Biomedical subjects

R C French

Publications and source records attributed to R C French.

16 recordsLinked to original sources

PubMed2000

Similarity and divergence among viruses in the genus Furovirus.

Nucleotide sequences of RNAs 1 and 2 of a Japanese strain of soil-borne wheat mosaic virus (SBWMV), the type species of the genus Furovirus, and sorghum chlorotic spot virus (SCSV) were determined from cloned cDNA. The relationship among the Japanese and US strains of SBWMV, SCSV, oat golden stripe virus (OGSV), and recently proposed Chinese wheat mosaic and European wheat mosaic viruses (CWMV and EWMV) were examined at the nucleotide and amino acid levels. Pairwise comparisons of genome-encoded proteins among the six viruses showed that the US strains of SBWMV and CWMV were the most closely related pair in RNA 1 and the Japanese strains of SBWMV and EWMV were most closely related in RNA 2. SCSV was most distantly related to the other five viruses. Phylogenetic analysis indicated that there may have been an ancient reassortment between RNAs 1 and 2 of the four wheat-infecting viruses and OGSV, while SCSV was shown to have separated from the rest before the other five viruses diverged. The fact that CWMV and EWMV have almost identical biological properties as well as the sequence similarities to the two strains of SBWMV suggests that they be regarded as strains of SBWMV, considering that SBWMV consists of genetically diverged strains. OGSV and SCSV are distinct in biological properties in addition to genetic divergence in the genus Furovirus.

Base Sequence↗

PubMed1997

Protein kinase C: a worthwhile target for anticancer drugs?

Protein kinase C (PKC) is an enzyme family with serine/threonine kinase function which is involved in the transduction of signals for cell proliferation and differentiation. The important role played in processes relevant to neoplastic transformation, carcinogenesis and tumor cell invasion renders PKC a potentially suitable target for anticancer therapy. Bryostatin 1, a macrocyclic lactone isolated from Bugula nerutina, is a partial PKC agonist, and has shown potent antineoplastic properties in vitro and in vivo. Staurosporine, an alkaloid isolated from microbial sources, is ine of the most potent PKC inhibitors and has shown high antiproliferative activity in vitro, but poor selectivity. Staurosporine analogs have thus been synthesize with the aim of obtaining more selective PKC inhibition; among these, CGP 41251 has shown reduced PKC inhibitory activity, but a higher degree of selectivity when assayed for inhibition of different kinases. Several studies indicate a role for PKC in the regulation of the multidrug resistance (MDR) phenotype, since several PKC inhibitors are able to partially reverse MDR and inhibit P-glycoprotein (Pgp) phosphorylation. The MDR phenotype is also associated with variation in PKC isoenzyme content, in particular with PKC-alpha overexpression. While adequate PKC modulation might offer an attractive concept to modulate MDR, other potential mechanisms of PKC interaction with anticancer drugs exist and have been documented, such as the enhancement of chemotherapy-induced apoptosis by safingol, a specific PKC inhibitor. Three phase I clinical trials with bryostatin have been completed so far and have shown that myalgia is the dose-limiting toxicity, while some antitumor activity is evident. Safingol is presently undergoing a phase I clinical trial in combination with doxorubicin. While no definitive data are presently available, it appears that safingol plasma levels approach those associated with chemopotentiation in animals and no pharmacokinetic interaction between the two drugs exists. Drugs targeting PKC are well work considering for clinical trials, particularly for their potential as modulators of currently available cytotoxic agents.

Animals↗

PubMed1995

Effect of human recombinant interferon-alpha on the activity of cis-diamminedichloroplatinum(II) in human non-small cell lung cancer xenografts.

Interferons (IFNs) augment the effect of some antitumor agents, including cis-diamminedichloroplatinum(II) (cDDP), in experimental systems. The effect of human recombinant interferon-alpha 2b (rIFN alpha) on the cDDP-dependent growth delay of a human non-small cell lung cancer established as a xenograft in nude mice (NX002) has been investigated. IFN (10(5) IU/mouse, s.c.) as a single agent had no effect on the growth of the xenograft. cDDP (4.2 mg/kg, i.p.) caused a specific growth delay of 0.42, and this delay was significantly enhanced (to 1.08) by concomitant dosing with the otherwise inactive IFN. Possible mechanisms for this supra-additive relationship between IFN and cDDP have been investigated: increased intratumoral accumulation of platinum was seen at late time points (maximally at 36 hr) during the pharmacokinetic beta-phase of cDDP elimination from the plasma of the nude mice. Tumor:plasma platinum concentration ratios at 36-48 hr indicated significantly increased accumulation of platinum in tumors from IFN-treated mice compared to controls (p < 0.05). Scheduling experiments suggest that this IFN-mediated effect can persist for 4 hr. These differences may account for the enhanced antitumor activity of cDDP when coadministered with IFN.

