Developing macrocyclic peptides that can reach intracellular targets is a significant challenge. This review discusses the most recent strategies used to develop cell permeable cyclic peptides that maintain binding to their biological target inside the cell. Macrocyclic peptides are unique from small molecules because traditional calculated physical properties are unsuccessful for predicting cell membrane permeability. Peptide synthesis and experimental membrane permeability is the only strategy that effectively differentiates between cell permeable and cell impermeable molecules. Discussed are chemical strategies, including backbone N‐methylation and stereochemical changes, which have produced molecular scaffolds with improved cell permeability. However, these improvements often come at the expense of biological activity as chemical modifications alter the peptide conformation, frequently impacting the compound's ability to bind to the target. Highlighted is the most promising approach, which involves side‐chain alterations that improve cell permeability without impact binding events.
Recent cancer therapies have focused on targeting biology networks through a single regulatory protein. Heat shock protein 90 (hsp90) is an ideal oncogenic target as it regulates over 400 client proteins and cochaperones. However, clinical inhibitors of hsp90 have had limited success; the primary reason being that they induce a heat shock response. We describe the synthesis and biological evaluation of a new hsp90 inhibitor, SM253. The previous generation on which SM253 is based (SM145) has poor overall synthetic yields, low solubility, and micromolar cytotoxicity. By comparison SM253 has relatively high overall yields, good aqueous solubility, and is more cytotoxic than its parent compound. Verification that hsp90 is SM253's target was accomplished using pull-down and protein folding assays. SM253 is superior to both SM145 and the clinical candidate 17-AAG as it decreases proteins related to the heat shock response by 2-fold, versus a 2-4-fold increase observed when cells are treated with 17-AAG.
The design, synthesis, and cell permeability of 19 hydrophilic macrocyclic peptides is presented. By systematically analyzing the impact of three different approaches (alkylated amino acids, asparagines, and d-amino acids) on the permeability of polar peptides, a well-defined strategy for optimizing cell permeability is provided. These three new methods can be used individually or in combination to effectively convert polar peptides into cell permeable molecules, and the results can be applied to the rapidly expanding peptide therapeutic industry.
Sixteen linear and cyclic peptides were designed de novo to target the C-terminus of heat shock protein 90 (Hsp90). Protein binding data indicates that three compounds directly block co-chaperone access to Hsp90's C-terminus and luciferase renaturation assays confirm Hsp90-mediated protein folding is disrupted. This is the first report of an inhibitor that binds directly to the C-terminal MEEVD region of Hsp90.
Herein, we describe
the synthesis and structure–activity
relationships of cyclic peptides designed to target heat shock protein
90 (Hsp90). Generating 19 compounds and evaluating their binding affinity
reveals that increasing electrostatic interactions allows the compounds
to bind more effectively with Hsp90 compared to the lead structure.
Exchanging specific residues for lysine improves binding affinity
for Hsp90, indicating some residues are not critical for interacting
with the target, whereas others are essential. Replacing l- for d-amino acids produced compounds with decreased binding
affinity compared to the parent structure, confirming the importance
of conformation and identifying key residues most important for binding.
Thus, a specific conformation and electrostatic interactions are required
in order for these inhibitors to bind to Hsp90.
Described are the design, synthesis, and biological evaluation of 5 N‐methylated analogs that are based on a lead drug structure LB51. LB51 is a cyclic pentapeptide that inhibits heat shock protein 90 and although a potent inhibitor of the protein function, it has poor cell permeability. Introduction of an N‐methyl moiety at each amino acid produces 5 analogs of LB51, where all 5 show significantly improved membrane permeability over the lead molecule despite the presence of 4 highly polar side chains.
Macrocycles have several advantages over small-molecule drugs when it comes to addressing specific protein-protein interactions as therapeutic targets. Herein we report the synthesis of seven new cyclic peptide molecules and their biological activity. These macrocycles were designed to understand how moving an N-methyl moiety around the peptide backbone impacts biological activity. Because the lead non-methylated structure inhibits the oncogenic regulator heat-shock protein 90 (Hsp90), two of the most potent analogues were evaluated for their Hsp90 inhibitory activity. We show that incorporating an N-methyl moiety controls the conformation of the macrocycle, which dramatically impacts cytotoxicity and binding affinity for Hsp90. Thus, the placement of an N-methylated amino acid within a macrocycle generates an unpredictable change to the compound's conformation and hence biological activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.