Determination of ifosfamide, 2- and 3-dechloroethyifosfamide using gas chromatography with nitrogen-phosphorus or mass spectrometry detection

A comparison was made between methods for determining ifosfamide (IF), 2- (2DCE) and 3-dechloroethylifosfamide (3DCE) using gas chromatography with nitrogen-phosphorus detection (GC-NPD) versus positive ion electron-impact ion-trap mass spectrometry (GC-MS2). Sample pretreatment involved liquid-liquid extraction with ethyl acetate after adding trofosfamide as internal standard and alkalinization. The GC-NPD was linear, specific, and sensitive for all analytes in the range of 0.0500-100 microg/mL with lower limits of quantification (LLQ) of 0.0500 microg/mL using a 50-microgL plasma sample. The GC-MS2 was linear, specific, and sensitive for IF, 2DCE, and 3DCE in the ranges of 0.250-100, 0.500-25.0, and 0.500-25.0 microg/mL, respectively, with LLQs of 0.250, 0.500, and 0.500 microg/mL. The ranges of accuracy, within-day precision, and between-day precision for analysis of all compounds with GC-NPD did not exceed 93.3% to 105.4%, 8.0% and 9.8%, respectively. The ranges of accuracy, within-day precision, and between-day precision for analysis of all compounds with GC-MS2 did not exceed 86.5% to 99.0%, 9.0% and 12.7%, respectively. In conclusion, GC-NPD proved to be superior to GC-MS2 in sensitivity, detection range, accuracy, and precisions. Therefore GC-NPD is the method of choice for fast un-derivatized determination of IF, 2DCE, and 3DCE in human plasma, and it can readily be used for clinical pharmacokinetic studies and routine monitoring of IF-treated patients in a hospital setting.

Combined 4-hydroxy-ifosfamide and vinorelbine treatment in established and primary human breast cell cultures

BACKGROUND

Vinorelbine and ifosfamide are active drugs against breast cancer, but the best treatment schedule has yet to be defined by preclinical or clinical studies. The antitumor activity of 4-hydroxy-ifosfamide (4-OH-IF), the active form of ifosfamide, and vinorelbine (VNB) and their interaction were investigated in two established breast cancer cell lines (MCF-7 and BRC-230) and in 10 primary breast cancer cultures.

MATERIALS AND METHODS

Cytotoxic activity was evaluated by a highly efficient clonogenic assay (HECA). The median-effect principle was applied to evaluate synergistic and antagonistic interactions and the corresponding combination index values were calculated. Cell cycle perturbations were analysed by flow cytometry.

RESULTS

In MCF-7 and BRC-230 cell lines the sequence VNB for 4 hours followed by 4-OH-IF for 24 hours produced an antagonistic effect. Conversely, the inverse sequential scheme, 4-OH-IF-->VNB provided synergistic effects on both cell lines. The synergism was associated with a strong block in the G2-M phase. Synergistic activity of 4-OH-IF-->VNB sequence was confirmed in 7 of 10 primary breast cancer cultures.

CONCLUSIONS

In conclusion, the sequence 4-OH-IF-->VNB appeared to be the most effective scheme both in established cell lines and in primary breast cancer cultures.

Biodegradability of antineoplastic compounds in screening tests: influence of glucosidation and of stereochemistry

Some pharmaceuticals such as antineoplastics are carcinogenic, mutagenic, teratogenic and fetotoxic. Antineoplastics and their metabolites are excreted by patients into waste water. In laboratory testing the frequently used isomeric anti-tumour agents cyclophosphamide (CP) and ifosfamide (IF) were shown to be not biodegradable. They are not eliminated in municipal sewage treatment plants and therefore detected in their effluents. Structural related compounds are beta-D-glucosylisophosphoramidmustard (beta-D-Glc-IPM; INN = glufosfamide) and beta-L-glucosylisophosphoramidmustard (beta-L-Glc-IPM). beta-L-Glc-IPM has no antineoplastic effects whereas beta-D-Glc-IPM is active against tumours. In contrast to IF and CP and almost all other investigated antineoplastics beta-D-Glc-IPM is inherently biodegradable. Improved biodegradability of beta-D-Glc-IPM compared to IF shows that reducing the impact of pharmaceuticals on the aquatic environment is feasible by changing the chemical structure of a given compound exerting a similar mode of action and therapeutic activity. Stereochemistry may be crucial for pharmaceutical activity of the compounds as well as for its biodegradability in the environment.

