The effect of phenobarbital on cyclophosphamide antitumor activity.

We have used the spleen colony assay system and survival duration studies in male DBA/2 mice with P388 leukemia to study the effects of microsomal enzyme induction by phenobarbital on the antileukemic activity and bone marrow toxicity of cyclophosphamide. Phenobarbital drinking water (0.5 mg/ml) was given for 7 days prior to cyclophosphamide (10 to 200 mg/kg i.p.). Average daily phenobarbital intake per mouse was 1.25 mg (equivalent to 4 mg/kg/day human dosage). Dose-response curves with and without phenobarbital pretreatment showed a constant 90% (1-log) reduction in the toxicity of cyclophosphamide to leukemic colony-forming units, whereas enzyme induction had no effect on the toxicity of the drug to normal bone marrow colony-forming units. Parallel survival studies confirmed the 1-log diminution in the antileukemic activity of cyclophosphamide in phenobarbital-pretreated mice. This phenobarbital-induced change in the antitumor activity of cyclophosphamide appears explainable on a pharmacokinetic basis. The Friedman and Boger assay for plasma alkylating metabolites showed that the reduction in the area under the plasma metabolite curve caused by enzyme induction exactly predicted the observed reduction in cyclophosphamide antitumor effect.     

Effect of cyclophosphamide on the bone marrow hematopoiesis in the mouse

This paper reports the effect of cyclophosphamide on the bone marrow hematopoiesis in the mouse. Cyclophosphamide 0.12 mg/g body weight was injected into the mice once and the observation lasted for 2 weeks. After the injection, peripheral leukocytes were reduced to the lowest level on day 4 and then increased higher than the control on day 7 to 14. The number of nucleated cell in the bone marrow was the lowest at the 48th hour and gradually became normal within two weeks. The pluripotent hemopoietic stem cells--CFU-S (colony forming unit-spleen) were depleted abruptly in 24 hours, then reproliferated exponentially to a peak on day 3, followed by a second decrease and came back to normal level on day 11 to 14. The changes of granulocytic progenitor cell CFU-D (colony forming unit-diffusion chamber) and CFU-C (colony forming unit-culture) were quite similar to that of CFU-S but their proliferation peak was on day 4. The peripheral leukocyte drop was slower and the return to normal was earlier than the hemopoietic cells. So the recovery of leukocyte count does not mean a real reconstruction of hematopoiesis. The bone marrow stroma observed by CFU-F (colony forming unit-fibroblastoid) assay and marrow microcirculation were also damaged and did not recover to normal during the observation. The bone marrow stroma and microcirculation showed a more serious damage.     

Glutathione and glutathione transferase levels in mouse granulocytes following cyclophosphamide administration

Following an initial depletion, glutathione and glutathione transferase levels are transiently increased in mouse bone marrow following the administration of a low dose of cyclophosphamide. Similar effects are observed on subsequent administration of the drug. The separation of various bone marrow populations on a fluorescence-activated cell sorter has shown that increase in glutathione and glutathione transferase levels are restricted to the granulocytic fraction. This may well provide an explanation for the protective effect of a low 'priming' dose of cyclophosphamide against a subsequent lethal dose. The changes in granulocytic glutathione and glutathione transferase levels can also be monitored in the peripheral circulation. The enhanced levels of glutathione in cells resulting from cytotoxic insult appear to be a general response of cells to cytotoxins and may be important in both antitumor therapy as well as the initiation of chemical toxicity and carcinogenicity.     

