Knockdown of CYP3A4 in BMSCs reversed the stromal-mediated FLT3 TKI resistance of FLT3/ITD AML cells. Clonogenic recovery of MV4-11 (A) and Molm14 (B) cells when cultured without F/STRO (Liq), with control F/STRO (CT Stro), or with shRNA CYP3A4 knockdown F/STRO (KD Stro) after treatment with 3 different FLT3 TKIs (20 nM sorafenib, 0.5 nM quizartinib, and 20 nM gilteritinib) for 72 hours. Data represent mean ± standard error of the mean (SEM) of 3 to 4 independent experiments. *P < .05, **P < .01, ***P < .001. CFU, colony-forming unit.