Separation of cells from a murine fibrosarcoma on the basis of size. II. Differential effects of cell size and age on lung retention and colony formation in normal and preconditioned mice

Metastatic abilities of murine sarcomas and carcinomas. II. Relationship to cell volume and DNA index

The cell volume and DNA content were determined in 12 murine tumors and correlated with the ability of these tumors to metastasize spontaneously or to form lung nodules when injected i.v. The cell volume significantly correlated with spontaneous metastatic potential of investigated tumors (r = 0.683; 0.02 less than P less than 0.05) but not with the ability of tumor cells to form artificial metastasis. The DNA index significantly correlated with both spontaneous metastasis (r = 0.594; 0.02 less than P less than 0.05), and lung colonization (r = 0.631; 0.02 less than P less than 0.05). The DNA index barely correlated with the cell volume (r = 0.564; P = 0.10).

Variant selection and blood-borne "clonogenic" tumour cells in metastasis of FSA cell clones

Our studies of the metastatic behaviour of FSA1231 and FSA1233 show that the role of selection processes of metastatic variants at the secondary sites is minimal in the spontaneous metastasis of these systems. In contrast, tumour-cell release efficiency (number of blood-borne clonogenic tumour-cells) correlates well with the difference in spontaneous lung metastasis efficiencies of the cell clones FSA1231 and FSA1233. Also, the different tumour-cell release efficiencies could explain the discrepancy between artificial and spontaneous metastasis of these cell clones.

Cytotoxic effects of vincristine on tumour subpopulations separated from pulmonary nodules

The cytotoxic and stathomokinetic effects of vincristine (VCR) on murine fibrosarcoma (FSa) cells, grown either in vitro as primary cultures or in vivo as micro- or macroscopic pulmonary nodules, were determined and compared. FSa cells 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, thus allowing determination of age-dependent cytotoxicity. The colony-forming efficiencies (CFE) of these cells were determined using a lung colony assay. Synchronized cell population of FSa cells, separated by centrifugal elutriation, were injected into recipient animals and exposed 20 min later to a single dose of VCR to determine their age-specific sensitivity. Under these conditions there appeared to be a suggestion of an enhanced killing of cells enriched in the G2 + M phase. However, following prolonged VCR exposure in vitro (e.g., 2.5 micrograms ml-1; 25 ml for 24 h) to primary cultures of FSa cells or in vivo (e.g., 0.25 mg kg-1 per fraction i.p.; 5 fractions in 24 h) to macroscopic pulmonary tumour nodules, elutriated FSa cell populations most enriched with G1 phase cells exhibited the lowest CFE. If under either condition exposed cells were allowed to recover in the absence of VCR for 24 h prior to their removal and separation, FSa cell survival increased in each of the elutriated populations. In contrast, while G1 enriched cell populations from in vitro exposed cultures still exhibited a significant reduction in CFE, no such age-specific response was observed for in vivo exposed macroscopic pulmonary nodules. The stathomokinetic effect of VCR on FSa cells was also readily observed in vitro using FMF analysis (e.g., an increase of from 20 to 38% in the G2 + M phase compartment). While no such effect was observed in vivo using FMF analysis, cluster of mitotic figures were observed. The mitotic indices (MI) of the in vivo exposed FSa cells increased from 2.5 to 8.4%.

Treatment of artificially-induced pulmonary metastases with fractionated doses of vincristine and/or radiation therapy

The cytotoxic effects in vivo of vincristine (VC), radiation, or both modalities in combination on murine fibrosarcoma (FSa) cells grown as pulmonary tumors were determined. Fourteen days following the i.v. injection of viable FSa cells, recipient mice developed between 100 and 150 visible pulmonary nodules. At that time, tumor-bearing animals were exposed to either single or combined modality treatments, as well as single and fractionated dose regimens. Animals were sacrificed 1 hour after the last treatment. Tumor nodules were excised and made into a single cell suspension and separated on the basis of cell size by centrifugal elutriation. Flow microfluorometry (FMF) was used to determine the cell-cycle parameters and the relative synchrony of the separated populations, as well as the percentage contamination by normal diploid cells in each of the tumor cell populations. Known numbers of viable cells from each elutriator fraction were injected into recipient mice to determine their colony-forming efficiency (CFE). Surviving fractions were determined by comparing the CFEs of treated FSa cells from each of the separated elutriator fractions with those of appropriate untreated controls. Following a single dose of VC (1 mg/kg), populations of cells enriched in late S and G2 + M were the most sensitive. However, following the administration of five doses (0.25 mg/kg each) over a 24 hour period, populations of cells most enriched in G1 cells exhibited the lowest percentage of survivors. A single dose of radiation (1000 rad) was most effective in killing S-phase cells. When administered in five fractions (250 rad per fraction), each separated by a 6 hour interval, no phase-specific sensitivity was observed. The combination of both modalities exhibited a marked schedule dependence, with a single dose (1000 rad) of radiation followed by five doses of VC (0.25 mg/kg) being the most effective treatment protocol observed.

