A streamlined process to phenotypically profile heterologous cDNAs in parallel using yeast cell-based assays

To meet the demands of developing lead drugs for the profusion of human genes being sequenced as part of the human genome project, we developed a high-throughput assay construction method in yeast. A set of optimized techniques allows us to rapidly transfer large numbers of heterologous cDNAs from nonyeast plasmids into yeast expression vectors. These high- or low-copy yeast expression plasmids are then converted quickly into integration-competent vectors for phenotypic profiling of the heterologous gene products. The process was validated first by testing proteins of diverse function, such as p38, poly(ADP-ribose) polymerase-1, and PI 3-kinase, by making active-site mutations and using existing small molecule inhibitors of these proteins. For less well-characterized genes, a novel random mutagenesis scheme was developed that allows a combination selection/screen for mutations that retain full-length expression and yet reverse a growth phenotype in yeast. A broad range of proteins in different functional classes has been profiled, with an average yield for growth interference phenotypes of approximately 30%. The ease of manipulation of the yeast genome affords us the opportunity to approach drug discovery and exploratory biology on a genomic scale and shortens assay development time significantly.

Novel inhibitors of poly(ADP-ribose) polymerase/PARP1 and PARP2 identified using a cell-based screen in yeast

Multicellular organisms must have means of preserving their genomic integrity or face catastrophic consequences such as uncontrolled cell proliferation or massive cell death. One response is a modification of nuclear proteins by the addition and removal of polymers of ADP-ribose that modulate the properties of DNA-binding proteins involved in DNA repair and metabolism. These ADP-ribose units are added by poly(ADP-ribose) polymerase (PARP) and removed by poly(ADP-ribose) glycohydrolase. Although budding yeast Saccharomyces cerevisiae does not possess proteins with significant sequence similarity to the human PARP family of proteins, we identified novel small molecule inhibitors against two family members, PARP1 and PARP2, using a cell-based assay in yeast. The assay was based on the reversal of growth inhibition caused by the heterologous expression of either PARP1 or PARP2. Validation of the assay was achieved by showing that the growth inhibition was relieved by a mutation in a single residue in the catalytic site of PARP1 or PARP2 or exposure of yeast to a known PARP1 inhibitor, 6(5H)-phenanthridinone. In separate experiments, when a putative protein regulator of PARP activity, human poly(ADP-ribose) glycohydrolase, was coexpressed with PARP1 or PARP2, yeast growth was restored. Finally, the inhibitors identified by screening the yeast assay are active in a mammalian PARP biochemical assay and inhibit PARP1 and PARP2 activity in yeast cell extracts. Thus, our data reflect the strength of using yeast to identify small molecule inhibitors of therapeutically relevant gene families, including those that are not found in yeast, such as PARP. The resultant inhibitors have two critical uses (a) as leads for drug development and (b) as tools to dissect cellular function.

Selenium causes growth inhibition and apoptosis in human brain tumor cell lines

We examined the effect of the trace element selenium on human glioma cell lines: T98G, U373MG, and U87MG, in addition to dermal fibroblast cells. Cultures were incubated with sodium selenite, and the following parameters were studied: cell growth, mitochondrial function, and ultrastructure. Cell growth was assayed by counting the number of viable cells after treatment with selenium. Mitochondrial function was analyzed using the MTT (tetrazolium salt reduction) assay. Apoptosis was determined by evaluating nuclear chromatin condensation by electron microscopy. The results indicated that selenium had a significant inhibitory effect on the growth of the tumor cells but had little effect upon dermal fibroblasts which had been passaged numerous times. Selenium also induced mitochondrial damage as shown by MTT assay in two brain tumor cell lines and in minimally passaged fibroblasts, but it had little effect upon the high-passage fibroblasts. Ultrastructurally, mitochondria had electron-dense inclusions resulting from selenium treatment. High rates of apoptosis were induced by selenium in the tumor cell lines and in the minimally passaged fibroblasts, whereas the fibroblasts with a high number of passages had some resistance to selenium treatment. This study correlates the adverse effects of selenium on mitochondrial function, inhibition of cell growth, and apoptosis and shows that selenium similarly affects three different brain tumor cell lines and minimally passaged fibroblasts. Further, the results with fibroblasts show that some types of cells after repeated passages can develop resistance to selenium damage.

