Mentor Name: Kyle MacQuarrie

Rhabdomyosarcoma (RMS), a pediatric tumor of skeletal muscle, has relatively poor survival, especially in the setting of relapsed disease. Chemotherapy resistance is one of the drivers of poor survival in the setting of relapse, and studies of resistance in RMS often focus on individual gene targets, while treating resistance as a static process. RMS cells share characteristics with normal skeletal muscle cells, but fail to undergo myogenesis, the process of terminal differentiation that occurs during normal muscle development. Myogenesis results not only in gene expression changes, but organizational changes in the components of the nucleus and the genome. Since studies in adult tumors have linked nuclear and genomic organizational changes to chemotherapy resistance and patient survival, this suggests that changes in nuclear and genome organization occur during the development of chemotherapy resistance in RMS cells and contribute mechanistically to the process. Our lab is testing this hypothesis by characterizing the organizational changes that occur in the genome and in multiple aspects of the nucleus during the development of chemo-resistance in vitro in RMS tumor cell lines and then mechanistically relating those changes to cell survival. In addition, we aim to use agents that have previously been shown to sensitize RMS cells to chemotherapy to test the hypothesis that such agents exert global effects on organization in addition to target-specific effects. During the POST award period, we will test one of those agents, S63845, an inhibitor of Mcl-1 (myeloid cell leukemia 1) to determine if it affects chromatin packing characteristics in RMS cells. Using tools including immunohistochemistry and partial wave spectroscopic imaging, the changes that occur during the exposure of in vitro RMS tumor cell lines to varying concentrations of S63845 – both ‘naïve’ RMS cells and those in which we have induced chemoresistance – will be characterized and quantitated. In addition to directly testing our hypothesis about the effect of sensitizing agents, this project will therefore also serve as the basis for future studies examining different classes of sensitizing agents.