In many cancers, mortality is associated with the emergence of relapse with multidrug resistance (MDR). Thus far, the investigation of cancer relapse mechanisms has largely focused on acquired genetic mutations. Using acute myeloid leukemia (AML) patient-derived xenografts (PDX), we systematically elucidated a basis of MDR and identified drug sensitivity in relapsed AML. We derived pharmacologic sensitivity for 22 AML PDX models using dynamic BH3 profiling (DBP), together with genomics and transcriptomics. Using in vivo acquired resistant PDXs, we found that resistance to unrelated, narrowly targeted agents in distinct PDXs was accompanied by broad resistance to drugs with disparate mechanisms. Moreover, baseline mitochondrial apoptotic priming was consistently reduced regardless of the class of drug-inducing selection. By applying DBP, we identified drugs showing effective in vivo activity in resistant models. This study implies evasion of apoptosis drives drug resistance and demonstrates the feasibility of the DBP approach to identify active drugs for patients with relapsed AML. Significance: Acquired resistance to targeted therapy remains challenging in AML. We found that reduction in mitochondrial priming and common transcriptomic signatures was a conserved mechanism of acquired resistance across different drug classes in vivo. Drugs active in vivo can be identified even in the multidrug resistant state by DBP.

TP53 mutations are among the worst prognostic factors in acute myeloid leukemia (AML), with affected patients facing relapse-free survival of just five-to-six months compared to TP53 wild-type patients. A major barrier to improving outcomes lies in the dearth of effective therapies, as TP53 mutant patients remain refractory to conventional cytotoxic chemotherapies, targeted therapies, and even allogeneic stem cell transplantation. In this review, we first summarize current clinical strategies and the major setbacks of p53 activators, MDM2/X regulators, and immunotherapy, highlighting the disconnect between promising pre-clinical studies and limited durable clinical responses. We next discuss the mechanisms of therapy resistance in TP53 mutant AML, with specific emphasis on dysfunction in the mitochondrial apoptotic pathway and clonal evolution of TP53 mutant hematopoietic stem cells. We then outline a roadmap for developing tailored therapies that may finally redefine prognosis for this high-risk patient population, including apoptotic activators, cell-cycle modulators, and immune- and metabolic-based therapies. We lastly call attention to new biomarker-driven approaches that can improve patient stratification and optimize identification of responders. By connecting mechanistic understanding with translational insights, this review underscores both the formidable challenges and the emerging opportunities in TP53 mutant AML.

Supplemental table legends 1-4.

Supplemental Figure 8 shows ex vivo DBP profiling in AML PDX models guides generation of drug-resistant PDXs.

Supplemental Figure 5 shows DBP identified drug sensitivities in resistant vs parental AML PDX models.