Discovering potent PTP4A3 phosphatase small molecule inhibitors for colorectal cancer

Abstract

Although there has been significant progress in understanding colorectal cancer pathogenesis, the 5‐year patient survival rate in the United States of ~60% underlines the need for better treatment options when surgical resection and current therapies are not sufficient. In recent years, protein tyrosine phosphatase 4A3 (PTP4A3) has garnered significant interest and extensive validation as an anticancer target. The Oncomine database documents PTP4A3 is in the top 1% of the most highly expressed colorectal cancer genes with >650 tumor samples. Moreover, it has been noted that increased PTP4A3 expression correlates with increased tumor invasiveness and poor patient prognosis. We synthesized the thienopyridone JMS‐631‐050, which is the most potent published PTP4A3 small molecule inhibitor. Using 6,8‐difluoro‐4‐methylumbelliferyl phosphate as an artificial substrate, we found JMS‐631‐050 non‐competitively inhibited recombinant PTP4A3 in vitro phosphatase activity with an IC50 value of 138 nM. We have generated the first NMR spectra of PTP4A3 in complex with JMS‐631‐050 to more thoroughly characterize the nature of their interaction. Preliminary analysis of NMR data suggests that JMS‐631‐050 binds to a region of the phosphatase outside of the active site, which we hypothesize decreases protein flexibility and proximity of the general acid to the catalytic cysteine. This binding site is also consistent with molecular docking simulation studies. Recently, we discovered a new, more potent thienopyridone analog, JMS‐631‐053, which inhibited recombinant PTP4A3 in vitro phosphatase activity with an IC50 value of 8 nM and showed limited or no inhibition against other phosphatases at concentrations < 1 μM. Both JMS‐631‐050 and JMS‐631‐053, which computationally have drug‐like properties, reduced cellular migration of mouse colorectal tumor cells and prevented the formation of cohesive spheroids in an extracellular matrix phenocopying results observed with PTP4A3 null colorectal cancer cells. JMS‐631‐050 and JMS‐631‐053 should be valuable reagents for further validation of PTP4A3 as a cancer target as well as potential leads for drug discovery.Support or Funding InformationNIH R21CA191944, the Farrow Fellowship, and NCI Cancer Center Support Grant P30 CA44579