Maintenance chemotherapy in limited small cell lung cancer: a randomised controlled clinical trial

In a prospective randomised study 68 patients with limited small cell bronchogenic carcinoma were assigned to induction treatment with combined alternating non-cross-resistant chemotherapy plus split course radiotherapy without (NM) or with (M) subsequent maintenance therapy. Induction chemotherapy consisted of cisplatinum and VP16213q. 3 weeks followed by cyclophosphamide, vincristine and methotrexate (CVM)q. 4 weeks. Three courses of this 7-week chemotherapy programme were given. Radiotherapy to the primary lesion of 25 Gy in 13 fractions was given after each of the first and second courses of chemotherapy. Those in complete remission following the induction phase received prophylactic cranial irradiation. Those assigned to maintenance received a further six cycles of CVM after induction. The overall survival of patients randomised to maintenance therapy was significantly inferior to that of those randomised to no maintenance therapy (median survival NM 19.2 vs M 14.1 months, P = 0.05 log rank). Among patients achieving a complete remission of disease on induction therapy those receiving maintenance also showed a trend towards inferior survival (median survival NM 26.8 vs 18.0 months, P = 0.06 log rank). Deaths in each group of patients were predominantly due to tumour progression. The results do not support the use of maintenance chemotherapy after the use of intensive combined therapy induction programmes in the management of limited small cell bronchogenic carcinoma.

Differentiation-regulated loss of the polysialylated embryonic form and expression of the different polypeptides of the neural cell adhesion molecule by cultured oligodendrocytes and myelin

The expression of the neural cell adhesion molecule (N-CAM) on cultured murine oligodendrocytes, their precursors, and myelin was examined by indirect immunofluorescence, biosynthetic radiolabeling followed by immunoprecipitation and Western blot analysis, using antibodies specific for various forms of the molecule. In all culture systems studied, whether the oligodendrocytes were cultured as an enriched fraction containing precursor cells or in the presence of astrocytes and neurons, a similar differentiation-stage-related expression of N-CAM was seen. At early developmental stages many tetanus toxin receptor- and A2B5 antigen-positive putative oligodendrocyte precursors with bipolar morphology were seen and found to express N-CAM in its embryonic form. Of the 04 antigen-positive immature oligodendrocytes with few slender processes most expressed N-CAM, but few the embryonic form of N-CAM. The more mature 01 or 010 antigen-positive oligodendrocytes were found to express exclusively the adult form of N-CAM. Oligodendrocytes synthesized the 120 and 140 kD forms of N-CAM (N-CAM 120 and N-CAM 140), but not N-CAM 180, although with differentiation, N-CAM 120 predominated in oligodendrocytes and also in pure myelin. N-CAM 120 could be released from oligodendrocytes and myelin by phosphatidylinositol-specific phospholipase C, suggesting that in both oligodendrocytes and myelin N-CAM 120 is inserted into the membrane by covalent linkage to phosphatidylinositol.

Expression of v-src arrests murine glial cell differentiation

A replication-defective retroviral vector carrying the v-src oncogene and the gene for neomycin resistance was used to infect neurone- and fibroblast-depleted embryonic mouse brain cells in vitro. Cells resistant to the antibiotic G418 were obtained and continually passaged. Several cell lines were isolated which express high levels of v-src mRNA and v-src tyrosine kinase activity. The antigenic marker profile of either the pooled cells from an individual infection or sublines isolated from individual foci showed the cells to be immature glia: most cells expressed vimentin, A2B5 antigen and/or J1/tenascin glycoproteins, but not fibronectin. Sublines expressed different antigen profiles suggesting that the immortalised cells were derived from glial cells of different phenotypes. The cell lines expressed the 120 and 140 but not the 180 kd components of N-CAM as well as voltage-activated potassium channels, typical for glial cells. 01 antigen-positive oligodendrocytes were never observed in the lines or sublines after long term passage (over 1 year), but some cells expressed glial fibrillary acidic protein, a marker for mature astrocytes. Thus, expression of v-src in murine glial cells appears to arrest their development and prevent their differentiation.

