Chemotherapeutic targeting of etoposide to regions of the brain on the basis of polyamine level

The effects of etoposide on body weight, regional weights, and the concentrations of putrescine, spermidine and spermine in the cerebellum, hippocampus, corpus striatum, cortex, the combined regions of the thalamus and hypothalamus and the diencephalon of the brain were examined in rats. Etoposide seems to be a better choice for management of cortical and hippocampal tumors because it reduces polyamines, which are associated with tumor cell growth, but not for the management of tumors of the diencephalon and corpus striatum because it increases polyamines.

Concentration change of chemotherapeutic agents in plasma and tissue after intraarterial and intravenous injection

OBJECTIVE

To study the concentration change of chemotherapeutic agents in plasma and tissue after intraarterial and intravenous injection.

METHODS

Ten mature female New Zealand rabbits were divided randomly into two groups. Fluorouracil, etopiside, and cisplatin were injected into the rabbits through the ear vein in one group and through the internal iliac artery in the other group. Blood samples and the uterus tissue specimens were collected at various time points after injection. Drug concentration in plasma and tissue was determined by high performance liquid chromatography (HPLC) method. The data were analyzed by the pharmacokinetic program 3P97.

RESULTS

Regular concentration change of the three drugs in plasma and tissue was observed after the intravenous and intraarterial injection, which met the two - compartment model. The pharmacokinetic parameters of the three drugs after intravenous and intraarterial injection were different. The peak concentration in plasma after intraarterial injection was lower than that after intravenous injection and the peak concentration and area under curve (AUC) value in tissue after intraarterial injections were higher than those after intravenous injection.

CONCLUSION

Intraarterial chemotherapy has advantages to intravenous chemotherapy in fluorouracil, etopiside and cisplatin. These advantages depend on the drug pharmacological properties.

Oral etoposide in patients with hematological malignancies: a clinical and pharmacokinetic study

Tumor responses after daily oral administration of low-dose etoposide have been demonstrated in both hematological and solid tumors. The aim of the present phase II trial was to determine tumor response, and toxicity and to delineate the pharmacokinetics of oral low-dose etoposide in patients with hematological malignancies in a palliative treatment setting. Thirty-two patients with non-Hodgkin's lymphoma (NHL), acute myeloblastic (AML) and lymphoblastic leukemia, multiple myeloma, and myelodysplastic syndrome (MDS) were included. Patients were given oral etoposide, 100 mg once daily for 14 d in a 21-d cycle. Serum etoposide concentrations were determined on d 1, 7, and 14 of every cycle before etoposide administration and, in addition, 1, 2, 3, 4, and 24 h after drug intake on d 1. The median age of patients was 68 yr (range: 50-89 yr). The median time from diagnosis to inclusion in the study was 21 mo (range: 0.5-144 mo) and most patients had advanced disease and were heavily pretreated. Eleven patients completed three or more cycles. Eight of 11 patients with acute leukemia and 1 of 2 with MDS received only 1 course because of toxicity (n = 5) or progression (n = 4). One patient with AML, a Jehovah's Witness, was treated up-front and achieved a complete remission and two patients with low-grade NHL gained a complete and a partial remission, respectively. Twenty-one of 32 patients were evaluable for toxicity during the first cycle. In 67%, the white blood cell count nadir was < 2.0 x 109/L and in 38% < 1.0 x 10(9)/L. Platelet count nadir was less than 25 x 10(9)/L in 24% of evaluable patients. During all cycles (n = 79), eight patients developed febrile neutropenia, four of whom with a fatal outcome. The correlation between the area under the curve (AUC) of the free fraction of etoposide and leukopenia was statistically significant at a log analysis (n = 12; p < 0.05). There was also a statistically significant correlation between the AUC and the 24-h concentration (n = 15; p < 0.005) and between the concentrations at 24 h and d 7 (n = 11; p < 0.005) of the free fractions of etoposide. In conclusion, etoposide had a moderate clinical effect in this group of heavily pretreated patients. Moreover, toxicity was substantial, in particular leukopenia, which correlated to the free-etoposide AUC.

Phase II and pharmacokinetic study of GL331 in previously treated Chinese gastric cancer patients

PURPOSE

A phase II and pharmacokinetic study was designed to assess the efficacy and toxicity profile of an epidophyllotoxin analogue, GL331, in previously treated Chinese gastric cancer patients, with concurrent pharmacokinetic evaluation of the drug's metabolism.

MATERIAL AND METHODS

GL331 was given at 200 mg/m(2) as a daily 3-h infusion for 5 days every 4 weeks.

RESULTS

Enrolled in the study were 15 patients. One patient died from neutropenic sepsis before evaluation, one patient did not receive the full dose for reasons unrelated to GL331, nine patients had progressive disease with a median survival of 80 days, and five had stable disease with a median survival of 240 days. Grade 3 and 4 myelosuppression occurred in 10 of the 15 patients, with one death from neutropenic sepsis. This patient's peak GL331 concentration was 16.8 microg/ml, which was high compared to the mean peak drug concentration of 6+/-4.1 microg/ml. The mean systemic GL331 clearance was 12.1+/-7.2 l/h per m(2), much lower than 23.3+/-8.2 l/h per m(2) found in the phase I trial. Topoisomerase IIalpha was determined by immunohistochemistry and overexpression was detected in 3 of 11 specimens.

CONCLUSIONS

GL331 was ineffective at this dose and schedule in this group of patients in spite of adequate blood levels of the drug.

