SHP2 inhibition reduces leukemogenesis in models of combined genetic and epigenetic mutations

Allosteric SHP2 inhibition increases apoptotic dependency on BCL2 and synergizes with venetoclax in FLT3- and KIT-mutant AML

Mutations in the receptor tyrosine kinases (RTKs) FLT3 and KIT are frequent and associated with poor outcomes in acute myeloid leukemia (AML). Although selective FLT3 inhibitors (FLT3i) are clinically effective, remissions are short-lived due to secondary resistance characterized by acquired mutations constitutively activating the RAS/MAPK pathway. Hereby, we report the pre-clinical efficacy of co-targeting SHP2, a critical node in MAPK signaling, and BCL2 in RTK-driven AML. The allosteric SHP2 inhibitor RMC-4550 suppresses proliferation of AML cell lines with FLT3 and KIT mutations, including cell lines with acquired resistance to FLT3i. We demonstrate that pharmacologic SHP2 inhibition unveils an Achilles' heel of RTK-driven AML, increasing apoptotic dependency on BCL2 via MAPK-dependent mechanisms, including upregulation of BMF and downregulation of MCL1. Consequently, RMC-4550 and venetoclax are synergistically lethal in AML cell lines and in clinically relevant xenograft models. Our results provide mechanistic rationale and pre-clinical evidence for co-targeting SHP2 and BCL2 in RTK-driven AML.

Adiponectin negatively regulates pigmentation, Wnt/β-catenin and HGF/c-Met signalling within human scalp hair follicles ex vivo

Adiponectin reportedly stimulates proliferation and elongation of human scalp hair follicles (HFs) ex vivo. In the current study, we investigated how adiponectin oligomers produced by perifollicular dermal white adipose tissue (dWAT), a potent source of adiponectin isoforms, influence human HF proliferation and pigmentation. To do so, we treated microdissected, organ-cultured HFs in the presence or absence of dWAT with a recombinant human adiponectin oligomer mix, or inhibited dWAT-derived adiponectin using a neutralizing antibody. Multiplex qPCR (Fluidigm) revealed that adiponectin oligomers downregulated pigmentation genes KITLG, PMEL and TYRP1 and Wnt genes AXIN2, LEF1 and WNT10B. In situ hybridization showed that adiponectin downregulated AXIN2 and LEF1, and up-regulated DKK1 within the dermal papilla (DP), a highly unusual transcriptional profile for a putative hair growth-promoting agent. Adiponectin oligomers also downregulated protein expression of the HGF receptor c-Met within the matrix and DP. However, adiponectin did not alter hair matrix keratinocyte proliferation within 48 h ex vivo, irrespective of the presence/absence of dWAT; HF pigmentation (Masson-Fontana histochemistry, tyrosinase activity) was also unchanged. In contrast, neutralizing adiponectin isoforms within HF + dWAT increased proliferation, melanin content and tyrosinase activity but resulted in fewer melanocytes and melanocytic dendrites, as assessed by gp100 immunostaining. These seemingly contradictory effects suggest that adiponectin exerts complex effects upon human HF biology, likely in parallel with the pro-pigmentation effects of dWAT- and DP-derived HGF. Our data suggest that dWAT-derived ratios of adiponectin isoforms and the cleaved, globular version of adiponectin may in fact determine how adiponectin impacts upon follicular pigmentation and growth.

Tumor PD-L1 engages myeloid PD-1 to suppress type I interferon to impair cytotoxic T lymphocyte recruitment

The cellular and molecular mechanisms underlying tumor cell PD-L1 (tPD-L1) function in tumor immune evasion are incompletely understood. We report here that tPD-L1 does not suppress cytotoxic T lymphocyte (CTL) activity in co-cultures of tumor cells and tumor-specific CTLs and exhibits no effect on primary tumor growth. However, deleting tPD-L1 decreases lung metastasis in a CTL-dependent manner in tumor-bearing mice. Depletion of myeloid cells or knocking out PD-1 in myeloid cells (mPD-1) impairs tPD-L1 promotion of tumor lung metastasis in mice. Single-cell RNA sequencing (scRNA-seq) reveals that tPD-L1 engages mPD-1 to activate SHP2 to antagonize the type I interferon (IFN-I) and STAT1 pathway to repress Cxcl9 and impair CTL recruitment to lung metastases. Human cancer patient response to PD-1 blockade immunotherapy correlates with IFN-I response in myeloid cells. Our findings determine that tPD-L1 engages mPD-1 to activate SHP2 to suppress the IFN-I-STAT1-CXCL9 pathway to impair CTL tumor recruitment in lung metastasis.

