Loss of PARP7 increases IFN-I signalling preventing pancreatic tumour growth by enhancing immune cell infiltration

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal forms of cancer, and despite low incidence rates, it remains the sixth leading cause of cancer related deaths worldwide. Immunotherapy, which aims to enhance the immune system’s ability to recognize and eliminate cancer cells, has emerged as a promising approach in the battle against PDAC. PARP7, a mono-ADP-ribosyltransferase, is a negative regulator of the type I interferon (IFN-I) pathway, thereby reducing antitumour immunity. By characterizing murine pancreatic cancer cells, we found that loss of PARP7 elevated the levels of interferon stimulated gene factor 3 (ISGF3) and its downstream target genes, even in the absence of STING. We also observed that cancer cells deficient in PARP7 resulted in smaller tumours when injected into wildtype mice. Transcriptomic analyses revealed that tumours knocked out for Parp7 (Parp7KO) had increased expression of genes involved in immunoregulatory interactions and interferon signalling pathways. Characterization of tumour infiltrating leukocyte (TIL) populations showed that Parp7KO tumours had higher proportions of natural killer cells, CD8+ T cells and a lower proportion of anti-inflammatory macrophages (M2). The overall TIL profile of Parp7KO tumours was suggestive of a better response to anti-PD-1 immune checkpoint therapy. Our data show that loss of PARP7 reduces PDAC tumour growth by increasing the infiltration of immune cells and enhancing antitumor immunity. These findings provide support to pursue PARP7 as a therapeutic target for PDAC CR705 cells derived from a spontaneous pancreatic tumour in a LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx1-Cre (KPC) mouse were used in this study. Total RNA was isolated from approximately 100 mg of tumours from CR705 WT or PARP7KO cells using the Aurum™ Total RNA isolation kit (BioRad) according to the manufacturer’s protocol.