CUCURBITACIN-E TARGETS PROLIFERATING ENDOTHELIA

Tumor vasculature offers a target for drugs directed against prolifera ting endothelia. We hypothesized that cucurbitacin E (CuE), an actin-d isrupting agent, would preferentially inhibit proliferating vs, quiesc ent endothelia. Log-phase and confluent ECV304 and HUVEC human endothe lial cells were exposed to 10-200 nM CuE for 1-96 hr, and toxicity was determined at 2-6 days by sulforhodamine B assay. Confluent ECV cells were scraped by Q-tip to allow proliferation at the margin and expose d to CuE at LD50, and the actin cytoskeleton was stained by rhodamine- phalloidin. Cell cycle analysis was performed by flow cytometry. Log-p hase cells were significantly inhibited compared to confluent. LD50's of log-phase cells were much less than for confluent cells (12 vs. 170 nM, ECV; 13 vs 76 nM, HUVEC), Persistent growth inhibition required 2 4-96 hr exposure to LD50. Followed less than 6 hr exposure. CuE induce d F-actin to accumulate centrally in clumps in newly proliferating cel ls; actin appeared normal in quiescent cells. CuE treated endothelial cells were not blocked at cytokinesis. CuE preferentially potently inh ibits proliferating human endothelia compared to quiescent cells in vi tro. CuE induces depolymerization of F-actin in proliferating cells. A t low concentrations, cucurbitacin E may potently inhibit vascular pro liferation by disrupting actin, (C) 1997 Academic Press.