Develop A Novel P110?[E545K] Binding Peptide That Inhibits The Oncogenic P110?[E545K]-IRS1 Interaction

Protein-protein interactions(PPIs)specify a large number of key intracellular signaling pathways.Specific blockers for a PPI that is crucial for cell survival would therefore be able to suppress cell growth.If an intracellular signaling pathway harboring such PPI is hijacked by tumor cells as the key pathway for cell survival;or such signaling pathway is only present in tumor cells,the blockers for such PPI would then be able to selectively or speficially suppress the tumor cell growth.Due to the flat and extended PPI interface,it would be conceivably difficult for small molecules to be effective blockers since they may not be able to effectively bind to the interface of a PPI,in this sense,peptides would be potentially more effective blockers.However,the proteolytic liability and cellular impermeability of linear peptides in general would render them non-effective intracellular PPI blockers in general.With the advent of the peptide stapling technology which has been demonstrated to be able to stabilize the ?-helical conformation of a linear peptide via bridging two neighboring amino acid side chains with a macrocycle(or a “molecular staple”),a linear parent peptide would be transformed into a stapled peptide with a stronger PPI blocking efficacy and enhanced proteolytic stability and cellular permeability.Prof.Weiping Zheng's research group and that of Prof.Zhenghe Wang at Case Western Reserve University School of Medicine,United States,recently collaboratively identified and validated the p110?[E545K]-IRS1 interaction,a PPIuniquely present in the colon cancer cells expressing p110?[E545K] instead of the wild-type p110?,as a novel druggable anti-colon cancer target.In the study,p110?[E545K],but not p110?[H1047R],was found to gain the ability to associate with IRS1 independent of the p85 regulatory subunit of PI3K?,so as to rewire this oncogenic signaling pathway in the colon cancer cell.This newly acquired PPI and its cognate signaling pathway,which exist only in the colon cancer cells expressing p110?[E545K] instead of the wild-type p110?,has proved to be necessary and sufficient for cell growth.An 18-amino acid all-hydrocarbon [i,i+4]-stapled p110?[E545K] peptide harboring an intra-chain olefinic macrocycle was shown in the study which was published in Cancer Cell in 2013 to be able to potently inhibit the intracellular p110?[E545K]-IRS1 interaction and the growth of the xenograft tumor formed from the colon cancer cell expressing p110?[E545K].However,this 18-mer stapled peptide exhibited relatively low % ?-helicity and proteolytic stability.In this thesis work,the above-mentioned stapled peptide was used as the lead compound for further structural derivatization by the following means,which afforded compounds with higher % ?-helicity and proteolytic stability.First,while the lead compound is an all-hydrocarbon [i,i+4]-stapled peptide,its derivative stapled peptides prepared in this thesis work employed the all-hydrocarbon [i,i+7]-stapling system,and the selected [i,i+7]-stapled peptides were then shortened at both N-term and C-term giving rise to two derivatives with enhanced % ?-helicity and the inhibitory potency against the intracellular p110?[E545K]-IRS1 interaction than the lead compound.Second,in this thesis work,the simple and highly efficient bis-lactam stapling was also employed to prepare the corresponding derivative stapledpeptides(harboring an intra-chain bis-lactam macrocycle)of the lead compound,and a few of these stapled peptides were found to exhibit higher % ?-helicity than the lead compound.The results from this thesis work have helped to lay a good foundation for the development of the next-generation anti-colon cancer drugs.