Micafungin

Improving the production of the micafungin precursor FR901379 in an industrial production strain

BACKGROUND

Micafungin is an echinocandin-type antifungal agent used for the clinical treatment of invasive fungal infections. It is semisynthesized from the sulfonated lipohexapeptide FR901379, a nonribosomal peptide produced by the filamentous fungus Coleophoma empetri. However, the low fermentation efficiency of FR901379 increases the cost of micafungin production and hinders its widespread clinical application.

RESULTS

Here, a highly efficient FR901379-producing strain was constructed via systems metabolic engineering in C. empetri MEFC09. First, the biosynthesis pathway of FR901379 was optimized by overexpressing the rate-limiting enzymes cytochrome P450 McfF and McfH, which successfully eliminated the accumulation of unwanted byproducts and increased the production of FR901379. Then, the functions of putative self-resistance genes encoding β-1,3-glucan synthase were evaluated in vivo. The deletion of CEfks1 affected growth and resulted in more spherical cells. Additionally, the transcriptional activator McfJ for the regulation of FR901379 biosynthesis was identified and applied in metabolic engineering. Overexpressing mcfJ markedly increased the production of FR901379 from 0.3 g/L to 1.3 g/L. Finally, the engineered strain coexpressing mcfJ, mcfF, and mcfH was constructed for additive effects, and the FR901379 titer reached 4.0 g/L under fed-batch conditions in a 5 L bioreactor.

CONCLUSIONS

This study represents a significant improvement for the production of FR901379 and provides guidance for the establishment of efficient fungal cell factories for other echinocandins.

Potent antifungal agents and use of nanocarriers to improve delivery to the infected site: A systematic review

There are four major classes of antifungals with the predominant mechanism of action being targeting of cell wall or cell membrane. As in other drugs, low solubility of these compounds has led to low bioavailability in target tissues. Enhanced drug dosages have effects such as toxicity, drug-drug interactions, and increased drug resistance by fungi. This article reviews the current state-of-the-art of antifungals, structure, mechanism of action, other usages, and toxic side effects. The emergence of nanoformulations to transport and uniformly release cargo at the target site is a boon in antifungal treatment. The article details research that lead to the development of nanoformulations of antifungals and potential advantages and avoidance of the lacunae characterizing conventional drugs. A range of nanoformulations based on liposomes, polymers are in various stages of research and their potential advantages have been brought out. It could be observed that under similar dosages, test models, and duration, nanoformulations provided enhanced activity, reduced toxicity, higher uptake and higher immunostimulatory effects. In most instances, the mechanism of antifungal activity of nanoformulations was similar to that of regular antifungal. There are possibilities of coupling multiple antifungals on the same nano-platform. Increased activity coupled with multiple mechanisms of action presents for nanoformulations a tremendous opportunity to overcome antifungal resistance. In the years to come, robust methods for the preparation of nanoformulations taking into account the repeatability and reproducibility in action, furthering the studies on nanoformulation toxicity and studies of human models are required before extensive use of nanoformulations as a prescribed drug.

Imp2, the PSTPIP homolog in fission yeast, affects sensitivity to the immunosuppressant FK506 and membrane trafficking in fission yeast

Cytokinesis is a highly ordered process that divides one cell into two cells, which is functionally linked to the dynamic remodeling of the plasma membrane coordinately with various events such as membrane trafficking. Calcineurin is a highly conserved serine/threonine protein phosphatase, which regulates multiple biological functions, such as membrane trafficking and cytokinesis. Here, we isolated imp2-c3, a mutant allele of the imp2(+) gene, encoding a homolog of the mouse PSTPIP1 (proline-serine-threonine phosphatase interacting protein 1), using a genetic screen for mutations that are synthetically lethal with calcineurin deletion in fission yeast. The imp2-c3 mutants showed a defect in cytokinesis with multi-septated phenotypes, which was further enhanced upon treatment with the calcineurin inhibitor FK506. Notably, electron micrographs revealed that the imp2-c3 mutant cells accumulated aberrant multi-lamella Golgi structures and putative post-Golgi secretory vesicles, and exhibited fragmented vacuoles in addition to thickened septa. Consistently, imp2-c3 mutants showed a reduced secretion of acid phosphatase and defects in vacuole fusion. The imp2-c3 mutant cells exhibited a weakened cell wall, similar to the membrane trafficking mutants identified in the same genetic screen such as ypt3-i5. These findings implicate the PSTPIP1 homolog Imp2 in Golgi/vacuole function, thereby affecting various cellular processes, including cytokinesis and cell integrity.

