Antigens associated with multidrug resistance in H69AR, a small cell lung cancer cell line

In a previous study (S.E.L. Mirski et al., Cancer Res., 47: 2594-2598, 1987), we described the derivation of a multidrug-resistant small cell lung cancer cell line, H69AR. The H69AR cell line does not over-express P-glycoprotein and is therefore a useful model for the investigation of alternate mechanisms of drug resistance. In this paper we report the production and preliminary characterization of six murine monoclonal antibodies (MAbs) which react selectively with the H69AR cell line compared to its drug-sensitive parent cell line, NCI-H69. One of these antibodies, MAb 2.54, detects a cell surface epitope and reacts with multiple proteins of molecular weight 24,500-34,500 on immunoblots. Non-cell surface membrane-associated epitopes are detected by the other five antibodies, MAbs 3.50, 3.80, 3.177, 3.187, and 3.186. MAbs 3.50 and 3.186 immunoprecipitate antigens of molecular weight 55,000 and 36,000, respectively, while MAbs 3.80, 3.177, and 3.187 all precipitate a molecular weight 47,000 protein, suggesting that they may detect epitopes on the same antigen. The epitopes detected by all six antibodies are present on greater than 80% of H69AR cells, as determined by flow cytometry. With the exception of MAb 2.54, the MAbs cross-react in an enzyme-linked immunosorbent assay with the multidrug-resistant human fibrosarcoma cell line HT1080/DR4. Thus, these MAbs react with two drug-resistant cell lines derived from different tumor types in which overexpression of P-glycoprotein is undetectable. These MAbs may detect novel markers for drug resistance and thus may have potential diagnostic or therapeutic value.