RESUMEN
Three tripeptidyl polyoxins were synthesized and found to inhibit Candida albicans. Compared with the naturally occurring polyoxin D, the three synthetic polyoxins had little effect on chitin synthetase when assayed with a C. albicans membrane preparation. However, all the compounds inhibited growth, affected cell morphology in a manner similar to that of polyoxin D, and were hydrolyzed by cell extracts of C. albicans. Hydrolysis did not occur extracellularly, and at least one of the synthetic polyoxins, leucyl-norleucyl-uracil polyoxin C, inhibited peptide uptake, suggesting entrance into the cell via the peptide transport system. Thus, the intact tripeptidyl polyoxins are inactive prodrugs that are converted to active moieties by cellular enzymes.
Asunto(s)
Antifúngicos/síntesis química , Candida albicans/efectos de los fármacos , Candida albicans/metabolismo , Quitina Sintasa/metabolismo , Oligopéptidos/síntesis química , Oligopéptidos/farmacología , Péptidos/síntesis química , Péptidos/farmacología , Nucleósidos de Pirimidina/síntesis química , Nucleósidos de Pirimidina/farmacologíaRESUMEN
We demonstrated that polyoxin D at millimolar concentrations caused marked morphological alterations of the human pathogens Candida albicans and Cryptococcus neoformans. C. albicans incubated in the presence of this drug grew in long chains that were severely swollen. Polyoxin D inhibited the growth of C. neoformans and killed cells of both the yeast and the hyphal phase of C. albicans. These observations give the first evidence that polyoxin antibiotics can kill zoopathogenic fungi.
Asunto(s)
Antifúngicos/farmacología , Candida albicans/efectos de los fármacos , Cryptococcus neoformans/efectos de los fármacos , Cryptococcus/efectos de los fármacos , Candida albicans/metabolismo , Quitina/biosíntesis , Nucleósidos de Pirimidina/farmacologíaRESUMEN
Oligopeptides and dipeptides are transported into Saccharomyces cerevisiae by a carrier-mediated system. In the dark, leucyl-p-nitroanilide (Leu-p-NA) and leucyl-leucyl-4-azido-2-nitrophenylalanine [Leu-Leu-Phe-(4N3,2NO2)] are competitive inhibitors of peptide transport by S. cerevisiae cells. The photolysis of yeast cells in the presence of Leu-p-NA or Leu-Leu-Phe(4N3,2NO2) at 350 nm results in an irreversible inactivation of peptide transport. Protection against this inactivation is afforded by an excess of trimethionine, a transported peptide. Photolysis with Leu-p-NA or Leu-Leu-Phe(4N3,2NO2) does not affect amino acid or sugar transport, and cell viability is maintained throughout the irradiation procedure. A 5-min irradiation of S. cerevisiae with 2.4 microM Leu-p-NA or 15 microM Leu-Leu-Phe(4N3,2NO2) causes 50% inhibition of trimethionine uptake. p-Nitroaniline, a possible hydrolysis product generated from Leu-p-NA by cellular peptidase activity, has no effect on peptide transport. An exogenous energy source is not required for photoinactivation. The results suggest that a component(s) of the peptide transport system of S. cerevisiae is irreversibly modified by photolysis with Leu-p-NA or Leu-Leu-Phe-(4N3,2NO2) and provide the first example of the use of amino acid p-nitroanilides as photoaffinity labels.
Asunto(s)
Luz , Oligopéptidos/metabolismo , Saccharomyces cerevisiae/metabolismo , Marcadores de Afinidad/farmacología , Anilidas/farmacología , Azidas/farmacología , Transporte Biológico/efectos de los fármacos , Transporte Biológico/efectos de la radiación , FotólisisRESUMEN
The ability of conjugates of peptides and 5-fluorocytosine or 5-fluoroorotic acid to enter Candida albicans was investigated. A number of conjugates of 5-fluoroorotic acid and peptides were synthesized using 1-(ethoxy-carbonyl)-2-ethoxy-1,2-dihydroquinoline as the coupling agent. Orotyl-L-leucyl-L-leucine, 5-fluoro-4-(N-succinamoyl-L-alanyl-L-leucine)-2(1H)-pyrimidinone [a 5-fluorocytosine derivative], and 5-fluoroorotyl-L-leucyl-L-leucine all inhibited the uptake of trimethionine into C. albicans WD 18-4. Inhibition by 5-fluoroorotyl-L-leucyl-L-leucine was competitive as judged using double-reciprocal plots. Evaluation of minimum inhibitory concentrations of peptide-5-fluorocytosine conjugates suggest that these conjugates enter C. albicans in the intact form. These results provide the first experimental evidence that peptides can carry pyrimidines into a eukaryote.
Asunto(s)
Antifúngicos/síntesis química , Candida albicans/efectos de los fármacos , Péptidos/síntesis química , Pirimidinas/síntesis química , Antifúngicos/metabolismo , Transporte Biológico , Candida albicans/metabolismo , Ácido Orótico/análogos & derivados , Ácido Orótico/síntesis química , Péptidos/metabolismo , Péptidos/farmacología , Pirimidinas/metabolismo , Pirimidinas/farmacología , Saccharomyces cerevisiae/efectos de los fármacosRESUMEN
An approach to the development of new anticandidal drugs is described that employs peptides as carriers of toxic agents into cells. 5-Flurorcytosine (5-FC) was chosen as a toxic agent with which to prepare 5-FC-peptide conjugates as models to test the carrier proposal. Model compounds were synthesized and then tested for antiyeast activity against S. Cerevisiae 9763, C. albicans 1-V, C. albicans WD 18-4, and C. Krusei 1-T. The 5-FC derivatives showed antiyeast activity comparable to 5-FC in all strains except C. krusei 1-T, in which case the compounds were less active. The solution stabilities of 5-FC conjugates at 37 degrees C were tested in the same growth medium used for susceptibility testing. The results indicated a range of stabilities where the half-life (t1/2) = 0.3--17.6 h. These results and those obtained in the susceptibility testing suggest extracellular hydrolysis and indicate that the type of linkage used to conjugate 5-FC to peptides will not provide appropriate compounds to evaluate the peptide-carrier concept.