Gemcitabine Metabolism Research Articles

Abstract 4168: Comprehensive characterisation of a newly established patient-derived pancreatic adenocarcinoma xenograft collection

Abstract There is a high medical need to identify new treatments for patients with pancreatic cancer, since in many cases only palliative treatment is possible. The standard 1st line chemotherapy in inoperable, locally advanced (stage II and III) and metastatic (stage IV) adenocarcinoma of the pancreas is Gemcitabine as a single agent with a median survival of about 6 month. In addition, Gemcitabine is indicated as adjuvant chemotherapy after surgery. Although the anti-metabolite 5-Flourouracil (5-FU) and the EGF-R inhibitor Tarceva (Erlotinib) have been approved for 2nd line treatment, new and more efficient drugs are urgently needed. In the present study, more than 60 samples of pancreatic carcinomas were transplanted subcutaneously (s.c.) into NMRI nude mice directly after tumor resection. In most cases, tumor material from chemonaive patients with defined histology and staging was used for implantation. Up to now, 17 tumor models were passaged in nude mice and characterized comprehensively. In general, the histology of the primary tumor was comparable to that of the established xenograft. Chemosensitivity in vivo was evaluated by treatment of tumor bearing nude mice with 5-FU (100 or 75mg/kg, q7dx3, i.p.), Gemcitabine (240mg/kg, q7dx3, i.v.) and Erlotinib (25 and 50mg/kg, qdx21, p.o.). In general, tumor growth was not inhibited with best T/C values >50% highlighting the general chemoresistance of pancreatic cancer. Only for two models (PAXF 1872 and PAXF 1998), a high sensitivity towards Gemcitabine was evident with best T/C values of 8% and 3.8%, respectively. There was no correlation to the transcriptional levels of proteins involved in transportation and metabolism of Gemcitabine. Concerning Erlotinib, best T/C values were ranging from 89.6% (PAXF 1876) to 38.5% (PAXF 1982) with no correlation to EGFR expression status. A more broad chemosensitivity profile was established with the ex-vivo clonogenic assay. Interestingly, several tumors responded strongly to treatment with Rapamycin (IC50 ≤ 10nM). Based on this data, in vivo treatment experiments with RAD001 (Everolimus) were done and data are presented. Mutational analysis of p53 (exons 4 to 10) revealed only 4 out of 13 models as p53 wild-type. Nevertheless, the p53 pathway is dysregulated in all tumor models and for selected tumors, an aneuploid cell population was identified by ex vivo cell cycle analysis. In summary, a unique collection of patient-derived pancreatic xenograft models of high clinical relevance has been established. These models are available for translational research studies including in-vivo efficacy testing of new investigational drugs. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4168.

Abstract 4549: Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice

Abstract Introduction Cytidine drugs, such as gemcitabine, undergo rapid, inactivating catabolism by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine drug metabolism. However, p.o. THU is at most 20% bioavailable (Beumer et al.), which limits its preclinical evaluation and clinical use. Therefore, the more lipophilic prodrug triacetyl THU (taTHU) was developed. We characterized THU pharmacokinetics after administration of taTHU to mice. Methods Mice were dosed 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters and p.o. bioavailability were calculated non-compartmentally and compartmentally. We assessed taTHU inhibition of metabolism of gemcitabine by recombinant CD. ResultsTHU parameterstaTHU i.v. 150 mg/kgtaTHU p.o. 150 mg/kgCmax (µg/mL)10611.8Tmax (min)560Half-life (min)235122AUC0-inf (mg/mL*min)7.553.36Vd/F (L/kg)4.495.26Cl/F (mL/min/kg)13.229.8F-THUi.v. (%)68.030.3% dose in 0-16 h urine405.6% dose in 0-24 h urine5512 THU, after 150 mg/kg taTHU i.v., had a 235 min terminal half-life and produced plasma THU concentrations >1 µg/mL, the concentration shown to inhibit CD, for 10 h. A multi-compartment model fit the data best. 150 mg/kg p.o. taTHU produced a concentration versus time profile with a plateau of approximately 10 µg/mL from 0.5-2 h, followed by a decline with a 122 min half-life. Approximately 68% of i.v. taTHU was converted to THU. Approximately 30% of p.o. taTHU reached the systemic circulation as THU. After i.v dosing, renal excretion accounted for 40-55% of the taTHU dose, 26-35% as THU and an additional 14-19% as acetylated forms of THU. After p.o. dosing, the renal excretion percentages were 6-12%, 5.2-11%, and 0.42-0.71%, respectively. taTHU did not inhibit recombinant CD. Conclusion The availability of THU after p.o. taTHU in mice is 30%, as compared to the 20% achieved after p.o. THU. Clinical studies are warranted to evaluate availability of THU from taTHU in humans. Support: N01-CM07106, N01-CM52202, P30-CA47904 from the NCI and P41-EB001978. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4549.

