BET bromodomain inhibition of MYC-amplified medulloblastoma.

MYC-amplified medulloblastomas are highly lethal tumors. Bromodomain and extraterminal (BET) bromodomain inhibition has recently been shown to suppress MYC-associated transcriptional activity in other cancers. The compound JQ1 inhibits BET bromodomain-containing proteins, including BRD4. Here, we investigate BET bromodomain targeting for the treatment of MYC-amplified medulloblastoma. We evaluated the effects of genetic and pharmacologic inhibition of BET bromodomains on proliferation, cell cycle, and apoptosis in established and newly generated patient- and genetically engineered mouse model (GEMM)-derived medulloblastoma cell lines and xenografts that harbored amplifications of MYC or MYCN. We also assessed the effect of JQ1 on MYC expression and global MYC-associated transcriptional activity. We assessed the in vivo efficacy of JQ1 in orthotopic xenografts established in immunocompromised mice. Treatment of MYC-amplified medulloblastoma cells with JQ1 decreased cell viability associated with arrest at G1 and apoptosis. We observed downregulation of MYC expression and confirmed the inhibition of MYC-associated transcriptional targets. The exogenous expression of MYC from a retroviral promoter reduced the effect of JQ1 on cell viability, suggesting that attenuated levels of MYC contribute to the functional effects of JQ1. JQ1 significantly prolonged the survival of orthotopic xenograft models of MYC-amplified medulloblastoma (P < 0.001). Xenografts harvested from mice after five doses of JQ1 had reduced the expression of MYC mRNA and a reduced proliferative index. JQ1 suppresses MYC expression and MYC-associated transcriptional activity in medulloblastomas, resulting in an overall decrease in medulloblastoma cell viability. These preclinical findings highlight the promise of BET bromodomain inhibitors as novel agents for MYC-amplified medulloblastoma.

Bandopadhayay P ，Bergthold G ，Nguyen B ，Schubert S ，Gholamin S ，Tang Y ，Bolin S ，Schumacher SE ，Zeid R ，Masoud S ，Yu F ，Vue N ，Gibson WJ ，Paolella BR ，Mitra SS ，Cheshier SH ，Qi J ，Liu KW ，Wechsler-Reya R ，Weiss WA ，Swartling FJ ，Kieran MW ，Bradner JE ，Beroukhim R ，Cho YJ ... -  《-》

BET bromodomain protein inhibition is a therapeutic option for medulloblastoma.

Henssen A ，Thor T ，Odersky A ，Heukamp L ，El-Hindy N ，Beckers A ，Speleman F ，Althoff K ，Schäfers S ，Schramm A ，Sure U ，Fleischhack G ，Eggert A ，Schulte JH ... -  《Oncotarget》

Inhibition of BRD4 attenuates tumor cell self-renewal and suppresses stem cell signaling in MYC driven medulloblastoma.

Venkataraman S ，Alimova I ，Balakrishnan I ，Harris P ，Birks DK ，Griesinger A ，Amani V ，Cristiano B ，Remke M ，Taylor MD ，Handler M ，Foreman NK ，Vibhakar R ... -  《Oncotarget》

BET protein inhibitor JQ1 attenuates Myc-amplified MCC tumor growth in vivo.

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin currently with no cure. In this study, we have first demonstrated that c-Myc overexpression is common in MCC. By targeting c-Myc, bromodomain inhibitors have demonstrated antitumor efficacy in several preclinical human cancer models. Thus, we interrogated the role of c-Myc inhibition in MCC with c-Myc amplification by using the BET inhibitor JQ1. We have uncovered that c-Myc can be regulated by JQ1 in MCC cells with pathologic c-Myc activation. Moreover, JQ1 potently abrogates c-Myc expression in MCC cells and causes marked G1 cell-cycle arrest. Mechanistically, JQ1-induced cell-cycle arrest coincides with downregulation of cyclin D1 and upregulation of p21, p27, and p57, whereas JQ1 exerts no effect on apoptosis in MCC cells. Further knockdown of p21, p27, or p57 by shRNA partially protects cells from JQ1-induced cell-cycle arrest. In addition, c-Myc knockdown by shRNA generates significant cell-cycle arrest, suggesting that c-Myc overexpression plays a role in MCC pathogenesis. Most importantly, JQ1 significantly attenuates tumor growth in xenograft MCC mouse models. Our results provide initial evidence, indicating the potential clinical utility of BET protein inhibitors in the treatment of MCC with pathologic activation of c-Myc.

Shao Q ，Kannan A ，Lin Z ，Stack BC Jr ，Suen JY ，Gao L ... -  《-》

A novel dual epigenetic approach targeting BET proteins and HDACs in Group 3 (MYC-driven) Medulloblastoma.

Medulloblastoma (MB) patients with MYC oncogene amplification or overexpression exhibit extremely poor clinical outcomes and respond poorly to current therapies. Epigenetic deregulation is very common in MYC-driven MB. The bromodomain extra-terminal (BET) proteins and histone deacetylases (HDACs) are epigenetic regulators of MYC transcription and its associated tumorigenic programs. This study aimed to investigate the therapeutic potential of inhibiting the BET proteins and HDACs together in MB. Using clinically relevant BET inhibitors (JQ1 or OTX015) and a pan-HDAC inhibitor (panobinostat), we evaluated the effects of combined inhibition on cell growth/survival in MYC-amplified MB cell lines and xenografts and examined underlying molecular mechanism(s). Co-treatment of JQ1 or OTX015 with panobinostat synergistically suppressed growth/survival of MYC-amplified MB cells by inducing G2 cell cycle arrest and apoptosis. Mechanistic investigation using RNA-seq revealed that co-treatment of JQ1 with panobinostat synergistically modulated global gene expression including MYC/HDAC targets. SYK and MSI1 oncogenes were among the top 50 genes synergistically downregulated by JQ1 and panobinostat. RT-PCR and western blot analyses confirmed that JQ1 and panobinostat synergistically inhibited the mRNA and protein expression of MSI1/SYK along with MYC expression. Reduced SYK/MSI expression after BET (specifically, BRD4) gene-knockdown further confirmed the epigenetic regulation of SYK and MSI1 genes. In addition, the combination of OTX015 and panobinostat significantly inhibited tumor growth in MYC-amplified MB xenografted mice by downregulating expression of MYC, compared to single-agent therapy. Together, our findings demonstrated that dual-inhibition of BET and HDAC proteins of the epigenetic pathway can be a novel therapeutic approach against MYC-driven MB.

Kling MJ ，Kesherwani V ，Mishra NK ，Alexander G ，McIntyre EM ，Ray S ，Challagundla KB ，Joshi SS ，Coulter DW ，Chaturvedi NK ... -  《JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH》