Promoter-specific activation defects by a novel yeast TBP mutant compromised for TFIIB interaction

TFIIB is an RNA polymerase II general transcription factor (GTF) that has also been implicated in the mechanism of action of certain promoter-specific activators (see, for examples, [1-11]). TFIIB enters the preinitiation complex (PIC) primarily through contact with the TATA box binding protein (TBP), an interaction mediated by three TBP residues [12-14]. To study the role of TFIIB in transcription activation in vivo, we randomly mutagenized these three residues in yeast TBP and screened for promoter-specific activation mutants. One mutant bearing a single conservative substitution, TBP-E186D, is the focus of this study. As expected, TBP-E186D binds normally to the TATA box but fails to support the entry of TFIIB into the PIC. Cells expressing TBP-E186D are viable but have a severe slow-growth phenotype. Whole-genome expression analysis indicates that transcription of 17% of yeast genes are compromised by this mutation. Chimeric promoter analysis indicates that the region of the gene that confers sensitivity to the TBP-E186D mutation is the UAS (upstream activating sequence), which contains the activator binding sites. Most interestingly, other TBP mutants that interfere with different interactions (TFIIB, TFIIA, or the TATA box) and a TFIIB mutant defective for interaction with TBP all manifest distinct and selective promoter-specific activation defects. Our results implicate the entry of TFIIB into the PIC as a critical step in the activation of certain promoters and reveal diverse mechanisms of transcription activation.

High-dose doxorubicin, dexrazoxane, and GM-CSF in malignant mesothelioma: a phase II study-Cancer and Leukemia Group B 9631

Doxorubicin is the most widely studied agent for the treatment of malignant mesothelioma. In conventional doses, the response rate is approximately 17%. Higher dose doxorubicin has been successfully employed in other tumor types. Dexrazoxane has been demonstrated to reduce the cardiac toxicity associated with long term, chronic use of doxorubicin. Based upon phase I data generated by the Cancer and Leukemia Group B (CALGB) indicating that doxorubicin at a dose of 120 mg/m(2) when combined with dexrazoxane and GM-CSF could be safely administered, the CALGB undertook a phase II study of high-dose doxorubicin in patients with malignant mesothelioma. Toxicity was excessive, necessitating protocol modification and ultimately protocol termination. There were no objective responses observed. We conclude that high-dose doxorubicin administered with dexrazoxane is unacceptably toxic in this patient population.

Genetic analysis of TAF68/61 reveals links to cell cycle regulators

In yeast, inactivation of certain TBP-associated factors (TAF(II)s) results in arrest at specific stages of the cell cycle. In some cases, cell cycle arrest is not observed because overlapping defects in other cellular processes precludes the manifestation of an arrest phenotype. In the latter situation, genetic analysis has the potential to reveal the involvement of TAF(II)s in cell cycle regulation. In this report, a temperature-sensitive mutant of TAF68/61 was used to screen for high-copy dosage suppressors of its growth defect. Ten genes were isolated: TAF suppressor genes, TSGs 1-10. Remarkably, most TSGs have either a genetic or a direct link to control of the G(2)/M transition. Moreover, eight of the 10 TSGs can suppress a CDC28 mutant specifically defective for mitosis (cdc28-1N) but not an allele defective for passage through start. The identification of these genes as suppressors of cdc28-1N has identified four unreported suppressors of this allele. Moreover, synthetic lethality is observed between taf68-9 and cdc28-1N. The isolation of multiple genes involved in the control of a specific phase of the cell cycle argue that the arrest phenotypes of certain TAF(II) mutants reflect their role in specifically regulating cell cycle functions.

