Effect of inhibition of Src and insulin/insulin-like growth factor-1 receptor (IR/IGF-1R) on tumor activity and bone turnover in prostate cancer (PCa) models in vivo relative to inhibition of either kinase alone

e15151

Background: Growth of prostate cancer (PCa) metastases relies on bidirectional interactions between the tumor and microenvironment.The Src family kinases (SFK) and insulin-like growth factor-1 receptor (IGF-1R) signaling axes are aberrantly activated in both PCa and the microenvironment of bone metastases. Dasatinib and BMS-754807 are small molecule inhibitors that target SFK and IGF-1R/IR, respectively. This study examined the in vitro and in vivo effects of BMS-754807 and dasatinib on PCa growth. Methods: Antitumor effects of both reagents were tested alone and in combination in vitro in PC3 and LNCaP cells, using proliferation and apoptosis assays. Signaling pathways were interrogated by western blots. Tumor growth in vivo was assessed by orthotopic and intratibial injection of PC3 cells and subcutaneous growth of primary human xenograft PCa-133b. Serum markers were measured by ELISA. Results: In vitro, dasatinib decreased proliferation and migration of PCa cells whereas BMS-754807 induced apoptosis. All observed anti-tumor effects were enhanced when dual blockade was used. IGF-1 induced phosphorylation of Akt1, but not Akt2, was partially inhibited by either drug alone and almost completely abrogated by the combination. Dasatinib and BMS-754807 inhibited in vivo orthotopic and intratibial tumor growth of PC3 cells more potently than either as a single agent alone with a corresponding decrease in bone turnover markers. Both drugs also exhibited synergism in primary human xenograft tumors. Potent target inhibition (p-Src, p-IGF-1R, p-Akt) by the drug combination was also demonstrated in xenografts. Conclusions: The combination of dasatinib and BMS-754807 may be a rational therapeutic approach in PCa by blocking both independent and complementary processes critical to tumor growth.

Pre-clinical mouse models of human prostate cancer and their utility in drug discovery

In vivo animal experiments are essential to current prostate cancer research, and are particularly critical to studying interactions between tumor cells and their microenvironment. Numerous pre-clinical animal models of prostate cancer are currently available, including transgenic mouse models and human prostate cancer xenograft mouse models. In contrast to transgenic mouse models producing more heterogeneous cohorts of tumors, xenograft mouse models provide more controlled approaches. This unit describes the detailed procedures necessary to establish several distinct pre-clinical mouse models of human prostate cancer, including an orthotopic prostate xenograft model, an orthotopic bone metastasis model, an experimental metastasis model of intra-cardiac injection, and a vossicle model of tumor-bone interaction.

Inhibition of Src and insulin/insulin-like growth factor-1 receptor (IR/IGF-1R) on tumors and bone turnover in prostate cancer (PCa) models in vivo compared with inhibition of either kinase alone

61

Background: The Src and IGF-1R axes are aberrantly activated in both PCa and the microenvironment of bone metastases. Dasatinib and BMS-754807 are clinically promising small molecule inhibitors with high potency against Src family kinases (SFK) and IR/IGF-1R, respectively. Based on a phase I/II clinical trial in which 9/19 pts treated with docetaxel + dasatinib were increased in serum IGF-1 levels after one cycle, the aim of this study was to establish potential antitumor cooperativity of inhibiting both IGF-1R and Src in experimental PCa models in vitro and in mice.

Methods: Inhibition of Src and IGF-1R pathways was accomplished by pharmacologic agents (dasatinib against Src and BMS-754807 against IR/IGF-1R) as well as by shRNA, in PC3 and LNCaP cells. In vivo studies were done after orthotopic and intratibial injection of PC3 cells in nude mice.

Results: SFK inhibition decreased proliferation and migration of PCa cells whereas IGF-1R blockade induced apoptosis. All anti-tumor effects were enhanced by dual blockade. IGF-1 induced phosphorylation of Akt1 and 2. Only Akt 1 phosphorylation was decreased by dasatinib; whereas Akt 1 and 2 phosphorylation were completely abrogated by the combination. Dasatinib and BMS-754807 inhibited orthotopic in vivo tumor growth of PC3 cells more potently than either inhibitor alone. Similarly, intratibial tumor growth and bone destruction was significantly reduced with the drug combination, accompanied by a decrease in serum bone turnover markers alkaline phosphatase and N-telopeptide.

Conclusions: Dual inhibition of Src and IGF-1R has greater anti-tumor effect in PCa cells compared to inhibiting either alone. In the presence of IGF-1, dasatinib and BMS-754807 are necessary to inhibit IGF-1-induced phosphorylation of Akt1 and 2 in tumor cells in culture. In intratibial models, decreased bone turnover markers in serum support the concept of targeting both the epithelial and bone microenvironment. The combination of dasatinib and BMS-754807 may be a rational therapeutic approach in PCa by blocking complementary processes of tumor growth and progression.

