Distribution of tritiated thymidine about a capillary sinusoid in a transplanted mouse tumour

Hypoxia in a human intracerebral glioma model

OBJECT

The development of hypoxia in human gliomas is closely related to functional vasculature and the presence of hypoxia has important biological and therapeutic consequences. Assessment of hypoxia is necessary to understand its role in treatment response and to evaluate treatment strategies to improve tumor oxygenation. In this study, the authors report findings of their analysis of the degree of hypoxia in relation to other vascular parameters in a human intracerebral glioma xenograft.

METHODS

In sections of tumor, hypoxic regions were identified immunohistochemically by using the hypoxic marker pimonidazole. The S-phase marker bromodeoxyuridine was used to detect cell proliferation, and the perfusion marker Hoechst 33342 was used to delineate perfused vessels. Vascular structures were stained with an endothelial marker. Hypoxic tumor regions were clearly present in this human intracerebral glioma model. Hypoxic areas were usually found in nonperfused regions, whereas tumor cell proliferation was especially marked in perfused tumor areas. Furthermore, by using in situ hybridization the authors identified infiltrating tumor cells in the normal brain. This feature is often observed in gliomas in patients.

CONCLUSIONS

This model is a representative human glioma model that provides the researcher with the opportunity to analyze the relationship between the degree of hypoxia and vascular parameters, as well as to examine the effects of treatments aimed at modification of the oxygenation status of a tumor.

Prognostic significance of the bromodeoxyuridine labeling index in primary colorectal carcinoma

The bromodeoxyuridine (BrdU) labeling index was determined in 40 primary colorectal carcinomas by DNA flow cytometry using a BrdU-specific monoclonal antibody. The labeling index, or the fraction of cells in the S-phase of the cell cycle, ranged from 12% to 52%, with a mean of 28% (SEM, 2%). The labeling index in 19 patients was over 30%, which was termed a higher labeling index. There was no significant difference in the labeling index based on the clinical stage of the disease. During the 5-year follow-up after the apparently curative resection, 14 patients died of the disease, 1 died of an unrelated cause, 1 is alive with a recurrence of the disease, and 24 are alive without the disease. The higher labeling index was thus associated with a significantly poorer patient survival (P = 0.03 based on the generalized Wilcoxon test). The present study therefore disclosed that the S-phase fraction of tumor cells thus determined had prognostic significance in primary colorectal carcinoma.

The effect of two fractions of radiation, delivered in air or in hyperbaric oxygen, on the Fib/T tumour in WHT mice pretreated with a hypoxic gas mixture

The response of the Fib/T tumour to equal fractions of radiation, spaced by an interval of 24 hours, was determined in tumour-bearing mice that were pretreated either with 8% oxygen for 48 h or with air. An increase in tumour cell kill occurred in the group of animals that received a low oxygen pretreatment. Tumour cell kill was further and significantly increased if mice were retained in the low oxygen environment for the 24-h interval between radiation fractions. Possible explanations for these findings are proposed and discussed. The effect of a 48 h 8% oxygen exposure in modifying the response of the Fib/T tumour to two fractions of radiation, both delivered in hyperbaric oxygen, was also investigated. The low oxygen pretreatment did not significantly alter the tumour response to radiation given under conditions of hyperbaric oxygenation.

In situ analysis of cell kinetics in human brain tumors. A comparative immunocytochemical study of S phase cells by a new in vitro bromodeoxyuridine-labeling technique, and of proliferating pool cells by monoclonal antibody Ki-67

A newly developed in vitro labeling method with bromodeoxyuridine (BrdU) identifies S phase cells in situ in freshly obtained surgical tissue of human brain tumors which is subsequently fixed and embedded in paraffin for BrdU immunovisualization. For the first time, the BrdU labeling index (LI) is successfully compared here with the LI obtained by immunostaining of frozen sections of the same tumors with monoclonal antibody Ki-67 which identifies all proliferating cells, i.e., the growth fraction. LIs were counted in at least five different areas with high density of labeled cells; at least 1,000 cells were counted. In 13 metastatic tumors, Ki-67 LI was 8.3%-62.6%, and BrdU LI was 5.1%-28.0%. In 18 gliomas, Ki-67 LI was 1.4%-19.3%, and BrdU LI was 0.2%-11.6%. In 7 meningiomas, Ki-67 LI was 0.3%-3.0%, and BrdU LI was 0%-2.0%. Statistical comparison of Ki-67 and BrdU LIs by linear regression analysis revealed a highly significant correlation: BrdU LI = 0.99 + 0.34 Ki-67 LI (r = 0.92, P less than 0.001). A significant heterogeneity of proliferation patterns may occur within one sample from area to area, as well as between different samples of the same tumor, especially in gliomas; thus, some subjective influence on LIs by arbitrary sampling and selection could occur in quantitative evaluation of in situ cell kinetics of human brain tumors. This study indicates that our in vitro BrdU-labeling method allows the in situ identification of S phase cells in excellently preserved fixed tumor tissue which is well suited for further histological examination.(ABSTRACT TRUNCATED AT 250 WORDS)

The validity of the labelling index in tumour studies

The distribution of labelled cells through 5 different mouse tumours was measured after a single injection of [3H]-thymidine [( 3H]-TdR) or [3H]-deoxyuridine [( 3H]-UdR). All the tumours had areas where the percentage of labelled cells (the labelling index, LI) was high and areas where the LI was very low. The total area with a low LI was greater after [3H]-TdR than after [3H]-UdR injection in all 5 tumours. In one of the tumours, carcinoma NT, repeated injections of [3H]-UdR at 2 h intervals caused the areas of high LI to spread, eliminating all areas of low LI in many specimens. When 5-fluorodeoxyuridine (FUdR) was injected, to block de novo DNA synthesis in carcinoma NT, [3H]-TdR was incorporated by many more cells. The LI was increased throughout the tumour and no area had a LI below 20% after FUdR plus [3H]-TdR. After flash-labelling with [3H]-TdR alone, nearly half the tumour had a LI below 20%. We conclude that the labelling seen after FUdR plus [3H]-TdR represented the true distribution of S phase cells in carcinoma NT. Routine flash-labelling with [3H]-TdR or [3H]-UdR left nearly half the S phase cells unlabelled and gave an erroneously low value for the proportion of DNA synthesising cells in the tumour. The results suggest that many tumour cells have very large endogenous nucleotide pools which cannot be flooded by a single injection, even of [3H]-UdR.

