G.J. Peters

Antitumor activity of prolonged as compared with bolus administration of 2@,2@-difluorodeoxycytidine in vivo against murine colon tumors

Abstractu20022′,2′-Difluorodeoxycytidine (gemcitabine) is a cytidine analogue with established antitumor activity against several experimental tumor types and against human ovarian and non-small-cell lung cancer. Both preclinical studies and most clinical trials involving patients with solid tumors have focused on short-term administration schedules; however, mechanistic studies indicate that a continuous-infusion schedule may be more effective. We determined the maximal tolerated dose (MTD) of gemcitabine in mice using various schedules. At these MTDs we observed considerably better antitumor activity of gemcitabine in two of three murine colon carcinoma lines using a prolonged administration as compared with a standard bolus protocol (i.p. 120u2005mg/kg q3d×4). On the latter schedule, Colon 26–10 grown in BALB/c mice was the most sensitive tumor line, showing a growth-delay factor (GDF, number of doubling times gained by the treatment) of 6.7, whereas Colon 38 (grown in C57/B16 mice) was the least sensitive tumor, displaying a GDF of 0.9. Prolonged treatment (q3d×6) of Colon 26–10 at a lower dose (100u2005mg/kg) enhanced the antitumor activity (GDF 9.6) while producing similar toxicity. A similar weight loss was found following the continuous infusion (c.i.) of gemcitabine using Alzet osmotic pumps s.c. for 3 or 7 days (2u2005mg/kg), but the GDF increased to 2.4 in Colon 38 (C57/B16) as compared with that provided by the bolus injections. Continuous infusion of gemcitabine at 15u2005mg/kg per 24u2005h q7d×2 i.v. via the tail vein was more effective than bolus injection against Colon 26–10, with the GDF being >17.7 and 73% of the tumors regressing completely. However, against Colon 38 tumors this schedule was not effective (GDF 0.4), even with a 25% higher dose. The plasma pharmacokinetics of gemcitabine was determined after one bolus dose (120u2005mg/kg). The peak concentration of gemcitabine was 225u2005μM and that of the deaminated catabolite 2′,2′-difluorodeoxyuridine (dFdU) was 79u2005μM. The elimination of gemcitabine was much faster than that of dFdU, with the t1/2ß values being 15u2005min and 8u2005h, respectively. For the c.i. schedules, plasma concentrations were below the detection limit of the assay (<0.5u2005μM). Our results suggest that prolonged infusion of gemcitabine can give a better antitumor activity than bolus injections and shows promise of being active in clinical trials.

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 25u2009μM 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 24u2009h exposure to 0.1u2009μM 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.

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

PURPOSEnTo 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.nnnPATIENTS AND METHODSnA 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.nnnRESULTSnA 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).nnnCONCLUSIONSnOf 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.

Gemcitabine–cisplatin: A schedule finding study

PURPOSEnTo evaluate the tolerability of four alternating cisplatin-gemcitabine schedules. A secondary aim was to evaluate the clinical efficacy of this combination.nnnPATIENTS AND METHODSnForty-one patients with advanced solid tumors received alternating sequences with a 4- and 24-hour interval of cisplatin and gemcitabine. Gemcitabine 800 mg/m2 was administered as a 30-min infusion on day 1, 8 and 15, and cisplatin 50 mg/m2 over 1 hour on day 1 and 8; in case of the 24-hour time interval the second drug was administered one day later. Four cisplatin-gemcitabine schedules were studied: gemcitabine four hour before cisplatin (10 patients), or vice versa (14 patients) and gemcitabine twenty-four hours before cisplatin (9 patients) or vice versa (8 patients). The sequence of drug administration was reversed in the second cycle of therapy in each individual patient, enabling the evaluation of sequence-dependent side effects. Twenty-six patients had received prior chemotherapy, of which twenty-one platinum-based.nnnRESULTSnThe main toxicity was myelosuppression. Overall, grade 3 and 4 thrombocytopenia was observed in 27 out of 41 patients (66%) and was not schedule dependent. No serious bleeding occurred. Leukopenia was significantly different between the 4 alternating schedules (P = 0.01); gemcitabine 24 hours before cisplatin was significantly less toxic compared to both cisplatin 4 hours and 24 hours before gemcitabine (P = 0.01 and P = 0.003, respectively). Furthermore, paired analysis of the 4-hour and 24-hour data sets showed that leukopenia was significantly more serious when cisplatin preceded gemcitabine (P = 0.005). Although most patients received prior treatment, both prior chemotherapy and radiotherapy were not related to toxicity. Overall, grade 3 and 4 leukopenia occurred in 19 out of 41 patients (46%). Anemia (Hb < or = 6.0 mmol/l) was not sequence dependent and was observed in 63% of patients. Myelotoxicity was cumulative between cycles and caused frequent omission of gemcitabine on day 15. Overall, in 51% of administered cycles there was no omission of gemcitabine. A mean of 3.5 therapy cycles was administered. Non-hematological toxicity was moderate, consisting mainly of grade 1 and 2 nausea/vomiting and fatigue, and was not schedule dependent. Recently, we described that the schedule in which cisplatin was administered 24 hours before gemcitabine produced the best pharmacological profile. Based on this and because toxicity was manageable, the schedule cisplatin 24 hours prior to gemcitabine was chosen for phase II evaluation. Nine out of thirty-six evaluable patients had an objective response. These responses were observed in head and neck squamous-cell carcinoma (HNSCC), non-small-cell lung cancer (NSCLC), melanoma, adenocarcinoma of unknown origin, ovarian and esophageal carcinoma.nnnCONCLUSIONSnMyelosuppression was the most important toxicity. Leukopenia was schedule dependent: gemcitabine before cisplatin was less toxic than the reversed sequence, in this respect. Some encouraging responses were seen in patients with esophageal cancer. Currently, a phase II study with cisplatin 24 hours before gemcitabine is ongoing in patients with advanced upper gastro-intestinal tumors.

