MYB-NFIB fusion and NOTCH1 mutation are common hallmark genetic events in salivary gland adenoid cystic carcinoma (SACC). However, abnormal expression of MYB and NOTCH1 is also observed in patients without MYB-NFIB fusion and NOTCH1 mutation. Here, we explore in-depth the molecular mechanisms of lung metastasis through single-cell RNA sequencing (scRNA-seq) and exome target capture sequencing in two SACC patients without MYB-NFIB fusion and NOTCH1 mutation. Twenty-five types of cells in primary and metastatic tissues were identified via Seurat clustering and categorized into four main stages ranging from near-normal to cancer-based on the abundance of each cell cluster in normal tissue. In this context, we identified the Notch signaling pathway enrichment in almost all cancer cells; RNA velocity, trajectory, and sub-clustering analyses were performed to deeply investigate cancer progenitor-like cell clusters in primary tumor-associated lung metastases, and signature genes of progenitor-like cells were enriched in the “MYC_TARGETS_V2” gene set. In vitro, we detected the NICD1-MYB-MYC complex by co-immunoprecipitation (Co-IP) and incidentally identified retinoic acid (RA) as an endogenous antagonist of genes in the “MYC_TARGETS_V2” gene set. Following this, we confirmed that all-trans retinoic acid (ATRA) suppresses the lung metastasis of SACC by correcting erroneous cell differentiation mainly caused by aberrant NOTCH1 or MYB expression. Bioinformatic, RNA-seq, and immunohistochemical (IHC) analyses of primary tissues and metastatic lung tissues from patients with SACC suggested that RA system insufficiency partially promotes lung metastasis. These findings imply the value of the RA system in diagnosis and treatment.

Background: Numerous studies have explored the anticancer effect of FTY720 (Fingolimod) in animal models, a sphingosine-1-phosphate (S1P) receptor antagonist and an immunosuppressant, but little clinical evidence guides the use of FTY720 in cancer patients.Methods: Strictly, only related published articles about the treatment with FTY720 for various cancers in vivo from January 1998 to January 2020 were selected from PubMed, Web of Science, Ovid, Embase, CNKI and Cochrane databases, and which were qualified. We acquired agreement through discussion. Then, we conducted meta-analysis, subgroups analysis, publication bias analysis and sensitivity analysis based on selected studies. In the last two sections, we summaried and compared side effects, drug combination effects and molecular pathways from selected studies.Results: In the 31 articles included from 2002 to 2019, FTY720 was found to reduce tumor volume (SMD =-2.58, 95% CI: -3.42, -1.75, Z = 6.09, P = 0.000), tumor weight (SMD = -3.69, 95% CI: -5.17, -2.21, Z = 4.88, P = 0.000) and body weight (SMD = -0.86, 95% CI: -1.61, -0.11, Z = 2.23, P = 0.025) in 14 types of cancer. Relevant frequent signal pathways include the Akt pathway, S1PRs-Caspase pathway and the STAT3-PP2A pathway. FTY720 has significant independent or in combination anticancer effects and a lower toxicity in renal cell carcinoma and neuroblastoma mice models. However, it should be noted that FTY720 achieved a significant therapeutic effect in immunodeficient mice, not in immunecompetent mice. Also, the dosage-safety of FTY720 alone in clinical use is a noteworthy issue. In mouse models, the mechanism of the FTY720 treatment of tumors lies in inducing the tumor cells apoptosis through important signaling moleculars.Conclusions: FTY720 alone or in combination exerted significant anti-tumor effects for neuroblastoma and renal cell carcinoma, however not for melanoma. Due to insufficient evidence, more specific studies of FTY720 only and in combination included in immunity, inflammation and melanoma should be carried out in the future preclinical and clinical studies.

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MYB-NFIB fusion and NOTCH1 mutation are hallmark genetic events familiar in SACC that promote lung metastasis. However, abnormal expression of MYB and NOTCH1 was also observed in without MYB-NFIB fusion and NOTCH1 mutation. Here, through single-cell RNA sequencing (scRNA-seq) and exome target capture sequencing in two SACC patients without MYB-NFIB fusion and NOTCH1 mutation, we explore in-depth the molecular mechanisms of lung metastasis. Twenty-five types of cells in primary and metastatic tissues were identified via Seurat clustering and categorized into four main stages ranging from near normal to cancer state based on the normal tissue occupancy for each cell cluster. In this context, we identified the Notch signalling pathway enrichment in almost all cancer cells; trajectory and sub-clustering analyses investigated deeply cancer progenitor-like cell clusters in primary tumour-associated lung metastases, in which signature genes enriched in the ‘MYC_TARGETS_V2’ gene set. In vitro, we detected the complexes of the NICD1-MYB-MYC by Co-immunoprecipitation (Co-IP) and incidentally identified retinoic acid (RA) signalling as endogenous antagonists of the ‘MYC_TARGETS_V2’ gene set. Following this, we validate that all-trans retinoic acid (ATRA) reduces the lung metastasis in SACC via correcting erroneous cell differentiation mainly caused by aberrant NOTCH1 or MYB expression. Bioinformatic and immunohistochemical (IHC) analyses of four primary tissues and eleven metastatic lung tissues from patients with SACC suggested that RA system insufficiency partially promotes lung metastasis. These findings imply the value of diagnosis and treatment of the RA system.