Sequential imaging and volumetric analysis of an intracerebral C6 glioma by means of a clinical MRI system

In this study, using high resolution coils; implanted growing rat brain tumors were imaged sequentially with 3-D volume measurements generated by means of a clinical magnetic resonance imaging system (CMRI) and commercially available wrist coil. Ten female Sprague-Dawley rats were used, eight were implanted with C6 rat glioma cells and two served as controls. The images that were used for the three-dimensional (3-D) measurements were obtained from T1 weighted post contrast sequences. A commercially available computer work station with 3-D image analysis software was used to generate the tumor volumes. In addition to the rat studies a mouse was included to see if the resolution would be adequate for imaging very small brains. Six rats had brain tumor growth after transplantation and two rats did not have any tumor growth, however, their images were similar to the controls animals. Tumor volumes varied widely among the implanted rats. The number of implanted tumor cells had no direct relationship to developing tumor volumes. This study demonstrates that high resolution images of a rat brain tumor can be obtained from a CMRI system using a commercially available wrist coil which is capable of imaging two rats at the same time or even a mouse brain. A commercially available computer work station was able to generate the tumor volumes. The ability to image brain tumor and generate volume measurements over time has potential for animal research.

Long-term remission of malignant brain tumors after intracranial infection: a report of four cases

OBJECTIVE

This report describes four patients with malignant brain tumors in whom regression or cure seems to be related to infection with bacteria.

METHODS

An analysis of the four clinical cases reported and a review of the literature produced a comprehensive body of both experimental and clinical data concerning the antineoplastic properties of bacteria.

RESULTS

Although direct oncolytic effects from bacteria have been suggested, immune adjuvant responses to tumor suppression are emphasized. In one of our patients, infiltration of numerous granulocytes and lymphocytes into the tumor at the time of initial surgery was observed, suggesting that a spontaneous immune reaction had begun. Also, in two other patients, tumor aggression occurred in association with a bacterial process that was not in direct contact with the tumor. In three of the cases described, Enterobacter aerogenes was recovered from the microbial cultures. Whether the presence of this organism was coincidental or whether this organism plays an important role in tumor defense is not known; however, a specific cross-reactive immunological attack to the tumor is suggested.

CONCLUSION

The case histories presented in conjunction with the relevant literature reviewed support the concept that microbial infections may influence immune responses in brain tumor defense.

A public health approach to nursing in the community

This article, the first in a three-part series on public health, promotes the case for community nurses to grasp the opportunities a public health approach to care offers to populations and communities. The importance of organisation and evaluation are emphasised as is the need for support from colleagues which, argue the authors, can only be obtained if the benefits of this approach are made clear. The second article in the series will appear next week.

Transformation-associated recombination between diverged and homologous DNA repeats is induced by strand breaks

Rearrangements within plasmid DNA are commonly observed during transformation of eukaryotic cells. One possible cause of rearrangements may be recombination between repeated sequences induced by some lesions in the plasmid. We have examined the mechanisms of transformation-associated recombination in the yeast Saccharomyces cerevisiae using a plasmid system which allowed the effects of physical state and/or extent of homology on recombination to be studied. The plasmids contain homologous or diverged (19%) repeats of the URA3 genes (from S. cerevisiae or S. carlsbergensis) separated by the genetically detectable ADE2 colour marker. Recombination during transformation for covalently closed circular plasmids was over 100-fold more frequent than during mitotic growth. The frequency of recombination is partly dependent on the method of transformation in that procedures involving lithium acetate or spheroplasting yield higher frequencies than electroporation. When present in the repeats, unique single-strand breaks that are ligatable, as well as double-strand breaks, lead to high levels of recombination between diverged and identical repeats. The transformation-associated recombination between repeat DNAs is under the influence of the RAD52 and RAD1 genes.

Inverted DNA repeats: a source of eukaryotic genomic instability

While inverted DNA repeats are generally acknowledged to be an important source of genetic instability in prokaryotes, relatively little is known about their effects in eukaryotes. Using bacterial transposon Tn5 and its derivatives, we demonstrate that long inverted repeats also cause genetic instability leading to deletion in the yeast Saccharomyces cerevisiae. Furthermore, they induce homologous recombination. Replication plays a major role in the deletion formation. Deletions are stimulated by a mutation in the DNA polymerase delta gene (pol3). The majority of deletions result from imprecise excision between small (4- to 6-bp) repeats in a polar fashion, and they often generate quasipalindrome structures that subsequently may be highly unstable. Breakpoints are clustered near the ends of the long inverted repeats (< 150 bp). The repeats have both intra- and interchromosomal effects in that they also create hot spots for mitotic interchromosomal recombination. Intragenic recombination is 4 to 18 times more frequent for heteroalleles in which one of the two mutations is due to the insertion of a long inverted repeat, compared with other pairs of heteroalleles in which neither mutation has a long repeat. We propose that both deletion and recombination are the result of altered replication at the basal part of the stem formed by the inverted repeats.

