Factors affecting in vitro protein binding of etoposide in humans

Selective fluorescence turn-on detection of combination cisplatin-etoposide chemotherapy based on N-CDs/GSH-CuNCs nanoprobe

Cisplatin (CIS) and etoposide (ETP) combination therapy is highly effective for treating various cancers. However, the potential for pharmacokinetic interactions between these drugs necessitates selective sensing methods to quantitate both CIS and ETP levels in patient's plasma. This work develops a dual fluorescence probe strategy using glutathione-capped copper nanoclusters (GSH-CuNCs) and nitrogen-doped carbon dots (N-CDs) for the simultaneous analysis of CIS and ETP. The fluorescence signal of GSH-CuNCs at 615 nm increased linearly with CIS concentration while the N-CD emission at 480 nm remained unaffected. Conversely, the N-CD fluorescence was selectively enhanced by ETP with no interference with the CuNC fluorescence. Extensive materials characterization including UV-vis, fluorescence spectroscopy, XRD, and TEM confirmed the synthesis of the nanoprobes. The sensor showed high sensitivity with limits of detection of 6.95 ng mL-1 for CIS and 7.63 ng mL-1 for ETP along with excellent selectivity against potential interferences in rabbit plasma. Method feasibility was demonstrated with application to real rabbit plasma samples. The method was further applied to estimate the pharmacokinetic parameters of CIS before and after ETP coadministration. The dual nanoprobe sensing strategy enables rapid and selective quantitation of CIS and ETP levels to facilitate therapeutic drug monitoring and optimization of combination chemotherapy regimens.

Pharmacokinetic modulation of oral etoposide by ketoconazole in patients with advanced cancer

PURPOSE

Etoposide is a widely used cytotoxic drug that is commercially available in both intravenous and oral formulations. High interpatient pharmacokinetic variability has been associated with oral etoposide administration. Various strategies used in the past to reduce such variability have not been successful. Hence, this study was designed to evaluate if pharmacokinetic modulation of oral etoposide with ketoconazole could lead to a favorable alteration of etoposide pharmacokinetics, and to assess the feasibility and safety of this approach.

METHODS

Thirty-two patients were treated with ketoconazole 200 mg daily with an escalating dose of oral etoposide starting at a dose of 50 mg every other day. Pharmacokinetic samples were obtained during the first treatment cycle after the administration of an oral etoposide and ketoconazole dose. Additional baseline pharmacokinetic studies of etoposide alone were performed 4 days prior to the first treatment cycle.

RESULTS

Dose limiting toxicities were neutropenia and fatigue. Ketoconazole increased the area under the plasma concentration-time curve (AUC) of oral etoposide by a median of 20% (p < 0.005). Ketoconazole did not reduce the interpatient variability in etoposide pharmacokinetics. Pretreatment bilirubin levels correlated with etoposide clearance (Spearman's r = -0.48, p = 0.008). The maximum tolerated dose was etoposide administered at 50 mg daily and ketoconazole 200 mg qd for 3 of 5 weeks.

CONCLUSIONS

Ketoconazole reduces the apparent clearance of oral etoposide, does not alter its toxicity profile and does not reduce interpatient pharmacokinetic variability. Other methods to reduce the pharmacokinetic variability of oral etoposide are needed.

Pharmacokinetic Optimisation of Treatment with Oral Etoposide

Etoposide is a derivative of podophyllotoxin widely used in the treatment of several neoplasms, including small cell lung cancer, germ cell tumours and non-Hodgkin's lymphomas. Prolonged administration of etoposide aims for continuous inhibition of topoisomerase II, the intracellular target of etoposide, thus preventing tumour cells from repairing DNA breaks. However, the clinical advantages of extended schedules as compared with conventional short-term infusions remain unclear. Oral administration of etoposide represents the most feasible and economic strategy to maintain effective concentrations of drug for extended times. Nevertheless, the efficacy of oral etoposide therapy is contingent on circumventing pharmacokinetic limitations, mainly low and variable bioavailability. Inhibition of small bowel and hepatic metabolism of etoposide with specific cytochrome P450 inhibitors or inhibition of the intestinal P-glycoprotein efflux pump have been attempted to increase the bioavailability of oral etoposide, but the best results were obtained with daily oral administration of low etoposide doses (50-100 mg/day for 14-21 days). Saturable absorption of etoposide was reported for doses greater than 200 mg/day, whereas lower doses were associated with increased bioavailability, although they were characterised by high inter- and intrapatient variability. Pharmacokinetic parameters such as plasma trough concentration between two oral administrations (C(24,trough)), drug exposure time above a threshold value and area under the plasma concentration-time curve have been correlated with the pharmacodynamic effect of oral etoposide. Pharmacokinetic-pharmacodynamic relationships indicate that severe toxicity is avoided when peak plasma concentrations do not exceed 3-5 mg/L and C(24,trough) is under the threshold limit of 0.3 mg/L. To maintain effective etoposide plasma concentrations during prolonged oral administration, pharmacokinetic variability must be monitored in each patient, taking account of factors from many pharmacokinetic studies of etoposide, including absorption, distribution, protein binding, metabolism and elimination. Dosage reduction is generally useful to avoid haematological toxicity in patients with renal dysfunction (creatinine clearance <50 mL/min). The need for dosage adjustment based on liver function in patients with liver dysfunction is not completely defined, but generally is not indicated in patients with minor liver dysfunction. Adaptive dosage adjustment based on individual pharmacokinetic parameters, estimated using limited sampling strategies and population pharmacokinetic models, is more appropriate. This approach has been used with success in different clinical trials to increase the etoposide dosage, without significantly increasing toxicity. Various pharmacodynamic models have been proposed to guide etoposide oral dosage. However, they lack precision and accuracy and need to be refined by considering other predictor variables in order to extend their application in current clinical practice.

