Targeting MYCN IRES in MYCN ‐amplified neuroblastoma with miR‐375 inhibits tumor growth and sensitizes tumor cells to radiation

The MYCN oncogene is amplified in 20% of neuroblastomas, leading to its overexpression at both the mRNA and protein levels. MYCN overexpression is strongly associated with advanced disease stage, rapid tumor progression and a worse prognosis. In the present study, we identified microRNA‐375 (miR‐375) as a negative regulator of MYCN: enforced expression of miR‐375 inhibited MYCN‐amplified neuroblastoma in vitro and in vivo. Upon searching the website miRbase for possible miR‐375 binding sites within the whole MYCN mRNA, we found that the MYCN 5′‐UTR had significant sequence complementarity to miR‐375, yet no complementary sequences existed within the MYCN 3′‐UTR and coding regions. Enforced overexpression of miR‐375 efficiently inhibited MYCN mRNA translation and protein synthesis, via an IRES‐dependent mechanism. In athymic nude mouse model with human MYCN‐amplified neuroblastoma, MYCN downregulation by miR‐375 led to inhibition of tumor cell growth and tumorigenicity. In particular, miR‐375‐regulated inhibition of MYCN translation was enhanced when MYCN‐amplified neuroblastoma cells were exposed to stress stimulation, such as ionizing irradiation (IR), resulting in a remarkable increase in the neuroblastoma's sensitivity to IR‐induced cell death. Our results identified a novel mechanism by which IRES‐dependent translation of MYCN is repressed by miR‐375, particularly during cellular stress, highlighting a potential anticancer strategy: the development of miR‐375 as a novel therapeutic agent to treat MYCN‐amplified neuroblastoma.