Pharmacokinetics and bioequivalence of etoposide following intravenous administration of etoposide phosphate and etoposide in patients with solid tumors

PURPOSE

To assess the pharmacokinetics and bioequivalence of etoposide following intravenous (i.v.) administration of etoposide phosphate (Etopophos; Bristol-Myers Squibb, Princeton, NJ), a prodrug of etoposide, and VePesid (Bristol-Myers Squibb).

PATIENTS AND METHODS

Forty-nine solid tumor patients were randomized to receive Etopophos or VePesid on day 1 of a day-1,3,5 schedule of treatment. The alternate drug was given on day 3 and repeated on day 5. The dose, 150 mg/m2 of etoposide equivalent, was administered by constant rate infusion over 3.5 hours. The plasma concentrations of etoposide phosphate and etoposide were determined using validated high-performance liquid chromatography (HPLC) assays. Pharmacokinetic parameters were calculated by a noncompartmental method. Etopophos was considered to be bioequivalent to VePesid if the 90% confidence limits for the differences in mean maximum concentration (Cmax) and AUCinf of etoposide were contained within 80% to 125% for the long-transformed data.

RESULTS

Forty-one patients were assessable for pharmacokinetics and bioequivalence assessment. Following i.v. administration, etoposide phosphate was rapidly and extensively converted to etoposide in systemic circulation, resulting in insufficient data to estimate its pharmacokinetics. The mean bioavailability of etoposide from Etopophos, relative to VePesid, was 103% (90% confidence interval, 99% to 106%) based on Cmax, and 107% (90 confidence interval, 105% to 110%) based on area under the concentration versus time curve from zero to infinity (AUCinf) values. Mean terminal elimination half-life (t1/2), steady-state volume of distribution (Vss), and total systemic clearance (CL) values of etoposide were approximately 7 hours, 7 L/m2, and 17 mL/min/m2 after Etopophos and VePesid treatments, respectively. The main toxicity observed was myelosuppression, characterized by leukopenia and neutropenia.

CONCLUSION

With respect to plasma levels of etoposide, i.v. Etopophos is bioequivalent to i.v. VePesid.

Phase I evaluation of a water-soluble etoposide prodrug, etoposide phosphate, given as a 5-minute infusion on days 1, 3, and 5 in patients with solid tumors

PURPOSE

To determine the toxicities, maximum-tolerated dose (MTD), and pharmacology of etoposide phosphate, a water-soluble etoposide derivative, administered as a 5-minute intravenous infusion on a schedule of days 1, 3, and 5 repeated every 21 days.

PATIENTS AND METHODS

Thirty-six solid tumor patients with a mean age of 63 years, performance status of 0 to 1, WBC count > or = 4,000/microL, and platelet count > or = 100,000/microL, with normal hepatic and renal function were studied. Doses evaluated in etoposide equivalents were 50, 75, 100, 125, 150, 175, and 200 mg/m2/d. Etoposide in plasma and urine and etoposide phosphate in plasma were measured by high-performance liquid chromatography (HPLC). Eleven of 36 patients were treated with concentrated etoposide phosphate at 150 mg/m2/d.

RESULTS

Grade I/II nausea, vomiting, alopecia, and fatigue were common. Leukopenia (mainly neutropenia) occurred at doses greater than 75 mg/m2, with the nadir occurring between days 15 and 19 posttreatment. All effects were reversible. Hypotension, bronchospasm, and allergic reactions were not observed in the first 25 patients. The MTD due to leukopenia was determined to be between 175 and 200 mg/m2/d. In 11 patients treated with concentrated etoposide phosphate, no local phlebitis was noted, but two patients did develop allergic phenomena. The conversion of etoposide phosphate to etoposide was not saturated in the dosages studied. Etoposide phosphate had peak plasma concentrations at 5 minutes, with a terminal half-life (t1/2) of 7 minutes. Etoposide reached peak concentrations at 7 to 8 minutes, with a t1/2 of 6 to 9 hours. Both etoposide phosphate and etoposide demonstrated dose-related linear increases in maximum plasma concentration (Cmax) and area under the curve (AUC).

CONCLUSION

Etoposide phosphate displays excellent patient tolerance in conventional dosages when administered as a 5-minute intravenous bolus. The suggested phase II dose is 150 mg/m2 on days 1, 3, and 5. The ability to administer etoposide phosphate as a concentrated, rapid infusion may prove of value both in the outpatient clinic and in high-dose regimens.

Pharmacokinetic analysis of combination chemotherapy with carboplatin and etoposide in small-cell lung cancer patients undergoing hemodialysis

BACKGROUND

The aim of this study was to use pharmacokinetic analysis to investigate the efficacy and toxicity of combined chemotherapy with carboplatin (CBDCA) and etoposide (ETP) in small-cell lung cancer (SCLC) patients with chronic renal failure undergoing hemodialysis (HD).

PATIENTS AND METHODS

Three SCLC patients with chronic renal failure undergoing HD were treated with CBDCA (300 mg/m(2)) on day 1 and ETP (50 mg/m(2)) on days 1 and 3, followed by HD 1 h after completing the administration of anticancer agents on each day. The pharmacokinetic analysis of CBDCA and ETP was planned for at least the first two courses of the chemotherapy in each patient.