Cerebrovascular histopathology after intracarotid infusion of Gelfoam in the rat

To evaluate the histopathology of Gelfoam on the cerebral vasculature, 42 Sprague-Dawley rats weighing 250 to 300 g received internal carotid artery infusions of 0.3 ml of Gelfoam solution (5 mg/ml) or normal saline (0.9%). The animals were killed at 1 hour, 5 hours, 3 days, 1 week, 2 weeks, and 4 weeks after the infusion. The brains were removed, sectioned, and stained with hematoxylin and eosin. Examination of brain sections revealed Gelfoam emboli lodged primarily in the small leptomeningeal arteries. At 5 hours after infusion, inflammatory cells were noted in the arterial walls with vessel occlusion. Further canalization of vessels was noted at 1 week. At 4 weeks, Gelfoam was not seen in the specimens. This study suggests that Gelfoam acts as an embolic agent in vessels over short periods of time with no residual inflammatory activity postinfusion.

Ascorbic acid-enhanced antiproliferative effect of flavonoids on squamous cell carcinoma in vitro

We examined the effects of flavone and two polyhydroxylated plant flavonoids (quercetin and fisetin), either singly or in combination with ascorbic acid, on the growth of a human squamous cell carcinoma cell line (HTB 43) in vitro. Fisetin and quercetin significantly impaired cell growth in the presence of ascorbic acid. Exposure of cells to ascorbic acid (2 micrograms/ml) and 2 micrograms/ml of either fisetin or quercetin resulted in 61 and 45% inhibition of cell growth, respectively, in 72 h, while treatment with ascorbic acid alone had no effect on cellular proliferation. Flavone and ascorbic acid, either as single agents or in combination, exhibited no significant inhibition at any of the concentrations tested. The enhancement of the antiproliferative effect of the above flavonoids by ascorbic acid may be due to its ability to protect these compounds against oxidative degradation.

Differential inhibition of proliferation of human squamous cell carcinoma, gliosarcoma and embryonic fibroblast-like lung cells in culture by plant flavonoids

We investigated the antiproliferative effect of two polyhydroxylated (quercetin and taxifolin) and two polymethoxylated (nobiletin and tangeretin) flavonoids against three cell lines in tissue culture. Tangeretin and nobiletin markedly inhibited the proliferation of a squamous cell carcinoma (HTB 43) and a gliosarcoma (9L) cell line at 2-8 micrograms/ml concentrations. Quercetin displayed no effect on 9L cell growth at these concentrations, while at 8 micrograms/ml it inhibited HTB 43 cell growth. Taxifolin slightly inhibited HTB 43 cell growth at 8 micrograms/ml, while moderately inhibiting HTB 43 cell growth at 2-8 micrograms/ml. The proliferation of a human lung fibroblast-like cell line (CCL 135) was relatively insensitive to low concentrations of the above flavonoids.

Use of allopurinol and deferoxamine in cellular protection during ischemia

During cellular ischemia and death, many changes occur in the cell. These include the build-up of purines and lipid peroxidation. In this study, we evaluated the effectiveness of allopurinol, which blocks purine breakdown, and deferoxamine, which inhibits lipid peroxidation, as cytoprotective agents. Rats were subjected to middle cerebral artery occlusion and were treated with high or low doses of allopurinol or high or low doses of deferoxamine, with normal saline used as a control. Treatments were given 1 hour before, 1 hour after, or 5 hours after occlusion. The outcome was based on neurological status and infarct size. Both infarct size and neurological status were found to be improved in all treatment groups when compared to controls. This study suggests that the use of these agents prevents cellular damage during ischemia.

