N-dechloroethylated Metabolites Research Articles

A molecular model of the enantioselective liquid chromatographic separation of (R,S)-ifosfamide and its N-dechloroethylated metabolites on a teicoplanin aglycon chiral stationary phase

The enantioselective separations of the chiral oxazaphosphorines (R,S)-ifosfamide (IF), (R,S)-2-N-dechloroethyl-IF (2-DCE-IF) and (R,S)-3-N-dechloroethyl-IF (3-DCE-IF) were achieved on teicoplanin-based chiral stationary phase using isopropanol:methanol (60:40, v/v) as the mobile phase. Computational models of the teicoplanin and teicoplanin aglycon (TAG) chiral selectors were constructed and used in docking experiments to examine the chiral recognition mechanism associated with the observed resolutions. Initial data showed no significant differences between the simulated selector–selectand complexes using teicoplanin and TAG, and the full study was conducted using TAG. The data from the study indicate that hydrophobic interactions arise between the chlorine atom present in the cholorethyl moieties of the oxazaphosphorine molecules and hydrophobic pockets within the TAG basket and that these interactions anchored and positioned the selectands within the selector–selectand complexes. The complexes were stabilized through the formation of a network of hydrogen bond and cation–π interactions, in which the latter involved the phosphorous atom of the phosphoramide moiety and aromatic components of the TAG aglycon basket. The chirality of the oxazaphosphorine molecule determined the number and strength of the stabilizing interactions which resulted in significant differences in the relative mean binding energies between the complexes formed by the (R) and (S) enantiomers of the selectands. These differences were consistent with the observed chromatographic enantioselectivity and suggest a multi-step chrial recognition mechanism involving the tethering of the selectand to the selector followed by conformational adjustments and stabilization of the selectand–selector complex.

Enantioselective liquid chromatography–mass spectrometry assay for the determination of ifosfamide and identification of the N-dechloroethylated metabolites of ifosfamide in human plasma

A sensitive and specific liquid chromatography–mass spectrometry (LC–MS) method has been developed and validated for the enantioselective determination of ifosfamide [( R)-IF and ( S)-IF] in human plasma and for the detection of the N-dechloroethylated metabolites of IF, 2- N-dechloroethylifosfamide [( R)-2-DCl-IF and ( S)-2-DCl-IF] and 3- N-dechloroethylifosfamide [( R)-3-DCl-IF and ( S)-3-DCl-IF]. IF, 2-DCl-IF and 3-DCl-IF were extracted from plasma using solid-phase extraction and resolved by liquid chromatography on a column containing a Chirabiotic T chiral stationary phase. The enantioselective separations were achieved using a mobile phase composed of 2-propanol:methanol (60:40, v/v) and a flow rate of 0.5 ml/min. The observed enantioselectivities ( α) for IF, 2-DCl-IF and 3-DCl-IF were 1.20, 1.17 and 1.20, respectively. The calibration curve was linear in the concentration range of 37.50–4800 ng/ml for each ifosfamide enantiomer ( r 2 > 0.997). The lower limit of detection (LLOD) was 5.00 ng/ml. The inter- and intra-day precision ranged from 3.63 to 15.8% relative standard deviation (R.S.D.) and 10.1 to 14.3% R.S.D., respectively, and the accuracy ranged from 89.2 to 101.5% of the nominal values. The method was applied to the analysis of plasma samples obtained from a cancer patient who received 3.75 g/m 2/day dose of ( R, S)-ifosfamide as a 96-h continuous infusion.

Enantioselective liquid chromatography–mass spectrometry assay for the determination of ifosfamide and identification of the N-dechloroethylated metabolites of ifosfamide in human plasma

Enantioselective liquid chromatography–mass spectrometry assay for the determination of ifosfamide and identification of the N-dechloroethylated metabolites of ifosfamide in human plasma

PII-80A sensitivity comparison study of ifosfamide and its 2- and 3- N-dechloroethylated metabolites using electrospray interface or atmospheric pressure chemical ionization interface on a liquid chromatography-mass spectrometry system

