Differentiation-inducing and growth-inhibitory activities of erythroid differentiation factor (EDF/activin A) toward mouse erythroleukemic cells in vivo

The in vivo differentiation-inducing activity of a purified human erythroid differentiation factor (EDF) toward mouse erythroleukemic cells (MEL cells) was examined. BDF₁ mice with diffusion chambers implanted in the peritoneal cavity were treated with continuous i.p. administration of EDF. MEL cells within a diffusion chamber differentiated into hemoglobin-positive cells when treated with EDF, the percentage of the positive cells being 32.3 ± 28.3 on day 5 as compared to 0.2 ± 0.3 in the controls. The anti-tumor activity of EDF was also examined in a nude mouse MEL solid tumor model. Daily intra-tumor treatment with EDF for 10 days resulted in 73% suppression of tumor growth on day 25. A histological study revealed that EDF-treated solid tumor cells became hemoglobin-positive, indicating the anti-tumor activity of EDF through induction of differentiation in vivo. EDF could induce in vitro the differentiation of human erythroleukemic cell lines K562 and HEL, as well as the murine cell line. These results indicate the possibility of differentiation therapy for erythroleukemia using EDF.