Investigation of a MMP-2 activity-dependent anchoring probe for nuclear imaging of cancer.

Since matrix metalloproteinase-2 (MMP-2) is an important marker of tumor malignancy, we developed an original drug design strategy, MMP-2 activity dependent anchoring probes (MDAP), for use in MMP-2 activity imaging, and evaluated the usefulness of this probe in in vitro and in vivo experiments. We designed and synthesized MDAP(1000), MDAP(3000), and MDAP(5000), which consist of 4 independent moieties: RI unit (111)In hydrophilic chelate), MMP-2 substrate unit (short peptide), anchoring unit (alkyl chain), and anchoring inhibition unit (polyethylene glycol (PEGn; where n represents the approximate molecular weight, n = 1000, 3000, and 5000). Probe cleavage was evaluated by chromatography after MMP-2 treatment. Cellular uptake of the probes was then measured. Radioactivity accumulation in tumor xenografts was evaluated after intravenous injection of the probes, and probe cleavage was evaluated in tumor homogenates. MDAP(1000), MDAP(3000), and MDAP(5000) were cleaved by MMP-2 in a concentration-dependent manner. MDAP(3000) pretreated with MMP-2 showed higher accumulation in tumor cells, and was completely blocked by additional treatment with an MMP inhibitor. MDAP(3000) exhibited rapid blood clearance and a high tumor accumulation after intravenous injection in a rodent model. Furthermore, pharmacokinetic analysis revealed that MDAP(3000) exhibited a considerably slow washout rate from tumors to blood. A certain fraction of cleaved MDAP(3000) existed in tumor xenografts in vivo. The results indicate the possible usefulness of our MDAP strategy for tumor imaging.