Synthesis and preliminary evaluation in tumor bearing mice of new ¹⁸F-labeled arylsulfone matrix metalloproteinase inhibitors as tracers for positron emission tomography

New fluorinated, arylsulfone-based matrix metalloproteinase (MMP) inhibitors containing carboxylate as the zinc binding group were synthesized as radiotracers for positron emission tomography. Inhibitors were characterized by K_i for MMP-2 in the nanomolar range and by a fair selectivity for MMP-2/9/12/13 over MMP-1/3/14. Two of these compounds were obtained in the ¹⁸F-radiolabeled form, with radiochemical purity and yield suitable for preliminary studies in mice xenografted with a human U-87 MG glioblastoma. Target density in xenografts was assessed by Western blot, yielding B _max/K_d = 14. The biodistribution of the tracer was dominated by liver uptake and hepatobiliary clearance. Tumor uptake of ¹⁸F-labeled MMP inhibitors was about 30% that of [ ¹⁸F]fluorodeoxyglucose. Accumulation of radioactivity within the tumor periphery colocalized with MMP-2 activity (evaluated by in situ zimography). However, specific tumor uptake accounted for only 18% of total uptake. The aspecific uptake was ascribed to the high binding affinity between the radiotracer and serum albumin.