A novel podophyllotoxin-derived compound GL331 is more potent than its congener VP-16 in killing refractory cancer cells

Purpose. GL331 is a new homolog of VP-16, and has demonstrated more efficac ious anti-cancer activity in both the in vitro and in vivo lymphoma systems . To extensively explore GL331's clinical value, we furthermore evaluate th e cytotoxicity and apoptosis-inducing activity of GL331 in several human ce ll lines from cancers that are not normally treated with VP-16. Methods. By MTT and clonogenic survival assays, the cytotoxicities of GL331 and VP-16 were evaluated in a variety of cell lines including nasopharynge al, hepatocellular, gastric, colon, cervical, and neuroblastoma cancer type s. Western blot analysis was performed to detect the MDR-1 level in these c ell lines. By Annexin V-staining flow cytometry and detection of DNA ladder s, the apoptosis-inducing activities of GL331 and VP-16 were also evaluated . Results. GL331 showed more efficacy than its congener VP-16 in killing canc er cells. The estimated ID50 of GL331 were 2.5 to 17-fold lower than those of VP-16. GL331 possessed more cell-killing activity even in MDR-1-overexpr essing cell lines such as HCC36 and SW620. Its higher cytotoxicity could be attributed by the elevated ability to induce apoptotic cell death. Conclusion. GL331's overriding drug resistance and higher cancer cell-killi ng activity suggest its superiority in clinical cancer therapy.