Preclinical Characterization of Prosetin, a Brain-Penetrant MAP4K Inhibitor for Treating ALS

The primary objective of the research outlined in this proposal is to complete the remaining studies required to submit an investigational new drug (IND) application to the Food and Drug Administration (FDA), and subsequently initiate a well-designed, informative phase 1 clinical trial, for prosetin, a potent mitogen activated protein kinase kinase kinase kinase (MAP4K) inhibitor that is efficacious across multiple models of ALS and has exceptional safety and pharmacokinetic profiles. Following completion of the activities described in this proposal, we would plan to submit an IND application almost immediately and initiate a clinical trial in people with ALS within 4-6 months.

Previously, we established a robust, consistent screening platform for the identification of small molecules that could protect stem cell-derived ALS motor neurons from endoplasmic reticulum stress (ER stress), a process thought to contribute to the widespread degeneration of spinal motor neurons in ALS. Using this screening assay, we identified compounds that protected ALS motor neurons from the detrimental effects of ER stress. We identified a top performer, URMC-099, and then optimized this compound to improve its potency, metabolic stability, and brain penetrance. Prosetin emerged as the strongest candidate among >50 analogs we developed and tested. In subsequent preclinical studies, prosetin demonstrated potent neuroprotection in our ER stress model of ALS motor neurons, and attenuated weight loss and motor deficits in the SOD1G93A mouse model of ALS.

Because ER stress-related pathologies are observed both in familial and sporadic forms of ALS, prosetin's mechanism of action may be broadly applicable to all forms of ALS. Through this proposal, we will evaluate prosetin's effects in a non-SOD1 model of ALS, allowing us to validate our hypothesis and more confidently determine the appropriate patient population for future clinical applications (Aim 1).

Many ALS clinical trials have suffered from the inability to assess their investigational treatment's target engagement in ALS patients, limiting their ability to interpret study results or contribute to more broadly informing ALS drug development. We have identified a blood-based pharmacodynamic biomarker for prosetin in our preclinical studies and will validate and further characterize it for incorporation into future clinical applications through this proposal (Aim 2).

Through this proposal, we will also partner with Patheon, a contract manufacturing and development organization, and Charles River Laboratories, a contract research organization, to complete the final FDA-required IND-enabling activities for prosetin. With Patheon, we will modify the existing synthesis route for prosetin to enable the generation of large quantities of pure test article for use in clinical trials (Aim 3). With Charles River Laboratories, we will evaluate the toxicity profile of prosetin in a non-rodent animal species under stringent Good Laboratory Practices as required by the FDA (Aim 4).

Based on preclinical data, we intend to study prosetin's potential as a disease-modifying treatment for ALS by evaluating its safety and efficacy in ALS clinical trials. As a non-profit academic effort, we will prioritize efficiency, as ALS's 2- to 5-year prognosis demands, and transparency, so that other researchers can implement discoveries from this program toward future ALS drug development efforts. While there are significant risks associated with any drug development effort, prosetin's favorable preclinical safety, tolerability, pharmacokinetic, and pharmacodynamic profile makes it a strong candidate for further investigation.

Prosetin is the first novel potential ALS drug that we identified in our ER stress model of ALS motor neurons. These studies, and intended subsequent clinical development, will provide critical insights to link this cellular model of ALS to the human condition, and in parallel inform future ALS drug screening efforts.