In vitro and in vivo profiles of ACH-702, an isothiazoloquinolone, against bacterial pathogens.

ACH-702, a novel isothiazoloquinolone (ITQ), was assessed for antibacterial activity against a panel of Gram-positive and Gram-negative clinical isolates and found to possess broad-spectrum activity, especially against antibiotic-resistant Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA). For Gram-negative bacteria, ACH-702 showed exceptional potency against Haemophilus influenzae, Moraxella catarrhalis, and a Neisseria sp. but was less active against members of the Enterobacteriaceae. Good antibacterial activity was also evident against several anaerobes as well as Legionella pneumophila and Mycoplasma pneumoniae. Excellent bactericidal activity was observed for ACH-702 against several bacterial pathogens in time-kill assays, and postantibiotic effects (PAEs) of >1 h were evident with both laboratory and clinical strains of staphylococci at 10 × MIC and similar in most cases to those observed for moxifloxacin at the same MIC multiple. In vivo efficacy was demonstrated against S. aureus with murine sepsis and thigh infection models, with decreases in the number of CFU/thigh equal to or greater than those observed after vancomycin treatment. Macromolecular synthesis assays showed specific dose-dependent inhibition of DNA replication in staphylococci, and biochemical analyses indicated potent dual inhibition of two essential DNA replication enzymes: DNA gyrase and topoisomerase IV. Additional biological data in support of an effective dual targeting mechanism of action include the following: low MIC values (≤0.25 µg/ml) against staphylococcal strains with single mutations in both gyrA and grlA (parC), retention of good antibacterial activity (MICs of ≤0.5 µg/ml) against staphylococcal strains with two mutations in both gyrA and grlA, and low frequencies for the selection of higher-level resistance (<10⁻¹°). These promising initial data support further study of isothiazoloquinolones as potential clinical candidates.

Selenophene-containing inhibitors of type IIA bacterial topoisomerases.

We investigated compounds related to the previously reported antistaphyloccocal agent AVE6971 in an effort to attenuate inhibition of hERG potassium channel current that has been noted for this and related antibacterial drug classes. While most modifications of the original thiophene group compromised antibacterial activity, one selenophene analogue displayed (i) improved activity against the primary target enzyme DNA gyrase, (ii) similar activities against a panel of MRSA clinical isolates, and (iii) reduced hERG channel inhibition.

Exploration of the activity of 7-pyrrolidino-8-methoxyisothiazoloquinolones against methicillin-resistant Staphylococcus aureus (MRSA).

A series of 7-(3'-substituted)pyrrolidino-8-methoxyisothiazoloquinolone (ITQ) analogues were prepared, and their antibacterial potency against methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and Escherichia coli were compared. Many of these analogues had MIC ≤ 0.25 µg/mL against quinolone-resistant MRSA strains. The stereochemical preference was explored for a series of 1''-methyl-3'-aminomethylpyrrolidine analogues. Antibacterial activity was generally more favorable with 3'-R, 1''-S configuration. Substitution on the 3'-aminomethyl nitrogen tended to decrease activity, while potency was maintained with disubstitution or aryl substitution at the 1''-carbon. The 7-[(R)-3-((S)-1-aminoethyl)pyrrolidin-1-yl] analogue (6a(R,S)) and the (R)-7-[3-(2-aminopropan-2-yl)pyrrolidin-1-yl] analogue (7a(R)) were found to be the ITQs with the most promising antibacterial profiles. The MICs of these select ITQs versus a panel of clinical MRSA strains were determined, and the ITQs were found to have 8- to 16-fold greater potency than linezolid. These analogues were also evaluated for inhibition of the target enzymes, topoisomerase IV and DNA gyrase, from both wild-type and multidrug resistant strains. The ITQs were up to >30 times more inhibitory against these targets than the fluoroquinolone moxifloxacin.

New quinolone antibiotics: a survey of the literature from 2005 to 2010.

IMPORTANCE OF THE FIELD: The quinolone class of antibacterial agents has a proven track record over the past several decades for the treatment of bacterial infections. Their unique mechanism of action and bactericidal properties make them attractive therapeutic agents. AREAS COVERED IN THIS REVIEW: Significant research efforts continue to the present day in both academia and industry, which have provided a number of promising drug candidates for further development. This review examines quinolones that have been approved for market, entered into clinical trials or reported in the literature during 2005 - 2010. WHAT THE READER WILL GAIN: The reader will be provided with background information on the quinolones as well as recent research findings that demonstrate the continued utility of the class as antibacterial agents. The review highlights a number of recently reported compounds of interest. TAKE HOME MESSAGE: Despite nearly 40 years of research, quinolones still provide new analogs of both scientific and clinical interest. Compounds that are active against antibiotic resistant strains including multiple drug-resistant Mycobacterium tuberculosis as well as compounds with improved pharmacokinetic and safety profiles are goals for current and future programs in this area.

Recent advances in bacterial topoisomerase inhibitors.

