Tetracycline-induced expression of an anti-c-Myb single-chain antibody andits inhibitory effect on proliferation of the human leukemia cell line K562

Ablation of c-Myb function might be an effective approach for the therapy o f chronic myelogenous leukemia or other c-myb-dependent malignancies. To th is end, we have previously used an intracellular anti-c-Myb single-chain an tibody (sFv) to achieve the functional knockout of the c-Myb oncoprotein. I n this study, we have employed a tetracycline-inducible system to control t he expression of the sFv. A nuclear-localizing form of an anti-c-Myb sFv wa s cloned into a tet-regulated plasmid vector. Using a transient expression system in COS-1 cells, we observed that doxycycline (Dox) induced expressio n of the sFv in a dose-dependent manner, and that the sFv was localized mai nly in the nucleus. The Dox-induced anti-c-Myb sFv also inhibited the trans activating activity of c-Myb in a dose-dependent manner. We subsequently co nfirmed the Dox-induced expression of the sFv in the leukemia cell line K56 2. Proliferation of the target leukemia cells was also inhibited. These res ults suggest that the anti-c-Myb sFv may represent a viable method for gene therapy of c-myb-dependent hematopoietic malignancies.