APR-246 and DNA polymerase theta inhibitor Novobiocinsynergize to eliminate TP53 mutant AML cells

Patients with TP53-mutant myelodysplasic syndromes (MDS) and acute myeloid leukemia (AML) are usually elderly and frail with highly resistant malignant clones and a median survival of less than one year. The molecule APR-246 targets mutant p53 but also perturbs redox homeostasis. APR-246 showed favorable safety in a phase 3 trial in TP53 mutant MDS/AML but did not meet efficacy endpoints in combination with azacitidine (AZA), highlighting the need for more effective combination strategies. Conversion of APR-246 to the active compound MQ releases formaldehyde which generates DNA-protein crosslinks. AML cells depend on DNA polymerase theta (Pol[O]) to repair such lesions and Pol[O] protects cells from ferroptosis. Using a panel of isogenic MOLM13 AML cell lines each carrying a common TP53 variant, we show that the Pol[O] inhibitor Novobiocin (NVB) synergizes with APR-246 to induce AML cell death. We demonstrate strong synergy with this combination in all TP53 mutant cell lines and to a lesser extent in the TP53 wildtype and null cells, indicating both p53-dependent and p53-independent mechanisms behind the synergy. APR-246 provides selectivity for TP53-mutated cells while NVB enhances p53-independent apoptosis and p53-dependent ferroptosis. Levels of ferroptosis induction correlate with the observed synergy in TP53-mutant and WT cells. Combination of APR-246 and NVB induces potent in vitro growth inhibition of primary TP53-mutated AML/CMML patient samples, with significant activity achieved at low micromolar or nanomolar concentrations of APR-246. Our findings hold promise for combination of APR-246 and NVB as a new therapeutic strategy tailored for TP53-mutated AML patients with high efficacy and low toxicity.