Antiangiogenic and antitumor effects of SRC inhibition in ovarian carcinoma

Dasatinib inhibits the growth of prostate cancer in bone and provides additional protection from osteolysis

Background:

Dasatinib is a small molecule kinase inhibitor that has recently been shown to inhibit Src family kinases (SFK) and also has activity against CaP. Of importance to metastatic CaP, which frequently metastasises to bone, SFK are also vital to the regulation of bone remodelling. We sought to determine the ability of dasatinib to inhibit growth of CaP in bone.

Methods:

C4-2B CaP cells were injected into tibiae of SCID mice and treated with dasatinib, alone or in combination with docetaxel. Serum prostate-specific antigen levels, bone mineral density, radiographs and histology were analysed.

Results:

Treatment with dasatinib alone significantly lowered sacrifice serum prostate-specific antigen levels compared to control, 2.3±0.4 vs 9.2±2.1 (P=0.004). Combination therapy improved efficacy over dasatinib alone (P=0.010). Dasatinib increased bone mineral density in tumoured tibiae by 25% over control tumoured tibiae (P<0.001).

Conclusion:

Dasatinib inhibits growth of C4-2B cells in bone with improved efficacy when combined with docetaxel. Additionally, dasatinib inhibits osteolysis associated with CaP. These data support further study of dasatinib in clinical trials for men with CaP bone metastases.

The role of Src in solid tumors

The proto-oncogene c-Src (Src) encodes a nonreceptor tyrosine kinase whose expression and activity are correlated with advanced malignancy and poor prognosis in a variety of human cancers. Nine additional enzymes with homology to Src have been identified and collectively are referred to as Src family kinases (SFKs). Together, SFKs represent the largest family of nonreceptor tyrosine kinases and interact directly with receptor tyrosine kinases, G-protein-coupled receptors, steroid receptors, signal transducers and activators of transcription, and molecules involved in cell adhesion and migration. These interactions lead to a diverse array of biological functions including proliferation, cell growth, differentiation, cell shape, motility, migration, angiogenesis, and survival. Studies investigating mutational activation of Src in human cancers suggest that this may be a rare event and that wild-type Src is weakly oncogenic. Thus, the role of Src in the development and progression of human cancer remains unclear. Recently, it was suggested that increased SFK protein levels and, more importantly, SFK tyrosine kinase activity are linked to cancer progression and metastatic disease by facilitating the action of other signaling proteins. This accumulating body of evidence indicates that SFKs may represent a promising therapeutic target for the treatment of solid tumors. This review discusses the role of SFKs in solid tumors and the recent therapeutic advances aimed at targeting this family of tyrosine kinases in cancer.

Proliferating cell nuclear antigen is protected from degradation by forming a complex with MutT Homolog2

Proliferating cell nuclear antigen (PCNA) has been demonstrated to interact with multiple proteins involved in several metabolic pathways such as DNA replication and repair. However, there have been fewer reports about whether these PCNA-binding proteins influence stability of PCNA. Here, we observed a physical interaction between PCNA and MutT homolog2 (MTH2), a new member of the MutT-related proteins that hydrolyzes 8-oxo-7,8-dihydrodeoxyguanosine triphosphate (8-oxo-dGTP). In several unstressed human cancer cell lines and in normal human fibroblast cells, PCNA and MTH2 formed a complex and their mutual binding fragments were confirmed. It was intriguing that PCNA and MTH2 were dissociated dependent on acetylation of PCNA, which in turn induced degradation of PCNA in response to UV irradiation, but not in response to other forms of DNA-damaging stress. To further explore the link between dissociation of PCNA-MTH2 and degradation of PCNA, RNAi against MTH2 was performed to mimic the dissociated status of PCNA to evaluate changes in the half-life of PCNA. Knockdown of MTH2 significantly promoted degradation of PCNA, suggesting that the physiological interaction of PCNA-MTH2 may confer protection from degradation for PCNA, whereas UV irradiation accelerates PCNA degradation by inducing dissociation of PCNA-MTH2. Moreover, secondary to degradation of PCNA, UV-induced inhibition of DNA synthesis or cell cycle progression was enhanced. Collectively, our data demonstrate for the first time that PCNA is protected by this newly identified partner molecule MTH2, which is related to DNA synthesis and cell cycle progression.