Micafungin: the US perspective

Invasive fungal infections cause considerable morbidity and mortality in nosocomial settings and amongst immunocompromised hosts. Invasive candidiasis and aspergillosis remain the most common invasive fungal infections, with Candida spp. constituting the fourth most common bloodstream infection in the USA. Currently available antifungal therapies include the polyene, antimetabolite, allylamine, azole and echinocandin drug classes. Micafungin, approved in March 2005 by the Food and Drug Administration for use in the USA, has shown safety and efficacy for the treatment of candidiasis and aspergillosis in clinical trials in Japan, Europe and South Africa. Micafungin holds promise as a first-line treatment option for candidiasis, as well as prophylaxis against invasive fungal infections during periods of neutropenia in high-risk patients.

Development and validation of a stability-indicating high performance liquid chromatographic (HPLC) method for the determination of related substances of micafungin sodium in drug substances

An isocratic, sensitive and stability-indicating high performance liquid chromatographic (HPLC) method for separation and determination of the related substances of micafungin sodium was developed. The chromatographic separation was achieved on Agilent Zorbax SB-C18 column (250 × 4.6 mm, 5 μm). Forced degradation study confirmed that the newly developed method was specific and selective to the degradation products. The performance of the method was validated according to the present ICH guidelines for specificity, linearity, accuracy, precision and robustness. Regression analysis showed correlation coefficient value greater than 0.999 for micafungin sodium and its six impurities. Limit of detection of impurities was in the range of 0.006%-0.013% indicating the high sensitivity of the newly developed method. Accuracy of the method was established based on the recovery obtained between 98.2% and 102.0% for all impurities. RSD obtained for the repeatability and intermediate precision experiments, was less than 1.0%. The method was successfully applied to quantify related substances of micafungin sodium in bulk drugs.

Comparison of echinocandin antifungals

The incidence of invasive fungal infections, especially those due to Aspergillus spp. and Candida spp., continues to increase. Despite advances in medical practice, the associated mortality from these infections continues to be substantial. The echinocandin antifungals provide clinicians with another treatment option for serious fungal infections. These agents possess a completely novel mechanism of action, are relatively well-tolerated, and have a low potential for serious drug-drug interactions. At the present time, the echinocandins are an option for the treatment of infections due Candida spp (such as esophageal candidiasis, invasive candidiasis, and candidemia). In addition, caspofungin is a viable option for the treatment of refractory aspergillosis. Although micafungin is not Food and Drug Administration-approved for this indication, recent data suggests that it may also be effective. Finally, caspofungin- or micafungin-containing combination therapy should be a consideration for the treatment of severe infections due to Aspergillus spp. Although the echinocandins share many common properties, data regarding their differences are emerging at a rapid pace. Anidulafungin exhibits a unique pharmacokinetic profile, and limited cases have shown a potential far activity in isolates with increased minimum inhibitory concentrations to caspofungin and micafungin. Caspofungin appears to have a slightly higher incidence of side effects and potential for drug-drug interactions. This, combined with some evidence of decreasing susceptibility among some strains of Candida, may lessen its future utility. However, one must take these findings in the context of substantially more data and use with caspofungin compared with the other agents. Micafungin appears to be very similar to caspofungin, with very few obvious differences between the two agents.