Imexon enhances gemcitabine cytotoxicity by inhibition of ribonucleotide reductase

Gemcitabine (GEM) is currently the standard first line treatment for pancreatic cancer; however, the overall survival of patients with this disease remains poor. Imexon is a pro-oxidant small molecule which produced a high response rate in combination with GEM in a phase I trial in pancreatic cancer. In this study, we investigate the combination of GEM with a novel redox-active agent, imexon, in vitro and in vivo. Median effect analysis was used for in vitro combination cytotoxicity. The effect of imexon on GEM metabolism and uptake into cells and into DNA and effects on ribonucleotide reductase (RNR) were examined in vitro. The pharmacokinetics and antitumor efficacy of the imexon/GEM combination was evaluated in mouse models. In three human pancreatic cancer lines, there was additivity for the imexon/GEM combination. There was significantly greater efficacy for the drug combination in Panc-1 xenograft tumors. A pharmacokinetic study in mice showed a near doubling in the AUC of imexon when GEM was co-administered, with no effect of imexon on GEM's pharmacokinetic disposition. In vitro, imexon did not alter GEM's metabolism or uptake into DNA, but significantly inhibited RNR, and this effect was greater when combined with GEM. These results suggest that the interaction between imexon and GEM may be due to complimentary inhibition of RNR plus an enhanced exposure to imexon when the GEM is administered in vivo. This combination is currently being tested in a randomized phase II trial in pancreatic cancer.

Expression of nucleoside transporters, deoxycitidine kinase, ribonucleotide reductase regulatory subunits, and gemcitabine catabolic enzymes in primary ovarian cancer

Gemcitabine (2',2'-difluorodeoxycytidine) (GEM) is one of the most actively investigated drugs in ovarian cancer. Many molecular mechanisms have been proposed to be involved in GEM sensitivity/resistance including the equilibrative nucleoside transporter-1 (hENT1), the concentrative nucleoside transporter-1 (hCNT1), and deoxycytidine kinase (dCK). The expression of the ribonucleotide reductase regulatory subunits M1 (RRM1) and M2 (RRM2), and the catabolic enzymes 5'nucleotidase (5'NT), and cytidine deaminase (CDA) play also an important role. The aim of the study is to investigate the potential clinical role of hENT1, hCNT1, dCK, RRM1, RRM2, CDA, and 5'NT in a single institutional series of 25 primary ovarian carcinomas. The expression levels of the target genes were assayed by means of real-time quantitative PCR. The clinical role of the expression levels of each parameter was analyzed by Kaplan and Meier method and the Cox's proportional hazards model. hENT1, hCNT1, dCK, CDA, 5'NT, RRM1, and RRM2 gene expression was documented in all samples; undifferentiated and clear cell carcinoma exhibited higher levels of hENT1, dCK, 5'NT, and RRM1 compared to serous ovarian tumors. As of May 2009, the median follow-up was 32 months (range 10-80), and death of disease were observed in 17 cases (68.0%). A statistically significant direct association of RRM2 expression levels and the relative risk of death was observed (Chi (2) = 8.18, P = 0.0043). Moreover, cases with high RRM2 expression had a shorter OS (median OS = 19 months) than cases with low RRM2 levels (median OS = 36 months) (P = 0.0506). We first reported that the most relevant genes involved in gemcitabine metabolism are expressed in ovarian carcinoma, and might be associated with more aggressive histotypes. The assessment of the expression levels of RRM2 as marker of clinical outcome deserves further investigation in a larger series of ovarian cancer patients.

