The potent antiproliferative/antitumor compound RAD001 (everolimus) is an mTOR pathway inhibitor in phase II cancer clinical trials. The mTOR pathway is involved in regulation of proangiogenic factor production by tumors and modulation of VEGFR signaling in endothelial cells. The antiangiogenic effects caused by RAD001 were examined, using tumors derived from cell lines considered sensitive (B16/BL6 melanoma, 0.7 nM IC50) or resistant (KB-31 epidermoid 1.8 μM IC50) to RAD001 in vitro. At 5 mg/kg/d, p.o., RAD001 elicited potent antitumor activity in mouse tumor models (T/C: B16/BL6, 24% in primary tumors [P] and 9% in lymph node metastases [M]; KB-31 26%) despite sub-optimal drug exposure in the resistant models (tumor Cmax ∼106 nM). RAD001 treatment reduced tumor vascularization (versus controls, B16/BL6 P, ∼50%, M, ∼65%, and KB-31, ∼54%), and also reduced plasma and tumor VEGF levels, and These effects of RAD001 on angiogenic processes may explain its activity against tumors formed by cells resistant to mTOR inhibition. Comparison of the anti-angiogenic effects of RAD001 with those of PTK787/ZK222584 [PTK787] (a potent, selective small molecule inhibitor of VEGFR tyrosine kinase in phase III clinical trials), indicated overlapping effects on VEGF-induced endothelial cell proliferation but not endothelial cell migration consistent with an integral role of the mTOR pathway in the VEGFR proliferative signaling. The two agents differed in their effects on vascular permeability (significantly reduced by PTK787, while RAD001 was without effect) and the vessel-associated smooth muscle cell population (absence in RAD001-treated tumors, but only reduced in PTK787-treated tumors). Combining RAD001 (1 mg/kg/d and PTK787 100 mg/kg/d) produced profound antitumor effects in the RAD001-sensitive B16/BL6 model (T/C: P 2%, M 9%) as compared with single agents (T/C: RAD001, P 45%, M 33% and PTK787 38% for both P and M). This also occurred with tumors from the RAD001-resistant KB-31 line (T/C, RAD001, 47%, PTK787 61%, combination 31%). In the B16/BL6 model, the combination potently inhibited tumor VEGF and tumor vascularization as compared with single agents. The differential effects of mTOR and VEGFR inhibition on antiangiogenic processes likely contribute to the drug combination effects. Hence, the combination of RAD001 and PTK787 holds strong promise for the treatment of human cancers.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]