Beneficial Diets and Pancreatic Cancer: Molecular Mechanisms and Clinical Practice

Raf/MEK/ERK Signaling Pathway Is Involved in the Inhibition of Glioma Cell Proliferation and Invasion in the Ketogenic Microenvironment

OBJECTIVE

A high-fat, low-carbohydrate ketogenic diet has been used to treat malignant glioma, in which the Raf/MEK/ERK signaling pathway is overactivated. However, whether the Raf/MEK/ERK signaling pathway is involved in the therapeutic effect of ketone bodies remains unknown. In this study, we investigated the effects of a major ketone body, 3-hydroxybutyric acid (3-HBA), on the proliferation and metastasis of malignant glioblastoma cells and the underlying mechanism.

METHODS

Two human malignant glioblastoma cell lines (U87 and U251) were treated with different concentrations of 3-HBA with or without the Raf inhibitor PAF C-16 for 24 h. Cell proliferation, cell cycle, cell invasion, and phospholipase D1 (PLD1) activity were determined. Protein and gene expression levels of Raf/MEK/ERK signaling pathway members were examined.

RESULTS

3-HBA significantly decreased cell proliferation, invasion, and intracellular PLD1 activity in both U87 and U251 glioblastoma cell lines. 3-HBA treatment significantly increased the proportion of cells in the G1 phase and decreased the proportion of cells in S phase in U87 cells. In the U251 line, the proportion of treated cells in S phase was increased and proportion of cells in G2 was decreased. 3-HBA treatment also significantly decreased the protein expression levels of Raf, MEK, p-MEK, ERK, p-ERK, and PLD1 while increasing p53 expression; an effect that was similar to treatment with the Raf inhibitor. Co-treatment of 3-HBA with the Raf inhibitor further enhanced the effects of the 3-HBA in both cell lines.

CONCLUSION

We confirmed that a ketogenic microenvironment can inhibit glioma cell proliferation and invasion by downregulating the expression of PLD1 through the Raf/MEK/ERK signaling pathway.

Bibliometric and visual analysis in the field of ketogenic diet on cancer from 2012 to 2021

Increasing evidence demonstrated that the ketogenic diet (KD) played a positive effect on cancer treatment. However, no systematic review and bibliometric analysis were conducted in this field. This study aimed to explore the current status, and reveal the potential trends and hotspots to provide a reference for future research. Publications were extracted from the Web of Science Core Collection. CiteSpace (5.6.R3) software and the website of bibliometrics were used for visual analysis. A total of 500 publications with 334 articles and 166 reviews were included, with the timespan of 2012 to 2021. The United States was the most productive country. Majority of the top 10 institutions were from the United States, and Harvard University was the top-contributing institution. The most prolific author and the co-cited author was Thomas N Seyfried from Boston College. The highest cited reference was published in PLoS ONE, authored by Abdelwahab Mohammed G, with 161 citations. Glioma and breast cancer were the most common types of cancer in this field, while hepatocellular carcinoma and pancreatic cancer were the new hotspots. The anti-tumor mechanism of KD mainly focused on regulating metabolism, decanoic acid, oxidative stress, fatty acid oxidation, and cell apoptosis. Additionally, the presence of "chemotherapy" and "radiotherapy" in the keywords indicated that KD combined with anti-tumor research was a topic, while "immunotherapy" has became a recent frontiers. Notably, as a metabolic therapy, KD was deserved more attention in the treatment of hepatocellular carcinoma and pancreatic cancer, and KD combined with immunotherapy was the new hotspot and frontier. Additionally, more molecular studies and high-quality uniformly, randomized, controlled clinical trials are urgently warranted to evaluate the effect of KD in multiple cancers.

Ketogenic HMG-CoA lyase and its product β-hydroxybutyrate promote pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDA) tumor cells are deprived of oxygen and nutrients and therefore must adapt their metabolism to ensure proliferation. In some physiological states, cells rely on ketone bodies to satisfy their metabolic needs, especially during nutrient stress. Here, we show that PDA cells can activate ketone body metabolism and that β-hydroxybutyrate (βOHB) is an alternative cell-intrinsic or systemic fuel that can promote PDA growth and progression. PDA cells activate enzymes required for ketogenesis, utilizing various nutrients as carbon sources for ketone body formation. By assessing metabolic gene expression from spontaneously arising PDA tumors in mice, we find HMG-CoA lyase (HMGCL), involved in ketogenesis, to be among the most deregulated metabolic enzymes in PDA compared to normal pancreas. In vitro depletion of HMGCL impedes migration, tumor cell invasiveness, and anchorage-independent tumor sphere compaction. Moreover, disrupting HMGCL drastically decreases PDA tumor growth in vivo, while βOHB stimulates metastatic dissemination to the liver. These findings suggest that βOHB increases PDA aggressiveness and identify HMGCL and ketogenesis as metabolic targets for limiting PDA progression.