Pharmacological Targeting of the Mitochondrial Phosphatase PTPMT1

Abstract

The dual-specificity protein tyrosine phosphatases (PTPs) play integral roles in the regulation of cell signaling. There is a need for new tools to study these phosphatases, and the identification of inhibitors potentially affords not only new means for their study, but also possible therapeutics for the treatment of diseases caused by their dysregulation. However, the identification of selective inhibitors of the protein phosphatases has proven somewhat difficult. PTP localized to mitochondrion 1 (PTPMT1) is a recently discovered dual-specificity phosphatase that has been implicated in the regulation of insulin secretion. Screening of a commercially available small-molecule library yielded alexidine dihydrochloride, a dibiguanide compound, as an effective and selective inhibitor of PTPMT1 with an in vitro concentration that inhibits response by 50% of 1.08 M. A related dibiguanide analog, chlorhexidine dihydrochloride, also significantly inhibited PTPMT1, albeit with lower potency, while a monobiguanide analog showed very weak inhibition. Treatment of isolated rat pancreatic islets with alexidine dihydrochloride resulted in a dosedependent increase in insulin secretion, whereas treatment of a pancreatic ␤-cell line with the drug affected the phosphorylation of mitochondrial proteins in a manner similar to genetic inhibition of PTPMT1. Furthermore, knockdown of PTPMT1 in rat islets rendered them insensitive to alexidine dihydrochloride treatment, providing evidence for mechanism-based activity of the inhibitor. Taken together, these studies establish alexidine dihydrochloride as an effective inhibitor of PTPMT1, both in vitro and in cells, and support the notion that PTPMT1 could serve as a pharmacological target in the treatment of type II diabetes.

Identification and Evaluation of Twin-Arginine Translocase Inhibitors

“…At the higher concentrations in our assay, alexidine-treated cells exhibited increased PlcH activity over the controls, consistent with leakage through the cell membrane (polymyxin B sulfate, another cationic basic protein which alters membrane structure, was also a hit in our initial screen). It is interesting that although alexidine dihydrochloride's antimicrobial activity has previously been ascribed to its nonspecific disruption of bacterial membranes (21), a recent study reports that it is also a selective and effective inhibitor of PTPMT1, a dual-specificity protein tyrosine phosphatase localized to mitochondria which has been implicated in the regulation of insulin secretion (17). Yet another study links the antifungal activity of alexidine dihydrochloride to possible inhibition of secreted and cytosolic fungal phospholipase B (20).…”

Maintenance of mouse hematopoietic stem cells ex vivo by reprogramming cellular metabolism

“…7 Ptpmt1 depletion blocks differentiation in ES cells and HSCs without affecting cell survival. 7,9 Inspired by these findings and given that a known antibiotic, alexidine dihydrochloride (AD), has been identified as a selective and potent Ptpmt1 inhibitor, 10 we investigated whether HSCs could be better maintained/expanded ex vivo by pharmacologic inhibition of Ptpmt1.…”

Novel Pharmacological Approaches to the Treatment of Type 2 Diabetes

“…Protein tyrosine phosphatase localized to mitochondrion 1 (PTPMT1) may be involved in the regulation of insulin secretion, because ATP and subsequently released insulin are increased in PTPMT1 knockdown rat islet experiments. Inhibitors were detected, such as the dibiguanides alexidine (IC 50 , 1.08 M) and chlorhexidine (more potent) (Doughty-Shenton et al, 2010). Phosphorylation of mitochondrial proteins is decreased by these compounds similar to PTPMT1 knockdown experiments (Doughty-Shenton et al, 2010).…”

“…Inhibitors were detected, such as the dibiguanides alexidine (IC 50 , 1.08 M) and chlorhexidine (more potent) (Doughty-Shenton et al, 2010). Phosphorylation of mitochondrial proteins is decreased by these compounds similar to PTPMT1 knockdown experiments (Doughty-Shenton et al, 2010). This enzyme may be a target for future therapies.…”