Drug testing platform using in vitro electrophysiology and in vivo rodent models for evaluating existing and novel cardiovascular drugs and their potential applications

Abstract

Ion channels play crucial roles in normal cardiac function and in maintaining intracellular ion homeostasis in both excitable and non-excitable cells. Cardiovascular diseases and malignancy are two of the major global causes of mortality and both may be related to channelopathies. Although current therapeutic agents often have limited efficacy or undesirable side effects, development of new drugs is hindered by the lack of a human drug testing platform to determine their efficacy and side effects at an early stage.

This dissertation first proposed an in vitro electrophysiological drug testing platform that utilized mouse cardiomyocytes and evaluated its effectiveness using digoxin. The effect of digoxin on lengthening of action potential duration was observed using the proposed platform. The effects were consistent through single cell level to monolayer and tissue level. Efforts were also made to test whether human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) offer a feasible cell source for human drug testing. The results obtained using iPSC-CMs were inconsistent with those observed using mouse cells. Nonetheless with careful optimization of protocols for the differentiation of iPSCs to yield a clone of cardiomyocytes with higher purity, there remains great promise for the application of human iPSCs in drug testing or even patient-specific drug testing.

Next, the pharmacological potential of a previously identified new synthetic molecule, C11, was evaluated as a novel anti-arrhythmic agent. C11 is capable of forming chloride channels on the cell membrane through self-assembly. Treatment with C11 has been shown to terminate and prevent electrical stimulation-induced ventricular tachycardia in rats through lengthening of the action potential duration. C11 creates artificial chloride channels and simultaneously enhances the calcium current. It may be a superior anti-arrhythmic drug to amiodarone, one of the most common antiarrhythmic drugs in current clinical use, because it does not affect ventricular contractility.

In the final study, HCN channels were identified as a possible oncogene in human small cell lung carcinoma (SCLC) as they are over-expressed in SCLC cell lines. Inhibition of HCN channels by a general HCN channel blocker, ivabradine, suppressed growth of the cancer cell lines both in vitro and in vivo. Ivabradine treatment also induced apoptosis, achieved, at least partially, through down regulation of anti-apoptotic Bcl-2 expression.

With the help of an in vitro electrophysiological drug testing platform and an in vivo rodent model, new therapeutic applications have been established for several drugs. These techniques can be further utilized to identify more potential drug candidates.