SHP2 deneddylation mediates tumor immunosuppression in colon cancer via the CD47/SIRPα axis

SIPRα on macrophages binds with CD47 to resist proengulfment signals, but how the downstream signal of SIPRα controls tumor-infiltrating macrophages (TIMs) is still poorly clarified. Here, we report that the CD47/signal regulatory protein α (SIRPα) axis requires the deneddylation of tyrosine phosphatase SHP2. Mechanistically, Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2) was constitutively neddylated on K358 and K364 sites; thus, its autoinhibited conformation was maintained. In response to CD47-liganded SIRPα, SHP2 was deneddylated by sentrin-specific protease 8 (SENP8), which led to the dephosphorylation of relevant substrates at the phagocytic cup and subsequent inhibition of macrophage phagocytosis. Furthermore, neddylation inactivated myeloid-SHP2 and greatly boosted the efficacy of colorectal cancer (CRC) immunotherapy. Importantly, we observed that supplementation with SHP2 allosteric inhibitors sensitized immune treatment-resistant CRC to immunotherapy. Our results emphasize that the CRC subtype that is unresponsive to immunotherapy relies on SIRPαhiSHP2hiNEDD8lo TIMs and highlight the need to further explore the strategy of SHP2 targeting in CRC therapy.

Amplifying STING activation by bioinspired nanomedicine for targeted chemo- and immunotherapy of acute myeloid leukemia

Chemotherapy resistance and the tumor immune microenvironment are dual reasons for the poor therapeutic efficacy of treating acute myeloid leukemia (AML), causing suboptimal clinical outcomes and high relapse rates. Activation of the stimulator of interferon genes (STING) pathway based on innate immunity can effectively improve antitumor immunity. However, traditional STING agonists are limited due to their easy degradation and difficult membrane transport. Here, a bioinspired nanomedicine synergizing chemo- and immunotherapy was developed by activating the STING pathway for targeted and systemic AML cell damage. We show that a leukemia cell membrane (LCM)-camouflaged hollow MnO₂ nanocarrier (HM) with encapsulated doxorubicin (DOX) (denoted LHMD) could bind specifically to AML cells with a homologous targeting effect. Then, MnO₂ was decomposed into Mn²⁺ in response to endosomal acid and glutathione (GSH), which improved the magnetic resonance imaging (MRI) signal for AML detection and activated the STING pathway. In mouse models, LHMD was confirmed to eradicate established AML and prevent the engraftment of AML cells. The percentages of T-helper 1 (Th1) and T-helper 17 (Th17) cells and the concentrations of type I interferon (IFN-Ⅰ) and proinflammatory cytokines increased, while the percentage of T-helper 2 (Th2) cells decreased, reflecting the anti-AML immune response induced by Mn²⁺ after treatment with LHMD. This nanotechnology-based therapeutic regimen may represent a generalizable strategy for generating an anti-leukemia immune response. STATEMENT OF SIGNIFICANCE: Relapse and chemotherapy refractoriness are main causes for the dismal prognosis of AML, making it urgent to develop more effective anti-AML therapies. This study proposes an innovative strategy to combat this issue by designing a biomimetic BM-targeted nanomedicine based on a MnO₂ nano-carrier to rationally deliver chemotherapeutic agents and to trigger Mn²⁺ mediated STING pathway activation for potent immune- and chemotherapy against AML cells. Hence, the nanomedicine design addresses the challenges associated with AML therapy and proposes a promising strategy to improve the therapeutic efficacy against AML.

