Synergistic Effects of Thiosemicarbazides with Clinical Drugs against S. aureus

Abstract

Antimicrobial resistance spurred by the overuse and misuse of antibiotics is a major global health concern, and of the Gram positive bacteria, S. aureus is a leading cause of mortality and morbidity. Alternative strategies to treat S. aureus infections, such as combination therapy, are urgently needed. In this study, a checkerboard method was used to evaluate synergistic interactions between nine thiosemicarbazides (4-benzoyl-1-(2,3-dichloro-benzoyl)thiosemicarbazides 1–5 and 4-aryl-1-(2-fluorobenzoyl)thiosemicarbazides 6–9) and conventional antibiotics against S. aureus ATCC 25923, which were determined as the fractional inhibitory concentration indices (FICIs). For these experiments, amoxicillin, gentamicin, levofloxacin, linezolid, and vancomycin were selected to represent the five antimicrobial classes most commonly used in clinical practice. With one exception of 7-vancomycin combination, none of the forty-five thiosemicarbazide-antibiotic combinations tested had an antagonistic effect, showing promising results with respect to a combination therapy. The synergic effect was observed for the 2-linezolid, 4-levofloxacin, 5-linezolid, 6-gentamicin, 6-linezolid, and 7-levofloxacin combinations. No interactions were seen in combination of the thiosemicarbazide with gentamicin or vancomycin, whereas all combinations with linezolid acted in additive or synergism, except for 6-gentamicin and 7-linezolid. The 4-(4-chlorophenyl)-1-(2-fluorobenzoyl)thiosemicarbazide 6 showed a clear preference for the potency; it affected synergistically in combinations with gentamicin or linezolid and additively in combinations with amoxicillin, levofloxacin, or vancomycin. In further studies, the inhibitory potency of the thiosemicarbazides against S. aureus DNA gyrase and topoisomerase IV was examined to clarify the molecular mechanism involved in their synergistic effect in combination with levofloxacin. The most potent synergist 6 at concentration of 100 µM was able to inhibit ~50% activity of S. aureus DNA gyrase, thereby suggesting that its anti-gyrase activity, although weak, may be a possible factor contributing to its synergism effect in combination with linezolid or gentamycin.

Antibacterial Activity of Fluorobenzoylthiosemicarbazides and Their Cyclic Analogues with 1,2,4-Triazole Scaffold

“…Taking this fact into account, the results of the MBC assay are not surprising. In fact, in our previous studies [ 23 ], on the thiosemicarbazides 9a and 10a, we showed that their inhibitory action against S. aureus DNA gyrase was very weak; compound 10a was able to inhibit ~50% of S. aureus DNA gyrase activity at as high a concentration as 100 µg/mL, whereas the inhibitory activity of 9a at this concentration was even lower (~33%). Collectively, the results of the MBC assay further confirm the assumption that, for our bacteriostatic thiosemicarbazides of sets I – III, bacterial topoisomerases are not primary factors contributing to their antibacterial activity.…”

“…The synthesis of ortho -, meta -, and para -fluorobenzoylthiosemicarbazides (sets I – III ) and their cyclic analogues with a 1,2,4-triazole-5-thione scaffold (sets IV – VI ) was performed according to a well-established synthetic route, described elsewhere [ 23 , 34 ] ( Scheme 1 ). The reaction of the corresponding fluorobenzoylhydrazide with related alkyl/aryl isothiocyanate in boiling ethanol gave 1-fluorobenzoyl-4-aryl/(alkyl)thiosemicarbazides (sets I – III ) in 40–90% yields.…”

“…For these reasons, we explored the antibacterial potential within the structure–activity relationship of a library of 1-fluorobenzoyl-4-aryl(alkyl)thiosemicarbazides. Previously, we had searched for the N1 substituents which would improve the antibacterial potency of thiosemicarbazide-based compounds and had found that the fluorobenzoyl group might constitute a particularly useful series [ 23 ]. Other research groups also confirmed the thiosemicarbazide structure as a novel scaffold for potential antibacterial agents [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], although a systematic survey of the effects of the N1 and N4 terminal substituents on antibacterial potency has not been presented thus far.…”

4-Arylthiosemicarbazide Derivatives as Toxoplasmic Aromatic Amino Acid Hydroxylase Inhibitors and Anti-inflammatory Agents

“…Additionally, thiosemicarbazide derivatives are biologically active, noncytotoxic organic compounds with proven antitumor, antiviral, antifungal, and antioxidant activities [ 27 , 28 , 29 , 30 , 31 , 32 ] but are also precursors for thiosemicarbazones, which are formed by the condensation of thiosemicarbazide or substituted thiosemicarbazide at the N4 position with a suitable aldehyde or ketone [ 33 ]. Last, thiosemicarbazone derivatives were described as anti-inflammatory factors, especially in the inflammatory response mediated by nuclear factor kappa light-chain-enhancer of activated B cells (NF-κB), by inhibiting NF-κB transactivation [ 33 , 34 , 35 , 36 ].…”

Imidazole-Thiosemicarbazide Derivatives as Potent Anti-Mycobacterium tuberculosis Compounds with Antibiofilm Activity

“…Thiosemicarbazides are biologically active, noncytotoxic organic compounds with proven antitumor, antiviral, antifungal, and antioxidant activities. Furthermore, the strong antibacterial potential of various thiosemicarbazide derivatives has also been documented [ 6 , 7 , 8 , 9 , 10 ]. Although the in vitro activity of imidazolo-thiosemicarbazide against the virulent Mtb H37Rv strain has not previously been described, other than in the present study, many derivatives containing thiosemicarbazide moieties have been synthesized and evaluated for their antibacterial activity.…”