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Biomedical subjects

G E Francis

Publications and source records attributed to G E Francis.

At least 19 recordsLinked to original sources
PubMed1992

Polyethylene glycol (PEG) modification of granulocyte-macrophage colony stimulating factor (GM-CSF) enhances neutrophil priming activity but not colony stimulating activity.

PEG-modified proteins have numerous advantages over their unmodified counterparts (increased half life, reduced antigenicity, improved solubility), but almost without exception, they show a modest to marked reduction in biological or enzymatic activity. However, while investigating a new protocol for the preparation of PEG-proteins, we compared PEG-modified and unmodified GM-CSF with respect to their polymorphonuclear neutrophil granulocyte (PMN) priming activities. PEG-GM-CSF was unexpectedly more active than GM-CSF in its ability to prime neutrophils to respond to the synthetic peptide n-formyl-methionyl-leucyl-phenylalanine (FMLP) with an oxidative burst (assessed both by nitroblue tetrazolium reduction and ferricytochrome c reduction). These results were in contrast to the findings for colony stimulating activity and with GM-CSF induced thymidine uptake, where the biological activity was unchanged or reduced. The enhanced neutrophil priming activity of PEG-GM-CSF was confirmed using FPLC fractionated PEG-modified GM-CSF. This showed changes in the bioactivity profile consistent with both the shift in protein elution profile and enhanced activity of the PEG-modified material (reflected in the increased area under the bioactivity curve). We also excluded a neutrophil priming action for PEG-modified fetal calf serum proteins, carrier proteins and 'irrelevant' cytokine, erythropoietin. The dissociation of the two bioactivities was confirmed using individual FPLC fractions. These results suggest the presence of differences in either binding, receptor/ligand processing or signal transduction for neutrophils versus progenitors, that are differentially affected by PEG-modification of GM-CSF. The demonstration that PEG-modification can partially dissociate two biological activities suggests the feasibility of using PEG-modification to produce proteins with subtly altered spectra of biological activity and hence new ranges of clinical applications.

Cells, Cultured↗
PubMed1992

The uses and properties of PEG-linked proteins.

Poly(ethylene glycol) (PEG) is a water soluble polymer that when covalently linked to proteins, alters their properties in ways that extend their potential uses. PEG-modified conjugates are being exploited in many different fields. The improved pharmacological performance of PEG-proteins when compared with their unmodified counterparts prompted the development of this type of conjugate as a therapeutic agent. Enzyme deficiencies for which therapy with the native enzyme was inefficient (due to rapid clearance and/or immunological reactions) can now be treated with equivalent PEG-enzymes. PEG-adenosine deaminase has already obtained FDA approval. PEG-modified cytokines have been constructed and, interestingly, one of the conjugates, PEG-modified granulocyte-macrophage colony-stimulating factor, showed dissociation of two biological properties. This novel observation may open new horizons to the application of PEGylation technology. The biotechnology industry has also found PEG-proteins very useful because PEG-enzymes can act as catalysts in organic solvents, thereby opening the possibility of producing desired stereoisomers, as opposed to the racemic mixture usually obtained in classical organic synthesis. Covalent attachment of PEG to proteins requires activation of the hydroxyl terminal group of the polymer with a suitable leaving group that can be displaced by nucleophilic attack of the epsilon-amino terminal of lysine residues (other nucleophilic groups can also interact). Several chemical groups have been exploited to activate PEG, thereby giving rise to a variety of PEG-proteins. Some of these varieties retain part of the activating group as a coupling moiety between PEG and protein and others provide a direct linkage. For each particular application, different coupling methods provide distinct advantages.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Polyethylene glycol (PEG)-modified granulocyte-macrophage colony-stimulating factor (GM-CSF) with conserved biological activity.

Polyethylene glycol (PEG) modification improves the pharmacological properties of proteins, usually extending plasma half-life and concomitantly increasing in vivo bioactivity, reducing both antigenicity and immunogenicity, and increasing solubility and resistance to proteolysis. Despite these established benefits, few PEG proteins are in use. Current coupling methods are either traumatic for the protein or involve lengthy and difficult procedures to activate monomethoxyPEG (MPEG). We have applied a new coupling method that allows coupling of MPEG directly to proteins under physiological conditions. Using this method with recombinant human (rh)granulocyte-macrophage colony-stimulating factor (GM-CSF) we were able to construct biologically active PEG-GM-CSF. Fast protein liquid chromatography (FPLC) and phase-partitioning confirmed the presence of PEG modification, and the former was used to fractionate modified and unmodified material. Bioactivity was measured in colony assays of normal human bone marrow cells and by tritiated thymidine uptake (of chronic myeloid leukemia cells and TF-1 cells). With both uptake and colony assays, using unfractionated material, we observed only a modest reduction in biological activity. Assays of FPLC-fractionated material confirmed that much of the bioactivity of the PEG-GM-CSF preparations was due to the modified species and any residual unmodified GM-CSF. Species uncontaminated by tresylmonomethoxyPEG (TMPEG; which was somewhat inhibitory in the thymidine uptake assay and eluted over a broad region of the FPLC profile) had no significant reduction in activity, but we cannot rule out the possibility that PEG-GM-CSF species eluting elsewhere in the profile had modest reduction of activity. Subcutaneous injection into mice confirmed the anticipated improved half-life in vivo and demonstrated a longer uptake from the injection site. This is, as far as we are aware, the first successful construction of PEG-GM-CSF with conserved biological activity.

