Bioelectricity to mature electrophysiological characteristics of human stem cell derived cardiomyocytes: a new competitive model in drug safety testing

Development of new drugs to treat any human disease is compromised by potential adverse side effects induced by the candidate drugs. A common and dangerous reason for attrition of a drug is the life-threathening disturbance of the heart rhythm. To exclude candidate drugs that disturb heart rhythm, drugs are tested in pre-clinical testing models with increasing complexity; beginning with drug-target binding assays and ending with complete large animals before clinical trails in human patients take place. Importantly, drugs are tested in animal models (cells and organs) before they are tested in humans. In this phase, drugs are rejected on basis of their adverse effects in animals, but it is well known that the mechanisms underlying animal heart rhythm (especially that in rodents) are significantly different from that in humans. As a result, candidate drugs are rejected that may very well have a desired performance in humans, or on the other hand considered safe in the animal while being detrimental in humans. As a consequence of the complex testing process, development of new drugs requires a large amount of animals, is very expensive, time consuming and heavily burdens the health care system. Through replacing the undesired animal testing with tests on human tissues or cells instead, it is anticipated that less valuable candidate drugs will be rejected unnecessarily. Moreover, costs will be reduced and drugs will enter the market more rapidly. Since healthy human cardiac tissue is unavailable, in the previous ZonMW-3V project (40-401000-96-8301) we have evaluated the possibility to develop a human drug-screening model based on human embryonic stem cell-derived heart cells (hSC-CM). In this project we started PPPs with leading companies within this field. We were able to identify the prerequisites with respect to the characteristics of the cells, standardized the conditions for measurements and showed that the system is sensitive and specific enough to recognize those drugs that are potentially pro-arrhythmic through interference with the repolarizing current Ikr. Sensitivity and selectivity appeared comparable to contemporary used animal models and superior to models including single cardiomyocytes isolated from these animals. However, the relative electrical immaturity of hSC-CM limits their usability for unbiased drug screening. An important factor in the immaturity is absence of one specific cardiac ion channel, Ik1, which is constituted by Kir2.1 proteins. The absence of this current negatively affects the functioning of other ion-currents and through this, limits the cells to respond appropriately to drugs that e.g. interfere with sodium or calcium channels. Application of a system biology approach with computer simulations learned that if we are able to introduce a well-balanced Ik1 current in those hSC-CM, they will become fully responsive and predictive for any ion-channel modulating drug. Next to hSC-CM we will perform the same experiments on cardiomyocytes generated from induced pluripotent stem cells. The latter source allows inclusion of patient-specific aspects of drug safety testing. To succeed in this we have defined 3 different strategies which we aim to explore in the current proposal 1) we will develop a hybrid model, in which hSC-CM are coupled to a real-time computer that adds simulated Kir2.1 channels to the hSC-CM (dynamic clamp). As a result, the hybrid model will behave with the necessary maturity. The hybrid hSC-CM model will be tested using well-evaluated drugs, and its predictive power with respect to heart rhythm disturbances will be compared with existing data from animal models and previous measurements on untreated hSC-CM. 2) We will use co-culture systems of hSC-CM and transfected cells expressing proteins that create the Ik1 current to introduce the current electrotonically into the hSC-CM. Arrhythmogenic testing will be performed at the host institute as described in 1. 3) We will stimulate and investigate the endogenous mechanisms that lead to electrical maturation of the hSC-CM. In this respect, a library screen of small molecules is under construction through our international collaboration. To achieve in this project we feel that we have collected a well-balanced and proven succesful consortium with input from both the academy and industry. We anticipate that we will be able to show that upon electrical maturation, such hSC-CM will generate a model which is sensitive and predictive enough and able to replace several phases in drug safety testing for which tests on a tremendous amount of animals can be prohibited.