Polymyxin derivatives

Kitamura-Matsunaga, H. Kimura, Y. Araki, T. Izumiya, N. A sodium-containing polymyxin derived from polymyxin-complex during chromatography. J.Antibiot.(Tokyo), 1984, 37, 1605-1610 [for colistin, polymyxin E anal3d ical preparative]... 

On the other hand, the negatively charged Kdo-lipid A domain constitutes a target for binding of certain antibiotics, such as polymyxin B (125) and basic peptides derived from host cells such as the bactericidal/perme-ability-increasing protein (BPI) (261). In this respect the Kdo-lipid A domain constitutes a weak site of the outer membrane, rendering bacteria vulnerable to the action of cationic agents. 

Polymyxines Polymyxines are a gronp of related polypeptide antibiotics that are produced by sporo-forming soil bacteria Bacillus polymyxa and B. circulans, and they differ in amino acid content. Five different polymyxines have been identified—polymyxines A, B, C, D, and E, which differ in the amino acid content and are differentiated by additional letter notations and names— polymyxine B (aerosporin) and polymyxine E (colistin). It is known that in the process of development, some strains of B. polymyxa only form polymyxines A and C, and others synthesize polymyxines B and D. Polymyxine M was later isolated, a snlfomethyl derivative of polymyxine E. 

Katz M, Tsubery H, Kolusheva S, Shames A, Fridkin M, Jelinek R. Lipid binding and membrane penetration of polymyxin B derivatives studied in a biomimetic vesicle system. Biochem J 2003 375 405-413. 

Mora and coworkers201 studied the in vivo interaction, in mice, of toxic levels of cationic macromolecules with the carboxyl and sulfate derivatives of polyglucose. Toxic levels of polymyxin, protamine, streptomycin, and neomycin could be counteracted, if the synthetic macroanions were injected five to ten minutes after administration of the proteins. Subcutaneous administration of the anionic polyglucoses prior to intra-peri toneal injection of toxic levels of basic proteins afforded protection to the mice, and also demonstrated that the animals could survive, even when the two injections were by different routes. 

Colistin (COL) is a multicomponent antibiotic (polymyxins E) that is produced by strains of inverse Bacillus polymyxa. It consists of a mixture of several closely related decapeptides with a general structure composed of a cyclic heptapeptide moiety and a side chain acetylated at the N-terminus by a fatty acid. Up to 13 different components have been identified. The two main components of colistin are polymyxins El and E2 they include the same amino acids but a different fatty acid (216). A selective and sensitive HPLC method was developed for the determination of COL residues in milk and four bovine tissues (muscle, liver, kidney, and fat). The sample pretreatment consists of protein precipitation with trichloracetic acid (TCA), solid-phase purification on Cl 8 SPE cartridges, and precolumn derivatization of colistin with o-phthalaldehyde and 2-mercaptoethanol in borate buffer (pH 10.5). The last step was performed automatically, and the resulting reaction mixture was injected into a switching HPLC system including a precolumn and the reversed-phase analytical column. Fluorescence detection was used. The structural study of El and E2 derivatives was carried out by HPLC coupled with an electrospray MS. Recoveries from the preseparation procedure were higher than 60%. 

Fig. 12.6 A transfer-NOE derived space-fill model of the polymyxin B (PMB) -lipid A complex. Bidendate ionic H-bonds between pairs of the y-amino groups of Dab residues of PMB and the phosphates of lipid A, as well as hydrophobic interactions between the methyloctanoate group of PMB and the polyacyl domain of lipid A stabilize the interactions...

The majority of these substances may be considered unique polypeptides which contain unusual amino acids or amino acids joined in some unusual manner. Antibiotics now definitely known to be in this class are the penicillins (2), gramicidin (2), tyrocidine (1), gramicidin-S 3), bacitracin (4), subtilin (-5), polymyxin (6), aerosporin (7) and others. The penicillins are produced by a mold. The others listed here are produced by related bacteria. Streptomycin is a very important antibiotic therapeutically but it does not belong to the polypeptide class, being a complex amino-sugar derivative. 

Some antibiotics that have been derived from peptides were mentioned in Chapter l. The biosynthesis of penicillins was discussed in Chapter 8. Many peptide antibiotics are known. Some find clinical applications but others such as gramicidin S (9.7), tyrocidine A (9.8) and polymyxins (9.9) are too toxic for use in humans. Cyclosporin A (Figure 1.4), however, has immunosuppressive properties and it has been used in transplant surgery for this reason rather than for its antibiotic properties. Peptide antibiotics have some non-standard structural features and these may explain in part their antibiotic properties. First, cyclic peptides are not found in animal cells. Secondly, peptide antibiotics usually contain some unusual amino acids they may have the d configuration, be A-methylated or have other non-standard structural features. Clearly, these features are not compatible with direct ribo-somal synthesis. 

