One of the challenges facing oncology today is the limited absorption of chemotherapeutics in the tumor microenvironment, with the vast majority of any drug being eliminated from the patient. Increasing the dosage to improve the therapeutic potential of a drug can often lead to dangerous side effects. Vasopermeation Enhancement Agents (VEAs) are a new class of biologics that are designed to increase the uptake of cancer therapeutics at the tumor site, resulting in a greater efficacy of the compounds, without increasing dosages given to the patient. VEAs comprise tumor-specific antibodies fused to vasoactive compounds that are co-administered with standard chemotherapeutics. The lead vasoactive compound under investigation is Interleukin-2 (IL-2) or fragments of that protein. Here we present the results of a comprehensive study to evaluate VEAs bearing eleven variants of human IL-2. The IL-2 variants include: 1) the full length wildtype molecule, 2) a deletion mutant of IL-2 missing regions of cytokine activity, 3) an IL-2 fragment referred to as the Permeability Enhancing Peptide (PEP) that is believed to have vasopermeable activity, 4) a fragment encompassing both PEP and the xDy motif at residue 20, a motif believed to also have vasoactivity, and 5) several structural variants that encompass both PEP and residue D20 but vary in the location of the carboxy terminus with respect to the overall protein’s structure. The potency of each candidate was evaluated by measuring the extravasation of blood into the surrounding tissue in a chorioallantoic membrane (CAM) assay. Using fluorescent reagents, dyes, and the CAM of an avian embryo as a vascular model, we have developed a quantitative assay that measures the amount of vasopermeation into the interstitial regions of an induced tumor. CAMs are highly vascularized extra-embryonic membranes connected to embryos through a continuous circulatory system. They have the advantage of easy accessibility for experimental manipulation, including the intravenous injection of drug candidates, the attachment and growth of tumor colonies, and the optical visualization of local responses using, in this case, fluorescent dextran to track the flow of blood. Sensitive quantitative measurements obtained in our novel in vivo assay have allowed us to determine the efficacy of these eleven vasoactive compounds, and this has allowed us to choose the most promising candidates for further pre-clinical studies in mice and monkeys. We believe this is the first report of an avian embryonic system being utilized for the commercial evaluation of clinical drug candidates prior to more costly investigations in traditional animal models.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA