Tubulin-Destabilizing Agent BPR0L075 Induces Vascular-Disruption in Human Breast Cancer Mammary Fat Pad Xenografts

BPR0L075, 6-methoxy-3-(39,49,59-trimethoxy-benzoyl)-1H-indole, is a tubulin-binding agent that inhibits tubulin polymerization by binding to the colchicine-binding site. BPR0L075 has shown antimitotic and antiangiogenic activity in vitro. The current study evaluated the vascular-disrupting activity of BPR0L075 in human breast cancer mammary fat pad xenografts using dynamic bioluminescence imaging. A single dose of BPR0L075 (50 mg/kg, intraperitoneally (i.p.)) induced rapid, temporary tumor vascular shutdown (at 2, 4, and 6 hours); evidenced by rapid and reproducible decrease of light emission from luciferase-expressing orthotopic MCF7 and MDA-MB-231 breast tumors after administration of luciferin substrate. A time-dependent reduction of tumor perfusion after BPR0L075 treatment was confirmed by immunohistological staining of the perfusion marker Hoechst 33342 and tumor vasculature marker CD31. The vasculature showed distinct recovery within 24 hours post therapy. A single i.p. injection of 50 mg/kg of BPR0L075 initially produced plasma concentrations in the micromolar range within 6 hours, but subsequent drug distribution and elimination caused BPR0L075 plasma levels to drop rapidly into the nanomolar range within 24 h. Tests with human umbilical vein endothelial (HUVEC) cells and tumor cells in culture showed that BPR0L075 was cytotoxic to both tumor cells and proliferating endothelial cells, and disrupted preestablished vessels in vitro and ex vivo. In conclusion, BPR0L075 caused rapid, albeit, temporary tumor vascular shutdown and led to reduction of tumor perfusion in orthotopic human breast cancer xenografts, suggesting that this antimitotic agent may be useful as a vascular-disrupting cancer therapy.