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K T Wheeler

Publications and source records attributed to K T Wheeler.

At least 55 records · Page 3Linked to original sources
PubMed1984

Detection of heterogeneity in the chemosensitivity of 9L brain tumor cell lines to 1,3-bis (2-chloroethyl)-1-nitrosourea by the sister chromatid exchange assay.

To investigate the potential use of the sister chromatid exchange assay to analyze the heterogeneity of drug response among tumor cell subpopulations, mixtures of 1,3-bis (2-chloroethyl)-1-nitrosourea-sensitive (9L) and -resistant (9L2) rat brain tumor cells were treated in vitro with 2 microM 1,3-bis (2-chloroethyl)-1-nitrosourea. When data were plotted as histograms representing the number of cells vs sister chromatid exchanges/metaphase, two regions corresponding to the 9L and 9L2 populations were obtained. The approximate percentages of 9L and 9L2 in each mixture could be predicted from these histograms. While these results were obtained with a limited model chosen for its simplicity, they suggest that the sister chromatid exchange assay may be useful in the analysis of heterogeneity in drug sensitivity among cell subpopulations in a tumor.

Animals↗
PubMed1984

Effect of alkali on the size dispersity of mammalian DNA measured by filter elution.

DNA from unirradiated and irradiated cultured 9L rat brain tumor cells was held for varying times in low ionic strength solutions at pH 11.0, 12.3, or 12.9. The effect of this exposure to alkali on the DNA size distribution was determined by comparing the DNA filter elution profiles obtained experimentally with those theoretically predicted for monodispersed and random distributions. At pH 12.3 or 12.9, DNA from cells irradiated with 300 rad eluted with first-order kinetics corresponding to a random DNA size distribution. The median size of the distribution decreased if the irradiated DNA was exposed to pH 12.3 for 24 h. At pH 12.3 or 12.9, DNA from unirradiated cells eluted initially with complex kinetics that later became linear (18-21 h for pH 12.3 or 13-15 h for pH 12.9), characteristic of a monodispersed DNA size distribution. Holding either unirradiated or irradiated DNA at pH 11.0, below the critical unwinding pH, produced no effect on the elution profiles. Analysis of these filter elution data indicated that after sufficient exposure to pH 12.3 or 12.9, undamaged DNA molecules from mammalian cells elute as a single-stranded monodispersed size distribution of approximately 1 X 10(10) daltons. While the possibility cannot be completely eliminated that this monodispersed size represents an upper limit determined by physical forces, these results, in conjunction with those obtained using other techniques, lend credence to the existence of a nonrandom higher-order structure in mammalian chromosomal DNA.

Alkalies↗
PubMed1984

Hypoxic cells and in situ chemopotentiation of the nitrosoureas by misonidazole.

Intracerebral (i.c.) and subcutaneous (s.c.) 9L tumours were treated simultaneously with various doses of the nitrosoureas, BCNU or CCNU, and 2.5 mmol kg-1 of misonidazole (MISO). After 24 h, tumours were removed, dissociated into single cell suspensions and the cells plated for colony formation. In both i.c. and s.c. tumours, no cell kill was observed after exposure to MISO alone, and no additional cell kill was observed when MISO was combined with either nitrosourea. If s.c. 9L tumours were clamped 30 min after i.p. injection of 2.5 mmol kg-1 MISO, then 2 h later the clamps were removed and the nitrosourea injected, an increase in cell kill was observed. This increase in cell kill was statistically significant (P less than 0.01) for each dose of BCNU administered, but not statistically significant (P greater than 0.05) for the moderate dose of CCNU administered. Clamping did not alter the colony forming efficiency of cells from untreated 9L s.c. tumours or from those treated with each drug alone. These data demonstrate that hypoxic cells are required for misonidazole to potentiate the cell-killing effects of the nitrosoureas and that s.c. 9L tumours contain no such cells.

