Biomedical subjects

S Seeber

Publications and source records attributed to S Seeber.

At least 109 records · Page 6Linked to original sources

PubMed1998

Bolus vincristine and epirubicin with cyclophosphamide and dexamethasone (VECD) as induction and salvage treatment in multiple myeloma.

The VAD regimen (infusional vincristine, doxorubicin and intermittent high-dose dexamethasone) is widely considered the standard salvage chemotherapy for multiple myeloma resistant to alkylating agents and is increasingly used for induction in previously untreated patients prior to high-dose chemotherapy. We investigated the VECD protocol, a VAD-based regimen using bolus injections of vincristine 1.5 mg day 1 and epirubicin 20 mg/m2 days 2 and 3 with 1 h infusions of cyclophosphamide 200 mg/m2 days 1-3 and oral dexamethasone 20 mg/m2 days 1-5 as induction and salvage treatment in multiple myeloma. Fifteen previously untreated and 25 patients with relapsed or refractory myeloma were included. Cycles were repeated every 3 weeks. In the group of previously untreated patients the response rate was 53% and the median survival has not been reached at 59 months. For relapsed and refractory patients the response rate was 44% and the median survival 13 months. In the group of patients with truly refractory disease on prior chemotherapy a response rate of 47% was achieved, which appears superior to the results observed for VAD alone. The main toxicities were leukocytopenia WHO grade IV and infections grade III/IV with both toxicities being significantly more pronounced in pretreated patients. VECD appears to be an effective regimen for induction and salvage therapy in multiple myeloma. Based on the limited number of patients treated the results are comparable to those reported for VAD, with the advantage that the infusional application of vincristine and the anthracycline is omitted.

Adult↗

PubMed1998

Structural and functional analysis of the cytidine deaminase gene in patients with acute myeloid leukaemia.

Gene transfer of the cytidine deaminase (CDD) cDNA has recently been shown to induce cellular resistance to cytarabine (AraC) in vitro. To investigate the role for CDD in acute myeloid leukaemia (AML) we analysed the CDD activity and CDD gene structure in blast material from well-defined patients with untreated and AraC refractory (RF) AML. Median CDD activity in previously untreated AML was significantly lower than in RF-AML blasts (P=0.015) and was significantly lower in patients with complete remission than with blast persistence following induction chemotherapy (P=0.043). Structural investigation of the CDD gene by Southern analyses and RT-PCR showed no detectable aberrations. Sequence analysis of the CDD cDNA from nine RF-AML patients showed inconsistent aberrations in three patients. Semiquantitative assessment of CDD mRNA expression revealed a significant correlation with CDD activity. In conclusion, concordant with another recent study our data suggest a correlation of pretherapeutic CDD activity with induction treatment response. Besides the previously described prognostic impact of mdrl expression, this result could be useful for the development of risk-adapted AML treatment strategies and warrants further studies of CDD activity in well-defined cohorts of AML patients and of the mechanisms involved in the regulation of CDD activity.

Acute Disease↗

PubMed1998

Phase II study with cisplatin and paclitaxel in combination with weekly high-dose 24 h infusional 5-fluorouracil/leucovorin for first-line treatment of metastatic breast cancer.

Results from our previous phase II study demonstrating high efficacy and low toxicity for a weekly schedule of 5-fluorouracil (5-FU)/leucovorin in intensively pretreated patients with metastatic breast cancer prompted addition of paclitaxel and cisplatin to this regimen for a phase II study of outpatient first-line treatment of metastatic breast cancer. (MBC). Twenty-eight patients with metastatic breast cancer have been evaluated. Pretreatment comprised adjuvant CTX in 24 out of 28 patients, but no prior CTX for MBC. Patients were treated with 5-FU 2 g/m2 (24 h infusion) plus leucovorin 500 mg/m2 (2 h infusion prior to 5-FU) weekly for 6 weeks (days 1, 8, 15, 22, 29 and 36); in addition, paclitaxel 175 mg/m2 (3 h infusion) was administered on days 0 and 21, and cisplatin 50 mg/m2 (1 h infusion) on days 1 and 22 prior to 5-FU/leucovorin, repeated every 50 days. All patients were treated as outpatients using Port-a-Cath systems and portable pumps. Aside from common total alopecia, neutropenia was common but only of short duration. No episodes of febrile neutropenia occurred. Non-hematologic toxicities (NCl CTC grade, percent of patients) consisted of mild to moderate diarrhea (2+3, 47%), mucositis (2, 14%), and nausea and vomiting (2+3, 60%). Out of 28 patients with bidimensionally measurable disease 25% (seven out of 28) achieved a CR, 57% (16 out of 28) achieved a PR, 11% (three out of 28) had a SD and 7% (two out of 28) had a PD. Overall RR was 82% (95% confidence interval 66-100%). Median remission duration was 8 months, median time to progression 9 months and median survival time 28 months with a median follow-up of 21 months. We conclude that the combination of paclitaxel, cisplatin and 5-FU/leucovorin is an effective non-anthracycline-containing regimen for the first-line treatment of MBC.

