Discovery of a SHP2 Degrader with In Vivo Anti-Tumor Activity.

Src homology 2 domain-containing phosphatase 2 (SHP2) is an attractive target for cancer therapy due to its multifaceted roles in both tumor and immune cells. Herein, we designed and synthesized a novel series of proteolysis targeting chimeras (PROTACs) using a SHP2 allosteric inhibitor as warhead, with the goal of achieving SHP2 degradation both inside the cell and in vivo. Among these molecules, compound P9 induces efficient degradation of SHP2 (DC50 = 35.2 ± 1.5 nM) in a concentration- and time-dependent manner. Mechanistic investigation illustrates that the P9-mediated SHP2 degradation requires the recruitment of the E3 ligase and is ubiquitination- and proteasome-dependent. P9 shows improved anti-tumor activity in a number of cancer cell lines over its parent allosteric inhibitor. Importantly, administration of P9 leads to a nearly complete tumor regression in a xenograft mouse model, as a result of robust SHP2 depletion and suppression of phospho-ERK1/2 in the tumor. Hence, P9 represents the first SHP2 PROTAC molecule with excellent in vivo efficacy. It is anticipated that P9 could serve not only as a new chemical tool to interrogate SHP2 biology but also as a starting point for the development of novel therapeutics targeting SHP2.

An Integrated Proteomic Strategy to Identify SHP2 Substrates.

Protein phosphatases play an essential role in normal cell physiology and the development of diseases such as cancer. The innate challenges associated with studying protein phosphatases have limited our understanding of their substrates, molecular mechanisms, and unique functions within highly coordinated networks. Here, we introduce a novel strategy using substrate-trapping mutants coupled with quantitative proteomics methods to identify physiological substrates of Src homology 2 containing protein tyrosine phosphatase 2 (SHP2) in a high-throughput manner. The technique integrates three parallel mass spectrometry-based proteomics experiments, including affinity isolation of substrate-trapping mutant complex using wild-type and SHP2 KO cells, in vivo global quantitative phosphoproteomics, and in vitro phosphatase reaction. We confidently identified 18 direct substrates of SHP2 in the epidermal growth factor receptor signaling pathways, including both known and novel SHP2 substrates. Docking protein 1 was further validated using biochemical assays as a novel SHP2 substrate, providing a mechanism for SHP2-mediated Ras activation. This advanced workflow improves the systemic identification of direct substrates of protein phosphatases, facilitating our understanding of the equally important roles of protein phosphatases in cellular signaling.

A head-to-head comparison of the EQ-5D-3L index scores derived from the two EQ-5D-3L value sets for China.

OBJECTIVE: Two EQ-5D-3L (3L) value sets (developed in 2014 and 2018) co-exist in China. The study examined the level of agreement between index scores for all the 243 health states derived from them at both absolute and relative levels and compared the responsiveness of the two indices. METHODS: Intraclass correlations coefficient (ICC) and Bland-Altman plot were adopted to assess the degree of agreement between the two indices at the absolute level. Health gains for 29,403 possible transitions between pairs of 3L health states were calculated to assess the agreement at the relative level. Their responsiveness for the transitions was assessed using Cohen effect size. RESULTS: The mean (SD) value was 0.427 (0.206) and 0.649 (0.189) for the 3L2014 and 3L2018 index scores, respectively. Although the ICC value showed good agreement (i.e., 0.896), 88.9% (216/243) of the points were beyond the minimum important difference limit according to the Bland-Altman plot. The mean health gains for the 29,403 health transitions was 0.234 (3L2014 index score) and 0.216 (3L2018 index score). The two indices predicted consistent transitions in 23,720 (80.7%) of 29,403 pairs. For the consistent pairs, Cohen effective size value was 1.05 (3L2014 index score) or 1.06 (3L2018 index score); and the 3L2014 index score only yielded 0.007 more utility gains. However, the results based on the two measures varied substantially according to the direction and magnitude of health change. CONCLUSION: The 3L2014 and 3L2018 index scores are not interchangeable. The choice between them is likely to influence QALYs estimations.

[Measurement Properties and Value Set of EuroQol Five-Dimensional Questionnaire-Youth Version].

