Abstract

Disseminated cancer cells (DCCs) identified in secondary organs, sometimes before the primary tumor becomes detectable and treated, can remain dormant for years to decades before manifesting. Microenvironmental and epigenetic mechanisms may control the onset and escape from dormancy, and here we reveal how a combination of the DNA methylation inhibitor 5-azacytidine (AZA) and retinoic acid receptor ligands all-trans retinoic acid (atRA), orchestrate a novel program of stable dormancy. Treatment of HNSCC tumor cells with AZA+atRA induced a SMAD2/3/4 dependent regulation of downstream transcriptional program that restored the anti-proliferative function of TGF{beta} signaling. Significantly, AZA+atRA or AZA+AM80, an RAR specific agonist, strongly suppresses lung metastasis formation. The metastatic suppression occurs via the induction and maintenance of phenotypically homogenous dormant SMAD4+/NR2F1+ non-proliferative DCCs. These findings suggest that strategies that maintain or induce dormancy programs may be a viable alternative strategy to improve patient outcomes by preventing or significantly delaying metastasis development.