E-3810 is a small molecule inhibitor of VEGFR-1, -2 and -3 and FGFR-1 tyrosine kinases with IC50 <30nM, currently in clinical Phase 1. We have previously shown that in vivo E-3810 as a single agent (s.a.) has potent antitumor activity and strong anti-angiogenic effects (Cancer Res. 2011 Feb 15;71(4):1396–405) and that, when combined with paclitaxel (PTX) in triple negative breast cancer MDA-MB-231 xenograft, E-3810 induces complete regressions with no major safety issues; the E-3810/PTX combination was more active than brivanib/PTX and sunitinib/PTX. PK studies suggested that the increased antitumor activity of the combination was not due to an increase in PTX tumor levels ((Poster #2574, AACR, April 2011, Orlando, FL). In vitro we observed no synergy in the cytotoxic activity of E-3810 and PTX on MDA-MB-231 cells, suggesting that host mediated mechanisms cause the tumor cures in vivo. MDA-MB-231 tumor-bearing mice (n = 4; tumor weight approximately 400 mg) were treated orally with E-3810 (20mg/kg), sunitinb (40mg/kg), brivanib (100 mg/kg) or vehicle for 10 days; on day 7 (4 hours from the anti-angiogenic drug), PTX (20 mg/kg) was administered i.v. and tumor and plasma samples were collected 24 and 72 hours thereafter to evaluate early and late biological pharmacodinamic effects on tumor cells and tumor vasculature. Immuno-histochemical staining of tumor cells for the proliferation marker Ki-67 showed that the positive population was around 30%, with no major differences in the experimental groups both at 24 and 72 hours. A 2- to 20-fold increase over controls in the percentage of cellular necrosis, detected after staining with hematossilin/eosin, was observed in all groups except for PTX s.a., with the highest increase in the E-3810 s.a and the E-3810/PTX groups; a similar trend was observed in the caspase 3/7 activity, indicative of apoptosis. PTX treatment caused no modification in CD31 count compared to controls, whereas a % decrease, ranging from 63 to 90, was seen with E-3810, sunitinb and brivanib s.a and PTX combinations. There was a decreasing trend vs. vehicle (significant at 72 hours) in the collagen IV immunoreactivity only for the E-3810/PTX combination. We assessed, by commercially available ELISA kits, the plasma concentrations of soluble factors including mVEGF, mFGF, msVEGFR and msCollagen IV. Plasma mVEGF values were increased only in E-3810 s.a. and E-3810/PTX treated mice. There was a statistically significant decrease in levels of msVEGFR in mice treated with PTX, E-3810 and brivanib alone and in combination with PTX compared to control mice, while no changes were observed in mice treated with sunitinb alone and in combination with PTX. No change versus controls in the levels of mFGF was found in any of the experimental groups. An increase in plasma levels of soluble collagen IV was observed in mice treated with E-3810 alone or in combination with PTX; an opposite trend was found in mice treated with sunitinb, PTX and their combination whereas levels were unaffected by brivanib treatment as s.a and in combination. Our data suggest that the synergistic activity of the combination E-3810/PTX observed in this model relies on complex and dynamic interactions between tumor cells and host factors and that further studies are warranted to fully understand the relevant mechanism.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C192.