dFdCTP Accumulation Research Articles

Ultrasound- and Microbubble-Assisted Gemcitabine Delivery to Pancreatic Cancer Cells.

Pancreatic ductal adenocarcinoma (PDAC) is a major cause of cancer death worldwide. Poor drug delivery to tumours is thought to limit chemotherapeutic treatment efficacy. Sonoporation combines ultrasound (US) and microbubbles to increase the permeability of cell membranes. We assessed gemcitabine uptake combined with sonoporation in vitro in three PDAC cell lines (BxPC-3, MIA PaCa-2 and PANC-1). Cells were cultured in hypoxic bioreactors, while gemcitabine incubation ± sonoporation was conducted in cells with operational or inhibited nucleoside membrane transporters. Intracellular active metabolite (dFdCTP), extracellular gemcitabine, and inactive metabolite (dFdU) concentrations were measured with liquid chromatography tandem mass spectrometry. Sonoporation with increasing US intensities resulted in decreasing extracellular gemcitabine concentrations in all three cell lines with inhibited membrane transporters. In cells with inhibited membrane transporters, without sonoporation, dFdCTP concentrations were reduced down to 10% of baseline. Sonoporation partially restored gemcitabine uptake in these cells, as indicated by a moderate increase in dFdCTP concentrations (up to 37% of baseline) in MIA PaCa-2 and PANC-1. In BxPC-3, gemcitabine was effectively inactivated to dFdU, which might represent a protective mechanism against dFdCTP accumulation in these cells. Intracellular dFdCTP concentrations did not change significantly following sonoporation in any of the cell lines with operational membrane transporters, indicating that the gemcitabine activation pathway may have been saturated with the drug. Sonoporation allowed a moderate increase in gemcitabine transmembrane uptake in all three cell lines, but pre-existing nucleoside transporters were the major determinants of gemcitabine uptake and retention.

Extensive Metabolism and Hepatic Accumulation of Gemcitabine After Multiple Oral and Intravenous Administration in Mice

In a clinical study with oral gemcitabine (2',2'-difluorodeoxycytidine, dFdC), we found that gemcitabine was hepatotoxic and extensively metabolized to 2',2'-difluorodeoxyuridine (dFdU) after continuous oral dosing. The main metabolite dFdU had a long terminal half-life after oral administration. Our hypothesis was that dFdU and/or phosphorylated metabolites of gemcitabine accumulated in the liver after multiple oral dosing. In this study, mice were treated with oral or i.v. dFdC at a single dose (1qdx1d) or at multiple doses once daily for 7 days (1qdx7d) or seven times daily (7qdx1d). Blood, liver, kidneys, and lungs were collected at several time points. Urine samples were collected after i.v. dFdC, and peripheral blood mononuclear cells were collected 7qdx1d dosing of dFdC. The nucleosides dFdC and dFdU as well as the nucleotides gemcitabine monophosphate (dFdC-MP), diphosphate, and triphosphate (dFdC-TP) and dFdU monophosphate, diphosphate (dFdU-DP), and triphosphate (dFdU-TP) were simultaneously quantified by high-performance liquid chromatography with ultraviolet and radioisotope detection. We demonstrate that phosphorylated metabolites of both dFdC and dFdU are formed in mice, primarily consisting of dFdC-MP, dFdC-TP, and dFdU-TP. Multiple dosing of dFdC leads to substantial hepatic and renal accumulation of dFdC-TP and dFdU-TP, which have a more pronounced liver accumulation after oral than after i.v. dosing. The presence of dFdC-MP, dFdC-TP, and dFdU-TP in plasma and urine suggests efflux of these potentially toxic metabolites. Our results show that dFdU, dFdC-TP, and dFdU-TP accumulate in the liver after multiple dosing of dFdC in mice and might be associated with hepatotoxicity of oral dFdC in patients.

Prolonged Versus Standard Gemcitabine Infusion: Translation of Molecular Pharmacology to New Treatment Strategy

Gemcitabine is frequently used in the treatment of patients with solid tumors. Gemcitabine is taken up into the cell via human nucleoside transporters (hNTs) and is intracellularly phosphorylated by deoxycytidine kinase (dCK) to its monophosphate and subsequently into its main active triphosphate metabolite 2',2'-difluorodeoxycytidine triphosphate (dFdCTP), which is incorporated into DNA and inhibits DNA synthesis. In addition, gemcitabine is extensively deaminated to 2',2'-difluorodeoxyuridine, which is largely excreted into the urine. High expression levels of human equilibrative nucleoside transporter type 1 were associated with a significantly longer overall survival duration after gemcitabine treatment in patients with pancreatic cancer. Clinical studies in blood mononuclear and leukemic cells demonstrated that a lower infusion rate of gemcitabine was associated with higher intracellular dFdCTP levels. Prolonged infusion of gemcitabine at a fixed dose rate (FDR) of 10 mg/m2 per minute was associated with a higher intracellular accumulation of dFdCTP, greater toxicity, and a higher response rate than with the standard 30-minute infusion of gemcitabine in patients with pancreatic cancer. In the current review, we discuss the molecular pharmacology of nucleoside analogues and the influence of hNTs and dCK on the activity and toxicity of gemcitabine, which is the basis for clinical studies on FDR administration, and the results of FDR gemcitabine administration in patients. These findings might aid optimal clinical application of gemcitabine in the future.

