New N-alkyl derivatives of amphotericin B. Synthesis and biological properties

Infections in acute myeloid leukemia: an analysis of 382 febrile episodes

Neutropenic fever is an important cause of morbidity and mortality during therapy of acute myeloid leukemia (AML). We retrospectively analyzed 382 febrile episodes encountered during induction and consolidation chemotherapy to determine the potential etiology, microbiologic spectrum, response/resistance to antibiotics and outcome. Between May, 2001 and December, 2006, 95 patients with de novo non-M3 AML received remission induction chemotherapy followed by consolidation in those who achieved complete remission. Patients median age was 28 years, ranging from 2 to 61 years, 26 patients were ≤15 years of age. There were 57 males and 38 females. Febrile neutropenia was defined as per international guidelines. A total of 382 febrile episodes were recorded; neutropenic 347 (induction phase 172, consolidation phase 175) and non-neutropenic 35 (induction 16, consolidation 19). Clinical, microbiological and radiological evidence of infection could be identified in 64% of the febrile episodes (74% during induction, 52% during consolidation). Pulmonary infections were most common, both during induction and consolidation phase. Microbiologically gram-negative infections predominated. There were 60 possible/probable/definite episodes of fungal infection. Six cases of tuberculosis (pulmonary 5 and spine 1) and 3 cases of malaria (including one case of cerebral malaria) were also identified. Nineteen patients died (17 during induction, 2 during consolidation); 17 deaths were infection related, 12/17 possibly due to fungal infections. We suggest that evaluation of antibacterial resistance patterns in an institution must be done routinely in order to choose empiric antibiotics therapy. Careful selection of antibiotics and early institution of antifungal therapy besides considering alternative diagnosis peculiar to the region (e.g. tuberculosis, malaria) may help in reducing morbidity and mortality during AML therapy.

Influence of a lipid bilayer on the conformational behavior of amphotericin B derivatives - A molecular dynamics study

Amphotericin B (AmB) is an effective but very toxic antifungal antibiotic. In our laboratory a series of AmB derivatives of improved selectivity of action was synthesized and tested. To understand molecular basis of this improvement, comparative conformational studies of amphotericin B and its two more selective derivatives were carried out in an aqueous solution and in a lipid membrane. These molecular simulation studies revealed that within a membrane environment the conformational behavior of the derivatives differs significantly from the one observed for the parent molecule. Possible reasons for such a difference are analyzed. Furthermore, we hypothesize that the observed conformational transition within the polar head of AmB derivatives may lead to destabilization of antibiotic-induced transmembrane channels. Consequently, the selective toxicity of the derivatives should increase as ergosterol-rich liquid-ordered domains are more rigid and conformationally ordered than their cholesterol-containing counterparts, and as such may better support less stable channel structure.

Synthesis and in vitro biological properties of novel cationic derivatives of amphotericin B

Novel cationic amphotericin B derivatives as highly potent antifungal agents are reported. These semi-synthetic derivatives of amphotericin B were elaborated through a series of modifications both on the nitrogen atom of the mycosamine and on the C-16 carboxylic acid moiety. The antifungal activity of the new conjugates was tested against Saccharomyces cerevisiae and also against nine different strains of Candida albicans and Candida glabrata, including an amphotericin resistant strain. High potency was observed in the case of polyamine derivatives bearing two 3-aminopropyl chains on the mycosamine. The evaluation of the biological properties also included the determination of the hemolytic activity of the compounds by measuring the EH50 values.

Interactions of amphotericin B derivatives with lipid membranes—A molecular dynamics study

Amphotericin B (AmB) is a well-known polyene macrolide antibiotic used to treat systemic fungal infections. AmB targets more efficiently fungal than animal membranes. However, there are only minor differences in the mode of action of AmB against both types of membranes, which is a source of AmB toxicity. In this work, we analyzed interactions of two low toxic derivatives of AmB (SAmE and PAmE), synthesized in our laboratory, with lipid membranes. Molecular dynamics simulations of the lipid bilayers containing ergosterol (fungal cells) or cholesterol (animal cells) and the studied antibiotic molecules were performed to compare the structural and dynamic properties of AmB derivatives and the parent drug inside the membrane. A number of differences was found for AmB and its derivatives' behavior in cholesterol- and ergosterol-containing membranes. We found that PAmE and SAmE can penetrate deeper into the hydrophobic region of the membrane compared to AmB. Modification of the amino and carboxyl group of AmB also resulted in the conformational transition within the antibiotic's polar head. Wobbling dynamics differentiation, depending on the sterol present, was discovered for the AmB derivatives. These differences may be interpreted as molecular factors responsible for the improved selectivity observed macroscopically for the studied AmB derivatives.

Significant improvement of antifungal activity of polyene macrolides by bisalkylation of the mycosamine

[reaction: see text] New derivatives of Amphotericin B (AmB) were synthesized through a double reductive alkylation of the mycosamine. These derivatives of AmB displayed superior antifungal activity against Saccharomyces cerevisiae wild-type strain and especially in the case of an AmB-resistant Candida albicans strain. Moreover, these compounds are potential drug candidates because of significantly reduced hemotoxicity compared to AmB. Furthermore, the same mycosamine modification can be applied to other polyene macrolides such as Nystatin and Pimaricin to improve their antifungal activity.

Interaction of amphotericin B and its selected derivatives with membranes: molecular modeling studies

Amphotericin B (AmB) is a well-known antifungal antibiotic that has been used in the clinic for about five decades. Despite its chemotherapeutic importance, AmB is quite toxic and many efforts have been made to improve its pharmacological properties, e.g., by chemical modifications. The lipid membrane is a molecular target for AmB, however, due to heterogeneity of its components, the molecular mechanism of AmB action is still unclear. The lack of this knowledge hinders rational designing of new and less toxic AmB derivatives. Our review is a critical presentation of the current understanding of AmB molecular mechanism of action at the membrane level. Except the experimental approach, the extensive overview of molecular modeling studies, performed mostly in our lab, is presented. The results of interactions between AmB or some of its derivatives and lipid model membranes are discussed. In our studies, different biomembrane models and different associate states of the antibiotic were included. Presented molecular modeling approach is especially valuable with regard to a new paradigm of the structure of lipid membrane containing liquid-ordered domains. Hopefully, all these complementary experimental/computational approaches are going to reach the point at which a new hypothesis about molecular mechanism of AmB activity and selectivity will be put forward.

Molecular aspects of the interaction between amphotericin B and a phospholipid bilayer: molecular dynamics studies

Amphotericin B (AmB) is a polyene macrolide antibiotic used to treat systemic fungal infections. The molecular mechanism of AmB action is still only partly characterized. AmB interacts with cell-membrane components and forms membrane channels that eventually lead to cell death. The interaction between AmB and the membrane surface can be regarded as the first (presumably crucial) step on the way to channel formation. In this study molecular dynamics simulations were performed for an AmB-lipid bilayer model in order to characterize the molecular aspects of AmB-membrane interactions. The system studied contained a box of 200 dimyristoylphosphatidylcholine (DMPC) molecules, a single AmB molecule placed on the surface of the lipid bilayer and 8,065 water molecules. Two molecular dynamics simulations (NVT ensemble), each lasting 1 ns, were performed for the model studied. Two different programs, CHARMM and NAMD2, were used in order to test simulation conditions. The analysis of MD trajectories brought interesting information concerning interactions between polar groups of AmB and both DMPC and water molecules. Our studies show that AmB preferentially took a vertical position, perpendicular to the membrane surface, with no propensity to enter the membrane. Our finding may suggest that a single AmB molecule entering the membrane is very unlikely.

Comparative study of a semisynthetic derivative of natamycin and the parent antibiotic on the spoilage of shredded cheddar cheese

A water-soluble N-alkyl semisynthetic derivative of natamycin was synthesized by the Michael addition reaction of the parent with an N-substituted malemide. A comparative study was carried out to investigate the effectiveness of the semisynthetic derivative and the parent antibiotic in suppressing mold growth on shredded Cheddar cheese stored in modified atmosphere packaging (MAP). The effects of 0-, 10-, and 20-ppm antimycotic treatments were examined. A 20-ppm natamycin treatment effectively suppressed visible mold growth (< 10(4) CFU/g) in MAP samples for up to 30 days after packages were opened. The performance of the 20-ppm semisynthetic derivative was similar to that of the 10-ppm natamycin treatment. For these treatments, visible mold growth did not occur in MAP samples until 20 days after packages were opened. These results indicate that the semisynthetic derivative of natamycin is less effective than the parent compound in suppressing mold growth on shredded Cheddar cheese.

