The JAK2 inhibitor AZD1480 potently blocks Stat3 signaling and oncogenesis in solid tumors

Identification of JAK2 as a mediator of FIP1L1-PDGFRA-induced eosinophil growth and function in CEL

The Fip1-like1 (FIP1L1)-platelet-derived growth factor receptor alpha fusion gene (F/P) arising in the pluripotent hematopoietic stem cell (HSC),causes 14% to 60% of patients with hypereosinophilia syndrome (HES). These patients, classified as having F/P (+) chronic eosinophilic leukemia (CEL), present with clonal eosinophilia and display a more aggressive disease phenotype than patients with F/P (–) HES patients. The mechanisms underlying predominant eosinophil lineage targeting and the cytotoxicity of eosinophils in this leukemia remain unclear. Given that the Janus tyrosine kinase (JAK)/signal transducers and activators of transcription (Stat) signaling pathway is key to cytokine receptor-mediated eosinophil development and activated Stat3 and Stat5 regulate the expression of genes involved in F/P malignant transformation, we investigated whether and how JAK proteins were involved in the pathogenesis of F/P-induced CEL. F/P activation of JAK2, Stat3 and Stat5, were confirmed in all the 11 F/P (+) CEL patients examined. In vitro inhibition of JAK2 in EOL-1, primary F/P(+) CEL cells (PC) and T674I F/P Imatinib resistant cells(IR) by either JAK2-specific short interfering RNA (siRNA) or the tryphostin derivative AG490(AG490), significantly reduced cellular proliferation and induced cellular apoptosis. The F/P can enhance the IL-5-induced JAK2 activation, and further results indicated that JAK2 inhibition blocked IL-5-induced cellular migration and activation of the EOL-1 and PC cells in vitro. F/P-stimulation of the JAK2 suppressed cells led to a significantly reduction in Stat3 activation, but relatively normal induction of Stat5 activation. Interestingly, JAK2 inhibition also reduced PI3K, Akt and NF-κB activity in a dose-dependent manner, and suppressed expression levels of c-Myc and Survivin. These results strongly suggest that JAK2 is activated by F/P and is required for F/P stimulation of cellular proliferation and infiltration, possibly through induction of c-Myc and Survivin expression via activation of multiple signaling pathways, including NF-κB, Stat3, and PI3K/Akt.

Extracellular and intracellular sphingosine-1-phosphate in cancer

Sphingosine-1-phosphate (S1P) was first described as a signaling molecule over 20 years ago. Since then, great strides have been made to reveal its vital roles in vastly different cellular and disease processes. Initially, S1P was considered nothing more than the terminal point of sphingolipid metabolism; however, over the past two decades, a large number of reports have helped unveil its full potential as an important regulatory, bioactive sphingolipid metabolite. S1P has a plethora of physiological functions, due in part to its many sites of actions and its different pools, which are both intra- and extracellular. S1P plays pivotal roles in many physiological processes, including the regulation of cell growth, migration, autophagy, angiogenesis, and survival, and thus, not surprisingly, S1P has been linked to cancer. In this review, we will summarize the vast body of knowledge, highlighting the connection between S1P and cancer. We will also suggest new avenues for future research.

Ruxolitinib for the treatment of myelofibrosis: its clinical potential

Ruxolitinib is an orally bioavailable, selective Janus kinase (JAK) 1 and 2 inhibitor approved for the treatment of myelofibrosis (MF), a bone marrow disease in which the JAK pathway is dysregulated, leading to impaired hematopoiesis and immune function. By inhibiting JAK1 and JAK2, ruxolitinib modulates cytokine-stimulated intracellular signaling. In a phase II clinical trial in patients with MF, ruxolitinib recipients exhibited durable reductions in spleen size, reductions in circulating pro-inflammatory cytokines, improvements in physical activity, weight gain, and alleviation of symptoms (including constitutional symptoms) in patients with and without JAK2 mutation. These findings were confirmed by two phase III clinical MF studies, in which a greater proportion of ruxolitinib recipients achieved a spleen volume reduction of ≥35% from baseline at week 24, compared with placebo in one study (41.9% versus 0.7%; P < 0.0001) and with best available therapy in the other (31.9% versus 0%; P < 0.0001). Alleviation of MF symptoms and improvements in quality of life were also significantly greater in ruxolitinib recipients. Overall survival of patients treated with ruxolitinib was significantly longer than of those receiving the placebo. Owing to risks of potentially serious adverse effects, eg, myelosuppression, ruxolitinib should be used under close physician supervision. Longer follow-up of the phase III MF studies is needed to reach firm conclusions regarding ruxolitinib’s capacity to modify the natural disease course.

Thrombopoietin receptor down-modulation by JAK2 V617F: restoration of receptor levels by inhibitors of pathologic JAK2 signaling and of proteasomes

The constitutively active JAK2 V617F mutant is the major determinant of human myeloproliferative neoplasms (MPNs). We show that coexpression of murine JAK2 V617F and the murine thrombopoietin (Tpo) receptor (TpoR, c-MPL) in hematopoietic cell lines or heterozygous knock-in of JAK2 V617F in mice leads to down-modulation of TpoR levels. Enhanced TpoR ubiquitinylation, proteasomal degradation, reduced recycling, and maturation are induced by the constitutive JAK2 V617F activity. These effects can be prevented in cell lines by JAK2 and proteasome inhibitors. Restoration of TpoR levels by inhibitors could be detected in platelets from JAK2 inhibitor-treated myelofibrosis patients that express the JAK2 V617F mutant, and in platelets from JAK2 V617F knock-in mice that were treated in vivo with JAK2 or proteasome inhibitors. In addition, we show that Tpo can induce both proliferative and antiproliferative effects via TpoR at low and high JAK2 activation levels, respectively, or on expression of JAK2 V617F. The antiproliferative signaling and receptor down-modulation by JAK2 V617F were dependent on signaling via TpoR cytosolic tyrosine 626. We propose that selection against TpoR antiproliferative signaling occurs by TpoR down-modulation and that restoration of down-modulated TpoR levels could become a biomarker for the treatment of MPNs.

Targeting the interleukin-6/Jak/stat pathway in human malignancies

The Janus kinase/signal transducer and activator of transcription (Jak/Stat) pathway was discovered 20 years ago as a mediator of cytokine signaling. Since this time, more than 2,500 articles have been published demonstrating the importance of this pathway in virtually all malignancies. Although there are dozens of cytokines and cytokine receptors, four Jaks, and seven Stats, it seems that interleukin-6-mediated activation of Stat3 is a principal pathway implicated in promoting tumorigenesis. This transcription factor regulates the expression of numerous critical mediators of tumor formation and metastatic progression. This review will examine the relative importance and function of this pathway in nonmalignant conditions as well as malignancies (including tumor intrinsic and extrinsic), the influence of other Stats, the development of inhibitors to this pathway, and the potential role of inhibitors in controlling or eradicating cancers.

Targeting JAK2 in the therapy of myeloproliferative neoplasms

INTRODUCTION

Myeloproliferative neoplasms (MPNs) are a group of stem cell diseases, including polycythemia vera, essential thrombocythemia and primary myelofibrosis. Currently, there is no curative therapy for these diseases other than bone marrow transplant; therefore there is an apparent need for palliative treatment. MPNs are frequently associated with activating mutations in JAK2; small-molecule drugs targeting this molecule have entered clinical trials.