Mechanistic aspects of the cytotoxic activity of glufosfamide, a new tumour therapeutic agent

Beta-D-glucosyl-ifosfamide mustard (D 19575, glc-IPM, INN = glufosfamide) is a new agent for cancer chemotherapy. Its mode of action, which is only partly understood, was investigated at the DNA level. In the breast carcinoma cell line MCF7 glufosfamide inhibited both the synthesis of DNA and protein in a dose-dependent manner, as shown by the decreased incorporation of [3H-methyl]-thymidine into DNA and [14C]-methionine into protein of these cells. Treatment of MCF7 cells with 50 microM glufosfamide was sufficient to trigger poly(ADP-ribose) polymerase (PARP) activation, as revealed by immunofluorescence analysis. Both CHO-9 cells, which are O6-methylguanine-DNA methyltransferase (MGMT)-deficient, and an isogenic derivative, which has a high level of MGMT, showed the same cytotoxic response to beta-D-glc-IPM, indicating that the O6 position of guanine is not the critical target for cytotoxicity. By contrast, a sharp decrease in survival of cross-link repair deficient CL-V5 B cells was observed already at concentrations of 0.1 mM beta-D-glc-IPM, whereas the wild-type V79 cells showed a 90% reduction in survival only after treatment with 0.5 mM of this compound. The therapeutically inactive beta-L-enantiomer of glufosfamide also showed genotoxic effects in the same assays but at much higher doses. This was probably due to small amounts of ifosfamide mustard formed under the conditions of incubation. The results indicate that the DNA crosslinks are the most critical cytotoxic lesions induced by beta-D-glc-IPM.

Clinical application of an in vitro chemosensitivity test, the Histoculture Drug Response Assay, to urological cancers: wide distribution of inhibition rates in bladder cancer and renal cell cancer

To investigate the variations in chemosensitivity of individual cancers, we performed an in vitro chemosensitivity test, the Histoculture Drug Response Assay (HDRA), on fresh biopsied or surgical specimens. They were 26 bladder cancers and 19 renal cell cancers. Ten anticancer drugs were tested. By prolonging the drug exposure time to 7 days, we obtained reliable results. The mean inhibition rates (IRs) were higher for bladder cancer than for renal cell cancer, and the difference was significant for cisplatin, carboplatin, vinblastine, mitomycin C, and adriamycin. There was no significant correlation between the histological grade of the tumor and HDRA sensitivity. IR values showed a wide distribution and cancers could be classified into two groups of sensitive and resistant. This was especially true for 4-hydroxy-ifosfamide. Three bladder cancer patients with evaluable lesions were treated with drugs selected on the basis of the results of the HDRA. One patient achieved a complete response and the other patients showed a partial response. Our results suggest that chemosensitivity is independent of the clinicopathological classification of cancer, and that the HDRA may be useful for selecting the effective anticancer drug for patients with urological cancer.

Synergistic antitumour effects of chemo-immunotherapy with an oxazaphosphorine drug and IL-2-secreting cells in a mouse colon cancer model