Inhibition of Src family kinases with dasatinib blocks migration and invasion of human melanoma cells

Src family kinases (SFK) are involved in regulating a multitude of biological processes, including cell adhesion, migration, proliferation, and survival, depending on the cellular context. Therefore, although SFKs are currently being investigated as potential targets for treatment strategies in various cancers, the biological responses to inhibition of SFK signaling in any given tumor type are not predictable. Dasatinib (BMS-354825) is a dual Src/Abl kinase inhibitor with potent antiproliferative activity against hematologic malignancies harboring activated BCR-ABL. In this study, we show that dasatinib blocks migration and invasion of human melanoma cells without affecting proliferation and survival. Moreover, dasatinib completely inhibits SFK kinase activity at low nanomolar concentrations in all eight human melanoma cell lines investigated. In addition, two known downstream targets of SFKs, focal adhesion kinase and Crk-associated substrate (p130(CAS)), are inhibited with similar concentrations and kinetics. Consistent with inhibition of these signaling pathways and invasion, dasatinib down-regulates expression of matrix metalloproteinase-9. We also provide evidence that dasatinib directly inhibits kinase activity of the EphA2 receptor tyrosine kinase, which is overexpressed and/or overactive in many solid tumors, including melanoma. Thus, SFKs and downstream signaling are implicated as having key roles in migration and invasion of melanoma cells.

Integrating biologically targeted therapy in head and neck squamous cell carcinomas

The integration of targeted therapies such as cetuximab to radiation therapy has revolutionized the management of head and neck cancers in the last decade. However, the use of targeted therapies raised several clinically relevant questions that have yet to be answered. These questions include the optimal patient and tumor profile for biologically targeted therapy, the optimal radiation fractionation to use with targeted therapies, how to integrate them into standard or new chemoradiation regimens, their schedule and duration of administration, their toxicity, and which direction to consider for novel targeted treatment. In this review, we highlight several of these important issues, discuss the clinical trials that are designed to address these issues, and introduce some novel targeted therapies that may contribute to the improvement of the therapeutic ratio for head and neck cancer therapy.

Targeting aurora kinase with MK-0457 inhibits ovarian cancer growth

PURPOSE

The Aurora kinase family plays pivotal roles in mitotic integrity and cell cycle. We sought to determine the effects of inhibiting Aurora kinase on ovarian cancer growth in an orthotopic mouse model using a small molecule pan-Aurora kinase inhibitor, MK-0457.

EXPERIMENTAL DESIGN

We examined cell cycle regulatory effects and ascertained the therapeutic efficacy of Aurora kinase inhibition both alone and combined with docetaxel using both in vitro and in vivo ovarian cancer models.

RESULTS

In vitro cytotoxicity assays with HeyA8 and SKOV3ip1 cells revealed >10-fold greater docetaxel cytotoxicity in combination with MK-0457. After in vivo dose kinetics were determined using phospho-histone H3 status, therapy experiments with the chemosensitive HeyA8 and SKOV3ip1 as well as the chemoresistant HeyA8-MDR and A2780-CP20 models showed that Aurora kinase inhibition alone significantly reduced tumor burden compared with controls (P values<0.01). Combination treatment with docetaxel resulted in significantly improved reduction in tumor growth beyond that afforded by docetaxel alone (P <or= 0.03). Proliferating cell nuclear antigen immunohistochemistry revealed that MK-0457 alone and in combination with docetaxel significantly reduced cellular proliferation (P values<0.001). Compared with controls, treatment with MK-0457 alone and in combination with docetaxel also significantly increased tumor cell apoptosis by approximately 3-fold (P<0.01). Remarkably, compared with docetaxel monotherapy, MK-0457 combined with docetaxel resulted in significantly increased tumor cell apoptosis.

CONCLUSIONS

Aurora kinase inhibition significantly reduces tumor burden and cell proliferation and increases tumor cell apoptosis in this preclinical orthotopic model of ovarian cancer. The role of Aurora kinase inhibition in ovarian cancer merits further investigation in clinical trials.

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.

Effect of interleukin-8 gene silencing with liposome-encapsulated small interfering RNA on ovarian cancer cell growth

BACKGROUND

Interleukin-8 (IL-8) is a proangiogenic cytokine that is overexpressed in many human cancers. We investigated the clinical and biologic significance of IL-8 in ovarian carcinoma using human samples and orthotopic mouse models.

