The effect of route of administration and fractionation of dose on the metabolism of ifosfamide

The glycine deportation system and its pharmacological consequences

The glycine deportation system is an essential component of glycine catabolism in man whereby 400 to 800mg glycine per day are deported into urine as hippuric acid. The molecular escort for this deportation is benzoic acid, which derives from the diet and from gut microbiota metabolism of dietary precursors. Three components of this system, involving hepatic and renal metabolism, and renal active tubular secretion help regulate systemic and central nervous system levels of glycine. When glycine levels are pathologically high, as in congenital nonketotic hyperglycinemia, the glycine deportation system can be upregulated with pharmacological doses of benzoic acid to assist in normalization of glycine homeostasis. In congenital urea cycle enzymopathies, similar activation of the glycine deportation system with benzoic acid is useful for the excretion of excess nitrogen in the form of glycine. Drugs which can substitute for benzoic acid as substrates for the glycine deportation system have adverse reactions that may involve perturbations of glycine homeostasis. The cancer chemotherapeutic agent ifosfamide has an unacceptably high incidence of encephalopathy. This would appear to arise as a result of the production of toxic aldehyde metabolites which deplete ATP production and sequester NADH in the mitochondrial matrix, thereby inhibiting the glycine deportation system and causing de novo glycine synthesis by the glycine cleavage system. We hypothesize that this would result in hyperglycinemia and encephalopathy. This understanding may lead to novel prophylactic strategies for ifosfamide encephalopathy. Thus, the glycine deportation system plays multiple key roles in physiological and neurotoxicological processes involving glycine.

The pharmacologic basis of ifosfamide use in adult patients with advanced soft tissue sarcomas

The treatment outcome of patients with locally advanced and metastatic soft tissue sarcomas is poor. Doxorubicin is regarded as standard treatment, but its use is featured by the occurrence of cardiotoxicity. This hinders the administration of this drug at high doses or in combination with, in theory, attractive newly developed targeted drugs, such as vascular endothelial growth factor (VEGF) pathway inhibitors. The combination of doxorubicin and VEGF pathway inhibitors has been shown to yield an unacceptable high rate of cardiomyopathy. Ifosfamide is the only drug that consistently shows response rates comparable to those of doxorubicin. The lack of cardiotoxicity renders this drug a much more attractive alternative than doxorubicin to be explored at high doses or as part of new drug combinations. This review addresses the clinical pharmacology, metabolism, and present role of ifosfamide in the treatment of locally advanced and/or metastatic soft tissue sarcomas, excluding gastrointestinal stromal tumors, the Ewing-like sarcomas, and other small blue round cell tumors. Furthermore, this review focuses on the anticipated growing role of ifosfamide in the development of new treatment strategies.

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 (alpha) 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.

Ifosfamide: pharmacokinetic properties for central nervous system metastasis prevention

The incidence of central nervous system (CNS) recurrence in patients with lymphoma is about 5%. Nevertheless, this complication is very serious because it is almost always fatal. Its incidence is not sufficiently high to warrant the use of CNS prophylaxis in all patients. The identification of subgroups for whom CNS prophylaxis may be of benefit is therefore important and the age-adjusted international prognostic index (aa-IPI) may be useful in this respect. Ifosfamide (IFO) is a widely used antitumor agent, requiring activation to isophosphoramide mustard (IPM) for DNA alkylation. IFO anabolism occurs through the hepatic microsomal cytochrome P450 system. As with the majority of antineoplastic agents, IFO has toxic side-effects. These include neurotoxicity due to the chloroacetaldehyde (CAA) catabolite. However, the incidence of neurotoxicity is low when IFO is administered as a continuous intravenous infusion. Both inactive IFO and active IPM cross the blood-brain barrier, making IFO treatment effective in the prevention of CNS metastasis in lymphoma patients at high risk of recurrence. The benefit/risk ratio for such patients should evaluated.

Activation of oxazaphosphorines by cytochrome P450: Application to gene-directed enzyme prodrug therapy for cancer

Cancer chemotherapeutic prodrugs, such as the oxazaphosphorines cyclophosphamide and ifosfamide, are metabolized by liver cytochrome P450 enzymes to yield therapeutically active, cytotoxic metabolites. The effective use of these prodrugs is limited by host toxicity associated with the systemic distribution of cytotoxic metabolites formed in the liver. This problem can, in part, be circumvented by implementation of cytochrome P450 gene-directed enzyme prodrug therapy (P450 GDEPT), a prodrug activation strategy for cancer treatment that augments tumor cell exposure to cytotoxic drug metabolites generated locally by a prodrug-activating cytochrome P450 enzyme. P450 GDEPT has been exemplified in preclinical rodent and human tumor models, where chemosensitivity to a P450 prodrug can be greatly increased by introduction of a prodrug-activating P450 gene. Further enhancement of the efficacy of P450-based gene therapy can be achieved: by co-expression of P450 with the flavoenzyme NADPH-P450 reductase, which provides electrons required for P450 metabolic activity; by metronomic (anti-angiogenic) scheduling of the prodrug; by localized delivery of the prodrug to the tumor; and by combination with anti-apoptotic factors, which slow the death of the P450 'factory' cells and thereby enhance the bystander cytotoxic response. P450 GDEPT has several important features that make it a clinically attractive strategy for cancer treatment. These include: the substantial bystander cytotoxicity of P450 prodrugs such as cyclophosphamide and ifosfamide; the ability to use human P450 genes and thereby avoid an immune response to the therapeutic gene; the use of well-established conventional chemotherapeutic prodrugs, as well as bioreductive drugs activated by P450/P450 reductase in a hypoxic tumor environment; and the potential to decrease systemic exposure to active drug metabolites by selective inhibition of hepatic P450 activity. Recent advances in this area of research are reviewed, and two proof-of-concept clinical trials that highlight the utility of this strategy are discussed.