Objective To summarize the research findings on the measurement properties and value set of EuroQol Five-Dimensional Questionnaire-Youth Version (EQ-5D-Y). Methods PubMed,Web of Science,CNKI,and Wanfang Data were searched for the studies involving the measurement properties and value set of EQ-5D-Y. Results According to the inclusion and exclusion criteria,38 studies were included for analysis.EQ-5D-Y had good feasibility,reliability,and validity in measuring health-related quality of life (HRQOL) of youth in different countries and populations.The advantages of 5-level EQ-5D-Y (Y-5L)over 3-level EQ-5D-Y (Y-3L) might be modest.The available studies have demonstrated that the EQ-5D value set for adults should not be adopted in youth,and the international protocol for constructing the Y-3L value set has been available.Many countries have established or are developing their own Y-3L value sets according to the protocol. Conclusion The study systematically elaborated the current status and trend of the measurement properties and value set of EQ-5D-Y,which could provide reference for the future research on the EQ-5D-Y in China.

Mechanistic insights explain the transforming potential of the T507K substitution in the protein-tyrosine phosphatase SHP2.

The protein-tyrosine phosphatase SHP2 is an allosteric enzyme critical for cellular events downstream of growth factor receptors. Mutations in the SHP2 gene have been linked to many different types of human diseases, including developmental disorders, leukemia, and solid tumors. Unlike most SHP2-activating mutations, the T507K substitution in SHP2 is unique in that it exhibits oncogenic Ras-like transforming activity. However, the biochemical basis of how the SHP2/T507K variant elicits transformation remains unclear. By combining kinetic and biophysical methods, X-ray crystallography, and molecular modeling, as well as using cell biology approaches, here we uncovered that the T507K substitution alters both SHP2 substrate specificity and its allosteric regulatory mechanism. We found that although SHP2/T507K exists in the closed, autoinhibited conformation similar to the WT enzyme, the interactions between its N-SH2 and protein-tyrosine phosphatase domains are weakened such that SHP2/T507K possesses a higher affinity for the scaffolding protein Grb2-associated binding protein 1 (Gab1). We also discovered that the T507K substitution alters the structure of the SHP2 active site, resulting in a change in SHP2 substrate preference for Sprouty1, a known negative regulator of Ras signaling and a potential tumor suppressor. Our results suggest that SHP2/T507K's shift in substrate specificity coupled with its preferential association of SHP2/T507K with Gab1 enable the mutant SHP2 to more efficiently dephosphorylate Sprouty1 at pTyr-53. This dephosphorylation hyperactivates Ras signaling, which is likely responsible for SHP2/T507K's Ras-like transforming activity.

A novel 15-spiro diterpenoid dimer from Andrographis paniculata with inhibitory potential against human carboxylesterase 2.

The phytochemical investigation of Andrographis paniculata resulted in the isolation of a novel 15-spiro diterpenoid dimer bisandrographolide G (1). Its structure was determined by 1D and 2D NMR, HRESIMS, electronic circular dichroism (ECD), and TD DFT calculations of ECD spectra. It showed potent inhibitory activity against human carboxylesterase 2 (CES 2) with an IC50 value of 4.61 ± 0.23 µM, and it was defined as a mixed-competitive type inhibitor with a Ki value of 8.88 µM based on the inhibition kinetics result. This finding gave us a hit to develop new generation of human CES 2 inhibitors.

Triterpenoids from Anchusa italica and their protective effects on hypoxia/reoxygenation induced cardiomyocytes injury.

Six new triterpenoids (1-6) and 22 known analogues (7-28), were separated from the aerial parts of Anchusa italica Retz., a traditional Uygur medicine for treating cardiovascular and cerebrovascular diseases in the Xinjiang region, China. The possible effects of compounds 1-28 on hypoxia/reoxygenation (H/R) induced cardiomyocytes injury were assayed, and compounds 4, 6-17, 21-22 and 26-28 showed significant protective effects. Further, the representative new compound 6 significantly suppressed the levels of H/R-induced apoptosis and autophagy in neonatal rat cardiomyocytes, with the reversing of the downregulated expression of Bcl-2 and upregulated expression of Bax and Beclin-1 by compound 6 treatment in neonatal rat cardiomyocytes following H/R injury. In addition, compound 6 protected cardiomyocyte from H/R injury, and pretreatment with 6 could decrease CK and LDH levels. Compound 6 also alleviated H/R-induced phosphorylation of p38 MAPK in neonatal rat cardiomyocytes. Therefore, tripterpenoid 6 and its analogues may be the pharmacodyamic material of A. italica, and offer a promising therapeutic approach for treating cardiomyocyte injury induced by H/R.