Animals↗

PubMed1993

Application of high-performance liquid chromatography for recognition of covalent nucleic acid modification with anticancer drugs.

Covalent modification of DNA by antineoplastic agents represents a potent biochemical lesion which can play a major role in drug mechanism of action. The ability to measure levels of DNA covalent modifications in target cells in vivo may, therefore, be seen as the ultimate form of therapeutic drug monitoring. Additionally, elucidation of the structure of critical DNA adducts and definition of their role in tumour cell cytotoxicity will provide more selective targets for rational drug design of new cancer chemotherapeutic agents. High-performance liquid chromatography has contributed significantly to all these areas. In vivo levels of nucleic acid covalent modifications are in the range of 1 in 10(5)-10(8) nucleotides precluding the use of conventional high-performance liquid chromatographic detection methods. Several classes of natural product anticancer drugs have been shown to bond covalently to nucleic acids under optimal laboratory conditions. These have proved more accessible to high-performance liquid chromatographic analysis because of their lipophilicity and strong UV chromophores. However, the majority of experimental evidence to date suggests that with the exception of mitomycin C and morpholino-anthracyclines these compounds do not exert their primary mechanism of action through nucleic acid covalent modification. DNA adducts of alkylating and platinating agents are more difficult to detect by high-performance liquid chromatography and can be chemically unstable. These compounds interact with DNA on the basis of chemical kinetics. Thus, the principle sites of attachment tend to be with the most nucleophilic base (guanine) at its most reactive centre (N-7 position). Limited in vivo high-performance liquid chromatographic studies with all classes of anticancer drugs indicate a much more complex pattern of adductation than would have been anticipated from in vitro studies alone. Some of these differences are probably due to methodological artefacts but these studies stress the need for sensitive detection methods and reliable sample preparation (nucleic acid extraction and digestion techniques) when attempting to determine nucleic acid covalent modifications by anticancer drugs.

Animals↗

PubMed1993

The comparative disposition of the pyrolloquinone GR63178A and its 9-hydroxy metabolite GR54374X in sensitive and resistant mouse colon adenocarcinoma.

The novel anticancer compound GR63178A is being evaluated in the clinic, having demonstrated activity against a wide range of experimental tumour systems in animals without significant toxic side-effects being apparent. In this work, we have demonstrated significant antitumour action of this compound against one murine colon cancer model (colon 38 tumour in BDF-1 mice, specific growth delay = 1.2) when given at 10 mg/kg over 21 consecutive days and in contrast shown minimal sensitivity of another similar murine colon adenocarcinoma, MAC 26, in NMRI mice with the same dose regime. We investigated the disposition of both the parent drug and the 9-OH metabolite (GR54374X) in plasma, tissues and tumours, using solid phase extraction followed by reversed-phase high performance liquid chromatography. Although plasma clearance profiles of GR63178A were similar, significant differences were seen in the disposition of the drug to major organs in two mouse strains. Noteably, the liver and kidneys of the sensitive model had higher levels of parent drug and 9-OH metabolite at both 30 min and 4 h post-injection. However, this was not apparent in the tumours themselves, and the levels of 9-OH metabolite were lower in the plasma and higher in the urine of the sensitive mice, indicating possible rapid renal clearance of this compound. Neither GR63178A nor GR54374X proved cytotoxic in in vitro experiments. The data presented here have revealed considerable variation in drug handling by these two mouse strains, but this did not produce different levels of either parent drug or GR54374X in the tumours, which are the presumed targets, suggesting that differences in disposition are probably not responsible for the different sensitivities of the two tumours. Other possible explanations include the production of a hitherto undetected ultimate cytotoxic metabolite in the sensitive, but not in the resistant, mouse/tumour combination, or differences in inherent tumour sensitivity, or in host-mediated effects. These possibilities are discussed.

Adenocarcinoma↗

PubMed1993

Stability of GR63178A, a novel pentacyclic pyrroloquinone anticancer compound, in aqueous solutions and biological fluids.

The effect of temperature, pH, light, drug concentration and aeration on the stability of aqueous solutions of GR63178A, a novel anticancer compound, has been investigated. The effect of light upon the stability of GR63178A in a clinical infusion system and in biological fluids, has also been investigated. A high performance liquid chromatographic assay was used to separate the parent compound from a number of degradation products. Data presented here demonstrate that GR63178A is stable in aqueous solutions at normal ambient temperatures in neutral or alkaline pH ranges. The compound is unstable when exposed to light (t1/2 3.2-233 min) and shows an inverse relationship between concentration and rate of degradation. The drug is also unstable under acidic conditions, but shows a more limited spectrum of degradation products than those arising from photolysis.

