Advantages of long-term evaluation of doxorubicin-induced cardiotoxicity using human iPSC-derived cardiomyocyte sheet tissues with continuous contractile force measurement under constant pacing

With advancements in anticancer therapy, concerns over delayed cardiotoxicity are increasing, creating demand for precise in vitro systems to evaluate long-term cardiotoxic effects in drug discovery. In this study, we examined the impact of doxorubicin on the contractility of cell sheet tissues made from human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) maintained at a steady pacing rate of 1 Hz. Using our system for continuous contractile force measurement over 5 days, tissues exposed to 0.3 µM doxorubicin exhibited progressive force decline and arrhythmias, despite no significant changes in 4 biomarkers, ANP, BNP, NT-proBNP, and cTnT, sampled post-measurement. These findings suggest that indirect biomarker-based assessment of the cardiotoxicity of doxorubicin may be challenging. Notably, an increased slope during the relaxation stage preceded reduction in contraction amplitude in 0.3 µM-exposed tissues. Further analysis, dividing the relaxation into early, middle, and terminal phases, indicated that doxorubicin induces a rapid force decline during the early phase, followed by a gradual decrease in the terminal phase. We discussed the mechanistic basis of this toxicity based on intracellular Ca2+ dynamics. These insights derive from a system that enables stable, long-term measurement of contractile force under a consistent beating rate, and such technological advancements promise to enable more reliable evaluation of delayed cardiotoxicity in future drug development. Thus, our rate-controlled, continuous force platform reveals early relaxation-phase changes not detected by soluble biomarkers and offers a more sensitive in vitro approach for preclinical cardiotoxicity screening.