RESULTS

Two complete responses and one partial response were achieved in the three patients. Two patients experienced grade 3/4 neutropenia and required blood transfusion due to thrombocytopenia and anemia. Non-hematological toxicities were moderate. The pharmacokinetic analysis revealed that the platinum and the ETP concentrations in the plasma were similar to those in patients with normal renal function during the first 24 h, while the platinum still remained in the plasma for over 90 h.

CONCLUSIONS

Chemotherapy with CBDCA (300 mg/m(2) on day 1) and ETP (50 mg/m(2) on day 1, 3) as used in the present study may be a suitable regimen for SCLC patients undergoing HD, although careful attention should be given to hematological toxicities.

Population pharmacokinetics of doxorubicin, etoposide and ifosfamide in small cell lung cancer patients: results of a multicentre study

AIMS

To determine the population pharmacokinetic (PK) parameters of doxorubicin (Dox), etoposide (Eto) and ifosfamide (Ifo) in small cell lung cancer (SCLC) patients, to assess the potential relationship between those parameters and to estimate the impact of individual morphological and biological covariates on patients' PK parameters.

METHODS

Twenty-four patients with either SCLC limited to the thorax or extensive SCLC entered the study. All but one received at least two 3 day courses of the standard AVI (Dox 50 mg m-2 day 1, Eto 120 mg m-2 day 1,2,3, Ifo 2000 mg m-2 day 1,2) regimen. Individual blood samples were collected during each course and data on 47 courses were available. Data were analysed with the NONMEM program. Dox, Eto and Ifo plasma concentrations were studied with multicompartment (3, 2 and 2, respectively) models. Inter-individual and interoccasion (course-to-course) variabilities were estimated. The influence of individual covariates (age, sex, stage of the disease, weight, height, body-surface area, serum creatinine, total protein, LDH, ASAT, ALAT, alkaline phosphatase, gamma-GT, bilirubin) on PK parameters was also assessed. Correlations between individual PK parameters of Dox, Eto and Ifo were explored by using Pearson's correlation coefficient.

RESULTS

Multiple data were available for each patient. Dox clearance (CL) and volume of distribution (Vd) were 32.0 l h-1 and 9.3 l (Inter-individual variability: 17.2% and 19.2%). Eto CL (l h-1) and Vd were, respectively, 3.34-0.0083* serum creatinine (micromol l-1) and 6.38 l (interindividual variability: 15.6% and 18.7%). Ifo CL and Vd at day 1 were 5.6 l h-1 and 26.0 l (interindividual variability: 10.1% and 17.2%, respectively). Estimation of course-to-course variability improved the precision of PK models in some cases. No correlation was observed between the respective PK parameters of each drug. Of individual covariates tested, only serum creatinine correlated with Eto CL (r = -0.37, P < 0.001). Self-induction of the metabolism of Ifo was apparent (mean CL increase from day 1 to day 2 : 42%) and individually correlated with the CL value at day 1 (r = -0.61, P < 0.001).

CONCLUSIONS

Assessment of potential relationships between individual systemic exposure of chemotherapy and therapeutic endpoints (tumour response, toxicity and survival) will be required to adjust drugs dosages based on individual PK parameters rather than questionable body-surface area. However, all three drugs in the AVI regimen should be monitored simultaneously.

Pharmacokinetics and pharmacodynamics of oral etoposide in children with relapsed or refractory acute lymphoblastic leukemia

PURPOSE

To study the pharmacokinetics and pharmacodynamics of once- versus twice-daily oral etoposide in children with relapsed or refractory acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Fifty-eight patients were randomly assigned to etoposide at 50 mg/m(2)/d with once- versus twice-daily doses for 22 days. On day 8, vincristine, asparaginase, and dexamethasone were started. Etoposide pharmacokinetics and pharmacodynamics were studied for 47, 28, and 26 patients on day 1, 8, and 22, respectively, of remission reinduction therapy.

RESULTS

Of 48 patients with pharmacokinetic data, 42 (87.5%) achieved complete remission, three (6.3%) failed to achieve remission, and three (6.3%) died during induction. Median etoposide day 8 area under concentration-time curve (AUC) and cumulative AUC tended to be greater (P =.06 and P =.07, respectively) in patients (n = 23) who achieved complete remission (24 and 522 micro mol/L x h, respectively) than in patients (n = 3) who did not (14 and 303 micro mol/L x h, respectively). Three of eight patients with plasma concentrations exceeding 1.7 micro M (1 micro g/mL) for more than 8 hours daily, compared with one of 20 patients with concentrations exceeding 1.7 micro M for <or= 8 hours daily, were unable to receive all 22 days of etoposide because of toxicity. There was no difference in the AUC at day 1 or day 8 with once- versus twice-daily doses (P =.55 and P =.86, respectively).

CONCLUSION

A pharmacodynamic relationship exists between systemic etoposide exposure and response to therapy when oral etoposide is used as part of remission induction regimens for relapsed or refractory childhood ALL.

Continuous low-dose oral chemotherapy for adjuvant therapy of splenic hemangiosarcoma in dogs

BACKGROUND

Hemangiosarcoma (HSA) is a highly metastatic and often rapidly fatal tumor in dogs. At present, conventional adjuvant chemotherapy provides only a modest survival benefit for treated dogs. Continuous oral administration of low-dose chemotherapy (LDC) has been suggested as an alternative to conventional chemotherapy protocols. Therefore, we evaluated the safety and effectiveness of LDC using a combination of cyclophosphamide, etoposide, and piroxicam as adjuvant therapy for dogs with stage II HSA.

