Toward more effective antifungal therapy: the prospects of combination therapy

Improved outcomes associated with advances in therapy for invasive fungal infections in immunocompromised hosts

Invasive fungal infections cause substantial morbidity and mortality in immunocompromised hosts. The response rate to therapy, in particular for invasive aspergillosis and invasive mould infections, has been poor. Recently a number of techniques to facilitate early diagnosis of these infections, in parallel with the development of a number of antifungals with increased potency and lower toxicity, have raised optimism that outcomes for invasive fungal infection can be improved upon. The availability of lipid formulations of amphotericin B, azoles with extended spectrum against filamentous fungi and the development of a new class of antifungal agents, the echinocandins, presents the clinician with a range of therapeutic choices. Recent clinical trials have provided important insights into how these agents should be used. In particular, voriconazole has demonstrated superior efficacy to amphotericin B in the management of invasive aspergillosis, posaconazole has been shown to have significant efficacy in the prophylaxis of invasive fungal infection in high-risk individuals and a role in salvage therapy of invasive aspergillosis, caspofungin has demonstrated efficacy in salvage therapy of invasive aspergillosis, and each of the echinocandins show activity without significant toxicity in invasive candidiasis. Nevertheless, many therapeutic areas of uncertainty remain, including the role of combination therapy, and will provide the focus for future studies.

Safety and efficacy of a caspofungin-based combination therapy for treatment of proven or probable aspergillosis in pediatric hematological patients

Background

Fungal infections are diagnosed increasingly often in patients affected by hematological diseases and their mortality has remained high. The recent development of new antifungal drugs gives the clinician the possibility to assess the combination of antifungal drugs with in-vitro or in animal-model synergistic effect.

Methods

We analyzed retrospectively the safety and efficacy of caspofungin-based combination therapy in 40 children and adolescents, most of them were being treated for a malignant disease, who developed invasive aspergillosis (IA) between November 2002 and November 2005.

Results

Thirteen (32.5%) patients developed IA after hematopoietic stem cell transplantation (HSCT), 13 after primary diagnosis, usually during remission-induction chemotherapy, and 14 after relapse of disease. Severe neutropenia was present in 31 (78%) out of the 40 patients. IA was classified as probable in 20 (50%) and documented in 20 (50%) patients, respectively. A favorable response to antifungal therapy was obtained in 21 patients (53%) and the probability of 100-day survival was 70%. Different, though not significant, 100-day survival was observed according to the timing of diagnosis of IA: 51.9% after HSCT; 71.4% after relapse; and 84.6% after diagnosis of underlying disease, p 0.2. After a median follow-up of 0.7 years, 20 patients are alive (50%). Overall, the combination therapy was well tolerated. In multivariate analysis, the factors that were significantly associated to a better overall survival were favorable response to antifungal therapy, p 0.003, and the timing of IA in the patient course of underlying disease, p 0.04.

Conclusion

This study showed that caspofungin-based combination antifungal therapy is an effective therapeutic option also for pediatric patients with IA. These data need to be confirmed by prospective, controlled studies.

New approaches to invasive fungal infections in acute leukemia and hematopoietic stem cell transplant patients

Recognition and treatment of invasive fungal infections in acute leukemia and hematopoietic stem cell transplant patients are important clinical challenges. New diagnostic tools, such as fungal serologic assays and high-resolution CT scans, offer the hope for earlier initiation of antifungal therapy and improved treatment results. New antifungal agents offer choices that in some cases are less toxic than older drugs and in other cases are more efficacious. Combining the new diagnostic tools with new drugs, novel strategies are being evaluated to change our approaches to these deadly infections.

