Multiple myeloma is a haematological disease that develops in the skeleton. The bone microenvironment supports myeloma growth and long-term survival of dormant myeloma cells. Despite new treatments, patients typically relapse, suggesting we need a better understanding of the regulation of dormant cells and their role in drug resistance. We developed a new approach to identify dormant myeloma cells in vivo and define the transcriptome profile of these cells in order to identify pathways that control dormancy. 5TGM1eGFP myeloma cells were labelled with the fluorescent membrane dye DiD. Dividing cells share DiD with daughter cells and become DiDneg, whereas, non-dividing dormant cells retain DiD (DiDhigh). DiD-labelled cells were injected (i.v.) into C57BLKalwRij mice and DiDhigh and DiDneg populations isolated by FACS at 7, 14, 21, or 28 days. Transcript profiling of each population was performed using mouse ST 2.0 whole genome arrays. DiDhigh dormant cells were identified in bone marrow across all time-points. DiDneg cells were first detected on day 14 and increased up to day 28. Over 300 genes were up-regulated and >300 genes were down-regulated in DiDhigh cells compared with DiDneg cells at day 28, (fold change >2, Q value <0.05). Gene set enrichment analysis (GSEA) confirmed the dormant status of DiDhigh cells, with down-regulation of gene sets involved in proliferation and cell cycle. Functional annotation and GSEA identified immune system-related pathways, cytokine and integrin signalling as important determinants of dormancy throughout time-points. Candidate genes, including Vcam-1, Axl1, Tyrobp, S100A6 were verified by qPCR and/or flow cytometry and were shown to be up-regulated in dormant cells. These data confirm the persistence of dormant myeloma cells in bone and demonstrate that they have a unique transcriptome profile. Furthermore, we have identified several novel pathways and candidate genes that control dormancy and may be new targets for therapeutic intervention.
Disclosure: The authors declared no competing interests.