Suppression of double-stranded RNA sensing in cancer: molecular mechanisms and therapeutic potential.

Immunotherapy has emerged as a therapeutic option for many cancers. For some tumors, immune checkpoint inhibitors show great efficacy in promoting anti-tumor immunity. However, not all tumors respond to immunotherapies. These tumors often exhibit reduced inflammation and are resistant to checkpoint inhibitors. Therapies that turn these 'cold' tumors 'hot' could improve the efficacy and applicability of checkpoint inhibitors, and in some cases may be sufficient on their own to promote anti-tumor immunity. One strategy to accomplish this goal is to activate innate immunity pathways within the tumor. Here we describe how this can be accomplished by activating double-stranded RNA (dsRNA) sensors. These sensors evolved to detect and respond to dsRNAs arising from viral infection but can also be activated by endogenous dsRNAs. A set of proteins, referred to as suppressors of dsRNA sensing, are responsible for preventing sensing 'self' dsRNA and activating innate immunity pathways. The mechanism of action of these suppressors falls into three categories: (1) Suppressors that affect mature RNAs through editing, degradation, restructuring, or binding. (2) Suppressors that affect RNA processing. (3) Suppressors that affect RNA expression. In this review we highlight suppressors that function through each mechanism, provide examples of the effects of disrupting those suppressors in cancer cell lines and tumors, and discuss the therapeutic potential of targeting these proteins and pathways.