Many studies have shown that metformin inhibits the tumor development of various cancer such as lung, breast, colon, and pancreatic cancer

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Long noncoding RNAs (lncRNAs) are a group of nonprotein coding transcripts that play a critical role in cancer progression. However, the role of lncRNA in metformin-induced inhibition of cell growth and its biological function in gastric cancer remain largely unknown. In this study, we identified an oncogenic lncRNA, Loc100506691, the expression of which was decreased in gastric cancer cells with metformin treatment. Moreover, Loc100506691 was significantly overexpressed in gastric cancer compared with adjacent normal tissues (p < 0.001), and high Loc100506691 expression was significantly correlated with poor survival of patients with gastric cancer. Additionally, Loc100506691 knockdown could significantly suppress gastric cancer cell growth in vitro, and ectopic Loc100506691 expression accelerated tumor growth in an in vivo mouse model. Analysis of the cell cycle revealed that Loc100506691 knockdown induced cell cycle arrest at the G2/M phase by impairing cell entry from the G2/M to G1 phase. Loc100506691 negatively regulated CHAC1 expression by modulating miR-26a-5p/miR-330-5p expression, and CHAC1 knockdown markedly attenuated Loc100506691 knockdown-induced gastric cancer cell growth and motility suppression. We concluded that anti-proliferative effects of metformin in gastric cancer may be partially caused by suppression of the Loc100506691-miR-26a-5p/miR-330-5p-CHAC1 axis.

 

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Introduction​

Gastric cancer is one of most the common malignancies and is the third leading cause of cancer-related mortality worldwide.
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Early gastric cancer has no associated symptoms and is often diagnosed at an advanced stage. Despite efforts, not much improvement has been observed in surgical techniques, chemotherapy, and radiochemotherapy, and the prognosis of advanced gastric cancer remains poor.
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Therefore, further investigation of the molecular mechanisms of gastric cancer progression is crucial for developing an effective therapy.
Metformin is an antidiabetic drug for type2 diabetes with a safe tolerability profile. Retrospective studies have demonstrated that the antidiabetic drug metformin has a potential antitumor effect because a significant reduction in the risk of malignancy has been observed in patients with diabetes treated with metformin.
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Many studies have shown that metformin inhibits the tumor development of various human cancer cell types, such as those of lung,
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breast,
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colon,
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and pancreatic cancer.
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Furthermore, studies have revealed that metformin inhibits cellular proliferation, induces cell death, and causes partial cell cycle arrest in gastric cancer.
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Long noncoding RNAs (lncRNAs) are a group of nonprotein coding transcripts more than 200 bp in length.
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They have been demonstrated to participate in several biological functions by modulating complicated signaling pathways, such as those responsible for chromosome dosage compensation, imprinting, epigenetic regulation, cell cycle control, nuclear and cytoplasmic trafficking, transcription, translation, splicing, and cell differentiation.
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Several lncRNAs were observed to be deregulated in a wide variety of gastric cancers. lncRNA MALAT1 was observed to promote cell proliferation by recruiting SF2/ASF and be overexpressed in gastric cancer.
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HOTAIR was upregulated in gastric carcinoma tissues compared with adjacent normal gastric tissues,
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and the overexpression of HOTAIR in gastric cancer cells resulted in the enhancement of metastases of the liver in vivo.
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Overexpression of lncRNA H19 enhances cell proliferation and invasion of gastric cancer cells.
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Moreover, lncRNA CCAT1 is markedly increased in gastric carcinoma, promotes cell proliferation and migration, and is activated by c-Myc.
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Studies have demonstrated that metformin regulates the expression of two ncRNAs in cancer cells, namely HULC and H19. Thus, lncRNA HULC is overexpressed in hepatocellular carcinoma, and a decrease in its expression can be observed in hepatocellular carcinoma cells treated with metformin. In addition, the knockdown of HULC can inhibit cell growth and motility ability.
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The H19 is a potential oncogenic lncRNA in many types of human cancer.
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Furthermore, a report revealed a positive relationship between H19 expression and tumor cell motility ability, and metformin downregulates H19 in part by inducing DNA methylation.
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However, the antitumor role of lncRNA in patients with gastric cancer undergoing metformin treatment is also largely unknown.
In this study, we comprehensively profiled the expression of lncRNAs in gastric cancer cells after metformin treatment by adopting a microarray approach. We identified an oncogenic lncRNA, Loc100506691, which was significantly increased in patients with gastric cancer and could be suppressed after metformin treatment, suggesting that the antiproliferation effects of metformin in gastric cancer cells might result from the modulation of Loc100506691-miR-26a-5p/miR-330-5p-CHAC1 axis signaling.

 

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Results​

Metformin inhibited gastric cancer cell proliferation and invasion ability​

Studies have revealed that metformin can inhibit cell proliferation in human cancer cells, including lung, breast, colon, and pancreatic cancer cells.
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We evaluated the effects of metformin treatment in three human gastric cells (AGS, HR, and TSGH) by applying metformin treatment of various concentrations (0, 1, 5, and 10 mM) for 4 days. In Figures S1A–S1C, the growth of gastric cancer cells was significantly suppressed in a dose-dependent manner. The invasion ability was also suppressed in gastric cancer cells with metformin treatment (Figures S1D–S1F). The distribution of the cell cycle was examined in HR cells with metformin treatment. Our data indicated that HR cells with metformin treatment could significantly induce cell cycle arrest at the G2/M phase (Figures S1G and S1H). Expression levels of cell-cycle-related protein expression noticeably decreased after metformin treatment (Figures S1I and S1J). In summary, our results demonstrated that metformin could significantly inhibit gastric cancer growth by impairing cell cycle progression.