GBM is the most aggressive type of brain tumour with a poor prognosis29. Hence, the development of molecular mechanisms of GBM is essential. Melatonin axis signaling plays a wide role in the development and progression of cancer30. As reported previously, melatonin reduces the morbidity and associated mortality of fatal viral infections, including COVID-19, due to its antioxidant, anti-inflammatory, and immunomodulatory activities31. The relationship between melatonin and GBM has rarely been explored, moreover, melatonin-based molecular subtypes in tumor repertoires was less frequent. In the present study, we made a comprehensive summarization of melatonin regulator genes via in silico analysis. We found that these signatures were significantly dysregulated in GBM and were associated with genomic and epigenetic modification. According to the expression pattern of these signatures, GBM patients could be subgrouped into two significantly different melatonin-associated subtypes (Cluster 1 and Cluster 2). Compared with Cluster 1, the Cluster 2 exhibited higher tumor mutation burden, and poorer survival. Furthermore, we established a reliable risk model based on subtype biomarkers and validated the model using external datasets.
Melatonergic system axis signaling have a synergistic anti-tumor effect with targeted therapy or immunotherapy. We compared the gene expression of the two clusters, we created a scoring model, called MT-RGs score (risk score), indicating that the higher the MT-RGs score, the worse the prognosis. Our results show remarkable differences in genomic alterations between the low-risk and high-risk groups, with the expression of ECE1, CYP1B1, IRAK1, being higher in the high-risk group, while the expression of ACHE and SIRT1 was higher in the low-risk group. As, previous studies, CircNDC80 promotes GBM multiforme tumorigenesis via the miR-139-5p/ECE1 pathway32, and ECE1 along with PODXL, ICAM1, ALCAM1, CD97, and CD44 contributing to breast cancer chemotherapy evasion and metastatic seeding33. Qimei Lin et al. reported that increased CYP1B1 expression in prostate cancer cells could promote tumor progression34. A study by Chao Xi et al. showed that miR-146a-5p enhances tumor epithelial-mesenchymal transition through disinhibition of the TRAF6-IRAK1 complex and IKK-dependent NF-κB signaling pathway35. Besides its role in synaptic transmission, ACHE also regulates multiple oncogenic signaling pathways involved in the classic function of tumors, as Kai Wang et al. proposed expression of the ACHE gene can significantly inhibit the proliferation of liver cancer cells in xenograft model36. A study by Tan et al. showed that SRT1720 inhibits bladder cancer growth by inhibiting the SIRT1-HIF pathway37. These results suggest that these MT-RGs have certain carcinogenic or anti-tumor functions to some extent. The effectiveness of MT-RGs score was also confirmed using CGGA datasets. Nonetheless, more datasets are needed in the future to verify the effectiveness of the model.
Both univariate and multivariate Cox regression analysis showed that MT-RGs score was an independent predictor of survival outcome in GBM patients. The ROC validated its predictive robustness for 3-, 5- and 7-year OS. Thus, MT-RGs score may have reliable predictive power for GBM patient prognosis. We also analyzed the correlation between MT-RGs score and immune cell infiltration. The results suggested that MT-RGs score was strongly correlated with immune cells. Neutrophils were markedly more abundant in high-risk cohort, while abundance of activated NK cells was significantly higher in low-risk cohort. Those cells played complex roles in tumor immunity. For example, a study suggested that enhanced neutrophils activity was associated with increased levels of IL-12p70 and correlated with worse patient outcome38. Ji Liang et al. also found that neutrophils promote glioma growth via induction of S100A4 expression in glioma cells39. NK cells have crucial roles in the innate immunosurveillance of cancer. The ex vivo activation, expansion and genetic modification of NK cells can greatly increase their anti-tumor activity and equip them to overcome resistance40. Laughney AM et al. found metastatasizing lung adenocarcinoma cells that express high levels of the transcription factor SOX9 can better evade NK cell-mediated killing, due to increased MHC-I expression, whereas SOX2high cells were more sensitive to NK cell attack, through downregulation of MHC-I and upregulation of activating receptor ligands41. Poznanski SM et al. found expansion of NK cells with IL-21 or treatment with an activator of the Nrf2 antioxidant pathway promote Warburg-like metabolism with increased glycolysis and reduced oxidative phosphorylation, resulting in substantially improved resistance to the oxidatively stressed and nutrient-deprived TME and enhanced antitumour responses42. The above results revealed that immune monitoring function of patients in high-risk group was weakened, which was conducive to immune escape.
The resistance to chemotherapy in GBM is the most important cause of recurrence43,44. Melatonin possesses the capability to sensitize various cancers, such as breast, lung, colon, hepatic, and hematologic cancers to the effects of antineoplastic agents like anthracyclines, alkylating agents, tyrosine kinase inhibitors, endogenous factors such as TNF-α, TRAIL, and FAS, as well as ionizing radiation45. The development of resistance to chemotherapy in GBM is often a problem for physicians and patients. GBM patients with lower MT-RGs score were more sensitive to Temozolomide, Cisplatin, Cytarabine, Doxorubicin, Eesclomol, Eoposide, Gemcitabine, Methotrexate, Mitomycin, Nilotinib, Temsirolimus, Viblastine, Vorinostat and multiple chemotherapeutic drugs. As in previous studies, co-treatment of melatonin with vorinostat promotes the therapeutic sensitivity of GBM by inhibiting the expression of transcription factor EB46. Our findings may provide more evidence for the follow-up study of MT-RGs and tumor resistance, which may help to reduce drug resistance and improve clinical outcomes.
In this work, we systematically explored the function of melatonin regulator genes and identified two molecular subtypes of GBM. There are also some limitations of our study. First, the main findings were based on bioinformatics analyses, which need to be further verified in subsequent experiments. Second, the risk model may be disturbed by some confounding factors. Thus, further independent and prospective datasets are warranted to confirm this risk model validity.