PTPN2: a tumor suppressor you want deleted?

A Medicinal Chemistry Perspective on Protein Tyrosine Phosphatase Nonreceptor Type 2 in Tumor Immunology

PTPN2 (protein tyrosine phosphatase nonreceptor type 2) is an important member of the protein tyrosine phosphatase (PTP) family. It plays a crucial role in dephosphorylating tyrosine-phosphorylated proteins and modulating critical signaling pathways associated with T-cell receptors, IL-2, IFNγ, and various cytokines. In recent years, the PTPN2's biological role has been clarified, particularly since its association with tumor immunology was gradually revealed in 2017, making it a star target for cancer immunotherapy. The dual inhibitor AC484, which targets both PTPN2 and PTP1B, is currently undergoing phase I clinical trials. This advancement has attracted great interest from researchers to develop new drugs based on its unique structure. This review outlines the structural modification processes of PTPN2-targeted agents, focusing primarily on inhibitors and degraders. Finally, this review endeavors to provide a comprehensive perspective on the evolving field of PTPN2-targeted drug discovery for tumor immunotherapy, offering valuable insights for future drug development.

Haploinsufficiency in PTPN2 leads to early-onset systemic autoimmunity from Evans syndrome to lupus

An exome sequencing strategy employed to identify pathogenic variants in patients with pediatric-onset systemic lupus or Evans syndrome resulted in the discovery of six novel monoallelic mutations in PTPN2. PTPN2 is a phosphatase that acts as an essential negative regulator of the JAK/STAT pathways. All mutations led to a loss of PTPN2 regulatory function as evidenced by in vitro assays and by hyperproliferation of patients' T cells. Furthermore, patients exhibited high serum levels of inflammatory cytokines, mimicking the profile observed in individuals with gain-of-function mutations in STAT factors. Flow cytometry analysis of patients' blood cells revealed typical alterations associated with autoimmunity and all patients presented with autoantibodies. These findings further supported the notion that a loss of function in negative regulators of cytokine pathways can lead to a broad spectrum of autoimmune manifestations and that PTPN2 along with SOCS1 haploinsufficiency constitute a new group of monogenic autoimmune diseases that can benefit from targeted therapy.

PTPN2 Regulates Metabolic Flux to Affect β-Cell Susceptibility to Inflammatory Stress

Protein tyrosine phosphatase N2 (PTPN2) is a type 1 diabetes (T1D) candidate gene identified from human genome-wide association studies. PTPN2 is highly expressed in human and murine islets and becomes elevated upon inflammation and models of T1D, suggesting that PTPN2 may be important for β-cell survival in the context of T1D. To test whether PTPN2 contributed to β-cell dysfunction in an inflammatory environment, we generated a β-cell-specific deletion of Ptpn2 in mice (PTPN2-β knockout [βKO]). Whereas unstressed animals exhibited normal metabolic profiles, low- and high-dose streptozotocin-treated PTPN2-βKO mice displayed hyperglycemia and accelerated death, respectively. Furthermore, cytokine-treated Ptpn2-KO islets resulted in impaired glucose-stimulated insulin secretion, mitochondrial defects, and reduced glucose-induced metabolic flux, suggesting β-cells lacking Ptpn2 are more susceptible to inflammatory stress associated with T1D due to maladaptive metabolic fitness. Consistent with the phenotype, proteomic analysis identified an important metabolic enzyme, ATP-citrate lyase, as a novel PTPN2 substrate.

ARTICLE HIGHLIGHTS

Small molecule. Big biology. Dual phosphatase inhibitor enters the immunotherapy fray

The advent and clinical success of immune checkpoint inhibitors Ipilimumab, Nivolumab and Pembrolizumab has had a seismic impact on our drug discovery focus and rationale. Novel extrinsic targets that enhance immune responses to cancer are actively being pursued, while tumor intrinsic targets that render cancer cells more sensitive to the immune system have joined traditional intrinsic targets (e.g. directly cytotoxic) in the drug discovery pipeline. The phosphatase PTPN2 (TC-PTP) and its paralog PTPN1 (PTP-1B) are negative regulators of several cytokine signaling pathways and T cell receptor (TCR) signaling. In a recent publication, Baumgartner et al. demonstrate the pre-clinical efficacy of a first-in-class dual PTPN1/N2 active site inhibitor (ABBV-CLS-484/AC484) in cancer models.

Discovery of PVD-06 as a Subtype-Selective and Efficient PTPN2 Degrader

Protein tyrosine phosphatase nonreceptor Type 2 (PTPN2) is an attractive target for cancer immunotherapy. PTPN2 and another subtype of PTP1B are highly similar in structure, but their biological functions are distinct. Therefore, subtype-selective targeting of PTPN2 remains a challenge for researchers. Herein, the development of small molecular PTPN2 degraders based on a thiadiazolidinone dioxide-naphthalene scaffold and a VHL E3 ligase ligand is described, and the PTPN2/PTP1B subtype-selective degradation is achieved for the first time. The linker structure modifications led to the discovery of the subtype-selective PTPN2 degrader PVD-06 (PTPN2/PTP1B selective index > 60-fold), which also exhibits excellent proteome-wide degradation selectivity. PVD-06 induces PTPN2 degradation in a ubiquitination- and proteasome-dependent manner. It efficiently promotes T cell activation and amplifies IFN-γ-mediated B16F10 cell growth inhibition. This study provides a convenient chemical knockdown tool for PTPN2-related research and a paradigm for subtype-selective PTP degradation through nonspecific substrate-mimicking ligands, demonstrating the therapeutic potential of PTPN2 subtype-selective degradation.