A Phase I Study of Prolonged Ambulatory Infusion of Ifosfamide with Oral Mesna

BACKGROUND

Oral mesna allows investigation of ifosfamide as a prolonged ambulatory infusion for dose-intense out-patient use.

METHODS

Cohorts of 3 patients received escalating doses of ifosfamide from 200 to 1,000 mg/m2/day as continuous ambulatory infusion with oral mesna at 30% of the ifosfamide dose every 6 h commencing 2 h prior to ifosfamide infusion as uroprotection on a 14-day schedule with cycles repeated every 28 days.

RESULTS

Fifteen patients received a median of three cycles. Dose-limiting toxicities with cycle 1 were lethargy and hepatotoxicity at 1,000 mg/m2/14 days. Transient transaminase elevation was seen at all dose levels. The other grade 3 toxicities were single episodes of anaemia, granulocytopenia, nausea and hypotension. The best response was stable disease in a patient with thyroid cancer.

CONCLUSION

Ambulatory infusion of 600 mg/m2 ifosfamide with 180 mg/m2 oral mesna was considered suitable for phase II trials and delivers dose-intense out-patient therapy without urotoxicity.

Phase I study of docetaxel plus ifosfamide in patients with advanced cancer

The aim of this study was to determine the maximum tolerated dose of a fixed dose of docetaxel when combined with continuous infusion ifosfamide, with and without G-CSF support, in the treatment of advanced cancer, and to evaluate anti-tumour activity of this combination. Thirty-one patients with advanced malignancies were treated with docetaxel 75 mg/m(2) intravenously on days 1, and ifosfamide at increasing dose levels from 1500 mg/m(2)/day to 2750 mg/m(2)/day as a continuous infusion from day 1-3, every 3 weeks. A total of 107 cycles of treatment were administered. Without G-CSF support dose-limiting toxicity of grade 4 neutropenia greater than 5 days duration occurred at dose level 1. With the addition of G-CSF the maximum tolerated dose was docetaxel 75 mg/m(2) on day 1 and ifosfamide 2750 mg/m(2)/day on days 1-3. Dose limiting toxicity (DLT) included ifosfamide-induced encephalopathy, febrile neutropenia and grade three mucositis. Three complete responses and 3 partial responses were seen. This combination of docetaxel and infusional ifosfamide is feasible and effective. The recommended dose for future phase II studies is docetaxel 75 mg/m(2) on day 1 and ifosfamide 2500 mg/m(2)/day continuous infusion on days 1-3.

Cyclophosphamide and related anticancer drugs

This article presents an overview of the methods of bioanalysis of oxazaphosphorines, in particular, cyclophosphamide, ifosfamide, and trofosfamide as well as their metabolites. The metabolism of oxazaphosphorines is complex and leads to a large variety of metabolites and therefore the spectrum of methods used is relatively broad. The various methods used are shown in a table and the particularly important assays are described.

Clinical pharmacokinetics and pharmacodynamics of ifosfamide and its metabolites

This review discusses several issues in the clinical pharmacology of the antitumour agent ifosfamide and its metabolites. Ifosfamide is effective in a large number of malignant diseases. Its use, however, can be accompanied by haematological toxicity, neurotoxicity and nephrotoxicity. Since its development in the middle of the 1960s, most of the extensive metabolism of ifosfamide has been elucidated. Identification of specific isoenzymes responsible for ifosfamide metabolism may lead to an improved efficacy/toxicity ratio by modulation of the metabolic pathways. Whether ifosfamide is specifically transported by erythrocytes and which activated ifosfamide metabolites play a key role in this transport is currently being debated. In most clinical pharmacokinetic studies, the phenomenon of autoinduction has been observed, but the mechanism is not completely understood. Assessment of the pharmacokinetics of ifosfamide and metabolites has long been impaired by the lack of reliable bioanalytical assays. The recent development of improved bioanalytical assays has changed this dramatically, allowing extensive pharmacokinetic assessment, identifying key issues such as population differences in pharmacokinetic parameters, differences in elimination dependent upon route and schedule of administration, implications of the chirality of the drug and interpatient pharmacokinetic variability. The mechanisms of action of cytotoxicity, neurotoxicity, urotoxicity and nephrotoxicity have been pivotal issues in the assessment of the pharmacodynamics of ifosfamide. Correlations between the new insights into ifosfamide metabolism, pharmacokinetics and pharmacodynamics will rationalise the further development of therapeutic drug monitoring and dose individualisation of ifosfamide treatment.

