Abrogation of signal transducer and activator of transcription 3 reactivation after Src kinase inhibition results in synergistic antitumor effects

A Redox-Silent Analogue of Tocotrienol May Break the Homeostasis of Proteasomes in Human Malignant Mesothelioma Cells by Inhibiting STAT3 and NRF1

6-O-Carboxypropyl-alpha-tocotrienol (α-T3E) is a multi-target redox-silent analogue of tocotrienol that exhibits cytotoxicity against many cancer cells, including malignant mesothelioma (MM) cells. α-T3E has several molecular targets to effectively induce cytotoxicity against MM cells; however, the mechanisms underlying this cytotoxicity remain unclear. In the present study, we demonstrated that the α-T3E-dependent disruption of the homeostasis of proteasomes strongly induced endoplasmic reticulum (ER) stress, which resulted in effective cytotoxicity against MM cells. The α-T3E-dependent disruption of the homeostasis of proteasomes depended on decreases in proteasome subunits via the inactivation of signal transducer and activator of transcription 3 (STAT3) and nuclear factor erythroid 2 related factor-1 (NRF1), which inhibited protease activity, such as chymotrypsin-like activity, in proteasomes. The α-T3E-dependent inhibition of this activity also induced severe ER stress and ultimately resulted in effective cytotoxicity against MM cells with chemoresistance. The present results indicate that α-T3E acts as an effective anti-mesothelioma agent by disrupting the homeostasis of proteasomes through the simultaneous inactivation of STAT3 and NRF1.

Vitamin K2 Inhibits Hepatocellular Carcinoma Cell Proliferation by Binding to 17β-Hydroxysteroid Dehydrogenase 4

Our previous studies have proved that 17β-hydroxysteroid dehydrogenase 4 (HSD17B4) is a novel proliferation-promoting protein. The overexpression of HSD17B4 promotes hepatocellular carcinoma (HCC) cell proliferation. Vitamin K2 (VK2), a fat-soluble vitamin, has the function of promoting coagulation and can inhibit the progression of liver cancer. A previous study demonstrated that VK2 could bind to HSD17B4 in HepG2 cells. However, the mechanism of VK2 in inhibiting HCC cell proliferation is not clear. In this study, we investigate whether VK2 can inhibit the proliferation of HCC cell induced by HSD17B4 and the possible mechanism. We detected the effect of VK2 on HSD17B4-induced HCC cell proliferation, and the activation of STAT3, AKT, and MEK/ERK signaling pathways. We measured the effect of HSD17B4 on the growth of transplanted tumor and the inhibitory effect of VK2. Our results indicated that VK2 directly binds to HSD17B4, but does not affect the expression of HSD17B4, to inhibit the proliferation of HCC cells by inhibiting the activation of Akt and MEK/ERK signaling pathways, leading to decreased STAT3 activation. VK2 also inhibited the growth of HSD17B4-induced transplanted tumors. These findings provide a theoretical and experimental basis for possible future prevention and treatment of HCC using VK2.

Targeting SRC Family Kinases in Mesothelioma: Time to Upgrade

Malignant mesothelioma (MM) is a deadly tumor mainly caused by exposure to asbestos. Unfortunately, no current treatment is able to change significantly the natural history of the disease, which has a poor prognosis in the majority of patients. The non-receptor tyrosine kinase SRC and other SRC family kinase (SFK) members are frequently hyperactivated in many cancer types, including MM. Several works have indeed suggested that SFKs underlie MM cell proliferation, survival, motility, and invasion, overall affecting multiple oncogenic pathways. Consistently, SFK inhibitors effectively counteracted MM cancerous features at the preclinical level. Dasatinib, a multi-kinase inhibitor targeting SFKs, was also assessed in clinical trials either as second-line treatment for patients with unresectable MM or, more recently, as a neoadjuvant agent in patients with resectable MM. Here, we provide an overview of the molecular mechanisms implicating SFKs in MM progression and discuss possible strategies for a more successful clinical application of SFK inhibitors. Our aim is to stimulate discussion and further consideration of these agents in better designed preclinical and clinical studies to make the most of another class of powerful antitumoral drugs, which too often are lost in translation when applied to MM.

Distinct characteristics of dasatinib-induced pyroptosis in gasdermin E-expressing human lung cancer A549 cells and neuroblastoma SH-SY5Y cells

Dasatinib, a multikinase inhibitor, is used in the treatment of chronic myeloid leukemia and was developed to overcome imatinib resistance. Its mechanism of action involves the induction of apoptosis, autophagy and necroptosis. However, it remains unclear whether dasatinib can induce pyroptosis. In the present study, gasdermin E (GSDME)-expressing SH-SY5Y and A549 cells were chosen for investigation. Typical pyroptotic features, such as cleavage of GSDME protein, leakage of lactate dehydrogenase and large bubbled morphology, were observed in both cell lines after exposure to dasatinib. The generation of GSDME fragments was inhibited by specific caspase-3 inhibitor zDEVD in SH-SY5Y cells and pan-caspase inhibitor zVAD in A549 cells. Moreover, distinct characteristics of pyroptosis were observed in A549 cells, which occurred only with a high percentage of Annexin V/propidium iodide double-stained cells and low level of GSDME protein cleavage. The sensitivity of A549 cells to dasatinib is significantly reduced by increasing cell numbers. The elevation of GSDMD and GSDME protein levels was induced by low concentrations of dasatinib, which was not influenced by the reduction of p53 protein with RNA interference. In conclusion, to the best of our knowledge, this is the first study to report that dasatinib can induce pyroptosis in tumor cells and increase the protein levels of GSDMD and GSDME in a p53-independent manner.

Combined Src/EGFR Inhibition Targets STAT3 Signaling and Induces Stromal Remodeling to Improve Survival in Pancreatic Cancer

Lack of durable response to cytotoxic chemotherapy is a major contributor to the dismal outcomes seen in pancreatic ductal adenocarcinoma (PDAC). Extensive tumor desmoplasia and poor vascular supply are two predominant characteristics which hinder the delivery of chemotherapeutic drugs into PDAC tumors and mediate resistance to therapy. Previously, we have shown that STAT3 is a key biomarker of therapeutic resistance to gemcitabine treatment in PDAC, which can be overcome by combined inhibition of the Src and EGFR pathways. Although it is well-established that concurrent EGFR and Src inhibition exert these antineoplastic properties through direct inhibition of mitogenic pathways in tumor cells, the influence of this combined therapy on stromal constituents in PDAC tumors remains unknown. In this study, we demonstrate in both orthotopic tumor xenograft and Ptf1a^cre/+;LSL-Kras^G12D/+;Tgfbr2^flox/flox (PKT) mouse models that concurrent EGFR and Src inhibition abrogates STAT3 activation, increases microvessel density, and prevents tissue fibrosis in vivo. Furthermore, the stromal changes induced by parallel EGFR and Src pathway inhibition resulted in improved overall survival in PKT mice when combined with gemcitabine. As a phase I clinical trial utilizing concurrent EGFR and Src inhibition with gemcitabine has recently concluded, these data provide timely translational insight into the novel mechanism of action of this regimen and expand our understanding into the phenomenon of stromal-mediated therapeutic resistance. IMPLICATIONS: These findings demonstrate that Src/EGFR inhibition targets STAT3, remodels the tumor stroma, and results in enhanced delivery of gemcitabine to improve overall survival in a mouse model of PDAC.

Increasing Antitumor Activity of JAK Inhibitor by Simultaneous Blocking Multiple Survival Signaling Pathways in Human Ovarian Cancer

Many signaling pathways, including the JAK/STAT3 pathway, are aberrantly activated and associated with ovarian cancer growth and progression. However, inhibition of STAT3 pathway alone was not sufficient to effectively block human ovarian cancer cell survival in vitro, which could be due to the activation and compensation of multiple survival pathways. In this study, we investigated a strategy that can enhance antitumor activity of JAK/STAT3 inhibitor by combining with inhibitors targeting other growth and survival pathways. We found that the in vitro activity of JAKi was remarkably increased when additional survival pathway was blocked. Blocking SRC pathway with SRC inhibitor (SRCi) increased the efficacy of JAKi more effectively than blocking AKT or MAPK pathway. The increased activity of JAKi in combination with SRCi is synergistic and associated with attenuation of p-STAT3, p-SRC, p-AKT and p-MAPK and increased inhibition of p-AKT. Simultaneous blockade of multiple survival pathways by combining JAKi with both AKT inhibitor (AKTi) and MEK inhibitor (MEKi) also resulted in a synergistic inhibition of cell survival. Furthermore, the combined treatment of JAKi and SRCi led to an increased apoptosis and greater inhibition of tumor growth and ascites formation. Taken together, our results demonstrate that the antitumor efficacy of JAKi is improved most effectively when combined with SRCi, providing a potential combination strategy for the treatment of advanced ovarian cancer.

