Biomedical subjects

F M Chen

Publications and source records attributed to F M Chen.

At least 73 records · Page 4Linked to original sources

PubMed1992

[Experimental study on early multiple organ failure after severe burns].

Forty-three male mongrel dogs (12.5 +/- 2.5 kg) were divided into normal control (n = 7), immediate infusion (n = 8), non-infusion (n = 13) and delayed infusion (n = 15) groups. A 50% TBSA third degree surface burn was produced by igniting 3% napalm for 30 seconds on the shaved back. Cardiac, pulmonary, hepatic, renal and gastrointestinal functions were monitored following the thermal injury. The findings of these studies showed that mean arterial pressure, cardiac index, left ventricular work, right ventricular work, ADP/O ratio and ATP were all significantly decreased (P less than 0.05). However pulmonary artery wedge pressure, pulmonary vascular resistance, systemic vascular resistance, P(A-a)O2, Beef, Cr, UN, ALT, LDH, TB, DB, and MDA were markedly increased (P less than 0.05). Severe shock occurred soon after burns. Thirteen dogs died within 12 hours in the non-infusion group. All the dogs were resuscitated when immediate infusion of lactic acid Ringers solution was given according to Parkland formula, and all of them tide over shock stage smoothly without obvious changes in visceral functions. However, dogs were not resuscitated when infusion was delayed 6 hours postburn. The changes in visceral were even more severe in this group than those in non-infusion group. These results demonstrated that delayed resuscitation was an important factor of MOF in the early postburn stage. The marked increase in MDA in the myocardiac, lung, liver, renal and gastrointestinal tissues indicated that lipoperoxidation by free oxygen radicals was closely related with visceral damages.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Intramolecular triplex formation of the purine.purine.pyrimidine type.

Six octadecamers with hairpin motifs have been synthesized and investigated for possible intramolecular triplex formation. Electrophoretic, hypochromic, and CD evidence suggest that d(CCCCTTTGGGGTTTGGGG) and d(GGGGTTTGGGGTTTCCCC) can form G.G.C intramolecular triplexes via double hairpin formation in neutral solutions, presumably with the terminal G tract folding back along the groove of the hairpin duplex. In contrast, d(GGGGTTTCCCCTTTGGGG) and the three corresponding 18-mers containing one G and two C tracts each forms a single hairpin duplex with a dangling single strand. The design of the sequences has led to the conclusion that the two G tracts are antiparallel to each other in such a triplex. Magnesium chloride titrations indicate that Mg2+ is not essential for such an intramolecular triplex formation. The main advantage of our constructs when compared to the intermolecular triplex formation is that the shorter triplex stem can be formed in a much lower DNA concentration. The merit of G.G.C triplex, in contrast to that of C+.G.C, lies in the fact that acidic condition is not required in its formation and will, thus, greatly expand our repertoire in the triplex strategy for the recognition and cleavage of duplex DNA. Spectral binding studies with actinomycin D (ACTD) and chromomycin A3 (CHR) as well as fluorescence lifetime measurements with ethidium bromide (EB) suggest that although hairpin duplexes bind these drugs quite well, the intramolecular triplexes bind poorly. Interestingly, the binding densities for the strong-binding hairpins obtained from Scatchard plots are about one ACTD molecule per oligomeric strand, whereas more than two drug molecules are found in the case of CHR, in agreement with the recent NMR studies indicating that CHR binds to DNA in the form of a dimer.

Base Composition↗

PubMed1991

Chromatographic methods for large-scale preparation of immunoglobulin G2a monoclonal antibodies Lym-1 and TNT-1 F(ab')2 fragments.

Lym-1 and TNT-1 are two murine immunoglobulin G2a monoclonal antibodies (MAbs) which have been used for clinical trials in cancer patients. This paper describes methods for large-scale preparation of F(ab')2 fragments from 50 mg to 4 g of MAbs Lym-1 and TNT-1. Digestion of MAbs with pepsin was optimized and performed at pH 3.8, a pepsin/antibody ratio of 1:250, and 3-4 h of incubation at 37 degrees C. The F(ab')2 fragments were purified by tandem column procedures using fast protein liquid chromatography. Quality control analyses of the products included protein purity, isoelectric point, immunoreactivity, and endotoxin level. The results revealed that the chromatographic procedures are practical, simple, and effective, and can be used to produce gram quantities of clinical-grade F(ab')2 fragments for the diagnosis of cancer in patients.

Antibodies, Monoclonal↗

PubMed1991

Reaction mechanisms in peptide synthesis. Part 1. Semiquantitative characteristics of the reactivity of 2-methyl-5(4H)-oxazolone with water and ammonia in the gas phase and weakly polar media.

