Design, synthesis, and biological evaluation of potent thiosemicarbazone based cathepsin L inhibitors

A small library of 36 functionalized benzophenone thiosemicarbazone analogs has been prepared by chemical synthesis and evaluated for their ability to inhibit the cysteine proteases cathepsin L and cathepsin B. Inhibitors of cathepsins L and B have the potential to limit or arrest cancer metastasis. The six most active inhibitors of cathepsin L (IC<sub>50</sub> < 85 nM) in this series incorporate a meta-bromo substituent in one aryl ring along with a variety of functional groups in the second aryl ring. These six analogs are selective for their inhibition of cathepsin L versus cathepsin B (IC<sub>50</sub> > 10,000 nM). The most active analog in the series, 3-bromophenyl-2′-fluorophenyl thiosemicarbazone 1, also efficiently inhibits cell invasion of the DU-145 human prostate cancer cell line