The vascular disrupting activity of OXi8006 in endothelial cells and its phosphate prodrug OXi8007 in breast tumor xenografts

This study describes the vascular disrupting ability and the mechanism of action of the indole-based tubulin-binding compound, OXi8006, and its water-soluble phosphate prodrug OXi8007. Treatment of rapidly proliferating human umbilical vein endothelial cells (HUVECs), used as a model for the tumor vasculature, with OXi8006 or OXi8007, caused potent microtubule disruption followed by extensive reorganization of the cytoskeletal network. The mechanism of action involved an increase in focal adhesion formation associated with an increase in phosphorylation of both non-muscle myosin light chain and focal adhesion kinase. These effects were dramatically diminished by an inhibitor of RhoA kinase, a downstream effector of RhoA. Cell cycle blockade at G2/M and cytotoxicity toward rapidly proliferating HUVECs were also observed. Capillary-like networks of HUVECs were disrupted by the action of both OXi8006 and OXi8007. The prodrug OXi8007 exhibited potent and rapid dose-dependent antivascular activity assessed by dynamic bioluminescence imaging (BLI) in an MDA-MB-231-luc breast cancer xenograft mouse model. By 6 hours post treatment, over 93% of the BLI signal was abolished with only a slight recovery at 24 hours. These findings were confirmed by histology. The results from this study demonstrate that OXi8007 is a potent vascular disrupting agent acting through an anti-microtubule mechanism involving RhoA.

KML001 displays vascular disrupting properties and irinotecan combined antitumor activities in a murine tumor model

KML001 is sodium metaarsenite, and has shown cytotoxic activity in human tumor cell lines. The anti-cancer mechanism of KML001 involves cancer cell destruction due to DNA damage at the telomeres of cancer cell chromosomes. In this study, we assessed the vascular disrupting properties of KML001 and investigated whether KML001 as VDA is able to increase anti-tumor activity in irinotecan combined treatment. We used a murine model of the CT26 colon carcinoma cell line. CT26 isograft mice treated intraperitoneally with 10 mg/kg KML001 displayed extensive central necrosis of tumor by 24 h. The vascular disrupting effects of KML001 were assessed by dynamic contrast enhanced magnetic resonance imaging. Gadopentetic acid-diethylene triaminepentaacetic acid contrast enhancement was markedly decreased in KML001-treated mice one day after treatment, whereas persistently high signal enhancement was observed in mice injected with saline. Rate constant K(ep) value representing capillary permeability was significantly decreased (p<0.05) in mice treated with KML001. Cytoskeletal changes of human umbilical vein endothelial cells (HUVECs) treated with 10 uM KML001 were assessed by immune blotting and confocal imaging. KML001 degraded tubulin protein in HUVECs, which may be related to vascular disrupting properties of KML001. Finally, in the mouse CT26 isograft model, KML001 combined with irinotecan significantly delayed tumor growth as compared to control and irinotecan alone. These results suggest that KML001 is a novel vascular disrupting agent, which exhibits significant vascular shut-down activity and enhances anti-tumor activity in combination with chemotherapy. These data further suggest an avenue for effective combination therapy in treating solid tumors.

Targeted agents in ovarian cancer

Despite recent advances in the treatment of ovarian cancer, a large majority of women with this diagnosis will die from recurrence of their disease. Targeted therapies, in the form of monoclonal antibodies and small molecule tyrosine kinase inhibitors have significantly altered the management of many solid tumors and hematologic malignancies. No such agents have been approved by the US FDA for use in ovarian cancer, although Phase II data suggests excellent single-agent activity of some of these drugs. Antiangiogenic agents in combination with chemotherapy are being evaluated in Phase III clinical trials, both in the adjuvant setting and in recurrent platinum-sensitive disease. Poly-ADP-ribose polymerase inhibitors are promising agents in BRCA1/2-mutated breast and ovarian cancers. Ongoing clinical trials are exploring the anti-tumor effect of poly-ADP-ribose polymerase inhibitors administered as single agents and in combination with chemotherapy. Many other new drugs are in earlier grades of development. In this article, we review the state of the art in targeted therapies for ovarian cancer and identify future directions for their development in the management of this often devastating disease.

Targeted therapies in epithelial ovarian cancer

Molecularly targeted therapy is relatively new to ovarian cancer despite the unquestionable success with these agents in other solid tumours such as breast and colorectal cancer. Advanced ovarian cancer is chemosensitive and patients can survive several years on treatment. However chemotherapy diminishes in efficacy over time whilst toxicities persist. Newer biological agents that target explicit molecular pathways and lack specific chemotherapy toxicities such as myelosuppression offer the advantage of long-term therapy with a manageable toxicity profile enabling patients to enjoy a good quality of life. In this review we appraise the emerging data on novel targeted therapies in ovarian cancer. We discuss the role of these compounds in the front-line treatment of ovarian cancer and in relapsed disease; and describe how the development of predictive clinical, molecular and imaging biomarkers will define the role of biological agents in the treatment of ovarian cancer.