AREAS COVERED

In this review novel JAK2 inhibitors are discussed and alternative approaches to inhibiting their transforming potential are highlighted. Current clinical approaches do not only aim at blocking JAK2 activity, but also at reducing its stability and expression are highlighted, including inhibition of heat shock protein 90 (HSP90) and deacetylases (DAC) have the potential to significantly enhance the efficacy of JAK2 inhibitors.

EXPERT OPINION

Preliminary results from clinical trials indicate the feasibility and efficacy of JAK2-targeted approaches. However, JAK2 inhibitor treatment is limited by dose-dependent toxicity and combination treatment might be required. The discovery of JAK2 mutations that cause secondary resistance in vitro would further highlight the need for the development of next-generation JAK2 inhibitors and novel synergistic approaches.

TSLP signaling network revealed by SILAC-based phosphoproteomics

Thymic stromal lymphopoietin (TSLP) is a cytokine that plays diverse roles in the regulation of immune responses. TSLP requires a heterodimeric receptor complex consisting of IL-7 receptor α subunit and its unique TSLP receptor (gene symbol CRLF2) to transmit signals in cells. Abnormal TSLP signaling (e.g. overexpression of TSLP or its unique receptor TSLPR) contributes to the development of a number of diseases including asthma and leukemia. However, a detailed understanding of the signaling pathways activated by TSLP remains elusive. In this study, we performed a global quantitative phosphoproteomic analysis of the TSLP signaling network using stable isotope labeling by amino acids in cell culture. By employing titanium dioxide in addition to antiphosphotyrosine antibodies as enrichment methods, we identified 4164 phosphopeptides on 1670 phosphoproteins. Using stable isotope labeling by amino acids in cell culture-based quantitation, we determined that the phosphorylation status of 226 proteins was modulated by TSLP stimulation. Our analysis identified activation of several members of the Src and Tec families of kinases including Btk, Lyn, and Tec by TSLP for the first time. In addition, we report TSLP-induced phosphorylation of protein phosphatases such as Ptpn6 (SHP-1) and Ptpn11 (Shp2), which has also not been reported previously. Co-immunoprecipitation assays showed that Shp2 binds to the adapter protein Gab2 in a TSLP-dependent manner. This is the first demonstration of an inducible protein complex in TSLP signaling. A kinase inhibitor screen revealed that pharmacological inhibition of PI-3 kinase, Jak family kinases, Src family kinases or Btk suppressed TSLP-dependent cellular proliferation making them candidate therapeutic targets in diseases resulting from aberrant TSLP signaling. Our study is the first phosphoproteomic analysis of the TSLP signaling pathway that greatly expands our understanding of TSLP signaling and provides novel therapeutic targets for TSLP/TSLPR-associated diseases in humans.

Differentiation and gene expression profile of tumor-associated macrophages

Tumor microenvironment is composed of proliferating neoplastic cells, a vascular network of endothelial cells, extra cellular matrix produced by fibroblasts, cellular compartments of adaptive immunity like lymphocytes and dendritic cells as well as cells of innate immunity, e.g., natural killer cells and macrophages. Many pre-clinical and clinical studies demonstrate an inversed correlation between macrophage infiltrate and patients' prognosis indicating a macrophage supporting role for tumor progression as producers of growth and angiogenic factors and as regulators of tissue remodelling. Based on in vitro models, macrophages have been classified in pro-inflammatory, classically activated macrophages (M1; stimulated by IFN-γ or LPS) and anti-inflammatory, alternatively activated macrophages (M2; stimulated by either IL-4/IL-13, IL-1β/LPS in combination with immune complexes or by IL-10/TGFβ/glucocorticoids). Tumor escape has been linked with a switch from M1 activation in the early tumor initiation process towards M2-like phenotype during tumor progression, a process that highlights the heterogeneity and plasticity of macrophage activation and which offers a possible therapeutic target directed against reversing the TAM phenotype in the tumor. Here, we review different tumor-environmental stimuli and signalling cascades involved in this switch in differentiation and the so connected gene regulation in TAMs. In addition, therapeutic applications deducted from this differentiation and gene regulatory processes are presented. Data from pre-clinical as well as clinical studies clearly support the notion, that TAMs are excellent novel therapeutic targets for the fight against cancer.

An HNF4α-miRNA inflammatory feedback circuit regulates hepatocellular oncogenesis

Hepatocyte nuclear factor 4α (HNF4α) is essential for liver development and hepatocyte function. Here, we show that transient inhibition of HNF4α initiates hepatocellular transformation through a microRNA-inflammatory feedback loop circuit consisting of miR-124, IL6R, STAT3, miR-24, and miR-629. Moreover, we show that, once this circuit is activated, it maintains suppression of HNF4α and sustains oncogenesis. Systemic administration of miR-124, which modulates inflammatory signaling, prevents and suppresses hepatocellular carcinogenesis by inducing tumor-specific apoptosis without toxic side effects. As we also show that this HNF4α circuit is perturbed in human hepatocellular carcinomas, our data raise the possibility that manipulation of this microRNA feedback-inflammatory loop has therapeutic potential for treating liver cancer.

STAT3 is activated by JAK2 independent of key oncogenic driver mutations in non-small cell lung carcinoma

Constitutive activation of STAT3 is a common feature in many solid tumors including non-small cell lung carcinoma (NSCLC). While activation of STAT3 is commonly achieved by somatic mutations to JAK2 in hematologic malignancies, similar mutations are not often found in solid tumors. Previous work has instead suggested that STAT3 activation in solid tumors is more commonly induced by hyperactive growth factor receptors or autocrine cytokine signaling. The interplay between STAT3 activation and other well-characterized oncogenic “driver” mutations in NSCLC has not been fully characterized, though constitutive STAT3 activation has been proposed to play an important role in resistance to various small-molecule therapies that target these oncogenes. In this study we demonstrate that STAT3 is constitutively activated in human NSCLC samples and in a variety of NSCLC lines independent of activating KRAS or tyrosine kinase mutations. We further show that genetic or pharmacologic inhibition of the gp130/JAK2 signaling pathway disrupts activation of STAT3. Interestingly, treatment of NSCLC cells with the JAK1/2 inhibitor ruxolitinib has no effect on cell proliferation and viability in two-dimensional culture, but inhibits growth in soft agar and xenograft assays. These data demonstrate that JAK2/STAT3 signaling operates independent of known driver mutations in NSCLC and plays critical roles in tumor cell behavior that may not be effectively inhibited by drugs that selectively target these driver mutations.

CD24(+) liver tumor-initiating cells drive self-renewal and tumor initiation through STAT3-mediated NANOG regulation

Tumor-initiating cells (T-ICs) are a subpopulation of chemoresistant tumor cells that have been shown to cause tumor recurrence upon chemotherapy. Identification of T-ICs and their related pathways are therefore priorities for the development of new therapeutic paradigms. We established chemoresistant hepatocellular carcinoma (HCC) xenograft tumors in immunocompromised mice in which an enriched T-IC population was capable of tumor initiation and self-renewal. With this model, we found CD24 to be upregulated in residual chemoresistant tumors when compared with bulk tumor upon cisplatin treatment. CD24(+) HCC cells were found to be critical for the maintenance, self-renewal, differentiation, and metastasis of tumors and to significantly impact patients' clinical outcome. With a lentiviral-based knockdown approach, CD24 was found to be a functional liver T-IC marker that drives T-IC genesis through STAT3-mediated NANOG regulation. Our findings point to a CD24 cascade in liver T-ICs that may provide an attractive therapeutic target for HCC patients.

