Fig. S1. RNA-seq analysis between MYC vs non-MYC amplified MB cell lines. Fig. S2. Synergistic effects of OTX and mTOR inhibitors on MYC-amplified MB cell growth. Fig. S3. JQ1 chemosensitizes the MB cells. Fig. S4. Flow cytometry plots for cell cycle distribution (as summarized in main Fig. 2A and 2D) in MB cell lines-treated with inhibitors alone or combined as indicated. Fig. S5. The representative Annexin-V flow plots for apoptosis (as summarized in main Fig. 2C and 2E) in HD-MB03 MB cell lines-treated with inhibitors alone or combined as indicated. Fig. S6. Combination effects of BET protein inhibitor OTX with mTOR inhibitors (BEZ/TEM) on cell cycle and apoptosis in MYC-driven HD-MB03 cells. Fig. S7. Combination effects of JQ1/BEZ or JQ1/TEM on associated pathways/molecules. Fig. S8. Effects of inhibitors on body weight and histology of the MB xenograft mice. Fig. S9. Combined in vivo effects of JQ1 and BEZ on the expression levels of target key proteins using subcutaneous MYC-amplified MB xenografts.
ARTICLE ABSTRACT
The MYC oncogene is frequently amplified in patients with medulloblastoma, particularly in group 3 patients, who have the worst prognosis. mTOR signaling–driven deregulated protein synthesis is very common in various cancers, including medulloblastoma, that can promote MYC stabilization. As a transcription factor, MYC itself is further known to regulate transcription of several components of protein synthesis machinery, leading to an enhanced protein synthesis rate and proliferation. Thus, inhibiting enhanced protein synthesis by targeting the MYC and mTOR pathways together may represent a highly relevant strategy for the treatment of MYC-driven medulloblastoma. Here, using siRNA and small-molecule inhibitor approaches, we evaluated the effects of combined inhibition of MYC transcription and mTOR signaling on medulloblastoma cell growth/survival and associated molecular mechanism(s) in MYC-amplified (group 3) medulloblastoma cell lines and xenografts. Combined inhibition of MYC and mTOR synergistically suppressed medulloblastoma cell growth and induced G1 cell-cycle arrest and apoptosis. Mechanistically, the combined inhibition significantly downregulated the expression levels of key target proteins of MYC and mTOR signaling. Our results with RNA-sequencing revealed that combined inhibition synergistically modulated global gene expression including MYC/mTOR components. In addition, the combination treatment significantly delayed tumor growth and prolonged survival of MYC-amplified medulloblastoma xenografted mice by downregulating expression of MYC and the key downstream components of mTOR signaling, compared with single-agent therapy. Together, our findings demonstrated that dual inhibition of MYC (transcription) and mTOR (translation) of the protein synthesis pathway can be a novel therapeutic approach against MYC-driven medulloblastoma.