Nitropyrazole derivatives such as 4-nitropyrazole, l-methyl-4-nitropyrazole and 4,4 -dinitro-l,r-methylene dipyrazole are known as antiparasitic agents <88Mi 30i-02>. It has been shown that 3,4-bis(2,4-dinitrobenzoyl-hydroxymethyl) pyrazole has remarkable antimicrobial activity it is more efficient than penicillin, levomycetin, and polymyxin <92Ml 30i-03>. The synthesis of A -pyrazoline-... 

Polymyxins are antibiotics produced by the bacterium Bacillus polymyxa. They are protein derivatives having one end that is hydrophobic because of an attached fatty add. The opposite end is hydrophilic. Because of these properties, the polymyxins bind to membranes with the hydrophobic end embedded within the membrane, while the hydrophihc end remains outside the cell. As a result, the integrity of the membrane is disrupted, and leakage of cellular constituents occurs, causing cell death. 

Synergistic action of colistin and polymyxin in combination with other antibiotics in vitro and in vivo has been reported by several investigators " . In clinical application the effect of these combinations seems to be more a broadening of the antimicrobial spectrum than a synergistic interaction. Several salts and derivatives of both colistin and polymyxin have been reported. Commercially available are the sulphates and also recently the sodium sulphomethyl derivatives which are prepared by treatment of the free bases of polymyxin and colistin with formaldehyde and sodium bisulphite . These derivatives have a lower toxicity than the sulphates, however, and their in vitro antimicrobial activity is also reduced. 

Several toxic side-effects have been reported when polymyxin B and colistin are administered parenterally. Besides local irritation and pain at the site of injection in intramuscular administration, marked nephrotoxic effects are observed manifested by proteinuria, and cylindruria accompanied occasionally by an increase in white, red and epithelical cells in the urinary sediment. The neurotoxic effects of the drugs are characterized by flushing of the face, drowsiness, and a feeling of weakness and irritability. These symptoms, however, are transitory and disappear upon removal of the drug. In patients with pre-existing renal damage polymyxin and colistin should be administered in lower doses under frequent control of the renal functions. The recently available sodium sulphomethyl derivatives of polymyxin B and colistin are stated to be less toxic, yet these derivatives are also less active than their parent compounds - . ... 

Polymyxin B-Mcthancsulfonic Acid. Polymyxin B N-sulfomethyl deriv sedinm alt polymyxin B-N.N.N.N.N-pentakis(methanesulfonic acid). Prepn of sodium salt from polymyxin B sulfate, formaldehyde, and sodium bisulfite Wilkinson, U.S. pat. 3,044,934 (1962 to Burroughs Wellcome). 

Since Hydrogenomonas strain H16 and many other strains of hydrogen bacteria are not affected by penicillin or its derivatives, the well-known penicillin technique for the selection of auxotrophic mutants cannot be applied. However, colistine (= polymyxine B) proved to be an effective agent which kills only growing cells leaving non-growing cells unimpaired (Schlegel et al, 1965). 

The polymyxins are a group of cyclic polypeptides derived from the Bacillus species. In addition to various amino acids, they contain 6-methyloctanoic or 6-methylheptanoic acid (Fig. 5) and are very stable substances. Solutions of the polymyxins retain their potency during storage for several months. Only polymyxin-B... 

On rare occasions, hepatotoxicity and toxic leukopenia have been observed during polymyxin-E (colistin) treatment, but a definite causal relationship has not been established. The most serious side effect of the polymyxins is their nephrotoxicity. Polymyxin-B is more nephrotoxic than polymyxin-E and the sulfate derivatives of both are more toxic than their corresponding methylsulfonates. The toxic effects are dose dependent and doses above the recommended range may be dangerous. The principal nephrotoxic effect of the polymyxins is on the epithelium of the renal... 

N Acylations largely resemble the condensation of various starter acyl-groups in polykc-tide formation. The respective acyl-CoA derivative, presumably derived from a pathway-integrated fatty acid or polyketide synthase, is transferred to the first amino group of a thioescer-bound aminoacyl residue, requiring the action of an acy [transferase. Such acyl-transferases have been partially purified from the polymyxin (107) and surfactin biosynthetic systems (108,109). So far, sequence data is missing, but presum ly similarity to known transferases from the polyketide field can be expected. 

Both these antibiotics damage the cytoplasmic membrane of sensitive bacteria. Newton has shown that a fluorescent i-dimethylaminonaph-thalene-5-sulphonyl derivative of polymyxin (DANSP) combines with the cytoplasmic membrane . 

---