Modulation of tumour colony growth by irradiated accessory cells

Radiation sensitivity of human ovarian carcinoma cell lines in vitro: effects of growth factors and hormones, basement membrane, and intercellular contact

The radiation sensitivity of six established human ovarian carcinoma cell lines was determined in vitro under five different experimental conditions. Cells from exponentially growing monolayer cultures were assayed under three different post-irradiation culture conditions, i.e., conventional conditions on a plastic surface, in the presence of growth factors and hormones, and on a basement membrane. Multicellular aggregates were dissociated either immediately before or immediately after irradiation and assayed under conventional conditions. The radiation sensitivity differed considerably among the cell lines; the initial slope alpha ranged from 0.05 +/- 0.03 Gy-1 to 0.36 +/- 0.07 Gy-1 and the surviving fraction at 2.0 Gy from 0.32 +/- 0.06 to 0.78 +/- 0.06 under conventional conditions. There was no significant effect of the growth factors and hormones and of the basement membrane on the survival curves for any of the cell lines. Only one of the lines showed a significant intercellular contact effect. The presence of this effect required that the cells were grown as aggregates, but was independent of whether the irradiation was performed on dissociated or intact aggregates. The present work with established cell lines indicates that the outcome of an in vitro predictive assay for clinical radioresponsiveness of ovarian carcinomas would probably not vary significantly among the five experimental conditions studied here. However, further studies using cells isolated directly from human ovarian carcinoma surgical specimens are warranted.

Enhancement of survival and proliferation of clonogenic cells by monocyte-derived growth factors

Human peripheral blood monocytes release a factor that enhances the clonal growth of human epithelial tumor cells in soft agar. The monocyte-derived growth factor was needed for both cellular proliferation and survival. Survival of SW-13 colony-forming cells decreased linearly in the absence of monocyte-conditioned media (MO-CM). Cells failed to respond to MO-CM after four days in culture. Although MO-CM enhanced growth when cells were plated at low density, growth was also enhanced when cell density was not a limiting factor. MO-CM increased DNA synthesis of SW-13 cells growing in monolayer culture as measured by tritiated-thymidine incorporation. These findings support evidence indicating inflammatory products may play a role in maintenance of the transformed phenotype.

The human tumor clonogenic assay as a model system in cell biology

The human tumor stem cell (clonogenic) assay (HTCA) is a soft agar system designed for growing fresh human tumor specimens in vitro. The assay has been extensively used in studies both of individual patients' response to chemotherapy and for screening new agents. The technical limitations of this assay have been extensively discussed. The use of this test as a model system to study fundamentals of tumor cell growth has not been stressed. The potentials and limitations of this assay for the study of the regulation of tumor growth are presented.

A radiobiological comparison of human tumor soft-agar clonogenic assays

Radiation survival curves have been generated for 3 human tumor cell lines as a means of comparing and evaluating the validity of human tumor soft-agar clonogenic assays. The assays investigated were the Hamburger-Salmon, Courtenay-Mills, Courtenay-Mills plus additions, soft agar (no additions), and soft agar plus additions. The additions were formulated to supplement the media used in soft agar assays of primary ovarian and cervical carcinoma specimens. Supplementing the media with additions led to a 2- to 3-fold increase in PE of CaSki cells but had no effect on the PEs of ME180 and OWI cells. Radiation survival curves were similar in all assays for CaSki and OWI but differed for ME180 cells. For ME180 cells, the Courtenay-Mills and soft agar assays plus additions produced the most radioresistant curves (Do = 2.2 Gy); the cells were more responsive when assayed by the Hamburger-Salmon method (Do = 1.5 Gy), and the soft agar and Courtenay-Mills assays gave the most radiosensitive curves (Do = 1.2 Gy). These results demonstrate that the PE of human tumor cell lines may be increased with no effect on radiation survival; radiation survival may be altered without changes in PE and neither may be altered by applying modifications and supplements to existing clonogenic assays.

