A New Toxicity Screen to Assess Mitochondrial DNA Content and Protein Synthesis

DESCRIPTION (provided by applicant): Investment in research and development by pharmaceutical companies has more than tripled since the early 1990's, but the number of the new molecular entity (NME) approvals has remained stagnant. The industry is still plagued by costly late stage attrition in phase II and phase III clinical trials. Around the turn of the millennium, lack of efficacy was the main reason clinical trials were halted. However, advances in pharmacokinetics have enhanced our predictive capabilities and toxicity is now the number one reason for clinical trial failures, accounting for approximately 30-40% of withdrawals. Just as advancements in pharmacokinetics enhanced our predictive abilities and reduced clinical trial failures due to problems with efficacy, similar improvements in toxicity screening are needed to reduce the number of late stage clinical trial withdrawals. Effective predictive assays and in vitro models that are introduced early in the drug development cycle could not only aid in decreasing clinical trial withdrawals but also reduce preclinical development costs by identifying toxic candidates early on, reducing the number and cost of animal trials, and allowing a more focused effort on high quality drug candidates. Assessing mitochondrial impairment as a mechanism of toxicity represents a significant problem in toxicity screening. Traditionally, mitochondrial toxicity has been considered retrospectively; more than half of the drugs that carry black box warnings for hepato- and cardiotoxicity have been shown to act as mitochondrial toxins. While several assays exist to measure the acute effects of drugs on the mitochondria such as changes in membrane potential, mitochondrial integrity and reactive oxygen species generation, there are few assays that can assess more long term effects such as mitochondrial DNA (mtDNA) depletion and inhibition of mitochondrial protein synthesis. These two mechanisms of mitochondrial related toxicity are associated with serious and potentially fatal side effects. A number of drugs including AIDS therapies, antibiotics, and chemotherapeutic agents are associated with toxic side effects related to mtDNA depletion and inhibition of mitochondrial protein synthesis. Additionally, the FDA has mandated that all new antiviral drugs must demonstrate that they do not result in mtDNA depletion. Regardless, there are no commercially available assays that directly measure mtDNA content and/or assess mitochondrial protein synthesis. Therefore, we are proposing the development of a new assay, and an associated software solution, for use with high content screening systems, to directly measure mtDNA content and assess mitochondrial protein synthesis. The assay will then be tested in hepatocyte and cardiac model systems against compounds known to cause mtDNA depletion and protein synthesis inhibition. We also proposing the development of a predictive, in vitro, model utilizing cardiomyocytes derived from human induced pluripotent stem cells for application to safety screening during the early stages of drug development. PUBLIC HEALTH RELEVANCE: Increasing pharmaceutical RandD costs are a major contributor to the overall cost of healthcare. A large proportion of these costs are incurred due to compound attrition during preclinical and clinical trial testing. Toxicity is the primary reason for compound attrition and identifying toxic compounds early in the drug development cycle is one of the most effective ways to reduce development costs. The proposed project aims to develop an assay and a stem cell based model system to provide better predictive capabilities during early stage testing, in order to identify that demonstrate toxicities related to mitochondrial DNA depletion and protein synthesis inhibition and eliminate them early on in the development scheme.