A novel costimulatory molecule gene-modified leukemia cell-derived exosome-targeted CD4+ T cell vaccine efficiently enhances anti-leukemia immunity

Previous studies demonstrated that CD4+ T cells can uptake tumor antigen-pulsed dendritic cell-derived exosomes (DEXO), which harbor tumor antigen peptide/pMHC I complex and costimulatory molecules and show potent effects on inducing antitumor immunity. However, in preliminary study, CD4+ T cells targeted by leukemia cell-derived exosomes (LEXs) did not show the expected effects in inducing effective anti-leukemia immunity, indicating that LEX is poorly immunogenetic largely due to an inadequate costimulatory capacity. Therefore, LEX-based anti-leukemia vaccines need to be optimized. In this study, we constructed a novel LEX-based vaccine by combining CD4+ T cells with costimulatory molecules gene-modified LEXs, which harbor upregulated CD80 and CD86, and the anti-leukemia immunity of CD80 and CD86 gene-modified LEX-targeted CD4+ T cells was investigated. We used lentiviral vectors encoding CD80 and CD86 to successfully transduced the L1210 leukemia cells, and the expression of CD80 and CD86 was remarkably upregulated in leukemia cells. The LEXs highly expressing CD80 and CD86 were obtained from the supernatants of gene-transduced leukemia cells. Our data have shown that LEX-CD8086 could promote CD4+ T cell proliferation and Th1 cytokine secretion more efficiently than control LEXs. Moreover, CD4+ TLEX-CD8086 expressed the acquired exosomal costimulatory molecules. With acquired costimulatory molecules, CD4+ TLEX-CD8086 can act as APCs and are capable of directly stimulating the leukemia cell antigen-specific CD8+ CTL response. This response was higher in potency compared to that noted by the other formulations. Furthermore, the animal study revealed that the CD4+ TLEX-CD8086 significantly inhibited tumor growth and prolonged survival of tumor-bearing mice than other formulations did in both protective and therapeutic models. In conclusion, this study revealed that CD4+ TLEX-CD8086 could effectively induce more potential anti-leukemia immunity than LEX-CD8086 alone, suggesting that the utilization of a costimulatory molecule gene-modified leukemia cell-derived exosome-targeted CD4+ T cell vaccine may have promising potential for leukemia immunotherapy.

Structural insights into the pSer/pThr dependent regulation of the SHP2 tyrosine phosphatase in insulin and CD28 signaling

Serine/threonine phosphorylation of insulin receptor substrate (IRS) proteins is well known to modulate insulin signaling. However, the molecular details of this process have mostly been elusive. While exploring the role of phosphoserines, we have detected a direct link between Tyr-flanking Ser/Thr phosphorylation sites and regulation of specific phosphotyrosine phosphatases. Here we present a concise structural study on how the activity of SHP2 phosphatase is controlled by an asymmetric, dual phosphorylation of its substrates. The structure of SHP2 has been determined with three different substrate peptides, unveiling the versatile and highly dynamic nature of substrate recruitment. What is more, the relatively stable pre-catalytic state of SHP2 could potentially be useful for inhibitor design. Our findings not only show an unusual dependence of SHP2 catalytic activity on Ser/Thr phosphorylation sites in IRS1 and CD28, but also suggest a negative regulatory mechanism that may also apply to other tyrosine kinase pathways as well.

SHP2 is an important human tyrosine phosphatase with key roles in cancer, immune responses and insulin signaling. Here, the authors explore its substrate recognition mechanism in molecular detail and uncover a complex regulatory mechanism for this enzyme that marks specific target sites for dephosphorylation.