Higher clearance of micafungin in neonates compared with adults: role of age-dependent micafungin serum binding

Micafungin, a new echinocandin antifungal agent, has been used widely for the treatment of various fungal infections in human populations. Micafungin is predominantly cleared by biliary excretion and it binds extensively to plasma proteins. Micafungin body weight-adjusted clearance is higher in neonates than in adults, but the mechanisms underlying this difference are not understood. Previous work had revealed the roles of sinusoidal uptake (Na(+) -taurocholate co-transporting peptide, NTCP; organic anion transporting polypeptide, OATP) as well as canalicular efflux (bile salt export pump, BSEP; breast cancer resistance protein, BCRP) transporters in micafungin hepatobiliary elimination. In the present study, the relative protein expression of hepatic transporters was compared between liver homogenates from neonates and adults. Also, the extent of micafungin binding to serum from neonates and adults was measured in vitro. The results indicate that relative expression levels of NTCP, OATP1B1/3, BSEP, BCRP and MRP3 were similar in neonates and in adults. However, the micafungin fraction unbound (f(u) ) in neonatal serum was about 8-fold higher than in the adult serum (0.033±0.012 versus 0.004±0.001, respectively). While there was no evidence for different intrinsic hepatobiliary clearance of micafungin between neonates and adults, our data suggest that age-dependent serum protein binding of micafungin is responsible for its higher clearance in neonates compared with adults.

In vitro investigation of the hepatobiliary disposition mechanisms of the antifungal agent micafungin in humans and rats

The purpose of the present study was to elucidate the transport mechanisms responsible for elimination of micafungin, a new semisynthetic echinocandin antifungal agent, which is predominantly cleared by biliary excretion in humans and rats. In vitro studies using sandwich-cultured rat and human hepatocytes were conducted. Micafungin uptake occurred primarily (∼75%) by transporter-mediated mechanisms in rat and human. Micafungin uptake into hepatocytes was inhibited by taurocholate (K(i) = 61 μM), Na(+) depletion (45-55% reduced), and 10 μM rifampin (20-25% reduced); these observations support the involvement of Na(+)-taurocholate-cotransporting polypeptide (NTCP/Ntcp) and, to a lesser extent, organic anion-transporting polypeptides in the hepatic uptake of micafungin. The in vitro biliary clearance of micafungin, as measured by the B-CLEAR technique, amounted to 14 and 19 μl/(min · mg protein) in human and rat, respectively. In vitro biliary excretion of micafungin was reduced by 80 and 75% in the presence of the bile salt export pump (BSEP) inhibitors taurocholate (100 μM) and nefazodone (25 μM), respectively. Biliary excretion of micafungin also was reduced in the presence of breast cancer resistance protein inhibitors [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) (10 μM) and fumitremorgin C (10 μM)]. In vitro biliary excretion of micafungin was not significantly altered by coincubation with P-glycoprotein or multidrug resistance-associated protein 2 inhibitors. These results suggest that NTCP/Ntcp and BSEP/Bsep are primarily responsible for hepatobiliary disposition of micafungin in human and rat. Interference with hepatic bile acid disposition could be one mechanism underlying hepatotoxicity associated with micafungin in some patients.

Intrapulmonary pharmacokinetics and pharmacodynamics of micafungin in adult lung transplant patients

