anticancer agents - philadelphia university · 2016-12-27 · anticancer agents dr. pran kishore...
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Anticancer Agents
Dr. Pran Kishore DebAssistant Professor,
Pharmaceutical Medicinal Chemistry
Faculty of Pharmacy, Philadelphia University-Jordan
Email: [email protected]
Medicinal Chemistry III
B Pharm
Learning Outcomes
At the end of this lesson students will be able to
– Outline the current status, causes and treatment strategies of cancer
– Explain the mechanism of action, SAR, therapeutic uses and side
effects of following classes of anti-cancer agents:
• Alkylating Agents
• Heavy metal compounds (Metallating Agents)
• Anti-metabolite
• Antibiotics
• Plant Extracts
• Topoisomerase inhibitors
• Hormones
• Monoclonal antibodies
• Others
The Status of Cancer
• Cancer is a leading cause of death worldwide,accounting for 12.6 million new cases and 7.6million deaths every year.
THIS IS EQUIVALENT TO
ONE PERSON,
EVERY 5 SECONDS
OF EVERYDAYSource: GLOBOCAN 2008
By 2020 the World Health Organisation (WHO) expects this rise to 16 million.
Cancer Cases and Deaths Worldwide for
Leading Cancer Sites, 2008
Source: Global Cancer Facts & Figures 2nd Edition (2011)
Cancer
• A new growth of tissue in which multiplication of cellsis uncontrolled and progressive (tumour).
• Abnormal cells can spread to other parts of the body(metastasise).
Cancer Types
Cancer types are categorized based on the functions/locations of the cells from which they originate:
Carcinoma: a tumor derived from epithelial cells, those cells thatline the inner or outer surfaces of our skin and organs (80-90% ofall cancer cases reported)
Sarcoma: a tumor derived from muscle, bone, cartilage, fat orconnective tissues.
Leukemia: a cancer derived from white blood cells or theirprecursors.
Lymphoma: a cancer of bone marrow derived cells that affectsthe lymphatic system.
Myelomas: a cancer involving the white blood cells responsiblefor the production of antibodies (B lymphocytes).
Causes of Cancer
What causes cells to divide out of control
???
Accumulation of faults in our DNA
What causes DNA faults?
• DNA mutations
– Inborn mutations of cancer susceptibility genes
– Acquired mutations
• Mutation:
– Germline (Germline mutations are mutations that can be passed
on to offspring) and
– Somatic (Somatic mutations are mutations that happen in any
other cell type and cannot be inherited by offspring)
• Genetic mutations within a single affected cell leads to monoclonal
development. Genes affected can be those controlling cell cycle,
DNA repair and/or differentiation, This leads to uncontrolled
proliferation and tumour formation.
Biochemical Basis of Cancer: Mutation
Development of cancer from Mutation produced by ionising
radiation
Cancer Treatment Four primary modalities are employed in the approach to cancer treatment
Surgery (solid localized tumor): It often offers the greatest chance for cure, especially if the cancer has not spread to other parts of the body.
Radiation (solid localized tumor): Radiation therapy uses high-energyparticles or waves to destroy or damage cancer cells. It is one of the mostcommon treatments for cancer, either by itself or along with other formsof treatment.
Chemotherapy
Chemotherapy (chemo) is the use of medicines or drugs to treatcancer. Accesses the systemic circulation and can theoretically treatthe primary tumor and any metastatic disease.
Biologic therapy (immunotherapy or targeted therapies)
Immunotherapy involves stimulating the host’s immune system tofight the cancer (Examples; interferons and interleukins)
Targeted therapies include monoclonal antibodies such as tyrosinekinase inhibitors and proteosome inhibitors 21
Phenotypic Drug Discovery
Screens used to measure the desired biological effect in cells, tissues or
whole organisms
Targets are unknown
Assay throughput is usually low
Potentially lead to the identification of a molecule that modifies a disease
phenotype by acting on a previously undescribed target or by acting
simultaneously on more than one target
Need to do target deconvolution to identify target
Terstappen et al, Nature Reviews Drug Discovery, 2007, 6, 891-903
Target-Based Drug Discovery
Based on targets that are identified and validated
Typically use recombinant proteins or cells over-expressing the target of
interest
Assay throughput is usually high
Screens used are to measure the compound’s effect on the target of interest
Need to confirm compound effects in biological effect assay
Terstappen et al, Nature Reviews Drug Discovery, 2007, 6, 891-903
How were new medicines discovered?
1960s-80s
‘Classical’ phenotypic screen
1980s-2000s
Target-based screen
Doxorubicin
(1950s)
Paclitaxel
(1960)
Temozolomide
(1970s)
Cyclophosphamide
(1954)
Imatinib
(1990s)
Gefitinib
(1994)
Bortezomib
(1995)
The Classification of Anticancer Drugs
According to chemical structure and resource of the drug:
– Alkylating Agents
– Heavy metal compounds (Metallating Agents)
– Anti-metabolite
– Antibiotics
– Plant Extracts
– Topoisomerase inhibitors
– Hormones
– Monoclonal antibodies
– Others
History of Chemotherapy
Era of modern chemotherapy began in early 1940s
Goodman and Gilman first administered nitrogen mustard to patients with
lymphoma
Nitrogen mustard was developed as a war gas rather than as a medicine
Toxic effects on the lymphatic system led to clinical trials
26
Chemotherapy
Chemotherapy attacks tumors at the cellular level by interrupting
processes or inhibiting substances necessary for cellular replication and life.