BACKGROUND/AIMS To evaluate the sensitivity of ifosfamide (IFF) and its 2- and 3-N-dechloroethylated metabolites (2-DCE-IFF and 3-DCE-IFF) using ES interface vs. APCI interface in LC/MS methods. METHODS Standard calibration curves were prepared by spiking an aliquot of 0.025 ml of standard containing ifosfamide, 2-DCE-IFF and 3-DCE-IFF into 0.1 ml drug-free human plasma, then liquid/liquid extracted with 3 ml of ethyl acetate. The resulting organic phase was evaporated to dryness and reconstituted in 0.5 ml methanol and 0.010 ml was injected. Enantioselective separations were achieved using a C18 column (4.6 × 150 mm) and a Chirobiotic T column (4.6 × 150 mm). The mobile phase was 2-propanol: NH4OAc (10 mM, pH 7.0) and a gradient from 5% to 18% 2-propanol, a flow rate of 0.5 ml/min. The detection and quantification of the compounds were achieved using selected-ion monitoring at m/z=261.1 for IFF and m/z=199.1 for the 2-DCE-IFF and 3-DCE-IFF. RESULTS Linear relationships between peak height and drug concentrations were obtained for all the analytes using each of the two interfaces separately (ES vs APCI): IFF showed a linear response in the range of 100–4000 ng/ml (LLOQ=100 ng/ml) in ES, versus 3–4000 ng/ml (LLOQ=3 ng/ml) in APCI. For 2-DCE-IFF from 50–2000 ng/ml in both interfaces. For 3-DCE-IFF from 6–4000 ng/ml in both interfaces. CONCLUSIONS IFF showed better sensitivity using APCI than ES (ratio APCI:ES = 32:1). No difference in sensitivity was found for 2-DCE-IFF and 3-DCE-IFF metabolites. Clinical Pharmacology & Therapeutics (2005) 79, P57–P57; doi: 10.1016/j.clpt.2005.12.205

Clinical Pharmacology of Cyclophosphamide and Ifosfamide

The oxazaphosphorine cyclophosphamide (CPA) and ifosfamide (IFO) are two commonly used DNA- alkylating agents in cancer chemotherapy. This review highlights the pharmacokinetics and pharmacodynamics of the two important agents. As alkylating agents, CPA and IFO are usually combined with other anticancer drugs in the chemotherapy of solid tumors and hematological malignancies to obtain synergistic or additive anticancer effect due to complementary mechanism of action. Both compounds are prodrugs that are activated via 4-hydroxylation by cytochrome P450s such as CYP2B6 and CYP3A4 to generate alkylating nitrogen mustards (phosphoramide mustard and ifosforamide mustard) and the byproduct acrolein. The resultant mustards can alkylate DNA to form DNA-DNA cross-links, leading to inhibition of DNA synthesis and cell apoptosis. Both CPA and IFO are also inactivated by N-dechloroethylation, resulting in N-dechloroethylated metabolites and the byproduct chloroacetaldehyde. Acrolein is the causative agent for hemorrhagic cystitis, whereas chloroacetaldehyde induces nephrotoxicity and neurotoxicity. Pharmacokinetics of CPA and IFO is markedly influenced by route of administration and duration of treatment, age, comedication, liver and renal function. Large interpatient variability in pharmacokinetics, clinical response rate and toxicity has been observed in cancer patients treated with CPA or IFO. Resistance to CPA or IFO occurs due to decreased activation by CYP3A4 and CYP2B6, increased deactivation of the agents, decreased entry into or increased efflux from tumor cells, increased cellular thiol level, increased DNA repair capacity, and/or deficient apoptotic response to DNA damage. A full understanding of factors affecting the pharmacokinetics, pharmacodynamics, toxicology and pharmacogenetics of CPA and IFO is important to optimize the dose and regimens of CPA and IFO in cancer chemotherapy.

