Validation of SNPs Highly Correlated with Pediatric Chemotherapy-Induced Cardiotoxicity

Anthracyclines, although some of the oldest anti-cancer agents, are highly effective in treating a wide range of malignancies and are still utilized in 50-60% of breast cancer and 70% of all childhood cancer treatment protocols. In children, the anthracycline doxorubicin has contributed to the improvement in 5-year survival to over 80% [1], however, its utility is limited by its cardiotoxicity. Initial reports documented the highest risk for doxorubicin cardiotoxicity at doses above 450 mg/m2 (2). However, with improved methods of detecting subtle changes in cardiac function [3), the incidence is now thought to be much higher, occurring in up to 65% of long­term survivors of childhood cancer, even at doses as low as 228 mg/m2 [4-6J. As many as 16% of children with abnormal echocardiograms will develop clinical heart failure [2, 7, 8] with a mortality rate of 72% [1, 7, 8). Long­term follow-up will likely increase this number substantially. With 1 in 750 adults now being survivors of childhood cancer, this problem is a major challenge in the emerging field of cardio-oncology. Our collaborators have recently completed two large multi-center pediatric studies (9, 10J, using a targeted genomic approach, demonstrating two SNPs associated with dramatically altered risk of anthracycline cardiotoxicity in both original and replication cohorts: one in SLC28A3, encoding the nucleoside/anti-cancer drug transporter and one in UGT1A6, encoding UDP glucuronosyltransferase 1A6. Screening the same populations using a GWAS approach, we discovered another candidate SNP in RARG, which encodes they retinoic acid receptor. Although these studies represent a potential major advance in applying a pharmacogenomic approach to cardio-oncology, the true connection between these SNPs and cardiotoxicity is far from proven, especially given the mixed track record of transitioning other GWAS data into clinical practice. Thus, before their application to clinical practice, several additional criteria must be met: first, these results must be confirmed in additional large replication cohorts; second, rational mechanisms for their effects (e.g. does a gain-of-function SNP in a drug transporter lead to increased intracellular levels and increased toxicity) must be developed and proven using model systems; third, reversion of tha SNP to wildtype should rescue the altered toxicity effect. Patient-derived hiPSC-CMs (human induced pluripotent stem cell-derived cardiomyocytes) represent a novel technology, which has already been successfully applied to understanding basic mechanisms of several cardiovascular diseases, as well as to screening drugs for efficacy and toxicity. Critical to our study, we have already confirmed that hiPSC-CMs from patients with clinical doxorubicin cardiotoxicity recapitulate this enhanced toxicity in vitro. We hypothesize that hiPSC-CMs represent a model platform for studying the mechanisms and validity of individual genomic hits in regulating anthracycline cardiotoxicity. Furthermore, we hypothesize that hiPSC-CMs represent a platform for testing the cardiotoxicity of new anthracycline derivatives, cardioprotective agents, and other anti-cancer agents.