Synergistic action of genistein and cisplatin on growth inhibition and cytotoxicity of human medulloblastoma cells

Objective: Recent experimental data have shown that dietary soy isoflavones such as genistein can significantly suppress invasiveness and growth of a number of human malignancies. In this study we examined whether genistein, at a concentration typical of plasma levels following soy formula intake, i n combination with cisplatin or vincristine exhibited an additive or synerg istic inhibitory effect on the growth of medulloblastoma cells. Methods: Th ree human medulloblastomas cell lines (HTB-186, CRL-8805 and MED-l)were tre ated with genistein at 6 muM, the maximum reported dietary plasma level in children, combined with cisplatin (0-10 muM) or vincristine (0-1 muM). Mono layer cell growth and cytotoxicity, as measured by colonigenic survival in soft agarose, were then compared in control and drug-treated cultures. Pres ence of apoptosis, using the DNA ladder assay and laser scanning cytometry, was investigated in all cell lines at those concentrations at which an enh ancement of antiproliferative effect of cisplatin and vincristine in presen ce of genistein was observed. Results: Genistein at 6 muM led to a 2.8-fold increase in the monolayer growth inhibitory effect of cisplatin (0.05 muM) in HTB-186 cells (p = 4.5 x 10(-4) by one-tailed t test). Genistein increa sed colonigenic survival inhibition of HTB-186 2.6-old at the same cisplati n concentration (p = 1.5 x 10-4). Genistein caused a 1.3-fold increase in a ntiproliferative effect of cisplatin (0.5 muM) in CRL-8805 cells (p = 3.1 x 10(-4)). Similarly the inhibition of colonigenic survival was enhanced 2.0 -fold in CRL-8805 (p = 1.22 x 10(-5)). The addition of genistein to 0.5 muM cisplatin led to a 1.7-fold increase in monolayer growth inhibition and 2. 4-fold increase in colonigenic survival inhibition of MED-1 cells (p = 8.3 x 10(-4) and p = 1.1 x 10(-4) respectively). These effects were primarily s ynergistic but also additive in nature. The combination of genistein and vi ncristine, as compared to vincristine alone, caused a minimal-to-modest inc rease in antiproliferative effect on medulloblastoma cells studied here. We were unable to detect apoptosis by two methodologies in any of the medullo blastoma lines when genistein was combined with cisplatin or vincristine. C onclusion: These results indicate that genistein at typical dietary plasma levels can significantly enhance the antiproliferative and cytotoxic action of cisplatin and, to a lesser extent, vincristine. The implication for tre atment of medulloblastomas of early childhood may be a reduction in the che motherapeutic dose recommendations of these agents and subsequently a decre ase in the risk of treatment sequelae for these patients. Copyright(C)2000S . Karger AG, Basel.