A novel peptide recognition mode revealed by the X-ray structure of a core U2AF35/U2AF65 heterodimer

U2 auxiliary factor (U2AF) is an essential splicing factor that recognizes the 3' splice site and recruits the U2 snRNP to the branch point. The X-ray structure of the human core U2AF heterodimer, consisting of the U2AF35 central domain and a proline-rich region of U2AF65, has been determined at 2.2 A resolution. The structure reveals a novel protein-protein recognition strategy, in which an atypical RNA recognition motif (RRM) of U2AF35 and the U2AF65 polyproline segment interact via reciprocal "tongue-in-groove" tryptophan residues. Complementary biochemical experiments demonstrate that the core U2AF heterodimer binds RNA, and that the interacting tryptophan side chains are essential for U2AF dimerization. Atypical RRMs in other splicing factors may serve as protein-protein interaction motifs elsewhere during spliceosome assembly.

Synergistic interaction between topotecan and microtubule-interfering agents

PURPOSE

Topotecan is a topoisomerase I inhibitor with demonstrated anticancer activity in preclinical and clinical studies. The purpose of the present study was to evaluate drug-drug interactions in therapeutic regimens that would combine topotecan with microtubule-interfering agents, such as Taxol and vinblastine.

METHODS

The cytotoxic activities of various drug combinations and schedules of administration were measured in a colon cancer cell line using the MTT assay. Western blot and flow cytometry were performed to determine the effects of Taxol and vinblastine on topoisomerase I and Bcl-xL protein levels and cell cycle distribution.

RESULTS

Brief incubation of colon cancer cells with low concentrations of either Taxol or vinblastine increased the efficacy of a subsequent treatment with topotecan. Preincubation of cells with vinblastine or Taxol reduced by 10- to 40-fold the concentration of topotecan necessary to induce a 50% decrease in cell survival. The effects were maximal when the cells were treated for 5 h with microtubule-interfering agents and then incubated for 19 h in drug-free medium before the addition of topotecan. Under these conditions, both Taxol and vinblastine caused an increase in topoisomerase I protein levels, fraction of S phase cells, and extent of Bcl-xL phosphorylation immediately prior to the addition of topotecan. All these factors may contribute to the increased efficacy of topotecan observed with sequential therapy.

CONCLUSION

Combinations of topotecan and microtubule-interfering agents result in synergistic anticancer activity when the drugs are administered sequentially. The promising preclinical data presented here encourage clinical testing of these drug combinations using a sequential schedule of administration.

Induction of apoptosis by a secreted lipocalin that is transcriptionally regulated by IL-3 deprivation

Many hematopoietic cells undergo apoptosis when deprived of specific cytokines, and this process requires de novo RNA/protein synthesis. Using DNA microarrays to analyze interleukin-3 (IL-3)-dependent murine FL5.12 pro-B cells, we found that the gene undergoing maximal transcriptional induction after cytokine withdrawal is 24p3, which encodes a secreted lipocalin. Conditioned medium from IL-3-deprived FL5.12 cells contained 24p3 and induced apoptosis in naive FL5.12 cells even when IL-3 was present. 24p3 also induced apoptosis in a wide variety of leukocytes but not other cell types. Apoptotic sensitivity correlated with the presence of a putative 24p3 cell surface receptor. We conclude that IL-3 deprivation activates 24p3 transcription, leading to synthesis and secretion of 24p3, which induces apoptosis through an autocrine pathway.

SAGA is an essential in vivo target of the yeast acidic activator Gal4p

Despite major advances in characterizing the eukaryotic transcriptional machinery, the function of promoter-specific transcriptional activators (activators) is still not understood. For example, in no case have the direct in vivo targets of a transcriptional activator been unambiguously identified, nor has it been resolved whether activators have a single essential target or multiple redundant targets. Here we address these issues for the prototype acidic activator yeast Gal4p. Gal4p binds to the upstream activating sequence (UAS) of GAL1 and several other GAL genes and stimulates transcription in the presence of galactose. Previous studies have shown that GAL1 transcription is dependent on the yeast SAGA (Spt/Ada/GCN5/acetyltransferase) complex. Using formaldehyde-based in vivo cross-linking, we show that the Gal4p activation domain recruits SAGA to the GAL1 UAS. If SAGA is not recruited to the UAS, the preinitiation complex (PIC) fails to assemble at the GAL1 core promoter, and transcription does not occur. SAGA, but not other transcription components, is also recruited by the Gal4p activation domain to a plasmid containing minimal Gal4p-binding sites. Recruitment of SAGA by Gal4p and stimulation of PIC assembly is dependent on several SAGA subunits but not the SAGA histone acetyl-transferase (HAT) GCN5. Based on these and other results, we conclude that SAGA is an essential target of Gal4p that, following recruitment to the UAS, facilitates PIC assembly and transcription.

