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R Schnell

Publications and source records attributed to R Schnell.

At least 19 recordsLinked to original sources
PubMed1996

Potent anti-tumor effects of an anti-CD24 ricin A-chain immunotoxin in vitro and in a disseminated human Burkitt's lymphoma model in SCID mice.

A new anti-CD24 immunotoxin (IT), SWA11.dgA, was constructed by coupling the MAb SWA11 via the bivalent linker SMPT to deglycosylated ricin A-chain (dgA). The effects of SWA11.dgA were evaluated in vitro against the B-precursor leukemia cell line REH, the non-B-non-T acute lymphoblastic leukemia cell line NALM-6 and the Burkitt's lymphoma cell lines BL-2 and BL-38. Binding of SWA11 to the CD24 antigen was assessed by flow cytometry demonstrating high affinity of the MAb for all cell lines tested. SWA11.dgA inhibited the protein synthesis of BL-38, NALM-6, REH and BL-2 cells by 50% at concentrations (IC50) of 4.0 x 10(-11) M, 6.0 x 10(-11) M, 8.0 x 10(-11) M and 3.0 x 10(-9) M, respectively. SWA11.dgA was subsequently used for the treatment of disseminated human BL-38 Burkitt's lymphoma in a newly developed SCID mouse model. The mean survival time (MST) of BL-38-bearing SCID mice was extended from 23 days in untreated controls to more than 230 days when 6 microg SWA11.dgA was applied intraperitoneally one day after tumor challenge. All of the animals achieved continuous complete remissions. SCID mice treated with SWA11.dgA 4 days after tumor cell challenge or a reduced dose of SWA11.dgA (67%) also had a significantly extended MST (45.0 and 51.4 days, respectively, as compared to 22.7 and 23.1 days in the controls). We conclude that SWA11.dgA might be of potential use for the treatment of lymphoma in man.

Animals↗
PubMed1996

Recent progress in oligonucleotide synthesis.

New blocking group combinations for the machine-aided oligoribonucleotide synthesis on solid phase material have been developed and tested regarding their general application. An acetal function for 2'-OH protection offers a series of advantages in the synthetic approach but special conditions have to be fulfilled in order to guarantee a selective cleavage of the temporary 5'-OH blocking group such as the dansylethoxycarbonyl or even the acid-labile dimethoxytrityl group in the chain elongation process. The final removal of the 2'-O-acetal function in the partially deblocked oligomer proceeds unexpectedly well under weak acidic conditions due to a supposed intramolecular acid catalysis.

Acetals↗
PubMed1995

The in vivo anti-tumor activity of immunotoxins containing two versus one deglycosylated ricin A chains.

We have compared the in vitro and in vivo activities of three deglycosylated ricin A chain (dgA)-containing immunotoxins (ITs) with one versus two molecules of dgA per molecule of IgG. Two of the ITs (anti-CD19-dgA2 and anti-CD25-dgA2) had 3-0-fold improvements over their dgA1 counterparts in vitro. However, the in vivo anti-tumor activity of both constructs of each IT was the same. In contrast, anti-CD22-dgA2 was 7-fold more potent in vitro and significantly more potent in vivo than its dgA1 counterpart. These studies suggest that monoclonal antibodies must be individually tested to determine whether the addition of two versus one dgA will improve cytotoxic activity in vivo.

Animals↗
PubMed1995

Development of new ricin A-chain immunotoxins with potent anti-tumor effects against human Hodgkin cells in vitro and disseminated Hodgkin tumors in SCID mice using high-affinity monoclonal antibodies directed against the CD30 antigen.

