Smac mimetics cooperate with STING to induce necroptosis in apoptosis-resistant pancreatic carcinoma cells

Introduction Pancreatic cancer (PC) still remains a major cause of cancer-related death worldwide and alternative treatments are urgently required.

Aim A panel of PC cell lines were investigated to explore alternative strategies in cell death induction to overcome apoptosis resistance.

Method The Smac mimetic BV6, that neutralize inhibitors of apoptosis proteins (IAP), was applied in combination with the STING ligand 2´3´-cGAMP, and apoptosis was blocked by the pan-caspase inhibitor zVAD.fmk or by Caspase 8 silencing via CRISPR/Cas9-mediated gene knockout.

Result We demonstrated that the Smac mimetic BV6 cooperates with the stimulator of interferon (IFN) genes (STING) ligand 2´,3´-cyclic guanosine monophosphate-adenosine monophosphate (2´3´-cGAMP) to trigger necroptosis in PC cells, when apoptosis is blocked. Pharmacological inhibition of key components of necroptosis signaling, such as receptor-interacting protein (RIPK)1, RIPK3 and mixed lineage kinase domain-like pseudokinase (MLKL), significantly rescues PC cells from 2´3´-cGAMP/BV6/zVAD.fmk-mediated cell death suggesting the induction of necroptosis. Consistently, 2´3´-cGAMP/BV6 co-treatment promotes phosphorylation of MLKL. Furthermore, we show that 2´3´-cGAMP stimulates the production of type I IFNs which cooperate with BV6 to trigger necroptosis when caspase activity is blocked. STING silencing via siRNA or CRISPR/Cas9-mediated gene knockout protects PC cells from 2´3´-cGAMP/BV6/zVAD.fmk-mediated cell death. Interestingly, we demonstrate the involvement of NF-κB and IFN-regulatory factor 1 signaling in the execution of 2´3´-cGAMP/BV6/zVAD.fmk-induced necroptosis.

Conclusion We show that activated STING and Smac mimetics act together to exert antitumor effects on PC cells with important implications for the design of new PC treatment concepts.

Abb.1 STING and the Smac mimetic BV6 act together to induce necroptosis in PC cells

Publication History

Article published online:
07 September 2021