Ji, Baoan

Animal models of pancreatitis are useful for elucidating the pathogenesis of pancreatitis and developing and testing novel interventions. In this review, we aim to summarize the most commonly used animal models, overview their pathophysiology, and discuss their strengths and limitations. We will also briefly describe common animal study procedures and refer readers to more detailed protocols in the literature. Although animal models include pigs, dogs, opossums, and other animals, we will mainly focus on rodent models because of their popularity. Autoimmune pancreatitis and genetically engineered animal models will be reviewed elsewhere.

Abstract Pancreatic cancer, one of the most lethal forms of human cancer, is largely resistant to many conventional chemotherapeutic agents. Although many therapeutic approaches focus on tumor growth, metastasis is a primary factor contributing to lethality. Therefore, novel therapies to target metastatic invasion could prevent tumor spread and recurrence resulting from local and distant metastasis. The protein Vav1 is aberrantly expressed in more than half of pancreatic cancers. Its expression promotes activation of Rac and Cdc42 and leads to enhanced invasion and migration, as well as increased tumor cell survival and proliferation, suggesting that Vav1 could be a potent therapeutic target for pancreatic cancer. The purine analogue azathioprine, well known for its function as an anti-inflammatory compound, was recently shown to function by inhibiting Vav1 signaling in immune cells. We therefore hypothesized that azathioprine could also inhibit Vav1 in pancreatic tumor cells to reduce its proinvasive functions. Indeed, we have found that treatment of cultured pancreatic tumor cells with azathioprine inhibited Vav1-dependent invasive cell migration and matrix degradation, through inhibition of Rac and Cdc42 signaling. Furthermore, azathioprine treatment decreased metastasis in both xenograft and genetic mouse models of pancreatic cancer. Strikingly, metastasis was dramatically reduced in Vav1-expressing tumors arising from p48Cre/+, KrasG12D/+, p53F/+ mice. These inhibitory effects were mediated through Vav1, as Vav1-negative cell lines and tumors were largely resistant to azathioprine treatment. These findings demonstrate that azathioprine and related compounds could be potent antimetastatic agents for Vav1-positive pancreatic tumors. Cancer Res; 75(14); 2907–15. ©2015 AACR.

Hepatic stellate cells (HSCs) generate matrix, which in turn may also regulate HSCs function during liver fibrosis. We hypothesized that HSCs may endocytose matrix proteins to sense and respond to changes in microenvironment. Primary human HSCs, LX2, or mouse embryonic fibroblasts (MEFs) [wild-type; c-abl−/−; or Yes, Src, and Fyn knockout mice (YSF−/−)] were incubated with fluorescent-labeled collagen or gelatin. Fluorescence-activated cell sorting analysis and confocal microscopy were used for measuring cellular internalization of matrix proteins. Targeted PCR array and quantitative real-time PCR were used to evaluate gene expression changes. HSCs and LX2 cells endocytose collagens in a concentration- and time-dependent manner. Endocytosed collagen colocalized with Dextran 10K, a marker of macropinocytosis, and 5-ethylisopropyl amiloride, an inhibitor of macropinocytosis, reduced collagen internalization by 46%. Cytochalasin D and ML7 blocked collagen internalization by 47% and 45%, respectively, indicating that actin and myosin are critical for collagen endocytosis. Wortmannin and AKT inhibitor blocked collagen internalization by 70% and 89%, respectively, indicating that matrix macropinocytosis requires phosphoinositide-3-kinase (PI3K)/AKT signaling. Overexpression of dominant-negative dynamin-2 K44A blocked matrix internalization by 77%, indicating a role for dynamin-2 in matrix macropinocytosis. Whereas c-abl−/− MEF showed impaired matrix endocytosis, YSF−/− MEF surprisingly showed increased matrix endocytosis. It was also associated with complex gene regulations that related with matrix dynamics, including increased matrix metalloproteinase 9 (MMP-9) mRNA levels and zymographic activity. HSCs endocytose matrix proteins through macropinocytosis that requires a signaling network composed of PI3K/AKT, dynamin-2, and c-abl. Interaction with extracellular matrix regulates matrix dynamics through modulating multiple gene expressions including MMP-9.

