CA-074, a synthetic analogue of E-64 developed through rational drug design, is an irreversible inhibitor of most lysosomal cysteine proteinases. It exploits the dipeptidylcarboxypeptidase activity of cathepsin B. With a Ki of 2 to 5 nM, CA-074 selectively inhibits cathepsin B within living cells, provided that experimental conditions allow significant fluid-phase endocytosis of the drug[2]. Notably, CA-074 demonstrates significantly greater inhibitory effects on purified rat cathepsin B (10000-30000 times) compared to cathepsin H and L, for which the initial Kis are about 40-200 μM[3].

The intraperitoneal injection of compound CA-074 into rats effectively and selectively inhibits cathepsin B activity[1]. Following intravenous administration of CA-074 immediately after the ischemic insult, it preserves 67% of CA1 neurons from delayed neuronal death on day 5 in eight monkeys undergoing 20 minutes of brain ischemia. The extent of inhibition is excellent in three of eight monkeys and good in five of eight monkeys[1].