Ruxolitinib: a new JAK1/2 inhibitor that offers promising options for treatment of myelofibrosis

Ruxolitinib (INCB018424) is the first potent, selective, oral inhibitor of JAK1 and 2 being developed for clinical use. Its major cellular and systemic effects are proliferation inhibition, apoptosis induction and reduction in cytokine plasma levels, all mediated by the drug's inhibition of JAKs' ability to phosphorylate STAT. In initial clinical trials of its use in myelofibrosis, ruxolitinib exhibited durable efficacy in reduction of splenomegaly and alleviation of constitutional symptoms. Patients also showed weight gain and improvement in general physical condition. The dose-limiting toxicity was thrombocytopenia. In preliminary findings of a Phase III trial in patients with primary, postpolycythemia-vera, or postessential-thrombocythemia myelofibrosis, administration at an initial dosage of 15 or 20 mg twice daily led to a spleen-volume response rate (≥ 35% reduction at 24 weeks) of 41.9 versus 0.7% for placebo (p < 0.0001); furthermore, 45.9% of the ruxolitinib recipients had ≥ 50% improvement in symptom score (on the modified Myelofibrosis Symptom Assessment Form version 2.0) versus 5.3% for placebo (p < 0.0001). Ruxolitinib recipients also showed improvement in parameters of quality of life.

Inhibition of Stat3 activation by sanguinarine suppresses prostate cancer cell growth and invasion

BACKGROUND

Signal transducer and activator of transcription 3 (Stat3) is an oncogenic transcriptional factor that plays a critical role in carcinogenesis and cancer progression and is a potential therapeutic target. Sanguinarine, a benzophenanthridine alkaloid derived primarily from the bloodroot plant, was identified previously as a novel inhibitor of survivin that selectively kills prostate cancer cells over "normal" prostate epithelial cells.

METHODS

DU145, C4-2B, and LNCaP cells were treated with sanguinarine. The phosphorylation status of Stat3 and related proteins were measured with Western blots. Activation of transcription by Stat3 was measured with luciferase reporter assay. The effect of sanguinarine on anchorage-independent growth was examined with soft agar assay, and on cell migration and invasion of DU145 cells were measured with scratch assay and invasion assay, respectively.

RESULTS

In this study, we identified sanguinarine as a potent inhibitor of Stat3 activation which was able to suppress prostate cancer growth, migration, and invasion. Sanguinarine inhibits constitutive as well as IL6-induced phosphorylation of Stat3 at both Tyr705 and Ser727 in prostate cancer cells. The inhibition of Stat3 phosphorylation by sanguinarine correlates with reduction of Janus-activated Kinase 2 (Jak2) and Src phosphorylation. Sanguinarine downregulates the expression of Stat3-mediated genes such as c-myc and survivin and inhibits the Stat3 responsive element luciferase reporter activity. Sanguinarine inhibits the anchorage-independent growth of DU145 and LN-S17 cells expressing constitutively activated Stat3. Migration and invasion abilities of DU145 cells were also inhibited by sanguinarine in a manner similar to the dominant negative form of Stat3.

CONCLUSIONS

These data demonstrate that sanguinarine is a potent Stat3 inhibitor and it could be developed as a therapeutic agent for prostate cancer with constitutive activation of Stat3.

Biology and clinical management of myeloproliferative neoplasms and development of the JAK inhibitor ruxolitinib

Myeloproliferative neoplasms (MPN) are debilitating stem cell-derived clonal myeloid malignancies. Conventional treatments for the BCR-ABL1-negative MPN including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) have, so far, been unsatisfactory. Following the discovery of dysregulated JAK-STAT signaling in patients with MPN, many efforts have been directed toward the development of molecularly targeted therapies, including inhibitors of JAK1 and JAK2. Ruxolitinib (previously known as INCB018424; Incyte Corporation, Wilmington, Delaware, USA) is a rationally designed potent oral JAK1 and JAK2 inhibitor that has undergone clinical trials in patients with PV, ET, and PMF. Ruxolitinib was approved on November 16, 2011 by the United States Food and Drug Administration for the treatment of intermediate or high-risk myelofibrosis (MF), including patients with PMF, post-PV MF, and post-ET MF. In randomized phase III studies, ruxolitinib treatment resulted in significant and durable reductions in splenomegaly and improvements in disease-related symptoms in patients with MF compared with placebo or best available therapy. The most common adverse events were anemia and thrombocytopenia, which were manageable and rarely led to discontinuation. This review addresses the cellular and molecular biology, and the clinical management of MPN.

Targeting the tumor stroma as a novel therapeutic approach for prostate cancer

Interactions between epithelium and the surrounding stroma are required to maintain organ function. These interactions provide proliferative and migratory restraints that define anatomical and positional information, mediated by growth factors and extracellular matrix components. When cancer develops, transformed cells lose these constraints while stroma adapts and coevolves to support the "function" of the tumor. The prostate is a good example of an organ that relies on its surrounding stroma during normal development and cancer progression. Carcinoma-associated fibroblasts (CAFs) constitute a substantial volume of the tumor stroma and play a pivotal role in tumor maintenance, dissemination, and even drug resistance. The origins of CAF and the exact mechanisms by which they promote tumor progression are still debated. CAF acquire an activated phenotype quite similar to the one seen during wound repair in sites of injury. Here, we describe the CAF ontogeny, the similarities with activated fibroblasts during physiological wound repair, and potential pathways that can be targeted to prevent their appearance in tumors and their protumorigenic functions in cancer progression. A strategy to identify aspects of stromal cell biology for therapeutic targeting is becoming increasingly plausible, driven by the increased understanding of the complex interplays between the cells and tissues of which tumors are comprised. Several preclinical and clinical studies show that targeting the stroma may be a promising and attractive therapeutic option for the treatment of cancer and has the potential to play an increasingly prominent role in future treatment strategies.

A phosphopeptide mimetic prodrug targeting the SH2 domain of Stat3 inhibits tumor growth and angiogenesis

Signal transducer and activator of transcription 3 (Stat3) is constitutively activated in a number of human cancers and cancer cell lines. Via its Src homology 2 (SH2) domain, Stat3 is recruited to phosphotyrosine residues on intracellular domains of cytokine and growth factor receptors, whereupon it is phosphorylated on Tyr705, dimerizes, translocates to the nucleus and is reported to participate in the expression of genes related to angiogenesis, metastasis, growth and survival. To block this process, we are developing cell-permeable, phosphatase-stable phosphopeptide mimics, targeted to the SH2 domain of Stat3, that inhibit the phosphorylation of Tyr705 of Stat3 in cultured tumor cells (Mandal et al., J. Med. Chem. 54, 3549-5463, 2011). At concentrations that inhibit tyrosine phosphorylation, these materials were not cytotoxic, similar to recent reports on JAK inhibitors. At higher concentrations, cytotoxicity was accompanied by off-target effects. We report that treatment of MDA-MB-468 human breast cancer xenografts in mice with peptidomimetic PM-73G significantly inhibited tumor growth, which was accompanied by reduction in VEGF production and microvessel density. No evidence of apoptosis or changes in the expression of the canonical genes cyclin D1 or survivin were observed. Thus selective inhibition of Stat3 Tyr705 phosphorylation may be a novel anti-angiogenesis strategy for the treatment of cancer.

