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At least 973 records · Page 54Linked to original sources
PubMed2001

Aza-[3,3]-Claisen enolate rearrangement in vinylaziridines: stereoselective synthesis of mono-, di-, and trisubstituted seven-membered lactams.

Several 2,3-disubstituted vinylaziridines have been N-acylated and subjected to LiHMDS in THF at -78 degrees C. Upon warming to room temperature, the resulting amide enolates underwent a highly stereoselective [3,3]-sigmatropic rearrangement to give mono-, di-, and trisubstituted seven-membered lactams in good yields. The scope and limitations of the process have been investigated by using variously substituted vinylaziridines. A kinetically controlled process proceeding through a six-membered boatlike transition state assembly has been invoked to explain the stereochemical outcome of the reaction.

Aziridines↗
PubMed1990

Treatment of relapsed and refractory acute myeloid leukemia with diaziquone and mitoxantrone: a CALGB phase I study.

Twenty-one patients with relapsed or refractory acute myeloid leukemia (AML) were treated with mitoxantrone (12 mg/m2/day, days 1-3) and diaziquone (continuous infusion days 1-5). The dosage of diaziquone was increased for sequential cohorts of seven patients from 20 mg/m2/day to 24 mg/m2/day, and finally to 28 mg/m2/day to determine the maximum tolerated dose for this chemotherapy combination. Myelosuppression was the dose-limiting toxicity. The median time to recovery of blood counts was greater at the highest dose of diaziquone (48 days) than at the lower two doses (31 and 28 days). Other toxic effects were minimal. Overall, 9/21 (43%, 95% confidence interval, 0.22 to 0.66) patients achieved complete remission. We conclude that this combination of drugs shows sufficient antileukemic activity with acceptable toxicity to warrant further trials.

Adult↗
PubMed1988

Corporate influence on threshold limit values.

Investigations into the historical development of specific Threshold Limit Values (TLVs) for many substances have revealed serious shortcomings in the process followed by the American Conference of Governmental Industrial Hygienists. Unpublished corporate communications were important in developing TLVs for 104 substances; for 15 of these, the TLV documentation was based solely on such information. Efforts to obtain written copies of this unpublished material were mostly unsuccessful. Case studies on the TLV Committee's handling of lead and seven carcinogens illustrate various aspects of corporate influence and interaction with the committee. Corporate representatives listed officially as "consultants" since 1970 were given primary responsibility for developing TLVs on proprietary chemicals of the companies that employed them (Dow, DuPont). It is concluded that an ongoing international effort is needed to develop scientifically based guidelines to replace the TLVs in a climate of openness and without manipulation by vested interests.

Acrylonitrile↗
PubMed1988

Successful chemotherapy for recurrent malignant oligodendroglioma.

Eight consecutive patients with recurrent malignant oligodendroglioma were treated with systemic chemotherapy. Six patients received a combination of procarbazine, lomustine (CCNU), and vincristine; 1 received carmustine (BCNU), and 1 diaziquone. All responded by clinical and computed tomographic scan criteria. One patient had a complete response for 78 weeks, and 7 patients had unequivocal partial responses lasting 30+ to 68+ weeks. Two partial responders had complete control of systemic metastases. Malignant oligodendroglioma is a uniquely chemosensitive glial tumor.

Adult↗
PubMed1990

A randomized controlled trial of ciamexon versus placebo in the immunomodulatory treatment of rheumatoid arthritis.

To determine the efficacy of the new immunosuppressive agent ciamexon in patients with rheumatoid arthritis (RA), we conducted a 6-month, prospective, double-blind, placebo-controlled study. The study included 21 outpatients with confirmed RA, who were randomized into 3 treatment groups of 7 patients each. Group 1 received 400 mg/day of ciamexon, group 2 received 100 mg/day of ciamexon, and group 3 received placebo. We investigated the influence of ciamexon on the clinical course, the systemic inflammatory activity, and the lymphocyte subsets in the peripheral blood. Significant, dose-dependent improvement was seen in both the clinical and the biochemical activity indexes at the end of the treatment period (P = 0.02 to P = 0.05). The proportion of activated T lymphocytes was significantly decreased (P = 0.05), and the proportion of CD8-positive lymphocytes was significantly increased (P = 0.03) in patients taking ciamexon. The major adverse effects were hepatotoxicity (2 patients) and rash (2 patients). This study documents the clinical efficacy of ciamexon therapy in RA patients and identifies the agent's potential toxicity.

Adjuvants, Immunologic↗
PubMed1980

Mass spectrometry as a technique for testing the purity of drugs for biological use: the case of new antitumor cyclophosphazenes.