2,4-Dialkyl-5(4H)-oxazolones are well-recognized intermediates in some aminolysis reactions in peptide synthesis. Using the MOPAC molecular orbital programs, detailed geometric and energetic characteristics of the elementary reaction pathways for the additions of water and ammonia to 2-methyl-5(4H)-oxazolone have been determined at the AM1 level. The results demonstrate that the additions must be parsed into a two-step mechanism involving formation of the alpha-hydroxyimine followed by tautomerization to the parent N-acetylamino acid or amide.

Ammonia↗

PubMed1991

Reaction mechanisms in peptide synthesis. Part 2. Tautomerism of the peptide bond.

We had concluded in previous work that ring opening of a 2-alkyl-5(4H)-oxazolone by water or ammonia leads to transient high-energy imidol intermediates which instantly tautomerize to the native amides. Using the MOPAC molecular orbital program, detailed geometric and energetic characteristics of the tautomerism of a peptide bond have been determined on the AM1 level. The results demonstrate that tautomerism of a peptide bond comprises a three-stage process involving three successive transition states and a bimolecular mechanism: (i) E----Z peptide bond isomerization followed by dimerization, (ii) concerted double-hydrogen exchange leading to an alpha-hydroxyimine (imidic acid) followed by splitting of the dimer, and (iii) Z----E N-methylimine inversion. While pathway (iii----ii----i) is predicted as a feasible route terminating in the formation of a peptide bond, the inverse route (iii----ii----i) is excluded as a possible initial step in the generation of a 5(4H)-oxazolone intermediate.

Ammonia↗

PubMed1991

Effects of 131I-labeled TNT-1 radioimmunotherapy on HT-29 human colon adenocarcinoma spheroids.

Radiolabeled murine monoclonal antibody TNT-1, directed against the nuclear histones of degenerating cells, was used to treat human colon adenocarcinoma HT-29 spheroids in vitro. The therapeutic effects of 131I-TNT-1 were investigated as a function of the radioactive dose, treatment time, and number of treatments. Efficacy of treatment was assessed by TNT-1 antibody uptake, spheroid growth delay, and morphological examination using light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). From these studies, it was determined that the therapeutic effect increased with the number of doses and the duration of treatment. Spheroids treated for 24 h showed approximately two to four times more cell death than those with a 2-h treatment. As previously shown in animal models, additional treatment with radiolabeled TNT-1 produced an expanding number of TNT-1 targets, and subsequent treatments were more effective as shown by antibody uptake studies. Microscopic examinations demonstrated that morphological changes consistent with spheroid destruction correlated well with antibody uptake data and increased gradually with dose, treatment time, and frequency of treatments. At the ultrastructural level, destruction of cells in the treated spheroids included the formation of porous cell membranes, crater-like holes (SEM), blebbing, and dissolution of cytoplasmic organelles (TEM). With continued culture, the injured spheroids were found to disaggregate after intensive 131I-TNT-1 therapy (e.g. 50 microCi/ml or 100 microCi/ml with two or three 24-h treatments). These findings suggest that tumor spheroids can be used as an in vitro model to evaluate monoclonal antibody therapy using TNT-1 and other candidate mAbs directed against intracellular antigens exposed in degenerating cells of tumors.

Adenocarcinoma↗

PubMed1991

An integrated multielectrode electrophysiology system.

An integrated system for recording and analyzing electrophysiological data from multiple channels is described. The system uses an MS-DOS microcomputer, a 16-channel amplifier, and multiple-tipped electrode arrays designed for use in intact and slice preparations. The system is designed for applications where the collection and analysis of multiple-channel electrophysiological data is desirable, including the construction of current source density (CSD) profiles from field potential data. The software incorporates on-line averaging, CSD and freeze-frame capabilities to guide the experiment in progress. Additional off-line analyses include multiple unit activity, power spectra, and automatic scans of data files for peak amplitude, area, latency, and slope within user-defined latency windows. All data and analyses can be exported to commercial statistical/graphical programs for the creation of publication-ready figures.

Amplifiers, Electronic↗

PubMed1991

Binding of Hg(II) to poly(dA): poly(dT) and its component single strands.