Gemcitabine uptake in glioblastoma multiforme: potential as a radiosensitizer

Glioblastoma multiforme (GBM), the most frequent malignant brain tumor, has a poor prognosis, but is relatively sensitive to radiation. Both gemcitabine and its metabolite difluorodeoxyuridine (dFdU) are potent radiosensitizers. The aim of this phase 0 study was to investigate whether gemcitabine passes the blood-tumor barrier, and is phosphorylated in the tumor by deoxycytidine kinase (dCK) to gemcitabine nucleotides in order to enable radiosensitization, and whether it is deaminated by deoxycytidine deaminase (dCDA) to dFdU. Gemcitabine was administered at 500 or 1000 mg/m(2) just before surgery to 10 GBM patients, who were biopsied after 1-4 h. Plasma gemcitabine and dFdU levels varied between 0.9 and 9.2 microM and 24.9 and 72.6 microM, respectively. Tumor gemcitabine and dFdU levels varied from 60 to 3580 pmol/g tissue and from 29 to 72 nmol/g tissue, respectively. The gene expression of dCK (beta-actin ratio) varied between 0.44 and 2.56. The dCK and dCDA activities varied from 1.06 to 2.32 nmol/h/mg protein and from 1.51 to 5.50 nmol/h/mg protein, respectively. These enzyme levels were sufficient to enable gemcitabine phosphorylation, leading to 130-3083 pmol gemcitabine nucleotides/g tissue. These data demonstrate for the first time that gemcitabine passes the blood-tumor barrier in GBM patients. In tumor samples, both gemcitabine and dFdU concentrations are high enough to enable radiosensitization, which warrants clinical studies using gemcitabine in combination with radiation.

5-Fluorouracil induced Fas upregulation associated with apoptosis in liver metastases of colorectal cancer patients

BACKGROUNDnIn vitro, thymidylate synthase (TS) inhibition by 5-fluorouracil (5-FU) induces thymineless apoptosis possibly via Fas receptor Fas ligand interactions and cell-cycle arrest. In colorectal cancer patients we evaluated whether 5-FU administration also resulted in apoptosis and cell-cycle arrest and which proteins might be involved.nnnPATIENTS AND METHODSnBiopsy specimens were taken from 36 patients 2, 22 or 46 hours after administration of 500 mg/m2 5-FU, and from 12 control patients who did not receive 5-FU. In frozen tissue-sections from liver metastases immunohistochemistry was performed with antibodies directed against p53, p21, E2F2, Rb, Ki67 and TS (cell-cycle related) and bax, BCL-2, BCL-x, mcl-1, PARP, caspase-3, Fas receptor and Fas ligand (apoptosis related). Apoptosis was determined by M30 immunostaining, which recognises a cleavage product of cytokeratin 18.nnnRESULTSnFas receptor expression was 50% higher (P = 0.036) 46 hours after 5-FU administration compared to the control group. This was associated with a 12% increase (P < 0.02) in M30 positive tumour cells and with elevation of caspase-3 and PARP expression. The expression of Ki67 and E2F2 was 30% lower after 46 hours compared to the control group, whereas TS was 56% lower after 2 hours and 32% higher again after 46 hours. No differences in the expression of the other proteins were found.nnnCONCLUSIONSnThese results suggest that 5-FU decreases proliferation status and induces apoptosis possibly via the Fas pathway. Since Fas mediated cell killing is important for cytotoxic T cells this indicates that clinical studies combining immunotherapy for activation of T cells and chemotherapy using 5-FU might be very effective.

