Microfilaments in human epithelial cancer cells

Exploiting the cytoskeletal filaments of neoplastic cells to potentiate a novel therapeutic approach

Although cytoskeletal-directed agents have been a mainstay in chemotherapeutic protocols due to their ability to readily interfere with the rapid mitotic progression of neoplastic cells, they are all microtubule-based drugs, and there has yet to be any microfilament- or intermediate filament-directed agents approved for clinical use. There are many inherent differences between the cytoskeletal networks of malignant and normal cells, providing an ideal target to attain preferential damage. Further, numerous microfilament-directed agents, and an intermediate filament-directed agent of particular interest (withaferin A) have demonstrated in vitro and in vivo efficacy, suggesting that cytoskeletal filaments may be exploited to supplement chemotherapeutic approaches currently used in the clinical setting. Therefore, this review is intended to expose academics and clinicians to the tremendous variety of cytoskeletal filament-directed agents that are currently available for further chemotherapeutic evaluation. The mechanisms by which microfilament directed- and intermediate filament-directed agents damage malignant cells are discussed in detail in order to establish how the drugs can be used in combination with each other, or with currently approved chemotherapeutic agents to generate a substantial synergistic attack, potentially establishing a new paradigm of chemotherapeutic agents.

Changes in the cytoskeleton pattern of tumor cells by cisplatin in vitro

The influence of the antitumor drug cis-diamminedichloroplatinum(II) ('cisplatin') upon the structural pattern of the main cytoskeletal components, i.e. microtubules, intermediate filaments and microfilaments, was investigated in squamous carcinoma cells derived from the mouse stomach (G 22) or the human lung (L 266) and growing in vitro as monolayer cultures. The studies were performed by the indirect immunofluorescence technique using monoclonal antibodies against alpha-tubulin, type 19 cytokeratin and actin at the end of a 90-min exposure to 2.5 x 10(-6), 5 x 10(-6) or 10(-5) mol cisplatin/l and a subsequent 24-h recovery period. Under the influence of cisplatin, the cytoskeletal tubules and filaments, which were distributed in untreated cells as a finely organized network spreading through the whole cytoplasm like a spider's web, collapsed and aggregated to dense and circularly arranged bands of bright immunofluorescence around the nucleus or to cap-like structures apposing the nucleus. These phenomena developed in clear dependence upon the dose of cisplatin applied and were observable in a modified manner and to a different degree with the three structural elements of the cytoskeleton. During the subsequent 24-h interval, during which the cells were allowed to recover in drug-free growth medium, the before-mentioned collapse of the cytoskeletal network was only partially reversible following previous treatment with the medium (5 x 10(-6) mol/l) and the high (10(-5) mol/l) dose of cisplatin and restored totally to the normal structural pattern of untreated control cells when the low dose of 2.5 x 10(-6) mol cisplatin/l had been administered before. These results give evidence that the DNA cannot be the only cellular target for the antitumor drug cisplatin, but that it also effects other intracellular lesions which cause structural alterations of cellular organelles independently of the primary molecular attack at nuclear DNA strands. Probably, these additional interactions fortify the antiproliferative effect and contribute to the achievement of important biological and cytological effects of cisplatin such as growth inhibition or giant cell formation.

Ultracytochemistry of the cell surface and microfilaments in dimethylhydrazine-induced colonic tumor cells

Studies were made of the ultracytochemical changes in the cell membrane and microfilaments of colonic epithelial cells during tumorigenesis induced by 1,2-dimethylhydrazine (DMH) in mice fed a high fat diet. The tumor cells showed reduced membrane ATPase activity and loss of contact with neighboring cells. Microfilaments in tumor cells showed an irregular intensity of fluorescent staining. Their actin filaments bound with heavy meromyosin (HMM) had an arrowhead pattern as in normal cells, but these complexes were shortened and detached from the cell membrane. The arrowheads were directed toward the interior in the terminal web of tumor cells. Microfilaments with long rootlets extended to the apical surface of some tumor cells. These results indicate that during development of colonic tumors, the structures of the cell membrane and microfilaments of the cells changes.

