title: Anti-tumor efficacy of BEZ235 is complemented by its anti-angiogenic effects via downregulation of PI3K-mTOR-HIF1alpha signaling in HER2-defined breast cancers.
abstract: Activation of the PI3K-mTOR pathway via HER2: HER3-mediated signaling in HER2+ breast cancers pose one of the major threats towards the success of trastuzumab. First, trastuzumab cannot perturb survival/proliferative signals following HER2: HER3 heterodimerization in HER2+ tumor cells. Second, trastuzumab treatment has been reported to cause drug-mediated resistance in over 50% of HER2+ breast cancers. We have reported that treatment with an anti-angiogenic drug imparted a significant anti-tumor advantage when combined with trastuzumab plus pertuzumab in the trastuzumab-resistant model of HER2+ breast cancers (PMID: 23959459). The very fact as revealed by our study that an inclusion of anti-angiogenic drug conferred a significant anti-tumor advantage when combined with dual anti-HER2 therapy clearly indicated a critical and indispensable role of angiogenesis in these tumors. Hence, we hypothesized that BEZ235 a dual PI3K/mTOR inhibitor will have an effect on the tumor as well as the angiogenic stromal compartments. In vitro and in vivo efficacy of BEZ235 was determined in HER2+ trastuzumab-sensitive, trastuzumab-resistant and HER2 amplified/PIK3CA mutated cell lines. BEZ235 alone and in combination with trastuzumab was tested on the tumor as well as stromal compartments. AKT-mTOR signal was suppressed following BEZ235 treatment in a concentration and time-dependent manner. AnnexinV, cl-CASPASE3, SURVIVIN and p-FOXO1 indicated that BEZ235-induced cell death occurred predominantly via an apoptotic pathway. Heregulin-induced HIF1α synthesis was also significantly decreased. Oncoprint data (cBioPortal) representing PAM50 Her2 enriched tumors (TCGA, Nature 2012) and Her2-positive breast tumors (TCGA, cell 2015) showed 91.4% genetic alterations and 79.2% genetic alterations in a set of four genes comprised of PIK3CA, ERBB2, VEGFA and HIF1alpha. The co-occurrence of HIF1alpha with VEGFA in PAM50 Her2 enriched tumors (TCGA, Nature 2012) and the co-occurrence of HIF1alpha with VEGFA pair as well as HIF1alpha with PIK3CA pair in Her2-positive breast tumors (TCGA, cell 2015) were found statistically significant. In xenograft models, BEZ235 blocked tumor growth and decreased Ki67, CD31, p-AKT, p-S6RP, p-4EBP1 IHC-expressions. These decreases were more pronounced when BEZ235 was combined with trastuzumab in HER2+/trastuzumab-sensitive, trastuzumab-resistant and HER2+/PIK3CA mutated models. We demonstrated that combined targeting of HER2 and the PI3K-AKT-mTOR pathway is superior to HER2-directed therapy alone. Mechanistically the inhibition of tumor-induced angiogenesis by BEZ235 caused by the down-regulation of PI3K-mTOR-HIF1alpha signaling irrespective of the trastuzumab-sensitivity status of HER2+ breast cancers proving evidence for the first time that the inhibition of angiogenesis is an important component of the anti-tumor efficacy of BEZ235 in HER2 defined breast cancers.
authors.affiliation: Genomic Oncology, Avera Cancer InstituteSioux Falls, SD; Departmental of Internal Medicine, University of South DakotaSioux Falls, SD.
authors.forename: Nandini
authors.initials: N
authors.lastname: Dey
authors.affiliation: Genomic Oncology, Avera Cancer Institute Sioux Falls, SD.
authors.forename: Yuliang
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Genomic Oncology, Avera Cancer Institute Sioux Falls, SD.
authors.forename: Jennifer H
authors.initials: JH
authors.lastname: Carlson
authors.affiliation: Emory school of Medicine, Emory University Atlanta, GA.
authors.forename: Hui
authors.initials: H
authors.lastname: Wu
authors.affiliation: Genomic Oncology, Avera Cancer Institute Sioux Falls, SD.
authors.forename: Xiaoqian
authors.initials: X
authors.lastname: Lin
authors.affiliation: Genomic Oncology, Avera Cancer InstituteSioux Falls, SD; Departmental of Internal Medicine, University of South DakotaSioux Falls, SD.
authors.forename: Brian
authors.initials: B
authors.lastname: Leyland-Jones
authors.affiliation: Genomic Oncology, Avera Cancer InstituteSioux Falls, SD; Departmental of Internal Medicine, University of South DakotaSioux Falls, SD.
authors.forename: Pradip
authors.initials: P
authors.lastname: De
keywords: Breast cancer; HER2+; PIK3CA mutation; angiogenesis; apoptosis; trastuzumab-sensitive and trastuzumab-resistant