Etoposide protein binding in cancer patients

The protein binding of etoposide was studied in vivo in 36 cancer patients receiving etoposide therapy. Free etoposide was separated from plasma using an ultrafiltration method and the etoposide concentrations (free and total) were measured by high-performance liquid chromatography (HPLC). Considerable interpatient variation in the protein binding of etoposide was observed. The protein binding of etoposide varied from 80% to 97% (mean, 93%). Univariate analysis showed a significant inverse correlation between the free fraction of etoposide and serum albumin (r = 0.74), daily dose (r = 0.37) and age (r = -0.34). Multivariate analysis demonstrated that serum albumin and age were independent predictors of the etoposide free fraction. Serum bilirubin showed no correlation with etoposide protein binding. There is wide variation in etoposide protein binding in cancer patients, which is mostly dependent on serum albumin concentration.

Decrease in penbutolol protein binding as a consequence of treatment with some alkylating agents

The effect of in vitro treatment of serum with the alkylating agents carmustine (BCNU) and mechlorethamine on the protein binding of penbutolol, a basic agent mainly bound to alpha 1-acid glycoprotein (AAG), was investigated. The free fraction of penbutolol increased significantly (P < 0.001) after the treatment of serum with BCNU (5.27+ +/- 0.47%) and with mechlorethamine (5.23% +/- 0.17%), being 1.98% +/- 0.18% in serum not treated with BCNU or mechlorethamine. In addition, after incubation with BCNU (2 h), the free fraction of penbutolol continued increasing (10.96% +/- 0.70% vs 5.27% +/- 0.47% at time 0; P < 0.001), whereas it remained unchanged after incubation with mechlorethamine. Moreover, dialysis against saline for 24 h did not restore the free fraction of penbutolol, which increased after treatment with carmustine (9.05% +/- 1.24% vs. 11.04% +/- 1.55%, nondialyzed). We concluded that the treatment of cancer patients with alkylating agents could alter the serum proteins and modify their binding capacity, and this should be taken into account in the simultaneous treatment of these patients with other basic drugs like penbutolol, e.g., methadone.

Use of etoposide in patients with organ dysfunction: pharmacokinetic and pharmacodynamic considerations

Etoposide is a podophyllotoxin deriverative with activity against a wide variety of malignancies. It is also used in many clinical conditions in which renal or hepatic function is impaired. To establish a basis for making initial dose adjustments in patients with renal or hepatic dysfunction, the clinical pharmacology (e.g., absorption, distribution, protein binding, metabolism, and elimination) of etoposide is presented. Studies of the use of etoposide in patients with renal or hepatic dysfunction are summarized. The importance of protein binding to etoposide disposition, especially in patients with hepatic dysfunction is discussed. Pharmacodynamics refers to the relationship between drug concentration at the site of action (receptor) and pharmacologic response (toxicity or efficacy). The pharmacodynamics of etoposide has been studied in only a few patients with renal and (or) hepatic dysfunction and must be studied in larger populations before definitive dosing guidelines can be recommended. However, some general initial dosing recommendations for the use of etoposide in patients with renal and hepatic dysfunction are presented.

Disposition of total and unbound etoposide following high-dose therapy

Total and unbound etoposide pharmacokinetics were studied in 16 adult patients (median age, 34 years; range, 18-61 years) undergoing autologous bone marrow transplantation for advanced lymphoma after receiving high-dose etoposide (35-60 mg/kg) as a single intravenous infusion. Pretreatment values for mean serum albumin and total bilirubin were 3.0 +/- 0.4 g/dl and 0.5 +/- 0.4 mg/dl, respectively. Etoposide plasma concentrations and protein binding (%unbound) were determined by high-performance liquid chromatography (HPLC) and equilibrium dialysis, respectively. Pharmacokinetic parameters for unbound and total etoposide were calculated by nonlinear regression analysis using a two-compartment model. The mean (+/- SD) parameters for total etoposide included: clearance (CL), 31.8 +/- 17.7 ml min-1 m-2; volume of distribution (Vss), 11.5 +/- 5.9 l/m2, and terminal half-life (t1/2 beta), 7.2 +/- 3.7 h. Mean unbound CL was 209.6 +/- 62.7 ml min-1 m-2 and %unbound was 16% +/- 5%. The mean etoposide %unbound was inversely related to serum albumin (r2 = 0.45, P = 0.0043). The mean %unbound at the end of the etoposide infusion was higher than that at the lowest measured concentration (21% vs 13%, respectively; P = 0.017), suggesting that concentration-dependent binding may occur after high etoposide doses. The median total CL was higher in patients with serum albumin concentrations of < or = 3.0 g/dl than in those with levels of > 3.0 g/dl (34.6 vs 23.5 ml min-1 m-2, P = 0.05). Total CL was directly related to %unbound (r2 = 0.61, P = 0.0004). Unbound CL was unrelated to either serum albumin or %unbound. These results demonstrate that hypoalbuminemia is independently associated with an increased etoposide %unbound and rapid total CL after the administration of high-dose etoposide. Unbound CL in hypoalbuminemic patients is unchanged in the presence of normal total bilirubin values.