Characterization of three B-cell lymphoma cell lines from chemotherapy resistant patients with respect to in vitro sensitivity to 21 antitumor agents, ABC-transporter expression and cellular redox status.

The aim of this study was to characterize three new, recently established non-Hodgkin lymphoma cell lines (GUMBUS, DOGUM, and DOGKIT), isolated from patients developing high-clinical resistance to cytotoxic therapy, with respect to sensitivity toward 21 antitumor drugs from different classes of action, expression of three ABC transporters: P glycoprotein (Pgp) (MDR1 and ABCB1), multidrug resistance related proteins (MRP1) (ABCC1), and MRP2 (ABCC2), as well as a range of antioxidative enzymes and glutathione (GSH). The results were compared to analogous data from the well-known HL-60 and U-937 cells. The MTT assay was used to measure cell growth inhibitory activity. Transporter expression was determined by using an electrophoresis/Western blot system. GSH and enzyme activities were measured by employing functional assays with photometric detection. Pre-incubation with hydrogen peroxide was chosen as a model for oxidative stress. Based on the 50% growth inhibitory values (GI(50) values) of 21 known antitumor agents, the cell lines were sensitive again to chemotherapeutics after being in culture for at least 15-18 weeks. DOGUM and DOGKIT were most sensitive toward antitumor drugs in in vitro cytotoxicity assays while DOGUM was the least sensitive. None of the cell lines expressed measurable levels of any of the three transporters investigated and showed only moderate variation in their antioxidative defense system. After pre-treatment with hydrogen peroxide, GSH peroxidase (GPx) activity increased and, in general, a decrease in the growth inhibitory activities of various platinum antitumor agents occurred. Furthermore, all three cell lines rapidly acquired resistance to doxorubicin, methotrexate, and cisplatin again in vitro after only 3-5 treatment cycles with the respective drug. The therapy-resistant lymphoma cell lines GUMBUS, DOGUM, and DOGKIT were sensitive to antitumor agents once again after they had been established in culture. However, their sensitivity to antitumor agents can be rapidly decreased in vitro by either introducing the cells to culture conditions favoring oxidative stress or by exposing the cells at regular intervals to an antitumor drug. The ability of these three cell lines to quickly adapt to toxic insults in their environment is probably the reason why clinical resistance occurred.