Fig. 2: Significant vulnerability of SCLC to inhibition of NAD salvage.

a Key metabolic enzymes involved in NAD biosynthesis (shown in green) and potential nutrient sources (blue) taken up by cells. Note that Nam and Trp are the only NAD precursors contained in normal culture medium. See also Fig. 1, which describes substrates required for each reaction. b Effects of siRNA-mediated knockdown of enzymes shown in (a) on NAD levels in 4 SCLC lines. Shown are values relative to those seen in mock-transfected cells, which were defined as 100%. Circles represent individual lines. P<0.0001 (NTC vs NAMPT). c Comparison of relative numbers of cells (relative to the number on day 0) in SCLC and NSCLC lines cultured 4 days with indicated NAMPT-inhibitors (FK866, GNE-617 or TLM-118), each at 20 nM. Each symbol represents an individual cell line. Shown are results of 8 (for FK866) or 7 (GNE-617 and TLM-118) SCLC lines and 8 NSCLC lines. P = 0.0069 (FK866); P = 0.0045 (GNE-617); P = 0.0073 (TLM-118). d Analysis of the DepMap dataset showing effects of NAMPT knock-out on proliferation of cell lines in the CCLE collection. Results were compared in pan-cancer, NSCLC and SCLC categories. P = 0.0001 (SCLC vs NSCLC); P = 0.0017 (SCLC vs Pan-cancer); P = 0.0652 (NSCLC vs Pan-cancer). e Time course analysis of NAD levels in 4 NAMPTi-treated SCLC lines (87-5, H209, Lu-139, and MS-1). Shown is data representative of >2 independent experiments. f Volcano plot of the metabolome of 4 SCLC lines in (e) treated 48 h with or without NAPMTi. Significantly increased or decreased metabolites compared to untreated controls are shown in blue and red, respectively. p values were based on a two-tailed t test. g Summary of ¹³C-glucose tracer experiments in SCLC cells. FK866 treatment blocked glucose metabolism at steps catalyzed by GAPDH, IMPDH and ADSS (thick red lines). Lac., lactate. TCA TCA cycle. h ATP levels in 5 SCLC lines treated 6 h with Koningic acid (KA) (a GAPDH inhibitor) or control vehicle. P = 0.0003. i Proposed model of NAMPT inhibition-induced death of SCLC cells. Data are presented as the mean of measurement duplicates (e) or the mean of biological replicates plus the SEM (b, c, h). **P < 0.01, ***P < 0.001, ****P < 0.0001 as determined by one-way ANOVA with a post hoc test (b, d) or by two-tailed t test (c, h). Source data are provided as a Source Data file.