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Pim-2 kinase is overexpressed in multiple myeloma (MM) cells, and regarded as an important therapeutic target. Here, we aimed to validate the therapeutic efficacy of different types of Pim inhibitors against MM cells for their possible clinical application. Intriguingly, the thiazolidine-2,4-dione-family compounds SMI-16a and SMI-4a reduced Pim-2 protein levels and impaired MM cell survival preferentially in acidic conditions, in contrast to other types of Pim inhibitors, including AZD1208, CX-6258 and PIM447. SMI-16a also suppressed the drug efflux function of breast cancer resistance protein, minimized the sizes of side populations, and reduced in vitro colony forming capacity and in vivo tumorigenic activity in MM cells, suggesting impairment of their clonogenic capacity. Pim-2 is known to be subject to ubiquitination-independent proteasomal degradation. Consistently, the proteasome inhibitors bortezomib and carfilzomib increased Pim-2 protein levels in MM cells without affecting its mRNA levels. However, SMI-16a mitigated the Pim-2 protein increase and cooperatively enhanced anti-MM effects in combination with carfilzomib. Collectively, the thiazolidine-2,4-dione-family compounds SMI-16a and SMI-4a uniquely reduce Pim-2 protein in MM cells, which may contribute to their profound efficacy in addition to their immediate kinase inhibition. Their combination with proteasome inhibitors is envisioned.


  • British Journal of Haematology

    British Journal of Haematology 180(2), 246-258, 2018-01-12

    John Wiley & Sons Ltd


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