The lymphocyte activation marker CD30 has been shown to be an excellent target for the immunotherapy of human Hodgkin's lymphoma. In order to develop new potent immunotoxins (ITs) against CD30, we chemically linked 6 recently described monoclonal antibodies (MAbs) via SMPT to deglycosylated ricin A-chain (dgA). Cross-blocking experiments demonstrated that these MAbs, termed Ki-2 to Ki-7, recognize 3 different clusters on the CD30 antigen: Ki-2, Ki-4, Ki-5 and Ki-7 recognize cluster A; Ki-6 recognizes cluster B; Ki-3 binds to cluster C. Staining of 29 sections of normal human organs revealed no major cross-reactivity of any MAbs tested. Binding to the CD30 antigen on L540Cy Hodgkin cells was assessed by flow cytometry, and demonstrated high affinities for Ki-2, Ki-3 and Ki-4. The concentration giving 50% of the mean fluorescence intensity (MFI50) was 0.58 micrograms/ml to 0.78 micrograms/l. MAbs Ki-5, Ki-6, and Ki-7 bound much more weakly. The staining intensity of the MAbs correlated with the cytotoxicity of the corresponding ITs. Ki-2.dgA, ki-3.dgA and Ki-4.dgA inhibited the protein synthesis of L540Cy cells by 50% at concentrations (IC50) of 3.5 x 10(-10)M to 4.0 x 10(-11)M. The most effective IT, Ki-4dgA, is 5-fold more potent than previously reported CD30 ricin A-chain ITs. Ki-4.dgA was subsequently used for the treatment of disseminated human Hodgkin's lymphoma in a SCID mouse model. The mean survival time (MST) of lymphoma-bearing SCID mice was extended from 42 days in untreated controls to more than 132 days when Ki-4.dgA was applied one day after tumor challenge. Ki-4.dgA is a new potent IT suitable for further evaluation against Hodgkin's lymphoma in man.

Animals↗
PubMed1995

Cocktails of ricin A-chain immunotoxins against different antigens on Hodgkin and Sternberg-Reed cells have superior anti-tumor effects against H-RS cells in vitro and solid Hodgkin tumors in mice.

Three ricin A-chain immunotoxins (ITs) recognizing different antigens on Hodgkin-Reed/Sternberg (H-RS) cells were evaluated for their anti-tumor effects when used in combination as "cocktails". These ITs, BB10.dgA (CD25), HRS3.dgA (CD30), and IRac.dgA (70 kDa), strongly inhibited the growth of L540Cy H-RS cells in vitro. The protein synthesis of this cell line was reduced more efficiently by the combination of 2 of these ITs than by BB10.dgA, HRS3.dgA or IRac.dgA alone. A cocktail of all 3 ITs was most effective in vitro. This was at least in part due to the non-homogeneous distribution of CD25, CD30 or IRac on the L540Cy H-RS target cells and to the fact that subpopulations deficient in one antigen nevertheless expressed appreciable levels of the other target antigens. IT cocktails were also superior as anti-tumor agents in nude mice with solid L540Cy tumors. Ninety percent of mice treated with cocktails containing 2 or 3 ITs had continuous complete remissions (CCR), as compared with only 40% of mice treated with the same dose of a single IT. Analysis of 7 L540Cy sub-lines re-established ex vivo from mice that relapsed after having achieved complete remission (CR) after therapy with a single IT showed that the surviving tumor cells were antigen-deficient variants which were resistant to the original IT, but which could be killed by ITs directed against other target antigens. Thus, IT cocktails give superior results against human H-RS cells, both in vitro and in vivo.

Animals↗
PubMed1989

Isolation and characterization of the nitrate reductase structural gene of Chlamydomonas reinhardtii.

The nitrate reductase structural gene of Chlamydomonas reinhardtii has been isolated from a genomic library by using a nitrate reductase cDNA probe from barley. Restriction fragment length polymorphism analyses mapped the Chlamydomonas clone (B6a) to the nitrate reductase structural gene locus nit-1. Overlapping inserts cover a region of the genome of about 24 kilobases containing the entire gene, which spans approximately 5-8 kilobases. Sequence analysis of DNA fragments from the B6a clone demonstrated a high degree of sequence similarity at the amino acid level with regions corresponding to portions of the heme and FAD/NADH-binding domains of tobacco and Arabidopsis thaliana nitrate reductases and human NADH cytochrome b5 reductase. The identity of the cloned gene as nitrate reductase was confirmed by its ability to complement a nit-1 mutation upon transformation. The nitrate reductase gene produced a 3.4-kilobase transcript in cells derepressed with nitrate; the transcript was undetectable in cells grown in the presence of ammonium. In cells that contain a mutation in the putative regulatory gene nit-2, significantly lower levels of the 3.4-kilobase transcript were found, indicating that the wild-type nit-2 gene is involved in the control of nitrate reductase transcript levels.