Combined heterozygosity of FLT3 ITD, TET2, and DNMT3A results in aggressive leukemia

Heterozygous mutations in FLT3ITD, TET2, and DNMT3A are associated with hematologic malignancies in humans. In patients, cooccurrence of mutations in FLT3ITD combined with TET2 (TF) or FLT3ITD combined with DNMT3A (DF) are frequent. However, in some rare complex acute myeloid leukemia (AML), all 3 mutations cooccur - i.e., FLT3ITD, TET2, and DNMT3A (TFD). Whether the presence of these mutations in combination result in quantitative or qualitative differences in disease manifestation has not been investigated. We generated mice expressing heterozygous Flt3ITD and concomitant for either heterozygous loss of Tet2 (TF) or Dnmt3a (DF) or both (TFD). TF and DF mice did not induce disease early on, in spite of similar changes in gene expression; during the same time frame, an aggressive form of transplantable leukemia was observed in TFD mice, which was mostly associated with quantitative but not qualitative differences in gene expression relative to TF or DF mice. The gene expression signature of TFD mice showed remarkable similarity to the human TFD gene signature at the single-cell RNA level. Importantly, TFD-driven AML responded to a combination of drugs that target Flt3ITD, inflammation, and methylation in a mouse model, as well as in a PDX model of AML bearing 3 mutations.

The Tyrosine Phosphatase SHP2: A New Target for Insulin Resistance?

The SH2 containing protein tyrosine phosphatase 2(SHP2) plays essential roles in fundamental signaling pathways, conferring on it versatile physiological functions during development and in homeostasis maintenance, and leading to major pathological outcomes when dysregulated. Many studies have documented that SHP2 modulation disrupted glucose homeostasis, pointing out a relationship between its dysfunction and insulin resistance, and the therapeutic potential of its targeting. While studies from cellular or tissue-specific models concluded on both pros-and-cons effects of SHP2 on insulin resistance, recent data from integrated systems argued for an insulin resistance promoting role for SHP2, and therefore a therapeutic benefit of its inhibition. In this review, we will summarize the general knowledge of SHP2’s molecular, cellular, and physiological functions, explaining the pathophysiological impact of its dysfunctions, then discuss its protective or promoting roles in insulin resistance as well as the potency and limitations of its pharmacological modulation.

Inhibition of BTK and PI3Kδ impairs the development of human JMML stem and progenitor cells

Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasia that lacks effective targeted chemotherapies. Clinically, JMML manifests as monocytic leukocytosis, splenomegaly with consequential thrombocytopenia. Most commonly, patients have gain-of-function (GOF) oncogenic mutations in PTPN11 (SHP2), leading to Erk and Akt hyperactivation. Mechanism(s) involved in co-regulation of Erk and Akt in the context of GOF SHP2 are poorly understood. Here, we show that Bruton's tyrosine kinase (BTK) is hyperphosphorylated in GOF Shp2-bearing cells and utilizes B cell adaptor for PI3K to cooperate with p110δ, the catalytic subunit of PI3K. Dual inhibition of BTK and p110δ reduces the activation of both Erk and Akt. In vivo, individual targeting of BTK or p110δ in a mouse model of human JMML equally reduces monocytosis and splenomegaly; however, the combined treatment results in a more robust inhibition and uniquely rescues anemia and thrombocytopenia. RNA-seq analysis of drug-treated mice showed a profound reduction in the expression of genes associated with leukemic cell migration and inflammation, leading to correction in the infiltration of leukemic cells in the lung, liver, and spleen. Remarkably, in a patient derived xenograft model of JMML, leukemia-initiating stem and progenitor cells were potently inhibited in response to the dual drug treatment.

Targeting SHP2 phosphatase in hematological malignancies

INTRODUCTION

Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) is a ubiquitously expressed, non-receptor protein tyrosine phosphatase encoded by the PTPN11 gene. Gain-of-function (GOF) mutations in PTPN11 are associated with the development of various hematological malignancies and Noonan syndrome with multiple lentigines (NS-ML). Preclinical studies performed with allosteric SHP2 inhibitors and combination treatments of SHP2 inhibitors with inhibitors of downstream regulators (such as MEK, ERK, and PD-1/PD-L1) demonstrate improved antitumor benefits. However, the development of novel SHP2 inhibitors is necessary to improve the therapeutic strategies for hematological malignancies and tackle drug resistance and disease relapse.

AREAS COVERED

This review examines the structure of SHP2, its function in various signaling cascades, the consequences of constitutive activation of SHP2 and potential therapeutic strategies to treat SHP2-driven hematological malignancies.

