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Combined PI3K/mTOR and MEK Inhibition Provides Broad Anti-Tumor Activity in Faithful Murine Cancer Models

ABSTRACT: Anticancer drug development is an inefficient process, with potential therapeutics demonstrating a high attrition rate due to lack of efficacy in Phase II/III testing. In an effort to develop improved pre-clinical predictors of efficacy, we and others have turned to testing in genetically engineered murine models (GEMMs) of cancer, which may offer some advantages to in vitro and xenograft systems. Specifically, we assessed the activity of 16 treatment regimens in a Ras-driven, Ink4a/Arf-deficient melanoma GEMM. Like human RAS-mutant melanoma, this GEMM was refractory to standard chemotherapy and single-agent small molecule therapies. Only one regimen exhibited significant anti-tumor activity in this model: combined treatment with AZD6244 (MEK inhibitor) and BEZ235 (dual PI3K/mTOR inhibitor), which produced marked tumor regression and improved survival. Given the surprising activity of the “AZD/BEZ” combination in a melanoma GEMM, we next tested this regimen in a Ras-driven orthotopic-transplant model of “claudin-low” breast cancer, which shares some gene expression features with melanoma. The AZD/BEZ regimen also exhibited significant activity in this related Ras-driven model, leading us to testing in even more diverse GEMMs of basal-like and luminal breast cancer. The AZD/BEZ combination was highly active in each of these distinct breast models, demonstrating equal or greater efficacy compared to any other regimen tested in studies of over 700 tumor-bearing mice. This regimen even exhibited activity in tumors selected for resistance to another effective chemotherapy agent, lapatinib, in HER2+ models. These results demonstrate the utility of credentialed murine models for large-scale efficacy testing of diverse anti-cancer regimens, and predict combinations of PI3K/mTOR and MEK inhibitors will demonstrate anti-tumor activity in a wide-range of human malignancies.

ORGANISM(S): Mus musculus

PROVIDER: GSE35722 | GEO | 2012/08/21

SECONDARY ACCESSION(S): PRJNA152123

REPOSITORIES: GEO

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Project description:Combining direct anti-tumor effects with targeting of tumor microenvironment is an attractive strategy that may lead to more effective therapies for advanced melanoma. Here, we tested whether association of TRAIL with co-targeting of MEK and PI3K/mTOR, or with MEK blockade, could have synergistic anti-melanoma activity mediated not only by induction of tumor cell death, but also by effects on the tumor microenvironment. Drug interaction analysis by the Chou-Talalay approach in a panel of 21 melanoma cell lines indicated that strong synergism could be achieved by association of the MEK1/2 inhibitor AZD6244, the PI3K/mTOR inhibitor NPV-BEZ235 and TRAIL, as well as by the AZD6244/TRAIL combination. Synergism was observed on most tumors including TRAIL- or inhibitor-resistant melanomas, irrespective of the BRAF, NRAS, p53 and PTEN status, and was explained by enhanced induction of caspase-dependent melanoma apoptosis. The AZD/BEZ/TRAIL and AZD/TRAIL combinatorial treatments induced strong modulation of key apoptosis regulators along the extrinsic and intrinsic cell death pathways, including c-FLIP down-regulation, caspase-8 cleavage, BIMs and BAXa upregulation, clusterin and Mcl-1 inhibition, enhanced mitochondrial depolarization, suppression of inhibitors of apoptosis c-IAP1, c-IAP2, XIAP and Apollon, and caspase 3/7 activation. In an in vivo model, the AZD6244/TRAIL combinatorial treatment induced highly significant growth inhibition of a TRAIL-resistant tumor associated not only with melanoma cell death, but even with suppression of pro-angiogenic molecules HIF1a, VEGFa, IL-8 and TGFb1, and with inhibition of tumor angiogenesis. These results provide a proof of principle supporting the rationale for combinatorial treatments with synergistic anti-melanoma activity based on direct and indirect anti-tumor effects. The human melanoma cell line Me13 was established in our laboratory from a surgical specimen. Cells were routinely maintained in RPMI medium 1640 (Lonza, Basel, Switzerland) supplemented with 10% FBS (Lonza) and 2 mM glutamine (Lonza). Cells were maintained at 37°C in a water-saturated atmosphere of 5% CO2 in air. 3x10^6 cells were seeded in 75 cm2 flasks; after 24 hours, cells were left untreated or treated with Selumetinib (Selleck Chemicals, Houston, TX) at 0.1 micromol/L, NVP-BEZ-235 (Selleck Chemicals, Houston, TX) at 0.1 micromol/L and sTRAIL (AdipoGen) at 25ng/ml as single drugs or in combination for 8 hours. Each treatment or combination was performed in triplicate. At the end of treatment, cells were collected and RNA extracted.

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Combined PI3K/mTOR and MEK Inhibition Provides Broad Anti-Tumor Activity in Faithful Murine Cancer Models

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