A multicentre randomised phase II study of carboplatin in combination with gemcitabine at standard rate or fixed dose rate infusion in patients with advanced stage non-small-cell lung cancer

Background: Intracellular gemcitabine triphosphate (dFdCTP) levels can be optimised by administering gemcitabine at a fixed dose rate infusion.Patients and methods: Patients with chemonaive advanced non-small cell lung cancer (NSCLC) were randomised to receive gemcitabine at a fixed dose rate gemcitabine 750mg/m2 over 75min (arm A) or gemcitabine 1000mg/m2 over 30min (arm B) on days 1 and 8 every three week cycle. Carboplatin at AUC of 5 was administered in both treatment arms on day 1 of each cycle. End points were activity, tolerability and pharmacokinetics of plasma and intracellular gemcitabine.Results: 76 patients were randomised. Response rate was 34% in arm A and 42% in arm B. Toxicity and quality of life scores were similar for both treatment arms. Mean plasma Cmaxgemcitabine and mean dFdCTP AUC in arm A was 20.8μm ± 17.2μm and 35079 ± 18216 μM*min respectively and in arm B, 41.2 ± 13.9μm and 32249 ± 11267 μM*min respectively. dFdCTP saturation was reached in Arm B but not in Arm A.Conclusion: The saturability of dFdCTP accumulation in Arm A suggests optimal delivery of gemcitabine is achieved using fixed rate infusion compared to 30-min infusion. Fixed dose rate gemcitabine is active and feasible, supporting the concept of fixed dosing rate of gemcitabine in advanced NSCLC. However, this entails a longer infusion time with associated higher costs involved.

Phase II study with the combination of gemcitabine and DTIC in patients with advanced soft tissue sarcomas

Based on the promising results of a Phase I study with a combination of gemcitabine and DTIC performed in advanced soft tissue sarcoma (ASTS) patients, and due to the limited efficacy of second or third line therapies in those patients, we designed a Phase II study to determine the activity of this new regimen. Patients with ASTS, measurable disease, pretreated with chemotherapy, received gemcitabine 1,800 mg/m2 infused over 180 min followed by DTIC 500 mg/m2 (one cycle), every 2 weeks. The pharmacokinetics (PK) of gemcitabine and 2',2'-difluorodeoxyuridine (dFdU), and the accumulation of gemcitabine triphosphate (dFdCTP) by peripheral blood mononuclear cells were studied. The influence of the sequence of administration on those parameters was examined to exclude potential drug interactions. Twenty-six patients received a total of 158 cycles (mean four cycles, range 1-18). Grade 3-4 anemia (23% of patients), granulocytopenia (46%) or thrombocytopenia (12%), and grade 3 increase in AST (18%), ALT (21%), or gamma-glutamyl-transferase (9%) were noted. Response rate in 23 patients was 4% (95% CI: 0-24%), and in 8 of 11 patients stable disease lasted > 6 months. Progression-free rate (PFR) at 3 and 6 months was, respectively, 48 and 28%, and median overall survival 37 weeks. Pooled data from the Phase I and Phase II studies showed clinical benefit in patients with leiomyosarcomas (LMS) (57%) and malignant fibrous histiocytomas (MFH) (33%). The sequence of administration did not influence PK of gemcitabine or dFdU. There was a trend (P = 0.11) toward a lower accumulation of dFdCTP when DTIC preceded gemcitabine. Although the remission rate was low, PFR figures indicate that this regimen has activity in patients with ASTS. It should be compared with DTIC, or other gemcitabine-containing combinations, in patients with LMS or MFH, to determine whether this combination offers advantages in PFR or in overall activity.

The relation between deoxycytidine kinase activity and the radiosensitising effect of gemcitabine in eight different human tumour cell lines

BackgroundGemcitabine (dFdC) is an active antitumour agent with radiosensitising properties, shown both in preclinical and clinical studies. In the present study, the relation between deoxycytidine kinase (dCK) activity and the radiosensitising effect of gemcitabine was investigated in eight different human tumour cell lines.MethodsTumour cells were treated with dFdC (0–100 nM) for 24 h prior to radiotherapy (RT) (γ-Co60, 0–6 Gy, room temperature). Cell survival was determined 7, 8, or 9 days after RT by the sulforhodamine B test. dCK activity of the cells was determined by an enzyme activity assay.ResultsA clear concentration-dependent radiosensitising effect of dFdC was observed in all cell lines. The degree of radiosensitisation was also cell line dependent and seemed to correlate with the sensitivity of the cell line to the cytotoxic effect of dFdC. The dCK activity of our cell lines varied considerably and differed up to three fold from 5 to 15 pmol/h/mg protein between the tested cell lines. In this range dCK activity was only weakly related to radiosensitisation (correlation coefficient 0.62, p = 0.11).ConclusionGemcitabine needs to be metabolised to the active nucleotide in order to radiosensitise the cells. Since dFdCTP accumulation and incorporation into DNA are concentration dependent, the degree of radiosensitisation seems to be related to the extent of dFdCTP incorporated into DNA required to inhibit DNA repair. The activity of dCK does not seem to be the most important factor, but is clearly a major factor. Other partners of the intracellular metabolism of gemcitabine in relation to the cell cycle effects and DNA repair could be more responsible for the radiosensitising effect than dCK activity.