Pharmacokinetic interactions of cyclosporine with etoposide and mitoxantrone in children with acute myeloid leukemia

The purpose of this study was to assess the effect of the multidrug resistance modulator cyclosporine (CsA) on the pharmacokinetics of etoposide and mitoxantrone in children with de novo acute myeloid leukemia (AML). Serial blood samples for pharmacokinetic studies were obtained in 38 children over a 24-h period following cytotoxin treatment with or without CsA on days 1 and 4. Drug concentrations were quantitated using validated HPLC methods, and pharmacokinetic parameters were determined using compartmental modeling with an iterative two-stage approach, implemented on ADAPT II software. Etoposide displayed a greater degree of interindividual variability in clearance and systemic exposure than mitoxantrone. With CsA treatment, etoposide and mitoxantrone mean clearance declined by 71% and 42%, respectively. These effects on clearance, in combination with the empiric 40% dose reduction for either cytotoxin, resulted in a 47% and 12% increases in the mean AUC for etoposide and mitoxantrone, respectively. There were no differences in the rates of stomatitis or infection between the two groups. CsA treatment resulted in an increased incidence of hyperbilrubinemia, which rapidly reversed upon conclusion of drug therapy. The variability observed in clearance, combined with the empiric 40% dose reduction of the cytotoxins, resulted in statistically similar systemic exposure and similar toxicity.

Dose-adjusted EPOCH chemotherapy for untreated large B-cell lymphomas: a pharmacodynamic approach with high efficacy

We hypothesized that incremental improvements in the cyclophosphamide-doxorubicin-vincristine-prednisone (CHOP) chemotherapy regimen through optimization of drug selection, schedule, and pharmacokinetics would improve outcome in patients with large B-cell lymphomas. A prospective multi-institutional study of administration of etoposide, vincristine, and doxorubicin for 96 hours with bolus doses of cyclophosphamide and oral prednisone (EPOCH therapy) was done in 50 patients with previously untreated large B-cell lymphomas. The doses of etoposide, doxorubicin, and cyclophosphamide were adjusted 20% each cycle to achieve a nadir absolute neutrophil count below 0.5 x 10(9)/L. The median age of the patients was 46 years (range, 20-88 years); 24% were older than 60 years; and 44% were at high-intermediate or high risk according to International Prognostic Index (IPI) criteria. There was a complete response in 92% of patients, and at the median follow-up time of 62 months, the progression-free survival (PFS) and overall survival (OS) rates were 70% and 73%, respectively. Neither IPI risk factors nor the index itself was associated with response, PFS, or OS. Doses were escalated in 58% of cycles, and toxicity levels were tolerable. Significant inverse correlations were observed between dose intensity and age for all adjusted agents, and drug clearance of doxorubicin and free etoposide was also inversely correlated with age (r = -0.54 and P(2) =.08 and r = -0.45 and P(2) =.034, respectively). Free-etoposide clearance increased significantly during successive cycles (P(2) =.015). Lymphomas with proliferation of at least 80% had somewhat lower progression and those expressing bcl-2 had significantly higher progression (P(2) =.04). Expression of bcl-2 may discriminate the recently described activated B-like from germinal-center B-like large-cell lymphomas and provide important pathobiologic and prognostic information. Dose-adjusted EPOCH may produce more cell kill than CHOP-based regimens. Dynamic dose adjustment may overcome inadequate drug concentrations, particularly in younger patients, and compensate for increased drug clearance over time.

Limited and optimal sampling strategies for etoposide and etoposide catechol in children with leukemia

Etoposide is used to treat childhood malignancies, and its plasma pharmacokinetics have been related to pharmacodynamic endpoints. Limiting the number of samples should facilitate the assessment of etoposide pharmacokinetics in children. We compared limited sampling strategies using multiple linear regression of plasma concentrations and clearance with Bayesian methods of estimating clearance using compartmental pharmacokinetic models. Optimal sampling times were estimated in the multiple linear regression method by determining the combination of two samples which maximized the correlation coefficient, and in the Bayesian estimation approach by minimizing the variance in estimates of clearance. Clearance estimates were compared to the actual clearances from Monte Carlo-simulated data and predicted clearances estimated using all available plasma concentrations in clinical data from children with acute lymphoblastic leukemia. Multiple linear regression poorly predicted clearance (mean bias 8.3%, precision 17.5%), but improved if plasma concentrations were logarithmically transformed (mean bias 1.4%, precision 12.5%). Bayesian estimation methods with optimal samples gave the best overall prediction (mean bias 2.5%, precision 6.8%) and also performed better than regression methods for abnormally high or low clearances. We conclude that Bayesian estimation with limited sampling gives the best estimates of etoposide clearance.

