cancidas and Disease-Models--Animal

We previously reported medicinal chemistry efforts that identified MK-5204, an orally efficacious β-1,3-glucan synthesis inhibitor derived from the natural product enfumafungin. Further extensive optimization of the C2 triazole substituent identified 4-pyridyl as the preferred replacement for the carboxamide of MK-5204, leading to improvements in antifungal activity in the presence of serum, and increased oral exposure. Reoptimizing the aminoether at C3 in the presence of this newly discovered C2 substituent, confirmed that the (R) t-butyl, methyl aminoether of MK-5204 provided the best balance of these two key parameters, culminating in the discovery of ibrexafungerp, which is currently in phase III clinical trials. Ibrexafungerp displayed significantly improved oral efficacy in murine infection models, making it a superior candidate for clinical development as an oral treatment for Candida and Aspergillus infections.

Topics: Administration, Oral; Animals; Antifungal Agents; Aspergillosis; Aspergillus; beta-Glucans; Candida albicans; Candidiasis; Disease Models, Animal; Glycosides; Half-Life; Mice; Structure-Activity Relationship; Triterpenes

The in vivo efficacy of posaconazole against 4 clinical Aspergillus fumigatus isolates with posaconazole MICs ranging from 0.03 to 16 mg/liter, as determined by CLSI method M38A, was assessed in a nonneutropenic murine model of disseminated aspergillosis. The underlying resistance mechanisms of the isolates included substitutions in the cyp51A gene at codon 220 (M220I), codon 54 (G54W), and codon 98 (L98H). The latter was combined with a 34-bp tandem repeat in the gene promoter region (TR L98H). The control isolate exhibited a wild-type phenotype without any known resistance mechanism. Oral posaconazole therapy was started 24 h after infection and was given once daily for 14 consecutive days. Mice were treated with four different doses (1 to 64 mg/kg of body weight), and survival was used as the end point. Survival was dependent both on the dose and on the MIC. The Hill equation with a variable slope fitted the relationship between the dose/MIC ratio and 14-day survival well (R2, 0.92), with a 50% effective dose (ED50) of 29.0 mg/kg (95% confidence interval [CI], 15.6 to 53.6 mg/kg). This also applied to the relationship between the area under the plasma concentration-time curve (AUC)/MIC ratio and 14-day survival (50% effective pharmacodynamic index [EI50], 321.3 [95% CI, 222.7 to 463.4]). Near-maximum survival was reached at an AUC/MIC ratio of nearly 1,000. These results indicate that treatment of infections with A. fumigatus strains for which MICs are 0.5 mg/liter requires doses exceeding the present licensed doses. Increasing the standard dosing regimen may have some effect and may be clinically useful if no alternatives are available.

Topics: Administration, Oral; Animals; Antifungal Agents; Area Under Curve; Aspergillosis; Aspergillus fumigatus; Cytochrome P-450 Enzyme System; Disease Models, Animal; Drug Administration Schedule; Female; Fungal Proteins; Mice; Microbial Sensitivity Tests; Mutation; Triazoles

A high-dose-step-down strategy for caspofungin treatment was evaluated in an experimental model of advanced-stage invasive pulmonary aspergillosis. The therapeutic efficacy of caspofungin in relation to the severity of invasive pulmonary infection caused by Aspergillus fumigatus in transiently neutropenic rats was investigated by using rat survival and the decrease in the fungal burden as the parameters of efficacy. When treatment was started at either 16 h or 24 h after fungal inoculation, caspofungin administered intraperitoneally at 4 mg/kg of body weight/day for 10 days was highly effective (100% and 93% rat survival, respectively). However, only 27% rat survival was obtained when treatment was started at 72 h, when the rats had advanced-stage infection. Increasing the dose from 4 to 10 mg/kg/day could compensate for the decrease in efficacy and resulted in 67% rat survival. The high dose of 10 mg/kg/day for 10 days did not appear to be necessary since a high-dose-step-down dosing schedule with 10 mg/kg/day for 3 days followed by 4 mg/kg/day for 7 days was equally effective. At 10 days after the end of treatment with 10 mg/kg/day caspofungin, the level of neither A. fumigatus DNA nor A. fumigatus galactomannan in the infected left lung was significantly decreased. In contrast, A. fumigatus galactomannan concentrations in serum were significantly decreased. The levels of creatinine, blood urea nitrogen, alanine aminotransferase, and asparate aminotransferase were not elevated during treatment. Caspofungin is effective for the treatment of invasive pulmonary aspergillosis in transiently neutropenic rats and is even effective in rats with advanced-stage infection. In this model, the administration of high-dose-step-down treatment was as effective as treatment with high doses for the whole treatment period.

Topics: Animals; Antifungal Agents; Aspergillosis; Aspergillus fumigatus; Caspofungin; Disease Models, Animal; Echinocandins; Humans; Lipopeptides; Lung; Lung Diseases, Fungal; Neutropenia; Rats; Severity of Illness Index; Treatment Outcome

Two clinical isolates of Aspergillus fumigatus, designated AT and DK, were recently obtained from patients failing caspofungin and itraconazole therapy, respectively. The isolates were tested by microdilution for susceptibility to itraconazole, voriconazole, posaconazole, ravuconazole, and caspofungin and by Etest for susceptibility to amphotericin B and caspofungin. Susceptibility testing documented that the DK isolate was azole resistant (itraconazole and posaconazole MICs, >4 microg/ml; voriconazole MIC, 2 microg/ml; ravuconazole MIC, 4 microg/ml), and the resistance was confirmed in a hematogenous mouse model, with mortality and the galactomannan index as the primary and secondary end points. Sequencing of the cyp51A gene revealed the M220K mutation, conferring multiazole resistance. The Etest, but not microdilution, suggested that the AT isolate was resistant to caspofungin (MIC, >32 microg/ml). In the animal model, this isolate showed reduced susceptibility to caspofungin. Sequencing of the FKS1 gene revealed no mutations; the enzyme retained full sensitivity in vitro; and investigation of the polysaccharide composition showed that the beta-(1,3)-glucan proportion was unchanged. However, gene expression profiling by Northern blotting and real-time PCR demonstrated that the FKS gene was expressed at a higher level in the AT isolate than in the susceptible control isolate. To our knowledge, this is the first report to document the presence of multiazole-resistant clinical isolates in Denmark and to demonstrate reduced susceptibility to caspofungin in a clinical A. fumigatus isolate with increased expression of the FKS gene. Further research to determine the prevalence of resistance in A. fumigatus worldwide, and to develop easier and reliable tools for the identification of such isolates in routine laboratories, is warranted.

Topics: Adult; Animals; Antifungal Agents; Aspergillosis; Aspergillus fumigatus; Azoles; Base Sequence; Caspofungin; Cytochrome P-450 Enzyme System; Disease Models, Animal; DNA, Fungal; Drug Resistance, Multiple, Fungal; Echinocandins; Fungal Proteins; Genes, Fungal; Glucosyltransferases; Humans; In Vitro Techniques; Itraconazole; Lipopeptides; Mice; Microbial Sensitivity Tests; Mutation