Randomized crossover study evaluating the effect of gemcitabine infusion dose rate: evidence of auto-induction of gemcitabine accumulation

Intracellular Pharmacokinetics of Pyrimidine Analogues used in Oncology and the Correlation with Drug Action

Pyrimidine analogues can be considered as prodrugs, like their natural counterparts, they have to be activated within the cell. The intracellular activation involves several metabolic steps including sequential phosphorylation to its monophosphate, diphosphate and triphosphate. The intracellularly formed nucleotides are responsible for the pharmacological effects. This review provides a comprehensive overview of the clinical studies that measured the intracellular nucleotide concentrations of pyrimidine analogues in patients with cancer. The objective was to gain more insight into the parallels between the different pyrimidine analogues considering their intracellular pharmacokinetics. For cytarabine and gemcitabine, the intracellular pharmacokinetics have been extensively studied over the years. However, for 5-fluorouracil, capecitabine, azacitidine and decitabine, the intracellular pharmacokinetics was only very minimally investigated. This is probably owing to the fact that there were no suitable bioanalytical assays for a long time. Since the advent of suitable assays, the first exploratory studies indicate that the intracellular 5-fluorouracil, azacitidine and decitabine nucleotide concentrations are very low compared with the intracellular nucleotide concentrations obtained during treatment with cytarabine or gemcitabine. Based on their pharmacology, the intracellular accumulation of nucleotides appears critical to the cytotoxicity of pyrimidine analogues. However, not many clinical studies have actually investigated the relationship between the intracellular nucleotide concentrations in patients with cancer and the anti-tumour effect. Only for cytarabine, a relationship was demonstrated between the intracellular triphosphate concentrations in leukaemic cells and the response rate in patients with AML. Future clinical studies should show, for the other pyrimidine analogues, whether there is a relationship between the intracellular nucleotide concentrations and the clinical outcome of patients. Research that examined the intracellular pharmacokinetics of cytarabine and gemcitabine focused primarily on the saturation aspect of the intracellular triphosphate formation. Attempts to improve the dosing regimen of gemcitabine were aimed at maximising the intracellular gemcitabine triphosphate concentrations. However, this strategy does not make sense, as efficient administration also means that less gemcitabine can be administered before dose-limiting toxicities are achieved. For all pyrimidine analogues, a linear relationship was found between the dose and the plasma concentration. However, no correlation was found between the plasma concentration and the intracellular nucleotide concentration. The concentration-time curves for the intracellular nucleotides showed considerable inter-individual variation. Therefore, the question arises whether pyrimidine analogue therapy should be more individualised. Future research should show which intracellular nucleotide concentrations are worth pursuing and whether dose individualisation is useful to achieve these concentrations.

Intracellular pharmacokinetics of gemcitabine, its deaminated metabolite 2',2'-difluorodeoxyuridine and their nucleotides

AIMS

Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdC) is a prodrug that has to be phosphorylated within the tumour cell to become active. Intracellularly formed gemcitabine diphosphate (dFdCDP) and triphosphate (dFdCTP) are considered responsible for the antineoplastic effects of gemcitabine. However, a major part of gemcitabine is converted into 2',2'-difluoro-2'-deoxyuridine (dFdU) by deamination. In the cell, dFdU can also be phosphorylated to its monophosphate (dFdUMP), diphosphate (dFdUDP) and triphosphate (dFdUTP). In vitro data suggest that these dFdU nucleotides might also contribute to the antitumour effects, although little is known about their intracellular pharmacokinetics (PK). Therefore, the objective of the present study was to gain insight into the intracellular PK of all dFdC and dFdU nucleotides formed during gemcitabine treatment.

METHODS

Peripheral blood mononuclear cell (PBMC) samples were collected from 38 patients receiving gemcitabine, at multiple time points after infusion. Gemcitabine, dFdU and their nucleotides were quantified in PBMCs. In addition, gemcitabine and dFdU plasma concentrations were monitored. The individual PK parameters in plasma and in PBMCs were determined.

RESULTS

Both in plasma and in PBMCs, dFdU was present in higher concentrations than gemcitabine [mean intracellular area under the concentration-time curve from time zero to 24 h (AUC_0-24 h ) 1650 vs. 95 μM*h]. However, the dFdUMP, dFdUDP and dFdUTP concentrations in PBMCs were much lower than the dFdCDP and dFdCTP concentrations. The mean AUC_0-24 h for dFdUTP was 312 μM*h vs. 2640 μM*h for dFdCTP.

