Antifungal activity of the pradimicin derivative BMS 181184 in the treatment of experimental pulmonary aspergillosis in persistently neutropenic rabbits

Recent Progress in the Discovery of Antifungal Agents Targeting the Cell Wall

Due to the limit of available treatments and the emergence of drug resistance in the clinic, invasive fungal infections are an intractable problem with high morbidity and mortality. The cell wall, as a fungi-specific structure, is an appealing target for the discovery and development of novel and low-toxic antifungal agents. In an attempt to accelerate the discovery of novel cell wall targeted drugs, this Perspective will provide a comprehensive review of the progress made to date on the development of fungal cell wall inhibitors. Specifically, this review will focus on the targets, discovery process, chemical structures, antifungal activities, and structure-activity relationships. Although two types of cell wall antifungal agents are clinically available or in clinical trials, it is still a long way for the other cell wall targeted inhibitors to be translated into clinical applications. Future efforts should be focused on the identification of inhibitors against novel conserved cell wall targets.

Pradimicin A, a carbohydrate-binding nonpeptidic lead compound for treatment of infections with viruses with highly glycosylated envelopes, such as human immunodeficiency virus

Pradimicin A (PRM-A), an antifungal nonpeptidic benzonaphtacenequinone antibiotic, is a low-molecular-weight (molecular weight, 838) carbohydrate binding agent (CBA) endowed with a selective inhibitory activity against human immunodeficiency virus (HIV). It invariably inhibits representative virus strains of a variety of HIV-1 clades with X4 and R5 tropisms at nontoxic concentrations. Time-of-addition studies revealed that PRM-A acts as a true virus entry inhibitor. PRM-A specifically interacts with HIV-1 gp120 and efficiently prevents virus transmission in cocultures of HUT-78/HIV-1 and Sup T1 cells. Upon prolonged exposure of HIV-1-infected CEM cell cultures, PRM-A drug pressure selects for mutant HIV-1 strains containing N-glycosylation site deletions in gp120 but not gp41. A relatively long exposure time to PRM-A is required before drug-resistant virus strains emerge. PRM-A has a high genetic barrier, since more than five N-glycosylation site deletions in gp120 are required to afford moderate drug resistance. Such mutated virus strains keep full sensitivity to the other known clinically used anti-HIV drugs. PRM-A represents the first prototype compound of a nonpeptidic CBA lead and, together with peptide-based lectins, belongs to a conceptually novel type of potential therapeutics for which drug pressure results in the selection of glycan deletions in the HIV gp120 envelope.

Pharmacological agents in development for invasive aspergillosis

The urgent medical need for new potent antifungal agents in the management of invasive aspergillosis (IA) has resulted in the development of several compounds which may be of value in the future for the treatment or prophylaxis of IA. In the past years, several novel types of drugs have been discovered and developed, some of which are already in late-stage clinical trials and ready to enter the market. This paper discusses the antifungal agents, classified by their mode of action, that are currently available and the agents which are still in development for treatment or prevention of IA.

Update on antifungals targeted to the cell wall: focus on beta-1,3-glucan synthase inhibitors

Currently available antifungal drugs for serious infections are either fungistatic and vulnerable to resistance (azoles) or fungicidal but toxic to the host (polyenes). Cell wall-acting antifungals are inherently selective and fungicidal, features that make them particularly attractive for clinical development. Three classes of such compounds, targeted respectively to chitin synthase (nikkomycins), beta-1,3-glucan synthase (echinocandins) and mannoproteins (pradimicins/benanomicins), have entered clinical development. While nikkomycins and pradimicins/benanomicins are no longer in development, echinocandins have emerged as potentially clinically useful and three compounds, caspofungin (MK-991, L-743,872), micafungin (FK-463) and anidulafungin (LY-303366) are in late clinical development (Phase II and III).

Antifungal pharmacodynamics: review of the literature and clinical applications

Invasive fungal infections are seen with growing frequency, likely due to increases in numbers of patients at risk of infection. Optimal selection and dosing of antifungal agents are important, as these infections are often refractory to available therapy. In contrast to antibacterials, studies examining the pharmacodynamic properties of antifungals and their application in treating invasive disease often are lacking. Agents administered for invasive infections are amphotericin B, flucytosine, and azole antifungals. Several drugs are under investigation, such as posiconazole, voriconazole, and the echinocandins, and preliminary pharmacodynamic data likely will help shape dosing regimens. Clinical trials that investigated dosage and administration, as well as the potential benefits of combination and sequential therapy, are addressed. In addition, antifungal susceptibility and animal models of infection are discussed.

New drugs and novel targets for treatment of invasive fungal infections in patients with cancer

Invasive fungal infections have emerged as important causes of morbidity and mortality in profoundly immunocompromised patients with cancer. Current treatment strategies for these infections are limited by antifungal resistance, toxicity, drug interactions, and expense. In order to overcome these limitations, new antifungal compounds are being developed, which may improve our therapeutic armamentarium for prevention and treatment of invasive mycoses in high-risk patients with neoplastic diseases.

Novel antifungal drugs

There have been many new developments in antifungal therapy in the past few years. Some antifungal drugs have been reformulated to reduce toxicity (e.g. new lipid formulations of polyenes), and new derivatives of drugs have been developed to enhance potencies. The search for unique drug targets will be enhanced by the availability of sequencing data from whole genome sequencing projects.

Activity of pradimicin BMS-181184 against Aspergillus spp

The pradimicins are a new class of antifungal agents with activity against the majority of human fungal pathogens. In this study, the in vitro activity of pradimicin BMS-181184 was investigated against a range of the most common species of Aspergillus. The results were compared with itraconazole and amphotericin B. BMS-181184 was found to be active against most Aspergillus spp., but at higher concentrations than itraconazole and amphotericin B.

The 1998 Garrod lecture. Current and future antifungal therapy: new targets for antifungal agents

Invasive fungal infections are a major problem in immunocompromised patients. The recent expansion of antifungal drug research has occurred because there is a critical need for new antifungal agents to treat these life-threatening invasive infections. The overview of the development of antifungal therapy which is provided herein reflects the increased interest in this very special area of infectious diseases. Although we have newer, less toxic, antifungal agents that are available for clinical use, their clinical efficacy in some invasive fungal infections, such as aspergillosis and fusariosis, is not optimal. Thus, intense efforts in antifungal drug discovery are still needed to develop more promising and effective antifungal agents for use in the clinical arena.