Animals↗
PubMed1984

Comparison of tumour age response to radiation for cells derived from tissue culture or solid tumours.

Direct comparison of the cell age response of 9L and KHT tumour cells derived either from tissue culture or solid tumours was achieved. Cells from dissociated KHT and 9L tumours (the latter implanted either subcutaneously or intracerebrally) and cells from tissue culture were separated into homogeneous sized populations by centrifugal elutriation. In both tumour models these homogeneous sized populations correspond to populations enriched at different stages of the cell cycle. The survival of these elutriated cell populations was measured after a single dose of Cs-137 gamma rays. For cells isolated from 9L solid tumours, there was little variation in radiosensitivity throughout the cell cycle; however, a very small but significant increase in resistance was found in late G1 cells. This lack of a large variation in radiosensitivity through the cell cycle for 9L cells from solid tumours also was seen in 9L cells growing in monolayer tissue culture. When similar experiments were performed using the KHT sarcoma tumour model, the results showed that KHT cells in vitro exhibited a fairly conventional increase in radioresistance in both mid G1 and late S. However, the cell age response of KHT cells from solid tumours was different; particularly in the late S and G2 + M phases. These data demonstrate that direct extrapolation of in vitro cell age responses to the in situ situation may not always be valid.

Animals↗
PubMed1984

Relationship between the repair of radiation-induced DNA damage and recovery from potentially lethal damage in 9L rat brain tumor cells.

The kinetics of repair of radiation-induced DNA damage and recovery from radiation-induced potentially lethal damage (PLD) for fed plateau-phase 9L/Ro rat brain tumor cells were compared after single doses of gamma-radiation and after combined treatment with 3 micrograms of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)/ml given 16 hr prior to irradiation. DNA damage and repair were assayed using alkaline filter elution, while cell survival was assayed by colony formation. Repair of radiation-induced DNA damage and recovery from radiation-induced PLD followed statistically identical biphasic kinetics; the fast-phase half-times were 4.1 +/- 0.3 (S.D.) min and 4.0 +/- 0.8 min, while the slow-phase half-times were 59.7 +/- 11.2 min and 78.7 +/- 34.1 min, respectively. Treatment with BCNU prior to irradiation resulted in both additional DNA damage and increased cell kill. When DNA damage and cell survival after the combined treatment were corrected for the contribution from BCNU given alone, no inhibition of either repair of radiation-induced DNA damage or of recovery from radiation-induced PLD was observed. However, postirradiation hypertonic treatment inhibited both DNA repair and recovery from radiation-induced PLD. These correlations between the kinetics of the molecular and cellular repair processes support a role for repair of radiation-induced DNA damage in recovery from radiation-induced PLD. The lack of inhibition by BCNU of both repair of radiation-induced DNA damage and of recovery from radiation-induced PLD also demonstrates that these are not the mechanisms by which BCNU enhances radiation-induced cytotoxicity in 9L cells.

Animals↗
PubMed1984

DNA repair kinetics in mammalian cells following split-dose irradiation.

The in situ DNA repair kinetics in intracerebral 9L tumor cells and cerebellar neurons following the second of two 1250- or 2500-rad doses separated by various times have been measured using alkaline sucrose gradients in zonal rotors. For both doses and all times employed, both cell types exhibited biphasic kinetics similar to those observed after single doses. When the two doses were separated by less than 2 hr in neurons (1 hr for tumor cells), the half-time (T1/2) of the slow phase was faster than that expected based on the amount of damage present and remained constant until the observed T1/2 coincided with the expected T1/2. When repair of the damage produced by the first dose was complete, the slow phase after the second dose exhibited the same T1/2 as after a single dose. These results suggest that the accessibility of a fraction of the chromatin is altered for a finite period during the repair process, and upon completion of repair is returned to a state indistinguishable from that existing prior to irradiation.

Animals↗
PubMed1983

DNA repair kinetics in irradiated undifferentiated and terminally differentiated cells.