HYPOTHESIS

We hypothesized that oral adjuvant therapy with LDC could be safely administered to dogs with HSA and that survival times would be comparable to those attained with conventional doxorubicin (DOX) chemotherapy.

ANIMALS

Nine dogs with stage II splenic HSA were enrolled in the LDC study. Treatment outcomes were also evaluated retrospectively for 24 dogs with stage II splenic HSA treated with DOX chemotherapy.

METHODS

Nine dogs with stage II splenic HSA were treated with LDC over a 6-month period. Adverse effects and treatment outcomes were determined. The pharmacokinetics of orally administered etoposide were determined in 3 dogs. Overall survival times and disease-free intervals were compared between the 9 LDC-treated dogs and 24 DOX-treated dogs.

RESULTS

Dogs treated with LDC did not develop severe adverse effects, and long-term treatment over 6 months was well-tolerated. Oral administration of etoposide resulted in detectable plasma concentrations that peaked between 30 and 60 minutes after dosing. Both the median overall survival time and the median disease-free interval in dogs treated with LDC were 178 days. By comparison, the overall survival time and disease-free interval in dogs treated with DOX were 133 and 126 days, respectively.

CONCLUSIONS

Continuous orally administered LDC may be an effective alternative to conventional high-dose chemotherapy for adjuvant therapy of dogs with HSA.

Synthesis and characterization of a catalytic antibody-HPMA copolymer-Conjugate as a tool for tumor selective prodrug activation

Selective chemotherapy remains a key issue for successful treatment in cancer therapy. The use of targeting approaches like the enhanced permeability and retention (EPR) effect of macromolecules, is consequently needed. Here, we report the preparation of a novel catalytic antibody-polymer conjugate for selective prodrug activation. HPMA copolymer was conjugated to catalytic antibody 38C2 through an amide bond formation between epsilon-amino group of lysine residue from the antibody molecule and a p-nitrophenyl ester of the polymer. The conjugate was purified over a size exclusion column using FPLC. In the isolated fraction, one or two molecules of polymer were conjugated to one molecule of antibody based on gel analysis. The resulting conjugate retained most of its catalytic activity (75-81%) in comparison to the free antibody. The activity was monitored with a fluorogenic substrate and a prodrug activation assay using HPLC. Furthermore, the conjugate was evaluated in vitro for its ability to activate an etoposide prodrug using two different cancer cell lines. Cells growth inhibition using the prodrug and the conjugate was almost identical to inhibition by the free antibody and the prodrug. For the first time, a catalytic antibody was conjugated to a passive targeting moiety while retaining its catalytic ability to activate a prodrug. The conjugate described in this work can be used for selective activation of prodrug in the PDEPT (polymer directed enzyme prodrug therapy) approach by replacing the enzyme component with catalytic antibody 38C2.

Etoposide phosphate, the water soluble prodrug of etoposide

Etoposide (Vepesid) is a widely used drug in a variety of neoplasms. To improve the pharmaceutical characteristics of etoposide, etoposide phosphate (Etopophos, Bristol-Myers Squibb) has been developed as a prodrug. Etoposide phosphate is the phosphate ester derivative of etoposide. In comparison to the parent compound, etoposide phosphate is highly soluble in water and can be readily formulated for intravenous use, resulting in higher clinical application. This paper presents information on the pharmaceutical properties and the current status of etoposide phosphate in clinical trials.

Carboplatin and etoposide pharmacokinetics in patients with testicular teratoma

The pharmacokinetics of carboplatin and etoposide were studied in four testicular teratoma patients receiving four courses each of combination chemotherapy consisting of etoposide (120 mg/m2 daily x 3); bleomycin (30 mg weekly) and carboplatin. The carboplatin dose was calculated so as to achieve a constant area under the plasma concentration vs time curve (AUC) of 4.5 mg carboplatin/ml x min by using the formula: dose = 4.5 x (GFR + 25), where GFR is the absolute glomerular filtration rate measured by 51Cr-EDTA clearance. Carboplatin was given on either day 1 or day 2 of each course and pharmacokinetic studies were carried out in each patient on two courses. Etoposide pharmacokinetics were also studied on two separate courses in each patient on the day on which carboplatin was given and on a day when etoposide was given alone. The pharmacokinetics of carboplatin were the same on both the first and second courses, on which studies were carried out with overall mean +/- SD values (n = 8) of 4.8 +/- 0.6 mg/ml x min, 94 +/- 21 min, 129 +/- 21 min, 20.1 +/- 5.41, 155 +/- 33 ml/min and 102 +/- 24 ml/min for the AUC, beta-phase half-life (t 1/2 beta), mean residence time (MRT), volume of distribution (Vd) and total body (TCLR) and renal clearances (RCLR), respectively. The renal clearance of carboplatin was not significantly different from the GFR (132 +/- 32 ml/min). Etoposide pharmacokinetics were also the same on the two courses studied, with overall mean values +/- SD (n = 8) of: AUC = 5.1 +/- 0.9 mg/ml x min, t 1/2 alpha = 40 +/- 9 min, t 1/2 beta = 257 +/- 21 min, MRT = 292 +/- 25 min, Vd = 13.3 +/- 1.31, TCLR = 46 +/- 9 ml/min and RCLR = 17.6 +/- 6.3 ml/min when the drug was given alone and AUC = 5.3 +/- 0.6 mg/ml x min, t 1/2 alpha = 34 +/- 6 min, t 1/2 beta = 242 +/- 25 min, MRT = 292 +/- 25 min, Vd = 12.5 +/- 1.81, TCLR = 43 +/- 6 ml/min and RCLR = 13.4 +/- 3.5 ml/min when it was given in combination with carboplatin. Thus, the equation used to determine the carboplatin accurately predicted the AUC observed and the pharmacokinetics of etoposide were not altered by concurrent carboplatin administration. The therapeutic efficacy and toxicity of the carboplatin-etoposide-bleomycin combination will be compared to those of cisplatin, etoposide and bleomycin in a randomised trial.