Adult↗

PubMed1998

Paclitaxel plus ifosfamide in advanced ovarian cancer: results of a phase I study.

Patients with advanced ovarian carcinoma and an inadequate response to first-line platinum-based combination chemotherapy (CTX) have a very poor prognosis and effective salvage regimens are clearly needed. This phase I study was performed in order to determine the maximum tolerable dose (MTD) and dose-limiting toxicity (DLT) of the combination paclitaxel (P) and ifosfamide (IFO). After premedication, patients received P as a 3 h i.v. infusion on day 1; IFO was given as 1 h i.v. infusion with the standard dose of mesna i.v. on days 2-5, q day 22. The following dose levels (dl) were investigated: (mg/m2/day) dl1, P 135/IFO 1500; dl2, P 135/IFO 2000; dl3, P 175/IFO 2000; and dl4, P 175/ IFO 1500. Eighteen patients with advanced ovarian cancer entered this trial. In eight patients treated with an IFO dose of 2000 mg/m2 during dl2 and 3, two required treatment interruptions because of CNS toxicity CTC grade 3 and one patient experienced nephrotoxicity CTC grade 3, Therefore the MTD of IFO used in combination with P and given over 4 days is reached with 2000 mg/m2/day. In the fourth dl we escalated the P dose up to 175 mg/m2, reduced the IFO dose to 1500 mg/m2 and treated an additional five patients. No DLT occurred at that dl. Objective responses were observed at all dls. The combination of P and IFO is feasible and active in pretreated advanced ovarian carcinoma. dl4 is the recommended dose for phase II trials.

Adult↗

PubMed1998

Phase II study of continuous 120 h infusion of mitomycin C as salvage chemotherapy in patients with progressive or rapidly recurrent colorectal cancer.

We evaluated the therapeutic activity and safety of continuously infused mitomycin C in patients with metastatic colorectal cancer who had recurred (less than 3 months) or progressed following first- or second-line 5-fluorouracil-based chemotherapy. Treatment consisted of mitomycin C 20 mg/m2 i.v. given over 120 h (5 days) followed by a 3 week rest period. Fifty-two consecutively enrolled patients were assessable for toxicity and 49 for response evaluation (three patients evaluable but not measurable), completing at least one full course of chemotherapy. Previous chemotherapy regimens consisted of bolus 5-fluorouracil/folinic acid (5-FU/FA) (Machover) n=26 (50%) or continuous (24 h) 5-FU+/-FA+/-interferon n=26 (50%). Forty-two percent of patients had received one previous chemotherapy regimen and 58% more than one. One partial remission (2%) lasting 7 months and 11 disease stabilizations (23%) with a median duration of 3.2 months (range 1-8) were achieved in 49 patients. Median survival time since start of mitomycin C was 4.7 months (1.2-28.1) resulting in a 6 month survival rate of 36%. The progression-free interval was 10 weeks (range 4-36). Delayed and cumulative thrombo- and leukocytopenia (WHO grade III/IV) were observed in 19 and 6%, and anemia in 2% of patients. WHO grade I/IV mucositis, diarrhea and fever/infection occurred each in 6% of patients. Treatment delays and dose reductions were necessary in 11 (21%) and 21 (40%) patients, respectively. In three cases treatment was stopped due to cumulative thrombocytopenia (6%). Continuous infusion of single-agent mitomycin C displays modest activity in heavily pretreated 5-FU refractory colorectal cancer patients combined with a low toxicity level.