Bacterial topoisomerase inhibitors continue to be actively developed as clinical antibacterial agents, largely owing to the success of the currently marketed inhibitors, the quinolones, and the increasing resistance to these agents. New quinolone analogs such as isothiazoloquinolones and quinazolinediones show some potential in overcoming this problem. Quinolones linked to other antibacterial agents such as rifamycins and oxazolidinones are designed to overcome both quinolone-specific resistance and resistance to the coupled agents. Novel inhibitors targeting non-quinolone-binding regions of topoisomerase continue to expand beyond the known coumarin class. The benzimidazoles and pyrazoles have shown promise but have been surpassed into the clinic by novel quinolines. Improved screening techniques and high-throughput methods offer new hope of further expanding the chemical space of topoisomerase inhibitors.

Dual targeting of DNA gyrase and topoisomerase IV: target interactions of heteroaryl isothiazolones in Staphylococcus aureus.

Heteroaryl isothiazolones (HITZs) are antibacterial agents that display excellent in vitro activity against Staphylococcus aureus. We recently identified a series of these compounds that show potent bactericidal activities against methicillin-resistant Staphylococcus aureus (MRSA). We report here the results of in vitro resistance studies that reveal potential underlying mechanisms of action. HITZs selected gyrA mutations exclusively in first-step mutants of wild-type S. aureus, indicating that in contrast to the case with most quinolones, DNA gyrase is the primary target. The compounds displayed low mutation frequencies (10(-9) to 10(-10)) at concentrations close to the MICs and maintained low MICs (< or =0.016 microg/ml) against mutants with single mutations in either gyrA or grlA (parC). These data suggested that HITZs possess significant inhibitory activities against target enzymes, DNA gyrase and topoisomerase IV. This dual-target inhibition was supported by low 50% inhibitory concentrations against topoisomerase IV as measured in a decatenation activity assay and against DNA gyrase as measured in a supercoiling activity assay. Good antibacterial activities (< or =1 microg/ml) against staphylococcal gyrA grlA double mutants, as well as low frequencies (10(-9) to 10(-10)) of selection of still higher-level mutants, also suggested that HITZs remained active against mutant enzymes. We further demonstrated that HITZs exhibit good inhibition of both S. aureus mutant enzymes and thus continue to possess a novel dual-targeting mode of action against these mutant strains. In stepwise acquisition of mutations, HITZs selected quinolone resistance determining region mutations gyrA(Ser84Leu), grlA(Ser80Phe), grlA(Ala116Val), and gyrA(Glu88Lys) sequentially, suggesting that the corresponding amino acids are key amino acids involved in the binding of HITZs to topoisomerases. The overall profile of these compounds suggests the potential utility of HITZs in combating infections caused by S. aureus, including multidrug-resistant MRSA.

Small molecule inhibitors of E. coli primase, a novel bacterial target.

Bacterial primase is essential for DNA replication in Gram-positive and Gram-negative bacteria. It is also structurally distinct from eukaryotic primases, and therefore an attractive, but under-explored, target for therapeutic intervention. We applied virtual screening to discover primase inhibitors, and subsequently several commercially available analogs of these initial hits showed potent primase inhibition and in vitro antibacterial activity. This work provides a 3D pharmacophore for primase ligands, SAR trends, and leads that can be further optimized.

Isothiazoloquinolones with enhanced antistaphylococcal activities against multidrug-resistant strains: effects of structural modifications at the 6-, 7-, and 8-positions.

We describe the biological evaluation of isothiazoloquinolones (ITQs) having structural modifications at the 6-, 7-, and 8-positions. Addition of a methoxy substituent to C-8 effected an increase in antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and a decrease in cytotoxic activity against Hep2 cells. Removal of fluorine from C-6 or replacement of the C-8 carbon with a nitrogen compromised anti-MRSA activity. When the groups attached at C-7 were compared, the anti-MRSA activity decreased in the order 6-isoquinolinyl > 4-pyridinyl > 5-dihydroisoindolyl > 6-tetrahydroisoquinolinyl. The compound with the most desirable in vitro biological profile was 9-cyclopropyl-6-fluoro-8-methoxy-7-(2-methylpyridin-4-yl)-9H-isothiazolo[5,4-b]quinoline-3,4-dione (7g). This ITQ demonstrated (i) strong in vitro anti-MRSA activity (MIC90 = 0.5 microg/mL), (ii) strong inhibitory activities against S. aureus DNA gyrase and topoisomerase IV, with weak activity against human topoisomerase II, (iii) weak cytotoxic activities against three cell lines, and (iv) efficacy in an in vivo murine thigh model of infection employing MRSA.

In vitro and in vivo antibacterial activities of heteroaryl isothiazolones against resistant gram-positive pathogens.