Metabolism and pharmacokinetics of oxazaphosphorines

The 2 most commonly used oxazaphosphorines are cyclophosphamide and ifosfamide, although other bifunctional mustard analogues continue to be investigated. The pharmacology of these agents is determined by their metabolism, since the parent drug is relatively inactive. For cyclophosphamide, elimination of the parent compound is by activation to the 4-hydroxy metabolite, although other minor pathways of inactivation also play a role. Ifosfamide is inactivated to a greater degree by dechloroethylation reactions. More robust assay methods for the 4-hydroxy metabolites may reveal more about the clinical pharmacology of these drugs, but at present the best pharmacodynamic data indicate an inverse relationship between plasma concentration of parent drug and either toxicity or antitumour effect. The metabolism of cyclophosphamide is of particular relevance in the application of high dose chemotherapy. The activation pathway of metabolism is saturable, such that at higher doses (greater than 2 to 4 g/m2) a greater proportion of the drug is eliminated as inactive metabolites. However, both cyclophosphamide and ifosfamide also act to induce their own metabolism. Since most high dose regimens require a continuous infusion or divided doses over several days, saturation of metabolism may be compensated for, in part, by auto-induction. Although a quantitative distinction may be made between the cytochrome P450 isoforms responsible for the activating 4-hydroxylation reaction and those which mediate the dechloroethylation reactions, selective induction of the activation pathway, or inhibition of the inactivating pathway, has not been demonstrated clinically. Mathematical models to describe and predict the relative contributions of saturation and autoinduction to the net activation of cyclophosphamide have been developed. However, these require careful validation and may not be applicable outside the exact regimen in which they were derived. A further complication is the chiral nature of these 2 drugs, with some suggestion that one enantiomer may have a favourable profile of metabolism over the other. That the oxazaphosphorines continue to be the subject of intensive investigation over 30 years after their introduction into clinical practice is partly because of their antitumour activity. Further advances in analytical and molecular pharmacological techniques may further optimise their use and allow rational design of more selective analogues.

Determination of ifosfamide by HPLC using on-line sample preparation

The Authors have developed a novel and easily applicable HPLC method for ifosfamide (IF) determination. This method involves on-line sample processing and its solid-phase extraction by means of an automatic preparator integrated with the chromatographic system. The calibration graph of the method is linear in the concentration range 6-200 microg/ml; minimum detectable concentration is 6 microg/ml. This highly accurate and easily reproducible method was used by the Authors in the treatment of osteosarcoma with slow infusion of ifosfamide.

The pharmacokinetics and metabolism of ifosfamide during bolus and infusional administration: a randomized cross-over study

In a randomized cross-over trial, 11 patients received ifosfamide (IFOS) in 21-day cycles, which alternated between 3 g m(-2) x (2 or 3) days given as a 1-h bolus doses, or the same total dose as a continuous infusion. Patients who received four or more cycles also alternated between two cycles on dexamethasone 4 mg 8 hourly for 3 days starting 8 h before IFOS, and two cycles off dexamethasone. A total of 34 patient cycles were studied and serum and urinary levels of IFOS, 2 dechloroethylifosfamide (2DC), 3 dechloroethylifosfamide (3DC), carboxyifosfamide (CX) and isophosphoramide mustard (IPM) were measured by thin-layer chromatography. No significant differences could be detected in the areas under the curve (AUCs) of serum concentration, nor in the proportion of IFOS or its metabolites found in the urine. There was no significant effect of dexamethasone on IFOS metabolism. These results indicate that there is no identifiable pharmacokinetic basis for insistence on either bolus or infusional methods of IFOS administration.

Analysis of ifosforamide mustard, the active metabolite of ifosfamide, in plasma

Ifosforamide mustard is the active metabolite of ifosfamide, a cytostatic drug. In this study a sensitive and selective method for the analysis of ifosforamide mustard in plasma is described. The method consists of direct derivatisation of ifosforamide mustard in plasma with diethyldithiocarbamate and subsequent solid-phase extraction of the resulting derivative. The analysis of the derivatisation product was performed by high-performance liquid chromatography with UV detection. The calibration graph was linear in the concentration range 0.45-45 microM and the minimum detectable concentration was 0.45 mumol. The samples were stabilised by addition of semicarbazide and sodium chloride. A patient's plasma sample was analysed by means of the described method. The ifosforamide mustard concentration was 2.3 microM.

Stereoselective pharmacokinetics of ifosfamide and its 2- and 3-N-dechloroethylated metabolites in female cancer patients

The pharmacokinetics of the R and S enantiomers of ifosfamide (IFF) and of its 2- and 3-N-dechloroethylated metabolites (2-DCE-IFF and 3-DCE-IFF) were investigated in 14 cancer patients treated with a 3-h infusion of (R,S)-IFF (3 g/m2) with mesna uroprotection. An enantioselective gas chromatographic-mass spectrometric (GC-MS) assay was used to determine the concentrations in plasma and urine. The AUCs of (R)-IFF were significantly larger than those of (S)-IFF (2480 +/- 200 vs 1960 +/- 150 microM.h). The terminal half-lives (7.57 +/- 0.99 h) and mean residence times (11.17 +/- 1.10 h) of (R)-IFF were significantly longer than those of (S)-IFF, 6.03 +/- 0.82 h and 9.37 +/- 0.88 h, respectively. The mean volume of distribution at steady rate of (R)-IFF (25.68 +/- 0.80 l/m2) was slightly smaller than that of (S)-IFF (27.35 +/- 0.89 l/m2). While the renal clearances of (R)-IFF and (S)-IFF were similar, the nonrenal clearance was significantly lower for (R)-IFF (30.20 +/- 2.70 vs 41.40 +/- 3.55 ml/m2 per min) as was total clearance (41.52 +/- 2.90 vs 52.37 +/- 3.75 ml/m(2) per min). The AUC values for all of the DCE metabolites from (S)-IFF were significantly greater than those from (R)-IFF with 47% of the measured AUC accounted for by DCE from (S)-IFF compared to only 20% for (R)-IFF. Therefore, the enantioselective difference in IFF elimination can be partially explained by differences in N-dechloroethylation.

