Effect of Interleukin-8 Gene 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.

Ovarian cancer remains the leading cause of death from gynecologic malignancy among women in the United States. Although tumor-reductive surgery and taxane- and platinum-based chemotherapy regimens are effective treatments for primary disease in the majority of ovarian cancer patients, recurrence is common and often leads to death. New therapeutic agents are needed to improve survival rates and to eventually cure patients of this deadly disease. Of the emerging therapeutic strategies, those that target stromal cells in the tumor microenvironment are particularly attractive because these cells are thought to be more genetically stable than the tumor cells themselves. Moreover, targeting the host vasculature by using anti-vascular endothelial growth factor therapy has been shown to improve survival among colorectal and lung cancer patients. However, the tumor vasculature is complex and the process of angiogenesis in cancers relies on many factors that are not fully understood.

Interleukin-8 (IL-8) is a potent proangiogenic cytokine that is overexpressed in most human cancers, including ovarian carcinoma. IL-8 is an 8-kDa molecule that is secreted by multiple cell types, including monocytes, neutrophils, endothelial and mesothelial cells, and tumor cells; it is responsible for recruiting neutrophils, T cells, and basophils during immune system activation. Induction of IL-8 expression is mediated primarily by the transcription factor nuclear factor kappa B (NF-κB); however, the Src/signal transducer and activator of transcription 3 (Stat3) pathway may also promote IL-8 production independent of NF-κB. IL-8 exerts its effects by binding to the G protein-coupled receptors CXCR1 and CXCR2. Both receptors are expressed on most tumor cells as well as on endothelial cells.

The extensive effects of increased IL-8 activity on tumor pathogenesis make it a unique therapeutic target in cancer therapy. For example, IL-8 promotes tumor growth, angiogenesis, and metastasis in murine models of several cancers. Moreover, blocking IL-8 activity with a monoclonal antibody has been shown to decrease tumor growth in two murine cancer models. However, there are limited data regarding the efficacy of other therapeutic approaches that target IL-8. We recently developed a novel method for highly efficient in vivo gene silencing using neutral liposome-encapsulated small interfering RNA (siRNA). Here we examined the clinical significance of IL-8 expression in human ovarian carcinoma and tested the therapeutic efficacy of IL-8-targeted siRNA in orthotopic mouse models of ovarian cancer.