Use of neuroendocrine markers, p53, and HER2 to predict response to chemotherapy in patients with stage III non-small cell lung cancer: a Cancer and Leukemia Group B study

Several studies have suggested that non-small cell lung cancer (NSCLC) patients whose tumors have neuroendocrine (NE) features may be more responsive to chemotherapy. In addition, increased expression of p53 and HER2 may confer relative chemotherapy resistance and shortened survival. The Cancer and Leukemia Group B performed a series of studies involving sequential chemotherapy followed by radiation for patients with unresectable stage III NSCLC. The objectives of this study were to analyze pathological specimens using immunohistochemistry for NE markers, p53 and HER2 to determine if there was a correlation between marker expression and response or survival. Of 160 eligible patients, 28 (18%) were not evaluable because of inadequate material. The percentage of specimens positive for markers was as follows: neuron-specific enolase 38%, Leu-7 2%, chromogranin A 0%, synaptophysin 5%, > or =2+NE markers 3%, p53 61%, and HER2 65%. There was no statistically significant correlation between any individual marker and response to induction chemotherapy or response to combined chemotherapy/radiation except for synaptophysin. Six of 6 (100%) synaptophysin positive tumors responded by the completion of all therapy compared with 69/125 (55%) synaptophysin negative tumors (P=0.04). None of the individual markers had a significant effect on survival in univariate analysis. Neuron-specific enolase was marginally significant in multivariate analysis (P=0.08). In conclusion, this study did not demonstrate that expression of NE markers, p53 and HER2 were predictive of response to chemotherapy, combined chemotherapy/radiation or for survival in this group of patients with stage III NSCLC. Future studies must employ either different markers or be performed on more adequate surgical specimens.

Beyond pancreatic cancer: irinotecan and gemcitabine in solid tumors and hematologic malignancies

Non-platinum combinations including gemcitabine and irinotecan (Gemzar; Eli Lilly and Company, Indianapolis, IN) for the management of a variety of malignancies have started to emerge. Gemcitabine and irinotecan are well-tolerated single agents, each with a broad spectrum of antitumor activity. Preclinical data suggests synergy for the two drugs when used in combination. A phase I trial has defined a well-tolerated combination regimen using both drugs on a day-1, -8 schedule every 3 weeks. Phase II data suggest activity for the combination in pancreatic cancer, and a phase III trial of the two-drug combination versus gemcitabine alone is underway in previously untreated pancreatic cancer patients. Other phase II trials evaluating the impact of this combination on a variety of other tumors, such as non-small cell lung, small cell lung, breast, colorectal, and non-Hodgkin's lymphoma, are either forthcoming or in progress. Semin Oncol 28 (suppl 10):34-43.

Sequence-specific interaction between HIV-1 matrix protein and viral genomic RNA revealed by in vitro genetic selection

The human immunodeficiency virus type-1 matrix protein (HIV-1 MA) is a multifunctional structural protein synthesized as part of the Pr55 gag polyprotein. We have used in vitro genetic selection to identify an RNA consensus sequence that specifically interacts with MA (Kd = 5 x 10(-7) M). This 13-nt MA binding consensus sequence bears a high degree of homology (77%) to a region (nt 1433-1446) within the POL open reading frame of the HIV-1 genome (consensus sequence from 38 HIV-1 strains). Chemical interference experiments identified the nucleotides within the MA binding consensus sequence involved in direct contact with MA. We further demonstrate that this RNA-protein interaction is mediated through a stretch of basic amino acids within MA. Mutations that disrupt the interaction between MA and its RNA binding site within the HIV-1 genome resulted in a measurable decrease in viral replication.