Antineoplastic Agents↗

PubMed1991

Chromatographic characterisation of six human metabolites of the new anticancer drug GR63178A.

GR63178A is the second pentacyclic pyrroloquinone to enter clinical trials as an anticancer drug. We developed a reversed-phase, gradient-elution high-performance liquid chromatography (HPLC) method along with a Bond Elut C2 mini-column sample-preparation technique for the analysis of GR63178A, its 9-hydroxy-metabolite GR54374X and internal standard GR70440A in human plasma and urine. The limit of detection is 2 ng/ml for both GR63178A and GR54374X. Analysis of GR63178A is complicated by its light instability, whereby a number of chromatographically distinct, stable degradation products can form. These can be practically eliminated if clinical specimens are frozen immediately and all subsequent sample preparation is performed in a darkroom. Using this methodology, a total of six metabolites (including GR54374X) were detected in human plasma and urine specimens. The five new metabolites were characterised according to polarity (HPLC retention time), UV-visible absorption maxima and the effect of incubation with beta-glucuronidase and aryl-sulphatase. Application of this methodology to the analysis of GR63178A will aid in the development of this novel synthetic anticancer drug.

Antineoplastic Agents↗

PubMed1987

Metabolic activation of 1-naphthol and phenol by a simple superoxide-generating system and human leukocytes.

Phenol and 1-naphthol, products of benzene and naphthalene biotransformation, are metabolized during O2- generation by xanthine oxidase/hypoxanthine and phorbol myristate acetate (PMA)-stimulated human neutrophils. The addition of 1-naphthol to xanthine oxidase/hypoxanthine incubations resulted in the formation of 1,4-naphthoquinone (1,4-NQ) whereas phenol addition yielded only small quantities of hydroquinone, catechol and a unidentified reducible product but not 1,4-benzoquinone. This formation of 1,4-NQ was dependent upon hypoxanthine, xanthine oxidase, and 1-naphthol and was inhibited by the addition of superoxide dismutase (SOD) demonstrating that the conversion was O2-mediated. During O2- generation by PMA-stimulated neutrophils, the addition of phenol interfered with luminol-dependent chemiluminescence and resulted in covalent binding of phenol to protein. Protein binding was 80% inhibited by the addition of azide or catalase to the incubations indicating that bioactivation was peroxidase-mediated. In contrast, the addition of 1-naphthol to PMA-stimulated neutrophils interfered with superoxide-dependent cytochrome c reduction as well as luminol-dependent chemiluminescence and also resulted in protein binding. Protein binding was only partially inhibited by azide or catalase. The addition of SOD in combination with catalase resulted in a significantly greater inhibition of binding when compared to that of catalase alone. The results of these experiments indicate that phenol and 1-naphthol are converted to reactive metabolites during superoxide generating conditions but by different mechanisms. The formation of reactive metabolites from phenol was almost exclusively peroxidase-mediated whereas the bioactivation of 1-naphthol could occur by two different mechanisms, a peroxidase-dependent and a direct superoxide-dependent mechanism.

Benzoquinones↗

PubMed1987

Metabolic activation of diethylstilbestrol by stimulated human leukocytes.

Previous studies have implicated both peroxidases and leukocytes in the metabolic activation of the human carcinogen diethylstilbestrol (DES). Here we demonstrate that DES is converted during the oxidative burst of human leukocytes to reactive protein binding species. Although luminol-dependent chemiluminescence indicated that peroxidase-dependent metabolism was occurring, the protein binding was not inhibitable by azide. This suggested that either peroxidase-mediated metabolism was not responsible for the formation of the reactive protein binding species or that this binding was occurring in a cellular compartment inaccessible to azide. The addition of catalase alone and in combination with superoxide dismutase (SOD) did, however, result in significant inhibition of binding. Hypochlorous acid was also shown to be capable of directly converting DES to protein binding species. These results indicate that a product of the oxidative burst, most likely a highly oxidizing species derived from H2O2, is capable of converting DES to a potentially carcinogenic binding species.

Catalase↗

PubMed1984

Detection of double-stranded RNA by serologically specific electron microscopy.

Details of a procedure for detecting double-stranded RNA (dsRNA) in virus and viroid infected tissue extracts using serologically specific electron microscopy are given. A method for staining dsRNA, based on in situ formation of uranyl phosphate, that consistently permits the examination of dsRNA by electron microscopy without shadowing with heavy metals, is described. The method provides for routine assays for dsRNA in crude extracts without the variable results associated with shadowing procedures. DsRNA was found to accumulate in older leaves of sorghum systemically infected with sugarcane mosaic virus. In contrast, dsRNA was not detected in older cowpea leaves systemically infected with cowpea mosaic virus but was readily found in inoculated leaves 4 days post inoculation and young systemically infected leaves.

Microscopy, Electron↗

PubMed1969