A phase II study of fixed dose rate gemcitabine in patients with relapsed mullerian tumors

Gemcitabine (2',2'-difluorodeoxycytidine) is a novel purine analog with clinical activity against ovarian cancer. Accumulation of gemcitabine triphosphate (dFdCTP) increases in a linear fashion with prolonged infusions of gemcitabine, and there is a strong relationship between intracellular accumulation of dFdCTP and DNA damage. Women with ovarian, fallopian tube, or primary peritoneal carcinoma and documented recurrent disease were eligible for the study. Patients could not have received more than four prior lines of chemotherapy and had to have measurable or evaluable disease. Gemcitabine 800 mg/m2 administered by intravenous infusion at 10 mg/m2/min (fixed dose rate [FDR]) on days 1 and 8 of a 21-day schedule. Twenty-eight patients with a median age 60 (range, 40-77) years were treated. Although 43% were Eastern Cooperative Oncology Group 0, 50% had liver metastases. Eighty-eight cycles of therapy were delivered (median 2 [range, 1-6]). Five of the first ten patients treated at 800 mg/m2 could not receive day 8 FDR-gemcitabine because of neutropenia, and the starting dose was reduced to 700 mg/m2. Even at this dose there was cumulative hematologic toxicity resulting in dose reductions. Vomiting, mucositis, diarrhea, allergy, rash, fever, and alopecia were mild. In 28 patients, there was only one partial response (4%, 95% CI 0-18%) and median time to progression was 1.7 (interquartile range, 1.2-3.9) months. FDR-gemcitabine 700 mg/m2 administered by intravenous infusion at an FDR of 10 mg/m2/min had minimal activity against heavily pretreated recurrent tumors of müllerian origin. The optimal dose and schedule of gemcitabine is yet to be defined in this population.

Paclitaxel (PAC) alters the metabolism of gemcitabine (GEM) to its active metabolite difluorodeoxycytidine triphosphate (dFdCTP)

2089 Background: Our group previously reported PAC significantly decreased the systemic clearance and volume of distribution of a fixed dose of GEM administered after PAC. Therefore, this study was conducted to determine the effects of PAC on the disposition and metabolism of GEM to difluordeoxyuridine (dFdU) in human hepatocytes and dFdCTP in human peripheral blood mononuclear cells (PBMC). Methods: PBMC or hepatocytes were treated with GEM 5, 15 or 30μM x 80 min alone or after PAC 3μM x 3 h. Extracellular GEM and dFdU concentrations were measured at 0, 40, and 80 min after adding GEM and 40 and 80 min after removing GEM and the intracellular accumulation of GEM, dFdU and dFdCTP were measured ∼80 min after removing GEM using high performance liquid chromatography. Results: In hepatocytes, mean extracellular gemcitabine concentrations were higher (17 to 95%) and mean extracellular dFdU concentrations were lower (19 to 73%) for cells treated with PAC+GEM compared to GEM alone. GEM, dFdU, and dFdCTP were not measurable in hepatocytes. In PBMC, mean extracellular GEM concentrations were similar for cells treated with PAC+GEM and GEM alone; however, intracellular dFdCTP accumulation was lower (21 to 44%) in cells treated with PAC+GEM. GEM and dFdU were not measurable in PBMC. Additional studies indicated TAXOL (formulated) similarly altered GEM metabolism and disposition and PAC did not alter the metabolism or disposition in cells treated with PAC after GEM. Conclusions: PAC reduced the formation of dFdCTP and dFdU at clinically achievable concentrations. PAC most likely reduced the intracellular accumulation of GEM or its metabolites and thus, reduced the metabolism of GEM to its inactive or active metabolite, respectively. The sequence of administration, but not the PAC formulation influenced this interaction. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration American Cancer Society Institutional Research Grant Program

Paclitaxel (PAC) alters the metabolism of gemcitabine (GEM) to its active metabolite difluorodeoxycytidine triphosphate (dFdCTP)

2089 Background: Our group previously reported PAC significantly decreased the systemic clearance and volume of distribution of a fixed dose of GEM administered after PAC. Therefore, this study was conducted to determine the effects of PAC on the disposition and metabolism of GEM to difluordeoxyuridine (dFdU) in human hepatocytes and dFdCTP in human peripheral blood mononuclear cells (PBMC). Methods: PBMC or hepatocytes were treated with GEM 5, 15 or 30μM x 80 min alone or after PAC 3μM x 3 h. Extracellular GEM and dFdU concentrations were measured at 0, 40, and 80 min after adding GEM and 40 and 80 min after removing GEM and the intracellular accumulation of GEM, dFdU and dFdCTP were measured ∼80 min after removing GEM using high performance liquid chromatography. Results: In hepatocytes, mean extracellular gemcitabine concentrations were higher (17 to 95%) and mean extracellular dFdU concentrations were lower (19 to 73%) for cells treated with PAC+GEM compared to GEM alone. GEM, dFdU, and dFdCTP were not measurable in hepatocytes. In PBMC, mean extracellular GEM concentrations were similar for cells treated with PAC+GEM and GEM alone; however, intracellular dFdCTP accumulation was lower (21 to 44%) in cells treated with PAC+GEM. GEM and dFdU were not measurable in PBMC. Additional studies indicated TAXOL (formulated) similarly altered GEM metabolism and disposition and PAC did not alter the metabolism or disposition in cells treated with PAC after GEM. Conclusions: PAC reduced the formation of dFdCTP and dFdU at clinically achievable concentrations. PAC most likely reduced the intracellular accumulation of GEM or its metabolites and thus, reduced the metabolism of GEM to its inactive or active metabolite, respectively. The sequence of administration, but not the PAC formulation influenced this interaction. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration American Cancer Society Institutional Research Grant Program