Delineating the contribution of secretory transporters in the efflux of etoposide using Madin-Darby canine kidney (MDCK) cells overexpressing P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP1), and canalicular multispecific organic anion transporter (cMOAT)

Multidrug resistance conferred to cancer cells is often mediated by the expression of efflux transporter "pumps". It is also believed that many of the same transporters are involved in drug efflux from numerous normal endothelial and epithelial cell types in the intestine, brain, kidney, and liver. Etoposide transport kinetics were characterized in Caco-2 cells and in well established Madin-Darby canine kidney (MDCKII) cell lines that were stably-transfected with a human cDNA encoding P-glycoprotein (Pgp), human multidrug resistance protein (MRP1), or the canalicular multispecific organic anion (cMOAT) transporters to determine the roles of these transporters in etoposide efflux. Etoposide transport kinetics were concentration-dependent in the MDCKII-MDR1 and MDCKII-cMOAT cells. The apparent secretory Michaelis constant (Km) and carrier-mediated permeability (Pc) values for Pgp and cMOAT were 254.96 +/- 94.39 microM and 5.96 +/- 0.41 x 10(-6) cm/s and 616.54 +/- 163.15 microM and 1.87 +/- 0.10 x 10(-5) cm/s, respectively. The secretory permeability of etoposide decreased significantly in the basal to apical (B to A) (i.e., efflux) direction, whereas the permeability increased 2.3-fold in the apical to basal (A to B) direction in MDCKII-MDR1 cells in the presence of elacridar (GF120918). Moderate inhibition of etoposide efflux by leukotriene C4 (LTC4) was observed in MDCKII-cMOAT cells. Furthermore, etoposide inhibited LTC4 efflux, confirming the involvement of cMOAT. The flux of etoposide in MDCKII-MRP1 cells was similar to that in MDCKII/wt control cells. The current results demonstrate that the secretory transport mechanism of etoposide involves multiple transporters, including Pgp and cMOAT but not MRP1. These results demonstrate that Pgp and cMOAT are involved in the intestinal secretory transport of etoposide. Since the intestinal secretion of etoposide was previously reported in the literature, it also suggests that they may be involved in the in vivo intestinal secretion of etoposide; however, mechanistic in vivo studies are required to confirm this.

Low dose--high dose: what is the right dose? Pharmacokinetic modeling of etoposide

PURPOSE

Some clinical studies on etoposide (Eto) have shown marked schedule dependency of the effect (starting at about 1 mg/l) and toxicity (over about 10 mg/l) whereas other studies have not confirmed these results. What are the conclusions we can draw from these inconsistent results when developing new low-dose (LD) and high-dose (HD) Eto schedules?

METHODS

A pharmacokinetic model for Eto based on individual pharmacokinetic data was used to simulate different LD (450 mg/m(2)) and HD (1800 mg/m(2)) schedules. The duration of exposure and the AUC of relevant concentration ranges (>1 mg/l, 1-10 mg/l, >10 mg/l) as well as peak levels were calculated in relation to the standard low dose (150 mg/m(2) over 2 h daily for 3 days).

RESULTS

The fourfold dose increase from the LD to the HD schedule was associated with a complementary increase in total AUC. However, variations in infusion time for the HD schedule were associated with large differences in AUC distribution and drug exposure with constant total AUC. Short infusions (0.5 h and 4 h) resulted in extreme peak levels (factors of 17.6+/-1.5 and 8.7+/-0.4 compared to the standard LD schedule) and an AUC >10 mg/l (factors of 17.5+/-4.9 and 17.2+/-4.8, and 83+/-2.4% and 82+/-2.4% of the corresponding total AUC), and the 96-h infusion yielded a long duration of exposure to concentrations >10 mg/l (factor 7.9+/-2.6), whereas continuous i.v. infusion over 55+/-11 days was associated with a multiple increase in the duration of exposure to "standard" drug concentrations (1 mg/l ).

CONCLUSIONS

According to evidence against schedule dependency, only target dose and pharmacokinetic variability would be appropriate rationales for Eto dosing. However, arguing for schedule dependency, simulated pharmacokinetic profiles for new Eto schedules over a wide range support that Eto-containing regimens should be designed on the basis of clear pharmacokinetic hypotheses of target levels, exposure times and AUC distributions, to allow subsequent development of pharmacokinetic/pharmacodynamic modeling.

Limited penetration of anticancer drugs through tumor tissue: a potential cause of resistance of solid tumors to chemotherapy

PURPOSE

Potential causes of drug resistance in solid tumors include genetically determined factors expressed in individual cells and those related to the solid tumor environment. Important among the latter is the requirement for drugs to penetrate into tumor tissue and to achieve a lethal concentration in all of the tumor cells. The present study was designed to characterize further the multicellular layer (MCL) method for studying drug penetration through tumor tissue and to provide information about tissue penetration for drugs used commonly in the treatment of human cancer.

EXPERIMENTAL DESIGN

EMT-6 mouse mammary and MGH-U1 human bladder cancer cells were grown on collagen-coated semiporous Teflon membranes to form MCLs approximately 200 microm thick. The properties of MCLs were compared with those of tumors grown in mice from the same cells. The penetration of drugs through the MCL was evaluated by using radiolabeled drugs or analytical methods.

RESULTS

The MCL developed an extracellular matrix containing both laminin and collagen, although there were some differences in expression of extracellular matrix proteins. Electron microscopy showed rare desmosomes in both MCL and tumors. The penetration of cisplatin, etoposide, gemcitabine, paclitaxel, and vinblastine through tissue in the MCL was slow compared with penetration through the Teflon support membrane alone.

CONCLUSIONS

Our results suggest limited ability of anticancer drugs to reach tumor cells that are distant from blood vessels. The limited penetration of anticancer drugs through tumor tissue may be an important cause of clinical resistance of solid tumors to chemotherapy.

