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Supplemental Figure S1. Tumor origins and specifications and primary cell characterization.

Supplemental Figure S2. ESFT-1 response to enoxacin in vivo.

Supplemental Table S1. Target genes of 5 TARBP2-dependent miRNAs.

Immunotherapy is revolutionizing cancer treatment but is often restricted by toxicities. What distinguishes adverse events from concomitant antitumor reactions is poorly understood. Here, using anti-CD40-treatment in mice as a model of Th1-promoting immunotherapy, we showed that liver macrophages promoted local immune-related adverse events. Mechanistically, tissue-resident Kupffer cells mediated liver toxicity by sensing lymphocyte-derived IFN-𝛾 and subsequently producing IL-12. Conversely, dendritic cells were dispensable for toxicity but drove tumor control. IL-12 and IFN-𝛾 were not toxic themselves, but prompted a neutrophil response that determined the severity of tissue damage. We observed activation of similar inflammatory pathways following anti-PD-1 and anti-CTLA4 immunotherapies in mice and humans. These findings implicated macrophages and neutrophils as mediators and effectors of aberrant inflammation in Th1-promoting immunotherapy, suggesting distinct mechanisms of toxicity and antitumor immunity.

Plasticity in cancer stem–like cells (CSC) may provide a key basis for cancer heterogeneity and therapeutic response. In this study, we assessed the effect of combining a drug that abrogates CSC properties with standard-of-care therapy in a Ewing sarcoma family tumor (ESFT). Emergence of CSC in this setting has been shown to arise from a defect in TARBP2-dependent microRNA maturation, which can be corrected by exposure to the fluoroquinolone enoxacin. In the present work, primary ESFT from four patients containing CD133+ CSC subpopulations ranging from 3% to 17% of total tumor cells were subjected to treatment with enoxacin, doxorubicin, or both drugs. Primary ESFT CSC and bulk tumor cells displayed divergent responses to standard-of-care chemotherapy and enoxacin. Doxorubicin, which targets the tumor bulk, displayed toxicity toward primary adherent ESFT cells in culture but not to CSC-enriched ESFT spheres. Conversely, enoxacin, which enhances miRNA maturation by stimulating TARBP2 function, induced apoptosis but only in ESFT spheres. In combination, the two drugs markedly depleted CSCs and strongly reduced primary ESFTs in xenograft assays. Our results identify a potentially attractive therapeutic strategy for ESFT that combines mechanism-based targeting of CSC using a low-toxicity antibiotic with a standard-of-care cytotoxic drug, offering immediate applications for clinical evaluation. Cancer Res; 74(22); 6610–22. ©2014 AACR.