A phase II study of fixed dose-rate gemcitabine in patients with relapsed Müllerian tumors

5151 Background: Gemcitabine (2',2'-difluorodeoxycytidine) is a novel purine analog with clinical activity against ovarian cancer. Accumulation of gemcitabine triphosphate (dFdCTP) increases in a linear fashion with prolonged infusions of gemcitabine and there is a strong relationship between intracellular accumulation of dFdCTP and DNA damage. Methods: Women with ovarian, fallopian tube or primary peritoneal carcinoma and documented recurrent disease were eligible for the study. Patients could not have received more than 4 prior lines of chemotherapy and had to have measurable or evaluable disease. Gemcitabine 800 mg/m2 was administered by i.v. infusion at 10 mg/m2/min (Fixed dose-rate (FDR)) on days 1 and 8 of a 21 day schedule. Results: Twenty-eight patients with a median age 60 (range, 40–77) years were treated. Although 43% were ECOG 0, 50% had liver metastases. Eighty-eight cycles of therapy were delivered (Median 2(Range, 1–6)). Five of the first 10 patients treated at 800 mg/m2 could not receive day 8 FDR-gemcitabine because of neutropenia and the starting dose was reduced to 700 mg/m2. Even at this dose there was cumulative hematologic toxicity resulting in dose reductions. Vomiting, mucositis, diarrhea, allergy, rash, fever and alopecia were mild. In 28 patients there was only one partial response (4%, 95% CI 0 –18%) and median time to progression was 1.7 (Interquartile range, 1.2 –3.9) months. Conclusions: FDR-Gemcitabine 700 mg/m2 administered by i.v. infusion at a fixed dose-rate of 10 mg/m2/min had minimal activity against recurrent tumors of Müllerian origin. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Eli Lilly Co. Eli Lilly Co.

A phase II study of fixed dose-rate gemcitabine in patients with relapsed Müllerian tumors

5151 Background: Gemcitabine (2',2'-difluorodeoxycytidine) is a novel purine analog with clinical activity against ovarian cancer. Accumulation of gemcitabine triphosphate (dFdCTP) increases in a linear fashion with prolonged infusions of gemcitabine and there is a strong relationship between intracellular accumulation of dFdCTP and DNA damage. Methods: Women with ovarian, fallopian tube or primary peritoneal carcinoma and documented recurrent disease were eligible for the study. Patients could not have received more than 4 prior lines of chemotherapy and had to have measurable or evaluable disease. Gemcitabine 800 mg/m2 was administered by i.v. infusion at 10 mg/m2/min (Fixed dose-rate (FDR)) on days 1 and 8 of a 21 day schedule. Results: Twenty-eight patients with a median age 60 (range, 40–77) years were treated. Although 43% were ECOG 0, 50% had liver metastases. Eighty-eight cycles of therapy were delivered (Median 2(Range, 1–6)). Five of the first 10 patients treated at 800 mg/m2 could not receive day 8 FDR-gemcitabine because of neutropenia and the starting dose was reduced to 700 mg/m2. Even at this dose there was cumulative hematologic toxicity resulting in dose reductions. Vomiting, mucositis, diarrhea, allergy, rash, fever and alopecia were mild. In 28 patients there was only one partial response (4%, 95% CI 0 –18%) and median time to progression was 1.7 (Interquartile range, 1.2 –3.9) months. Conclusions: FDR-Gemcitabine 700 mg/m2 administered by i.v. infusion at a fixed dose-rate of 10 mg/m2/min had minimal activity against recurrent tumors of Müllerian origin. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Eli Lilly Co. Eli Lilly Co.

Increased sensitivity to gemcitabine of P-glycoprotein and multidrug resistance-associated protein-overexpressing human cancer cell lines.

