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Biomedical subjects

W C Dewey

Publications and source records attributed to W C Dewey.

At least 145 records · Page 8Linked to original sources
PubMed1978

Effects of heat on the centrosomes of Chinese hamster ovary cells.

Chinese hamster ovary cells were heated either at 45.5 degrees for 15 min or at 42 degrees for 1 hr and then were either fixed immediately or allowed to recover at 37 degrees for intervals of up to 12 hr. In addition control cells and cells heated at 45.5 degrees for 15 min were immediately subjected to a cell fractionation procedure that yielded partially purified centrosome preparations. In 100% of the cells fixed and examined immediately after heating, the centrosomes were damaged. The osmiophilic cloud increased in density and became aggregated. The majority of the pericentriolar particles or virus-like particles disappeared, and in some cases the tubules of the wall of the centriole appeared disrupted. These changes were also noted in the much more abundant population of centrosomes in the partially purified cell fraction. Furthermore, in those cells heated at 45.5 degrees for 15 min, no recovery of the centrosomes or return of virus-like particles occurred even after incubation at 37 degrees for 12 hr.

Cell Fractionation↗
PubMed1977

Effect of pH on hyperthermic cell survival.

Chinese hamster ovary cells incubated with various concentrations of CO2, to obtain extracellular pH values in the range of 6.40-7.85, were heated at 45.5C for 5, 10, or 20 minutes. Thermal sensitivity increased sharply from pH 7.35 to 6.65 (i.e., survival decreased from 1 X 10(-2) to 3 X 10(-5) for 20 minutes of heating), but remained constant from pH 7.35 to 7.85. The enhanced thermal sensitivity at pH values below pth 7.35 suggested that tumors should be preferentially destroyed by heat relative to normal tissue, since reports indicated that tumors were more acidic than the surrounding normal tissue.

Cell Survival↗
PubMed1977

Cellular responses to combinations of hyperthermia and radiation.

The two principal rationales for applying hyperthermia in cancer therapy are that: (a) the S phase, which is relatively radioresistant, is the most sensitive phase to hyperthermia, and can be selectively radiosensitized by combining hyperthermia with x-irradiation; the cycling tumor cells in S phase which would normally survive an x-ray dose could thus be killed by subjecting these cells to hyperthermia; and (b) the relatively radioresistant hypoxic cells in the tumor may be selectively destroyed by combinations of hyperthermia and x-irradiation. Both of these rationales have been mentioned as reasons for using high LET irradiation in cancer therapy; therefore where such irradiation may be of use, hyperthermia may also be advantageous.

Animals↗
PubMed1977

Visualization of interphase chromosomes.

Using a modified Giemsa-banding technique we have observed what appear to be chromosomes during interphase in nuclei from Allium cepa root tips and Chinese hamster cells (CHO line). During telophase through G1 chromosomes progressively uncoil and decondense. During S chromosomes are comparatively decondensed, but some segments have structure similar to chromosomes in G1 and G2. During G2 the chromosomes progressively recondense and coil in apparent preparation for prophase. Although specific structural modifications of chromosomes occur in G1, Sand G2 nuclei, chromosomes appear never to decondense to the point that they lose their 3-dimensional integrity, but remain in distinct domains throughout interphase.

Animals↗
PubMed1976

X-ray-induced mutants resistant to 8-azaguanine. I. Effects of cell density and expression time.

Asynchronous Chinese hamster ovary cells were irradiated and colony survival in Alpha MEM medium with dialyzed serum was determined with or without 15 mug/ml 8-Azaguanine (AG). Data indicated that a reproducible assay for the system was dependent upon controlling cell density at least two days prior to induction as well as throughout the expression period. Generally, spontaneous and radiation-induced mutant frequencies decreased when cell densities exceeded a critical density of 3-6 X 10(4) cells/cm2. Infrequently, the critical density was exceeded by a factor of two with no observed decrease, possibly correlated with a longer cell doubling time. Drug depletion artifacts can occur because of drug degradation, or because wild-type cells utilize the drug or produce conditions which reduce uptake of the drug. Thus, as the effective drug concentration is lowered, the observed mutant frequency increases because a spectrum of mutants resistant to only low concentrations can now survive. In fact, refeeding with AG at intervals during the incubation period lowered spontaneous and radiation-induced frequencies approx. 5-fold. Therefore, to standardize conditions, cells were trypsinized at the end of the expression time and replated at a constant cell number for mutant selection by AG. Over two generations of growth during the expression period were required for optimal manifestation of induced mutants, and when densities were kept below 4 X 10(4) cells/cm2 at all times, observed mutant frequencies did not change significantly over a period between 80 and 140 h post-induction (over 4 generations for irradiated cells and over 6 generations for controls). Previous reports of observed mutant frequencies decreasing beyond three generations may be due to cell interaction prior to mutant selection.

