Response to X-radiation and cytotoxic drugs of clonal subpopulations of different ploidy and metastatic potential isolated from RIF-1 mouse sarcoma

Selection, establishment and characterization of cell lines derived from a chemically-induced rat mammary heterogeneous tumor, by flow cytometry, transmission electron microscopy, and immunohistochemistry

In order to isolate, characterize, and establish culture cell lines with different diagnostic and prognostic significance, derived from multiclonal neoplasms, a ductal infiltrating mammary tumor was induced in rats by 7,12-dimethylbenz[a]anthracene. Clones with different DNA/protein content, being the DI of 1.16, 1.30, and 1.60, respectively, were observed in the primary tumor. Biparametric flow cytometry suggested that the clone at 1.30 is made up of two subpopulations with different protein and slightly different DNA contents. The culture, after a few passages, exhibited the presence of aneuploid cells and the absence of diploid components, demonstrating that only tumor cells survived. The limiting dilution method gave rise to four lines with DI of 1.16, 1.25, 1.30, and 1.50; a mean chromosome number of 45, 46, 47, and 88, respectively; and different morphological and ultrastructural features. These characteristics were stable during the experimental procedure, that is, for about 20 passages. Conversely, the detection of cytoskeletal proteins indicated that the tumor epithelial cells underwent early dedifferentiation into sarcoma-like cells showing markers of stromal cell type and thus exhibiting phenotypic instability in vitro, a feature reported in many advanced human breast cancers in vivo. In conclusion, this cellular model represents the in vivo situation and appears suitable for in vitro studies of tumor cell characteristics and might be used to predict clinical behavior.

Heterogeneity of chemosensitivity in six clonal cell lines derived from a spontaneous murine astrocytoma and its relationship to genotypic and phenotypic characteristics

Heterogeneity in drug sensitivity must, in part, account for the relative lack of success with single agent chemotherapy for glioblastoma multiforme (GBM). In order to develop in vitro model systems to investigate this, clones derived from the VM spontaneous murine astrocytoma have been characterised with regard to drug sensitivity. Six clonal cell lines have been tested for sensitivity to a panel of cytotoxic drugs using an intermediate duration 35S-methionine uptake assay. These lines have previously been extensively characterised with regard to morphological, antigenic, kinetic, tumourigenic potential in syngeneic animals and chromosomal properties and display considerable heterogeneity. The present study indicates that heterogeneity extends to sensitivity to all classes of cytotoxic drugs. The greatest difference in sensitivity between the clones was seen in response to cell cycle-specific drugs like the Vinca alkaloids (14-fold and 20-fold for vincristine (VCR) and vindesine (VIND) respectively), while the nitrosoureas, CCNU and BCNU displayed a smaller fold difference in sensitivity (4.3 and 3.6-fold difference respectively). All the clones were considerably more resistant to the adriamycin (ADM), cis-platinum (C-PLAT) and the Vinca alkaloids than the parental cell line although the difference in sensitivity between the clones and parental cell line were less marked for the nitrosoureas and procarbazine (PCB). It has also been possible to examine the relationship between drug sensitivity and the phenotypic and genotypic properties of these clonal cell lines. There is a relationship between chromosome number and sensitivity of a wide variety of cytotoxic drugs including the nitrosoureas, Vinca alkaloids, PCB, C-PLAT, BLEO but not ADR or 5-FU. Clones with small numbers of chromosomes were more resistant than clones with gross polyploidy. Similarly, sensitivity to Vinca alkaloids and ADM, but not other classes of drugs, was greatest in cells with numerous cytoplasmic processes and which did not express large amounts of cell surface fibronectin. Preliminary experiments have been conducted on reconstituting clonal mixtures of cells with different sensitivity to Vinca alkaloids and results from these studies indicate that the drug resistance phenotype is dominant, with clonal mixtures of sensitive and resistant cell adopting the sensitivity of the more resistant partner. These cell lines should prove to be useful models for examining the cell biological basis of drug resistance in glioma and may lead to the identification and exploitation of novel cellular targets in new therapies for GBM.

Feasibility of measuring radiation-induced DNA double strand breaks and their repair by pulsed field gel electrophoresis in freshly isolated cells from the mouse RIF-1 tumor

PURPOSE

To examine the technical feasibility of pulsed field gel electrophoresis (PFGE) as a predictive assay for the radioresponsiveness of tumors. Induction and repair of DNA double strand breaks (DSBs) in a freshly prepared cell suspension from a RIF-1 tumor (irradiated ex vivo) was compared with DSB induction and repair in exponentially growing RIF-1 cells in culture (irradiated in vitro).