Growth factors for human tumor clonogenic cells elaborated by macrophages isolated from human malignant effusions

We previously demonstrated that macrophages isolated from human malignant effusions support colony formation of autologous tumor cells in soft agar. We now demonstrate that macrophages (derived from effusions of patients with ovarian, breast, colon, or lung adenocarcinomas) secrete a soluble factor(s) that enhances the ability of a human epithelial tumor cell line (SW-13) to clone in soft agar. Macrophages increased colony growth 5 to 10-fold in a concentration dependent manner, although inhibition of cell growth was observed in the presence of high concentrations of macrophages. We attempted to increase production of tumor colony stimulating factor by exposing macrophages to lipopolysaccharide, concanavalin A, or phytohemagglutinin. Exposure of macrophages to these agents failed to increase their ability to secrete stimulatory factors. Macrophages were cultured for 1 day to 6 weeks in the presence of GCT-CM, a source of granulocyte-macrophage colony stimulating factor and the ability of these cultured macrophages to support colony growth assessed. The ability of macrophages to support colony growth declined gradually with time in culture reaching 50% of control values at 14 days, but remained at this level until 5 weeks of culture. The results of this study indicate the SW-13 cells may provide a quantitative assay for studying monocyte-derived tumor colony stimulating factors.

Non-linearity of colony formation by human tumour cells from biopsy samples

The relationship between colony numbers and concentration of cells plated is an important parameter of clonogenic assay systems. The cloning efficiency for an ideal sample should be independent of cell concentration, thus giving a straight line through the origin when colony numbers are plotted against cell concentration. A simple statistical method has been developed to test if this is the case for individual tumour samples. Colony data from 51 freshly obtained tumour samples, which had sufficient cells to plate 3 or more dilutions and gave at least 20 colonies per plate at one or more of the dilutions, were tested. The results indicated that colony formation was linear for 27 (53%) of the samples. The remaining 24 samples could be classified into 2 groups: type I, in which cloning efficiencies increased with increasing cell concentration and type II, which had reduced cloning efficiencies at high cell concentrations. Fifteen (29%) of the samples had type I non-linearity and 9 (18%) exhibited non-linearity of type II. These findings indicate that the relationship between colonies and cells plated should be examined for each biopsy sample particularly in each experiment where the effects of cytotoxic drugs are tested.

Percoll density gradient separation of cells from human malignant effusions

A simple method is described for the separation of cells derived from effusions of patients with adenocarcinomas in discontinuous density gradients of Percoll. After separation, cells from different fractions were analyzed by morphologic, histochemical and immunologic criteria. Total cell recovery from 27 experiments was 67 +/- 4%. Macrophages (82%) were recovered in the intermediate density fraction (1.056-1.067 g ml-1) with a purity of 90%. Recovered lymphocytes (98%) were found in the high density fraction (1.067-1.077 g ml-1) with a purity of 92%. The majority of the lymphocytes recovered were T cells. Malignant adenocarcinoma cells (90%) were recovered in the lowest density fractions (up to 1.056 g ml-1) with a purity of 79%. Use of effective cell separation procedures should facilitate the analysis of the functional capacities of both normal and neoplastic cells derived from human malignant effusions.

Mechanism of enhancing effect of irradiation on production of IL-2

In order to explain the mechanism of enhancing effect of irradiation on IL-2 production, assumption that radio-induced free radicals could act as a signal for mitogenesis and/or increase lipid peroxidation of T lymphocyte membrane phospholipids was made. Thus, production of metabolites of the lipoxygenase pathway in the arachidonic acid (AA) cascade, known to increase T cell proliferation and lymphokine production could be enhanced by irradiation. We have shown that (1) hydroxyl radical scavenger (DMSO) abolished IL-2 production, (2) inhibitor of the lipoxygenase pathway (NDGA) strongly decreased IL-2 production, (3) thin layer chromatography demonstrated a polar metabolite(s) of AA in increasing amounts according to the following order: non-irradiated resting cells, non-irradiated stimulated cells, irradiated resting cells, and irradiated stimulated cells. Investigations are in progress to identify this metabolite.

Enhancement of rat ACT-1 tumor clonogenicity by xenogeneic mouse macrophages

In vitro growth of rat atriocaval epithelial tumor cells (ACT-1) was enhanced by the inclusion of xenogeneic mouse adherent peritoneal exudate cells (PECs) in a two-layer soft agar system. A linear relationship was found between the number of cells plated and the number of colonies when ACT-1 tumor cells were plated at plating densities of between 1 and 5 X 10(5) cell/60 mm plate (r = 0.9, P less than 0.001). Inclusion of irradiated PECs in the bioassay for tumor stem cells resulted in a two and a half-fold increase in colony formation in three separate experiments (P less than 0.001).