VHR Phosphatase Research Articles

Abstract C044: Discovery and characterization of novel fragment binders of the VHR phosphatase as a drug target for cervix cancer

Abstract The dual-specificity phosphatase 3 (DUSP3), also known as Vaccinia H1-related phosphatase (VHR) was reported to exhibit elevated protein level in cervix cancer cell lines compared to normal keratinocytes implicating VHR as a novel target for cervical cancer therapeutic. VHR belongs to the superfamily of protein tyrosine phosphatases (PTPs), a large class of human enzymes that is notoriously difficult to target with small molecules. Recent studies have demonstrated some PTP functions as oncogenes to promote tumor development including SHP2 (PTPN11), PTP1B (PTPN1), and VHR (DUSP3). Fragment-based drug discovery (FBDD) has merged as an effective strategy to provide potent ligands, particularly for challenging drug targets such as PTPs. In this study, we present an NMR-based discovery platform designed to discovery fragment hits that exhibit binding affinity to VHR. Our platform employed fluorine NMR, a robust ligand-observed NMR method, to screen fragment library. Subsequent validation of confirmed hits was accomplished through a series of biophysical and biochemical experiments. Structural study such as X-ray crystallography provide binding mode of action of potent molecules with the VHR protein. Using this platform, we have successfully identified several potent fragments that displayed relative selectivity for VHR. Furthermore, We discovered novel ligand binding sites distinguished from the active site. Initial structure-activity relationship (SAR) studies were also conducted, enabling us to explore a set of validated fragment hits that serve as starting point for medicinal chemistry optimization. Moreover, our fragment discovery platform is a promising strategy for discovering potent and selective fragments targeting other PTPs, thereby offering potential therapeutic options for a boarder spectrum of cancer types. Citation Format: Jiaqian WU, Marek R Baranowski, Nicholas D.P. Cosford, Lutz Tautz. Discovery and characterization of novel fragment binders of the VHR phosphatase as a drug target for cervix cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C044.

ChemInform Abstract: Identification of Two Novel VHR Phosphatase Inhibitors with Structure‐Based Virtual Screening.

AbstractCompounds (I) and (II) exhibit significant inhibitory activity against VHR phosphatase.

Identification of Two Novel VHR Phosphatase Inhibitors with Structure-Based Virtual Screening

Identification of Two Novel VHR Phosphatase Inhibitors with Structure-Based Virtual Screening

Discovery of VHR Phosphatase Inhibitors with Micromolar Activity based on Structure‐Based Virtual Screening

Human VHR phosphatase has been shown to be involved in the regulation of cell-cycle progression and is itself modulated during the cell cycle, indicating that VHR can serve as a therapeutic target for cancer. In the present study, we identify new VHR inhibitors by means of a structure-based drug design protocol involving the virtual screening with docking simulations and in vitro enzyme assay.

Novel benzofuran inhibitors of human mitogen-activated protein kinase phosphatase-1

Protein tyrosine phosphatases have a central role in the maintenance of normal cellular functionality. For example, PTP1B has been implicated in insulin-resistance, obesity, and neoplasia. Mitogen-activated protein kinase phosphatase-1 (MKP-1 or DUSP1) dephosphorylates and inactivates mitogen-activated protein kinase (MAPK) substrates, such as p38, JNK, and Erk, and has been implicated in neoplasia. The lack of readily available selective small molecule inhibitors of MKP family members has severely limited interrogation of their biological role. Inspired by a previously identified inhibitor (NSC 357756) of MKP-3, we synthesized seven NSC 357756 congeners, which were evaluated for in vitro inhibition against several protein phosphatases. Remarkably, none displayed potent inhibition against MKP-3, including the desamino NSC 357756 analog NU-154. Interestingly, NU-154 inhibited human PTP1B in vitro with an IC 50 value of 24 ± 1 μM and showed little inhibition against Cdc25B, MKP-1, and VHR phosphatases. NU-126 [2-(( E)-2-(5-cyanobenzofuran-2-yl)vinyl)-1 H-indole-6-carbonitrile] inhibited MKP-1 and VHR in vitro but was less active against human MKP-3, Cdc25B, and PTP1B. The inhibition of MKP-1 by NU-126 was independent of redox processes. The benzofuran substructure represents a new potential scaffold for further analog development and provides encouragement that more selective and potent inhibitors of MKP family members may be achievable.

