Amelioration of an undesired action of deguelin

Abstract

The pharmaceutical world has greatly benefited from the well-characterized structure-function relationships of toxins with endogenous biomolecules, such as ion-channels, receptors, and signaling molecules. Thus, therapeutics derived from toxins have been aggressively pursued. However, the multifunctional role of various toxins may lead to undesirable off-target effects, hindering their use as therapeutic agents. In this paper, we suggest that previously unsuccessful toxins (due to off-target effects) may be revisited with mixtures by utilizing the pharmacodynamic response to the potential primary therapeutic as a starting point for finding new targets to ameliorate the unintended responses. In this proof of principle study, the pharmacodynamic response of HepG2 cells to a potential primary therapeutic (deguelin, a plant-derived chemopreventive agent) was monitored, and a possible secondary target (p38MAPK) was identified. As a single agent, deguelin decreased cellular viability at higher doses (> 10 μM), but inhibited oxygen consumption over a wide dosing range (1.0 – 100 μM). Our results demonstrate that inhibition of oxygen consumption is related to an increase in p38MAPK phosphorylation, and may only be an undesired side effect of deguelin (i.e., one that does not contribute to the decrease in HepG2 viability). We further show that deguelin’s negative effect on oxygen consumption can be diminished while maintaining efficacy when used as a therapeutic mixture with the judiciously selected secondary inhibitor (SB202190, p38MAPK inhibitor). These preliminary findings suggest that an endogenous response-directed mixtures approach, which uses a pharmacodynamic response to a primary therapeutic to determine a secondary target, allows previously unsuccessful toxins to be revisited as therapeutic mixtures.

Deguelin exerts potent nematocidal activity via the mitochondrial respiratory chain

“…Complex I is involved in both oxidative phosphorylation and the phosphoenolpyruvate carboxykinase-succinate pathway, which could account for the increased gene expression in both respiratory pathways. The proposal that deguelin is a complex I inhibitor in H. contortus is consistent with previous results for mammalian cells (6,32,33) and with the current observation of a substantial increase in transcription linked to energy metabolism-related pathways-that is, oxidative phosphorylation, citric acid cycle, mitoribosome biosynthesis, and glycolysis-24 h before a significant reduction in worm motility, most likely reflecting a compensatory/negative feedback response to the inhibition of complex I. We tested this hypothesis by using a fluorescent dye that is sequestered by active mitochondria and assessed mitochondrial activity in response to various concentrations of deguelin at 48 h. Here, exposure of H. contortus to high concentrations of deguelin ablated the activity of mitochondria, whereas low concentrations of deguelin increased their activity, which supports the RNA sequencing results.…”

“…Although most of the up-regulated pathways in deguelin-treated worms represent aerobic respiration, anaerobic pathways were also identified as being significantly up-regulated and associated with carbon fixation and glycolysis. On the basis of these findings and what is already known about the mode of action of deguelin in other organisms (6,32,33), we hypothesize that deguelin induces a loss in parasite viability, mainly by modulating or disrupting the function of the oxidative phosphorylation pathway, likely acting as a complex I inhibitor of the electron transport chain. Complex I is involved in both oxidative phosphorylation and the phosphoenolpyruvate carboxykinase-succinate pathway, which could account for the increased gene expression in both respiratory pathways.…”

“…Particularly over the past 2 decades, there has been a considerable focus on studying deguelin as a chemopreventative, since the discovery of its antiproliferative properties on cells (70). These properties have been attributed to the modulation of myriad molecular pathways in various cancer cell types (6,13,17,(24)(25)(26)(27)(28)(29)(30)(31)(32)(33), and the question arose as to whether deguelin might also have antiparasitic effects.…”

“…For many years, relatively disappointing results were obtained using the latter approach; however, today, this approach is highly successful (4). Recognition that biologically relevant chemical diversity is crucial-combined with progress in genomics, bioinformatics-the biosynthesis of natural products and the availability of advanced analytical techniques are ABBREVIATIONS: IC 50 , 50% inhibitory concentration; KEGG, Kyoto Encyclopedia of Genes and Genomes; LB, Luria Bertani; L3, third-stage larva; L4, fourthstage larva; NFF, neonatal foreskin fibroblast;NGM,nematodegrowthmedium; SEM, scanning electron microscopy; SI, selectivity index; TMRE, tetramethylrhodamine ethyl ester; UPR mt , mitochondrial unfolded protein response At the biochemical level, deguelin has been demonstrated to inhibit phorbol ester-induced ornithine decarboxylase activity (6,13) as well as oxygen consumption by down-regulating NADH:ubiquinone or complex I of the m i t o c h o n d r i a le l e c t r o nt r a n s p o r tc h a i ni nb o v i n eh e a r t cells, a human breast cancer cell line (MCF- 7), and a human liver carcinoma cell line (HepG2) (6,32,33). In contrast, nothing is known about how deguelin affects parasitic nematodes.…”

Suppressive function of low‐dose deguelin on the invasion of oral cancer cells by downregulating tumor necrosis factor alpha–induced nuclear factor‐kappa B signaling

“…As a single agent, deguelin decreased cellular viability at higher doses (>1 µM), but inhibited the activities of some signaling molecules over a wide dosing range (0.1–10 µM). Unfortunately, treatment of deguelin at high dose exhibits undesirable side effects, such as respiratory depression and cardiotoxicity . Recently, a number of studies showed that low dose of deguelin (<1 µM) preserved its antitumor activity in triple‐negative breast cancer, lung cancer, colon cancer, and glioblastoma multiforme .…”