Cells positive for the O4 surface antigen isolated by cell sorting are able to differentiate into astrocytes or oligodendrocytes

Cells expressing the surface antigen O4 were isolated as pure populations from cultures of murine brain or cerebellum using fluorescence activated cell sorting. When these O4-positive cells were further cultured in the presence of fetal calf serum (FCS) many cells expressed both O4 and the astrocyte marker glial fibrillary acidic protein (GFAP) after 4 days of culture. Cells not exposed to FCS expressed O4, but never GFAP. GFAP-positive cells in the presence of fetal calf serum very rarely expressed the myelin associated glycoprotein (MAG) or O1, both of which are expressed on more differentiated oligodendrocytes, and never expressed O10 that is characteristic of even more mature oligodendrocytes. These results show that glial cells expressing O4, but not MAG, O1, O10 or GFAP are bipotential precursor cells able to differentiate into astrocytes or oligodendrocytes depending on the culture conditions and suggest that bipotentiality of glial precursor cells is retained up to a later developmental stage than that of the O2A progenitor cell.

Channel expression correlates with differentiation stage during the development of oligodendrocytes from their precursor cells in culture

Membrane currents in cultured murine oligodendrocytes and their precursors were characterized using the patch-clamp technique. Prior to recording, cells were identified by immunofluorescence using monoclonal antibodies characteristic of two types of precursor cells and two differentiation stages of oligodendrocytes. The most immature, A2B5 antigen-positive glial precursors, expressed four types of voltage-activated K+ currents and tetrodotoxin-sensitive Na+ currents. The more differentiated cells, O4 antigen-positive glial precursors, expressed similar K+ currents, but Na+ currents were recorded in only a minority of cells. In differentiated O1 and O10 antigen-positive oligodendrocytes the channels characteristic of precursor cells were no longer observed, but an inwardly rectifying K+ current was apparent. Thus, channel expression by cells of the oligodendrocyte lineage correlates with differentiation stage and is more complex in precursor cells than in oligodendrocytes.

Qualitative and quantitative heterogeneity in Pgp-1 expression among murine thymocytes

A proportion of Pgp-1+ cells in the thymus have been shown to have progenitor activity. In adult AKR/Cum mice the total Pgp-1+ population in the thymus differs from that of the bulk of thymocytes and is antigenically heterogeneous when examined by flow cytometry. Pgp-1+ thymocytes are enriched for several minor cell populations compared to total thymocytes: B2A2-, interleukin-2-receptor+ (IL-2R+), and Lyt-2-, L3T4-. However, these subsets are still a minor proportion of the Pgp-1+ cells, the majority being Lyt-2+ and/or L3T4+ and B2A2+. Pgp-1+ thymocytes also differ from the bulk of thymocytes in having lower amounts of Thy-1 and in showing a higher proportion of single positive (Lyt-2+, L3T4- or Lyt-2-, L3T4+) cells. Populations of adult thymocytes that are enriched in progenitor cells can be isolated by cytotoxic depletion using either anti-Thy-1 antibody (Thy-1 depletion) or anti-Lyt-2 and anti-L3T4 antibody (Lyt-2, L3T4 depletion). Pgp-1+ cells in progenitor cell-enriched populations are also phenotypically heterogeneous. Pgp-1+ cells in both populations may be IL-2R+ or IL-2R- and B2A2+ or B2A2-. The population of Pgp-1+ cells in progenitor cell-enriched populations in the adult differs from that of the fetus at 14 days of gestation in that in the 14-day fetus, most Pgp-1+ cells are IL-2R+. By Day 15 of gestation, distinct populations of Pgp-1+, IL-2R-; Pgp-1+, IL-2R+; and Pgp-1-, IL-2R+ cells are observed. In the 15-day fetus, as in the adult, many Pgp-1+ thymocytes express low to moderate levels of Thy-1. The total percentage of Pgp-1+ cells in the thymus varies among different mouse strains, ranging from 4 to 35% in the thymus of young adult mice. Pgp 1.1 strains contain more detectably Pgp-1+ thymocytes than Pgp 1.2 strains; however, there is variability in the proportion of Pgp-1+ cells, even among Pgp 1.2 strains. In contrast to AKR/Cum mice, the Pgp-1+ thymocyte population in BALB/c mice, which contain a high proportion of Pgp-1+ thymocytes, closely resembles the total thymocyte population.