Paclitaxel alters the expression and specific activity of deoxycytidine kinase and cytidine deaminase in non-small cell lung cancer cell lines

BackgroundWe observed that paclitaxel altered the pharmacokinetic properties of gemcitabine in patients with non-small cell lung cancer (NSCLC) and limited the accumulation of gemcitabine and its metabolites in various primary and immortalized human cells. Therefore, we classified the drug-drug interaction and the effects of paclitaxel on deoxycytidine kinase (dCK) and cytidine deaminase (CDA) in three NSCLC cell lines. These enzymes are responsible for the metabolism of gemcitabine to its deaminated metabolite dFdU (80% of the parent drug) and the phosphorylated metabolites dFdCMP, dFdCDP and dFdCTP. These metabolites appear to relate to sensitivity and tolerability of gemcitabine based on previous animal and laboratory studies.MethodsThree immortalized human cells representative of the most common histological subtypes identified in patients with advanced NSCLC were exposed to the individual drugs or combinations to complete a multiple drug effect analysis. These same cell lines were exposed to vehicle-control or paclitaxel and the mRNA levels, protein expression and specific activity of dCK and CDA were compared. Comparisons were made using a two-tailed paired t-test or analysis of variance with a P value of < 0.05 considered significant.ResultsThe multiple drug effect analysis indicated synergy for H460, H520 and H838 cells independent of sequence. As anticipated, paclitaxel-gemcitabine increased the number of G2/M cells, whereas gemcitabine-paclitaxel increased the number of G0/G1 or S cells. Paclitaxel significantly decreased dCK and CDA mRNA levels in H460 and H520 cells (40% to 60%, P < 0.05) and lowered dCK protein (24% to 56%, P < 0.05) without affecting CDA protein. However, paclitaxel increased both dCK (10% to 50%) and CDA (75% to 153%) activity (P < 0.05). Paclitaxel caused substantial declines in the accumulation of the deaminated and phosphorylated metabolites in H520 cells (P < 0.05); the metabolites were not measurable in the remaining two cell lines. The ratio of dCK to CDA mRNA levels corresponded to the combination index (CI) estimated for sequential paclitaxel-gemcitabine.ConclusionIn summary, paclitaxel altered the mRNA levels and specific activity of dCK and CDA and these effects could be dependent on histological subtype. More cell and animal studies are needed to further characterize the relationship between mRNA levels and the overall drug-drug interaction and the potential to use histological subtype as a predictive factor in the selection of an appropriate anticancer drug regimen.

Correlation of RRM1 expression in muscle invasive locally advanced urothelial cancer with age

e16021 Background: RRM1, the regulatory subunit of ribonucleotide reductase, plays a role in DNA repair after chemotherapy damage and in gemcitabine metabolism. Prior studies demonstrated a survival benefit to high expression in resected early stage lung cancer and a trend toward longer time to progression with low expression in advanced bladder cancers treated with gemcitabine and cisplatin. We hypothesized that patients with resected locally advanced (T2–4NxM0) urothelial transitional cell carcinoma (TCC) whose tumors had higher RRM1 expression would have longer overall survival (OS). Methods: 84 radical cystectomy specimens with muscle invasive TCC were identified from existing tissue microarrays (TMAs) containing 343 specimens. The medical records of these patients were retrospectively reviewed to confirm pathology and stage. Presence of muscle invasion was required. Specimens were analyzed for RRM1 expression using AQUA. The median value of RRM1 was established a priori as the cutoff for high and low expression. Results: Median age of the patients was 69.3 years. There was near equal distribution of stages: 30%, 38%, and 32% for stage II, III, and IV respectively. The majority were high grade (99%) with no nodal involvement (69%). Median OS was 2.0 years (0–13.1). Median RRM1 expression was 1493.3. Degree of RRM1 expression did not correlate with OS, but when adjusted for age, adding an interaction term, high RRM1 expression in younger patients correlated with increased OS (p = 0.0278). Median OS for high expressors age &lt;69.3 years was 6 years compared to 2.3 years for low expressors. 35% of patients less than 70 years were high expressors. Conclusions: Our results suggest that high RRM1 expression may be a prognostic factor for improved survival in locally advanced TCC patients less than 70 years old. These results deserve further study in a larger prospective analysis with disease-specific survival assessment and correlation with other possible prognostic genes such as ERCC1. [Table: see text]

Pharmacogenomic analysis of the triplet combination of gemcitabine, oxaliplatin, and cetuximab as salvage therapy for metastatic colorectal cancer (mCRC) patients