Regulation of cisplatin-resistant head and neck squamous cell carcinoma by the SRC/ETS-1 signaling pathway

BACKGROUND

We investigated the role of the ETS-1 transcription factor in Head and Neck Squamous Cell Carcinoma (HNSCC) in multiple cisplatin-resistant HNSCC cell lines.

METHODS

We examined its molecular link with SRC and MEK/ERK pathways and determined the efficacy of either MEK/ERK inhibitor PD0325901 or SRC inhibitor Dasatinib on cisplatin-resistant HNSCC inhibition.

RESULTS

We found that ETS-1 protein expression levels in a majority of cisplatin-resistant HNSCC cell types were higher than those in their parental cisplatin sensitive partners. High ETS-1 expression was also found in patient-derived, cisplatin-resistant HNSCC cells. While ETS-1 knockdown inhibited cell proliferation, migration, and invasion, it could still re-sensitize cells to cisplatin treatment. Interestingly, previous studies have shown that MER/ERK pathways could regulate ETS-1 through its phosphorylation at threonine 38 (T38). Although almost all cisplatin-resistant HNSCC cells we tested showed higher ETS-1 phosphorylation levels at T38, we found that inhibition of MEK/ERK pathways with the MEK inhibitor PD0325901 did not block this phosphorylation. In addition, treatment of cisplatin-resistant HNSCC cells with the MEK inhibitor completely blocked ERK phosphorylation but did not re-sensitize cells to cisplatin treatment. Furthermore, we found that, consistent with ETS-1 increase, SRC phosphorylation dramatically increased in cisplatin-resistant HNSCC, and treatment of cells with the SRC inhibitor, Dasatinib, blocked SRC phosphorylation and decreased ETS-1 expression. Importantly, we showed that Dasatinib, as a single agent, significantly suppressed cell proliferation, migration, and invasion, in addition to survival.

CONCLUSIONS

Our results demonstrate that the SRC/ETS-1 pathway plays a crucial role and could be a key therapeutic target in cisplatin-resistant HNSCC treatment.

Effect of Tyrosin Kinase Inhibitors on NK Cell and ILC3 Development and Function

Tyrosin kinase inhibitors (TKI) sharply improved the prognosis of Chronic Myeloid Leukemia (CML) and of Philadelphia+ Acute Lymphoblastic Leukemia (Ph+ALL) patients. However, TKI are not curative because of the development of resistance and lack of complete molecular remission in the majority of patients. Clinical evidences would support the notion that patient's immune system may play a key role in preventing relapses. In particular, increased proportions of terminally differentiated CD56+CD16+CD57+ NK cells have been reported to be associated with successful Imatinib therapy discontinuation or with a deep molecular response in Dasatinib-treated patients. In view of the potential role of NK cells in immune-response against CML, it is important to study whether any TKI have an effect on the NK cell development and identify possible molecular mechanism(s) by which continuous exposure to in vitro TKI may influence NK cell development and repertoire. To this end, CD34+ hematopoietic stem cells (HSC) were cultured in the absence or in the presence of Imatinib, Nilotinib, or Dasatinib. We show that all compounds exert an inhibitory effect on CD56+ cell recovery. In addition, Dasatinib sharply skewed the repertoire of CD56+ cell population, leading to an impaired recovery of CD56+CD117-CD16+CD94/NKG2A+EOMES+ mature cytotoxic NK cells, while the recovery of CD56+CD117+CD94/NKG2A-RORγt+ IL-22-producing ILC3 was not affected. This effect appears to involve the Dasatinib-mediated inhibition of Src kinases and, indirectly, of STAT5-signaling activation in CD34+ cells during first days of culture. Our studies, reveal a possible mechanism by which Dasatinib may interfere with the proliferation and maturation of fully competent NK cells, i.e., by targeting signaling pathways required for differentiation and survival of NK cells but not of ILC3.

Dasatinib induces DNA damage and activates DNA repair pathways leading to senescence in non-small cell lung cancer cell lines with kinase-inactivating BRAF mutations

Improved therapies are greatly needed for non-small cell lung cancer (NSCLC) that does not harbor targetable kinase mutations or translocations. We previously demonstrated that NSCLC cells that harbor kinase-inactivating BRAF mutations (^KIBRAF) undergo senescence when treated with the multitargeted kinase inhibitor dasatinib. Similarly, treatment with dasatinib resulted in a profound and durable response in a patient with ^KIBRAF NSCLC. However, no canonical pathways explain dasatinib-induced senescence in ^KIBRAF NSCLC. To investigate the underlying mechanism, we used 2 approaches: gene expression and reverse phase protein arrays. Both approaches showed that DNA repair pathways were differentially modulated between ^KIBRAF NSCLC cells and those with wild-type (WT) BRAF. Consistent with these findings, dasatinib induced DNA damage and activated DNA repair pathways leading to senescence only in the ^KIBRAF cells. Moreover, dasatinib-induced senescence was dependent on Chk1 and p21, proteins known to mediate DNA damage-induced senescence. Dasatinib also led to a marked decrease in TAZ but not YAP protein levels. Overexpression of TAZ inhibited dasatinib-induced senescence. To investigate other vulnerabilities in ^KIBRAF NSCLC cells, we compared the sensitivity of these cells with that of ^WTBRAF NSCLC cells to 79 drugs and identified a pattern of sensitivity to EGFR and MEK inhibitors in the ^KIBRAF cells. Clinically approved EGFR and MEK inhibitors, which are better tolerated than dasatinib, could be used to treat ^KIBRAF NSCLC. Our novel finding that dasatinib induced DNA damage and subsequently activated DNA repair pathways leading to senescence in ^KIBRAF NSCLC cells represents a unique vulnerability with potential clinical applications.

KDR Amplification Is Associated with VEGF-Induced Activation of the mTOR and Invasion Pathways but does not Predict Clinical Benefit to the VEGFR TKI Vandetanib

PURPOSE

VEGF pathway inhibitors have been investigated as therapeutic agents in the treatment of non-small cell lung cancer (NSCLC) because of its central role in angiogenesis. These agents have improved survival in patients with advanced NSCLC, but the effects have been modest. Although VEGFR2/KDRis typically localized to the vasculature, amplification ofKDRhas reported to occur in 9% to 30% of the DNA from different lung cancers. We investigated the signaling pathways activated downstream ofKDRand whetherKDRamplification is associated with benefit in patients with NSCLC treated with the VEGFR inhibitor vandetanib.

METHODS

NSCLC cell lines with or withoutKDRamplification were studied for the effects of VEGFR tyrosine kinase inhibitors (TKI) on cell viability and migration. Archival tumor samples collected from patients with platinum-refractory NSCLC in the phase III ZODIAC study of vandetanib plus docetaxel or placebo plus docetaxel (N= 294) were screened forKDRamplification by FISH.

RESULTS

KDRamplification was associated with VEGF-induced activation of mTOR, p38, and invasiveness in NSCLC cell lines. However, VEGFR TKIs did not inhibit proliferation of NSCLC cell lines withKDRamplification. VEGFR inhibition decreased cell motility as well as expression of HIF1α inKDR-amplified NSCLC cells. In the ZODIAC study,KDRamplification was observed in 15% of patients and was not associated with improved progression-free survival, overall survival, or objective response rate for the vandetanib arm.

CONCLUSIONS

Preclinical studies suggestKDRactivates invasion but not survival pathways inKDR-amplified NSCLC models. Patients with NSCLC whose tumor hadKDRamplification were not associated with clinical benefit for vandetanib in combination with docetaxel.

Current and future intratumoral targeted treatment for pancreatic cancer

Pancreatic cancer is an insidious type of cancer with its symptoms manifested upon extensive disease. The overall 5-year survival rates between 0.4 and 4%. Surgical resection is an option for only 10% of the patients with pancreatic cancer. Local recurrence and hepatic metastases occur within 2 years after surgery. There are currently several molecular pathways investigated and novel targeted treatments are on the market. However; the nature of pancreatic cancer with its ability to spread locally in the primary site and lymph nodes indicates that further experimentation with local interventional therapies could be a future treatment proposal as palliative care or adjunct to gene therapy and chemotherapy/radiotherapy. In the current review, we will summarize the molecular pathways and present the interventional treatment options for pancreatic cancer.