The therapeutic efficacies of two chemical agents-cyclophosphamide (CY) and compound CBM-11-were compared in a chemo-immunotherapy protocol combining a single injection of a cytotoxic agent with a series of weekly peritumoural (p.t.) administrations of non-tumourigenic plasmocytoma cells engineered to produce interleukin-2 (IL-2). Compound CBM-11, an optically active S(-) isomeric form of a bromine-substituted analogue of ifosfamide, is currently used in Phase I clinical trials in Poland. The treatment was applied to mice bearing well-established subcutaneous (s.c.) MC-38 colon tumours. Single intraperitoneal injection of 200 mg/kg of CY or of an equitoxic dose of 140 mg/kg of CBM-11 alone resulted in a tumour growth delay (TGD) of 10-13 and 17-21 d, respectively. This effect was accompanied by an increase in life-span (ILS) of at most 42 and 62% over control. Complete responses (CR) were not observed. Combination of CY or CBM-11 with 6-7 p.t. injections of IL-2-secreting cells resulted in potentiation of the therapeutic effects: TGD and ILS values were considerably increased and long-lasting CRs were observed. The overall incidence of CR after combined treatment was ca 16% and 42% for CY and CBM-11, respectively (P=0.049). A specific anti-MC-38 immunity was induced by the treatment, as verified by rechallenge of cured mice with MC-38 tumour cells 3-4 months post therapy cessation. Our results indicate that tumour destruction by chemotherapy (even if not complete) and prolonged local delivery of IL-2 secreted by allogeneic cells of an easy to culture line are sufficient to secure long-lasting specific antitumour immunity in cured mice.

Determination of 4-hydroxyifosfamide concomitantly with ifosfamide and its dechloroethylated metabolites using gas chromatography and a nitrogen phosphorus-selective detector

A sensitive gas chromatographic (GC)/nitrogen phosphorus detection (NPD) system was developed for the determination of the antitumor drug ifosfamide (Ifos) and its 2-dechloroethylifosfamide (2-Difos), 3-dechloroethylifosfamide (3-Difos) and 4-hydroxyifosfamide (4-OHIfos) metabolites in human blood. 4-OHIfos was analyzed after coupling with a trapping agent and was used as an indicator of isophosphoramide mustard (IPM). Ifos and its metabolites 2-DIfos, 3-DIfos, 4-OHIfos and the internal standard (trofosfamide) were extracted into chloroform and then resolved by gas chromatography using a Hewlett Packard HP5 capillary column cross-linked with 5% phenyl methyl silicone (30 m; 530 microm I.D.; 2.65 microm film thickness). Precision and accuracy of the assay were determined over a three-day period and a concentration range of 3.25-50 microg/ml for Ifos, 0.8-14 microg/ml for 2D-Ifos, 0.6-10 microg/ml for 3D-Ifos and 0.08-1.40 microg/ml for 4-OHIfos. The limit of quantitation was set at 3.25, 0.80, 0.62 and 0.08 microg/ml, respectively, for Ifos, 2-DIfos, 3-DIfos and 4-OHIfos. The intra- and inter-day coefficients of variation and accuracies were less than 20%, except for a low concentration 4-OHIfos. This assay was then used to provide pharmacokinetic data on antitumor and toxicologic effects following intravenous infusion of Ifos.

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.

Effects of 4-hydroperoxy ifosfamide in combination with other anticancer agents on human cancer cell lines

Ifosfamide is one of the currently available anticancer agents with a broad spectrum of clinical activity against a variety of tumors. To investigate its optimal combinations, we studied the effect of 4-hydroperoxy ifosfamide (the active form of ifosfamide) in combination with other anticancer agents against two human cancer cell lines, MG-63 (an osteosarcoma cell line) and MOLT-3 cells (a T-cell leukemia cell line). The cells were incubated for 4 days and 3 days, respectively, in the presence of 4-hydroperoxy ifosfamide and the other agent. Cell growth inhibition was determined by MTT assay. The effects of these drug combinations at the concentration producing 50% inhibition (IC50) were analyzed by the isobologram method. 4-Hydroperoxy ifosfamide showed additive effects with bleomycin, cisplatin, cytarabine, doxorubicin, etoposide, 5-fluorouracil, and mitomycin C, while it showed a protective effect with methotrexate in both cell lines. 4-Hydroperoxy ifosfamide showed an additive effect with vincristine in the MG-63 cell line, while it showed a sub-additive effect in the MOLT-3 cell line. No anticancer agents tested showed a supra-additive effect with 4-hydroperoxy ifosfamide. These data suggest that ifosfamide is advantageous for simultaneous administration with a majority of the anticancer agents we studied. Methotrexate is an inappropriate drug for simultaneous administration with ifosfamide.

