In vitro and in vivo evaluation of antifungal agents

Silver Complexes of Miconazole and Metronidazole: Potential Candidates for Melanoma Treatment

Melanoma, arguably the deadliest form of skin cancer, is responsible for the majority of skin-cancer-related fatalities. Innovative strategies concentrate on new therapies that avoid the undesirable effects of pharmacological or medical treatment. This article discusses the chemical structures of [(MTZ)2AgNO3], [(MTZ)2Ag]2SO4, [Ag(MCZ)2NO3], [Ag(MCZ)2BF4], [Ag(MCZ)2SbF6] and [Ag(MCZ)2ClO4] (MTZ-metronidazole; MCZ-miconazole) silver(I) compounds and the possible relationship between the molecules and their cytostatic activity against melanoma cells. Molecular Hirshfeld surface analysis and computational methods were used to examine the possible association between the structure and anticancer activity of the silver(I) complexes and compare the cytotoxicity of the silver(I) complexes of metronidazole and miconazole with that of silver(I) nitrate, cisplatin, metronidazole and miconazole complexes against A375 and BJ cells. Additionally, these preliminary biological studies found the greatest IC50 values against the A375 line were demonstrated by [Ag(MCZ)2NO3] and [(MTZ)2AgNO3]. The compound [(MTZ)2AgNO3] was three-fold more toxic to the A375 cells than the reference (cisplatin) and 15 times more cytotoxic against the A375 cells than the normal BJ cells. Complexes of metronidazole with Ag(I) are considered biocompatible at a concentration below 50 µmol/L.

Repurposing antifungal drugs for cancer therapy

BACKGROUND

Repurposing antifungal drugs in cancer therapy has attracted unprecedented attention in both preclinical and clinical research due to specific advantages, such as safety, high-cost effectiveness and time savings compared with cancer drug discovery. The surprising and encouraging efficacy of antifungal drugs in cancer therapy, mechanistically, is attributed to the overlapping targets or molecular pathways between fungal and cancer pathogenesis. Advancements in omics, informatics and analytical technology have led to the discovery of increasing "off-site" targets from antifungal drugs involved in cancerogenesis, such as smoothened (D477G) inhibition from itraconazole in basal cell carcinoma.

AIM OF REVIEW

This review illustrates several antifungal drugs repurposed for cancer therapy and reveals the underlying mechanism based on their original target and "off-site" target. Furthermore, the challenges and perspectives for the future development and clinical applications of antifungal drugs for cancer therapy are also discussed, providing a refresh understanding of drug repurposing.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review may provide a basic understanding of repurposed antifungal drugs for clinical cancer management, thereby helping antifungal drugs broaden new indications and promote clinical translation.

Antifungal Activity of 1,4-Dialkoxynaphthalen-2-Acyl Imidazolium Salts by Inducing Apoptosis of Pathogenic Candida spp

Even though Candida spp. are staying commonly on human skin, it is also an opportunistic pathogenic fungus that can cause candidiasis. The emergence of resistant Candida strains and the toxicity of antifungal agents have encouraged the development of new classes of potent antifungal agents. Novel naphthalen-2-acyl imidazolium salts (NAIMSs), especially 1,4-dialkoxy-NAIMS from 1,4-dihydroxynaphthalene, were prepared and evaluated for antifungal activity. Those derivatives showed prominent anti-Candida activity with a minimum inhibitory concentration (MIC) of 3.125 to 6.26 μg/mL in 24 h based on microdilution antifungal susceptibility test. Among the tested compounds, NAIMS 7c showed strongest antifungal activity with 3.125 μg/mL MIC value compared with miconazole which showed 12.5 μg/mL MIC value against Candida spp., and more importantly >100 μg/mL MIC value against C. auris. The production of reactive oxygen species (ROS) was increased and JC-1 staining showed the loss of mitochondrial membrane potential in C. albicans by treatment with NAIMS 7c. The increased release of ultraviolet (UV) absorbing materials suggested that NAIMS 7c could cause cell busting. The expression of apoptosis-related genes was induced in C. albicans by NAIMS 7c treatment. Taken together, the synthetic NAIMSs are of high interest as novel antifungal agents given further in vivo examination.

