Cysteine proteases as therapeutic targets: does selectivity matter? A systematic review of calpain and cathepsin inhibitors

Cysteine proteases continue to provide validated targets for treatment of human diseases. In neurodegenerative disorders, multiple cysteine proteases provide targets for enzyme inhibitors, notably caspases, calpains, and cathepsins. The reactive, active-site cysteine provides specificity for many inhibitor designs over other families of proteases, such as aspartate and serine; however, a) inhibitor strategies often use covalent enzyme modification, and b) obtaining selectivity within families of cysteine proteases and their isozymes is problematic. This review provides a general update on strategies for cysteine protease inhibitor design and a focus on cathepsin B and calpain 1 as drug targets for neurodegenerative disorders; the latter focus providing an interesting query for the contemporary assumptions that irreversible, covalent protein modification and low selectivity are anathema to therapeutic safety and efficacy.

Novel GHRH antagonists suppress the growth of human malignant melanoma by restoring nuclear p27 function

Malignant melanoma is the deadliest form of skin cancer; the treatment of advanced and recurrent forms remains a challenge. It has recently been reported that growth hormone-releasing hormone (GHRH) receptor is involved in the pathogenesis of melanoma. Therefore, we investigated the effects of our new GHRH antagonists on a human melanoma cancer cell line. Antiproliferative effects of GHRH antagonists, MIA-602, MIA-606 and MIA-690, on the human melanoma cell line, A-375, were studied in vitro using the MTS assay. The effect of MIA-690 (5 μg/day 28 d) was further evaluated in vivo in nude mice bearing xenografts of A-375. Subcellular localization of p27 was detected with Western blot and immunofluorescent staining. MIA-690 inhibited the proliferation of A-375 cells in a dose-dependent manner (33% at 10 μM, and 19.2% at 5 μM, P < 0 .05 vs. control), and suppressed the growth of xenografted tumors by 70.45% (P < 0.05). Flow cytometric analysis of cell cycle effects following the administration of MIA-690 revealed a decrease in the number of cells in G2/M phase (from 19.7% to 12.9%, P < 0.001). Additionally, Western blot and immunofluorescent studies showed that exposure of A-375 cells to MIA-690 triggered the nuclear accumulation of p27. MIA-690 inhibited tumor growth in vitro and in vivo, and increased the translocation of p27 into the nucleus thus inhibiting progression of the cell cycle. Our findings indicate that patients with malignant melanoma could benefit from treatment regimens, which combine existing chemotherapy agents and novel GHRH-antagonists.