EXPERT OPINION

While SHP2 inhibitors have exhibited promise in preclinical trials, numerous challenges remain in translation to the clinic, including drug resistance. Although PROTAC-based SHP2 degraders show better efficacy than SHP2 inhibitors, novel strategies need to be designed to improve SHP2-specific therapies in hematologic malignancies. Genome-wide CRISPR screening should also be used to identify molecules that confer resistance to SHP2 inhibitors. Targeting these molecules together with SHP2 can increase the target specificity and reduce drug resistance.

Phosphorylation of SHP2 at Tyr62 enables acquired resistance to SHP2 allosteric inhibitors in FLT3-ITD-driven AML

The protein tyrosine phosphatase SHP2 is crucial for oncogenic transformation of acute myeloid leukemia (AML) cells expressing mutated receptor tyrosine kinases (RTK). SHP2 is required for full RAS-ERK activation to promote cell proliferation and survival programs. Allosteric SHP2 inhibitors act by stabilizing SHP2 in its auto-inhibited conformation and are currently being tested in clinical trials for tumors with overactivation of the RAS/ERK pathway, alone and in various drug combinations. In this study, we established cells with acquired resistance to the allosteric SHP2 inhibitor SHP099 from two FLT3-ITD-positive AML cell lines. Label-free and isobaric labeling quantitative mass spectrometry-based phosphoproteomics of these resistant models demonstrated that AML cells can restore phosphorylated ERK (pERK) in the presence of SHP099, thus developing adaptive resistance. Mechanistically, SHP2 inhibition induced tyrosine phosphorylation and feedback-driven activation of the FLT3 receptor, which in turn phosphorylated SHP2 on tyrosine 62. This phosphorylation stabilized SHP2 in its open conformation, preventing SHP099 binding and conferring resistance. Combinatorial inhibition of SHP2 and MEK or FLT3 prevented pERK rebound and resistant cell growth. The same mechanism was observed in a FLT3-mutated B-ALL cell line and in the inv(16)/KitD816Y AML mouse model, but allosteric inhibition of Shp2 did not impair the clonogenic ability of normal bone marrow progenitors. Together, these results support the future use of SHP2 inhibitor combinations for clinical applications.

Gab2 deficiency prevents Flt3-ITD driven acute myeloid leukemia in vivo

Internal tandem duplications (ITD) of the FMS-like tyrosine kinase 3 (FLT3) predict poor prognosis in acute myeloid leukemia (AML) and often co-exist with inactivating DNMT3A mutations. In vitro studies implicated Grb2-associated binder 2 (GAB2) as FLT3-ITD effector. Utilizing a Flt3-ITD knock-in, Dnmt3a haploinsufficient mouse model, we demonstrate that Gab2 is essential for the development of Flt3-ITD driven AML in vivo, as Gab2 deficient mice displayed prolonged survival, presented with attenuated liver and spleen pathology and reduced blast counts. Furthermore, leukemic bone marrow from Gab2 deficient mice exhibited reduced colony-forming unit capacity and increased FLT3 inhibitor sensitivity. Using transcriptomics, we identify the genes encoding for Axl and the Ret co-receptor Gfra2 as targets of the Flt3-ITD/Gab2/Stat5 axis. We propose a pathomechanism in which Gab2 increases signaling of these receptors by inducing their expression and by serving as downstream effector. Thereby, Gab2 promotes AML aggressiveness and drug resistance as it incorporates these receptor tyrosine kinases into the Flt3-ITD signaling network. Consequently, our data identify GAB2 as a promising biomarker and therapeutic target in human AML.

Extramedullary Hematopoiesis of the Liver and Spleen

Hematopoiesis is the formation of blood cellular components and, consequently, immune cells. In a more complete definition, this process refers to the formation, growth, maturation, and specialization of blood cells, from the hematopoietic stem cell, through the hematopoietic progenitor cells, to the s pecialized blood cells. This process is tightly regulated by several elements of the bone marrow microenvironment, such as growth factors, transcription factors, and cytokines. During embryonic and fetal development, hematopoiesis takes place in different organs: the yolk sac, the aorta–gonad mesonephros region, the lymph nodes, and not lastly, the fetal liver and the spleen. In the current review, we describe extramedullary hematopoiesis of the spleen and liver, with an emphasis on myeloproliferative conditions.

