Brefeldin A Induces Apoptosis, Inhibits BCR-ABL Activation, and Triggers BCR-ABL Degradation in Chronic Myeloid Leukemia K562 Cells

Background: Chronic Myeloid Leukemia (CML) is a myeloproliferative disease caused by BCR-ABL oncoprotein. Tyrosine kinase inhibitors have been developed to inhibit the activity of BCR-ABL; however, drug resistance and side effect occur in clinic application. Therefore, it is urgent to find novel drugs for CML treatment. Under the guidance of cytotoxic activity, crude extracts of 55 fungal strains from the medicinal mangrove Acanthus ilicifolius were evaluated, and one potent cytotoxic natural compound, brefeldin A (BFA), was discovered from Penicillium sp. (HS-N-29). Objective: This study was aimed to determine the cytotoxic activity of BFA and the effect on the activation and expression of BCR-ABL in K562 cells. Methods: We evaluated cytotoxic activity by MTT assay and soft agar clone assay; apoptosis and cell cycle distribution by Muse cell analyzer. The protein level of BCR-ABL and signaling molecules was detected by western blotting, and the mRNA level of BCR-ABL was determined by RT-PCR. Results: BFA inhibited cell proliferation, induced G2/M cell cycle arrest, and stimulated cell apoptosis in K562 cells. Importantly, for the first time, we revealed that BFA inhibited the activation of BCR-ABL and consequently inhibited the activation of its downstream signaling molecules in K562 cells. Moreover, we found BFA degraded BCR-ABL without affecting its transcription in K562 cells, and BFA-induced BCR-ABL degradation was related to caspase activation, while not to autophagy or ubiquitinated proteasome degradation pathway. Conclusion: Our present results indicate that BFA acts as a dual functional inhibitor and degrader of BCR-ABL, and BFA is a potential compound for chemotherapeutics to overcome CML.