Silibinin suppresses NPM-ALK, potently induces apoptosis and enhances chemosensitivity in ALK-positive anaplastic large cell lymphoma

Abstract

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), an oncogenic fusion protein carrying constitutively active tyrosine kinase, is known to be central to the pathogenesis of ALK-positive anaplastic large cell lymphoma (ALK(+)ALCL). Here, it is reported that silibinin, a non-toxic naturally-occurring compound, potently suppressed NPM-ALK and effectively inhibited the growth and soft agar colony formation of ALK(+)ALCL cells. By western blots, it was found that silibinin efficiently suppressed the phosphorylation/activation of NPM-ALK and its key substrates/downstream mediators (including STAT3, MEK/ERK and Akt) in a time- and dose-dependent manner. Correlating with these observations, silibinin suppressed the expression of Bcl-2, survivin and JunB, all of which are found to be upregulated by NPM-ALK and pathogenetically important in ALK(+)ALCL. Lastly, silibinin augmented the chemosensitivity of ALK(+)ALCL cells to doxorubicin, particularly the small cell sub-set expressing the transcriptional activity of Sox2, an embryonic stem cell marker. To conclude, the findings suggest that silibinin might be useful in treating ALK(+)ALCL.