETRON) for

treatment of chronic hepatitis C in patients with compensated liver function not

treated previously with interferon alfa-2b or who have relapsed after interferon

alfa-2b therapy.

Adverse Effects

Flu-like symptoms, including fever, chills, and headache, are the most common

adverse effects after interferon alfa-2b administration.

Adverse experiences involving the cardiovascular system (hypotension,

arrhythmias, and rarely cardiomyopathy and myocardial infarction) and CNS

(depression, confusion) are less-frequent side effects.

Interferon gamma-1b (ACTIMMUNE)

Is a recombinant polypeptide that activates phagocytes and induces their

generation of oxygen metabolites that are toxic to a number of microorganisms.

It is indicated to reduce the frequency and severity of serious infections associated

with chronic granulomatous disease.

Adverse reactions include fever, headache, rash, fatigue, GI distress, anorexia,

weight loss, myalgia, and depression.

Interferon beta-1a (AVONEX, REBIF) a 166-amino acid recombinant glycoprotein

Interferon beta-1b (BETASERON), a 165-amino acid recombinant protein

Have antiviral and immunomodulatory properties.

They are FDA approved for the treatment of relapsing and relapsing-remitting

multiple sclerosis to reduce the frequency of clinical exacerbations.

The mechanism of their action in multiple sclerosis is unclear.

Flu-like symptoms (fever, chills, myalgia) and injection-site reactions have been

common adverse effects.

43


Interleukin-2

Human recombinant interleukin-2 (Aldesleukin, PROLEUKIN; des-alanyl-1,

serine-125 human IL-2) is produced by recombinant DNA technology in E. coli.

This recombinant form differs from native IL-2 in that it is not glycosylated, has

no amino terminal alanine, and has a serine substituted for the cysteine at amino

acid 125.

The potency of the preparation is represented in International Units in a

lymphocyte proliferation assay such that 1.1 mg of recombinant IL-2 protein

equals 18 million International Units.

Aldesleukin has the following in vitro biologic activities of native IL-2:

Enhancement of lymphocyte proliferation and growth of IL-2-

dependent cell lines;

Enhancement of lymphocyte-mediated cytotoxicity and killer cell

activity; and induction of interferon-g activity.

In vivo administration of Aldesleukin in animals produces multiple immunologic

effects in a dose-dependent manner.

Cellular immunity is profoundly activated with lymphocytosis, eosinophilia,

thrombocytopenia, and release of multiple cytokines (e.g., TNF, IL-1, and

interferon-g).

Therapeutic Uses

Aldesleukin is indicated for the treatment of adults with metastatic renal cell

carcinoma and melanoma.

Adverse Effects

Administration of Aldesleukin has been associated with serious cardiovascular

toxicity resulting from capillary leak syndrome, which involves loss of vascular

tone and leak of plasma proteins and fluid into the extravascular space.

Hypotension, reduced organ perfusion, and death may occur.

An increased risk of disseminated infection due to impaired neutrophil function

also has been associated with Aldesleukin treatment.

Tretinoin

Tretinoin, or all-trans retinoic acid (ATRA), is a ligand of the retinoic acid receptor

(RAR). ATRA is used in the treatment of acute promyelocytic leukemia.

This disease is characterized by a translocation t(15;17) in which part of the RAR

gene is fused to the PML gene, creating a fusion protein that induces a block to

differentiation and thereby allows development of the leukemia.

Treatment with ATRA stimulates differentiation of these cells into more normal

granulocytes.

44


In some patients, the induction of differentiation can lead to a life-threatening

over-production of white blood cells.

ATRA can also induce a rapidly progressive syndrome of fever, acute respiratory

distress with pulmonary infiltrates, edema and weight gain, and multisystem

organ failure.

Therapy with high doses of glucocorticoids is often an effective treatment for this

ATRA syndrome.

References

Laurence Brunton, Bruce Chabner, Bjorn Knollman, Goodman & Gilmans

The Pharmacological Basis Of Therapeutics, 12th Edition, Mc Graw Hill

Medical, 2011 Pg No: 1005-1023

David E.Golan, Armen H.Tashjian, Ehrin J. Armstrong, April W. Armstrong,

Principles of Pharmacology, The Pathophysiologic Basis Of Drug

Therapy,3rd Edition, Lippincott Williams & Wilkins, 2012 Pg no: 790-806

H.P.Rang, M.M. Dale, J.M. Ritter, R.J. Flower, Rang and Dales

Pharmacology, 6th Edition, Churchill Livingstone Elsevier, 2007

Bertram G. Katzung, Susan B. Masters, Anthony J. Trevor, Basic & Clinical

Pharmacology, 12th Edition, Tata McGraw Hill Education Private Limited,

New Delhi, 2012, Pg No: 977-999

final immunomodulators & immunosuppressants

Documents

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