The many faces of Janus kinase

Janus kinases have proved to be essential for many immunological processes but there is growing evidence that they also play a critical role in pathogenesis of many diseases including inflammatory diseases and cancer where they promote multiple steps of tumorigenesis. Several companies are in late stage clinical programs for the development of JAK kinase inhibitors and the first small molecule JAK inhibitor, Jakafi® (ruxolitinib) has been just approved for treatment of myeloproliferative neoplasms. Several other molecules are on the rise to treat arthritis, psoriasis and multiple types of cancer. This commentary will provide a review of the JAK kinase field as it pertains to small molecule inhibition for the treatment of cancer and autoimmune diseases with an emphasis on JAK2. The use of experimental and clinical inhibitors of JAK will be discussed for solid tumor and hematological malignancies, lupus, arthritis, colitis, neurological disorders, pain, diabetes and cardiovascular disease. In addition, it will review current paradigms in the field and treatment programs which could be complemented by small molecule inhibitors of Janus kinase.

Antitumor activity of a novel oncrasin analogue is mediated by JNK activation and STAT3 inhibition

Background

To optimize the antitumor activity of oncrasin-1, a small molecule identified through synthetic lethality screening on isogenic K-Ras mutant tumor cells, we developed several analogues and determined their antitumor activities. Here we investigated in vitro and in vivo antitumor activity of NSC-743380 (1-[(3-chlorophenyl) methyl]-1H-indole-3-methanol, oncrasin-72), one of most potent analogues of oncrasin-1.

Methodology and Principal Findings

In vitro antitumor activity was determined in NCI-60 cancer cell line panel using cell viability assay. In vivo antitumor activity was determined in parallel with NSC-741909 (oncrasin-60) in xenograft tumors established in nude mice from A498, a human renal cancer cell line. Changes in gene expression levels and signaling pathway activities upon treatment with NSC-743380 were analyzed in breast and renal cancer cells by Western blot analysis. Apoptosis was demonstrated by Western blot analysis and flow cytometric analysis. NSC-743380 is highly active against a subset of cancer cell lines derived from human lung, colon, ovary, kidney, and breast cancers. The 50% growth-inhibitory concentration (GI₅₀) for eight of the most sensitive cell lines was ≤10 nM. In vivo study showed that NSC-743380 has a better safety profile and greater antitumor activity than NSC-741909. Treatment with NSC-743380 caused complete regression of A498 xenograft tumors in nude mice at the tested doses ranging from 67 mg/kg to 150 mg/kg. Mechanistic characterization revealed that NSC-743380 suppressed the phosphorylation of C-terminal domain of RNA polymerase II, induced JNK activation, inhibited JAK2/STAT3 phosphorylation and suppressed cyclin D1 expression in sensitive human cancer cells. Blocking JNK activation or overexpression of constitutively active STAT3 partially blocked NSC-743380-induced antitumor activity.

Conclusions

NSC-743380 induces antitumor activity through modulation of functions in multiple cancer related pathways and could be a potential anticancer agent for some solid tumors.

NVP-BKM120, a novel PI3K inhibitor, shows synergism with a STAT3 inhibitor in human gastric cancer cells harboring KRAS mutations

Aberrations of Phosphoinositide 3-kinase (PI3K)/AKT signaling are frequently observed in many types of cancer, promoting its emergence as a promising target for cancer treatment. PI3K can become activated by various pathways, one of which includes RAS. RAS can not only directly activate the PI3K/AKT pathway via binding to p110 of PI3K, but also regulates mTOR via ERK or RSK independently of the PI3K/AKT pathway. Thus, actively mutated RAS can constitutively activate PI3K signaling. Additionally, in RAS tumorigenic transformation, signal transducer and activator of transcription 3 (STAT3) has been known also to be required. In this study, we examined the efficacy of NVP-BKM120, a pan-class I PI3K inhibitor in human gastric cancer cells and hypothesized that the combined inhibition of PI3K and STAT3 would be synergistic in KRAS mutant gastric cancer cells. NVP-BKM120 demonstrated anti-proliferative activity in 11 human gastric cancer cell lines by decreasing mTOR downstream signaling. But NVP-BKM120 treatment increased p-AKT by subsequent abrogation of feedback inhibition by stabilizing insulin receptor substrate-1. In KRAS mutant gastric cancer cells, either p-ERK or p-STAT3 was also increased upon treatment of NVP-BKM120. The synergistic efficacy study demonstrated that dual PI3K and STAT3 blockade showed a synergism in cells harboring mutated KRAS by inducing apoptosis. The synergistic effect was not seen in KRAS wild-type cells. Together, these findings suggest for the first time that the dual inhibition of PI3K and STAT3 signaling may be an effective therapeutic strategy for KRAS mutant gastric cancer patients.

STAT3 activation in monocytes accelerates liver cancer progression

Background

Signal transducer and activator of transcription 3 (STAT3) is an important transcription factor ubiquitously expressed in different cell types. STAT3 plays an essential role in cell survival, proliferation, and differentiation. Aberrantly hyper-activated STAT3 signaling in cancer cells and in the tumor microenvironment has been detected in a wide variety of human cancers and is considered an important factor for cancer initiation, development, and progression. However, the role of STAT3 activation in monocytes in the development of HCC has not been well understood.

Methods

Immunohistochemical analysis of phosphorylated STAT3 was performed on tissue microarray from HCC patients. Using a co-culture system in vivo, HCC cell growth was determined by the MTT assay. In vivo experiments were conducted with mice given diethylinitrosamine (DEN), which induces HCC was used to investigate the role of STAT3 expression in monocytes on tumor growth. Real-time PCR was used to determine the expression of cell proliferation and cell arrest associated genes in the tumor and nontumor tissue from liver.

Results

Phosphorylated STAT3 was found in human hepatocellular carcinoma tissue samples and was expressed in tumor cells and also in monocytes. Phosphorylated STAT3 expression in monocyte was significantly correlated to advanced clinical stage of HCC and a poor prognosis. Using a co-culture system in vivo, monocytes promoted HCC cell growth via the IL-6/STAT3 signaling pathway. The STAT3 inhibitor, NSC 74859, significantly suppressed tumor growth in vivo in mice with diethylinitrosamine (DEN)-induced HCC. In this animal model, blockade of STAT3 with NSC 74859 induced tumor cell apoptosis, while inhibiting both tumor cells and monocytes proliferation. Furthermore, NSC 74859 treatment suppressed cancer associated inflammation in DEN-induce HCC.

Conclusion

Our data suggest constitutively activated STAT3 monocytes promote liver tumorigenesis in clinical patients and animal experiments. Thus, STAT3 in tumor infiltrating inflammatory cells may an attractive target for liver cancer therapy.

