Abstract 5472: Systems pharmacogenomics approach identifies synergistic molecular action of combined MTOR/HDAC inhibition on MYC

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Multiple myeloma (MM) and murine plasmacytoma (PCT) are rare mature B-lymphoid malignancies. Allelic variants of Mtor and Cdkn2a affect susceptibility to PCT, and functional alterations in the PI3K/MTOR and CYCLIN/CDK/CDKI/RB (RB) pathways are common to both malignancies. We found that combining sirolimus (rapamycin), an inhibitor of mechanistic target of rapamycin (MTOR), with entinostat (MS-275), a selective class I histone deacytlase (HDAC) inhibitor, was synergistic in controlling 90% of tested cell lines derived from B cell malignancies in vitro, effective in limiting xenograft growth in vivo, and diminished cellular viability in ex vivo patient samples. Similarly, the combination reduced tumor burden and volume and increased survival in a long-term, in-vivo study in C.B6-Bcl2l1 mice. To examine the core synergistic consequence of combining entinostat with sirolimus, an integrated, systems-level approach was used. Weighted gene co-expression analysis (WGCNA) of GEP data from MM cells treated individually and in combination was used to identify a distinct module of 126 genes cooperatively affected by both drugs. Of the cooperatively affected genes, 37 were found to be differentially expressed in MM and predictive of survival (p<0.01). Ingenuity upstream analysis identified MYC as a potential core regulator of the synergistic transcriptional response. MYC protein, but not mRNA, decreased in response to the drug combination when examined by Western blot and NanoString analyses, respectively. Using tet-off, MYC-inducible transformed P493 cells, the necessity of MYC for the drop in cellular viability and response of the gene signature to the combination was evident. Using the translational and proteasomal inhibitors, cycloheximide and MG132, respectively, it was determined that MYC protein half-life decreased with the combination, largely due to proteasomal degradation. Utilizing a systems-level approach and biological filters, an alternative route to MYC inhibition was determined. Biologically relevant, this methodology can be used to define the molecular underpinnings of drug combinations, applicable to many diseases. Citation Format: Benjamin J. Gamache, John K. Simmons, Aleksandra Michalowski, Jyoti Patel, Ke Zhang, Shuling Zhang, Wendy DuBois, Adriana Zingone, Michael Kuehl, Jing Huang, Ola Landgren, Beverly Mock. Systems pharmacogenomics approach identifies synergistic molecular action of combined MTOR/HDAC inhibition on MYC. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5472. doi:10.1158/1538-7445.AM2014-5472