Bioorthogonal Reaction-Mediated Tumor-Selective Delivery of CRISPR/Cas9 System for Dual-Targeted Cancer Immunotherapy

CRISPR system-assisted immunotherapy is an attractive option in cancer therapy. However, its efficacy is still less than expected due to the limitations in delivering the CRISPR system to target cancer cells. Here, we report a new CRISPR/Cas9 tumor-targeting delivery strategy based on bioorthogonal reactions for dual-targeted cancer immunotherapy. First, selective in vivo metabolic labeling of cancer and activation of the cGAS-STING pathway was achieved simultaneously through tumor microenvironment (TME)-biodegradable hollow manganese dioxide (H-MnO2 ) nano-platform. Subsequently, CRISPR/Cas9 system-loaded liposome was accumulated within the modified tumor tissue through in vivo click chemistry, resulting in the loss of protein tyrosine phosphatase N2 (PTPN2) and further sensitizing tumors to immunotherapy. Overall, our strategy provides a modular platform for precise gene editing in vivo and exhibits potent antitumor response by boosting innate and adaptive antitumor immunity.

Enhancing CAR T-cell therapies against solid tumors: Mechanisms and reversion of resistance

Chimeric antigen receptor (CAR) T-cell therapy, belonging to adoptive immune cells therapy, utilizes engineered immunoreceptors to enhance tumor-specific killing. By now new generations of CAR T-cell therapies dramatically promote the effectiveness and robustness in leukemia cases. However, only a few CAR T-cell therapies gain FDA approval till now, which are applied to hematologic cancers. Targeting solid tumors through CAR T-cell therapies still faces many problems, such as tumor heterogeneity, antigen loss, infiltration inability and immunosuppressive micro-environment. Recent advances provide new insights about the mechanisms of CAR T-cell therapy resistance and give rise to potential reversal therapies. In this review, we mainly introduce existing barriers when treating solid tumors with CAR T-cells and discuss the methods to overcome these challenges.

Macromolecular crowding amplifies allosteric regulation of T-cell protein tyrosine phosphatase

T-cell protein tyrosine phosphatase (TC-PTP) is a negative regulator of T-cell receptor and oncogenic receptor tyrosine kinase signaling and implicated in cancer and autoimmune disease. TC-PTP activity is modulated by an intrinsically disordered C-terminal region (IDR) and suppressed in cells under basal conditions. In vitro structural studies have shown that the dynamic reorganization of IDR around the catalytic domain, driven by electrostatic interactions, can lead to TC-PTP activity inhibition; however, the process has not been studied in cells. Here, by assessing a mutant (³⁷⁸KRKRPR³⁸³ mutated into ³⁷⁸EAAAPE³⁸³, called TC45^E/A) with impaired tail-PTP domain interaction, we obtained evidence that the downmodulation of TC-PTP enzymatic activity by the IDR occurs in cells. However, we found that the regulation of TC-PTP by the IDR is only recapitulated in vitro when crowding polymers that mimic the intracellular environment are present in kinetic assays using a physiological phosphopeptide. Our FRET-based assays in vitro and in cells confirmed that the effect of the mutant correlates with an impairment of the intramolecular inhibitory remodeling of TC-PTP by the IDR. This work presents an early example of the allosteric regulation of a protein tyrosine phosphatase being controlled by the cellular environment and provides a framework for future studies and targeting of TC-PTP function.

PTPN2, A Key Predictor of Prognosis for Pancreatic Adenocarcinoma, Significantly Regulates Cell Cycles, Apoptosis, and Metastasis

Objective

This study conducted a comprehensive analysis of the members of the PTPN family and emphasized the key role of PTPN2 as a potential therapeutic target and diagnostic biomarker in improving the survival rate of PAAD.

Method

Oncomine was used to analyze the pan-cancer expression of the PTPN gene family. The Cancer Genome Atlas (TCGA) data as well as Genotype-Tissue Expression (GTEx) data were downloaded to analyze the expression and prognosis of PTPNs. The diagnosis of PTPNs was evaluated by the experimental ROC curve. The protein-protein interaction (PPI) network was constructed by combining STRING and Cytoscape. The genes of 50 proteins most closely related to PTPN2 were screened and analyzed by GO and KEGG enrichment. The differentially expressed genes of PTPN2 were found by RNA sequencing, and GSEA enrichment analysis was carried out to find the downstream pathways and targets, which were verified by online tools and experiments. Finally, the relationship between PTPN2 and immune cell infiltration in PAAD, and the relationship with immune score and immune checkpoint were studied.

