Utilization of Proton Pump Inhibitors in Combination Regimen for Breast Cancer Treatment by Targeting Fatty Acid Synthase

Abstract

Fatty acid synthase (FASN) over-expression has been associated with poor prognosis and recurrence in cancer patients. In addition, it has also been found that overexpression of FASN causes resistance to DNA-damaging treatments by up-regulating the non-homologous end joining (NHEJ) repair of DNA double-strand break. Proton pump inhibitors (PPIs), were originally designed to decrease gastric acid production by binding irreversibly with gastric hydrogen potassium ATPase. PPIs have recently been reported to reduce drug resistance in cancer cells when used in combination with other chemotherapeutics, although the mechanism of resistance reduction is uncertain. In our lab, previous investigation showed that PPIs decreased FASN thioesterase (TE) domain activity and cancer cell proliferation in a dose-dependent manner. In this study, I tested the hypothesis that PPIs sensitize breast cancer cells to doxorubicin and ionizing radiation (IR) treatments by inhibiting FASN. When administered to breast cancer cells as single-agent, lansoprazole exhibited the highest potency in inhibiting both FASN activity and breast cancer cell proliferation, among four PPIs tested. In addition, treatment of breast cancer cells with lansoprazole decreased the mRNA and protein levels of poly (ADP-ribose) polymerase-1 (PARP-1) and NHEJ activity, accompanied by elevated γ-H2AX expression. Following a 3-day treatment with lansoprazole, a dose-dependent disruption in cell cycle disruption and increased apoptosis were also detected. Combination of lansoprazole with either doxorubicin or IR caused profoundly higher levels of DNA damage accumulation than doxorubicin or IR treatment alone, suggesting synergistic effects. Taken together, our observations suggest that PPIs synergistically suppress breast cancer cells in combination with DNA damaging treatments by inhibiting FASN. These findings may provide a potential route to overcome resistance to DNA-damaging chemo/radiation treatments in refractory breast cancers.