Human model systems based on induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) with patient-specific characteristics have the potential to revolutionize biomedical as well as translational cardiovascular research. Due to their human origin, high availability, and application possibilities in long-term culture, iPSC-CMs have decisive advantages over animal models or primary cells. One aspect represents the establishment of iPSC-CM-based drug screening platforms to identify pro-arrhythmogenic or cardiotoxic molecules. However, the use of iPSC-CM in vitro models to ultimately guide the selection of particular drugs for individual patients in the clinic remains a vision. A major limitation is the immature phenotype of iPSC-CMs, which affects their response to physiological stimuli and to cardioactive drugs, in comparison to adult CMs.

We have recently established an advanced culture protocol, which combines the use of a lipid-supplemented maturation medium (MM), nanopatterning surface (NP) and electrical stimulation (ES), to generate iPSC-CMs with strongly improved structural, metabolic as well as functional properties. In this study, we aimed to investigate whether the enhanced maturation state of iPSC-CMs correlates with an altered response to cardioactive drugs and thus better reflects clinical safety. Multi-electrode array (MEA) measurements revealed a step-wise increase in conduction velocity and spike amplitude by MM, MM+NP and MM+NP+ES, in comparison to iPSC-CMs cultured in widely used RPMI/B27 standard medium. These results demonstrate a significantly increased maturation state of iPSC-CMs cultivated under the influence of MM+NP+ES (mat-CMs) versus iPSC-CMs in RPMI/B27 medium (imm-CMs). To investigate the influence of the maturation state on drug response, we performed MEA recordings to study the effect of different cardioactive substances in mat-CMs in comparison to imm-CMs. We tested the influence of isoprenaline and found that mat-CMs had a stronger chronotropic response and higher sensitivity (decreased EC50) to β-adrenergic stimulation. As MEA allows detection of field potential duration (FPDc) as a surrogate for the clinically relevant QT-interval and thus arrhythmogenic potential, we examined the influence of the hERG-channel blocker E-4031. Although E-4031 prolonged the FPDc in both imm-CMs and mat-CMs, this effect was more pronounced in mat-CMs, indicating that mat-CMs have a higher sensitivity for the identification of proarrhythmic compounds. Moreover, testing of TTX demonstrated that the beating activity of mat-CMs was diminished in the presence of low concentrations of TTX, while the imm-CMs still beat spontaneously. As these findings point towards different mechanisms underlying depolarization of imm-CMs and mat-CMs, we investigated the effect of the L-type calcium channel (LTCC) blocker verapamil. Interestingly, verapamil diminished spontaneous beating activity in imm-CMs but not in mat-CMs, demonstrating that LTCC is important for depolarization of imm-CMs. In contrast, depolarization of mat-CMs mainly relied on sodium channel activity, better resembling the behavior of adult CMs.

Taken together, we demonstrated that the maturation of iPSC-CMs under the combined influence of MM, NP and ES strongly improves their electrophysiological functionality and drug response profile, which may provide the basis for iPSC-CM-based drug screening platforms with high translational potential.

https://herzmedizin.de/fuer-aerzte-und-fachpersonal/kongresse/dgk-jahrestagung-2024/programm/ipsc-based_models_in_cardiovascular_disease/p1706.html