Bortezomib Synergizes with DFMO to Inhibit Neuroblastoma Cell Proliferation via Reversal of the LIN28/Let-7 Axis

Abstract

As scientists and physicians continue to search for better and long-term treatment for cancer, greater focus has recently been placed on molecular guided therapy and the targeting of cancer stem cells (CSCs). One pathway associated with targeting CSCs is the LIN28/Let-7 pathway due to the inductive role of LIN28 in stem cell growth and glycolytic metabolism. LIN28 protein is characteristically overexpressed and correlates with poor outcome in many different malignancies including Neuroblastoma (NB), the most common extracranial solid pediatric tumor. Therefore, drugs that target the LIN28/Let-7 axis could be beneficial in treating NB patients by targeting CSCs and preventing relapse of disease. This study investigated the drug combination therapy of Difluoromethylornithine (DFMO)—an inhibitor of ornithine decarboxylase—coupled with bortezomib—a proteasome inhibitor—as a new therapeutic upstream target of LIN28/Let-7 pathway and glycolytic metabolism. Cell proliferation assays and isobologram experiments suggest synergistic cytotoxicity of the drug combination in two NB cell lines. Western blot analysis demonstrated regulation of the Lin28/Let-7 pathway with inhibition of LIN28 protein expression. Decrease in ATP-per-cell when treated with combination drug therapy suggests inhibition of glycolytic metabolic activity in NB cells. In vivo studies showed a trend in decreased tumor size for combination treatment compared to control or DFMO-treated mice. Results indicate that DFMO and bortezomib act synergistically to inhibit glycolytic metabolism via the LIN28/Let-7 pathway and prevent NB CSC survival. Given the current lack of effective treatments and the high incidence of relapse and metastatic disease for patients, bortezomib in combination with DFMO offers a potential new therapeutic treatment for children with NB.