Azaguanine↗
PubMed1976

X-ray-induced mutants resistant to 8-azaguanine. II. Cell cycle dose response.

Synchronous Chinese hamster ovary cells were irradiated in G1 or S phase. Colony survival in Alpha MEM medium with dialyzed serum was determined with or without 15 mug/ml 8-azaguanine (AG). An expression period of over three generations (multiplicity of 20) was utilized, with expression times ranging from 58 to 114 h. Both G1 and S phase were practically identical in sensitivity to X-ray-induced mutations, with mutant frequency/viable cell/rad ranging from 1 X 10(-7) (75-100 rad) to 8 X 10(-7) (1000 rad). The spontaneous mutation rate, shown by Luria-Delbruck fluctuation analysis, was 5 X 10(-7) per generation. Thirty-three mutants, isolated at random and grown for over 30 generations in the absence of AG, were analyzed for plating efficiency (PE) in different concentrations of AG or in hypoxanthine-aminopterin-thymidine (HAT) medium. Of these, 64% were resistant (PE greater than 0.1) to 7.5 mug/ml AG, 85% to 5.0 mug/ml, and 91% to 3.5 mug/ml. Only 42% showed possible hypoxanthine-phosphoribosyltransferase (hprtase) deficiency as evidenced by HAT sensitivity (PE less than 0.1). Wild type controls exhibited PE's in 3.5 mug/ml AG of less than 0.001 and in HAT of greater than 0.5. Of ten mutants studied, all demonstrated survival response to radiation similar to wild type cells (D0 of approx. 120 rad). For radiation protection standards, the radiation dose required to induce mutations at a rate equal to that occurring spontaneously is called the doubling dose. The doubling dose observed for acute irradiation was about 3 rad and was estimated to be 10-60 rad for chronic irradiation, similar to that often reported for in vivo studies.

Aminopterin↗
PubMed1976

Fragmentation of chromatin with 125I radioactive disintegrations.

The DNA in Chinese hamster cells was labeled first for 3 h with [3H]TdR and then for 3 h with [125I]UdR. Chromatin was extracted, frozen, and stored at -30 degrees C until 1.0 X 10(17) and 1.25 X 10(17) disintegrations/g of labeled DNA occurred for 125I and 3H respectively. Velocity sedimentation of chromatin (DNA with associated chromosomal proteins) in neutral sucrose gradients indicated that the localized energy from the 125I disintegrations, which gave about 1 double-strand break/disintegration plus an additional 1.3 single strand breaks, selectively fragmented the [125I] chromatin into pieces smaller than the [3H] chromatin. In other words, 125I disintegrations caused much more localized damage in the chromatin labeled with 125I than in the chromatin labeled with 3H, and fragments induced in DNA by 125I disintegrations were not held together by the associated chromosomal proteins. Use of this 125I technique for studying chromosomal proteins associated with different regions in the cellular DNA is discussed. For these studies, the number of disintegrations required for fragmenting DNA molecules of different sizes is illustrated.

Cell Line↗
PubMed1976

X-irradiation of equine peripheral blood lymphocytes stimulated with phytohaemagglutinin in vitro.

Small lymphocytes were isolated from the peripheral blood of horses and incubated at 37 degrees C in Eagle's medium supplemented with 20 per cent foetal calf serum. The addition of phytohaemagglutinin (PHA) to the cultures resulted in: increased RNA and protein synthesis; the enlargement of the small lymphocyte into a lymphoblast-like cell; the initiation of DNA synthesis, and cell division. When survival was measured 24 hours after X-irradiation by means of phase-contrast microscopy, the lymphoblast-like cell was much more radio-resistant (D0 = 250 rad) than the small lymphocyte (D0 = 20 rad). This increase in radioresistance, however, was not observed until 12-24 hours after PHA treatment. To investigate which of the changes occurring during the transformation of the small lymphocyte was responsible for the increased resistance to irradiation, the percentage of cells surviving irradiation was compared with the percentage of cells incorporating significant amounts of 3HTdR, 3H-UR, or 3H-leucine at the time of irradiation. For this comparison, a dose of 100 rad was used because 100 rad killed essentially all of the small lymphocytes, but less than 35 percent of the cells which had become radioresistant from the PHA treatment. The results indicated that the increase in radioresistance was not associated with DNA synthesis, but instead correlated with the increase in RNA and protein synthesis which the cells had attained at the time of irradiation.

Animals↗