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Biomedical subjects

R S Wong

Publications and source records attributed to R S Wong.

10 recordsLinked to original sources
PubMed1991

Enhancement of SR 2508 (etanidazole) radiosensitization by buthionine sulphoximine at low-dose-rate irradiation.

SR 2508 (etanidazole) (1 mM) or buthionine sulphoximine (BSO, 50 microM) or both drugs together did not radiosensitize oxic V79 Chinese hamster cells irradiated at either an acute dose rate (2.35 Gy/min) or at a low dose rate (0.117 Gy/min). BSO pretreatment (15 h at 37 degrees C) depleted cellular glutathione (GSH) to less than or equal to 1% of control level and radiosensitized hypoxic cells at both dose rates with an enhancement ratio (ER) of 1.2. SR 2508 alone radiosensitized hypoxic cells equally at both dose rates with an ER of 1.5. However, ER values of 2.2 and 2.5 were obtained with 1 mM SR 2508 in GSH-depleted cells at acute and low dose rate, respectively, with no significant difference between the two, i.e. there is no dose rate dependence for this potentiation. Since BSO increases SR 2508 radiosensitization and the combined BSO + SR 2508 treatment is extremely cytotoxic to hypoxic cells, our results suggest that combining BSO with SR 2508 will be useful in brachytherapy as well as external-beam therapy if the toxicity from both drugs in vivo is less than the gain in radiosensitization achieved.

Animals↗
PubMed1990

Glutathione depletion and cytotoxicity of buthionine sulphoximine and SR2508 in rodent and human cells.

SR2508 (1 mM) increases the rate of glutathione (GSH) depletion by L-buthionine-S-R-sulphoximine (BSO) in hypoxic V79 rodent and A549 human cells. Specifically, the GSH content for V79 and A549 cells, after incubating for about 6 hr with 50 and 100 microM BSO, respectively, was lower by at least 10-fold when 1 mM SR2508 was present. In addition, 1 mM SR2508 is extremely toxic to hypoxic cells with lower GSH content. Survival probabilities of GSH-depleted V79 and A549 cells are about 10(-3) after 10 hr incubation with 1 mM SR2508. By itself, 1 mM SR2508 or 50-100 microM BSO decreased cellular viability by about 50% with a 10 hr treatment period. Both the phenomena described above are preferential towards hypoxic cells with minimal effect on aerobic cells.

Animals↗
PubMed1990

DNA technology.

With the availability of DNA recombinant technology and DNA and RNA sequencing techniques, diseases can now be studied and treated at a molecular level, while unlimited quantities of a pure protein product can be produced through gene cloning. Before the end of this century, gene therapy will be used to repair genetic defects. This article explains these advances in genetic technology and suggests their relevance in clinical problems and practice.

Amino Acid Sequence↗
PubMed1990

Thermal tolerance during S phase for cell killing and chromosomal aberrations.

Synchronous Chinese hamster ovary cells in early S phase were obtained by selecting mitotic cells, accumulating them at the G1/S border by incubating them in aphidicolin for 12 h, and then incubating them for 2 h after releasing them from the aphidicolin block. To determine if thermotolerance could be induced, the cells were heated at 43 degrees C for 20 min in early S phase, incubated for 160 min, and then heated a second time at 43 degrees C for different durations (30-100 min). For the control, nontolerant population, the cells in early S phase were incubated for 50 min and then heated once at 43 degrees C for different durations (20-60 min). Flow cytometric analysis indicated that the population receiving the second heat dose was in the same part of S phase as the population receiving the single heat dose. A comparison of the heat response for the two populations indicated that heating during early S phase induced thermotolerance for both cell killing and chromosomal aberrations; i.e., for 10% survival, which corresponded to 10% of the cells being cytologically normal, the thermal dose was twofold greater in the thermotolerant cells than in the control, nontolerant cells. Furthermore, this thermotolerance developed during S phase. These observations support the hypothesis that heating during S phase kills cells primarily by inducing chromosomal aberrations.

Acclimatization↗
PubMed1990

Cell killing, chromosomal aberrations, and division delay as thermal sensitivity is modified during the cell cycle.

Synchronous Chinese hamster ovary cells were treated in G1 or S phase with cycloheximide or procaine hydrochloride before and during heating at 43 degrees C. Cycloheximide and procaine apparently act by different mechanisms, with cycloheximide inhibiting protein synthesis and procaine hydrochloride supposedly affecting cellular membranes. Both agents, however, modify the heat damage expressed as chromosomal aberrations, cell killing, or division delay. Furthermore, the approximately twofold protection with cycloheximide treatment or twofold sensitization with procaine treatment is the same for the three end points and for heating during either G1 or S phase. However, heat induces chromosomal aberrations observed in metaphase when cells are heated in S phase but not when they are heated in G1. Finally, for the three end points, the activation energy is about 140-152 kcal/mol. Therefore, heat may induce a common intracellular phenomenon involving protein denaturation or aggregation that is responsible for the damage observed by division delay, chromosomal aberrations, and cell-killing. There are great differences in division delay induced during the cell cycle by heat or radiation. Division delay is the same when cells are heated in the relatively heat-resistant G1 phase or the relatively heat-sensitive S phase, with about 15 min of delay for 1 min of heating at 43 degrees C. This contrasts with the increase in division delay observed when cells are irradiated in the relatively radioresistant S phase compared with the relatively radiosensitive G1 phase. Quantitatively, division delay for a treatment that reduces survival to about 0.1 is 15 or 25 h for heating in S or G1, respectively, compared with only 6 or 1.5 h for irradiation in S or G1, respectively.