Abstract A65: Contribution of stromal-derived IL-8 on prostate cancer progression

Background: Prostate cancer (PCa) is the second leading cause of cancer deaths. Deaths invariably result from metastasis, most commonly to the bone. Tumor-microenvironment interactions of metastatic PCa in the bone are critical for growth at the metastatic site. These interactions suggest that therapies will need to target both tumor cells and the microenvironment to be successful. One target in both tumor and microenvironment is Src family kinases (SFKs), for which a phase three trial in combination with docetaxel is completed. Better targeting of SFKs will depend on understanding the tumor-stromal interactions that lead to its activation in both compartments. Aberrant Src activation de-represses cytokines including IL-8, contributing to the “vicious cycle” of metastatic growth in the bone. Stromal cells are a rich source of IL-8, but there is little information on how they affect tumor cells and viceversa. Here, we describe a feed-forward loop and paracrine mechanism of IL-8-mediated Src activation in PCa, both of which lead to increased tumor cell migration and invasion.

Methods/Results: We demonstrate IL-8 and Src are overexpressed in more metastatic PC3-MM2 cells versus less metastatic PC3 cells. Previous work in the laboratory has demonstrated activated Src increases IL-8 expression. Through lentiviral knockdown of IL-8 in PC3-MM2 (PC3-MM2shIL-8) cells, we demonstrate that decreased IL-8 expression decreases Src activity in tumor cells. We also demonstrate that decreased IL-8 expression decreases migration and invasion while exogenous IL-8 rescues this phenotype. We next asked the effect of immortalized bone marrow-derived human stromal cells (HS5) on tumor cells. HS5 cells secrete high levels of IL-8. To determine if stromal-produced IL-8 affects Src activity in PCa, conditioned media from HS5 cells was added to PC3, PC3- MM2 and PC3-MM2shIL-8 cells. Src activity was increased in all cell lines. Conditioned media also increased migration and invasion of these cell lines. To determine if these increases were due, in part to IL-8, HS5 cells were infected with a lentivirus driving the expression of shIL-8 (HS5shIL-8) and conditioned media was collected. Addition of conditioned media from HS5shIL-8 cells to PC3 or PC3-MM2shIL-8 cell lines resulted in reduced Src activation, migration and invasion relative to HS-5 cells infected with a control vector.

Conclusions/Future Directions: These results demonstrate stromal production of IL-8 increases Src activity and that stromal cells play a major role in metastatic properties of PCa cells. To confirm these in vitro studies, in vivo studies are being performed using co-injections of stromal cells and PCa cells. We will determine if: (1) stromal cells co-inoculated with tumor cells increase tumor growth and/or metastatic potential of PC3; (2) if knockdown of Src and/or IL-8 in stromal cells inhibits the ability to increase metastatic potential induced by stromal cells. Recent data from the Phase I/II dasatinib + docetaxel trial suggest that decreases in IL-8 levels after 21 days of treatment are associated with patient response (Araujo et al., unpublished). These results suggest that IL-8 from both tumor and stromal cells may be important inmetastatic potential and growth of prostate tumor cells in the bone. Understanding the roles of IL-8 and Src in PCa and the stromal microenvironment are important in better understanding PCa metastasis.

Citation Format: Lynnelle Thorpe, John C. Araujo, Nila U. Parikh, Menashe Bar Eli, Gary E. Gallick. Contribution of stromal-derived IL-8 on prostate cancer progression [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A65.

Small-molecule protein tyrosine kinase inhibitors for the treatment of metastatic prostate cancer

The microenvironment is critical to the growth of prostate cancer (PCa) in the bone. Thus, for clinical efficacy, therapies must target tumor-microenvironment interactions. Several protein tyrosine kinases have been implicated in the development and growth of PCa bone metastasis. In this review, specific protein tyrosine kinases that regulate these complex interactions, including PDGFR, the EGFR family, c-Src, VEGFR, IGF-1R, FGFR and c-Met will be discussed, with an emphasis on why these kinases are promising therapeutic targets for metastatic PCa treatment. For each of these kinases, small-molecule inhibitors have reached clinical trials. Current results of these trials and future prospects for the use of tyrosine kinase inhibitors for the treatment of PCa bone metastases are also discussed.

The role of HGF/c-Met signaling in prostate cancer progression and c-Met inhibitors in clinical trials

INTRODUCTION

An increasing number of basic, translational and clinical studies demonstrate the importance of the protein tyrosine kinase receptor, c-Met, in the progression of prostate cancer. c-Met is overexpressed in primary prostate cancers, further increased in expression in bone metastases and is associated with the development of castrate-resistant disease. Because of its importance as a target, c-Met inhibitors have reached clinical trial for advanced, castrate-resistant prostate cancer.

AREAS COVERED

In this review, altered expression of c-Met and hepatocyte growth factor in prostate tumors and the microenvironment and how they contribute to growth and invasion of prostate cancer cells is described. Next, preclinical studies providing the support for use of c-Met inhibitors are discussed. Finally, early promising results from c-Met inhibitors in clinical trial, and future prospects for c-Met inhibitors in the treatment of advanced stage prostate cancer, are discussed.

EXPERT OPINION

An emerging theme in treating metastatic prostate cancer is the requirement to target both the epithelial and stromal compartments. Results from clinical trials suggest that inhibitors of c-Met that block stromal-mediated c-Met activation in prostate tumors may be important therapeutic agents in at least a subset of patients with metastatic prostate cancer. However, as many of the inhibitors have multiple targets, the efficacy of targeting c-Met alone remains to be determined.

