Preclinical Development Obatoclax Interacts Synergistically with the Irreversible Proteasome Inhibitor Carfilzomib in GC- and ABC-DLBCL Cells In Vitro and In Vivo

Interactions between the irreversible proteasome inhibitor carfilzomib and the pan-BH3 mimetic obatoclax were examined in germinal center (GC)and activated B-cell–diffuse large B-cell lymphoma (ABC-DLBCL) cells. Cotreatment with minimally toxic concentrations of carfilzomib (i.e., 2–6 nmol/L) and subtoxic concentrations of obatoclax (0.05–2.0mmol/L) synergistically increased apoptosis inmultipleDLBCL cell lines and increased lethality toward primary human DLBCL but not normal CD34þ cells. Synergistic interactions were associated with sharp increases in caspase-3 activation, PARP cleavage, p-JNK induction, upregulation of Noxa, and AKT dephosphorylation. Combined treatment also diminished carfilzomib-mediated Mcl-1 upregulation whereas immunoprecipitation analysis revealed reduced associations between Bak and Mcl1/Bcl-xL and Bim and Mcl-1. The carfilzomib/obatoclax regimen triggered translocation, conformational change, and dimerization of Bax and activation of Bak. Genetic interruption of c-jun-NH2-kinase (JNK) and Noxa by short hairpin RNA knockdown, ectopic Mcl-1 expression, or enforced activation of AKT significantly attenuated carfilzomib/obatoclax-mediated apoptosis. Notably, coadministration of carfilzomib/obatoclax sharply increased apoptosis inmultiple bortezomib-resistant DLBCLmodels. Finally, in vivo administration of carfilzomib and obatoclax to mice inoculated with SUDHL4 cells substantially suppressed tumor growth, activated JNK, inactivated AKT, and increased survival compared with the effects of single-agent treatment. Together, these findings argue that a strategy combining carfilzomib and obatoclax warrants attention in DLBCL. Mol Cancer Ther; 11(5); 1122–32. 2012 AACR.