Inhibition of autophagy with chloroquine potentiates carfilzomib-induced apoptosis in myeloma cells in vitro and in vivo

• Carfilzomib induces apoptosis through Puma and Noxa up-regulation and interaction with Bax.
• Carfilzomib induces autophagy, which is disrupted as apoptosis progresses.
• Inhibition of autophagy potentiates carfilzomib-induced apoptosis in vitro and in vivo.
• Carfilzomib induces immunogenic cell death of myeloma cells.

The proteasome inhibitor bortezomib is now the cornerstone of combination therapy of multiple myeloma (MM). Carfilzomib, a second-generation inhibitor, has shown a substantial benefit vs bortezomib in combination regimes. Here we have analyzed in detail the mechanism of cell death induced by carfilzomib and its crosstalk with autophagy and applied the results to the in vivo treatment of MM in a mouse model. Carfilzomib induced apoptosis essentially by the intrinsic pathway, through the up-regulation of Puma and Noxa proteins followed by the interaction of Puma, Noxa and Bim with Bax and of Noxa with Bak. Carfilzomib also produces an increase in the formation of autophagosomes but, as apoptosis progresses, autophagy is disrupted, probably owing to Beclin 1 and p62 inactivation. Cotreatment with chloroquine, which blocks autophagy, strongly potentiated apoptosis in vitro and in vivo. Accordingly, combination therapy with carfilzomib plus chloroquine was highly effective in the treatment of MM in a mouse xenograft model. Chloroquine also enhanced carfilzomib-induced calreticulin exposure in MM cells undergoing apoptosis, increasing the immunogenic ability of carfilzomib. These results support design of trials combining carfilzomib with chloroquine to improve MM therapy.