Novel therapies for metastatic castrate-resistant prostate cancer

Recent advances in tumor biology have made remarkable achievements in the development of therapy for metastatic castrate-resistant prostate cancer. These advances reflect a growing appreciation for the role of the tumor microenvironment in promoting prostate cancer progression. Prostate cancer is no longer viewed predominantly as a disease of abnormally proliferating epithelial cells but rather as a disease of complex interactions between prostate cancer epithelial cells (epithelial compartment) and the surrounding tissues (stromal compartment) in which they reside. For example, prostate cancers frequently metastasize to bone, an organ that contains a microenvironment rich in extracellular matrix proteins and stromal cells including hematopoietic cells, osteoblasts, osteoclasts fibroblasts, endothelial cells, adipocytes, immune cells, and mesenchymal stem cells. Multiple signaling pathways provide crosstalk between the epithelial and the stromal compartments to enhance tumor growth, including androgen receptor signaling, tyrosine kinase receptor signaling, and immune surveillance. The rationale to disrupt this "two-compartment" crosstalk has led to the development of drugs that target tumor stromal elements in addition to the cancer epithelial cell.

Targeting SRC in mucinous ovarian carcinoma

PURPOSE

Mucinous ovarian carcinomas have a distinct clinical pattern compared with other subtypes of ovarian carcinoma. Here, we evaluated (i) stage-specific clinical significance of mucinous ovarian carcinomas in a large cohort and (ii) the functional role of Src kinase in preclinical models of mucinous ovarian carcinoma.

EXPERIMENTAL DESIGN

A total of 1,302 ovarian cancer patients including 122 (9.4%) cases of mucinous carcinoma were evaluated for survival analyses. Biological effects of Src kinase inhibition were tested using dasatinib-based therapy in a novel orthotopic mucinous ovarian cancer model (RMUG-S-ip2).

RESULTS

Patients with advanced-stage mucinous ovarian cancer had significantly worse survival than those with serous histology: median overall survival, 1.67 versus 3.41 years, P = 0.002; median survival time after recurrence of 0.53 versus 1.66 years, P < 0.0001. Among multiple ovarian cancer cell lines, RMUG-S-ip2 mucinous ovarian cancer cells showed the highest Src kinase activity. Moreover, oxaliplatin treatment induced phosphorylation of Src kinase. This induced activity by oxaliplatin therapy was inhibited by concurrent administration of dasatinib. Targeting Src with dasatinib in vivo showed significant antitumor effects in the RMUG-S-ip2 model but not in the serous ovarian carcinoma (SKOV3-TR) model. Combination therapy of oxaliplatin with dasatinib further showed significant effects on reducing cell viability, increasing apoptosis, and in vivo antitumor effects in the RMUG-S-ip2 model.

CONCLUSIONS

Our results suggest that poor survival of women with mucinous ovarian carcinoma is associated with resistance to cytotoxic therapy. Targeting Src kinase with a combination of dasatinib and oxaliplatin may be an attractive approach for this disease.

Dasatinib combined with docetaxel for castration-resistant prostate cancer: results from a phase 1-2 study

BACKGROUND

To determine the potential efficacy of targeting both the tumor and bone microenvironment in patients with castration-resistant prostate cancer (PC), the authors conducted a phase 1-2 trial combining docetaxel with dasatinib, an oral SRC inhibitor.

METHODS

In phase 1, 16 men received dasatinib 50 to 120 mg once daily and docetaxel 60 to 75 mg/m(2) every 21 days. In phase 2, 30 additional men received dasatinib 100 mg once daily/docetaxel 75 mg/m(2) every 21 days. Efficacy endpoints included changes in prostate-specific antigen (PSA), measurable disease, bone scans, and markers of bone metabolism. Safety and pharmacokinetics were also studied.

RESULTS

Combination dasatinib and docetaxel therapy was generally well tolerated. Thirteen of 46 patients (28%) had a grade 3-4 toxicity. Drug-drug interactions and a maximum tolerated dose were not identified. Durable 50% PSA declines occurred in 26 of 46 patients (57%). Of 30 patients with measurable disease, 18 (60%) had a partial response. Fourteen patients (30%) had disappearance of a lesion on bone scan. In bone marker assessments, 33 of 38 (87%) and 26 of 34 (76%) had decreases in urinary N-telopeptide or bone-specific alkaline phosphatase levels, respectively. Twenty-eight patients (61%) received single-agent dasatinib after docetaxel discontinuation and had stabilization of disease for an additional 1 to 12 months.

CONCLUSIONS

The high objective response rate and favorable toxicity profile are promising and justify randomized studies of docetaxel and dasatinib in castration-resistant PC. Parallel declines in levels of PSA and bone markers are consistent with cotargeting of epithelial and bone compartments of the cancer. Treatment with single-agent dasatinib following docetaxel cessation warrants further study. Cancer 2012;. © 2011 American Cancer Society.