Mercuric binding studies at pH 10 revealed that poly(dA): poly(dT) exhibits a more dramatic absorption spectral alteration than the alternating polymer poly(dA-dT):poly(dA-dT) and induces a unique intense positive CD band at 296 nm during the spectral titrations. Comparative studies with its component single strands suggest that the spectral alterations exhibited by poly(dA): poly(dT) are consistent with a binding model in which the mercuric ions initially bind to thymines and cause the eventual strand separation of the duplex, with subsequent high cooperative binding to the poly(dA) strands. This interpretation is supported by the binding isotherms indicating much stronger mercuric binding to poly(dT) than to poly(dA), with saturation binding densities of 1 Hg(II) per 2 bases and 1 Hg(II) per base, respectively, and very high binding cooperativity for poly(dA). Striking spectral alterations are exhibited by the mercuric binding to poly(dA), likely the consequence of binding to the amino group of dA in an alkaline solution. The mononucleoside dA exhibits minor spectral alterations upon similar mercuric chloride additions whereas the dinucleoside monophosphate d(AA) exhibits significant spectral changes, albeit less pronounced than those of poly(dA). Some sequence effects on the mercuric binding are observed in the dinucleotide studies. Our CD results on the mercuric binding to polynucleotides do not support the contention of (psi)-type condensed complex formation.

Circular Dichroism↗

PubMed1991

Cell based radioimmunoassays to quantitate the immunoreactivity of TNT monoclonal antibodies directed against intracellular antigens.

Direct and indirect radioimmunoassay (RIA) procedures to determine the amount of binding of a mouse monoclonal antibody (MoAb) reactive with an intracellular antigen present in human cells are described. In these RIAs, mouse IgG2a MoAb, designated as Tumor Necrosis Treatment (TNT-1) antibody, paraformaldehyde/acetone fixed cells, and Sephadex beads were used to standardize the assay conditions. In the direct RIA, 83% of the 125I-labeled TNT-1 MoAb was bound to the target cells within 30 min after the addition of reagents. The amount of binding of the MoAb was directly proportional to the amount of antigen present in the assay. When the direct RIA was carried out using different types of target cells, 125I-labeled TNT-1 MoAb showed greater than 70% binding. In the indirect RIA, the amount of binding of secondary 125I-labeled goat anti-mouse IgG antibody to the target cells was linear. These results suggest that the indirect RIA can be used to estimate the immunoreactivity of the unlabeled TNT-1 MoAb present in crude protein preparations. Based on the results of RIAs the following two conclusions are drawn: 1) the direct RIA can be used to estimate rapidly the amount of immunoreactive TNT-1 MoAb present in 125I-labeled antibody preparations and 2) the indirect RIA which estimates the amount of immunoreactivity of unlabeled TNT-1 MoAb can be used to monitor the purification and study the characteristics of the MoAb present in crude protein preparations. These methods enable the quantitative measurement of MoAbs reactive against intracellular antigens using standard RIA procedures.

Animals↗

PubMed1991

Preparation of N-9-fluorenylmethoxycarbonylamino acid chlorides from mixed anhydrides by the action of hydrogen chloride.

N-9-Fluorenylmethoxycarbonyl-(Fmoc) amino-acid chlorides have been prepared by reaction of hydrogen chloride on purified mixed Fmoc-amino acid-monoalkyl carbonic acid anhydrides in dichloromethane. The products partially undergo subsequent conversion to the corresponding esters due to the presence of the liberated alcohol, the extent depending on the nature of the alkyl group. Esterification occurred to 5-20% when the alkyl group was isopropyl. Anhydrides of monoisopropenyl carbonic acid which liberate acetone instead of an alcohol gave products uncontaminated with ester. The three components in a reaction mixture could be determined as the reaction progressed by normal phase high-performance liquid chromatography of aliquots, which had been freed of excess hydrogen chloride, on a mu Porasil (underivatized silica) column using tert.-butanol-hexane (1.5:98.5) as solvent.

Acylation↗

PubMed1991

Studies on asymmetric induction associated with the coupling of N-acylamino acids and N-benzyloxycarbonyldipeptides.

The asymmetric induction occurring during aminolysis by an amino acid benzyl ester of the 5(4H)-oxazolones obtained from N-acyl-DL-valine for acyl = formyl, acetyl, benzoyl, trifluoroacetyl and N-benzyloxycarbonyl-Xaa where Xaa = Gly, Ala and Leu in dichloromethane and dimethylformamide at +5 degrees and -5 degrees was determined by analysis of the epimeric products by high-performance liquid chromatography after removal of protecting groups by hydrogenolysis. The influence of the side-chain of the activated residue on induction was assessed by examining aminolysis of the 5(4H)-oxazolones from N-benzyloxycarbonyl glycyl-Xaa-OH for Xaa = Ala, Leu, Val, and Phe. The contribution of induction to the epimeric content of products obtained from couplings mediated by N,N'-dicyclohexylcarbodiimide in the presence and absence of l-hydroxybenzotriazole, and by the mixed-anhydride method, were calculated. The induction was affected at varying levels by the nature of the N-acyl group, the side-chain of Xaa, the nature of the aminolyzing nucleophile, the nature of the solvent, and the temperature, with diastereomeric excesses reaching -32 and +53. The influence of the side-chain of Xaa on the induction was different in the two solvents. For the N-acyl series, the epimeric content of products did not always correctly reflect the relative tendencies of the derivatives to racemize. The order for epimeric content of the products also depended on the method of coupling.