Effect of cyclophosphamide pretreatment on the short-term disposition and biliary excretion of adriamycin metabolites in rat

Summary The effect of pretreatment with cyclophosphamide 180 mg/kg upon the short-term disposition of adriamycin in anesthetized rat 4 days later was studied. There was a significant decrease in plasma adriamycin clearance, from 125 to 48 ml/min/kg, and a significant decrease in the apparent volume of the peripheral compartment of adriamycin distribution, from 51.7 to 25.6 l/kg, in cyclophosphamide-pretreated as against control rats. Biliary excretion of adriamycin over 2.5 h was increased significantly by 114% in cyclophosphamide-pretreated rats and there was a small but nonsignificant increase in biliary adriamycinol excretion and a decrease in excretion of adriamycin aglycones. Cyclophosphamide pretreatment was associated with an 83% increase in bile flow. Cyclophosphamide pretreatment had no significant effect upon the utilization of adriamycin or upon the formation of adriamycin metabolites by rat isolated hepatocytes. The results suggest that NADPH-cytochrome P-450 reductase, which is decreased 40% by cyclophosphamide pretreatment, is not rate-limiting in elimination of adriamycin. Biliary excretion of adriamycin is increased when plasma adriamycin clearance is decreased, suggesting that cyclophosphamide pretreatment affects a pathway besides biliary excretion that is responsible for the short-term removal of adriamycin from plasma.     

Pharmacokinetics of cyclophosphamide and its metabolites in paediatric patients receiving high-dose myeloablative therapy

Introduction

In order to better understand the impact of high-dose on the pharmacokinetics and metabolism of cyclophosphamide, a pharmacological study was performed in children with malignant mesenchymal tumours with metastatic disease.

Methods

Patients received four courses of chemotherapy including two courses of cyclophosphamide. Plasma concentrations of cyclophosphamide and the metabolites 4-ketocyclophosphamide, dechloroethylcyclophosphamide and carboxyphosphamide were determined on days 1, 2 and 3 of each course. A population pharmacokinetic model for cyclophosphamide was developed using non-linear mixed effects modelling and metabolite AUC values were compared between days and courses.

Results

Data were available on 21 cyclophosphamide courses from 15 patients. A one compartment model, incorporating a term in surface area for both CL and V, best described cyclophosphamide pharmacokinetics. Typical CL and V on day 1 of treatment for a patient with a SA of 1.4 m² were 4.3 L/h and 28.5 L, respectively. On days 2 and 3 CL increased by 88% (95% CI, 72-105%) and 125% (95% CI, 108-145%) over day 1 levels; V increased by 14% (95% CI, 5-23%) on days 2 and 3. V tended to be larger for males than similarly sized females but no effect of age was found upon CL or V. Significant increases in metabolite AUCs were observed on days 2 and 3 compared to day 1 and a significant increase in CXCP AUC from course 1 to course 3.

Conclusion

Administration of high-dose cyclophosphamide over several days results in an increase in metabolism, possibly by induction of the activation pathway. This induction is effectively reversed following a four week period between cyclophosphamide doses. The degree of intersubject variation in cyclophosphamide elimination is largely accounted for by body surface area and is less than previously reported.     

Uridine-induced hypothermia in mice and rats in relation to plasma and tissue levels of uridine and its metabolites

Summary Administration of high-dose uridine or cytidine (3500 mg/kg) resulted in severe hypothermia of 6–10°C in mice. This effect of uridine was observed in three different mouse strains, C57B1/6, Balb/c, and Swiss. A high-dose of uridine also caused hypothermia in Wistar rats. Co-infusion of uridine with benzylacyclouridine, an inhibitor of uridine phosphorylase, partially prevented uridine-mediated hypothermia in mice. A low dose of uridine (100 mg/kg) resulted in a slight increase in temperature. Plasma pharmacokinetics of uridine (at 3500 mg/kg) were studied in two mouse strains, C57B1/6 and Balb/c, and those of cytidine only in C57B1/6 mice. Peak plasma concentrations of uridine in both strains after uridine administration were about 20 mM (at 30–60 min). The peak plasma concentration of cytidine in C57B1/6 mice after cytidine administration was about 12 mM and that of uridine, 1.3 mM. The mean residence time for uridine was about 105 min. The area under the plasma concentration-time curve for uridine was about 50 mmol h/l, and that for cytidine, about 25 mmol h/l. In various tissues of C57B1/6 mice the levels of uridine, uracil and total uracil and cytosine nucleotide pools were determined before and 2 h after uridine administration. Uridine levels increased about 53-fold in liver, about 70-fold in a colon tumor, and only about 7-fold in brain, while the corresponding uracil levels increased about 9-fold, 4-fold and 11-fold, respectively. Total uracil nucleotide pools increased about 8-fold, 3.2-fold and 1.6-fold, respectively. Cytosine nucleotide pools did not increase in the brain. In conclusion, high-dose uridine administration caused severe hypothermia. Plasma levels of uridine and uracil were enhanced to a considerably higher extent than the levels in the tissues. The hypothermia might be related to breakdown products of uridine, since inhibition of uridine breakdown partially prevented hypothermia and since in brain uracil nucleotide levels were only slightly increased after uridine administration, while those of uracil were more markedly increased than in other tissues.Abbreviations TCA trichloroacetic acid - GPT 1-(2-deoxy--D-glucopyranosyl) thymine - BAU benzylacyclouridine - THU tetrahydrouridine - MRT mean residence time - AUC area under the plasma concentration-time curve - V_D volume of distribution - 5FU 5-fluorouracil     

