Search for novel anti-tumor agents from ridaifens using JFCR39, a panel of human cancer cell lines.

To overcome the heterogeneous nature of cancer, the search for potent anti-cancer drug candidates with new modes of action is essential. For that purpose, we prepared forty-eight Ridaifens (RIDs), a novel series of tamoxifen-derivatives. Then, we screened them, searching for novel candidates for a new class of anti-cancer drug using a panel of human cancer cell lines (JFCR39) and by a binding assay to estrogen receptor α (ERα). First, the growth inhibition of the forty-eight RIDs against JFCR39 was evaluated. Forty RIDs showed higher growth-inhibitory activity than that of tamoxifen. The structure-activity relationship (SAR) study revealed that the aminoalkoxyphenyl groups at the C-1 position and the common central ethylenic bond were important in retaining a high level of growth-inhibitory activity. Subsequently, the ERα binding activity of all the RIDs was measured by a competitive binding assay. The SAR study for ERα binding activity indicated that both the phenyl group and the ethyl group at the C-2 position in the ethylenic bond were essential. Based on the screenings, we identified RID-SB1 and RID-SB8, which demonstrated potent tumor growth inhibition but had completely lost ERα binding activity. Furthermore, the COMPARE analysis using JFCR39 suggested that RID-SB1 and RID-SB8 had different molecular modes of action compared to those of the current anti-cancer drugs including tamoxifen. These results indicate that RID-SB1 and RID-SB8 are interesting candidates for novel anti-cancer agents with unique modes of action.