Invasive pulmonary aspergillosis is a life-threatening infection in lung transplant recipients; however, no studies of the pharmacokinetics and pharmacodynamics (PKPD) of echinocandins in transplanted lungs have been reported. We conducted a single-dose prospective study of the intrapulmonary and plasma PKPD of 150 mg of micafungin administered intravenously in 20 adult lung transplant recipients. Epithelial lining fluid (ELF) and alveolar cell (AC) samples were obtained via bronchoalveolar lavage performed 3, 5, 8, 18, or 24 h after initiation of infusion. Micafungin concentrations in plasma, ELF, and ACs were determined using high-pressure liquid chromatography. Noncompartmental methods, population analysis, and multiple-dose simulations were used to calculate PKPD parameters. Cmax in plasma, ELF, and ACs was 4.93, 1.38, and 17.41 microg/ml, respectively. The elimination half-life in plasma was 12.1 h. Elevated concentrations in ELF and ACs were sustained during the 24-h sampling period, indicating prolonged compartmental half-lives. The mean micafungin concentration exceeded the MIC90 of Aspergillus fumigatus (0.0156 microg/ml) in plasma (total and free), ELF, and ACs throughout the dosing interval. The area under the time-concentration curve from 0 to 24 h (AUC0-24)/MIC90 ratios in plasma, ELF, and ACs were 5,077, 923.1, and 13,340, respectively. Multiple-dose simulations demonstrated that ELF and AC concentrations of micafungin would continue to increase during 14 days of administration. We conclude that a single 150-mg intravenous dose of micafungin resulted in plasma, ELF, and AC concentrations that exceeded the MIC90 of A. fumigatus for 24 h and that these concentrations would continue to increase during 14 days of administration, supporting its potential activity for prevention and early treatment of pulmonary aspergillosis.

Echinocandins: The Newest Class of Antifungals

Objective:

To review the mechanism of action, antifungal spectrum of activity, pharmacodynamics, pharmacokinetics, clinical efficacy, and safety of the echinocandins.

Data Sources:

A MEDLINE search (1982–May 2009) was conducted for articles published in the English language using the key words caspofungin, micafungin, anidulafungin, and echinocandins.

Study Selection and Data Extraction:

Medicinal chemistry, in vitro, and animal studies, as well as human trials were reviewed for information on the pharmacodynamics, pharmacokinetics, efficacy, and safety of each echinocandin. Clinical trials were reviewed and included to compare and contrast the available echinocandins.

Data Synthesis:

Three echinocandin antifungal agents are currently approved for use in the US: caspofungin, micafungin, and anidulafungin. The echinocandins have a unique mechanism of action, inhibiting β-(1,3)-d-glucan synthase, an enzyme that is necessary for the synthesis of an essential component of the cell wall of several fungi. The echinocandins display fungistatic activity against Aspergillus spp. and fungicidal activity against most Candida spp., including strains that are fluconazole-resistant. The echinocandins have been shown to be efficacious for the treatment of esophageal candidiasis, candidemia, and invasive candidiasis. In addition, caspofungin has demonstrated efficacy as empiric treatment of febrile neutropenia and salvage therapy for the treatment of invasive aspergillosis, and it is the only echinocandin approved for use in pediatric patients. Micafungin is the only echinocandin approved for use as prophylaxis against Candida infections in patients undergoing hematopoietic stem cell transplantation. Overall, resistance to echinocandins is still rare, and all agents are well tolerated, with similar adverse effect profiles and few drug–drug interactions.

Conclusions:

Echinocandins, the newest addition to the arsenal of antifungals, offer potential advantages over other classes of agents. Clinicians should assess their distinguishing characteristics, including route of metabolism, drug interaction profile, and approved indications for use, when determining which agent to include on a formulary.

Recent advances and challenges in the treatment of invasive fungal infections

The frequency of invasive fungal infections (IFIs) has increased over the last decade with the rise in at-risk populations of patients. The morbidity and mortality of IFIs are high and management of these conditions is a great challenge. With the widespread adoption of antifungal prophylaxis, the epidemiology of invasive fungal pathogens has changed. Non-albicans Candida, non-fumigatus Aspergillus and moulds other than Aspergillus have become increasingly recognised causes of invasive diseases. These emerging fungi are characterised by resistance or lower susceptibility to standard antifungal agents. Invasive infections due to these previously rare fungi are therefore more difficult to treat. Recently developed antifungal agents provide the potential to improve management options and therapeutic outcomes of these infections. The availability of more potent and less toxic antifungal agents, such as second-generation triazoles and echinocandins, has led to considerable improvement in the treatment of IFIs. This article reviews the changing spectrum of invasive mycosis, the properties of recently developed antifungal agents and their role in the management of these infections.

