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PubMed1980

Antitumor activity of monomeric and polymeric cyclophosphamide derivatives compared with in vitro hydrolysis.

Relatively stable sulfhydryl derivatives of 4-hydroxycyclophosphamide and these same derivatives covalently bound to a polymeric carrier were studied in vitro and in vivo. The rate of release of 4-hydroxycyclophosphamide from monomeric and polymeric derivatives was examined under physiological conditions (pH 7.0, 37.0 degrees) in vitro. Hydrophobicity and length of alkyl chain of substituents at the 4-position of the phosphamide ring decreased the rate of hydrolysis. The polymeric derivatives were more slowly hydrolyzed than were their corresponding monomers. Toxicity in mice indicated that the rate of hydrolysis in vitro is related to toxicity in vivo. The optimal antitumor activity (maximum 270% increase in life span in L1210-bearing mice) and effective dose range of each derivative of low molecular weight were similar to cyclophosphamide. The polymeric derivatives exhibited much less antitumor activity (maximum 50% increase in the life span) than did cyclophosphamide. The short-alkyl-chain monomeric derivatives such as propanol and propionic acid caused acute lethal toxicity, which limited the upper dose usable for antitumor activity. Polymeric derivatives, when compared on a molar basis to their corresponding monomers, were relatively more toxic to the mice which limited their maximum dose.

Animals↗
PubMedDate not supplied

Biocompatibility of visible light-polymerized denture base resins.

The biocompatibility of three commercial formulations of visible light-polymerized denture base resins was studied to determine its effects on the RNA and DNA synthesis of oral epithelial cells in vitro. Isotope incorporation into RNA or DNA was measured after 24 hours of incubation with isotope and 48 hours of exposure to resin. The resins were shown to significantly inhibit the synthesis of both nucleotides as compared to a heat-processed resin control. Increasing the polymerization time can mitigate the toxicity of some of the resins. The air barrier coatings used to prevent oxygen inhibition of polymerization increased the toxic effects of two resins and decreased that of one of the materials. These investigations suggest that visible light-polymerized denture resins may impair the replication of oral epithelial cells. DNA synthesis is more sensitive to the toxic effects of the materials, which may relate to the ability to cause mucosal pathology. The cytotoxic effects may relate to the presence of unpolymerized resin constituents or polymerization by-products.

Acrylic Resins↗
PubMed1995

Tubulin polymerization by paclitaxel (taxol) phosphate prodrugs after metabolic activation with alkaline phosphatase.

Paclitaxel (taxol) phosphate derivatives BMY46366, BMY-46489, BMS180661 and BMS180820 were used to determine the ability of alkaline phosphatase to convert these water-soluble potential prodrugs to tubulin-polymerizing metabolites (i.e., paclitaxel). Compounds were treated up to 180 min with an in vitro metabolic activation system composed of 10% bovine alkaline phosphatase in 0.2 M tris, pH 7.4, or in 0.2 M glycine, pH 8.8, plus 0.05 M MgCl2. Samples were tested (either by direct addition or after methylene chloride extraction/dimethyl-sulfoxide resuspension) in spectrophotometric tubulin polymerization assays utilizing bovine-derived microtubule protein. Pretreatment of 2'- and 7-phosphonoxyphenylpropionate prodrugs BMS180661 and BMS180820 with alkaline phosphatase for 30 to 120 min yielded relative initial slopes of about 20 to 100% at test concentrations equimolar to paclitaxel. High-performance liquid chromatography/mass spectrometry of BMS180661 treated with alkaline phosphatase confirmed the production of paclitaxel from the prodrug. In contrast, 2'- and 7-phosphate analogs BMY46366 and BMY46489 treated with alkaline phosphatase were not active in tubulin assays. None of the paclitaxel phosphate prodrugs polymerized tubulin in the absence of metabolic activation. The differences in tubulin polymerization with metabolic activation may be related both to accessibility of the phosphate group to the enzyme and to anionic charge effects. These results demonstrate that certain paclitaxel phosphate prodrugs can be metabolized by alkaline phosphatase to yield effective tubulin polymerization.

