ABSTRACT DEVELOPING A PRECLINICAL MODEL OF HUMAN SUNITINIB CARDIOTOXICITY TO ASSESS THE ROLE OF MECHANICAL LOADING USING ENGINEERED CARDIAC MICROTISSUES Rachel Elizabeth Truitt Kenneth B. Margulies, MD Sunitinib, a multi-targeted oral tyrosine kinase inhibitor used to treat many solid tumors, has led to important survival gains. However, this agent carries a significant risk of cardiotoxicity, with left ventricular dysfunction reported in up to 9.7% of treated individuals, and hypertension in 11-43%. There are a number of proposed mechanisms for sunitinib cardiotoxicity, however the relative contribution of each remains poorly understood. In particular, the relationship between increased left ventricular afterload toward inducing cardiac dysfunction remains unknown. Shortcomings of conventional cell culture and rodent models have hampered the identification of pivotal mechanisms of cardiotoxicity such as increased afterload. We instead chose to utilize a recently developed 3D in vitro microtissue model, where rat myocytes self-assemble to form microtissues. Our model of human sunitinib cardiotoxicity recapitulated characteristics observed by other research groups, specifically, cardiomyocyte death, decreases in force generation and spontaneous beating, and demonstrated the dependence of these characteristics on sunitinib dose and treatment duration. Additionally, we observed decreases in mitochondrial membrane potential consistent with findings of mitochondrial abnormalities in patient biopsies. We demonstrated that increased in vitro afterload augments sunitinib cardiotoxicity. Finally, we created microtissues from cardiomyocytes derived from human pluripotent stem cells and found that afterload is required for sunitinib induced apoptosis at clinically relevant exposure concentrations. Our finding that afterload is a key mediator suggests that anti-hypertensive therapy may be important for avoiding eventual LV dysfunction in patients treated with sunitinib.