CONCLUSIONS

The study provides the first complete picture of all nucleotides that are formed intracellularly during gemcitabine treatment. Low intracellular dFdU nucleotide concentrations were found, which calls into question the relevance of these nucleotides for the cytotoxic effects of gemcitabine.

SLC28A3 genotype and gemcitabine rate of infusion affect dFdCTP metabolite disposition in patients with solid tumours

Background:

Gemcitabine is used for the treatment of several solid tumours and exhibits high inter-individual pharmacokinetic variability. In this study, we explore possible predictive covariates on drug and metabolite disposition.

Methods:

Forty patients were enrolled. Gemcitabine and dFdU concentrations in the plasma and dFdCTP concentrations in peripheral blood mononuclear cell were measured to 72 h post infusion, and pharmacokinetic parameters were estimated by nonlinear mixed-effects modelling. Patient-specific covariates were tested in model development.

Results:

The pharmacokinetics of gemcitabine was best described by a two-compartment model with body surface area, age and NT5C2 genotype as significant covariates. The pharmacokinetics of dFdU and dFdCTP were adequately described by three-compartment models. Creatinine clearance and cytidine deaminase genotype were significant covariates for dFdU pharmacokinetics. Rate of infusion of <25 mg m⁻² min⁻¹ and the presence of homozygous major allele for SLC28A3 (CC genotype) were each associated with an almost two-fold increase in the formation clearance of dFdCTP.

Conclusion:

Prolonged dFdCTP systemic exposures (⩾72 h) were commonly observed. Infusion rate <25 mg m⁻² min⁻¹ and carriers for SLC28A3 variant were each associated with about two-fold higher dFdCTP formation clearance. The impacts of these covariates on treatment-related toxicity in more selected patient populations (that is, first-line treatment, single disease state and so on) are not yet clear.

Safety and pharmacology of gemcitabine and capecitabine in patients with advanced pancreatico-biliary cancer and hepatic dysfunction

PURPOSE

We assessed the impact of hepatic dysfunction on the safety and pharmacology of gemcitabine/capecitabine in patients with advanced pancreatico-biliary cancer.

METHODS

We included 12 patients receiving 3 weekly gemcitabine 1,000 mg/m(2) day 1, 8 and oral capecitabine 650 mg/m(2) b.i.d. over 2 weeks until disease progression or intolerable toxicity. Patients were included into one normal hepatic function cohort [total bilirubin (TB) ≤15 μmol/L] and 3 cohorts with increasing TB (16-39, 40-80, >80 μmol/L). Three patients with a creatinine clearance <60 ml/min were also included. Patients were sampled for gemcitabine, difluoro-deoxy uridine, intracellular gemcitabine triphosphates, capecitabine, 5'-deoxy-5-fluorocytidine, 5'-deoxy-5-fluorouridine and 5-fluorouracil up to 4 h after initiation of chemotherapy on day 1, and up to 90 min on day 8. All compounds were analyzed using validated liquid chromatography-tandem mass spectrometry. Nonlinear mixed-effect modeling was used for population analysis.

RESULTS

Hepatic dysfunction was caused by intrahepatic cholestasis in 4 out of 8 patients (50 %) and extrahepatic cholestasis in another 4 patients (50 %). Dose-limiting toxicity was increasing hyperbilirubinemia and severe neutropenia in 2 patients each. Hepatic dysfunction was not associated with dose-limiting toxicity or severe hematological or non-hematological toxicity. However, hepatic dysfunction was associated with low clearance of both gemcitabine (p = 10(-3)) and capecitabine (p = 10(-5)), and low intracellular gemcitabine triphosphate concentrations (p = 10(-3)).

CONCLUSIONS

Gemcitabine/capecitabine can be given at the standard dose in patients with severe hyperbilirubinemia, though the present data suggest that gemcitabine's activity may be limited due to poor intracellular activation. In patients with severe hyperbilirubinemia, initial monotherapy with capecitabine should be considered, followed by the addition of gemcitabine with improving hyperbilirubinemia.

Equilibrative nucleoside transporter 1 genotype, cytidine deaminase activity and age predict gemcitabine plasma clearance in patients with solid tumours

AIM

Gemcitabine (GEM) enters normal and tumour cells via concentrative (CNT) and equilibrative nucleoside transporters (ENT) and is subsequently deaminated to the inactive difluorodeoxyurine (dFdU) by cytidine deaminase (CDA). The aim of our study was to ascertain whether the nucleoside transporter genotype and the CDA activity phenotype can predict total GEM plasma clearance.