Alkaline Phosphatase↗
PubMed1993

Template-directed pausing of DNA synthesis by HIV-1 reverse transcriptase during polymerization of HIV-1 sequences in vitro.

Replication of human immunodeficiency virus type 1 (HIV-1) requires reverse transcriptase (RT) to synthesize double-stranded proviral DNA (9.7 kilobases) through a complex mechanism utilizing both RNA and DNA templates. We have examined DNA synthesis by HIV-1 RT on RNA and DNA templates derived from the HIV-1 genome using a primer extension assay in vitro. Analysis of polymerization products on sequencing gels revealed strong pauses in synthesis, on both RNA and DNA templates, in homopolymeric nucleotide runs, and at regions of predicted secondary structure. Polymerization pauses occurred in runs of template rGs (> or = 4 bases) and rCs (> or = 3 bases) during minus-strand synthesis on RNA templates, and in most runs (> or = 4 bases) of template dTs and dAs during plus-strand synthesis on DNA templates. Pausing also occurred on both templates within the first few nucleotides of the predicted hairpin structures of the Rev response element. The locations of pauses were dependent on template sequence and were unaffected by primer positioning, RT concentration, and ionic strength. Recombinant and virion-derived HIV-1 RTs showed similar pausing patterns. DNA products that accumulated at HIV-1 RT pause sites on RNA templates were extended by continued incubation with excess RT from Moloney murine leukemia virus, showing that the RNA templates were not broken or otherwise unable to support polymerization. Polymerizations conducted in the presence of a poly(rA) oligo(dT) trap showed that pausing results from two mechanisms: 1) RT remaining bound to the primer-template and polymerizing at a greatly reduced rate, or 2) RT dissociating from the primer-template. These results demonstrate that specific HIV-1 RNA and DNA template sequences are capable of interrupting processive DNA synthesis by HIV-1 RT in vitro. Pausing may serve specific functions in HIV-1 replication and mutagenesis. Moreover, these data suggest that one or more accessory factors are required to complete proviral DNA synthesis in vivo and that efficient HIV-1 DNA synthesis may require multiple origins.

Base Sequence↗
PubMed1995

Addition of a mu-tailpiece to IgG results in polymeric antibodies with enhanced effector functions including complement-mediated cytolysis by IgG4.

The 18-amino acid carboxyl-terminal tailpiece from IgM (mutp) has now been added to the carboxyl-termini of IgG1, IgG2, IgG3, and IgG4 constant regions to produce recombinant IgM-like IgGs. Polymeric IgGs obtained by this approach possess up to six Fcs and 12 antigen-combining sites, greatly increasing the avidity of their interactions with other molecules. Not surprisingly, the C activity of normally active IgG1 and IgG3 and somewhat less active IgG2 Abs is shown to be dramatically enhanced upon polymerization. The multiple Fcs present in a single molecule apparently allow for more efficient interactions with the multiple C1q heads present in C1, the first component of the classical C cascade. An unexpected result however, is that IgG4, normally devoid of C activity, when polymerized in the same fashion directs C-mediated lysis of target cells almost as effectively as the other polymers. Interestingly though, IgG4mutp does not deplete C activity in a standard consumption assay using soluble Ag. The other gamma mutp isotypes are capable of depleting 100% of the serum lytic ability even in the absence of Ag, whereas IgG4mutp shows no evidence of activity in this assay under any of the conditions tested. Additionally, we show that, in contrast to monomeric IgG, polymeric IgGs bind with very high affinity to Fc gamma receptor II (Fc gamma RII), a low affinity receptor for wild-type antibodies; however, binding to Fc gamma Rl, the high affinity receptor, appears to be unaltered. Finally, the in vivo t1/2 of the gamma mutp proteins is decreased relative to wild-type IgG, apparently because of rapid clearance of the polymeric fraction.

Amino Acid Sequence↗
PubMed1994

Polymerization and instability of a recombinant hemoglobin containing valine beta 7.