The effect of radiosensitizers on the pharmacokinetics of melphalan and cyclophosphamide in the mouse.

Misonidazole (MISO) has been shown to affect the pharmacokinetics of both cyclophosphamide (CY) and melphalan (MEL) in WHT mice resulting in increased plasma levels of the cytotoxic drugs. The effect is not solely due to the reduction in body temperature observed with large single doses of MISO, as a change in MEL pharmacokinetics was still observed when the mice were maintained at 37 degrees C. Inhibition of cytotoxic drug metabolism may also be a possible mechanism. Such a pharmacokinetic effect could account for part of the potentiation of MEL and CY action observed in tumours with large single doses of MISO. However, a chronic low dosing schedule of MISO did not affect the plasma half-life of either cytotoxic drug, although a significant potentiation of each drug in combination with a chronic MISO dose has been obtained in some tumours. These results suggest that potentiation of chemotherapeutic drug action by MISO in the clinical situation is unlikely to be due to changes in drug pharmacokinetics.     

Rapid esterase-sensitive breakdown of polysorbate 80 and its impact on the plasma pharmacokinetics of docetaxel and metabolites in mice.

We have developed and validated an analytical methodology for the quantification of docetaxel and its four major human oxidation metabolites in mouse plasma. We have used this procedure to study the pharmacokinetics and metabolism of docetaxel in female FVB mice, receiving 2.5, 10, or 33 mg/kg of docetaxel by i.v. injection. We have also studied the pharmacokinetics of polysorbate 80, because it was shown previously that the vehicle substance Cremophor EL, which is used in the formulation of paclitaxel, exerts a profound effect on the pharmacokinetics of this compound. Linear pharmacokinetics of docetaxel was observed at dose levels between 2.5 and 10 mg/kg, where plasma levels corresponded to those in patients receiving the maximum tolerated dose. At the highest dose level of 33 mg/kg, a deviation from the linear kinetics was observed. Compared with humans, mice could tolerate much higher plasma levels, suggesting that the toxic side effects are related to a certain plasma threshold concentration instead of area under the curve or Cmax. At the highest dose level, three docetaxel metabolites could be detected in the plasma samples of mice for up to 4 h after drug administration. The hydroxy metabolite of the tert-butoxy group (metabolite II) was the major metabolite, followed by the two epimeric hydroxyoxazolone-type compounds (metabolites I and III). A fourth putative metabolite (e.g., the cyclic oxazolidinedione derivative) was not detected. Because of rapid degradation of polysorbate 80 by esterases in plasma, the concentration of this vehicle substance declined very rapidly. Consequently, this substance was not able to interfere in the disposition of docetaxel.     

Effect of phorbol myristate acetate on cyclic nucleotide levels in mouse epidermis.

Basal levels of cyclic adenosine 3':5'-monophosphate and cyclic guanosine 3':5'-monophosphate were determined in mouse epidermis in vivo after a single topical treatment with the tumor promoter phorbol myristate acetate. No changes in cyclic adenosine 3':5'-monophosphate levels were found from 0 to 72 hr after treatment. A twofold increase in cyclic guanosine 3':5'-monophosphate was found 36 hr after treatment. This increase had subsided by 72 hr. The effect of phorbol myristate acetate on DNA, RNA, and protein synthesis in the epidermis of Ha/ICR mice was also measured.     