Transposon Tn5 excision in yeast: influence of DNA polymerases alpha, delta, and epsilon and repair genes

Interaction between short repeats may be a source of genomic rearrangements and deletions. We investigated possible interactions between short (9 base pairs) direct repeats in yeast by using our previously described system for analyzing bacterial transposon Tn5 excision in yeast. Mutations of either POL3 or POL1, the proposed structural genes for polymerases delta and alpha, respectively, yield high levels of excision at semipermissive temperatures. pol2 (corresponding to polymerase epsilon) and pol2 pol3 double mutants do not exhibit enhanced excision. A majority of excision events involve direct repeats and are precise; the remaining imprecise excisions occur within or in the vicinity of the repeats. The three DNA repair pathways identified by rad1, rad6 and rad18, rad50 and rad52 mutations were examined for their possible role in Tn5 excision; no enhancement was observed in mutants. However, the pol3-stimulated Tn5 excision was reduced in rad52 and rad50 mutants. This suggests the potential for interaction between the systems for DNA double-strand break/recombinational repair and DNA synthesis. Based on the suggestion of Morrison et al. [Morrison, A., Araki, H., Clark, A. B., Hamatake, R. H. & Sugino, A. (1990) Cell 62, 1143-1151] that polymerases delta and alpha are responsible for lagging-strand synthesis and that polymerase epsilon is responsible for leading-strand synthesis, we suggest that Tn5 excision is stimulated under conditions of altered lagging-strand synthesis, possibly due to extended opportunities for single-strand interactions between the inverted insertion sequence I550 repeats of Tn5.

Antiproliferative effects of citrus flavonoids on a human squamous cell carcinoma in vitro

We examined the effects of four plant flavonoids (quercetin, taxifolin, nobiletin and tangeretin) on the in vitro growth of a human squamous cell carcinoma cell line (HTB43). Cell cultures were treated with each flavonoid (2-8 micrograms/ml) for 3-7 days. Cell viability, as determined by counting cells, correlated well with that obtained from a colorimetric assay for cellular growth utilizing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The polymethoxylated flavonoids, nobiletin and tangeretin, markedly inhibited cell growth at all concentrations tested on days 5 and 7. On day 3, the inhibition observed was 70-72% at 8 micrograms/ml, while on day 5, it ranged from 61-88% at 2-4 micrograms/ml. Quercetin and taxifolin exhibited no significant inhibition at any of the concentrations tested. This difference in activity may be due to the relatively greater membrane uptake of the polymethoxylated flavonoids since methoxylation of the phenolic groups decreases hydrophilicity of the flavonoid.

Microleakage of glass ionomer/composite laminate Class V restorations

The aim of this investigation was to evaluate the effects on microleakage of pretreating dentin with polyacrylic acid (PAA), prior to placing a glass ionomer base/composite laminate restoration. Class V erosion-type lesions with the incisal margin on enamel and the cervical margin below the cemento-enamel junction (CEJ), were prepared in 50 sound extracted teeth. These teeth were divided into five dentin treatment groups: A) 10% PAA; B) 20% PAA; C) and D) 40% PAA; E) no dentin preconditioning. In groups A, B, C and E, a glass ionomer base was placed within 1 mm of the margins. In group D the glass ionomer base extended to the cervical margin. The glass ionomer base and the incisal enamel were etched with 37% phosphoric acid prior to placing a bonding agent and restoring with a composite. The restorations were finished and polished and the teeth were stored in distilled water at 37 degrees C for 7 days. They were thermocycled in 0.5% fuchsin dye for 500 cycles (5 degrees C to 60 degrees C), embedded in epoxy resin, and sectioned at 250 mu intervals through the restorations. The section of each tooth exhibiting the most severe dye penetration along the tooth/restoration interface was evaluated and scored both incisally and cervically: 0 = no leakage; 1 = leakage up to the glass ionomer base; 2 = leakage up to 1/2 the wall length; 3 = leakage exceeding 1/2 the wall length. Cervically, the median leakage for all groups was 3.0. Incisally, the median leakage for all the groups was 0.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterization of the maltose permease in genetically defined Saccharomyces strain

Saccharomyces yeasts ferment several alpha-glucosides including maltose, maltotriose, turanose, alpha-methylglucoside, and melezitose. In the utilization of these sugars transport is the rate-limiting step. Several groups of investigators have described the characteristics of the maltose permease (D. E. Kroon and V. V. Koningsberger, Biochim. Biophys. Acta 204:590-609, 1970; R. Serrano, Eur. J. Biochem. 80:97-102, 1977). However, Saccharomyces contains multiple alpha-glucoside transport systems, and these studies have never been performed on a genetically defined strain shown to have only a single permease gene. In this study we isolated maltose-negative mutants in a MAL6 strain and, using a high-resolution mapping technique, we showed that one class of these mutants, the group A mutants, mapped to the MAL61 gene (a member of the MAL6 gene complex). An insertion into the N-terminal-coding region of MAL61 resulted in the constitutive production of MAL61 mRNA and rendered the maltose permease similarly constitutive. Transformation by high-copy-number plasmids containing the MAL61 gene also led to an increase in the maltose permease. A deletion-disruption of MAL61 completely abolished maltose transport activity. Taken together, these results prove that this strain has only a single maltose permease and that this permease is the product of the MAL61 gene. This permease is able to transport maltose and turanose but cannot transport maltotriose, alpha-methylglucoside, or melezitose. The construction of strains with only a single permease will allow us to identify other maltose-inducible transport systems by simple genetic tests and should lead to the identification and characterization of the multiple genes and gene products involved in alpha-glucoside transport in Saccharomyces yeasts.

