The cytotoxicity of methyl protoneogracillin (NSC-698793) and gracillin (NSC-698787), two steroidal saponins from the rhizomes of Dioscorea collettii var. hypoglauca, against human cancer cells in vitro

In our continuous studies of anticancer activity of steroidal saponins from the rhizomes of Dioscorea collettii var. hypoglauca (Dioscoreaceae), methyl protoneogracillin (NSC-698793) and gracillin (NSC-698787) were tested for cytotoxicity against human cancer cell lines from leukemia and eight solid tumor diseases. As a result, methyl protoneogracillin was cytotoxic against all the test cell lines with GI(50) < 100 muM, especially selectively against two leukemia lines (CCRF-CEM and RPMT-8226), one colon cancer line (KM12), two central nervous system (CNS) cancer lines (SF-539 and U251), one melanoma line (M14), one renal cancer line (786-0), one prostate cancer line (DU-145), and one breast cancer line (MDA-MB-435), with GI(50) less than or equal to 2.0 muM. Leukemia, CNS cancer, and prostate cancer were the most sensitive subpanels, while ovarian cancer was the least sensitive subpanels. The preliminary toxicity studies showed that the maximum tolerant dose was 600 mg/kg for methyl protoneogracillin to mice. Gracillin was cytotoxic against most cell lines with GI(50), TGI and LC50 at micromolar levels, but no activity against EKVX (non-small cell lung cancer), HT29 (colon cancer), OVCAR-5 (ovarian cancer), and SN12C (renal cancer). Based on structure-activity relationship, C-25 R/S configuration was critical for leukemia selectivity between methyl protoneogracillin and methyl protogracillin. F-ring was critical to selectivity between furostanol (methyl protoneogracillin and methyl protogracillin) and spirostanol (gracillin) saponins in this study. By an analysis of COMPARE software, no compounds in the NCI's database had similar mean graphs to those of methyl protoneogracillin and gracillin, respectively, indicating potential novel mechanism(s) of action involved. Put all in together, methyl protoneogracillin has been selected as a potential anticancer candidate for hollow fiber assay to nude mice, but gracillin will not be pursued due to lack of selectivity against human cancer diseases. Copyright (C) 2003 John Wiley Sons, Ltd.