Targeting Intracellular CD38 to Reduce Ischemia-Reperfusion Injury in Liver Transplantation - PROJECT SUMMARY End-stage liver disease causes over 2.2 million deaths annually worldwide. Despite performing ~10,000 liver transplants yearly in the U.S., we discard ~10% of recovered organs, with rates exceeding 30% for donation after cardiac death (DCD) donors. The principal barrier is ischemia-reperfusion injury (IRI), which precipitates early allograft dysfunction and may lead to graft loss. No FDA-approved drugs exist to repair donor organs. Although CD38 has been studied as a biomarker in transplantation, our data identify CD38, the body's major NADase, as a key driver of liver IRI. CD38 exists in two membrane topologies: a well-characterized ectoenzyme (type II) and a poorly characterized endoenzyme (type III). Our studies demonstrate that type III CD38, not type II, mediates hepatic IRI. Genetic CD38 ablation confers robust hepatoprotection, while type II inactivation fails to prevent injury. Existing CD38 inhibitors lack topology selectivity: the small molecule 78c requires doses over 100-fold higher than its type II IC50 to achieve hepatoprotection, creating translational barriers including off-target effects. This proposal aims to develop potent, selective type III CD38 inhibitors as first-in-class therapeutics for donor organ repair. Our hypothesis is that type III CD38 drives liver IRI through cell-specific mechanisms, with hepatocyte NAD+ depletion as the primary driver, and that potent type III-selective inhibitors (IC50 < 100 nM) will provide superior protection, improving transplantation outcomes. Aim 1 defines cell-type-specific and temporal mechanisms using Cre-inducible CD38 knockout mice with hepatocyte, LSEC, and myeloid-lineage-specific drivers to determine which cell types drive injury and when CD38 activity is critical. We will test inhibitors at multiple timepoints (30 minutes before through 6 hours after reperfusion) and assess rate-limiting pathways (NAD+ depletion versus Ca2+ signaling) using mouse hilar clamp and arterialized orthotopic liver transplant models. Aim 2 identifies and optimizes inhibitors using our Fluorescent Probe Cellular Binding Assay (FPCBA), which quantitatively measures type III CD38 engagement in living cells. Through high-throughput screening and rational design, we will screen approved drugs, clinical candidates, diverse chemical libraries, and focused heterocyclic warhead libraries, and design novel analogues and molecular glues as potential type III degraders. Our novel proof-of-concept compound CDD1285088 demonstrates approximately 10-fold greater potency than 78c. Aim 3 validates efficacy in mouse DCD transplantation and human tissue. We will test existing compounds (Years 2-3) and Aim 2 leads (Years 3-4), targeting at least 70% injury reduction and over 85% survival. Human validation includes precision-cut liver slices from DCD donors (n=30) and clinical correlation with transplant outcomes (n=30). Clinical impact, such as modestly expanding DCD utilization from 20-30% to 35-45% would enable 300-400 additional U.S. transplants annually. Our robust NMP program may enable Phase I trials to be initiated within 5 years. Beyond transplantation, type III CD38 inhibitors could address ischemic injuries affecting over 15 million Americans annually, establishing first-in-class therapeutics with broad applications.