Twenty-two years of phase III trials for patients with advanced non-small-cell lung cancer: sobering results

PURPOSE

To determine the changes in clinical trials and outcomes of patients with advanced-stage non-small-cell lung cancer (NSCLC) treated on phase III randomized trials initiated in North America from 1973 to 1994.

PATIENTS AND METHODS

Phase III trials for patients with advanced-stage NSCLC were identified through a search of the National Cancer Institute's Cancer Therapy Evaluation Program database from 1973 to 1994, contact with Cooperative Groups, and by literature search of MEDLINE. Patients with advanced NSCLC treated during a similar time interval were also examined in the SEER database. Trends were tested in the number of trials, in the number and sex of patients entered on the trials, and in survival over time.

RESULTS

Thirty-three phase III trials were initiated between 1973 and 1994. Twenty-four trials (73%) were initiated within the first half of this period (1973 to 1983) and accounted for 5,359 (64%) of the 8,434 eligible patients. The median number of patients treated per arm of the trials rose from 77 (1973 to 1983) to 121 (1984 to 1994) (P <.001). Five trials (15%) showed a statistically significant difference in survival between treatment arms, with a median prolongation of the median survival of 2 months (range, 0.7 to 2.7 months).

CONCLUSION

Analysis of past trials in North America shows that the prolongation in median survival between two arms of a randomized study was rarely in excess of 2 months. Techniques for improved use of patient resources and appropriate trial design for phase III randomized therapeutic trials with patients with advanced NSCLC need to be developed.

Irinotecan/gemcitabine combination chemotherapy in pancreatic cancer

Gemcitabine (Gemzar) and irinotecan (CPT-11, Camptosar) are active cytotoxic drugs against pancreatic cancer. Preclinical data evaluating the combination of gemcitabine and irinotecan suggest dose-dependent synergistic interactions in SCOG small-cell lung cancer and MCF-7 breast cancer cell lines. Two phase I trials of this combination have been reported to date: the day 1 and 8 every-3-week schedule (IrinoGem trial), and the day 1, 8, and 15 every-4-week schedule (MSKCC trial). Both trials aimed to determine the maximum tolerated dose of irinotecan when administered as a 90-minute i.v. infusion either immediately after (IrinoGem) or before or immediately after (MSKCC) gemcitabine at 1,000 mg/m2 by 30-minute i.v. infusion in patients with solid tumors. The achieved maximum tolerated dose of IrinoGem has a higher dose intensity of irinotecan (100 mg/m2 on days 1 and 8, every-3-week cycle) compared with the MSKCC schedule (60 mg/m2 on days 1, 8, and 15, every-4-week trial). In IrinoGem, two of three previously untreated metastatic pancreas cancer patients had durable radiologic partial responses. The third had stable disease with clinical benefit for eight cycles. In addition, a patient with metastatic adenocarcinoma of unknown primary--potentially pancreatic--has had a durable response and is alive more than 30 months after the diagnosis. Preliminary results of a 45-patient multicenter phase II trial with IrinoGem in advanced and metastatic pancreas cancer were recently reported. Toxicity was modest, with no toxic deaths or neutropenic fever. Radiologic response rate was 20% of patients (9 out of 45), and a CA 19-9 decrease of more than 50% from baseline values occurred in 32.5% of patients (13 out of 40). Median survival was 6 months (range: 0.9 to 12.2+ months) and median time to treatment failure was 2.9 months (range: 0.1 to 11.3+ months). A pivotal international multicenter phase III trial comparing IrinoGem to single-agent gemcitabine in advanced and metastatic pancreas cancer is ongoing.

Expressing the human genome

We have searched the human genome for genes encoding new proteins that may be involved in three nuclear gene expression processes: transcription, pre-messenger RNA splicing and polyadenylation. A plethora of potential new factors are implicated by sequence in nuclear gene expression, revealing a substantial but selective increase in complexity compared with Drosophila melanogaster and Caenorhabditis elegans. Although the raw genomic information has limitations, its availability offers new experimental approaches for studying gene expression.