Cancer stem cell phosphatases

Cancer stem cells (CSCs) are involved in the initiation and progression of human malignancies by enabling cancer tissue self-renewal capacity and constituting the therapy-resistant population of tumor cells. However, despite the exhausting characterization of CSC genetics, epigenetics, and kinase signaling, eradication of CSCs remains an unattainable goal in most human malignancies. While phosphatases contribute equally with kinases to cellular phosphoregulation, our understanding of phosphatases in CSCs lags severely behind our knowledge about other CSC signaling mechanisms. Many cancer-relevant phosphatases have recently become druggable, indicating that further understanding of the CSC phosphatases might provide novel therapeutic opportunities. This review summarizes the current knowledge about fundamental, but yet poorly understood involvement of phosphatases in the regulation of major CSC signaling pathways. We also review the functional roles of phosphatases in CSC self-renewal, cancer progression, and therapy resistance; focusing particularly on hematological cancers and glioblastoma. We further discuss the small molecule targeting of CSC phosphatases and their therapeutic potential in cancer combination therapies.

SSMD: a semi-supervised approach for a robust cell type identification and deconvolution of mouse transcriptomics data

Deconvolution of mouse transcriptomic data is challenged by the fact that mouse models carry various genetic and physiological perturbations, making it questionable to assume fixed cell types and cell type marker genes for different data set scenarios. We developed a Semi-Supervised Mouse data Deconvolution (SSMD) method to study the mouse tissue microenvironment. SSMD is featured by (i) a novel nonparametric method to discover data set-specific cell type signature genes; (ii) a community detection approach for fixing cell types and their marker genes; (iii) a constrained matrix decomposition method to solve cell type relative proportions that is robust to diverse experimental platforms. In summary, SSMD addressed several key challenges in the deconvolution of mouse tissue data, including: (i) varied cell types and marker genes caused by highly divergent genotypic and phenotypic conditions of mouse experiment; (ii) diverse experimental platforms of mouse transcriptomics data; (iii) small sample size and limited training data source and (iv) capable to estimate the proportion of 35 cell types in blood, inflammatory, central nervous or hematopoietic systems. In silico and experimental validation of SSMD demonstrated its high sensitivity and accuracy in identifying (sub) cell types and predicting cell proportions comparing with state-of-the-arts methods. A user-friendly R package and a web server of SSMD are released via https://github.com/xiaoyulu95/SSMD.

Therapeutic vaccination against leukaemia via the sustained release of co-encapsulated anti-PD-1 and a leukaemia-associated antigen

Therapeutic leukaemia vaccines have shown modest potency. Here, we show that the co-encapsulation of a leukaemia-associated epitope peptide highly expressed in leukaemia patients and of the immune checkpoint inhibitor anti-programmed-cell-death-protein-1 (anti-PD-1) in degradable poly(lactic acid) microcapsules resulted in the sustained release of the peptide and of the antibody, which led to the recruitment of activated antigen-presenting cells to the injection site, their uptake of the peptide and the transportation of the anti-PD-1 antibody to lymph nodes, enhancing the expansion of epitope-specific T cells and the activation of cytotoxic T cells. After single subcutaneous injections of vaccine formulations with different epitope peptides, mice bearing leukaemia xenografts derived from humanized cell lines or from primary cells from patients showed better therapeutic outcomes than mice receiving repeated injections of free antigen, antibody and a commercial adjuvant. The sustained release of a tumour-associated peptide and of anti-PD-1 may represent a generalizable strategy for boosting antitumour immune responses to leukaemia.

