Therapeutically Active RIG-I Agonist Induces Immunogenic Tumor Cell Killing in Breast Cancers

Abstract

Cancer immunotherapies that remove checkpoint restraints on adaptive immunity are gaining clinical momentum but have not achieved widespread success in breast cancers, a tumor type considered poorly immunogenic and which harbors a decreased presence of tumor-infiltrating lymphocytes. Approaches that activate innate immunity in breast cancer cells and the tumor microenvironment are of increasing interest, based on their ability to induce immunogenic tumor cell death, type I IFNs, and lymphocyte-recruiting chemokines. In agreement with reports in other cancers, we observe loss, downregulation, or mutation of the innate viral nucleotide sensor retinoic acid-inducible gene I (RIG-I/) in only 1% of clinical breast cancers, suggesting potentially widespread applicability for therapeutic RIG-I agonists that activate innate immunity. This was tested using an engineered RIG-I agonist in a breast cancer cell panel representing each of three major clinical breast cancer subtypes. Treatment with RIG-I agonist resulted in upregulation and mitochondrial localization of RIG-I and activation of proinflammatory transcription factors STAT1 and NF-κB. RIG-I agonist triggered the extrinsic apoptosis pathway and pyroptosis, a highly immunogenic form of cell death in breast cancer cells. RIG-I agonist also induced expression of lymphocyte-recruiting chemokines and type I IFN, confirming that cell death and cytokine modulation occur in a tumor cell-intrinsic manner. Importantly, RIG-I activation in breast tumors increased tumor lymphocytes and decreased tumor growth and metastasis. Overall, these findings demonstrate successful therapeutic delivery of a synthetic RIG-I agonist to induce tumor cell killing and to modulate the tumor microenvironment These findings describe the first in vivo delivery of RIG-I mimetics to tumors, demonstrating a potent immunogenic and therapeutic effect in the context of otherwise poorly immunogenic breast cancers..

RIG-I-based immunotherapy enhances survival in preclinical AML models and sensitizes AML cells to checkpoint blockade

“…Targeting RIG-I with ppp-RNA has been described in preclinical studies as a promising strategy in the treatment of various solid tumors [4,5,7,17,20,32]. However, no data exist suggesting similar efficacy for hematologic malignancies.…”

“…RIG-I-like receptor ligands have been used as a promising strategy for the treatment of solid malignancies including melanoma [4,5], pancreatic cancer [6] and breast cancer [7] in preclinical models and just recently qualified for a combined phase I/II study in patients with advanced solid tumors (NCT03065023). Serving as a cytoplasmic antiviral pattern recognition receptor, RIG-I senses short double-stranded RNAs with an uncapped 5′-triphosphate moiety (ppp-RNA), a common motif found in viral RNAs [8][9][10][11][12].…”

“…MAVS, once activated, assembles a downstream signaling complex culminating in the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and interferon regulatory factor 3/7 (IRF3/IRF7), resulting in the release of type I interferons (IFN) and proinflammatory cytokines (reviewed in Chow et al [16]). Furthermore, ppp-RNA has been shown to induce an immunogenic form of cell death (ICD) in different tumor entities [7,[17][18][19]. The cytokine release combined with direct sensing of viral RNA by immune cells leads to an adaptive cellular immune response directed against infected cells [4].…”

“…By applying an exogenous short ppp-RNA, a viral infection can be mimicked, allowing direction of the immune response towards otherwise altered or potentially harmful targets, such as cancerous cells. While this approach has shown survival benefits in different solid tumor models [4,6,7,20], the treatment efficacy of RIG-I ligands for non-solid tumors in vivo remains elusive. We therefore investigated the potential of ppp-RNA therapy for AML as an example of a hematological malignancy.…”

Harnessing the immune system to fight cancer with Toll-like receptor and RIG-I-like receptor agonists

“…RIG-I agonists are synthetic RNA oligonucleotides with specific phosphorylation patterns that have shown potent antitumoral effects in preclinical studies [19][20][21][22][23][24] . Interestingly, these agonists not only stimulate anticancer immune responses, but also have a pro-apoptotic effect in cancer cells 19 .…”