The current status of docetaxel for advanced non-small cell lung cancer

Docetaxel is an active single agent in both first- and second-line therapy of patients with advanced non-small cell lung cancer (NSCLC). Randomized trials versus best supportive care have documented an improvement in overall survival for docetaxel therapy in both settings. Docetaxel also produced a significant 1-year survival rate improvement when compared with vinorelbine or ifosfamide as second-line therapy. Docetaxel has been extensively investigated in phase I/II studies in combination with cisplatin, carboplatin, irinotecan and gemcitabine. Substantial activity has been demonstrated. In a randomized phase II trial comparing docetaxel plus cisplatin with docetaxel plus gemcitabine, the efficacy of the two regimens was almost identical (response rates 32 and 34%; 1-year survival rates 42 and 38%). However, the combination of docetaxel with gemcitabine was associated with significantly less grade III/IV neutropenia, diarrhea and nausea/vomiting. Three drug regimens combining docetaxel with, for example, gemcitabine and carboplatin or with ifosfamide and cisplatin, are producing very high response rates in phase II trials. Whether three-drug combinations including docetaxel will result in an improved outcome for patients with advanced NSCLC remains to be determined.

Carboplatin/Etoposide/Paclitaxel in the Treatment of Patients with Extensive Small-Cell Lung Cancer

The purpose of this study was to examine the safety and efficacy of carboplatin/etoposide/paclitaxel in patients with untreated stage IV non-small-cell lung cancer (NSCLC) and extensive small-cell lung cancer (SCLC). Carboplatin was administered intravenously (i.v.) at an area under the curve (AUC) of 6 with etoposide at either 80 or 100 mg/m2 i.v. days 1-3 and paclitaxel at 175 or 200 mg/m2 i.v. over 3 hours along with 5 g/kg of granulocyte colony-stimulating factor subcutaneously on days 4-18, repeated every 3 weeks for 6 courses. Thirty-one patients (five NSCLC and 26 SCLC) entered into this phase I study. The median age was 63 (range, 42 to 74 years), with 24 males and seven females. The recommended dose level for phase II testing was carboplatin AUC = 6, etoposide 80 mg/m2 days 1-3, and paclitaxel 175 mg/m2 over 3 hours. With seven patients at this level, 14% had grade 4 neutropenia, 14% had grade 4 thrombocytopenia, none had grade 2/3 neurotoxicity, and no toxic deaths occurred. One of five (20%) patients with NSCLC responded, and 19 of 22 (86%) evaluable SCLC patients experienced a response to therapy. SCLC patients had a median survival of 10 months. The combination of carboplatin/etoposide/paclitaxel has significant activity with acceptable toxicity in patients with extensive SCLC.

Gemcitabine for malignant mesothelioma: A phase II trial by the Cancer and Leukemia Group B

PURPOSE

The CALGB conducted a phase II multicenter trial to evaluate the activity of gemcitabine in malignant mesothelioma (CALGB protocol 9530).

PATIENTS AND METHODS

Seventeen patients were accrued between February 1996 and May 1996 and received gemcitabine 1500 mg/m(2) by intravenous infusion over 30 min weekly for 3 weeks, followed by a 1 week break. Eligibility included a performance status of 0-2 by CALGB criteria, and no prior chemotherapy. Nine patients had epithelial cell type and eight had mixed or sarcomatoid cell types. There were 11 cases with measurable disease and six with evaluable disease.

RESULTS

There were no complete or partial responders. Eight patients had stable disease, seven developed progressive disease, and two were not evaluable for tumor response. Two patients had minor responses. Median survival from study entry was 4.7 months (95% CI 3.1-12.9 months); one year survival was 24% (95% CI 10-55%). One patient remains alive at 37 months. There were two early deaths, one from disease progression and one from pneumonia. Toxicity was mild and included anemia, lymphopenia and infection; no patient experienced grades three or four thrombocytopenia.

CONCLUSION

No antitumor activity was observed for single-agent gemcitabine in patients with malignant mesothelioma in this multicenter phase II study.

