Pancreatic Ductal Adenocarcinoma Cells Regulate NLRP3 Activation to Generate a Tolerogenic Microenvironment

Abstract

Defining feature of pancreatic ductal adenocarcinoma (PDAC) that participates in the high mortality rate and drug resistance is the immune-tolerant microenvironment which enables tumors to progress unabated by adaptive immunity. In this study, we report that PDAC cells release CSF-1 to induce nucleotide-binding domain, leucine-rich containing family, pyrin domain-containing-3 (NLRP3) activation in myeloid cells. Increased NLRP3 expression was found in the pancreas of PDAC patients when compared to normal pancreas which correlated with the formation of the NLRP3 inflammasome. Using human primary cells and an orthotopic PDAC mouse model we show that NLRP3 activation is responsible for the maturation and release of the inflammatory cytokine interleukin-1β (IL-1β) which selectively drives Th2-type inflammation via COX2/PGE2 induction. As a result of this inflammation, primary tumors were characterized by reduced cytotoxic CD8+ T cell activation and increased tumor expansion. Genetic deletion and pharmacological inhibition of NLRP3 enabled the development of Th1 immunity, increased intratumoral levels of IL 2, CD8+ T cell–mediated tumor suppression, and ultimately limited tumor growth. Additionally, we observed that NLRP3 inhibition in combination with gemcitabine significantly increased the efficacy of the chemotherapy. In conclusion, this study provides a mechanism by which tumor-mediated NLRP3 activation exploits a distinct adaptive immunity response that facilitates tumor escape and progression. Considering the ability to block NLRP3 activity with safe and small orally active molecules, this protein represents a new promising target to improve the limited therapeutic options in PDAC.

The Co-Localization of NLRP3 and ASC Specks Does Not Automatically Entail NLRP3 Inflammasome Functionality in PDAC Cell Lines

“…A high expression of ASC protein is often used as a marker for inflammasome formation in multiple types of cancer [21,31,[43][44][45][46][47][48][49]. The ASC protein levels [13] and PYCARD gene expression [50] (Figure 5e) were increased in the PDAC tissue, but our results imply that the ASC amount alone may be a poor marker for inflammasome formation.…”

“…Upon inflammasome activation, ASC polymerizes into a large speck-like structure, which functions as a scaffold for caspase-1 cleavage and activation, a process which also requires the intracellular redistribution of ASC [11,12]. The formation of ASC specks is therefore often used as a readout for inflammasome formation [13].…”