Leucovorin enhances curcumin-induced inhibition of cell viability and ferroptosis in colorectal cancer cells.

Colorectal cancer (CRC) is one of the leading causes of cancer-related mortality. Curcumin can inhibit the viability and induce ferroptosis in CRC cells, while leucovorin is known to enhance the cytotoxic effects of fluorouracil in the same cells. Therefore, the present study aimed to investigate whether leucovorin could potentiate curcumin-induced inhibition of cell viability and induce ferroptosis in CRC cells. The CRC cell lines, Caco-2 and HCT116, were treated with 50 µM curcumin, 2 µM leucovorin, a combination of curcumin and leucovorin, or leucovorin pre-treatment followed by co-treatment with curcumin and leucovorin. Cell viability and ferroptosis were assessed after 24 h of treatment. The results indicated that curcumin suppressed the viability of both Caco-2 and HCT116 cells. Furthermore, it also reduced glutathione, mitochondrial membrane potential and the protein expression levels of solute carrier family 7 member 11, while increasing the levels of malondialdehyde, reactive oxygen species, ferrous iron and the expression levels of acyl-CoA synthetase long chain family member 4, thus indicating that curcumin could induce ferroptosis in these cells. Cell treatment with curcumin and leucovorin further suppressed cell viability compared with curcumin alone in both cell lines. Furthermore, this combination, compared with curcumin alone, more notably promoted ferroptosis in HCT116 cells compared with that in Caco-2 cells. However, pre-treatment with leucovorin followed by co-treatment with curcumin and leucovorin had no further effect on cell viability or ferroptosis compared with the synchronous treatment of Caco-2 and HCT116 cells with curcumin and leucovorin. In conclusion, leucovorin could potentiate curcumin-induced inhibition of CRC cell viability and ferroptosis. However, additional leucovorin pre-treatment did not display further benefits compared with curcumin and leucovorin co-treatment. The findings of the present study suggested that curcumin and leucovorin may serve as a potential regimen for the treatment of CRC.