CORE C: Drug Discovery and Development Core – SUMMARY The overall goal of this multi-disciplinary, multi-site PPG application is to build a firm foundation of discovery science in cellular senescence that leads to a pipeline of therapeutic strategies that slow or prevent age- associated diseases. Each of the three PPG Projects focus on the role of senescent cells in specific age-related health outcomes: Project 1, Skeletal Fragility (Khosla/Monroe); Project 2, Skeletal Muscle Loss and Dysfunction (LeBrasseur) and Project 3, Brain aging (Jurk). To establish cause and effect, each project will use genetic and pharmacologic approaches to ablate senescent cells. In addition, each of these projects will test the efficacy of senotherapeutic compounds (drugs that induce apoptosis specifically of senescent cells [senolytics] or suppress markers of senescence, in particular SASP [senomorphics]) in treating their health outcome focus. The identification and characterization of effective senotherapeutics for different lineages of senescent cells will be performed by the Drug Discovery and Development Core C (DDDC), working with PIs of each of the three projects and three additional cores. Importantly, the collaborative published and preliminary data from PPG members establishes that no single senotherapeutic is effective in all senescent cell types. Thus, it is imperative to have a centralized Core as part of this PPG to continue to develop and utilize standardized measures of senescence and senotherapeutic activity to identify the most efficacious drugs or drug combinations. During the previous funding period, the DDDC identified and optimized multiple types of senotherapeutics including improved analogs of fisetin, a senolytic natural lipid that induces senescent cell death via ferroptosis, zoledronic acid and optimized analogs, several natural products including tomatidine and multiple drugs targeting epigenetic regulators. These drugs were identified and validated in our established workflow of screening for activity in primary cells or cell lines from multiple species, testing in vivo in a rapid model of accelerated senescence/aging, followed by testing in naturally aged mice. In addition, we identified multiple miRNAs able to drive or prevent senescence as well as used bioinformatic analysis of the targets of senescence-associated miRNAs to identify new senotherapeutic targets. Furthermore, we have used machine learning approaches to identify a novel class of natural senolytics. Finally, we have collaborated with Dr. Daohong Zhou to test the efficacy of optimized PROTACs targeting Bcl-2 family members and are co-developing novel PROTACs. Importantly, using scRNAseq of senescent cells, we have identified subsets of SnCs with differential sensitivity to these senolytics including differential sensitivity of p16INK4a and p21CIP1-positive SnCs. Thus, the role of the DDDC within this multi-site PPG is to continue to develop and implement assays for measuri...