A first-in-class small-molecule modulator of the p300/CBP interactome exhibits broad efficacy in xenograft models of solid tumors and hematologic malignancies

Background: Dysregulation of the cellular transcription machinery is a fundamental feature of cancer. E1A binding protein (p300) and CREB binding protein (CBP) are two closely related paralog transcription co-activators involved in the expression of oncogenic drivers in cancer cells. Methods: Small molecule ligands of the CH1/TAZ1 domain of p300/CBP were rationally designed and optimized for their anti-proliferative activity in vitro. Subsequent characterization focused on their ability to modulate downstream biological processes controlled by p300/CBP, including hormone-dependent androgen receptor signalling, the HIF-1 alpha/VEGF pathway and reactivation of p53 in HPV-positive carcinomas. The in vivo efficacy of this novel compound class was assessed in a variety of patient and cell line derived xenograft models, and pharmacodynamic effects were investigated. Results: Several modulators of p300/CBP exhibited anti-proliferative effects at low nanomolar concentrations in more than 60 cancer cell lines inducing both senescence and apoptosis in a highly context dependent manner. Transcriptome analyses revealed the downregulation of various drivers of cell cycle progression. Once daily oral administration triggered strong growth-inhibitory effects in several xenograft models up to complete tumor eradication at well tolerated doses. p300/CBP dependent biomarkers like VEGF (colon cancer) and PSA (prostate cancer) were significantly downregulated in the tumors of treated animals. In an orthotopic model of acute myeloid leukemia, the growth of primary tumors and metastasis was almost completely inhibited. Conclusions: Reprogramming the transcriptional profile of cancer cells by modulation of p300/CBP activity by targeting the CH1/TAZ1 domain represents a novel and broadly applicable approach for the treatment of cancer. The presented data illustrate the clinical potential of this new class of therapeutics against a broad variety of tumor types, including prostate and colon cancer as well as hematological malignancies. Citation Format: Bernd Hentsch, Valentino Cattori, Marc Labelle, Ulrich Kessler. A first-in-class small-molecule modulator of the p300/CBP interactome exhibits broad efficacy in xenograft models of solid tumors and hematologic malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2694.