| dc.description.abstract | This dissertation describes the development of new therapeutic leads for retinal (chapter 1-3) and infectious diseases (chapter 4). More than 40% of patients with retinal inflammatory diseases are refractory to the standard of care treatment, direct intraocular injection of anti-VEGF antibodies. The inability to effectively treat these diseases accounts for >20% of healthcare expenditures and impacts the quality of life of >30 million people in the United States alone. Considering population growth rates and aging demographics, the prevalence of retinal diseases continues to increase. Frontline approaches require frequent injections, are destructive, demand specialized facilities, suffer from poor response rates, and produce significant burdens on the healthcare system. Fenofibrate, one of two approved drugs known to agonize peroxisome proliferative-activated receptor alpha (PPARα), has demonstrated beneficial effects on DR in several experimental and clinical studies (FIELD and ACCORD). Fenofibrate, however, is a relatively weak PPARα agonist, exhibits poor selectivity over other PPAR isoforms, exhibits poor distribution to the eye, and suffers from dose-limiting side effects, all of which will preclude its use as a viable therapy for DR. I was charged with developing small molecules with improved potency and selectivity for PPARα as potential treatments for DR.
Our collaborator identified a 4-carboxy-quinoline (Y-0452) as a chemically distinct PPARα agonist and inducer. My initial optimization efforts on Y-0452 produced novel PPARα agonists that exhibit better potency (~10-fold) and efficacy (~1.5-fold increase in agonism) than both fenofibric acid (FA, the active metabolite of fenofibrate) and Y-0452 in our primary luciferase assay. More detailed biochemical evaluation of A91, the top lead from these first-generation studies, by our collaborator confirms typical downstream responses of PPARα agonism, including PPARα upregulation, induction of target genes, and inhibition of cell migration. A91 reduces retinal vascular leakage in diabetic rats – a major culprit behind diabetic macular edema and consequential vision loss. Interestingly, A91 seems to lack signs of hepatomegaly, a common side-effect of fenofibrate that may impose dose-limiting toxicity. These results provide proof-of-concept that the A91 chemotype 1) demonstrates in vivo efficacy in a relevant DR model following systemic (i.p) administration, 2) is bioavailable, 3) survives first-pass metabolism and clearance mechanisms well enough to maintain efficacy, and 4) demonstrates a relatively safe profile (no observable toxicity) after daily i.p. injection for one-month. Initial pharmacokinetic assessment of A91 reveals 1) good stability in human and rat microsomes, 2) low clearance, 3) no evidence of irreversible inhibition of any of the five major drug metabolizing CYP450s, and 4) low risk of hERG inhibition. Leveraging our structural modification approach, I developed second generation analogs that exhibit EC50 values <50 nM with >2,700-fold selectivity for PPARα over other PPAR isoforms in cellular luciferase assays. To date >200 analogs have been designed, synthesized, and evaluated for PPARα agonistic properties. This work sets the stage for future SAR campaigns on the developed and new chemotypes and sets a foundation for detailed PK/PD and preclinical assessment.
Currently, the status quo for antibiotic development is to inhibit essential processes in bacteria, thus leading to cell death. The development of chemical probes and antimicrobial agents that operate through pathway/enzyme activation, rather than inhibition, thus provides a clearly differentiated avenue to uncover new biology and represents an innovative therapeutic strategy. In this regard, caseinolytic protease P (ClpP) represents a promising new antibacterial target, as ClpP chemo-activation leads to uncontrolled proteolysis and bactericidal activity. Activation of ClpP has been validated and proven safe in vivo as an antibacterial strategy against systemic lethal infections of Enterococcus faecium, E. faecalis, Staphylococcus aureus, and Streptococcus pneumonia. In each case, activation of ClpP with a small molecule acyldepsipeptide (ADEP) outperforms clinically utilized antibiotics, including linezolid and ampicillin. Although potent ClpP activators have been identified, the structural diversity of compounds is limited. In addition, poor physicochemical properties, a limited spectrum of utility, and/or susceptibility to drug efflux pumps have hindered the clinical development of known activators. ClpP is a promising target, but new compounds are needed to allow for pre-clinical and clinical validation.
Structure-activity relationship studies of the ADEP scaffold have produced extremely potent analogs against Gram-positive pathogens. However, several physicochemical liabilities have hindered the clinical development of this class. Specifically, hydrolysis of the ADEP depsipeptide ester under basic or acidic conditions has been a major concern regarding this natural product family. One approach to address depsipeptide stability is to replace the ester linkage. Previously, our group provided direct evidence that ester to amide linkage substitution maintained the in vitro biochemical activity but resulted in a significant drop in the whole-cell activity, likely due to a disruption of a key intramolecular hydrogen bond interaction thought to influence membrane permeability.
To provide more insight into the influence of the depsipeptide core on whole-cell activity, we hypothesized that a -CH2- substitution will improve stability while maintaining the intramolecular hydrogen bond interaction. This new family of ADEP was envisioned to be accessible through a convergent approach comprised of three fragments: tripeptide, linkage, and F-Phe-heptenamide fragments. In a little over 8-months, several synthetic challenges were addressed in order to complete the total synthesis. | en_US |