Gemcitabine (2′,2′-difluorodeoxycytidine) is a deoxycytidine analogue that is activated by deoxycytidine kinase (dCK) to its monophosphate and subsequently to its triphosphate dFdCTP, which is incorporated into both RNA and DNA, leading to DNA damage. Multidrug resistance (MDR) is characterised by an overexpression of the membrane efflux pumps P-glycoprotein (P-gP) or multidrug resistance-associated protein (MRP). Gemcitabine was tested against human melanoma, non-small-cell lung cancer, small-cell lung cancer, epidermoid carcinoma and ovarian cancer cells with an MDR phenotype as a result of selection by drug exposure or by transfection with the mdr1 gene. These cell lines were nine- to 72-fold more sensitive to gemcitabine than their parental cell lines. The doxorubicin-resistant cells 2R120 (MRP1) and 2R160 (P-gP) were nine- and 28-fold more sensitive to gemcitabine than their parental SW1573 cells, respectively (P<0.01), which was completely reverted by 25 μM verapamil. In 2R120 and 2R160 cells, dCK activities were seven- and four-fold higher than in SW1573, respectively, which was associated with an increased dCK mRNA and dCK protein. Inactivation by deoxycytidine deaminase was 2.9- and 2.2-fold decreased in 2R120 and 2R160, respectively. dFdCTP accumulation was similar in SW1573 and its MDR variants after 24 h exposure to 0.1 μM gemcitabine, but dFdCTP was retained longer in 2R120 (P<0.001) and 2R160 (P<0.003) cells. 2R120 and 2R160 cells also incorporated four- and six-fold more [3H]gemcitabine into DNA (P<0.05), respectively. P-glycoprotein and MRP1 overexpression possibly caused a cellular stress resulting in increased gemcitabine metabolism and sensitivity, while reversal of collateral gemcitabine sensitivity by verapamil also suggests a direct relation between the presence of membrane efflux pumps and gemcitabine sensitivity.

3′-Azido-2′,3′-dideoxythymidine induced deficiency of thymidine kinases 1, 2 and deoxycytidine kinase in H9 T-lymphoid cells

Continuous cultivation of T-lymphoid H9 cells in the presence of 3′-azido-2′,3′-dideoxythymidine (AZT) resulted in a cell variant cross-resistant to both thymidine and deoxycytidine analogs. Cytotoxic effects of AZT, 2′,3′-didehydro-3′-deoxythymidine as well as different deoxycytidine analogs such as 2′,3′-dideoxycytidine, 2′,2′-difluoro-2′-deoxycytidine (dFdC) and 1-ß-D-arabinofuranosylcytosine (Ara-C) were strongly reduced in H9 cells continuously exposed to AZT when compared to parental cells (>8.3-, >6.6-, >9.1-, 5×10 4-, 5×10 3-fold, respectively). Moreover, anti-HIV-1 effects of AZT, d4T, ddC and 2′,3′-dideoxy-3′-thiacytidine (3TC) were significantly diminished (>222-, >25-, >400-, >200-fold, respectively) in AZT-resistant H9 cells. Study of cellular mechanisms responsible for cross-resistance to pyrimidine analogs in AZT-resistant H9 cells revealed decreased mRNA levels of thymidine kinase 1 (TK1) and lack of deoxycytidine kinase (dCK) mRNA expression. The loss of dCK gene expression was confirmed by western blot analysis of dCK protein as well as dCK enzyme activity assay. Moreover, enzyme activity of TK1 and TK2 was reduced in AZT-resistant cells. In order to determine whether lack of dCK affected the formation of the active triphosphate of the deoxycytidine analog dFdC, dFdCTP accumulation and retention was measured in H9 parental and AZT-resistant cells after exposure to 1 and 10 μM dFdC. Parental H9 cells accumulated about 30 and 100 pmol dFdCTP/10 6 cells after 4 hr, whereas in AZT-resistant cells no dFdCTP accumulation was detected. These results demonstrate that continuous treatment of H9 cells in the presence of AZT selected for a thymidine analog resistant cell variant with cross-resistance to deoxycytidine analogs, due to deficiency in TK1, TK2, and dCK.

Collateral sensitivity to gemcitabine (2′,2′-difluorodeoxycytidine) and cytosine arabinoside of daunorubicin- and VM-26-resistant variants of human small cell lung cancer cell lines

Multidrug resistance (MDR), characterized by a cross-resistance to many natural toxin-related compounds, may be caused either by overexpression of a drug efflux pump such as P-glycoprotein, (P-gP), multidrug resistance proteins MRP1–3, or BCRP/MXR or, in the case of DNA topoisomerase II active drugs, by a decrease in the enzymatic activity of the target molecule termed altered topoisomerase MDR (at-MDR). However, human small cell lung carcinoma (SCLC) cell lines showed a collateral sensitivity to 2′,2′-difluorodeoxycytidine (gemcitabine, dFdC) and 1-β- d-arabinofuranosylcytosine (ara-C). H69/DAU, a daunorubicin (DAU)-resistant variant of H69 with a P-gP overexpression, and NYH/VM, a VM-26 (teniposide)-resistant variant of NYH with an at-MDR, were both 2-fold more sensitive to gemcitabine and 7- and 2-fold more sensitive to ara-C, respectively. MDR variants had a 4.3- and 2.0-fold increased activity of deoxycytidine kinase (dCK), respectively. dCK catalyzes the first rate-limiting activation step of both gemcitabine and ara-C. In addition, deoxycytidine deaminase, responsible for inactivation of dFdC and ara-C, was 9.0-fold lower in H69/DAU cells. The level of thymidine kinase 2, a mitochondrial enzyme that can also phosphorylate deoxycytidine and gemcitabine, was not significantly different between the variants. These differences most likely caused an increased accumulation of the active metabolites (dFdCTP, 2.1- and 1.6-fold in NYH/VM and H69/DAU cells, respectively) and of ara-CTP (1.3-fold in NYH/VM cells). Ara-CTP accumulation was not detectable in either H69 variant. The pools of all ribonucleoside and deoxyribonucleoside triphosphates were at least 3- to 4-fold higher in the NYH variants compared to the H69 variants; for dCTP and dGTP this difference was even larger. The higher ribonucleotide pools might explain the >10-fold higher accumulation of dFdCTP in NYH compared to H69 variants. Since dCTP is low, H69 cells might not need a high ara-CTP accumulation to inhibit DNA polymerase. This might be related to the lack of ara-CTP in H69 variants. In addition, the increased CTP, ATP, and UTP pools in the MDR variants might explain the increased ara-CTP and dFdCTP accumulation. In conclusion, the MDR variants of the human SCLC cell lines were collaterally sensitive due to an increased dCK activity, and consequently an increased ara-CTP and dFdCTP accumulation.