Pharmacokinetically guided dosing of carboplatin and etoposide during peritoneal dialysis and haemodialysis

Two patients with relapsed Wilms' tumour and renal failure requiring dialysis were given carboplatin and etoposide by pharmacokinetically guided dosing. The target area under the drug plasma concentration vs time curve (AUC) was 6 mg ml-1 min for carboplatin and 18 and 21 mg ml-1 min for etoposide. On course 1 measured AUCs of carboplatin and etoposide were 6 and 20 mg ml-1 min for patient 1 and 6 and 21 mg ml-1 min for patient 2 respectively. Peritoneal dialysis did not remove carboplatin or etoposide from the plasma, however carboplatin but not etoposide was cleared by haemodialysis. Therapy with carboplatin and etoposide is possible in children and adults with renal failure who require dialysis, but in this situation pharmacokinetic monitoring is essential.

Treatment of childhood acute myelogenous leukemia with an intensive regimen (AML-87) that individualizes etoposide and cytarabine dosages: short- and long-term effects

The purpose of this study was to assess the feasibility and efficacy of a treatment regimen for pediatric acute myelogenous leukemia (AML) that uses four rotating drug pairs and adjusts dosages of etoposide and cytarabine to target specific plasma concentrations. Thirty-one girls and 27 boys (median age, 9.7 years) with de novo AML were treated on the protocol. Six cycles of chemotherapy were planned. Cycles 1 to 4 comprised the drug combinations cytarabine plus etoposide, cytarabine plus daunomycin, etoposide plus amsacrine, and etoposide plus azacitidine, respectively. For cycles 5 and 6, the first two combinations were repeated. Dosages were adjusted to achieve plasma concentrations of 1.0 microM +/- 0.1 microM cytarabine and 30 microM +/- 0.3 microM etoposide. Forty-four patients (76%) entered complete remission. Of those, 24 have had relapses; 23 remain alive in first or subsequent remission. The 5-year event-free survival (EFS) estimate was 31.0% +/- 5.9%; the 5-year survival estimate was 41.4% +/- 6.3%. Six patients (10%) died of the toxic effects of therapy. Severe neutropenia occurred in all cycles. Long-term complications of therapy included hepatitis C, cardiac insufficiency, and hearing loss. Adjustment of cytarabine and etoposide dosage was feasible for achieving targeted plasma drug concentrations; however, the potential clinical efficacy of this approach was offset by substantial acute and long-term toxicity.

Pharmacokinetics of oral etoposide in patients with hepatocellular carcinoma

Etoposide dosage in patients with liver dysfunction remains controversial. Since etoposide has a hepatic component to its clearance (CL) and shows a high degree of protein binding, hepatic impairment could affect etoposide disposition. However, the empiric recommendation that the dose of etoposide be decreased in such patients may reduce systemic exposure and be detrimental to its antitumor activity. To address these issues we studied the pharmacokinetics (PK) of etoposide in patients with hepatocellular carcinoma (HCC) and underlying cirrhosis (n = 17) treated with daily oral etoposide. Unbound etoposide was obtained by ultrafiltration. Etoposide concentrations (total and free drug) were measured by high-performance liquid chromatography (HPLC) and analyzed by noncompartmental equations. The patients had mild or moderate liver dysfunction. Albuminemia was in the normal range for all the patients. Creatininemia was normal in all but two patients. PK results (mean and range) showed that etoposide disposition was unchanged in patients with liver dysfunction. We found slightly high etoposide bioavailability [F, 61% (17-95%)] and clearance [CL, 1.1 (0.7-2.3)l h(-1) m(-2)] resulting in a normal degree of systemic exposure (AUC(oral) 27 microg h ml(-1)). Normal protein binding [PB 93.2% (84.4-98.1%)] contributed to a normal level of exposure to free drug (AUC(f, oral) 1.9 microg h ml(-1)). The distribution volume [V(SS) 8.4 (6.1-13.2) l/m2] and the effective half-life [t1/2eff, 5.1 (3.0-9.6) h] were normal. Median CL and protein binding did not differ in the seven patients with total bilirubin value of > 1.2 mg/dl as compared with the ten patients with total bilirubin levels of < or = 1.2 mg/dl (1.3 versus 1.01 h(-1) m(-2) and 92.5% versus 93.4%, respectively). In agreement with this PK finding, we observed no clinical evidence of increased toxicity in patients with hyperbilirubinemia as compared with patients with normal bilirubinemia (mean WBC decrease 38% versus 47%). The only case of severe (grade 4) hematological toxicity was observed in one patient with reduced glomerular filtration. Since the pharmacological effects of etoposide correlate with the level of systemic exposure to the free drug, our data suggest that no dose reduction is needed in patients with HCC. It is even possible to increase the dose intensity in patients with favorable PK parameters under appropriate hematological and therapeutic drug monitoring.

