In solid tumors, [vascular disrupting agents] VDA’s, such as ZYBRESTAT™, rapidly disrupt the vasculature within the tumor, reduce blood-flow, and deprive the tumor of oxygen and nutrients, resulting in tumor cell death. This disruption of the newly formed blood vessels contrasts with the action of anti-angiogenic therapies (e.g., bevacizumab/Avastin™), which are designed to prevent new blood vessel formation. … Specifically, Zybrestat™ was tested on advanced solid malignancies in Phase I clinical trial involving 14 patients. … Nine of fourteen patients experienced disease stabilization for greater than 12 weeks. Three patients experienced disease stabilization for greater than 24 weeks, with two of these patients continuing with stable disease at 47 and 29 weeks, respectively.
Based upon an abstract presentation made at the 2008 American Society of Clinical Oncology (ASCO) Annual Meeting recently held in Chicago on May 30th through June 3rd, the new vascular disrupting agent (VDA) Zybrestat™ (fosbretabulin) produced an advanced solid tumor disease stabilization rate of 64 percent.
Vascular disruption represents a new approach to a validated therapeutic strategy: depriving tumors of blood supply. In solid tumors, VDA’s, such as ZYBRESTAT™, rapidly disrupt the vasculature within the tumor, reduce blood-flow, and deprive the tumor of oxygen and nutrients, resulting in tumor cell death. This disruption of the newly formed blood vessels contrasts with the action of anti-angiogenic therapies (e.g., bevacizumab/Avastin™), which are designed to prevent new blood vessel formation. OXiGENE Inc. (OXiGENE) believes its VDA product candidates may offer advantages over current anti-angiogenic drugs, including superior efficacy and reduced side-effects.
In addition, there is a strong scientific rationale for combining VDA and anti-angiogenesis therapies. OXiGENE and its scientific collaborators have published preclinical research results showing that the combination of OXiGENE VDAs and certain anti-angiogenic drugs (i.e., monoclonal antibodies targeting vascular endothelial growth factor, or VEGF) have synergistic anti-tumor effects. Building upon these results, OXiGENE has undertaken the first-ever human clinical trial of a VDA (ZYBRESTAT) in combination with an anti-angiogenic agent (bevacizumab / AVASTIN.) The additional benefits of vascular disrupting agents include:
- This method of treatment is designed to target newly formed abnormal blood vessels, rather than the established blood vessels found in healthy tissue, resulting in fewer side effects in the oncology setting than conventional disease treatments such as radiation and chemotherapy. VDAs are designed to address the complete spectrum of solid tumors, whereas other approaches, which directly target tumor cells, require the development of different drugs for different types of solid tumors.
- VDAs are designed to target endothelial cells associated with new blood vessel formation, so drug resistant mutations are unlikely to occur.
- Damaging one or two blood vessels can cause thousands of tumor cells to die.
- The ability of VDAs to selectively target newly formed or abnormal blood vessels makes them well-suited for certain ocular diseases, such as age-related macular degeneration, in which the formation of new, abnormal blood vessels in the eye plays a key role in disease.
Specifically, Zybrestat™ was tested on advanced solid malignancies in Phase I clinical trial involving 14 patients. The patients were divided into three separate dosage cohorts, representing 45mg/m2 (cohort 1), 54mg/m2 (cohort 2) or 63mg/m2 (cohort 3) of Zybrestat™ every 14 days followed by bevacizumab (Avastin™) at a dosage of 10mg/kg four hours later. The study results indicated two grade 3/4 drug dosage limiting toxicities. Nine of fourteen patients experienced disease stabilization for greater than 12 weeks. Three patients experienced disease stabilization for greater than 24 weeks, with two of these patients continuing with stable disease at 47 and 29 weeks, respectively. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) showed statistically significant reductions in tumor perfusion/vascular permeability which reversed when Zybrestat™ was used as a monotherapy, but were sustained following the use of bevacizumab (Avastin™). The clinical trial investigators concluded that Zybrestat™ was safe and tolerable at the three dosage levels used, and noted that Zybrestat™ induced profound vascular changes in the solid tumor which were maintained by the presence of bevacizumab (Avastin™).
- OXiGENE Announces Clinical Trials Data to be Presented At the 2008 Annual Meeting of the American Society of Clinical Oncology, OXiGENE Inc. News Release, May 28, 2008.
- A phase I study of combretastatin A4 phosphate (CA4P) and bevacizumab in subjects with advanced solid tumors; P.D. Nathan et. al., J.Clin. Oncol. 26: 2008 (May 20 suppl; abstr 3550).
- ZYBRESTATTM (combretastatin / CA4P parenteral) – ONCOLOGY Section, OXiGENE Inc website.
Comment: ZYBRESTAT™ has broad potential therapeutic utility across a wide range of different solid tumor types, and can potentially be combined with mainstay oncology treatment modalities: chemotherapy, radiation therapy and newer, “molecularly-targeted therapies,” such as tumor angiogenesis inhibitors. Preclinical studies have demonstrated that ZYBRESTAT™ has synergistic or additive effects when incorporated in various combination regimens with all of these treatment modalities. There is a strong scientific rationale for combining ZYBRESTAT™ and tumor angiogenesis inhibiting drugs, and ZYBRESTAT™ is the first VDA to be tested in humans in combination with a tumor-angiogenesis-inhibiting drug (bevacizumab / AVASTIN®).