Analysis of ifosfamide, 4-hydroxyifosfamide, N2-dechloroethylifosfamide, N3-dechloroethylifosfamide and iphosphoramide mustard in plasma by gas chromatography-mass spectrometry

A sensitive and specific method for the simultaneous quantitation of ifosfamide (IF), 4-hydroxylifosfamide (4-OHIF), N2-dechloroethylifosfamide (N2D), N3-dechloroethylifosfamide (N3D) and iphosphoramide mustard (IPM) has been developed using gas chromatography-mass spectrometry (GC-MS) with an ion-trap mass spectrometer. Deuterium labeled analogues for each of these analytes were synthesized as the internal standards. The labile 4-OHIF in plasma was first converted to the more stable cyanohydrin adducts before dichloromethane extraction. IPM was extracted by C18 reversed-phase resin. All analytes were converted to their silyl derivatives before GC-MS analysis. The sensitivity limits ranged from 0.1 to 0.5 microgram/ml when 100 microliters of plasma was used. This method was validated with within-run coefficients of variation less than 5% (n = 8) and between-run coefficients of variation less than 12% (n = 6). The method was applied to the determination of plasma levels of IF and metabolites in the rat.

Pharmacokinetics, metabolism and clinical effect of ifosfamide in breast cancer patients

Ifosfamide (IFO) at a dose of 5 g/m2, was administered as a 24-h infusion to 15 patients with metastatic (12) or locally advanced (3) breast cancer (age range 33-59 years, median 46). Concurrent chemotherapy was doxorubicin (40 mg/m2) or epirubicin (60 mg/m2). Ifosfamide and its metabolites were measured in plasma and urine during and for 24 h after the infusion using a high performance thin layer chromatography (HPTLC) technique. Patients' haematological toxicity and biochemistry were monitored during treatment and patients were followed for up to 2 years after therapy. At the time of evaluation, 5 of the patients were alive, 2 of whom had not relapsed. A marked variation was observed in the pharmacokinetics and metabolism of ifosfamide in the evaluable patients. Clearance, volume of distribution and half-life of the drug were 3.48 +/- 0.88 1/h/m2, 0.56 +/- 0.22 l/kg and 4.68 +/- 2.01 h, respectively. There was no apparent correlation between these pharmacokinetic variables and patient age, weight or renal function. AUCs of the ultimate alkylating species isophosphoramide mustard (IPM) varied over 6-fold, as did those of the inactivated metabolite carboxyifosfamide (CX). AUCs of dechloroethylated metabolites varied 4-fold (3-dechloroethylifosfamide, 3-DCI) or 8-fold (2-DCI), while that of the parent compound varied only 2.5-fold. Variation in recovery of the metabolites in urine varied over an even wider range, total recovery varying from 17.5 to 81.8% of the dose administered. There was little apparent correlation between pharmacokinetic and metabolite parameters of IFO and haematological toxicity. However, there was a marked negative correlation between both progression-free interval and survival and the AUCs of the products of IFO activation (IPM and CX). In addition, the recovery of IPM in urine was higher in patients experiencing a partial response compared to those with progressive or stable disease. Recovery of dechloroethylated metabolites correlated positively with survival, if 1 poor prognosis patient was excluded. Although far from conclusive, these results give some insight into a possible mechanism of action of ifosfamide and indicate that some species other than IPM, as measured systemically, is responsible for the pharmacological effects of this drug.

The kinetics of the auto-induction of ifosfamide metabolism during continuous infusion

It has often been reported that the oxazaphosphorines ifosfamide and cyclophosphamide induce their own metabolism. This phenomenon was studied in 21 paediatric patients over 35 courses of therapy. All patients received 9 gm-2 of ifosfamide as a continuous infusion over 72 h. Plasma concentrations of parent drug and of the major metabolite in plasma, 3-dechloroethylifosfamide (3DC) were determined, using a quantitative thin-layer chromatography (TLC) technique. A one-compartment model was fitted simultaneously to both ifosfamide and 3DC data. The model included a time-dependent clearance term, increasing asymptotically from an initial value to a final induced clearance and characterised by a first-order rate constant. A time lag, before induction of clearance began, was determined empirically. Metabolite kinetics were characterised by an elimination rate constant for the metabolite and a composite parameter comprising a formation clearance, proportional to the time-dependent clearance of parent drug, divided by the volume of distribution of the metabolite. Thus, the parameters to estimate were the volume of distribution of parent drug (V), initial clearance (Cli), final clearance (Cls), the rate constant for changing clearance (Kc), the elimination rate constant for the metabolite (Km) and Vm/fm, the metabolite volume of distribution divided by the fractional clearance to 3DC. The model of drug and metabolite kinetics produced a good fit to the data in 22 of 31 courses. In a further 4 courses an auto-inductive model for parent drug alone could be used. In the remaining courses, auto-induction could be demonstrated, but there were insufficient data to fit the model. For some patients this was due to a long time lag (up to 54 h) relative to the infusion time. The time lag varied from 6 to 54 (median, 12)h and values for the other parameters were Cli, 3.27 +/- 2.52 lh-1 m-2, Cls, 7.50 +/- 3.03 lh-1 m-2, V, 22.0 +/- 11.0 1 m-2, Kc, 0.086 +/- 0.074 h-1; Km, 0.159 +/- 0.077 h-1 and Vm/fm, 104 +/- 82 1m-2. The values of Kc correspond to a half-life of change in clearance ranging from 2 to 157 h, although for the majority of the patients the half-life was less than 7 h and a new steady-state level was achieved during the 72 h infusion period. This model provides insight into the time course of enzyme induction during ifosfamide administration, which may continue for up to 10 days in some protocols.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism of ifosfamide during a 3 day infusion