Targeting SHP2 as a therapeutic strategy for inflammatory diseases

With the change of lifestyle and the acceleration of aging process, inflammatory diseases have increasingly become one of the most vital threats to global human health. SHP2 protein is a non-receptor tyrosine phosphatase encoded by PTPN11 gene, and it is widely expressed in various tissues and cells. Numerous studies have shown that SHP2 plays important roles in the regulation of inflammatory diseases, including cancer-related inflammation, neurodegenerative diseases and metabolic diseases. In this paper, the roles of SHP2 in inflammatory diseases of various physiological systems were reviewed. At the same time, the latest SHP2 inhibitors were summarized, which will hold a promise for the therapeutic potential in future.

Tyrosine phosphatase SHP2 inhibitors in tumor-targeted therapies

Src homology containing protein tyrosine phosphatase 2 (SHP2) represents a noteworthy target for various diseases, serving as a well-known oncogenic phosphatase in cancers. As a result of the low cell permeability and poor bioavailability, the traditional inhibitors targeting the protein tyrosine phosphate catalytic sites are generally suffered from unsatisfactory applied efficacy. Recently, a particularly large number of allosteric inhibitors with striking inhibitory potency on SHP2 have been identified. In particular, few clinical trials conducted have made significant progress on solid tumors by using SHP2 allosteric inhibitors. This review summarizes the development and structure–activity relationship studies of the small-molecule SHP2 inhibitors for tumor therapies, with the purpose of assisting the future development of SHP2 inhibitors with improved selectivity, higher oral bioavailability and better physicochemical properties.

Novel Approaches to Target Mutant FLT3 Leukaemia

Simple Summary

Acute myeloid leukemia (AML) is a haematologic disease in which oncogenic mutations in the receptor tyrosine kinase FLT3 frequently lead to leukaemic development. Potent treatment of AML patients is still hampered by inefficient targeting of leukemic stem cells expressing constitutive active FLT3 mutants. This review summarizes the current knowledge about the regulation of FLT3 activity at cellular level and discusses therapeutical options to affect the tumor cells and the microenvironment to impair the haematological aberrations.

Abstract

Fms-like tyrosine kinase 3 (FLT3) is a member of the class III receptor tyrosine kinases (RTK) and is involved in cell survival, proliferation, and differentiation of haematopoietic progenitors of lymphoid and myeloid lineages. Oncogenic mutations in the FLT3 gene resulting in constitutively active FLT3 variants are frequently found in acute myeloid leukaemia (AML) patients and correlate with patient’s poor survival. Targeting FLT3 mutant leukaemic stem cells (LSC) is a key to efficient treatment of patients with relapsed/refractory AML. It is therefore essential to understand how LSC escape current therapies in order to develop novel therapeutic strategies. Here, we summarize the current knowledge on mechanisms of FLT3 activity regulation and its cellular consequences. Furthermore, we discuss how aberrant FLT3 signalling cooperates with other oncogenic lesions and the microenvironment to drive haematopoietic malignancies and how this can be harnessed for therapeutical purposes.

Y772 phosphorylation of EphA2 is responsible for EphA2-dependent NPC nasopharyngeal carcinoma growth by Shp2/Erk-1/2 signaling pathway

EphA2 is an important oncogenic protein and emerging drug target, but the oncogenic role and mechanism of ligand-independent phosphorylation of EphA2 at tyrosine 772 (pY772-EphA2) is unclear. In this study, we established nasopharyngeal carcinoma (NPC) cell lines with stable expression of exogenous EphA2 and EphA2-Y772A (phosphorylation inactivation) using endogenous EphA2-knockdown cells, and observed that pY772A EphA2 was responsible for EphA2-promoting NPC cell proliferation and anchorage-independent and in vivo growth in mice. Mechanistically, EphA2-Y772A mediated EphA2-activating Shp2/Erk-1/2 signaling pathway in the NPC cells, and Gab1 (Grb2-associated binder 1) and Grb2 (growth factor receptor-bound protein 2) were involved in pY772-EphA2 activating this signaling pathway. Our results further showed that Shp2/Erk-1/2 signaling mediated pY772-EphA2-promoting NPC cell proliferation and anchorage-independent growth. Moreover, we observed that EphA2 tyrosine kinase inhibitor ALW-II-41-27 inhibited pY772-EphA2 and EphA2-Y772A decreased the inhibitory effect of ALW-II-41-27 on NPC cell proliferation. Collectively, our results demonstrate that pY772-EphA2 is responsible for EphA2-dependent NPC cell growth in vitro and in vivo by activating Shp2/Erk-1/2 signaling pathway, and is a pharmacologic target of ALW-II-41-27, suggesting that pY772-EphA2 can serve as a therapeutic target in NPC and perhaps in other cancers.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

