Combined treatment with vitamin C and methotrexate inhibits triple-negative breast cancer cell growth by increasing H2O2 accumulation and activating caspase-3 and p38 pathways.

Methotrexate (MTX) is widely used as both an anticancer and anti-rheumatoid arthritis drug. Although MTX has been used to inhibit the growth of many cancer cells, it cannot effectively inhibit growth of triple-negative breast cancer cells (TNBC cells). Vitamin C is an antioxidant that can prevent oxidative stress. In addition, vitamin C has been applied as adjunct treatment for growth inhibition of cancer cells. Recent studies indicated that combined treatment with vitamin C and MTX may inhibit MCF-7 and MDA-MB-231 breast cancer cell growth through G2/M elongation. However, the mechanisms remain unknown. The aim of the present study was to determine whether combined treatment with low-dose vitamin C and MTX inhibits TNBC cell growth and to investigate the mechanisms of vitamin C/MTX-induced cytotoxicity. Neither low-dose vitamin C alone nor MTX alone inhibited TNBC cell growth. However, combined low-dose vitamin C and MTX had synergistic anti-proliferative/cytotoxic effects on TNBC cells. In addition, co-treatment increased H2O2 levels and activated both caspase-3 and p38 cell death pathways.