Induced pluripotent stem cells in cardiovascular drug discovery

Abstract

The unexpected discovery that somatic cells can be reprogrammed to a pluripotent state yielding induced pluripotent stem cells has made it possible to produce cardiovascular cells exhibiting inherited traits and disorders. Use of these cells in high throughput analyses should broaden our insight into fundamental disease mechanisms and provide many benefits for patients, including new therapeutics and individually tailored therapies. Here we review recent progress in generating induced pluripotent stem cell-based models of cardiovascular disease and their multiple applications in drug development.

Figure 1. Utility of iPSC technology for drug discovery

Drug discovery starts with patient biopsies used for the generation of induced pluripotent stem cells (iPSCs), followed by the directed differentiation to specialized cardiac cell types that are used in disease models for screening. The assays are then screened in high throughput, moderate throughput or small-scale assays that are tailored for a range of activities, from primary drug screens to the design of individualized patient therapies. (Illustration Credit: Ben Smith).

Figure 2. High throughput assay readouts

High throughput screening (HTS) readouts measure parameters of entire wells, such as luciferase or fluorescence, and read out by a plate reader (left). Monitoring whole well fluorescence or luminescence over time is also feasible (not shown). In contrast, high content screening (HCS) is based on the quantification of images and has the potential to report multiple parameters on a cell-by-cell (cytometric) basis, such as cardiomyocyte hypertrophy (middle panels). Kinetic imaging cytometry is the quantification of fluorescent probes over time and enables cell-by-cell analysis of physiological responses, such as for Ca²⁺ transients recorded under spontaneous or stimulated conditions, exemplified by the effect of an arrhythmogenic drug (right panels). (Illustration Credit: Ben Smith).

Figure 3. iPSC-based disease-in-dish modelling to discover novel drug targets

iPSC technology can contribute the human disease context to multiple points in a pharmaceutical development pipeline (indicated as red in the flow diagram at bottom). Screening disease-in-dish assays against focused libraries of molecules represents a powerful functional and chemical genomics approach to identify new drug targets. The key property of the indicated libraries, except for diversity collections of small molecules, is that the cellular targets can be determined in sufficient throughput and reliability to be used in subsequent pathway analysis and validation steps. In contrast, it remains challenging to identify biologically relevant target of small molecule hits from diversity collections since they are promiscuous and largely uncharacterized. Systems biology tools are employed to create an interaction network consisting of the candidate targets and interacting genes/proteins, the key nodes of which can be validated by re-screening using specific small molecule or siRNA/shRNA agents. Following validation and refinement, the network is analyzed for druggable targets that can be entered into conventional drug discovery at the level of high throughput screening (HTS).