Etoposide and teniposide. Bioanalysis, metabolism and clinical pharmacokinetics

Etoposide (VP 16-213) and teniposide (VM 26) are semisynthetic epipodophyllotoxin derivatives active against a variety of tumours. The clinical efficacy has led to an increasing interest in these compounds. This review presents information on the mechanism of action, biochemical pharmacology, bioanalysis, metabolism and pharmacokinetics of etoposide and teniposide.

Etoposide bioavailability after oral administration of the prodrug etoposide phosphate in cancer patients during a phase I study

PURPOSE

The purpose of this study was to determine the bioavailability (F) of etoposide (E;VP-16) after oral administration of the water-soluble prodrug etoposide phosphate (EP;BMY-40481) during a phase I trial in cancer patients.

PATIENTS AND METHODS

Twenty-nine patients received oral EP (capsules, 50 to 150 mg/m2/d of E equivalent) for 5 days in week 1 (course 1), followed every 3 weeks thereafter by a daily intravenous (i.v.) infusion for 5 days of E (80 mg/m2, 1-hour i.v. infusion; course 2); in three patients, the i.v. E course was given before oral EP. Plasma and urine E pharmacokinetics (high-performance liquid chromatography [HPLC]) were performed on the first day of oral EP administration and on the first day of i.v. E.

RESULTS

Twenty-six of 29 patients completed two courses or more, whereas three patients received only one course due to toxicity. Myelosuppression was dose-dependent and dose-limiting, with grade 4 leukoneutropenia in four of 15 patients at 125 mg/m2 and in five of seven patients at 150 mg/m2. One patient died of meningeal hemorrhage related to grade 4 thrombocytopenia. Other toxicities were infrequent and/or manageable. No objective response was observed. The maximum-tolerated dose (MTD) is therefore 150 mg/m2, and the recommended oral dose of EP for phase II trials in this poor-risk patient population is 125 mg/m2. Twenty-six patients had pharmacokinetic data for both oral EP and i.v. E, whereas three had pharmacokinetic data on the i.v. E course only. After oral administration of EP, the pharmacokinetics of E were as follows: mean absorption rate constant (Ka), 1.7 +/- 1.7 h-1 (mean +/- SD); lag time, 0.3 +/- 0.2 hours; time of maximum concentration (t(max)), 1.6 +/- 0.8 hours; and mean half-lives (t1/2), 1.6 +/- 0.2 (first) and 10.3 +/- 5.8 hours (terminal); the increase in the area under the plasma concentration-versus-time curve (AUC) of E was proportional to the EP dose. After the 1-hour i.v. infusion of E, maximum concentration (C(max)) was 15 +/- 3 micrograms/mL; mean AUC, 88.0 +/- 22.0 micrograms.h/mL; mean total-body clearance (CL), 0.97 +/- 0.24 L/h/m2 (16.2 mL/min/m2); and mean t1/2, 0.9 +/- 0.6 (first) and 8.1 +/- 4.1 hours (terminal). The 24-hour urinary excretion of E after i.v. E was significantly higher (33%) compared with that of oral EP (17%) (P < .001). Significant correlation was observed between the neutropenia at nadir and the AUC of E after oral EP administration (r = .58, P < .01, sigmoid maximum effect [E(max)] model). The mean F of E after oral administration of EP in 26 patients was 68.0 +/- 17.9% (coefficient of variation [CV], 26.3%; F range, 35.5% to 111.8%). In this study, tumor type, as well as EP dose, did not significantly influence the F in E. There was no difference in F of E, whether oral EP was administered before or after i.v. E. Compared with literature data on oral E, the percent F in E after oral prodrug EP administration was 19% higher at either low ( < or = 100 mg/m2) or high ( > 100 mg/m2) doses.

CONCLUSION

Similarly to E, the main toxicity of the prodrug EP is dose-dependent leukoneutropenia, which is dose-limiting at the oral MTD of 150 mg/m2/d for 5 days. The recommended oral dose of EP is 125 mg/m2/d for 5 days every 3 weeks in poor-risk patients. Compared with literature data, oral EP has a 19% higher F value compared with oral E either at low or high doses. This higher F in E from oral prodrug EP appears to be a pharmacologic advantage that could be of potential pharmacodynamic importance for this drug.

Phase I clinical and pharmacokinetic study of a 14-day infusion of etoposide in patients with lung cancer

PURPOSE

A phase I study was conducted to determine the maximum-tolerated dose (MTD) of a 14-day continuous infusion of etoposide, and to evaluate the pharmacokinetics in patients with lung cancer.

PATIENTS AND METHODS

Etoposide was administered continuously through a central venous catheter using a pump. The starting dose level was 300 mg/m2 over 14 days, with dose escalations of 100 mg/m2 over 14 days until unacceptable toxicities occurred. Pharmacokinetic studies were performed in all patients.