Blocking the bFGF/STAT3 interaction through specific signaling pathways induces apoptosis in glioblastoma cells

We have reported that basic fibroblast growth factor (bFGF) demonstrates an intimate connection with signal transducer and activator of transcription 3 (STAT3) in malignant brain tumor cells. However, its mechanisms are still unclear. In this study, we used inhibitors to block specific signaling pathways, including JAK, PI3K/Akt, and Src pathways, to explore how bFGF mediates crosstalk with STAT3 in two glioblastoma(GBM) cell lines: U251 (mutant p53) and U87 (wild-type p53). Furthermore, we explored how the bFGF/STAT3 pathway affects GBM cell apoptosis. Our results suggest that bFGF can induce the activation of STAT3 mainly through the JAK and PI3K/Akt pathways, and that siRNA-mediated knockdown of STAT3 markedly reduces the bFGF levels in U251 cells. Our results also suggest that STAT3 knockdown increases the expression of pro-apoptotic genes and decreases the expression of anti-apoptotic genes, subsequently collapsing the mitochondrial membrane potentials in vitro and impairs tumor growth in vivo.

Resistance of Cancer Cells to Targeted Therapies Through the Activation of Compensating Signaling Loops

The emergence of low molecular weight kinase inhibitors as “targeted” drugs has led to remarkable advances in the treatment of cancer patients. The clinical benefits of these tumor therapies, however, vary widely in patient populations and with duration of treatment. Intrinsic and acquired resistance against such drugs limits their efficacy. In addition to the well studied mechanisms of resistance based upon drug transport and metabolism, genetic alterations in drug target structures and the activation of compensatory cell signaling have received recent attention. Adaptive responses can be triggered which counteract the initial dependence of tumor cells upon a particular signaling molecule and allow only a transient inhibition of tumor cell growth. These compensating signaling mechanisms are often based upon the relief of repression of regulatory feedback loops. They might involve cell autonomous, intracellular events or they can be mediated via the secretion of growth factor receptor ligands into the tumor microenvironment and signal induction in an auto- or paracrine fashion. The transcription factors Stat3 and Stat5 mediate the biological functions of cytokines, interleukins and growth factors and can be considered as endpoints of multiple signaling pathways. In normal cells this activation is transient and the Stat molecules return to their non-phosphorylated state within a short time period. In tumor cells the balance between activating and de-activating signals is disturbed resulting in the persistent activation of Stat3 or Stat5. The constant activation of Stat3 induces the expression of target genes, which cause the proliferation and survival of cancer cells, as well as their migration and invasive behavior. Activating components of the Jak-Stat pathway have been recognized as potentially valuable drug targets and important principles of compensatory signaling circuit induction during targeted drug treatment have been discovered in the context of kinase inhibition studies in HNSCC cells [1]. The treatment of HNSCC with a specific inhibitor of c-Src, initially resulted in reduced Stat3 and Stat5 activation and subsequently an arrest of cell proliferation and increased apoptosis. However, the inhibition of c-Src only caused a persistent inhibition of Stat5, whereas the inhibition of Stat3 was only transient. The activation of Stat3 was restored within a short time period in the presence of the c-Src inhibitor. This process is mediated through the suppression of P-Stat5 activity and the decrease in the expression of the Stat5 dependent target gene SOCS2, a negative regulator of Jak2. Jak2 activity is enhanced upon SOCS2 downregulation and causes the reactivation of Stat3. A similar observation has been made upon inhibition of Bmx, bone marrow kinase x-linked, activated in the murine glioma cell lines Tu-2449 and Tu-9648. Its inhibition resulted in a transient decrease of P-Stat3 and the induction of a compensatory Stat3 activation mechanism, possibly through the relief of negative feedback inhibition and Jak2 activation. These observations indicate that the inhibition of a single tyrosine kinase might not be sufficient to induce lasting therapeutic effects in cancer patients. Compensatory kinases and pathways might become activated and maintain the growth and survival of tumor cells. The definition of these escape pathways and their preemptive inhibition will suggest effective new combination therapies for cancer.

Proteomics and phosphoproteomics provide insights into the mechanism of action of a novel pyrazolo[3,4-d]pyrimidine Src inhibitor in human osteosarcoma

Osteosarcoma (OS) is a highly malignant bone tumour, affecting mainly children and young adults between 10 and 20 years of age. It represents the most frequent primitive malignant tumour of the skeletal system and is characterized by an extremely aggressive clinical course, with rapid development of lung metastases. In the last few years, targeting Src in the treatment of OS has become one of the major challenges in the development of new drugs, since an elevated Src kinase activity has been associated with the development and the maintenance of the OS malignant phenotype. Recently, SI-83, a novel pyrazolo[3,4-d]pyrimidine derivate Src inhibitor, was selected as a promising OS therapeutic drug because of its elevated anti-tumour effects toward human OS. In the present study, gel-based proteomics and phosphoproteomics revealed significant changes in proteins involved in many cancer related processes. We got insight into SI-83 proapoptotic and antiproliferative properties (overrepresentation of GRIA1, GRP78, and CALR and underrepresentation of NPM1, RCN, and P4HB). Nevertheless, the most significant findings of our work are the SI-83 induced dephosphorylation of ARPC5L, a subunit of the actin related Arp2/3 complex, and the decrease of other cytoskeleton proteins. These data, together with a dramatic impairment of SaOS-2 cell migration and adhesion, suggest that SI-83 may have antimetastatic features that enhance its use as a potent OS chemotherapeutic drug.

Dasatinib promotes the expansion of a therapeutically superior T-cell repertoire in response to dendritic cell vaccination against melanoma

Dasatinib (DAS) is a potent inhibitor of the BCR-ABL, SRC, c-KIT, PDGFR, and ephrin tyrosine kinases that has demonstrated only modest clinical efficacy in melanoma patients. Given reports suggesting that DAS enhances T cell infiltration into the tumor microenvironment, we analyzed whether therapy employing the combination of DAS plus dendritic cell (DC) vaccination would promote superior immunotherapeutic benefit against melanoma. Using a M05 (B16.OVA) melanoma mouse model, we observed that a 7-day course of orally-administered DAS (0.1 mg/day) combined with a DC-based vaccine (VAC) against the OVA_257–264 peptide epitope more potently inhibited tumor growth and extended overall survival as compared with treatment with either single modality. The superior efficacy of the combinatorial treatment regimen included a reduction in hypoxic-signaling associated with reduced levels of immunosuppressive CD11b⁺Gr1⁺ myeloid-derived suppressor cells (MDSC) and CD4⁺Foxp3⁺ regulatory T (Treg) populations in the melanoma microenvironment. Furthermore, DAS + VAC combined therapy upregulated expression of Type-1 T cell recruiting CXCR3 ligand chemokines in the tumor stroma correlating with activation and recruitment of Type-1, vaccine-induced CXCR3⁺CD8⁺ tumor-infiltrating lymphocytes (TILs) and CD11c⁺ DC into the tumor microenvironment. The culmination of this bimodal approach was a profound “spreading” in the repertoire of tumor-associated antigens recognized by CD8⁺ TILs, in support of the therapeutic superiority of combined DAS + VAC immunotherapy in the melanoma setting.

MLS-2384, a new 6-bromoindirubin derivative with dual JAK/Src kinase inhibitory activity, suppresses growth of diverse cancer cells

Janus kinase (JAK) and Src kinase are the two major tyrosine kinase families upstream of signal transducer and activator of transcription (STAT). Among the seven STAT family proteins, STAT3 is constitutively activated in many diverse cancers. Upon activation, JAK and Src kinases phosphorylate STAT3, and thereby promote cell growth and survival. MLS-2384 is a novel 6-bromoindirubin derivative with a bromo-group at the 6-position on one indole ring and a hydrophilic group at the 3'-position on the other indole ring. In this study, we investigated the kinase inhibitory activity and anticancer activity of MLS-2384. Our data from in vitro kinase assays, cell viability analyses, western blotting analyses, and animal model studies, demonstrate that MLS-2384 is a dual JAK/Src kinase inhibitor, and suppresses growth of various human cancer cells, such as prostate, breast, skin, ovarian, lung, and liver. Consistent with the inactivation of JAK and Src kinases, phosphorylation of STAT3 was inhibited in a dose-dependent manner in the cancer cells treated with MLS-2384. STAT3 downstream proteins involved in cell proliferation and survival, such as c-Myc and Mcl-1, are downregulated by MLS-2384 in prostate cancer cells, whereas survivin is downregulated in A2058 cells. In these two cancer cell lines, PARP is cleaved, indicating that MLS-2384 induces apoptosis in human melanoma and prostate cancer cells. Importantly, MLS-2384 suppresses tumor growth with low toxicity in a mouse xenograft model of human melanoma. Taken together, MLS-2384 demonstrates dual JAK/Src inhibitory activity and suppresses tumor cell growth both in vitro and in vivo. Our findings support further development of MLS-2384 as a potential small-molecule therapeutic agent that targets JAK, Src, and STAT3 signaling in multiple human cancer cells.

