AVPI analogs and conjugates: Molecular docking studies and in vitro biological evaluation

In recent years, small peptide and non-peptide AVPI-/Smac-mimetics have been developed as IAP antagonists and are in clinical trials to overcome resistance to apoptosis in various cancer types. In this study, we present molecular modeling studies and in vitro biological evaluation of a set of AVPI-mimetics, including parent AVPI, tetrapeptide AVPI-mimetics and AVPI-conjugates.

Combined molecular modeling studies and HYDE analyses provided valuable information regarding the protein–ligand interactions within the binding site of cIAP1-BIR3 and XIAP-BIR3 domains, showing that the binding part of both domains (cIAP1- and XIAP-BIR3) are formed from 22 amino acid residues, and their active part of 11 AAs. Moreover, 5 amino acids are defined common for both targets, namely Lys299, Gly306, Leu307, Trp310, and Trp323. Based on the observed docking models, six amino acid residues for cIAP1-BIR3 and five amino acids for XIAP-BIR3 are recognized actively involved in the formation of H-bonds with the respective ligand. The amino acid sequence 308 (Arg308 in cIAP1-BIR3, Thr308 in XIAP-BIR3), simultaneously forming two H-hydrogen bonds, seems to plays a key role in improvement of binding affinity.

Apart from docking results the synthesized set of AVPI-mimetics was tested in vitro using cell biology (MTT assay) and parallel artificial membrane permeability assay (PAMPA). The results showed that the double modification of AVPI via substitution of Pro³ with Hyp³, as well as elongation of AVPI’s C-terminus by its conjugation with RGD-analogs, significantly increase the antiproliferative effects of AVPI-conjugates on all tested cancer cell lines (MDA-MB-231, MCF-7, HepG2 and HT-29 cells) compared to the parent AVPI peptide. SARs analysis defined this modification beneficial for the overall biological activity of the AVPI-mimetics and pointed out AVHypI-AgbGD as the most active conjugate with an IC₅₀ of 348 µM for MDA-MB-231, 457 µM for MCF-7, 399 µM for HepG2, and 578 µM for HT-29 cells. Though the calculated IC₅₀ values were still high, we consider AVHypI-AgbGD peptide as a good basis for further modifications. In addition, PAMPA results showed that substitution of Pro with Hyp improved the BBB permeability of AVHypI peptide compared to its parent molecule.