Adult↗

PubMed1998

Comparison between short or long exposure to 5-fluorouracil in human gastric and colon cancer cell lines: biochemical mechanism of resistance.

Recent preclinical and clinical data indicate that the main mechanisms of 5-fluorouracil (5-FU) cytotoxicity depend on the mode of administration. To gather further insight into the major causes of acquired 5-FU resistance, drug-sensitive human gastric (M2), colon (HT29) and breast (MCF7) cancer cell lines were repeatedly exposed to a fixed concentration of 5-FU given either for 1 or 24 h. Although equieffective doses (IC50) of 5-FU were used, resistance to a 1 h exposure of 5-FU developed faster in all models than to a 24 h exposure. Cell lines with acquired resistance to a 1 h application of 5-FU were only partly cross-resistant to a 24 h exposure, whereas lines with resistance to protracted application of 5-FU displayed significant cross-resistance to the 1 h schedule. Resistance to methotrexate was only seen in cell lines with acquired resistance to 24 h of 5-FU. All 5-FU-resistant cell lines showed reduced incorporation of 5-FU into cellular RNA. Furthermore, elevations of thymidylate synthase were seen in all cell lines with resistance to 24 h of 5-FU but also in one cell line with resistance to a bolus schedule. No alterations in folylpolyglutamate synthase developed in the resistant cell lines. These data support the concept that the main mechanisms of 5-FU cytotoxicity depend on the mode of application. Incorporation of fluorouridine triphosphate into RNA appears to be the most important mechanism of action for 5-FU bolus schedules, whereas inhibition of thymidylate synthase becomes more important as the infusion time is prolonged. These data could have implications on the interaction of 5-FU given at different schedules with various other cytostatic agents.

Adenocarcinoma↗

PubMed1998

Preoperative chemotherapy followed by concurrent chemoradiation therapy based on hyperfractionated accelerated radiotherapy and definitive surgery in locally advanced non-small-cell lung cancer: mature results of a phase II trial.

PURPOSE: To evaluate the feasibility and efficacy of an intensive multimodality approach with combination chemotherapy, hyperfractionated accelerated chemoradiotherapy, and definitive surgery in prognostically unfavorable subgroups of locally advanced non-small-cell lung cancer stages IIIA and IIIB (LAD-NSCLC). PATIENTS AND METHODS: Following staging, including mediastinoscopy, 94 patients with inoperable LAD-NSCLC were treated preoperatively with chemotherapy (three courses of split-dose cisplatin and etoposide [PE]) followed by concurrent chemoradiotherapy (one course of PE combined with 45 Gy hyperfractionated accelerated radiotherapy). After repeat mediastinoscopy, patients underwent surgery 4 weeks postradiation. RESULTS: Of 94 consecutive patients (52 stage IIIA [> or = two lymph node levels involved] and 42 stage IIIB [no pleural effusion, no supraclavicular nodes]), 62 (66%) completed induction and underwent surgery. Complete resection (R0) was achieved in 50 (53% of all patients) and pathologic complete response (PCR) in 24 (26%). After a median follow-up of 43 months, the median survival time was 20 months for IIIA, 18 months for IIIB, and 42 months for R0 patients. Calculated survival rates at 4 years were 31%, 26%, and 46%. Two patients died of sepsis preoperatively and four died postoperatively of pleural empyema (n = 1), stump insufficiency (n = 2), and cardiac failure (n = 1). Other toxicities were acceptable-mainly hematologic during chemotherapy or chemoradiotherapy and esophagitis during chemoradiotherapy. CONCLUSION: This intensive multimodality treatment is feasible and demonstrates high efficacy in prognostically unfavorable LAD-NSCLC subgroups with high R0 rates and improved long-term survival compared with historical controls

Adult↗

PubMed1998

Fluorouracil-based combinations in the treatment of metastatic breast cancer.