Molecular profiling of direct xenograft tumors established from human pancreatic adenocarcinoma after neoadjuvant therapy

BACKGROUND

Pancreatic adenocarcinoma is among the most resistant of human cancers, yet specific mechanisms of treatment resistance remain poorly understood. Models to study pancreatic cancer resistance remain limited and should reflect in vivo changes that occur within patient tumors. We sought to identify consistent, differentially expressed genes between treatment of naive pancreatic tumors and those exposed to neoadjuvant therapy using a strict, in vivo direct xenograft model system.

METHODS

Over a 42-week period, 12 untreated and treated patient tumors were successfully engrafted into NOD/SCID mice. RNA from each treatment group (5 untreated and 4 treated) was isolated in triplicate and subjected to global gene expression analysis. Consistent gene expression changes with treatment were identified and confirmed using RT-PCR and immunohistochemistry.

RESULTS

Engraftment of untreated patient tumors was more frequent than treated tumors (17 of 21 versus 16 of 49, P = .0002) but without differences in observed time until tumor formation. The histology of patient tumors was recapitulated in direct xenograft tumors. Relative to untreated tumors, treated tumors consistently demonstrated more than a 2-fold reduction in TGFβ-R2 mRNA expression and more than a 5-fold increase in IGFBP3 expression (P < .0218) and were confirmed by immunohistochemistry.

CONCLUSION

Engraftment of human pancreatic tumors into immunodeficient mice prior to and following neoadjuvant therapy is possible and provides an in vivo platform for comparison of global gene expression patterns. The decreased TGFβ-R2 expression and increased IGFBP3 expression among direct xenograft tumors derived from treated tumors relative to untreated tumors suggests a role in therapy resistance and warrants further study.

ALDH activity selectively defines an enhanced tumor-initiating cell population relative to CD133 expression in human pancreatic adenocarcinoma

Background

Multiple studies in recent years have identified highly tumorigenic populations of cells that drive tumor formation. These cancer stem cells (CSCs), or tumor-initiating cells (TICs), exhibit properties of normal stem cells and are associated with resistance to current therapies. As pancreatic adenocarcinoma is among the most resistant human cancers to chemo-radiation therapy, we sought to evaluate the presence of cell populations with tumor-initiating capacities in human pancreatic tumors. Understanding which pancreatic cancer cell populations possess tumor-initiating capabilities is critical to characterizing and understanding the biology of pancreatic CSCs towards therapeutic ends.

Methodology/Principal Findings

We have isolated populations of cells with high ALDH activity (ALDH^high) and/or CD133 cell surface expression from human xenograft tumors established from multiple patient tumors with pancreatic adenocarcinoma (direct xenograft tumors) and from the pancreatic cancer cell line L3.6pl. Through fluorescent activated cell sorting (FACs)-mediated enrichment and depletion of selected pancreatic cancer cell populations, we sought to discriminate the relative tumorigenicity of cell populations that express the pancreatic CSC markers CD133 and aldehyde dehydrogenase (ALDH). ALDH^high and ALDH^low cell populations were further examined for co-expression of CD44 and/or CD24. We demonstrate that unlike cell populations demonstrating low ALDH activity, as few as 100 cells enriched for high ALDH activity were capable of tumor formation, irrespective of CD133 expression. In direct xenograft tumors, the proportions of total tumor cells expressing ALDH and/or CD133 in xenograft tumors were unchanged through a minimum of two passages. We further demonstrate that ALDH expression among patients with pancreatic adenocarcinoma is heterogeneous, but the expression is constant in serial generations of individual direct xenograft tumors established from bulk human pancreatic tumors in NOD/SCID mice.

Conclusions/Significance

We conclude that, in contrast to some previous studies, cell populations enriched for high ALDH activity alone are sufficient for efficient tumor-initiation with enhanced tumorigenic potential relative to CD133⁺ and ALDH^low cell populations in some direct xenograft tumors. Although cell populations enriched for CD133 expression may alone possess tumorigenic potential, they are significantly less tumorigenic than ALDH^high cell populations. ALDH^high/CD44⁺/CD24⁺ or ALDH^low/CD44⁺/CD24⁺ phenotypes do not appear to significantly contribute to tumor formation at low numbers of inoculated tumor cells. ALDH expression broadly varies among patients with pancreatic adenocarcinoma and the apparent expression is recapitulated in serial generations of direct xenograft tumors in NOD/SCID. We have thus identified a distinct population of TICs that should lead to identification of novel targets for pancreatic cancer therapy.

