Research paperHomoharringtonine enhances bortezomib antimyeloma activity in myeloma cells adhesion to bone marrow stromal cells and in SCID mouse xenografts

•Co-culture with bone marrow stroma can induce Bortezomib resistance in U266 cells.•Activated NF-κB signaling pathway plays a vital role in Bortezomib resistance.•HHT enhances anti-myeloma effects of Bortezomib both in vitro and in vivo.

Despite the great progress in the treatment, multiple myeloma (MM) still remains incurable. Bortezomib (BTZ), a reversible inhibitor of the 26S proteasome, is very effective against MM but unable to eradicate the MM cells in bone marrow niche eventually causing the disease relapse. Homoharringtonine (HHT) is a known anti-leukemia drug that inhibits MM both in vitro and in vivo. This study aimed to investigate whether HHT could potentiate the anti-tumor activity of BTZ in MM cells cocultured with bone marrow stromal cells and in vivo xenograft models. We found that coculture of myeloma cells with a human stroma cell line significantly decreased the sensitivity of myeloma cells to BTZ treatment. HHT inhibited the proliferation of MM cells and potentiated the anti-myeloma effects of BTZ by inhibition of both canonical and noncanonical NF-κB pathways. HHT also enhanced the anti-myeloma effect of BTZ in vivo xenograft models. Taken together, our data suggest that HHT can enhance the anti-myeloma activity of BTZ both in vitro and in vivo, which may represent a new clinical treatment in MM.