High-performance liquid chromatographic determination of stabilized 4-hydroxyifosfamide in human plasma and erythrocytes

A method using reversed-phase high-performance liquid chromatography (RP-HPLC) is described for the measurement of the stabilized activated metabolite of ifosfamide, 4-hydroxyifosfamide (4-OHIF), in human plasma and erythrocytes. Immediately after sample collection and plasma-erythrocyte separation at 4 degrees C, 4-OHIF was stabilized by derivatization with semicarbazide (SCZ). The sample pretreatment involved liquid-liquid extraction with ethyl acetate. RP-HPLC was executed with a C8 column and acetonitrile-0.025 M potassium dihydrogenphosphate buffer (pH 7.40)-triethylamine (13.5:86:0.5, v/v) as mobile phase. The analyte was determined with UV detection at 230 nm. Complete validation, optimisation and stability studies were performed and the method proved to be specific, sensitive and with a stable analyte in the range of clinically relevant concentrations (0.1-10 microg/ml) after conventional dosing. The lower limit of quantitation was 100 ng/ml using 1.00 ml of sample. Accuracy was between 94.1 and 107.0%. Within-day and between-day precisions were less than 6.2% and 7.2%, respectively. 4-OHIF-SCZ was found to be stable in the biological matrix at -20 degrees C for at least 1 month. A pharmacokinetic study conducted in a patient receiving 9 g/m2 over 3 days by means of a continuous infusion, demonstrated the applicability of this method.

Excretion kinetics of ifosfamide side-chain metabolites in children on continuous and short-term infusion

Ifosfamide (IFO) requires metabolic activation by hydroxylation of the ring system to exert cytotoxic activity. A second metabolic pathway produces the cytostatically inactive metabolites 2-dechloroethyl-ifosfamide (2-D-IFO) and 3-dechloroethyl-ifosfamide (3-D-IFO) under release of chloroacetaldehyde. This side-chain metabolism has been suggested to be involved in CNS- and renal toxicity. The total urinary excretion of ifosfamide and its metabolites was investigated during 23 cycles in 22 children at doses ranging from 400 mg/m2 to 3 g/m2. The kinetics of the excretion were compared following short-term and continuous ifosfamide infusion at a dosage of 3 g/m2. IFO and side-chain metabolites were analyzed by gas chromatography, the active metabolites by indirect determination of acrolein (ACR) and IFO mustard (IFO-M) with the NBP test. 59+/-15% of the applied dose could be recovered in the urine, 23+/-9% as unmetabolized IFO. The main metabolite was 3-D-IFO (14+/-4%) followed by isophosphoramide mustard (IFO-M) (13+/-4%) and 2-D-IFO (8+/-3%). Neither the total amount recovered nor the excretion kinetics of ifosfamide and side-chain metabolites showed obvious schedule dependency. The excretion kinetics of side-chain metabolites as well as unmetabolized IFO were nearly superimposable on short-term and continuous infusion. Even after 1-hour infusion there was a lag of 3 - 6 hours until dechloroethylation became relevant. Therefore, differences in toxicity and efficacy cannot be explained by an influence of the application time on the metabolic profile of ifosfamide.

Pharmacokinetics of ifosfamide and some metabolites in children

The pharmacokinetics of ifosfamide and some metabolites in children was investigated. The patients received various doses of ifosfamide, mostly by continuous infusion, over several days. The penetration of ifosfamide and its metabolites into the cerebrospinal fluid was also studied in four cases. Ifosfamide and 4-hydroxyifosfamide pass the blood-brain barrier, reaching cerebrospinal fluid concentrations that are almost as high as plasma concentrations.