Urinary drug metabolites were measured in 21 patients receiving ifosfamide by continuous infusion over 3 days. Mean values for the proportion of drug excreted as parent compound, 2-dechloroethylifosfamide (2-DC), 3-dechloroethylifosfamide (3-DC), carboxyifosfamide (CX) and ifosforamide mustard (IPM) were 19, 6, 10, 7 and 8% of dose respectively. The proportion of urinary drug products in the form of ifosfamide fell considerably over the course of the 3 days. This was mirrored by an increase in the proportion of 2-DC, 3-DC and CX. The proportion in the form of IPM, however, remained unchanged. With successive cycles the amount of 2-DC and IPM increased by about 10% per course. A very wide variation in the amount of each metabolite was reproducibly seen between patients, but no evidence for a genetic polymorphism was found. Urinary dechloroethyl metabolites correlated positively with each other and negatively with CX. Although autoinduction increases 'activation' of ifosfamide when given over 3 days, our evidence suggests that competing metabolic pathways prevent an increase in the amount of active metabolite formed.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Determination of the urinary excretion of ifosfamide and its phosphorated metabolites by phosphorus-31 nuclear magnetic resonance spectroscopy

Phosphorus-31 nuclear magnetic resonance spectroscopy was used to analyze urine samples obtained from patients treated with ifosfamide (IF). This technique allows the individual assay of all phosphorated metabolites of IF in a single analysis without the need for prior extraction. In addition to the classic IF metabolites 2-dechloroethylifosfamide (2DEC1IF), 3-dechloroethylifosfamide (3DEC1IF), carboxyifosfamide (CARBOXYIF), and isophosphoramide mustard (IPM), several signals corresponding to unknown phosphorated compounds were observed. Four of them were identified: one is alcoifosfamide (ALCOIF), two come from the degradation of 2,3-didechloroethylifosfamide (2,3-DEC1IF), and one results from the decomposition of 2DEC1IF. The total cumulative drug excretion as measured over 24 h in nine patients was 51% of the injected IF dose; 18% of the dose was recovered as unchanged IF. The major urinary metabolites were the dechloroethylated compounds, with 3DEC1IF excretion (11% of the injected dose) always being superior to 2DEC1IF elimination (4% of the injected dose). Degradation compounds of 2DEC1IF and 2,3DEC1IF represented 0.4% of the injected dose. The metabolites of the dechloroethylation pathway always predominated over those of the activation pathway (CARBOXYIF, ALCOIF, and IPM, representing 3%, 0.8%, and 0.2% of the injected dose, respectively). In all, 14% of the injected dose was excreted as unknown phosphorated compounds. The interpatient variation in levels of IF metabolites was obvious and involved all of the metabolites. Renal excretion was not complete at 24 h, since 11% of the injected dose was recovered in the 24- to 48-h urine samples.

Comparative pharmacokinetics of ifosfamide, 4-hydroxyifosfamide, chloroacetaldehyde, and 2- and 3-dechloroethylifosfamide in patients on fractionated intravenous ifosfamide therapy

The initial metabolism of the oxazaphosphorine cytostatic ifosfamide (IF) consists of two different pathways: ring oxidation at carbon-4 forms the cytostatically active metabolite 4-hydroxyifosfamide (4-OH-IF, "activated ifosfamide"), whereas side-chain oxidation with liberation of the presumably neurotoxic compound chloroacetaldehyde (CAA) that may also be responsible for IF-associated nephrotoxicity results in the formation of the cytostatically inactive metabolites 2-dechloroethylifosfamide (2-DCE-IF) and 3-dechloroethylifosfamide (3-DCE-IF). The pharmacokinetics of IF and its metabolites were investigated in 11 patients with bronchogenic carcinoma receiving IF on a 5-day divided-dose schedule (1.5 g/m2 daily). Blood samples were drawn on days 1 and 5 for up to 24 h after the start of the IF infusion. IF, 2-DCE-IF, and 3-DCE-IF were simultaneously quantified by gas chromatography (GC) with an NIP flame-ionization detector (NPFID), CAA was determined by GC with an electron-capture detector (ECD), and the highly unstable compound 4-OH-IF was measured using a high-performance liquid chromatography (HPLC) assay with fluorometric detection of 7-OH-quinoline, which is formed by the condensation of 4-OH-IF-derived acrolein with m-aminophenol. As compared with the values obtained on day 1, on day 5 the terminal half-life and AUC values determined for IF were reduced by 30% (6.36 vs 4.06 h and 1781 vs 1204 nmol h ml-1, respectively), whereas the maximal concentration (Cmax) values were not affected significantly (199.1 vs 181.1 nmol ml-1). This known phenomenon is explained by autoinduction of hepatic IF metabolism and was paralleled by increased metabolite levels. The mean Cmax values determined for 4-OH-IF, CAA, 3-DCE-IF, and 2-DCE-IF (on day 1/on day 5) were 1.51/2.59, 2.69/4.85, 12.9/26.5, and 8.6/16.7 nmol ml-1, respectively. The corresponding AUC values were 11.3/16.5, 30.3/34.3, 146/354, and 111/209 nmol h ml-1, respectively. As calculated by intraindividual comparison, the mean Cmax (day 5): Cmax (day 1) ratios for 4-OH-IF, CAA, 3-DCE-IF, and 2-DCE-IF were 1.94*, 2.05*, 2.52*, and 2.33*, respectively; the corresponding AUC (day 5): AUC (day 1) ratios were 1.51*, 1.29, 2.34*, and 2.23*, respectively (* P < 0.05). These data reveal that during fractionated-dose IF therapy the cancerotoxic effect of the drug increases. If the assumed role of CAA in IF-associated neurotoxicity and nephrotoxicity is a dose-dependent phenomenon, the probability of developing these side effects would also increase during prolonged IF application.