e14531 Background: We have previously reported that biweekly gemcitabine-based therapy was active in pretreated mCRC pts (De la Cruz et al, ASCO GI 2008, abstr 377). We aimed to investigate whether germ line polymorphisms may be predictors of clinical outcome in mCRC pts treated with this combination. Methods: We evaluated SNPs of genes involved in gemcitabine metabolism (CDA, dCDK, RRM1, DCTD, SLC28A1), DNA repair (XRCC1, XRCC 3, ERCC1, XPD) and two IgG Fcγ R polymorphisms (Fcγ RIIa- H131R and Fcγ RIIIa-V158F), reported to be predictive of cetuximab-based therapy, even in K-ras mutated pts. Whole blood was collected and DNA extracted from peripheral lymphocytes using a DNA isolation Kit (Qiagen, CA). Polymorphisms were detected using the TaqMan genotyping assays (Applied Biosystems, CA). Clinical response was evaluated according to RECIST criteria. Univariate analysis (Fisher´s exact test for response; log-rank test for TTP and OS) was performed to examine associations between polymorphisms and clinical outcome. Results: Blood samples of 35 out of 39 enrolled pts were tested for genomic analysis. Patient‘s characteristics are as follows; M/F: 26/13, median age: 59 years, median number of prior chemotherapy lines: 2 (1–4), Köhne risk groups; low: 8 pts, intermediate: 18 pts, high: 13 pts. After a median follow-up of 20 months, median progression-free survival (PFS) is 6.7 months (95% CI; 5.2–8.3) and median overall survival 15.4 m (95% CI; 14.7–16.1). Overall response rate (ORR) was 53.8%. RRM1 R284R SNPs (p=0.06), T741T (p=0.02) and RRM1–524CT (p=0.04) were linked to clinical responsiveness. All pts possessing 2 or 3 favourable RRM1 SNPs responded. ORR was 53.3% for pts with no favourable SNPs versus 85% for pts with any favourable SNP (p=0.04). ORR was also significantly higher in pts with any histidine allele in the Fcγ RIIa polymorphism (93% vs. 60%, p=0.034). Median PFS was adversely affected in pts harbouring no favourable RRM1 SNPs (4.2m versus 6.7 months, p=0.019) and in those pts with homozygous Fcγ RIIa-131R allele (4.4 vs. 7.5 months, p=0.007). Conclusions: Polymorphic variants of RRM1 and Fcγ RIIa may play a key role in the efficacy of gemcitabine and cetuximab-based therapy for mCRC pts. No significant financial relationships to disclose.

Phase I study of oral gemcitabine prodrug (LY2334737) alone and in combination with erlotinib in patients (pts) with advanced solid tumors

2576 Background: LY2334737 (LY) is an orally available valproic acid prodrug of gemcitabine that was developed to overcome the extensive first-pass metabolism of gemcitabine to 2',2'-difluorodeoxyuridine (dFdU). The objectives of this study were to determine the maximum tolerated dose (MTD), dose limiting toxicity (DLT) and pharmacokinetics (PK) of LY as monotherapy and in combination with erlotinib. Methods: Eligible pts had ECOG PS &lt; 2 and adequate hematologic, renal and hepatic function. In Arm A, LY was given daily for 14 days in a 3-week cycle. Pts assigned to Arm B also received erlotinib daily 100 mg continuously. Dose escalation was based on observed toxicity and the modified continual reassessment method (mCRM). The dose was maximally increased by 100% depending on the toxicity observed in the previous cohort. PK of LY, gemcitabine, dFdU and intracellular metabolites were determined. Results: 33 pts (21 m, 12 f, median age 60 yrs (range 24–81)) were treated at 5 different dose-levels (range 5–50 mg/day). Pts received a median of 3 cycles (range 2–17). Three out of 7 pt treated with 50 mg experienced 5 dose limiting toxicities (DLT). DLTs observed at 40 and 50 mg include fatigue (4 pt), thrombocytopenia (1 pt), GGT elevation (1 pt), AST/ALT elevation (1 pt), fever (1 pt), and pulmonary embolism (1 pt). One death was possibly related to LY intake. This pt, treated with 40 mg LY, developed on day 15 dyspnea, hypovolemic shock, and suddenly died. No grade 3 or 4 toxicities were reported at dose-levels &lt; 40 mg. The most common adverse events were fatigue, vomiting, nausea, pyrexia, anorexia, and diarrhea. Two pts with mesothelioma were stable for &gt; 9 months. One pt with refractory prostate cancer presented a PSA CR as assessed by investigator. The PK show dose-proportional increase in exposure of both LY and gemcitabine. Both LY and gemcitabine are rapidly cleared, thus no accumulation occurs. The metabolite dFdU accumulates due to its long half life. Conclusions: LY displays linear PK. The dose level of 50-mg is non-tolerable and 40-mg is being confirmed as the MTD as single agent and in combination with 100 mg erlotinib. Antitumor activity warrants further development. Pt accrual is ongoing. [Table: see text]

