Neuromuscular and cardiac organoids and assembloids: Advanced platforms for drug testing.

The inherent technical difficulties, ethical/regulatory issues and costs of experimental studies in animal models is prompting investigators to replace as much as possible living organisms with in vitro physiological models named organoids and assembloids. Generated from induced pluripotent stem cells, these three-dimensional structures approximate the complexity of tissues and their interactions, enabling personalized disease modelling and drug testing. The integration of multiple components in assembloids further enhances their predictive value for multi-system interactions and toxicities. This review describes how neuromuscular organoids, incorporating functional neuromuscular junctions and contractile muscle tissue, have been used to replicate, in vitro, complex neuromuscular morpho-functional structures, offering very valuable platforms to study molecular mechanisms and drug effects in models of incurable diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis. In the cardiological field, cardiac organoids and assembloids are proving reliable models for testing drug effects at molecular, morphological, electrophysiological and mechanical level. Recently, the integration of neuronal components into cardiac organoids has provided a potential approach to investigate autonomic function, a fundamental aspect of many neurological, neuromuscular and cardiac diseases. Challenges and limitations still remain, including the non-uniform differentiation protocols across studies, the incomplete maturation of cell phenotypes, and the lack of integrated pharmacokinetic modelling. We discussed some future developments aimed at overcoming such hurdles. Despite their current limitations, organoids and assembloids clearly hold great promises and will help advancing many fields of biomedicine.