Stereoisomers in clinical oncology: why it is important to know what the right and left hands are doing

BACKGROUND

In the past few years it has become clear that the individual stereoisomers, especially the enantiomers, of a biologically active chiral molecule may differ in potency, pharmacological action, metabolism, toxicity, plasma disposition and urine excretion kinetics. The situation exists in all classes of therapeutically active agents including chiral agents used in clinical oncology. Chiral anticancer agents which exist as a pair of enantiomers are commonly administered as racemic (50:50) mixtures of the two isomers. The possibility exists that only one of the enantiomers possesses the desired pharmacological activity while the other is responsible for part or all of the observed toxicity. The toxicity due to the non-efficacious isomer may be the difference between a clinically useful anticancer drug and one which is too toxic to use.

RESULTS

The chiral compounds used in standard and experimental cancer chemotherapy include leucovorin, ifosfamide and verapamil. Only one stereoisomer of leucovorin, (6S)-leucovorin is active and data suggests that the administration of just the single isomer may enhance the activity of the agent as well as improve therapeutic monitoring. Both enantiomers of verapamil, (R)-verapamil and (S)-verapamil, are active in reversing adriamycin resistance in some tumor lines. The standard clinical formulation of verapamil is a mixture of the two isomers and cannot be used in clinical treatment of resistant disease due to the cardiotoxicity of the (S)-isomer. (S)-verapamil is the active calcium channel blocking agent while (R)-verapamil has no effect in this area. Thus, an effective anticancer drug would be (R)-verapamil. Data also exists which suggests that the use of a single isomer of ifosfamide may reduce dose limiting CNS toxicity.

CONCLUSION

The existence of stereoisomeric forms of a chemical has been a recognized fact for almost 150 years. However, the clinical consequences of symmetry and asymmetry are only just beginning to be considered. Within the three-dimensional structures of the human body lie tremendous potentials for differential drug actions and, perhaps, new keys to the treatment of cancer and other diseases. The next few years should see the end to the two-dimensional clinical pharmacology we are accustomed to and the growth of stereochemical clinical pharmacology; where we always know what the right and left hands are doing.

Gas chromatographic determination of 2- and 3-dechloroethylifosfamide in plasma and urine

The metabolic oxidation of one of the chloroethyl groups of the antitumour drug ifosfamide leads to the formation of the inactive metabolites 2- and 3-dechloroethylifosfamide together with the neurotoxic metabolite chloroacetaldehyde. A very sensitive capillary gas chromatographic method, requiring only 50 microliters of plasma or urine, has been developed to measure the amounts of the drug and the two inactive metabolites in a single run. Calibration curves were linear (r > 0.999) in the concentration ranges from 50 ng/ml to 100 micrograms/ml in plasma and from 100 ng/ml to 1 mg/ml in urine.

Combined thin-layer chromatography-photography-densitometry for the quantification of ifosfamide and its principal metabolites in urine, cerebrospinal fluid and plasma

A method has been devised for the determination of the anticancer drug ifosfamide and its principal metabolites in urine, plasma and cerebrospinal fluid (CSF). The urine and CSF samples are absorbed onto Amberlite XAD-2 eluting the compounds of interest with methanol. Plasma is deproteinated using cold acetonitrile and centrifuged to yield a clear supernatant. The eluate and supernatant are analyzed by thin-layer chromatography, with spot visualization using 4-(4-nitrobenzyl)pyridine. The plates are photographed for subsequent densitometeric analysis. The intra-assay coefficient of variation for each compound in both urine and plasma was less than 10% and the lower limit of detection was 1 microgram/ml. The method provides a means of determining the full spectrum of metabolic products of ifosfamide in patients and will allow detailed investigation of variability in metabolism and pharmacokinetics of this drug.

Determination of urinary 2- and 3-dechloroethylated metabolites of ifosfamide by high-performance liquid chromatography

In vivo oxidation of chloroethyl side-chains on ifosfamide produces the toxin chloroacetaldehyde. Production of this labile metabolite can be indirectly quantitated by monitoring the excretion of the residual 2- and 3-dechloroethylated ifosfamide. Urinary ifosfamide and the two dechloroethylated metabolites were extracted into chloroform from alkalinized salt-saturated urine, followed by high-performance liquid chromatographic separation using an acetonitrile gradient on a reversed-phase column and ultraviolet detection at 190 nm. In five patients given 1.6 g/m2 ifosfamide, 11-30% of the dose was excreted over 24 h as unchanged drug, 11-21% as 3-dechloroethylated and 3-10% as 2-dechloroethylated ifosfamide.

