Proapoptotic activity of a monomeric smac mimetic on human fibroblast-like synoviocytes from patients with rheumatoid arthritis.

Inhibitors of apoptosis proteins (IAPs) block cell death in response to diverse stimuli. The mitochondrial protein, second mitochondria-derived activator of caspase (Smac), negatively regulates IAP inhibition of caspase activity. We investigated the proapoptotic activity of a synthetic Smac (Smac 066) on fibroblast-like synoviocytes (FLS) derived from patients with active rheumatoid arthritis (RA). We found that Smac 066 induced significant apoptosis in all RA-FLS samples. Furthermore, IAPs, which are upregulated in RA-FLS, were downregulated by Smac 066. This suggested that IAPs upregulation was responsible for RA-FLS sensitivity to Smac 066. Next, we analysed caspase activation and found that Smac 066 was associated with caspase 8 and caspase 3 activities. We then investigated the mechanism underlying Smac 066 downregulation of IAPs in RA-FLS with an apoptotic pathway array. Interestingly, Smac 066 significantly upregulated IGFBP-5, a protein involved in differentiation, apoptosis, and osteoblastic activation. Smac 066 may represent a new therapeutic approach to RA treatment.

Peptide aldehydes as inhibitors of HIV protease.

We have recently shown that alpha-MAPI, a peptidic aldehyde of microbial origin, inhibits the HIV protease with a potency comparable to pepstatin, having, differently from pepstatin, no activity on other aspartic proteases. In this study different peptide derivatives containing a C-terminal aldehyde have been tested to assess the potential of this function for the inhibition of HIV protease. The results of our analysis correspond with the recently published subsite preferences of the viral enzyme, indicating that aldehydes bind to the active site of the HIV protease. Our data suggest that peptide aldehydes can act in their hydrated forms as transition state analogues with the most potent inhibitor having an IC50 of 0.9 microM.