Assessment of glucosylifosfamide mustard biodistribution in rats with prostate adenocarcinomas by means of in vivo 31P NMR and in vitro uptake experiments

A combined in vitro/in vivo study was performed to evaluate the possible application of phosphorus (31P) NMR spectroscopy for therapy monitoring and to investigate glucosylifosfamide mustard (Glc-IPM) transport and biodistribution by radiotracer techniques. Dynamic in vivo 31P NMR measurements were performed in rats with prostate adenocarcinoma after i.v. injection of 1 mmol/kg body weight (bw) of ifosfamide (IFO) (n = 4) and 1 mmol/kg bw (n = 4) or 2.15 mmol/kg bw (n = 9) of Glc-IPM. In a biodistribution study with 14C-labeled Glc-IPM and a final dose of 0.8 mmol Glc-IPM/kg bw, the animals were killed 5, 30, 60, and 120 min after drug administration, an ethanol extraction was performed from several tissues, and the dose per g tissue was calculated. The same tumor cell line was used in saturation and competition experiments to further elucidate the transport mechanism. The 31P NMR signals of IFO and Glc-IPM showed no overlap with the endogenous phosphorus peaks. A rapid washout with a half-life between 25.9 +/- 5.6 min for the lower dose and 34.3 +/- 4.2 min for the higher dose of Glc-IPM was observed in the tumor. No statistically significant change of the pH value was observed during the examination period. The beta-nucleoside 5'-triphosphate (NTP)/inorganic phosphate (Pi) signal intensity ratio showed a tendency to decrease but without statistical significance. A rapid elimination was demonstrated by both the noninvasive NMR technique and the biodistribution study. No saturation was found in vitro for the Glc-IPM uptake, even at the concentration of 5 mM. Furthermore, the Glc-IPM uptake was not inhibited by the presence of 2-deoxyglucose and vice versa. The data show that the pharmacokinetics of Glc-IPM in the tumor can be followed in vivo by 31P NMR. The results presented are evidence for diffusion as the transport mechanism for Glc-IPM in this tumor model. However, the better visualization of Glc-IPM as compared to ifosfamide may be due to metabolic trapping of a negatively charged metabolite after deglycosylation.

Transport of the new chemotherapeutic agent beta-D-glucosylisophosphoramide mustard (D-19575) into tumor cells is mediated by the Na+-D-glucose cotransporter SAAT1

For beta-D-glucosylisophosphoramide mustard (beta-D-Glc-IPM), a new alkylating drug in which isophosphoramide mustard is stabilized, a higher selectivity and lower myelotoxicity was observed than for the currently used cytostatic ifosfamide. Because beta-D-Glc-IPM is hydrophilic and does not diffuse passively through the lipid bilayer, we investigated whether a transporter may be involved in the cellular uptake. A variety of cloned Na+-sugar cotransporters were expressed in Xenopus oocytes, and uptake measurements were performed. By tracer uptake and electrical measurements it was found that beta-D-Glc-IPM was transported by the low-affinity Na+-D-glucose cotransporter SAAT1, which had been cloned from pig and is also expressed in humans. At membrane potentials between -50 and -150 mV, a 10-fold higher substrate affinity (Km approximately 0.25 mM) and a 10-fold lower Vmax value were estimated for beta-D-Glc-IPM transport than for the transport of D-glucose or methyl-alpha-D-glucopyranoside (AMG). Transport of beta-D-Glc-IPM and glucose by SAAT1 is apparently performed by the same mechanism because similar sodium dependence, dependence on membrane potential, electrogenicity, and phlorizin inhibition were determined for beta-D-Glc-IPM, D-glucose, and AMG. Transcription of human SAAT1 was demonstrated in various human carcinomas and tumor cell lines. In one of these, the human carcinoma cell line T84, phlorizin inhibitable uptake of beta-D-Glc-IPM was demonstrated with substrate saturation and an apparent Km of 0.4 mM. The data suggest that the Na+-D-glucose cotransporter SAAT1 transports beta-D-Glc-IPM into human tumor cells and may accumulate the drug in the cells. They provide an example for drug targeting by employing a plasma membrane transporter.

Combined effects of ionizing radiation and 4-hydroperoxyfosfamide in vitro

BACKGROUND AND PURPOSE

Combined radiochemotherapy has gained increasing interest in clinical applications. The effects of combined exposure of ionizing radiation and 4-hydroperoxyifosfamide (4HOOIF) on cell survival were investigated in vitro.

