Abstract 1017: The BRD-inhibitor OTX015 affects proliferation and gene expression of cells derived from mature lymphoid neoplasms.
Authors: Bonetti Paola , Boi Michela , Bernasconi Elena , Rinaldi Andrea , Kwee Ivo , Gaudio Eugenio , Ponzoni Maurilio , Tibiletti Maria Grazia , Stathis Anastasios , Riveiro Eugenia , Inghirami Giorgio , Zucca Emanuele , Bertoni Francesco 
Published: August 2014

Inhibitors of the BET family members BRD2/3/4 are a promising new class of anti-cancer drugs. Here, we assessed the antitumor activity and the mechanism of action of OTX015, a selective orally bioavailable BRD2/3/4 inhibitor, in cells derived from human mature lymphoid neoplasms.

OTX015 was evaluated in 31 B-cell malignancies cell lines: 13 diffuse large B-cell lymphomas (DLBCL), 8 anaplastic large T-cell lymphomas (ALCL), 4 mantle cell lymphomas (MCL), 3 splenic marginal zone lymphomas (SMZL), and 3 multiple myelomas (MM). Anti-proliferative effect was seen in the majority of the cell lines. The median IC50s, calculated at 72h, were: DLBCL, 0.19μM (range 0.07-12.68); ALCL, 0.48μM (0.04-9.1); SMZL, 0.16μM (0.1-0.24); MM, 0.45μM (0.06-0.7); MCL, 2μM (1.22- &gt;15). There were apparently no IC50 differences based on the cell of origin (DLBCL) or ALK-positivity status (ALCL). Apoptosis did not appear as the main effect of the drug, being not observed in 11 cell lines treated with the IC50 defined by MTT test after 72-hour exposure. However, OTX105 determined a dose-dependent G1 cell cycle arrest in 12/12 cell lines (DLBCL, MM and ALCL), and an increased percentage of senescent cells in 3/3 sensitive cell lines (DLBCL and ALCL).

MYC mRNA was suppressed in a dose-dependent manner in 4/5 DLBCL, 4/4 ALCL and 2/2 MM cell lines. Down-regulation was usually seen within 1h. Real-time PCR showed that MYC and also NFKB target genes were affected. Gene expression profiling (GEP), using the Illumina HumanHT-12 v4 Expression BeadChip array, was done in 3 sensitive DLBCL cell lines, exposed to DMSO or OTX015 (0.5μM) for 4h and 8h. MYC was the most down-regulated gene. Functional annotation of the down-regulated genes identified an over-representation of genes involved in RNA and DNA metabolism and cell cycle, putative MYC target genes and transcripts reported as down-regulated after treatment with aminopeptidase inhibitors and HDAC-inhibitors. Up-regulated transcripts were enriched of genes coding for proteins involved in chromatin structure, as well as putative MYC target genes and transcripts reported as up-regulated after treatment with HDAC-inhibitors, demethylating agents or aplidine. Also, GEP signature was similar to what reported for the BRD-inhibitor JQ1.

In conclusion, OTX015 showed in vitro anti-tumoral activity in a large series of mature lymphoid neoplasms. The activity was largely cytostatic, with cell cycle G1 arrest and induction of senescence. Down-regulation of MYC and its putative targets appeared as the main effect, but it might not be the only mechanism of action, since a few cell lines did not appear to down-regulate MYC after exposure to OTX015, which also induced down-regulation of NFKB target genes and modulation of transcripts similar to what observed with HDAC-inhibitors. The compound appears worth of further investigation as a new promising therapeutic agent in lymphomas.

Citation Format: Paola Bonetti, Michela Boi, Elena Bernasconi, Andrea Rinaldi, Ivo Kwee, Eugenio Gaudio, Maurilio Ponzoni, Maria Grazia Tibiletti, Anastasios Stathis, Eugenia Riveiro, Giorgio Inghirami, Emanuele Zucca, Francesco Bertoni. The BRD-inhibitor OTX015 affects proliferation and gene expression of cells derived from mature lymphoid neoplasms. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1017. doi:10.1158/1538-7445.AM2013-1017