Protein tyrosine phosphorylation is a key regulatory process in virtually all aspects of cellular functions. Dysregulation of protein tyrosine phosphorylation is a major cause of human diseases, such as cancers, diabetes, autoimmune disorders, and neurological diseases. Indeed, protein tyrosine phosphorylation-mediated signaling events offer ample therapeutic targets, and drug discovery efforts to date have brought over two dozen kinase inhibitors to the clinic. Accordingly, protein tyrosine phosphatases (PTPs) are considered next-generation drug targets. For instance, PTP1B is a well-known targets of type 2 diabetes and obesity, and recent studies indicate that it is also a promising target for breast cancer. SHP2 is a bona-fide oncoprotein, mutations of which cause juvenile myelomonocytic leukemia, acute myeloid leukemia, and solid tumors. In addition, LYP is strongly associated with type 1 diabetes and many other autoimmune diseases. This review summarizes recent findings on several highly recognized PTP family drug targets, including PTP1B, Src homology phosphotyrosyl phosphatase 2(SHP2), lymphoid-specific tyrosine phosphatase (LYP), CD45, Fas associated phosphatase-1 (FAP-1), striatal enriched tyrosine phosphatases (STEP), mitogen-activated protein kinase/dual-specificity phosphatase 1 (MKP-1), phosphatases of regenerating liver-1 (PRL), low molecular weight PTPs (LMWPTP), and CDC25. Given that there are over 100 family members, we hope this review will serve as a road map for innovative drug discovery targeting PTPs.

The Src homology 2 domain containing protein tyrosine phosphatase-2 (SHP2) is an oncogenic phosphatase associated with various kinds of leukemia and solid tumors. Thus, there is substantial interest in developing SHP2 inhibitors as potential anticancer and antileukemia agents. Using a structure-guided and fragment-based library approach, we identified a novel hydroxyindole carboxylic acid-based SHP2 inhibitor 11a-1, with an IC50 value of 200 nM and greater than 5-fold selectivity against 20 mammalian PTPs. Structural and modeling studies reveal that the hydroxyindole carboxylic acid anchors the inhibitor to the SHP2 active site, while interactions of the oxalamide linker and the phenylthiophene tail with residues in the β5–β6 loop contribute to 11a-1’s binding potency and selectivity. Evidence suggests that 11a-1 specifically attenuates the SHP2-dependent signaling inside the cell. Moreover, 11a-1 blocks growth factor mediated Erk1/2 and Akt activation and exhibits excellent antiproliferative activity in lung cancer and breast cancer as well as leukemia cell lines.

Protein tyrosine phosphatases (PTP) are exciting and novel targets for cancer drug discovery that work in concert with protein tyrosine kinases (PTK) in controlling cellular homeostasis. Given the activating role that some PTKs play in initiating growth factor-mediated cellular processes, PTPs are usually perceived as the negative regulators of these events and therefore tumor suppressive in nature. However, mounting evidence indicate that PTPs do not always antagonize the activity of PTKs in regulating tyrosine phosphorylation, but can also play dominant roles in the initiation and progression of signaling cascades that regulate cell functions. It follows, therefore, that PTP malfunction can actively contribute to a host of human disorders, in particular, cancer, metabolic syndromes, and autoimmune diseases. The Src homology domain containing phosphatase 2 (SHP2) and the three-membered family of phosphatases of regenerating liver (PRL) are infamously oncogenic members of the PTP superfamily. Both are established regulators of major cancer pathways such as Ras/ ERK1/2, Src, JAK/STAT, JNK, NF-κB, and PTEN/PI3K/AKT. Furthermore, upregulation, mutation, or other dysregulation of these PTPs has been positively correlated with cancer initiation and progression. This review will provide topical coverage of target validation and drug discovery efforts made in targeting these oncogenic PTPs as compelling candidates for cancer therapy.

The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) is a critical signal transducer downstream of growth factors that promotes the activation of the RAS-ERK1/2 cascade. In its basal state, SHP2 exists in an autoinhibited closed conformation because of an intramolecular interaction between its N-SH2 and protein tyrosine phosphatase (PTP) domains. Binding to pTyr ligands present on growth factor receptors and adaptor proteins with its N-SH2 domain localizes SHP2 to its substrates and frees the active site from allosteric inhibition. Germline mutations in SHP2 are known to cause both Noonan syndrome (NS) and LEOPARD syndrome (LS), two clinically similar autosomal dominant developmental disorders. NS-associated SHP2 mutants display elevated phosphatase activity, while LS-associated SHP2 mutants exhibit reduced catalytic activity. A conundrum in how clinically similar diseases result from mutations to SHP2 that have opposite effects on this enzyme’s catalytic functionality exists. Here we report a comprehensive investigation of the kinetic, structural, dynamic, and biochemical signaling properties of the wild type as well as all reported LS-associated SHP2 mutants. The results reveal that LS-causing mutations not only affect SHP2 phosphatase activity but also induce a weakening of the intramolecular interaction between the N-SH2 and PTP domains, leading to mutants that are more readily activated by competing pTyr ligands. Our data also indicate that the residual phosphatase activity associated with the LS SHP2 mutant is required for enhanced ERK1/2 activation. Consequently, catalytically impaired SHP2 mutants could display gain-of-function properties because of their ability to localize to the vicinity of substrates for longer periods of time, thereby affording the opportunity for prolonged substrate turnover and sustained RAS-ERK1/2 activation.

