One of the strategies employed by novel anticancer
therapies is to put the process of apoptosis back on track by blocking the interaction between
inhibitor of apoptosis proteins (IAPs) and
caspases. The activity of
caspases is modulated by the
caspases themselves in a
caspase/procaspase proteolytic cascade and by their interaction with IAPs.
Caspases can be released from the inhibitory influence of IAPs by proapoptotic
proteins such as secondary mitochondrial activator of
caspases (Smac) that share an IAP binding motif (IBM). The main purpose of the present study was the design and synthesis of
phosphorus-based peptidyl antagonists of IAPs that mimic the endogenous Smac
protein, which blocks the interaction between IAPs and
caspases. Based on the structure of the IAP antagonist and recently reported
thiadiazole derivatives, we designed and evaluated the biochemical properties of a series of phosphonic
peptides bearing the N-Me-Ala-Val/Chg-Pro-
OH motif (Chg: cyclohexylglycine). The ability of the obtained compounds to interact with the binding groove of the
X-linked inhibitor of apoptosis protein baculovirus
inhibitor of apoptosis protein repeat (XIAP BIR3) domain was examined by a fluorescence polarization assay, while their potential to induce autoubiquitination followed by proteasomal degradation of cellular IAP1 was examined using the MDA-MB-231
breast cancer cell line. The highest potency against BIR3 was observed among
peptides containing C-terminal phosphonic
phenylalanine analogs, which displayed nanomolar Ki values. Their antiproliferative potential as well as their proapoptotic action, manifested by an increase in
caspase-3 activity, was examined using various cell lines.