Cancer Therapy Using Intravenous Liposomal Delivery of an Antiangiogenic Snake Venom Disintegrin

Francis S. Markland, Stephen D. Swenson, Fritz K. Costa and Radu O. Minea

Dept. of Biochemistry & Molecular Biology, and Norris Comprehensive Cancer Center, University of Southern California, Keck School of Medicine

Breast cancer (BC) is the second most common form of cancer among women in the United States with ~216,000 new cases anticipated in 2004, and it is the second leading cause of cancer death with 40,110 deaths expected.  Despite significant improvements in the management of BC, for women with distant metastases, the 5-year survival rate is very poor, 23%.  It is critical, therefore, that new treatment options be made available for patients with metastatic disease.  BC has been labeled an angiogenesis-dependent cancer and a unique target for antiangiogenic therapy.

Ovarian cancer (OC) represents the most lethal gynecological cancer.  The American Cancer Society estimates that about 25,580 new cases of OC will be diagnosed in the United States and there will be about 16,090 deaths from OC in 2004.  The 5-year survival in women with distant disease is only 31%.  It is imperative that new therapeutic modalities be developed for this disease.  As in BC, angiogenesis plays an important role in OC growth and dissemination.  Antiangiogenic therapy, therefore, offers an attractive strategy for enhanced long-term survival for this “silent killer”. 

We have been studying a snake venom disintegrin, contortrostatin (CN), with antitumor/antiangiogenic activity in animal models of BC and OC.  We previously described the antitumor efficacy of daily intratumor injection of CN in a BC model, but these studies employed a method of delivery that was not clinically translatable.  Recently we developed a liposomal delivery system and showed that CN, delivered by this mechanism, effectively limits tumor progression in orthotopic, xenograft models of human BC and OC in immunodeficient mice.  CN (Mr 13,500) is a homodimeric protein isolated from venom of the southern copperhead snake.  CN possesses two RGD sites, which modulates its interaction with integrins on cells.  CN binds to integrins on tumor cells including v3, v5, and 51.  This binding effectively prevents cell adhesion, migration, and invasion.  CN also binds to integrins on angiogenic vascular endothelial cells, thereby interfering with angiogensis. 

We now show that intravenous (i.v.) liposomal delivery of CN (L-CN) effectively controls both tumor growth and angiogenesis, and is a method of administration that is translatable to the clinic.  Several distinct advantages of liposomal delivery of CN were observed: (i) L-CN has a significantly prolonged circulatory half-life compared to native CN; (ii) L-CN passively accumulates in the tumor; (iii) L-CN exhibits no platelet reactivity; and (iv) L-CN is not recognized by the immune system.  In addition to these significant advantages, twice weekly i.v. delivery of L-CN is as effective, if not more so, than daily intratumor (i.t.) delivery of native CN, not only in limiting tumor growth, but also in reducing angiogenesis in both tumor models (reduction of angiogenesis is ~90%).  In the BC study, L-CN was delivered i.v. twice weekly (105 g/dose) while native CN was delivered i.t. daily (30g/dose).  Both forms of treatment revealed a significant decrease in tumor growth, but there was a distinct advantage to L-CN delivery in terms of antiangiogenic activity.  In the OC study, L-CN was delivered i.v. twice weekly (105 or 210 g/dose) while native CN was delivered intraperitoneally (i.p.) daily (30 g/dose).  Both forms of treatment showed a significant decrease in tumor growth and angiogenesis.  However, i.v. administration of L-CN revealed a dose-dependent response and greater antiangiogenic activity than i.p. delivery.

In summary, we have developed a clinically relevant method for delivery of L-CN that involves twice weekly intravenous administration.  Full retention of biological activity is observed for the potent antitumor agent with this method of delivery.