Drug-drug interactions of antifungal agents and implications for patient care

Drug interactions in the gastrointestinal tract, liver and kidneys result from alterations in pH, ionic complexation, and interference with membrane transport proteins and enzymatic processes involved in intestinal absorption, enteric and hepatic metabolism, renal filtration and excretion. Azole antifungals can be involved in drug interactions at all the sites, by one or more of the above mechanisms. Consequently, azoles interact with a vast array of compounds. Drug-drug interactions associated with amphotericin B formulations are predictable and result from the renal toxicity and electrolyte disturbances associated with these compounds. The echinocandins are unknown cytochrome P450 substrates and to date are relatively devoid of significant drug-drug interactions. This article reviews drug interactions involving antifungal agents that affect other agents and implications for patient care are highlighted.

Serum differentially alters the antifungal properties of echinocandin drugs

Antifungal efficacies of the echinocandin drugs caspofungin, micafungin, and anidulafungin were reduced significantly in the presence of 50% human serum, which yielded nearly equivalent MICs or minimum effective concentrations against diverse Candida spp. and Aspergillus spp. Consistent with a direct drug interaction, serum decreased the sensitivity of glucan synthase to echinocandin drugs.

Valproic acid affects membrane trafficking and cell-wall integrity in fission yeast

Valproic acid (VPA) is widely used to treat epilepsy and manic-depressive illness. Although VPA has been reported to exert a variety of biochemical effects, the exact mechanisms underlying its therapeutic effects remain elusive. To gain further insights into the molecular mechanisms of VPA action, a genetic screen for fission yeast mutants that show hypersensitivity to VPA was performed. One of the genes that we identified was vps45+, which encodes a member of the Sec1/Munc18 family that is implicated in membrane trafficking. Notably, several mutations affecting membrane trafficking also resulted in hypersensitivity to VPA. These include ypt3+ and ryh1+, both encoding a Rab family protein, and apm1+, encoding the mu1 subunit of the adaptor protein complex AP-1. More importantly, VPA caused vacuolar fragmentation and inhibited the glycosylation and the secretion of acid phosphatase in wild-type cells, suggesting that VPA affects membrane trafficking. Interestingly, the cell-wall-damaging agents such as micafungin or the inhibition of calcineurin dramatically enhanced the sensitivity of wild-type cells to VPA. Consistently, VPA treatment of wild-type cells enhanced their sensitivity to the cell-wall-digesting enzymes. Altogether, our results suggest that VPA affects membrane trafficking, which leads to the enhanced sensitivity to cell-wall damage in fission yeast.

Rho2 is a target of the farnesyltransferase Cpp1 and acts upstream of Pmk1 mitogen-activated protein kinase signaling in fission yeast

We have previously demonstrated that knockout of the calcineurin gene or inhibition of calcineurin activity by immunosuppressants resulted in hypersensitivity to Cl- in fission yeast. We also demonstrated that knockout of the components of the Pmk1 mitogen-activated protein kinase (MAPK) pathway, such as Pmk1 or Pek1 complemented the hypersensitivity to Cl-. Using this interaction between calcineurin and Pmk1 MAPK, here we developed a genetic screen that aims to identify new regulators of the Pmk1 signaling and isolated vic (viable in the presence of immunosuppressant and chloride ion) mutants. One of the mutants, vic1-1, carried a missense mutation in the cpp1+ gene encoding a beta subunit of the protein farnesyltransferase, which caused an amino acid substitution of aspartate 155 of Cpp1 to asparagine (Cpp1(D155N)). Analysis of the mutant strain revealed that Rho2 is a novel target of Cpp1. Moreover, Cpp1 and Rho2 act upstream of Pck2-Pmk1 MAPK signaling pathway, thereby resulting in the vic phenotype upon their mutations. Interestingly, compared with other substrates of Cpp1, defects of Rho2 function were more phenotypically manifested by the Cpp1(D155N) mutation. Together, our results demonstrate that Cpp1 is a key component of the Pck2-Pmk1 signaling through the spatial control of the small GTPase Rho2.