Result

The expression patterns and the prognostic value of multiple PTPNs in PAAD have been reported through bioinformatic analyzes. Among these members, PTPN2 is the most important prognostic signature that regulates the progression of PAAD by activating JAK-STAT signaling pathway. Comparison of two PAAD cell lines with normal pancreatic epithelial cell lines revealed that PTPN2 expression was up-regulated as a key regulator of PAAD, which was associated with poor prognosis. Knockdown of PTPN2 caused a profound decrease in PAAD cell growth, migration, invasion, and induced PAAD cell cycle and apoptosis. In addition, we conducted a series of enrichment analyses to investigate the PTPN2-binding proteins and the PTPN2 expression-correlated genes. We suggest that STAT1 and EGFR are the key factors to regulate PTPN2, which are involved in the progression of PAAD. Meanwhile, the silencing of PTPN2 induced the repression of STAT1 and EGFR expression.

Conclusion

These findings provide a comprehensive analysis of the PTPN family members, and for PAAD, they also demonstrate that PTPN2 is a diagnostic biomarker and a therapeutic target.

Macrophage Membrane-Camouflaged shRNA and Doxorubicin: A pH-Dependent Release System for Melanoma Chemo-Immunotherapy

Improving the efficacy of melanoma treatment remains an important global challenge. Here, we combined chemotherapy with protein tyrosine phosphatase nonreceptor type 2(Ptpn2) based immunotherapy in an effort to address this challenge. Short-hairpin RNA (shRNA) targeting Ptpn2 was coencapsulated with doxorubicin (DOX) in the cell membrane of M1 macrophages (M1HD@RPR). The prepared nanoparticles (NPs) were effectively phagocytosed by B16F10 cells and M1 macrophages, but not by M0 macrophages. Hence, NP evasion from the reticuloendothelial system (RES) was improved and NP enrichment in tumor sites increased. M1HD@RPR can directly kill tumor cells and stimulate immunogenic cell death (ICD) by DOX and downregulate Ptpn2. It can promote M1 macrophage polarization and dendritic cell maturation and increase the proportion of CD8⁺ T cells. M1HD@RPR killed and inhibited the growth of primary melanoma and lung metastatic tumor cells without harming the surrounding tissue. These findings establish M1HD@RPR as a safe multifunctional nanoparticle capable of effectively combining chemotherapy and gene immunotherapies against melanoma.

Programmable Unlocking Nano-Matryoshka-CRISPR Precisely Reverses Immunosuppression to Unleash Cascade Amplified Adaptive Immune Response

Immune checkpoint blockade (ICB) is an attractive option in cancer therapy, but its efficacy is still less than expected due to the transient and incomplete blocking and the low responsiveness. Herein, an unprecedented programmable unlocking nano-matryoshka-CRISPR system (PUN) targeting programmed cell death ligand 1 (PD-L1) and protein tyrosine phosphatase N2 (PTPN2) is fabricated for permanent and complete and highly responsive immunotherapy. While PUN is inert at normal physiological conditions, enzyme-abundant tumor microenvironment and preternatural intracellular oxidative stress sequentially trigger programmable unlocking of PUN to realize a nano-matryoshka-like release of CRISPR/Cas9. The successful nucleus localization of CRISPR/Cas9 ensures the highly efficient disruption of PD-L1 and PTPN2 to unleash cascade amplified adaptive immune response via revoking the immune checkpoint effect. PD-L1 downregulation in tumor cells not only disrupts PD-1/PD-L1 interaction to attenuate the immunosurveillance evasion but also spurs potent immune T cell responses to enhance adaptive immunity. Synchronously, inhibition of JAK/STAT pathway is relieved by deleting PTPN2, which promotes tumor susceptibility to CD8+ T cells depending on IFN-γ, thus further amplifying adaptive immune responses. Combining these advances together, PUN exhibits optimal antitumor efficiency and long-term immune memory with negligible toxicity, which provides a promising alternative to current ICB therapy.

PTPN2 phosphatase deletion in T cells promotes anti-tumour immunity and CAR T-cell efficacy in solid tumours

Although adoptive T-cell therapy has shown remarkable clinical efficacy in haematological malignancies, its success in combating solid tumours has been limited. Here, we report that PTPN2 deletion in T cells enhances cancer immunosurveillance and the efficacy of adoptively transferred tumour-specific T cells. T-cell-specific PTPN2 deficiency prevented tumours forming in aged mice heterozygous for the tumour suppressor p53. Adoptive transfer of PTPN2-deficient CD8+ T cells markedly repressed tumour formation in mice bearing mammary tumours. Moreover, PTPN2 deletion in T cells expressing a chimeric antigen receptor (CAR) specific for the oncoprotein HER-2 increased the activation of the Src family kinase LCK and cytokine-induced STAT-5 signalling, thereby enhancing both CAR T-cell activation and homing to CXCL9/10-expressing tumours to eradicate HER-2+ mammary tumours in vivo. Our findings define PTPN2 as a target for bolstering T-cell-mediated anti-tumour immunity and CAR T-cell therapy against solid tumours.