Spliceosome inhibition induces Z-RNA and ZBP1-driven Cell Death in Small Cell Lung Cancer

Spliceosome inhibitors emerged as promising anticancer agents. Recent studies have demonstrated that spliceosome targeted-therapies (STTs) trigger antitumor immune responses by inducing the accumulation of right-handed double-stranded (ds)RNA (A-RNA), resulting in activation of RIG-I-like receptors and Type I interferon-driven antiviral responses. Here, we show that pharmacological spliceosome inhibition or genetic neutralization of SF3B1 activity induces the accumulation of endogenous left-handed dsRNAs (Z-RNAs) derived from intron-retained RNAs. These Z-RNAs activate the Z-form nucleic acid-sensor ZBP1, which triggers cell death in mouse embryonic fibroblasts (MEFs) and small cell lung cancer (SCLC) cells. Spliceosome inhibition induced potent ZBP1-dependent cell death in cancer-associated fibroblasts (CAFs), which was essential for enhancing immunotherapy response in mouse models of SCLC. Collectively, these results demonstrate that spliceosome inhibitors or STTs, can be used to generate Z-RNA and trigger on-demand ZBP1-dependent cell death in cells of the tumor microenvironment (TME) as a therapeutic strategy to enhance immunotherapy responses in resistant-cancers. To elucidate the Z-RNA species accumulated post spliceosome perturbation, we treated EV MEFs with DMSO or Pladienolide B (PlaB) for 18 hours followed by Z22-antibody RNA immunoprecipitation.