Goals of Cancer Chemotherapy:
Cure
Prolong survival
Palliation
Radiosensitive
The Cell Cycle
G1 phase: cell prepares for DNA synthesis
S phase: cell generates complete copy of genetic material
G2 phase: cell prepares for mitosis
M phase: replicated DNA is condensed and segregated into chromosomes
G0 phase: resting state
27
https://www.youtube.com/watch?v=Q6ucKWIIFmg
Chemotherapy
Cell cycle phase – specific
Agents with major activity in a particular phase of cell cycle
Schedule dependent
Cell cycle phase – nonspecific
Agents with significant activity in multiple phases
Dose dependent
28
How Cells Divide and How Chemotherapy Works
https://www.youtube.com/watch?v=VRhz3DhjG5M
CHEMOTHERAPY
29
Backbone of cancer chemotherapy regimens
Cytotoxicity is not selective
Problems with chemotherapy
• Treatments are non-specific, attack healthy cells as well as normal cells
since cancer cells are derived from normal cells.
• Cancers can develop resistance: for example with platinum-drugs,
cancer cells became resistant by many ways:
– Decreased drug uptake/increased efflux
– Enhanced tolerance of DNA adducts
– Enhanced repair of DNA adducts
– Increased drug deactivation by intracellular glutathione
Ideal cytotoxic drugs should:
– Selectively target cancer cells without causing damage to normal cells.
– Reduce size of tumors + minimize risks of metastases.
Unfortunately, most of the available agents are not selective, they also
affect rapidly-proliferating normal tissues (bone marrow, gastro
intestinal epithelium, hair cells etc.) causing serious side-effects (bone
marrow suppression, nausea, vomiting etc.).
Treatment Side effects - Terminology
Neutropenia (is a hematological disorder characterised by an
abnormally low number of neutrophil granulocytes (a type of
white blood cell).
Myelosuppression is a decrease in the production of blood cells.
(Red blood cells and platelets).
Ototoxicity is damage of the ear, specifically the cochlea or
auditory nerve.
Nephrotoxicity is kidney damage. Results in decreased kidney
function.
Hepatotoxicity is liver damage. Results in decreases liver function.
Neuropathy is usually short for peripheral neuropathy, and means a
damage to peripheral nerve(s).
Hypomagnesaemia is an abnormally low level of magnesium in
blood serum.
Extravasation: a dreaded complication of chemotherapy
Most chemotherapeutic agents are given by intravenous (IV)
administration, which cause few side-effects at the site of injection.
A tissue reaction varying from irritation to necrosis.
Extravasation is defined either as the escape of a chemotherapeutic
agent from a vessel into the surrounding tissues by leakage or as an
involuntary injection of a drug into the tissues.
The severity of tissue injury is dependent on the type and concentration of
the chemotherapeutic agent and the quantity injected.
Cytotoxic agents may be classified as IRRITANTS or VESICANTS
Irritants are drugs that can cause an inflammatory reaction,
aching, swelling, pain or phlebitis, hyperpigmentation at the injection site
or along the vein. These symptoms are self-limiting and there are no
long-term sequelae.
Vesicants are drugs that may cause severe and lasting tissue injury and
necrosis. Symptoms may arise immediately after extravasation or appear
after several days or weeks.
Chemotherapeutic Agents
IRRITANTS or VESICANTS
Part – I
Alkylating agents
• Nitrogen mustard
• Nitrosoureas: Carmustine, Lomustine
• Busulfan
• Aziridines: Thiotepa
• Methylhydrazines: Dacarbazine and Procarbazine
• Mitomycin C
• Cisplatin and Cisplatin Analogues
Alkylating agent
The alkylating agents are among the oldest and most useful of
antineoplastic drugs.
Evolved from the observation of bone marrow suppression and lymph
node shrinkage in soldiers exposed to sulfur mustard gas warfare
during World War I
35
Cl
Cl
NR
Cl
Cl
S
Sulfur Mustard
(chemical weapon) not used clinically
Nitrogen Analog
Less-reactive derivatives were synthesized to treat cancerous overgrowths
of lymphoid tissues
The nitrogen mustards were the first alkylating agents used
medically, as well as the first modern cancer chemotherapies.
Cl
Cl
NR
Cl
Cl
S
Sulfur Mustard
(chemical weapon) not used clinically
Nitrogen Analog
36
Contain highly electrophilic groups
Form covalent bonds to nucleophilic groups in DNA (e.g. 7-N of
guanine)
Prevent replication of DNA and transcription
Useful anti-tumour agents
Toxic side effects (e.g. alkylation of proteins)
Can cause interstrand and intrastrand cross-linking of DNA if two
electrophilic groups are present
Alkylation of nucleic acid bases can result in miscoding
Alkylating agents
Interstrand cross linkingIntrastrand cross linking
NuNu
X X
Nu
Nu Nu
Nu
X X
Nu
Nu
37
Nucleophilic groups on nucleic acid bases
nucleophilicgroups
nucleophilicgroups
NH2
N
N
N
N
1
3
R
H2N
HN
N N
N
O
7
R
NH2
N
NR
O
3
CytosineGuanineAdenine
Alkylating agents
Miscoding resulting from alkylated nucleic acid bases
Guanine prefers keto tautomer
Normal base pairing
Alkylated guanine prefers enol tautomerAbnormal base pairing
Thymine Alkylated guanine
N
NH
O
O
Me
R
N
N
N
NHO
R
H2N
DRUGCytosine Guanine
N
N
NH2
OR
HN
N
N
NO
H2N
R
Alkylating Agents
Mechanism of Action of nitrogen mustard
• Nitrogen mustards inhibit cell reproduction by formation of
irreversible covalent binding with the nucleic acids (DNA). The
specific type of chemical bonding involved is alkylation.
• After alkylation, DNA is unable to replicate and therefore unable
to synthesize proteins and other essential cell metabolites.
• Consequently, cell reproduction is inhibited and the cell eventually
dies from the inability to maintain its metabolic functions.
Chlormethine (Mechlorethamine)
Used medicinally in 1942
MOA: Causes intrastrand and interstrand cross-linking
Prevents replication of DNA
Monalkylation of guanine also possible
Used mainly to treat Hodgkin's disease and non-Hodgkin's lymphoma.