Antifungal Susceptibility Testing of Fusarium: A Practical Approach

In vitro susceptibility testing of Fusarium is becoming increasingly important because of frequency and diversity of infections and because resistance profiles are species-specific. Reference methods for antifungal susceptibility testing (AFST) are those of Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility (EUCAST), but breakpoints (BPs) have not yet been established. One of the problems is that phylogenetic distances between Fusarium species are much smaller than between species of, e.g., Candida. Epidemiological cutoff values (ECVs) for some Fusarium species have been determined in order to differentiate wild-type from non-wild-type isolates. In clinical routine, commercially available assays such as Etest, Sensititre or others provide essential agreement with reference methods. Our objective is to summarize antifungal susceptibility testing of Fusarium genus in the clinical laboratory: how to do it, when to do it, and how to interpret it.

An ex-vivo oral mucosa infection model for the evaluation of the topical activity of antifungal agents

Although Nystatin has been used since 1950s as a non-absorbable antifungal agent, there is still no reliable in-vivo data available stating a dose-effect relationship of Nystatin-suspension in the treatment of oropharyngeal infection with Candida albicans. Here, we studied the efficacy of a commercially available topical Nystatin suspension in a new ex-vivo model of candidiasis using porcine oral mucosa. After 48 and 96 h of C. albicans infection, 230 IU Nystatin (standard dosage), 100 IU and 20 IU proved to be equally efficacious. Multiple applications of Nystatin were not superior compared with single application. In dosages of 10 and 0.1 IU the activity of Nystatin suspension against C. albicans was no longer confirmed. In an agar diffusion model, the minimal biocidal concentration of Nystatin proved to be 0.25 IU. Our results suggest that the proposed porcine ex-vivo model is much closer to the in-vivo situation compared with other established in-vitro models of the treatment of muco-cutaneous candidiasis and may provide a substitute for animal models in the investigation of antifungal agents. Additionally, it seems to be a valuable tool for further investigations of the pathogenesis of C. albicans infections.

Amphotericin B-induced nephrotoxicity: a review

Amphotericin B is the gold standard for antifungal treatment for the most severe mycoses. However, adverse effects are common, with nephrotoxicity being the most serious, occurring early in the course of treatment, and usually being reversible in most patients. Tubular damage is a well known problem associated with amphotericin B therapy but acute renal failure is the most serious complication. Recent studies have examined ways to ameliorate the well-known toxicities of amphotericin B. A new approach has been to complex the drug with lipids or entrap it in liposomes. This review will concern amphotericin B-induced nephrotoxicity, whose mechanisms are not completely clear. Nephrotoxicity seems related to direct amphotericin B action on the renal tubules as well as to drug-induced renal vasoconstriction. The main mechanisms of nephrotoxicity suggested in the literature are presented. The clinical picture at different ages (adults, children, newborns), interactions of clinical significance, strategies for prevention of amphotericin B-induced nephrotoxicity are summarized. To provide optimal patient care, it is imperative that the clinician understand the etiology of and the signs and symptoms associated with nephrotoxicity, as well as interventions to prevent nephrotoxicity in patients receiving amphotericin B.

In vitro susceptibility of chromoblastomycosis and phaeohyphomycosis agents to antifungal drugs

The in vitro susceptibility of chromoblastomycosis and phaeohyphomycosis agents to antifungal drugs was appraised using the reference macrodilution method proposed by the National Committee for Clinical Laboratory Standards (NCCLS) for yeasts modified for filamentous fungi. The antifungal drugs amphotericin B, 5-fluorocytosine, itraconazole and fluconazole were tested against one environmental and 18 clinical isolates. This work amended the macrodilution methods proposed by NCCLS and suggests that a conidial suspension free of hyphae leads to a more reliable assay and provides for better reproducibility. The macrodilution method was performed with 10(4) conidia ml-1. The MIC values ranged from 1.0 to 16.0 micrograms ml-1 for amphotericin B and 3.12 to 25.0 micrograms ml-1 for 5-fluorocytosine. A MIC range of 0.06 to 1.95 micrograms ml-1 was determined for itraconazole while 2.0 to 64.0 micrograms ml-1 was detected for fluconazole.