MATERIALS AND METHODS

Clonogenic survival of log phase V79, Caski (squamous carcinoma), Widr (colon carcinoma) and MRI-221 cells (human melanoma) was determined after combined exposure to 4HOOIF and radiation. Measurement of cell survival for different cell cycle phases was performed after mitotic shake-off (V79) or appropriate intervals after serum stimulation of plateau phase cells (Widr). Control of cell cycle distribution was performed using flow cytometry.

RESULTS

In all cell lines tested, a combined exposure resulted in cell killing that was greater than for independent action. While this type of radiosensitization was of minor magnitude for log-phase cells or cells in G1 substantial radiosensitization was detected for S-phase cells with enhancement ratios (calculated from the respective mean inactivation doses) of up to 1.5.

CONCLUSIONS

The results demonstrate the interaction of 4HOOIF and radiation-induced cell damage with marked cell cycle specificity. Since the largest combination effect was observed for the most radioresistant S-phase cells, damage interaction could be mediated by an interference of 4HOOIF with the repair/fixation pathway of radiation-induced potentially lethal damage.

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.

Pharmacokinetic-stereoselective differentiation of some isomeric analogues of ifosfamide

Three bromine-ifosfamide analogues: racemic chlorobromofosfamide (+/-)-(R,S)-1, its levorotatory enantiomer (-)-(S)-2 and racemic bromofosfamide (+/-)-(R,S)-3 showed considerable stereoselective differences in their pharmacokinetics and bioavailability depending on the route of administration and regimen of dosage studies in rats. Remarkable differences in the AUCi.p. parameters (212, 54, 89 mumol x min x ml-1, respectively) were demonstrated in comparison with a standard ifosfamide (158 mumol x min x ml-1). However, the AUCp.o. established for (+/-)-(R,S)-1 and (-)-(S)-2 were similar and different from the value measured for (+/-)-(R,S)-3. A wide variability in the determined parameters after i.p. injection and similarities after p.o. administration were finally confirmed by the AUCp.o./AUCi.p. mean ratio which equaled 0.24; 0.79;, 0.54, respectively, as well as by different bioavailability data. The results showed that the pharmacokinetic bioequivalance between i.v. and p.o. treatment is possible to approach by adjustment of fractionated oral dosage.

Ifosfamide cytotoxicity on human tumor and renal cells: role of chloroacetaldehyde in comparison to 4-hydroxyifosfamide

The initial metabolism of ifosfamide (IFO) consists of two different pathways, which lead to the alkylating metabolite 4-hydroxy-IFO and to chloroacetaldehyde (CAA). CAA has been reported to cause side effects, such as neuro- and nephrotoxicity, whereas no direct antitumor effect has been described thus far. Therefore, two human tumor cell lines (MXI and S117) and a renal tubular cell line (Landa Leiden) were exposed to 4-hydroxy-IFO, CAA, and a combination of both. The concentrations used were in the same range as measured in the blood of 10 patients treated with 5 g/m2 IFO. The cell survival was measured using the MTT assay. Similar dose-response curves were found for both metabolites. For the MX1 tumor, the IC50s of 4-hydroxy-IFO and CAA were 10.8 and 8.6 microM, respectively. For the reduction of S117 cell survival, higher concentrations of the metabolites were needed (25.0 microM 4-hydroxy-IFO and 15.3 microM CAA). Combination treatment of the cells resulted in an approximately additive effect. Both metabolites exhibited similar toxicity against Landa Leiden cells. Our results indicate that CAA has its own cytotoxic profile against tumor cells. Hence, we conclude that the molecular mechanism of action of IFO seems to be only in part an alkylating effect and that CAA may play an important role in the therapeutic efficacy of IFO.