Although combination chemotherapy regimens may prolong survival for selected patients with metastatic breast cancer, few, if any, are cured. The standard regimens used in treatment, e.g., CMF (cyclophosphamide, methotrexate, and fluorouracil [5-FU]), FAC (5-FU, Adriamycin, and cyclophosphamide), and FEC (5-FU, epirubicin, and cyclophosphamide), were developed over a decade ago. Current efforts to improve therapeutic efficacy have concentrated on decreasing drug toxicity and increasing drug doses (e.g., high-dose chemotherapy with peripheral stem-cell support). An important alternative approach to increasing therapeutic efficacy focuses on altering the administration schedules of well-known chemotherapeutic agents and introducing active new agents. One of the most frequently used cytotoxic drugs, fluorouracil (5-FU), has documented activity in a variety of malignancies, most notably, breast cancer and gastrointestinal tract cancers. However, despite broad clinical experience with 5-FU, our knowledge about the mechanisms of resistance to the various administration schedules used is limited. In vitro data and clinical experience show that resistance to one schedule of 5-FU can be overcome by using alternative schedules, in particular, a protracted infusion. This article discusses our clinical experience with weekly high-dose 24-hour infusions of 5-FU in combination with folinic acid (leucovorin) alone and together with paclitaxel (Taxol) for the treatment of advanced breast cancer.

Adult↗

PubMed1998

Ifosfamide and gemcitabine: a phase II trial in advanced inoperable non-small cell lung cancer.

The novel nucleoside agent gemcitabine has demonstrated antitumor activity against a variety of solid tumors and is associated with low toxicity. A phase I trial in Germany of gemcitabine combined with the alkylating agent ifosfamide has shown encouraging activity against non-small cell lung cancer. The efficacy and toxicity of this combination was further evaluated in a phase II trial involving chemotherapy-naive patients with non-small cell lung cancer (mostly stage IV disease). Gemcitabine was administered at a dose of 1,000 mg/m2 on days 1, 8, and 15, followed by a 1-week rest, while ifosfamide was given at a dose of 1,500 mg/m2 on days 8 through 12. Fifty-five patients were treated, 49 of whom are evaluable for response. Six patients were not evaluable because they had not received sufficient therapy (less than one complete cycle) because of early disease progression or early death. Twelve patients responded, for an overall objective response rate of 24.5%. The median survival time was 8.9 months, and the 1-year survival rate was 30.9%. Grades 3 and 4 neutropenia occurred in 30.2% and 24.5% of patients, respectively, but the incidence of infection was low. These results indicate that the combination of gemcitabine and ifosfamide is active against non-small cell lung cancer and has a mild toxicity profile, and suggest that further evaluation of this combination is warranted.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1998

Recombinant gene products of two natural variants of the human cytidine deaminase gene confer different deamination rates of cytarabine in vitro.

The recent cloning of human cytidine deaminase (CDD) revealed two variants with a nonconservative amino acid deviation (Gln<-->Lys) at codon 27 within a region of structural homology to a core domain of bacterial CDDs. We here confirm the occurrence of both CDD sequences by cDNA cloning and show that at cytarabine (ara-C) concentrations of 1x10(-8) to 2x10(-2) M, the recombinant enzyme corresponding to the Lys-carrying natural variant (CDD-2) exerts a 1.3- to 3.3-fold higher in vitro deamination rate of ara-C than the Gln-carrying enzyme (CDD-1). These results suggest that this genetic polymorphism contributes to the different deamination phenotypes of ara-C observed in vivo, and that investigation of CDD allelotype frequencies and their correlation with ara-C resistance in patients with acute leukemia may be warranted. In addition, our data may be relevant to recently considered CDD gene transfer strategies for the detoxification of hematopoietic stem cells during high-dose therapy with cytosine nucleoside analogs.

Cytarabine↗

PubMed1998

In acute myeloid leukemia, coexpression of at least two proteins, including P-glycoprotein, the multidrug resistance-related protein, bcl-2, mutant p53, and heat-shock protein 27, is predictive of the response to induction chemotherapy.