How the EQ-5D utilities are derived matters in Chinese diabetes patients: a comparison based on different EQ-5D scoring functions for China.

OBJECTIVES: In China, multiple approaches to calculating EQ-5D utilities are available, including the two EQ-5D-3L (3L2014 and 3L2018) scoring functions, the EQ-5D-5L (5L) scoring function, and the crosswalk function linking the 3L utilities and 5L health states. The study compared utilities derived from them in terms of agreement and discriminative power; and assessed whether the use of different approaches may affect QALY estimation in Chinese type 2 diabetes (T2D) patients. METHODS: Cross-sectional data of 289 T2D patients who self-completed both the 5L and 3L questions were used. Agreement were examined using intraclass correlation coefficient (ICC) and Bland-Altman plots. The ability of the EQ-5D utilities in differentiating the patients with and without clinical conditions was evaluated using F-statistics. Their influence on QALY estimation was assessed adopting mean absolute difference (MAD) in utility values between the patients. RESULTS: The ICC values were 0.881 (3L2014-3L2018), 0.958 (5L-c5L2014), and 0.806 (5L-c5L2018). The two 3L utilities and the three 5L utilities had poor agreement at the lower end of utility scale according to Bland-Altman plots. The 3L2018 utilities had lower F-statistics compared to the 3L2014 utilities; the two c5L utilities had larger or similar F-statistics compared to the 5L utilities. The mean MADs were 0.138 (5L), 0.116 (3L2014), 0.115 (c5L2014), 0.055 (c5L2018), and 0.055 (3L2018). CONCLUSION: The 3L2014 utilities is more discriminative than the 3L2018 utilities; and the two c5L utilities have no worse discriminative power compared with the 5L utilities. The choice of the approach to calculating the EQ-5D utilities is likely to affect QALY estimates.

Quinic Acid-Conjugated Nanoparticles Enhance Drug Delivery to Solid Tumors via Interactions with Endothelial Selectins.

Current nanoparticle (NP) drug carriers mostly depend on the enhanced permeability and retention (EPR) effect for selective drug delivery to solid tumors. However, in the absence of a persistent EPR effect, the peritumoral endothelium can function as an access barrier to tumors and negatively affect the effectiveness of NPs. In recognition of the peritumoral endothelium as a potential barrier in drug delivery to tumors, poly(lactic-co-glycolic acid) (PLGA) NPs are modified with a quinic acid (QA) derivative, synthetic mimic of selectin ligands. QA-decorated NPs (QA-NP) interact with human umbilical vein endothelial cells expressing E-/P-selectins and induce transient increase in endothelial permeability to translocate across the layer. QA-NP reach selectin-upregulated tumors, achieving greater tumor accumulation and paclitaxel (PTX) delivery than polyethylene glycol-decorated NPs (PEG-NP). PTX-loaded QA-NP show greater anticancer efficacy than Taxol or PTX-loaded PEG-NP at the equivalent PTX dose in different animal models and dosing regimens. Repeated dosing of PTX-loaded QA-NP for two weeks results in complete tumor remission in 40-60% of MDA-MB-231 tumor-bearing mice, while those receiving control treatments succumb to death. QA-NP can exploit the interaction with selectin-expressing peritumoral endothelium and deliver anticancer drugs to tumors to a greater extent than the level currently possible with the EPR effect.

Molecular basis of gain-of-function LEOPARD syndrome-associated SHP2 mutations.

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.

Protein tyrosine phosphatases as potential therapeutic targets.

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.

Off-target autophagy inhibition by SHP2 allosteric inhibitors contributes to their anti-tumor activity in RAS-driven cancers.

Aberrant activation of RAS-MAPK signaling is common in cancer, and efforts to inhibit pathway components have yielded drugs with promising clinical activities. Unfortunately, treatment-provoked adaptive resistance mechanisms inevitably develop, limiting their therapeutic potential. As a central node essential for receptor tyrosine kinase mediated RAS activation, SHP2 has emerged as an attractive cancer target. Consequently, many SHP2 allosteric inhibitors are now in clinical testing. Here we discovered a previously unrecognized off-target effect associated with SHP2 allosteric inhibitors. We found that these inhibitors accumulate in the lysosome and block autophagic flux in a SHP2-independent manner. We showed that off-target autophagy inhibition by SHP2 allosteric inhibitors contributes to their anti-tumor activity. We also demonstrated that SHP2 allosteric inhibitors harboring this off-target activity not only suppress oncogenic RAS signaling but also overcome drug resistance such as MAPK rebound and protective autophagy in response to RAS-MAPK pathway blockage. Finally, we exemplified a therapeutic framework that harnesses both the on- and off-target activities of SHP2 allosteric inhibitors for improved treatment of mutant RAS driven and drug resistant malignancies such as pancreatic and colorectal cancers. Brief Summary: SHP2 allosteric inhibitors elicit off-target autophagy blockade that can be exploited for improved treatment of RAS-driven and drug-resistant cancers.

SPSiPs, a Class of Diphosphine Ligands Based on SPSiOL with a Large Dihedral Angle.

The development and the synthetic applications of a novel class of diphosphine ligands (SPSiPs) based on chiral spirosilabiindane diol (SPSiOL) are presented. Starting from SPSiOL, the diphosphine ligands could be readily prepared in three steps with high efficiency. This novel class of diphosphine ligands features rigid configuration, a large dihedral angle, a large P-M-P angle, and a long P-P distance. The potentials of SPSiPs in asymmetric catalysis have also been preliminarily disclosed.

A fluorometric assay for high-throughput screening targeting nicotinamide phosphoribosyltransferase.

Nicotinamide adenine dinucleotide (NAD) plays a crucial role in many cellular processes. As the rate-limiting enzyme of the predominant NAD biosynthesis pathway in mammals, nicotinamide phosphoribosyltransferase (Nampt) regulates the cellular NAD level. Tumor cells are more sensitive to the NAD levels, making them more susceptible to Nampt inhibition than their nontumorigenic counterparts. Experimental evidence has indicated that Nampt might have proangiogenic activity and supports the growth of some tumors, so Nampt inhibitors may be promising as antitumor agents. However, only four Nampt inhibitors have been reported, and no high-throughput screening (HTS) strategy for Nampt has been proposed to date, largely limiting the drug discovery targeting Nampt. Therefore, the development of a robust HTS strategy for Nampt is both imperative and significant. Here we developed a fluorometric method for a Nampt activity assay by measuring the fluorescence of nicotinamide mononucleotide (NMN) derivative resulting from the enzymatic product NMN through simple chemical reactions. Then we set up an HTS system after thorough optimizations of this method and validated that it is feasible and effective through a pilot screening on a small library. This HTS system should expedite the discovery of Nampt inhibitors as antitumor drug candidates.

4-Phenyl butyric acid does not generally reduce glucose levels in rodent models of diabetes.

1. Endoplasmic reticulum (ER) stress plays a role in the pathogenesis of diabetes. The aim of the present study was to investigate the effect of 4-phenyl butyric acid (PBA), a novel chemical chaperone reducing ER stress, on serum glucose level in different strains of normal and diabetic rodents. 2. 4-Phenyl butyric acid (1 g/kg per day, i.g.) was administered to ob/ob Type 2 diabetic mice, alloxan-induced Type 1 diabetic mice and hydrocortisone (HC)-induced Type 2 diabetic mice as well as normal C57BL/6J mice and Kumming mice for 14 days to evaluate its effect on serum glucose levels. In addition, mice were treated simultaneously with PBA (1 g/kg per day) and HC for 9 days to determine its preventive effect against the development of insulin resistance. PBA (0.7 and 1.4 g/kg per day) was administered to non-obese Type 2 diabetic Goto-Kakizaki (GK) and normal Wistar-Kyoto (WKY) rats for 14 and 7 days, respectively, to determine its effects on serum glucose levels. 3. 4-Phenyl butyric acid significantly reduced serum glucose levels in obese Type 2 diabetic ob/ob mice. Normoglycaemia was obtained in ob/ob mice after 4 days of PBA treatment and was maintained for up to 14 days treatment. 4. 4-Phenyl butyric acid had no glucose-lowering effect in alloxan-induced Type 1 diabetic mice, HC-induced Type 2 diabetic mice and non-obese Type 2 diabetic GK rats. In addition, it had no beneficial effects on insulin resistance in HC-treated mice. 5. 4-Phenyl butyric acid did not affect normal serum glucose levels in C57BL/6 J mice, Kunming mice or WKY rats. 6. In conclusion, PBA does not generally reduce glucose levels in rodent models of diabetes, although it can normalize glucose levels in ob/ob diabetic mice, indicating that restoration of ER function as diabetes therapy is limited to conditions under which ER stress is involved in the high glucose levels.