METHODS AND MATERIALS

A murine RIF-1 tumor grown in vivo was digested, and cells were exposed to x-rays (ex vivo) at doses of 1 to 75 Gy. DNA damage was measured using CHEF (clamped homogeneous electric fields) electrophoresis. Repair kinetics were studied at 37 degrees C for 4 h after irradiation. Radiosensitivity was determined by clonogenic assay, and cell cycle distributions by flow cytometry. For comparison, a trypsinized suspension of exponentially growing RIF-1 cells in vitro was run parallel with each ex vivo experiment.

RESULTS

Induction of DSBs, expressed as % DNA extracted from the plug, was similar in the in vitro and ex vivo irradiated cells. Compared to repair rates in vitro cultured RIF-1 cells, repair kinetics in a freshly prepared cell suspension from the tumor were decreased, unrelated to differences in radiosensitivity. Differences in repair could not be explained by endogenous DNA degradation, nor by influences of enzymes used for digestion of the tumor. A lower plating efficiency and differences in ploidy (as revealed by flow cytometry) were the only reproducible differences between in vivo and in vitro grown cells that may explain the differences in repair kinetics.

CONCLUSIONS

The current results do not support the idea that PFGE is a technique robust enough to be a predictive assay for the radiosensitivity of tumor cells.

The intrinsic radiosensitivity of cervical carcinoma: correlations with clinical data

PURPOSE

The aims of the work were to study the intrinsic radiosensitivity of tumor biopsies from patients with cervical carcinoma and to correlate the data with information on patient age, disease stage, differentiation status, tumor volume, and tumor ploidy.

METHODS AND MATERIALS

Radiosensitivity was assessed for 145 tumors in vitro as surviving fraction at 2 Gy (SF2) using a clonogenic assay.

RESULTS

Although the clonogens in tumors classified as Stage I or II tended to be more radiosensitive than in Stage III or IV disease, the difference was not statistically significant (p > 0.15). There was also no significant difference in the intrinsic radiosensitivity of well, moderately, or poorly differentiated tumors or between squamous cell carcinoma and adenocarcinoma (p > 0.53). There was no correlation between patient age and tumor radiosensitivity (p = 0.49). Large volume (> or = 4 cm) disease was more radioresistant than small volume (< 4 cm) disease, but the difference was not significant (p = 0.08). Finally, diploid tumors tended to be more radioresistant than aneuploid tumors (p = 0.07).

CONCLUSION

The intrinsic radiosensitivity of cervix tumors is independent of disease stage, tumor grade, and patient age. Weak trends, however, were observed of increased tumor radioresistance for large volume disease and diploid tumors, suggesting that tumor SF2 may not be a completely independent parameter.

Resistance to photodynamic therapy in radiation induced fibrosarcoma-1 and Chinese hamster ovary-multi-drug resistant. Cells in vitro

A degree of resistance to photodynamic therapy (PDT) has been induced in radiation-induced fibrosarcoma-1 (RIF-1) tumor cells by repeated photodynamic treatment with Photofrin (4 or 18 h incubation) in vitro to the 0.1-1% survival level, followed by regrowth from single surviving colonies. The resistance is shown as increased cell survival in the strain designated RIF-8A, compared to the wild-type RIF-1 cells, when exposed to increasing Photofrin concentration for 18 h incubation and fixed light exposure. No difference was found between RIF-1 and RIF-8A in the uptake of Photofrin per unit cell volume at 18 h incubation. Resistance to PDT was also observed in Chinese hamster ovary-multi-drug resistant (CHO-MDR) cells compared to the wild-type CHO cells, possibly associated with decreased cellular concentration of Photofrin in the former. By contrast, the PDT-resistant RIF-8A cells did not show any cross-resistance to Adriamycin, nor was there any significant drug concentration difference between RIF-1 and RIF-8A. These findings suggest that different mechanisms are responsible for PDT-induced resistance and multi-drug resistance.

