The technique of labelled mitoses: analysis by automatic curve-fitting

Effect of X-Irradiation at Different Stages in the Cell Cycle on Individual Cell-Based Kinetics in an Asynchronous Cell Population

Using an asynchronously growing cell population, we investigated how X-irradiation at different stages of the cell cycle influences individual cell–based kinetics. To visualize the cell-cycle phase, we employed the fluorescent ubiquitination-based cell cycle indicator (Fucci). After 5 Gy irradiation, HeLa cells no longer entered M phase in an order determined by their previous stage of the cell cycle, primarily because green phase (S and G2) was less prolonged in cells irradiated during the red phase (G1) than in those irradiated during the green phase. Furthermore, prolongation of the green phase in cells irradiated during the red phase gradually increased as the irradiation timing approached late G1 phase. The results revealed that endoreduplication rarely occurs in this cell line under the conditions we studied. We next established a method for classifying the green phase into early S, mid S, late S, and G2 phases at the time of irradiation, and then attempted to estimate the duration of G2 arrest based on certain assumptions. The value was the largest when cells were irradiated in mid or late S phase and the smallest when they were irradiated in G1 phase. In this study, by closely following individual cells irradiated at different cell-cycle phases, we revealed for the first time the unique cell-cycle kinetics in HeLa cells that follow irradiation.

Interaction between three subpopulations of Ehrlich carcinoma in mixed solid tumours in nude mice: evidence of contact domination

Clonal interaction between three subpopulations of Ehrlich carcinoma were studied during growth as mixed solid tumours and as ascites tumours in immune-incompetent nude NMRI mice. The tumour cell lines differed in DNA content as determined by DNA flow cytometry (FCM). Tumour growth was evaluated by tumour growth curves including calculation of tumour volume doubling times, tumour weight on day 14, cell cycle times (per cent labelled mitoses) and cell cycle distributions (FCM). Two subpopulations (E1.15 and E1.95) showed nearly identical growth characteristics during both solid and ascites tumour growth. The third subpopulation (E1.80) grew more slowly. FCM on fine-needle tumour aspirates was used to determine the relative proportions of the cell populations in mixed solid tumours in which E1.95 showed a growth-dominating effect on E1.15. No such effect was demonstrated during single-cell tumour growth in ascitic fluid in which the cells had no intimate contact. Ascitic fluid from E1.95-bearing animals or radiation-killed E1.95 cells had no effect on the growth of E1.15, and no remote effect was seen when the two cell lines were growing in opposite flanks. This indicates that only viable E1.95 cells in close in vivo contact were able to induce growth inhibition of the E1.15 subpopulation. Both the E1.95 and the E1.15 cells dominated the E1.80 cells, but in these cases cell kinetic differences may have played a role as the E1.95 and the E1.15 lines grew faster than the E1.80. The E1.80 cell line had no dominating effect on the E1.15 or E1.95. It is concluded that non-immunologically mediated cellular dominance in heterogeneous tumours may contribute to the evolution of these tumours and may be involved in fundamental tumour biological phenomena.

Proliferative activity of human tumors: assessment using bromodeoxyuridine and flow cytometry

Cell kinetics of human carcinoma xenografts and human solid tumors were evaluated by means of two-color flow cytometry using single sampling at appropriate time intervals after bromodeoxyuridine (BrdU) labeling. The tumors were resected several hours after the administration of BrdU, and flow cytometry was used to measure the DNA content and BrdU incorporation. Once the BrdU labeling index (LI) and DNA synthesis time (Ts) were obtained, the potential doubling time (Tpot) was calculated from these values. In 11 xenografts, the cell kinetic data were compared with the actual tumor doubling time (Td), and a good correlation between Tpot and Td was obtained (r = 0.91, P less than 0.005). In a clinical study, 33 patients with gastric cancer, colorectal cancer, lung cancer, or other solid tumors were analyzed. Aneuploid tumors had a significantly higher LI value (P less than 0.01) and a shorter Tpot than diploid tumors. The cell loss rate of human tumors ranged from 40% to 80%. These cell kinetic parameters therefore accurately indicated the level of proliferative activity of human tumors.

Growth kinetics of four human breast carcinomas grown in nude mice

The immune-deficient nude mouse with human tumor xenografts is an appropriate model system for performing detailed growth kinetic examinations. In the present study one estrogen and progesterone receptor-negative (T60) and three receptor-positive (Br-10, MCF-7, T61) human breast cancer xenografts in nude mice were investigated. The proliferative tumor characteristics were examined by growth curves, thymidine labelling technique, and flow cytometric DNA analysis performed on fine-needle aspirations. The results showed that the tumors had growth kinetics comparable to other human tumor types with cell generation times of 42 to 60 hours. The three receptor-positive tumors had slower growth rate, larger tumor volume doubling time, and smaller growth fraction and labelling index than the receptor-negative tumor. However, no single proliferation parameter was sufficient to characterize the growth kinetics of individual tumors or to describe proliferative differences between the tumors.