Identification and characterization of yUAP/Sub2p, a yeast homolog of the essential human pre-mRNA splicing factor hUAP56

The human 56-kD U2AF(65)-associated protein (hUAP56), a member of the DExD/H box protein family of RNA-dependent ATPases, is required for the stable binding of U2 snRNP to the pre-mRNA branchpoint. Here we identify a highly conserved Saccharomyces cerevisiae homolog of hUAP56, yUAP/Sub2p. yUAP/Sub2p can be functionally substituted for by hUAP56 and, like its human counterpart, is an essential pre-mRNA splicing factor. yUAP/Sub2p is required for formation of the commitment complex, the precursor for U2 snRNP addition. In conjunction with previous studies, we conclude that at least two DExD/H box proteins, Prp5p and yUAP/Sub2p, mediate the U2 snRNP-branchpoint interaction.

Rapid identification and characterization of hammerhead-ribozyme inhibitors using fluorescence-based technology

The ability to rapidly identify small molecules that interact with RNA would have significant clinical and research applications. Low-molecular-weight molecules that bind to RNA have the potential to be used as drugs. Therefore, technologies facilitating the rapid and reliable identification of such activities become increasingly important. We have applied a fluorescence-based assay to screen for modulators of hammerhead ribozyme (HHR) catalysis from a small library of antibiotic compounds. Several unknown potent inhibitors of the hammerhead cleavage reaction were identified and further characterized. Tuberactinomycin A, for which positive cooperativity of inhibition in vitro was found, also reduced ribozyme cleavage in vivo. The assay is applicable to the screening of mixtures of compounds, as inhibitory activities were detected within a collection of 2,000 extracts from different actinomycete strains. This approach allows the rapid, reliable, and convenient identification and characterization of ribozyme modulators leading to insights difficult to obtain by classical methodology.

Docetaxel followed by gemcitabine and irinotecan in solid tumors

Docetaxel (Taxotere), gemcitabine (Gemzar), and irinotecan (Camptosar, CPT-11) are active single agents in a variety of solid tumors. In combination, synergism may be schedule dependent. Preclinical studies suggested synergistic interactions when docetaxel was administered 24 hours before gemcitabine or irinotecan. The objective of this phase I trial in patients with refractory solid tumors was to determine the maximum tolerated dose of docetaxel followed 24 hours later by gemcitabine and irinotecan. Two different schedules were tested: docetaxel escalated by 5 mg/m2/cohort from an initial dose of 20 mg/m2 on days 1 and 8 (schedule A) or escalated by 15 mg/m2/cohort from 45 mg/m2 on day 8 only (schedule B). In both schedules, docetaxel was given over 1 hour. Gemcitabine and irinotecan were given on days 2 and 9 (arm A) or 1 and 9 (arm B) at fixed doses of 1,000 mg/m2 over 30 minutes and 100 mg/m2 over 90 minutes, respectively. Escalation of docetaxel was planned in groups of three patients, with three additional patients added at the first indication of dose-limiting toxicity. Four dose levels in arm A and one dose level in arm B have been tested. Seventeen patients were evaluable in arm A; one died of an unrelated cause on cycle 1, and another withdrew consent before beginning treatment. Five of six patients were evaluable in arm B; one patient inadvertently received G-CSF on cycle 1. Forty-two cycles have been delivered in arm A (mean; 2.2 cycles/patient), and 25 cycles in arm B (mean, 4.2 cycles/patient); the maximum tolerated dose of docetaxel on arm A was 20 mg/m2. The dose-limiting toxicities were grade 3 diarrhea in one patient, grade 3 infection in two patients, and grade 4 neutropenia for > 4 days in one patient at the 25 mg/m2 level. The dose-limiting toxicities on arm B occurred at the first dose level and included grade 3 diarrhea in one patient, grade 4 diarrhea in one patient, and grade 4 neutropenia for 4 days in another patient. Accrual to schedule B was closed after testing the cohort 1 dose level because testing of a single deescalated docetaxel dose given on day 8 was not considered clinically relevant.