Prevention of extravasation: 0.16 M sodium thiosulfate and ice packs
Analogues with better properties have been prepared
Alkylating agents
H 3C N
C l
C l
+
-
Nucleophile
Electrophilic carbon
CH3 N
Cl
Cl
Mechlorethamine
+
Cl
NCH3
Aziridinium ion
highly reactive
alkylating agent
G = Guanine
DNA
G
N
HN
N
N
N
NNH
N
O
O
NH2
NH2
G
DNA
N
N
N
NN
HN
NH
N
O
NH2
O NH2
CH3 N
Cl
+
DNA
N
N
N
NNH
N
O
NH2
N
HNO NH2
NCH3
DNA
CH3
N
N
N
N
N
N
HN
NH
N
O NH2
O
NH2
Crosslinked DNA
Mechanism of Action of Chlormethine
Generation of highly reactive “aziridinium ions” that act as alkylating
agents to cross-link DNA producing defective DNA and abnormal
cellular function and eventually cell death.
• Substituting an aromatic ring for methyl group can be predicted to
increase chemical stability and thereby decrease the rate of alkylation
because of electron-withdrawing effect.
• This also, will lead to good oral bioavailability, tissue distribution,
before alkylation is widespread.
E.g. Chlorambucil, and melphalan.
Rationales used to improve nitrogen mustards
C l
N
C l
C H 3
M e c h l o r e t h m i n e
Cl
N
Cl
COOH
Chlorambucil
C l
N
C l
C O O H
N H 2
H
M e l p h a l a n
ClS
Cl ClS
NuH
ClS
Nu
+ HCl
Slow
less stable than N-aanalog
Moderate
ClN
Cl ClN
NuH
ClN
Nu
+ HCl
Fast
Moderate
R
R
2- order kinetics
1. order kinetics(1. step rat lim)
R=Alkyl
R
ClN
Cl ClN
NuH
ClN
Nu
+ HCl
Slow
ModeratePh
Lone pair delocalizedLess nucleophilic
Ph
1. order kinetics(1. step rat lim)
..
..
..
• Attachment of amino acid, nucleic acid base or hormone to nitrogen
mustards improve their uptake by using the carrier protein.
N
C l
C l
H 2 N
C O O HH
L-phenylalanine(amino acid)
Melphalan
C H 3
H
H
H
O H
H
O
O
NC l
C l
Estradiol(sex hormone)
NH
H N
O
O
N
C H 3
C H 3
Uracil Mustard
Uracil
(nucleic base)
Estramustine
Rationales used to improve nitrogen mustards
To increase selectivity, nitrogen mustards was bonded with natural
carrier e.g. Estramustine which is active against prostate cancer.
Estramustine phosphate: Estracyt®
Prodrug
O
O P
O
O
O
Na
Na
N
O
Cl
Cl
Water solubility
1) Oral absorb2) Fast metabol.
O
OH
N
O
Cl
Cl
Main comp. plasma
EstradiolCarry to cells with estrogenic receptors
Estrogenic (Anti-androgenic) effect protate cancerCleaved to active alkylating agent?
Synthesis of Chlorambucil
(CH2)3-COO-
Cl
Cl
N(CH2)3-COO-
OH
OH
N
CH3
CH3
CH3
CH3
(CH2)3-COO-NH2
CH3
CH3
(CH2)3-COO-O2N
(CH2)3-COOHO2N(CH2)3-COOH
CH3
CH3
O
CH3
CH3
OH
Nitration
4-Phenylbutyric acid
2
Hydrolysis
POCl3
Chlorambucil (CH2)3-COOH
Cl
Cl
N
Ethylene oxide(oxirane)
Phosphoryl chloride
Aromatic ring is electron-withdrawing
Lowers nucleophilic strength of nitrogen
Less reactive alkylating agent
Less side reactions and less toxic
Aromatic ring is present
Less reactive alkylating agent
Mimics phenylalanine
Transported into cells by transport proteins
N
Cl
Cl
HN
NH
O
O
Uracil mustard
Uracil ring is electron-withdrawing
Less reactive alkylating agent
Mimics a nucleic acid base
Concentrated in fast growing cells
Alkylating agents
Chlormethine analogues
Cl
N
Cl
HOOC
Chlorambucil
C l
N
C l
H O O C
N H 2
H
M e l p h a l a n
•Urethane group is electron-withdrawing
•Lowers nucleophilic strength of nitrogen
•Alkylating group is attached to oestradiol
•Steroid is hydrophobic
•Capable of crossing cell membranes
OHMe
ON
O
Cl
Cl
H
HH
H
Estramustine
Urethane
Alkylating agents
Chlormethine analogues
O
P
H2N O
NR2
O
H
H
O
P
NH O
NR2
HO
Cytochrome
P450 enzymes
H+
HO
P
Cl
Cl
N
OH2N
H
O
Alkylating agent Acrolein
O
P
NH O
NR2
Cyclophosphamide
• Cyclophosphamide is the most commonly used alkylating agent
• Non-toxic prodrug (Orally active) and requires CYP450 for activation
• Acrolein is toxic metabolite responsible for hemorragic cystitis
Cyclophosphamide
Mechanism of action
toxic
Indications: Malignant lymphomas, mycosis
fungoides and leukemias; several non-
malignant diseases: severe rheumatoid
arthritis and systemic lupus erythematosus.
Other Toxicity: Myelosuppression, Alopecia,
Cardiotoxicity, immunosuppressive
Acrolein toxicity can be avoided by co-administration with
N-acetylcysteine, or mercaptoethanesulfonate.