METHODS

Forty-seven patients received GEM 1000-1250mgm(-2) i.v. over 30min. Plasma concentrations of GEM and dFdU were measured and individual pharmacokinetic profiles were determined. CDA activity was measured ex vivo in plasma samples. The two most common hENT1 and hCNT1 polymorphisms were determined from genomic DNA.

RESULTS

Multivariate analysis revealed that GEM plasma clearance (CL) was positively correlated with the end of infusion dFdU : GEM ratio (P < 0.0001), which is a marker of in vivo CDA activity. The ENT1 genotype characterized by high transport capacity (G/G) and age were inversely correlated with CL (P= 0.027 and 0.048, respectively). A strong correlation was found between end of infusion GEM concentration and area under the concentration-time curve from time 0 to infinity (AUC(0,∞)) (r(2) = 0.77).

CONCLUSIONS

Our results confirm the role of CDA and age on the interindividual variability of GEM CL and show the contribution of the hENT1 genotype for the first time.

Gemcitabine for unresectable, locally advanced or metastatic bladder cancer

BACKGROUND

The prognosis for unresectable, locally advanced or metastatic transitional cell carcinoma of the bladder is poor with most patients succumbing to their disease within 2 to 3 years. Clinical management at this stage of the disease is palliative with systemic chemotherapy the main treatment of choice. A number of cytotoxic agents have shown activity in metastatic disease including cisplatin, methotrexate, doxorubicin and vinblastine. However, response rates still need improving and toxicities may sometimes be severe, and so the search for newer agents with improved benefit-to-risk ratios is constantly being pursued. One such agent that shows promise is gemcitabine.

OBJECTIVES

Evaluate the effectiveness and toxicity of gemcitabine for the management of unresectable, locally advanced or metastatic bladder cancer.

SEARCH STRATEGY

A search strategy was developed for MEDLINE to identify randomised trials of gemcitabine for the treatment of unresectable, locally advanced or metastatic bladder cancer. The searches were from 1966 to July 2010.  Other databases searched included EMBASE, CINAHL, the Cochrane Database of Systematic Reviews, LILACS, and the Web of Science®. There were no language or location restrictions.

SELECTION CRITERIA

The titles and abstracts of the combined electronic and hand searching searches were manually screened by two authors to determine if they met the inclusion criteria of this review. Studies were selected if they were randomised, controlled trials or quasi-randomised clinical trials that included gemcitabine in at least one arm of a comparative study.

DATA COLLECTION AND ANALYSIS

Data extraction was carried out in duplicate by two authors. The information retrieved included the author's details, the study design, the characteristics of the recruited patients, details of the interventions and data relating to the primary and secondary outcomes measures.

MAIN RESULTS

Three randomised trials used gemcitabine plus cisplatin (GCis) as one of the arms in each trial. The first randomised trial compared GCis with MVAC (methotrexate, vinblastine, doxorubicin and cisplatin) and showed no significant difference in overall survival (hazard ratio1.09, 95% CI 0.88 to 1.34, P = 0.443) however the GCis regime had fewer incidences of neutropenic sepsis (1% versus 12%, P = 0.001) and mucositis (1% versus 22%, P = 0.001). A second randomised trial compared GCis to gemcitabine plus carboplatin (GCarbo) and reported an improved, but non-significant 1-year survival rate with GCis (64% versus 37%). A third randomised trial compared GCis with gemcitabine plus cisplatin plus paclitaxel (GCisPac) and again found no significant difference in overall survival (respective medians 49 weeks versus 61 weeks).One randomised trial evaluated GCarbo against methotrexate plus carboplatin plus vinblastine (MCarboV) in patients "unfit" for cisplatin-based chemotherapy. There were more overall responses (38% versus 20%) and less severe acute toxicities (14% versus 23%) with GCarbo.In one randomised study evaluating 3-weekly gemcitabine plus paclitaxel (GPac3) versus a 2-weekly regimen overall survival was not significantly different (respective medians 13 and 9 months) however toxicities were worse with GPac3 especially alopecia (76% versus 32%).A larger trial compared gemcitabine (1 g/m(2)) (grams per metre squared) plus paclitaxel (175 mg/m(2)) (milligrams per metre squared) as a 3-weekly schedule for 6 cycles with a 2-weekly maintenance schedule. There was no significant difference in response rates, progression-free survival, disease-specific survival, and overall survival.

