Cationic steroid antimicrobials (CSAs or ceragenins) are a novel class of synthetic, cholic acid-based mimics of endogenous antimicrobial peptides. These small molecule compounds display broad bactericidal activity against gram-negative and gram-positive bacteria, potent ability against fungal pathogens, and cidal effects against drug resistant and multidrug resistant microbes. Implantable medical devices provide an abiotic surface upon which bacteria and fungi can accumulate--thereby leading to localized or systemic infection. We proposed that CSA antibiotics can be incorporated into medical device surface coatings which can be optimized for the active release or elution of the CSA compounds over time to prevent device-associated infections. This report will discuss the progress of developing and testing coating systems for 3 such devices: cardiac implantable electronic devices (CIED), silicone nasal splints, and breast tissue expanders. In the case of CIEDs, an envelope material containing CSA was created using bioresorbable polymers. We found that this envelope elutes CSA antibiotics and kills all surrounding bacteria or fungi in both planktonic and biofilm forms within 1 hour of exposure. We also developed a nasal splint coating which is directly adhered to the surface of the silicone splint. This coating system demonstrated more than 8 days of protective ability (full microbicidal activity to the detection limit) against Candida albicans, and reduced microbial growth of P. aeruginosa, Candida auris, and MRSA for approximately 6 days. Lastly, in the case of tissue expanders, we developed a layered coating which displays fully-reductive antimicrobial activity against MRSA for 8 days with reintroduction of bacteria every 24 hours. Additionally, this work will discuss our investigations into the secondary properties of ceragenin compounds. On the basis of studies which have demonstrated the pro-osteogenic properties of CSA, we probed the mechanism of this effect. We studied the potential effects of ceragenins on the proliferation, differentiation, and migration of bone-derived mesenchymal stem cells (MSCs). We have determined the absence of any positive proliferative effects of ceragenins on these cells; however, we have demonstrated the significant migration-promoting chemoattractant properties of CSA. In the case of CSA-13, we have observed up to a 400% increase in migration compared to the control. Also, we demonstrated that the P2X7 receptor is strongly implicated in the cellular mechanism of this effect. Our studies of the differentiation-promoting properties of CSA on MSCs have been largely inconclusive, but further investigations are proposed in this report. Lastly, this work includes a report on our investigations into the potential synergistic interactions between CSA-131/CSA-44 with amphotericin B or caspofungin, two commonly used antifungal agents.

CHAPTER 1 Aggregation of receptors for IgE (Fc RI) causes mast cells and basophils to release preformed contents of granules, including histamine and a variety of enzymes. This process, called degranulation plays a central role in allergic reactions. Methods to study this process are to create multivalent ligands which can interact with the receptors and, in turn, lead to aggregation of the receptors. We prepared a series of fluorophore-labeled divalent and trivalent antigens to study the degranulation of mast cells. Trivalent antigens proved to be much better stimulators for degranulation of mast cells than divalent antigens. These results indicate that aggregates formed by trivalent antigens are more complicated than those of divalent antigens. CHAPTER 2 Membrane-active antibiotics include antimicrobial peptides (AMPs) and a class of amphiphilic steroids termed ceragenins. Recent studies of membrane-active antibiotics show that cationic, facially amphiphilic molecules could disrupt bacterial membranes. It was found recently that some antibiotics, including AMPs and ceragenins, may share both antibacterial and antiviral activity. We prepared a series of ceragenins to optimize the antiviral activity of ceragenins against vaccinia virus (VV). The results show that ceragenins exhibit potent activity against VV, protect keratinocytes against VV-mediated cell death, and preferentially target the virus. It also shows that antibacterial and antiviral activities do not correlate with each other. Although ceragenins show good antiviral activity against VV, the mechanism for this activity still remains unclear.

The continuous emergence of drug-resistance pathogens is a global concern. As a result, substantial effort is being expended to develop new therapeutics and mechanisms for controlling microbial growth to avoid entering a "post-antibiotic" era in which commonly used antibiotics are no longer effective in treating infections. In this work, we investigate the efficacy and application of ceragenins as non-peptide mimics of antimicrobial peptides (AMPs). First, this work examines the susceptibility of drug-resistant Gram-negative bacteria. The susceptibility of colistin-resistant clinical isolates of Klebsiella pneumoniae to ceragenins and AMPs suggests that there is little to no cross-resistance between colistin and ceragenins/AMPs. Furthermore, Lipid A modifications are found in bacteria with modest changes in susceptibility to ceragenins and with high levels of resistance to colistin. Next, we investigated the potential for cross resistance between chlorhexidine, colistin, AMPs and ceragenins as repeated exposure of bacteria to chlorhexidine might result in cross resistance with colistin, AMPs or ceragenins. Furthermore, a proteomics study on the chlorhexidine-resistant strains showed that chlorhexidine resistance is associated with upregulation of proteins involved in the assembly of LPS for outer membrane biogenesis and virulence factors in Pseudomonas aeruginosa.Second, this dissertation describes the antifungal activity of ceragenins against an emerging multidrug-resistant fungus, Candida auris. We found that lead ceragenins displayed activities comparable to known antifungal agents against C. auris isolates. We also found that fungal cell morphology was altered in response to ceragenin treatment, that ceragenins exhibited activity against sessile organisms in biofilms, and that gel and cream formulations including CSA-44 and CSA-131 resulted in a significant log reduction against established fungal infections in ex vivo mucosal tissues. Finally, a hydrogel film containing CSA-131 was generated on endotracheal tubes (ETTs). ETTs provide an abiotic surface on which bacteria and fungi form biofilms that cause serious infections. In this study, the eluting ceragenin prevented fungal and bacterial colonization of coated ETTs for extended periods while uncoated tubes were colonized by bacteria and fungi. Coated tubes were well tolerated in intubated pigs. The ability of ceragenins to eradicate established biofilms make them attractive potential therapeutics for persistent infections in the lung, including those associated with cystic fibrosis. In ex vivo studies, we initially found that this ceragenin, at concentrations necessary to eradicate established biofilms, also causes loss of cilia function. However, by formulating CSA-131 in poloxamer micelles, cilia damage was eliminated and antimicrobial activity was unaffected. These findings suggest that CSA-131, formulated in micelles, may act as a potential therapeutic for polymicrobial and biofilm-related infections in the lung and trachea.