Amino Acid Sequence↗

PubMed1990

Observation of an anomalously slow association kinetics in the binding of actinomycin D to d(CATGGCCATG).

An unusually slow association process which accounts for the bulk of its dichroic changes at 293 nm is observed for d(CAT-GGCC-ATG) when it reacts with actinomycin D (ACTD). This is in contrast to an order of magnitude faster association rates exhibited by oligomers containing a self-complementary tetranucleotide ACTD binding sequence (-TGCA-, -AGCT-, or -CGCG-). The number of drug molecules bound and the melting temperature increase upon ACTD binding are significantly higher for d(CAT-GGCC-ATG) than for other decamers studied. Temperature-dependent spectral measurements of this oligomer in the presence of ACTD suggest additional drug binding prior to denaturation. This particular decamer sequence may be unique, as other decamers containing central -GGCC- sequence and even those differing only by the terminal bases such as d(TAT-GGCC-ATA) and d(GAT-GGCC-ATC) are only weakly binding and do not exhibit such anomalously slow ACTD association kinetics, whereas the dodecamer d(CCAT-GGCC-ATGG) does. CD evidence indicates that, in contrast to the other -GGCC- containing oligomers, both d(CCAT-GGCC-ATGG) and its parent decamer exhibit nonstandard B conformations. The observed slow association kinetics and its interesting D/P dependence are rationalized in terms of a model in which the ACTD molecules initially end-stack and distort the oligomer duplex to a favorable ACTD-binding conformation so that intercalation at the central G-C sequence can occur via DNA breathing.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed1990

Localization of monoclonal antibody TNT-1 in experimental kidney infarction of the mouse.

An experimental kidney infarction model was developed in the mouse to study the uptake of a radiolabeled monoclonal antibody previously shown to bind to degenerating cells in malignant tumors. To determine if this approach is applicable to normal tissue and cell degeneration, kidney infarction was produced by clamping the mouse renal artery for 3 h using surgical procedures. Various groups of mice were injected with 131I-labeled TNT-1 F(ab')2 monoclonal antibody directed against nuclear histone antigens at varying intervals after surgery. Imaging, biodistribution, autoradiography, and histological studies were performed on each group of mice, including sham-operated controls, to quantitate the level of binding and localize the uptake of label in clamped and unclamped (contralateral) kidneys. As additional controls, clamped mice were administered radiolabeled irrelevant monoclonal antibody Lym-1 or mouse albumin. The results showed a marked selective uptake of radiolabeled TNT-1 F(ab')2 in the injured clamped kidney compared with the untreated kidney and other normal organs of the mouse. These studies define a model of normal organ necrosis that may be useful for study of the kinetics of antibody uptake in infarcted tissues.

Animals↗

PubMed1990

High-performance liquid chromatography of 2,4-disubstituted-5(4H)-oxazolones, anhydrides and other activated forms of N-acyl- and N-alkoxycarbonylamino acids.

Normal phase high-performance liquid chromatography has been achieved of the common activated forms of valine on a LiChrosorb-CN or a muPorasil (underivatized silica) column using hexane containing 1.5 or 5% tert.-butanol as solvent. Compounds examined include the 2-alkoxy-5(4H)-oxazolones and symmetrical and mixed anhydrides of N-tert.-butoxycarbonyl-, N-benzyloxycarbonyl-, and N-9-fluorenylmethoxycarbonylvaline, the chloride of the latter, a p-nitrophenyl ester, 2-methyl-4-isopropyl-5(4H)-oxazolone, valine-N-carboxyanhydride, and the N- and O-ethoxycarbonyl adducts of l-hydroxybenzotriazole. The 5(4H)-oxazolones from N-tert.-butoxycarbonylvaline and N-benzyloxycarbonylglycylvaline decomposed during chromatography on the muPorasil but not the LiChrosorb-CN column. The method allows direct monitoring of reactions involving generation or consumption of activated forms of amino acids.

Amino Acids↗

PubMed1990

[The causes of death of early endometrial cancer].

