[Bortezomib and obatoclax for dual blockade of protein degradation pathways show synergistic anti-tumor effect in human acute T lymphoblastic leukemia cells].

OBJECTIVE

To explore whether bortezomib and a Bcl-2 inhibitor exhibit synergistic anti-tumor effect in human acute T lymphoblastic leukemia cells.

METHODS

MTT assay was used to determine the cytotoxicity of bortezomib in the absence or presence of Bcl-2 inhibitors (obatoclax, AT-101 and ABT-199) in Jurkat cells. The effects of drug treatment on the expression of Bcl-2 family proteins, LC3B, p62, ubiquitin, BiP/Grp78, p-JNK, p-p38 and CHOP proteins were examined by Western blotting. Flow cytometry was used to determine the effects of bortezomib and Bcl-2 inhibitors (obatoclax, AT-101 and ABT-199) on cell apoptosis. Quantitative real-time PCR was used to measure the mRNA expression levels of the key regulatory factors of unfolded protein reaction (UPR). A zebrafish xenograft model was used to study the anti-tumor effect of bortezomib, obatoclax and their combination in vivo.

RESULTS

Bortezomib or Bcl-2 inhibitors alone inhibited the cell viability of Jurkat cells, but only obatoclax and bortezomib showed synergistic cytotoxicity and pro-apoptotic effect. Obatoclax, rather than AT-101 and ABT- 199, blocked autophagic flux in the cells evidenced by concomitant accumulation of LC3B-Ⅱ and p62. Both bortezomib and obatoclax alone caused accumulation of polyubiquinated proteins, and their combination showed a synergistic effect, which was consistent with their synergistic cytotoxicity. The dual blockade of proteasome and autophagy by the combination of bortezomib and obatoclax triggered unfolded protein response followed by cell apoptosis. Preventing UPS dysfunction by tauroursodeoxycholic acid (TUDCA) significantly attenuated the cytotoxicity and pro-apoptotic effect of bortezomib in combination with obatoclax. In zebrafish xenograft models, bortezomib combined with obatoclax significantly decreased tumor foci formation.

CONCLUSIONS

Bortezomib and obatoclax for dual blockade of protein degradation pathways show synergistic anti-tumor effect in human acute T lymphoblastic leukemia cells.