Abstract 2351: MYC gene copy number determine MYC expression and sensitivity to a MYC-inhibitor in multiple myeloma cells
Authors: Holien Toril , Misund Kristine , Buene Glenn , Olsen Oddrun E. , Baranowska Katarzyna A. , Waage Anders , Sundan Anders 
Published: May 2015

Abstract
Background
The role of MYC in multiple myeloma has been under debate, but evidence now point to an important role for this oncogene in disease initiation, progression and maintenance. The key role of MYC in maintenance of tumor cell survival makes MYC a potential target for therapy. Acting as a transcription factor, MYC binds to its obligate partner MAX. Small-molecule inhibitors that target MYC-MAX heterodimerization prevent DNA binding and hence the transactivation of MYC target genes.
Purpose
We have previously shown that in many myeloma cell clones inhibition of MYC activity leads to apoptosis, but to varying degrees. The relation between the cells' response to inhibition of MYC, and levels of MYC gene, RNA and/or protein has not been thoroughly investigated earlier. Thus, we wanted to explore this using a panel of myeloma cell lines and primary myeloma cells.
Methods
A panel of myeloma cell lines was treated with the MYC-MAX inhibitor 10058-F4 before assessment of relative cell growth using CellTiter Glo, that measures the cells' ATP content. To determine MYC expression we analyzed DNA copy numbers using PCR, mRNA content using Nanostring technology and protein levels using Western Blotting. To screen primary myeloma cells for sensitivity to MYC-inhibition, we used our newly developed method for screening of cell viability in cocultures with bone marrow stromal cells.
Results
Myeloma cell lines showed a great variation in number of MYC gene copy number as well as MYC mRNA and protein levels. Interestingly, there was a good correlation between DNA copy numbers and mRNA levels, indicating that in general the MYC gene copy number is determining for the level of MYC mRNA in myeloma cells. Moreover, protein levels also showed a relatively high degree of correlation with MYC mRNA. The relative sensitivity for MYC-inhibition for each cell clone was compared with MYC expression. We could not see a clear correlation between sensitivity to MYC-inhibition and MYC expression in cell lines. However, cell lines with high MYC gene copy number and MYC expression tended to be among the most sensitive cell lines to MYC-MAX inhibition. We also tested a number of primary myeloma cells for sensitivity to the MYC-MAX-inhibitor in a cell viability assay in the presence of stromal cells. The presence of pooled patient bone marrow stromal cells (BMSC) did not affect the sensitivity of patient cells to the 10058-F4 MYC-MAX-inhibitor. Results on the correlation of MYC expression and sensitivity of primary cells to inhibition of MYC activity will be presented.
Citation Format: Toril Holien, Kristine Misund, Glenn Buene, Oddrun E. Olsen, Katarzyna A. Baranowska, Anders Waage, Anders Sundan. MYC gene copy number determine MYC expression and sensitivity to a MYC-inhibitor in multiple myeloma cells. [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 2351. doi:10.1158/1538-7445.AM2014-2351