Future randomized trials for non small-cell lung cancer

Combination chemotherapy is the standard of care for management of previously untreated, good performance status patients with advanced non small-cell lung cancer. Most of the regimens in use worldwide are platinum-based doublets. Recent data from the Eastern Cooperative Oncology Group suggest that multiple different platinum-based regimens produce similar response rates and overall survival when used as first-line treatment. In upcoming randomized trials designed to explore possible improvements in therapy, three different strategies are being evaluated. One involves head-to-head comparisons of new, often non-platinum-based doublet combinations with standard platinum-based, two-drug regimens. A second emphasizes the possible benefits of combinations using three cytotoxic agents compared to a two-drug standard. The third is focused on adding a new molecular targeting agent, such as an anti growth factor, growth factor receptor antibody, or an intracellular signal transduction inhibitor, to a standard combination of two cytotoxic drugs. This paper reviews some of the randomized phase III trials exemplifying each of these approaches to therapy for patients with advanced non small-cell lung cancer.

Irinotecan in the management of patients with pancreatic cancer

Synergy with no overlapping toxicities has been demonstrated for the combination of irinotecan (Camptosar, CPT-11) and gemcitabine (Gemzar) in vitro. Results of a single-institution phase I study in which patients with previously untreated pancreatic cancer were given irinotecan and gemcitabine were promising, with two of three patients achieving a partial response. Because of the favorable outcome of the phase I study, a multicenter phase II trial was undertaken in previously untreated patients with pancreatic carcinoma. Data from other sites entering patients in this phase II study have been analyzed, and a multicenter phase III trial of single-agent gemcitabine vs the irinotecan combination in first-line treatment of patients with locally advanced or metastatic pancreatic cancer is underway.

Atmospheric oxygen accelerates the induction of a post-mitotic phenotype in human dermal fibroblasts: the key protective role of glutathione

It has been proposed that ageing of human dermal fibroblasts occurs as a multi-stage process during which cells progress from a mitotic to a post-mitotic state. We describe the development of a simple and novel cell-cloning model for identifying and quantifying the different fibroblast morphotypes associated with the induction of post mitotic behaviour. We have found that under atmospheric (20%) oxygen tension a significant proportion of human dermal fibroblasts are rapidly induced to switch from a mitotic to a post-mitotic phenotype. In contrast, under more physiological (4%) oxygen conditions, the induction of a post-mitotic phenotype is largely prevented. Increasing oxidative stress by addition of hydrogen peroxide or depletion of glutathione also induced a switch from a mitotic to a post-mitotic phenotype in these cells, whereas addition of the anti-oxidant N-acetylcysteine under atmospheric (20%) oxygen tension potently inhibited this process. In addition, a statistically significant correlation was observed between the magnitude of intracellular glutathione depletion and the reduction in the population of mitotic cells in this model. We propose that the switch from a mitotic to a post-mitotic phenotype represents a process of cellular ageing and that standard atmospheric oxygen tension imposes a substantial oxidative stress on dermal fibroblasts which accelerates this process in culture. The data also suggest that intracellular glutathione levels strongly influence the induction of a post-mitotic phenotype and that, by implication, depletion of glutathione may play a significant role in the progression of cellular ageing in human skin.

Radiation and chemotherapy for patients with stage III non-small cell lung cancer

Nearly 50,000 people in the United States will be diagnosed with stage III non-small cell lung cancer during the year 2000. Over the past 10 years, combined modality therapy has become the standard of care for primary treatment of most of these patients. Numerous studies and meta-analyses document an improvement in survival for patients with stage III disease treated with sequential chemotherapy followed by chest radiation, compared with radiation alone. Some more recent studies have shown a further improvement in survival when the chemotherapy and full-dose radiation are given concurrently. Acute toxicity is increased compared with sequential chemotherapy followed by radiation, but late toxicities seem similar. A current question under study is whether the use of initial chemotherapy followed by concurrent chemoradiotherapy will further improve median and overall survival compared with immediate concurrent therapy alone.