The identification of peptide precursors of two bradykinin-like peptides from the protective skin secretion of a North American frog, and assessment of their activity from both a physiological and an anti-cancer perspective

• Main Author: McCrudden, Cian Michael
• Published: Queen's University Belfast 2008
• Subjects: 572
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485004

To protect themselves from predation, frogs produce and secrete venom that contains bioactive peptides that oft~n mimic those of their mammalian predators. Bradykinin (BK) (RPPGFSPFR) is a nonapeptide that elicits vasodilation, smooth muscle contraction and inflammation in mammals, and it is. present in the protective ·secretions of even the' most primitive frogs. BK is known to be involved in a range of pathological conditions including cancer by proliferation induction and stimulation of angiogenesis. This thesis documents the determination of the therapeutic potential oftwo previously identified BKlike peptides (I-ll-R and R-I3-R) from Ranapalustris venom. Molecular cloning of peptide precursor cDNA from Rana palustris venom revealed that this frog produces a wide range of BK-Iike peptides in a very economical manner, with eight peptides (including I-II-R and R-13-R) being encoded by three precursor cDNAs of 1,076, 812 and 680 bp. I-II-R and R-I3-R did not evoke a BK-like response in rat aorta, tail artery or ileum. Rather, they inhibited the BK response competitively and dose-dependently, and acted at both the B1 and B2 BK receptors. Both I-II-R and R-13-R inhibited the migration of, and formation of tubules by, human endothelial cells, and limited the development of , . vessel-like structures originating from rat aortic ring explants. Both also inhibited BK-elicited proliferation of prostate (PC3 and DUI45) and breast (MCF-7) cancer cell lines. In MCF-7, antagonism of the BK receptors with I-II-R and R-13-R before BK exposure resulted in a drop in quiescent cell number, and slowed the proliferation rate of dividing cells. Due to the probable susceptibility of 1- t'I-R and R-13-R to protease degradation, the potential of these peptides may be limited, however their anti-angiogenic and anti-cancer abilities could make them interesting drug leads.