Predicting sensitivity to azacytidine in non-small cell cancer lines by absence of activating mutations.

e18147 Background: A completed clinical trial has demonstrated activity of a combination of epigenetic therapies: entinostat, a histone deacetylase inhibitor, and azacytidine (AZA), a hypomethylating agent. A plasma-based biomarker assaying methylation status of key gene promoters from circulating DNA was developed. In order to test the relationship of activating mutations to sensitivity to epigenetic therapy, we treated non-small cell lung cancer (NSCLC) lines with AZA and assessed tumor growth in xenografts. Tumor from patients on trial was analyzed for mutational status. Methods: Nine NSCLC lines were treated in vitro for 72 hours with 500 nM AZA and injected to form flank tumors in NOG mice. Four lines contain no activating mutations. Of the five mutant lines, three were KRAS and two were EGFR mutations. Lines with no activating mutations are termed “mutation-negative” for known oncogenic drivers. Growth of mock versus treated tumors was compared over time to determine treatment phenotypes. Lines were grouped into four categories: augmented growth compared to mock, no treatment effect, mild inhibition of tumor growth, and marked inhibition. Seventeen tumors from the clinical trial were analyzed by SNaPshot multiplex PCR. Results: Among mutation negative lines three showed marked tumor growth inhibition and one showed mild inhibition. Among cell lines with activating mutations, one showed mild inhibition, three showed no effect, and one showed augmented tumor growth. Among 17 tumor samples from patients on study, four driver mutations were identified: 3 KRAS and one PTEN mutation. All four patients experienced progressive disease on study. Among thirteen patients with mutation negative tumors, three had stable disease and one had a complete response. Conclusions: The association between driver mutation negative status and treatment outcome in NSCLC cell lines in patients receiving AZA and entinostat merits further exploration. Future trials of epigenetic therapy in NSCLC may benefit from a biomarker enrichment strategy and the data presented here represents a potential way forward.