Polymorphisms of genes involved in gemcitabine metabolism correlate with prognosis in patients receiving neoadjuvant therapy for pancreatic cancer

4501 Background: Genetic variations in gemcitabine transport and metabolism may affect the clinical response, toxicity, and prognosis of pancreatic cancer patients treated with gemcitabine. Methods: We evaluated 17 single nucleotide polymorphisms (SNPs) of 8 genes (CDA, dCK, RRM1, DCTD, hCNT1, hCNT2, hCNT3, and hENT1) involved in gemcitabine metabolism in a homogeneous population of 126 patients with resectable pancreatic cancer treated with neoadjuvant gemcitabine- based chemotherapy plus radiation therapy. Whole blood was collected from patients at the time of enrollment, and DNA was extracted from peripheral lymphocytes using a DNA isolation kit (Qiagen Valencia, CA). Polymorphisms were detected using the TaqMan genotyping assays provided by Applied Biosystems (Foster City, CA). Survival was determined from pathologic diagnosis to death or last follow-up. Kaplan-Meier plot, log-rank test, and Cox regression were used to compare survival of patients according to genotype. Results: Six of the 17 SNPs had...

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.

Ribonucleotide reductase subunits M1 and M2 mRNA expression levels and clinical outcome of lung adenocarcinoma patients treated with docetaxel/gemcitabine

Ribonucleotide reductase subunits M1 (RRM1) and M2 (RRM2) are involved in the metabolism of gemcitabine (2′,2′-difluorodeoxycytidine), which is used for the treatment of nonsmall cell lung cancer. The mRNA expression of RRM1 and RRM2 in tumours from lung adenocarcinoma patients treated with docetaxel/gemcitabine was assessed and the results correlated with clinical outcome. RMM1 and RMM2 mRNA levels were determined by quantitative real-time PCR in primary tumours of previously untreated patients with advanced lung adenocarcinoma who were subsequently treated with docetaxel/gemcitabine. Amplification was successful in 42 (79%) of 53 enrolled patients. Low levels of RRM2 mRNA were associated with response to treatment (P< 0.001). Patients with the lowest expression levels of RRM1 had a significantly longer time to progression (P=0.044) and overall survival (P=0.02) than patients with the highest levels. Patients with low levels of both RRM1 and RRM2 had a significantly higher response rate (60 vs 14.2%; P=0.049), time to progression (9.9 vs 2.3 months; P=0.003) and overall survival (15.4 vs 3.6; P=0.031) than patients with high levels of both RRM1 and RRM2. Ribonucleotide reductase subunit M1 and RRM2 mRNA expression in lung adenocarcinoma tumours is associated with clinical outcome to docetaxel/gemcitabine. Prospective studies are warranted to evaluate the role of these markers in tailoring chemotherapy.

Randomized Crossover Study Evaluating the Effect of Gemcitabine Infusion Dose Rate: Evidence of Auto-Induction of Gemcitabine Accumulation

Controversy exists over the optimal dose rate for administration of gemcitabine. There is a strong pharmacologic rationale for increased intracellular accumulation with prolonged infusions, but this failed to translate into a significant benefit in a large randomized study. The purpose of this study was to compare the intracellular pharmacokinetics of gemcitabine given for 30 minutes or for 100 minutes in a crossover design. We randomly assigned 33 patients to a standard dose of 1,000 mg/m2 over either 30 minutes or 100 minutes. At the second week, they were transferred to the alternate schedule. Blood samples were collected at various times after the gemcitabine infusion. Gemcitabine and difluorodeoxyuridine were measured in plasma by high-performance liquid chromatography (HPLC), and gemcitabine-triphosphate was measured by HPLC in leukocytes. Intracellular accumulation was greater during the 100-minute infusion, which was consistent with previous data. This effect was confounded by an increase in gemcitabine-triphosphate accumulation between weeks 1 and 2, which was consistent with self-induction of gemcitabine accumulation. There was significant heterogeneity: 27% of patients had greater WBC accumulation during the 30-minute infusion (regardless of treatment order). Patients with relatively greater levels of gemcitabine-triphosphate in WBCs tended to have less under-dosing and a greater reduction in midcycle neutrophils. However, this observation did not correlate with plasma gemcitabine levels. This work identifies significant variations in intracellular gemcitabine-triphosphate accumulation between and within individuals, and it provides evidence that this variation has potential clinical significance. The observed self-induction of gemcitabine metabolism has broad implications for the dosing of nucleoside analogs.