Comparative study of the in vitro antifungal activity of bifonazole, naftifine and sertaconazole against yeasts

The in vitro activity of three antifungal agents was tested and compared against 151 yeast strains, including ten Candida species, Cryptococcus neoformans, Rhodotorula rubra, and Trichosporon cutaneum. Minimum inhibitory concentrations (MICs) were determined by a microdilution technique in Shadomy modified liquid medium. The mean MICs of sertaconazole (0.34 mg/L) were lower than those of naftifine (16.3 mg/L) and bifonazole (13.2 mg/L). These results suggest that sertaconazole is more active against Candida spp than other topical agents such as bifonazole and naftifine.

Chromoblastomycosis murine model and in vitro test to evaluate the sensitivity of Fonsecaea pedrosoi to ketoconazole, itraconazole and saperconazole

An experimental model of murine chromoblastomycosis and in vitro tests with Fonsecaea pedrosoi were used to test the sensitivity of this fungus to three different antimycotics. The experimental model was standardized in BALB/c mice inoculated intraperitoneally with a 10(6) CFU/ml suspension of a F. pedrosoi isolate. Clinical infection was evident after 5 days of inoculation. Three groups of 27 mice each were used in the experiment. One group was treated with ketoconazole (KTZ), another with itraconazole (ITZ) and the other with saperconazole (SPZ). Antimycotic therapy was continued for 21 days. The control group consisted of 40 mice which were inoculated, but not treated. Infection was documented by macroscopic and microscopic examination of affected tissue in addition to culture of tissue macerates. Minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC) for the F. pedrosoi strain used were done. The in vitro results showed that SPZ was the most active with MIC 0.01 microgram/ml and MFC 0.1 microgram/ml, followed by ITZ. SPZ was also the most effective in vivo since 63% of the treated animals (p = 0.01) showed a curative effect after the observation period. We concluded that SPZ had the best in vitro and in vivo activity against F. pedrosoi.

Correlation between in vitro resistance to fluconazole and clinical outcome of oropharyngeal candidiasis in HIV-infected patients

Fifty episodes of oropharyngeal candidiasis in HIV-infected patients were analyzed prospectively in order to evaluate the clinical response to fluconazole. The minimum inhibitory concentrations (MICs) of fluconazole for the Candida strains isolated from the pharynx were correlated with the clinical response. Treatment with fluconazole (100 mg/day) was successful in 86% of the cases. A good clinical outcome followed in 97% of the cases when a strain sensitive to fluconazole was isolated. This figure fell to 22% when the strain was resistant to fluconazole (p < 0.001). The rate of post-treatment colonization was high (87%), and selection of non-albicans Candida species occurred in 23% of the cases. In conclusion, fluconazole treatment for oropharyngeal candidiasis of HIV-infected patients was useful in most cases, but less sensitive non-albicans species can be selected. Most treatment failures were associated with increased MICs of fluconazole for the strains isolated before treatment; therefore, susceptibility testing is recommended as an aid in clinical decision-making for the use of the azole group of drugs.

Early detection of amphotericin B induced nephrotoxicity by 99mTc-DTPA: a useful test

Amphotericin B (AMB) with a broad spectrum of antifungal activity is used for the treatment of life-threatening mycoses, especially in immunocomprised patients. Since measurements of the blood level of AMB and of creatinine do not provide early warning of AMB induced renal toxicity, we studied the effects of AMB on biodistribution of a glomerular agent, 99mTc-DTPA. In Swiss mice, the toxicity of AMB was studied at single intravenous doses of 0.5-3.5 mg/kg body weight. Dose dependent effects consisted of decreased blood clearance and urinary excretion. Recovery of function was shown in dose ranges corresponding to high level clinical schedules. Serum creatinine changes lagged behind the 99mTc-DTPA alterations. This suggests that AMB toxicity might be monitored by blood/urinary clearance of 99mTc-DTPA.