RESULTS

Twenty-one patients, 20 with non-small-cell lung cancer and one with refractory small-cell lung cancer, received 37 courses. No World Health Organization (WHO) grade III or greater toxicity occurred at doses up to 400 mg/m2 over 14 days. At 700 mg/m2 over 14 days, all four patients experienced grade III or IV leukocytopenia, and two developed grade III stomatitis. No cumulative toxicity was observed. A steady concentration of etoposide was achieved 24 hours after the start of chemotherapy, and it was significantly correlated with surviving fractions of leukocytes (r = -.64, P = .001) and platelets (r = -.68, P < .001). The leukocyte count at the termination of chemotherapy predicted the nadir count (r = .93, P < .001).

CONCLUSION

Steady blood levels of etoposide were maintained for prolonged periods, during 14-day continuous infusions. Leukocytopenia and stomatitis were dose-limiting. Nadir counts and surviving fractions of leukocytes were predicted by the leukocyte count at the end of chemotherapy and the concentration of etoposide, respectively. The recommended dose for phase II trials is 600 mg/m2 over 14 days.

Circadian modulation in the intestinal absorption of P-glycoprotein substrates in monkeys

Recent studies in laboratory rodents have revealed that circadian oscillation in the physiologic functions affecting drug disposition underlies the dosing time-dependent change in pharmacokinetics. However, it is difficult to predict the circadian change in the drug pharmacokinetics in a diurnal human by using the data collected from nocturnal rodents. In this study, we used cynomolgus monkeys, diurnal active animals, to evaluate the relevance of intestinal expression of P-glycoprotein (P-gp) to the dosing time dependency of the pharmacokinetics of its substrates. The rhythmic phases of circadian gene expression in the suprachiasmatic nuclei (the mammalian circadian pacemaker) of cynomolgus monkeys were similar to those reported in nocturnal rodents. On the other hand, the expression of circadian clock genes in the intestinal epithelial cells of monkeys oscillated at opposite phases in rodents. The intestinal expression of P-gp in the small intestine of monkeys was also oscillated in a circadian time-dependent manner. Furthermore, the intestinal absorption of P-gp substrates (quinidine and etoposide) was substantially suppressed by administering the drugs at the times of day when P-gp levels were abundant. By contrast, there was no significant dosing time-dependent difference in the absorption of the non-P-gp substrate (acetaminophen). The oscillation in the intestinal expression of P-gp appears to affect the pharmacokinetics of its substrates. Identification of circadian factors affecting the drug disposition in laboratory monkeys may improve the predictive accuracy of pharmacokinetics in humans.

A tool for neutrophil guided dose adaptation in chemotherapy

Chemotherapy dosing in anticancer treatment is a balancing act between achieving concentrations that are effective towards the malignancy and that result in acceptable side-effects. Neutropenia is one major side-effect of many antitumor agents, and is related to an increased risk of infection. A model capable of describing the time-course of myelosuppression from administered drug could be used in individual dose selection. In this paper we describe the transfer of a previously developed semi-mechanistic model for myelosuppression from NONMEM to a dosing tool in MS Excel, with etoposide as an example. The tool proved capable to solve a differential equation system describing the pharmacokinetics and pharmacodynamics, with estimation performance comparable to NONMEM. In the dosing tool the user provides neutrophil measures from a previous treatment course and request for the dose that results in a desired nadir in the upcoming course through a Bayesian estimation procedure.

The cytoplasmic trafficking of DNA topoisomerase IIalpha correlates with etoposide resistance in human myeloma cells

In this study we have investigated the role of topoisomerase (topo) IIalpha trafficking in cellular drug resistance. To accomplish this, it was necessary to separate the influence of cell cycle, drug uptake, topo protein levels, and enzyme trafficking on drug sensitivity. Thus, we developed a cell model (called accelerated plateau) using human myeloma H929 cells that reproducibly translocates topo IIalpha to the cytoplasm. Compared to log-phase cells, the cytoplasmic redistribution of topo IIalpha in plateau-phase cells correlated with a 10-fold resistance to VP-16 and a 40-60% reduction in the number of drug-induced double-strand DNA breaks. In addition, 7-fold more VP-16 was necessary to achieve 50% topo IIalpha band depletion, suggesting that there are fewer drug-induced topo-DNA complexes formed in quiescent cells than in log-phase cells. The total cellular amount of topo IIalpha and topo IIbeta protein in log- and plateau-phase cells was similar as determined by Western blot analysis. There was a 25% reduction in S-phase cell number in plateau cells (determined by bromodeoxyuridine (BrdU) incorporation), while there was no significant difference in the equilibrium concentrations of [(3)H]-VP-16 when log cells were compared with plateau cells. Furthermore, the nuclear/cytoplasmic ratio of topo IIalpha is increased 58-fold in accelerated-plateau H929 cells treated with leptomycin B (LMB) when compared to untreated cells. It appears that the nuclear-cytoplasmic shuttling of topo IIalpha, which decreases the amount of nuclear target enzyme, is a major mechanism of drug resistance to topo II inhibitors in plateau-phase myeloma cells.

Transduction of hepatocellular carcinoma (HCC) using recombinant adeno-associated virus (rAAV): in vitro and in vivo effects of genotoxic agents

BACKGROUND/AIMS

Adeno-associated virus (AAV) is an attractive tool for gene therapy. Here we investigated the in vitro and in vivo transduction of hepatocellular carcinoma (HCC) cells by an AAV vector and the efficacy of different strategies to enhance the transduction of the tumor.