METHODS

Tumor expression of IL-8 was assessed by immunohistochemistry among ovarian cancer patients (n = 102) with available clinical and survival data. We examined the effect of IL-8 gene silencing with small interfering RNAs incorporated into neutral liposomes (siRNA-DOPCs), alone and in combination with docetaxel, on in vivo tumor growth, angiogenesis (microvessel density), and tumor cell proliferation in mice (n = 10 per treatment group) bearing orthotopic taxane-sensitive (HeyA8 and SKOV3ip1) and taxane-resistant (SKOV3ip2.TR) ovarian tumors. All statistical tests were two-sided.

RESULTS

Of the 102 cancer specimens, 43 (42%) had high IL-8 expression and 59 (58%) had low or no IL-8 expression; high IL-8 expression was associated with advanced tumor stage (P = .019), high tumor grade (P = .031), and worse survival (median survival for patients with high vs low IL-8 expression: 1.62 vs 3.79 years; P < .001). Compared with empty liposomes, IL-8 siRNA-DOPC reduced the mean tumor weight by 32% (95% confidence interval [CI] = 14% to 50%; P = .03) and 52% (95% CI = 27% to 78%; P = .03) in the HeyA8 and SKOV3ip1 mouse models, respectively. In all three mouse models, treatment with IL-8 siRNA-DOPC plus the taxane docetaxel reduced tumor growth the most compared with empty liposomes (77% to 98% reduction in tumor growth; P < .01 for all). In the HeyA8 and SKOV3ip1 models, tumors from mice treated with IL-8 siRNA-DOPC alone had lower microvessel density than tumors from mice treated with empty liposomes (HeyA8: 34% lower, 95% CI = 32% to 36% lower [P = .002]; SKOV3ip1: 39% lower, 95% CI = 34% to 44% lower [P = .007]). Compared with empty liposomes, IL-8 siRNA-DOPC plus docetaxel reduced tumor cell proliferation by 35% (95% CI = 25% to 44%; P < .001) and 38% (95% CI = 28% to 48%; P < .001) in the HeyA8 and SKOV3ip1 models, respectively.

CONCLUSIONS

Increased IL-8 expression is associated with poor clinical outcome in human ovarian carcinoma, and IL-8 gene silencing decreases tumor growth through antiangiogenic mechanisms.

Early Events in the Pathogenesis of Epithelial Ovarian Cancer

Ovarian carcinogenesis, as in most cancers, involves multiple genetic alterations. A great deal has been learned about proteins and pathways important in the early stages of malignant transformation and metastasis, as derived from studies of individual tumors, microarray data, animal models, and inherited disorders that confer susceptibility. However, a full understanding of the earliest recognizable events in epithelial ovarian carcinogenesis is limited by the lack of a well-defined premalignant state common to all ovarian subtypes and by the paucity of data from early-stage cancers. Evidence suggests that ovarian cancers can progress both through a stepwise mutation process (low-grade pathway) and through greater genetic instability that leads to rapid metastasis without an identifiable precursor lesion (high-grade pathway). In this review, we discuss many of the genetic and molecular disorders in each key process that is altered in cancer cells, and we present a model of ovarian pathogenesis that incorporates the role of tumor cell mutations and factors in the host microenvironment important to tumor initiation and progression.

Curcumin inhibits tumor growth and angiogenesis in ovarian carcinoma by targeting the nuclear factor-kappaB pathway

PURPOSE

Curcumin, a component of turmeric, has been shown to suppress inflammation and angiogenesis largely by inhibiting the transcription factor nuclear factor-kappaB (NF-kappaB). This study evaluates the effects of curcumin on ovarian cancer growth using an orthotopic murine model of ovarian cancer.

EXPERIMENTAL DESIGN

In vitro and in vivo experiments of curcumin with and without docetaxel were done using human ovarian cancer cell lines SKOV3ip1, HeyA8, and HeyA8-MDR in athymic mice. NF-kappaB modulation was ascertained using electrophoretic mobility shift assay. Evaluation of angiogenic cytokines, cellular proliferation (proliferating cell nuclear antigen), angiogenesis (CD31), and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) was done using immunohistochemical analyses.