Comparative efficacy of amphotericin B, clotrimazole and itraconazole against Aspergillus spp. An in vitro study

The susceptibilities of two isolates of Aspergillus flavus, one from a human case of recalcitrant mycotic keratitis, and an environmental isolate of A. fumigatus, to itraconazole, clotrimazole and amphotericin B were measured. Observations of macroscopic growth and microscopic evaluations of conidia germination both indicated that the two isolates of A. flavus were markedly more resistant to amphotericin B than to itraconazole and clotrimazole. Itraconazole was more effective than clotrimazole for all isolates. Our in vitro susceptibility results suggest the use of itraconazole should be a primary consideration in the treatment of Aspergillus keratitis.

Evaluation of five commercial antifungal susceptibility testing systems

Five commercial antifungal susceptibility testing systems were studied for repeatability and reproducibility as well as concordance of results with the MICs for ten reference strains belonging to six different species. Repeatability was determined by testing each strain in triplicate on the same day, and reproducibility by repeating this triple determination on three different days. On the basis of 630 yeast-antifungal agent results for Mycototal and Mycostandard, 540 for Candifast, and 450 for ATB Fungus and Diff Test, repeatability was consistently equal to or greater than 95%. Reproducibility was 80.07% for Candifast and greater than 95% for the other systems. The concordance with the reference MICs was 51.65% for Candifast, 75.33% for ATB Fungus, 80.89% for Diff Test, 90.16% for Mycostandard and 90.32% for Mycototal. Although the performance of Diff Test and ATB Fungus was satisfactory, Mycototal and Mycostandard gave notably better results with imidazoles. Mycostandard, which is easier to use and includes tests for fluconazole and itraconazole, would seem to be potentially the most useful antifungal susceptibility test available at present.

Effects of temperature on anti-Candida activities of antifungal antibiotics

The relative growth (percentage of growth relative to control growth) of 767 Candida isolates representing five species was measured in microcultures at 25 and 37 degrees C. In the presence of 10(-4) M flucytosine, the distribution of relative yeast growth data indicated that Candida albicans isolates were less susceptible at 25 degrees C than at 37 degrees C, while the opposite was found with 4 x 10(-5) M amorolfine for most of the isolates tested. Repetition of the experiments at four different temperatures with 99 C. albicans isolates and five antifungal agents confirmed a direct relationship between growth inhibition and increasing temperature from 25 to 40 degrees C with amphotericin B, flucytosine, and terconazole; a strong inverse relationship between inhibition and temperature with amorolfine; and a weak inverse relationship with terbinafine. However, these relationships were not always noted with other Candida spp.: in particular, the growth of C. glabrata and C. parapsilosis isolates tended to be greater at 37 degrees C than at 25 degrees C in the presence of the azole-derivative antifungal agents itraconazole and terconazole. These findings stress the species-specific individuality of yeast susceptibility to azole antifungal agents. The results with C. albicans and amorolfine and terbinafine accord with their known in vivo efficacy in mycoses involving low-temperature superficial sites and poor activity against mycoses involving deep body sites. The data also reinforce the need for control of experimental variables such as temperature in the design of standardized yeast susceptibility tests.

