EXOSOMES AS BIOMARKERS FOR EARLY DIAGNOSIS AND PROGNOSTIC PREDICTION OF ESOPHAGEAL CANCER
Studies have confirmed that the number or contents (including RNA and proteins) of exosomes in the circulating blood are of use as a biomarker for cancers, such as lung cancer, prostate cancer, colorectal cancer, as well as EC[18,28,43,49].
MiRNAs, a large family of small, noncoding RNAs, are enriched in exosomes and could regulate the expression of their target genes. MiRNAs are relatively stable, which can in part represent the level of miRNAs in its donor cell. Numerous studies have indicated that aberrant expression levels of exosomal miRNAs are closely related to the onset of multiple diseases, including cancer. MiR-21, miR-25, miR-93, miR-192, and miR-210 are widely studied oncogenic miRNAs, and have been studied as biomarkers for some kinds of human cancers[50,51].
MiR-93-5p: MicroRNA-93-5p can be transferred between EC9706 cells by exosomes and promote the proliferation of recipient EC9706 cells. Liu et al also found that the expression of miR-93-5p was statistically different (P = 0.035) between EC patients and healthy participants (the former being 1.39 times higher than the latter). The upregulation of plasma miR-93-5p in ESCC patients increased the risk of EC. The Cancer Genome Atlas data analysis also showed that miR-93-5p expression differs in tissues and is associated with patient survival. Therefore, miR-93-5p may be a plasma biomarker for the diagnosis and prognosis of EC.
MiR-1246: MiR-1246 is another cancer associated miRNA dysregulated in many malignant tumors[52,53]. Takeshita et al used ESCC cell lines (including TE1, TE2, TE4, TE6 and TE11) to evaluate the diagnostic and prognostic values of the exo-miR-1246 and estimated the miR-1246 level in peripheral blood of ESCC patients. In the serum samples of ESCC patients, the sensitivity and specificity of miR-1246 were 57.4% and 67.4%, respectively. The area under the curve of receiver operating characteristic curve was 0.665 when setting the optimal cut-off value to 1.15 for squamous cell carcinoma (SCC)-Ag. Furthermore, the miR-1246 expression level of the lymph nodes in adjacent stations was apparently higher than that of the distant lymph nodes.
MiR-21: One microarray data analysis showed that a total of 15 miRNAs were upregulated in the plasma of ESCC patients compared with healthy control participants. They were hsa-miR-16-5p, hsa-miR-130a-3p, hsa-miR-15a-5p, hsa-miR-144-3p, hsa-miR-19b-3p, hsa-miR-5196-5p, hsa-miR-25a-3p, hsa-miR1914-3p, hsa-miR-93-5p, hsa-miR-107, hsa-miR-3911, hsa-miR-21-5p, hsa-let-7d-3p, hsa-let7i-5p and hsa-miR-1290. In contrast, four miRNAs including hsa-miR-1238-3p, hsa-miR-6069, hsa-miR-191-3p, hsa-miR-4665-3p and hsa-miR-937-5p were downregulated. One case-control study on the correlation between exosome-shuttling miR-21 and EC morbidity indicated that the relative expression of miR-21 was 2.95 times higher in EC patient plasma compared to healthy controls. Furthermore, conditional logistic regression analysis showed that the higher miR-21 was expressed, the higher the EC incidence risk was (odds ratio: 1.107; 95% confidence interval: 1.012-1.21; P = 0.026). The area under the curve value was 0.60 to show the diagnostic value of exosome-shuttling miR-21 in ESCC patients.
MiR-223-3p: Exo-miRNAs are also important biomarkers for EA diagnosis and progression. Warnecke-Eberz et al first isolated exosomes from serum of EA patients and compared exosomal miRNA profiles in matching primary tumors with adjacent tissues. Results showed that a total of eight miRNAs (miR-126-5p, miR-146a-5p, miR-192-5p, miR-196b-5p, miR-223-3p, miR-223-5p, miR-409-3p and miR-483-5p) were significantly overexpressed. Conversely, ten miRNAs (miR-22-3p, miR-23b-5p, miR-27b-3p, miR-149-5p, miR-203-5p, miR-224-5p, miR-452-5p, miR-671-3p, miR-944-5p and miR-1201-5p) were significantly downregulated. They also detected that miR-223-3p was overexpressed in T2-staged adenocarcinoma patients and was higher than that in T3 tumors. There was no statistical difference in the overexpression of miR-223-5p and miR-483-5p in EA and ESCC. This result is consistent with the research of Zhou et al.
MiR-584: A four-stage study including screening, training, testing and validating identified that miR-106a, miR-18a, miR-20b, miR-486-5p and miR-584 were upregulated, but miR-223-3p was downregulated in the plasma of patients with ESCC. MiR-584 was also overexpressed in ESCC tissues. This result is consistent with the data in The Cancer Genome Atlas database. Furthermore, exosome miR-584 in plasma was consistently dysregulated. Therefore, miR-584 could play an important role in the early diagnosis of ESCC.
Stathmin-1 was abundant in exosomes and could enter peripheral blood loaded by exosomes. Yan et al found that the serum levels of stathmin-1 in ESCC patients with lymph node metastasis were significantly higher compared with the cases without lymph node metastasis. As the stage increased, its sensitivity improved accordingly. They also measured the serum levels of stathmin-1 in patients with various cancers. When setting the diagnostic critical value to 4.47ng/mL, the positive rates of stathmin-1 were 81.0% (295/364) for ESCC, 68.8% (33/48) for head and neck squamous cell carcinoma, 71.2% (37/52) for lung squamous cell carcinoma, 50.9% (27/53) for lung adenocarcinoma, 27.1% (16/59) for gastric cancer, 43.9% (25/57) for colorectal cancer and 45.3% (24/53) for hepatocellular carcinoma. The area under the curve value of stathmin-1 for SCC was over 0.8, but it was lower than 0.7 for other types of cancer. Thus, stathmin-1 showed excellent diagnostic capability for SCC and may be a serology biomarker for SCC in the clinic, especially for ESCC.