Anti-angiogenic thrombospondin-1 (TSP1) binds CD36 receptor to trigger apoptosis in vascular endothelium. This causes a secondary signal via CD95/Fas, a death receptor expressed independent of TSP1 by remodeling endothelium. TSP1 increases CD95 cognate ligand, FasL, which binds inducer-generated Fas causing apoptosis. DI-TSP, a short TSP-derived inhibitory peptide generates identical signal. Thus the sensitivity to inhibitory TSP1/DI-TSP is limited by the availability of its primary (CD36), or secondary (CD95) signaling receptors.
We aim to improve susceptibility to DI-TSP by modulating the levels of these rate-limiting signaling mediators. We will modulate CD36 using synthetic ligands of the PPARy nuclear receptor. CD95 we will alter with low-dose continuous (metronomic) chemotherapy. We propose to study: 1. The effects of the low-dose genotoxic agents on DI-TSP specific activity. We will measure Fas and FasL in human microvascular cells (HMVECs) treated with DI-TSP and/or low dose chemotherapy and compare the effects of DI-TSP and/or chemotherapy on the endothelial (EC) and cancer cell phenotype, Fas and FasL presentation, apoptosis and migration. Antibodies, Fas decoy receptor and metabolic inhibitors will be used to link CD95 increase with TSP1 augmented activity. 2. The effects of metronomic chemotherapy DI-TSP angiosuppression in vivo. Mice bearing bFGF-containing Matrigel plugs will be treated with DI-TSP and/or metronomic chemotherapy. The effect on vascularity, Fas and FasL expression, the extent of endothelia l cell apoptosis and pericyte recruitment will be measured. Antibodies, Fas decoy receptor and metabolic inhibitors will be used to link CD95 increase with TSP1 augmented activity. 3. The effects of thiazolinediones (TZDs, synthetic PPARy ligands) on CD36 expression and TSP1 anti-angiogenic activity. EC apoptosis, inhibition of migration, proliferation will be used to determine non-cytotoxic doses of troglitazone, rosiglitazone and pioglitazone, to achieve maximal CD36 increase. These doses will be tested in vivo in matrigel plug assay. CD36 neutralizing antibodies will be used to determine its contribution in vitro and in vivo. 4. The effect of TSP-based combination therapies on tumor growth and angiogenesis. TZDs and metronomic chemotherapy will be used alone and in combination with DI-TSP to block or delay the growth of invasive PC-3 or of less aggressive LNCaP prostate carcinoma. Tumor volume, angiogenesis, EC and non-EC apoptosis will be measured. Angiogenesis inhibitors comprise a new class of anti-cancer drugs. We showed that combining anti-angiogenics with chemotherapy offers possibility to significantly cut the dose and therefore the toxicity of chemotherapy while achieving substantial improvement in the efficacy of an anti-angiogenic. Such combined therapies present a promising new approach to the treatment of cancer and other angiogenesis dependent diseases.
