Antifungals Campoy, Sonia; Adrio, José L.
Biochemical pharmacology,
06/2017, Letnik:
133
Journal Article
Recenzirano
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The need for new antifungal agents is undeniable. Current therapeutic choices for the treatment of invasive fungal infections are limited to three classes of drugs. Most used ...antifungal agents are not completely effective due to the development of resistance, host toxicity and undesirable side effects that limit their use in medical practice. Invasive fungal infections have significantly increased over the last decades and the mortality rates remain unacceptably high. More threatening, new resistance patterns have been observed including simultaneous resistance to different antifungal classes.
In the last years, deeper insights into the molecular mechanisms for fungal resistance and virulence have yielded some new potential targets for antifungal therapeutics. Chemical genomics-based screenings, high throughput screenings of natural products and repurposing of approved drugs are some of the approaches being followed for the discovery of new antifungal molecules. However, despite the emerging need for effective antifungal agents, the current pipeline contains only a few promising molecules, with novel modes of action, in early clinical development stages.
Antifungal proteins (AFPs) of fungal origin have been described in filamentous fungi. AFPs are small, highly stable, cationic cysteine-rich proteins (CRPs) that are usually secreted in high amounts ...and show potent antifungal activity against non-self fungi. The role of AFPs in the biology of the producer fungus remains unclear. AFPs have been proposed as promising lead compounds for the development of new antifungals. The analyses of available antifungal CRP sequences from fungal origin and their phylogenetic reconstruction led us to propose a new classification of AFPs in three distinct classes: A, B and C. We initiate for the first time the characterization of an AFP in a fungal pathogen, by analysing the functional role of the unique afpB gene in the citrus fruit pathogen Penicillium digitatum. Null ΔafpB mutants revealed that this gene is dispensable for vegetative growth and fruit infection. However, strains that artificially express afpB in a constitutive way (afpB C) showed a phenotype of restricted growth, distortion of hyphal morphology and strong reduction in virulence to citrus fruits. These characteristics support an antifungal role for AfpB. Surprisingly, we did not detect the AfpB protein in any of the P. digitatum strains and growth conditions that were analysed in this study, regardless of high gene expression. The afpB C phenotype is not stable and occasionally reverts to a wild type-like phenotype but molecular changes were not detected with this reversion. The reduced virulence of afpB C strains correlated with localized fruit necrosis and altered timing of expression of fruit defence genes.
Background Voriconazole pharmacokinetic and pharmacodynamic data are lacking in children. Methods Records at the Childrens Hospital Los Angeles were reviewed for children with ⩾ 1 serum voriconazole ...concentration measured from 1 May 2006 through 1 June 2007. Information on demographic characteristics, dosing histories, serum concentrations, toxicity and survival, and outcomes was obtained. Results A total of 207 voriconazole measurements were obtained from 46 patients (age, 0.8–20.5 years). A 2-compartment Michaelis-Menten pharmacokinetic model fit the data best but explained only 80% of the observed variability. The crude mortality rate was 28%, and each trough serum voriconazole concentration < 1000 ng/mL was associated with a 2.6-fold increased odds of death (95% confidence interval, 1.6–4.8; P p.002). Serum voriconazole concentrations were not associated with hepatotoxicity. Simulations predicted an intravenous dose of 7 mg/kg or an oral dose of 200 mg twice daily would achieve a trough >1000 ng/mL in most patients, but with a wide range of possible concentrations. Conclusions We found a pharmacodynamic association between a voriconazole trough >1000 ng/mL and survival and marked pharmacokinetic variability, particularly after enteral dosing, justifying the measurement of serum concentrations.
Amphotericin B (AmB) is a prototypical small molecule natural product that can form ion channels in living eukaryotic cells and has remained refractory to microbial resistance despite extensive ...clinical utilization in the treatment of life-threatening fungal infections for more than half a century. It is now widely accepted that AmB kills yeast primarily via channel-mediated membrane permeabilization. Enabled by the iterative cross-coupling-based synthesis of a functional group deficient derivative of this natural product, we have discovered that channel formation is not required for potent fungicidal activity. Alternatively, AmB primarily kills yeast by simply binding ergosterol, a lipid that is vital for many aspects of yeast cell physiology. Membrane permeabilization via channel formation represents a second complementary mechanism that further increases drug potency and the rate of yeast killing. Collectively, these findings (i) reveal that the binding of a physiologically important microbial lipid is a powerful and clinically validated antimicrobial strategy that may be inherently refractory to resistance, (ii) illuminate a more straightforward path to an improved therapeutic index for this clinically vital but also highly toxic antifungal agent, and (iii) suggest that the capacity for AmB to form proteinlike ion channels might be separable from its cytocidal effects.