The effects of the bioflavonoid quercetin on squamous cell carcinoma of head and neck origin

Quercetin exhibits antitumor activity. We investigated the effect of quercetin on the in vitro and in vivo growth of two squamous cell carcinoma cell lines and a normal human lung fibroblast-like cell line. The in vivo effect was evaluated using implantable cell growth chambers implanted subcutaneously in immunocompetent rats. Quercetin was injected intraperitoneally, and multiple dosages were tested. Cells were counted on days 1, 3, 5, and 7, and growth curves were constructed. Quercetin caused inhibition of growth in both squamous cell carcinoma lines. Effect on the fibroblast-like human lung cells was noted only at the maximum concentration. Significant growth inhibition of squamous cell carcinoma was observed in implantable cell growth chambers retrieved 3 days after quercetin treatment. Quercetin appears to possess a cytotoxic effect on squamous cell carcinoma of head and neck origin both in vivo and in vitro. The inhibitory effect on malignant cells appears to be selective and dose-dependent.

Preservation of brain tumor specimens for drug sensitivity testing

To examine the feasibility of shipment of brain tumor specimens to a central laboratory for drug sensitivity testing, an experimental gliosarcoma (9L) was grown subcutaneously in rats, harvested, stored, and disaggregated. Growth of the disaggregated tumor cells in monolayer culture was evaluated after storage for various times at 2 to 6 degrees C and 37 degrees C in saline and minimum essential medium. Growth potential was maintained for 24 hours when tumor specimens were stored under refrigerated conditions and was best maintained when specimens were stored in saline. Specimens stored at 37 degrees C grew best when stored in minimum essential medium, but growth potential was lost after 12 hours unless the specimens were refrigerated. Shipment of tumor specimens to a central laboratory for drug sensitivity testing appears to be feasible, since under most circumstances, specimens should reach the laboratory for processing within 24 hours of their removal. Storage and transport of specimens in saline on wet ice appears to be optimal.

Chemosensitivity of squamous cell carcinoma grown in implantable chambers

This study was motivated by the need to develop new methods to predict tumor response to chemotherapeutic agents. Using implantable cell-growth chambers, squamous carcinoma cells from head and neck tumors were xenografted into the peritoneal cavity of immunocompetent rats. Animals were divided into control and treatment groups. The treatment groups received intravenous cisplatin (CDDP) or 5-fluorouracil (5-FU) v normal saline solution for the control. Animals from each group were randomly selected and killed on days 3, 5, and 7 postimplantation. The chambers were retrieved, the media aspirated, and cells counted. Exponential growth curves were derived for the control and treatment groups. Statistically significant growth inhibition was observed for both treatment arms, compared with controls. This method of chemosensitivity testing proved to be inexpensive and reliable, and demonstrated tumor cell killing by 5-FU and CDDP.

MAL63 codes for a positive regulator of maltose fermentation in Saccharomyces cerevisiae

Genetic analysis of the MAL6 locus has previously yielded mal6 mutants which fall into a single complementation group and which are noninducible for maltase and maltose permease. However, the strains used in these studies contained additional partially functional copies of MAL1 (referred to as MAL1g) and MAL3 (referred to as MAL3g). Using a strain lacking MALg genes, we have isolated two classes of mutants and these classes correspond to mutations in MAL63 and MAL61, two genes of the MAL6 complex. Disruptions of MAL63 are noninducible for maltase and maltose permease and for their corresponding mRNAs. The mal6 mutants are shown to map to MAL63. Inducer exclusion as a cause of the noninducible phenotype of the mal63 mutations has been eliminated by constructing a mal63 mutant in a strain constitutive for maltose permease; the strain remains noninducible. These results rigorously demonstrate that MAL63 is a regulatory gene which plays a positive role in the regulation of maltose fermentation.