The brains of male Fisher 344 rats bearing 80-150 mg intracerebral 9L/Ro tumors were irradiated with doses of 1,250-5,000 rads of x- or gamma-rays. At various times after irradiation, the cerebellum and tumor were excised, dissociated into single cells and the DNA from these cells sedimented through alkaline sucrose gradients in zonal rotors with slow gradient reorienting capability. Quantitation of the DNA repair kinetics demonstrated that the process in both tumor cells and neurons has a fast and slow phase. Although all other alternatives cannot be completely eliminated, we suggest that these two phases are most reasonably interpreted as representing repair of lesions in very accessible and less accessible regions of the genome rather than 1) repair of different types of lesions such as single- or double-strand breaks or 2) removal of immediate breaks and breaks induced during excision repair of latent base damage. The slow repair phase is saturable, but not inducible in both tumor cells and neurons. The data suggest that tumor cells restore their chromosomal DNA structure to the unirradiated state faster than neurons because 1) they contain more of the repair system per unit of DNA and 2) a larger proportion of their genetic material is comprised of very accessible regions. The data also suggest that the entire tumor cell genome may be accessible to the repair enzyme(s), while it is possible that a portion of the neuronal genome may be completely inaccessible.

Animals↗
PubMed1983

DNA accessibility: a determinant of mammalian cell differentiation?

Rats bearing intracerebral 9L tumors were whole-brain irradiated with 1250 to 5000 rad, and the in situ DNA repair kinetics of the undifferentiated tumor cells and terminally differentiated cerebellar neurons were examined by alkaline sucrose gradient sedimentation in zonal rotors with gradient reorienting capability. Biphasic repair kinetics were observed for both tumor cells and cerebellar neurons. Quantitation and analysis of the slow phase of the repair process suggest that the dividing tumor cell genome is completely accessible to the enzymatic repair machinery, while it is possible that the genome of the permanently nondividing neuron may contain a region that is inaccessible to this repair machinery.

Animals↗
PubMed1982

Chemotherapeutic approaches to brain tumors. Experimental observations with dianhydrogalactitol and dibromodulcitol.

Dianhydrogalactitol (DAG) or its active cell-killing moiety has a relatively long biological half-life in 9L cells cultured in vitro. The shape of the DAG dose-response curves was similar to that of those observed for most oncolytic agents. The prominent shoulder on the 24-h dose-response curve indicates that 9L cells can accumulate a reasonable amount of DAG-induced sublethal damage before they are killed. The appearance of 9L colonies in petri dishes was delayed 3-5 days after a DAG treatment that killed more than 99% of the cells, an observation not previously made with radiation, hyperthermia, the nitrosoureas, or other chemotherapeutic agents. Comparison of the in vitro exposure integral and the in vivo tumor tissue integral indicated that DAG would have to be administered at a dose in excess of its LD10 to achieve an in vivo 2 log cell kill. The lack of a significant increase in lifespan after a LD10 dose confirmed this prediction. While DAG alone is active against IC ependymoblastoma, it had very limited activity against IC glioma 26; however, the combination of DAG with BCNU was curative in 85%-100% of animals at 120 days. BCNU alone achieved no more than 4%-16% survival at 120 days. The combination of DBD and BCNU was not consistently better than BCNU alone against IC glioma 26. It appears that DAG may have a limited place in CNS chemotherapy for specific kinds of tumors. BCNU-DAG combination studies suggest that we may, under the right conditions, enhance the antitumor activity of the hexitol epoxides by drug combination therapies, although the mechanism for this enhanced antitumor activity is presently unknown.

Animals↗
PubMed1982

Cell survival as a determinant of tumor cure for rat 9L subcutaneous tumors following microwave-induced hyperthermia.

