Therapeutic Angiogenesis: Protein and Gene Therapies offer Hope to Patients with Myocardial Ischemia

Ryan McAuleyDept. of Biology

Furman UniversityGreenville, SC

• Palo Alto Veterans Affairs Healthcare System• Stanford University School of Medicine

Department of Cardiology

Outline

• Overview of Myocardial Ischemia: etiology, diagnosis, symptoms, and conventional treamtents

• Angiogenesis: history and development

• Overview of current studies

• Results from clinical trials

• Future Studies

Myocardial Ischemia

• Gr. ischein “to hold back” + haima “blood”• Caused by:

-Stenosis of coronary arteries

-Acute blockage• Coronary blood flow inadequate for maintaining

cardiac function• Result: cardiac muscle is deprived of essential

nutrients and gas exchange• Symptoms: most common is angina pectoris

Diagnosis• Electrocardiogram (ECG)

• Exercise Tolerance Test (ETT)

• Myocardial Perfusion Imaging

Treatment

• Complications include: myocardial infarction, cardiac arrhythmias, CHF, and low quality of life

• Pharmacotherapy: combination of drugs-antiplatelet agents-antithrombotic drugs-lipid-lowering drugs-anti-anginal drugs

• Invasive Therapies: -CABG and PCI

Limitations

• Symptoms not relieved by drugs• Patient is not good candidate for invasive

procedures

Angiogenesis• Offers hope to these “no-option” patients.• Current clinical trials to assess safety and efficacy for

FDA approval• Definition: extension of already formed primitive blood

vessels by budding of new capillaries through proliferation and migration of endothelial cells

• Takes place during embryonic development and combined with vasculogenesis, is responsible for development of the circulatory system

• Naturally-occurring process in adults that is prompted by hypoxia or ischemia after occlusion of an artery

Meet the Growth Factors

• Fibroblast Growth Factor (FGF)

-Peptide Family

-Cross-species homology

-Targets: endothelial cells, smooth muscle cells, fibroblasts, myocytes, and some tumor cells

• Vascular Endothelial Growth Factor (VEGF)

-Glycoprotein Family

-Targets endothelial cells exclusively

The Process

• Hypoxic conditions• VEGF upregulation occurs within 6 hours

due to:-stabilization of mRNA coding-increased transcription due to

activation of Hypoxia-Inducible Factor-1 (HIF-1) in the promoter region of VEGF

• If this is a naturally-occurring process, why do pts. still have disabling chest pain??

The Problem

• Animal studies have shown impaired angiogenesis and reduced endothelial cell viability in olderolder animals

• Decreased angiogenic activity also noted in diabeticdiabetic and hypercholesterolemichypercholesterolemic mice

• Since many patients. with myocardial ischemia have other health problems such as these, angiogenesis does not sufficiently improve coronary blood flow

• Don’t be sad…

BE GLAD!!!

• In all of these cases VEGF supplementation produced favorable results with regards to

and

Endothelial Cell Response

Growth

Early Work• Discovered by Folkman in early 1970’s• Link between vascular GF’s and neovascularization

associated with tumor growth• In 1983, Kumar et al. studied the presence of an

“angiogenesis factor” in the human heart following MI• Mid-1980’s: several polypeptide growth factors

associated with angiogenesis identified and purified• As a result, animal and human studies could be

expanded• Pre-clinical animal studies used an ameroid constrictor to

gradually occlude one of the coronary arteries.• Pigs, dogs, and rabbits have been used for models of

therapeutic angiogenesis

Animal Studies

• VEGF and FGF administered in various amounts and by different routes

• Effectiveness measured by many means including:

-size and number of vessels

-measurement of coronary blood flow

-quantitation of endothelial cell markers• Positive results for protein and genes, but a few

problems

Current Studies

• Endpoints• Gene Therapy Vs. Protein Therapy• Administration Route• Dosage

-Placebo?