Effect of Brahma Rasayana on antioxidant systems and cytokine levels in mice during cyclophosphamide administration

Intraperitoneal administration of cyclophosphamide (CTX) 25 mg/kg.b.wt. dose/mouse for 10 days was found to suppress the tissue and serum level of reduced glutathione (GSH), blood glutathione peroxidase (GPX) and tissue levels of superoxide dismutase (SOD) and catalase (CAT). Tissue levels of glutathione reductase (GR) and glutathione-S-transferase (GST) were unaltered by CTX treatment while serum and tissue lipid peroxide levels were significantly increased. Oral administration of Brahma Rasayana BR-50 mg/dose/mouse for 10 days and 30 days significantly enhanced the tissue levels of SOD, CAT, GST, GPX, serum and tissue GSH and significantly reduced the serum and tissue lipid peroxidation. BR treatment was also found to enhance the serum cytokine level of interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and granulocyte macrophage-colony stimulating factor (GM-CSF) in normal and CTX treated mice. The results are indicative of the use of BR to reduce the oxidant stress induced by CTX treatment and its effect in cellular function.     

Early morphologic alterations in mouse skin after topical application of 3-methylcholanthrene and its metabolites.

The effects of topical administration of 3-methylcholanthrene (MCA) or its metabolites on BALB/cKi mice were reported on inflammatory skin reactions, the alterations in epidermal thickness, the number of nucleated cells, pyknotic nuclei and/or nuclear fragments, and mitotic figures in the interfollicular epidermis (IFE). In the two-stage carcinogenesis system, MCA, the powerful complete carcinogen, induced an ordered sequence of cell changes strikingly similar to those caused by tumor-promoting agents such as the phorbol esters. These changes were absent after application of the "K-region" oxide of MCA. Other MCA metabolites also failed to induce notable inflammation, epidermal hyperplasia, and/or hypertrophy. Several MCA derivatives, however, caused a thinning of IFE paralleled by an increase in the relative number of pyknotic nuclei and a decrease in the total number of epithelial cells. The inhibitor of polycyclic hydrocarbon metabolism alpha-naphthoflavone did not prevent MCA-mediated skin reactions but, under suitable conditions, apparently potentiated the hyperplastic effects of MCA. The findings indicate that important events in the promotion phase of MCA-mediated skin carcinogenesis might be associated with the parent compound rather than with one of its metabolites.     

Pharmacokinetics of amifostine and its metabolites in the plasma and ascites of a cancer patient

 The pharmacokinetics of amifostine, a protector against chemotherapy and radiation-induced toxicities, was investigated in the plasma and ascites of a cancer patient. A high-performance liquid chromatography (HPLC) procedure with electrochemical detection was used to measure amifostine, its active metabolite, WR 1065, and the disulfides (symmetrical plus mixed disulfides). Both amifostine and WR 1065 were rapidly cleared from the plasma (95% and 50% of the peak concentration within 1 h, respectively). The disulfides, which were rapidly formed from WR 1065, were cleared much more slowly (final half-life 13.6 h). Multiple dosing resulted in a tendency toward increasing peak levels of WR 1065 and decreasing peak levels of the disulfides. Only 1% of the delivered dose appeared in the ascites. Therefore, it is not plausible that the presence of ascites or other third spaces would have an impact on the pharmacokinetics of amifostine. Received: 21 January 1996 / Accepted: 24 June 1996     

Effect of hepatic dysfunction due to liver metastases on the pharmacokinetics of capecitabine and its metabolites.