To identify prognostic factors alternative or additional to P-glycoprotein (Pgp), we studied the impact of the multidrug resistance-related protein (MRP), bcl-2 (flow cytometry), mutant p53 (single-strand conformation polymorphism), and heat-shock protein 27 (HSP27, Western blotting) in myeloid blasts obtained at the time of diagnosis in patients with de novo acute myeloid leukemia (AML). We collected bone marrow samples from untreated AML patients, prepared the cells as well as the cellular protein, and froze all the material. We then analyzed 20 patients who responded with complete remission (CR) and 20 patients who had blast persistence (BP). The purpose of the study was to determine whether leukemic blasts from patients with BP were more resistant to chemotherapy than those from patients with CR. There was no significant correlation between the expression of any of these proteins alone and treatment outcome in both groups studied. In contrast, there was a significant correlation between the coexpression of at least two of these proteins and response (p = 0.0298), which turned out to be a significant independent prognostic factor for treatment failure (p = 0.0329, relative risk = 1.5) according to multivariate analysis. We conclude that drug resistance in AML is multifactorial. Thus, coexpression of different resistance mechanisms may be responsible for the primary drug resistance in de novo AML.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Expression of p21WAF1 predicts outcome of esophageal cancer patients treated by surgery alone or by combined therapy modalities.

The p21WAF1 protein is an important regulator of the cell cycle. Its expression and prognostic significance were investigated immunohistochemically in samples of normal esophageal squamous epithelium (n = 10), severe squamous cell dysplasia (n = 20), carcinoma in situ (n = 14), permanent esophageal squamous cell carcinoma cell lines (n = 3), and invasive squamous cell carcinomas treated either by potentially curative resection (n = 172) or by combined modality therapy (radiochemotherapy +/- surgery; n = 38). Whereas p21WAF1 expression in the normal epithelium was restricted to a few cells adjacent to the basal cell layer, p21WAF1 overexpression was frequently found in preneoplasias and invasive carcinomas. Expression of p21WAF1 in invasive carcinomas was not correlated with tumor differentiation, pT category, or pN category. Among carcinomas treated by potential curative resection, univariate (P = 0.0025) and multivariate (P = 0.0081) survival analysis showed significant correlation of strong p21WAF1 expression (> or =50% p21WAF1-positive tumor cells) with poor overall survival. Univariate survival analysis (P = 0.0006) revealed the same prognostic influence in the group of patients treated by combined modality therapy. We conclude that overexpression of p21WAF1 protein is a frequent event in preneoplasias and neoplasias of the esophagus. Immunohistochemical examination of p21WAF1 expression may provide important prognostic information for decision-making in the treatment of patients with esophageal cancer.

Adult↗

PubMed1998

Phase I clinical and pharmacokinetic study of titanocene dichloride in adults with advanced solid tumors.

This Phase I dose-escalation clinical trial of a lyophilized formulation of titanocene dichloride (MKT4) was conducted to determine the maximum tolerated dose, the dose-limiting toxicity (DLT), and pharmacokinetics of titanium (Ti) after a single i.v. infusion of MKT4. Forty patients with refractory solid malignancies were treated with a total of 78 courses. Using a modified Fibonacci scheme, 15 mg/m2 initial doses of titanocene dichloride were increased in cohorts of three patients up to level 11 (560 mg/m2) if DLT was not observed. The maximum tolerated dose was 315 mg/m2, and nephrotoxicity was DLT. Two minor responses (bladder carcinoma and non-small cell lung cancer) were observed. The pharmacokinetics of plasma Ti were assessed in 14 treatment courses by atomic absorption spectroscopy. The ratio for the area under the curve(0-infinity) in plasma and whole blood was 1.2. The following pharmacokinetic parameters were determined for plasma, as calculated in a two-compartment model: biological half-life t1/2beta in plasma was 22.8+/-11.2 h (xh +/- pseudo-SD), peak plasma concentration cmax approximately 30 microg/ml at a dose of 420 mg/m2, distribution volume Vss= 5.34+/-2.1 L (xa +/- SD), and a total clearance CItotal = 2.58+/-1.23 ml/min (xa +/- SD). There was a linear correlation between the area under the curve(0-infinity) of Ti in plasma and the titanocene dichloride dose administered with a correlation coefficient r2 of 0.8856. Plasma protein binding of Ti was in the 70-80% range. Between 3% and 16% of the total amount of Ti administered were renally excreted during the first 36 h. The recommended dose for Phase II evaluation is 240 mg/m2 given every 3 weeks with i.v. hydration to reduce renal toxicity.

Adult↗

PubMed1998

Expression of apoptosis-regulating proteins and outcome of esophageal cancer patients treated by combined therapy modalities.

