Marrow Microenvironmental Pathobiology and Therapeutic Opportunities for TP53-Mutated Myelodysplastic Syndrome/Acute Myeloid Leukemia.

Mutations in TP53 inhibit p53 protective behaviors including cell cycle arrest, DNA damage repair protein recruitment, and apoptosis. The ubiquity of p53 in genome-stabilizing functions leads to an aberrant tumor microenvironment in TP53-mutated myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Profound immunosuppression mediated by myeloid-derived suppressor cells, the upregulation of cytokines and cell-surface receptors on leukemic cells, the suppression of native immune regulator cells, and metabolic aberrations in the bone marrow are features of the TP53-mutated AML/MDS marrow microenvironment. These localized changes in the bone marrow microenvironment (BMME) explain why traditional therapies for MDS/AML, including chemotherapeutics and hypomethylating agents, are not as effective in TP53-mutated myeloid neoplasms and demonstrate the dire need for new treatments in this patient population. The unique pathophysiology of TP53-mutated disease also provides new therapeutic approaches which are being studied, including intracellular targets (MDM2, p53), cell-surface protein biologics (immune checkpoint inhibitors, BiTE therapy, and antibody-drug conjugates), cell therapies (CAR-T, NK-cell), signal transduction pathways (Hedgehog, Wnt, NF-κB, CCRL2, and HIF-1α), and co-opted biologic pathways (cholesterol synthesis and glycolysis). In this review, we will discuss the pathophysiologic anomalies of the tumor microenvironment in TP53-mutant MDS/AML, the hypothesized mechanisms of chemoresistance it imparts, and how novel therapies are leveraging diverse therapeutic targets to address this critical area of need.