The contribution of low‐abundance microbial species to soil ecosystems is easily overlooked because there is considerable overlap between metabolic abilities (functional redundancy) of dominant and ...subordinate microbial species. Here we studied how loss of less abundant soil bacteria affected the production of antifungal volatiles, an important factor in the natural control of soil‐borne pathogenic fungi. We provide novel empirical evidence that the loss of soil bacterial species leads to a decline in the production of volatiles that suppress root pathogens. By using dilution‐to‐extinction for seven different soils we created bacterial communities with a decreasing number of species and grew them under carbon‐limited conditions. Communities with high bacterial species richness produced volatiles that strongly reduced the hyphal growth of the pathogen Fusarium oxysporum. For most soil origins loss of bacterial species resulted in loss of antifungal volatile production. Analysis of the volatiles revealed that several known antifungal compounds were only produced in the more diverse bacterial communities. Our results suggest that less abundant bacterial species play an important role in antifungal volatile production by soil bacterial communities and, consequently, in the natural suppression of soil‐borne pathogens.
Background. Voriconazole is the therapy of choice for aspergillosis and a new treatment option for candidiasis. Liver disease, age, genetic polymorphism of the cytochrome CYP2C19, and comedications ...influence voriconazole metabolism. Large variations in voriconazole pharmacokinetics may be associated with decreased efficacy or with toxicity. Methods. This study was conducted to assess the utility of measuring voriconazole blood levels with individualized dose adjustments. Results. A total of 181 measurements with high-pressure liquid chromatography were performed during 2388 treatment days in 52 patients. A large variability in voriconazole trough blood levels was observed, ranging from ⩽1 mg/L (the minimum inhibitory concentration at which, for most fungal pathogens, 90% of isolates are susceptible) in 25% of cases to >5.5 mg/L (a level possibly associated with toxicity) in 31% of cases. Lack of response to therapy was more frequent in patients with voriconazole levels ⩽1 mg/L (6 46% of 13 patients, including 5 patients with aspergillosis, 4 of whom were treated orally with a median dosage of 6 mg/kg per day) than in those with voriconazole levels >1 mg/L (15 12% of 39 patients; P=.02). Blood levels >1 mg/L were reached after increasing the voriconazole dosage, with complete resolution of infection in all 6 cases. Among 16 patients with voriconazole trough blood levels >5.5 mg/L, 5 patients (31%) presented with an encephalopathy, including 4 patients who were treated intravenously with a median voriconazole dosage of 8 mg/kg per day, whereas none of the patients with levels ⩽5.5 mg/L presented with neurological toxicity (P=.002). Comedication with omeprazole possibly contributed to voriconazole accumulation in 4 patients. In all cases, discontinuation of therapy resulted in prompt and complete neurological recovery. Conclusions. Voriconazole therapeutic drug monitoring improves the efficacy and safety of therapy in severely ill patients with invasive mycoses.
Background. There is a practical need to investigate the performance of the serum galactomannan (GM) assay in hematology patients with a potentially low pretest risk of invasive aspergillosis ...following effective antimold prophylaxis. Methods. We present a 4-year study with 262 unselected consecutive high-risk episodes, prospectively managed with posaconazole primary prophylaxis and a uniform diagnostic algorithm, including biweekly serum GM quantification for early detection of invasive aspergillosis. Results. A total of 2972 serum GM tests were performed (median, 11 per episode range, 3–30); the vast majority were negative (96.7% of tests and 83.6% of episodes). The incidence of breakthrough invasive aspergillosis was 1.9% (5/262), all with true-positive GM test results. Our study identified 30 false-positive GM evaluable episodes (85.7%; 13.8% of all evaluable episodes), validating with real-life data the low positive predictive value of the assay in this setting (12%). In 26 of these 30 episodes (86.7%), the false-positive result(s) occurred in tests performed as preemptive surveillance only. Conversely, in evaluable cases with positive GM tests and a clinical suspicion of invasive fungal disease, the performance of diagnostic-driven GM tests improved, with a positive predictive value of 89.6%. Conclusions. The low pretest risk of invasive aspergillosis in the context of effective antimold prophylaxis renders serum GM surveillance of asymptomatic patients unreliable, as all results would be either negative or false positive. The test remains useful to diagnose patients with a clinical suspicion of invasive fungal disease, calling for a more efficient copositioning of effective prophylaxis and GM testing in this clinical setting.