The JAK inhibitor AZD1480 regulates proliferation and immunity in Hodgkin lymphoma

Aberrant activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway has been reported to promote proliferation and survival of Hodgkin and Reed–Sternberg cells of Hodgkin lymphoma (HL). We investigated the activity of the JAK inhibitor AZD1480 in HL-derived cell lines and determined its mechanisms of action. AZD1480 at low doses (0.1–1 μ) potently inhibited STATs phosphorylation, but did not predictably result in antiproliferative effects, as it activated a negative-feedback loop causing phosphorylation of JAK2 and extracellular signal-regulated kinases 1 and 2 (ERK1/2), and increased IP-10, RANTES and interleukin (IL)-8 concentrations in the supernatants. Inhibition of the ERK activity by mitogen-activated extracellular signal regulated kinase (MEK) inhibitors (UO126 and PD98059) enhanced the cytotoxic activity of AZD1480. Interestingly, submicromolar concentrations of AZD1480 demonstrated significant immunoregulatory effects by downregulating T-helper 2 cytokines and chemokines, including IL-13 and thymus- and activation-regulated chemokine, and the surface expression of the immunosuppressive programmed death ligands 1 and 2. Higher concentrations of AZD1480 (5 μ) induced G2/M arrest and cell death by inhibiting Aurora kinases. Our study demonstrates that AZD1480 regulates proliferation and immunity in HL cell lines and provides mechanistic rationale for evaluating AZD1480 alone or in combination with MEK inhibitors in HL.

Stat3 mediates expression of autotaxin in breast cancer

We determined that signal transducer and activator of transcription 3 (Stat3) is tyrosine phosphorylated in 37% of primary breast tumors and 63% of paired metastatic axillary lymph nodes. Examination of the distribution of tyrosine phosphorylated (pStat3) in primary tumors revealed heterogenous expression within the tumor with the highest levels found in cells on the edge of tumors with relatively lower levels in the central portion of tumors. In order to determine Stat3 target genes that may be involved in migration and metastasis, we identified those genes that were differentially expressed in primary breast cancer samples as a function of pStat3 levels. In addition to known Stat3 transcriptional targets (Twist, Snail, Tenascin-C and IL-8), we identified ENPP2 as a novel Stat3 regulated gene, which encodes autotaxin (ATX), a secreted lysophospholipase which mediates mammary tumorigenesis and cancer cell migration. A positive correlation between nuclear pStat3 and ATX was determined by immunohistochemical analysis of primary breast cancer samples and matched axillary lymph nodes and in several breast cancer derived cell lines. Inhibition of pStat3 or reducing Stat3 expression led to a decrease in ATX levels and cell migration. An association between Stat3 and the ATX promoter, which contains a number of putative Stat3 binding sites, was determined by chromatin immunoprecipitation. These observations suggest that activated Stat3 may regulate the migration of breast cancer cells through the regulation of ATX.

Optimization of a novel kinase inhibitor scaffold for the dual inhibition of JAK2 and FAK kinases

The elaboration of a novel scaffold for the inhibition of JAK2 and FAK kinases was targeted in order to provide a dual inhibitor that could target divergent pathways for tumor cell progression.

Discovery of potent and highly selective thienopyridine Janus kinase 2 inhibitors

Developing Janus kinase 2 (Jak2) inhibitors has become a significant focus for small molecule drug discovery programs in recent years due to the identification of a Jak2 gain-of-function mutation in the majority of patients with myeloproliferative disorders (MPD). Here, we describe the discovery of a thienopyridine series of Jak2 inhibitors that culminates with compounds showing 100- to >500-fold selectivity over the related Jak family kinases in enzyme assays. Selectivity for Jak2 was also observed in TEL-Jak cellular assays, as well as in cytokine-stimulated peripheral blood mononuclear cell (PBMC) and whole blood assays. X-ray cocrystal structures of 8 and 19 bound to the Jak2 kinase domain aided structure-activity relationship efforts and, along with a previously reported small molecule X-ray cocrystal structure of the Jak1 kinase domain, provided structural rationale for the observed high levels of Jak2 selectivity.

The therapeutic potential of inhibitors of the signal transducer and activator of transcription 3 for central nervous system malignancies

Background:

High-grade primary and metastatic central nervous system (CNS) tumors are common, deadly, and refractory to conventional therapy and continue to be therapeutically challenging. A key nodal transcriptional factor, the signal transducer and activator of transcription 3 (STAT3), drives the fundamental components of tumor malignancy and metastases in the CNS by enhancing proliferation, angiogenesis, invasion, metastasis, and immunosuppression. The introduction of STAT3 inhibitors in clinical trials for this patient population is imminent.

Methods:

STAT3 inhibitors have been extensively tested in a variety of preclinical murine models.

Results:

The STAT3 inhibitor, WP1066, has displayed marked efficacy with minimal toxicity against malignancy in murine models, including established intracerebral tumors. The mechanism of this in vivo efficacy of the STAT3 blockade agents is a combination of direct tumor cytotoxicity and immune cytotoxic clearance.

Conclusions:

Given their direct antitumor cytotoxic effects, STAT3 inhibitors may exert therapeutic activity in the monotherapy setting but may also have compelling use as immunotherapeutic modulators or as a salvage therapy.

Protein-network modeling of prostate cancer gene signatures reveals essential pathways in disease recurrence

Objective

Uncovering the dominant molecular deregulation among the multitude of pathways implicated in aggressive prostate cancer is essential to intelligently developing targeted therapies. Paradoxically, published prostate cancer gene expression signatures of poor prognosis share little overlap and thus do not reveal shared mechanisms. The authors hypothesize that, by analyzing gene signatures with quantitative models of protein–protein interactions, key pathways will be elucidated and shown to be shared.

Design

The authors statistically prioritized common interactors between established cancer genes and genes from each prostate cancer signature of poor prognosis independently via a previously validated single protein analysis of network (SPAN) methodology. Additionally, they computationally identified pathways among the aggregated interactors across signatures and validated them using a similarity metric and patient survival.

Measurement

Using an information-theoretic metric, the authors assessed the mechanistic similarity of the interactor signature. Its prognostic ability was assessed in an independent cohort of 198 patients with high-Gleason prostate cancer using Kaplan–Meier analysis.

Results

Of the 13 prostate cancer signatures that were evaluated, eight interacted significantly with established cancer genes (false discovery rate <5%) and generated a 42-gene interactor signature that showed the highest mechanistic similarity (p<0.0001). Via parameter-free unsupervised classification, the interactor signature dichotomized the independent prostate cancer cohort with a significant survival difference (p=0.009). Interpretation of the network not only recapitulated phosphatidylinositol-3 kinase/NF-κB signaling, but also highlighted less well established relevant pathways such as the Janus kinase 2 cascade.

Conclusions

SPAN methodolgy provides a robust means of abstracting disparate prostate cancer gene expression signatures into clinically useful, prioritized pathways as well as useful mechanistic pathways.

Therapeutic potential of AZD1480 for the treatment of human glioblastoma

Aberrant activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway has been implicated in glioblastoma (GBM) progression. To develop a therapeutic strategy to inhibit STAT-3 signaling, we have evaluated the effects of AZD1480, a pharmacologic inhibitor of JAK1 and JAK2. In this study, the in vitro efficacy of AZD1480 was tested in human and murine glioma cell lines. AZD1480 treatment effectively blocks constitutive and stimulus-induced JAK1, JAK2, and STAT-3 phosphorylation in both human and murine glioma cells, and leads to a decrease in cell proliferation and induction of apoptosis. Furthermore, we used human xenograft GBM samples as models for the study of JAK/STAT-3 signaling in vivo, because human GBM samples propagated as xenografts in nude mice retain both the hallmark genetic alterations and the invasive phenotype seen in vivo. In these xenograft tumors, JAK2 and STAT-3 are constitutively active, but levels vary among tumors, which is consistent with the heterogeneity of GBMs. AZD1480 inhibits constitutive and stimulus-induced phosphorylation of JAK2 and STAT-3 in these GBM xenograft tumors in vitro, downstream gene expression, and inhibits cell proliferation. Furthermore, AZD1480 suppresses STAT-3 activation in the glioma-initiating cell population in GBM tumors. In vivo, AZD1480 inhibits the growth of subcutaneous tumors and increases survival of mice bearing intracranial GBM tumors by inhibiting STAT-3 activity, indicating that pharmacologic inhibition of the JAK/STAT-3 pathway by AZD1480 should be considered for study in the treatment of patients with GBM tumors.