Phase-specific cytotoxicity in vivo of hydroxyurea on murine fibrosarcoma pulmonary nodules

The cytotoxic effects in vivo of hydroxyurea (HU) on murine fibrosarcoma (FSa) cells grown as pulmonary tumours were determined. Tumour cells from 13-day-old nodules were made into suspension and separated on the basis of cell size by centrifugal elutriation. Flow microfluorometry (FMF) was used to determine the cell-cycle parameters and the relative synchrony of the separated populations, as well as the degree of contamination by normal diploid cells in each of the tumour-cell populations. HU cytotoxicity was tested by administering both a single 1 mg/g i.p. dose into mice that had been injected i.v. 20 min earlier with known numbers of synchronized viable FSa cells, and i.p. doses of 1 mg/g each into mice bearing 13-day-old pulmonary nodules. In the latter experiments, animals were killed 1 h after the last dose, and the tumour nodules were excised and made into a single-cell suspension and elutriated. Known numbers of cells from each fraction were injected into recipient mice to determine survival. In both sets of experiments, cell killing by HU correlated with the percentage of S-phase cells. The treatment of 13-day-old pulmonary nodules with 3 doses of HU also depleted the (G2+M) phase tumour cells and increased the heterogeneity between tumour subpopulations, as determined by FMF analysis.

Cytotoxic effect in vivo of selected chemotherapeutic agents on synchronized murine fibrosarcoma cells

The cytotoxic effects in vivo of single doses of either adriamycin (ADM), 1-beta-D-arabinofuranosylcytosine (Ara-C), bleomycin (BLM), cis-diamminedichloroplatinum (II) (cis-DDP), or cyclophosphamide (CY) on murine fibrosarcoma (FSa) cell populations were determined. Tumour cells were separated and synchronized by centrifugal elutriation. Viable tumour cells from selected elutriator fractions were then injected i.v. into whole-body-irradiated mice. Twenty minutes later selected doses of ADM, Ara-C, BLM, cis-DDP or CY were administered to selected groups of these animals. Fourteen days later the mice were killed. Killing of injected tumour cells by each of the chemotherapeutic agents was evidenced by a reduction in the lung cells by each of the chemotherapeutic agents was evidenced by a reduction in the lung colonies per cell injected in treated animals. Under these conditions the response of FSa cells in vivo to the 5 drugs tested differed both qualitatively and quantitatively. Ara-C was S-phase-specific in toxicity. ADM, BLM, and cis-DDP were preferentially toxic to S, G2+M and G1 cells respectively. CY, a drug requiring bioactivation to form alkylating metabolites, was found to be equally toxic to G1 and G2+M enriched populations, but less effective in killing cell populations enriched with early-S cells.

Inhibition of artificial lung metastases in mice by pre-irradiation of abdomen

A phenomenon by which pre-irradiation of the abdomen of mice reduced the lung-colony-forming efficiency of i.v.-injected tumour cells is described. The extent of lung-colony inhibition was shown to depend on both the dose and timing of abdominal irradiation. The maximum inhibitory effect was obtained when mice received 1200 rad gamma-irradiation to the abdomen 5--7 days before tumour-cell challenge, but there was no effect when abdominal irradiation was given 1 or greater than or equal to 14 days before challenge, or when radiation doses were less than 600 rad. In mice less than 3 weeks old, the effect was much less marked than in adults. The target tissue which, when irradiated, exerted the inhibitory influence on lung-colony formation was located in the ventral half of the abdomen in all 4 quadrants, and was probably gut. Radioactively labelled tumour cells were arrested normally in the lungs of irradiated mice, but were cleared more rapidly without evidence of sequestration in the irradiated gut. The most plausible mechanism seems to be that irradiation of the gut induces the production of natrual killer cells with anti-tumour activity, though this has not been conclusively established.

Centrifugal elutriation (counterstreaming centrifugation) of cells

Lindahl first described the separation of cells by velocity sedimentation utilizing a special technique (counterstreaming centrifugation) that was later modified slightly and renamed centrifugal elutriation. Centrifugal elutriation has been applied, with variable degrees of success, to the separation of hemopoietic cells, mouse tumor cells, testicular cells, and a variety of other specialized cells as well as cells in particular phases of the cell cycle. The capacity of the elutriator to separate large numbers of cells is its chief advantage. The purities of the separated cells have not been compared with the purities of cells separated by other methods in most cases; such comparisons would permit more sophisticated comparison of elutriation with other techniques for velocity sedimentation.