Ifosfamide/mesna. A review of its antineoplastic activity, pharmacokinetic properties and therapeutic efficacy in cancer

Ifosfamide is an oxazaphosphorine alkylating agent with a broad spectrum of antineoplastic activity. It is a prodrug metabolised in the liver by cytochrome P450 mixed-function oxidase enzymes to isofosforamide mustard, the active alkylating compound. Mesna, a uroprotective thiol agent, is routinely administered concomitantly with ifosfamide, and has almost eliminated ifosfamide-induced haemorrhagic cystitis and has reduced nephron toxicity. Therapeutic studies, mostly noncomparative in nature, have demonstrated the efficacy of ifosfamide/mesna alone, or more commonly as a component of combination regimens, in a variety of cancers. In patients with relapsed or refractory disseminated nonseminomatous testicular cancer, a salvage regimen of ifosfamide/mesna, cisplatin and either etoposide or vinblastine produced complete response in approximately one-quarter of patients. As a component of both induction and salvage chemotherapeutic regimens, ifosfamide/mesna has produced favourable response rates in small cell lung cancer, paediatric solid tumours, non-Hodgkin's and Hodgkin's lymphoma, and ovarian cancer. Induction therapy with ifosfamide/mesna-containing chemotherapeutic regimens has been encouraging in non-small cell lung cancer, adult soft-tissue sarcomas, and as neoadjuvant therapy in advanced cervical cancer. As salvage therapy, ifosfamide/mesna-containing combinations have a palliative role in advanced breast cancer and advanced cervical cancer. Ifosfamide/mesna can elicit responses in patients refractory to numerous other antineoplastic drugs, including cyclophosphamide. With administration of concomitant mesna to protect against ifosfamide-induced urotoxicity, the principal dose-limiting toxicity of ifosfamide is myelosuppression; leucopenia is generally more severe than thrombocytopenia. Reversible CNS adverse effects ranging from mild somnolence and confusion to severe encephalopathy and coma can occur in approximately 10 to 20% of patients after intravenous infusion, and the incidence of neurotoxicity may be increased to 50% after oral administration because of differences in the preferential route of metabolism between the 2 routes of administration. Other adverse effects of ifosfamide include nephrotoxicity, alopecia, and nausea/vomiting. In general, intravenously administered mesna is associated with a low incidence of adverse effects; however, gastrointestinal disturbances are common following oral administration. Thus, ifosfamide/mesna is an important and worthwhile addition to the currently available range of chemotherapeutic agents. It has a broad spectrum of antineoplastic activity and causes less marked myelosuppression than many other cytotoxic agents. At present, the role of ifosfamide/mesna in refractory germ cell testicular cancer is clearly defined; however, its overall place in the treatment of other forms of cancer awaits delineation in future well-controlled comparative studies.

Continuous 5-day infusion of ifosfamide with mesna in inoperable pancreatic cancer patients: a phase II study

Phase II studies on ifosfamide and mesna in pancreatic cancer have mostly been inconclusive. In all of these studies ifosfamide was administered as an i.v. bolus or by short infusions. Since dose fractionation of ifosfamide over several days increases its therapeutic index, we chose to maximize the dose fractioning by selecting a continuous-infusion schedule (1.75 g/m2 on days 1-5 every 21-28 days, with mesna 60%-100% of the ifosfamide dose up to 12 h after ifosfamide). Since 1987 29 patients (performance status less than or equal to 2) with advanced inoperable adenocarcinoma of the pancreas were studied (8 women and 21 men; median age 58 years: 36-73 years). A total of 25 patients are evaluable for response (1 ineligible; 3 inevaluable: 2 early deaths due to disseminated intravascular coagulation, 1 refusal). One female patient with a complete response on computed tomography scan (after five cycles) but residual liver metastases on surgical exploration survived for 473 days. Three male patients with partial response survived for 205, 335 and 355 days. Six more patients with minor response (3) or no change (3) but significant decrease of tumour marker CA 19-9 had a median survival of 213 days (106-243). Responders seemed to benefit in terms of pain relief and general well-being. The median overall survival of all patients was 148 days (21-473). Haematotoxicity was rarely dose-limiting [median nadirs: white blood cells = 2.1 x 10(9)/l (0.45-6.4), Hb = 10.7 g/dl (7.5-13), platelets = 137 x 10(9)/l (21-411)]. Nausea and vomiting were mild with prophylactic oral metoclopramide. No central nervous system toxicity or urotoxicity was observed. Alopecia was seen in all patients who had received at least two cycles. Continuous infusion of ifosfamide was generally well tolerated and useful for palliation in 10 of 25 patients. A higher dose intensity is recommended.