Cl
HN
Cl
O P
Cl
Cl
Cl
-HCl
Cl
N
Cl
P
Cl
Cl
O(C2H5)2NH
Dioxane (20-30 0C)
H2N
HO
Cl
N
Cl
P
O
HN
O
Cyclophosphamidebis(2-chloroethyl)amine
Synthesis of Cyclophosphamide
Ifosfamide
It is closely related in structure, clinical use,
toxicity with Cyclophosphamide
Prodrug: requires CYP450 for activation
Acrolein is toxic metabolite
Indications: Germ cell testicular cancer
Side effects: Hemorrhagic cystitis, CNS problems such as confusion and coma
O
N NH
NO
Cl Cl
Carmustine
O
N NH
NO
Cl
Lomustine
Alkylating agents: Nitrosoureas
Carmustine
• Indications: Palliative treatment for brain tumors, multiple myeloma,
Hodgkin’s and non-Hodgkin’s lymphomas
• Non-vesicant, I.V. or topical
• Highly lipid soluble (may cross BBB)
• Long delay in bone marrow suppression (6 weeks) - do not give more often
than every 6 weeks
Lomustine
• Indications: Brain tumors and Hodgkin’s disease
• Bone marrow toxicity is cumulative - delayed for 6 weeks
• Capsule: take on empty stomach to avoid N/V
• Highly lipid soluble allows 50% higher CNS levels
Cl
N2 + HO
Alkylatingagent
ClN N
N
O
O
R
H
Nitrosoureas
• Decompose in the body to form an alkylating agent and a carbamoylating agent
• Alkylating agent causes interstrand cross-linking between G-G or G-C
• Carbamoylating agent reacts with lysine residues on proteins
• May inactivate DNA repair enzymes
O C N R
ClN
NOH
+
Isocyanate(carbamoylating agent)
H O
ClDNA
X Y
Cl
X Y
Cross-linking
DNA DNA
AlkylationAlkylatingagent
O C N R
Isocyanate
Protein-Lys-NH2
Protein-Lys-NH
O
HN RCarbamoylation
Sulfonate
(good leaving group)
Busulfan: Myleran®, Busulfex ®
Notes
• Synthetic agent used as an anticancer agent
• Causes interstrand cross-linking
• Very well tolerated drug but severe myelosuppression
• Discontinue at first sign of bone marrow abnormalities
• Can cause hyperuricemia—use allopurinol to avoid
OO
SMe
OO
SMe
OO
OO
SMe
OO
SMe
OO
HN
N N
N
O
H2N
Guanine
DNA
N
N
DNA
-MeSO3-
OSO2Me
N
N
DNA
-MeSO3-
N
N
DNA
N
N
DNA
Other Alkylating Agents
Mechanism of Action
Thiotepa: Thioplex®
Other Alkylating Agents: Aziridines
N
N
NP
S
Thiotepa - Thioplex®
Tris-1-aziridinylphosphine sulfide
• MOA: Alkylates by ethyleneimine radical disrupting DNA
• Monitor renal and hepatic function - decrease dosage as
appropriate
• Monitor blood counts for at least three weeks following cessation
of therapy - very highly toxic to bone marrow - discontinue if
sharp drop in WBC’s or platelets
• Indications: Adenocarcinoma of the
breast or ovary, urinary bladder
papillary carcinoma, lymphomas
• IV use only
Procarbazine HCl: Matulane®
Other Alkylating Agents: Methylhydrazines
• Indications: Hodgkin’s disease
• MOA: Free radical methylation of
DNA: results in cessation of protein,
DNA and RNA synthesis
NH
NH
CH3
NH
CH3
OCH3
Procarbazine HCl - Matulane®
Caution
• Initial treatment should be considered via hospitalization due to
hepatic and renal impairment - metabolism in liver and kidneys
produce cytotoxic metabolites.
• Capsules, warn patients of ethanol-disulfiram like reactions,
avoid sympathomimetics such as cold-cough preps and tyramine
containing foods due to possibility of hypertensive crisis.
Procarbazine
Mechanism of Action
Other Alkylating Agents: Methylhydrazines
HN N
CONH2NN
NH3C
CH3
Dacarbazine:
• Prodrug activated by demethylation in liver
• Decomposes to form a methyldiazonium ion
• Alkylates guanine groups
HN N
CONH2NN
NH3C
CH3
Cyt P-450
liver
HN N
CONH2NN
N
CH3OHH
HN N
CONH2NHN
N
CH3
-CH2O
H
HN N
CONH2H2N
N N CH3
AIC
Methyldiazonium ion
N2 + CH3
O6-Methylguanine-DNA
DNA
Mechanism of Action
O
O
N
H2N
Me
CH2OCONH2
NH
OMe
Mitomycin C
Prodrug activated in the body to form an alkylating agent
One of the most toxic anticancer drugs in clinical use
Other Alkylating Agents
-MeOH
O
OH
N
H2N
Me
CH2OCONH2
NH
H
H
Ring
opening
-H +
O
OH
N
H2N
Me
CH2OCONH2
NH2
Alkylating agent
OH
OH
N
H2N
Me
CH2
NH2
NH-DNA
O
C
O
NH2
H2N-DNA
H
-CO2
-NH3
OH
OH
N
H2N
Me
CH2
NH2
NH-DNA
NH-DNA
Crosslinked DNA
Reduction
OH
OH
N
H2N
Me
CH2OCONH2
NH
OMe
OH
OH
N
H2N
Me
CH2
NH2
NH
NH
HN
N N
N
O
HN
N N
N
O Guanine
Guanine
H
H2N-DNA
O
O
N
H2N
Me
CH2OCONH2
NH
OMe
Mitomycin C
• Neutral inactive molecule acting as a prodrug
• Platinum covalently linked to chloro substituents
• Ammonia molecules act as ligands that bound irreversibly by
coordinate covalent bonds
MOA
• Activated in cells with low chloride ion concentration
• Chloro substituents are replaced with neutral water ligands
• Produces positively charged species that react with DNA
Cisplatin: Platinol®
PtNH3Cl
NH3Cl
H2O
Pt
NH3H2O
NH3Cl
Pt
NH3H2O
NH3H2O
+ 2+
+
DNAPt
NH3DNA
NH3DNA
Cisplatin
Metallating agentsPt
Cl
Cl
H3N
H3NCisplatin
Diamminedichloroplatinum
• Binds to DNA in regions rich in guanine units
• Intrastrand links are formed rather than interstrand link
• It binds to N-7 and O-6 positions of adjacent guanine molecules
• Hydrogen bond involved in base-paring guanine to cytosine are
disrupted by the cross-links
• Causes localised unwinding of the DNA double helix
• Inhibits transcription
Pt
NH3Cl
NH3Cl
Metallating agents
Cisplatin
HN
N N
N
O
CH3
H2N
1
23
4
56
7
8
9
Guaninehttps://www.youtube.com/watch?v=Wq_up2uQRDo
https://www.youtube.com/watch?v=Wq_up2uQRDo
Cisplatin
Mechanism of Action
PtH3N
H3NO
O
O
O
Pt
OAc
OAc
ClCl
H3NNH2
H2N
NH2
Pt
O
O O
O PtNH3Cl
NCl
Me
Carboplatin
Less side effects
JM216
First orally
active analogue
Oxaliplatin
Approved in 1999
Picoplatin
Metallating agents
Cisplatin analogues
Adverse effects Cisplatin Carboplatin Oxaliplatin
Nephrotoxicity ++ + -
GI toxicity +++ + +
Peripheral neurotoxicity +++ - ++
Ototoxicity + - -
Hematologic toxicity + ++ +
Hypersensitivity - + -
Comparative adverse effect profiles of platinum drugs
Part II
Drugs acting on enzyme
(Antimetabolites)
ANTIMETABOLITES
Antimetabolite are structurally related tonormal compounds within the cell.
