Abstract A36: Combined inhibition of PI3K isoforms and mTOR kinase is critical for cancer stem cell inhibition by VS-5584

We report here that VS-5584 is up to 30-fold more potent at inhibiting the proliferation and survival of CSCs than non-CSCs in breast cancer cell lines using multiple orthogonal CSC assays. Moreover, VS-5584 preferentially induced apoptosis in Aldefluor-positive CSCs relative to Aldefluor-negative non-CSCs as measured by Annexin V and Caspase 3/7 assays. In contrast, paclitaxel induced more apoptosis in non-CSCs than CSCs cells. VS-5584 also preferentially diminished CSCs in human breast and small cell lung cancer xenograft models in vivo, as evidenced by marked reduction of tumor-initiating capacity in an in vivo limiting dilution re-implantation assay. Likewise, ex vivo VS-5584 treatment of surgically removed breast and ovarian patient tumors preferentially reduced CSC populations. In contrast, cytotoxic chemotherapeutic agents such as paclitaxel and cisplatin preferentially eliminate non-CSCs and thus enrich the CSC population. Interestingly, preferential targeting of CSCs requires inhibition of multiple components of the PI3K/mTOR pathway; simultaneous knockdown of PI3Kα, PI3Kβ, and mTOR by siRNA phenocopied the effect of VS-5584 and exhibited the strongest preferential targeting of CSCs, while knocking down of individual PI3K isoform or mTOR failed to do so. Consistent with its strong suppression of CSCs, VS-5584 effectively delayed tumor regrowth following chemotherapy in small cell lung cancer xenograft models including a patient-derived primary tumor model....

Source: Molecular Cancer Therapeutics - July 6, 2015 Category: Cancer & Oncology Authors: Kolev, V. N., Wright, Q. G., Weaver, D. T., Padval, M. V., Pachter, J. A., Xu, Q. Tags: Preclinical and Clinical Studies in Breast Cancer: Poster Presentations - Proffered Abstracts Source Type: research