New xenografts of human megakaryoblastic cell line (MEG-01) for evaluating anti-tumor agents

A human megakaryoblastic cell line (MEG-01) was successfully transplanted into athymic nude mice. MEG-01 cells (5 x 10(7)) were inoculated subcutaneously in KSN-nu/nu mice, none of which were pretreated with irradiation or chemotherapeutic agents. All mice developed solid tumors at the site of injection after incubation for 10-14 days reaching a size of 200-400 mm2 (product of cross-sectional diameters) after 30 days. These tumors, designated as MEG-01/nu, were transplanted into other nude mice. The transplanted tumors infiltrated the liver and spleen, and leukemic megakaryoblastic cells appeared in the blood of some transplanted mice. Cells resuspended from MEG-01/nu tumors exhibited almost the same megakaryocytic characteristics as the original MEG-01 cells, and underwent in vitro differentiation to a mature form of megakaryocyte upon addition of phorbol diesters. MEG-01/nu was evaluated for sensitivity to cytosine arabinoside, vincristine, and daunorubicin in vitro and in vivo. Daunorubicin exhibited significant anti-tumor activity against MEG-01/nu in vivo, while cytosine arabinoside did so in vitro. Vincristine showed no activity against these cells. This cell line may provide a useful model for testing the in vivo efficacy of anti-tumor agents and immunotoxins, and for studying the pathophysiological mechanisms of human megakaryoblastic leukemia.