AUTHORS' CONCLUSIONS

A review of the published evidence found that one trial reported gemcitabine plus cisplatin had a better safety profile than MVAC and may be considered the first choice for treatment of metastatic bladder cancer. However, the data are limited to one trial only. Patients unable to tolerate cisplatin may benefit from gemcitabine plus carboplatin.

The pharmacological advantage of prolonged dose rate gemcitabine is restricted to patients with variant alleles of cytidine deaminase c.79A>C

AIM

Controversy exists over the optimal dosing for the nucleoside analogue gemcitabine. A pharmacological advantage is achieved by prolonging infusion times but evidence for a clinical benefit has been conflicting. We hypothesized that polymorphisms in genes involved in gemcitabine accumulation, particularly the cytidine deaminase CDA c.79A>C, may influence the optimal dosing regimen in individual patients.

METHODS

DNA was collected from 32 patients participating in a randomized crossover study comparing 30-min with 100-min infusions of gemcitabine. The relationships between seven polymorphisms among three genes (CDA, RRM1 and DCK) and (i) gemcitabine triphosphate accumulation; (ii) gemcitabine-induced toxicity; and (iii) dose delivery were examined for each infusion time and week of administration.

RESULTS

There were trends for increased accumulation of gemcitabine-triphosphate (GEM-TP) with the variant alleles of CDA c.79A>C, and RRM1-37C>A and -524T>C but none of these reached statistical significance in a univariate analysis. In a multivariable model there were significant effects of infusion duration and week of administration on GEM-TP accumulation. There were significant interactions between CDA c.79A>C (P=0.01) and RRM1-37C>A (P=0.019) genotypes, infusion time, and arm. More patients with one or two CDA c.79 variant alleles had doses delays (57 vs 13 %, P=0.03) and a pharmacological advantage for prolonged infusion after week 1.

CONCLUSION

It is important to consider both pharmacokinetics and pharmacogenetics in optimizing gemcitabine accumulation. This represents a classical interaction between genes and environment and provides support for the consideration of both CDA genotype and infusion duration in development of an individualized dosing strategy.

Phase I-II trial of prolonged gemcitabine infusion plus paclitaxel as a biweekly schedule for advanced breast cancer patients pretreated with anthracyclines

PURPOSE

Paclitaxel (PACL) plus gemcitabine (GEM) is an effective regimen for advanced breast cancer patients pretreated with anthracyclines. A prolonged GEM infusion at a fixed dose rate (FDR) of 10 mg/m²/min produces higher levels of intracellular active metabolites of GEM when compared with a standard 30-min infusion. In the present phase I/II trial, we investigated the association of FDR GEM plus PACL.

METHODS

1,200 mg/m² was the dose of GEM recommended for the phase II study, in which patients received PACL at 150 mg/m², followed by FDR GEM at 1,200 mg/m² (total GEM infusion time = 120 min), both drugs administered biweekly.

RESULTS

Forty-two anthracycline-pretreated advanced breast cancer patients with disease recurrence following at least one line of chemotherapy were enrolled. Two (4.8%) and 12 (33.3%) patients experienced a complete and partial response, respectively, for an overall response rate of 38.1% (95% CI 23.4-52.8%). Median progression free survival and overall survival were 5 and 19.9 months, respectively. No statistically significant association was noted between in situ protein expression of RRM1 and BRCA1 (as assessed by immunofluorescence combined with automated quantitative analysis) and response to treatment in 15 patients with tissue available for analysis. Toxicity was mostly mild to moderate, mainly consisting of G3-G4 neutropenia (9.6%) and hypertransaminasemia (9.5%).

CONCLUSIONS

Biweekly FDR GEM in combination with PACL is an active and safe regimen for advanced breast cancer patients pretreated with anthracyclines. A prolonged infusion regimen of GEM does not seem to improve the efficacy of a standard 30-min infusion.

Pharmacokinetics of gemcitabine at fixed-dose rate infusion in patients with normal and impaired hepatic function

BACKGROUND AND OBJECTIVES

Gemcitabine (2,2-difluorodeoxycytidine [dFdC]) can be administered in a standard 30-minute infusion or in a fixed-dose-rate (FDR) infusion to maximize the rate of accumulation of triphosphate, its major intracellular metabolite. The standard 30-minute infusion requires dose adjustment in patients with organ dysfunction, especially in patients with elevated baseline serum bilirubin levels. On the other hand, the FDR infusion is burdened by increased haematological toxicity. The primary aim of this study was to evaluate the pharmacokinetics of dFdC and its metabolite difluorodeoxyuridine (dFdU) in patients with normal and impaired hepatic function.