Characterization of BMS-911543, a functionally selective small-molecule inhibitor of JAK2

We report the characterization of BMS-911543, a potent and selective small-molecule inhibitor of the Janus kinase (JAK) family member, JAK2. Functionally, BMS-911543 displayed potent anti-proliferative and pharmacodynamic (PD) effects in cell lines dependent upon JAK2 signaling, and had little activity in cell types dependent upon other pathways, such as JAK1 and JAK3. BMS-911543 also displayed anti-proliferative responses in colony growth assays using primary progenitor cells isolated from patients with JAK2(V617F)-positive myeloproliferative neoplasms (MPNs). Similar to these in vitro observations, BMS-911543 was also highly active in in vivo models of JAK2 signaling, with sustained pathway suppression being observed after a single oral dose. At low dose levels active in JAK2-dependent PD models, no effects were observed in an in vivo model of immunosuppression monitoring antigen-induced IgG and IgM production. Expression profiling of JAK2(V617F)-expressing cells treated with diverse JAK2 inhibitors revealed a shared set of transcriptional changes underlying pharmacological effects of JAK2 inhibition, including many STAT1-regulated genes and STAT1 itself. Collectively, our results highlight BMS-911543 as a functionally selective JAK2 inhibitor and support the therapeutic rationale for its further characterization in patients with MPN or in other disorders characterized by constitutively active JAK2 signaling.

The JAK2/STAT3 signaling pathway is required for growth of CD44⁺CD24⁻ stem cell-like breast cancer cells in human tumors

Intratumor heterogeneity is a major clinical problem because tumor cell subtypes display variable sensitivity to therapeutics and may play different roles in progression. We previously characterized 2 cell populations in human breast tumors with distinct properties: CD44+CD24- cells that have stem cell-like characteristics, and CD44-CD24+ cells that resemble more differentiated breast cancer cells. Here we identified 15 genes required for cell growth or proliferation in CD44+CD24- human breast cancer cells in a large-scale loss-of-function screen and found that inhibition of several of these (IL6, PTGIS, HAS1, CXCL3, and PFKFB3) reduced Stat3 activation. We found that the IL-6/JAK2/Stat3 pathway was preferentially active in CD44+CD24- breast cancer cells compared with other tumor cell types, and inhibition of JAK2 decreased their number and blocked growth of xenografts. Our results highlight the differences between distinct breast cancer cell types and identify targets such as JAK2 and Stat3 that may lead to more specific and effective breast cancer therapies.

Prolactin regulation of the prostate gland: a female player in a male game

Prolactin is best known for its actions on the mammary gland. However, circulating prolactin is also detected in males and its receptor (PRLR) is expressed in the prostate, suggesting that the prostate is a target of prolactin. Germline knockout of prolactin or its receptor has failed to reveal a key role for prolactin signaling in mouse prostate physiology. However, several studies involving rodent models and human prostate cell lines and specimens have supported the contribution of the canonical PRLR-Jak2-Stat5a/b pathway to prostate cancer tumorigenesis and progression. Increased expression of prolactin in the prostate itself (rather than changes in circulating prolactin levels) and crosstalk with androgen receptor (AR) signaling are potential mechanisms for increased Stat5a/b signaling in prostate cancer. In the mouse prostate, prolactin overexpression results in disorganized expansion of the basal/stem cell compartment, which has been proposed to house putative prostate tumor-initiating cells. These findings provide new insight into the molecular and cellular targets by which locally produced prolactin could contribute to prostate cancer initiation and progression. A number of pharmacological inhibitors targeting various levels of the PRLR-Jak2-Stat5a/b pathway have been developed and are entering clinical trials for advanced prostate cancer.

Constitutive activation of JAK2 in mammary epithelium elevates Stat5 signalling, promotes alveologenesis and resistance to cell death, and contributes to tumourigenesis

Signalling through the janus kinase (JAK)/signal transducer and activator of transcription (Stat) pathway is required at different stages of mammary gland development, and this pathway is frequently hyper-activated in cancer, including tumours of the breast. Stats 3, 5 and 6 have important roles in the differentiation and survival of mammary alveolar cells, but somewhat paradoxically, both Stat3 and 5 can have oncogenic activity in the mammary gland. Constitutive activation of JAK2 could be anticipated to result in hyper-activation of Stats 1, 3, 5 and 6 with concomitant cell transformation, although the outcome is difficult to envisage, particularly since Stats 3 and 5 play opposing roles in normal mammary gland development. Here, we show that expression of a constitutively active JAK2 mutant, JAK2 V617F, leads to hyper-activation of Stat5 in mammary epithelial cells (MECs), and transgenic mice expressing JAK2 V617F specifically in the mammary gland exhibit accelerated alveologenesis during pregnancy and delayed post-lactational regression. Overexpressing JAK2 V617F in MECs in vitro results in elevated proliferation and resistance to cell death. Furthermore, constitutively active JAK2 enhances anchorage-independent cell growth in the presence of a co-operating oncogene and accelerates tumourigenesis in a xenograft model. Taken together, our results provide insights into signalling downstream of constitutively active JAK2 and could be important for understanding the molecular mechanisms of breast tumourigenesis.

Kinase domain mutations confer resistance to novel inhibitors targeting JAK2V617F in myeloproliferative neoplasms

The transforming JAK2V617F kinase is frequently associated with myeloproliferative neoplasms and thought to be instrumental for the overproduction of myeloid lineage cells. Several small molecule drugs targeting JAK2 are currently in clinical development for treatment in these diseases. We performed a high-throughput in vitro screen to identify point mutations in JAK2V617F that would be predicted to have potential clinical relevance and associated with drug resistance to the JAK2 inhibitor ruxolitinib (INCB018424). Seven libraries of mutagenized JAK2V617F cDNA were screened to specifically identify mutations in the predicted drug-binding region that would confer resistance to ruxolitinib, using a BaF3 cell-based assay. We identified five different non-synonymous point mutations that conferred drug resistance. Cells containing mutations had a 9- to 33-fold higher EC(50) for ruxolitinib compared with native JAK2V617F. Our results further indicated that these mutations also conferred cross-resistance to all JAK2 kinase inhibitors tested, including AZD1480, TG101348, lestaurtinib (CEP-701) and CYT-387. Surprisingly, introduction of the 'gatekeeper' mutation (M929I) in JAK2V617F affected only ruxolitinib sensitivity (fourfold increase in EC(50)). These results suggest that JAK2 inhibitors currently in clinical trials may be prone to resistance as a result of point mutations and caution should be exercised when administering these drugs.