Tumor grafts derived from patients with head and neck squamous carcinoma authentically maintain the molecular and histologic characteristics of human cancers

BACKGROUND

The patient-derived xenograft (PDX) model is likely to reflect human tumor biology more accurately than cultured cell lines because human tumors are implanted directly into animals; maintained in an in vivo, three-dimensional environment; and never cultured on plastic. PDX models of head and neck squamous cell carcinoma (HNSCC) have been developed previously but were not well characterized at the molecular level. HNSCC is a deadly and disfiguring disease for which better systemic therapy is desperately needed. The development of new therapies and the understanding of HNSCC biology both depend upon clinically relevant animal models. We developed and characterized the patient-derived xenograft (PDX) model because it is likely to recapitulate human tumor biology.

METHODS

We transplanted 30 primary tumors directly into mice. The histology and stromal components were analyzed by immunohistochemistry. Gene expression analysis was conducted on patient tumors and on PDXs and cell lines derived from one PDX and from independent, human tumors.

RESULTS

Five of 30 (17%) transplanted tumors could be serially passaged. Engraftment was more frequent among HNSCC with poor differentiation and nodal disease. The tumors maintained the histologic characteristics of the parent tumor, although human stromal components were lost upon engraftment. The degree of difference in gene expression between the PDX and its parent tumor varied widely but was stable up to the tenth generation in one PDX. For genes whose expression differed between parent tumors and cell lines in culture, the PDX expression pattern was very similar to that of the parent tumor. There were also significant expression differences between the human tumors that subsequently grew in mice and those that did not, suggesting that this model enriches for cancers with distinct biological features. The PDX model was used successfully to test targeted drugs in vivo.

CONCLUSION

The PDX model for HNSCC is feasible, recapitulates the histology of the original tumor, and generates stable gene expression patterns. Gene expression patterns and histology suggested that the PDX more closely recapitulated the parental tumor than did cells in culture. Thus, the PDX is a robust model in which to evaluate tumor biology and novel therapeutics.

Intelligent design of multifunctional lipid-coated nanoparticle platforms for cancer therapy

Nanotechnology is rapidly evolving and dramatically changing the paradigms of drug delivery. The small sizes, unique chemical properties, large surface areas, structural diversity and multifunctionality of nanoparticles prove to be greatly advantageous for combating notoriously therapeutically evasive diseases such as cancer. Multifunctional nanoparticles have been designed to enhance tumor uptake through either passive or active targeting, while also avoiding reticuloendothelial system uptake through the incorporation of PEG onto the surface. First-generation nanoparticle systems, such as liposomes, are good carriers for drugs and nucleic acid therapeutics, although they have some limitations. These lipid bilayers are now being utilized as excellent carriers for drug-loaded, solid core particles such as iron oxide, mesoporus silica and calcium phosphate. In this article, their design, as well as their multifunctional role in cancer therapy are discussed.

Dual inhibition of Janus and Src family kinases by novel indirubin derivative blocks constitutively-activated Stat3 signaling associated with apoptosis of human pancreatic cancer cells

Constitutively-activated JAK/Stat3 or Src/Stat3 signaling plays a crucial role in tumor cell survival, proliferation, angiogenesis and immune suppression. Activated JAK/Stat3 or Src/Stat3 has been validated as a promising molecular target for cancer therapy. However, prolonged inhibition of Src family kinases (SFKs) leads to reactivation of signal transducer and activator of transcript 3 (Stat3) and tumor cell survival through altered JAK/Stat3 interaction. This compensatory feedback suggests that dual inhibition of Janus kinases (JAKs) and SFKs might be a promising strategy for targeting downstream Stat3 signaling in the clinic. In this study, we identify that the natural product derivative E738 is a novel dual inhibitor of JAKs and SFKs. The IC(50) values of E738 against recombinant JAKs and SFKs in vitro are in the ranges of 0.7-74.1 nM and 10.7-263.9 nM, respectively. We observed that phosphorylation of both Jak2 and Src was substantially inhibited in the submicromolar range by E738 in cultured human pancreatic tumor cells, followed by blockade of downstream Stat3 activation. E738 down-regulated expression of the Stat3 target proteins Mcl-1 and survivin, associated with induction of apoptosis. Computational models and molecular dynamics simulations of E738/Tyk2 or E738/Src in silico suggest that E738 inhibits both tyrosine kinase 2 (Tyk2) and Src as an ATP-competitive ligand. Moreover, the planar E738 molecule demonstrates a strong binding affinity in the compact ATP-binding site of Tyk2. In sum, E738 is the first dual inhibitor of JAKs and SFKs, followed by inhibition of Stat3 signaling. Thus, according to in vitro experiments, E738 is a promising new therapeutic agent for human pancreatic cancer treatment by blocking both oncogenic pathways simultaneously.

Degradation of epidermal growth factor receptor mediates dasatinib-induced apoptosis in head and neck squamous cell carcinoma cells

Epidermal growth factor receptor (EGFR) is an important oncoprotein that promotes cell growth and proliferation. Dasatinib, a bcr-abl inhibitor, has been approved clinically for the treatment of chronic myeloid leukemia and demonstrated to be effective against solid tumors in vitro through Src inhibition. Here, we disclose that EGFR degradation mediated dasatinib-induced apoptosis in head and neck squamous cell carcinoma (HNSCC) cells. HNSCC cells, including Ca9-22, FaDu, HSC3, SAS, SCC-25, and UMSCC1, were treated with dasatinib, and cell viability, apoptosis, and underlying signal transduction were evaluated. Dasatinib exhibited differential sensitivities against HNSCC cells. Growth inhibition and apoptosis were correlated with its inhibition on Akt, Erk, and Bcl-2, irrespective of Src inhibition. Accordingly, we found that down-regulation of EGFR was a determinant of dasatinib sensitivity. Lysosome inhibitor reversed dasatinib-induced EGFR down-regulation, and c-cbl activity was increased by dasatinib, indicating that dasatinib-induced EGFR down-regulation might be through c-cbl-mediated lysosome degradation. Increased EGFR activation by ligand administration rescued cells from dasatinib-induced apoptosis, whereas inhibition of EGFR enhanced its apoptotic effect. Estrogen receptor α (ERα) was demonstrated to play a role in Bcl-2 expression, and dasatinib inhibited ERα at the pretranslational level. ERα was associated with EGFR in dasatinib-treated HNSCC cells. Furthermore, the xenograft model showed that dasatinib inhibited HSC3 tumor growth through in vivo down-regulation of EGFR and ERα. In conclusion, degradation of EGFR is a novel mechanism responsible for dasatinib-induced apoptosis in HNSCC cells.

GSK3 inhibition prevents lethal GVHD in mice

Graft-versus-host disease (GVHD) is a major contributor to transplant-related mortality and morbidity after allogeneic stem cell transplantation. Despite advancements in tissue-typing techniques, conditioning regimens, and therapeutic intervention, the incidence rate of GVHD remains high. GVHD is caused by alloreactive donor T cells that infiltrate and destroy host tissues (e.g., skin, liver, and gut). Therefore, GVHD is prevented and treated with therapeutics that suppress proinflammatory cytokines and T-cell function (e.g., cyclosporine, glucocorticoids). Here we report that the small molecule inhibitor of glycogen synthase kinase 3, 6-bromoindirubin 3'-oxime (BIO), prevents lethal GVHD in a humanized xenograft model in mice. BIO treatment did not affect donor T-cell engraftment, but suppressed their activation and attenuated bone marrow and liver destruction mediated by activated donor T cells. Glycogen synthase kinase 3 inhibition modulated the Th1/Th2 cytokine profile in vitro and suppressed activation of signal transducers and activators of transcription 1 and 3 signaling pathways both in vitro and in vivo. Importantly, human T cells derived from BIO-treated mice were able to mediate anti-tumor effects in vitro, and BIO did not affect stem cell engraftment and multilineage reconstitution in a mouse model of transplantation. These data demonstrate that inhibition of glycogen synthase kinase 3 can potentially abrogate GVHD without compromising the efficacy of transplantation.

Yes is a central mediator of cell growth in malignant mesothelioma cells

The constitutive activation of the Src family kinases (SFKs) has been established as a poor prognostic factor in malignant mesothelioma (MM), however, the family member(s) which contribute to the malignancy have not been defined. This study aimed to identify the SFK member(s) contributing to cell growth using RNA interference in various MM cell lines. Silencing of Yes but not of c-Src or Fyn in MM cells leads to cell growth suppression. This suppressive effect caused by Yes silencing mainly depends on G1 cell cycle arrest and partly the induction of apoptosis. Also, the knockout of Yes induces the inactivation of β-catenin signaling and subsequently decreases the levels of cyclin D necessary for G1-S transition in the cell cycle. In addition, Yes knockout has less effect on cell growth suppression in β-catenin-deficient H28 MM cells compared to other MM cells which express the catenin. Overall, we conclude that Yes is a central mediator for MM cell growth that is not shared with other SFKs such as c-Src.

