Assessing the role of ATF4 dependent signaling in limiting pancreatic cancer by tomatidine.
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Date
2022-03
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Abstract
BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC), comprising of 90% pancreatic cancer cases, is a highly aggressive cancer with a five-year survival rate of 10.8%. Current therapies include surgery and chemotherapy, which are mostly ineffective because of metastasis to different organs of the body and dysfunctional immune cell populations in the tumor microenvironment. Plant based metabolites have been used as chemotherapy agents to target cancer as a less toxic alternative therapeutic for several decades. Tomatidine, a natural metabolite present in the tomato plant, has anti-cancer and anti-inflammatory properties. Further, tomatidine is reported to inhibit Activating Transcription Factor 4 (ATF4) dependent signaling in a range of diseases such as skeletal muscle atrophy, dengue virus infection, neurons, and myoblasts. ATF4, a master regulator of cellular stress, has been implicated in different cancers including PDAC by promoting cancer cell survival, as well as by affecting anti-tumor immunity and inducing chemotherapy resistance.
HYPOTHESIS: Tomatidine can inhibit pancreatic cancer by regulating ATF4-dependent signaling.
METHODS: Miapaca-2 (human) and MT5 (mouse) pancreatic tumor cell lines were treated with tomatidine for 72 hours and assayed for cell growth. ATF4 and its downstream protein expressions were evaluated. Pancreatic cancer bearing immunocompetent mice and immunocompromised mice were treated with 5 mg/kg daily injections of tomatidine or vehicle control and monitored for tumor growth. RNA from the tumor bearing immunocompetent mice were assayed for ATF4 and related gene expression. ATF4 expression was silenced in human pancreatic cancer cells and assayed for cell growth. Further, healthy donor immune cells were treated with tomatidine in presence or absence of factors that help differentiate these cells into a dysfunctional immunosuppressive population called as myeloid derived suppressor cells (MDSCs). Quantity of MDSCs before and after treatment were compared along with assaying for ATF4 and related gene expression.
RESULTS: Tomatidine can inhibit pancreatic tumor growth in vitro (cell culture) and in vivo (in mice). However, there was little effect of tomatidine on tumor growth when pancreatic cancer cells were implanted into immunocompromised mice. Lack of an effect in an immunocompromised animal model suggests tomatidine may affect anti-tumor immunity. Treatment with tomatidine reduced expression of downstream protein p-4EBP1 (direct ATF4 target) in vitro. Tumor-bearing mice treated with tomatidine have reduced mRNA expression of ATF4 and downstream gene eIF4EBP1 compared to vehicle control treated animals. Further, reducing expression of ATF4 in MiaPaca-2 cells in vitro reduced cell viability. Tomatidine can affect the rate of MDSC differentiation without causing immune cell death and reduce expression of ATF4 and related gene expression in immune cells.
CONCLUSION: Tomatidine can inhibit pancreatic tumor growth and reduce ATF4 expression in PDAC and immune cells. Tomatidine can also affect the activity of immunosuppressive cells present in PDAC tumor microenvironment.
SIGNIFICANCE: Therefore, this study sheds light on a novel plant derived anti-cancer treatment strategy that targets an upregulated pathway (ATF4 dependent signaling) in pancreatic cancer and can be used to develop a new holistic therapeutic strategy for targeting both the pancreatic tumor and its microenvironment.
Description
Health Sciences: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
Pancreatic cancer, ATF4, Anti-tumor immunity, ER Stress, Tomatidine