[Chemotherapy for small-cell lung cancer (SCLC) patients with renal failure]

We administered chemotherapy in three cases of small-cell lung cancer (SCLC) with renal failure under different situations. Hemodialysis (HD) was used in 2 out of the 3 cases. Case 1 was complicated by acute renal failure from extensive bilateral tumor invasion. After chemotherapy (CBDCA + ETP) under HD, renal metastases regressed and renal function improved, although the final response was PD. In case 2, HD had been introduced for diabetic nephropathy. After 2 cycles of chemotherapy (CBDCA + ETP) under HD, the patient attained a PR. Case 3 is an example of paraneoplastic nephrotic syndrome with renal failure. Chemotherapy including CBDCA or CDDP was performed and the QOL of the patient improved. Pro-GRP and serum creatinine changed in parallel during the clinical course of 6 admissions. In conclusion, individualized therapy is necessary to increase survival time of SCLC patients with renal failure. Although chemotherapy is useful, further study is needed for the selection of suitable chemotherapeutic regimens, optimal dosage of each drug and the timing of HD.

Population pharmacokinetics of high-dose etoposide in children receiving different conditioning regimens

Pharmacokinetics after high-dose (HD) etoposide (Eto) (40 mg/kg i.v. once as 4-h infusion, one patient 20 mg/kg i.v. as 4-h infusion, for 3 consecutive days) were studied in 31 children and young adults (age 0.8-23.7 years, median: 8.0 years) undergoing bone marrow transplantation after different conditioning regimens. Blood samples were collected until 97 h after the end of infusion. The population analysis of the first part of data (112 samples/21 patients, well documented) served to establish the pharmacokinetic model. The same data combined with the second part of data (50 samples/10 patients, 'intention to treat') then served to calculate the final population model. Data were best described by a three-compartment model with t1/2alpha = 0.28 h +/- 3.2%, t1/2beta = 3.6 h +/- 16.9% and t1/2gamma = 44.2 h +/- 56.5%, respectively (mean(geom) +/- CV(geom)). Clearance (CL) was 15.5 ml/min/m2 +/- 30.6% (mean(geom) +/- CV(geom)) and thus at the lower range of data reported in the literature. The fraction of unbound Eto (fu) was 7.0% (4.3-11.9%) [median (range)], with high intra-individual variability. An increase in f(u) with increasing total Eto was observed. The question of a principally lower Eto CL in children, as compared to adults, after HD treatment remains open.

Randomized cross-over clinical trial to study potential pharmacokinetic interactions between cisplatin or carboplatin and etoposide

AIMS

Cisplatin and carboplatin are often used in combination with etoposide. In a randomized cross-over study, the potential interaction between the two platinum drugs and the metabolism of etoposide was explored. In vitro investigations using human liver microsomes were also performed.

METHODS

Etoposide was administered to 15 patients over 3 days, with the platinum drug administered on day 2. The alternate platinum drug was administered on the second course. The pharmacokinetics of etoposide were determined on all 3 days of each cycle. The effect of platinum drugs on etoposide metabolism by human liver enzymes was explored in vitro.

RESULTS

Neither cisplatin nor carboplatin coadministration affected the pharmacokinetics of etoposide during cycle 1. When carboplatin was administered on course 2, etoposide AUC was 8% higher on day 2 compared with day 1 or day 3 (for day 2 vs day 3, 95% CI: -0.72, -0.08 mg ml(-1) min). In contrast, cisplatin on course 2 increased the AUC of etoposide (28%) on day 3 (day 3 vs day 1, 95% CI: 0.67, 2.09 mg ml(-1) min), with no effect on day 2. In vitro carboplatin and cisplatin (10-100 microm) inhibited the metabolism of etoposide, if rat liver microsomes were preincubated (30 min) with NADPH and the platinum complexes. With human liver microsomes a small effect on etoposide metabolism, but not on catechol formation, was observed.

CONCLUSIONS

The interaction between etoposide and platinum drugs is small and, given the pharmacokinetic variability seen with etoposide, the clinical impact is unlikely to be significant.

Pro-oxidant and antioxidant mechanisms of etoposide in HL-60 cells: role of myeloperoxidase

Etoposide is an effective anticancer agent whose antitumor activity is associated with its phenolic E-ring, which can participate in intracellular redox cycling reactions. Myeloperoxidase (MPO)-catalyzed one-electron oxidation of the etoposide phenolic ring and/or interaction of this phenolic moiety with reactive radicals yields its phenoxyl radical, whose reactivity may determine the pro- or antioxidant effects of this molecule in cells. Using MPO-rich HL-60 cells, we directly demonstrated that both anti- and pro-oxidant activities of etoposide are realized in cells. Etoposide acted as an effective radical scavenger and antioxidant protector of phosphatidylethanolamine, phosphatidylcholine, and other intracellular phospholipids against H2O2-induced oxidation in HL-60 cells with constitutively high MPO activity and in HL-60 cells depleted of MPO by an inhibitor of heme synthesis, succinyl acetone. MPO-catalyzed production of etoposide phenoxyl radicals observed directly in HL-60 cells by electron paramagnetic resonance (EPR) did not result in oxidation of these membrane phospholipids, suggesting that the radicals were not reactive enough to trigger lipid oxidation. MPO-dependent pro-oxidant activity of etoposide was directly demonstrated by (a) the ability of intracellular reduced glutathione (GSH) to eliminate EPR-detectable etoposide phenoxyl radicals, (b) the ability of etoposide phenoxyl radicals to oxidize GSH and protein thiols (after preliminary depletion of intracellular GSH with a maleimide reagent, ThioGlo-1), and (c) the disappearance of these effects after depletion of MPO by pretreatment of cells with succinyl acetone. In addition, titration of intracellular GSH (in intact cells) using the maleimide reagent ThioGlo-1 resulted in remarkably augmented EPR-detectable etoposide phenoxyl radicals and enhanced etoposide-induced topoisomerase II-DNA covalent complexes. In conclusion, the phenolic moiety of etoposide acts as an effective free radical scavenger, accounting for its antioxidant action. Whereas one-electron oxidation of etoposide by free radical scavenging and/or by MPO results in a phenoxyl radical with low reactivity toward lipids, its high reactivity toward thiols is a determinant of its pro-oxidant effects in HL-60 cells.

