Activation of Host-NLRP3 Inflammasome in Myeloid Cells Dictates Response to Anti-PD-1 Therapy in Metastatic Breast Cancers.

Tumor-associated inflammation leads to dysregulated cytokine production that promotes tumor immune evasion and anti-tumor immunity dysfunction. In advanced stage breast cancer, the proinflammatory cytokine IL-1β is overexpressed due to large proportions of activated myeloid cells in the tumor microenvironment (TME). Here, we demonstrate the role of the host nucleotide-binding domain, leucine-rich containing family, pyrin domain-containing 3 (NLRP3) inflammasome in metastatic breast cancer. In vitro, we show that stimulation of THP-1 cells with conditioned media collected from MDA-MB-468 cells induced NLRP3 activation and increased Pdcd1l1 expression. In vivo, mice deficient in NLRP3 orthotopically implanted with metastatic breast cancer cell line (E0771) showed significant reduction in tumor growth ( p < 0.05) and increased survival ( p < 0.01). Inhibition of NLRP3 with the small molecule OLT1177 ® reduced expression of Pdcd1l1 ( p < 0.001), Casp1 ( p < 0.01) and Il1b ( p < 0.01) in primary tumors. Furthermore, tumor-bearing mice receiving OLT1177 ® showed reduced infiltration of myeloid-derived suppressor cells (MDSCs) ( p < 0.001) and increased CD8 + T cells ( p < 0.05) and NK cells ( p < 0.05) in the TME. NLRP3 inhibition in addition to anti-PD-1 treatment significantly reduced tumor growth from the monotherapies ( p < 0.05). These data define NLRP3 activation as a key driver of immune suppression in metastatic breast cancers. Furthermore, this study suggests NLRP3 as a valid target to increase efficacy of immunotherapy with checkpoint inhibitor in metastatic breast cancers.