The present study retrospectively examines the correlation between the outcome of patients with locally advanced esophageal squamous cell carcinoma (LAEC) after multimodal treatment (radiochemotherapy +/- surgery) and the expression of apoptosis-regulating proteins in pretherapeutic biopsies. Thirty-eight patients with LAEC who took part in a prospective multicentric trial received radiochemotherapy, optionally followed by surgery. Pretreatment tumor biopsies were immunohistochemically investigated for expression of p53, Bcl-2, Bax (bcl-2-associated X protein), and Bcl-X(L) (bcl-2-related X protein). The overall expression of p53, Bcl-2, Bax, and Bcl-X(L) was 52.6, 57.9, 100, and 97.4% respectively. Tumors without p53 expression and tumors with weak Bcl-X(L) expression showed response to chemotherapy more frequently (55.6 and 52.6%, respectively) than tumors positive for p53 expression and tumors with strong Bcl-X(L) expression (30.0 and 31.6%, respectively); however, these differences did not attain statistical significance. No correlations were found between the expression of Bcl-2 and Bax and the response to chemotherapy. In patients treated by radiochemotherapy and surgery, p53-negative tumors showed a significantly better outcome than p53-positive tumors (mean survival, 31.1 months versus 11.3 months; P = 0.0378). Additionally, a more favorable outcome was observed in tumors positive for Bcl-2 (not significant), whereas no differences in survival were observed in relation to the expression of Bax or Bcl-X(L). No differences in survival were observed in patients treated by radiochemotherapy without subsequent resection therapy in relation to the expression of apoptosis-regulating proteins. Immunohistochemical examination of pretherapeutic tumor biopsies for expression of apoptosis-regulating proteins may help to identify patients with LAEC who may benefit from multimodal treatment and those who may not.

Adult↗

PubMed1997

[Comparison of stress echocardiography and radionuclide ventriculography in the diagnosis of cardiomyopathy in patients receiving chemotherapy for malignant diseases].

BACKGROUND AND OBJECTIVE: Early evidence of drug-induced cardiomyopathy (CMP) is of great importance in haematological treatment, especially with anthracyclines. Stress echocardiography (SEC) has proved of value in determining left ventricular function at rest and under stress in patients with heart disease. The study was undertaken to assess the value of SEC in comparison with radionuclide ventriculography (RNV). PATIENTS AND METHODS: 63 unselected patients with malignant tumour (20 women, 43 men; mean age 49 +/- 15 years) underwent SEC and RNV. No chemotherapy had yet been started in 17 of them, 43 had received anthracyclines as main component of the chemotherapy (mean anthracycline dose 339 +/- 251 mg/m2). Left ventricular ejection fraction (LVEF) was measured by both SEC and RNV at rest and during standardized stress (recumbent ergometry). Both methods were applied and results measured independently by two examiners. RESULTS: The time interval between the two tests averaged 1 = 2 days. EC could be performed at rest in 62 of 63 and under stress in 59 of 63 patients (RNV: 63 of 63 and 54 of 63, respectively). Resting LVEF was 61 +/- 8% by SEC and 64 +/- 9% by RNV (P < 0.05). LVEF during stress, measured by SEC, was 71 +/- 11% and 73 +/- 10% by RNV (not significant). Mean LVEF increase between rest and stress was 9 +/- 10% by SEC and 9 +/- 8% by RNV (not significant). CONCLUSION: SEC is a satisfactory alternative to RNV in the assessment of ventricular function in patients receiving chemotherapy. It is less involved and more cost-effective than RNV, avoids radiation exposure and provides additional information on heart size and segmental contraction abnormalities.

Acute Disease↗

PubMed1997

Carbamoylation of glutathione reductase by N,N-bis(2-chloroethyl)-N- nitrosourea associated with inhibition of multidrug resistance protein (MRP) function.