METHODS

Transduction efficiency was determined by analyzing AAV-mediated beta-galactosidase gene (rAAV/lacZ) expression.

RESULTS

Adenovirus help or pretreatment of HCC cells with y-irradiation or with the topoisomerase inhibitor etoposide resulted in marked enhancement of cell transduction in vitro. In vivo studies in nude mice with subcutaneous HCC tumors showed that HCC cells were not transduced by AAV vector alone. However, co-infection of the tumor with adenovirus allowed an efficient expression of the reporter gene but only at the sites of vector injection. Previous gamma-irradiation of subcutaneous tumors with 1800 rad was able to improve transduction of HCC cells (up to 30%) using recombinant AAV. Continuous i.p. infusion of etoposide in buffalo rats harboring HCC tumors in the liver resulted in transduction of normal liver tissue and also of very small neoplastic lesions (<2 mm) but no transduction was observed in tumors bigger than 2 mm. To analyze this phenomenon we determined etoposide concentration in hepatic tissue. Our results revealed high concentrations of the drug in non-tumoral tissue but almost undetectable levels in big tumor nodules.

CONCLUSIONS

Our results indicate that while both radiotherapy and etoposide enhance transduction of tumor cells by rAAV in vitro, only radiotherapy increases tumor transduction in vivo. Our data suggest the existence of a barrier which limits in vivo the diffusion of chemotherapeutic agents to well-established HCC nodules.

Pharmacokinetics of etoposide: correlation of pharmacokinetic parameters with clinical conditions

The pharmacokinetic parameters of etoposide were established in 35 patients receiving the drug parenterally within the framework of different polychemotherapy protocols. A total of 62 data for 24-h kinetics were analysed. After sample extraction and high-performance liquid chromatography (HPLC) or thin-layer chromatographic (TLC) separation, etoposide was measured by means of [252Cf]-plasma desorption mass spectrometry (PDMS). This highly specific detection system proved to be very practicable and reproducible. The present study comprised two parts that were absolutely comparable in terms of clinical and pharmacokinetic parameters. In part II of the study, sensitivity was improved by modifying the analytical technique. After the exclusion of patients who had previously been given cisplatin or who exhibited renal impairment and of one patient who showed extremely high levels of alkaline phosphatase, gamma-GT and SGPT, the mean values calculated for the pharmacokinetic parameters evaluated were: beta-elimination half-life (t 1/2 beta), 4.9 +/- 1.2 h; mean residence time (MRT), 6.7 +/- 1.4 h; area under the concentration-time curve (AUC), 5.43 +/- 1.74 mg min ml-1; volume of distribution at steady state (Vdss), 6.8 +/- 2.7 l/m2; and clearance (Cl), 18.8 +/- 5.3 ml min-1 m-2. The pharmacokinetic parameters were correlated with 12 different demographic or biochemical conditions. Impaired renal function, previous application of cisplatin and the age of patients were found to influence etoposide disposition to a statistically significant extent. We suggest that the dose of etoposide should be reduced in elderly patients and/or in individuals with impaired renal function, especially in those exhibiting general risk factors such as reduced liver function with regard to the polychemotherapy.

Modeling interpatient pharmacodynamic variability of etoposide

This report describes approaches to modeling interpatient pharmacodynamic variability of etoposide effect as measured by white blood cell count nadir. Such models may be utilized in adaptive control dosing to individualize the dose administered to a patient with the aim of lessening the risk of severe myelosuppression. We have successfully employed adaptive control dosing of etoposide administered by 72-hour continuous infusion based on our prior pharmacodynamic model for white blood cell count nadir. Data from our most recent series of 41 patients were used to investigate new linear and nonlinear pharmacodynamic models. We then cross-validated our best models on data from an independent series of 27 similarly treated patients. We identified an unbiased model that exhibited high precision in both data sets (root mean square errors of 1.11 x 10(3) and 1.20 x 10(3) cells/microL, respectively). The optimal model was a nonlinear Hill model defined by 24-hour etoposide concentration, pretreatment white blood cell count, and pretreatment serum albumin level. The level of albumin was found to be both a component of kinetic (protein binding) and dynamic (patient health) variability. Patients with lower pretreatment albumin levels are at higher risk of severe myelosuppression during etoposide therapy.

A limited-sampling strategy for estimation of etoposide pharmacokinetics in cancer patients

Etoposide (VP16), a widely used anticancer drug, is a topoisomerase II inhibitor. A number of studies have highlighted a correlation between hematologic toxicity and pharmacokinetic or physiological parameters. Other studies have also suggested that the anti-tumor response could be related to the plasma etoposide concentration. Therefore, it would seem of interest to individualize VP16 dose regimens on the basis of pharmacokinetic parameters. The aim of this study was to develop and validate a limited-sampling strategy allowing VP16 pharmacokinetic evaluation with minimal disturbance to the patient. A total of 34 patients (54 kinetics) received VP16 at various dose regimens, with doses ranging between 30 and 200 mg and infusion times varying between 0.5 and 2 h. The statistical characteristics of the pharmacokinetic parameters were assessed from the first courses of treatment performed in 23/34 patients; then the following three-sample protocol was designed: the end of the infusion and 5 and 24 h after the start of the infusion. For validation of the model the main pharmacokinetic parameters (clearance, half-lives, volume of distribution) were estimated in the 11 remaining patients by maximum-likelihood estimation (ML) and by Bayesian estimation (BE) using the three sampling times designed. Statistical comparison showed a good concordance between ML and BE estimates (the bias for clearance was -1.72%). The limited-sampling strategy presented herein can thus be used for accurate estimation of VP16 pharmacokinetic parameters.