Mass spectrometry has been used for testing the chemical purity of some new antitumor cyclophosphazene compounds. the spectrum of N3P3Az6 (code name MYKO 63)--which exhibits noticeable activity on murine P 388, L 1210 and B 16 tumors--appeared to be remarkably simple, as most of the fragmentations arose from successive losses of the aziridino radicals. Traces of the pentaziridinomonochloro impurity formed by an incomplete substitution of N3P3Cl6 chlorine atoms under aziridinolysis could be detected in an impure and toxic sample by spectral subtraction. Quantification of this impurity was performed by selected ion monitoring in the direct inlet mode of sample introduction. The mass spectra of other derivatives of this class of compounds are slightly more complex, since the decomposition pathways showed more intense H-transfers associated with the loss of substituents.

Antineoplastic Agents↗
PubMed1990

Supercritical fluid chromatography/chemical ionization/mass spectrometry of some anticancer drugs in a thermospray ion source.

A packed-column supercritical-fluid chromatograph was interfaced with a mass spectrometer via a modification of a thermospray probe. This modification allowed a capillary restrictor for the supercritical fluid (CO2) and reagent gas for chemical ionization to be introduced directly into a thermospray source. Chemical ionization conditions were observed when either the filament or discharge electrode was used and the source pressure was above 0.5 torr. The discharge electrode produced more efficient ionization, resulting in approximately a tenfold larger signal than that observed in the filament mode. The usefulness of this instrumentation was demonstrated on several anticancer drugs. Methanol positive ion chemical ionization (PICI) spectra were recorded for cyclophosphamide, diaziquone, mitomycin C and thiotepa. Methane PICI spectra of thiotepa were obtained in the absence of methanol as a mobile-phase modifier. A 50 ng on-column injection of diaziquone produced approximately a 6:1 signal to noise ratio in the scanning mode.

Antineoplastic Agents↗
PubMed1991

Genotoxicity studies with the unstable zeste-white (UZ) system of Drosophila melanogaster: results with ten carcinogenic compounds.

To increase the number of chemicals tested using the zeste-white (UZ) somatic mutation assay, ten selected carcinogens (acetamide, acrylamide, benzo(alpha)pyrene, cyclophosphamide, diethylstilbestrol, 4-nitroquinoline N-oxide, propyleneimine, safrole, thiourea, and o-toluidine) have been evaluated in this assay. Our results show that all the compounds tested produce significant increases in the eye spot frequency at, at least, one of the concentrations assayed, indicating that the zeste-white assay appears to be highly sensitive to these carcinogenic compounds. That is in agreement with data previously reported by other authors.

4-Nitroquinoline-1-oxide↗
PubMed1988

Persistence of SCE-inducing lesions in lymphocytes of mice exposed to diaziquone.

Male C57B1/6 mice were injected i.p. with either 1.25 or 5.0 mg/kg diaziquone (AZQ) and killed at various time intervals from 1 to 99 days post treatment for examination of sister chromatid exchange (SCE) persistence in the peripheral blood lymphocytes (PBLs) and splenocytes. SCE frequencies were found to decay steeply during the first week after exposure in both PBLs and splenocytes. This pattern was followed by a slower decline to baseline over the next week. However, high-frequency cell (HFC) analysis indicates that significant numbers of HFCs persist in the PBLs through day 28 and splenocytes at day 99 post exposure. Mathematical modeling of the time-response curves indicates that the average life span of the majority of AZQ-induced SCE-producing lesions in murine PBLs and splenocytes responsive to phytohemagglutinin is between 3 and 5 days.

Animals↗
PubMed2001

Inducible ablation of astrocytes shows that these cells are required for neuronal survival in the adult brain.

To study the function of astrocytes in the adult brain, we have targeted the expression of E. coli nitroreductase (NTR) to the astrocytes of transgenic mice under the control of the GFAP promoter. The astrocytes expressing NTR were selectively ablated after administration of the prodrug CB1954, resulting in motor discoordination. Histological examination showed that the region most affected in the brain was the cerebellum, in which the Bergmann glia were eliminated and the granular neurons had degenerated. Specific effects were also noted on the dendrites of the Purkinje cells, and the junction between these neurons and granular layer was disrupted. Astrocyte ablation was associated with a dramatic decrease in the expression of glutamate transporters, which may account for the degeneration of granular neurons since the excitotoxic effects of glutamate result in a similar phenotype. These results provide the first evidence that astrocytes are important for the survival of neurons in the adult brain in vivo.

ATP-Binding Cassette Transporters↗
PubMed1998

Regulation of cyclin G1 during murine hepatic regeneration following Dipin-induced DNA damage.