Amphotericin B is the archetype for small molecules that form transmembrane ion channels. However, despite extensive study for more than five decades, even the most basic features of this channel ...structure and its contributions to the antifungal activities of this natural product have remained unclear. We herein report that a powerful series of functional group-deficient probes have revealed many key underpinnings of the ion channel and antifungal activities of amphotericin B. Specifically, in stark contrast to two leading models, polar interactions between mycosamine and carboxylic acid appendages on neighboring amphotericin B molecules are not required for ion channel formation, nor are these functional groups required for binding to phospholipid bilayers. Alternatively, consistent with a previously unconfirmed third hypothesis, the mycosamine sugar is strictly required for promoting a direct binding interaction between amphotericin B and ergosterol. The same is true for cholesterol. Synthetically deleting this appendage also completely abolishes ion channel and antifungal activities. All of these results are consistent with the conclusion that a mycosamine-mediated direct binding interaction between amphotericin B and ergosterol is required for both forming ion channels and killing yeast cells. The enhanced understanding of amphotericin B function derived from these synthesis-enabled studies has helped set the stage for the more effective harnessing of the remarkable ion channel-forming capacity of this prototypical small molecule natural product.
Background. Invasive aspergillosis is an important cause of morbidity and mortality in immunocompromised patients. Current treatments provide limited benefit. Posaconazole is an extended-spectrum ...triazole with in vitro and in vivo activity against Aspergillus species. Methods. We investigated the efficacy and safety of posaconazole oral suspension (800 mg/day in divided doses) as monotherapy in an open-label, multicenter study in patients with invasive aspergillosis and other mycoses who were refractory to or intolerant of conventional antifungal therapy. Data from external control cases were collected retrospectively to provide a comparative reference group. Results. Cases of aspergillosis deemed evaluable by a blinded data review committee included 107 posaconazole recipients and 86 control subjects (modified intent-to-treat population). The populations were similar and balanced with regard to prespecified demographic and disease variables. The overall success rate (i.e., the data review committee—assessed global response at the end of treatment) was 42% for posaconazole recipients and 26% for control subjects (odds ratio, 4.06; 95% confidence interval, 1.50–11.04; P = .006). The differences in response between the modified intent-to-treat treatment groups were preserved across additional, prespecified subsets, including infection site (pulmonary or disseminated), hematological malignancy, hematopoietic stem cell transplantation, baseline neutropenia, and reason for enrollment (patient was refractory to or intolerant of previous antifungal therapy). An exposure-response relationship was suggested by pharmacokinetic analyses. Conclusions. Although the study predates extensive use of echinocandins and voriconazole, these findings demonstrate that posaconazole is an alternative to salvage therapy for patients with invasive aspergillosis who are refractory to or intolerant of previous antifungal therapy.
is a multidrug-resistant yeast which has emerged in health care facilities worldwide; however, little is known about identification methods, patient colonization, environmental survival, spread, and ...drug resistance. Colonization on both biotic (patients) and abiotic (health care objects) surfaces, along with travel, appear to be the major factors for the spread of this pathogen across the globe. In this investigation, we present laboratory findings from an ongoing
outbreak in New York (NY) from August 2016 through 2018. A total of 540 clinical isolates, 11,035 patient surveillance specimens, and 3,672 environmental surveillance samples were analyzed. Laboratory methods included matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for yeast isolate identification, real-time PCR for rapid surveillance sample screening, culture on selective/nonselective media for recovery of
and other yeasts from surveillance samples, antifungal susceptibility testing to determine the
resistance profile, and Sanger sequencing of the internal transcribed spacer (ITS) and D1/D2 regions of the ribosomal gene for
genotyping. Results included (a) identification and confirmation of
in 413 clinical isolates and 931 patient surveillance isolates as well as identification of 277 clinical cases and 350 colonized cases from 151 health care facilities, including 59 hospitals, 92 nursing homes, 1 long-term acute care hospital (LTACH), and 2 hospices, (b) successful utilization of an in-house developed
real-time PCR assay for the rapid screening of patient and environmental surveillance samples, (c) demonstration of relatively heavier colonization of
in nares than in the axilla/groin, and (d) predominance of the South Asia clade I with intrinsic resistance to fluconazole and elevated MIC to voriconazole (81%), amphotericin B (61%), flucytosine (5FC) (3%), and echinocandins (1%). These findings reflect greater regional prevalence and incidence of
and the deployment of better detection tools in an unprecedented outbreak.
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