ENANTIOSELECTIVE METABOLISM AND CYTOTOXICITY OFR-IFOSFAMIDE ANDS-IFOSFAMIDE BY TUMOR CELL-EXPRESSED CYTOCHROMES P450

The anticancer prodrug ifosfamide (IFA) contains a chiral phosphorous atom and is administered in the clinic as a racemic mixture of R-IFA and S-IFA. Hepatic cytochrome P450 (P450) enzymes exhibit enantioselective preferences in the metabolism of R-IFA and S-IFA; however, the impact of this selectivity on P450-dependent anticancer activity is not known. Presently, the metabolism and cytotoxicity of R-IFA and S-IFA were determined in 9L gliosarcoma and Chinese hamster ovary tumor cells expressing an IFA-activating P450 enzyme and by in vitro steady-state kinetic analysis using cDNA-expressed P450 enzymes. Tumor cells expressing P450 enzyme CYP3A4 were the most sensitive to R-IFA cytotoxicity, whereas tumor cells expressing CYP2B1 or CYP2B6 were most sensitive to cyclophosphamide (CPA), an isomer of IFA. Correspondingly, CYP3A4-expressing cells and cDNA-expressed CYP3A4 metabolized R-IFA to yield the active, 4-hydroxylated metabolite at a 2- to 3-fold higher rate than they metabolized S-IFA or CPA. CYP2B cells and cDNA-expressed CYP2B enzymes metabolized CPA almost exclusively by 4-hydroxylation, whereas R-IFA and S-IFA were substantially converted to inactive, N-dechloroethylated metabolites. Further investigation revealed that CYP3A1, a rat enzyme, exhibited superior kinetic properties compared with the human enzyme CYP3A4, with R-IFA and S-IFA both metabolized with high catalytic efficiency by 4-hydroxylation and with a K(m) value of 200 microM, approximately 5-fold lower than CYP3A4. Based on these kinetic parameters and metabolic profiles, R-IFA is expected to exert greater anticancer activity than S-IFA or CPA against tumors that express CYP3A enzymes, whereas tumors expressing CYP2B enzymes may be more sensitive to CPA treatment.

Chemical stability and fate of the cytostatic drug ifosfamide and its N-dechloroethylated metabolites in acidic aqueous solutions.

31P NMR spectroscopy was used to study the products of the decomposition of the antitumor drug ifosfamide (IF, 1d) and its N-dechloroethylated metabolites, namely, 2,3-didechloroethylIF (1a) and 2- (1b) and 3-dechloroethylIF (1c), in buffered solutions at acidic pH. The first stage of acid hydrolysis of these four oxazaphosphorines is a P-N bond cleavage of the six-membered ring leading to the phosphoramidic acid monoesters (2a-d) of type R'HN(CH(2))(3)OP(O)(OH)NHR, with R and/or R' = H or (CH(2))(2)Cl. The electron-withdrawing chloroethyl group at the endocyclic and/or exocyclic nitrogens counteracts the endocyclic P-N bond hydrolysis. This effect is even more marked when the N-chloroethyl group is in the exocyclic position since the order of stability is 1d > 1c > 1b > 1a. In the second stage of hydrolysis, the remaining P-N bond is cleaved together with an intramolecular attack at the phosphorus atom by the non-P-linked nitrogen of the compounds 2a-d. This leads to the formation of a 2-hydroxyoxazaphosphorine ring with R = H (3a coming from compounds 2a,c) or (CH(2))(2)Cl (3b coming from compounds 2b,d) and to the release of ammonia or chloroethylamine. The third step is the P-N ring opening of the oxazaphosphorines 3a,b leading to the phosphoric acid monoesters, H(2)N(CH(2))(3)OP(O)(OH)(2) (4a) and Cl(CH(2))(2)HN(CH(2))(3)OP(O)(OH)(2) (4b-1), respectively. For the latter compound, the chloroethyl group is partially (at pH 5.5) or totally (at pH 7.0) cyclized into aziridine (4b-2), which is then progressively hydrolyzed into an N-hydroxyethyl group (4b-3). Compounds 3a,b are transient intermediates, which in strongly acidic medium are not observed with (31)P NMR. In this case, cleavage of the P-N bond of the type 2 phosphoramidic acid monoesters leads directly to the type 4 phosphoric acid monoesters. The phosphate anion, derived from P-O bond cleavage of these latter compounds, is only observed at low levels after a long period of hydrolysis. Compounds 1a-c and some of their hydrolytic degradation products (4b-1, 4b-2, diphosphoric diester [Cl(CH(2))(2)NH(CH(2))(3)OP(O)(OH)](2)O (5), and chloroethylamine) did not exhibit, as expected, any antitumor efficacy in vivo against P388 leukemia. (31)P NMR determination of the N-dechloroethylated metabolites of IF or its structural isomer, cyclophosphamide (CP), and their degradation compounds could provide an indirect and accurate estimation of chloroacetaldehyde amounts formed from CP or IF.

Alkaline Hydrolysis of the Cytostatic Drug, Ifosfamide, and its N-Dechloroethylated Metabolites

I fosfamide (IF) is an alkylating antitumor agent used in the treatment of solid tumors. Up to 50% of IF administered to patients undergoes an oxidative N-dealkylation reaction resulting in the loss or one, other or both chloroethyl side chain(s) to produce 2- or 3-dechloioethylIF (ZDCIF, 3DCIF) or 2,3-didechloroethyllF (DDCIF). The hydrolytic pathway of these four oxazaphosphorines has been studied earlier but only at acidic and neutral pHs[l] In the present work, we monitored their time courses of hydrolysis at basic pHs using phosphorus-3 1 NMR. The structures of the compounds formed were determined by NMR (13C and 1H) and mass spectrometry. The results are reported in the following scheme.