Structural Insights into Molecular Function of the Metastasis-associated Phosphatase PRL-3

Phosphatases and kinases are the cellular signal transduction enzymes that control protein phosphorylation. PRL phosphatases constitute a novel class of small (20 kDa), prenylated phosphatases with oncogenic activity. In particular, PRL-3 is consistently overexpressed in liver metastasis in colorectal cancer cells and represents a new therapeutic target. Here, we present the solution structure of PRL-3, the first structure of a PRL phosphatase. The structure places PRL phosphatases in the class of dual specificity phosphatases with closest structural homology to the VHR phosphatase. The structure, coupled with kinetic studies of site-directed mutants, identifies functionally important residues and reveals unique features, differentiating PRLs from other phosphatases. These differences include an unusually hydrophobic active site without the catalytically important serine/threonine found in most other phosphatases. The position of the general acid loop indicates the presence of conformational change upon catalysis. The studies also identify a potential regulatory role of Cys(49) that forms an intramolecular disulfide bond with the catalytic Cys(104) even under mildly reducing conditions. Molecular modeling of the highly homologous PRL-1 and PRL-2 phosphatases revealed unique surface elements that are potentially important for specificity.

Tyrosine phosphorylation of VHR phosphatase by ZAP-70.

The ZAP-70 tyrosine kinase is a key component of the signaling machinery for the T cell antigen receptor (TCR). Whereas recruitment and activation of ZAP-70 are relatively well understood, the proteins phosphorylated by ZAP-70 are incompletely known. We report here that VHR, a Vaccinia virus VH1-related dual-specific protein phosphatase that inactivates the mitogen-activated kinases Erk2 and Jnk, is phosphorylated at Y138 by ZAP-70. Tyr138 phosphorylation was required for VHR to inhibit the Erk2-Elk-1 pathway and, conversely, the VHR(Y138F) mutant augmented TCR-induced Erk2 kinase and activation of the gene encoding interleukin 2. These results suggest that VHR is a target for ZAP-70 and tempers activation of the Erk2 pathway in a ZAP-70-controlled manner.

The catalytic role of Cys124 in the dual specificity phosphatase VHR.

The recombinant human Vaccinia virus H1-related protein tyrosine phosphatase, (VHR PTPase) possesses intrinsic Tyr and Thr/Ser phosphatase activities. Both activities were abolished by a single amino acid substitution, C124S. When VHR was incubated with a 32P-labeled phosphotyrosine-containing substrate and then rapidly denatured, enzyme-associated 32P was evident following SDS-polyacrylamide gel electrophoresis. The formation of 32P-labeled protein could be blocked in the presence of an unlabeled substrate. VHR-associated 32P was sensitive to iodine but insensitive to pyridine and hydroxylamine. The catalytically inactive C124S mutant would not form a 32P-labeled enzyme. Furthermore, VHR phosphatase could be selectively inactivated by the alkylating agent iodoacetate. The inactivation resulted from the specific covalent modification of Cys124. Collectively these results suggest that a thiol-phosphate enzyme intermediate is formed when Cys124 of VHR accepts a phosphate from the substrate. Our results also demonstrate that the dual specificity phosphatases and the tyrosine-specific PTPases employ similar catalytic mechanisms.

The detailed characterisation of a 400 kb cosmid walk in the BRCA1 region: identification and localisation of 10 genes including a dual-specificity phosphatase

We have produced a detailed physical and transcriptional map of a 400 kb region within the narrowest flanking markers known to contain the hereditary breast and ovarian susceptibility gene, BRCA1. The approach described here has avoided the problems of chimaerism, instability and rearrangements commonly observed in yeast artificial chromosomes by converting the YAC clones into ordered chromosome 17-specific cosmid contigs and joining these contigs by cosmid end-walking. A detailed long-range restriction map provided a framework for the cosmid contig assembly and further refines existing physical mapping data. We have used a combined approach towards the isolation of the genes housed within these cosmids. This has resulted in the isolation and precise localisation of eight novel genes, including a novel G protein and an endogenous retrovirus related to the HERV-K family, and the previously described dual-specificity VHR phosphatase and MOX1 homeobox genes.