Modeling the combination of amphotericin B, micafungin, and nikkomycin Z against Aspergillus fumigatus in vitro using a novel response surface paradigm

Response surface methods for the study of multiple-agent interaction allow one to model all of the information present in full concentration-effect data sets and to visualize and quantify local regions of synergy, additivity, and antagonism. In randomized wells of 96-well plates, Aspergillus fumigatus was exposed to various combinations of amphotericin B, micafungin, and nikkomycin Z. The experimental design was comprised of 91 different fixed-ratio mixtures, all performed in quintuplicate. After 24 h of drug exposure, drug effect on fungal viability was assessed using the tetrazolium salt 2,3-bis {2-methoxy-4-nitro-5-[(sulfenylamino) carbonyl]-2H-tetrazolium-hydroxide} (XTT) assay. First, we modeled each fixed-ratio combination alone using the four-parameter Hill concentration-effect model. Then, we modeled each parameter, including the 50% inhibitory concentration (IC(50)) effect, versus the proportion of each agent using constrained polynomials. Finally, we modeled the three-agent response surface overall. The overall four-dimensional response surface was complex, but it can be explained in detail both analytically and graphically. The grand model that fit the best included complex polynomial equations for the slope parameter m and the combination index (equivalent to the IC(50) for a fixed-ratio concentration, but with concentrations normalized by the respective IC(50)s of the drugs alone). There was a large region of synergy, mostly at the nikkomycin Z/micafungin edge of the ternary plots for equal normalized proportions of each drug and extending into the center of the plots. Applying this response surface method to a huge data set for a three-antifungal-agent combination is novel. This new paradigm has the potential to significantly advance the field of combination antifungal pharmacology.

An open study of the comparative efficacy and safety of caspofungin and liposomal amphotericin B in treating invasive fungal infections or febrile neutropenia in patients with haematological malignancy

In a clinical non-trial setting, the efficacy and safety of caspofungin was compared with liposomal amphotericin B for the management of febrile neutropenia or invasive fungal infections in 73 episodes in patients with haematological malignancy. There were fewer episodes of drug toxicity with caspofungin than liposomal amphotericin B (58.3 vs 83.7 %, P=0.02). The favourable response rate for episodes of febrile neutropenia treated with caspofungin or liposomal amphotericin B was similar at 37.5 and 53.8 %, respectively, but more breakthrough fungal infections occurred with caspofungin than with liposomal amphotericin B (33.3 vs 0 %, P<0.05) in these patients who did not receive antifungal prophylaxis. None of four episodes of candidaemia or hepatosplenic candidiasis responded to caspofungin compared with three of four episodes treated with liposomal amphotericin B. Mortality was significantly higher with caspofungin treatment compared with liposomal amphotericin B (6/24 vs 2/49, P=0.01), mainly due to an excess of fungal infections (P=0.04). Caspofungin treatment was a significant independent predictor of mortality [odds ratio=7.6 (95 % confidence interval 1.2-45.5)] when sepsis severity, prolonged neutropenia and length of antifungal therapy were considered in a multiple logistic regression model. In clinical practice, there is a suggestion that caspofungin may not be as effective as liposomal amphotericin B in preventing breakthrough invasive fungal infections in febrile neutropenia or in preventing fungus-related deaths. Because of the potential biases in this observational study, these preliminary findings should be interpreted with caution and clarified with a larger cohort of patients.

Antifungal therapy in febrile neutropenic patients: review of treatment choices and strategies for aspergillar infection

RATIONALE

Invasive fungal infections, especially aspergillosis, are a major problem in patients who undergo aggressive therapy for haematological malignancies. Presently, the standard therapy for demonstrated aspergillar infection is voriconazole. Because the morbidity and the mortality of proven aspergillar infection is relatively high, empirical and preemptive approaches have been explored.

FINDINGS

Empirical therapy is effective at the cost of overtreatment in a significant number of patients. This can be reduced through the preemptive approach; however, its equivalence in terms of successful therapy and mortality should be studied further and, optimally, in prospective controlled clinical trials.

Decision making in antifungal monotherapy versus combination therapy

The availability of new antifungal agents with novel mechanisms of action and improved tolerability has widened the possibilities for combination therapy for difficult-to-treat opportunistic mycoses. However, empiricism largely governs this therapy, especially in patients with invasive mould infections for whom there is a dire need to improve outcomes. Because of difficulties associated with the design and conduct of clinical trials of combination therapy for opportunistic mycoses, most studies are still performed in the laboratory or in animal models. Methods to assess combined antifungal effects in vitro and in animals are poorly standardized, and little evidence suggests that the data generated from these studies are relevant to treating patients. Even without solid evidence to support routine combination therapy, certain principles can guide its use in select patients.