The activities of several tricyclic heteroaryl isothiazolones (HITZs) against an assortment of gram-positive and gram-negative clinical isolates were assessed. These compounds target bacterial DNA replication and were found to possess broad-spectrum activities especially against gram-positive strains, including antibiotic-resistant staphylococci and streptococci. These included methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-nonsusceptible staphylococci, and quinolone-resistant strains. The HITZs were more active than the comparator antimicrobials in most cases. For gram-negative bacteria, the tested compounds were less active against members of the family Enterobacteriaceae but showed exceptional potencies against Haemophilus influenzae, Moraxella catarrhalis, and Neisseria spp. Good activity against several anaerobes, as well as Legionella pneumophila and Mycoplasma pneumoniae, was also observed. Excellent bactericidal activity against staphylococci was observed in time-kill assays, with an approximately 3-log drop in the numbers of CFU/ml occurring after 4 h of exposure to compound. Postantibiotic effects (PAEs) of 2.0 and 1.7 h for methicillin-susceptible S. aureus and MRSA strains, respectively, were observed, and these were similar to those seen with moxifloxacin at 10x MIC. In vivo efficacy was demonstrated in murine infections by using sepsis and thigh infection models. The 50% protective doses were

Isothiazolopyridones: synthesis, structure, and biological activity of a new class of antibacterial agents.

We report the syntheses of first-generation derivatives of isothiazolopyridones and their in vitro evaluation as antibacterial agents. These compounds, containing a novel heterocyclic nucleus composed of an isothiazolone fused to a quinolizin-4-one (at C-2 and C-3 of the quinolizin-4-one), were prepared using a sequence of seven synthetic transformations. The solid-state structure of 7-chloro-9-ethyl-1-thia-2,4a-diazacyclopenta[b]naphthalene-3,4-dione was determined by X-ray diffraction. The prepared derivatives of desfluoroisothiazolopyridones exhibited (a) antibacterial activity against Gram-negative and Gram-positive organisms, (b) inhibitory activities against DNA gyrase and topoisomerase IV, and (c) no inhibitory activity against human topoisomerase II.

Biological evaluation of isothiazoloquinolones containing aromatic heterocycles at the 7-position: In vitro activity of a series of potent antibacterial agents that are effective against methicillin-resistant Staphylococcus aureus.

We synthesized a diverse series of 9H-isothiazolo[5,4-b]quinoline-3,4-diones containing heteroaromatic groups at the 7-position via palladium-catalyzed cross-coupling. Many of these compounds demonstrated potent antistaphylococcal activity (MICs 2 microg/mL) against a multi-drug-resistant strain (ATCC 700699) and low cytotoxic activity (CC(50)>100 microM) against the human cell line Hep2 (laryngeal carcinoma).

Isothiazoloquinolones containing functionalized aromatic hydrocarbons at the 7-position: synthesis and in vitro activity of a series of potent antibacterial agents with diminished cytotoxicity in human cells.

This report describes 9H-isothiazolo[5,4-b]quinoline-3,4-diones (ITQs) containing aromatic groups at the 7-position that were prepared using palladium-catalyzed cross-coupling and tested against a panel of susceptible and resistant bacteria. In general, these compounds were more effective against Gram-positive than Gram-negative organisms. Many of the ITQs were more potent than contemporary quinolones and displayed a particularly strong antistaphylococcal activity against a clinically important, multi-drug-resistant strain. In contrast with ITQs reported previously, several of the analogues described in this Letter demonstrated low cytotoxic activity against a human cell line.

Synthesis and complement inhibitory activity of B/C/D-ring analogues of the fungal metabolite 6,7-diformyl-3',4',4a',5',6',7',8',8a'-octahydro-4,6',7'-trihydroxy- 2',5',5',8a'-tetramethylspiro[1'(2'H)-naphthalene-2(3H)-benzofuran].

This paper reports the synthesis and the bioassay of 4-methoxy- and 4-hydroxyspiro[benzofuran-2(3H)-cyclohexane] partial analogues (5) of the complement inhibitory sesquiterpene fungal metabolite 6,7-diformyl-3',4',4a',5',6',7',8',8a'-octahydro-4,6',7'-trihydroxy-2',5',5',8a'-tetramethylspiro[1'(2'H)-naphthalene-2(3H)-benzofuran] (1a, K-76) and its silver oxide oxidized product (1b, K-76COOH). The described target compounds represent spirobenzofuran B/C/D-ring analogues lacking the A-ring component of the prototype structure. The target compounds were evaluated by the inhibition of total hemolytic complement activity in human serum. It was observed that the structurally simplified analogue 4-methoxyspiro[benzofuran-2(3H)-cyclohexane]-6-carboxylic acid (5a) exhibited an IC(50) = 0.53 mM similar to the IC(50) = 0.57 mM that was observed for the natural product derivative 1b. Exhibiting an IC(50) = 0.16 mM, the three-ringed partial structure 6-carboxy-7-formyl-4-methoxyspiro[benzofuran-2(3H)-cyclohexane] (5k)was found to be the most potent target compound. Like the natural product, 5k appears to inhibit primarily at the C5 activation step and inhibits both the classical and alternative human complement pathways. Several other analogues inhibited complement activation in vitro at concentrations similar to those required for inhibition by the natural product 1b.