Background: Prolactinoma is the most common hormone-secreting pituitary adenoma. Dopamine receptor agonists (DAs) are effective in reducing prolactin levels and tumor mass, but some prolactinoma patients are resistant to DAs. Treating patients with DA-resistant prolactinoma is challenging. In this study, we examined the anti-prolactinoma effect of artesunate (ART), a potential new treatment option for prolactinoma, and its mechanism of action.Methods: Cell Counting Kit-8 (CCK8) and flow cytometry were used to detect the effect of ART on the proliferation, cycle, and apoptosis of rat pituitary adenoma cell line MMQ. The subcellular localization of ART was observed using confocal fluorescence microscopy. The JC-1 mitochondrial membrane potential (MMP) detection and Seahorse assays were used to detect the effect of ART on mitochondrial function.Real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis were used to detect the effect of ART on the expression of prolactin (PRL) and apoptosis-related proteins. A mouse xenograft model of prolactinoma was used to detect the inhibitory effect of ART on MMQ in vivo.Results: ART specifically inhibited MMQ proliferation and PRL synthesis, induced G0/G1 phase arrest and apoptosis in vitro. ART accumulated in the mitochondria of MMQ cells, inhibiting mitochondrial respiratory function and mediating apoptosis through the mitochondrial pathway. ART also inhibited proliferation and activated the apoptosis of MMQ cells in vivo.Conclusions: ART has a strong inhibitory effect on prolactinoma both in vitro and in vivo, and its effects rely on high MMP to inhibit mitochondrial metabolism and induce apoptosis. Our results provide evidence for ART as a candidate drug for the treatment of prolactinoma.
Background: Growth hormone (GH)-secreting pituitary adenomas can be divided into densely and sparsely granulated subtypes, based on electron microscopic studies. The latter are frequently associated with more invasive behavior, and respond worse to somatostatin analogues. The underlining mechanisms are largely unknown. Increasing evidence showed that N6-methyladenosine (m6A) of messenger RNAs (mRNAs) participated in the development of various tumors. We aimed to investigate the role of RNA m6A modification in the classification of GH-secreting pituitary adenomas. Methods: The main components of m6A methyltransferase complex, demethylase, and RNA m6A levels were compared between sparsely and densely GH-secreting tumors. The role of METTL3 was functionally studied. Results: The level of m6A methyltransferases (METTL3, WTAP and METTL14) and demethylase (FTO and ALKBH5) were significantly downregulated in GH adenomas, comparing to the normal pituitary tissues. However, only METTL3 and METTL14 were shown to significantly higher in densely granulated tumors than those in sparsely ones. Consistently, the level of RNA m6A was markedly increased in densely granulated GH adenomas. In addition, the expression of METTL3 was positively correlated with the level of RNA m6A among tumor samples, and METTL3 silencing decreased RNA m6A of GH3 cells. METTL3 was demonstrated to function as a tumor suppressor based on in vivo and in vitro evidence, using patient-derived and GH3 cells. Moreover, the sensitivity of GH3 cells to pasireotide was increased with METTL3 overexpression, but decreased when METTL3 was silenced. Consistently, METTL3 silencing inhibited GH secretory, and decreased the expression of SSTR2 and SSTR5. Conclusions: METTL3 functions as a tumor suppressor in GH secreting adenomas, and enhance tumor cells sensitivity to medical treatment. Our work uncovers the critical roles of METTL3 in the pathogenesis of GH adenomas, since it potentially promotes the transition from sparsely to densely granulated subtypes.
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