Hidenori Ohki

In vitro activities of a new lipopeptide antifungal agent, FK463, against a variety of clinically important fungi

ABSTRACT The in vitro antifungal activity and spectrum of FK463 were compared with those of amphotericin B, fluconazole, and itraconazole by using a broth microdilution method specified by National Committee for Clinical Laboratory Standards document M27-A (National Committee for Clinical Laboratory Standards, Wayne, Pa., 1997). FK463 exhibited broad-spectrum activity against clinically important pathogens including Candida species (MIC range, ≦0.0039 to 2 μg/ml) and Aspergillus species (MIC range, ≦0.0039 to 0.0313 μg/ml), and its MICs for such fungi were lower than those of the other antifungal agents tested. FK463 was also potently active against azole-resistant Candida albicans as well as azole-susceptible strains, and there was no cross-resistance with azoles. FK463 showed fungicidal activity against C. albicans, i.e., a 99% reduction in viability after a 24-h exposure at concentrations above 0.0156 μg/ml. The minimum fungicidal concentration (MFC) assays indicated that FK463 was fungicidal against most isolates of Candida species. In contrast, the MFCs of FK463 for A. fumigatus isolates were much higher than the MICs, indicating that its action is fungistatic against this species. FK463 had no activity against Cryptococcus neoformans,Trichosporon species, or Fusarium solani. Neither the test medium (kind and pH) nor the inoculum size greatly affected the MICs of FK463, while the addition of 4% human serum albumin increased the MICs for Candida species and A. fumigatus more than 32 times. Results from preclinical in vitro evaluations performed thus far indicate that FK463 should be a potent parenteral antifungal agent.

Synthesis and SAR of novel parenteral anti-pseudomonal cephalosporins: discovery of FR264205.

We describe herein the synthesis and biological evaluation of a series of novel cephalosporins with potent activity against Pseudomonas aeruginosa. Introduction of various amino groups to the 4-position of a 3-amino-2-methylpyrazole cephalosporin 3-side chain resulted in enhanced MIC values against multiple Pseudomonas aeruginosa strains and ultimately led to the discovery of FR264205 (15) with excellent anti-bacterial activity and weak convulsion effect by direct intracerebroventricular injection assay.

Role of Micafungin in the Antifungal Armamentarium

Serious infections caused by opportunistic molds remain a major problem for public health. Immune deficiency following organ transplantation and aggressive cancer treatment has greatly increased the incidence of systemic mycoses, and invasive aspergillosis in patients with AIDS is associated with significant morbidity and mortality. Amphotericin B is the first-line therapy for systemic infection because of its broad-spectrum and fungicidal activity. However, considerable side effects limit its clinical utility. The echinocandins are large lipopeptide molecules that inhibit the synthesis of 1,3-beta-D-glucan, a key component of the fungal cell wall. Three echinocandins have reached the market, and some others are in early clinical development. Caspofungin was the first echinocandin to be licensed for clinical use in most countries. Micafungin is licensed for clinical use in Japan, China, Taiwan, Jordan, Korea, Hong-Kong and the US, and anidulafungin is currently licensed in the US. The novel class of echinocandins represents a milestone in antifungal drug research that has further expanded our therapeutic options. Studies to date have shown that micafungin exhibits extremely potent antifungal activity against clinically important fungi, including Aspergillus and azole-resistant strains of Candida. In animal studies, micafungin is as efficacious as amphotericin B with respect to improvement of survival rate. Micafungin is also characterized by a linear pharmacokinetic profile and substantially fewer toxic effects. Micafungin is a poor substrate for the cytochrome P450 enzymes, and compared to azoles, fewer drug interactions are described. No dose adjustments of the drug are required in the presence of mycophenolate mofetil, cyclosporin, tacrolimus, prednisolone, or sirolimus. Strategies using this new echinocandin agent will benefit a large number of patients with severe immune dysfunction.

Novel echinocandin antifungals. Part 2: Optimization of the side chain of the natural product FR901379. Discovery of micafungin.

Further optimization of the potent antifungal activity of side chain analogs of the natural product FR901379 led to the discovery of compound 8 with an excellent, well-balanced profile. Potent compounds with reduced hemolytic potential were designed based upon a disruption of the linearity of the terphenyl lipophilic side chain. The optimized compound (8, FK463, micafungin) displayed the best balance and was selected as the clinical candidate.

