The role of hydrogen bond acceptor groups in the interaction of substrates with Pdr5p, a major yeast drug transporter.

The yeast ABC (ATP-binding cassette protein) multidrug transporter Pdr5p transports a broad spectrum of xenobiotic compounds, including antifungal and antitumor agents. Previously, we demonstrated that substrate size is an important factor in substrate-transporter interaction and that Pdr5p has at least three substrate-binding sites. In this study, we use a combination of whole cell transport assays and photoaffinity labeling of Pdr5p with [(125)I]iodoarylazidoprazosin in purified plasma membrane vesicles to study the behavior of two series of novel substrates: trityl (triphenylmethyl) and carbazole derivatives. The results indicate that site 2, defined initially by tritylimidazole efflux, requires at least a single hydrogen bond acceptor group (electron pair donor). In contrast, complete inhibition of rhodamine 6G efflux and [(125)I]iodoarylazidoprazosin binding at site 1 requires substrates with three electronegative groups. Carbazole and trityl substrates with two groups show saturating, incomplete inhibition at this site. This type of inhibition is frequently observed in bacterial multidrug-binding proteins that use a pocket with multiple binding sites. The presence of multiple sites with different requirements for substrate-Pdr5p interaction may explain the broad specificity of xenobiotic compounds transported by this protein.

AZT: farmacologia, benefícios e aplicaçÆes clínicas / AZT: pharmacology, general considerations and clinical effects

Este trabalho consiste numa revisåo dos principais tópicos referentes ao uso do AZT, como histórico, consideraçÆes gerais, mecanismo de açåo, farmacocinética, uso terapêutico e efeitos clínicos, reaçÆes adversas e interaçÆes medicamentosas. Pretender uma introduçåo para a descriçåo de nossa experiência com a droga, através de dois grupos de pacientes, 40 no total, a ser publicada num futuro próximo

Protection by unsaturated lecithin against the imidazole antimycotics, clotrimazole and miconazole.

The activity of egg lecithin in preventing the antifungal action of the two imidazole antimycotics, clotrimazole and miconazole, was confirmed. However, addition of this phospholipid could not relieve an existing imidazole inhibition. Compared with egg lecithin, reduced egg lecithin showed no such protective effect. The addition of egg lecithin to an aqueous suspension of the imidazole drugs changed the absorption profile of the imidazole, suggesting a low solubility and, consequently, a lower effective concentration; however, the addition of reduced egg lecithin did not produce any change in the adsorption. These results indicate that the preventive effect of egg lecithin on imidazole inhibition may be a consequence of preferential in vitro interaction of the drug with unsaturated phospholipid to form a hydrophobic complex.

Antagonistic action of lipid components of membranes from Candida albicans and various other lipids on two imidazole antimycotics, clotrimazole and miconazole.

The growth-inhibitory activity of two imidazole antimycotics, clotrimazole and miconazole, against Candida albicans was significantly reversed when lipid extracts from protoplast membranes of the same organism were added to the assay medium together with the drugs. Of four major classes of lipids further separated from them, viz., phospholipids, triglycerides, sterol esters, and free sterols, the former two were capable of counteracting both drugs, whereas the latter two were not. However, even with phospholipids or triglycerides, no antagonism was noted when they were saturated by catalytic hydrogenation before use. The antagonistic effect of varying classes of commercial lipids, including phospholipids, acylglycerides, sterols, and fatty acids, was also studied by means of the agar diffusion technique. Significant antagonism to both drugs was observed with: (i) phospholipids with an unsaturated acyl group; (ii) acylglycerides, the ester portion of which consists of unsaturated fatty acid; (iii) ultraviolet-activated sterols; and (iv) unsaturated fatty acids of cis-configuration. By contrast, none of the saturated phospholipids and acylglycerides nor sterols was effective as an antagonist. With the exception only of lauric acid, all of a series of saturated fatty acids and unsaturated trans-fatty acids ranging from C(8) to C(18) in chain length were either minimally effective or completely ineffective. Essentially, there was no qualitative difference between clotrimazole and miconazole in the response to these various lipids.

Effect of culture media on the antifungal activity of miconazole and amphotericin B methyl ester.

The capacity of four culture media to obfuscate the antifungal activity of miconazole and amphotericin B methyl ester was evaluated qualitatively by examination of five isolates each of Candida albicans, Candida tropicalis, Candida parapsilosis, Torulopsis glabrata, and Cryptococcus neoformans, and quantitatively by determination of the absolute minimal inhibitory concentrations for a strain of C. albicans. Miconazole, like the predecessor imidazole (clotrimazole), was antagonized by two complex, undefined media (Sabouraud's glucose and brain-heart infusion agars) but not by either of two synthetic formulations (synthetic amino acid medium, fungal and modified yeast-nitrogen base). The antifungal activity of amphotericin B methyl ester, like that of the parent compound amphotericin B, was not materially affected by the culture medium used for testing. When added separately to synthetic amino acid medium (fungal), neither purines nor pyrimidines antagonized miconazole. Ether extraction of Sabouraud's glucose agar failed to diminish the antagonism of this medium for miconazole.