Complexity in the signaling network: insights from the use of targeted inhibitors in cancer therapy

Cancer often arises when normal cellular growth goes awry due to defects in critical signal transduction pathways. A growing number of inhibitors that target specific components of these pathways are in clinical use, but the success of these agents has been limited by the resistance to inhibitor therapy that ultimately develops. Studies have now shown that cancer cells respond to chronic drug treatment by adapting their signaling circuitry, taking advantage of pathway redundancy and routes of feedback and cross-talk to maintain their function. This review focuses on the compensatory signaling mechanisms highlighted by the use of targeted inhibitors in cancer therapy.

Role of STAT3 in Transformation and Drug Resistance in CML

Chronic myeloid leukemia (CML) is initially driven by the bcr-abl fusion oncoprotein. The identification of bcr-abl led to the discovery and rapid translation into the clinic of bcr-abl kinase inhibitors. Although, bcr-abl inhibitors are efficacious, experimental evidence indicates that targeting bcr-abl is not sufficient for elimination of minimal residual disease found within the bone marrow (BM). Experimental evidence indicates that the failure to eliminate the leukemic stem cell contributes to persistent minimal residual disease. Thus curative strategies will likely need to focus on strategies where bcr-abl inhibitors are given in combination with agents that specifically target the leukemic stem cell or the leukemic stem cell niche. One potential target to be exploited is the Janus kinase (JAK)/signal transducers and activators of transcription 3 (STAT3) pathway. Recently using STAT3 conditional knock-out mice it was shown that STAT3 is critical for initiating the disease. Interestingly, in the absence of treatment, STAT3 was not shown to be required for maintenance of the disease, suggesting that STAT3 is required only in the tumor initiating stem cell population (Hoelbl et al., 2010). In the context of the BM microenvironment, STAT3 is activated in a bcr-abl independent manner by the cytokine milieu. Activation of JAK/STAT3 was shown to contribute to cell survival even in the event of complete inhibition of bcr-abl activity within the BM compartment. Taken together, these studies suggest that JAK/STAT3 is an attractive therapeutic target for developing strategies for targeting the JAK-STAT3 pathway in combination with bcr-abl kinase inhibitors and may represent a viable strategy for eliminating or reducing minimal residual disease located in the BM in CML.

Molecular pathogenesis of pancreatic cancer and clinical perspectives

Pancreatic cancer remains stubbornly resistant to many key cytotoxic chemotherapeutic agents and novel targeted therapies. The molecular heterogeneity of this cancer may account for therapy failures to date, although our growing arsenal of novel targeted agents could translate into patient survival. The main objectives of this review are to elucidate histological subtypes of pancreatic neoplasms that exhibit the characteristic of a gradual process of differentiation from benign entities to malignant ones. In addition, important genes, molecular abnormalities, and significant pathways of pancreatic cancer are analyzed and a potential clinical interpretation is presented (p16/cdkn2a, k-ras mutations, smad-4/tgf-/stat3, stk-11, braf, brca-2, neurotensin, mucs proteins, palb2, mitochondrial mutations, DNA mismatch repair genes, methylation, microrna expression, epithelial-to-mesenchymal transition, egfr mutations, the pi3k-akt-mtor pathway, the vegf pathway, heat shock proteins, cxcr4, the cox pathway, the src pathway, the hedgehog pathway, pancreatic stellate cells, a progression model, and molecular events in uncommon pancreatic tumors). Finally, future therapeutic directions are elucidated.

STAT5A-mediated SOCS2 expression regulates Jak2 and STAT3 activity following c-Src inhibition in head and neck squamous carcinoma

PURPOSE

The inhibition of c-Src results in a striking reduction in cancer cell invasion, but the effect on cell survival is modest. Defining mechanisms that limit apoptosis following c-Src inhibition could result in an ideal therapeutic approach that both inhibits invasion and leads to apoptosis. In this regard, we discovered a novel feedback loop that results in STAT3 reactivation following sustained c-Src inhibition. Here we define the mechanism underlying this feedback loop and examine the effect of inhibiting it in vivo.

EXPERIMENTAL DESIGN

We measured levels and activity of pathway components using PCR, Western blotting, and kinase assays following their manipulation using both molecular and pharmacologic approaches. We used a heterotransplant animal model in which human oral squamous cancer is maintained exclusively in vivo.

RESULTS

Following c-Src inhibition, STAT5 is durably inhibited. The inhibition of STAT5A, but not STAT5B, subsequently reduces the expression of suppressors of cytokine signaling 2 (SOCS2). SOCS2 inhibits Janus kinase 2 (Jak2) activity and Jak2-STAT3 binding. SOCS2 expression is necessary for STAT3 inhibition by c-Src inhibitors. Overexpression of SOCS2 is adequate to prevent STAT3 reactivation and to enhance the cytotoxic effects of c-Src inhibition. Likewise, the combination of Jak and c-Src inhibitors led to significantly more apoptosis than either agent alone in vivo.

CONCLUSIONS

To our knowledge, ours is the first study that fully defines the mechanism underlying this feedback loop, in which sustained c-Src inhibition leads to diminished SOCS2 expression via sustained inhibition of STAT5A, allowing activation of Jak2 and STAT3, Jak2-STAT3 binding, and survival signals.

Nanoparticle delivery of a peptide targeting EGFR signaling

EGFR serves as an important therapeutic target because of its over-expression in many cancers. In this study, we investigated a peptide-based therapy aimed at blocking intracellular protein-protein interactions during EGFR signaling and evaluated a targetable lipid carrier system that can deliver peptides to intracellular targets in human cancer cells. EEEEpYFELV (EV), a nonapeptide mimicking the Y845 site of EGFR which is responsible for STAT5b phosphorylation, was designed to block EGFR downstream signaling. EV was loaded onto LPH nanoparticles that are comprised of a membrane/core structure including a surface-grafted polyethylene glycol (PEG) used to evade the reticuloendothelial system (RES) and anisamide (AA) for targeting the sigma receptor over-expressed in H460 human lung cancer cells. EV formulated with PEGylated and targeted LPH (LPH-PEG-AA) was taken up by the tumor cells and trafficked to the cytoplasm with high efficiency. Using this approach, EV acted as a dominant negative inhibitor of STAT5b phosphorylation, arrested cell proliferation, and induced massive apoptosis. Intravenous administration of EV loaded in LPH-PEG-AA led to efficient EV peptide delivery to the tumor in a xenograft mouse model, and multiple injections inhibited tumor growth in a dose-dependent manner. Our findings offer proof-of-concept for an intracellular peptide-mediated cancer therapy that is delivered by carefully designed nanoparticles.

Regulation of soluble interleukin-6 (IL-6) receptor release from corneal epithelial cells and its role in the ocular surface

PURPOSE

Interleukin (IL)-6 signaling through its soluble receptor (sIL-6R) (IL-6 trans-signaling) plays an important role in various inflammatory states. We investigated production of sIL-6R in the corneal epithelium and examined the role of IL-6 trans-signaling in the cornea.

METHODS

In-vitro experiments were performed using SV40-transformed human corneal epithelial cells (HCEC) and primary human corneal fibroblasts (HCF, keratocytes). Ectodomain shedding in HCEC was stimulated by adding phorbol myristate acetate (PMA, 3 μM: ) both with and without ectodomain shedding inhibition using TNF-α processing inhibitor-1 (TAPI-1, 250 ng/mL), and the concentration of sIL-6R in the culture medium was determined by enzyme-linked immunosorbent assay (ELISA). Expression of differential sIL-6R mRNA splicing (DS-sIL-6R) in HCEC was examined by using reverse transcription (RT)-PCR. The recombinant IL-6 or combination of recombinant IL-6/sIL-6R was added to HCF culture medium and phosphorylation of STAT3 was analyzed by Luminex assay. Tear fluid from patients with Sjögren syndrome was collected and analyzed by ELISA for sIL-6R concentration.

RESULTS

In HCEC culture medium, sIL-6R release was increased significantly (P < 0.01) by adding PMA and this increased release of sIL-6R was inhibited significantly by adding TAPI-1, indicating the participation of ectodomain shedding in sIL-6R production. In RT-PCR, DS-sIL-6R expression was noted in HCEC. IL-6/sIL-6R-induced STAT3 phosphorylation was recognized in cultured HCF, suggesting IL-6 trans-signaling induced inflammatory cellular signaling in HCF. In the tear fluid of the patients with Sjögren syndrome, sIL-6R expression was up-regulated (Sjögren syndrome; 2.38 ± 0.98 ng/mL, normal control; 0.16 ± 0.34 ng/mL).

