Rituximab synergizes with hydroxyurea or vincristine in the killing of Ramos Burkitt's lymphoma B cell line.

Rituximab is an effective immunotherapy for CD20-positive B-cell non-Hodgkin's lymphoma. However, some patients show resistance, particularly those suffering from more aggressive lymphoma types, such as Burkitt's lymphoma. Hence, Rituximab is commonly combined with several chemotherapeutic drugs. With a view to reduce the number of such drugs, we examined the effect of combining Rituximab individually with hydroxyurea, vincristine, or etoposide on the killing of Ramos Burkitt lymphoma cell line type I. Cell death was examined by using Annexin-V/propidium iodide staining. Combining Rituximab with hydroxyurea or vincristine resulted in a synergistic effect, whereas combining it with etoposide resulted in a subadditive effect. In single treatments, the percentage of cell death ranged from 23% (Rituximab) to 36% (hydroxyurea). Combining Rituximab with hydroxyurea or vincristine resulted in a synergistic effect (83% and 74% killing, respectively). In contrast, only a subadditive effect was noticed with etoposide (36%). We conclude that the synergistic effect of Rituximab with hydroxyurea or vincristine is worthy of further study, and that further in vitro screening of chemotherapeutics might identify chemo-immunotherapeutic combinations that are effective in vivo but less toxic than currently used regimens.