Mesenchymal Stem Cells Rescue Patient-Specific Cardiomyocyte Viability And Function Following Doxorubicin Injury Via Microvesicle Mediated Mitochondrial Transfer To Recapitulate Human Clinical Trial Results

Introduction: Anthracyclines are effective chemotherapeutic agents associated with cardiac toxicity. Anthracycline induced cardiomyopathy (AIC) carries a mortality of 20% at four years. Effective therapies for AIC have not been established. The NIH-sponsored Stem Cell Injection for Cancer Survivors (SENECA) Trial examined the role of allogeneic mesenchymal stem cells (MSC) to treat AIC. To predict the efficacy of MSC in the SENECA patients, we performed an in vitro clinical trial to study the restorative effects of MSC on patient-specific iPSC-derived cardiomyocytes (iCM) by assessing the effects in vitro following doxorubicin (dox) exposure. Hypothesis: MSC secretome will rescue SENECA Trial patient-specific iCM from dox injury. Methods and Results: We generated three SENECA patient-specific iPSC lines. In vitro iCM dox sensitivity was shown to be comparable to published values. iCM were cultured in 1μM dox for 24hrs, treated with MSC or MSC-secretome, and assessed for viability and apoptosis. Co-culture of MSC with iCM using a 1μm trans-well system improved iCM viability by 43% (p-value < 0.005) and reduced apoptosis (p-value = 0.013). To better define the paracrine mechanism, MSC-secretome was divided into microvesicles >200nm (MV) and exosomes <200nm (Ex) using a novel filtration system. MV recapitulated the effect of co-culture, improving iCM viability by 87.8% (p-value = 0.006) and reducing apoptosis by 60% (p-value = 0.013). Treatment with Ex had no effect. MV restore contractility and calcium transients in the dox-injured iCM. MV were found to contain mitochondria (MT), which are taken up by iCM. Treated iCM demonstrate increased MT-copy number and augmented MT-biogenesis. Inhibition of MT function in MV attenuated therapeutic efficacy. We were unblinded to SENECA outcomes. In our cohort, the MSC-treated patient improved across all endpoints while placebo treated patients did not consistent with our in vitro findings. Conclusion: Allogeneic MSC attenuate apoptosis and restore contractility following dox injury in patient-specific iCM. MV and MT-transfer appear to be the putative mechanism. Our findings correlate with the SENECA results, demonstrating proof-of-concept that iPSC-derivatives can be used to predict trial outcomes.