PRL oncoproteins are phosphatases overexpressed in numerous types of human cancer. Elevated levels of PRL associate with metastasis and poor clinical outcomes. In principle, PRL phosphatases offer appealing therapeutic targets, but they remain underexplored due to the lack of specific chemical probes. In this study, we address this issue by exploiting a unique property of PRL phosphatases, namely, that they may function as homotrimers. Starting from a sequential structure-based virtual screening and medicinal chemistry strategy, we identified Cmpd-43 and several analogs which disrupt PRL1 trimerization. Biochemical and structural analyses demonstrate that Cmpd-43 and its close analogs directly bind the PRL1 trimer interface and obstruct PRL1 trimerization. Cmpd-43 also specifically blocks the PRL1-induced cell proliferation and migration through attenuation of both ERK1/2 and Akt activity. Importantly, Cmpd-43 exerted potent anticancer activity both in vitro and in vivo in a murine xenograft model of melanoma. Our results validate a trimerization-dependent signaling mechanism for PRL and offer proof-of-concept for trimerization inhibitors as candidate therapeutics to treat PRL-driven cancers

Protein tyrosine phosphatases (PTPs) are potential therapeutic targets for many diseases. Unfortunately, despite considerable drug discovery efforts devoted to PTPs, obtaining selective and cell permeable PTP inhibitors remains highly challenging. We describe a strategy to explore the existing drug space for previously unknown PTP inhibitory activities. This led to the discovery of cefsulodin as an inhibitor of SHP2, an oncogenic phosphatase in the PTP family. Crystal structure analysis of SHP2 interaction with cefsulodin identified sulfophenyl acetic amide (SPAA) as a novel phosphotyrosine (pTyr) mimetic. A structure-guided and SPAA fragment-based focused library approach produced several potent and selective SHP2 inhibitors. Notably, these inhibitors blocked SHP2-mediated signaling events and proliferation in several cancer cell lines. Thus, SPAA may serve as a new platform for developing chemical probes for other PTPs. KEYWORDS:Protein tyrosine phosphatase, pTyr mimetics, SHP2 inhibitors, fragment-based library, anticancer agents P roper level of protein tyrosine phosphorylation is vital for cell growth and survival. Aberrant tyrosine phosphorylation, due to imbalance of activities of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), is linked to numerous human diseases and offers enormous opportunities for therapeutic intervention. The success for such targeted approach has been well established by the more than two-dozen PTK inhibitors already used in clinic. 1 However, acquired resistance to PTK inhibitors limit durable responses. Therefore, there is great potential to modulate disease progression at the level of PTPs. To this end, the Src homology 2 (SH2) domain containing PTP2 (SHP2), encoded by the PTPN11 gene, is a positive signal transducer, required for most receptor PTKmediated Ras/ERK1/2 activation. 2,3 In addition, considerable evidence indicates that SHP2 is a bona fide oncoprotein as activating SHP2 mutations are found in leukemia and solid tumors. 4,5 Moreover, given the obligatory requirement of SHP2 in growth factor-mediated pathways, thwarting SHP2 activity may also prove effective for cancers caused by abnormal activation of receptor PTKs, some of which respond poorly to kinase inhibitor monotherapy. Hence there is strong interest in developing small molecule SHP2 inhibitors as novel anticancer agents. 6 However, the conserved PTP active site (i.e., pTyr-binding pocket) 7 makes it difficult to develop isozyme-specific inhibitors. One useful paradigm for the design of potent and selective PTP inhibitors is to engage both the active site and unique peripheral binding pockets by tethering appropriately functionalized moieties to a nonhydrolyzable pTyr mimetic. 8,9 Application of this strategy has enabled the development of a number of small molecule PTP probes. 10 Unfortunately, most existing pTyr mimetic-containing PTP inhibitors lack appropriate cellular efficacy, which represents a major obstacle in developing PTP-based therapeutics. Consequently, there is ...

Melanoma ranks among the most aggressive and deadly human cancers. Although a number of targeted therapies are available, they are effective only in a subset of patients and the emergence of drug resistance often reduces durable responses. Thus there is an urgent need to identify new therapeutic targets and develop more potent pharmacological agents for melanoma treatment. Herein we report that SHP2 levels are frequently elevated in melanoma, and high SHP2 expression is significantly associated with more metastatic phenotype and poorer prognosis. We show that SHP2 promotes melanoma cell viability, motility, and anchorage-independent growth, through activation of both ERK1/2 and AKT signaling pathways. We demonstrate that SHP2 inhibitor 11a-1 effectively blocks SHP2-mediated ERK1/2 and AKT activation and attenuates melanoma cell viability, migration and colony formation. Most importantly, SHP2 inhibitor 11a-1 suppresses xenografted melanoma tumor growth, as a result of reduced tumor cell proliferation and enhanced tumor cell apoptosis. Taken together, our data reveal SHP2 as a novel target for melanoma and suggest SHP2 inhibitors as potential novel therapeutic agents for melanoma treatment.

mPTPB is a virulent phosphatase from Mycobacterium tuberculosis and a promising therapeutic target for tuberculosis. To facilitate mPTPB-based drug discovery, we identified α-sulfophenylacetic amide (SPAA) from cefsulodin, a third generation β-lactam cephalosporin antibiotic, as a novel pTyr pharmacophore for mPTPB. Structure-guided and fragment-based optimization of SPAA led to the most potent and selective mPTPB inhibitor 9, with a K i of 7.9 nM and more than 10,000-fold preference for mPTPB over a large panel of 25 phosphatases. Compound 9 also exhibited excellent cellular activity and specificity in blocking mPTPB function in macrophage. Given its novel structure, modest molecular mass, and extremely high ligand efficiency (0.46), compound 9 represents an outstanding lead compound for anti-TB drug discovery targeting mPTPB.