Amino Acid Sequence↗
PubMed1989

Genetic and molecular characterization of suppressors of SIR4 mutations in Saccharomyces cerevisiae.

In order to learn more about other proteins that may be involved in repression of HML and HMR in Saccharomyces cerevisiae, extragenic suppressor mutations were identified that could restore repression in cells defective in SIR4, a gene required for function of the silencer elements flanking HML and HMR. These suppressor mutations, which define at least three new genes, SAN1, SAN2 and SAN3, arose at the frequency expected for loss-of-function mutations following mutagenesis. All san mutations were recessive. Suppression by san1 was allele-nonspecific, since san1 could suppress two very different alleles of SIR4, and was locus-specific since san1 was unable to suppress a SIR3 mutation or a variety of mutations conferring auxotrophies. The SAN1 gene was cloned, sequenced, and used to construct a null allele. The null allele had the same phenotype as the EMS-induced mutations and exhibited no pleiotropies of its own. Thus, the SAN1 gene was not essential. SAN1-mediated suppression was neither due to compensatory mutations in interacting proteins, nor to translational missense suppression. SAN1 may act posttranslationally to control the stability or activity of the SIR4 protein.

Alleles↗
PubMed1986

A position effect on the expression of a tRNA gene mediated by the SIR genes in Saccharomyces cerevisiae.

The SIR genes of Saccharomyces cerevisiae are responsible for the position-dependent regulation of the a and alpha mating-type genes. Previous work by others has shown that the products of the SIR genes prevent the accumulation of stable transcripts of the a and alpha genes at HML and HMR. Results of this study establish that this regulation is a region-specific effect rather than a gene-specific effect since expression of a tRNA gene placed at HMR is repressed by the products of the SIR genes.

DNA Restriction Enzymes↗
PubMed1985

Possible approaches to the simulation of antibiotic kinetics and the determination of antibacterial activity in vitro.

Various methods of determining antibacterial effects in vitro by simulation of antibiotic kinetics were investigated. MICs were determined in fluids with and without proteins. Only concentrations of free drug were antibacterially active, and these concentrations should therefore be simulated in culture media without protein. Varying drug concentrations can easily be simulated in our in-vitro system, but the question remains which of the concentrations found in the different body fluids is the most representative. Cephalosporins were more active when phagocytosis was simulated, as shown by the continuous elimination of approximately 90% of the bacteria. If phagocytosis was not simulated, the effects of long-lasting concentrations were not decreased as much as those of concentrations corresponding to short half-lives and repeated doses.

Anti-Bacterial Agents↗
PubMed1983

[Determination of protein in cerebrospinal fluid: comparison of the Coomassie-Blue method and the Cu-Folin differential test].

Comparison of within-run and between-day imprecision of protein assays using CSF controls as well as 96 random CSF samples from the routine laboratory shows that the Cu-Folin differential test and the Coomassie-Brilliant-Blue method from Bio-Rad are equally suited to total protein determination in cerebrospinal fluid. Problems possibly arising with very low concentrations of CSF or urine protein and the influence of some drugs often used in the neurological clinic are presented and discussed.

Cerebrospinal Fluid Proteins↗
PubMed1982

Histone hypoacetylation following release of HTC cells from butyrate.

Exposure of HTC cells to 6 mM sodium butyrate for 20 h results in significantly reduced amounts of nuclear histone acetyltransferase. While the direct butyrate inhibition of histone deacetylases is rapidly reversed upon removal of cells from butyrate, histone acetyltransferase activity increases only gradually following release of cells from butyrate, requiring several hours to regain control cell levels. As a result, HTC cells released from a 20-h exposure to butyrate display normal kinetics of histone acetate turnover but markedly reduced rates of histone acetylation, the imbalance in these two processes produces histone hypoacetylation.

Acetylation↗