SYNTHESIS AND CHARACTERIZATION OF MODIFIED BH3 PEPTIDES
Hector Nieves-Rosado1, Amy Keating2.
1University of Puerto Rico, Mayaguez Campus, Mayaguez, PR, 2Massachusetts Institute of Technology, Cambridge, MA.
A series of small molecules and engineered peptides that inhibit some anti-apoptotic Bcl-2 proteins have been identified; however, they are not effective against cells that overexpress Mcl-1. Hence, the effort to abrogate the cancer cell survival triggered by Mcl-1 is a major focus in experimental therapeutics. One approach uses pro-death BH3 peptides to re-establish mitochondrial sensitivity. However, the application of small peptides to block cancer has been hindered by some characteristic features of natural peptides such as loss of their natural architecture and protease degradation. The goal of this project was to optimize a promising lead peptide inhibitor of Mcl-1 using unnatural elements to provide enhanced peptide stability and affinity. A side-chain, lactam bridge, linking i with i + 4 spaced amino acid pairs is a powerful helix-stabilizing tool for inhibitors that bind their receptors in an a-helical conformation. Therefore, selected lactam bridged BH3 peptides were prepared by solid-phase synthesis. Biophysical analysis of these peptides in solution confirmed helical contents of these peptides. Remarkably, the ability to inhibit Mcl-1 was reduced in lactam-bridged peptides in comparison with i, i + 4 hydrocarbon-stapled analogue. Moreover, new peptides including bulky and helix-inducing nonnatural amino acids that can potentially improve binding to Mcl-1 were synthesized and characterized.