RESULTS

Curcumin inhibited inducible NF-kappaB activation and suppressed proliferation in vitro. In vivo dose-finding experiments revealed that 500 mg/kg orally was the optimal dose needed to suppress NF-kappaB and signal transducers and activators of transcription 3 activation and decrease angiogenic cytokine expression. In the SKOV3ip1 and HeyA8 in vivo models, curcumin alone resulted in 49% (P = 0.08) and 55% (P = 0.01) reductions in mean tumor growth compared with controls, whereas when combined with docetaxel elicited 96% (P < 0.001) and 77% reductions in mean tumor growth compared with controls. In mice with multidrug-resistant HeyA8-MDR tumors, treatment with curcumin alone and combined with docetaxel resulted in significant 47% and 58% reductions in tumor growth, respectively (P = 0.05). In SKOV3ip1 and HeyA8 tumors, curcumin alone and with docetaxel decreased both proliferation (P < 0.001) and microvessel density (P < 0.001) and increased tumor cell apoptosis (P < 0.05).

CONCLUSIONS

Based on significant efficacy in preclinical models, curcumin-based therapies may be attractive in patients with ovarian carcinoma.

Efficacy and antivascular effects of EphA2 reduction with an agonistic antibody in ovarian cancer

BACKGROUND

EphA2 is an oncoprotein and tyrosine kinase receptor that is overexpressed in ovarian and many other cancers. We investigated the effects of reduced EphA2 levels on tumor growth and the tumor microenvironment in an orthotopic ovarian cancer model.

METHODS

The effect of the EphA2-agonistic monoclonal antibody EA5, alone or in combination with paclitaxel, on the growth of ovarian cancer cells (SKOV3ip1, HeyA8, and HeyA8MDR [taxane-platinum resistant]) was determined in vitro and in vivo by immunoblotting, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, and immunohistochemical analysis. Expression of EphA2 and markers of angiogenesis (CD31, vascular endothelial growth factor [VEGF], and basic fibroblast growth factor), proliferation (proliferating cell nuclear antigen), and endothelial cell apoptosis (CD31-terminal deoxynucleotidyl transferase biotin-deoxyuridine triphosphate nick-end labeling colocalization) and phosphorylation of Src were analyzed by immunoblotting, immunohistochemistry, immunofluorescence, and in situ hybridization in tumors from treated mice. Statistical tests were two-sided.

RESULTS

EA5 antibody treatment led to a more than 90% reduction in EphA2 expression in HeyA8 tumors in vivo. In mice bearing orthotopic SKOV3ip1 or HeyA8 tumors, 4 weeks of EA5 treatment resulted in tumors that weighed 31% and 45% less, respectively, than those in control (IgG-treated) mice (95% confidence interval [CI] = -0.09% to 71% and 20% to 70%, P = .27 and .01, respectively). Combination therapy with EA5 and paclitaxel reduced tumor weight by 77% and 80% (95% CI = 63% to 91% and 68% to 91%), respectively, compared with paclitaxel alone and by 92% and 88% (95% CI = 87% to 97% and 80% to 94%), respectively, compared with IgG alone. Combination therapy also reduced the weight of HeyA8MDR tumors by 47% (95% CI = 24% to 72%) compared with paclitaxel. Mice bearing SKOV3ip1 or HeyA8 tumors that were treated with combination therapy survived longer than those treated with paclitaxel alone (median survival = 144 versus 69 days and 46 versus 37 days, respectively). EA5-treated tumors had reduced microvascular density, proliferation, and VEGF protein and mRNA levels, with increased endothelial cell apoptosis. EphA2 was associated with Src, which was rapidly dephosphorylated after EA5 treatment.

CONCLUSIONS

EA5 in combination with paclitaxel decreased tumor growth in an orthotopic ovarian cancer mouse model through antiangiogenic mechanisms associated with reduced levels of VEGF and phosphorylated Src. Humanized antibody constructs against EphA2 are worthy of future study.

[Experimental animal models of diabetes mellitus]

Vascular endothelial growth factor (VEGF) plays a critical role in angiogenesis, which is required for tumor growth and metastasis. In this article, a review of the functional and biological roles of the VEGF pathway in driving angiogenesis and growth of gynecologic malignancies was performed. Based on the biological functions of VEGF, multiple approaches for targeting the VEGF/VEGF-receptor complex have been developed and many of these have demonstrated substantial activity in preclinical models. These promising data have led to rapid clinical development of VEGF-targeted agents. Therefore, we also assessed the status of VEGF-targeted therapies and associated toxicities in gynecologic malignancies. However, many questions remain related to optimal dosing, sequencing of therapies, management of toxicities, appropriate patient selection, and assessment of response, which will require further studies. Nevertheless, VEGF-targeted therapies offer hope for improving the outcome of cancer patients.