Elucidating Protective Mechanisms for Cardiotoxicity of Kinase Inhibitors

ABSTRACT Modern, molecularly targeted oncology therapeutics have revolutionized cancer treatment, prolonging cancer survivorship. As patients’ lives are extended, cardiovascular toxicities caused by treatments have emerged as a major clinical problem. This problem persists despite the development of advanced therapeutics, including covalent tyrosine kinase inhibitors (KIs) that were expected to have reduced toxicity due to their increased specificity. Project 3 of this Program Project Grant (PPG) is focused at developing pharmacological strategies to protect the heart from drug-induced cardiac toxicities. We will focus on ibrutinib as a paradigm because as a covalent, irreversible inhibitor of the BTK receptor, it represents an important class of modern oncology drugs, and because it is a first-line therapeutic for B-cell malignancies. Our approach builds on our expertise in high throughput, automated assays of cardiac arrhythmia in hiPSC- derived atrial and ventricular cardiomyocytes (hiPSC-aCMs and hiPSC-vCMs), and the use of deep learning algorithms to recognize and quantify the incidences of arrhythmic waveforms in these cells. hiPSC-CMs treated with ibrutinib exhibit arrhythmic waveforms consistent with presentations of atrial fibrillation and arrhythmia in patients. Our pipeline to discover therapeutic strategies is based on identifying targets that block ibrutinib- induced arrhythmia using hiPSC-aCMs and vCMs, and then testing candidates in a mouse model. We take two orthogonal approaches to identify therapeutic targets. Specifically, we will delineate the regulatory elements in chromatin (Aims 1 and 2) and key transcriptional inputs (Aim 3) that mediate the adverse effect of the drug on cardiomyocytes. We will experimentally test each DNA element and each TF for the ability to block or exacerbate ibrutinib-induced arrhythmia, thereby functionally defining genes and factors that are potential therapeutic targets to revert the adverse effects of ibrutinib on the cardiomyocyte. Candidates suggested from preliminary data and promising new targets emerging from these proposed studies will be evaluated for protective activity in a mouse model of ibrutinib-induced cardiotoxicity. Project 3 synergizes with Project 2 since some of the factors and chromatin elements that we will discover are expected to coincide with eQTLs for drug susceptibility. Hence, our joint efforts will provide human genetic evidence supporting protective loci with verified functional effects that can be targeted pharmacologically. Project 3 also synergizes with Project 1 by using its expertise in mouse models as well as its data on human susceptibility loci. Key deliverables of Project 3 include identification of therapeutic targets and possibly therapeutics to mitigate ibrutinib toxicity, as well as a discovery paradigm to improve the quality of life and survivorship of cancer patients.