INHIBITION OF MITOSIS AND MICROTUBULE FUNCTION THROUGH DIRECT TUBULINBINDING BY A NOVEL ANTIPROLIFERATIVE NAPHTHOPYRAN LY290181

The mechanism of action of a novel antiproliferative compound LY290181 (3-pyridyl)-4H-naphtho(1,2-b)pyran-3-carbonitrile] was characterized. LY290181 is a potent inhibitor of cell proliferation, producing 50% i nhibition of vascular smooth muscle, endothelial, Chinese hamster ovar y, HeLa, and human erythroleukemia cells at concentrations of 8-40 nM. Cell cycle analysis showed that LY290181 caused accumulation of smoot h muscle cells at the G(2)/M phase and induced mitotic arrest in Chine se hamster ovary cells and HeLa cells. At low concentrations (3-30 nM) , LY290181 blocked transition of cells from metaphase to anaphase and disrupted mitotic spindle organization. At high concentrations (greate r than or equal to 100 nM), LY290181 produced a concentration-dependen t loss of cytoplasmic and spindle microtubules. LY290181 inhibited the polymerization of purified bovine brain microtubule protein into micr otubules, and it depolymerized preformed microtubules. Using tubulin-1 -anilino-8-naphthalene sulfonate complex fluorescence, we have shown t hat LY290181 directly interacted with tubulin in a unique manner. Thes e studies show that LY290181 induces cell growth arrest in prometaphas e/metaphase, and tubulin appears to be its molecular target.