An etoposide-resistant lung cancer subline overexpresses the multidrug resistance-associated protein

We have characterised an etoposide-resistant subline of the small-cell lung cancer cell line, UMCC-1, derived at our centre. Subline UMCC-1/VP was developed by culturing the parent line in increasing concentrations of etoposide over 16 months. UMCC-1/VP is 20-fold resistant to etoposide by MTT assays, relative to the parent line, and is cross-resistant to doxorubicin, vincristine and actinomycin D, but not to taxol, cisplatin, melphalan, thiotepa or idarubicin. Topoisomerase II immunoblotting demonstrates a 50% reduction of the protein in the resistant subline. The UMCC-1/VP subline demonstrates a marked decrease in the accumulation of [3H]etoposide relative to the parent line, as well as a modest reduction in the accumulation of daunorubicin. Reverse transcription-polymerase chain reaction assays demonstrate no detectable mdr1 expression but marked expression of the multidrug resistance-associated protein (MRP) gene in the resistant subline. Northern blotting with an MRP cDNA probe confirms marked overexpression of the MRP gene only in the UMCC-1/VP subline. Western blotting with antisera against MRP peptide confirms a 195 kDa protein band in the UMCC-1/VP subline. Southern blotting experiments demonstrate a 10-fold amplification of the MRP gene in the resistant subline. Depletion of glutathione with buthionine sulphoximine sensitised UMCC-1/VP cells to daunorubicin and etoposide. Our studies indicate that MRP gene expression may be induced by etoposide and may lead to reduced accumulation of the drug.

Pharmacokinetics of undiluted or diluted high-dose etoposide with or without busulfan administered to patients with hematologic malignancies

PURPOSE

We used two different methods to administer high-dose etoposide (VP-16) during a myeloablative conditioning chemotherapy regimen before bone marrow transplantation (BMT). VP-16 was administered either diluted (0.5 mg/mL) or undiluted (20 mg/mL), with or without busulfan.

PATIENTS AND METHODS

Blood samples were drawn from 17 patients during the infusion (6 hours) and thereafter daily until 2 days after BMT. VP-16 concentrations were measured in all plasma samples by high-performance liquid chromatography (HPLC) and electrochemical detection, and the results were analyzed with a pharmacokinetic data analysis system.

RESULTS

All calculated pharmacokinetic parameters in the two patient groups (VP-16 administered diluted or undiluted) were similar. There were no statistically significant differences in half-lives, mean residence time (MRT), volume of distribution, total clearance, or area under the curve (AUC). VP-16 was found in blood samples from eight of 17 patients at the time of BMT. Significant differences in systemic drug exposure and systemic clearance were found when patients were grouped according to treatment with busulfan or with total-body irradiation (TBI).

CONCLUSION

The two administration modes for VP-16, either diluted or undiluted, are bioequivalent in pharmacokinetic terms. The terminal half-lives were longer than expected and resulted in significant VP-16 plasma levels at the time of BMT. The biologic significance remains unclear. Busulfan and/or concomitant medication with phenytoin influence plasma clearance (clp) and systemic drug exposure significantly.

Human splicing factor SPF45 (RBM17) confers broad multidrug resistance to anticancer drugs when overexpressed--a phenotype partially reversed by selective estrogen receptor modulators

The splicing factor SPF45 (RBM17) is frequently overexpressed in many solid tumors, and stable expression in HeLa cells confers resistance to doxorubicin and vincristine. In this study, we characterized stable transfectants of A2780 ovarian carcinoma cells. In a 3-day cytotoxicity assay, human SPF45 overexpression conferred 3- to 21-fold resistance to carboplatin, vinorelbine, doxorubicin, etoposide, mitoxantrone, and vincristine. In addition, resistance to gemcitabine and pemetrexed was observed at the highest drug concentrations tested. Knockdown of SPF45 in parental A2780 cells using a hammerhead ribozyme sensitized A2780 cells to etoposide by approximately 5-fold relative to a catalytically inactive ribozyme control and untransfected cells, suggesting a role for SPF45 in intrinsic resistance to some drugs. A2780-SPF45 cells accumulated similar levels of doxorubicin as vector-transfected and parental A2780 cells, indicating that drug resistance is not due to differences in drug accumulation. Efforts to identify small molecules that could block SPF45-mediated drug resistance revealed that the selective estrogen receptor (ER) modulators tamoxifen and LY117018 (a raloxifene analogue) partially reversed SPF45-mediated drug resistance to mitoxantrone in A2780-SPF45 cells from 21-fold to 8- and 5-fold, respectively, but did not significantly affect the mitoxantrone sensitivity of vector control cells. Quantitative PCR showed that ERbeta but not ERalpha was expressed in A2780 transfectants. Coimmunoprecipitation experiments suggest that SPF45 and ERbeta physically interact in vivo. Thus, SPF45-mediated drug resistance in A2780 cells may result in part from effects of SPF45 on the transcription or alternate splicing of ERbeta-regulated genes.