Abstract Background: Obesity is postulated to be a major risk factor for pancreatic ductal carcinoma (PDAC), which is the fourth deadliest cancer in the US. Although the association between obesity and pancreatic cancer has been reported, the molecular mechanisms are not yet known. Since K-Ras mutations are almost universal in PDAC, and we have recently shown that endogenous levels of oncogenic K-Ras make cells susceptible to otherwise benign levels of inflammation, we hypothesize that high fat intake can act as a persistent low level inflammatory mechanism capable of inducing PDAC in cells expressing a single copy of oncogenic K-Ras. In the current study, we examined the effects of high dietary fat on the development of precancerous lesions and fibrosis, as well as the activation of K-Ras signaling pathways in mice expressing mutant K-Ras in pancreatic acinar cells. Methods: Transgenic mice LSL-K-Ras were cross with Ela-CreER (Pancreatic-Ras) and treated with tamoxifen to “knock-in” oncogenic K-Ras in adult pancreatic acinar cells. Pancreatic-Ras and littermate control mice were administered a low fat diet with 10.2% kcal fat or a high fat diet with 61.6% kcal fat for 30 days starting at 50 days of age. Mice were then sacrificed and analyzed histologically for fibrosis development, presence of precancerous lesions, and activation of K-Ras signaling pathways. Results: Mice expressing endogenous levels of oncogenic K-Ras and fed a high fat diet developed abundant fibrosis, low grade precancerous lesions throughout the pancreas and had higher levels of phospho-ERK when compared to littermate controls and mice fed a low fat diet. Conclusions: These findings suggest that consumption of high dietary fat acts as an inflammatory stimulus that enhances the activation of oncogenic K-Ras downstream signaling pathways, leading to the early development of precancerous lesions and fibrosis in the pancreas. Therefore, efforts aimed at inhibiting inflammation and K-Ras activation would be expected to prevent cancer development. Citation Format: Zobeida Cruz-Monserrate, Bincy Philips, Baoan Ji, Jaroslaw Daniluk, Craig D. Logsdon. High-fat diet accelerates development of precancerous lesions and fibrosis in mice expressing mutant K-Ras in pancreatic acinar cells. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B113.

Abstract Increased Ras activity levels due to active mutations of Ras are critical for tumorigenesis. These oncogenic Ras mutations are considered to be locked in a permanent “On” state and “constitutively active”. Yet, surprisingly, expression of oncogenic Ras at physiologically levels in genetically engineered mice with “knock-in” mutant Ras has little effect on most cells. Here, we demonstrated that oncogenic K-Ras is not at all constitutively active. Rather, oncogenic K-Ras can be readily activated by upstream stimulants such as diet-induced hormones (eg. Cholecystokinin) and inflammatory stimuli (eg. PGE2 or LPS). However, unlike wild-type Ras, oncogenic K-Ras is very slow to inactivate. This effect on oncogenic K-Ras signaling kinetics leads to dramatically amplified levels of Ras activity initiated by physiologic stimuli. Sustained increase of Ras activity involves a feed-forward loop in which increased Ras activity generates more inflammatory mediators which act as Ras stimulants. High Ras activity led to acinar cell senescence and generated inflammation and fibrosis resembling the histological features of chronic inflammation with abundant precancerous lesions that spontaneously progressed to cancer only in animals expressing physiologic levels of oncogenic Ras. In summary, oncogenic Ras is not constitutively active but predisposes cells to pathological alterations dependent upon Ras activity levels. Since a large population of normal healthy humans harbors Ras mutations, in addition to targeting Ras downstream signaling pathways a reduction of factors that can activate Ras signaling may provide an important alternative cancer preventive value. These data also provide a mechanistic explanation for the link between inflammation, Ras and cancer and provide insights for cancer prevention. Citation Format: Ji Baoan, Huang Haojie, Liu Yan, Daniluk Jaroslaw, Logsdon Craig. Targeting oncogenic Ras activation for cancer prevention. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A31.

Abstract Elevated Ras activity is critical for Ras induced tumorigenesis. However, the underlying mechanisms that lead to pathological levels of Ras activity are unclear. Here, we found that stimulation of Ras signaling by typical inflammatory stimuli was transient and had no long term sequelae in wild-type mice. In contrast, these stimuli generated prolonged Ras signaling and led to chronic inflammation and precancerous lesions (PanINs) in mice expressing endogenous levels of oncogenic K-Ras. The effects of inflammatory stimuli on oncogenic Ras expressing mice were disrupted by deleting IKK2 or inhibiting Cox-2. Likewise, the expression of active IKK2 or Cox-2, or treatments with LPS generated chronic inflammation and PanINs only in mice expressing oncogenic Ras. The data support that in the presence of oncogenic Ras, inflammatory stimuli trigger an NF-κB mediated positive feedback mechanism involving Cox-2 that amplifies Ras activity to pathological levels. Because a large portion of the adult human population possesses Ras mutations in tissues including colon, pancreas, and lung, disruption of this positive feedback loop may be an important strategy for cancer prevention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-425. doi:1538-7445.AM2012-LB-425