Circulating Cell-Free miR-25-3p Is Upregulated in Brazilian Patients with Prostate Cancer and Contributes to Tumor Aggressiveness.

Background/Objectives: Prostate cancer (PCa) has a high incidence worldwide, yet reliable prognostic biomarkers to distinguish indolent from aggressive forms are lacking. MicroRNAs (miRNAs), a class of small non-coding RNAs, are stable molecules that play an important role in cancer development and can be detected in circulation by non-invasive methods. This study aimed to examine the influence of the cell-free (cf) miRNAs levels on PCa risk and aggressiveness using plasma samples and cell models. Methods: Four overexpressed miRNAs in prostate cancer tissue were selected from The Cancer Genome Atlas database: miR-25-3p, miR-92a-1-5p, miR-92a-2-5p, and miR-148a-3p. Cf-miRNA levels were validated via quantitative reverse transcription polymerase chain reaction (RT-qPCR) in plasma samples from 80 PCa patients and 40 controls in a Brazilian cohort. Clinicopathological associations were analyzed to determine prognostic value. Subsequently, functional analyses were performed using transient transfection of miR-25-3p in the LNCaP cell line, assessing proliferation, migration, invasion, and target gene regulation. Results: Among the miRNAs analyzed, only miR-25-3p was upregulated in the plasma of PCa patients compared to controls (p = 0.013). Patients with International Society of Urological Pathology (ISUP) grade ≥2 presented higher expression levels of miR-25-3p (p = 0.020) compared to patients with ISUP grade 1. Overexpression of miR-25-3p significantly increased cell proliferation, colony formation, migration, and invasion capacity and modulated the expression of BCL2L11, CDH1, CDKN1C, EHZ2, and TP53 genes. Conclusions: miR-25-3p had an oncogenic role in PCa, showing a potential marker to assess PCa development and progression using liquid biopsy.