The cytoskeleton in tumor cells

During the past few years several laboratories investigated the occurrence of cytoskeletal components in epithelial and mesenchymal cells by electron microscopy and/or immunocytochemical methods in a number of tumor types growing in vitro or in the body. Since it is well established that antibodies to different intermediate-sized filament proteins can distinguish cells and tissues of epithelial, mesenchymal, muscle, astrocytic and neural origin special attention has been paid to the behaviour of these filaments in neoplastic cells recently. While the organisation of the cytoskeleton in tumor cells growing in vitro is very variable, regularities relevant for the diagnosis and the determination of the histogenetic origin of tumors have been observed in tumor cells growing in the body. In general, ultrastructural and immunological features of intermediate filaments are maintained during neoplastic transformation in the body. Thus immunofluorescence microscopy with antibodies to cytoskeletal proteins is a powerful tool for the classification and differential diagnosis of tumors, especially for the distinction between epithelial and mesenchymal tumors, including metastases. The concept that presence of an excess of contractile proteins such as actin is an important prerequisite for the metastatic spread of malignant cells has not been unequivocally supported by more recent results. However, an accumulation of various types of intermediate filaments (e.g. prekeratin, vimentin, acidic glial fibrillar protein) has been shown in different tumor types. The further elucidation of this alteration could contribute to a better understanding of the molecular mechanisms of neoplastic cell transformation.

Ultrastructural changes of epithelium-connective tissue junction in experimental lingual tumors

In this study, plaque-like lesions, epithelial hyperplasias, and papillary invasive carcinomas were produced in the tongues of hamsters by the application of DMBA combined with trauma for 16 weeks. The junction between the neoplastic epithelial cells and the connective tissue was studied ultrastructurally. In plaque-like lesions, the basal lamina was partially decreased in both thickness and density or partially discontinuous. In epithelial hyperplasias, cytoplasmic projections were observed in the portion of the basal cell near the intercellular space, and the basal lamina was absent around these cytoplasmic projections. In papillary invasive carcinomas, however, numerous cytoplasmic projections extended from various portions of the basal surface of the basal cells into the underlying connective tissue. The basal lamina was also absent around these projections. In epithelial hyperplasias and papillary invasive carcinomas, some of the cytoplasmic projections appeared almost empty, some contained a small number of tonofilaments and ribosomes, and others were filled with a large number of ribosomes but did not contain the tonofilaments. The collagen fibrils were markedly reduced in number in the area around cytoplasmic projections. The cytoplasm of some fibroblasts in that area contained many intracellular collagen fibrils.

Epithelial-stromal interface in normal and neoplastic human bladder epithelium

The ultrastructure of the epithelial-stromal interface of the human urinary bladder was studied in biopsy specimens that included 7 normal controls, 1 inverted papilloma, 18 noninvasive papillary carcinomas, and 19 invasive transitional cell carcinomas. In the invasive foci of the transitional cell carcinomas, the underlying basal lamina was attenuated or absent and the number of hemidesmosomes was decreased. These neoplastic cells displayed notably increased numbers of lysosomes, some of which appeared to be in the process of exocytosis. Increased numbers of cytoplasmic filaments adjacent to the plasma membranes at the invading pole of these cells were also observed. Tight junctions and junctional complexes were noticed adjacent to the tumor-stromal interface. None of the aforementioned features was observed in normal transitional epithelium, in inverted papilloma, in noninvasive papillary carcinomas, or in the noninvasive portions of invasive transitional cell carcinomas. Alterations of the epithelial-stromal interface deserve additional studies for they may constitute important parameters in the evaluation of actual or potential invasiveness in the various types of carcinoma of the bladder.

The role of myoepithelial cells in the morphogenesis of induced mammary tumours

The localization and cytomorphology of myoepithelial (ME) cells and their role in the morphogenesis of the mammary gland tumours of Wistar rats induced by 7,12-Dimethylbenz-a-anthracene-DMBA- were studied. Cells which do not participate in secretion and contain cytoplasmic myofibrillar bundles in a typical arrangement are considered to be of ME origin. In the histogenesis of induced mammary gland tumours no difinite role can be attributed to mature ME cells or their precursors. Decreased differentiation is associated with reduced numbers of ME cells. No ME cells can be detected in the anaplastic, stromafree portions of the solid tumour. The sarcomatous component of the induced carcinosarcomas originates from connective tissue. ME cells may give rise to leiomyoma-like tumours comparable with the human benign mammary myoepithelioma. The atrophic areas of mammary gland tumours consisted mostly of preserved ME cells. The ME cells of induced mammary gland tumours were, in every respect, identical with the normal ME cells of control mammary glands.