BMP4 promotes prostate tumor growth in bone through osteogenesis

Induction of new bone formation is frequently seen in the bone lesions from prostate cancer. However, whether osteogenesis is necessary for prostate tumor growth in bone is unknown. Recently, 2 xenografts, MDA-PCa-118b and MDA-PCa-133, were generated from prostate cancer bone metastases. When implanted subcutaneously in severe combined immunodeficient (SCID) mice, MDA-PCa-118b induced strong ectopic bone formation while MDA-PCa-133 did not. To identify the factors that are involved in bone formation, we compared the expression of secreted factors (secretome) from MDA-PCa-118b and MDA-PCa-133 by cytokine array. We found that the osteogenic MDA-PCa-118b xenograft expressed higher levels of bone morphogenetic protein BMP4 and several cytokines including interleukin-8, growth-related protein (GRO), and CCL2. We showed that BMP4 secreted from MDA-PCa-118b contributed to about a third of the osteogenic differentiation seen in MDA-PCa-118b tumors. The conditioned media from MDA-PCa-118b induced a higher level of osteoblast differentiation, which was significantly reduced by treatment with BMP4 neutralizing antibody or the small molecule BMP receptor 1 inhibitor LDN-193189. BMP4 did not elicit an autocrine effect on MDA-PCa-118b, which expressed low to undetectable levels of BMP receptors. Treatment of SCID mice bearing MDA-PCa-118b tumors with LDN-193189 significantly reduced tumor growth. Thus, these studies support a role of BMP4-mediated osteogenesis in the progression of prostate cancer in bone.

Steps in prostate cancer progression that lead to bone metastasis

Prostate cancer is a complex disease in which metastasis to the bone is the main cause of death. Initial stages of metastasis are generally similar to those for most solid tumors; however, the mechanisms that underlie the homing of prostate tumor cells to the bone are not completely understood. Prostate cancer bone metastasis is also a microenvironment-driven disease, involving bidirectional interactions between the tumor and the bone microenvironment. In this review, we discuss the current understanding of the biologic processes and regulatory factors involved in the metastasis of prostate cancer cells, and their specific properties that promote growth in bone. Although many of these processes still need to be fully elucidated, a better understanding of the complex tumor/microenvironment interplay is slowly leading to more effective therapies for patients with prostate cancer bone metastases.

Abstract 937: Molecular dynamics of SrcS17 activation in chronic stress-induced tumor growth

Clinical studies have demonstrated that chronic stress can influence cancer progression. However, the underlying mechanisms are not fully understood. To determine the molecular drivers of downstream signaling networks activated in response to chronic stress, we performed a phosphoproteomic analysis and determined that the non-receptor tyrosine kinase, Src, was the key regulator of these networks. Since Src plays an important role in cancer biology, we examined the biological and clinical significance of Src in stress-mediated tumor growth. Norepinephrine (NE) rapidly activated SrcY419 in β-adrenergic receptor (ADRB) positive ovarian cancer cell lines, but not in ADRB-null cells. Confocal microscopy showed that Src was rapidly recruited to the cellular membrane after NE exposure in ADRB positive ovarian cancer cells. Furthermore, treatment with different ADRB agonists and blockers determined that ADRB2 is required for SrcY419 phosphorylation. Treatment with a cAMP agonist or PKA agonist/antagonists demonstrated that cAMP/PKA signaling is required for NE-induced Src activation. The unexpected Src activation via cAMP/PKA was found to be mediated by direct phosphorylation of SrcS17 following NE treatment. In Src-/- cells transiently expressing WT Src, NE caused SrcY419 phosphorylation, which was not observed when cells were transfected with a Src S17A construct. In order to investigate how S17 phosphorylation leads to Src activation, we performed molecular dynamic simulations and observed that upon SrcS17 phosphorylation, Src undergoes significant structural changes that expose its Y419 residue. To understand the functional consequences of stress-induced Src activation, we performed migration and invasion assays. Exposure to NE resulted in an increase in ovarian cancer cell migration and invasion that was completely abrogated by Src-targeted siRNA (P &lt; 0.01). In various orthotopic mouse models of ovarian carcinoma, chronic restraint stress significantly increased tumor weights (P &lt; 0.05). Increased tumor growth was completely blocked by Src silencing with Src siRNA-DOPC or by the non-specific beta-blocker, propranolol (P &lt; 0.05). To test the clinical significance of our biological findings, we examined 91 epithelial ovarian cancer samples. Elevated pSrcY419 was associated with worse patient survival (P &lt; 0.001), high tumoral NE levels (P &lt; 0.001) and high scores on the Center for Epidemiologic Studies Depression Scale (P = 0.008). To examine the potential clinical impact of our findings, we investigated whether beta-blocker usage by patients affected cancer-related mortality. This analysis revealed that beta-blockers reduced mortality by 17% across all major cancer types and 14.6% among patients with ovarian and other gynecologic cancers. This work is the first to demonstrate that an ADRB-PKA-Src axis mediates the effect of chronic stress on tumor growth and progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 937. doi:10.1158/1538-7445.AM2011-937

Functional roles of Src and Fgr in ovarian carcinoma

PURPOSE

Src is an attractive target because it is overexpressed in a number of malignancies, including ovarian cancer. However, the effect of Src silencing on other Src family kinases (SFKs) is not known. We hypothesized that other SFK members could compensate for the lack of Src activity.

EXPERIMENTAL DESIGN

Cell viability after either Src or Fgr silencing was examined in ovarian cancer cell lines by MTT assay. Expression of SFKs after Src silencing in ovarian cancer cells was examined by real-time reverse transcriptase (RT)-PCR. Therapeutic effect of in vivo Src and/or Fgr silencing was examined using siRNA incorporated into chitosan nanoparticles (siRNA/CH-NP). Microvessel density, cell proliferation, and apoptosis markers were determined by immunohistochemical staining in ovarian tumor tissues.