The relationship of cell survival to tumor cure after local hyperthermia treatment was studied in subcutaneous 9L rat tumors. Tumors weighing 0.2-0.4 g were heated to 42.5, 43.0, 44.0 and 45.0 degrees C by local exposure to 2450 MHz microwaves. Cell survival data was obtained by an in vivo to in vitro colony forming technique and a cell survival curve was constructed for each temperature as a function of exposure duration (0-180 min). Cell survival followed a simple exponential function with an increasingly steeper slope as temperature increased. At 44 degrees C, it was observed that cells from large tumors (1.0-1.4 g) were inactivated at the same rate as those from small tumors. When tumor response was monitored in the small tumors for 90 days following treatment, a direct correlation between the percentage of tumor cures and time at 44 degrees C (0-60 min) was observed; therefore, at 44 degrees C, tumor cure was exponentially related to cell survival in this range. However, when approximately the same cell survival was obtained with 3 other temperature--time regimens, the resulting percentage of tumor cures was not the same. These results indicate that while cell survival is related to tumor cure, it is probably not the primary determinant of tumor response following local hyperthermia in these 9L subcutaneous tumors.

Animals↗
PubMed1982

High-dose radiation therapy with low-dose (pulsed) BCNU in malignant gliomas: an Eastern Cooperative Oncology Group (ECOG) report.

Based on preliminary favorable results with the use of postoperative high-dose radiation therapy for malignant gliomas and encouraging experimental studies which indicated that fractionated does of BCNU given 16 hours before irradiation significantly enhanced the effect of radiation both in vitro and in vivo, the Eastern Cooperative Oncology Group (ECOG) decided to explore the use of high-dose radiation therapy in combination with pulsed low doses of Group (ECOG) decided to explore the use of high-dose radiation therapy in combination with pulsed low doses of BCNU in a high-risk Phase I-II pilot study. The radiation therapy consisted of delivering 6000 rad to the whole brain plus a boost of 1000 rad to the tumor. BCNU was given i.v. 16 hours before the next radiation fraction with doses of 20 mg/M2 twice weekly for six weeks beginning on the second day of irradiation. Twelve patients were treated (5 with Grade III and 7 with Grade IV Astrocytomas). The median survival for the entire group was 80 weeks (30 weeks for Grade IV and 210 weeks for Grade III tumors). These results are not difficult from what was achieved by high-dose radiation alone. Subsequent experimental data seem to indicate that probably the smallest dose of BCNU that should be used in pulsed BCNU combined modality therapy is 80 mg/M2. In general, the treatment as offered in this study was well tolerated. There were no fatal or life-threatening hematologic toxicities and only one patient exhibited a transitory leukopenia of 1600.

Adult↗
PubMed1981

Characterization of the separation properties of the Beckman elutriator system.

The role of fluid flow in the elutriation process was visualized by pumping dye solution through the Beckman JE-6 elutriator rotor. Three major fluid flow disturbances were observed in the separation chambers, namely; jet-streaming, ripple flow, and whirl flow. In order to evaluate the effects of these non-ideal fluid flow patterns on the separation of homogeneous populations of particles or cells, 12--35 micron diameter latex spheres and 9L rat brain tumor cells were fractionated with the Beckman elutriator system. The elutriator system was evaluated on the basis of: (1) recovery, (2) elution loss during loading, (3) homogeneity of the size distributions, and (4) the relationship of the median volume of eluted particles or cells to the rotor speed and the collection fluid velocity. Both a conventional collection method (two 40-mL fractions at ech collection rotor speed) and a long collection method (10--15 40-mL fractions at several collection rotor speeds) were compared to determine if collection procedures could compensate for some of the difficulties caused by the non-ideal fluid flow patterns. Although more than 90% of the particles or cells were always recovered, about 5% eluted during the loading procedure. Neither collection method altered this phenomenon. The long collection method significantly improved the homogeneity of the collected populations, but this was accompanied by a reduction in cell yield. The median particle or cell volume of each fraction agreed with that expected under ideal fluid flow conditions except at high and low rotor speeds when the conventional collection method was used.

Animals↗