Antimetabolite generally interfere with the availability of normalpurine or pyrimidine nucleotide precursors either
by inhibiting their synthesis or
by competing with them in DNA or RNA synthesis.
Antimetabolites are S phase-specific drugs that are structuralanalogues of essential metabolites and that interfere with DNAsynthesis.
Myelosuppression is the dose-limiting toxicity for all drugs in thisclass.
Antimetabolites: Sites of Drug Action
ANTIMETABOLITES
Pyrimidine Antagonists
Methotrexate, Fluorouracil, Floxuridine, Tegafur
Purine Antagonists
Mercaptopurine, Thioguanine
DNA Polymerase/ DNA Chain Elongation Inhibitors
Cytarabine, Gemcitabine, Fludarabine, Cladribine, Clofarabine
Miscellaneous Antimetabolite
Hydroxyurea
Antimetabolites
Pyrimidine Antagonists: deoxythymidine monophosphate (dTMP)
Synthesis Inhibitors
Indirect Inhibitors: Dihydrofolate reductase (DHFR) inhibitors
Methotrexate
Direct Inhibitors: Thymidylate synthase inhibitors
Fluorouracil, Floxuridine, Tegafur
Antimetabolites
Pyrimidine Antagonists: Dihydrofolate reductase (DHFR) inhibitors
Methotrexate (MTX)
The structures of MTX and folic acid are similar.
MTX is actively transported into mammalian cells and inhibits
dihydrofolate reductase (DHFR), the enzyme that normally converts
dietary folate to the tetrahydrofolate (THF) form required for thymidine
and purine synthesis.
Adverse Effects:
MTX is myelosuppressive, producing severe leukopenia, bone marrow
aplasia, and thrombocytopenia.
This agent may produce severe gastrointestinal disturbances.
Renal toxicity may occur because of precipitation (crystalluria) of the 7-OH
metabolite of MTX.
Methotrexate
Methotrexate
Methotrexate: Mechanism of Action
The structures of MTX, folic acid and DHF are similar
MTX inhibits dihydrofolate reductase (DHFR) and prevents conversion of
THF to cofactor N5,N10-THF
Depletion of cofactor (N5,N10-THF) effects thymidylate synthase and
lowered synthesis of dTMP (DNA synthesis)
Methotrexate
Methotrexate
Methotrexate: Mechanism of Action
DHFR
DHFR
Pyrimidine Antagonists: Thymidylate synthase inhibitors
5-Fluorouracil
5-Fluorouracil (5-FU) act as a prodrug which is converted to the
fluorinated analogue of 2’-deoxyuridylic acid monophosphate (5-FdUMP)
5-FdUMP competes with deoxyuridine monophosphate (dUMP) for the
enzyme thymidylate synthetase
5-FdUMP inhibits thymidylate synthetases and prevents the synthesis
of dTMP, a major building block of DNA.
H N
N
O
O
R
H
R = H U r a c i l
R = F 5 - F l u o r o u r a c i l
R = C H 3 T h y m i n e
H N
N
O
O
R
O
H 2 C
OP
- O O H
O
O H
H N
N
O
O
R
O
H 2 C
O H
O H
T h y m i d y la t e s y n t h a s e
R = H d U M P
R = F 5 - F d U M P
R = H
R = C H 3 d T M P
R = F 5 - F d T M P
5-Fluorouracil: Mechanism of Action
(major building block of DNA)
5-Fluorouracil (5-FU)
Adverse Effects:
• Fluorouracil may cause nausea and vomiting, myelosuppression,and oral and gastrointestinal ulceration.
• With fluorouracil, myelosuppression is more problematic after
bolus injections, whereas mucosal damage is dose-limiting with
continuous infusions.
Tegafur
• It’s a 3-tetrahydrofuranyl derivative of 5-FU
• It is a prodrug slowly metabolized to 5-FU
H N
N
O
O
O
F
T e g a fu r
Antimetabolites
Purine Antagonists:
All thiopurines: azathioprine, 6-mercaptopurine, 6-thioguanine are prodrugs
Azathioprine is converted to 6-mercaptopurine (6-MP) by non-enzymatic
activation in red blood cells
N
N NH
N
Purine
6-Mercaptopurine (6-MP)
N
N NH
N
S H
1
2
6
4
5
3
7
8
9
6-Thioguanine (6-TG)
N
N NH
N
S H
H 2 N
6
N
N NH
N
H 2N
Guanine
Incorporated into
DNA & RNA
causing cell death
Purine
biosynthesis
HGPRT
HGPRT
(Inactive)
(Inactive)
Mechanism of Action of Azathioprine, 6-Mercaptopurine, 6-Thioguanine
HGPRT = Hypoxanthine–guanine
phosphoribosyltransferase
TPMT =Thiopurine S-methyltransferase
XO = Xanthine oxidase
TIMP = Thio inosine monophosphate
TGMP = thio guanosine monophosphate5-phosphoribosylamine5-phosphoribosylpyrophosphate
• Azathioprine is converted to 6-mercaptopurine (6-MP) by non-enzymatic
activation in red blood cells.
