NAPRT and B-cell chronic lymphocytic leukemia: Notably, nicotinic acid (NA) supplementation, which blocks FK866 cytotoxic activity by allowing NAD+ biosynthesis through an alternative pathway (via nicotinic acid phosphoribosyltransferase, NAPRT1), completely prevented AMPK phosphorylation in primary B-CLL (Fig. 3b, Additional file 3E), confirming that NAD+ depletion is responsible for AMPK activation.