Rb, mcl-1 and p53 expression correlate with clinical outcome in patients with liver metastases from colorectal cancer

BACKGROUNDnThymidylate synthase (TS) has been associated with clinical outcome in disseminated colorectal cancer. However, many patients with low TS expression still fail to respond to treatment. Therefore, we studied the cell cycle proteins, Rb, E2F2, Ki67, p21 and p53 and the apoptotic proteins, mcl-1, hax, bcl-xl, bcl-2, Fas receptor, Fas ligand, caspase-3, M30 and PARP as potential predictive factors.nnnPATIENTS AND METHODSnIn biopsy specimens of liver metastases from 31 colorectal cancer patients, protein expression was retrospectively determined by immunohistochemistry and related to response to hepatic arterial or intravenous (i.v.) 5-fluorouracil (5-FU) treatment, time to tumour progression (TTP) and overall survival.nnnRESULTSnExpression of both p53 and Rb correlated with survival benefit after 5-FU treatment. A median survival time of 79 weeks was found in patients with high levels of p53 or Rb compared to 36 and 44 weeks for patients expressing low levels of p53 (P = 0.027) or Rb (P = 0.030), respectively. Multivariate analysis showed that p53 was the best predictor of survival independent of sex, age or prior treatment. Following 5-FU hepatic arterial infusion, patients with a high TS expression had a shorter survival time than those with a low expression (P = 0.025). The anti-apoptotic protein mcl-1 was the only factor, which correlated with response to 5-FU treatment. Thirty-five percent of patients with a diffuse mcl-1 expression responded whereas ninety percent of patients with a peri-nuclear expression responded (P = 0.041).nnnCONCLUSIONSnThese results indicate that besides TS, also Rb, p53 and mcl-1 are correlated with clinical outcome in patients with liver metastases from colorectal cancer.

Cross-resistance in the 2′,2′-difluorodeoxycytidine (gemcitabine)-resistant human ovarian cancer cell line AG6000 to standard and investigational drugs

Gemcitabine (2-2-difluorodeoxycytidine; dFdC) is a deoxycytidine analogue which is effective against solid tumours, including lung cancer and ovarian cancer. dFdC requires phosphorylation by deoxycytidine kinase (dCK) for activation. In the human ovarian cancer cell line A2780 and its 30,000-fold dFdC-resistant variant AG6000 (P<0.001), we investigated the cross-resistance profile to several drugs. AG6000, which has a complete dCK deficiency, was approximately 1000-10,000-fold resistant to other deoxynucleoside analogues such as 1-beta-D-arabinofuranosyl cytosine, 2-chloro-deoxyadenosine, aza-deoxycytidine and 2, 2-difluorodeoxyguanosine (dFdG) (P<0.001). dFdG can be activated by dCK and deoxyguanosine kinase (dGK), but the latter enzyme was not altered in AG6000 cells. Thus dFdG resistance was only due to dCK deficiency. AG6000 was 1.6- and 46.7-fold resistant to 5-fluorouracil (5-FU) and ZD1694, respectively (the latter was significant; P<0.01), which may be due to the 1.7-fold higher thymidylate synthase (TS) activity, but AG6000 cells were also 2. 7-fold resistant to the lipophilic TS inhibitor AG337 (P<0.05). Remarkably, AG6000 cells were 2.5-fold more sensitive to methotrexate (MTX) (P<0.01) than A2780 cells, but 1.6-fold more resistant to trimetrexate (TMQ) (P<0.10). However, no differences in reduced folate carrier activity, folylpolyglutamate synthetase (FPGS) activity and polyglutamation of MTX were found between the cell lines. AG6000 cells were approximately 2 to 7.5-fold more resistant to doxorubicin (DOX), daunorubicin (DAU), epirubicin and vincristine (VCR) (the latter was significant; P<0.02) and approximately 4-fold more resistant to the microtubule inhibitors paclitaxel and docetaxel (P<0.001). Fluorescent activated cell sorter (FACS) analysis revealed no P-glycoprotein (Pgp) or multidrug resistance-associated protein (MRP) expression, but less fluorescence of intercalated DAU in AG6000 cells. An approximately 2-fold resistance to the topoisomerase I and II inhibitors etoposide, CPT-11 and SN38 was found in AG6000 cells. Topoisomerase I and IIalpha RNA expression was decreased in AG6000 cells. AG6000 was 2.4, 2.4, 2.3 and 3.7-fold more resistant to EO9 (P<0.02), mitomycin-C (MMC) (P<0.05), cisplatin (CDDP) (P<0.10) and maphosphamide (MAPH), respectively. DT-diaphorase (DTD), which activates EO9, was 2.2-fold lower in AG6000 cells. CDDP resistance might be related to a reduced retention of DNA adducts in AG6000. However, glutathione levels were equal in A2780 and AG6000 cells. A 24 h exposure to DOX, VCR and paclitaxel at equimolar and equitoxic concentrations, resulted in more double-strand breaks (1.5- to 2-fold) in A2780 than in AG6000 cells. MAPH at 1120 nM and 17 nM of EO9 did not cause DNA damage in either cell line. In conclusion, AG6000 is a cell line highly cross-resistant to a wide variety of drugs. This cross-resistance might be related to altered enzyme activities and/or increased DNA repair.

