The Mechanism of Inhibition of the Undrugged Oncogenic Phosphatase PTP4A3 by a Novel Small Molecule JMS‐053

Abstract

The oncogenic tyrosine phosphatase PTP4A3 is an attractive cancer therapeutic target because it is overexpressed in many types of cancer and promotes tumor metastasis, contributing to poor patient prognosis. We recently synthesized JMS‐053, which is a potent, selective, reversible, iminothienopyridinedione inhibitor of PTP4A3. We modeled possible interactions between JMS‐053 and PTP4A3 and the goal of our current work was to test the model and further define the crucial amino acids involved in the PTP4A3 inhibition by JMS‐053. We generated three PTP4A3 single amino acid mutants: C104S, K144I and C49S. The enzymatic activities of these phosphatases were determined in vitro in the absence and presence of JMS‐053, using the artificial substrate 6,8‐difluoro‐4‐methylumbelliferyl phosphate. The C104S mutant showed no catalytic activity, consistent with C104 being the catalytic cysteine. The K144I mutant retained full enzymatic activity. In contrast to our molecular modeling predictions, the K144I mutant was inhibited by JMS‐053 to the same extent as the wild type enzyme. We concluded K144 was not primarily involved in JMS‐053 inhibition. Tyrosine phosphatases are known to be inhibited by intramolecular disulfide bond formation and C49S has been reported to be the only cysteine involved with disulfide bond formation with the catalytic C104. The C49S mutant had reduced catalytic activity compared to the wild type PTP4A3 but JMS‐053 retained partial inhibition. Thus, C49‐C104 disulfide bond formation does not appear to be the primary mode of JMS‐053 inhibition, although we cannot completely exclude involvement of C49. We are now examining the oxidation state of C104 after JMS‐053 treatment and new analogs of JMS‐053. The information obtained from mapping the critical amino acids involved in PTP4A3 inhibition should assist in the design of the next generation phosphatase inhibitors.Support or Funding InformationThe Department of Defense (BC170507), the Fiske Drug Discovery Fund and the Ivy Foundation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.