Abstract 788: Modeling tumor microenvironmental heterogeneity identifies CREBBP as a novel tumor suppressor in breast cancer

Solid tumors display significant histological, genetic and micro-environmental intra-tumor heterogeneity that can change substantially over the course of their evolutionary trajectory. In particular, changes in the micro-environmental complexity within breast cancer such as hypoxic and nutrient deplete environments are associated with aggressive disease and a poor patient outcome. We sought to identify novel driver alterations in aggressive disease by employing a functional genomics screen in a 3-dimensional model of breast cancer progression that more accurately recapitulates in vivo micro-environmental heterogeneity. Screening of the top 200 recurrently mutated genes in breast cancer in cancer cell line spheroids identified several genes whose silencing impacted growth. A second targeted validation screen in a larger panel of triple negative cell line models showed that silencing of the histone acetyltransferase CREBBP, promoted growth in 3D but had limited effect under traditional 2D culture conditions. Investigation of TCGA and METABRIC datasets showed that CREBBP was more frequently mutated in triple negative breast cancers (TNBCs) and at least a third of TNBCs also displayed gene haploinsufficiency or complete loss of CREBBP. Interrogation of expression and proteomic datasets showed that loss of CREBBP resulted in the upregulation of the pro-proliferative transcription factor FOXM1. Significantly, this conserved FOXM1-driven transcriptional programme was also seen in multiple solid tumors with CREBBP alterations including lung, oesophageal, bladder and endometrial cancers. This was recapitulated in several CREBBP deficient cells where we identified that FOXM1 is driving altered metabolism, allowing cancer cells to grow under nutrient stress conditions. In summary, CREBBP is a bona fide tumor suppressor in up to a third of TNBCs, as well as a wide range of other solid tumors. CREBBP-altered tumors display up-regulation of FOXM1, which alters cancer cell metabolism under nutrient stress conditions. Moreover, CREBBP-altered tumors are selectively sensitive to small molecule inhibitors that target FOXM1 activity, suggesting that this maybe a viable targeted therapeutic approach for CREBBP altered cancers. Citation Format: Barrie Peck, Philip J. Bland, Patty T. Wai, Hannah Cottom, Sarah L. Maguire, Eamonn Morrison, Holly E. Barker, Divya Kriplani, Rebecca Marlow, Kalnisha Naidoo, Gareth Muirhead, Syed Haider, Frances Daley, Frederik Wallberg, Andrew N. Tutt, Rachael C. Natrajan. Modeling tumor microenvironmental heterogeneity identifies CREBBP as a novel tumor suppressor in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 788.