A recombinant hemoglobin containing Val beta 7 (Hb beta E7V) was engineered and expressed in yeast to evaluate amino acid specificity of the Glu beta 6-->Val mutation (Hb beta E6V) in promoting polymer formation of deoxyhemoglobin. The purified CO Hb beta E7V migrated as a single band on electrophoresis with a slightly decreased positive charge compared with CO Hb S. The oxygen affinity of Hb beta E7V was slightly higher than Hb S, while the absorption spectrum of the mutant was similar to Hb S. Critical concentrations for polymerization in 1.8 M phosphate of the deoxy forms of Hb beta E7V and Hb A were 15- and 25-fold, respectively, higher than Hb S. Oversaturated deoxy Hb beta E7V polymerized without a delay time prior to polymerization like deoxy Hb beta E6F and Hb beta E6W. These results demonstrate that Val beta 6 in Hb S is critical for rapid polymerization of deoxyhemoglobin. The oxy form of Hb beta E7V was approximately 2-3-fold more unstable to heat and mechanical agitation than oxy Hb S, suggesting that instability and polymerization of hemoglobin are distinct properties.

Biopolymers↗
PubMed1994

Phosphorylation and supramolecular organization of murine small heat shock protein HSP25 abolish its actin polymerization-inhibiting activity.

Characteristic features of mammalian small heat shock proteins are their rapid phosphorylation in response to stress and mitogenic signals and their ability to form multimeric particles of 200-700 kDa and large aggregates up to 5000 kDa. Recently, a chaperoning function and an actin polymerization-inhibiting activity were demonstrated for the recombinant murine and turkey small heat shock protein, respectively. In this paper, we demonstrate that the actin polymerization-inhibiting activity of the murine small heat shock protein HSP25 is dependent on the degree of its phosphorylation and structural organization. Non-phosphorylated and phosphorylated HSP25 monomers, as well as non-phosphorylated multimeric HSP25 particles, were isolated from Ehrlich ascites tumor cells by ammonium sulfate precipitation, column chromatography, and ultracentrifugation and tested for their actin polymerization-inhibiting activity. Fluorescence spectroscopy and electron microscopy were used to monitor actin polymerization. Non-phosphorylated HSP25 monomers were active in inhibiting actin polymerization with about 90% inhibition at a 1:1 ratio of actin to HSP25, while phosphorylated HSP25 monomers and non-phosphorylated multimeric HSP25 particles were inactive. Furthermore, we present electron microscopic data on the structure of HSP25 particles.

Actins↗
PubMed1993

The amino acids that constitute sequence gamma 268-282 of fibrinogen are not involved in fibrin monomer polymerization.

Congenitally abnormal fibrinogens with impaired fibrin monomer polymerization have been described to contain single amino-acid substitutions localized in certain positions of the gamma 275-330 peptide region. To evaluate the role of the amino-acid sequence in the vicinity of Arg275 in fibrin monomer polymerization, the peptide fragment corresponding to gamma 268-282 was synthesized and used to obtain peptide-specific antibodies. These antibodies, when purified immunochemically on the immobilized peptide, bound to the intact fibrinogen and fibrin monomers with the same binding affinity. However, they did not recognize the gamma 268-282 epitopes on the denatured and reduced fibrinogen molecules. The lack of influence of antipeptide antibodies on fibrin monomer polymerization indicates that the gamma 268-282 peptide is not directly involved in the structure of the polymerization site in the D domain of fibrinogen. It is suggested that substitution of Arg275 either by His or Cys in abnormal fibrinogens results probably in conformational changes which disturb a proper orientation of the polymerization site and reduce its expression.

Amino Acid Sequence↗
PubMed1993

Thermodynamical aspects of the polymerization reaction of PMMA cement mixed with phosphatic mineral phases.

The main problem related to the use of polymeric cement in orthopaedics is the high temperature reached during the polymerization, causing necrosis. This paper reports a thermodynamical study of the polymerization reaction of an acrylic cement mixed with powdered phosphatic phases. In particular, mixing of alpha-tricalciumphosphate, beta-tricalciumphosphate and hydroxyapatite was proposed. Important preliminary results indicated that amounts of about 66% by weight of alpha-tricalciumphosphate reduced the polymerization temperature to about 58 degrees C in respect to 100 degrees C of pure acrylic cement. In addition, a special chamber was designed and realized to monitor the temperature variations involved during the polymerization reaction of the different mixtures.