Pharmacokinetics-pharmacodynamics of micafungin in Japanese patients with deep-seated mycosis

The objective of this study was to describe the pharmacokinetic profile and investigate the effective concentration of micafungin in Japanese male patients with deep-seated mycosis. 66 patients were treated with i.v. micafungin 12.5-150 mg intravenously for up to 56 days. At this dose range, micafungin showed linear pharmacokinetics, and the mean values of Cmax and Cmin amounted to 3.16-12.9 microg/mL and 0.70-3.68 microg/mL, respectively. The mean value for the elimination half-life was 13.5 h (95 samples from 65 patients), and it remained almost constant over the dose range. In addition, the elimination half-life was not influenced by age, gender or weight, and was similar to that found in healthy subjects. The active metabolites M1 and M2 were detectable, but their exposure was lower than that of the unchanged drug. The pharmacokinetic-pharmacodynamics ob micafungin were then investigated. The overall clinical response rate against aspergillosis and candidiasis showed good results at a dose of 50 mg and over. The Cmax and Cmin at the latter dose amounted to 5.16 and 1.41 microg/mL, respectively. In conclusion, micafungin showed linear pharmacokinetics at doses ranging from 12.5 to 150 mg, and the effective concentration was considered to be over 5 microg/mL as maximum level in Japanese patients with deep-seated mycosis such as candidiasis and aspergillosis.

Genetic and functional interaction between Ryh1 and Ypt3: two Rab GTPases that function in S. pombe secretory pathway

We have previously isolated ypt3-i5 mutant and showed that Ypt3 GTPase functions in the fission yeast secretory pathway. Here, the same genetic screen led to the isolation of ryh1-i6, a mutant allele of the ryh1+ gene encoding a homolog of Rab6. The ryh1-i6 mutant showed phenotypes that support its role in retrograde traffic from endosome to the Golgi. Interestingly, ryh1+ gene deletion was synthetically lethal with ypt3-i5 mutation. Consistently, the over-expression of the GDP-conformational mutant, Ryh1T25 N, inhibited the growth of ypt3-i5 mutant but had no effect on that of wild-type cells. Furthermore, the over-expression of the Ryh1T25N mutant inhibited the acid phosphatase glycosylation and exacerbated the cell wall integrity of ypt3-i5 mutant, but had no effect on those of wild-type cells. GFP-Ryh1 and GFP-Ypt3 both localized at the Golgi/endosome, but showed distinct subcellular localizations. The localization of GFP-Ryh1 in ypt3-i5 mutant and that of GFP-Ypt3 in ryh1-i6 mutant were distinct from those in wild-type cells. In addition, Ryh1 as well as Ypt3 were shown to be involved in acid phosphatase secretion. These results suggest that Ryh1 is involved in the secretory pathway and may have a potential overlapping function with Ypt3 in addition to its role in recycling.

Micafungin: a new echinocandin

Micafungin, a potent inhibitor of 1,3-beta-D-glucan synthase, has become the second available agent in the echinocandins class that is approved for use in clinical practice. This agent shares with caspofungin an identical spectrum of in vitro activity against Candida albicans, non-albicans species of Candida, and Aspergillus species, as well as several but not all pathogenic molds. If anything, its in vitro activity appears to be superior to that of caspofungin, although the clinical relevance of this observation is unclear. The clinical role of micafungin appears to be similar to that of caspofungin, although clinical data are still lacking at this stage, with initial approval only for treatment of esophageal candidiasis and prophylaxis in subjects with neutropenia. Pharmacokinetic and pharmacodynamic studies and reports of adverse effects and safety have reported similar but not identical results to those of other agents in the echinocandin class. Factors such as acquisition costs and the potential for resistance development may be more relevant to its widespread use than in vitro and in vivo data comparisons with caspofungin.