Multicenter evaluation of a broth macrodilution antifungal susceptibility test for yeasts

Thirteen laboratories collaborated to optimize interlaboratory agreement of results of a broth macrodilution procedure for testing three classes of antifungal drugs against pathogenic yeasts. The activities of amphotericin B, flucytosine, and ketoconazole were tested against 100 coded isolates of Candida albicans, Candida tropicalis, Candida parapsilosis, Candida lusitaniae, Torulopsis (Candida) glabrata, and Cryptococcus neoformans. Two starting yeast inoculum sizes (5 x 10(4) and 2.5 x 10(3) cells per ml) were compared, and readings were taken after 24 and 48 h of incubation. All other test conditions were standardized. The resultant turbidities in all tubes were estimated visually on a scale from 0 to 4+ turbidity, and MIC-0, MIC-1, and MIC-2 were defined as the lowest drug concentrations that reduced growth to 0, 1+, or 2+ turbidity, respectively. For flucytosine, agreement among laboratories varied between 57 and 87% for different inocula, times of incubation, and end point criteria. Agreement was maximized (85%) when the lower inoculum was incubated for 2 days and the MICs were defined as 1+ turbidity or less. For amphotericin B, variations in test conditions produced much smaller differences in interlaboratory agreement. For ketoconazole, interlaboratory agreement was poorer by all end point criteria. However, MIC-2 endpoints distinguished T. glabrata as resistant compared with the other species. Overall, the studies indicated that readings from the lower inoculum obtained on the second day of reading result in the greatest interlaboratory agreement. In combination with data from previous multicenter studies (National Committee for Clinical Laboratory Standards, Antifungal Susceptibility Testing: Committee Report, Vol. 5, No. 17, 1988; M. A. Pfaller, L. Burmeister, M. S. Bartlett, and M. G. Rinaldi, J. Clin. Microbiol. 26:1437-1441, 1988; M. A. Pfaller, M. G. Rinaldi, J. N. Galgiani, M. S. Bartlett, B.A. Body, A. Espinel-Ingroff, R.A. Fromtling, G.S. Hall, C.E. Hughes, F. C. Odds, and A. M. SUgar, J. Clin. Microbiol. 34:1648-1654, 1990), these findings will be used by the National Committee for Clinical Laboratory Standards to develop a standardized method for in vitro antifungal susceptibility testing for yeasts.

Antifungal susceptibility testing of Candida spp. by relative growth measurement at single concentrations of antifungal agents

The relative growth (percentage of growth relative to control growth) of 496 isolates representing six Candida species was assessed as a means of determining in vitro susceptibilities of the isolates in microdilution plate wells containing single concentrations of each of seven antifungal agents. The relative growth data were highly reproducible. With flucytosine and amorolfine they correlated well with MICs, but for an azole antifungal agent, terconazole, they did not correlate with MICs. Distributions of relative growth percentages for different Candida spp. showed significant differences in species susceptibility to individual agents. For example, C. albicans was less susceptible than the other species to amorolfine; C. parapsilosis isolates were particularly susceptible to terbinafine; and C. glabrata, C. guilliermondii, and C. krusei isolates were less susceptible than C. albicans to fluconazole and ketoconazole but equally susceptible as or more susceptible than C. albicans to itraconazole. Differential patterns of susceptibility to individual azole antifungal agents were noted for some individual strains as well as for Candida spp.

Effects of amphotericin B and fluconazole on the extracellular and intracellular growth of Candida albicans

The effects of amphotericin B and fluconazole on the extracellular and intracellular growth of Candida albicans were studied. With respect to the extracellular growth of C. albicans, antifungal activity was measured in terms of MICs and minimal fungicidal concentrations as well as by determination of the concentration that effectively killed (greater than 99.9%) C. albicans in the absence or presence (amphotericin B only) of serum. Amphotericin B was highly active in terms of killing, even at an increased inoculum size. In the presence of serum, amphotericin B activity was substantially reduced. For fluconazole, activity was restricted to inhibition of fungal growth, even after the inoculum size was reduced. With respect to the intracellular growth of C. albicans, antifungal activity was measured by using monolayers of murine peritoneal macrophages infected with C. albicans and was measured in terms of inhibition of germ tube formation as well as effective killing (greater than 99%) of C. albicans. Amphotericin B was highly active against C. albicans. At an increased ratio of infection, amphotericin B activity was slightly reduced. Fluconazole had no antifungal activity. Neither a reduction in the ratio of infection nor exposure of C. albicans to fluconazole prior to macrophage ingestion resulted in activity against intracellular C. albicans by fluconazole. Previous exposure of C. albicans to amphotericin B resulted in increased intracellular activity of amphotericin B. The intracellular antifungal activity of the combination of fluconazole with amphotericin B was less than that of amphotericin B alone. Amphotericin B showed fungicidal activity against C. albicans growing both extracellularly and intracellularly, whereas fluconazole inhibited growth only of extracellular C. albicans. A slight antagonistic effect between fluconazole and amphotericin B was found with respect to intracellular as well as extracellular C. albicans.

