Synergetic Antimicrobial Activity and Mechanism of Clotrimazole-Linked CO-Releasing Molecules

Abstract

Several metal-based carbon monoxide-releasing molecules (CORMs) are active CO donors with established antibacterial activity. Among them, CORM conjugates with azole antibiotics of type [Mn(CO) 3 (2,2′-bipyridyl)(azole)] + display important synergies against several microbes. We carried out a structure−activity relationship study based upon the lead structure of [Mn(CO) 3 (Bpy)(Ctz)] + by producing clotrimazole (Ctz) conjugates with varying metal and ligands. We concluded that the nature of the bidentate ligand strongly influences the bactericidal activity, with the substitution of bipyridyl by small bicyclic ligands leading to highly active clotrimazole conjugates. On the contrary, the metal did not influence the activity. We found that conjugate [Re(CO) 3 (Bpy)(Ctz)] + is more than the sum of its parts: while precursor [Re(CO) 3 (Bpy)Br] has no antibacterial activity and clotrimazole shows only moderate minimal inhibitory concentrations, the potency of [Re(CO) 3 (Bpy)(Ctz)] + is one order of magnitude higher than that of clotrimazole, and the spectrum of bacterial target species includes Gram-positive and Gram-negative bacteria. The addition of [Re(CO) 3 (Bpy)(Ctz)] + to Staphylococcus aureus causes a general impact on the membrane topology, has inhibitory effects on peptidoglycan biosynthesis, and affects energy functions. The mechanism of action of this kind of CORM conjugates involves a sequence of events initiated by membrane insertion, followed by membrane disorganization, inhibition of peptidoglycan synthesis, CO release, and break down of the membrane potential. These results suggest that conjugation of CORMs to known antibiotics may produce useful structures with synergistic effects that increase the conjugate's activity relative to that of the antibiotic alone.

Antimicrobial Activity of Rhenium Di- and Tricarbonyl Diimine Complexes: Insights on Membrane-Bound S. aureus Proteins Binding

“…ranging from ca. -9 to -11 kcal/mol) are fully consistent with the experimental results reported by Wenzel et al [31] and Mendes et al [48], in that inhibition of these proteins would lead to membrane disorganization and affect peptidoglycan/wall biosynthesis [76,[80][81][82][83][84].…”

“…compound 14 in Figure 4, targets the cytoplasmic membrane of Bacillus subtilis, affecting its architecture and disrupting essential cellular processes taking place at the membrane, such as respiration, and cell wall biosynthesis and integrity [31]. Similarly Mendes et al have shown that the mechanism of action of the fac-[Re(CO)3(bpy)(ctz)] + complex (17 in Figure 4, where ctz = the drug clotrimazole) involves a sequence of events initiated by membrane insertion, followed by membrane disorganization, inhibition of peptidoglycan biosynthesis, and break down of the membrane potential [48].…”

“…We found that none of the dicarbonyl complexes showed antimicrobial potential. Only compounds 4b, 5b and 11 were weakly active against S. aureus strains, but their MIC values (25 and 50 µM, respectively) are much higher than active rhenium complexes 13-19 (Figure 4) [32,33,[48][49][50]. [33]; complex 14 [32]; complexes 15, 16, 18 and 19 [49,50]; complex 17 [48].…”

“…In the last decade, complexes of virtually all transition metals have been evaluated as antimicrobial agents [25][26][27][28], with rhenium (Re), among others [29,30], showing promising potential for new antibiotic development [31][32][33][34]. While some transition metal complexes [35][36][37][38][39][40], predominantly of group 8 [41][42][43] and 9 [44][45][46][47], act against Gram-negative bacteria, carbonyl rhenium complexes have demonstrated very potent activity towards Gram-positive pathogens, particularly towards Staphylococcus aureus involving both methicillin-resistant (MRSA) and methicillin-sensitive (MSSA) strains [32][33][34][48][49][50].…”

Metal Complexes as Antifungals? – From a Crowd-Sourced Compound Library to First In Vivo Experiments

“…The few in-depth studies on the mechanism of action of metallobiotics in recent years have indicated that metal compounds are likely to affect multiple targets inside of microbes. 17,26,[112][113] This makes them well suited to avoid rapid resistance development but also increases the difficulty in narrowing down their exact mode of action. 114 On behalf of CO-ADD we invite researchers around the world to submit their (well characterized) metal complexes for antimicrobial testing to advance our collective knowledge on this promising and underexplored compound class.…”