Subcutaneous continuous infusion of ifosfamide and cyclophosphamide in ambulatory cancer patients: bioavailability and feasibility

The oxazaphosphorines ifosfamide (IFO) and cyclophosphamide (CTX) are standard alkylating agents. Both drugs show an increased therapeutic index when given as a fractionated dosage over several days. Maximal fractionation is achieved by continuous infusion. We have studied the feasibility and bioavailability of a subcutaneously (s.c.) administered isotonic and neutral (pH 7) solution of IFO (10 h up to 5 days infusion) and CTX (12-24 h infusion) in patients with advanced cancer. A portable disposable gas-driven infusor syringe was used for ambulatory patients. Our results show 90%-100% bioavailability of s.c. IFO and CTX. The isotonic solution of IFO and CTX (pH 7) showed no significant local toxicity (one local infection in 51 cycles) during or after s.c. administration of 33 cycles with IFO and 18 with CTX. Haematotoxicity of both drugs was equal after s.c. and i.v. application. For IFO-treated patients no uro- or neurotoxicity was observed. We conclude that this novel continuous s.c. oxazaphosphorine infusion over a prolonged period is a rational, well-tolerated and economic way of delivering this drug on an outpatient basis.

Dosing and side-effects of ifosfamide plus mesna

In clinical practice and in most ongoing studies in adult and pediatric tumours, daily short-time infusions of ifosfamide (IFO) on 2-5 consecutive days with cycle doses between 6 g/m2 and 12 g/m2 are used at present. The continuous i.v. infusion of IFO/mesna over 1-5 days is still experimental. Since mesna prevents IFO-induced urotoxicity, the IFO dose could be increased to 16 g/m2 per cycle. As the dose and schedules of IFO/mesna were increased and varied, CNS and renal toxicity became more evident. CNS toxicity seems not to be dependent on i.v., but on oral dosing of IFO. Renal dysfunction and previous administration of cisplatinum predispose for CNS toxicity. The incidence or severity of CNS toxicity does not increase with subsequent courses of IFO i.v. The nephrotoxicity of IFO is dependent on IFO dose, diuresis, mesna dose and whether there has been previous cisplatinum and seems to involve preferentially the tubulus system, leading to 25 cases of Fanconi renal syndrome as published in 1988-1990. Fanconi's syndrome depends on the cumulative IFO dose, the previous administration of nephrotoxic drugs such as cisplatinum and the age of the children. Studies are continuing to determine the least nephrotoxic dose and schedule of IFO plus mesna. Leucopenia and thrombopenia are well-known dose-dependent side-effects of IFO, with similar incidence after i.v. short-time and continuous infusion.

Clinical pharmacokinetics of cyclophosphamide

Cyclophosphamide has been in clinical use for the treatment of malignant disease for over 30 years. It remains one of the most useful anticancer agents, and is also widely used for its immunosuppressive properties. Cyclophosphamide is inactive until it undergoes hepatic transformation to form 4-hydroxycyclophosphamide, which then breaks down to form the ultimate alkylating agent, phosphoramide mustard. Sensitive and specific methods are now available for the measurement of cyclophosphamide, its metabolites and its stereoisomers in plasma and urine. The pharmacokinetics of cyclophosphamide have been understood for many years; those of the cytotoxic metabolites have been described more recently. The pharmacokinetics are not significantly altered in the presence of hepatic or renal insufficiency. As activity resides exclusively in the metabolites, whose pharmacokinetics are not predicted by those of the parent compound, correlations between cyclophosphamide pharmacokinetics and pharmacodynamics have not been demonstrated. Cyclophosphamide is used in doses that range from 1.5 to 60 mg/kg/day. A steep dose-response curve exists, and reductions in dose can lead to unfavourable outcomes. Myelosuppression is the dose-limiting toxicity, although in the setting of bone marrow transplantation, escalation beyond that dosage range is limited by cardiac toxicity. Longer term complications of cyclophosphamide therapy include infertility and an increased incidence of second malignancies. Cellular sensitivity to cyclophosphamide is a function of cellular thiol concentration, metabolism by aldehyde dehydrogenases to form inactive metabolites, and the ability of DNA to repair alkylated nucleotides. Whether alteration of these cellular functions will lead to further improvements in clinical outcomes is an area of active investigation.

Urinary excretion of the enantiomers of ifosfamide and its inactive metabolites in children

The precondition for the antineoplastic effect of ifosfamide (ifo) is the oxidation of the oxazaphosphorine ring system, which contains a chiral centre at the phosphorous atom. This "ring oxidation" leads to the formation of alkylating mustard via several steps. A second metabolic pathway produces the cytostatically inactive metabolites 2- and 3-dechloroethyl-ifosfamide (2-d- and 3-d-ifo). The urinary excretion of the optical isomers of unmetabolised ifo and of 2- and 3-d-ifo, which represents the amount of ifo that has not been activated, was investigated by capillary gas chromatography for 18 treatment cycles in 14 children on various therapeutic schedules. The total cumulative excretion in 12 completely sampled cycles ranged from 27% to 50% of the ifo dose. Between 14% and 34% of the dose could be detected as ifo; 9% to 29%, as 3-d-ifo; and 2% to 8%, as 2-d-ifo. At 24 h after the end of therapy, excretion was nearly complete. Without exception, slightly more R-ifo (53%-61%) than S-ifo was excreted. S-2-d-ifo (50%-73%) was the main 2-d-metabolite. S-3-d-ifo (deriving from R-ifo) predominated in 6 of 14 children and R-3-d-ifo, in 8. Enantiomer-specific excretion increased after the end of infusion (up to 73% for R-ifo and 27% for S-ifo). We demonstrated stereospecific metabolism of ifo in children, with two different patterns of side-chain oxidation being observed. There was no evidence of important stereospecific ring oxidation in most children. A benefit should not be expected from the therapeutic application of pure enantiomers.