CONCLUSIONS

Production of sIL-6R was induced by both ectodomain shedding and mRNA splicing in the corneal epithelium. IL-6 trans-signaling can induce an inflammatory response in corneal fibroblasts. The up-regulation of sIL-6R in inflamed ocular surfaces suggests a pivotal role of sIL-6R at the ocular surface.

Curcumin enhances dasatinib-induced inhibition of growth and transformation of colon cancer cells

Colorectal cancer is the third most common form of malignancy, behind prostate and lung cancers. Despite recent advances in medicine, mortality from colorectal cancer remains high, highlighting the need for improved therapies. Numerous studies have demonstrated increased activation of EGFR and its family members (EGFRs), IGF-1R as well as c-Src in colorectal cancer. The current study was undertaken to examine the effectiveness of combination therapy of dasatinib (BMS-354825; Bristol-Myers Squibb), a highly specific inhibitor of Src family kinases (SFK) and a nontoxic dietary agent; curcumin (diferuloylmethane), in colorectal cancer in in vitro and in vivo experimental models. For the latter, we utilized C57BL/6 APC(Min+/-) mice. Initial in vitro studies revealed synergistic interactions between the two agents. Additionally, we have observed that combination treatment causes a much greater inhibition of the following metastatic processes than either agent alone: (i) colony formation, (ii) invasion through extracellular matrix and (iii) tubule formation by endothelial cells. Dasatinib affects the cell adhesion phenotype of colon cancer HCT-116 cells whereas the combination therapy enhances this effect to a greater extent. Preclinical investigation revealed that the combination therapy to be highly effective causing an over 95% regression of intestinal adenomas in Apc(Min+/-) mice, which could be attributed to decreased proliferation and increased apoptosis. In conclusion, our data suggest that combination treatment of dasatinib and curcumin could be a potential therapeutic strategy for colorectal cancer.

JAK1 activates STAT3 activity in non-small-cell lung cancer cells and IL-6 neutralizing antibodies can suppress JAK1-STAT3 signaling

Members of the signal transducer and activator of transcription (STAT) family of transcription factors are potential targets for the treatment and prevention of cancers including non-small-cell lung cancer. STAT proteins can be phosphorylated and activated by diverse upstream kinases including cytokine receptors and tyrosine kinases. We examined STAT protein activation in lung cancer cell lines including those with activating mutations in the EGFR and examined upstream kinases responsible for STAT3 phosphorylation and activation using small molecules, antibodies, and RNA interference. We found more pronounced STAT3 activation in cells with activating EGFR mutations, yet inhibition of EGFR activity had no effect on STAT3 activation. Inhibition of JAK1 with small molecules or RNA interference resulted in loss of STAT3 tyrosine phosphorylation and inhibition of cell growth. An interleukin-6 neutralizing antibody, siltuximab (CNTO 328) could inhibit STAT3 tyrosine phosphorylation in a cell-dependent manner. Siltuximab could completely inhibit STAT3 tyrosine phosphorylation in H1650 cells, and this resulted in inhibition of lung cancer cell growth in vivo. Combined EGFR inhibition with erlotinib and siltuximab resulted in dual inhibition of both tyrosine and serine STAT3 phosphorylation, more pronounced inhibition of STAT3 transcriptional activity, and translated into combined effects on lung cancer growth in a mouse model. Our results suggest that JAK1 is responsible for STAT3 activation in lung cancer cells and that indirect attacks on JAK1-STAT3 using an IL-6 neutralizing antibody with or without EGFR inhibition can inhibit lung cancer growth in lung cancer subsets.

Distinct interactions between c-Src and c-Met in mediating resistance to c-Src inhibition in head and neck cancer

PURPOSE

c-Src inhibition in cancer cells leads to an abrogation of invasion but a variable effect on apoptosis. The pathways downstream of c-Src promoting survival are not well characterized. Because cancer therapy that both decreases invasion and induces significant apoptosis would be ideal, we sought to characterize the mechanisms of resistance to c-Src inhibition.

EXPERIMENTAL DESIGN

c-Src was inhibited in a panel of oral cancer cell lines and subsequent survival and signaling measured. The interactions between c-Src and c-Met were evaluated using immunoprecitation and an in vitro kinase assay. Cytotoxicity was measured and the Chou-Talalay combination index calculated. An orthotopic model of oral cancer was used to assess the effects of c-Met and c-Src inhibitors.

RESULTS

Inhibition of c-Src resulted in c-Met inhibition in sensitive cells lines, but not in resistant cell lines. Isolated c-Met was a c-Src substrate in both sensitive and resistant cells, but there was no interaction of c-Src and c-Met in intact resistant cells. To examine the biological consequences of this mechanism, we demonstrated synergistic cytotoxicity, enhanced apoptosis, and decreased tumor size with the combination of c-Src and c-Met inhibitors.

CONCLUSIONS

Sustained c-Met activation can mediate resistance to c-Src inhibition. These data suggest that the differences between c-Met and c-Src signaling in sensitive and resistant cells are due to distinct factors promoting or inhibiting interactions, respectively, rather than to intrinsic structural changes in c-Src or c-Met. The synergistic cytotoxic effects of c-Src and c-Met inhibition may be important for the treatment of head and neck cancers.

Dasatinib: a potent SRC inhibitor in clinical development for the treatment of solid tumors

SRC is a tyrosine kinase that plays a role in oncogenic, invasive and bone-metastatic processes. It has therefore been prioritized as a candidate therapeutic target in patients with solid tumors. Several SRC inhibitors are now in development, of which dasatinib has been most explored. Preclinical studies in a wide variety of solid tumor cell lines, including prostate, breast and glioma, have shown that that dasatinib acts as a cytostatic agent, inhibiting the processes of cell proliferation, invasion and metastasis. Dasatinib also inhibits the activity of osteoclasts, which have a major role in the development of metastatic bone lesions. Dasatinib has additive or synergistic activity in combination with a number of other agents, including cytotoxic agents and targeted therapies, providing a rationale for combination treatment in a clinical setting. Emerging clinical data with dasatinib support experimental observations, with preliminary phase 1 and 2 data demonstrating activity, both as a single agent and as combination therapy, in a range of solid tumors. Future clinical trials will further assess the clinical value of SRC inhibition with dasatinib.

ErbB-inhibitory protein: a modified ectodomain of epidermal growth factor receptor synergizes with dasatinib to inhibit growth of breast cancer cells

Many solid tumors, including breast cancer, show increased activation of several growth factor receptors, specifically epidermal growth factor receptor (EGFR) and its family members as well as c-Src, a nonreceptor tyrosine kinase that promotes proliferation, inhibits apoptosis, and induces metastasis. We hypothesize that inhibition of c-Src and EGFRs will be an effective therapeutic strategy for triple-negative breast cancer. To test our hypothesis, we used a c-Src-specific inhibitor dasatinib (BMS-354825; Bristol-Myers Squibb) and our newly developed ErbB-inhibitory protein (EBIP), a potential pan-ErbB inhibitor, in breast cancer cells. EBIP is composed of 1 to 448 amino acids of the ectodomain of human EGFR to which the 30-amino acid epitope (known as "U" region) of rat EGFR-related protein is fused at the COOH-terminal end. The combination of dasatinib and EBIP was found to be highly effective in inhibiting the growth of four different breast cancer cells (MDA-MB-468, SKBr-3, MDA-MB-453, and MDA-MB-231) that express different levels of EGFRs. In EGFR-overexpressing MDA-MB-468 cells, the combination, but not monotherapy, markedly stimulated apoptosis mediated by caspase-9 and caspase-8 and attenuated activation of EGFR and Src as well as tyrosine kinase activity. EBIP also inhibited heregulin-induced activation of HER-2 and HER-3 in MDA-MB-453 breast cancer cells. The combination therapy was highly effective in suppressing tumor growth ( approximately 90% inhibition) in MDA-MB-468-derived xenografts in severe combined immunodeficient mice. The latter could be attributed to induction of apoptosis. We conclude that combining dasatinib and EBIP could be an effective therapeutic strategy for breast cancer by targeting EGFRs and Src signaling.

