Cross resistance to diverse anticancer nicotinamide phosphoribosyltransferase inhibitors induced by FK866 treatment

Cross-resistance to drugs remains an unsolved problem in Cancer chemotherapy. This study elucidates a molecular mechanism of cross-resistance to diverse inhibitors of nicotinamide phosphoribosyltransferase (NAMPT) with Anticancer activity. We generated a variant of the human colon Cancer cell line HCT116, HCT116R^FK866, which exhibited primary resistance to the potent NAMPT Inhibitor FK866, and was approximately 1,000-fold less sensitive to the drug than the parental HCT116. HCT116R^FK866 was found to be cross-resistant to diverse NAMPT inhibitors, including CHS-828, GNE-617, and STF-118804. Whole-exon Sequencing revealed two point mutations (H191R and K342R) in NAMPT in HCT116R^FK866, only one of which (K342R) was present in the parental HCT116. Importantly, the protein level, NAMPT Enzyme activity, and intracellular NAD⁺ level were similar between HCT116R^FK866 and HCT116. Hence, we investigated NAMPT-binding partners in both cell lines by focused proteomic analyses. The amount of NAMPT precipitated with anti-NAMPT monoclonal antibody was much higher in HCT116R^FK866 than in the parental. Furthermore, in HCT116, but not in HCT116R^FK866, NAMPT was revealed to interact with POTE ankyrin domain family member E and beta-actin. Thus, these results suggest that NAMPT usually interacts with the two partner proteins, and the H191R mutation may prevent the interactions, resulting in resistance to diverse NAMPT inhibitors.