RESULTS

Src silencing enhanced cytotoxicity of docetaxel in both SKOV3ip1 and HeyA8 cells. In addition, Src silencing using siRNA/CH-NP in combination with docetaxel resulted in significant inhibition of tumor growth compared with control siRNA/CH-NP (81.8% reduction in SKOV3ip1, P = 0.017; 84.3% reduction in HeyA8, P < 0.005). These effects were mediated by decreased tumor cell proliferation and angiogenesis, and increased tumor cell apoptosis. Next, we assessed the effects of Src silencing on other SFK members in ovarian cancer cell lines. Src silencing resulted in significantly increased Fgr levels. Dual Src and Fgr silencing in vitro resulted in increased apoptosis that was mediated by increased caspase and AKT activity. In addition, dual silencing of Src and Fgr in vivo using siRNA/CH-NP resulted in the greatest reduction in tumor growth compared with silencing of either Src or Fgr alone in the HeyA8 model (68.8%, P < 0.05).

CONCLUSIONS

This study demonstrates that, in addition to Src, Fgr plays a biologically significant role in ovarian cancer growth and might represent an important target.

Loss of tyrosine phosphatase-dependent inhibition promotes activation of tyrosine kinase c-Src in detached pancreatic cells

Despite an intense focus on novel therapeutic strategies, pancreatic adenocarcinoma remains one of the deadliest human malignancies. The frequent and rapid mortality associated with pancreatic cancer may be attributed to several factors, including late diagnosis, rapid tumor invasion into surrounding tissues, and formation of distant metastases. Both local invasion and metastasis require disruption of tumor cell contacts with the extracellular matrix. Detachment of normal cells from the extracellular matrix leads to a form of programmed cell death termed anoikis. Pancreatic cancer cells avert anoikis by activation of signaling pathways that allow for adhesion-independent survival. In the present studies, cellular signaling pathways activated in detached pancreatic cancer cells were examined. We demonstrate a rapid and robust activation of Src kinase in detached pancreatic cancer cells, relative to adherent. Src autophosphorylation rapidly returned to baseline levels upon reattachment to tissue culture plastic, in the presence or absence of specific extracellular matrix proteins. Treatment of pancreatic cancer cells with tyrosine phosphatase inhibitors increased steady-state Src autophosphorylation in adherent cells and abrogated the detachment-induced increase in Src autophosphorylation. Src was found to co-immunoprecipitate with the Src homology 2 (SH2) domain containing protein tyrosine phosphatase (SHP-2) in pancreatic cancer cells, suggesting that SHP-2 may participate in regulation of Src autophosphorylation in adherent cells. Src family kinase (SFK) dependent increases in Akt and Jun N-terminal kinase (JNK) phosphorylation were observed in detached cells, indicating the potential for Src-dependent activation of survival and stress pathways in pancreatic cancer cells that have detached from the extracellular matrix.

AMPK/TSC2/mTOR-signaling intermediates are not necessary for LKB1-mediated nuclear retention of PTEN tumor suppressor

The regulation of the subcellular localization of phosphatase and tensin homologue (PTEN) is critical to its tumor-suppressing functions. Previously, we found that the activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR/S6 protein kinase (S6K) cascade triggers the nuclear export of PTEN during the G1/S transition. Because mTOR can be alternatively downregulated by tuberous sclerosis complex 2 (TSC2) activation mediated by 5' adenosine monophosphate-activated protein kinase (AMPK), we proposed that the activation of AMPK α1/2 by LKB1 and/or by calmodulin-dependent protein kinase kinase (CaMKK) would also block the nuclear export of PTEN in a manner similar to that of inhibitors of PI3K, mTOR, and S6K. We found that in LKB1-null A549 lung adenocarcinoma cells, an AMPK activator, metformin, failed to block the nuclear export of PTEN, and the reintroduction of functional LKB1 into these cells restored the metformin-mediated inhibition of the nuclear export of PTEN. In addition, the nuclear export of PTEN was blocked in cells treated with the CaMKK activator ATP, and this inhibition was reversed by the addition of inhibitors of either AMPK (compound C) or CaMKK (STO-609). Although the nuclear export of PTEN is blocked by metformin in MCF-7 breast cancer cells carrying wild-type LKB1, this inhibition could not be reversed by an AMPK inhibitor, suggesting that LKB1 could regulate the nuclear export of PTEN by bypassing AMPK α1/2. Moreover, ATP could not block the nuclear export of PTEN in AMPK α1/2(-/-) or TSC2(-/-) mouse embryonic fibroblasts. However, metformin was still able to induce the LKB1-mediated inhibition of the nuclear export of PTEN in these cells. Taken together, these findings strongly suggest that although CaMKK mediates the nuclear retention of PTEN mainly through the activation of AMPK, LKB1 can regulate the nuclear-cytoplasmic trafficking of PTEN, with or without the AMPK/TSC2/mTOR/S6K-signaling intermediates.

GWAS meets microarray: are the results of genome-wide association studies and gene-expression profiling consistent? Prostate cancer as an example

BACKGROUND

Genome-wide association studies (GWASs) and global profiling of gene expression (microarrays) are two major technological breakthroughs that allow hypothesis-free identification of candidate genes associated with tumorigenesis. It is not obvious whether there is a consistency between the candidate genes identified by GWAS (GWAS genes) and those identified by profiling gene expression (microarray genes).