Population pharmacokinetics and pharmacodynamics of oral etoposide

AIMS

To study the population pharmacokinetics and pharmacodynamics of oral etoposide in patients with solid tumours.

METHODS

A prospective, open label, cross-over, bioavailability study was performed in 50 adult patients with miscellaneous, advanced stage solid tumours, who were receiving oral (100 mg capsules) etoposide for 14 days and i.v. (50 mg) etoposide on day 1 or day 7 in randomised order during the first cycle treatment. Total and unbound etoposide concentration were assayed by h.p.l.c. Population PK parameters estimation was done by using the P-Pharm software (Simed). Haematological toxicity and tumour response were the main pharmacodynamic endpoints.

RESULTS

Mean clearance was 1.14 l h(-1) (CV 25%). Creatinine clearance was the only covariable to significantly reduce clearance variability (residual CV 18%). (CL = 0.74 + 0.0057 CLCR; r(2) = 0.32). Mean bioavailability was 45% (CV 22%) and mean protein binding 91.5% (CV 5%). Exposure to free, pharmacologically active etoposide (free AUC p.o.) was highly variable (mean value 2.8 mg l(-1) h; CV 64%; range 0.4-9.5). It decreased with increased creatinine clearance and increased with age which accounted for 9% of the CV. Mean free AUC p.o. was the best predictor of neutropenia. Free AUC50 (exposure producing a 50% reduction in absolute neutrophil count) was 1.80 mg l(-1) h. In patients with lung cancer, the free AUC p.o. was higher in the two patients with responsive tumour (5.9 mg l(-1) h) than in patients with stable (2.1 mg l-1 h) or progressive disease (2.3 mg l-1 h) (P = 0.01).

CONCLUSIONS

Exposure to free etoposide during prolonged oral treatment is highly variable and is the main determinant of pharmacodynamic effects. The population PK model based on creatinine clearance is poorly predictive of exposure. Therapeutic drug monitoring would be necessary for dose individualization or to study the relationship between exposure and antitumour effect.

Bioequivalence investigation of high-dose etoposide and etoposide phosphate in lymphoma patients

PURPOSE

To compare etoposide pharmacokinetics following administration of high-dose etoposide and etoposide phosphate, a water-soluble prodrug of etoposide. Bioequivalence was assessed using a two-treatment randomized crossover design.

METHODS

Ten patients with high-risk or relapsed lymphoma were treated with a sequential high-dose chemotherapy. They were randomized to receive either 3 x 400 mg/m2 etoposide or an equimolar amount of etoposide phosphate (as 1-h infusions on three consecutive days) in the first course and the alternative drug in the second course. Serial plasma and ultrafiltered plasma samples were collected and analysed for etoposide by a reversed-phase HPLC method with UV and electrochemical detection. Pharmacokinetic parameters were estimated using a two-compartment model. Bioequivalence was assessed calculating the 90% confidence intervals (CI) for the ratios of the geometric means of AUC(0-infinity) and additionally of Cmax of etoposide derived from etoposide phosphate relative to etoposide in plasma and ultrafiltered plasma as point estimates (level of significance alpha < 0.05).

RESULTS

Pharmacokinetic parameters of etoposide were comparable in both treatment arms except that terminal half-life was significantly shorter and apparent Vss in ultrafiltered plasma was significantly larger following administration of the prodrug. The point estimates for AUC(0-infinity) of etoposide derived from etoposide phosphate relative to etoposide were 102.9% and 88.4% for plasma and ultrafiltered plasma, respectively. The 90% CIs were in the range from 80% to 125% where bioequivalence can be assumed. The point estimates of Cmax on day 3 of chemotherapy were 96.5% and 81.7% in plasma and ultrafiltrate with the 90% CI in ultrafiltered plasma being out of the range from 80% to 125%.

CONCLUSION

With respect to total drug exposure, represented by AUC(0-infinity), high-dose etoposide phosphate is bioequivalent to high-dose etoposide.

Simultaneous determination of etoposide and its catechol metabolite in the plasma of pediatric patients by liquid chromatography/tandem mass spectrometry

The anticancer drug etoposide is associated with leukemias with MLL gene translocations and other translocations as a treatment complication. The genotype of cytochrome P450 3A4 (CYP3A4), which converts etoposide to its catechol metabolite, influences the risk. In order to perform pharmacokinetic studies aimed at further elucidation of the translocation mechanism, we have developed and validated a liquid chromatography/electrospray/tandem mass spectrometry assay for the simultaneous analysis of etoposide and its catechol metabolite in human plasma. The etoposide analog teniposide was used as the internal standard. Liquid chromatography was performed on a YMC ODS-AQ column. Simultaneous determination of etoposide and its catechol metabolite was achieved using a small volume of plasma, so that the method is suitable for pediatric patients. The limits of detection were 200 ng ml(-1) etoposide and 10 ng ml(-1) catechol metabolite in human plasma and 25 ng ml(-1) etoposide and 2.5 ng ml(-1) catechol metabolite in protein-free plasma, respectively. Acceptable precision and accuracy were obtained for concentrations in the calibration curve ranges 0.2--100 microg ml(-1) etoposide and 10--5000 ng ml(-1) catechol metabolite in human plasma. Acceptable precision and accuracy for protein-free human plasma in the range 25--15 000 ng ml(-1) etoposide and 2.5--1500 ng ml(-1) etoposide catechol were also achieved. This method was selective and sensitive enough for the simultaneous quantitation of etoposide and its catechol as a total and protein-free fraction in small plasma volumes from pediatric cancer patients receiving etoposide chemotherapy. A pharmacokinetic model has been developed for future studies in large populations.

