therapeutic angiogenesis
TRANSCRIPT
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
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
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
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.