Capecitabine (Xeloda) is a rationally designed oral, tumor-selective fluoropyrimidine carbamate aimed at preferential conversion to 5-fluorouracil (5-FU) within the tumor. Because capecitabine is extensively metabolized by the liver, it is important to establish whether liver dysfunction altered the pharmacokinetics of capecitabine and its metabolites. This was investigated in 14 cancer patients with normal liver function and in 13 with mild to moderate disturbance of liver biochemistry due to liver metastases. They received a single oral dose of capecitabine (1255 mg capecitabine/m2) with serial blood and urine samples collected up to 72 h after administration. Concentrations of capecitabine and its metabolites were determined in plasma by high-performance liquid chromatography or liquid chromatography coupled to mass spectrometry and in urine by 19F-nuclear magnetic resonance spectroscopy. Although plasma concentrations of capecitabine, 5'-deoxy-5-fluorouridine, 5-FU, dihydro-5-FU, and alpha-fluoro-beta-alanine were, in general, higher in patients with liver dysfunction, the opposite was found for 5'-deoxy-5-fluorocytidine. These effects were not clinically significant. Total urinary recovery of capecitabine and its metabolites was 71% of the administered dose in patients with normal hepatic function and 77% in patients with hepatic impairment. The absolute bioavailability of 5'-deoxy-5-fluorouridine was estimated as 42% in patients with normal hepatic function and 62% in patients with impaired hepatic function. In summary, mild to moderate hepatic dysfunction had no clinically significant influence on the pharmacokinetic parameters of capecitabine and its metabolites. Although caution should be exercised when capecitabine is administered to patients with mildly to moderately impaired hepatic function, there is no need for, a priori, adjustment of the dose.     

Clinical role of determination of plasma mitotane and its metabolites levels in patients with adrenal cancer: results of a long-term follow-up

Our study aimed at evaluation of the relations between the plasma levels of mitotane (o,p'-DDD) and its metabolites, o,p'-DDA and o,p'-DDE, and the efficacy of Mitotane therapy during a long-term follow-up. Eighteen patients, aged 11 to 70 years, were included to the study. Metastatic or regional stage was diagnosed in 15 patients, while localized disease in three patients. Mitotane has been administered in daily doses of 3.0 to 10.0 g in metastatic and regional stages, and 1.5 to 4.0 g in the localized disease, simultaneously with hydrocortisone, prednisolone and fludrocortisone. Mitotane and its metabolites were determined by a high-pressure liquid chromatographic method. The plasma o,p'-DDD level exceeding 44 _M/L, considered as curative one, was reached in nine cases. The o,p'-DDA/o,p'-DDD ratio rose significantly mainly in the first 1-3 months of therapy. The o,p'-DDE levels rose slowly, reaching higher values in long-term therapy, over 12 months of mitotane administration. In the group of patients with regional or metastatic stage, both the o,p'-DDE levels and the o,p'-DDE/o,p'-DDD ratios were higher in the survivors than in non-survivors. The results of our study suggest that the plasma concentrations of o,p'-DDE were more closely related to clinical improvement or remission than the o,p'-DDD levels.     

Optimised analysis of tamoxifen and its main metabolites in the plasma and cytosol of mammary tumours

Recent biochemical and pharmacological findings concerning tamoxifen (TMX) have proven that both the unchanged drug and the main metabolites, N-desmethyltamoxifen (NDT) and 4-hydroxytamoxifen (4OHT) are biologically active. An HPLC method based on on-line post-column UV irradiation with fluorescence detection is described. Optimized conditions allowed complete and rapid separation of TMX 4OHT, NDT and two other recently reported metabolites, Y and Z. This method was applied to plasma and cytosol drug and metabolite analyses. In plasma, from the moment of initial drug administration until the steady state (after 1 month or more of continuous oral TMX treatment), the values of NDT to TMX ratios were completely reversed: 22 to 215 in mean %, P less than 0.01. The presence of metabolites Y and Z is significant. 4OHT, hardly detectable at the first dose, was measured at the steady state with high interpatient variability. It is hypothesized that metabolite evolution with time may be due to auto-induction of drug metabolism. In cytosols, which were all obtained during continuous TMX treatment, the ratios between TMX and metabolites were comparable to those observed in plasma, but with greater interpatient variability. Metabolite Y was not detectable in cytosols. This variability was not linked to the levels of cytosolic oestradiol receptors before initiation of treatment.