Abstract 3530: Gene expression profile of OTX015, a BET bromodomain inhibitor, in preclinical models of non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) models
Authors: Riveiro Maria Eugenia , Kwee Ivo , Astorgues-Xerri Lucile , Bekradda Mohamed , Vazquez Ramiro , Rinaldi Andrea , Cvitkovic Esteban , Bertoni Francesco 
Published: August 2015

Background. BET bromodomain proteins recognize chromatin modifications and act as epigenetic readers contributing to gene transcription. OTX015, a novel BET bromodomain inhibitor currently in clinical Phase Ib studies in hematologic malignancies and solid tumors, including lung cancer. We have shown in vitro and in vivo activity of OTX015 in NSCLC and SCLC models (Riveiro et al; EORTC 2014), however the mechanism of action and relevant affected genes are not fully characterized. This study aimed to elucidate pathways and genes affecting response/resistance to OTX015 in lung models.Methods. OTX015 (OncoEthix SA, Switzerland), GI50 values were determined with the MTT assay after 72h exposure in 5 NSCLC cell lines (H2228, H3122, A549, HOP62, HOP92) and 4 SCLC cell lines (H82, H69, DMS79, DMS114). For cell cycle analysis, cells were stained with propidium iodide and analyzed with a FACScan flow cytometer. RNA was isolated after treatment with DMSO or OTX015 (500 nM) for 2, 4, 8 or 12 and 24h and gene expression profiles (GEP) were obtained in all NSCLC and 2 SCLC (H82 and DMS114) cell lines with Illumina HumanHT-12 Expression BeadChips.

Results. OTX015 displayed antiproliferative effects in 4 of the 5 NSCLC cell lines with GI50 values from 110 to 940 nM, whereas A549 cells (harboring mutations in KRAS and LKB1 genes) were resistant to OTX015. Among SLCL models, DMS114 cells showed dose-dependent sensitivity to OTX015 [GI50 = 120nM], while H82, H69, and DMS79 cells were resistant [GI50 &gt;6 μM], despite overexpressing CMYC and/or NMYC. In sensitive-NSCLC models we observed an increase in cells in the S phase after OTX015 treatment, whereas an increase in the G1 phase was observed in the sensitive DMS114 cell line. GEP showed that changes in expression levels of EFR3B and genes related to RNA biogenesis were higher in SCLC cells with reduced sensitivity to OTX015 than in sensitive cells. On the other hand, genes related to histones and chromatin structure were the most differentially expressed after OTX015 exposure in both sensitive and resistant cell lines. In NSCLC models, EFR3B and FOS gene up-regulation, IL7R and IL6-related gene down-regulation were associated with higher OTX015 sensitivity Expression changes more prominent in OTX015-resistant cells affected the transcription factor FOXD1 and genes related to RNA processing.

Conclusions. Our data contribute to elucidate the mechanisms associated with OTX015 sensitivity in several lung cancer in vitro models, supporting the rationale for the ongoing clinical Phase Ib study in solid tumors including NSCLC patients (KRAS+; ALK+).

Citation Format: Maria Eugenia Riveiro, Ivo Kwee, Lucile Astorgues-Xerri, Mohamed Bekradda, Ramiro Vazquez, Andrea Rinaldi, Esteban Cvitkovic, Francesco Bertoni. Gene expression profile of OTX015, a BET bromodomain inhibitor, in preclinical models of non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3530. doi:10.1158/1538-7445.AM2015-3530