De Novo Design of Flavonoid-Based Mimetics of Cationic Antimicrobial Peptides: Discovery, Development, and Applications

ConspectusThe alarming rate at which pathogens are developing resistance to conventional antibiotics represents one of the major global challenges to public health care. The prevalence of multidrug-resistant microorganisms is a major impetus for the discovery and development of new antimicrobials. Nature has, to date, been the source of most of the antibiotics discovered and used, including cationic antimicrobial peptides (CAMPs). CAMPs are key components of the innate immune system that are widely found in humans, animals, plants, and microorganisms and that serve as a first line of defense for the host. The attractive features of CAMPs have led to their recognition as potential new antimicrobials. However, they possess several inherent flaws that limit their clinical application including low stability, poor oral bioavailability, poor in vivo efficacy, and a high production cost. To address these issues, small molecule-based peptidomimetic antimicrobials have been designed to biomimic the structural features and biological function of CAMPs. Plant-derived flavonoids (e.g., xanthones and flavones) are active components in traditional herbal medicines and have been reported to contain a variety of significant pharmacological actions including antibacterial, antiviral, antioxidant, and anticancer activities. Over the past decade, we have developed a new chemical strategy to design, discover, and develop xanthone- or flavone-based peptidomimetics and have designed, synthesized, and biologically evaluated a library of approximately 450 new xanthone or flavone derivatives. The designed, structurally diverse compounds can be generally classified into two subfamilies, namely, peptidic and nonpeptidic amphiphilic xanthone or flavone derivatives. In this Account, we describe our efforts on the design, synthesis, biological property evaluation, and mechanism of action model studies of synthetic mimics of CAMPs. The flavonoid compounds are an important component of these rationally designed mimics because they function as hydrophobic aromatic moieties conjugated with different length lipid moieties, behave like an unnatural hydrophobic residue, and provide a rigid scaffold, with the reduced conformational flexibility more likely to provide an active conformation. The mimics can effectively disrupt the integrity of the bacterial membranes. Our endeavors encompass design principles, chemical synthesis, in vitro screening, structural optimization, extensive structural-activity relationship analysis, and a mechanism of action study through biophysical technologies including NMR spectroscopy techniques and computer dynamics simulations, drug resistance assays, in vivo pharmaceutical kinetics (PK) analyses, and in vivo efficacy evaluations of selected promising compounds against drug-resistant bacteria and fungi. Our major contributions to the discovery and development of flavonoid-based mimics as antimicrobials include effectively addressing several limitations associated with CAMPs and have led to promising compounds with a notable potential for further development as new therapeutic antimicrobial agents for the treatment of drug-resistant bacteria- or fungi-induced infections.