This is an analysis of 136 patients with clinical stage I and II endometrial carcinoma treated with primarily surgery at the Columbia Presbyterian Hospital between 1978 and 1985. There was a minimum three years follow up. Of 136 patients, 28 (21%) died with recurrent cancer. Tumor upstaging, histology, grade, depth of myometrial invasion, peritoneal cytology were of important factors in prognosis. Therefore, a clinically sophisticated study during initial operation and a deliberate planning of adjuvant treatment should further improve the survival rate of early endometrial cancer.

Aged↗

PubMed1990

A comparative autoradiographic study demonstrating differential intratumor localization of monoclonal antibodies to cell surface (Lym-1) and intracellular (TNT-1) antigens.

Autoradiography was utilized to explore the patterns of distribution of two different monoclonal antibodies (Lym-1 and TNT-1) in tumor-bearing nude mice. Lym-1 is an antibody against a cell surface B-cell antigen. In comparison, TNT-1 represents a novel approach and is an antibody against an intracellular (nuclear) antigen that is selectively revealed in degenerating tumor cells. Experimentally iodine-125-(125I) labeled Lym-1 or TNT-1 was injected intravenously into nude mice bearing either the Raji lymphoma or the ME-180 human cervical carcinoma. Qualitative autoradiographic analyses performed after injection revealed that Lym-1 accumulated at the periphery of the target tumor where vascular permeability is marked and where Lym-1 positive cells are first encountered. By contrast, TNT-1 lost its initial peripheral distribution and demonstrated progressive concentration in the center of the tumor where binding to its nuclear antigen is facilitated by the presence of cell degeneration and necrosis. These studies confirm the ability of TNT-1 to bind areas deep within tumor that traditionally are considered inaccessible to antibodies administered for imaging and therapy.

Animals↗

PubMed1989

Characterization of the high pH wobble structure of the 2-aminopurine.cytosine mismatch by N-15 NMR spectroscopy.

Transition mutations induced by the base analogue 2-aminopurine arise via the formation of AP.C base pairs during DNA replication. We report here the results of N-15 NMR studies on a duplex oligonucleotide containing N-15 enriched AP and C residues. At high pH (8.6) the AP.C base pair is predominantly wobble. This is the first report on use of a site specifically N-15 enriched oligonucleotide as a probe of aberrant base pairing in DNA.

2-Aminopurine↗

PubMed1989

Tumor necrosis treatment of ME-180 human cervical carcinoma model with 131I-labeled TNT-1 monoclonal antibody.

In contrast to normal tissues, many malignant tumors contain a high proportion of dead and dying cells. The loss of membrane integrity that accompanies cellular degeneration permits macromolecules, including antibodies, to freely enter the cell cytoplasm. Based upon these observations, it was hypothesized that monoclonal antibodies to intracellular antigens, which are integral structural components and are retained by degenerating cells, may be used to target a wide range of human malignancies. Previous studies by our laboratory utilizing these principles have demonstrated the feasibility of imaging four different histological types of human cancer in a nude mouse model, using monoclonal antibodies directed against insoluble intranuclear antigens. The present study describes the application of this approach, designated tumor necrosis treatment, for the radioimmunotherapy of transplantable ME-180 human cervical carcinomas in the nude mouse. Groups of tumor-bearing nude mice received three weekly treatments of 150 or 300 microCi of 131I-labeled experimental (TNT-1) or control (Lym-1) monoclonal antibodies. Detailed biodistribution data, dosimetric evaluations, and therapeutic results are presented to demonstrate the effective and preferential targeting of 131I-labeled TNT-1 monoclonal antibody within the tumor. In the experimental groups, the dose delivered to the tumor was sufficient to induce clinical regressions in 88% of treated animals, without evidence of toxicity to normal tissues. Complete regressions were obtained in 25% of the mice treated with high dose TNT-1. Microscopic examination of the implantation sites of these mice demonstrated the presence of acute radiation damage and residual keratin-positive tumor cells showing marked evidence of degeneration. Dosimetric data obtained over the 3-week treatment period showed that, unlike control treated mice, which received approximately 500 cGy each week, the experimental animals received increasing doses of radiolabeled antibody with each treatment (averages for weeks 1, 2, and 3: 1066, 2046, and 2476 cGy, respectively). In accordance with these data, enhanced imaging and therapeutic responses were observed with each therapeutic dose in the TNT-1-treated groups, compared with controls. These results indicate that TNT-1 therapy produces an ever expanding population of TNT-1-positive targets in the tumor as a result of the centrifugal killing of adjacent viable tumor cells. To help illustrate these results, a four-compartment model of the dose distribution kinetics of TNT-1 is presented for discussion with respect to the possible application of this method for the imaging and treatment of cancer in

Animals↗