Enantioselective induction of cyclophosphamide metabolism by phenytoin

The objective of this study was to investigate the effect of phenytoin (PHE) on cyclophosphamide (CP) disposition. CP was administered to 6 adult patients in a preparative regimen for bone marrow transplantation consisting of busulfan and CP. Three of the patients received PHE and the other 3 “control” patients received diazepam (DZP) as anti-epileptic prophylactic treatment. Plasma samples were collected at intervals up to 24 h after CP administration. The plasma concentrations of (R)- and (S)-CP and their respective N-dechloroethylated metabolites, (R)- and (S)-DCE-CP were simultaneously fitted using an enantiospecific 2-compartment pharmacokinetic (PK) model with Bayesian control estimation. DZP had no significant effect on the metabolism of CP and any of its PK parameters. PHE, however, increased significantly the formation of (S)-DCE-CP while having no effect on the formation of (R)-DCE-CP. These results suggest that different enzymes are responsible for the formation of (S)-DCE-CP from (S)-CP and (R)-DCE-CP from (R)-CP. Additionally, assuming that PHE does not affect the passive renal elimination of (R)- and (S)-CP, this analysis suggests that the clearance of both (R)- and (S)-CP to 4-hydroxy-CP (the activation pathway) is increased by PHE. Chirality 11:569–574, 1999. © 1999 Wiley-Liss, Inc.

The N-dechloroethylation of ifosfamide: using stereochemistry to obtain an accurate picture of a clinically relevant metabolic pathway.

The cumulative urinary excretions of the enantiomers of ifosfamide [(R)-IFF, (S)-IFF)] and their 2-N-dechlorethylated (2-DCE-IFF) and 3-N-dechloroethylated (3-DCE-IFF) metabolites were determined in 11 adult cancer patients who received a single 3-h infusion of IFF (3 g/m2) with mesna uroprotection. The urine samples were analyzed for the compounds of interest using an enantioselective gas chromatographic-mass spectrometric assay. The results indicated an enantioselective excretion of the parent and N-dechloroethylated metabolites: the urinary recovery of (R)-IFF was significantly greater than that of (S)-IFF (1.73 +/- 0.45 vs 1.43 +/- 0.41 mmol, P < 0.0001); the excretion of (S)-2-DCE-IFF (0.75 +/- 0.53 mmol) was greater than that of (R)-2-DCE-IFF (0.42 +/- 0.22 mmol, P = 0.071) while the excretion of (R)-3-DCE-IFF (1.64 +/- 0.76 mmol) was greater than that of (S)-3-DCE-IFF (0.77 +/- 0.59 mmol, P = 0.012). The study also revealed two distinct metabolic patterns in which the urinary recoveries of (R)-2-DCE-IFF and (R)-3-DCE-IFF were linked as were those of (S)-2-DCE-IFF and (S)-3-DCE-IFF. The results suggest that at least two enzymes are involved in the N-dechlorethylation of IFF. The data also demonstrate the importance of following the metabolic fate of (R)-IFF and (S)-IFF and of determining the relative urinary excretion of all dechloroethylated metabolites.

Studies on the urinary metabolites of isophosphamide and its activated species in rabbits.

Investigations on the urinary metabolites of isophosphamide, 4-hydroxyisophosphamide and 4-hydroxyisophosphamide including stereoisomers of the C4-oxidized derivatives in rabbits revealed that their metabolic behaviors were different from each other and also form those of cyclophosphamide. Administration of isophosphamide to rabbits resulted in the urinary excretion of carboxyisophosphamide and two N-dechloroethylated metabolites besides considerable amount of unchanged isophosphamide, while 4-hydroxyisophosphamide was metabolized principally into carboxyisophosphamide. In the case of 4-hydroxyisophosphamide, carboxyisophosphamide was excreted as a major metabolite, but considerable amount of a new metabolite which might be produced from 4-ketoisophosphamide via a hitherto unknown pathway was also excreted besides small amount of 4-ketoisophosphamide. Mechanism of the formation of this new metabolite was proposed based on the chemical conversion of a suggested intermediate into the metabolite. PHosphorus configuration of the C4-oxidized isophosphamides was found to have no significant effect upon their metabolism. It was suggested that the results of the present studies could account for the great differences in in vivo antitumor activities between isophosphamide and its pre-activated derivatives and also between isophosphamide and cyclophosphamide.