Schedule-dependent pharmacodynamic effects of gemcitabine and cisplatin in mice bearing Lewis lung murine non-small cell lung tumours

The combination of 2′,2′-difluorodeoxycytidine (gemcitabine, dFdC) and cis-diammine-dichloroplatinum(II) (cisplatin, CDDP) is increasingly applied in clinical oncology. We studied the underlying mechanisms of the in vivo schedule dependency and supra-additive interaction between dFdC and CDDP in C57/Bl6 mice bearing Lewis lung (LL) tumours. Mice were treated with CDDP (6 mg/kg) and dFdC (60 mg/kg) either simultaneously or in a 4 or 24 h interval with dFdC preceding CDDP or vice versa. Four, 8 (in some cases 12) and 24 h after treatment mice were sacrificed and tumours, kidneys, blood and bone marrow (BM) were collected. Since CDDP acts by formation of Platinum (Pt)–DNA adducts and dFdC by incorporation of its triphosphate (dFdCTP) into DNA, we measured total Pt levels, dFdCTP accumulation and Pt–DNA adducts by atomic absorption spectrometry (AAS), high performance liquid chromatography (HPLC) and 32P-postlabelling, respectively. These levels were related to the previously determined antitumour efficacy and toxicity of the dFdC/CDDP combination. Peak dFdCTP accumulation in tumours (11 pmol/mg) was found 4 h after dFdC treatment, while CDDP tended to reduce this in a time-dependent way. Peak levels of total Pt in tumours were found 4 h after CDDP treatment (581 fmol/mg) and dropped 1.8-fold after simultaneous treatment with dFdC ( P=0.04). Treatment with dFdC 4 h after or simultaneously with CDDP increased Pt retention (level 24 h after CDDP treatment) 1.4- and 1.6-fold ( P=0.04 and P=0.03, respectively). Peak Pt–DNA adduct levels in tumours were also found 4 h after CDDP treatment (7 fmol/μg DNA) and were decreased 3-fold by dFdC treatment 24 h prior to CDDP ( P=0.04). Pt–DNA adduct retention was only decreased when dFdC was given 4 h before CDDP (8-fold ( P<0.01)). The retention and the area-under the concentration–time curve of Pt–DNA adducts were related to decreased tumour doubling time (linear regression coefficient ( R)=0.95; P<0.05, 0.96 P=0.04 and 0.90; P=0.04. Pt–DNA adduct levels in the BM cells reached a plateau level 4–24 h after CDDP treatment (approximately 10 fmol/μg DNA), which was increased by dFdC when given either simultaneously with, 4 h before or 4 h after CDDP (6-, 3- and 5-fold at 28 h, 8 h and 28 h, respectively ( P⩽0.04)). Peak Pt–DNA adduct formation (24 h: 8 fmol/μg DNA) in kidneys was enhanced by dFdC when given simultaneously with or 4 h before CDDP (4 h timepoint) ( P<0.01). However, retention was 4- and 6-fold decreased when dFdC was given 4 or 24 h after CDDP, respectively ( P⩽0.01). dFdC given 24 h before CDDP decreased all Pt–DNA adduct levels in kidneys 3-fold or more ( P⩽0.03). Pt–DNA adduct levels were inversely related to kidney toxicity when the most toxic schedule was excluded from the analysis. Peak levels of total Pt in kidneys were reached 24 h after CDDP treatment (4.3 fmol/mg) and the 8 h levels were increased 2-fold by dFdC when given 4 h after CDDP ( P=0.07).

Sequence dependent effect of paclitaxel on gemcitabine metabolism in relation to cell cycle and cytotoxicity in non-small-cell lung cancer cell lines.