Ultrastructure of mucoepidermoid carcinoma in minor salivary glands

Three cases of mucoepidermoid carcinoma of minor salivary glands were studied by electron microscopy. Mucus-secreting cells contained numerous mucous globules and bundles of fine cytoplasmic filaments. Another cell type contained a large number of glycogen particles, akin to tumor cells in glycogen-rich adenocarcinoma, and it is postulated that these cells represent the intermediate cells observed by light microscopy. Epidermoid cells contained a moderate amount of tonofilaments and various numbers of organelles. Mucus-secreting and epidermoid cells that surrounded a cystic space exhibited many microvilli. Results of this study support the theory that mucoepidermoid carcinoma develops from salivary gland duct cells with different cellular differentiation potentials and, in general, agree with the conventional grading system of mucoepidermoid carcinoma.

The fate of hemidesmosomes in laryngeal carcinoma

The ultrastructural morphology of the hemidesmosomes in malignant epithelial cells of invasive squamous cell carcinoma of the human larynx was studied by electron microscopy. In the more advanced carcinomas the hemidesmosomes are reduced in number or absent over extensive areas of the epithelial stromal junction. In some places the hemidesmosomes are observed to be in the process of being dislodged from their normal sites at the plasma membrane of the basal carcinoma cell. After dislodgment from the basal plasmalemma into the subepithelial connective tissue the hemidesmosomes are seen to round off with the cytoplasmic attachment plaques lying on their inner circumference. A constant feature of the detached hemidesmosomes is the absence of inserting tonofilaments. Frequently, the detached hemidesmosomes are found to be in close association with detached multilayered basement membrane material in the stroma. The detached hemidesmosome-structures appear to migrate down into the deeper layers of the connective tissue space apparently loosing their distinct ultrastructure. These observations indicate that the detachment of hemidesmosomes and their subsequent downward dermal migration may result in a loss of epithelial-stromal adherence in invasive epithelial cancer of the larynx.

Fine structural studies of radiation-resistant human squamous cell carcinomas

Squamous cell carcinomas of the oral cavity are relatively common lesions, and often can be controlled by radiation therapy. Recently, a series of these tumors has been encountered which did not respond positively to irradiation, necessitating subsequent extensive surgery. This report describes some fine structural changes which were observed in squamous cell carcinomas following exposure to x-irradiation. In addition to the common, keratin-forming differentiated cell, others which were observed were secretory-like, undifferentiated and phagocytic cells. Undifferentiated tumor cells occasionally became incorporated, at least temporarily, as a component of the blood vessel wall, perhaps reflecting metastatic potentiality. It is proposed that irradiation may either increase potential avenues of tumor cell differentiation or inactivate inhibitors thereof.

Ultrastructure of oral squamous-cell carcinoma

Fresh surgical specimens of sixteen cases of oral squamous-cell carcinoma were processed for electron microscopic study. All cases were histologically graded as moderately differentiated carcinoma. As compared to normal oral stratified squamous epithelium, some unusual ultrastructural features were present in carcinoma. These features were spherical or ovoid nuclear bodies composed of concentrically arranged filaments and granules, clustered ribosomes, many lysosomal bodies, cell residues in other cells, absence and multilayering of basal lamina, pseudopodal cytoplasmic projections, microfilaments in peripheral cytoplasm, clusters of swirled tonofilaments, intracytoplasmic desmosomes, and a small amount of glycogen. These features are interpreted as being related to hyperactivity, phagocytosis, locomotion, and differentiation of cancer cells.

Benign human mammary myoepithelioma

A leiomyoma-like, multifocal tumour developed from intraductal papillomatosis in the breast of a 42 year old woman. The spindle-shaped tumour cells were examined by light, electron and polarizing microscopy, which revealed that they originated from immature "precursor" myoepithelial cells. The author suggests that the tumour be called "myoepithelioma". From the morphological characteristics of the tumour the myoepithelial cells appear to be capable of producing leiomyoma-like benign or malignant tumours. The role that has been attributed by some to the myoepithelial cell in the production of epithelial tumours is problematical, in the light of the present finding.