Bone Cements↗
PubMedDate not supplied

Effect of light-tip distance on polymerization of resin composite.

The inability to place a light tip in close approximation to a resin restoration may affect the resultant polymerization and clinical durability of the restoration. This research measured light intensity at the surface of a resin composite, as well as 2 mm within its bulk, as the tip-to-resin distance is moved from 0 to 10 mm. The polymerization of the resin composite at both locations was measured for the various tip distances using exposure durations of 10, 20, 40, and 60 seconds. Light intensity did not decrease with the inverse square of the tip distance. The polymerization on the surface was greatly dependent upon the duration of exposure. The extent of polymerization 2 mm below the surface was still dependent primarily upon exposure duration, but intensity had a significant affect. For exposure durations of 10, 20, and 40 seconds, a tip distance greater than 4 mm demonstrated a significant decrease in resin polymerization 2 mm below the resin composite surface.

Composite Resins↗
PubMed1993

Alpha 1-antitrypsin Siiyama (Ser53-->Phe). Further evidence for intracellular loop-sheet polymerization.

Antitrypsin Siiyama is a rare example of the deficiency variants of antitrypsin that accumulate in the endoplasmic reticulum of the hepatocyte. The common example is Z antitrypsin, which has a mutation (Glu342-->Lys) at the junction of the head of the fifth strand of the A sheet and the base of the reactive center loop. It was previously shown that Z antitrypsin spontaneously polymerizes due to the insertion of the reactive center loop of one molecule into the A sheet of a second. The mutation in antitrypsin Siiyama (Ser53-->Phe) affects a residue that provides a ridge for the sliding movement that opens the A sheet, and it had been predicted that this would result in the same type of loop-sheet polymerization observed with the Z variant. We confirm this here and show that virtually all the plasma antitrypsin in a homozygote for the Siiyama variant was polymerized due to non-covalent bonding with a loss of accessibility of the reactive center loop. The common basis of the polymerization of Z and Siiyama antitrypsin is supported by identical findings on electron microscopy. Taken together these results confirm that loop-sheet polymerization is a general mechanism and as such is likely to be responsible for the intracellular inclusions associated with liver pathology.

Adult↗
PubMedDate not supplied

Effect of die material hue and value on polymerization of indirect resin inlays.

This study investigated the effects of hue and value of mold materials on the polymerization of resin composite inlays fabricated by an indirect process. Three colors of molds were used, and 10 specimens each of three resin composite materials were light polymerized on each of the die materials for each test. The specimens were postirradiation heat polymerized. Compressive strength, flexural strength, Knoop hardness, and bond strength to enamel and dentin were measured. Although differences in properties between specimens polymerized on different die materials were not always significant, the values obtained from the white mold were highest in all tests followed by those obtained on the gray and then the black molds. Correlations (r2) between lightness or value and compressive and flexural strength, hardness, and bond to enamel and dentin values were greater than 0.90. Die color and value appear to be important factors influencing the properties of indirect resin composite inlays even though they are heat polymerized after light activation.

Analysis of Variance↗
PubMed1993

The polymerization of fibrinogen Dusart (A alpha 554 Arg-->Cys) after removal of carboxy terminal regions of the A alpha-chains.

The six polypeptide chains of normal fibrinogen are covalently linked by interchain disulphide bonds, and there are no free sulphydryl groups. Fibrinogen Dusart is a congenital fibrinogen variant in which A alpha 554 Arg is replaced by Cys; albumin is disulphide linked to these fibrinogen molecules, possibly at A alpha 554 Cys. Functionally, Dusart fibrinogen displays markedly abnormal fibrin polymerization, characterized by delayed lateral fibril association and matrix fibre bundles that are thinner than normal fibrin bundles. These observations are consistent with experiments suggesting that the carboxy terminal region of the A alpha-chain contains a polymerization domain that participates in lateral fibril associations. In order to investigate the location and the effect of albumin binding to Dusart fibrinogen, we examined the fibrinogen by electron microscopy, and compared the polymerization and ultrastructure of fibrin prepared from normal fibrinogen containing intact A alpha-chains (fraction I-2) or plasmin degraded fibrinogen molecules lacking carboxy terminal regions of A alpha-chains (fraction I-9D), with fibrin prepared from Dusart fraction I-2 and I-9D. Most bound albumin was released from Dusart fibrinogen by plasmin degradation involving the A alpha-chains. Nevertheless, we were able to visualize albumin molecules remaining covalently bound to Dusart I-9D as well as to Dusart I-2 fibrinogen, as distinct globular domains situated near the fibrinogen D domain. The presence of albumin in these fractions was confirmed by Western blotting using anti-albumin. Dusart fibrin polymerized much more slowly than normal I-2, as previously reported, whereas polymerization of Dusart I-9D fibrin was faster than Dusart I-2 and nearly the same as normal I-9D fibrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1996