• The enzyme hypoxanthine–guanine phosphoribosyltransferase (HGPRT)
convert (activate) 6-MP into thio inosine monophosphate (TIMP) and 6-TG
into thio guanosine monophosphate (TGMP).
• In catabolic reactions, thiopurine S-methyltransferase (TPMT) inactivates
6-MP and 6-TG by S-methylation and form Me-6-MP and Me-6-TG
xanthine oxidase (XO) converts 6-MP to 6-thiouric acid.
• TIMP and TGMP are also TPMT substrates.
• TIMP and Methylated TIMP (meTIMP), but not meTGMP, is an effective
inhibitor of de novo purine biosynthesis by preventing the first step
conversion of 5-phosphoribosyl pyrophosphate in to 5-phosphoribosylamine.
• TIMP that escapes catabolism is further metabolized by inosine monophosphate
dehydrogenase (IMPDH) and guanine monophosphate synthetase (GMPS) to
TGMP.
• TGMP is converted into thioGTP and thio-dGTP (by deoxynucleoside kinases
and reductase) that incorporates into RNA and DNA leading to cell death.
Mechanism of Action of Azathioprine, 6-Mercaptopurine, 6-Thioguanine
6-MP & Allopurinol:
• 6-mercaptopurine is rapidly metabolized in the liver by xanthene oxidase
(XO) enzyme into the inactive metabolite (6-thiouric acid) which are
excreted in the urine.
• So when 6-mercaptopurine is co-administered with allopurinol
(xanthine oxidase inhibitor) its half-life will be increased.
• Allopurinol is used frequently to treat/prevent hyperuricemia caused by
many anticancer drugs.
• If Allopurinol is used with 6-MP then the dose of 6-MP is reduced by
more than 75%
Indications:
• Mercaptopurine is used primarily for the maintenance of remission inpatients with acute lymphocytic leukemia and is given in combinationwith MTX for this purpose.
Adverse Effects:
• Well tolerated.
• Myelosuppression is generally mild with thioguanine.
• Long-term mercaptopurine use may cause hepatotoxicity.
DNA Polymerase/ DNA Chain Elongation Inhibitors:
Cytarabine
• DNA Polymerase catalyse the synthesis of DNA using
the four DNA building blocks (dATP, dGTP, dCTP, dTTP)
• Cytarabine is an analogue of 2’-deoxycytidine
• Cytarabine act as a prodrug.
• In cell, Cytarabine is phosphorylated to triphosphate (ara-CTP) which act as a
competitive inhibitor.
• In addition, ara-CTP can act a substrate for DNA polymerases and become
incorporated into the growing DNA chain leading to chain termination or
prevent replication of the modified DNA causing inhibition of DNA synthesis
• Formulation: Cytarabine is available as a water soluble sterile powder for
intravenous, intrathecal and subcutaneous use.
• Indications: ALL (Acute lymphoblastic leukemia), AML (Acute myelogenous
leukemia), chronic myelocytic leukemia, meningeal leukemia.
• Adverse Effects: High doses can damage the liver, heart, and cause bone marrow
depression.
• Metabolism: metabolized to an inactive product, arabinofuranosyluracil.
O
H O
C H 2
O H
H O
N
N
N H 2
O
DNA Polymerase/ DNA Chain Elongation Inhibitors
O
H O
C H 2
O H
H O
N
N
N H 2
O
O
F
C H 2
O H
H O
N
N
N H 2
O
H
C l -
F
Cytarabine Gemcitabine
N
N N
N
N H 2
F
O
H O
C H 2
O H
OP
O
H O
O H
N
N N
N
N H 2
C l
OC H 2
O H
H O
N
N N
N
N H 2
C l
OC H 2
O H
H O
F
Cladribine Clofarabine
Fludarabine phosphate
Miscellaneous Antimetabolites
Hydroxyurea
• Prevent DNA synthesis and DNA repair by inhibiting
ribonucleotide reductase.
• Orally bioavailable
Pentostatin and Hydroxyurea (self study)
Pentostatin
Hydroxyurea
Classification of Antibiotics:
• Anthracycline
• Mitomycin C
• Bleomycin
• Actinomycin D
Part III: Anticancer Agents
Antibiotics
Antibiotics
• They are DNA intercalating agents followed by inhibition oftopoisomerase II resulting in strand breakage leading to apoptosis.
• These agents are primarily toxic during the S phase of cell cycle.
• Doxorubicin is probably the most important anticancer drugavailable because of its relatively broad spectrum of activity.
Anthracyclines
O
O
O
O
O
OH
OH
OH
NH2
OH
O
R
CH3
CH3
Doxorubicin: R= CH2OH
Daunorubicin: R=CH3
• Anthracycline antibiotics are
characterized by a planner oxidized
anthracene nucleus fused to a
cyclohexane ring that is connected by a
glycosidic linkage to a amino suger.
• They are initially discovered and
isolated from Streptomyces peucetius.
83
Doxorubicin & DaunorubicinThey:
intercalate between base pairs
inhibit topoisomerase II
generate free radicals
They block RNA and DNA synthesis and cause strand scission
• Doxorubicin is used to treat a broadspectrum of solid tumors as well as acuteleukaemias, lymphomas, and childhoodtumors.
• Daunorubicin is indicated for acuteleukaemias.
Antibiotics
• It is a natural product isolated from Streptomyces verticillataus aswell as from other sources.
