Anti-miRNA- 155 - 5p enhances the cytotoxic efficacy of temozolomide in brain cancer stem cells.

This study aimed to assess the molecular effects of the miR- 155 - 5p in modulating Temozolomide chemosensitivity, which was examined utilizing in silico and in vitro methods on brain cancer stem cells (BCSCs) that exhibit high differentiation, apoptosis avoidance, and a remarkable capacity for self-renewal as a mechanism of chemotherapeutic resistance. The hypothesis of the study is how miR- 155 - 5p modulates temozolomide chemosensitivity in brain cancer stem cells (BCSCs) and their differentiated counterparts (BSCs) and whether it influences the molecular mechanisms underlying tumour recurrence and treatment failure. By silencing miR- 155 - 5p using anti-miR oligonucleotides, the knockdown efficiency of miR- 155 - 5p was confirmed via quantitative qRT-PCR. The increased chemosensitivity effect of miR- 155 - 5p against temozolomide in BCSCs and BCSs was measured by cytotoxicity assay. Subsequently, all studied groups were evaluated by performing cell viability, cell cycle, and apoptosis tests. miRNA-mRNA-pathway interactions were analyzed using different bioinformatics tools and databases. Cell viability was significantly reduced by 42.9% in the combined treatment (anti-miR- 155 - 5p + temozolomide) group compared to the untreated group. Temozolomide treatment in combination with anti-miR- 155 - 5p showed a significant decrease in cell viability compared to temozolomide alone. In contrast, late apoptosis increased 2.10-fold (p < 0.0001), indicating a synergistic effect in promoting late apoptosis. Combining temozolomide and anti-miR- 155 - 5p inhibits DNA synthesis by causing G2 phase arrest. mRNAs targeted by miR- 155 - 5p and significantly down-regulated in glioblastoma included GABRA1, GABRB2, SCN1A, GRIN2A, and SGIP1. By survival analysis, low expression of SCN1A was associated with poor prognosis (p < 0.05; HR = 0.7), highlighting its potential prognostic role. The combination of temozolomide treatment with suppression of miR- 155 - 5p may provide a more effective and side-effect minimized brain cancer treatment strategy by reducing resistance.