Cyclin G1 has been linked to both positive and negative growth regulation. The expression of cyclin G1 is induced by transforming growth factor beta1 and p53, as well as by multiple mitogenic stimuli in mammalian cells in culture. However, the physiological role of cyclin G1 remains unclear. To examine the cell-cycle regulation of cyclin G1 in vivo, two models of coordinated cell proliferation induced by partial hepatectomy (PH) in the presence or absence of DNA damage were used. To introduce DNA damage, mice were treated with the alkylating drug, 1,4-bis[N,N'-di(ethylene)-phosphamide]piperazine (Dipin) 2 hours before PH. Cell-cycle progression was monitored by 5-bromo-2-deoxyuridine (BrdU) incorporation into the DNA, the frequency of mitoses, the expression of cell-cycle control genes, and by flow cytometry. Dipin treatment resulted in cell-cycle arrest at the G2/M boundary without affecting G0/G1 and G1/S transitions. While the hepatocytes progressively entered G2 phase arrest, the cyclin G1 mRNA and protein levels increased more than five- and eightfold, respectively. Cyclin G1 had a nuclear localization in all interphase cells with clear absence from nucleoli. In contrast, during mitosis, cyclin G1 was undetectable by immunohistochemistry. Taken together, our data provide evidence for a putative role of cyclin G1 in G2/M checkpoint control.

Animals↗
PubMed2003

Immune enhancement of nitroreductase-induced cytotoxicity: studies using a bicistronic adenovirus vector.

The nitroreductase (NR)/CB1954 enzyme prodrug system has given promising results in preclinical studies and is currently being assessed in phase I clinical trials. It is well established that there is an immune component to the bystander effect observed with other systems such as thymidine kinase and cytosine deaminase; however, such an effect has not previously been described using NR. We have preliminary data suggesting an immune bystander effect with NR to further examine these effects and their potential enhancement by cytokines, an adenoviral vector containing CMV-NR, an internal ribosome entry site (IRES) and the gene for murine GM-CSF (mGM-CSF) was constructed. The NR-GM-CSF virus was validated in 2 experimental models and demonstrated increased therapeutic efficacy in the MC26 murine colorectal tumour model. These data illustrate that the combination of suicide gene therapy using NR and CB1954 with immune stimulation via GM-CSF gives an improved response compared to either modality alone and suggests that the immune component of this response may be beneficial in combating unresectable, metastatic disease and preventing tumour recurrence.

Adenocarcinoma↗
PubMed2001

Appropriate subcellular localisation of prodrug-activating enzymes has important consequences for suicide gene therapy.

Escherichia coli B nitroreductase (NR) has been expressed stably in MDA-MB-361 human breast adenocarcinoma cells either as the wild-type protein (wtNR), which is distributed evenly between the cytoplasmic and nuclear compartments, or targeted to the mitochondrion (mtNR). Whereas bacterial NR is active as a dimer, a proportion of wtNR is monomeric. In contrast, mtNR is mostly dimeric, suggesting that it adopts a more stable, native conformation. Despite this, when tested in gene-directed enzyme prodrug therapy cell cytotoxicity studies, cells expressing wtNR or mtNR had similar sensitivity to the prodrug CB1954 and mounted similar bystander killing effects. Furthermore, when short prodrug exposures were given, wtNR was more efficient at killing cells than mtNR. These data demonstrate that the site of enzyme expression and prodrug activation is an important variable that requires consideration in suicide gene therapy approaches.

Adenocarcinoma↗
PubMed1994

Unusually marked hypoxic sensitization to indoloquinone EO9 and mitomycin C in a human colon-tumour cell line that lacks DT-diaphorase activity.

Studies with purified DT-diaphorase have shown that the enzyme is capable of catalyzing a two-electron reduction of the novel indoloquinone EO9 to a DNA-damaging alkylating species. The aim of this study was to determine to what extent DT-diaphorase may be involved in the metabolic activation of EO9 and mitomycin C in both aerobic and hypoxic conditions. Two human colon-carcinoma cell lines were used; HT29 has high levels of DT-diaphorase whilst BE lacks this activity because of a point mutation in the NQOI gene. In aerobic conditions the 2 cell lines show similar sensitivities to a number of cytotoxic drugs including cisplatin, doxorubicin and etoposide. They are equally sensitive to the benzotriazine di-N-oxide SR 4233 but HT29 is more sensitive than BE to mitomycin C and EO9. Sensitivity to SR 4233 is increased by about 100-fold for both cell lines in hypoxic conditions. DT-diaphorase-deficient BE cells show markedly increased sensitivity to mitomycin C and particularly EO9 in hypoxic conditions, whereas DT-diaphorase-rich HT29 cells show little hypoxic sensitization to these agents unless exposed in the presence of dicoumarol. These results suggest that DT-diaphorase can reduce EO9 and mitomycin C to potent cytotoxic species in aerobic conditions, and this activity predominates over the one-electron-reducing enzymes even in hypoxic conditions. In the absence of DT-diaphorase activity, EO9 and mitomycin C are reduced in hypoxic conditions, presumably by one-electron-reducing enzymes, to a similar or greater extent than is achieved with DT-diaphorase.

Aerobiosis↗