Chromatographic analysis of the enantiomers of ifosfamide and some of its metabolites in plasma and urine

The enantiomers of the cytostatic drug ifosfamide and the two metabolites 2- and 3-dechloroethylifosfamide were isolated from plasma and urine by liquid-liquid extraction with ethyl acetate, resolved on a Chirasil-L-val gas chromatographic column and detected by a nitrogen-phosphorus-selective flame ionisation detector. Resolution of the racemic compounds for identification purposes was also accomplished with high-performance liquid chromatography on a chiral column. The validated gas chromatographic method was suitable to determine the total concentrations and the enantiomeric composition of ifosfamide and its dechloroethylated metabolites in plasma and urine samples from treated patients. Some metabolic preferences in the metabolism of ifosfamide were found.

Enantioselective cytotoxic activity of bromine-substituted analogues of ifosfamide. A microsomal implication

Nine investigated chlorobromine-, bromine-, and dibromine-ifosfamide analogues including 3 racemates and 6 enantiomers, caused about 10-fold increase in in vitro cytotoxic activity, similar to reference standards ifosfamide and cyclophosphamide in HeLa (KB) human tumor cell culture systems with the addition of rat liver microsomal preparations (ED50 = 0.11 - 0.27 x 10(-3) mole/l) as compared to microsomally non induced samples. The chlorobromine-analogues (ED50 = 0.11 - 0.20 x 10(-3) mole/l) demonstrated the highest cytotoxicity in comparison with bromine-, or dibromine-analogues (SAR). Their levorotatory (-)-(S)- enantiomers (ED50 = 0.11 : 0.21 : 0.24 x 10(-3) mole/l) appear to be more active than their dextrorotatory (+)-(R)-antipodes (ED50 = 0.20 : 0.26 : 0.27 x 10(-3) mole/l, respectively) (ESAR). The stereodifferentiated enhancement of their in vitro cytotoxicity, correlated with the decreasing of in vivo L1210 antileukemic effect following phenobarbital metabolic induction in terms of a whole--strong antitumor activity, indicate that their cytostatic activity depends enantioselectively on the mixed function oxidases-system activity, and presumably on the efficacy of the rate of drug metabolic transformation to their cytostatically active metabolites/intermediates.

Determination of 4-hydroxyifosfamide in biological matrices by high-performance liquid chromatography

A high-performance liquid chromatographic method has been developed for the determination of 4-hydroxyifosfamide, a metabolite of ifosfamide, in plasma of cancer patients. The analyte is derivatized to 7-hydroxyquinoline, which can be detached fluorimetrically. The calibration graph is linear in the concentration range 0.05-25 microM, the limit of detection being 40 nM. Any inference from acrolein, another metabolite of ifosfamide, was ruled out. 4-Hydroxyifosfamide is very unstable in plasma and a stabilization procedure by adding citric acid has been developed. Thus treated, the samples were stable for 4 days. Analysis of a patient's plasma samples revealed that the 4-hydroxifosfamide concentration did not exceed 10 microM.

Urinary excretion of ifosfamide, 4-hydroxyifosfamide, 3- and 2-dechloroethylifosfamide, mesna, and dimesna in patients on fractionated intravenous ifosfamide and concomitant mesna therapy

The oxazaphosphorine antineoplastic ifosfamide (IF) is metabolized by two different initial pathways: ring oxidation ("activation"), forming 4-OH-IF ("activated IF"), and side-chain oxidation with liberation of chloroacetaldehyde (CAA), forming the inactive metabolites 3-dechloroethylifosfamide or 2-dechloroethylifosfamide (3-DCE-IF, 2-DCE-IF). 4-OH-IF and 4-OH-IF-derived acrolein are thought to be responsible for IF-induced urotoxicity (hemorrhagic cystitis), whereas CAA may be involved in IF-associated nephrotoxicity (renal tubular damage). The thiol compound 2-mercaptoethane sulfonate sodium (mesna) has proved to inactivate sufficiently the urotoxic metabolites of oxazaphosphorine cytostatics and is therefore routinely given to patients receiving IF chemotherapy. The cumulative urinary excretion of IF, 4-OH-IF, 3-DCE-IF, 2-DCE-IF, mesna, and its disulfide dimesna was studied in 11 patients with bronchogenic carcinoma receiving IF on a 5-day divided-dose schedule (1.5 g/m2 daily) with concomitant application of mesna (0.3 g/m2 at 0,4, and 8 h after IF infusion). On day 1 the mean cumulative 24-h urinary recoveries (percentage of the IF dose) recorded for IF, 4-OH-IF, 3-DCE-IF, and 2-DCE-IF were 13.9%, 0.52%, 4.8%, and 1.5%, respectively. On day 5 the corresponding values were 12.2%, 0.74%, 9.9%, and 3.6%, respectively. This time-dependent increase in urinary excretion of IF metabolites, which is caused by rapid autoinduction of hepatic oxidative metabolism, may result in a higher probability for the development of urotoxic and nephrotoxic side effects during prolonged IF application. The mean 24-h urinary recoveries (percentage of the daily mesna dose) recorded for mesna/dimesna on day 1 (day 5) were 23.8%/45.2% (21.2%/39.8%), respectively. The mean molar excess of urinary reduced ("free") mesna over 4-OH-IF ranged from 11 to 72 on day 1 and from 6 to 40 on day 5. This indicates that although urinary excretion of 4-OH-IF rises with repeated IF application, mesna in standard doses should sufficiently inactivate the urotoxic IF metabolites.

