Sensitive gas chromatographic determination of the cyclophosphamide metabolite 2-dechloroethylcyclophosphamide in human plasma

Analysis of the Fragmentation Pathways for the Collision-Induced Dissociation of Protonated Cyclophosphamide: A Mass Spectrometry and Quantum Mechanical Study

Cyclophosphamide is a well-known anticancer agent acting by means of DNA alkylation. Associated with its tumor selectivity, it also possesses a wide spectrum of toxicities. As the requirement of metabolic activation before cyclophosphamide exerts either its therapeutic or toxic effects is well recognized, research aiming at elucidating the pathways that lead to the activation of this drug is of key importance. This has created the necessity for developing an effective analytical method for detecting cyclophosphamide and its breakdown products. In this paper, an Acquity TQ tandem quadrupole mass spectrometer equipped with electrospray ionization in positive-ion mode was employed for detecting cyclophosphamide in its protonated form. The full-scan mass spectrum of cyclophosphamide shows two ion clusters displaying the characteristic isotopic pattern of two chlorine atoms and assigned as sodiated cyclophosphamide, [CP + Na]⁺, and protonated cyclophosphamide, [CP + H]⁺ or PCP. With the aid of quantum mechanical DFT calculation, free energy differences in the gas phase among PCP protomers were computed with respect to the most stable protomer being protonated on the 2-oxide oxygen of the 1,3,2-oxazaphosphorine-2-oxide ring. In addition, the interconversion mechanisms among the different protomers were also proposed by intercepting the corresponding transition states in the gas phase. Collision-induced dissociation (CID) of PCP generated six characteristic product ions. Fragmentation mechanisms were proposed and supported by computation. The calculated energy barriers for all of the located transition states were found to be accessible under the reported experimental conditions.

Fast quantification of cyclophosfamide and its N-dechloroethylated metabolite 2-dechloroethylcyclophosphamide in human plasma by UHPLC-MS/MS

A rapid, novel and reliable UHPLC-MS/MS method was developed and validated for simultaneous determination of cyclophosphamide (CP) and its dechloroethylated metabolite, 2-dechloroethylcyclosphamide (2-DCECP) in human plasma. The plasma samples were conducted by protein precipitation with 3-fold acetonitrile, containing 0.1% formic acid. Mass spectrometric detection was performed using electrospray positive ionization with multiple reaction monitoring mode, using tinidazole as internal standard (IS). Chromatographic separation was performed on an Agilent poroshell 120 SB-C18 column (2.1 × 75 mm, 2.7 µm) using gradient elution of acetonitrile and 0.1% formic acid at a flow rate of 0.5 mL/min, the total run time was 2.5 min. The limit of quantification (LOQ) was 20 ng/mL for both CP and 2-DCECP. Accuracies and precisions were <15% at LOQ and below 10% at quality control concentration levels. This UHPLC-MS/MS method was successfully applied for the estimation of CP and 2-DCECP in human plasma, which was also useful for clinical toxicology studies and therapeutic drug monitoring of CP.

Population pharmacokinetics of cyclophosphamide and its metabolites 4-hydroxycyclophosphamide, 2-dechloroethylcyclophosphamide, and phosphoramide mustard in a high-dose combination with Thiotepa and Carboplatin