Defining the role of the JAK-STAT pathway in head and neck and thoracic malignancies: implications for future therapeutic approaches

Although the role of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway has been most extensively studied in hematopoietic cells and hematologic malignancies, it is also activated in epithelial tumors, including those originating in the lungs and head and neck. The canonical pathway involves the activation of JAK following ligand binding to cytokine receptors. The activated JAKs then phosphorylate STAT proteins, leading to their dimerization and translocation into the nucleus. In the nucleus, STATs act as transcription factors with pleiotropic downstream effects. STATs can be activated independently of JAKs, most notably by c-Src kinases. In cancer cells, STAT3 and STAT5 activation leads to the increased expression of downstream target genes, leading to increased cell proliferation, cell survival, angiogenesis, and immune system evasion. STAT3 and STAT5 are expressed and activated in head and neck squamous cell carcinoma (HNSCC) where they contribute to cell survival and proliferation. In HNSCC, STATs can be activated by a number of signal transduction pathways, including the epidermal growth factor receptor (EGFR), alpha7 nicotinic receptor, interleukin (IL) receptor, and erythropoietin receptor pathways. Activated STATs are also expressed in lung cancer, but the biological effects of JAK/STAT inhibition in this cancer are variable. In lung cancer, STAT3 can be activated by multiple pathways, including EGFR. Several approaches have been used to inhibit STAT3 in the hopes of developing an antitumor agent. Although several STAT3-specific agents are promising, none are in clinical development, mostly because of drug delivery and stability issues. In contrast, several JAK inhibitors are in clinical development. These orally available, ATP-competitive, small-molecule kinase inhibitors are being tested in myeloproliferative disorders. Future studies will determine whether JAK inhibitors are useful in the treatment of HNSCC or lung cancer.

TOM1L is involved in a novel signaling pathway important for the IL-2 production in Jurkat T cells stimulated by CD3/CD28 co-ligation

TOM1L (target of Myb-1 Like) was identified as a binding partner for the full length and catalytically-active Lck in a yeast 2-hybrid screening assay. Here we show that in Jurkat T cells stimulated by CD3/CD28 coligation where the expression of TOM1L is reduced by lenti virus mediated-siRNA results in a dramatically lower IL-2 production. The production of IL-2 in siRNA treated cells stimulated with PMA/ionomycin was not affected indicating an involvement of TOM1L in a pathway proximal of TCR and CD28. The coexpression of Fyn with TOM1L increased the level of the phosphorylated form of Fyn indicating that TOM1L has the ability to activate Fyn. The ability of TOM1L to activate Fyn was further shown in a kinase assay using angiotensin II as a substrate. By confocal microscopy, we show that the expression of TOM1L in non-treated HeLa and SK-N-SH cells colocalizes with the mitochondrial membrane but not with lysosomal compartments or the trans-Golgi network. Furthermore, we show that the over-expression of TOM1L in Jurkat cells causes an increase of the STAT3 expression . Based on our results, we here propose that TOM1L is involved in a novel signaling pathway that is important for the IL-2 production in T cells.

Enhanced sensitivity of pancreatic cancer cells to concurrent inhibition of aberrant signal transducer and activator of transcription 3 and epidermal growth factor receptor or Src

Many molecular aberrations occur in pancreatic cancer. Although aberrant epidermal growth factor receptor (EGFR), Src, and signal transducer and activator of transcription 3 (Stat3) are implicated in pancreatic cancer, therapies that target only one of these entities are undermined by signaling cross-talk. In the human pancreatic cancer lines, Panc-1 and Colo-357, pY845EGFR, pY1068EGFR, pY1086EGFR, and pY1173EGFR levels and pY416c-Src are concurrently elevated with aberrantly active Stat3 in a complex signaling cross-talk. Thus, understanding the signaling integration would facilitate the design of effective multiple-targeted therapeutic modalities. In Panc-1 and Colo-357 lines, pY845EGFR, pY1068EGFR, and pY1086EGFR levels are responsive to c-Src inhibition in contrast to pY1173EGFR, which is EGFR kinase-dependent. Constitutively active Stat3 is sensitive to both EGFR and Src inhibition, but the early suppression of aberrantly active Stat3 in response to the inhibition of EGFR and Src is countered by a Janus kinase (Jaks)-dependent reactivation, suggesting that Jaks activity is a compensatory mechanism for Stat3 induction. The inhibition of EGFR, Src, or Stat3 alone induced weak biological responses. By contrast, the concurrent inhibition of Stat3 and EGFR or Src induced greater viability loss and apoptosis and decreased the migration/invasion of pancreatic cancer cells in vitro. Significantly, the concurrent inhibition, compared with monotargeting modality, induced stronger human pancreatic tumor growth inhibition in xenografts. We infer that the tumor growth inhibition in vivo is caused by the simultaneous suppression of the abnormal functions of Stat3 and EGFR or Src. These studies strongly suggest that the concurrent targeting of Stat3 and EGFR or Src could be a beneficial therapeutic approach for pancreatic cancer.

Reciprocal regulation of c-Src and STAT3 in non-small cell lung cancer

PURPOSE

Signal transducer and activator of transcription-3 (STAT3) is downstream of growth factor and cytokine receptors, and regulates key oncogenic pathways in non-small cell lung cancer (NSCLC). Activation of STAT3 by cellular Src (c-Src) promotes tumor progression. We hypothesized that c-Src inhibition could activate STAT3 by inducing a homeostatic feedback loop, contributing to c-Src inhibitor resistance.

EXPERIMENTAL DESIGN

The effects of c-Src inhibition on total and phosphorylated STAT3 were measured in NSCLC cell lines and in murine xenograft models by Western blotting. c-Src and STAT3 activity as indicated by phosphorylation was determined in 46 human tumors and paired normal lung by reverse phase protein array. Modulation of dasatinib (c-Src inhibitor) cytotoxicity by STAT3 knockdown was measured by MTT, cell cycle, and apoptosis assays.

RESULTS

Depletion of c-Src by small interfering RNA or sustained inhibition by dasatinib increased pSTAT3, which could be blocked by inhibition of JAK. Similarly, in vivo pSTAT3 levels initially decreased but were strongly induced after sustained dasatinib treatment. In human tumors, phosphorylation of the autoinhibitory site of c-Src (Y527) correlated with STAT3 phosphorylation (r = 0.64; P = 2.5 x 10(-6)). STAT3 knockdown enhanced the cytotoxicity of dasatinib.

CONCLUSIONS

c-Src inhibition leads to JAK-dependent STAT3 activation in vitro and in vivo. STAT3 knockdown enhances the cytotoxicity of dasatinib, suggesting a compensatory pathway that allows NSCLC survival. Data from human tumors showed a reciprocal regulation of c-Src and STAT3 activation, suggesting that this compensatory pathway functions in human NSCLC. These results provide a rationale for combining c-Src and STAT3 inhibition to improve clinical responses.

Emerging drugs in the treatment of pancreatic cancer

BACKGROUND

Pancreatic cancer is the fourth leading cause of cancer-related death in the US. However, there is a growing belief that novel biological agents could improve survival of patients with this cancer. Gemcitabine-based chemotherapy remains the cornerstone treatment for advanced pancreatic cancers. So far, the current targeted agents that have been used in combination with gemcitabine have failed to improve clinical outcomes. This failure may stem from the heterogeneous molecular pathogenesis of pancreatic cancers, which involves several oncogenic pathways and defined genetic mutations.

OBJECTIVE

The aims of this review are: i) to define the existing treatments available at present for patients with pancreatic cancers in the neo-adjuvant, adjuvant, locally advanced and metastatic settings; ii) to highlight the molecular heterogeneity of the cancers and the rationale for targeting specific oncogenic pathways; iii) to give an overview of targeted agents that may potentially have an impact in the treatment of pancreatic cancers.

CONCLUSIONS

Molecular pathogenesis of pancreatic cancer involves several pathways and defined genetic mutations. Targeting these complex molecular pathways with a combination of novel biological and chemotherapeutic agents could potentially improve patient outcome.

Antitumor effects and biomarkers of activity of AZD0530, a Src inhibitor, in pancreatic cancer

PURPOSE

To determine the efficacy of AZD0530, an orally active small molecule Src inhibitor, in human pancreatic cancer xenografts and to seek biomarkers predictive of activity.

EXPERIMENTAL DESIGN

Sixteen patient-derived pancreatic cancer xenografts from the PancXenoBank collection at Johns Hopkins were treated with AZD0530 (50 mg/kg/day, p.o.) for 28 days. Baseline gene expression profiles of differently expressed genes in 16 tumors by Affymetrix U133 Plus 2.0 gene array were used to predict AZD0530 sensitivity in an independent group of eight tumors using the K-Top Scoring Pairs (K-TSP) method.

RESULTS

Three patient tumors of 16 were found to be sensitive to AZD0530, defined as tumor growth <50% compared with control tumors (100%). Western blot and/or immunohistochemistry results showed that AZD0530 administration resulted in the down-regulation of Src, FAK, p-FAK, p-paxillin, p-STAT-3, and XIAP in sensitive tumor xenografts compared with control tumors. The K-TSP classifier identified one gene pair (LRRC19 and IGFBP2) from the 16 training cases based on a decision rule. The classifier achieved 100% and 83.3% of sensitivity and specificity in an independent test set that consists of eight xenograft cases.