Use of a serum‐based antifungal susceptibility assay to predict the in vivo efficacy of novel echinocandin compounds

In vitro susceptibility assays of antifungal activity do not always accurately predict in vivo efficacy. As well as having a clear clinical importance, the ability to predict efficacy is also essential for effective screening of novel drug compounds. Initial screening of novel compounds must often be based on in vitro data. The present report describes the use of serum‐MIC, an in vitro test of antifungal susceptibility, to accurately predict in vivo efficacy of echinocandin drugs in a mouse model of disseminated candidiasis. The basis of the serum‐MIC method was to measure the inhibitory activity of a test compound against Candida albicans hyphal growth in the presence of pooled mouse serum. For 13 previously uncharacterized echinocandin compounds, as well as for the known echinocandin drugs, micafungin and caspofungin, serum‐MIC determinations were shown to give better correlation to efficacy in the animal model than conventional, CLSI standard, in vitro antifungal susceptibility tests. The most accurate prediction of efficacy was obtained when the serum‐MIC was adjusted in relation to the serum concentration at 30 min post‐treatment. Furthermore, when the efficacy of micafungin was determined by measuring C. albicans kidney burden in the mouse model of infection, the adjusted serum‐MIC consistently reflected the effective serum concentrations. Our data indicate that determination of serum‐MIC values will facilitate prediction of the in vivo potency of new antifungal compounds such as novel echinocandins.

Novel echinocandin antifungals. Part 1: Novel side-chain analogs of the natural product FR901379

A series of novel acylated analogs of the novel water-soluble echinocandin FR901379 have been prepared and evaluated for antifungal and hemolytic activity. A relationship between antifungal activity and lipophilicity of the acyl side chain, expressed as ClogP was demonstrated, and an analog (3c) with 5.5- to 8-fold superior in vivo activity relative to the previously disclosed 4-(n-octyloxy)benzoyl side chain analog, FR131535 obtained.

Synthesis and biological activity of novel macrocyclic antifungals: acylated conjugates of the ornithine moiety of the lipopeptidolactone FR901469.

A series of acylated analogues of the novel macrocyclic lipopeptidolactone FR901469 has been prepared and evaluated for antifungal and hemolytic activity. Several analogues displayed markedly reduced hemolytic potential and comparable protective effects to the natural product in a mouse model of candidiasis.

Studies on 3'-quaternary ammonium cephalosporins--III. Synthesis and antibacterial activity of 3'-(3-aminopyrazolium) cephalosporins.

The synthesis and in vitro antibacterial activity of 7 beta-[(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]cephalos porins bearing N-mono or dialkyl and carbamoyl aminopyrazolium, and five- or six-membered rings fused to the 3-aminopyrazolium methyl groups at the 3-position, are described. Aminopyrazolium methyl cephalosporins (23e, f, i), with fused saturated and unsaturated rings were especially effective against Staphylococcus strains compared to 3-amino-2-methylpyrazolium methyl cephalosporin (1). Among the cephalosporins prepared in this work, 7 beta-[(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]-3-(4,5, 6, 7-tetrahydro-1-pyrazolo[1,5-a]pyrimidinio)methyl-3-cephem-4-carbox ylate (23f) showed a good balance of antibacterial activity against both Gram-positive bacteria including Staphylococcus aureus and Gram-negative bacteria including P. aeruginosa. An imidazopyrazolium group at the 3-position in, for example, cephalosporin (23i) was particularly effective for improving antibacterial activity against MRSA.

Determination of Antifungal Activities in Serum Samples from Mice Treated with Different Antifungal Drugs Allows Detection of an Active Metabolite of Itraconazole

To establish an in vitro method of predicting in vivo efficacy of antifungal drugs against Candida albicans and Aspergillus fumigatus, the antifungal activities of fluconazole, itraconazole, and amphotericin B were determined in mouse serum. The minimum inhibitory concentration (MIC) of each drug was measured using mouse serum as a diluent. For C. albicans, the assay endpoint of azoles was defined as inhibition of mycelial extension (mMIC) and for A. fumigatus, as no growth (MIC). The MICs of amphotericin B for both pathogens were defined as the MIC at which no mycelial growth occurred. Serum MIC or mMIC determinations were then used to estimate the concentration of the drugs in serum of mice treated with antifungal drugs by multiplying the antifungal titer of the serum samples by the serum (m)MIC. The serum drug concentrations were also determined by HPLC. The serum concentrations estimated microbiologically showed good agreement with those determined by HPLC, except for itraconazole. Analysis of the serum samples from itraconazole‐treated mice by a sensitive bioautography revealed the presence of additional spots, not seen in control samples of itraconazole. The bioautography assay demonstrated that the additional material detected in serum from mice treated with itraconazole was an active metabolite of itraconazole. The data showed that the apparent reduction in the itraconazole serum concentration as determined by HPLC was the result of the formation of an active metabolite, and that the use of a microbiological method to measure serum concentrations of drugs can provide a method for prediction of in vivo efficacy of antifungal drugs.