METHODOLOGY/PRINCIPAL FINDINGS

We used the Cancer Genetic Markers Susceptibility database to retrieve single nucleotide polymorphisms from candidate genes for prostate cancer. In addition, we conducted a large meta-analysis of gene expression data in normal prostate and prostate tumor tissue. We identified 13,905 genes that were interrogated by both GWASs and microarrays. On the basis of P values from GWASs, we selected 1,649 most significantly associated genes for functional annotation by the Database for Annotation, Visualization and Integrated Discovery. We also conducted functional annotation analysis using same number of the top genes identified in the meta-analysis of the gene expression data. We found that genes involved in cell adhesion were overrepresented among both the GWAS and microarray genes.

CONCLUSIONS/SIGNIFICANCE

We conclude that the results of these analyses suggest that combining GWAS and microarray data would be a more effective approach than analyzing individual datasets and can help to refine the identification of candidate genes and functions associated with tumor development.

Epithelial to mesenchymal transition contributes to drug resistance in pancreatic cancer

A better understanding of drug resistance mechanisms is required to improve outcomes in patients with pancreatic cancer. Here, we characterized patterns of sensitivity and resistance to three conventional chemotherapeutic agents with divergent mechanisms of action [gemcitabine, 5-fluorouracil (5-FU), and cisplatin] in pancreatic cancer cells. Four (L3.6pl, BxPC-3, CFPAC-1, and SU86.86) were sensitive and five (PANC-1, Hs766T, AsPC-1, MIAPaCa-2, and MPanc96) were resistant to all three agents based on GI(50) (50% growth inhibition). Gene expression profiling and unsupervised hierarchical clustering revealed that the sensitive and resistant cells formed two distinct groups and differed in expression of specific genes, including several features of "epithelial to mesenchymal transition" (EMT). Interestingly, an inverse correlation between E-cadherin and its transcriptional suppressor, Zeb-1, was observed in the gene expression data and was confirmed by real-time PCR. Independent validation experiment using five new pancreatic cancer cell lines confirmed that an inverse correlation between E-cadherin and Zeb-1 correlated closely with resistance to gemcitabine, 5-FU, and cisplatin. Silencing Zeb-1 in the mesenchymal lines not only increased the expression of E-cadherin but also other epithelial markers, such as EVA1 and MAL2, and restored drug sensitivity. Importantly, immunohistochemical analysis of E-cadherin and Zeb-1 in primary tumors confirmed that expression of the two proteins was mutually exclusive (P = 0.012). Therefore, our results suggest that Zeb-1 and other regulators of EMT may maintain drug resistance in human pancreatic cancer cells, and therapeutic strategies to inhibit Zeb-1 and reverse EMT should be evaluated.

Synergistic activity of the SRC family kinase inhibitor dasatinib and oxaliplatin in colon carcinoma cells is mediated by oxidative stress

Chemotherapeutic regimens for the treatment of colorectal cancer generally include oxaliplatin, although inherent and acquired resistance is common. One potential mediator of oxaliplatin sensitivity is the nonreceptor protein tyrosine kinase, Src, the activity of which correlates with disease stage and patient survival. Therefore, we investigated the effects of Src inhibition using the tyrosine kinase inhibitor dasatinib on oxaliplatin sensitivity. We show that oxaliplatin acutely activates Src and that combination treatment with dasatinib is synergistic in a cell-line dependent manner, with the level of Src activation correlating with extent of synergy in a panel of six cell lines. Intracellular reactive oxygen species (ROS) are generated after oxaliplatin treatment, and ROS potently activates Src. Pretreatment with antioxidants inhibits oxaliplatin-induced Src activation. In oxaliplatin-resistant cell lines, Src activity is constitutively increased. In a mouse model of colorectal liver metastases, treatment with oxaliplatin also results in chronic Src activation. The combination of dasatinib and oxaliplatin results in significantly smaller tumors compared with single-agent treatment, corresponding with reduced proliferation and angiogenesis. Therefore, we conclude that oxaliplatin activates Src through a ROS-dependent mechanism. Src inhibition increases oxaliplatin activity both in vitro and in vivo. These results suggest that Src inhibitors combined with oxaliplatin may have efficacy in metastatic colon cancer and may provide the first indication of a molecular phenotype that might be susceptible to such combinations.