Common Endpoints

•Change in total ETT time at baseline and after treatment

•Frequency of angina: # of doses of nitro per week

•Perfusion Imaging: MRI, angiography

ETT Evaluation

ST Segment

ST Segment Depression =

ST segment depression

Normal

Myocardial Ischemia

Data Points from ETT• Time to onset of angina• Time to >1mm change in ST segment• Measurement of HR, BP, and ST segment

depression at maximal exercise (angina pain rated as a 3 out of 4 or exhaustion)

• Measurement of ST segment depression at 1, 3, and 5 minutes recovery

Overview of Current Studies

• Comparisons:-Protein Therapy Vs. Gene Therapy-Administration Route-Dosage

• FDA approval:-Phase I to determine safety/feasibility-All subsequent phases must include

placebo group to determine efficacy

Physical Properties of GF

• GOAL: HighHigh exposure to coronary vessels, LowLow systemic exposure

• Protein Therapy:

-recombinant form of FGF or VEGF• Gene Therapy:

-VEGF or FGF inserted into a viral vector

-Naked DNA plasmid encoding for transcription of VEGF or FGF

Exposure to GF

Need for repeat dose

Readministration

Exposure to foreign genetic material

Systemic Exposure

Protein Therapy Gene TherapyCharacteristicShort-lived Prolonged

More likely Less likely

Easier Potential risk for

inflammatory response if viral

vector used

No Yes

Short-term, Long-term,

but high level but low level

Administration Routes

• GOAL: LeastLeast invasive procedure that allows for OptimalOptimal uptake of GF’s

• Many have been used

• Most common are Intracoronary and Intramyocardial

Dosage• GOAL: Dose is LargeLarge enough to be effective in

coronary arteries, but SmallSmall enough that systemic exposure is not a concern

• Protein Therapy: µg/kg or ng/kg• Gene Therapy:

-number of viral particles-DNA plasmids in units of µg

• Escalating dose groups to determine how side effects and effectiveness are related to the amount of GF administered

• Placebo group shows objective comparison to treatment group and randomization removes physician bias

Results of Phase I Studies

• In all studies, favorable results were reported

• Increased myocardial perfusion shown on MRI and angiography, increased ETT time compared to baseline, and decreased angina

• However, small sample size, lack of placebo group, and nonrandomization result in poor predictive value

Rosengart et al. 1999• n=21

• Randomized: No

• Angiogenic Factor: VEGF121 viral vector

• Administration Route: Intramyocardial

• Results: Improved angiography results, increased exercise time, decreased angina

Results of Phase II Studies

• Not consistently significant

• Dramatically demonstrate normalizing effect of placebo group

Kleiman and Califf 2000FIRST multicenter study

• n=337 total in 3:1 ratio of active agent to placebo• Randomized: Yes• Angiogenic Factor: FGF-2• Administration Route: Intracoronary• Results:

-No significant improvement in exercise time or stress nuclear perfusion imaging at 90 days

-Less angina in treatment group (P=0.057)-Trend toward greater improvement in

older and more symptomatic pts.

What Happened?

• Small sample size

• Insensitive end-points

• Single-administration of GF

• Acute myocardial ischemia in animal models Vs. chronic myocardial ischemia in humans

So…

• While angiogenesis has great potential, more research needed

• Short term goal: prove efficacy in large-scale, placebo-controlled trials

• Determine long-term safety by addressing concerns…

Some Clinical Concerns• Cancer• Abnormal vascular growth in non-target tissues• Immune consequences of using viral vectors

with foreign genetic material• Risks associated with local myocardial delivery• Note: these concerns have not all been validated

in research and the list will most likely evolve in the future

The Future• Variations on the theme that increased

exposure to GF’s yields optimal vascularization

• Multiple doses and/or sustained release of recombinant proteins

• Administration of multiple GF’s

• Administration of HIF-1

• Autologous bone marrow injection

THE ENDSpecial thanks to Dr. Thompson for her support and guidance

through this entire project. To Victor Froelicher, MD and Jonathan Myers, PhD for allowing me the opportunity to work with them and for their

help with my paper. To my uncle Paul McAuley, PhD for the “referral” to the

aforementioned Docs. To Soon-to-be-Dr. Schammel for her encouragement and

technological assistance.To Dr. Turgeon for her help and enthusiasm.

And finally, to Dean Charles Brock, PhD for allowing Furman students the opportunity to participate in internships such as

these through Furman Advantage funding.