[Anti-CD20 monoclonal antibody RTX enhances radiosensitivity of lymphoma cells]

This study was aimed to investigate the effects of rituximab (RTX), a chimeric human anti-CD20 monoclonal antibody, on lymphoma cell injury induced by X ray irradiation. The human Burkitt EBV-infected and moderate radioresistance lymphoma cells (Namalwa) were used in the this study. Cytotoxicity of rituximab combined with X ray irradiation on Namalwa cells was measured by sulforhodamine B (SRB)-staining; the apoptosis of Namalwa cells was detected by flow cytometry with FITC-Annexin V/PI double staining; the morphologic changes of cells were observed under transmission electron microscope (TEM) and the change of intracellular free calcium level ([Ca(2+)]i) in response to irradiation and rituximab was determined by means of the fluorescent dye fluo-3 and confocal microscopy. The results showed that the growth inhibition in Namalwa cells exposed to irradiation was enhanced by treatment with rituximab. Compared with irradiation alone, rituximab combined with irradiation significantly induced the cell apoptosis and a sustained rise of intracellular free calcium ([Ca(2+)]i) level in Namalwa cells; the serial apoptotic appearances of cells could be observed under TEM. It is concluded that rituximab can enhance the sensitivity of lymphoma cells on X ray irradiation as to induce cell more apoptosis, in this process the intracellular free calcium ([Ca(2+)]i), as an intracellular signaling molecule probably plays an important role.