Acquisition of epithelial-mesenchymal transition phenotype of gemcitabine-resistant pancreatic cancer cells is linked with activation of the notch signaling pathway

Despite rapid advances in many fronts, pancreatic cancer (PC) remains one of the most difficult human malignancies to treat due, in part, to de novo and acquired chemoresistance and radioresistance. Gemcitabine alone or in combination with other conventional therapeutics is the standard of care for the treatment of advanced PC without any significant improvement in the overall survival of patients diagnosed with this deadly disease. Previous studies have shown that PC cells that are gemcitabine-resistant (GR) acquired epithelial-mesenchymal transition (EMT) phenotype, which is reminiscent of "cancer stem-like cells"; however, the molecular mechanism that led to EMT phenotype has not been fully investigated. The present study shows that Notch-2 and its ligand, Jagged-1, are highly up-regulated in GR cells, which is consistent with the role of the Notch signaling pathway in the acquisition of EMT and cancer stem-like cell phenotype. We also found that the down-regulation of Notch signaling was associated with decreased invasive behavior of GR cells. Moreover, down-regulation of Notch signaling by siRNA approach led to partial reversal of the EMT phenotype, resulting in the mesenchymal-epithelial transition, which was associated with decreased expression of vimentin, ZEB1, Slug, Snail, and nuclear factor-kappaB. These results provide molecular evidence showing that the activation of Notch signaling is mechanistically linked with chemoresistance phenotype (EMT phenotype) of PC cells, suggesting that the inactivation of Notch signaling by novel strategies could be a potential targeted therapeutic approach for overcoming chemoresistance toward the prevention of tumor progression and/or treatment of metastatic PC.

Therapeutic targeting of Id2 reduces growth of human colorectal carcinoma in the murine liver

During development inhibitor of DNA-bind-2 (Id2) regulates proliferation and differentiation. Id2 expression has been detected in cancer cells, yet its cellular function and validity as a therapeutic target remains largely unknown. Immunohistochemical analysis of colorectal cancer (CRC) specimens revealed that Id2 was undetectable in normal colonic mucosa, but occurs in 40% of primary tumors and in most CRC liver metastases (P<0.0001). Additionally, Id2 was expressed in all CRC cell lines assayed. CRC cells with reduced Id2 expression demonstrated reduced proliferation. Analysis of CRC cell cycle regulatory proteins showed that reducing Id2 levels reduces cyclin D1 levels and increased p21 levels. Reduction of Id2 expression also enhanced tumor cell apoptosis, increasing levels of the pro-apoptotic protein Bim/Bod, and cleavage of caspase-7 and poly (ADP-ribose) polymerase. In vivo studies show tumors derived from cells with decreased Id2 levels formed smaller tumors with fewer metastases compared with tumors with normal levels (P<0.05). Furthermore, intraperitoneal administration of Id2 small interfering RNA (siRNA) conjugated with the neutral liposome 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine decreased tumor burden in mice compared with control treatment (P=0.006). We conclude that Id2 is upregulated in CRC, and is important in promoting cell survival. In vivo targeting of Id2 by siRNA establishes that it is a valid therapeutic target where its expression occurs.

Targeting Lyn inhibits tumor growth and metastasis in Ewing's sarcoma

Src family tyrosine kinases (SFK) play an important role in growth and metastasis of many types of human malignancies. However, their significance in Ewing's sarcoma remains to be elucidated. The purpose of this study was to evaluate the role of Lyn, one member of the SFK, in Ewing's sarcoma growth and metastasis and to determine whether a SFK inhibitor can induce Ewing's tumor regression. Lyn was expressed and activated in TC71, A4573, and SK-ES human Ewing's sarcoma cells. Lyn expression was seen in 13 of 15 patient tumor samples, 6 of which showed Lyn activation. Specific inhibition of Lyn using small interfering RNA significantly decreased primary tumor growth and lytic activity, and also reduced lung metastases in vivo. Down-regulation of Lyn resulted in decreased invasive capacity of tumor cells in vitro. AP23994, a small-molecule SFK inhibitor, decreased Lyn kinase activity and suppressed TC71 cell growth in vitro in a dose-dependent manner. Furthermore, treatment of mice bearing s.c. TC71 tumors with AP23994 or with polyethylenimine/Lyn-small interfering RNA gene therapy resulted in reduced Lyn kinase activity and significant tumor growth suppression. EWS/FLI-1, which is translocation fusion protein associated with Ewing's sarcoma, regulated Lyn gene expression and kinase activity. These data suggest that targeting Lyn may be a new therapeutic approach in treatment of Ewing's sarcoma.

Extracellular Alix regulates integrin-mediated cell adhesions and extracellular matrix assembly

Alix (ALG-2-interacting protein X), a cytoplasmic adaptor protein involved in endosomal sorting and actin cytoskeleton assembly, is required for the maintenance of fibroblast morphology. As Alix has sequence similarity to adhesin in Entamoeba histolytica, and we observed that Alix is secreted, we determined whether extracellular Alix affects fibroblast morphology. Here, we demonstrate that secreted Alix is deposited on the substratum of non-immortalized WI38 fibroblasts. Antibody binding to extracellular Alix retards WI38 cell adhesion and spreading on fibronectin and vitronectin. Alix knockdown in WI38 cells reduces spreading and fibronectin assembly, and the effect is partially complemented by coating recombinant Alix on the cell substratum. Immortalized NIH/3T3 fibroblasts deposit less Alix on the substratum and have defects in alpha5beta1-integrin functions. Coating recombinant Alix on the culture substratum for NIH/3T3 cells promotes alpha5beta1-integrin-mediated cell adhesions and fibronectin assembly, and these effects require the aa 605-709 region of Alix. These findings demonstrate that a sub-population of Alix localizes extracellularly and regulates integrin-mediated cell adhesions and fibronectin matrix assembly.