Animals↗
PubMed1991

A method for the purification of DNA/protein complexes applied to DNA topoisomerase II cleavage sites.

The object of this study was to devise a purification method for DNA/topoisomerase II complexes, with which to examine the enzyme's cleavage site specificity in cellular differentiation. Retinoic acid-induced differentiation involves topoisomerase II-mediated transient changes in DNA supercoiling, but it is not known whether this occurs at specific sites in the genome. Topoisomerase II forms a covalent DNA enzyme complex as it acts, which can be recovered by the sodium dodecyl sulfate (SDS)/KCl precipitation method, but this method fails to recover significantly more DNA from cells induced to differentiate. This may in part reflect the low numbers of retinoic acid-induced protein-linked breaks in DNA and also the method's relative inefficiency for DNA with few attached topoisomerase molecules. This suggested that an additional purification method would be required to enrich sufficiently for cleavage site DNA to address the issue of site specificity. The principle of our method is to couple poly(ethylene glycol) (PEG) to topoisomerase while it is covalently attached to DNA and then to use phase partitioning in an aqueous two-phase system of PEG and phosphate to separate free DNA from DNA bound to PEG-modified topoisomerases (which have high affinities for the phosphate-rich and PEG-rich phases, respectively). The method can be used in conjunction with DNase protection and, unlike the SDS/KCl method, can fractionate short fragments of DNA to which single protein molecules are attached. Using the SDS/KCl precipitation and new method in series, we have recovered protein-linked DNA from HL60 cells induced to differentiate to the granulocyte lineage (by retinoic acid) or to the monocyte/macrophage lineage (by phorbol myristate acetate) and have demonstrated that specific sequences become protein linked, probably to topoisomerase II, during induced differentiation.

Chemical Fractionation↗
PubMed1991

Separation of cell mixtures by immunoaffinity cell partitioning: strategies for low abundance cells.

The partitioning of cells in aqueous two-phase systems formed by poly(ethylene glycol) (PEG) and dextran can be changed by incubating the cells with a PEG-modified antibody directed specifically against its surface. We have developed a new approach for immunoaffinity cell partitioning (IACP) in which the antibodies are first reacted with tresylated monomethoxy PEG (TMPEG) in sodium phosphate buffer, pH 7.5, the excess TMPEG is quenched by reaction with bovine serum albumin, and the resulting preparation is used directly for incubation with the cells without any isolation of the monomethoxyPEG (MPEG)-antibody conjugates. We have demonstrated the specificity of this IACP method by showing that MPEG-modified anti-human red blood cell antibody increases the partition of human erythrocytes from the interface to the PEG-rich top phase (up to 100%) but not the partitioning of either neutrophils or HL60 cells. Irrelevant antibodies do not affect the partitioning of red blood cells. The partitioning behaviors of erythrocytes and HL60 cells in mixtures varying from 75 to 10% red blood cells subjected to IACP are similar to those of the pure cell population, i.e., erythrocytes ca. 100% and HL60 cells 3% in top phase. Thus, the population of erythrocytes can be almost completely extracted into the top phase in a single step. The contaminant cells represent only a small percentage (less than 5% in most of the cases) of the cell mixture recovered in top phase. Both cell populations can be completely separated by countercurrent distribution (CCD).(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody Affinity↗
PubMed1991

Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer.

Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-1 gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raf/c-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.

Amsacrine↗
PubMed1990

Dissociation of the proliferation and differentiation stimuli of granulocyte colony-stimulating factor (G-CSF).

