Molecular Design Implications for Esterified Therapeutic Peptides and Their Delivery Vehicles

As naturally potent molecules with low off-site toxicity, peptides have massive therapeutic potential, highlighted by successful drugs like insulin; however, their low cell membrane permeability and short in vivo half-lives prevent their clinical translation. In this thesis, we tailor both therapeutic peptides and relevant carrier systems towards overcoming these drawbacks and realizing the therapeutic potential of peptides. Historically, efforts to overcome these two drawbacks involve increasing the hydrophobicity and net cationic charge of therapeutic peptides through chemical modifications to peptide sequence, which can increase cell membrane permeability and/or enable encapsulation into relevant carriers. Yet, these modifications are often permanent, which comes at the expense of structurally-related activity or release from carriers. To reversibly modify the hydrophobicity and net cationic charge of therapeutic peptides to enable access to intracellular targets or encapsulation and release into relevant carriers, we have developed esterification of therapeutic peptides, where hydrophilic, anionic carboxylic acids are replaced with hydrophobic, but hydrolytically cleavable, ester groups. Hydrolysis of the esters enables restoration of the unesterified form of the therapeutic so as to return any structurally-related activity, a reaction that can be accelerated in the presence of endogenous esterases. In Chapter 2, we show that the number and position of esters installed onto the therapeutic peptide α carboxyl terminus 11 (αCT11, RPRPDDLEI) affect peptide hydrophobicity and hydrolytic stability of the ester caps, with the C-terminal ester being the most influential in modifying αCT11 properties. In vitro proof-of-concept experiments showed esterifying αCT11 to increase cell migration into a scratch, indicative of increased wound healing activity. In Chapter 3, we leverage the reversible increase in net cationic charge afforded by esterification to reversibly encapsulate αCT11 into polyelectrolyte complexes (PECs) through electrostatic interactions with anionic poly(methacrylic acid) (PMAA). We then study αCT11 ester hydrolysis in the presence and absence of PMAA, showing it to not only proceed slower in the presence of PMAA, but also correspond to a decrease in turbidity in mixtures of PMAA and esterified αCT11, suggesting hydrolysis to cause PEC dissociation and peptide release. In Chapter 4, we design polymer metal organic framework (MOF) composite gels, materials that combine the high sorptive capacity of MOFs into a processable polymer hydrogel template, as potential carriers for the anti-inflammatory peptide angiotensin 1-7 (Ang 1-7). Through investigating how polymer chemistry influences MOF formation and how MOF formation in turn influences gelation, we find that interactions between weakly metal-binding polymer functional groups (i.e., hydroxyls) and MOF metal nodes as well as polymer entrapment within MOF crystals simultaneously enables the formation of crystalline, self-supporting composite gels. Further, polymer-MOF composite hydrogels were capable of sorbing Ang 1-7 and showed sustained release of a small molecule dye relative to the individual polymer and MOF constituents. Altogether, this dissertation serves to influence the future design of both therapeutic peptides and their carriers, and in particular showcases the potential of therapeutic peptide esterification to reversibly tailor the properties of therapeutic peptides and expand their clinical implementation.