Intracellular glutathione (GSH) concentrations have been implicated recently as a regulatory determinant of multidrug resistance protein (MRP)-mediated drug efflux. Inhibition of glutathione reductase (GR) activity of N,N-bis(2-chloroethyl)-N-nitrosourea (BCNU) has been employed extensively to investigate the role of GSH redox cycle in cellular function. The present study examined the effect of BCNU on the MRP-mediated efflux of doxorubicin in the multidrug-resistant human fibrosarcoma cell line HT1080/DR4 overexpressing MRP. No significant difference in GR activity between HT1080 (parental) and multidrug-resistant HT1080/DR4 cells was detected (38.6 +/- 2.2 and 37.8 +/- 5.28 nmol/min/10(6) cells, respectively). Exposure of HT1080 and HT1080/DR4 cells to 100-500 microM BCNU decreased GR activity concentration dependently with subsequent reduction in cellular GSH pools in both cell lines. Inhibition of GSH biosynthesis by D,L-buthionine-(S,R)-sulfoximine (D,L-BSO), a specific inhibitor of gamma-glutamylcysteine synthetase, significantly reduced MRP-mediated drug efflux and potentiated the cytotoxicity of doxorubicin in MRP-expressing HT1080/DR4 cells (dose modifying factor 20.8). While equally effective inhibition of GR activity by BCNU was observed in parental and resistant cells, a significant increase in intracellular retention of doxorubicin was only achieved in MRP-expressing HT1080/DR4 cells. Furthermore, inhibition of MRP function following treatment with BCNU or D,L-BSO was directly related to the degree of GSH depletion in MRP-expressing tumor cells [r = 0.94 (P < 0.001) and 0.99 (P < 0.001), respectively]. Based on northern blot analysis of MRP mRNA levels, exposure of HT1080/DR4 cells to BCNU did not produce down-regulation of MRP gene expression. The results reported herein indicate that derivatives of nitrosourea with carbamoylating properties are potent inhibitors of MRP function. Depletion of intracellular GSH pools by inhibition of the GSH redox cycle or GSH de novo biosynthesis significantly inhibited MRP-mediated doxorubicin transport and restored intracellular drug concentrations in vitro.

ATP-Binding Cassette Transporters↗

PubMed1997

DNA excision repair profiles of normal and leukemic human lymphocytes: functional analysis at the single-cell level.

Recent evidence has linked cellular DNA repair capacity to the chemosensitivity of cancer cells to alkylating agents. Using single-cell gel electrophoresis ("comet assay"), we have analyzed the induction and differential processing of DNA damage in human lymphocytes derived from healthy donors and from patients with chronic lymphatic leukemia (CLL) after exposure to N-ethyl-N-nitrosourea in vitro. The extent of comet formation in lymphocytes after N-ethyl-N-nitrosourea exposure appears to depend predominantly on the processing of DNA repair intermediates, because strand breaks in plasmid DNA were not induced by ethylation before the addition of nuclear proteins. Although the initial level of a specific alkylation product (O6-ethylguanine) in nuclear DNA was uniform, different dose-response curves were obtained for the comet size in individual cell samples immediately after exposure, with small intercellular variation. The individual kinetics of DNA repair varied significantly between specimens derived from both healthy individuals and CLL patients; for the DNA repair half-time (t1/2), large difference was found. Pretreatment of cells with methoxyamine as a DNA repair modifier blocking the base excision repair pathway revealed a quite similar extent of base excision repair-independent DNA incision in almost all normal lymphocyte samples. In contrast, this portion varied relatively and absolutely to a great extent among individual samples of CLL lymphocytes, suggesting a loss of stringent control of DNA repair processes in these cells. The comet assay can thus be used to gain information about interindividual variation in the efficiency of different DNA repair processes in small samples of normal cells and their malignant counterparts.

Carcinogens↗

PubMed1997

Identification of novel 'expressed sequence tags' within the FHIT gene locus in human chromosome region 3p14.2.

Losses of genetic material within human chromosome regions (HCR) 3p12-p14 and 3p21-p22 are observed in various neoplasias, suggesting tumor suppressor gene (TSG) loci within these regions. HCR 3p14 is particularly interesting as it contains the t(3;8) translocation breakpoint of a hereditary renal cell carcinoma, the FRA3B fragile site, and DNA markers deleted in several types of human cancer. We here report on the identification of five novel 'expressed sequence tags' (ESTs) within 3p14.2 which map proximal to exon 9 of the candidate TSG, FHIT. These ESTs may be valuable for elucidation of the supposed TSG content in 3p14.2.

Acid Anhydride Hydrolases↗