Linear Pharmacokinetics of Micafungin and Its Active Metabolites in Japanese Pediatric Patients with Fungal Infections

The objective of this study was to propose the appropriate dosage regimen of micafungin for pediatric use, considering the effects of dose-linearity, age and other cofactors on the pharmacokinetics. Pharmacokinetic analysis of micafungin and its active metabolites (M1 and M2) after intravenous infusion at doses of 1 to 3 mg/kg was conducted for 19 Japanese pediatric patients (3 infants, 7 toddlers, and 9 pupils) with deep mycosis caused by either Aspergillus or Candida species. One patient was given the maximum dose of 6 mg/kg. The Cmax of micafungin increased in proportion to the dose. The mean values (S.D.) were 5.03 (2.33), 10.25 (4.45), 14.8 (5.52) and 21.1 microg/ml at 1, 2 , 3 and 6 mg/kg, respectively. These parameters were comparable to those seen in adults when the parameter was normalized by body weight. The elimination half life (t1/2) of micafungin over the dose range was apparently constant with the value of 13.1 h. There was no difference between the age groups observed. In fact, the metabolite concentrations were almost the same as those obtained for non-pediatric patients. Thus, micafungin showed the same dose-proportional pharmacokinetics in pediatric patients as it did in adults. No age dependent pharmacokinetics were observed in this study. It was concluded that the body weight adjustment was adequate for the treatment of micafungin in pediatric patients.

Population Pharmacokinetic Analysis of Micafungin in Japanese Patients with Fungal Infections

The object of this analysis was to develop a population pharmacokinetic model of micafungin, a new anti-fungal agent of the echinocandin class, to optimize dosing in Japanese patients with fungal infections. Population pharmacokinetics parameters were determined using NONMEM based on pharmacokinetic data from 198 subjects in seven clinical studies, comprising four phase I, two phase II and one pediatric phase III study. The healthy subjects received intravenous infusion of 2.5-150 mg micafungin. Adult and pediatric patients, age range of 8 month to 15 yeras old, were received 25-150 mg and 1-6 mg/kg daily, respectively. A total of 1825 micafungin plasma samples were available for this analysis. Two-compartment pharmacokinetic model was adopted. The clearance of micafungin was influenced by body weight in children and platelet counts (PLT). However the PLT accounted for less than 20% of the variation of micafungin clearance in Japanese subjects. In conclusions, body weight is the primary covariate factor in pediatric patients. The dose adjustment by body weight would be required only pediatric patients for the micafungin therapy in Japanese patients with fungal infection.

Myocardial infarction caused by Aspergillus embolization in a patient with aplastic anemia

A 38-year-old Japanese man with severe aplastic anemia had invasive pulmonary aspergillosis as a complication. He was treated with amphotericin B for six weeks, but the aspergillosis did not improve. Then he experienced a fatal myocardial infarction. An autopsy revealed disseminated aspergillosis involving pericarditis and Aspergillus embolization to the coronary arteries. This led to the acute myocardial infarction. Cardiac aspergillosis is rare, but should be included within the differential diagnosis when chest pain of unknown origin occurs in an immunosuppressed patient.

An update on antifungal targets and mechanisms of resistance in Candida albicans

Much progress has been made in the last decade in identifying genes responsible for antifungal resistance in Candida albicans. Attention has focused on five major C. albicans genes: ABC transporter genes CDR1 and CDR2, major facilitator efflux gene MDR1, and ergosterol biosynthesis genes ERG11 and ERG3. Resistance involves mutations in 14C-lanosterol demethylase, targeted by fluconazole (FLZ) and encoded by ERG11, and mutations that up-regulate efflux genes that probably efflux the antifungals. Mutations that affect ERG3 mutations have been understudied as mechanism resistance among clinical isolates. In vitro resistance in clinical isolates typically involves step-wise mutations affecting more than one of these genes, and often unidentified genes. Different approaches are needed to identify these other genes. Very little is understood about reversible adaptive resistance of C. albicans despite its potential clinical significance; most clinical failures to control infections other than oropharyngeal candidiasis (OPC) occur with in vitro susceptible strains. Tolerance of C. albicans to azoles has been attributed to the calcineurin stress-response pathway, offering new potential targets for next generation antifungals. Recent studies have identified genes that regulate CDR1 or ERG genes. The focus of this review is C. albicans, although information on Saccharomyces cerevisiae or Candida glabrata is provided in areas in where Candida research is underdeveloped. With the completion of the C. albicans genomic sequence, and new methods for high throughput gene overexpression and disruption, rapid progress towards understanding the regulation of resistance, novel resistance mechanisms, and adaptive resistance is expected in the near future.

