PROJECT SUMMARY PTP1B, a non-receptor–type oncogenic PTP, also known as PTPN1, is involved in growth factor signaling. The PTP1B gene is frequently amplified in cancers and correlates with poor prognosis. However, despite the attractiveness of PTP1B as a therapeutic target, the development of drug-like inhibitors of this enzyme has proven difficult, primarily due to low cell permeability and a lack of selectivity towards other PTPs. While numerous investigators are developing traditional types of inhibitors that target the reduced, active form of PTP1B, targeting PTP1B-ox has important advantages relating to inhibitor bioavailability and selectivity. The goal of this proposal is to develop charge neutral inhibitors that specifically target the oxidized form of PTP1B (PTP1B-ox), which exists principally in the disease state. This approach was validated in a recent study showing that single-chain variable fragment antibodies can stabilize oxPTP1B and, in so doing, modulate signaling pathways related to energy metabolism and cancer. In Aim 1, we will prepare and evaluate diverse sulfenic acid-reactive combinatorial libraries. In Aim 2, we will screen libraries prepared in Aim 1 to identify compounds that target oxidized PTP1B. Based on our expertise in targeting distinct redox forms of therapeutically important proteins and innovative chemistry (Nat. Chem. Biol. 2012, 2018, 2023 and Nat. Chem. 2021), we will almost certainly identify molecules that target and stabilize the oxidized form of PTP1B. These nucleophilic compounds will lay the foundation for future studies on this topic as an R21 proposal to examine potency and SAR in cellular assays.