Density gradient centrifugation of cells separated from multicellular tumor spheroids

Cells from a murine fibrosarcome (FSa) have been grown in vitro as multicell tumor spheroids (MTS). The growth rate of these MTS was determined. Following selected periods of growth, MTS were made into a single cell suspension and separated on linear density gradients of Renografin. While only 1 population of cells were separated from small spheriods (400 mum diameter), at least 3 subpopulations of tumor cells were separated and isolated from large spheroids (800 mum in diameter).

Phase-specific cytotoxicity in vivo of hydroxyurea on murine fibrosarcoma cells synchronized by centrifugal elutriation

The S-phase-specific cytotoxicity of hydroxyurea (HU) was tested on synchronized murine fibrosarcoma (FSa) cells lodged in the lungs of C3Hf/Bu mice. FSa cells from primary asynchronous cultures were separated and synchronized on the basis of size by centrifugal elutriation. Flow microfluorometry (FMF) was used to determine the cell-cycle parameters and the relative synchrony of the separated populations. After elutriation, 8000 viable FSa cells from each fraction, along with 10(6) heavily irradiated tumour cells (unseparated) were injected i.v. into whole-body-irradiated mice (20 per group). Under these conditions, 95% of the injected cells, regardless of size or position in the cell cycle, are arrested in the lungs. Twenty minutes later, hydroxyurea (HU, 1 mg/g) was administered i.p. into 10 animals of each group. Fourteen days later the animals were killed, their lungs removed and fixed, and the number of macroscopic tumour nodules counted. Killing of the initially injected cells by HU, as evidenced by a reduction in lung colonies in treated animals, correlated with the precentage of S-phase cells in each fraction. The greatest effect, an 80% reduction in colony number, was seen in Fraction 8, containing the largest percentage of S-phase cells (65%). These results demonstrate the usefulness of this procedure as a rapid method for characterizing the phase specificity of chemotherapeutic drugs in vivo.

Response of selected tumour cell populations separated from a fibrosarcoma following irradiation in situ with fast neutrons

We have characterized selected populations of fibrosarcoma cells separated on density gradients of Renografin with respect to distribution in the cell cycle, clonogenic ability, and response to radiation. The latter two parameters have been observed to be related to the density of the cells, the denser populations being less clonogenic but more resistant to both low and high LET radiation. We have determined that these cells effectively repair potentially lethal damage if allowed to remain in situ following exposure to low LET radiation. This repair ability is not observed, however, following neutron irradiation. In addition, cells left in situ are relatively more sensitive to low doses of either low or high LET radiation. This difference in response is believed to be due to differences in the expression of damage by cells left in situ as compared to those assayed immediately. These data reflect the usefulness of cell separation methods in the study of solid tumour systems. Specifically, these methods reduce the heterogeneity found in the solid tumour by allowing for the isolation of subpopulations which then can be studied either individually or in relation to the entire tumour.

Relevance of density, size and DNA content of tumour cells to the lung colony assay

Mouse fibrosarcoma tumours were dissociated and divided into subpopulations of viable cells by centrifugation in linear density gradients of Renografin. Two of these subpopulations, designated Band 2 and Band 4, differed in their clonogenic ability in lung colony assay. The less dense Band 2 cells were significantly more clonogenic than the Band 4 cells (2.9 percent vs 1.4 percent respectively). Each band was further separated on the basis of cell size by centrifugal elutriation. Each size class of cells comprising Band 2 showed higher clonogenic ability than the corresponding size class in Band 4. Thus cell size differences were not responsible for the clonogenic differences between these bands. To determine whether cell-cycle distribution of the tumour cells was responsible for differences in cloning efficiency, flow microfluorometric and premature chromosome condensation methods were utilized. The unseparated and Band 4 populations showed a higher percentage of cells in S and G2 than did the Band 2 populations, but many of the S and G2 tumour cells showed extensive chromosome damage. From this study we conclude that the increased clonogenic ability of the lighter tumour cells is not due to differences in cell size or cell-cycle parameters.

Separation of cells from mouse solid tumors by centrifugal elutriation

Centrifugal elutriation was used to separate cells dissociated from two hypotetraploid mouse solid tumors, a fibrosarcoma and a sarcoma derived from L-P59 cells, based on their sedimentation rates. The separation was rapid, requiring less than 1 hr; yielded about 80 percent cell recovery; and resulted in little loss of cell viability. Aanlysis of DNA content by flow cytometry demonstrated the synchrony obtained with these tumor cells. The fractions with the lowest sedimentation rates contained predominantly normal cells, those with intermediate sedimentation rates contained predominantly tumor cells in the G1 phase of the cell cycle, and those with the highest sedimentation rates contained mostly tumor cells in S or G2. The clonogenicity of L-P59 cells, assayed in culture, markedly increased with increasing sedimentation rates. In contrast, the clonogencity of fibrosarcoma cells, assayed in vivo by a lung colony assay, was lower for the smaller cells, but was essentially constant among the larger cells. Autoradiography of cells labeled in vivo with tritiated thymidine demonstrated no differences in the proportions of cycling cells in various fractions. These results demonstrate that subpopulations differing in cell type, phase of the cell cycle, and clonogencity can be rapidly separated from solid tumors by centrifugal elutriation.

Cell cycle dependency of metastatic lung colony formation

Exponentially growing FSA 1233 cells, one of the clones isolated from a mouse fibrosarcoma, were synchronized by fractionation according to cell size by centrifugal elutriation. Cells from each fraction were analyzed by flow microfluorometry to determine the stages of the cell cycle and were injected i.v. to determine lung colony-forming efficiency. In vitro plating efficiency of these cells was similar throughout the cell cycle except for a slight reduction at G2 + M. On the other hand, lung colony-forming efficiency showed marked cell cycle and cell size dependencies, being lowest at G1, highest at S, and declining slightly at G2.

In vitro destruction of tumor cells by macrophages from mice treated with Corynebacterium granulosum

Peritoneal macrophages from C3Hf/Bu mice treated with killed Corynebacterium granulosum bacteria were tested for their effect on in vitro growth of syngeneic fibrosarcoma cells, tumorigenic mouse L-P59 cells, human malignant melanoma cells, allogeneic fibroblasts, erythrocytes, and epithelial kidney cells. Only the cell cultures having neoplastic properties were destroyed by stimulated macrophages; the rate of tumor cell destruction was greater as the ratio of effector to target cells was increased. Neither irradiation nor trypsinization of macrophage monolayers altered the cytotoxicity of stimulated macrophages. The results indicated that C. granulosum activated macrophages to destroy tumor cells in an immunologically nonspecific manner but had no cytotoxic effect on normal allogeneic cells.