Development and cell kinetics of colonic tumors induced in mice by dimethylhydrazine

Gene expression of CD24 core polypeptide molecule in normal rat tissues and human tumor cell lines

CD24 antigen is a glycoprotein expressed on haematopoietic cells, including B cells, T cells and granulocytes and on non-haematopoietic cells, including neural cells, ganglion cells and the cells of the adrenal medulla. The antigen is also expressed on renal cell carcinoma, small cell lung carcinoma and neuroblastoma. We have cloned rat cDNA encoding core polypeptide of CD24 antigen from embryonic brain and shown that the core molecule is highly expressed in embryonic brain and non-neural tissues. Rat tissue and various human neoplastic cell lines were investigated for the gene expression of CD24 core polypeptide by in situ hybridization. The transcript was localized in gastrointestinal epithelia, ductal and acinar epithelia of the salivary gland, the bronchiolar epithelium, renal tubular epithelium, the epithelium of the oviduct, follicular cells of the thyroid, medullary cells of the adrenal gland, Auerbach's plexus, B blastoid cells in lymph nodes, hair follicles, and the sweat glands of the skin. Among the various human neoplastic cell lines investigated, the transcript was detected in squamous cell carcinoma of the lung, gastric carcinoma, colon carcinoma, choriocarcinoma and renal cell carcinoma. The result suggest that the core molecule of CD24 antigen may be expressed in a wider range of epithelial cells and carcinoma cell lines than has been reported. Furthermore, we show that gene expression of CD24 core polypeptide is confined to the proliferative zone of the gastrointestinal mucosa, suggesting that core molecule is transiently expressed on the surface of epithelial cells in the process of cellular maturation. We discuss a possible role for CD24 antigen in the maturation of epithelial cells in the gastrointestinal tract.

A quantitative study of epithelial alterations during the early stages of experimental colonic tumorigenesis in mice

The weekly administration of 1,2-dimethyl-hydrazine (DMH) by subcutaneous injection for a period of 16-20 weeks is a well known procedure for producing colonic tumors in mice and rats. Quantitative histomorphological, histochemical and kinetic studies, as well as investigation of the significance of epithelial cell density were carried out in mice between the 7th and the 91st day after the first DMH injection. These studies showed that between the 28th and the 35th day, several simultaneous alterations in the colonic epithelium involving modification of glandular form, decreased mucus secretion, an increase in epithelial cell density and an increase in the number of S phase cells (BrdU labeling index: LI). Around the 35th day, the glands tended to expand and from the 35th to the 63rd day, they were stretched and displayed compartments of dedifferentiated and non-mucinous crypts (DNMC). In these crypts the cell density became very high, reaching twice the control value on the 91st day. This feature was accompanied by alteration in cell morphology and by an increase in the available basement membrane area. A decrease in mucus secretion was apparent from the 14th day and by the 63rd day, mucus secretion was only about 60% of the control value in all crypts. The LI was increased until the 35th day following which a paradoxical and progressive decrease occurred in all glandular compartments.

Basic and clinical investigations of dietary calcium in the prevention of colorectal cancer

Long-standing investigations into the role of diet in colon cancer have generally supported the notion that some aspect of dietary fats acts to promote cancer at this site. Understanding of the chemical behavior of lipids in the colon led to a hypothesis suggesting that depletion of calcium could partly explain the tumor-promoting effects of dietary fat. Calcium levels may control critical intracellular events in the course of proliferation. Lack of availability or loss of calcium may result in abnormalities in the regulation of colonic proliferation. Basic and clinical studies suggest that calcium supplementation reduces colonic proliferation implying a potential reduction in cancer risk. The current evidence supporting calcium as a cancer chemoprevention agent is reviewed.

Antitumor effects of inhibitors of arachidonic acid cascade on experimentally induced intestinal tumors

The antitumor action of inhibitors of cyclooxygenase (indomethacin) and lipoxygenase activity (nordihydroguaiaretic acid) of arachidonic acid cascade was investigated in the chemically induced large bowel tumors in Sprague-Dawley rats. Indomethacin treatment completely prevented the carcinogenic effect of methylazoxymethanol. Thus, no tumors were found in the 14 rat test group, compared with 13 of 14 tumor-bearing rats in the untreated control group. Although nordihydroguaiaretic acid treatment does not abolish prostaglandin synthesis, it does reduce the effect of the carcinogen and tumors were found in only five of 14 treated rats. From this study it can be postulated that not only is reduction in prostaglandin formation responsible for the inhibition of tumor growth, but also leukotrienes may play some role.

