Tyrosine phosphatase SHP2 inhibitors in tumor-targeted therapies

Strategies to overcome drug resistance using SHP2 inhibitors

Encoded by PTPN11, the SHP2 (Src homology-2 domain-containing protein tyrosine phosphatase-2) is widely recognized as a carcinogenic phosphatase. As a promising anti-cancer drug target, SHP2 regulates many signaling pathways such as RAS-RAF-ERK, PI3K-AKT and JAK-STAT. Meanwhile, SHP2 plays a significant role in regulating immune cell function in the tumor microenvironment. Heretofore, five SHP2 allosteric inhibitors have been recruited in clinical studies for the treatment of cancer. Most recently, studies have proved the therapeutic potential of SHP2 inhibitor in overcoming drug resistance of kinase inhibitors and programmed cell death-1 (PD-1) blockade. Herein, we review the structure, function and small molecular inhibitors of SHP2, and highlight recent progress in overcoming drug resistance using SHP2 inhibitor. We hope this review would facilitate the future clinical development of SHP2 inhibitors.

Small-Molecule Inhibitors and Degraders Targeting KRAS-Driven Cancers

Drug resistance continues to be a major problem associated with cancer treatment. One of the primary causes of anticancer drug resistance is the frequently mutated RAS gene. In particular, considerable efforts have been made to treat KRAS-induced cancers by directly and indirectly controlling the activity of KRAS. However, the RAS protein is still one of the most prominent targets for drugs in cancer treatment. Recently, novel targeted protein degradation (TPD) strategies, such as proteolysis-targeting chimeras, have been developed to render "undruggable" targets druggable and overcome drug resistance and mutation problems. In this study, we discuss small-molecule inhibitors, TPD-based small-molecule chemicals for targeting RAS pathway proteins, and their potential applications for treating KRAS-mutant cancers. Novel TPD strategies are expected to serve as promising therapeutic methods for treating tumor patients with KRAS mutations.

Colony Stimulating Factor-1 and its Receptor in Gastrointestinal Malignant Tumors

Gastrointestinal malignant tumor is the fourth most common cancer in the world and the second cause of cancer death. Due to the susceptibility to lymphatic metastasis and liver metastasis, the prognosis of advanced tumor patients is still poor till now. With the development of tumor molecular biology, the tumor microenvironment and the cytokines, which are closely related to the proliferation, infiltration and metastasis, have become a research hotspot in life sciences. Colony stimulating factor-1 (CSF-1), a polypeptide chain cytokine, and its receptor CSF-1R are reported to play important roles in regulating tumor-associated macrophages in tumor microenvironment and participating in the occurrence and development in diversities of cancers. Targeted inhibition of the CSF-1/CSF-1R signal axis has broad application prospects in cancer immunotherapy. Here, we reviewed the biological characters of CSF-1/CSF-1R and their relationship with gastrointestinal malignancies.

Synthesis and biological evaluation of 2,5-diaryl-1,3,4-oxadiazole derivatives as novel Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2) inhibitors

The Src homology-2 domain containing-protein tyrosine phosphatase-2 (SHP2) is a convergent node for oncogenic cell-signaling cascades including the PD-L1/PD-1 pathway. As an oncoprotein as well as a potential immunomodulator, SHP2 has now emerged as an attractive target for novel anti-cancer agents. Although significant progress has been made in identifying chemotypes of SHP2 inhibitors, these specific compounds might not be clinically useful to inhibit frequently encountered mutated SHP2 variants. Consequently, it is highly desirable to develop chemically different SHP2 inhibitors sensitive to SHP2 mutants. This work developed a new type of SHP2 inhibitors with 2,5-diaryl-1,3,4-oxadiazole scaffold. The representative compound 6l exhibited SHP2 inhibitory activity with IC₅₀ of 2.73 ± 0.20 µM, showed about 1.56-fold, 5.26-fold, and 7.36-fold selectivity for SHP2 over SHP1, PTP1B and TCPTP respectively. Further investigations confirmed that 6l behaved as mixed-type inhibitor sensitive to leukemia cell TF-1 and inhibited SHP2 mediated cell signaling and proliferation. Molecular dynamics simulation provided more detailed information on the binding modes of compounds and SHP2 protein. These preliminary results could provide a possible opportunity for the development of novel SHP2 inhibitors sensitive to SHP2 mutants with optimal potency and improved pharmacological properties.