Urinary stability of carboxycyclophosphamide and carboxyifosfamide, two major metabolites of the anticancer drugs cyclophosphamide and ifosfamide

Phosphorus-31 nuclear magnetic resonance spectroscopy was used to evaluate the stability of carboxycyclophosphamide (CXCP) and carboxyifosfamide (CXIF) in human urine at pH 7.0 and 5.5 at 25 degrees, 8 degrees, -20 degrees, and -80 degrees C. At 25 degrees C and pH 7.0, CXCP and CXIF are relatively stable (approximately 10% degradation in 24 h). In contrast, they are much less stable at pH 5.5 (approximately 80% degradation of CXIF and approximately 50% degradation of CXCP in 24 h). The rate of degradation of CXCP and CXIF was a function of the storage temperature of the urine samples but, even at -80 degrees C, was not negligible: approximately 30% degradation for CXCP irrespective of pH and approximately 40% and 50% degradation for CXIF at pH 7.0 and 5.5, respectively, after storage for 6 months. CXCP was more stable than CXIF at either pH (7.0 or 5.5) and at all storage temperatures (8 degrees, -20 degrees, or -80 degrees C) of the urine samples. CXCP and CXIF were more stable at pH 7.0 than at pH 5.5, although this difference fell with decreasing temperatures to be almost negligible at -80 degrees C. To ensure a true estimate of CXCP and CXIF levels, urine samples must be frozen and stored at -80 degrees C within a few hours of micturition. CXCP and CXIF assays should also be carried out within 2 months and 1 month of storage, respectively.

Influence of mesna on urotoxic effects of selected bromosubstituted analogs of ifosfamide

Bromofosfamides, the group of novel compounds closely related to ifosfamide, are currently in the stage of advanced preclinical evaluation. Ifosfamide, although itself the effective antineoplastic drug useful in situations which have proved refractory to cyclophosphamide therapy, has the side-effect toxicities caused by its metabolities that pose clinically a very real problem. One of their manifestations is the severe urinary tract toxicity which now could be adequately managed by conjunctive administration of mesna (sodium 2-mercaptoethane sulphonate). In this study we have compared the magnitude of urotoxic effects elicited by ifosfamide and two bromofosfamide compounds--racemate and S(-) isomer of chlorobromofosfamide (ClBrs)--selected previously on the base of their superior antitumor activity in advanced animal tumor models. The urotoxic effects, expressed by the increase of urinary bladder weight and histopathologically defined organ wall edema, were estimated in healthy mice 24 h following single intraperitoneal or oral administrations of tested compounds which were applied in amounts equal to curative, sublethal or lethal doses. It was found that the expression of toxic effects revealed by both ClBrs was statistically significantly lower as compared to ifosfamide. Mesna coadministration prevented urotoxic effects almost completely in mice treated with ifosfamide or racemic ClBr. Somewhat lower efficacy of uroprotection with mesna was observed in the case of S(-) isomer of ClBr.