Contribution of in vivo proliferation/differentiation studies toward the development of a combined functional and morphologic system of classification of neoplastic diseases

A role for the putative tumor suppressor Bin1 in muscle cell differentiation

Bin1 is a Myc-interacting protein with features of a tumor suppressor. The high level of Bin1 expression in skeletal muscle prompted us to investigate its role in muscle differentiation. Significant levels of Bin1 were observed in undifferentiated C2C12 myoblasts, a murine in vitro model system. Induction of differentiation by growth factor withdrawal led to an upregulation of Bin1 mRNA and to the generation of higher-molecular-weight forms of Bin1 protein by alternate splicing. While Bin1 in undifferentiated cells was localized exclusively in the nucleus, differentiation-associated isoforms of Bin1 were found in the cytoplasm as well. To examine the function of Bin1 during differentiation, we generated stable cell lines that express exogenous human Bin1 cDNA in the sense or antisense orientation. Cells overexpressing Bin1 grew more slowly than control cells and differentiated more rapidly when deprived of growth factors. In contrast, C2C12 cells expressing antisense Bin1 showed an impaired ability to undergo differentiation. Taken together, the results indicated that Bin1 expression, structure, and localization are tightly regulated during muscle differentiation and suggested that Bin1 plays a functional role in the differentiation process.

The myelodysplastic syndromes in 1996: complex stem cell disorders confounded by dual actions of cytokines

Based upon recent studies of apoptosis, proliferation, cytokines and genic abnormalities, a new hypothesis regarding the pathology of myelodysplastic syndromes is being proposed. The transforming abnormality which affects an early progenitor hemopoietic stem cell is poorly defined so far but confers a growth advantage on this cell eventually leading to monoclonal hemopoiesis at least affecting the non-lymphoid bone marrow cells. Several cytokines confound the picture by exerting dual effects of stimulating the proliferation of immature cells while inducing the apoptosis in their maturing progeny thereby producing the clinical syndrome of cytopenias despite cellular marrows. Since a number of these offending cytokines share the same common lipid intracellular signalling pathway, interfering with the generation of specific phospholipid second messengers should hypothetically result in a dual effect as well. Alleviation of cytopenias (due to attenuation of apoptosis) should be accompanied by a decrease in the progeny of the transformed stem cell (due to suppression of proliferation) eventually allowing for resumption of polyclonal hemopoiesis.

Tumor cell complementation groups based on myogenic potential: evidence for inactivation of loci required for basic helix-loop-helix protein activity

Basic helix-loop-helix (bHLH) proteins mediate terminal differentiation in many lineages. By using the bHLH protein MyoD, which can dominantly activate the myogenic differentiation program in numerous cell types, we demonstrated that recessive defects in bHLH protein function are present in human tumor lines. In contrast to prior work with primary cell cultures, MyoD did not activate the myogenic program in six of the eight tumor lines we tested. Cell fusions between the MyoD-defective lines and fibroblasts restored MyoD activity, indicating that the deficiency of a gene or factor prevents bHLH protein function in the tumor lines. Fusions between certain pairings of the MyoD-defective lines also restored MyoD activity, allowing the tumor lines to be assigned to complementation groups on the basis of their ability to execute the myogenic program and indicating that multiple mechanisms exist for abrogation of bHLH protein activity. These groups provide a basis for identifying genes critical for bHLH-mediated differentiation and tumor progression by using genetic complementation.

Cell proliferation kinetics of normal and tumour tissue in vitro: quiescent reproductive cells and the cycling reproductive fraction

Current methods for measuring the cell kinetics of human tumours are made and interpreted within the context of a simplistic two compartment model for cell proliferation, consisting of cells that are cycling and those that are not. It is now recognized that the non-cycling compartment of many tumours is heterogeneous, composed of non-reproductive end-stage cells and reproductive cells that are dormant/quiescent. We have developed an in vitro analysis that distinguishes for the first time quiescent reproductive cells from non-reproductive end-stage cells and have integrated this analysis with monolayer clonogenic and suicide assays to simultaneously quantitate the duration of the cell cycle and reproductive cells that are: cycling, quiescent, clonogenic, and non-reproductive end-stage cells. We have defined a new parameter, the Cycling Reproductive Fraction (CRF), which is the cycling cell population referenced specifically to the reproductive cell population. Measurements of CRF from 72 tumour biopsies and from 5 normal foreskins showed that CRF approached 100% in some tumours; however, CRF showed near normal values (< 1%) in others suggesting that cell cycle control may be maintained in some tumours. Because of CRF's improved specificity, we believe that CRF may enhance classification, prognostication, and the optimization and prediction of response to chemotherapy.

Cell kinetics of human ovarian cancer with in vivo administration of bromodeoxyuridine

BACKGROUND

Cell kinetics could have prognostic significance in human ovarian cancer and might also help in designing optimal therapy. No data are available on the in vivo kinetics of this tumor using bromodeoxyuridine (BrdU) infusion before surgery.

PATIENTS AND METHODS

The kinetic parameters of human ovarian carcinoma were investigated in vivo using BrdU incorporation and bivariate BrdU/DNA flow cytometric (FCM) analysis. Fifty-five previously untreated patients with ovarian cancer (F.I.G.O. clinical stage III and IV) were studied. BrdU (250 mg/sqm) was given i.v. 6 h before surgery and samples of primary tumor and metastasis biopsies were fixed in 70% ethanol. By coupling the BrdU immunoreaction with biparametric FCM analysis, the nuclear DNA content (i.e., ploidy status), the tumor labelling index (LI), the synthesis time (TS) and the potential doubling time of the tumor mass (Tpot) were obtained. BrdU immunodetection was done on histological sections of the same tumors.

RESULTS

The majority of the tumors had a DNA aneuploid content (71.5%). The amount of BrdU-positive S-phase cells varied in different tumor samples and when several samples were taken from the same tumor. The proportion of BrdU-negative S-phase cells was large (50% of the total S phase cells) in almost all cases. The mean LI was 6.1% using FCM and 7.2% on visual count of the slide. The mean TS and Tpot were 14.7 h and 12.5 days, respectively. LI and TS were not correlated with clinical tumor stage, histological grading, residual tumor size or DNA ploidy, but Tpot was significantly higher (p < 0.05) in patients with residual tumor size < 2 cm. Univariate analysis showed that Tpot was significantly associated with the response after first-line chemotherapy (p < 0.009). In multivariate analysis only residual tumor size was related to the response.

CONCLUSION

Although this in vivo BrdU technique provides information on the kinetic features of human ovarian cancers, it remains questionable whether this information has any additional value compared to currently used prognostic factors which are assessable clinically and surgically.

The serial study of c-myc expression in bone marrow biopsy specimens during treatment for acute myelogenous leukaemia

The AMEX method of fixation permitted the serial study of c-myc expression in bone-marrow (BM) biopsies obtained from 6 patients with acute myelogenous leukaemia (AML) and one with myelodysplastic syndrome (MDS) during therapy with various cytotoxic and bioactive agents. BM cytotoxic therapy and therapy with bioactive agents was capable of altering c-myc expression in vivo. While cytotoxic therapy was generally associated with a fall in myc expression, it did not produce a dramatic effect on myc expression. Recombinant human granulocyte-macrophage colony-stimulating factor (RhGM-CSF) can increase and retinoic acid/alpha-interferon can decrease c-myc expression in myeloid cells in vivo.