Date of Award
Ph.D. in Pharmaceutical Sciences
Ikhlas A. Khan
Robert J. Doerksen
University of Mississippi
ABSTRACT After the validation of our in silico models by using the previous knowledge in this area the alerting phytochemicals from two Glycyrrhiza species (G. glabra and G. uralensis) were clustered. Exhaustive computational mining of licorice metabolome against selected endocrinal and metabolic targets led to the discovery of a unique class of compounds which belong to the dihydrostilbenoids (DHS) class appended with prenyl groups at various positions. To the best of our knowledge this interesting group of compounds has not been studied for their estrogenic activities or PXR activation. In addition some of the bis-prenylated DHS have been reported to be present only in G. uralensis. Another aspect of the current project was to predict the phase I primary metabolites of compounds found in both species of Glycyrrhiza and assess them with computational tools to predict their binding potential against both isoforms of hERs or drug metabolizing enzymes such as (CYP) inhibition models. Our investigations revealed estrogenic character for most of the predicted metabolites and have confirmed earlier reports of potential CYP3A4 and CYP1A2 inhibition. Compilation of such data is essential to gain a better understanding of the efficacy/safety of licorice extracts used in various botanical formularies. This approach with the involved cheminformatic tools has proven effective to yield rich information to support our understanding of traditional practices. It also can expand the role of botanical drugs for introducing new chemical entities (NCEs) and/or uncovering their liabilities at early stages. In this work we endeavored to comprehend the mechanism associated with the efficacy and safety of components reported in the licorice plant. We utilized smart screening techniques such as cheminformatics tools to reveal the high number of secondary metabolites produced by licorice which are capable of interfering with the human Estrogen Receptors (hERs) and/or PXR or other vital cytochrome P450 enzymes. The genus Glycyrrhiza encompasses several species exhibiting complex structural diversity of secondary metabolites and hence biological activities. The intricate nature of botanical remedies such as licorice rendered them obsolete for scientific research or medical industry. Understanding and finding the mechanisms of efficacy or safety for a plant-based therapy is very challenging yet it remains crucial and warranted. The licorice plant is known to have Selective Estrogen Receptor Modulatory effects (SERMs) with a spectrum of estrogenic and anti-estrogenic activities attributed to women’s health. On the contrary licorice extract was shown to induce pregnane xenobiotic receptor (PXR) which may manifest as a potential route for deleterious effects such as herb-drug interaction (HDI). While many studies attributed these divergent activities to a few classes of compounds such as liquiritigenin (a weak estrogenic SERM) or glycyrrhizin (weak PXR agonist) no attempt was made to characterize the complete set of compounds responsible for these divergent activities. A plethora of licorice components is undermined which might have the potential to be developed into novel phytoSERMS or to trigger undesirable adverse effects by altering drug metabolizing enzymes and thus pharmacokinetics. Thus we have ventured to synthesize a set of constitutional isomers of stilbenoids and DHS (archetypal of those found in licorice) with different prenylation patterns. Sixteen constitutional isomers of stilbenoids (M2-M10) and DHS (M12-M18) were successfully synthesized of which six of them (M8 M9 M14 M15 M17 and M18) were synthesized for the first time to be further tested and validated with cell-based methods for their estrogenic activities. We have unveiled a novel class of compounds which possess a strong PXR activation. These results which were in accord with the in silico prediction were observed for multiple synthesized prenylated stilbenoid and DHS by the luciferase reporter gene assay at µM concentrations. Moreover this activation was further validated by the six-fold increase in mRNA expression of Cytochrome P450 3A4 (CYP3A4) where three representative compounds (M7 M10 and M15) exceeded the activation fold of the positive control.
Alhusban, Manal Mohammad, "Cheminformatic Approach for Deconvolution of Active Compounds in a Complex Mixture - phytoserms in Licorice" (2019). Electronic Theses and Dissertations. 1954.