Recently, miRNA has been proved as one of the critical regulators during glioma progression. Mitomycin C ic50 Both up-regulation and down-regulation of miRNAs are involved

in the development of glioblastomas and chemoresistance. Shi et al. showed that over-expression of miR-21 could attenuate TMZ-induced apoptosis in U87MG cells through up-regulation of Bax, reduction of Bax/Bcl-2 ratio and caspase-3 activity, demonstrated that miR-21 over-expression is associated with resistance to chemotherapeutic drug TMZ [31]. Furthermore, Li et al. demonstrated that miRNA-21 targets LRRFIP1 which inhibits NF-κB activation. NF-κB pathway is activated upon miR-21 over-expression, exhibits significant anti-apoptotic efficacy, and contributes to VM-26 resistance in glioblastoma [32]. Based on these findings, miR-21 could be a potential target to increase the chemotherapeutic efficacy during glioblastoma treatment. Another study indicated that using an established U251 cell line resistant to temozolomide, Ujifuku et al. performed an analysis of miRNA expression in this cell line and its parental cell line. Three miRNAs miR-195, miR-455-3P, and miR-10a were identified as the most up-regulated miRNAs in the U251 cell line resistant to temozolomide. Knockdown of miR-195 inhibited tumor cell growth,

suggesting Proteases inhibitor that it could be a potential target for treatment of glioblastoma with acquired TMZ resistance [33]. In our study, Let-7b was down-regulated in acquired cisplatin-resistant U251R cells. Furthermore, ectopic Let-7b can increase the sensitivity of U251R cells to cisplatin through inhibition of cyclin D1 expression. In this regard, Let-7b could overcome cisplatin resistance in glioblastoma cells, indicating that it could be applied to treat glioblastoma patients with cisplatin resistance. It is known that Let-7 modulates chemosensitivity in various types of cancer. Let-7 inhibited gemcitabine chemoresistance in pancreatic cancer [34], and could also negatively modulate the chemoresistance

in Head and neck cancer [35]. Sugimura et al. showed that Let-7b and Let-7c expression were down-regulated in cisplatin-resistant Nintedanib (BIBF 1120) esophageal cancer cell lines compared with their parent cell lines [36]. Transfection of Let-7 into esophageal cancer cell lines restored their sensitivity to cisplatin. Furthermore, low expression of Let-7b and Let-7c in before-treatment patients is correlated with poor response to cisplatin-based chemotherapy, so Let-7 can also be used as a marker to predict the sensitivity to cisplatin treatment [36]. Moreover, Let-7b down-regulated cyclin D1 expression through targeting 3’-UTR of cyclin D1 mRNA, and inhibited cell cycle progression in melanoma cells [37]. Let-7 also regulates cyclin D1 in other types of tumors.