Towards kit-like 18F-labeling of marimastat, a noncovalent inhibitor drug for in vivo PET imaging cancer associated matrix metalloproteases

Abstract

Marimastat, a clinically trialed drug developed to treat breast cancer by inhibiting cancer-associated matrix metalloproteases (MMPs), was linked to an aryl boronic ester for single-step [18F]-aqueous fluoride capture and the labeled product revealed tumor associated MMP activity in vivo. Herein, we report important radiosynthetic attributes for labeling marimastat that enabled the first PET images of breast cancer-associated matrix metalloproteases in a syngenic murine model. The advantages of this method include one-step post synthetic labeling in less than one hour at ambient temperature, the ability to work in aqueous media without drying the 18F-fluoride, observation of high radiochemical purity, and the potential for tripling the specific activity of the fluoride used in labeling. Using low levels of activity e.g. 60 mCi in low volumes this method affords reasonable yields of labeled marimastat with decay-corrected specific activities of 0.39 and 0.75 Ci/μmol, and real specific activities of 0.16 and 0.39 Ci/μmol. Current limitations of this method along with anticipated improvements are discussed.