The Oncogene MYCN Modulates Glycolytic and Invasive Genes to Enhance Cell Viability and Migration in Human Retinoblastoma

SIMPLE SUMMARY: Retinoblastoma (RB) is a cancer in children, caused by loss of function of RB1 gene. Additional factors such as increase in gene copy numbers of oncogenes MYCN, MDM4 and E2F3 contribute to RB pathogenesis, though their mechanism(s) are not completely understood. We sought to explain the role of MYCN in RB pathogenesis. Our data indicate that MYCN is overexpressed in RB, and that may contribute to the disease progression by altering the cancer metabolism (glucose metabolism) and cell migration related genes. We also observed that a combination of MYCN-inhibition with carboplatin, a drug that is currently used in the treatment of RB has a good synergistic activity against RB. Development of drug-related toxicity and associated long-term side effects is a problem in treatment of RB. MYCN-inhibition, in combination with existing drugs, could be a novel, effective therapeutic strategy to reduce high doses of chemotherapy for children that receive prolonged chemotherapy. ABSTRACT: Retinoblastoma is usually initiated by biallelic RB1 gene inactivation. In addition, MYCN copy number alterations also contribute to RB pathogenesis. However, MYCN expression, its role in disease progression and correlation with RB histological risk factors are not well understood. We studied the expression of MYCN in enucleated RB patient specimens by immunohistochemistry. MYCN is overexpressed in RB compared to control retina. Our microarray gene expression analysis followed by qRT-PCR validation revealed that genes involved in glucose metabolism and migration are significantly downregulated in MYCN knockdown cells. Further, targeting MYCN in RB cells using small molecule compounds or shRNAs led to decreased cell survival and migration, increased apoptosis and cell cycle arrest, suggesting that MYCN inhibition can be a potential therapeutic strategy. We also noted that MYCN inhibition results in reduction in glucose uptake, lactate production, ROS levels and gelatinolytic activity of active-MMP9, explaining a possible mechanism of MYCN in RB. Taking clues from our findings, we tested a combination treatment of RB cells with carboplatin and MYCN inhibitors to find enhanced therapeutic efficacy compared to single drug treatment. Thus, MYCN inhibition can be a potential therapeutic strategy in combination with existing chemotherapy drugs to restrict tumor cell growth in RB.