Nitrogen mustards metabolites

According to a hypothesis launched by Larionov et al in the 1960s, some new nitrogen mustard derivatives were developed. They contain metabolites and heterocyclic structures as carriers of the cytotoxic chloroethylamine groups. By this way the synthesis of aliylating metabolites started melphalan (sarcolysine) as L- or DL-phenylalanine derivative prospidine with a tricyclic piperazine moiety and chlorambucil as butyric acid derivative. It was proven that each alkylating metabolite has its own spectrum of selective antitumor activity. 

The drug melphalan (phenylalanine mustard, 11.33, R = R = Cl) is another good example of a nitrogen mustard that undergoes hydrolytic dechlorination. Melphalan administered to cancer patients gives rise to the monohydroxy (11.33, R = Cl, R = OH) and dihydroxy metabolites (11.33, R = R = OH), which were detected in the plasma with a combined AUC (area-under-the-curve) amounting to 29% of the AUC of the drug [68],... 

Since the formation of the ethyleniminium ion is crucial for the cytotoxic activity of the nitrogen mustards, it is not surprising that stable ethylenimine derivatives have antitumor activity. Thiophospho-ramide or thiotepa is the best known compound of this type that has been used clinically. Both thiotepa and its primary metabolite, triethylenephos-phoramide (TEPA), to which it is rapidly converted by hepatic mixed-function oxygenases form crosslinks with DNA. It is mainly used as an intravesicu-lar agent in bladder cancer. Thiotepa produces little toxicity other than myelosuppression. 

Cyclophosphamide (Cytoxan) is the most versatile and useful of the nitrogen mustards. Preclinical testing showed it to have a favorable therapeutic index and to possess the broadest spectrum of antitumor activity of all alkylating agents. As with the other nitrogen mustards, cyclophosphamide administration results in the formation of cross-links within DNA due to a reaction of the two chloroethyl moieties of cyclophosphamide with adjacent nucleotide bases. Cyclophosphamide must be activated metabofically by microsomal enzymes of the cytochrome P450 system before ionization of the chloride atoms and formation of the cyclic ethylenimmonium ion can occur. The metabolites phosphoramide mustard and acrolein are thought to be the ultimate active cytotoxic moiety derived from cyclophosphamide. 

A number of modifications/improvements to methods for the analysis of metabolites of sulfur and nitrogen mustards, and hydrolysis products of nerve agents, have been reported in a special issue of the Journal of Analytical Toxicology, 28 (5) (2004) pp. 305-392. 

Brock N. 1976. Comparative pharmacologic study in vitm and in vivo with cyclophosphamide (NSC-26271), cyclophosphamide metabolites, and plain nitrogen mustard compounds. Cancer Treat Rep 60 301-307. 

Phensedyl, 932 Phensuximide, 889 Phentanyl, 617 Phentermine, 890 (metabolite), 732 Phentermine hydrochloride, 890 Phentolamine, 891 Phentolamine hydrochloride, 891 Phentolamine mesylate, 891 Phentolamine methanesulphonate, 891 Phenurone, 869 Phenyl aminosalicylate, 343 Phenyl hydrate, 884 Phenyl hydride, 380 Phenyl salicylate, 967 Phenylacetamide, 312 Phenylacetamidopenicillanic acid, 390 Phenylacetic acid mustard, 442 Phenylacetone, 350 Phenylacetylglutamine, 877 Phenylacetylurea, 869 Phenylalanine nitrogen mustard, 728 Phenylamine, 356... 

Cyclophosphamide, a nitrogen mustard alkylating agent, is a widely used cancer chemotherapeutic drug to treat lymphomas, leukemias, multiple myeloma and a numerous solid tumors. Cyclophosphamide can induce nephrotoxicity characterized as decreased water excretion and an inappropriate concentration of urine. These effects are due to a direct effect of one or more alkylating cyclophosphamide metabolites at distal tubules and collecting ducts. Special caution is warranted to avoid water-induced diuresis or diuretic therapy in these patients as hyponatremia can become a problem. 

Cyclophosphamide and ifosfamide are nitrogen mustard derivatives, and are widely used alkylating agents (Table 124—14). They are closely related in structure, clinical use, and toxicity. Neither agent is active in its parent form and must be activated by mixed hepatic oxidase enzymes. The active metabolite of cyclophosphamide is phosphoramide mustard. Another metabolite, 4-hydroxycyclophos-phamide is cytotoxic, but is not an alkylating agent. Ifosfamide is hepaticaUy activated to ifosfamide mustard. Acrolein, a metabolite of both cyclophosphamide and ifosfamide, has little antitumor activity, but is responsible for some of their toxicity. ... 

Alkylating agent nitrogen mustard derivative cross-links DNA-DNAor DNA-protein inhibits DNA synthesis activated by hepatic microsomal (CYP450) mixed function oxidases acrolein metabolite (no antitumor activity) associated with hemorrhagic cystitis... 

As described below, urinary metabolites have been identified for vesicants, nerve agents, 3-quinuclidinyl benzilate (BZ), hydrogen cyanide and the RCAs, CS, CR and capsaicin. Protein adducts have been identified for vesicants, nerve agents and phosgene, and DNA adducts for sulphur and nitrogen mustards. With the rapid advances being made in proteomics and metabo-nomics, new biological markers of exposure will undoubtedly be identified in the near future. 

Ifosfamide is a nitrogen mustard. Ifosfamide requires metabolic activation by microsomal liver enzymes to produce biologically active metabolites. Enzymatic oxidation of the chloroethyl side chains and subsequent dealkylation produces the major urinary metabolites, dichloroethyl ifosfamide and dichloroethyl cyclophosphamide. The alkylated metabolites of ifosfamide interact with DNA. It is indicated in germ cell testicular cancer. 

No data on the biodegradation of nitrogen mustards were located. Nitrogen mustards can theoretically be biodegraded via reductive dehalogenation and de-hydrohalogenation mechanisms, but these processes would be very slow. HNl and HN2 can be degraded via oxidation dealkylation (N-dealkylation for HNl and C-dealkylation for HN2) the metabolites would possess vesicant properties (Morrill et al. 1985). 

Suppression of cell membrane transport plays a role in the resistance to nitrogen mustard (HN2) by the Yoshida sarcoma cells. Metabolism of cyclophosphamide (3a, cytoxan) by rat hepatic microsomes has been reported. The active metabolite 4 is formed by a three-step enzymatic reaction. 

Wils et al. (25,26) previously reported an entirely different approach to TDG analysis. TDG in urine was converted back to sulfur mustard by treatment with concentrated HC1. The sample treatment is less straightforward than the methods described above, but analysis as sulfur mustard is facile. Urine, plus 2H8-TDG as internal standard, was cleaned up by elution through two C18 cartridges. Concentrated HC1 was added and the sample stirred and heated at 120 °C. Nitrogen was blown over the solution and sulfur mustard isolated from the headspace by adsorption onto Tenax-TA. The method was used to detect TDG in urine from casualties of CW attacks (see below). A disadvantage of this method is that it may convert metabolites other than TDG to sulfur mustard. This is supported by the detection of relatively high levels of analytes in urine from control subjects. Vycudilik (27) used a similar procedure, but recovered the mustard by steam distillation and extraction. 

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