Functional interrogation and therapeutic targeting of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) counteract the enzymatic activity of protein tyrosine kinases to modulate levels of both normal and disease-associated protein tyrosine phosphorylation. Aberrant activity of PTPs has been linked to the progression of many disease states, yet no PTP inhibitors are currently clinically available. PTPs are without a doubt a difficult drug target. Despite this, many selective, potent, and bioavailable PTP inhibitors have been described, suggesting PTPs should once again be looked at as viable therapeutic targets. Herein, we summarize recently discovered PTP inhibitors and their use in the functional interrogation of PTPs in disease states. In addition, an overview of the therapeutic targeting of PTPs is described using SHP2 as a representative target.

Double-edged roles of protein tyrosine phosphatase SHP2 in cancer and its inhibitors in clinical trials

Phosphorylation is a reversible post-translational modification regulated by phosphorylase and dephosphorylase to mediate important cellular events. Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) encoded by PTPN11 is the first identified oncogenic protein in protein tyrosine phosphatases family. Serving as a convergent node, SHP2 is involved in multiple cascade signaling pathways including Ras-Raf-MEK-ERK, PI3K-AKT, JAK-STAT and PD-1/PD-L1 pathways. Especially, the double-edged roles of SHP2 based on the substrate specificity in various biological contexts dramatically increase the effect complexity in different SHP2-associated diseases. Evidences suggest that by collaborating with other mutations in associated pathways, dysregulation of SHP2 contributes to the pathogenesis of different cancers, making SHP2 a promising therapeutic target for cancer treatment. SHP2 can either act as oncogenic factor or tumor suppressor in different diseases, and both the conserved catalytic dephosphorylation mechanism and the unique allosteric regulation mechanism of SHP2 provide opportunities for the development of SHP2 inhibitors and activators. To date, several small-molecule SHP2 inhibitors have advanced into clinical trials for mono- or combined therapy of cancers. Moreover, SHP2 activators and proteolysis-targeting chimera (PROTAC)-based degraders also display therapeutic promise. In this review, we comprehensively summarize the overall structures, regulation mechanisms, double-edged roles of SHP2 in both physiological and carcinogenic pathways, and SHP2 inhibitors in clinical trials. SHP2 activators and degraders are also briefly discussed. This review aims to provide in-depth understanding of the biological roles of SHP2 and highlight therapeutic potential of targeting SHP2.

Targeting Canonical and Non-Canonical STAT Signaling Pathways in Renal Diseases

Signal transducer and activator of transcription (STAT) plays an essential role in the inflammatory reaction and immune response of numerous renal diseases. STATs can transmit the signals of cytokines, chemokines, and growth factors from the cell membrane to the nucleus. In the canonical STAT signaling pathways, upon binding with their cognate receptors, cytokines lead to a caspase of Janus kinases (JAKs) and STATs tyrosine phosphorylation and activation. Besides receptor-associated tyrosine kinases JAKs, receptors with intrinsic tyrosine kinase activities, G-protein coupled receptors, and non-receptor tyrosine kinases can also activate STATs through tyrosine phosphorylation or, alternatively, other post-translational modifications. Activated STATs translocate into the nucleus and mediate the transcription of specific genes, thus mediating the progression of various renal diseases. Non-canonical STAT pathways consist of preassembled receptor complexes, preformed STAT dimers, unphosphorylated STATs (U-STATs), and non-canonical functions including mitochondria modulation, microtubule regulation and heterochromatin stabilization. Most studies targeting STAT signaling pathways have focused on canonical pathways, but research extending into non-canonical STAT pathways would provide novel strategies for treating renal diseases. In this review, we will introduce both canonical and non-canonical STAT pathways and their roles in a variety of renal diseases.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Diacylglycerol Kinase alpha in X Linked Lymphoproliferative Disease Type 1

Diacylglycerol kinases are intracellular enzymes that control the balance between the secondary messengers diacylglycerol and phosphatidic acid. DGKα and DGKζ are the prominent isoforms that restrain the intensity of T cell receptor signalling by metabolizing PLCγ generated diacylglycerol. Thus, their activity must be tightly controlled to grant cellular homeostasis and refine immune responses. DGKα is specifically inhibited by strong T cell activating signals to allow for full diacylglycerol signalling which mediates T cell response. In X-linked lymphoproliferative disease 1, deficiency of the adaptor protein SAP results in altered T cell receptor signalling, due in part to persistent DGKα activity. This activity constrains diacylglycerol levels, attenuating downstream pathways such as PKCθ and Ras/MAPK and decreasing T cell restimulation induced cell death. This is a form of apoptosis triggered by prolonged T cell activation that is indeed defective in CD8⁺ cells of X-linked lymphoproliferative disease type 1 patients. Accordingly, inhibition or downregulation of DGKα activity restores in vitro a correct diacylglycerol dependent signal transduction, cytokines production and restimulation induced apoptosis. In animal disease models, DGKα inhibitors limit CD8⁺ expansion and immune-mediated tissue damage, suggesting the possibility of using inhibitors of diacylglycerol kinase as a new therapeutic approach.

