The different response to NAD+ observed in the 2 cancer cell lines could be due to heterogeneities in the NAD+ pathways, as differences in nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in NAD+ biosynthesis, allows for selective killing in gastric cancer cells without harming normal tissues.52 Further characterization of NAD+ metabolism is needed to shed light on the various effects in cancer by NAD+. Here, NAMPT is linked to cancer.