A randomized, blinded, multicenter trial of lipid-associated amphotericin B alone versus in combination with an antibody-based inhibitor of heat shock protein 90 in patients with invasive candidiasis

BACKGROUND

Mycograb (NeuTec Pharma) is a human recombinant monoclonal antibody against heat shock protein 90 that, in laboratory studies, was revealed to have synergy with amphotericin B against a broad spectrum of Candida species.

METHODS

A double-blind, randomized study was conducted to determine whether lipid-associated amphotericin B plus Mycograb was superior to amphotericin B plus placebo in patients with culture-confirmed invasive candidiasis. Patients received a lipid-associated formulation of amphotericin B plus a 5-day course of Mycograb or placebo, having been stratified on the basis of Candida species (Candida albicans vs. non-albicans species of Candida). Inclusion criteria included clinical evidence of active infection at trial entry plus growth of Candida species on culture of a specimen from a clinically significant site within 3 days after initiation of study treatment. The primary efficacy variable was overall response to treatment (clinical and mycological resolution) by day 10.

RESULTS

Of the 139 patients enrolled from Europe and the United States, 117 were included in the modified intention-to-treat population. A complete overall response by day 10 was obtained for 29 (48%) of 61 patients in the amphotericin B group, compared with 47 (84%) of 56 patients in the Mycograb combination therapy group (odds ratio [OR], 5.8; 95% confidence interval [CI], 2.41-13.79; P<.001). The following efficacy criteria were also met: clinical response (52% vs. 86%; OR, 5.4; 95% CI, 2.21-13.39; P<.001), mycological response (54% vs. 89%; OR, 7.1; 95% CI, 2.64-18.94; P<.001), Candida-attributable mortality (18% vs. 4%; OR, 0.2; 95% CI, 0.04-0.80; P = .025), and rate of culture-confirmed clearance of the infection (hazard ratio, 2.3; 95% CI, 1.4-3.8; P = .001). Mycograb was well tolerated.

CONCLUSIONS

Mycograb plus lipid-associated amphotericin B produced significant clinical and culture-confirmed improvement in outcome for patients with invasive candidiasis.

Posaconazole Is Effective as Salvage Therapy in Zygomycosis: A Retrospective Summary of 91 Cases

To evaluate the activity of posaconazole for treatment of zygomycosis, a disease for which therapeutic options are limited, we conducted a retrospective study including 91 patients with zygomycosis (proven zygomycosis, 69 patients; probable zygomycosis, 22 patients). Patients had infection that was refractory to prior antifungal treatment (n=81) or were intolerant of such treatment (n=10) and participated in the compassionate-use posaconazole (800 mg/day) program. The rate of success (i.e., either complete or partial response) at 12 weeks after treatment initiation was 60%, and 21% of patients had stable disease. The overall high success and survival rates reported here provide encouraging data regarding posaconazole as an alternative therapy for zygomycosis.

Of Yeasts and Hyphae: A Hematologist’s Approach to Antifungal Therapy

Improvements in anticancer treatments, the ability to modify myelosuppression profiles, greater duration and intensity of immunosuppression, and the variety of available antimicrobial therapies have influenced the spectrum of pathogens associated with invasive fungal infection complicating treatment of hematological malignancies and hematopoietic stem cell transplantation. The approaches to the management of these infections encompass strategies of prevention for all those at risk, pre-emptive therapy based upon surrogates of infection before the onset of clinical disease, empirical therapy for patients with clinical evidence of early disease, and directed or targeted therapy for infected patients with established disease. Chemoprophylaxis is effective if applied to the highest risk patients over the duration of the risk. Pre-emptive strategies, while promising, have yet to be validated and linked to reliably predictive nonmicrobiological diagnostic techniques. Empirical antifungal therapy, as it is currently applied, now seems questionable. Patients with probable or proven invasive fungal infection still have suboptimal outcomes despite the availability of promising anti-fungal agents. Strategies examining the concept of dose-intensity and combination regimens require careful study and cannot yet be regarded as an acceptable standard of practice.

