Anti-infectives: Overview Pradimicins: Potential antifungal and anti-HIV agents

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.

Pradimicins: a novel class of broad-spectrum antifungal compounds

Pradimicins are a new class of antifungal compounds currently undergoing preclinical and early phase I clinical trials. The pradimicin structure is characterized by an aglycone of dihydrobenzo (alpha) naphthacenequinone with substitutions by a D-amino acid and hexose sugar. Pradimicins possess a novel mechanism of action consisting of a specific binding recognition to terminal D-mannosides of the cell wall of Candida albicans, resulting in the formation of a ternary complex consisting of D-mannoside, pradimicin, and calcium that leads to disruption of the integrity of the fungal cell membrane. Pradimicin in the form of BMS-181184 has broad-spectrum in vitro antifungal activity against Candida spp., Cryptococcus neoformans, Aspergillus spp., dematiaceous molds, and the Zygomycetes. Fusarium spp. are comparatively resistant to high concentrations of pradimicin. Initial vivo studies indicate that pradimicins have antifungal activity against experimental murine disseminated candidiasis and disseminated aspergillosis. Early studies indicate an excellent therapeutic index with no major end-organ toxicity. Pradimicins warrant further investigation for treatment of opportunistic mycoses in immuno-compromised hosts.