One of the topical areas of fundamental oncology in recent years is the study of epigenetic disruptions in the development and progression of malignancies, including breast cancer. Particular attention is given to the study of miRNAs, as they are the major regulators of genes involved in carcinogenesis. MicroRNAs are small non-coding RNAs about 22 nucleotides in length that regulate the level of expression of target mRNAs by interacting with their specific regions.
MicroRNAs regulate more than 30% of human genes involved in many vital processes such as proliferation, differentiation, apoptosis, regulation of the immune response, etc. That is why the disruption of miRNA regulation can affect all stages of carcinogenesis - from the initiation of malignancy to its progression. MiRNAs that have the high prognostic potential for monitoring the breast cancer course are already identified. However, clinical data are often controversial. Due to above mentioned, there is a need to validate them as markers of breast cancer course.
The dissertation is devoted to the actual problem of oncology - to study the profile of miRNA expression in in vitro and ex vivo systems. In addition, we aimed to justify the expediency of miRNAs usage for the evaluation of the aggressiveness of the breast cancer course and estimation of the sensitivity to chemotherapy.
In the in vitro experimental system, we defined the miRNA expression profile in breast cancer cell lines of different malignancy levels and different sensitivity to anticancer drugs. We established an increased expression of oncogenic (miR-10b, miR-221) and decreased expression of oncosuppressive miRNAs (miR-200b, miR-34a). -320a) (p <0.05) in the human breast cancer cells of high malignancy degree (MDA-MB-468 and MDA-MB-231). We find out that the development of cisplatin and doxorubicin resistance is accompanied by an increase in the expression level of miR-21 in parallel with a decrease in the expression levels of miR-29b, -34a, -133a, -200b and -320a (p <0.05).
Significant differences in the expression of miR-10b, -21, -200b, and -320a in cell lines of a high malignancy degree and with the phenotype of drug resistance gave grounds for their further study in tumors of patients with breast cancer.
We established the relationship of expression of tumor miR-21 (r = 0.56), -200b (r = -0.67) and -320a (r = -0.69) with the stage of tumor process (r= 0.56, -0.67 and -0.69 respectively) and proliferative activity of tumor cells (r = 0.68, -0.65 and -0.56, respectively).
For miR-10b, -200b, and -320a we found strong correlation with metastases in regional lymph nodes (r = 0.65, -0.67, -0.63 respectively) and the differentiation degree of the breast cancer (r = -0.59, 0.53, 0.57 respectively). The association of miR-10b, -21, -200b and -320a with the adhesive properties of breast tumors was established.
The features of miR-10b, -21, -200b, -320a expression in tumors of different molecular subtypes were established (p <0.05). A high level of miR-10b expression (5.95 ± 0.54) and -21 (12.40 ± 0.99) was observed in the breast tumors of basal molecular subtype against the low miR-200b expression (0.12 ± 0.05) and -320a (0.60 ± 0.05) in luminal A and luminal B subtypes.
The overall 5-year survival of patients with breast cancer with levels of miR-10b >3.8, -21 >10.26, -200b <0.3 and -320a <0.26 is significantly lower than in other cohorts (p <0.05). Recurrences of the disease at 3 years in patients with miR-10b expression >3.8, -21> 11.01, -200b <0.5 and -320a <0.52 was observed more frequently than in the ones with expression values of mentioned miRNAs <2.1, <8.2, >1.2 and >0.9 respectively.
Analysis of the expression profile of tumor miR-21, -200b, -320a showed a correlation of their levels with the response to neoadjuvant polychemotherapy: in most patients with resistance to anthracycline-containing therapy regimens, the expression rates of miR-21 were higher than 10.3 and the expression level of miR-200b and -320a was lower than 0.6 and 0.4 respectively. In the group of patients with sensitive tumors, the expression levels of miR-21 were lower 6.0 and the expression level of miR-200b and -320a was higher than 2.0 and 1.2 respectively.
Thus, we have substantiated the possibility of using the expression of miR-10b, -21, -200b, -320a in tumor cells to predict the aggressiveness of the breast cancer course, the risk of recurrence and the effectiveness of neoadjuvant treatment.
Summarizing obtained data, we can confirm the prognostic and predictive significance of the panel miR-10b, -21, -200b, -320a to assess the aggressiveness of the clinical course of breast cancer, the risk of disease recurrence, as well as determine the sensitivity to anthracycline-containing therapy.
