Anti- Toxoplasma Activities of 24 Quinolones and Fluoroquinolones In Vitro: Prediction of Activity by Molecular Topology and Virtual Computational Techniques

Abstract

The apicoplast, a plastid-like organelle of Toxoplasma gondii, is thought to be a unique drug target for quinolones. In this study, we assessed the in vitro activity of quinolones against T. gondii and developed new quantitative structure-activity relationship models able to predict this activity. The anti-Toxoplasma activities of 24 quinolones were examined by means of linear discriminant analysis (LDA) using topological indices as structural descriptors. In parallel, in vitro 50% inhibitory concentrations (IC 50 s) were determined in tissue culture. A multilinear regression (MLR) analysis was then performed to establish a model capable of classifying quinolones by in vitro activity. LDA and MLR analysis were applied to virtual structures to identify the influence of each atom or substituent of the quinolone ring on anti-Toxoplasma activity. LDA predicted that 20 of the 24 quinolones would be active against T. gondii. This was confirmed in vitro for most of the quinolones. Trovafloxacin, grepafloxacin, gatifloxacin, and moxifloxacin were the quinolones most potent against T. gondii, with IC 50 s of 0.4, 2.4, 4.1, and 5.1 mg/liter, respectively. Using MLR analysis, a good correlation was found between measured and predicted IC 50 s (r 2 ‫؍‬ 0.87, cross-validation r 2 ‫؍‬ 0.74). MLR analysis showed that the carboxylic group at position C-3 of the quinolone ring was not essential for anti-Toxoplasma activity. In contrast, activity was totally dependent on the presence of a fluorine at position C-6 and was enhanced by the presence of a methyl group at C-5 or an azabicyclohexane at C-7. A nucleophilic substituent at C-8 was essential for the activity of gatifloxacin and moxifloxacin.The discovery of a novel organelle in apicomplexan parasites and its characterization in Toxoplasma gondii offers new opportunities for pharmacological research on several protozoa of major medical importance (16). This organelle, the apicoplast, is a plastid-like structure which was probably acquired by secondary endosymbiosis from a green alga (15). The function of the apicoplast is still not clear, but the presence of this procaryotic structure within T. gondii presents a unique therapeutic target. Fichera and Roos showed that several antibiotics, such as azithromycin and ciprofloxacin, could inhibit DNA replication within the apicoplast and thus inhibited Toxoplasma growth (6). That study confirmed the previously wellknown effect of macrolides on T. gondii but also revealed fluoroquinolones as candidate anti-Toxoplasma drugs. However, other studies performed in vitro and in vivo failed to confirm the activity of ciprofloxacin against T. gondii and showed that, among the fluoroquinolones, only trovafloxacin and some of its derivatives inhibited Toxoplasma growth at micromolar concentrations (9, 10). Better knowledge of the structure-activity relationships of quinolones against T. gondii is thus needed.The aims of this work were (i) to assess quinolone activity against T. gondii by using a previously described model of virtual predicti...

In Vitro Activities of 25 Quinolones and Fluoroquinolones against Liver and Blood Stage Plasmodium spp

“…One remarkable characteristic of the effect of quinolones or fluoroquinolones on Plasmodium growth was a progressive inhibitory effect corresponding to the duration of the incubation with the drug. This has already been observed by other groups for ciprofloxacin, norfloxacin, and ofloxacin (13,23) and for other protozoa such as Toxoplasma gondii (7,9). The reasons for this delayed effect are still unknown.…”

Use of a serum-free medium to produce in vitro Neospora caninum and Toxoplasma gondii tachyzoites on Vero cells

“…Although convenient and reliable, this technique is ethically undesirable. Alternative in vitro methods, using MRC5 fibro-blasts complemented with FCS, were used for short studies assessing the effect of antimicrobial agents on T. gondii [3,10,21]. Additionally, continuous cell lines such as HeLa, LLC and Vero were also found to be suitable for the propagation of tachyzoites of T. gondii for the needs of a general hospital laboratory [19].…”

“…In vitro cultures are also used to screen potential chemotherapeutic agents [3,10,21,29,30] to study the process of cell invasion by the parasite [24] or perform genetic manipulation on the parasite [25,38]. The presence of serum proteins, or even specific antibodies, could hamper these experiments.…”

Antimicrosporidial activity of (fluoro)quinolones in vitro and in vivo

“…Norfloxacin also was reported to be effective for treating P. falciparum and Plasmodium vivax infections in India (Sarma 1989, Tripathi et al 1993), but ciprofloxacin was ineffective against multidrug resistant P. falciparum infections in Thailand (Watt et al 1991). Trovafloxacin, grepafloxacin, gatifloxacin, and moxifloxacin were among the most effective of 24 (fluoro)quinolones tested for their ability to inhibit Toxoplasma gondii replication in vitro (Gozalbes et al 2000). Ciprofloxacin also was found to inhibit in vitro replication of Giardia lamblia (Sousa and Poiares-da-Silva 2001) and T. gondii (Fichera and Roos 1997), particularly during the second infectious cell cycle in the latter case which was associated with reduction in plastid replication.…”