Bioavailability and pharmacokinetic features of etoposide in childhood acute lymphoblastic leukemia patients

The bioavailability and pharmacokinetic characteristics of etoposide were studied in 12 relapsed B-lineage acute lymphoblastic leukemia (ALL) patients after both intravenous (i.v.) infusion and oral administration. Following a 1 hour i.v. infusion of 50 mg/m2 etoposide, the elimination half-life ranged from 49.8 min to 509.4 min (mean +/- SD = 218.6 +/- 134.7 min), the MRT ranged from 71.8 to 734.9 min (mean +/- SD = 315.4 +/- 194.3 min) and the systemic clearance of etoposide ranged from 15.7 to 38.0 ml/min/m2 (mean +/- SD = 24.1 +/- 7.0 ml/min/m2). The AUC ranged from 2234.9 to 5427.0 microM.min) (mean +/- SD = 3827.8 +/- 1069.5 microM.min) and Vc ranged from 2026.9 to 13,505.2 ml/m2 (mean +/- SD = 6825.4 +/- 3278.5 ml/m2). The maximum plasma etoposide levels ranged from 6.0 to 28.4 microM (mean +/- SD = 13.6 +/- 6.3 microM). The bioavailability of oral etoposide was determined by comparing the AUC following i.v. infusion to the AUC following oral administration in the same patient. The overall bioavailability (mean +/- SD) was 60.6 +/- 22.4% (ranged from 17.6% to 91.2%). The elimination half-life following oral administration (mean +/- SD) was 209.8 +/- 196.3 min (ranged from 51.0 to 794.2 min). The time required to reach the maximum plasma etoposide concentration was 145.4 +/- 118.7 min (ranged from 23.7 to 396.9 min). To our knowledge, this is the first report concerning the bioavailability of etoposide in pediatric leukemia patients. All of the other pharmacokinetic properties of etoposide in pediatric B-lineage ALL leukemia patients reported here were similar to those described previously.

In vivo activity in a catalytic antibody-prodrug system: Antibody catalyzed etoposide prodrug activation for selective chemotherapy

Effective chemotherapy remains a key issue for successful cancer treatment in general and neuroblastoma in particular. Here we report a chemotherapeutic strategy based on catalytic antibody-mediated prodrug activation. To study this approach in an animal model of neuroblastoma, we have synthesized prodrugs of etoposide, a drug widely used to treat this cancer in humans. The prodrug incorporates a trigger portion designed to be released by sequential retro-aldol/retro-Michael reactions catalyzed by aldolase antibody 38C2. This unique prodrug was greater than 10(2)-fold less toxic than etoposide itself in in vitro assays against the NXS2 neuroblastoma cell line. Drug activity was restored after activation by antibody 38C2. Proof of principle for local antibody-catalyzed prodrug activation in vivo was established in a syngeneic model of murine neuroblastoma. Mice with established 100-mm3 s.c. tumors who received one intratumoral injection of antibody 38C2 followed by systemic i.p. injections with the etoposide prodrug showed a 75% reduction in s.c. tumor growth. In contrast, injection of either antibody or prodrug alone had no antitumor effect. Systemic injections of etoposide at the maximum tolerated dose were significantly less effective than the intratumoral antibody 38C2 and systemic etoposide prodrug combination. Significantly, mice treated with the prodrug at 30-fold the maximum tolerated dose of etoposide showed no signs of prodrug toxicity, indicating that the prodrug is not activated by endogenous enzymes. These results suggest that this strategy may provide a new and potentially nonimmunogenic approach for targeted cancer chemotherapy.

Feasibility of intraventricular administration of etoposide in patients with metastatic brain tumours

As the systemic administration of etoposide is effective in the treatment of relapsed and metastatic brain tumours, a pilot trial was designed to study the feasibility of intraventricular administration of etoposide in such patients. 14 patients aged 2.1 to 33.2 years were treated with intraventricular etoposide simultaneously with either oral or intravenous chemotherapy with trofosfamide or carboplatin and etoposide. In 59 courses (1-12/patient) 0.5 mg etoposide was administered daily via an indwelling subcutaneous reservoir for 5 consecutive days every 2-5 weeks over a period of 0-11 months. During 15 courses in 5 patients serial CSF samples were obtained and etoposide levels were determined by reversed-phase HPLC. Side effects included transient headache and bacterial meningitis, each during 2 courses. Pharmacokinetic data analysis in the CSF (11 courses, 4 patients) revealed a terminal half-life of 7.4+/-1.2 hours and an AUC of 25.0 +/- 9.5 microg h ml(-1)(mean +/- standard deviation). The volume of distribution at steady state and total clearance exhibited a large interindividual variability with mean values of 0.16 l and 0.46 ml min(-1)respectively. Intraventricularly administered etoposide is well tolerated. CSF peak levels exceed more than 100-fold those achieved with intravenous infusions. Further studies should be focused on optimizing the dose and schedule and on determining the effectiveness of intraventricularly administered etoposide.