Platinum Resistance Related to a Functional NER Pathway

Tobacco carcinogens induce DNA adducts that are repaired by the nucleotide excision repair (NER) pathway.1 Inhaled combustion-derived particles, such as cigarette smoke, cause a local pulmonary inflammatory response that is characterized by the influx of neutrophils into the airways. On entering the lung, neutrophils are activated and release reactive oxygen species and an array of proteins, such as myeloperoxidase. A significant reduction of NER in human alveolar epithelial cells was observed when they were cocultured with activated neutrophils.2 NER, a highly versatile pathway for DNA damage removal, is often dysfunctional in non-small cell lung cancer (NSCLC) and could, therefore, be the Achilles heel for customizing chemotherapy. NER removes numerous types of DNA helix-distorting lesions, including cisplatinand ultraviolet-induced photo products.1 Inherited defects in the NER process cause serious repair disorders: xeroderma pigmentosum (XP), with extreme risk of ultraviolet-induced skin cancer, and Cockayne syndrome. NER functions by a “cutand-paste” mechanism in which cisplatin damage recognition, local opening of the DNA helix around the lesion, damage excision, and gap filling occur in successive steps1,3–5 (Figure 1). NER is composed of two subpathways: global genome NER (GG-NER) and transcription-coupled NER (TC-NER), which share the same core mechanism but differ in the way lesions are recognized.6 NER-defective XP is classified into seven complementation groups, XPA to XPG. XPC and XPE are specifically defective in GG-NER, which repairs the damage on the nontranscribed strand, whereas the other XP groups involve deficiencies in both TC-NER and GG-NER.7 The first step in GG-NER is damage recognition by the heterodimer XPC/hHR23B, which binds with higher affinity to helix-distorting DNA lesions than to nondamaged, doublestranded DNA1 (Figure 1A). Various NER factors, including transcription factor IIH (TFIIH, a general transcription factor for RNA polymerase II), XPA, replication protein A (RPA), and XPG work together to repair DNA damage (Figure 1B). TFIIH can be divided into two subcomplexes: the core TFIIH (composed of XPB, p62, p52, p44, p34, and p8) and a cdk-activating kinase subcomplex (containing cdk7, cyclin H, and MAT1).7 Both subcomplexes are bridged by XPD. In NER, TFIIH unwinds the duplex DNA around the lesion to allow the recruitment of the NER factors XPA, RPA, XPG, and excision repair cross-complementing 1 (ERCC1)/XPF (Figure 1B). TFIIH, with the two helicases XPB and XPD, opens an approximately 30-base-long DNA segment around the platinum damage. This open intermediate is stabilized by RPA and XPA (Figure 1C). The DNA strand that contains the damaged base(s) is excised by the two NER endonucleases XPG and ERCC1/XPF (Figure 1D). XPG cleaves the damaged DNA strand 3= from the lesion, and ERCC1/XPF cleaves the damaged strand 5= from the lesion (Figure 1D). The resulting gap is filled by DNA polymerase or in the presence of replication factors8 (Figure 1E). Importantly, the ERCC1/XPF structure-specific nuclease has an additional role in the repair of cisplatin adducts besides its function in NER: the recombination repair of interstrand cross-links.9 Moreover, colocalization of ERCC1 foci and RAD51 foci in response to cisplatin treatment has recently been found and may represent recruitment of ERCC1/XPF to sites of recombination repair.10 Nevertheless, in addition to NER, cisplatininduced cytotoxicity requires the interaction of components from several different DNA damage-processing systems.11

Pharmacogenomics of gemcitabine: can genetic studies lead to tailor-made therapy?

Gemcitabine is a deoxycytidine analogue that has a broad spectrum of antitumour activity in many solid tumours including pancreatic cancer. We have recently carried out a pharmacogenomic study in cancer patients treated with gemcitabine, and found that one genetic polymorphism of an enzyme involved in gemcitabine metabolism can cause interindividual variations in the pharmacokinetics and toxicity of this agent. In this paper, we review recent genetic studies of gemcitabine, and discuss the possibility of individualised cancer chemotherapy based on a pharmacogenomic approach.

