Design, Synthesis, and Evaluation of Potent, Nonpeptidic Mimetics of Second Mitochondria-Derived Activator of Caspases

Abstract

A series of new Smac mimetics have been designed, synthesized and evaluated. The most potent compound 10 binds to XIAP, cIAP-1 and cIAP-2 BIR3 proteins with K i values of 3.9, 0.37 and 0.25 nM, respectively. Compound 10 antagonizes XIAP in a cell-free functional assay and induces rapid cIAP-1 degradation in cancer cells. Compound 10 inhibits cell growth in the MDA-MB-231 cancer cell line with an IC 50 value of 8.9 nM.Apoptosis is a critical cell process in normal development and homeostasis of multicellular organisms to eliminate unwanted or damaged cells. Evasion of apoptosis is now recognized as a hallmark of all cancers. 1-2 Targeting key apoptosis regulators with a goal to promote apoptosis in cancer cells is a new strategy for anticancer drug design. [3][4] Inhibitor of apoptosis proteins (IAPs) a are a class of key apoptosis regulators. 5,6 Among them, cellular IAP-1 (cIAP-1) and cIAP-2 play a critical role in regulation of tumor necrosis factor (TNF) receptor-mediated apoptosis, 7 and X-linked IAP (XIAP) is a central regulator of both death-receptor-mediated and mitochondria-mediated apoptosis pathways. 8 XIAP inhibits apoptosis through direct binding to and inhibition of three cysteine proteases, an initiator caspase-9 and the two effectors caspase-3 and -7. 5,6 XIAP contains three Baculoviral IAP Repeats (BIR) domains. While the third BIR domain (BIR3) of XIAP selectively targets caspase-9, the BIR2 domain, together with the immediate preceding linker, inhibits both caspase-3 and caspase-7. 6,8 Since these caspases play a critical role in the execution of apoptosis, XIAP functions as an efficient inhibitor of apoptosis. 6,8 Accordingly, these IAP proteins, especially XIAP, are considered as promising cancer therapeutic targets. [8][9] Smac (Second Mitochondria-derived Activator of Caspases) is a potent pro-apoptotic protein and an endogenous antagonist of IAP proteins. 10,11 Previous studies have firmly established that Smac interacts with XIAP and cIAP-1/2 proteins via its AVPI tetra-peptide motif. 15 Smac, in its dimeric form, interacts with both BIR2 and BIR3 domains in XIAP and effectively removes the inhibition of XIAP to not only caspase-9 but also caspase-3/-7.In the last few years, intense research efforts have been devoted to the design and development of small molecules to mimic the AVPI binding motif as antagonists of IAP proteins and as a new class of anticancer drugs. 4,[16][17][18][19][20][21][22][23] These small molecules are called Smac mimetics. To date, two different types of Smac mimetics have been reported, namely monovalent and bivalent Smac mimetics ( Figure 1). 4,[16][17][18][19][20][21][22][23] Monovalent Smac mimetics such as 1-4 are designed to mimic a single AVPI binding motif, [16][17][18][19] whereas the bivalent compounds, such as 5 and 6, contain mimetics of two AVPI binding motifs tethered together through a linker. 4,[20][21][22][23] Bivalent Smac mimetics can achieve much higher affinities to XIAP and can be much more potent than the corresponding monovalent Sma...

Inhibitor of apoptosis protein family as diagnostic markers and therapeutic targets of colorectal cancer

“…44 Since then, intense efforts have been made in many laboratories to develop small molecules to mimic the AVPI binding motif as antagonists of IAP molecules, and these agents are now collectively referred to as Smac mimetics. 45 Among these agents, AT-406, 46 developed by Ascenta Therapeutics, is the fi rst Smac mimetic registered for clinical trials ( Table 2) In addition, fucoxanthin and fucoxanthinol, which are classifi ed as carotenoids, could be potentially useful therapeutic agents targeting the IAP family. Other new drugs under development targeting the IAP family include (1) SPC3042, which is a 16-mer locked ASO, (2) capped tripeptide XIAP antagonists from Abbott Laboratories, (3) TWX024, which is a nonpeptide smallmolecule inhibitor of BIR2/caspase-3 interaction, and (4) embelin, which is an herbal cell-permeable XIAP inhibitor.…”

Theoretical studies on the interactions of XIAP-BIR3 domain with bicyclic and tricyclic core monovalent Smac mimetics

“…1. The chemical structures of Smac mimetics are shown in Table 1, which are taken from the experiments of Wang's groups [26][27][28]. Geometries of Smac mimetics were fully optimized using Gaussian 03 program [31] at the level of B3LYP/6-31G.…”

“…Since monovalent Smac mimetics are of lower molecular weight and good bioavailability, intense efforts have focused on designing and synthesizing monovalent mimetics [22], of which Wang's groups reported a number of conformationally constrained bicyclic Smac mimetics [22][23][24][25]. To improve the cell activity of these mimetics, they modified them by using a structure-based approach to generate a series of new anticancer drugs [26][27][28]. They found these structurally diverse mimetics exhibited distinct cell activity.…”

“…Although Wang's groups have predicted the binding sites of some Smac mimetics by molecular modeling [26,28], and Yang et al have calculated the binding free energy of some mimetics [29], the specific binding modes and different structural effect on the binding were not addressed. We previously reported the mechanism of bicyclic core Smac mimetics interacting with XIAP-BIR3 domain [30], which indicated that the bicyclic core segments of mimetics play important roles for ligand binding, and only one of two terminal phenyls locates in the hydrophobic pocket.…”

“…However, how the modifications on the bicyclic core segments and terminal groups affect the interactions between Smac mimetics and XIAP-BIR3 has not been discussed theoretically in detail. Based on the modifications on the bicyclic core segment and terminal group of mimetics designed by Wang's group [26][27][28], we used docking and molecular dynamics simulations to investigate the interactions of these mimetics with XIAP-BIR3, and gained an insight into the effect of structural variations of bicyclic core segments on their binding affinity and binding modes, which may be helpful for designing and synthesizing novel anticancer drugs.…”