ROR2 regulates cellular plasticity in pancreatic neoplasia and adenocarcinoma

Cellular plasticity is a hallmark of pancreatic ductal adenocarcinoma (PDAC) starting from the conversion of normal cells into precancerous lesions to the progression of carcinoma subtypes associated with aggressiveness and therapeutic response. We discovered that normal acinar cell differentiation, maintained by the transcription factor Pdx1, suppresses a broad gastric cell identity that is maintained in metaplasia, neoplasia, and the classical subtype of PDAC in mouse and human. We have identified the receptor tyrosine kinase Ror2 as marker of a gastric metaplasia (SPEM)-like identity in the pancreas. Ablation of Ror2 in a mouse model of pancreatic tumorigenesis promoted a switch to a gastric pit cell identity that largely persisted through progression to the classical subtype of PDAC. In both human and mouse pancreatic cancer, ROR2 activity continued to antagonize the gastric pit cell identity, strongly promoting an epithelial to mesenchymal transition, conferring resistance to KRAS inhibition, and vulnerability to AKT inhibition.

Arginase 1 is a key driver of immune suppression in pancreatic cancer

An extensive fibroinflammatory stroma rich in macrophages is a hallmark of pancreatic cancer. In this disease, it is well appreciated that macrophages are immunosuppressive and contribute to the poor response to immunotherapy; however, the mechanisms of immune suppression are complex and not fully understood. Immunosuppressive macrophages are classically defined by the expression of the enzyme Arginase 1 (ARG1), which we demonstrated is potently expressed in pancreatic tumor-associated macrophages from both human patients and mouse models. While routinely used as a polarization marker, ARG1 also catabolizes arginine, an amino acid required for T cell activation and proliferation. To investigate this metabolic function, we used a genetic and a pharmacologic approach to target Arg1 in pancreatic cancer. Genetic inactivation of Arg1 in macrophages, using a dual recombinase genetically engineered mouse model of pancreatic cancer, delayed formation of invasive disease, while increasing CD8+ T cell infiltration. Additionally, Arg1 deletion induced compensatory mechanisms, including Arg1 overexpression in epithelial cells, namely Tuft cells, and Arg2 overexpression in a subset of macrophages. To overcome these compensatory mechanisms, we used a pharmacological approach to inhibit arginase. Treatment of established tumors with the arginase inhibitor CB-1158 exhibited further increased CD8+ T cell infiltration, beyond that seen with the macrophage-specific knockout, and sensitized the tumors to anti-PD1 immune checkpoint blockade. Our data demonstrate that Arg1 drives immune suppression in pancreatic cancer by depleting arginine and inhibiting T cell activation.

Abstract B052: Uncovering the lineage of chemosensory cells in the progression of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is predicted to become the second leading cause of cancer-related death in 2025 and has a 5-year survival rate of only 11%. Progression of the pancreatic disease is in part driven by the transdifferentiation of acinar cells into metaplastic ducts in the pancreas. Metaplastic tuft cells (MTCs) are a specialized subset of the metaplastic epithelium that has the potential to drive tumor progression through communication with the microenvironment and modulate PDA progression. Also known as solitary chemosensory cells, tuft cells were first discovered in rodent luminal surfaces, including the nose, stomach, intestine, and bladder, more than 60 years ago. They are characterized by the “tuft” of microvilli reaching into the lumen and, only recently, have studies started to determine the role of normal tuft cells in different organs. These studies determined that tuft cells have different roles depending on the organ in which they reside. Tuft cells are found in several different organs during normal development; however, studies have shown that tuft cells are not present in a normal pancreas. MTCs are only present in the pancreas in PanINs during PDA progression in both humans and mice. Furthermore, the population of MTCs in the pancreas disappears as PDA progresses into invasive carcinoma when using canonical markers of tuft cells. We know little about the role of MTCs in the pancreas, but prior studies have suggested their role as a progenitor cell during PDA. However, these studies do not exclusively mark MTCs during their genesis in a progressive model of PDA due to a lack of a mouse model as well as the complexity of culturing them ex vivo. We have generated a unique mouse model to drive lineage tracing of MTCs during PDA, and I have preliminary data to suggest that MTCs are not disappearing as PDA progresses but can transdifferentiate into another cell type that is correlated with lower survival in patients.

Citation Format: Daniel Salas-Escabillas, Howard Crawford, Megan Hoffman. Uncovering the lineage of chemosensory cells in the progression of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B052.