Protein-based cellular therapeutics have been limited by getting molecules into cells and the fact that many proteins require accurate cellular localization for function. Cytoplasmic transduction peptide (CTP) is a newly designed transduction peptide that carries molecules across the cell membrane with a preference to localize in the cytoplasmic compartment and is, therefore, applicable for cytoplasmic targeting. The Bcr-Abl fusion protein, playing major causative role in chronic myeloid leukemia (CIVIL), is a cytoplasmic oncoprotein that contains an N-terminus oligomerization domain (013) mediating homodimerization of Bcr-Abl proteins, and an intact CD in Bcr-Abl is required both for the activation of its transforming activity and tyrosine kinase. Therefore, disrupting Bcr-Abl oligomerization represents a potential therapeutic strategy for inhibiting Bcr-Abl oncogenicity. In this study, we explored the possible homodimerization-disrupting and tyrosine kinase inhibiting effect of the transduction of OD in Bcr-Abl positive K562 cells. By expressing in Escherichia coli a CTP-OD-HA fusion protein followed by Ni+-NTA affinity purification, immunoblot identification and enterokinase cleavage, we showed that the CTP-OD-HA protein was structurally and functionally active in that it potently transduced and primarily localized into the cytoplasmic compartment, heterodimerized with Bcr-Abl, and potently inhibited the phospho-tyrosine pathways of Bcr-Abl oncoprotein at a low concentration of 4 mu M. These results delineate strategies for the expression and purification of therapeutic molecules for intracytoplasmic protein based therapeutics and the CTP-OD-HA-mediated killing strategy could be explored as a promising anti-leukemia agent or an adjuvant to the conventional therapeutic modalities in chronic myeloid leukemia, such as in vitro purging. (C) 2008 Elsevier Inc. All rights reserved.