Novel “Add-On” Molecule Based on Evans Blue Confers Superior Pharmacokinetics and Transforms Drugs to Theranostic Agents

Abstract

One of the major design considerations for a drug is its pharmacokinetics in the blood. A drug with a short half-life in the blood is less available at a target organ. Such a limitation dictates treatment with either high doses or more frequent doses, both of which may increase the likelihood of undesirable side effects. To address the need for additional methods to improve the blood half-life of drugs and molecular imaging agents, we developed an "add-on" molecule that contains 3 groups: a truncated Evans blue dye molecule that binds to albumin with a low micromolar affinity and provides a prolonged half-life in the blood; a metal chelate that allows radiolabeling for imaging and radiotherapy; and maleimide for easy conjugation to drug molecules. Methods: The truncated Evans blue molecule was conjugated with the chelator NOTA or DOTA, and the resulting conjugate was denoted as NMEB or DMEB, respectively. As a proof of concept, we coupled NMEB and DMEB to c(RGDfK), which is a small cyclic arginine-glycine-aspartic acid (RGD) peptide, for targeting integrin a v b 3 . NMEB and DMEB were radiolabeled with 64 Cu and 90 Y, respectively, and tested in xenograft models. Results: The resulting radiolabeled conjugates showed a prolonged circulation half-life and enhanced tumor accumulation in integrin a v b 3 -expressing tumors. Tumor uptake was markedly improved over that with NOTA-or DOTA-conjugated c(RGDfK). Tumor radiotherapy experiments in mice with 90 Y-DMEB-RGD showed promising results; existing tumors were eliminated. Conclusion: Conjugation of our novel add-on molecule, NMEB or DMEB, to potential tracers or therapeutic agents improved blood half-life and tumor uptake and could transform such agents into theranostic entities. Thegoalofdr ug development is to achieve high activity and specificity for a desired biologic target. However, many potential pharmaceuticals that meet these criteria fail as therapeutics because of unfavorable pharmacokinetics, in particular, rapid blood clearance, which prevents the achievement of therapeutic concentrations. For some drugs, the administration of large or frequently repeated doses is required to achieve and maintain therapeutic levels (1) but can, in turn, increase the probability of undesired side effects. One chemical modification that delays the rate of drug clearance and has been effective for some drugs is the addition of polyethylene glycol (PEG) (2). However, recent studies showed that PEGylation of drugs has disadvantages, including immunogenicity caused by the development of anti-PEG antibodies, heterogeneity of the PEGylated drugs, and decreased biologic activity and bioavailability of the drugs (1,3).To address the need for additional methods to improve the blood half-life of drugs and molecular imaging agents, we made use of molecules with a high affinity for albumin. We previously developed a radiolabeled truncated derivative of Evans blue (EB) that allowed imaging of the blood volume because of the affinity of EB for albumin (4). This result encouraged us to e...

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