Polydopamine-Based Multifunctional Antitumor Nanoagent for Phototherapy and Photodiagnosis by Regulating Redox Balance.

The development of multifunctional nanoagents for the simultaneous achievement of high diagnostic and therapeutic performances is significant for precise cancer treatment. Herein, we report on a polydopamine (PDA)-based multifunctional nanoagent, PML, in which the methylene blue (MB) photosensitizer (PS) and l-arginine (l-Arg) tumor-targeting species are equipped. After selectively accumulating in tumor sites, glutathione (GSH)-responsive PML degradation can controllably release loaded MB to produce singlet oxygen (1O2) under near-infrared (NIR) photoirradiation. This GSH-depleted PS release process can not only weaken the body's antioxidant defence ability but also synergistically increase the 1O2 concentration. Therefore, GSH depletion-enhanced photodynamic therapy (PDT) efficiency is logically achieved by regulating the intracellular redox balance. In addition, our nanoagent can guide photoacoustic/NIR thermal dual-modal imaging and convert light into heat for cooperative cancer phototherapy because of the inherent photothermal conversion nature of PDA. As a result, excellent in vivo antitumor phototherapy (PDT + PTT) is achieved under the precise guidance of dual-modal imaging. This work not only realizes the integration of cancer diagnosis and treatment through PDA-based nanocarriers but also delivers dimensions in designing the next generation of multifunctional antitumor nanoagents for enhanced phototherapy and photodiagnosis by regulating the redox balance.

Highly Potent and Selective N-Aryl Oxamic Acid-Based Inhibitors for Mycobacterium tuberculosis Protein Tyrosine Phosphatase B.

Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis (Mtb). Mtb protein tyrosine phosphatase B (mPTPB) is a virulence factor required for Mtb survival in host macrophages. Consequently, mPTPB represents an exciting target for tuberculosis treatment. Here, we identified N-phenyl oxamic acid as a highly potent and selective monoacid-based phosphotyrosine mimetic for mPTPB inhibition. SAR studies on the initial hit, compound 4 (IC50 = 257 nM), resulted in several highly potent inhibitors with IC50 values lower than 20 nM for mPTPB. Among them, compound 4t showed a Ki of 2.7 nM for mPTPB with over 4500-fold preference over 25 mammalian PTPs. Kinetic, molecular docking, and site-directed mutagenesis analyses confirmed these compounds as active site-directed reversible inhibitors of mPTPB. These inhibitors can reverse the altered host cell immune responses induced by the bacterial phosphatase. Furthermore, the inhibitors possess molecular weights <400 Da, log D7.4 < 2.5, topological polar surface area < 75, ligand efficiency > 0.43, and good aqueous solubility and metabolic stability, thus offering excellent starting points for further therapeutic development.

Therapeutic Targeting of Oncogenic Tyrosine Phosphatases.

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. Cancer Res; 77(21); 5701-5. ©2017 AACR.

Inhibition of Low Molecular Weight Protein Tyrosine Phosphatase by an Induced-Fit Mechanism.

The low molecular weight protein tyrosine phosphatase (LMW-PTP) is a regulator of a number of signaling pathways and has been implicated as a potential target for oncology and diabetes/obesity. There is significant therapeutic interest in developing potent and selective inhibitors to control LMW-PTP activity. We report the discovery of a novel class of LMW-PTP inhibitors derived from sulfophenyl acetic amide (SPAA), some of which exhibit greater than 50-fold preference for LMW-PTP over a large panel of PTPs. X-ray crystallography reveals that binding of SPAA-based inhibitors induces a striking conformational change in the LMW-PTP active site, leading to the formation of a previously undisclosed hydrophobic pocket to accommodate the α-phenyl ring in the ligand. This induced-fit mechanism is likely a major contributor responsible for the exquisite inhibitor selectivity.