The effect of atovaquone on etoposide pharmacokinetics in children with acute lymphoblastic leukemia

PURPOSE

The use of trimethoprim/sulfamethoxazole in the prevention of Pneumocystis carinii pneumonia in patients with acute lymphoblastic leukemia (ALL) may cause undesirable adverse effects: fungal overgrowth, neutropenia, and drug resistance. A possible alternative is atovaquone, a hydroxynaphthoquinone with anti-Pneumocystis carinii activity. However, it is not known if atovaquone alters the disposition or adverse effects of antileukemic drugs.

METHODS

Using a crossover study design, we compared the pharmacokinetics of etoposide and its CYP3A4-formed catechol metabolite when given as a 300 mg/m2 i.v. infusion following daily atovaquone versus trimethoprim/sulfamethoxazole in nine patients.

RESULTS

The area under the concentration time curve (AUC) of etoposide, etoposide catechol and the catechol to etoposide AUC ratio were slightly higher (a median of 8.6%, 28.4%, and 25.9%) following atovaquone as compared to trimethoprim/sulfamethoxazole (P=0.055, P= 0.031 and P=0.023), respectively. In vitro analysis in human liver microsomes showed modest inhibition of etoposide catechol formation in the presence of atovaquone. Using uptake of 3H-vinblastine in L-MDR1 cells, atovaquone was shown to inhibit P-glycoprotein with an apparent Ki of 95.6 microM.

CONCLUSIONS

Although the effect of atovaquone on etoposide disposition was modest, in light of the fact that the risk of etoposide-related secondary acute myeloid leukemia has been linked to minor changes in schedule and concurrent therapy, we suggest caution with the simultaneous administration of atovaquone and etoposide, particularly if used with other CYP3A4/P-glycoprotein substrates.

Body surface area as a determinant of pharmacokinetics and drug dosing

Body surface area (BSA) was introduced into medical oncology in order to derive a safe starting dose for phase I studies of anticancer drugs from preclinical animal toxicology data. It is not clear however, as to why dosing by BSA was extended to the routine dosing of antineoplastic agents. Several formulas exist to estimate BSA, but the formula derived by DuBois and DuBois is the one used in adult medical oncology. This formula was derived based on data from only nine patients; subsequent attempts to validate the formula have found the DuBois formula to either over or underestimate the actual determined BSA. While cardiac output does correlate with BSA, the relationship between BSA and other physiologic measures relevant for drug metabolism and disposition, such as, renal and hepatic function, is weak or nonexistent. Further only epirubicin, etoposide, and carboplatin have been studied to determine if dosing by BSA would reduce interpatient variability, and none of these drugs were found to have significant relationships between their pharmacokinetics and BSA. Future clinical trials of new agents should not presume that dosing based on BSA reduces interpatient variability. Studies should examine the role, if any, BSA has in dosing new chemotherapeutic agents in initial phase I studies.

Differential sensitivity to etoposide (VP-16)-induced S phase delay in a panel of small-cell lung carcinoma cell lines with G1/S phase checkpoint dysfunction

PURPOSE

The highly schedule-dependent cytotoxic agent etoposide (VP-16) is initially effective in the treatment of small-cell lung cancer (SCLC), particularly in multidrug combination chemotherapy. Heterogeneity in cellular sensitivity to cell cycle arrest may underpin the inadequacy of low-dose extended-cycle single-agent regimes in tumours with partially dysfunctional apoptotic signalling pathways. We have studied the longevity and dose dependency of cell cycle and to a limited extent the apoptotic responses of a panel of seven unselected SCLC cell lines, screened for TP53 status.

METHODS

Cells were analysed using flow cytometry for the cell cycle responses and field inversion gel electrophoresis for apoptotic patterns. The mitotic inhibitor nocodazole was used to assess and correct cell line response data for differences in cell cycle traverse per se.

RESULTS

An overall lack of G1/S arrest and muted DNA fragmentation were consistent with the presence of TP53 gene abnormalities. Maximal G2 arrest but with clear recovery potential occurred at an exposure dose (ED, concentration of drug x time) value of approximately 24 microM h. Higher doses (ED values >48 microM h) revealed a wide variation in S phase delay that was independent of population doubling time and could not be compensated for by drug concentration changes alone.

CONCLUSION

The results suggest that heterogeneity in the in vitro sensitivity of unselected SCLC cell lines to S phase arrest is demonstrable at ED values projected to be critical for clinical activity. Such variation in S phase responsiveness may reflect differences in checkpoint activation and offer a functional target for the design of more-effective combination therapy.

Phase II and pharmacokinetic/pharmacodynamic trial of sequential topoisomerase I and II inhibition with topotecan and etoposide in advanced non-small-cell lung cancer

PURPOSE

In vitro and in vivo preclinical models have demonstrated synergistic activity when topoisomerase I and II inhibitors are administered sequentially. Topoisomerase I inhibitors increase topoisomerase II levels and increase cell kill induced by topoisomerase II poisons. We evaluated this hypothesis in a cohort of patients with advanced non-small-cell lung cancer (NSCLC).

