Protein kinase D1 - A targetable mediator of pancreatic cancer development

Members of the Protein kinase D (PKD) kinase family each play important cell-specific roles in the regulation of normal pancreas functions. In pancreatic diseases PKD1 is the most widely characterized isoform with roles in pancreatitis and in induction of pancreatic cancer and its progression. PKD1 expression and activation increases in pancreatic acinar cells through macrophage secreted factors, Kirsten rat sarcoma viral oncogene homolog (KRAS) signaling, and reactive oxygen species (ROS), driving the formation of precancerous lesions. In precancerous lesions PKD1 regulates cell survival, growth, senescence, and generation of doublecortin like kinase 1 (DCLK1)-positive cancer stem cells (CSCs). Within tumors, regulation by PKD1 includes chemoresistance, apoptosis, proliferation, CSC features, and the Warburg effect. Thus, PKD1 plays a critical role throughout pancreatic disease initiation and progression.

Inflammatory and alternatively activated macrophages independently induce metaplasia but cooperatively drive pancreatic precancerous lesion growth

The innate immune system has a key role in pancreatic cancer initiation, but the specific contribution of different macrophage populations is still ill-defined. While inflammatory (M1) macrophages have been shown to drive acinar-to-ductal metaplasia (ADM), a cancer initiating event, alternatively activated (M2) macrophages have been attributed to lesion growth and fibrosis. Here, we determined cytokines and chemokines secreted by both macrophage subtypes. Then, we analyzed their role in ADM initiation and lesion growth, finding that while M1 secrete TNF, CCL5, and IL-6 to drive ADM, M2 induce this dedifferentiation process via CCL2, but the effects are not additive. This is because CCL2 induces ADM by generating ROS and upregulating EGFR signaling, thus using the same mechanism as cytokines from inflammatory macrophages. Therefore, while effects on ADM are not additive between macrophage polarization types, both act synergistically on the growth of low-grade lesions by activating different MAPK pathways.

Abstract 4775: Knockout of Sod2 accelerates KrasG12D-driven formation of pancreatic cancerous lesions

Recent studies demonstrate that mitochondrially-generated reactive oxygen species (ROS) downstream of oncogenic KRAS drive acinar-to-ductal metaplasia (ADM), a key first step in the pancreatic ductal adenocarcinoma (PDA) progression model. MnSOD/SOD2 is a mitochondrial enzyme that converts superoxide into hydrogen peroxide. Previous studies have shown that SOD2 is biologically relevant to the study of pancreatic cancer. Some patients with a SOD2 polymorphism resulting in less active MnSOD at the mitochondrial matrix are at increased risk of developing pancreatic cancer. Additionally, MnSOD is lost in high-grade human PanIN, further suggesting a role in tumor development. To elucidate the role of MnSOD in pancreatic cancer initiation and progression, we crossed Sod2lox/lox mice into the p48Cre;LSL-KrasG12D (KC) mouse model. We found increased ROS, abundantly more abnormal tissue development and presence of flat lesions indicating accelerated early progression. However, Kaplan Meyer survival analysis of KC and KC;Sod2−/− mice did not indicate faster progression to cancer, suggesting that for later steps additional signaling is needed. In summary, we identify MnSOD as a key antioxidant molecule preventing initiation of PDA.

Citation Format: Alicia K. Fleming Martinez, Brandy H. Edenfield, Irene Esposito, Peter Storz. Knockout of Sod2 accelerates KrasG12D-driven formation of pancreatic cancerous lesions. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4775.

Ym1+ macrophages orchestrate fibrosis, lesion growth, and progression during development of murine pancreatic cancer

Desmoplasia around pancreatic lesions is a barrier for immune cells and a hallmark of developing and established pancreatic cancer. However, the contribution of the innate immune system to this process is ill-defined. Using the KC mouse model and primary cells in vitro, we show that alternatively activated macrophages (AAM) crosstalk with pancreatic lesion cells and pancreatic stellate cells (PSCs) to mediate fibrosis and progression of lesions. TGFβ1 secreted by AAM not only drives activation of quiescent PSCs but also in activated PSCs upregulates expression of TIMP1, a factor previously shown as crucial in fibrosis. Once activated, PSCs auto-stimulate proliferation via CXCL12. Furthermore, we found that TIMP1/CD63 signaling mediates PanIN lesion growth and TGFβ1 contributes to a cadherin switch and drives structural collapse of lesions, indicating a potential progression step. Taken together, our data indicate TGFβ1 produced by Ym1+ AAM as a major driver of processes that initiate the development of pancreatic cancer.

Dysfunctional EGFR and oxidative stress-induced PKD1 signaling drive formation of DCLK1+ pancreatic stem cells

Doublecortin-like kinase 1 (DCLK1)-positive pancreatic cancer stem cells develop at a precancerous stage and may contribute to the lack of efficacy of pancreatic cancer therapy. Although PanIN cells express oncogenic KRas and have an increased activity of epidermal growth factor receptor (EGFR), we demonstrate that, in DCLK1⁺ PanIN cells, EGFR signaling is not propagated to the nucleus. Mimicking blockage of EGFR with erlotinib in PanIN organoid culture or in p48^cre;Kras^G12D mice led to a significant increase in DCLK1⁺ PanIN cells. As a mechanism of how EGFR inhibition leads to formation of DCLK1⁺ cells, we identify an increase in hydrogen peroxide contributing to activation of Protein Kinase D1 (PKD1). Active PKD1 then drives stemness and abundance of DCLK1⁺ cells in lesions. Our data suggest a signaling mechanism that leads to the development of DCLK1⁺ pancreatic cancer stem cells, which can be exploited to target this population in potential therapeutic approaches.

Mimicking and Manipulating Pancreatic Acinar-to-Ductal Metaplasia in 3-dimensional Cell Culture

The differentiation of acinar cells to ductal cells during pancreatitis and in the early development of pancreatic cancer is a key process that requires further study. To understand the mechanisms regulating acinar-to-ductal metaplasia (ADM), ex vivo 3D culture and differentiation of primary acinar cells to ductal cells offers many advantages over other systems. With the technique herein, modulation of protein expression is simple and quick, requiring only one day to isolate, stimulate or virally infect, and begin culturing primary acinar cells to investigate the ADM process. In contrast to using basement membrane matrix, the seeding of acinar cell clusters in collagen I extracellular matrix, allows acinar cells to retain their acinar identity before manipulation. This is vital when testing the contribution of various components to the induction of ADM. Not only are the effects of cytokines or other ectopically administered factors testable through this technique, but the contribution of common mutations, increased protein expression, or knockdown of protein expression is testable via viral infection of primary acinar cells, using adenoviral or lentiviral vectors. Moreover, cells can be re-isolated from collagen or basement membrane matrix at the endpoint and analyzed for protein expression.