One novel strategy for increasing cancer chemotherapy efficacy and reversing chemoresistance involves co-administration of natural chemopreventive compounds alongside standard chemotherapeutic protocols. Sulforaphane is a particularly promising chemopreventive agent, which has been shown to exert proapoptotic effects on tumor cells containing p53 mutations. The p53(Ser220) mutation has been implicated in reduced efficacy and drug resistance in the context of osteosarcomas and breast tumors treated with doxorubicin-based protocols. We investigated the effects of a combination of doxorubicin and sulforaphane on cell viability and apoptosis induction in fibroblasts characterized by different p53 status (p53 wild-type, p53 knock-out, and p53(Ser220) mutation), and identified some of the molecular pathways triggered by the drug combination. Very high concentrations of doxorubicin were necessary to decrease the viability of p53(Ser220) and p53 knock-out (but not wild-type) cells. Treatment of p53(Ser220) and p53 knock-out cells with doxorubicin did not induce apoptosis, also at very high concentrations (10muM). Sulforaphane restored chemosensitivity and induced apoptosis in doxorubicin-resistant p53(Ser220) and p53 knock-out cells, irrespective of p53 status. The induction of apoptosis was caspase-3 dependent and caspase-8 independent. Bongkrekic acid, a mitochondrial membrane stabilizer, partially prevented the effects of doxorubicin plus sulforaphane on mitochondrial permeability but was unable to prevent the induction of apoptosis. N-acetyl-cysteine, a glutathione precursor, blocked the induction of apoptosis by doxorubicin plus sulforaphane. Considering the negligible safety profile of sulforaphane, our findings could prompt innovative clinical studies designed to investigate whether its coadministration can enhance the efficacy of doxorubicin-based regimens.
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