A monoclonal antibody against the c-erbB-2 protein enhances the cytotoxicity of cis-diamminedichloroplatinum against human breast and ovarian tumor cell lines.

A monoclonal antibody (TAb 250) specific to an extracellular epitope of the c-erbB-2 protein (gp185) inhibited the in vitro proliferation of human breast tumor cell lines that overexpress c-erbB-2 in a dose-dependent manner. Treatment of cells with combinations of cis-diammedichloroplatinum (CDDP) and TAb 250 resulted in a significantly enhanced cytotoxic effect. This synergistic cytotoxicity was apparent over a wide range of antibody concentrations (200 pg/ml-100 micrograms/ml) including concentrations that showed no inhibitory effect alone. TAb 250 did not increase the cytotoxic effect of CDDP in a cell line exhibiting no detectable level of gp185. Athymic mice bearing s.c. xenografts of human tumor cells expressing high levels of gp185 showed a greatly enhanced inhibition of tumor growth when treated with TAb 250 and CDDP compared to treatment with the antibody or CDDP alone. This effect was specific inasmuch as TAb 250 did not enhance the growth-inhibitory effect of CDDP on tumor xenografts which were not expressing gp185.

DNA amplification is rare in normal human cells.

Three types of normal human cells were selected in tissue culture with three drugs without observing a single amplification event from a total of 5 x 10(8) cells. No drug-resistant colonies were observed when normal foreskin keratinocytes were selected with N-(phosphonacetyl)-L-aspartate or with hydroxyurea or when normal mammary epithelial cells were selected with methotrexate. Some slightly resistant colonies with limited potential for growth were obtained when normal diploid fibroblast cells derived from fetal lung were selected with methotrexate or hydroxyurea but careful copy-number analysis of the dihydrofolate reductase and ribonucleotide reductase genes revealed no evidence of amplification. The rarity of DNA amplification in normal human cells contrasts strongly with the situation in tumors and in established cell lines, where amplification of oncogenes and of genes mediating drug resistance is frequent. The results suggest that tumors and cell lines have acquired the abnormal ability to amplify DNA with high frequency.

Immortalization in culture: occurrence at a late stage in the progression of breast cancer.

The properties in culture of 3 breast cancer effusion metastases, obtained over approximately 2 years from the same patient, were examined. Despite repeated attempts with cryopreserved cells, only the last specimen reproducibly exhibited immortality in culture; the first 2 specimens grew initially but failed to develop into cell lines. Each specimen was unique in morphology and growth properties, although karyotypic markers indicated a common origin. Aberrations of chromosomes 1 and 11 marked these near-diploid cells, and further structural alterations of chromosome 11 accompanied the transition of biological properties observed in the third specimen.

Invasiveness and ploidy of human mammary carcinomas in short-term culture.

Invasiveness and ploidy were examined in cultures of human epithelial cells derived from nonmalignant breast tissue, primary breast carcinomas, and breast cancer effusion metastases. Successful short-term culture was achieved from approximately 70% of the primary breast cancers. These primary cancers were essentially diploid by flow cytometry and karyotype in contrast to the effusion metastases, which were mostly aneuploid. The diploid tumor cells retained their malignant phenotype in culture as demonstrated by invasion into a denuded human amnion basement membrane. In contrast, epithelial cells cultured from nonmalignant mammary tissue did not invade the amnion. We suggest that the diploid carcinoma cultures may be useful for investigating the essential differences between normal and malignant cells and may complement information derived from studies of tumor cell lines with grossly aberrant karyotypes.

Phenotypic variability in anchorage-independent growth by a human breast tumor cell line.

Possible mechanisms responsible for expression of anchorage independence were investigated with the use of the human breast carcinoma cell line Hs578T. This phenotype was not stable and most likely occurred via alterations in gene expression, causing secretion of growth factor (s). Colony-forming efficiency in methylcellulose was proportional to initial plating density at low passage number and increased with passage in culture. At high passages, there was less sensitivity to initial plating density, suggesting less dependence on surrounding cells for feeding effects. Clonal variants isolated in methylcellulose maintained a higher plating efficiency when kept in suspension, and removal of selective pressure resulted in the loss of the high level of expression upon subsequent challenge in suspension. In contrast to other systems, anchorage-dependent clones acquired the ability to grow in methylcellulose after only one passage in culture. This suggests that rapid variation at rates not typical of classical somatic mutation plays a role in expression of anchorage independence. Exposure to 5-azacytidine, which decreases methylation of DNA and may thereby activate gene transcription, increased the incidence of anchorage-independent growth 20 times; whereas treatment with 6-azacytidine had no effect. Unconcentrated medium conditioned by cells previously exposed to 5-azacytidine or by cells at high passage stimulated growth in suspension by as much as 10.9 times. The factor(s) present in this conditioned medium was stable to heat up to 63 degrees C for 30 minutes and was larger than 12,000-14,000 mol wt as determined by dialysis.