In vitro response to hyperthermia or X-irradiation of diploid and tetraploid RIF-1 cells separated by centrifugal elutriation

The RIF-1 cell line at the University of Utah is comprised of approximately 65 per cent diploid and 35 per cent tetraploid cells. Because sensitivity to heat cell killing has been shown to be ploidy dependent (Lucke-Huhle 1978), the responses of these subpopulations were examined independently. Diploid and tetraploid cells were separated from stock in vitro cultures by centrifugal elutriation and maintained entirely in vitro. No influence of ploidy on Do or Dq of heat dose survival curves could be detected. Neither did ploidy affect sensitivity to X-irradiation. However, separation of the diploid and tetraploid subpopulations was imperfect. The ratio of diploid to tetraploid cells in the separated and parent (mixed ploidy) lines was therefore monitored at each passage. Tetraploid contamination of the diploid cell subline was undetectable at the time of separation but regrew to 35 per cent by 40 days after separation. Diploid contamination of the tetraploid subline was initially less than 5 per cent and remained quite low until it became undetectable at 74 days. Differences in regrowth of the contaminating subline could not be accounted for by differences in plating efficiency or doubling time, but might result from subpopulation interactions. If so, such phenomena should be considered when using ploidy-dependent cytotoxic treatments.

Expression of p21ras in fresh primary and metastatic human colorectal tumors

Activation of the cellular oncogene ras has been implicated in many types of human malignancies. In this study, the relative levels of p21 protein product of ras (p21ras) in primary and metastatic colon tumors were compared to those in adjacent normal tissues. Nine of the 17 primary tumors had substantially elevated levels of p21ras with respect to adjacent normal tissues. Eight of these tumors were from Dukes' B and C stages. Four of the five tumors classified as "D" stage (in which distant metastases are present) did not show elevated levels of p21ras. In metastases from primary colon tumors, nine of nine were considerably reduced in p21ras expression regardless of the site of metastasis. These data suggest that elevation of p21ras may be a common event in early stages of colon tumors, and tumor progression may lead to a more autonomous population of cells in which other growth factors supplant the role of this protein.

Clinical pharmacokinetics of oral CCNU (lomustine)

The plasma pharmacokinetics of orally administered CCNU (130 mg/m2) were studied in four patients using reversed-phase high-performance liquid chromatography (HPLC) analysis. Parent CCNU was not detected in the plasma of any of the patients, probably due to complete conversion to monohydroxylated metabolites during the 'first pass' through liver and gut. However, two monohydroxylated metabolites, trans-4-hydroxy CCNU and cis-4-hydroxy CCNU, were found at high concentrations, the relative amounts being about 6:4. Peak concentrations of the metabolites were reached 2-4 h after administration and were remarkably similar for all four patients, the total being 0.8-0.9 micrograms/ml. The metabolites were also detected in a tumour biopsy. Plasma clearance half-lives of the two metabolites were similar in each patient but showed a two-fold variation between patients, from 1.3 to 2.9 h. These results suggest that the antitumour activity and systemic toxicity of CCNU when given orally are due mainly to its monohydroxylated metabolites. Finally, comparison with data obtained in vitro and in mice showed that the nitrosourea exposures in these patients were at the lower limit of those required for significant antineoplastic activity.

Patterns of cross-sensitivity in the responses of clonal subpopulations isolated from the RIF-1 mouse sarcoma to selected nitrosoureas and nitrogen mustards

The response of clonal subpopulations isolated from the RIF-1 mouse sarcoma to melphalan treatment is independent of cell ploidy, whereas a clear relationship exists between ploidy and cell sensitivity to CCNU treatment. In the present study RIF-1 clones have been exposed to nitrogen mustard, aniline mustard and chlorambucil, and to nitrosoureas BCNU, MeCCNU and chlorozotocin, in order to evaluate whether or not the different physiochemical and biological activities of these agents would affect the patterns of drug sensitivity obtained for melphalan and CCNU. Irrespective of the different lipophilicities, transport properties and chemical reactivities of the nitrogen mustards, RIF-1 clones showed the same pattern of sensitivity as previously observed for melphalan. Similarly, RIF-1 clones when exposed to nitrosoureas BCNU, MeCCNU and chlorozotocin, showed the same pattern of sensitivity as that obtained for CCNU exposure. These data suggest (a) that the variation in the sensitivity of RIF-1 clones to treatment by the nitrogen mustards is unlikely to reflect differences in either membrane permeability or in drug transport and (b) that the ploidy dependent nitrosourea responses shown by RIF-1 clones similarly do not reflect differences in drug uptake.