An Improved Small-Molecule Inhibitor of FtsZ with Superior In Vitro Potency, Drug-Like Properties, and In Vivo Efficacy

Abstract

The bacterial cell division protein FtsZ is an attractive target for small-molecule antibacterial drug discovery. Derivatives of 3-methoxybenzamide, including compound PC190723, have been reported to be potent and selective antistaphylococcal agents which exert their effects through the disruption of intracellular FtsZ function. Here, we report the further optimization of 3-methoxybenzamide derivatives towards a drug candidate. The in vitro and in vivo characterization of a more advanced lead compound, designated compound 1, is described. Compound 1 was potently antibacterial, with an average MIC of 0.12 g/ml against all staphylococcal species, including methicillin-and multidrug-resistant Staphylococcus aureus and Staphylococcus epidermidis. Compound 1 inhibited an S. aureus strain carrying the G196A mutation in FtsZ, which confers resistance to PC190723. Like PC190723, compound 1 acted on whole bacterial cells by blocking cytokinesis. No interactions between compound 1 and a diverse panel of antibiotics were measured in checkerboard experiments. Compound 1 displayed suitable in vitro pharmaceutical properties and a favorable in vivo pharmacokinetic profile following intravenous and oral administration, with a calculated bioavailability of 82.0% in mice. Compound 1 demonstrated efficacy in a murine model of systemic S. aureus infection and caused a significant decrease in the bacterial load in the thigh infection model. A greater reduction in the number of S. aureus cells recovered from infected thighs, equivalent to 3.68 log units, than in those recovered from controls was achieved using a succinate prodrug of compound 1, which was designated compound 2. In summary, optimized derivatives of 3-methoxybenzamide may yield a first-in-class FtsZ inhibitor for the treatment of antibiotic-resistant staphylococcal infections.

In Vivo Pharmacodynamic Evaluation of an FtsZ Inhibitor, TXA-709, and Its Active Metabolite, TXA-707, in a Murine Neutropenic Thigh Infection Model

“…Note that methoxybenzamide derivatives have been shown to be equipotent against susceptible as well as beta-lactam-resistant S. aureus isolates (53). Indeed, we found a very narrow MIC range with similar potencies for MSSA and MRSA isolates, similarly to previous reports.…”

“…Prior in vivo study of methoxybenzamide compounds which inhibit FtsZ was limited to a few proof-of-concept studies (14,52,53). In two of these studies, a single dose of the study compound led to improved survival in a murine methicillin-susceptible S. aureus (MSSA) septicemia model, whereas a third study demonstrated a decrease in bacterial burden for a single dose in a murine MSSA thigh model.…”

Strategies for Circumventing Bacterial Resistance Mechanisms

“…) in vitro, oral activity in infection models, and an acceptable frequency of FtsZ point mutation resistance selection (4.1 Â 10 À9 ) given the evidence for impaired in vitro fitness accompanying the point mutation (Stokes et al 2013). PC190723 also acts synergistically with b-lactam antibiotics against S. aureus, possibly as a result of mislocalization of FtsZ with concomitant disruption of its binding partner (and target of the b-lactams), the PBP bifunctional enzyme(s) (Tan et al 2012).…”

Small molecules targeting at the bacterial cell division protein FtsZ as potential antimicrobial agents

“…The C5 position of the oxazole moiety can be modified with alkyl, aryl or halogen substituents to achieve higher potency. In this series of compounds, 5-bromo-and 5-chlorooxazolyl analogs exhibit high activity against a mutant strain of S. aureus, G196A [94,95]. To increase the pharmacokinetic parameters of the compounds, polar groups such as alcohol, amine, carboxylic acid and heterocycles were incorporated to the pseudobenzylic position (−CH(R)−O− moiety).…”

“…In order to further increase the solubility of compound 18, a prodrug 19 was synthesized. The solubility of 19 was 2-fold higher than its parent compound [94,95] To further increase the pharmacological properties of PC190723, Pilch and coworkers synthesized 1-methylpiperidine-4-carboxamide TXY541 (20, Figure 4), which is a prodrug of PC190723. The compound was effective against MRSA [96].…”