Dephosphorylation of a 34kd triton-insoluble F-actin pool protein is associated with phorbol ester-induced actin polymerization in human polymorphonuclear leukocytes.

Activation of human polymorphonuclear leukocytes (PMNs) by chemotactic peptide (FMLP) or phorbol ester (PMA) results in actin reorganization and PMN motility. Evidence suggests that PMA and FMLP activate PMN actin reorganization by different mechanisms. For example, the protein phosphatase inhibitor, okadaic acid (OA), inhibits PMA- but not FMLP-induced actin rearrangement, suggesting protein dephosphorylation is key to PMA but not FMLP actin changes and that PMN actin reorganization occurs by multiple mechanisms. Further support for multiple actin polymerization mechanisms is the recent description of distinct F-actin pools coexisting with G-actin in PMNs, Triton insoluble F-actin (TIF) and Triton soluble F-actin (TSF). These studies examine quantitative actin pool-specific actin polymerization in PMA- and FMLP-activated PMNs using quantitative SDS-PAGE and the phosphorylation of proteins in each actin pool using 32P orthophosphate (32P) labeling. The results show: (1) OA alone has no effect on actin pool content; (2) PMA induces actin growth only in the TIF pool similar to results with FMLP, and (3) OA pretreatment has no effect on FMLP actin polymerization, but inhibits PMA-induced changes. 32P results show that in basal PMNs, multiple phosphoproteins are found in the TIF including a protein of MW 34kd (pp34), the TSF pool contains a pp34 and a pp69 and the G-actin pool a pp34. PMA induces dephosphorylation of pp34 in the TIF (0.59 +/- 0.14 x basal, n = 3). OA prior to PMA prevents TIF pp34 dephosphorylation and actin shifts between the TIF, TSF, and G pools. OA alone results in phosphorylation of pp34 in all actin pools but no shift in actin content. The results show that (1) phosphoproteins exist in all three actin pools of PMNs-TIF-actin, TSF-actin, and G-actin; (2) both PMA and FMLP cause quantitatively identical actin polymerization in the TIF; and (3) in contrast, PMA but not FMLP TIF growth requires dephosphorylation of a pp34. This as yet unidentified phosphoprotein appears crucial to PMA- but not FMLP-induced actin polymerization.

Actins↗
PubMedDate not supplied

Bond strength of six soft denture liners processed against polymerized and unpolymerized poly(methyl methacrylate).

The bond strength of six commercial soft denture liners was evaluated by a two-phase tensile test. The soft denture liners investigated were VinaSoft, Prolastic, Flexor, Molloplast-B, Novus, and SuperSoft. The samples were fabricated by processing them (1) against polymerized poly(methyl methacrylate), and (2) against unpolymerized poly(methyl methacrylate). The soft denture liners were processed according to the manufacturers recommendations. The samples were tested using an Instron Universal Testing Machine. The mode of failure, adhesive or cohesive, was also recorded. The bond strength when processed against unpolymerized poly(methyl methacrylate) ranged from 0.48 to 2.60 MPa, and when processed against polymerized poly(methyl methacrylate) the bond strength ranged from 0.94 to 2.56 MPa. A two-way analysis of variance (P = .05) revealed a significant increase in bond strength when the liners were processed against polymerized poly(methyl methacrylate), except for Novus, which had no change, and VinaSoft, which decreased. The Tukey interval between materials was .22 and between methods of polymerization was .08. Four of the six liners investigated demonstrated increased bond strength when processed against polymerized poly(methyl methacrylate). It was concluded that bonding can be influenced by the processing method.