Antiangiogenic and antimetastatic activity of JAK inhibitor AZD1480

STAT3 has important functions in both tumor cells and the tumor microenvironment to facilitate cancer progression. The STAT regulatory kinase Janus-activated kinase (JAK) has been strongly implicated in promoting oncogenesis of various solid tumors, including the use of JAK kinase inhibitors such as AZD1480. However, direct evidence that JAK drives STAT3 function and cancer pathogenesis at the level of the tumor microenvironment is yet to be established clearly. In this study, we show that AZD1480 inhibits STAT3 in tumor-associated myeloid cells, reducing their number and inhibiting tumor metastasis. Myeloid cell-mediated angiogenesis was also diminished by AZD1480, with additional direct inhibition of endothelial cell function in vitro and in vivo. AZD1480 blocked lung infiltration of myeloid cells and formation of pulmonary metastases in both mouse syngeneic experimental and spontaneous metastatic models. Furthermore, AZD1480 reduced angiogenesis and metastasis in a human xenograft tumor model. Although the effects of AZD1480 on the tumor microenvironment were important for the observed antiangiogenic activity, constitutive activation of STAT3 in tumor cells themselves could block these antiangiogenic effects, showing the complexity of the JAK/STAT signaling network in tumor progression. Together, our results indicated that AZD1480 can effectively inhibit tumor angiogenesis and metastasis mediated by STAT3 in stromal cells as well as tumor cells.

Signal transducer and activator of transcription 3 (STAT3): a promising target for anticancer therapy

Signal transducer and activator of transcription 3 (STAT3) is an oncogenic protein whose inhibition is sought for the prevention and treatment of cancer. In this review, the validated therapeutic strategy to block aberrant activity of STAT3 in many tumor cell lines is evaluated by presenting the most promising inhibitors to date. The compounds are discussed in classes based on their different mechanisms of action, which are critically explained. In addition, their future clinical development as anticancer agents is considered. Furthermore, the efforts devoted to the comprehension of the structure-activity relationships and to the identification of the biological effects are brought to attention. The synthetic and technological approaches recently developed to overcome the difficulties in the obtainment of clinically suitable drugs are also presented.

Dihydroxypentamethoxyflavone down-regulates constitutive and inducible signal transducers and activators of transcription-3 through the induction of tyrosine phosphatase SHP-1

Because constitutive activation of signal transducers and activators of transcription-3 (STAT3) has been linked with cellular transformation, survival, proliferation, chemoresistance, and angiogenesis of various tumor cells, agents that can suppress STAT3 activation have potential as cancer therapeutics. In the present report, we identified a flavone from the leaves of a Thai plant, Gardenia obtusifolia, 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF), that has the ability to inhibit STAT3 activation. PMF inhibited both constitutive and interleukin-6-inducible STAT3 activation in multiple myeloma (MM) cells, as indicated by suppression of STAT3 phosphorylation, nuclear translocation, DNA binding, and STAT3-regulated gene expression. The inhibition of STAT3 by PMF was reversible. We found that the activation of various kinases including Janus-like kinase (JAK)-1, JAK-2, c-Src, extracellular signal-regulated kinases 1 and 2, AKT, and epidermal growth factor receptor, implicated in STAT3 activation, were inhibited by the flavone. It is noteworthy that pervanadate suppressed the ability of PMF to inhibit the phosphorylation of STAT3, suggesting that protein tyrosine phosphatase was involved. PMF induced the expression of SHP-1 and was linked to the dephosphorylation of STAT3, because its deletion by small interfering RNA abolished the PMF-induced constitutive and inducible STAT3 inhibition. STAT3 inhibition led to the suppression of proteins involved in proliferation (cyclin D1 and c-myc), survival (survivin, Mcl-1, Bcl-xL, Bcl-2, and cIAP-2), and angiogenesis (vascular endothelial growth factor). Finally, PMF inhibited proliferation and induced apoptosis of MM cells. PMF also significantly potentiated the apoptotic effects of Velcade and thalidomide in MM cells. Overall, these results suggest that PMF is a novel blocker of STAT3 activation and thus may have potential in suppression of tumor cell proliferation and reversal of chemoresistance in MM cells.

Nuclear JAK2: form and function in cancer

The conventional view of Janus kinase 2 (JAK2) is a nonreceptor tyrosine kinase which transmits information to the nucleus via the signal transducer and activator of transcriptions (STATs) without leaving the cytoplasm. However, accumulating data suggest that JAK2 may signal by exporting from cytoplasm to nucleus, where it guides the transcriptional machinery independent of STATs protein. Recent studies demonstrated that JAK2 is a crucial component of signaling pathways operating in the nucleus. Especially the latest landmark discovery confirmed that JAK2 goes into the nucleus and directly interacts with nucleoproteins, such as histone H3 at tyrosine 41 (H3Y41), nuclear factor 1-C2 (NF1-C2) and SWI/SNF-related helicases/ATPases (RUSH)-1α, indicating that JAK2 has a fresh nuclear function. Nuclear JAK2 is linked to a variety of cellular functions, such as cell cycle progression, apoptosis and genetic instability. The balance between these functions is an essential factor in determining whether a cell remains benign or becomes malignant. The aim of this review is intended to summarize the state of our knowledge on nuclear localization of JAK2 and nuclear JAK2 pathways, and to highlight the emerging roles for nuclear JAK2 in carcinogenesis.

Inhibiting signal transducer and activator of transcription 3: rationality and rationale design of inhibitors

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3) controls a key signaling pathway in the development of many malignant diseases. Several genetic studies have proven its central role in the regulation of apoptosis, proliferation, angiogenesis and immune responses making it an attractive target for cancer therapy.

AREAS COVERED

This article addresses the role of STAT3 in immune response modulation and highlights the contribution of STAT3 in inflammation-mediated tumorigenesis. We also review the rationale to use novel STAT3 inhibitors and list some of these inhibitors such as STA-21, IS3 295, S3I- M2001 and small molecule JAK2 inhibitors AZD1480 and AZ960 that have been found to be efficient against tumors. We summarize the efforts that have been made so far in identifying promising compounds and mention the barriers that need to be overcome for successful application of STAT3 inhibitors in clinics.

EXPERT OPINION

STAT3 is an important target in tumor biology based on its frequent activation in various tumors and its pleiotropic effects on different cell types. Screening large libraries of logically synthesized small molecule inhibitors is one way to rapidly generate many potential molecules, which can then be tested in different biologically relevant models. The stage is, therefore, set for the identification and development of novel STAT3 inhibitors that will, in the very near future, enter the clinical realm.

New JAK2 inhibitors for myeloproliferative neoplasms

INTRODUCTION

The discovery of the JAK(V617F) kinase established a common pathogenetic link to the most important types of Philadelphia-chromosome-negative myeloproliferative neoplasms (MPNs): polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). More importantly, the demonstration of constitutive kinase activity emanating from the JAK2 protein provided the rationale for the development of small-molecule JAK2 kinase inhibitors.

AREAS COVERED

Several JAK2 kinase inhibitors are being tested in clinical trials for patients with MPNs. In PMF trials, JAK2 inhibitors have been shown to produce rapid reductions in spleen size and marked improvements in constitutional symptoms and quality of life. In ET and/or PV, JAK2 inhibitors normalize hematocrit, platelets and WBC, and spleen size in a large number of patients that are resistant or intolerant to hydroxyurea. JAK2 inhibitors are not specific for the JAK2V617F mutant protein. Rather, they inhibit the JAK2- signal transducer and activator of transcription (STAT) pathway and therefore any patient with MPN may benefit from therapy regardless of JAK2 mutational status.

