Targeting p300 Addiction in CBP-Deficient Cancers Causes Synthetic Lethality by Apoptotic Cell Death due to Abrogation of MYC Expression.

UNLABELLED Loss-of-function mutations in the CBP/CREBBP gene, which encodes a histone acetyltransferase (HAT), are present in a variety of human tumors, including lung, bladder, gastric, and hematopoietic cancers. Consequently, development of a molecular targeting method capable of specifically killing CBP-deficient cancer cells would greatly improve cancer therapy. Functional screening of synthetic-lethal genes in CBP-deficient cancers identified the CBP paralog p300/EP300 Ablation of p300 in CBP-knockout and CBP-deficient cancer cells induced G1-S cell-cycle arrest, followed by apoptosis. Genome-wide gene expression analysis revealed that MYC is a major factor responsible for the synthetic lethality. Indeed, p300 ablation in CBP-deficient cells caused downregulation of MYC expression via reduction of histone acetylation in its promoter, and this lethality was rescued by exogenous MYC expression. The p300-HAT inhibitor C646 specifically suppressed the growth of CBP-deficient lung and hematopoietic cancer cells in vitro and in vivo; thus p300 is a promising therapeutic target for treatment of CBP-deficient cancers. SIGNIFICANCE Targeting synthetic-lethal partners of genes mutated in cancer holds great promise for treating patients without activating driver gene alterations. Here, we propose a "synthetic lethal-based therapeutic strategy" for CBP-deficient cancers by inhibition of the p300 HAT activity. Patients with CBP-deficient cancers could benefit from therapy using p300-HAT inhibitors.