Gemcitabine and paclitaxel are active agents in the treatment of non-small-cell lung cancer (NSCLC). To optimize treatment drug combinations, simultaneously and 4 and 24 h intervals, were studied using DNA flow cytometry and multiple drug effect analysis in the NSCLC cell lines H460, H322 and Lewis Lung. All combinations resulted in comparable cytotoxicity, varying from additivity to antagonism (combination index: 1.0–2.6). Gemcitabine caused a S (48%) and G1 (64%) arrest at IC-50 and 10 × IC-50 concentrations, respectively. Paclitaxel induced G2/M arrest (70%) which was maximal within 24 h at 10 × IC-50. Simultaneous treatment increased S-phase arrest, while at the 24 h interval after 72 h the first drug seemed to dominate the effect. Apoptosis was more pronounced when paclitaxel preceded gemcitabine (20% for both intervals) as compared to the reverse sequence (8%, P = 0.173 for the 4 h and 12%, P = 0.051 for the 24 h time interval). In H460 cells, paclitaxel increased 2-fold the accumulation of dFdCTP, the active metabolite of gemcitabine, in contrast to H322 cells. Paclitaxel did not affect deoxycytidine kinase levels, but ribonucleotide levels increased possibly explaining the increase in dFdCTP. Paclitaxel did not affect gemcitabine incorporation into DNA, but seemed to increase incorporation into RNA. Gemcitabine almost completely inhibited DNA synthesis in both cell lines (70–89%), while paclitaxel had a minor effect and did not increase that of gemcitabine. In conclusion, various gemcitabine–paclitaxel combinations did not show sequence dependent cytotoxic effects; all combinations were not more than additive. However, since paclitaxel increased dFdCTP accumulation, gemcitabine incorporation into RNA and the apoptotic index, the administration of paclitaxel prior to gemcitabine might be favourable as compared to reversed sequences. © 2000 Cancer Research Campaign

Differential effects of gemcitabine on ribonucleotide pools of twenty-one solid tumour and leukaemia cell lines

To gain a more detailed insight into the metabolism of 2′,2′-difluoro-2′-deoxycytidine (dFdC, gemcitabine, Gemzar) and its effect on normal ribonucleotide (NTP) metabolism in relation to sensitivity, we studied the accumulation of dFdCTP and the changes in NTP pools after dFdC exposure in a panel of 21 solid tumour and leukaemia cell lines. Both sensitivity to dFdC and accumulation of dFdCTP were clearly cell line-dependent: in this panel of cell lines, the head and neck cancer (HNSCC) cell line 22B appeared to be the most sensitive, whereas the small cell lung cancer (SCLC) cell lines were the least sensitive to dFdC. The human leukaemia cell line CCRF-CEM accumulated the highest concentration of dFdCTP, whereas the non-SCLC cell lines accumulated the least. Not only the amount of dFdCTP accumulation was clearly related to the sensitivity for dFdC ( R=−0.61), but also the intrinsic CTP/UTP ratio ( R=0.97). NTP pools were affected considerably by dFdC treatment: in seven cell lines dFdC resulted in a 1.7-fold depletion of CTP pools, in two cell lines CTP pools were unaffected, but in 12 cell lines CTP pools increased about 2-fold. Furthermore, a 1.6–1.9-fold rise in ATP, UTP and GTP pools was shown in 20, 19 and 20 out of 21 cell lines, respectively. Only the UTP levels after treatment with dFdC were clearly related to the amount of dFdCTP accumulating in the cell ( R=0.64 ( P<0.01)), but not to the sensitivity to dFdC treatment. In conclusion, we demonstrate that besides the accumulation of dFdCTP, the CTP/UTP ratio was clearly related to the sensitivity to dFdC. Furthermore, the UTP levels and the CTP/UTP ratio after treatment were related to dFdCTP accumulation. Therefore, both the CTP and UTP pools appear to play an important role in the sensitivity to dFdC.

Mechanisms of synergism between cisplatin and gemcitabine in ovarian and non-small-cell lung cancer cell lines.

2′,2′-Difluorodeoxycytidine (gemcitabine, dFdC) and cis-diammine-dichloroplatinum (cisplatin, CDDP) are active agents against ovarian cancer and non-small-cell lung cancer (NSCLC). CDDP acts by formation of platinum (Pt)–DNA adducts; dFdC by dFdCTP incorporation into DNA, subsequently leading to inhibition of exonuclease and DNA repair. Previously, synergism between both compounds was found in several human and murine cancer cell lines when cells were treated with these drugs in a constant ratio. In the present study we used different combinations of both drugs (one drug at its IC25 and the other in a concentration range) in the human ovarian cancer cell line A2780, its CDDP-resistant variant ADDP, its dFdC-resistant variant AG6000 and two NSCLC cell lines, H322 (human) and Lewis lung (LL) (murine). Cells were exposed for 4, 24 and 72 h with a total culture time of 96 h, and possible synergism was evaluated by median drug effect analysis by calculating a combination index (CI; CI < 1 indicates synergism). With CDDP at its IC25, the average CIs calculated at the IC50, IC75 IC90 and IC95 after 4, 24 and 72 h of exposure were < 1 for all cell lines, indicating synergism, except for the CI after 4 h exposure in the LL cell line which showed an additive effect. With dFdC at its IC25, the CIs for the combination with CDDP after 24 h were < 1 in all cell lines, except for the Cls after 4 h exposure in the LL and H322 cell lines which showed an additive effect. At 72 h exposure all Cls were < 1. CDDP did not significantly affect dFdCTP accumulation in all cell lines. CDDP increased dFdC incorporation into both DNA and RNA of the A2780 cell lines 33- and 79-fold (P < 0.01) respectively, and tended to increase the dFdC incorporation into RNA in all cell lines. In the AG6000 and LL cell lines, CDDP and dFdC induced > 25% more DNA strand breaks (DSB) than each drug alone; however, in the other cell lines no effect, or even a decrease in DSB, was observed. dFdC increased the cellular Pt accumulation after 24 h incubation only in the ADDP cell line. However, dFdC did enhance the Pt–DNA adduct formation in the A2780, AG6000, ADDP and LL cell lines (1.6-, 1.4-, 2.9- and 1.6-fold respectively). This increase in Pt–DNA adduct formation seems to be related to the incorporation of dFdC into DNA (r = 0.91). No increase in DNA platination was found in the H322 cell line. dFdC only increased Pt–DNA adduct retention in the A2780 and LL cell lines, but decreased the Pt–DNA adduct retention in the AG6000 cell line. In conclusion, the synergism between dFdC and CDDP appears to be mainly due to an increase in Pt–DNA adduct formation possibly related to changes in DNA due to dFdC incorporation into DNA. © 1999 Cancer Research Campaign