CONCLUSIONS

AZD0530 treatment significantly inhibits the tumor growth in a subset of human pancreatic tumor xenografts. One gene pair (LRRC19 and IGFBP2) identified by the K-TSP classifier has high predictive power for AZD0530 sensitivity, suggesting the potential for this gene pair as biomarker for pancreatic tumor sensitivity to AZD0530.

ErbB2-mediated Src and signal transducer and activator of transcription 3 activation leads to transcriptional up-regulation of p21Cip1 and chemoresistance in breast cancer cells

Overexpression of the ErbB2 receptor tyrosine kinase is prevalent in approximately 30% of human breast cancers and confers Taxol resistance. Our previous work has shown that ErbB2 inhibits Taxol-induced apoptosis in breast cancer cells by transcriptionally up-regulating p21(Cip1). However, the mechanism of ErbB2-mediated p21(Cip1) up-regulation is unclear. Here, we show that ErbB2 up-regulates p21(Cip1) transcription through increased Src activity in ErbB2-overexpressing cells. Src activation further activated signal transducer and activator of transcription 3 (STAT3) that recognizes a SIE binding site on the p21(Cip1) promoter required for ErbB2-mediated p21(Cip1) transcriptional up-regulation. Both Src and STAT3 inhibitors restored Taxol sensitivity in resistant ErbB2-overexpressing breast cancer cells. Our data suggest that ErbB2 overexpression can activate STAT3 through Src leading to transcriptional up-regulation of p21(Cip1) that confers Taxol resistance of breast cancer cells. Our study suggests a potential clinical application of Src and STAT3 inhibitors in Taxol sensitization of ErbB2-overexpressing breast cancers.

Src inhibitor dasatinib inhibits growth of breast cancer cells by modulating EGFR signaling

EGF-receptor family members (EGFRs) as well as c-Src are over expressed in approximately 70% of breast cancer, and in most of the tumors c-Src is co-over expressed with at least one of the EGFRs, suggesting that they may interact functionally and play a role in the development and progression of the malignancy. We hypothesize that a small molecule inhibitor of c-Src dasatinib (BMS-354825; Bristol Myers Squibb), exerts its effects on breast cancer cells by modulating EGFR signaling. Indeed, we found that dasatinib causes inhibition of breast cancer cells overexpressing EGFR, HER-2 and HER-3 (MDA-MB-468, SKBR3, MDA-MB-453, and MDA-MB-231) in a dose and time-dependent manner. Dasatinib also stimulated apoptosis in MDA-MB-468 cells, which could be attributed to activation of both caspase-9 and -8 and arrest of the cell cycle at G0/G1 cycle. Furthermore, dasatinib markedly inhibited colony formation, cell invasion, migration and angiogenesis, accompanied by decreased phosphorylation of EGFR and c-Src and their downstream effector molecules Akt and Erks. Our data suggest that dasatinib mediates its action in part through EGFR signaling and could be a potential therapeutic agent for breast cancer.

ZD6474 inhibits Src kinase leading to apoptosis of imatinib-resistant K562 cells

ZD6474 is an orally available, small-molecule tyrosine kinase inhibitor. This study explores the effect of ZD6474 on imatinib-resistant K562 cell lines, which show markedly increased SRC family kinases (SFKs) activity. ZD6474 induces growth arrest and apoptosis of imatinib-resistant and parental K562 cells, as well as inhibition of Src activity and its downstream effectors, the anti-apoptotic Bcl-2 family. ZD6474 treatment also inhibits the activity of STAT3 and reactivation of its activity results in suppression of the anti-tumor effects of SFKs inhibitors. A single oral administration of ZD6474 produced dose-dependent inhibition of imatinib-resistant K562 cells xenograft tumors. These results suggest that clinical assessment of ZD6474 against imatinib-resistant CML is warranted.

Novel molecular and cellular therapeutic targets in acute lymphoblastic leukemia and lymphoproliferative disease

While the outcome for pediatric patients with lymphoproliferative disorders (LPD) or lymphoid malignancies, such as acute lymphoblastic leukemia (ALL), has improved dramatically, patients often suffer from therapeutic sequelae. Additionally, despite intensified treatment, the prognosis remains dismal for patients with refractory or relapsed disease. Thus, novel biologically targeted treatment approaches are needed. These targets can be identified by understanding how a loss of lymphocyte homeostasis can result in LPD or ALL. Herein, we review potential molecular and cellular therapeutic strategies that (i) target key signaling networks (e.g., PI3K/AKT/mTOR, JAK/STAT, Notch1, and SRC kinase family-containing pathways) which regulate lymphocyte growth, survival, and function; (ii) block the interaction of ALL cells with stromal cells or lymphoid growth factors secreted by the bone marrow microenvironment; or (iii) stimulate innate and adaptive immune responses.

Characterization of STAT3 activation and expression in canine and human osteosarcoma

Background

Dysregulation of signal transducer and activator of transcription 3 (STAT3) has been implicated as a key participant in tumor cell survival, proliferation, and metastasis and is often correlated with a more malignant tumor phenotype. STAT3 phosphorylation has been demonstrated in a subset of human osteosarcoma (OSA) tissues and cell lines. OSA in the canine population is known to exhibit a similar clinical behavior and molecular biology when compared to its human counterpart, and is often used as a model for preclinical testing of novel therapeutics. The purpose of this study was to investigate the potential role of STAT3 in canine and human OSA, and to evaluate the biologic activity of a novel small molecule STAT3 inhibitor.

Methods

To examine STAT3 and Src expression in OSA, we performed Western blotting and RT-PCR. OSA cells were treated with either STAT3 siRNA or small molecule Src (SU6656) or STAT3 (LLL3) inhibitors and cell proliferation (CyQUANT), caspase 3/7 activity (ELISA), apoptosis (Western blotting for PARP cleavage) and/or viability (Wst-1) were determined. Additionally, STAT3 DNA binding after treatment was determined using EMSA. Expression of STAT3 targets after treatment was demonstrated with Western blotting, RT-PCR, or gel zymography.

Results

Our data demonstrate that constitutive activation of STAT3 is present in a subset of canine OSA tumors and human and canine cell lines, but not normal canine osteoblasts. In both canine and human OSA cell lines, downregulation of STAT3 activity through inhibition of upstream Src family kinases using SU6656, inhibition of STAT3 DNA binding and transcriptional activities using LLL3, or modulation of STAT3 expression using siRNA, all resulted in decreased cell proliferation and viability, ultimately inducing caspase-3/7 mediated apoptosis in treated cells. Furthermore, inhibition of either Src or STAT3 activity downregulated the expression of survivin, VEGF, and MMP2, all known transcriptional targets of STAT3.

Conclusion

These data suggest that STAT3 activation contributes to the survival and proliferation of human and canine OSA cells, thereby providing a potentially promising target for therapeutic intervention. Future investigational trials of LLL3 in dogs with spontaneous OSA will help to more accurately define the role of STAT3 in the clinical setting.

Sustained Src inhibition results in signal transducer and activator of transcription 3 (STAT3) activation and cancer cell survival via altered Janus-activated kinase-STAT3 binding

Locoregional and distant recurrence remains common and usually fatal for patients with advanced head and neck squamous cell carcinoma (HNSCC). One promising molecular target in HNSCC is the Src family kinases (SFK). SFKs can affect cellular proliferation and survival by activating the signal transducer and activator of transcription (STAT) family of transcription factors, especially STAT3. Surprisingly, sustained SFK inhibition resulted in only transient inhibition of STAT3. We investigated the mechanism underlying STAT3 activation and its biological importance. Specific c-Src knockdown with small interfering RNA (siRNA) resulted in STAT3 activation showing specificity, which was inhibited by Janus-activated kinase (JAK; TYK2 and JAK2) depletion with siRNA. Sustained SFK inhibition also resulted in recovered JAK-STAT3 binding and JAK kinase activity after an initial reduction, although JAK phosphorylation paradoxically decreased. To determine the biological significance of STAT3 activation, we combined specific STAT3 depletion with a pharmacologic SFK inhibitor and observed increased cell cycle arrest and apoptosis. Likewise, the addition of STAT3- or JAK-specific siRNA to c-Src-depleted cells enhanced cytotoxicity relative to cells incubated with c-Src siRNA alone. These results show that reactivation of STAT3 after sustained, specific c-Src inhibition is mediated through altered JAK-STAT3 binding and JAK kinase activity and that this compensatory pathway allows for cancer cell survival and proliferation despite durable c-Src inhibition. To our knowledge, this novel feedback pathway has never been described previously. Given that pharmacologic SFK inhibitors are currently being evaluated in clinical trials, these results have potential clinical implications for cancer therapy.