EXPERT OPINION

JAK2 inhibitors induce clinically relevant responses in a large proportion of patients with MPNs. Because JAK kinase activation underlies the pathogenesis of other disorders, such as autoimmune and rheumatological disorders, the paradigm of JAK inhibition may translate into novel therapies for a variety of human diseases.

STAT3: a target to enhance antitumor immune response

Signal transducer and activator of transcription 3 (Stat3) has emerged as a critical regulator for tumor-associated inflammation. Activation of Stat3 negatively regulates the Th1-type immune response and promotes expansion of myeloid-derived suppressor cells (MDSCs) and regulatory T-cell functions in the tumor microenvironment. Mounting evidence suggests that Stat3 and related pathways may serve as a target for changing the tumor immunologic microenvironment to benefit cancer immunotherapies. Many recent studies support the use of certain tyrosine kinase inhibitors, through inhibition of Stat3, in decreasing immunosuppression in the tumor microenvironment. Other potential therapeutic avenues include the use of targeted delivery of Stat3 siRNA into immune cells. Here, we describe the role of Stat3 in regulating the immunologic properties of tumors as a background for Stat3-based therapeutic interventions.

Signal transducer and activator of transcription 5a/b: biomarker and therapeutic target in prostate and breast cancer

The search for new therapeutic strategies for prostate and breast cancer is of significant interest. Signal transducer and activator of transcription 5a/b (Stat5a/b) controls viability and growth of prostate cancer. Nuclear active Stat5a/b expression is clustered to high grade prostate cancers, predicts early disease recurrence and promotes metastatic dissemination of prostate cancer. In breast cancer, the role of Stat5a/b is more complex. In rodent model systems, Stat5a/b may promote malignant transformation and enhance growth of the breast tumors. In contrast, Stat5a/b activation in established human breast cancer positively correlates with tumor differentiation, prevents metastatic dissemination, and predicts favorable clinical outcome of node-negative breast cancer. Here we review the molecular structure and biological functions of Stat5a/b and discuss the potential applications of Stat5a/b for therapy development and as a prognostic marker for prostate and breast cancer.

Natural innate and adaptive immunity to cancer

The immune system can identify and destroy nascent tumor cells in a process termed cancer immunosurveillance, which functions as an important defense against cancer. Recently, data obtained from numerous investigations in mouse models of cancer and in humans with cancer offer compelling evidence that particular innate and adaptive immune cell types, effector molecules, and pathways can sometimes collectively function as extrinsic tumor-suppressor mechanisms. However, the immune system can also promote tumor progression. Together, the dual host-protective and tumor-promoting actions of immunity are referred to as cancer immunoediting. In this review, we discuss the current experimental and human clinical data supporting a cancer immunoediting process that provide the fundamental basis for further study of immunity to cancer and for the rational design of immunotherapies against cancer.

6-Bromoindirubin-3'-oxime inhibits JAK/STAT3 signaling and induces apoptosis of human melanoma cells

STAT3 is persistently activated and contributes to malignant progression in various cancers. Janus activated kinases (JAK) phosphorylate STAT3 in response to stimulation by cytokines or growth factors. The STAT3 signaling pathway has been validated as a promising target for development of anticancer therapeutics. Small-molecule inhibitors of JAK/STAT3 signaling represent potential molecular-targeted cancer therapeutic agents. In this study, we investigated the role of JAK/STAT3 signaling in 6-bromoindirubin-3'-oxime (6BIO)-mediated growth inhibition of human melanoma cells and assessed 6BIO as a potential anticancer drug candidate. We found that 6BIO is a pan-JAK inhibitor that induces apoptosis of human melanoma cells. 6BIO directly inhibited JAK-family kinase activity, both in vitro and in cancer cells. Apoptosis of human melanoma cells induced by 6BIO was associated with reduced phosphorylation of JAKs and STAT3 in both dose- and time-dependent manners. Consistent with inhibition of STAT3 signaling, expression of the antiapoptotic protein Mcl-1 was downregulated. In contrast to the decreased levels of phosphorylation of JAKs and STAT3, phosphorylation levels of the Akt and mitogen-activated protein kinase (MAPK) signaling proteins were not inhibited in cells treated with 6BIO. Importantly, 6BIO suppressed tumor growth in vivo with low toxicity in a mouse xenograft model of melanoma. Taken together, these results show that 6BIO is a novel pan-JAK inhibitor that can selectively inhibit STAT3 signaling and induces tumor cell apoptosis. Our findings support further development of 6BIO as a potential anticancer therapeutic agent that targets JAK/STAT3 signaling in tumor cells.

STAT3 plays a critical role in KRAS-induced pancreatic tumorigenesis

The STAT3 transcription factor is an important regulator of stem cell self-renewal, cancer cell survival, and inflammation. In the pancreas, STAT3 is dispensable for normal development, whereas the majority of pancreatic ductal adenocarcinomas (PDAC) show constitutive activation of STAT3, suggesting its potential as a therapeutic target in this cancer. Here, we sought to define the mechanisms of STAT3 activation and its functional importance in PDAC pathogenesis. Large-scale screening of cancer cell lines with a JAK2 inhibitor that blocks STAT3 function revealed a more than 30-fold range in sensitivity in PDAC, and showed a close correlation of sensitivity with levels of tyrosine-phosphorylated STAT3 and of the gp130 receptor, an upstream signaling component. Correspondingly, upregulation of the IL6/LIF-gp130 pathway accounted for the strong STAT3 activation in PDAC subsets. To define functions of STAT3 in vivo, we developed mouse models that test the impact of conditional inactivation of STAT3 in KRAS-driven PDAC. We showed that STAT3 is required for the development of the earliest premalignant pancreatic lesions, acinar-to-ductal metaplasia (ADM) and pancreatic intraepithelial neoplasia (PanIN). Moreover, acute STAT3 inactivation blocked PDAC initiation in a second in vivo model. Our results show that STAT3 has critical roles throughout the course of PDAC pathogenesis, supporting the development of therapeutic approaches targeting this pathway. Moreover, our work suggests that gp130 and phospho-STAT3 expression may be effective biomarkers for predicting response to JAK2 inhibitors.

Targeting miR-375 in gastric cancer

INTRODUCTION

Gastric cancer remains a major cancer burden in the world, with a poor 5-year survival rate. It is necessary to develop new effective therapeutic strategies to improve the long-term clinical outcome. MicroRNA (miRNA), a class of small non-coding RNA, has been identified as a key regulator of gene expression, and is implicated in the pathogenesis of gastric cancer.

AREAS COVERED

This review summarizes the role of miRNAs in gastric carcinogenesis, with an emphasis on the expression and function of miR-375 in gastric cancer and beyond. It also discusses the opportunities and challenges of miR-375 as a potential therapeutic target for gastric cancer. The genes targeted by miR-375, including JAK2 and 3'-phosphoinositide dependent protein kinase-1 (PDK1), are also candidates for gastric cancer therapy.

EXPERT OPINION

Although radical surgery and rational chemotherapy are still the main treatment for gastric cancer, targeting miRNAs, in combination with other conventional therapies, may serve as a promising therapy strategy to improve the clinical outcome.