Echinocandins: role in antifungal therapy, 2005

Novel therapies to treat invasive fungal infections have revolutionised the care of patients with candidiasis, aspergillosis and other less common fungal infections. Physicians in the twenty first century have access to safer versions of conventional drugs (i.e., lipid amphotericin B products), extended-spectrum versions of established drugs (i.e., voriconazole), as well as a new class of antifungal agents; the echinocandins. The increased number of options in the antifungal armamentarium is well timed, as the incidence of both invasive candidiasis and invasive aspergillosis, and the financial burden associated with these infections, have increased significantly in the past several decades. The increasing incidence of fungal infections has risen in parallel with the increase in critically ill and immunocompromised patients. Candida is the fourth most common bloodstream isolate, approximately 50% of which are non-albicans species. Estimates suggest there to be 9.8 episodes of invasive candidiasis per 1000 admissions to surgical intensive care units, with attributable mortality at 30% and cost per episode of US44,000 dollars. The burden of candidiasis is even higher in the paediatric population, with Candida being the second most common bloodstream infection. The increase in non-albicans candidiasis mandates the introduction of new antifungal agents capable of treating these often azole-resistant isolates. In addition, there has been a rise in the incidence of invasive aspergillosis, the most common invasive mould infection following haematopoietic stem cell transplantation, with an estimated incidence of 10 - 20%. The mortality associated with invasive aspergillosis has increased by 357% since 1980. Unfortunately, the overall survival rate among patients treated with amphotericin B, and even voriconazole, remains suboptimal, as evidenced by the failure of treatment in 47% of patients in the landmark voriconazole versus amphotericin B trial. Given the increasing incidence and suboptimal outcomes of these serious fungal infections, novel therapies represent an opportunity for significant advancement in clinical care. The current challenge is to discover the optimal place for the echinocandins in the treatment of invasive fungal infections.

Phosphatidylinositol-4-phosphate 5-kinase regulates fission yeast cell integrity through a phospholipase C-mediated protein kinase C-independent pathway

Fission yeast its3-1 mutant is an allele of the essential gene its3+ that encodes a phosphatidylinositol-4-phosphate 5-kinase (PIP5K) that produces phosphatidylinositol 4,5-bisphosphate. We found that the its3-1 mutant is sensitive to micafungin, a (1,3)-beta-D-glucan synthase inhibitor, suggesting a cell wall integrity defect. Consistently, its3-1 mutation caused synthetic lethality with a (1,3)-beta-D-glucan synthase mutant, bgs1-i2, and its3-1 mutant cells showed aberrant localization of green fluorescent protein-Bgs1. Similar aberrant localization of green fluorescent protein-tagged Rgf1, a putative phosphatidylinositol 4,5-bisphosphate-binding guanine nucleotide exchange factor for Rho protein, in its3-1 mutants was observed, suggesting a defective Rgf1/Rho pathway. To unravel the molecular mechanism(s), putative downstream components of PIP5K signaling were analyzed. Unexpectedly, overexpression of phospholipase C (Plc1), but not that of protein kinase C (PKC; Pck1 and Pck2), suppressed the phenotypes of the its3-1 mutant. These findings indicate that PKCs are not involved in the suppression, and further analysis revealed that PKCs are not downstream of Plc1 in fission yeast. Also, the enzymatic activity of Plc1 is essential for the suppression of the phenotypes and for the viability of the its3-1 mutant. These findings suggest that Its3 PIP5K regulates cell integrity through a Plc1-mediated PKC-independent pathway, in addition to the Rho/PKC pathway.