Abstract 953: JARID1 family inhibitor reduces generation of drug-resistant EGFR mutation-positive lung cancer cells
Authors: Ariga Shin , Kinoshita Ichiro , Kikuchi Junko , Shimizu Yasushi , Dosaka-Akita Hirotoshi 
Published: August 2019

Abstract
Epigenetic alteration contributes to tumor initiation, progression and invasion. Epigenetic machinery has become a major focus for the new development of molecular targeted cancer therapeutics. H3K4 trimethylation (H3K4me3) is epigenetic marks which exist surrounding transcription start site of active genes. JARID1 family is demethylase of H3K4me2/me3. JARID1a and JARID1b have been suggested, especially to have oncogenic properties and associations with anti-cancer drug resistance. We previously showed that JARID1 family inhibitor, 2-4(4-methylphenyl)-1,2-benzisothiazol-3(2H)-one (PBIT), recovers sensitivity of drug-resistant lung cancer cells. Here we examined whether PBIT affect the generation of drug resistant cells. A recent report revealed that “secretomes” induced by targeted therapies paradoxically stimulate the outgrowth of drug-resistant subpopulation, which are driven by downregulation of transcription factor FRA1. We confirmed that EGFR mutation-positive PC9 and H1975 cells treated with EGFR-TKIs produced the secretomes that promoted EGFR-TKIs-resistant cell growth. Interestingly, PC9 and H1975 cells pre-treated with 1 μM PBIT did not produce such tumor-promoting secretomes. IGF-1 was upregulated in the secretomes by the EGFR-TKI treatment, but the upregulation was disrupted by the 1 μM PBIT pre-treatment. Immunoblot assay showed that PC9 and H1975 decreased expression of FRA1 after the treatment with EGFR-TKIs, while PC9 and H1975 pre-treated with PBIT mitigated such decrease in FRA1 expression after treatment with EGFR-TKIs. Consistently, chromatin immunoprecipitation assay showed that H3K4me3 at FRA1 promoter region was decreased after treatment with gefitinib in PC9, while the decrease did not occur in PC9 pre-treated with PBIT. To investigate whether PBIT inhibits generation of drug resistant cells, we treated 100 small groups (100 cells each) of cells with EGFR-TKIs with or without 1 μM PBIT for 4 weeks. EGFR-TKI-resistant cells were significantly reduced in combination with PBIT. Of note, 1 μM PBIT alone did not affect clonogenic cell growth in soft agar colony formation assay. Immunoblot assay showed that expression of IGF-1-AKT-S6 pathway molecules in TKI-resistant cells was mitigated by the PBIT combination therapy. These results indicate that PBIT reduces EGFR-TKI-induced secretomes containing IGF-1 as a relevant mediator by preventing downregulation of FRA1 expression via prevention of decrease of active marker H3K4me3 at FRA1 promoter regions. JARID1 inhibitor may have potential to overcome EGFR-TKI-resistance in lung cancer, especially via off-target mechanisms.
Citation Format: Shin Ariga, Ichiro Kinoshita, Junko Kikuchi, Yasushi Shimizu, Hirotoshi Dosaka-Akita. JARID1 family inhibitor reduces generation of drug-resistant EGFR mutation-positive lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 953.