Posaconazole: a broad-spectrum triazole antifungal

Posaconazale is a new triazole drug being investigated in phase III clinical trials for the treatment and prevention of invasive fungal infections. In-vitro and in-vivo studies showed that posaconazole has broad-spectrum activity against most Candida species, Cryptococcus neoformans, Aspergillus species, Fusarium species, zygomycetes, and endemic fungi. Posaconazole is given orally two to four times daily. This triazole is widely distributed in the body, metabolised mainly by the liver, and is well tolerated, even in long-term courses. Adverse events are generally mild and include headache and gastrointestinal complaints. Posaconazole has shown promising clinical efficacy against life-threatening fungal infections that are often refractory to the currently available antifungal therapies-eg, invasive aspergillosis, fusariosis, and the emerging zygomycosis.

Effectiveness of amphotericin B lipid complex (ABLC) treatment in allogeneic hematopoietic cell transplant (HCT) recipients with invasive aspergillosis (IA)

A total of 85 allogeneic hematopoietic cell transplant (HCT) recipients with invasive aspergillosis treated with amphotericin B lipid complex (ABLC) were identified from the Collaborative Exchange of Antifungal Research (CLEAR) database. Of these patients, 78% (66/85) presented with pulmonary aspergillosis. Graft-versus-host disease (GVHD) was present in 24 of 85 patients. The response rate to ABLC was 31% (26/85) overall and 21% (5/24) in patients with GVHD. The overall response rate to first-line ABLC treatment was 41% (11/27). Four of nine (44%) patients with GVHD responded to first-line treatment with ABLC, while only one of 13 (8%) responded to ABLC as second-line therapy. Five of 18 (28%) and four of 14 (29%) patients, respectively, responded to sequential or concurrent treatment with ABLC and itraconazole. None of seven patients responded who continued receiving itraconazole after the start of ABLC therapy. At the end of ABLC therapy, serum creatinine had doubled in 12% of patients (10/85), and 2% (2/85) had developed a requirement for dialysis. These data suggest that ABLC, especially when administered as first-line therapy, can result in clinical response even in the most immunocompromised patients, that is, HCT recipients with GVHD, with minimal effects on renal function.

The structure of the Candida albicans Ess1 prolyl isomerase reveals a well-ordered linker that restricts domain mobility

Ess1 is a peptidyl-prolyl cis/trans isomerase (PPIase) that binds to the carboxy-terminal domain (CTD) of RNA polymerase II. Ess1 is thought to function by inducing conformational changes in the CTD that control the assembly of cofactor complexes on the transcription unit. Ess1 (also called Pin1) is highly conserved throughout the eukaryotic kingdom and is required for growth in some species, including the human fungal pathogen Candida albicans. Here we report the crystal structure of the C. albicansEss1 protein, determined at 1.6 A resolution. The structure reveals two domains, the WW and the isomerase domain, that have conformations essentially identical to those of human Pin1. However, the linker region that joins the two domains is quite different. In human Pin1, this linker is short and flexible, and part of it is unstructured. In contrast, the fungal Ess1 linker is highly ordered and contains a long alpha-helix. This structure results in a rigid juxtaposition of the WW and isomerase domains, in an orientation that is distinct from that observed in Pin1, and that eliminates a hydrophobic pocket between the domains that was implicated as the main substrate recognition site. These differences suggest distinct modes of interaction with long substrate molecules, such as the CTD of RNA polymerase II. We also show that C. albicans ess1(-)() mutants are attenuated for in vivo survival in mice. Together, these results suggest that CaEss1 might constitute a useful antifungal drug target, and that structural differences between the fungal and human enzymes could be exploited for drug design.