Mir-34a Mimics Are Potential Therapeutic Agents for p53-Mutated and Chemo-Resistant Brain Tumour Cells

Chemotherapeutic drug resistance and relapse remains a major challenge for paediatric (medulloblastoma) and adult (glioblastoma) brain tumour treatment. Medulloblastoma tumours and cell lines with mutations in the p53 signalling pathway have been shown to be specifically insensitive to DNA damaging agents. The aim of this study was to investigate the potential of triggering cell death in p53 mutated medulloblastoma cells by a direct activation of pro-death signalling downstream of p53 activation. Since non-coding microRNAs (miRNAs) have the ability to fine tune the expression of a variety of target genes, orchestrating multiple downstream effects, we hypothesised that triggering the expression of a p53 target miRNA could induce cell death in chemo-resistant cells. Treatment with etoposide, increased miR-34a levels in a p53-dependent fashion and the level of miR-34a transcription was correlated with the cell sensitivity to etoposide. miR-34a activity was validated by measuring the expression levels of one of its well described target: the NADH dependent sirtuin1 (SIRT1). Whilst drugs directly targeting SIRT1, were potent to trigger cell death at high concentrations only, introduction of synthetic miR-34a mimics was able to induce cell death in p53 mutated medulloblastoma and glioblastoma cell lines. Our results show that the need of a functional p53 signaling pathway can be bypassed by direct activation of miR-34a in brain tumour cells.化疗耐药与复发仍是儿童髓母细胞瘤（medulloblastoma）与成人胶质母细胞瘤（glioblastoma）脑肿瘤治疗面临的主要难题。携带p53信号通路（p53 signalling pathway）突变的髓母细胞瘤组织及细胞系，已被证实对DNA损伤剂存在特异性耐药性。本研究旨在探索通过直接激活p53下游促死亡信号通路，诱导p53突变型髓母细胞瘤细胞发生死亡的可行性。由于非编码微小RNA（microRNAs，miRNAs）可对多种靶基因的表达进行精细调控，并协同介导多种下游生物学效应，本研究提出假说：激活p53靶标miRNA的表达，能够在化疗耐药细胞中诱导细胞死亡。依托泊苷（etoposide）处理可通过p53依赖的方式提升miR-34a的表达水平，且miR-34a的转录水平与细胞对依托泊苷的敏感性呈正相关。通过检测其已被广泛证实的靶标之一——NADH依赖型沉默信息调节因子1（SIRT1）的表达水平，验证了miR-34a的活性。尽管直接靶向SIRT1的药物仅在高浓度下才可有效诱导细胞死亡，但引入合成miR-34a模拟物，能够在p53突变型髓母细胞瘤与胶质母细胞瘤细胞系中诱导细胞死亡。本研究结果表明，在脑肿瘤细胞中通过直接激活miR-34a，可绕过对功能性p53信号通路的依赖。