Investigating the function of subclonal cooperation in breast cancer progression

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Project Summary/Abstract Intratumor genetic heterogeneity is present in a vast majority of solid cancers and correlates with tumor aggressiveness and poor therapeutic response. Whether tumor heterogeneity promotes tumor growth and survival, and the potential mechanisms driving these phenotypic changes, are open areas of investigation. To explore this fundamental gap in knowledge, I generated a model for studying subclonal cooperation and tumor heterogeneity in vitro and in vivo, respectively, using isogenic MCF10A cell lines that either overexpress MYC (MYC) or oncogenic HRASG12V (HRAS). MYC and oncogenic RAS are two canonical oncogenes that are known to signal in distinct pathways, though studies focused on MYC and HRAS interactions have primarily explored cell intrinsic mechanisms of cooperation. Therefore, I will use MYC and HRAS as an exemplar for subclonal cooperation to study their cooperativity in distinct cell populations. In preliminary studies using the MYC and HRAS model, I made the exciting observation that individual subclones expressing MYC or HRAS cooperate non-cell autonomously: cell proliferation increases when subclones are grown together in vitro and tumor growth is more rapid when subclones are co-injected into mice. Importantly, these data suggest targeting clonal interdependence may be necessary to improve therapeutic strategies. We hypothesize tumor subclones cooperate to elicit emergent tumor properties promoting tumor growth, and, potentially, tumor metastasis and drug resistance. The three Experimental Aims of this proposed research will rigorously test my hypothesis, studying the phenomenon of subclonal cooperation in cell culture and in orthotopic and patient derived xenograft (PDX) models. Experimental Aim 1 will test if subclonal cooperation is necessary for more rapid tumor initiation and proliferation, by deconstructing heterogenous tumors at distinct timepoints during tumor progression. Experimental Aim 2 will explore how tumor heterogeneity is functional by defining how exosome mediated protein transfer contributes to subclonal cooperation. Finally, in Experimental Aim 3, I will test whether subclonal interactions promote therapeutic resistance in orthotopic mouse mammary tumors generated using human- derived cell lines. Additionally, I will validate our findings of subclonal heterogeneity by characterizing the subclonal expression of specific oncogenes present in in a library of readily available PDX models. Together, these data will improve our understanding of subclonal cooperation in tumor progression, providing key insights for future work aimed at efficiently deconstructing and treating complex, heterogenous tumors.