Genetic biomarkers of drug resistance: A compass of prognosis and targeted therapy in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly aggressive hematological malignancy with complex heterogenous genetic and biological nature. Thus, prognostic prediction and targeted therapies might contribute to better chemotherapeutic response. However, the emergence of multidrug resistance (MDR) markedly impedes chemotherapeutic efficacy and dictates poor prognosis. Therefore, prior evaluation of chemoresistance is of great importance in therapeutic decision making and prognosis. In recent years, preclinical studies on chemoresistance have unveiled a compendium of underlying molecular basis, which facilitated the development of targetable small molecules. Furthermore, routing genomic sequencing has identified various genomic aberrations driving cellular response during the course of therapeutic treatment through adaptive mechanisms of drug resistance, some of which serve as prognostic biomarkers in risk stratification. However, the underlying mechanisms of MDR have challenged the certainty of the prognostic significance of some mutations. This review aims to provide a comprehensive understanding of the role of MDR in therapeutic decision making and prognostic prediction in AML. We present an updated genetic landscape of the predominant mechanisms of drug resistance with novel targeted therapies and potential prognostic biomarkers from preclinical and clinical chemoresistance studies in AML. We particularly highlight the unfolded protein response (UPR) that has emerged as a critical regulatory pathway in chemoresistance of AML with promising therapeutic horizon. Futhermore, we outline the most prevalent mutations associated with mechanisms of chemoresistance and delineate the future directions to improve the current prognostic tools. The molecular analysis of chemoresistance integrated with genetic profiling will facilitate decision making towards personalized prognostic prediction and enhanced therapeutic efficacy.

SHP2 promotes proliferation of breast cancer cells through regulating Cyclin D1 stability via the PI3K/AKT/GSK3β signaling pathway

Objective: The tyrosine phosphatase SHP2 has a dual role in cancer initiation and progression in a tissue type-dependent manner. Several studies have linked SHP2 to the aggressive behavior of breast cancer cells and poorer outcomes in people with cancer. Nevertheless, the mechanistic details of how SHP2 promotes breast cancer progression remain largely undefined. Methods: The relationship between SHP2 expression and the prognosis of patients with breast cancer was investigated by using the TCGA and GEO databases. The expression of SHP2 in breast cancer tissues was analyzed by immunohistochemistry. CRISPR/Cas9 technology was used to generate SHP2-knockout breast cancer cells. Cell-counting kit-8, colony formation, cell cycle, and EdU incorporation assays, as well as a tumor xenograft model were used to examine the function of SHP2 in breast cancer proliferation. Quantitative RT-PCR, western blotting, immunofluorescence staining, and ubiquitination assays were used to explore the molecular mechanism through which SHP2 regulates breast cancer proliferation. Results: High SHP2 expression is correlated with poor prognosis in patients with breast cancer. SHP2 is required for the proliferation of breast cancer cells in vitro and tumor growth in vivo through regulation of Cyclin D1 abundance, thereby accelerating cell cycle progression. Notably, SHP2 modulates the ubiquitin-proteasome-dependent degradation of Cyclin D1 via the PI3K/AKT/GSK3β signaling pathway. SHP2 knockout attenuates the activation of PI3K/AKT signaling and causes the dephosphorylation and resultant activation of GSK3β. GSK3β then mediates phosphorylation of Cyclin D1 at threonine 286, thereby promoting the translocation of Cyclin D1 from the nucleus to the cytoplasm and facilitating Cyclin D1 degradation through the ubiquitin-proteasome system. Conclusions: Our study uncovered the mechanism through which SHP2 regulates breast cancer proliferation. SHP2 may therefore potentially serve as a therapeutic target for breast cancer.