• It act as a prodrug activated in the body to form an alkylating agent
Mechanism of action:
• Mitomycin C is an antineoplastic antibiotic that alkylates DNA and thereby causes strand breakage and inhibition of DNA synthesis.
Adverse Effects:
• Mitomycin produces prolonged myelosuppression that preferentially affects platelets and leukocytes.
O
O
N
H2N
Me
CH2OCONH2
NH
OMeMitomycin C
Antibiotics
• The actinomycins are a class of polypeptide antibiotics isolated
from soil bacteria of the genus Streptomyces, of which the most
significant is actinomycin D.
• Actinomycin D intercalates DNA and thereby prevents DNA
transcription and messenger RNA synthesis.
• The drug is given intravenously, and its clinical use is limited to the
treatment of trophoblastic (gestational) tumors and the treatment
of pediatric tumors.
Actinomycin D
Planar phenoxazinonering system
Bleomycin
Planar bi-thiazole ring system:intercalate DNA double helix
primaryamine
pyrimidine
disaccharide
imidazole
very rich electron functional group;
chelate with intracellular Fe2+
• Bleomycins were first discovered in 1966.• Bleomycin is a mixture of Bleomycin A2 and B2 isolated from
Streptomyces verticillus. It is used by IV/IM in combination therapy fortreatment of certain types of skin cancer, and testicular carcinoma.
Antibiotics
Mechanism of Action:• The drug has its greatest effect on
neoplastic cell in the G2 phase of thecell replication cycle.
• Bleomycin intercalates DNA, andacts through binding to DNA, whichresults in single and double strandbreaks following free radicalformation and inhibition of DNAsynthesis.
• The DNA fragmentation is due tooxidation of a DNA-bleomycin-Fe(II) complex and leads tochromosomal aberrations
Bleomycin
Clinical indication: carcinoma of cervix, head and neck, larynx, penis,skin, testes, Hodgkin’s and non-Hodgkin’s lymphoma.
Adverse Effects: Myelosuppression, Pneumonitis/pulmonary fibrosis
88
Plant Alkaloids
Vinca Alkaloids
Vinblastine
Podophyllotoxins
Etoposide
Camptothecins
Topotecan
Taxanes
Paclitaxel
Part IV: Anti-Cancer Plant Alkaloids
Mitotic inhibitors
• Mitotic inhibitors are often plant alkaloids and other compounds
derived from natural products. They can stop mitosis or inhibit
enzymes from making proteins needed for cell reproduction.
Paclitaxel Vincristine
Tubulin-Binding Agents
Vinca Alkaloids: Vinicristine and vinblastine
• These are obtained from Catharanthus roseus (Vinca rosea).
• They are dimeric indole-dihydroindole derivatives.
• These drugs block the formation of mitotic spindle/filaments for
nuclear and cell division by preventing the
assembly/polymerization of tubulin dimers into microtubules.
N
NH
NH
+
NH+
R
O
OH
O
OO
O
O
O
OH
CH3
CH3
CH3
CH3
CH3
CH3
H
S
O-
O-
O
O
Vincristine R = CHO
Vinblastine R = CH3
Vinka alkaloids
×
Vincristine sulfate (Oncovin®)
Uses:
• Leukemias, lymphomas, sarcomas,
and some carcinomas
Vinblastine sulfate (Velban®)
Uses:
• Vinblastine, the more active compound, has much wide clinical
application, including solid tumors, especially in combination with
drugs such as cisplatin and BLM (bleomycin)
• Testicular tumor
• Advanced Hodgkin’s disease
• Breast carcinoma
Anti-Cancer Plant Alkaloids
• Paclitaxel and the semisynthetic analogue Docetaxel represent the
taxane family of drugs that inhibit tubulin depolymerisation.
• Paclitaxel was isolated from the bark of Yew trees Taxus brevifola in
1962.
• A full synthesis was achieved in 1994.
• The semisynthetic route involves docetaxel as an intermediate.
• The term Taxoids is used generally for paclitaxel and its derivatives.
• MAO: The taxoids binds to β-subunit of tubulin and accelerates
polymerisation as well as stabilises the resultant microtubules,
which means that depolymerisation is inhibited. As a result, the cell
division cycle is halted.
Mitotic Inhibitors
(Tubulin-Binding Agents)
Paclitaxel (Taxol) and Docetaxel
Vinka alkaloids
×
×
Indirect
Paclitaxel (Taxol)
Direct
√
Stabilise
Paclitaxel (Taxol)
NH
O
O
OO
O O
O
O
O
OHO
O
CH3
OH
OH
CH3
CH3
CH3
CH3
CH3
Uses
• Leukemias, sarcomas,
• Lung cancer
• Ovarian and breast carcinoma
Side effects: Hair loss, muscle
and joint pains, and diarrhea
Uses
• Lung cancer
• Ovarian and breast carcinoma
Docetaxel
• Podophyllum resin is obtained from rhizomes or roots of Podophyllumpeltatum (American podophyllum) or Podophyllum emodi (Indianpodophyllum). Family: Berberidaceae.
• It is known as May apple.
Constituents:
• It contains 3.5 - 6% of resin.
• The active principle is the lignans, these include podophyllotoxin 20%,-peltatin 10%, and -Peltatin 5%.
• Etoposide is a lignan derivative obtained semi-synthetically frompodophylotoxin and is used for treatment of small-cell lung cancer,testicular cancer as well as lymphomas and leukemias.
• Etoposide cause inhibition of topoisomerase II resulting in strandbreakage leading to apoptosis.
• Teniposide (synthetic derivative of podophyllotoxin) is also used for the treatment of brain cancer.
96
Podophyllum
Podophyllotoxin TeniposideEtoposide
• It is obtained from the Chinese tree Camptotheca acuminata, and familyNyssaceae.
• This alkaloid showed broad spectrum activity as anticancer but itstoxicity is too high.
• The natural 10-hydroxy camptothecin is more active and is used in Chinafor neck and head cancer.
• The synthetic analogues are 9-aminocamptothecin.