One proposed therapeutic application of granulocyte colony-stimulating factor (G-CSF) is in differentiation induction therapy of myelodysplastic states (MDS) or acute myeloid leukemia (AML). G-CSF however has a substantial growth including effect which limits its potential as a differentiation inducing agent. We have therefore made a systematic search for agents which might restrain the proliferative effects of G-CSF whilst retaining the differentiation stimulus. Of all the agents we have tested on human bone marrow progenitor cells: (6-thioguanine, all-trans retinoic acid, vincristine, recombinant human alpha-2b and gamma-interferon) only the latter abolished the stimulation of cell growth and retained, or possibly increased, the differentiation effect of G-CSF. The antiproliferative drugs 6-thioguanine and vincristine both antagonized the neutrophil-granulocyte differentiation inducing action of G-CSF. Retinoic acid and alpha-2b interferon both had weak effects on proliferation and failed to enhance differentiation. These results suggest that it may be possible, by combining G-CSF with a suitable second agent, to utilize its substantial differentiation inducing effect without incurring the potentially hazardous effects of increased leukemic cell growth.

Cell Differentiation↗
PubMed1990

Coupling of poly(ethylene glycol) to albumin under very mild conditions by activation with tresyl chloride: characterization of the conjugate by partitioning in aqueous two-phase systems.

Poly(ethylene glycol) activated with tresyl chloride has been covalently linked to albumin as a result of a 2-h incubation in 0.05 M sodium phosphate buffer, pH 7.5, containing 0.125 M sodium chloride (0.344 OSM). The coupling of poly(ethylene glycol) to albumin was demonstrated by the increase in the partition coefficient of the protein in poly(ethylene glycol)-dextran aqueous two-phase systems. A linear relationship between the log of the partition coefficient of the poly(ethylene glycol)-albumin conjugate and the degree of modification (measured as the amino groups consumed during the coupling step) has been demonstrated. Countercurrent distribution in the two-phase system showed that poly(ethylene glycol)-albumin was heterogeneous with respect to its partitioning behavior, indicating that the albumin was not uniformly modified with poly(ethylene glycol).

Chemical Phenomena↗
PubMed1989

Differentiation stage-specific expression of a gene during granulopoiesis.

Differential screening of a recombinant cDNA library using cDNAs transcribed from poly(A)+ RNA of normal or leukemic leukocytes revealed a number of recombinants homologous to mRNAs characteristic of particular leukemias. The occurrence of one of these (pCG14) in high abundance was shown to be sufficiently characteristic of the circulating leukocyte population of chronic granulocytic leukemia (CGL) patients to distinguish them from all other populations of leukocytes. We have now characterized the gene encoding this mRNA and shown that its expression is specific to the granulocyte lineage in hemopoietic cells and is, moreover, limited to a narrow stage of differentiation during granulopoiesis. Our results explain why high levels of pCG14 RNA are characteristic of chronic granulocytic leukemia peripheral blood leukocytes.

Animals↗
PubMed1988

Acidic isoferritin stimulates differentiation of normal granulomonocytic progenitors.

Acidic isoferritin (AIF) has been shown to be released by cells from patients with leukemia and to have an inhibitory effect on the growth of normal granulomonocytic (GM) progenitors (leukemia-inhibitory activity) during the S phase of the cell cycle. AIF is also produced by normal mature cells of the monocyte-macrophage lineage. We studied the effects of AIF on the differentiation of normal GM progenitors and found an increase in the number of mature cells in AIF-exposed cultures. This increase did not occur when AIF was pretreated with anti-heart ferritin antiserum or when basic isoferritin was used in the place of AIF. The influence of AIF was not mimicked by removing S phase cells by pretreatment with a pulse of high specific activity tritiated thymidine. Thus, the apparent differentiation-stimulating effect of AIF is not likely to be due to selective removal of immature dividing cells. The results suggest that AIF-inhibitory activity on the proliferation of GM progenitors might at least in part be mediated by a stimulus for differentiation of the target cells, thus regulating the number of mature cells which might be formed by a single progenitor cell.

Cell Differentiation↗
PubMed1987

Differentiation-linked secretion of urokinase and tissue plasminogen activator by normal human hemopoietic cells.

Previous studies have shown that the response of patients with acute myeloid leukemia to induction chemotherapy can be predicted by the species of plasminogen activator that their cells secrete. Patients whose cells secreted tissue plasminogen activator (tPA) only failed to respond to combination chemotherapy. Individuals whose leukemic cells display features of the early progenitor phenotype also respond poorly to therapy. This suggested that the two species of plasminogen activator secreted by leukemic cells might be produced by normal cells at distinct stages of differentiation. These results indicate that the secretion of the two enzyme types is a differentiation-linked property of normal cells with tPA being produced by granulocyte/macrophage progenitors and urokinase by more differentiated cells and by mature neutrophils and macrophages.

Bone Marrow↗