Synergistic interaction of novel lactate dehydrogenase inhibitors with gemcitabine against pancreatic cancer cells in hypoxia.

Background:Hypoxia is a driving force in pancreatic-ductal-adenocarcinoma (PDAC) growth, metastasis and chemoresistance. The muscle-isoform of lactate dehydrogenase (LDH-A) constitutes a major checkpoint for the switch to anaerobic glycolysis, ensuring supply of energy and anabolites in hypoxic-environments. Therefore, we investigated the molecular mechanisms underlying the pharmacological interaction of novel LDH-A inhibitors in combination with gemcitabine in PDAC cells.Methods:Lactate dehydrogenase A levels were studied by quantitative RT–PCR, western blot, immunofluorescence and activity assays in 14 PDAC cells, including primary-cell-cultures and spheroids, in normoxic and hypoxic conditions. Cell proliferation, migration and key determinants of drug activity were evaluated by sulforhodamine-B-assay, wound-healing assay, PCR and LC-MS/MS.Results:Lactate dehydrogenase A was significantly increased under hypoxic conditions (1% O2), where the novel LDH-A inhibitors proved to be particularly effective (e.g., with IC50 values of 0.9 vs 16.3u2009μM for NHI-1 in LPC006 in hypoxia vs normoxia, respectively). These compounds induced apoptosis, affected invasiveness and spheroid-growth, reducing expression of metalloproteinases and cancer-stem-like-cells markers (CD133+). Their synergistic interaction with gemcitabine, with combination index values <0.4 in hypoxia, might also be attributed to modulation of gemcitabine metabolism, overcoming the reduced synthesis of phosphorylated metabolites.Conclusion:Lactate dehydrogenase A is a viable target in PDAC, and novel LDH-A inhibitors display synergistic cytotoxic activity with gemcitabine, offering an innovative tool in hypoxic tumours.

Postconfluent multilayered cell line cultures for selective screening of gemcitabine

The in vitro cytotoxicity of gemcitabine (dFdC) was tested in ovarian and colon cancer cell lines grown as monolayers and three-dimensional multilayered cell cultures. In our model, dFdC showed slight selectivity in cytotoxicity against ovarian over colon cancer cells, when cell lines were grown as monolayers. However, when cell lines were grown as multilayers, this selectivity was accentuated: A2780 multilayers were 14 times less sensitive than monolayers, but the colon cancer cell lines were more than 1000 times more resistant than their corresponding monolayers. The accumulation of the active metabolite, dFdCTP, after 24 h exposure to 1 microM dFdC varied between 1100 and 1900 pmol/10(6) cells in monolayers. This was 5 times lower in multilayers compared with monolayers of all four cell lines, which can, in part, explain the lower sensitivity of the multilayers. In addition, it appears that the amount of the active metabolite retained is more important than the amount accumulated initially, since the differences between the ovarian and the colon cancer cell lines were more evident in retention experiments. Exposure to dFdC caused a 2-3-fold increase in the levels of several nucleotides, except for the CTP pools in the colon cancer lines, which were reduced by 3-fold at the highest dFdC concentration (10 microM). The findings with the multilayer model are in better agreement with in vivo activity in ovarian cancer and colon cancer than those with the monolayer system. This indicates the potential of the multilayer system to be a better predictive model than the conventionally used monolayer cultures.