Phenotypic diversity in leukemia cell populations

Acute leukemia comprises a large group of different diseases that can be identified by morphology in combination with immunological markers. Such studies suggest that phenotypic heterogeneity may be expressed in individual leukemia cell populations. This was verified in the murine AKR leukemia that was found to be composed of four antigenically different subtypes of leukemia cells, and it was shown that this feature has a severe negative impact on the use of leukemia cell specific monoclonal antibodies (Mabs) as therapeutical reagents. Twenty-four human T-lymphoblastic leukemias were analyzed with Mabs against HLA class I, HLA class II, and T-lymphocyte differentiation antigens, and 21 were found to be intratumoral heterogeneous with respect to these antigens. Mabs with high specificity were generated against AML cells and subsequently used to analyze more than 50 AML samples from different patients. The reactivity pattern of the Mabs differed significantly among the various AML samples. Further, a pronounced intratumoral antigenic heterogeneity (IAH) was found in most AML samples with regard to reactivity of the Mabs against AML and expression of major histocompatibility antigens. The negative impact of IAH on the use of Mabs in clinical oncology is described. It is argued that IAH exemplifies the phenotypic diversity of malignant neoplasms which is also suggested to be a basic and necessary feature of malignant cell populations. Mabs against subsets of malignant cell populations may have a profound effect on cancerous cell populations, and it is therefore of crucial importance that such subsets are identified and characterized. It is conceivable that this may result in generation of Mabs with potentially high value in cancer diagnosis and therapy, particularly in combination with drugs that induce differentiation in the malignant cell mass.

Autoradiographic investigations about the proliferation rate in different areas of human head and neck carcinomas

Up to five biopsies from the margin of the cancerous area of 10 human laryngeal and pharyngeal carcinomas have been labeled in vitro and partly in vivo after xenotransplantation on thymus-aplastic nude mice. The question should be answered whether or not one single biopsys will represent the proliferation rate of the complete tumor. The results demonstrate that under consideration of the methodical source of error the DNA-synthesizing cells are distributed regularly in the periphery of the carcinomas. One biopsy, therefore, represents the proliferation rate of the whole tumor. This result is only valid for examining the labeling index but not, as discussed, for calculating, e.g., the length of single cell cycle phases. For this purpose, laboratory animals are necessary. The most suitable animals seem to be thymus-aplastic nude mice.

Growth characteristics of human colorectal tumours during serial passage in immune-deprived mice

The growth characteristics of 6 human colorectal tumours have been examined during serial passage in both male and female immune-deprived mice. Exponential growth is a characteristic feature, especially on very early passages. Growth rates in 5 out of the 6 tumour lines increase during the first few transplant generations. This is accompanied by a shorter exponential growth phase and an increased slope of the growth curves. Lag phases and growth rates for individual tumours are variable within a passage. Growth rates for tumours maintained within the same host are similar, and are at least partially influenced by the host. In one tumour line examined in detail, the increased growth rate is attributable to a decreased cell-loss factor, and the difference in growth rate between human colorectal tumours and their corresponding xenografts may therefore largely be due to a difference in the contribution of this factor.

The growth kinetics of xenografts of human colorectal tumours in immune deprived mice

The technique of labelled mitoses was used to examine cell proliferation within grafts of human colonic and rectal tumours in immune deprived mice. Most of the data were obtained on the first passage but in some cases up to the third passage was used. It was found to be difficult to obtain precise kinetic data on this type of tumour material, but the results did allow some estimates to be made, particularly of the duration of the G2 and S phases of the mitotic cycle. The average G2 duration was 6 h and the average S phase was 14 h. It is concluded that whilst xenografts may differ in a number of respects from the tumour in the patient, they nevertheless constitute a type of experimental tumour that is worthy of further study.

Do cells cycle?

We propose that a cell's life is divided into two fundamentally different parts. Some time after mitosis all cells enter a state (A) in which their activity is not directed towards replication. A cell may remain in the A-state for any lenght of time, throughout which its probability of leaving A-state remains constant. On leaving A-state, cells enter B-phase in which their activities are deterministic, and directed towards replication. Initiation of cell replication processes is thus random, in the sense that radioactive decay is random. Cell population growth rates are determined by the probability with which cells leave the A-state, the duration of the B-phase, and the rate of cell death. Knowledge of these parameters permits precise calculation of the distribution of intermitotic times within populations, the behavior of synchronized cell cultures, and the shape of labeled mitosis curves.

Thymidine labelling studies in a transmissible venereal tumour of the dog

The cell population kinetics of the transmissible venereal tumour of the dog was studied at two different stages of tumour growth using the labelled mitoses technique. At the first stage the tumours were growing with a doubling time of about 4 days; at the second stage their growth rate was limited, probably by an immune reaction on the part of the host, to a doubling time greater than 20 days.Labelling of the tumour cells was found to be extremely heterogeneous throughout the tumour. Mitotic figures, however, were present in well labelled as well as in poorly labelled fields, suggesting that thymidine did not reach all regions of the tumour nodules. The data were therefore analysed assuming that the cells in well labelled areas were representative of the total cell population in the neoplasm. The timing of the cell cycle was found to be similar in the rapidly growing tumours and in those growing more slowly. It is concluded that the slowing of growth was due to a considerable increase in the rate of cell loss as a result of the immune reaction.

Cell proliferation during immunological perturbation in three transplanted tumours

The cell population kinetics of 3 transplantable tumours has been studied under circumstances in which the tumour growth rate was modified by a disturbance of the immunological status of the host. In 2 cases a complete arrest of growth was achieved but in spite of this there was a barely significant change in the median intermitotic time of proliferating cells. The data indicate that growth retardation was associated with a reduction in the proportion of actively proliferating cells and the rate of cell production, with or without an increase in the absolute rate of cell loss.