Abstract 2812: mTOR kinase mediates dissemination and colonization of breast cancer metastasis

Background: Early events of metastatic dissemination arise from the ability of tumor cells to acquire a number of biological changes which allow for their survival in distal microenvironments. Among the early events that initiate disseminated tumor populations include epithelial-to-mesenchymal transition (EMT) and increased potential for invasion that will ultimately lead to colonization of distal sites. The PI3K/mTOR pathway has been linked to clinic-pathalogical features of invasion and metastasis of multiple tumor types. Results: We sought to investigate using both in vitro and in vivo models of metastasis a panel of PI3K/mTOR selective inhibitors, in which INK128, a selective mTOR kinase inhibitor in clinical development was included. Using live-cell time lapse imaging experiments to monitor cell migration and invasion we found that INK128 significantly inhibited motility and velocity of metastatic breast cancer models in wound assays and decreased the ability of tumor cells to migrate through membranes and matrigel. The ability of INK128 to selectively inhibit tumor cell migration in vitro prompted us to assess whether INK128 can prevent tumor dissemination in vivo. In metastatic breast cancer xenograft models we monitored the growth of tumors implanted in mammary fat pads (MFP) and metastatic dissemination by serial noninvasive whole body bioluminescent imaging. We first assessed and characterized the degree of spontaneous metastasis to the lung, liver, auxillary lymph nodes, chest cavity of mice and subsequently the effect of mTOR kinase inihibition on primary tumor growth on the MFP versus overt metastatic dissemination upon daily, oral treatment with INK128. We show that INK128 blocked drastically metastatic spread in a dose-dependent manner without significantly affecting the growth of primary tumors. Interestingly, we found that INK128 did not affect the ability of breast cancer cells to enter into the lungs following an alternative experimental lung metastasis model by lateral tail vein injection but INK128 greatly diminished the capacity of breast cancer cells to subsequently colonize and expand. Conclusion: Our results position mTOR on a metastasis-sustaining axis that engages downstream pathways to support the biological machinery of migration, invasion, and fitness of initiating breast cancer cells during the establishment of thoracic metastases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2812. doi:1538-7445.AM2012-2812