Human equilibrative nucleoside transporter 1 is associated with the chemosensitivity of gemcitabine in human pancreatic adenocarcinoma and biliary tract carcinoma cells

Gemcitabine has been one of the most commonly used agents for pancreatic adenocarcinoma chemotherapy, but the determinants of the sensitivity of and resistance to this agent are not yet fully understood. In this study with pancreatic carcinoma and biliary tract carcinoma cell lines, we examined the gene expression levels of nucleotide transporters and others related to the metabolism of gemcitabine in the light of sensitivity to this agent. Quantitative RT-PCR demonstrated that one of the nucleotide transporter genes; human equilibrative nucleoside transporter 1 (hENT1) was associated with the sensitivity to gemcitabine as represented by IC50, while the other genes for nucleotide transporter and metabolism were not. We conclude that increased hENT1 expression is a most important determinant of gemcitabine sensitivity at least in an in vitro study.

Gene expression profile of enzymes involved in gemcitabine (Gem) metabolism in bone marrow mononuclear cells as predictors of myelosuppression

2007 Background: The dose-limiting toxicity of gemcitabine (Gem) is hematologic toxicity (heme tox), and there is wide intra-patient variability in the degree of heme tox. This study was done to assess the possible impact of gene expression of enzymes involved in Gem metabolism or mechanism of action on heme tox. Methods: Pre-therapy mononuclear cells were isolated from bone marrow aspirates collected from 71 consenting patients with various advanced malignancies enrolled in an IRB-approved phase I trial in which single agent Gem was given over 30 min weekly for 2 of 3 weeks during cycle 1 at doses ranging from 750–1,560 mg/m2. Gene expression of deoxycytidine kinase (DCK), an activating enzyme, cytidine deaminase (CD) and deoxycytidylate deaminase (DCD), deactivating enzymes, and ribonucleotide reductase M2 (RNR), which is inhibited by Gem diphosphate, was measured by real-time RT-PCR. Target gene expression was relative to beta-actin. Heme tox was calculated as the % decrease in white blood cells (WBC), neutrophils (ANC) and platelets (PLT) from baseline. Results: 71 patients (26 females, 35 males) with a median age of 56 years (range: 20–75) were included in the analysis. The median (25th %, 75th %) gene expression was as follows (x10e3/beta-actin): DCK, 0.34 (0.19, 0.64); CD, 1.88 (1.33, 2.92); DCD, 2.48 (1.15, 7.78); and RNR, 0.39 (0.19, 0.80). A strong linear correlation was noted only between RNR &amp; DCD gene expression (Pearson r = 0.89). When gene expression was categorized as above or below the median value, only CD appeared to influence heme tox (mean ± std dev) ( Table ). T-test p value is shown. Conclusions: Gem is rapidly metabolized to its inactive metabolite by CD. Subjects with a higher relative gene expression of CD tended to have a lesser degree of heme tox following Gem. Correlation with Gem pharmacokinetics in these subjects is planned. [Table: see text] No significant financial relationships to disclose.

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.

Immunohistochemical and Genetic Evaluation of Deoxycytidine Kinase in Pancreatic Cancer: Relationship to Molecular Mechanisms of Gemcitabine Resistance and Survival

Gemcitabine is considered the standard first-line therapy for patients with advanced pancreatic cancer. More recent strategies have focused on improving the efficacy of gemcitabine by either improving the method of delivery or by combining gemcitabine with other non-cross-resistant chemotherapy agents or with small-molecule drugs. However, the clinical benefits, response rates, and duration of responses have been modest. Deoxycytidine kinase (dCK) is the rate-limiting enzyme involved in the metabolism of gemcitabine. The expression of dCK has been postulated to be correlative of gemcitabine resistance. We determined the relationship of dCK immunohistochemical protein expression and/or genetic status of dCK in a panel of human pancreatic cancer tissues and pancreatic cancer cell lines and determined the relationship of these variables to the clinical outcome of patients treated with gemcitabine. We report that dCK protein expression is expressed in the majority of pancreatic cancers analyzed (40 of 44 cases, 91%) and showed a range of labeling intensities ranging from 1+ (labeling weaker in intensity than normal lymphocytes present in same section) to 3+ (labeling greater in intensity than normal lymphocytes present in same section). When labeling intensity was compared with survival, low dCK expression (1+ labeling) was correlated with both overall survival (P < 0.009) and progression-free survival following gemcitabine treatment (P < 0.04). Low dCK labeling intensity was also significantly correlated with patient age (70.3 +/- 8.1 versus 59.8 +/- 7.4 years; P < 0.0006), suggesting that age-related methylation of the dCK gene may account in part for the observed differences. Sequencing of the entire dCK coding sequence in 17 cell lines and 9 patients' cancer tissues with disease progression while on gemcitabine did not identify any mutations, suggesting that genetic alterations of dCK are not a common mechanism of resistance to gemcitabine for this tumor type. Moreover, dCK labeling showed similar patterns and intensities of labeling among matched pretreatment and post-treatment tissues. In summary, pretreatment levels of dCK protein are most correlated with overall survival following gemcitabine treatment and are stable even after resistance to gemcitabine is clinically documented.