Vascular occlusion and tumour cell death

Vascular occlusion has been tested as a means of inducing regrowth delay, local control, reduced cell viability and prolonged alteration of blood flow in mouse tumours. The occlusion has been achieved by applying D-shaped metal clamps across the base of subcutaneously implanted tumours. The period of clamping has been varied from 30 min to 24 hr. Marked tumour regression, delayed growth and long-term tumour control were seen, with the magnitude of the response being proportional to the duration of clamping. Vessel occlusion for at least 15 hr is necessary to achieve local cure of the tumour. The overall effect results partly from an immediate loss of cell viability and partly from a failure of the capillary network to recover its normal perfusion pattern after the clamp has been removed. The implications of this for anti-proliferative endothelial therapy is discussed.

The relation between tumor cell proliferation and vascularization in differentiated and undifferentiated colon carcinomas in the rat

Tumor cell proliferation and tumor vascularization were investigated in differentiated and undifferentiated colon carcinomas of the rat. The following results were found: 1, in both tumor types, vascularization is developed equally well; 2, both in the differentiated and in the undifferentiated carcinomas, the number of proliferating tumor cells decreases with increasing distance from the capillaries; at a distance of about 80 microns, there is no longer any noteworthy tumor cell proliferation; 3, the differentiated and undifferentiated carcinomas differ both in the level of the mitosis index and 3H-thymidine labeling index as well as in their local proliferation pattern despite equal vascularization; 4, these differences must be based on factors which are independent of vascularization; they are attributed to proliferation properties which are inherent in the differently differentiated tumor cell populations. It is concluded from this that the actual proliferation behavior of a carcinoma is primarily dependent on the proliferation properties of the tumor cell population.

Endothelial-cell proliferation in experimental tumours

The proliferation characteristics of vascular endothelium have been studied in 131 individual experimental tumours, representing 18 transplanted tumour lines. The labelling index (LI) is high in most tumours, with a mean value of 0.9%, regardless of the growth rate of the tumours, or whether different tumour types are considered or individual tumours from within one line are studied in detail. A similar high LI value has been found by others for a human tumour. These high LI values may even underestimate the proliferation in new capillary buds. The high proliferative index of tumour endothelium is in marked contrast with the previously reported low 3HTdR uptake into normal tissue blood vessels. It seems likely that it is the type of new vessels formed that will influence tumour growth rates more than the simple rate of endothelial-cell proliferation. The large difference between the proliferation characteristics of tumour endothelium and normal tissue endothelium, recently identified as a possible approach for tumour therapy, has now been confirmed for a range of animal tumours and a human tumour.

Tumour cell proliferation in relation to the vasculature

The proliferation pattern of a transplantable mouse mammary carcinoma has been studied in relation to its macroscopic and microscopic structure. No significant differences were seen in the labelling or mitotic indices or in the percentage labelled mitoses curves for the peripheral 2.0 mm rim or for the central tumour core. When these parameters were scored for cells classified according to their position in relation to capillaries or to necrotic regions, marked differences were observed in all the parameters. Higher labelling and mitotic indices and higher grain counts were seen adjacent to the capillaries. These appear to result from a shorter cell cycle duration and a higher growth fraction. The variation in cell cycle is mainly due to a change in the duration of G1.

Kinetics of cell proliferation and cell loss in the peripheral and central parts of Walker tumours growing in rats and nude mice

In previous experiments it was shown that, in the submucosal part of Walker tumours transplanted to the gastric wall of rats, a lower rate of cell proliferation was seen in the peripheral zone, defined as the outer 100-120 mu of the tumours, than in the main tumour mass. The purpose of the present experiments was to investigate whether such differences are independent of the location of the Walker tumour, or were caused by local factors specific for the gastric mucosa, and whether specific cellular immunity cell proliferation at the periphery of a transplanted tumour. Cells from Walker 256 tumour were injected into the subcutaneous space in rats and in mutant nude mice, which lack T lymphocytes. In one series, the rats and mice were injected with 3H-TDR at different time intervals before sacrifice. In a second series vinblastine sulfate was injected 3 hours before sacrifice. Although all the animals were given the same tumour dose, the tumours in mice increased in size more slowly than those in rats. In the first-mentioned series, the mitotic counts, the labelled cells and the percentage labelled mitoses (PLM) in the main tumour mass and at the tumour perphery were counted. In the second series the mitotic rate in the same two regions was determined. A significantly lower rate of cell proliferation was demonstrated at the periphery compared to the main tumour mass in both rats and mice. Differences between the PLM curves in the two regions were also found. Possible explanations of these findings are discussed. It is concluded that the described growth pattern is probably a general characteristic of the Walker tumour, and that the low rate of proliferation at the periphery is not caused by specific immunological mechanisms mediated through T lymphocytes. If the growth rates were calculated on the assumtion that the actual tumour growth followed a Gompertz function, then the rate of cell loss in the tumour in mice was higher than that in the tumour in rats.

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.