Conformational properties of amphotericin B amide derivatives--impact on selective toxicity

Even though it is highly toxic, Amphotericin B (AmB), an amphipathic polyene macrolide antibiotic, is used in the treatment of severe systemic fungal infections as a life-saving drug. To examine the influence of conformational factors on selective toxicity of these compounds, we have investigated the conformational properties of five AmB amide derivatives. It was found that the extended conformation with torsional angles (phi,psi)=(290 degrees,180 degrees) is a common minimum of the potential energy surfaces (PES) of unsubstituted AmB and its amide derivatives. The extended conformation of the studied compounds allows for the formation of an intermolecular hydrogen bond network between adjacent antibiotic molecules in the open channel configuration. Therefore, the extended conformation is expected to be the dominant conformer in an open AmB (or its amide derivatives) membrane channel. The derivative compounds for calculations were chosen according to their selective toxicity compared to AmB and they had a wide range of selective toxicity. Except for two AmB derivatives, the PES maps of the derivatives reveal that the molecules can coexist in more than one conformer. Taking into account the cumulative conclusions drawn from the earlier MD simulation studies of AmB membrane channel, the results of the potential energy surface maps, and the physical considerations of the molecular structures, we hypothesize a new model of structure-selective toxicity of AmB derivatives. In this proposed model the presence of the extended conformation as the only well defined global conformer for AmB derivatives is taken as the indicator of their higher selective toxicity. This model successfully explains our results. To further test our model, we also investigated an AmB derivative whose selective toxicity has not been experimentally measured before. Our prediction for the selective toxicity of this compound can be tested in experiments to validate or invalidate the proposed model.

Oligonucleotide delivery by a cationic derivative of the polyene antibiotic amphotericin B. I: interaction oligonucleotide/vector as studied by optical spectroscopy and electron microscopy

Antisense strategy requires efficient systems for the delivery of oligodeoxyribonucleotides (ODN) into target cells. Cationic amphiphiles have shown good efficiency in vitro and a lot of attention is currently paid to their interaction with nucleic acids. In the present study, this interaction was, for the first time, analysed at the molecular level, taking advantage of the spectroscopic properties of the positively charged chiral polyene molecule amphotericin B 3-dimethylaminopropyl amide (AMA), the efficiency of which, as delivery system, has been demonstrated [Garcia et al., Pharmacol. Ther. (2000), in press]. By UV-visible absorption and circular dichroism (CD) we studied its self-association properties in pure water, saline and RPMI medium. Drastic changes were observed upon ODN addition, stronger in pure water than in media of high ionic strength. At low AMA concentration (<10(-6) M), the strong increase of the CD signal, characteristic of self-association, indicated condensation of AMA on the ODN molecules. At a higher concentration (10(-4) M), and for a nucleic acid negative charge/AMA positive charge ratio higher than 1, spectra were interpreted as a reorganisation of free self-associated AMA species into smaller ones 'decorating' the nucleic acid molecule. Electron microscopy data were interpreted according to this scheme.

The role of amphotericin B amino group basicity in its antifungal action. A theoretical approach

The role of basicity of the amine group of amphotericin B in the molecular mechanism of antifungal activity of this antibiotic has been investigated by AM1 and MNDO quantum chemistry methods. Calculations of proton affinity of the amine group, as a measure of its basicity, for appropriate models of free amphotericin B and its N-alkyl derivatives were carried out. These studies were preceded by a critical examination of the usefulness and reliability of both methods to predict the proton affinities of several aliphatic amines. It has been concluded that the diminution of protonability of the substituted amine group of amphotericin B correlates with the decrease of antifungal activity of the appropriate derivatives of antibiotic. It was experimentally demonstrated (A. Czerwiński et al., J. Antibiot. 44 (1991) 979) that the introduction of additional amine groups in such a derivative restores antifungal activity of the compound. In our studies it was evidenced, using theoretical methods, that the proton affinity of this additional amine group is similar to that in free amphotericin B.