A thiol-bound drug reservoir enhances APR-246-induced mutant p53 tumor cell death

The tumor suppressor gene TP53 is the most frequently mutated gene in cancer. The compound APR‐246 (PRIMA‐1Met/Eprenetapopt) is converted to methylene quinuclidinone (MQ) that targets mutant p53 protein and perturbs cellular antioxidant balance. APR‐246 is currently tested in a phase III clinical trial in myelodysplastic syndrome (MDS). By in vitro, ex vivo, and in vivo models, we show that combined treatment with APR‐246 and inhibitors of efflux pump MRP1/ABCC1 results in synergistic tumor cell death, which is more pronounced in TP53 mutant cells. This is associated with altered cellular thiol status and increased intracellular glutathione‐conjugated MQ (GS‐MQ). Due to the reversibility of MQ conjugation, GS‐MQ forms an intracellular drug reservoir that increases availability of MQ for targeting mutant p53. Our study shows that redox homeostasis is a critical determinant of the response to mutant p53‐targeted cancer therapy.
Tumor suppressor TP53 is mutated in a large fraction of tumors. APR‐246/Eprenetapopt is the most clinically advanced mutant p53‐targeting drug candidate (Phase III). Besides restoring wild type p53 activity, the active product MQ also disrupts the redox balance, resulting in cancer cell death.