Phenoxodiol, a synthetic analog of genistein, generates ceramide and is equipotent in wild-type and multidrug-resistant human tumor cells

Abstract

2075 Background: Multidrug resistance (MDR) continues to undermine the success of chemotherapy against cancer. Phenoxodiol (PXD, 2H-1-benzopyran-7–0,1,3-[4-hydroxylphenyl]) is a flavonoid derivative that inhibits growth of ovarian, prostate, breast, leukemia, and other human tumor cell lines. We evaluated the potency of PXD in MDR tumor cell lines and their wild-type isogenic variants. We hypothesized that its cytotoxic effect might be linked to increased intracellular production of ceramide, an agonist of apoptosis, and that its efficacy might be independent of MDR status. Methods: Three sets of wild-type and MDR cells were evaluated: KB-3–1 and KB-V1 head/neck epidermoid cancer; MCF-7 and MCF-7-AdrR breast cancer; and SKOV-3 and SKOVBL1.0 ovarian cancer. Cells were seeded into 96-well plates. After 24 hours, PXD was added and cells were incubated for 5 days. Cell viability was determined by colorimetric assay, and the PDX concentration causing 50% cell kill (EC50) was determined. Separate experiments examined the effects of PXD on accumulation of paclitaxel in a paclitaxel-resistant human ovarian cancer line (Igrov/P200) and an MDR1-transfected mouse fibroblast line (77.1/MDR1); both are rich in P-glycoprotein. Ceramide and paclitaxel levels were measured by radiotracer assay. Results: EC50 values of wild-type and MDR isogenic variants were 2.3 and 2.2 μM in head/neck lines, 2.4 and 3.0 μM in breast cancer lines, and 10.8 and 2.7 μM in ovarian lines, respectively. In Igrov/P200 and 77.1/MDR1 cells, PXD concentrations as high as 64 μM had no influence on taxane accumulation. A 24-hour exposure to 4.6 μM of PXD increased ceramide by 2.3-fold in KB-3–1 cells and by similar levels in other cell lines. Conclusions: PXD, which was developed to be more stable than its chemical cousin genistein, does not interfere with taxane uptake and shows high potency in MDR cancer cells. Increased production of intracellular ceramide indicates that PXD induces death-signaling complexes associated with sphingolipid metabolism. The cytotoxicity of PXD in highly drug-resistant tumor cells suggests its clinical utility in patients with advanced, chemorefractory cancer. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novogen