Brentuximab vedotin (ADCETRIS®) is an antibody-drug conjugate (ADC) directed against CD30. This ADC consists of monoclonal antibodies conjugated to the auristatin monomethyl auristatin E (MMAE) a microtubule-disrupting agent. ADC antitumor activity is thought to be primarily the result of intracellular payload release leading to mitotic arrest and apoptotic cell death. We have recently demonstrated that brentuximab vedotin induces surface expression of calreticulin and HSP70 as well as activation of the transcription factor ATF6 which are classical hallmarks of immunogenic cell death (ICD) associated with unfolded protein/ER stress response. In this study, we provide evidence that additional ER stress response pathways are activated.

Treatment of CD30+ Hodgkin lymphoma (HL) cells or xenografts with brentuximab vedotin resulted in the phosphorylation of the ER-associated, unfolded-protein response transmembrane protein inositol-requiring transmembrane kinase/endonuclease 1 (IRE1). Activation of IRE1 was confirmed by the increase in phosphorylation of the downstream effector Jun N-terminal kinase (JNK). Kinetics of tubulin disruption, ER stress induction, evidence of ICD, mitotic arrest, and apoptosis was assessed. Onset of ICD occurred concurrently with induction of ER stress response pathways including induction of pIRE1 and pJNK. Interestingly, induction of ER stress response and ICD preceded mitotic arrest and caspase activation. These results indicate that brentuximab vedotin-mediated disruption of the microtubule network contributes to ER stress, which maybe an apoptotic mechanism mediated by auristatin-ADCs in addition to mitotic arrest at G2/M phase of the cell cycle. Induction of ICD may also be a class effect of the auristatin-based ADCs, as the small molecule payload MMAE, was able to activate IRE1 and JNK and induced surface expression of calrecutilin on target cells.

Previously, brentuximab vedotin-killed HL cells were shown to induce innate immune cell activation in vitro and in vivo. Addition of ADC-killed tumor-like cells to autologous PBMCs results in the expansion of INFã-secreting cytotoxic T-cells. Via induction of ER stress, tumor cells killed by auristatin-based ADCs may initiate an antitumor immune response and provides a rationale for exploring therapeutic strategies that combine ADCs with other immune stimulatory regimens.

Citation Format: Anthony Cao, Ryan Heiser, Che-Leung Law, Shyra J. Gardai. Auristatin-based antibody drug conjugates activate multiple ER stress response pathways resulting in immunogenic cell death and amplified T-cell responses. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4914.