Acrylic Resins↗
PubMed1997

Colchicine activates actin polymerization by microtubule depolymerization.

Swiss 3T3 fibroblasts were treated with the microtubule-disrupting agent colchicine to study any interaction between microtubule dynamics and actin polymerization. Colchicine increased the amount of filamentous actin (F-actin), in a dose- and time-dependent manner with a significant increase at 1 h by about 130% over control level. Confocal microscopic observation showed that colchicine increased F-actin contents by stress fiber formation without inducing membrane ruffling. Colchicine did not activate phospholipase C and phospholipase D, whereas lysophosphatidic acid did, indicating that colchicine may have a different mechanism of actin polymerization regulation from LPA. A variety of microtubule-disrupting agents stimulated actin polymerization in Swiss 3T3 and Rat-2 fibroblasts as did colchicine, but the microtubule-stabilizing agent taxol inhibited actin polymerization induced by the above microtubule-disrupting agents. In addition, colchicine-induced actin polymerization was blocked by two protein phosphatase inhibitors, okadaic acid and calyculin A. These results suggest that microtubule depolymerization activates stress fiber formation by serine/threonine dephosphorylation in fibroblasts.

3T3 Cells↗
PubMed1997

Fibrinogen and fibrin polymerization: appraisal of the binding events that accompany fibrin generation and fibrin clot assembly.

Fibrinogen is a complex multifunctional protein comprised of three major domains (two outer D and one central E) which contains constitutive binding sites (e.g. Da, Db, gammaXL, D:D, gamma', thrombin substrate, platelet receptor) as well as binding sites that become exposed or expressed as a result of fibrinogen proteolysis by thrombin and/or that are exposed as a consequence of the polymerization process itself (tPA binding sites). Fibrin-dependent tPA-mediated activation of plasminogen is associated with exposure of polymerization-dependent epitopes (Aalpha148-160, gamma312-324) that are expressed in assembled fibrin and in crosslinked (polymerized) fibrinogen but not in unpolymerized fibrinogen or fibrin. Fibrin polymerization is initiated by thrombin cleavage of fibrinopeptide A from fibrinogen Aalpha chains, exposing two E domain E(A) sites. Cleavage of fibrinopeptide B from fibrinogen Bbeta chains exposes other E domain polymerization sites, termed E(B), that also interact with platelets, fibroblasts and endothelial cells. Fibrin generation is followed by an assembly process of intermolecular end-to-middle D to E associations to form linear and branched double-stranded fibrin fibrils, lateral fibril-fibril associations to form fibers and a branched fiber network. Binding sites in fibrinogen play their roles in fibrin assembly by self-association (gammaXL to gammaXL and D:D to D:D) or by complementary association with exposed sites in fibrin (Da to E(A) and Db to E[B]). Other binding sites in fibrinogen include thrombin substrate recognition sites in each E domain and a non-substrate high affinity thrombin binding site in the carboxy-terminal region of each gamma' chain, which also binds plasma factor XIII. Fibrin possesses low affinity thrombin binding sites in each E domain and retains the gamma' chain nonsubstrate thrombin-binding site.

Animals↗
PubMed1963

Polymerization-depoly-merization of tobacco mosaic virus protein. I. Kinetics.

It was shown that a reversible endothermic association of TMV protein subunits (A protein) can take place at pH values below the isoelectric point as well as at pH 6.5. The polymerization occurring below the isoelectric point was found to be more complex than that at pH 6.5 probably because products other than the usual TMV-like rods were formed in addition to those rods and also because side-to-side aggregation of the rods took place readily. Kinetic studies indicated that polymerization can be treated as a second-order linear condensation. The rate of polymerization was found to be a critical function of pH, having a maximum value near pH 4.3. This behavior is at variance with the hypothesis that hydrogen-bonded carboxyl pairs play a dominant rate-determining role in the association of subunits. The dependence of the rate on pH was interpreted to indicate that electrostatic forces between subunits are a significant controlling factor in the polymerization of TMV protein.

Isoelectric Point↗