• Particularly, water-soluble derivatives topotecan, irinotecan showed goodfor the treatment of ovarian cancer and colorectal cancer, whilebelotecan (camtobell ® available in USA) is available for small cell lungcancer and ovarian cancer.
• Irinotecan inhibits the action of topoisomerase I by binding totopoisomerase I-DNA complex, and causes double-strand DNA breakageand cell death.
• Side effect of irinotecan: Diarrhea, anemia, hair loss, abdominal cramps,vomiting and nausea (common almost to all chemotherapy).
98
Campetothecine
99
Campetothecine TopotecanIrinotecan
Camptotheca acuminata
Topoisomerase inhibitors
• Interfere with enzymes called topoisomerases, which help
separate the strands of DNA so they can be copied
Topotecan
(topoisomerase I inhibitor)Etoposide
(topoisomerase II inhibitor)
Topoisomerase I and II
https://www.youtube.com/watch?v=EYGrElVyHnU
Hormone therapy
• Drugs in this category are sex hormones, or hormone-like drugs, that
change the action or production of female or male hormones.
• They are used to slow the growth of breast, prostate, and
endometrial (uterine) cancers, which normally grow in response to
natural hormones in the body.
• These cancer treatment hormones do not work in the same ways as
standard chemotherapy drugs, but rather by preventing the cancer
cell from using the hormone it needs to grow, or by preventing
the body from making the hormones.
Tamoxifen Exemestane Estrone
Common Chemotherapy Side Effects
• Although chemotherapy is given to kill cancer cells, it also damages normal
cells.
• The normal cells most likely to be damaged are those that divide
rapidly, for instance:
– Bone marrow/blood cells
– Cells of hair follicles
– Cells lining the digestive tract
– Cells lining the reproductive tract
• Common side effects
– Hair loss
– Anemia
– Infertility
– Infections
– Nausea and Vomiting
– Peripheral Neuropathy
– Second Cancers Caused by Cancer Treatment
Combination of chemotherapy with
other treatments
• Adjuvant chemotherapy
After surgery to remove the cancer, there may still be some cancer
cells left behind that cannot be seen. When drugs are used to kill
those unseen cancer cells, it’s called adjuvant chemotherapy.
Adjuvant treatment can also be given after radiation. An
example of this would be adjuvant hormone therapy after radiation
for prostate cancer.
• Neoadjuvant chemotherapy
Chemotherapy can be given before the main cancer treatment
(such as surgery or radiation). Giving chemotherapy first can
shrink a large cancerous tumor, making it easier to remove with
surgery. Shrinking the tumor may also allow it to be treated more
easily with radiation. Neoadjuvant chemotherapy also can kill small
deposits of cancer cells that cannot be seen on scans or x-rays.
Other types of chemotherapy drugs
• Targeted therapies - e.g. imatinib (Gleevec®), gefitinib (Iressa®),
– Attack cancer cells more specifically than traditional chemotherapy drugs
– Most attack cells with mutant versions of certain genes, or cells that
express too many copies of a particular gene
• Differentiating agents – e.g. retinoids, tretinoin (ATRA or Atralin®)
– Make cancer cell mature into normal cells
• Immunotherapy – e.g. rituximab (Rituxan®), cancer vaccines
– Stimulate natural immune systems to recognize and attack cancer cells
– Active immunotherapies stimulate the body’s own immune system to
fight the disease
– Passive immunotherapies do not rely on the body to attack the disease;
instead, they use immune system components (such as antibodies) created
outside the body.
What is targeted therapy?
• Cytotoxic chemotherapy preferentially selects for rapidly dividing cells,
which means that it affects both highly proliferative normal tissues (e.g.,
hair, the linings of the gastrointestinal tract, bone marrow) and malignant
cells.
• Targeted therapy
– Medication or drug that targets a specific pathway in the growth and
development of a tumor cell.
– The targets themselves are typically various molecules (or small
particles) in the body that are known or suspected to play a role in
cancer formation.
– Monoclonal antibodies or small molecule inhibitors directed against
molecules that are either overexpressed or mutated in cancerous cells.
– Many of these targets are tyrosine kinases, which are enzymes found
within cells that transfer phosphate groups and affect molecular
signaling.
Epidermal Growth Factor Receptor (EGFR)
• EGFR exists on the cell surface and is activated
by binding of its specific ligands
• Upon activation by its growth factor ligands,
EGFR undergoes a transition from an inactive
monomeric form to an active homodimer.
• EGFR dimerization stimulates its intrinsic
intracellular protein-tyrosine kinase activity.
• As a result, autophosphorylation of several
tyrosine (Y) residues in the C-terminal domain
of EGFR occurs.
• This autophosphorylation elicits downstream
activation and signaling leading to DNA
synthesis and cell proliferation.
• Mutations that lead to EGFR overexpression or
overactivity have been associated with a number
of cancers, including lung cancer.
Gefitinib (IRESSA®)
• Gefitinib targets the
EGFR family of receptors
mainly in lung cancer.
• Inhibits EGFR tyrosine
kinase by binding to the
adenosine triphosphate
(ATP)-binding site of the
enzyme.
• Thus the function of the
EGFR tyrosine kinase
transduction cascade is
inhibited, and malignant
cells are inhibited.
HER2 and cancer
• Amplification or over-expression of the HER2 (human epidermal growth
factor receptor 2) oncogene occurs in approximately 15-30% of breast
cancers.
• Over expression of HER2 is strongly associated with increased disease
recurrence and a poor prognosis.
• Signalling through this receptors promotes cell proliferation and opposes
apoptosis, and therefore must be tightly regulated to prevent
uncontrolled cell growth from occurring.
Trastuzumab (Herceptin)
It is a monoclonal antibody that interferes with the HER2/neu
receptor.
Trastuzumab is effective only in cancers where HER2 is over-expressed.
Hallmarks of Cancer: The Next Generation
Source: Cell , Volume 144, Issue 5, Pages 646-674
(DOI:10.1016/j.cell.2011.02.013)