Tumor dedifferentiation: an important step in tumor invasion

Tumor invasion in vivo was studied by light and electron microscopy as well as by immunofluorescence microscopy. Special regard was paid to the grade of tumor differentiation. Dimethylhydrazine-induced murine colonic carcinomas comprising a differentiated and an undifferentiated tumor type with low and high invasiveness respectively, were used. At the invasion front of both tumor types a striking dissociation of the organized tumor cell complexes into isolated tumor cells was found together with a loss of most of the cytological features of differentiation. It is supposed that this process mobilizes the tumor cells from the main tumor bulk enabling them to invade the host tissue by active locomotion. This view is strongly supported by the demonstration of morphological equivalents of active cell movement such as pseudopodia-like cytoplasmic extrusions, adaptive changes of the cell shape and microfilament bundles. Although the proposed mechanism of tumor invasion is essentially the same in both tumor types, the grade of differentiation is nevertheless critical, as in the undifferentiated carcinomas only subtle dedifferentiation steps (loss of basement membrane and cell junctions) are necessary to acquire an invasive status. This fact may explain the comparatively high invasiveness and poor prognosis of undifferentiated carcinomas.

Histological and autoradiographic study on development of group III lesion (dysplasia grade III) in the stomach

In order to elucidate the biological behaviour of the Group III lesion of the stomach, morphogenesis of the lesion was studied from cell kinetic point of view. In most Group III lesions, the proliferative cell zones were found at the upper third level of the mucosa, whereas they were confined to the middle third and to the lower third level in the normal pyloric and in the intestinalized mucosa, respectively. The smallest Group III lesion was a single gland dysplasia, in which the Group III cells were confined to the middle level of the mucosa. These findings suggested that the Group III lesion must be a change initiated in the neck stem cells of the pyloric mucosa as is the case in the intestinal metaplasia. The Group III cells arising at the neck region surge upwards and then accumulate in the upper part of the foveola to form an aberrant proliferative focus from which a lesion develops by budding. This morphogenesis manifests an adenomatous nature of the lesion. However, there was apparently a spectrum of cytological and histological abnormalities which varied from the lesions which might be considered to be a kind of intestinalized tubule, to the typical Group III lesion. Some Group III lesions imitating the intestinal metaplasia contained the proliferative cell zones at the middle level of the mucosa, indicating that a group of the dysplastic tubules arose zonally, not from a single gland. This morphogenesis reflects a metaplastic nature of the lesion. (ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of tumor invasion: evidence from in vivo observations

The major mechanisms of tumor invasion in vivo are discussed in the present review. A special emphasis is placed on tumor dedifferentiation which has proved to be of paramount importance for the invasion process. Based on in vivo observations obtained from various human and animal tumors a concept for the mechanism of tumor invasion is proposed which mainly comprises the following basic events: the first and essential step in tumor invasion is the tumor dedifferentiation and dissociation at the invasion front. This apparently temporary and reversible process mobilizes the tumor cells out of the main tumor bulk and enables them to invade the host tissue by active locomotion. This mechanism is essentially supported by an interstitial edema in the host tissue adjacent to the tumor periphery, which causes an 'opening and widening' of the host intercellular spaces. Enzymatic changes in the micromilieu of the extracellular matrix may contribute to this process. The tumor cell proliferation completes the invasion process in so far, as the invading tumor cells are still able to proliferate, leading this way to expanding tumor cell nests in the host tissue which have the potency to redifferentiate. The expansive growth of these tumor cell nests results in a progressive atrophy of the host tissue, mainly caused by an increasing compression and a competitive withdrawal of oxygen and other nutrients by the tumor cells. The overall picture of tumor invasion can therefore be considered as a repetitive cycle of active tumor cell locomotion followed by focal tumor cell proliferation in the host tissue.