Acclimatization↗
PubMed1989

DNA fork displacement rate measurements in heated Chinese hamster ovary cells.

DNA fork displacement rates (FDR) were measured in Chinese hamster ovary (CHO) cells heated at either 43.5 degrees C or 45.5 degrees C for various times. The inhibition of fork movement rate by heat was both time and temperature dependent, i.e., 10-20 min at 43.5 degrees C or 5 min at 45.5 degrees C was required to decrease the FDR to 20-30% of the control rate of 1 micron/min. Following heating, the reduced FDR was found to be constant for at least 75 min. The observed effects of heat on reduced rates of DNA replicon initiation and chain elongation and the increase in DNA with single-stranded regions could be explained by the heat sensitivity of the FDR. Any of these alterations in the DNA replication process may lead to many opportunities for abnormal DNA and/or protein interactions to occur which ultimately may lead to the observed formation of chromosomal aberrations.

Animals↗
PubMed1989

Growth factors, oncogenes and the autocrine hypothesis.

Many aspects must be studied when considering theories of oncogenesis. Growth factors, the polypeptide hormones that are necessary for cell growth, and oncogenes, the genes that produce cancer, are only two aspects. Proto-oncogenes are found in normal cellular DNA and are believed to play regulatory roles in differentiation and development. Oncoviruses, mutation of DNA and chromosomal damage can activate proto-oncogenes and cause malignant change. Oncogenes can render transformed cells independent of growth factors. A cell can bypass the need for outside growth factors by producing the growth factor and its receptor, thereby using an autostimulatory impetus for growth. This is autocrine growth. An oncogene can also bypass the need for growth factors by activating or modifying growth factor receptors, or by stimulating intracellular events, such as tyrosine phosphorylation, both of which ultimately lead to cell division. The various mechanisms by which oncogenes act provide specific targets for treatment. Specific antigrowth factor or antireceptor antibodies or antagonists could interfere with autocrine regulation. Further research on the activation of oncogenes could provide valuable insight on regulation of the growth of tumors. Ultimately, the understanding of the molecular pathogenesis of cellular transformation will be a key to the prevention and treatment of cancer.

Cell Transformation, Neoplastic↗
PubMed1989

Mechanism of killing Chinese hamster ovary cells heated in G1: effects on DNA synthesis and blocking in G2.

To determine where in the cell cycle Chinese hamster ovary cells die following heating in G1, a mild hyperthermia treatment, i.e., 10 or 11.5 min at 45.5 degrees C, resulting in 40-50% cell kill was used. After a 7-14-h delay in G1, the cells heated in G1 eventually entered S phase and replicated all their DNA. Both an autoradiographic analysis with tritiated thymidine and a bromodeoxyuridine-propidium iodide bivariate analysis by flow cytometry revealed that both clonogenic and nonclonogenic cells were delayed in progression through S phase for at least 4 h. Then they completed replication of all their DNA and entered G2. Alkaline sucrose gradient sedimentation analysis revealed that these heated cells could complete replicon elongation into cluster-sized molecules of 120-160 S which persisted for 2-12 h after heating. However, further replicon elongation into multicluster-sized molecules greater than 160 S required an additional 12 h in heated cells compared to the 4 h needed in unheated control cells. Our results when compared with the literature suggest that when G1 cells are heated to a survival level of about 50%, the nonclonogenic cells recover from a long delay in G1, traverse S at a reduced rate, and then die either in G2 or as multinucleated cells after an aberrant division.

Animals↗
PubMed1979

The complete primary structure of a proline-rich phosphoprotein from human saliva.

The complete amino acid sequence of a calcium-binding "proline-rich phosphoprotein," named Protein A, from human saliva was determined by automated and manual Edman degradation of peptides obtained by enzymatic and chemical cleavage of the intact protein. The NH2-terminal pyrrolidone carboxylic acid was identified by means of NMR. The protein consists of 106 amino acids, including 24 residues of proline. The NH2-terminal 32 residues contain 13 of the 15 negatively charged residues including 2 phosphoserines, but only 1 proline. In spite of a high concentration of proline in the COOH-terminal part of the molecule, the longest oligoproline sequence is tetraproline. The protein contains a number of repeated sequences and there are also several sequences of 3 or 4 residues identical with known sequences of collagen, but the characteristic occurrence of glycine in every third position in collagen is not found in salivary Protein A.

Amino Acid Sequence↗