Out of the Frying Pan and into the Fire: hiPSC-CM as Potential Tool for Preclinical Cancer Drug Cardiotoxicity Testing

“Diseases desperate grown, by desperate appliance are relieved, or not at all.”

William Shakespeare, Hamlet

In 2017, cardiovascular disease and cancer were the top two leading causes of death and morbidity.¹ Advances in the development of oncogenic therapies have improved their efficacy and thereby, increasing the survival rate in patients with cancers. However, oncology drugs can have adverse cardiovascular side effects causing irreversible cardiac injury that may manifest days or years after treatment. The mechanism of how these drugs induce these effects is largely unknown, partly as a result of limitations of current models to effectively reflect the response of cancer drugs on the heart. Moreover, limitations of preclinical animal models to gauge and predict the cardiotoxic effects of drugs on human cardiovascular system have further contributed to this problem. The development of more predictive human in vitro models of cardiac cells for cancer drug toxicity assessment might be key to solve this limitation. However, limited availability of adult human cardiac tissues and cardiomyocytes and difficulties associated with in vitro culture propagation of primary adult human cardiomyocytes severely limit this option.

The discovery of human induced pluripotent cells (hiPSCs) and the streamlining of successful protocols for obtaining large quantities of hiPSC-derived cardiomyocytes has led to the availability of a cell source that is considered to be more representative of human cardiac physiology and recapitulate the effects of certain drugs.^2,3 Therefore, it is now possible to study contractile and electrophysiologic dysfunction in human cardiomyocytes in relation to oncogenic drug therapy and cardiotoxicity. The AHA Scientific Statement on the use of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) in preclinical cancer drug cardiotoxicity testing provides a comprehensive and up to date review and discussion on the advantages and limitations of hiPSC-CMs in vitro and its potential impact on the development of screening strategies for the future preclinical cardiotoxicity testing.⁴

Human iPSC-derived cardiomyocytes represent a powerful tool because of its multiple implications, from aiding in the understanding of heart development, epigenetic control of cardiac differentiation, to drug discovery, toxicology testing, and ultimately in regenerative medicine. Not only do hiPSC-CMs provide an unlimited source of cells for drug safety testing but also they appear to recapitulate many properties of human primary cardiomyocytes and heart tissue, including physiological, structural and genetic profiles. Thus, one of the great advantages of hiPSC-CMs is the cost-effectiveness and feasibility in large scale production of cardiomyocytes for cardiotoxicity testing of oncogenic drugs.⁵ The AHA statement concisely illustrates hiPSC-CM flexibility of use and limitations that allow researchers the ability to develop and use different constructs to study cardiotoxicity based on a particular interest.⁴ Notably, hiPSCs can be used to generate organoids and organs on a chip that incorporate the biochemical and mechanical aspects of the target organ. Skardal et al. micro-engineered heart-lung-liver model using a 3D printed liver, heart organoid, and lung tissues perfused with a common media in a closed loop, found cardiotoxicity of a chemotherapeutic drug as a result of cytokine-mediated cross talk.⁶ Ramme et al. created a four organ model called patient-on- a- chip containing miniaturized iPSC-derived organoids of the human intestine, liver, brain, and kidney integrated into a microphysiological system from a single donor to aid in preclinical drug safety and efficacy testing.⁷ There are however, many challenges that must be addressed including the maturation status of the CM/tissue, standardized differentiation protocols, and medium composition.

Oncogenic drugs can induce cardiotoxicity by changes in electrophysiology, contractility, and structural organization. Gintant et al. highlight the advantages of using hiPSC-CMs that address both proarrhythmic and non-proarrhythmic cardiotoxicity.⁴ Interestingly, hiPSC-CMs also respond to major ion channel blockers and can be a useful tool to study cell surface receptor binding, mitochondrial damage and oxidative stress as the result of oncogenic drugs.⁸ Recently, Sharma et al. developed a cardiac safety index using hiPSC-CMs for screening FDA approved cancer chemotherapeutic tyrosine kinase inhibitors measuring cardiomyocyte viability, contractility, electrophysiology, and calcium handling.⁹ However, further research is needed on the effect of using combinational therapeutics, often used in cancer patients to increase efficacy of treatment, on cardiotoxicity. For example, inhibition of ErbB signaling with trastuzumab increased sensitivity to doxorubicin-induced cardiotoxicity.³ Oncogenic therapies can also induce DNA breaks activating a DNA damage response that can contribute to heart failure, hiPSC-CMs can potentially aid in the mechanistic understanding of how these oncogenic drugs contribute to heart failure.^10,11

Human induced PSCs are generated from somatic cells from individuals that allow its use as a personalized therapy to screen for cardiotoxicity effects of oncogenic drugs increasing efficacy of treatment while reducing risk of cardiotoxicity.¹² Magdy et al. in particular highlight the ability of hiPSCs to model disease phenotypic state such as diabetic cardiomyopathy.¹³ Further research is needed in developing hiPSCs diseased phenotypes models from individuals with cardiovascular risk factors such as obesity and diabetes, known to increase susceptibility to cardiotoxicity.¹⁴ Human-induced PSC-CMs also can be used as a platform to study gene variants found from Genome Wide Association Studies (GWAS) that can affect how individuals respond to oncogenic drugs.¹⁵

Although hiPSCs have characteristics of adult cardiomyocytes, there is still a need for the development of a more functionally mature phenotype without self-renewing capabilities.⁶ In order to address this, there needs to be a standardized differentiation protocol that can universally applied across laboratories to improve validity of hiPSCs in preclinical drug screening and therapeutic potential of hiPSCs.

Further investigation is needed in understanding the role of biologically active extracellular vesicles content (mRNA, microRNA, proteins, non-coding RNA) secreted by hiPSCs.⁴ The content is transferred to a target cell that can induce changes in the cell’s metabolism, cell cycle, gene expression, and anti-apoptotic effects. However, how extracellular vesicle content affects sensitivity to cardiotoxicity is still not well understood.

In summary this comprehensive AHA statement highlights these and many other important issues on the use of hiPSC-CMs for the screening of cytotoxic effects of cancer drugs. Authors argue for the importance of early assessment for cardiotoxicity from oncogenic drugs prior to clinical trials and development of effective preventive approaches that have the potential to replace the use of animal models to screen for cardiotoxicity of new compounds during preclinical drug development.