Genistein interferes with antitumor effects of cisplatin in an ovariectomized breast cancer xenograft tumor model

Genistein (GEN) has been demonstrated to interfere with antitumor effects of cisplatin (CIS) in vitro. To analyze whether these findings are also relevant in vivo, we examined the effects of combined GEN and CIS treatment in an ovariectomized nude mouse breast cancer xenograft model. Tumor growth and markers for antitumor activity were determined after three weeks of treatment. Furthermore, the concentrations of GEN metabolites were measured in serum, liver, and xenograft tumor tissues using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Three weeks’ oral exposure to GEN at a dose of 5 mg kg-1·d-1 resulted in an average concentration of total GEN metabolite equivalent as high as 0.2729 nmol·g-1 wet weight in xenograft tumor tissues. At this dosage, GEN significantly antagonized the antitumor effects of CIS. Mechanistically, GEN blocked both the inhibition of cell proliferation and induction of apoptosis triggered by CIS. Moreover, GEN concentrations in xenograft tumor tissues were found to be significantly higher than in serum and liver. In conclusion, our findings suggested that oral GEN exposure at a level comparable to dietary exposure in humans could interfere with CIS chemotherapy.