Drug toxicity is a significant cause of clinical failure, accounting for approximately one third of all pipeline attrition . This has driven huge interest across the pharmaceutical industry to understand drug toxicity early within the drug development pipeline. The aim of this is to de-risk drug candidates from a safety perspective before they enter the clinic, as well as reducing the substantial costs associated with drug development.

We spoke with Steve Rees, Vice President Discovery Biology at AstraZeneca, to discuss how the evolution of robust iPSC-based renal toxicity assays is of critical importance in identifying nephrotoxicity liabilities:

What is driving the development of iPSC assays for toxicity studies?

Somatic cells that are reprogrammed to iPSCs can be differentiated into any cell type in the body. These translational models can be applied to the in vitro evaluation of compound safety, allowing researchers to compare efficacy under native and diseased conditions.

iPSC-derived cells offer significant advantages over primary cells and immortalized cell lines. Concerns over the biological and physiological relevance of immortalized cells have seen these fall from favor, whereas iPSC-derived cells align with preclinical models. Toxicity assays performed using primary cells are often subject to variability due to factors including the method of preparation and the characteristics of the donor. In contrast, iPSC-derived cells are extremely consistent from batch to batch.

The quantity of a specific cell type that can be prepared from iPSCs enables the screening of hundreds of compounds per week, making iPSC-derived cells ideal for lead optimization. The development of plate-based iPSC assays that are highly predictive of organ-specific toxicities, have significantly reduced the reliance on in vivo models. This has also contributed to a reduction in projects failing within the clinic. Such assays are increasingly complemented by co-cultures, 3D cell culture systems and organ-on-a-chip technologies to further leverage their potential.

Multiple toxicities contribute to pipeline attrition

Hepatotoxicity, cardiotoxicity and renal toxicity are all causes of clinical compound failure. The well-known Cytochrome P450 and hERG assays, for assessing hepatoxicity and cardiotoxicity respectively, have been in use for decades yet it has long been known that these do not always translate accurately to preclinical studies. This has led to an increasing adoption of primary human hepatocytes and iPSC-derived cardiomyocytes when assessing compound toxicity .

Assays to predict renal toxicity have been more challenging to develop. While primary cell-based approaches have had some success , the various issues associated with primary cells indicate that iPSC assays are preferred.

Current assessment of renal toxicity during drug development

Researchers currently assess drug-induced renal toxicity through histopathology in preclinical studies. This is mainly because in vitro prediction of nephrotoxicity is challenging. A consequence of this is that renal toxicity is only being detected at the later stages of the development process. This is not an ideal process as in vivo models often do not fully translate to how renal toxicity acts in man.

The in vitro assessment of nephrotoxicity has historically relied on the use of immortalized cell lines which do not express a relevant repertoire of influx and efflux transporters. Assays are utilizing these cells to detect non-sensitive endpoints, providing only a crude indication of overall cytotoxicity rather than identifying more subtle cellular changes. In vitro conditionally immortalized proximal tubule epithelial cell (ciPTEC) high content models have shown recent promise as a screening model for first tier compound profiling within the drug development process, however these have yet to become established .

iPSC-derived renal proximal tubular cells can advance the drug development process

Drug-induced nephrotoxicity typically affects the renal proximal tubular cells (PTC) due to the roles they play in glomerular filtrate concentration and drug transport. PTC generated from embryonic stem cells have recently been used to predict tubular toxicity in humans with high accuracy, yet these cells exhibit a slow differentiation rate and relatively low sensitivity. This has led researchers to continue exploring iPSC-derived PTCs as an alternative. In vitro compound screening using an iPSC-based renal model has subsequently been shown to be an accurate and more efficient method.

Steve Rees speaks about renal toxicity assays
Steve Rees talked us through the imprortance of understanding drug toxicity within the early stages of drug discovery research and how the development of robust iPSC-based renal toxicity assays can help towards this direction.

Axol’s iPSC-derived renal proximal tubular cells provide researchers with a plate-based system for in vitro evaluation of renal toxicity. They are derived from integration-free iPSCs of a healthy male donor and express critical functional, epithelial and renal cell markers. These include the phosphate transporter SLC34A1, the organic ion transporter crucial for baso-lateral uptake of organic anions OAT1 and the apical glucose transporter SGLT2, key in glucose reabsorption from the glomerular filtrate. These cells are ready for endpoint assays within just four days of plating, providing an easy-to-use, assay-ready system.

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