Crossing the Rubicon in Lung Adenocarcinoma: The Conundrum of EGFR Tyrosine Kinase Mutations

Keyowrds: adenocarcinoma, epidermal growth factor, nonsmall cell lung cancer, tyrosine kinase mutations Chemotherapy in lung cancer: the state of the art In 2004 in Europe, there were an estimated 2,886,800 cases of cancer diagnosed, including data recorded in the 25 member states of the European Union. Lung cancer was the most common form, with a total of 381,500 cases (13.2%) and an estimated mortality of 341,800 cases (20% of the total) [1]. Approximately 85% of lung cancers are non-small cell lung cancer (NSCLC), and the majority of patients present with advanced disease, with dismal prognosis. A landmark study in NSCLC showed that the combination of gemcitabine (Gemzar®) plus cisplatin attained a median survival of 9.1 months in comparison with 7.6 months with cisplatin alone [2]. A Phase III trial of the European Organization for Research and Treatment of Cancer (EORTC) showed similar results with paclitaxel (Taxol®)– cisplatin and gemcitabine–cisplatin, with median survival times of 8.1 and 8.9 months, respectively. A third arm of paclitaxel–gemcitabine showed a shorter survival of 6.7 months [3]. A recent meta-analysis, which included a study encompassing 4556 patients, showed a median survival of 9 months for gemcitabine-based chemotherapy in contrast with 8.2 months for non-gemcitabine combinations [4]. One of the mechanisms of tumor resistance to cisplatin is increased nucleotide excision repair (NER) activity, in particular increased levels of excision repair cross-complementing (ERCC)1. The 5 incision made by the ERCC1–xeroderma pigmentosum group F (ERCC1–XPF) complex is thought to be a rate-limiting step in the NER pathway, as demonstrated by an increase in excision activity in extracts from non-cisplatin-resistant cells after addition of purified ERCC1–XPF protein, compared with no increase in excision activity after addition of ERCC1–XPF to extracts from cisplatin-resistant cells [5]. The potential use of ERCC1 mRNA expression as a predictive marker for the effectiveness of cisplatin-based chemotherapy is an important area of clinical translational research. Together with ERCC1, ribonucleotide reductase (RR) subunit M1 is also involved in gemcitabine metabolism as a participant in the NER pathway, providing nucleotides that fill gaps created by ERCC1 excision of the DNA strand-containing cisplatin bulky adducts. Tumor overexpression of RRM1 mRNA in gemcitabine/cisplatin-treated NSCLC patients was associated with a short median survival of 3.6 months in contrast with 13.7 months for patients with low RRM1 mRNA expression (p = 0.009) [6]. This data brings a new era of customized chemotherapy based on NER transcripts.

Mismatch repair proficiency is not required for radioenhancement by gemcitabine

Mismatch repair (MMR) proficiency has been reported to either increase or decrease radioenhancement by 24-h incubations with gemcitabine. This study aimed to establish the importance of MMR for radioenhancement by gemcitabine after short-exposure, high-dose treatment and long-exposure, low-dose treatment. Survival of MMR-deficient HCT116 and MMR-proficient HCT116 + 3 cells was analyzed by clonogenic assays. Mild, equitoxic gemcitabine treatments (4 h, 0.1 microM vs. 24 h, 6 nM) were combined with gamma-irradiation to determine the radioenhancement with or without recovery. Gemcitabine metabolism and cell-cycle effects were evaluated by high-performance liquid chromatography analysis and bivariate flow cytometry. Radioenhancement after 4 h of 0.1 microM of gemcitabine was similar in both cell lines, but the radioenhancement after 24 h of 6 nM of gemcitabine was reduced in MMR-proficient cells. No significant differences between both cell lines were observed in the gemcitabine metabolism or cell-cycle effects after these treatments. Gemcitabine radioenhancement after recovery was also lower in MMR-proficient cells than in MMR-deficient cells. Mismatch repair proficiency decreases radioenhancement by long incubations of gemcitabine but does not affect radioenhancement by short exposures to a clinically relevant gemcitabine dose. Our data suggest that MMR contributes to the recovery from gemcitabine treatment.