LP533401 hinders leukemia by osteoblast-specific, leukemic blast–independent actions. (A-C) Albino C57BL/6 mice were injected at 2 months of age with EL4-GFP-Luc cells pretreated with serotonin, LP533401, or vehicle for 24 hours. Luminescence intensity at different time points (A), whole body luminescence representative images (B), and overall survival (C) (A-C, n = 9-10 mice per group). (D-F) EL4 cells were infected with either Htr2a shRNA or scrambled shRNA oligos and injected into albino C57BL/6 mice at 3 months of age. Tumor burden and survival were assessed: Luminescence intensity at different time points (D), whole body luminescence images (E), and overall survival (F) (D-F, n = 6-10 mice per group). shRNA, short hairpin RNA.