Effects of ranitidine and sucralfate on ketoconazole bioavailability

Ketoconazole is an oral imidazole antifungal agent useful in the treatment of opportunistic fungal infections. Gastrointestinal absorption of this agent is variable and dependent on the presence of gastric acid. This study compared the effects of concomitant sucralfate administration with ranitidine administration on the pharmacokinetic disposition of a 400-mg ketoconazole dose. Six healthy male volunteers were randomized to receive 400 mg of ketoconazole alone, 1.0 g of sucralfate concomitantly with a 400-mg ketoconazole dose, or ranitidine, administered 2 h prior to a 400-mg ketoconazole dose to titrate to a gastric pH of 6. All subjects received all three regimens in crossover fashion. Gastric pH was measured continuously for 4 h after ketoconazole administration in all subjects by using a Heidelberg radiotelemetry pH capsule. Relative ketoconazole bioavailability was compared between treatments. With sucralfate, five of six subjects demonstrated a decrease in the peak drug concentration in serum as well as an increase in the time to peak concentration, indicating a delay in ketoconazole absorption. The mean area under the concentration-time curve from 0 to 12 h for ketoconazole following gastric alkalinization was significantly different from that of either ketoconazole alone or ketoconazole with sucralfate (P less than 0.01). Continuous gastric pH monitoring allowed correlation between the decrease in ketoconazole bioavailability observed with ranitidine and the increase in gastric pH. The apparent decrease in ketoconazole bioavailability observed with sucralfate appears to be caused by an alternative mechanism since a change in gastric pH was not observed. On the basis of these findings, separating the administration of ketoconazole and sucralfate should be considered to decrease the potential for interaction of sucralfate on ketoconazole bioavailability.

Comparison study of broth macrodilution and microdilution antifungal susceptibility tests

An evaluation of broth dilution antifungal susceptibility tests was performed by determining both the micro- and macrodilution MICs of amphotericin B, flucytosine, fluconazole, ketoconazole, and cilofungin against 38 isolates of Candida albicans, Candida lusitaniae, Candida parapsilosis, Candida tropicalis, Cryptococcus neoformans, and Torulopsis glabrata. The following preliminary antifungal working group recommendations of the National Committee for Clinical Laboratory Standards for broth macrodilution tests with antifungal agents were used: inocula standardized to 1 x 10(4) to 5 x 10(4) CFU/ml with a spectrophotometer, RPMI 1640 medium buffered with morpholinopropanesulfonic acid (pH 7.0), incubation at 35 degrees C for 24 to 48 h, and an additive drug dilution procedure. Broth microdilution MICs were higher (two or more dilutions) than broth macrodilution MICs for all isolates tested with amphotericin B and for most isolates tested with ketoconazole, fluconazole, and cilofungin. MICs of flucytosine were the same by both techniques or lower by the broth microdilution test except in tests with C. neoformans. However, the only statistically significant differences between the two tests were observed with amphotericin B against all isolates (P = 0.01 to 0.07), ketoconazole against C. neoformans (P = 0.01 to 0.02), and cilofungin against C. albicans (P = 0.05 to 0.14). Tests performed with less dense inocula (1 x 10(3) to 5 x 10(3] produced similar results.