PATIENTS AND METHODS

In this prospective study, patients with pancreatic or biliary tract carcinoma and normal or impaired hepatic function tests were considered eligible for recruitment. Patients were recruited according to the following criteria: (i) serum bilirubin <1.6 mg/dL and AST and ALT <2 times the upper the limit of normal (ULN) [cohort I]; and (ii) serum bilirubin >1.6 mg/dL and/or AST/ALT >2 times the ULN (cohort II). An FDR infusion of gemcitabine 1000 mg/m2 was administered on days 1, 8 and 15 every 4 weeks. The pharmacokinetic analysis of gemcitabine and dFdU was performed with high-performance liquid chromatography-tandem mass spectrometry assay in cycles 1 and 2.

RESULTS

Thirteen patients were enrolled, four in cohort I and nine in cohort II. All patients were assessable for toxicity and pharmacokinetic analysis. The grade and rate of toxicities were similar in both groups, and patients with elevation of bilirubin and/or transaminases did not require dose reduction of gemcitabine. Pharmacokinetic analysis revealed a reduction of the experimental area under the plasma concentration-time curve for gemcitabine and dFdU in patients with hepatic dysfunction when compared with patients with normal hepatic function. All other pharmacokinetic parameters were similar in the two cohorts. No statistical difference was demonstrated for all parameters evaluated between cycle 1 and cycle 2 in the two groups.

CONCLUSION

Gemcitabine 1000 mg/m2 can be administered as an FDR infusion in patients with altered hepatic function without causing additional toxicity compared with patients with normal hepatic function.

Improving gemcitabine-mediated radiosensitization using molecularly targeted therapy: a review

In the last three decades, gemcitabine has progressed from the status of a laboratory cytotoxic drug to a standard clinical chemotherapeutic agent and a potent radiation sensitizer. In an effort to improve the efficacy of gemcitabine, additional chemotherapeutic agents have been combined with gemcitabine (both with and without radiation) but with toxicity proving to be a major limitation. Therefore, the integration of molecularly targeted agents, which potentially produce less toxicity than standard chemotherapy, with gemcitabine radiation is a promising strategy for improving chemoradiation. Two of the most promising targets, described in this review, for improving the efficacy of gemcitabine radiation are epidermal growth factor receptor and checkpoint kinase 1.

Modulation of gemcitabine (2',2'-difluoro-2'-deoxycytidine) pharmacokinetics, metabolism, and bioavailability in mice by 3,4,5,6-tetrahydrouridine

PURPOSE

In vivo, 2',2'-difluoro-2'-deoxycytidine (dFdC) is rapidly inactivated by gut and liver cytidine deaminase (CD) to 2',2'-difluoro-2'-deoxyuridine (dFdU). Consequently, dFdC has poor oral bioavailability and is administered i.v., with associated costs and limitations in administration schedules. 3,4,5,6-Tetrahydrouridine (THU) is a potent CD inhibitor with a 20% oral bioavailability. We investigated the ability of THU to decrease elimination and first-pass effect by CD, thereby enabling oral dosing of dFdC.

EXPERIMENTAL DESIGN

A liquid chromatography-tandem mass spectrometry assay was developed for plasma dFdC and dFdU. Mice were dosed with 100 mg/kg dFdC i.v. or orally with or without 100 mg/kg THU i.v. or orally. At specified times between 5 and 1,440 min, mice (n = 3) were euthanized. dFdC, dFdU, and THU concentrations were quantitated in plasma and urine.

RESULTS

THU i.v. and orally produced concentrations >4 microg/mL for 3 and 2 h, respectively, whereas concentrations of >1 microg/mL have been associated with near-complete inhibition of CD in vitro. THU i.v. decreased plasma dFdU concentrations but had no effect on dFdC plasma area under the plasma concentration versus time curve after i.v. dFdC dosing. Both THU i.v. and orally substantially increased oral bioavailability of dFdC. Absorption of dFdC orally was 59%, but only 10% passed liver and gut CD and eventually reached the systemic circulation. Coadministration of THU orally increased dFdC oral bioavailability from 10% to 40%.

CONCLUSIONS

Coadministration of THU enables oral dosing of dFdC and warrants clinical testing. Oral dFdC treatment would be easier and cheaper, potentially prolong dFdC exposure, and enable exploration of administration schedules considered impractical by the i.v. route.