Rongjun He

Small molecule tools for functional interrogation of protein tyrosine phosphatases

The importance of protein tyrosine phosphatases (PTPs) in the regulation of cellular signalling is well established. Malfunction of PTP activity is also known to be associated with cancer, metabolic syndromes and autoimmune disorders, as well as neurodegenerative and infectious diseases. However, a detailed understanding of the roles played by the PTPs in normal physiology and in pathogenic conditions has been hampered by the absence of PTP‐specific small molecule agents. In addition, the therapeutic benefits of modulating this target class are underexplored as a result of a lack of suitable chemical probes. Potent and specific PTP inhibitors could significantly facilitate functional analysis of the PTPs in complex cellular signal transduction pathways and may constitute valuable therapeutics in the treatment of several human diseases. We highlight the current challenges to and opportunities for developing PTP‐specific small molecule agents. We also review available selective small molecule inhibitors developed for a number of PTPs, including PTP1B, TC‐PTP, SHP2, lymphoid‐specific tyrosine phosphatase, haematopoietic protein tyrosine phosphatase, CD45, PTPβ, PTPγ, PTPRO, Vaccinia H1‐related phosphatase, mitogen‐activated protein kinase phosphatase‐1, mitogen‐activated protein kinase phosphatase‐3, Cdc25, YopH, mPTPA and mPTPB.

Bicyclic benzofuran and indole-based salicylic acids as protein tyrosine phosphatase inhibitors

Protein tyrosine phosphatases (PTPs) constitute a large and structurally diverse family of signaling enzymes that control the cellular levels of protein tyrosine phosphorylation. Malfunction of PTP activity has significant implications in many human diseases, and the PTP protein family provides an exciting array of validated diabetes/obesity (PTP1B), oncology (SHP2), autoimmunity (Lyp), and infectious disease (mPTPB) targets. However, despite the fact that PTPs have been garnering attention as novel therapeutic targets, they remain largely an untapped resource. The main challenges facing drug developers by the PTPs are inhibitor specificity and bioavailability. Work over the last ten years has demonstrated that it is feasible to develop potent and selective inhibitors for individual members of the PTP family by tethering together small ligands that can simultaneously occupy both the active site and unique nearby peripheral binding sites. Recent results with the bicyclic salicylic acid pharmacophores indicate that the new chemistry platform may provide a potential solution to overcome the bioavailability issue that has plagued the PTP drug discovery field for many years. Structural analysis of PTP-inhibitor complexes reveals molecular determinants important for the development of more potent and selective PTP inhibitors, thus offering hope in the medicinal chemistry of a largely unexploited protein class with a wealth of attractive drug targets.

Double Click Reaction for the Acquisition of a Highly Potent and Selective mPTPB Inhibitor

Tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), is a major worldwide threat to public health. Mycobacterium protein tyrosine phosphatase B (mPTPB) is a virulent phosphatase secreted by Mtb, which is essential for the survival and persistence of the bacterium in the host. Consequently, small‐molecule inhibitors of mPTPB are expected to serve as anti‐TB agents with a novel mode of action. Herein, we report the discovery of highly potent and selective mPTPB inhibitors using a novel, double Click chemistry strategy. The most potent mPTPB inhibitor from this approach possesses a Ki value of 160 nM and a >25‐fold selectivity for mPTPB over 19 other protein tyrosine phosphatases (PTBs). Molecular docking study of the enzyme–inhibitor complex provides a rationale for the high potency and selectivity of the lead compound and reveals an unusual binding mode, which may guide further optimization effort.

A facile hydroxyindole carboxylic acid based focused library approach for potent and selective inhibitors of Mycobacterium protein tyrosine phosphatase B.

Focused on Mtb: A facile hydroxyindole carboxylic acid based focused amide library was designed to target both the PTP active site and a unique nearby pocket for enhanced affinity and selectivity. HTS of the library led to the identification of a highly potent and selective inhibitor, 11 a, of mPTPB, an essential virulence factor for Mycobacterium tuberculosis. Compound 11 a shows high cellular activity and is capable of reversing the altered immune responses induced by mPTPB in macrophages.

Organocatalytic multicomponent reaction for the acquisition of a selective inhibitor of mPTPB, a virulence factor of tuberculosis.

Mycobacterium protein tyrosine phosphatase B (mPTPB) is essential for the survival and persistence of Mycobacterium in the host. Thus small molecule inhibitors of mPTPB are potential anti-TB agents. We developed an efficient organocatalytic multicomponent reaction (MCR) between pyrrole, formaldehyde and aniline, affording a potent and selective mPTPB inhibitor with an IC(50) value of 1.5 μM and >50-fold specificity. Our studies provide a successful example of using organocatalysis as a discovery tool for the acquisition of PTP inhibitors.

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.

Chapter 6:Recent Advances in PTP1B Inhibitor Development for the Treatment of Type 2 Diabetes and Obesity

Reversible phosphorylation of protein residues is a key strategy for cells to convey and conduct cellular signals, such as growth, differentiation, migration, and apoptosis. Aberrant phosphorylations either initiate inappropriate or block functional signal pathways, which results in the pathogenesis...

Diversity-oriented synthesis for novel, selective and drug-like inhibitors for a phosphatase from Mycobacterium tuberculosis

Mycobacterium protein tyrosine phosphatase B (mPTPB) is a potential drug target of Tuberculosis (TB). Small molecule inhibitors of mPTPB could be a treatment to overcome emerging TB drug resistance. Using a Diversity-Oriented Synthesis (DOS) strategy, we successfully developed a salicylic acid based and drug-like mPTPB inhibitor with an IC50 of 2 μM and >20-fold specificity over many human PTPs, making it an excellent lead molecule for anti-TB drug discovery. In addition, DOS generated bicyclic salicylic acids are also promising starting points for acquiring inhibitors targeting other PTPs.

Current Status of PTP-Based Therapeutics

Protein tyrosine phosphorylation regulates virtually all aspects of cellular function. Proper levels of protein tyrosine phosphorylation are controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs). Deregulation of tyrosine phosphorylation-mediated signaling is a major cause of cancer. Indeed, PTKs represent an important class of anti-cancer drug targets with more than 20 drugs already approved by the FDA. Several PTPs are also implicated in tumor onset, progression and metastasis, and have attracted attention as potential therapeutic targets for cancer treatment. The most recognized members of the PTP family include PTP1B, SHP2, CDC25, and PRLs. PTP1B plays a positive role in breast cancer progression; SHP2 germ line and somatic gain-of-function mutations cause Noonan Syndrome, juvenile myelomonocytic leukemia, acute myeloid leukemia, and solid tumors; CDC25 regulates cell cycle progression and is overexpressed in a number of human cancers; and the PRLs are overexpressed in cancer and have been linked to tumor metastasis. Hence, inhibitors directed against these PTPs can serve as potential novel anti-cancer agents. This chapter provides an overview of the mechanisms of these oncogenic PTPs in promoting cancer, the approaches for inhibitor discovery, as well as the current status of drug development targeting these phosphatases.