Pharmacokinetic schedule finding study of the combination of gemcitabine and cisplatin in patients with solid tumors

To determine possible schedule dependent pharmacokinetic and pharmacodynamic interactions between gemcitabine (2',2'-difluorodeoxycytidine, dFdC) and cisplatin (cis-diammine-dichloroplatinum, CDDP) in patients with advanced stage solid tumors in a phase I trial. A total of 33 patients with advanced stage solid tumors were treated with gemcitabine (30-min infusion, 800 mg/m2) and cisplatin (one-hour infusion, 50 mg/m2). Sixteen patients had a four-hour interval between gemcitabine (days 1, 8, 15) and cisplatin (days 1 and 8), followed by the reverse schedule and seventeen patients had a 24-hour interval between gemcitabine (days 1, 8, 15) and cisplatin (days 2 and 9), followed by the reverse schedule. Gemcitabine and cisplatin pharmacokinetics were measured in plasma and white blood cells (WBC), isolated from blood samples taken at several time points after the start of treatment. A four-hour time interval between both agents did not reveal major differences in plasma pharmacokinetics of gemcitabine, dFdU (deaminated gemcitabine) and platinum (Pt), and of gemcitabine-triphosphate (dFdCTP) accumulation and Pt-DNA adduct formation in WBC between the two different sequences of gemcitabine and cisplatin. In the patients treated with the 24-hour interval, cisplatin before gemcitabine did not significantly change peak gemcitabine levels and the AUC of plasma dFdU, but tended to increase dFdCTP AUC in WBC 1.5-fold (P < 0.06). Gemcitabine before cisplatin decreased the plasma AUC of Pt 2.1-fold (P = 0.03). No significant differences in Pt-DNA adduct levels in WBC were found, although gemcitabine before cisplatin tended to increase the 24-hour retention of Pt-DNA adducts. Creatinine clearance on day 28 was related to the peak plasma levels of total Pt (linear regression coefficient (r) = 0.47, P = 0.02, n = 26). Furthermore, the increase in the Pt-GG to Pt-AG ratio 24 hours after cisplatin treatment was related to the overall response of patients (r = 0.89, P < 0.01, n = 8). Of all schedules the treatment of patients with cisplatin 24 hours before gemcitabine led to the highest dFdCTP accumulation in WBC and total Pt levels in plasma. These characteristics formed the basis for further investigation of this schedule in a phase II clinical study.

Decreased resistance to gemcitabine (2′,2′-difluorodeoxycitidine) of cytosine arabinoside-resistant myeloblastic murine and rat leukemia cell lines: role of altered activity and substrate specificity of deoxycytidine kinase

We determined the potential activity of 2′,2′-difluorodeoxycytidine (gemcitabine, dFdC) in 1-β- d-arabinofuranosylcytidine (ara-C)-sensitive and-resistant leukemia cell lines. Both drugs are phosphorylated by deoxycytidine kinase (dCK); the triphosphates, dFdCTP and ara-CTP, respectively, are incorporated into DNA. In the murine leukemia cell line L1210, induction of resistance to ara-C resulted in the 2200-fold resistant subline L4A6. The Brown Norway rat myelocytic leukemia ara-C-sensitive cell line (BCLO) was >300-fold more sensitive to ara-C than its variant Bara-C. In L1210 cells, gemcitabine was 8-fold more active than ara-C; in L4A6, BCLO, and Bara-C cells, gemcitabine was 16-, 28-, and more than 3-fold more active than ara-C, respectively. A partial explanation for these differences may be the higher dCK activity in the parental cell lines L1210 and BCLO with gemcitabine compared to ara-C as a substrate. DCK activity was not or hardly detectable in the resistant L4A6 and Bara-C cell. In the rat leukemia cell lines, deoxycytidine (dCyd) phosphorylation activity showed an aberrant pattern, since the activity with dCyd was 1.5-fold higher in the Bara-C cell line compared with BCLO, possibly due to thymidine kinase 2. The wild-type L1210 cells accumulated at least 3-fold more ara-CTP and dFdCTP than the rat leukemia cell line BCLO. The ara-C-resistant variants L4A6 and Bara-C did not accumulate dFdCTP or ara-CTP. In conclusion, gemcitabine was more active than ara-C in all leukemia cell lines tested. The sensitivity of the wild-type cell lines correlates with the accumulation of dFdCTP and ara-CTP, but is independent of dCK. However, both resistant variants had decreased dCK activities, but were relatively more sensitive to dFdC than to ara-C.