byl719 and Cocarcinogenesis

Estrogen dependence is major driver of ER + breast cancer, which is associated with PI3K mutation. PI3K inhibition (PI3Ki) can restore dependence on ER signaling for some hormone therapy-resistant ER + breast cancers, but is ineffective in others. Here we show that short-term supplementation with estrogen strongly enhanced Pik3caH1047R-induced mammary tumorigenesis in mice that resulted exclusively in ER + tumors, demonstrating the cooperation of the hormone and the oncogene in tumor development. Similar to human ER + breast cancers that are endocrine-dependent or endocrine-independent at diagnosis, tumor lines from this model retained ER expression but were sensitive or resistant to hormonal therapies. PI3Ki did not induce cell death but did cause upregulation of the pro-apoptotic gene BIM. BH3 mimetics or PI3Ki were unable to restore hormone sensitivity in several resistant mouse and human tumor lines. Importantly however, combination of PI3Ki and BH3 mimetics had a profound, BIM-dependent cytotoxic effect in PIK3CA-mutant cancer cells while sparing normal cells. We propose that addition of BH3 mimetics offers a therapeutic strategy to markedly improve the cytotoxic activity of PI3Ki in hormonal therapy-resistant and ER-independent PIK3CA-mutant breast cancer.

Topics: Aniline Compounds; Animals; Antineoplastic Agents, Hormonal; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; BH3 Interacting Domain Death Agonist Protein; Cell Line, Tumor; Class I Phosphatidylinositol 3-Kinases; Cocarcinogenesis; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Drug Synergism; Estradiol; Estrogen Receptor alpha; Female; Fulvestrant; Gene Expression Regulation, Neoplastic; Gene Knock-In Techniques; Mammary Neoplasms, Experimental; Mice; Mice, Nude; Mutation, Missense; Neoplasm Proteins; Neoplasms, Hormone-Dependent; Neuropeptides; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Sulfonamides; Thiazoles