Topoisomerase II levels and drug response in small cell lung cancer

Acquired resistance to chemotherapy is the major obstacle to cure of small cell lung cancer (SCLC). Some of the most active drugs in the treatment of this tumor exert their cytotoxicity by interacting with the nuclear enzyme topoisomerase II (topo II), which in mammalian cells occurs in two isoforms, alpha and beta. We examined the relationship between levels of topo II alpha and beta and drug response in a panel of 25 unselected SCLC cell lines. Chemosensitivity to several topo II-interactive drugs, as well as other chemotherapeutic agents, was quantitated previously using a modified MTT assay. Topo II levels were determined by immunoblot analysis of whole cell lysates, with topo II alpha and beta isoform-specific antibodies, and results were expressed relative to levels found in NCI-H209 cells which had the highest topo II alpha in this series of cell lines. Levels of topo II alpha and beta mRNA were determined by Northern blotting. Pearson correlation analysis was used to determine the significance of the relationship between topo II alpha and beta levels and response to the various chemotherapeutic drugs, as well as the treatment history of the patients from whom the cell lines were derived. These analyses revealed an inverse correlation between topo II alpha levels and resistance to all of the tested drugs, including several drugs which are not known to interact with topo II. This correlation was statistically significant for doxorubicin, cisplatin, epirubicin, melphalan, nitrogen mustard, and vinblastine. With one exception (cisplatin), there were no significant correlations between topo II beta levels and drug response. There was no significant correlation between topo II alpha and beta levels and treatment history. Taken together, our results are consistent with the hypothesis that levels of topo II alpha are important determinants of drug response in SCLC.

Cellular and karyotypic characterization of two doxorubicin resistant cell lines isolated from the same parental human leukemia cell line

Separate mechanisms underlying the multidrug resistant (MDR) phenotype were identified in 2 independent approaches to select tumour cells resistant to low concentrations of doxorubicin (Dox) from the sensitive T cell leukemia cell line CCRF-CEM. The CEM/A7 cell line was selected at an initial concentration of 0.005 microgram/ml of Dox and maintained at 0.07 microgram/ml. In contrast, the CEM/A5 line was selected using an initial concentration of 0.01 microgram/ml and maintained in Dox at a concentration of 0.05 microgram/ml. P-glycoprotein expression was demonstrated in the CEM/A7 line but not the CEM/A5 line. Amplification of the mdrI gene was not observed in the CEM/A7 cell line. Both cell lines showed cross-resistance to a number of structurally unrelated cytotoxic drugs including anthracyclines and etoposide (VP-16), although only the CEM/A7 line was cross resistant to Vinca alkaloids. Immunoblots of total cell lysates of the CEM/A5 line have revealed almost undetectable levels of topoisomerase II alpha and beta in this line. Cytogenetic analyses of both lines revealed numerous karyotypic abnormalities which were present in the parental cell line as well as both resistant cell lines. The CEM/A7 line also demonstrated a duplication of part of the long arm of chromosome 7 which included the region containing the mdrI gene, a finding not seen in the parental or CEM/A5 line. CEM/A5, however, demonstrated an abnormality of chromosome 7, outside the region of the mdrI gene, and it also contained a deletion of the short arm of chromosome 2. Abnormalities in this latter region of genome have been associated with non-P-glycoprotein-mediated MDR.

Differential expression of the Leu-7 antigen on human lung tumor cells

The HNK-1 monoclonal antibody detects an antigen (Leu-7) on a subpopulation of large granular lymphocytes which have natural killer cell function. Recently this antigen has been found on nonhemopoietic tissues. In the present study human lung tumor cells were examined for the presence of Leu-7 antigen using an enzyme-linked immunosorbent assay, immunoperoxidase staining, and fluorescence-activated cell sorter analysis. All small cell lung tumor cells tested were Leu-7 positive. In contrast only two of seven biopsy specimens from small cell lung cancer patients were Leu-7 positive. Several large cell lung tumor lines were Leu-7 positive while an adenocarcinoma and squamous cell carcinoma were negative. These results indicate that expression of Leu-7 antigen on lung tumor cells is heterogeneous both in vitro and in vivo. Small cell lung tumor lines have been reported to undergo histological conversion in vitro accompanied by the loss of a number of biochemical markers. In our study histologically converted cells exhibited much less reactivity with HNK-1 than did the parent cells. These results indicate that the degree of expression of Leu-7 antigen may be under the control of differentiation-related events. Thus monoclonal antibody HNK-1 has been very useful in studying heterogeneity within and among lung tumor cells.

Regulation of lymphoblast traffic and localization in mucosal tissues, with emphasis on IgA

A fundamentally important factor in the expression of immunity at mucosal sites is the migration of primed lymphocytes to, from, and among mucosal tissues. Despite considerable information in recent years on the selective localization of B lymphoblasts, especially those destined to make IgA antibodies in mucosal tissues, the basis for this remains obscure. Several cell-associated factors such as surface characteristics, histo-compatibility type, and organ derivation of the cells play a significant role for T and B lymphoblast localization. Factors that regulate lymphoblast delivery to tissues, such as blood flow, or control emigration from tissues, such as arachidonic acid metabolites, are discussed. Finally, factors such as the presence or absence of high endothelial venules, isotype-specific T helper cells, sex hormones, antigen, macrophages, and iron all may play a significant role in mucosal lymphoblast localization.