Abstract. Renal cell carcinoma (RCC) is resistant to chemotherapy partly due to the overexpression of the P-glycoprotein. Several tumor suppressor genes have been reported to be silenced by hypermethylation of the promoter region in RCC. We recently reported that the in vitro cytotoxicity of vinblastine (VBL) was enhanced by pre-treatment with the demethylating agent, 5-aza-2'-deoxycytidine (Aza), in the RCC cell line, Caki-1. In this study, we investigated the combined effect of Aza and VBL in a Caki-1 xenograft model and in other RCC cell lines in vitro. In the xenograft model, tumor volume and weight were significantly suppressed in the co-treatment group, compared to the control, and the expressions of P-glycoprotein, Bcl-2 and cyclin B1 were reduced. Thus, this combined effect could be mediated by the accumulation of intracellular VBL and the enhancement of apoptosis and cell cycle arrest. Moreover, the cytotoxicity of VBL was enhanced in vitro in three RCC cell lines by Aza treatment. These findings suggest that the combination treatment with Aza and VBL is effective against RCC.

Abstract. In this study, we describe the antitumor activity of QO-1, one of the new 2-aryl-1,4-naphthoquinone-1-oxime methyl ether derivatives. QO-1 is a derivative of macarpine, a natural occurring product from Rutaceae plant. It could potently inhibit cell growth when tested on 19 cancer cell lines. To investigate its mechanism, two cell lines (HeLa and MCF-7) sensitive to QO-1 were selected. Based on flow cytometry, it was found to induce G 2 /M-phase arrest. Moreover, it could cause microtubule depolymerization both in vitro and in vivo. On the other hand, QO-1 activated spindle assembly checkpoint (SAC) proteins. Expression of Bub1, one of the SAC, was gradually increased, reaching a peak after 16 -20 h, and then gradually decreased. Instead, QO-1 increased the sub-G 1 population, which suggested a cell death population. Actually, expression of Bcl-2 family proteins and activation of caspase-3/7 were evidences of apoptosis. Consistent with these results, cells with DNA fragmentation and multinucleated cells were increased timedependently after QO-1 exposure. In conclusion, QO-1 has promising antitumor effects via microtubule depolymerization.