The BCL-XL–specific BH3-mimetic drug A-1331852 inhibits tumor growth in NSG mice that had been transplanted with SNK6 cells. NSG mice were injected subcutaneously (SC) or intraperitoneally (IP) with SNK6, SNT15, or MEC04 cells on day 0. From day 7, A-1331852 or vehicle were delivered once daily to mice by oral gavage for 7 consecutive days. Mice were then monitored for tumor burden. Platelet levels in peripheral blood were examined pretreatment (day 7), posttreatment (day 14), and immediately prior to euthanization. NSG mice were injected intraperitoneally with SNK6 cells (5 × 10⁶ cells) (A), subcutaneously with SNK6 cells (2 × 10⁶ cells) (B), subcutaneously with SNT15 cells (2 × 10⁶ cells) (C), or intraperitoneally with MEC04 cells (5 × 10⁶ cells) (D). Mouse survival curves were assessed for significant differences by the Mantel-Cox test. Platelet and tumor weight data are shown with mean ± standard error (SE), and statistical significance were determined by unpaired Student t test. *P < .05; ***P < .0001. ND, not done.