Estrogen Decreases Cytoskeletal Organization by Forming an ERα/SHP2/c-Src Complex in Osteoclasts to Protect against Ovariectomy-Induced Bone Loss in Mice

Loss of ovarian function is closely related to estrogen (E₂) deficiency, which is responsible for increased osteoclast (OC) differentiation and activity. We aimed to investigate the action mechanism of E₂ to decrease bone resorption in OCs to protect from ovariectomy (OVX)-induced bone loss in mice. In vivo, tartrate-resistant acid phosphatase (TRAP) staining in femur and serum carboxy-terminal collagen crosslinks-1 (CTX-1) were analyzed upon E₂ injection after OVX in mice. In vitro, OCs were analyzed by TRAP staining, actin ring formation, carboxymethylation, determination of reactive oxygen species (ROS) level, and immunoprecipitation coupled with Western blot. In vivo and in vitro, E₂ decreased OC size more dramatically than OC number and Methyl-piperidino-pyrazole hydrate dihydrochloride (MPPD), an estrogen receptor alpha (ERα) antagonist, augmented the OC size. ERα was found in plasma membranes and E₂/ERα signaling affected receptor activator of nuclear factor κB ligand (RANKL)-induced actin ring formation by rapidly decreasing a proto-oncogene tyrosine-protein kinase, cellular sarcoma (c-Src) (Y416) phosphorylation in OCs. E₂ exposure decreased physical interactions between NADPH oxidase 1 (NOX1) and the oxidized form of c-Src homology 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2), leading to higher levels of reduced SHP2. ERα formed a complex with the reduced form of SHP2 and c-Src to decrease c-Src activation upon E₂ exposure, which blocked a signal for actin ring formation by decreased Vav guanine nucleotide exchange factor 3 (Vav3) (p-Y) and Ras-related C3 botulinum toxin substrate 1 (Rac1) (GTP) activation in OCs. E₂/ERα signals consistently inhibited bone resorption in vitro. In conclusion, our study suggests that E₂-binding to ERα forms a complex with SHP2/c-Src to attenuate c-Src activation that was induced upon RANKL stimulation in a non-genomic manner, resulting in an impaired actin ring formation and reducing bone resorption.

A multifunctional cross-validation high-throughput screening protocol enabling the discovery of new SHP2 inhibitors

The protein tyrosine phosphatase Src homology phosphotyrosyl phosphatase 2 (SHP2) is implicated in various cancers, and targeting SHP2 has become a promising therapeutic approach. We herein described a robust cross-validation high-throughput screening protocol that combined the fluorescence-based enzyme assay and the conformation-dependent thermal shift assay for the discovery of SHP2 inhibitors. The established method can effectively exclude the false positive SHP2 inhibitors with fluorescence interference and was also successfully employed to identify new protein tyrosine phosphatase domain of SHP2 (SHP2-PTP) and allosteric inhibitors. Of note, this protocol showed potential for identifying SHP2 inhibitors against cancer-associated SHP2 mutation SHP2-E76A. After initial screening of our in-house compound library (∼2300 compounds), we identified 4 new SHP2-PTP inhibitors (0.17% hit rate) and 28 novel allosteric SHP2 inhibitors (1.22% hit rate), of which SYK-85 and WS-635 effectively inhibited SHP2-PTP (SYK-85: IC50 = 0.32 μmol/L; WS-635: IC50 = 4.13 μmol/L) and thus represent novel scaffolds for designing new SHP2-PTP inhibitors. TK-147, an allosteric inhibitor, inhibited SHP2 potently (IC50 = 0.25 μmol/L). In structure, TK-147 could be regarded as a bioisostere of the well characterized SHP2 inhibitor SHP-099, highlighting the essential structural elements for allosteric inhibition of SHP2. The principle underlying the cross-validation protocol is potentially feasible to identify allosteric inhibitors or those inactivating mutants of other proteins.