The anticancer prodrug cyclophosphamide (CP) is activated by the formation of 4-hydroxycyclophosphamide (4OHCP), which decomposes into phosphoramide mustard (PM). This activation pathway is inhibited by thiotepa. CP is inactivated by formation of 2-dechloroethylcyclophosphamide (2DCECP). The aim of this study was to develop a population pharmacokinetic model describing the complex pharmacokinetics of CP, 4OHCP, 2DCECP, and PM when CP is administered in a high-dose combination with thiotepa and carboplatin. Patients received a combination of CP (1000-1500 mg/m/d), carboplatin (265-400 mg/m/d), and thiotepa (80-120 mg/m/d) administered in short infusions over 4 days. Twenty blood samples were collected per patient per course. Concentrations of CP, 4OHCP, 2DCECP, PM, thiotepa, and tepa were determined in plasma. Using NONMEM, an integrated population pharmacokinetic model was used to describe the pharmacokinetics of CP, 4OHCP, 2DCECP, and PM, including the already described processes of autoinduction of CP and the interaction with thiotepa. Data were available on 35 patients (70 courses). The pharmacokinetics of CP were described with a 2-compartment model, and those of 4OHCP, 2DCECP, and PM with 1-compartment models. Before onset of autoinduction, it was assumed that CP is eliminated through a noninducible pathway accounting for 20% of total CP clearance, whereas 2 inducible pathways resulted in formation of 4OHCP (75%) and 2DCECP (5%). It was assumed that 4OHCP was fully converted to PM. Induction of CP metabolism was mediated by 2 hypothetical amounts of enzyme whose quantities increased in time in the presence of CP (kenz=0.0223 and 0.0198 hours). Induction resulted in an increased formation of 4OHCP (approximately 50%), PM (approximately 50%), and 2DCECP (approximately 35%) during the 4-day course, and concomitant decreased exposure to CP (approximately 50%). The formation of 2DCECP was not inhibited by thiotepa. Apparent volumes of distribution of CP, PM, and 2DCECP could be estimated being 43.7, 55.5, and 18.5 L, respectively. Exposure to metabolites varied up to 9-fold. The complex population pharmacokinetics of CP, 4OHCP, 2DCECP, and PM in combination with thiotepa and carboplatin has been established and may form the basis for further treatment optimization with this combination.

Mono- and diiodocyclophosphamide as possible internal standards for cyclophosphamide quantification: characterization by ion trap multi-stage mass spectrometry and effects of iodine-chlorine substitution on the fragmentation pattern

Hospital personnel involved in antineoplastic drug preparation and administration to patients are exposed to large amounts of these drugs. Labour legislation indicates the necessity of planning monitoring strategies aimed at prevention and/or reduction of drug exposure. Monitoring strategies consist of quantitative determinations of indicators, present in environmental and biological matrices. Among the antineoplastic drugs widely used, cyclophosphamide (CP) has been identified as a suitable indicator of potential exposure to mixtures of antineoplastic drugs. Many literature methods for quantitative analysis of CP involve either liquid (LC) or gas chromatography (GC) with mass spectrometry (MS), both of which require use of a suitable internal standard. The present work focuses on the synthesis of mono- and diiodocyclophosphamide (CPI and CPI(2)) to be used as internal standard. These compounds were analyzed by GC/EI-MS/MS and LC/ESI-MS(n) using ion trap mass spectrometry. The product ion mass spectra are interpreted in terms of proposed structures of fragment ions. Iodine-chlorine substitution resulted in a weakening of the carbon-halogen bond with a noteworthy influence on the ion fragmentation processes. The proposed suitability of CPI and CPI(2) as internal standards was based on similarities to CP as regards ionization and fragmentation processes. The results obtained suggest that CPI could be used as internal standard for CP quantification by LC/ESI-MS/MS, and CPI(2) for GC/EI-MS/MS analyses.

Highly sensitive high-performance liquid chromatography/selective reaction monitoring mass spectrometry method for the determination of cyclophosphamide and ifosfamide in urine of health care workers exposed to antineoplastic agents

In recent years, the potential for exposure of health care workers to antineoplastic agents has led to the establishment of more restrictive government and professional standards and procedures for handling cytotoxic drugs. Therefore, the detection of low exposure levels is a new and important aim of biological monitoring. In the present paper we report an assay for the simultaneous determination of cyclophosphamide (CP) and ifosfamide (IF) in urine, using electrospray ionization liquid chromatography/tandem mass spectrometry with selective reaction monitoring (HPLC/SRM-MS). A rapid sample preparation procedure uses a solid-phase extraction stage with C18 columns. The urine assay is linear over the range 0.02 to 0.4 microg/L, with lower limits of quantification (LLOQs) of 0.02 and 0.04 microg/L for CP and IF. The accuracy and precision have been carried out through the validation study. The intra-day precision, expressed as relative standard deviation (RSD), is found to be always less than 14.7% for both analytes. The overall precision, assessed on three different days, is less than 15.0%. The recovery of ozaxaphosphorines ranges from 83.5% (CP) to 88.5% (IF) with a RSD always less than 14.6%. The uncertainty of the overall method was also evaluated, to identify possible sources of error. The combined uncertainty was less than 25% over all the days of the validation study. This method is selective and sensitive enough to determine trace levels of CP and IF in a range of urine concentrations relevant to performing low exposure assessment.