METHODS

A group of 19 patients with advanced NSCLC (70% adenocarcinoma) received topotecan at a dose of 0.85 mg/m2 per day as a continuous 72-h infusion from days 1 to 3. Etoposide was administered orally at a dose of 100 mg twice daily for 3 days on days 7-9 (schedule and dose derived from prior phase I trials). Total and lactone topotecan concentrations were measured at the end of the 72-h infusion. Blood samples were obtained immediately after each 72-h topotecan infusion in order to measure the mutational frequency at the hypoxanthine phosphoribosyl transferase (HPRT) locus in peripheral lymphocytes.

RESULTS

A total of 55 cycles were administered. Toxicity was mainly hematologic with grade 4 neutropenia occurring in 7% of courses. Only one partial response and two stable diseases were observed. The 1-year survival rate was 33%. There was a statistically significant difference between steady-state lactone concentrations between cycle 1 and cycle 2 with decreasing concentrations with cycle 2 (P = 0.02). This was explained by a statistically significant increase in the clearance of topotecan lactone during cycle 2 (P = 0.03). Total but not lactone concentrations correlated with nadir WBC, ANC and platelet levels. Steady-state plasma lactone levels correlated with the mutational frequency at the HPRT locus (P = 0.06). In the one patient with a partial response a sixfold increase in HPRT mutational frequency was observed, which was not seen in patients with progressive disease.

CONCLUSION

The combination of topotecan and etoposide in this schedule of administration has minimal activity in adenocarcinoma of the lung. This lack of activity may be due to the delay in administration of etoposide after the topotecan as studies have shown that the compensatory increase in topoisomerase II levels after treatment with topoisomerase I inhibitors is shortlived (<24 h). The HPRT mutational frequency results suggest that the lack of clinical response may be associated with failure to achieve sufficient cytotoxic dose as indicated by a lack of increase in mutational frequency in those patients with progressive disease. HPRT mutational frequency may correlate with plasma steady-state topotecan lactone levels. Future studies should be directed toward earlier administration of topoisomerase II inhibitors after topoisomerase I inhibition.

Fractionated doses of oral etoposide in the treatment of patients with aids-related kaposi sarcoma: a clinical and pharmacologic study to improve therapeutic index

The purpose of this study was to examine the antitumor activity, toxic effects, and plasma pharmacokinetics of fractionated doses of oral etoposide aiming at the achievement of prolonged safe and active plasma drug levels in patients with AIDS-related Kaposi sarcoma (KS). This was designed as a phase II trial in which consecutive patients with progressing AIDS-KS after at least 3 months of active antiretroviral therapy received oral etoposide at the dose of 20 mg/m2 every 8 hours daily for 7 days every 21 days, with the study of its plasma pharmacokinetics. Eligible patients were 18 to 60 years old, with a histopathologically confirmed diagnosis of AIDS-related KS, human immunodeficiency virus-positive test, progressing after at least 3 months of active antiretroviral therapy, World Health Organization (WHO) performance status 0 to 3, New York University staging IIA or greater, no active infection except oral candidiasis, normal bone marrow, liver, and renal function, and who signed an informed consent. Objective tumor responses were evaluated after at least one full treatment course according to a modified WHO criteria, and toxicity was evaluated weekly and graded using the National Cancer Institute-Common Toxicity Criteria (NCI-CTC) criteria. For the pharmacokinetic study, plasma was obtained from patients during the first drug administration immediately before and at various time points thereafter. Etoposide was measured after extraction from plasma by a standard high-performance liquid chromatography. Twenty-one patients were accrued for the study, and 18 of them met the eligibility criteria. They were all men, with median age of 36 years old (range: 25-50 years), median WHO performance status 0 (range: 0-3) median CD4+ count (cells/mm3) 67 (range: 8-443), prior AIDS diagnosis in 10 of 18 cases, NYU staging IIA (1 patient), IIB (1), IIIA (7), IIIB (1), IVA (4), and IVB (4) sites of disease: mucocutaneous only (5), mucocutaneous/lymph nodes (5), mucocutaneous/lung (5) and mucocutaneous/lymph nodes/lung (2); and prior cytotoxic treatment in two patients. Seventy-two percent of cases presented some form of toxic effect (NCI-CTC). Leukopenia was documented in 50% of cases, anemia occurred in 61%, whereas thrombocytopenia was documented in 17% of the patients. The main nonhematologic toxicities were nausea and vomiting in 17% of cases and alopecia in 44%. The overall objective response rate was 83%, with 2 complete remissions documented (11%). The median duration of responses was 12 weeks (range: 3-45 weeks). The median t1/2 of etoposide in plasma was 4.11 hours (range: 1.95-9.64), area under the curve was 13.51 microg/h/ml (range: 7.12-24.42), Cmax was 2.17 microg/ml (1.40-4.41), tmax (1.00-2.00), mean residence time 4.62 hours (range: 3.75-5.20 hours), CIt (total clearance) 3.13 l/m2/h (range: 1.49-5.20 l/m2/h), Vd 13.08 l/m2 (range: 6.23-19.65 l/m2), and the median etoposide plasma concentration time greater than 1 microg/ml was 3.69 hours (range: 1.00-6.80 hours). The use of fractionated oral daily doses of etoposide produced significant antitumor activity with manageable clinical toxicity in the individuals with AIDS-KS included in this trial. This more favorable therapeutic index of etoposide could be due to the achievement of more sustained plasma levels of the drug within safe but active concentrations.