A dual inhibitor of matrix metalloproteinases and a disintegrin and metalloproteinases, [18F]FB-ML5, as a molecular probe for non-invasive MMP/ADAM-targeted imaging

BACKGROUND: Numerous clinical studies have shown a correlation between increased matrix metalloproteinase (MMP)/a disintegrin and metalloproteinase (ADAM) activity and poor outcome of cancer. Various MMP inhibitors (MMPIs) have been developed for therapeutic purposes in oncology. In addition, molecular imaging of MMP/ADAM levels in vivo would allow the diagnosis of tumors. We selected the dual inhibitor of MMPs and ADAMs, ML5, which is a hydroxamate-based inhibitor with affinities for many MMPs and ADAMs. ML5 was radiolabelled with (18)F and the newly obtained radiolabelled inhibitor was evaluated in vitro and in vivo. MATERIALS AND METHODS: ML5 was radiolabelled by direct acylation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB) for PET (positron emission tomography). The resulting radiotracer [(18)F]FB-ML5 was evaluated in vitro in human bronchial epithelium 16HBE cells and breast cancer MCF-7 cells. The non-radioactive probe FB-ML5 and native ML5 were tested in a fluorogenic inhibition assay against MMP-2, -9, -12 and ADAM-17. The in vivo kinetics of [(18)F]FB-ML5 were examined in a HT1080 tumor-bearing mouse model. Specificity of probe binding was examined by co-injection of 0 or 2.5mg/kg ML5. RESULTS: ML5 and FB-ML5 showed high affinity for MMP-2, -9, -12 and ADAM-17; indeed IC50 values were respectively 7.4±2.0, 19.5±2.8, 2.0±0.2 and 5.7±2.2nM and 12.5±3.1, 31.5±13.7, 138.0±10.9 and 24.7±2.8nM. Radiochemical yield of HPLC-purified [(18)F]FB-ML5 was 13-16% (corrected for decay). Cellular binding of [(18)F]FB-ML5 was reduced by 36.6% and 27.5% in MCF-7 and 16HBE cells, respectively, after co-incubation with 10μM of ML5. In microPET scans, HT1080 tumors exhibited a low and homogeneous uptake of the tracer. Tumors of mice injected with [(18)F]FB-ML5 showed a SUVmean of 0.145±0.064 (n=6) which decreased to 0.041±0.027 (n=6) after target blocking (p