Results represent the mean SD of one representative experiment performed in duplicate (*< 0

Results represent the mean SD of one representative experiment performed in duplicate (*< 0.05, **< 0.01, ***< 0.001 respect to controls). in translational models of neuroblastoma [15]. OTX015 is the first BET inhibitor to have moved into the medical center, with three phase Ib clinical trials initiated in hematologic malignancies ("type":"clinical-trial","attrs":"text":"NCT01713582","term_id":"NCT01713582"NCT01713582) [21, 22], selected solid tumors ("type":"clinical-trial","attrs":"text":"NCT02259114","term_id":"NCT02259114"NCT02259114) and glioblastoma multiforme ("type":"clinical-trial","attrs":"text":"NCT02296476","term_id":"NCT02296476"NCT02296476). We statement here preclinical findings of the BET inhibitor OTX015 in NSCLC and SCLC cell lines harboring oncogenic mutations recurrently found in lung cancer patients. In NSCLC models, OTX015 was equally active in both EML4-ALK positive and negative cell lines harboring other oncogenic mutations. OTX015-exposure resulted in quick and sustained downregulation of MYC or MYCN, together with an downregulation of stemness markers in sensitive NSCLC models. Conversely, we observed that despite broad amplification of MYC family genes, OTX015 did not show potent or antitumor effects in the SCLC models evaluated. RESULTS OTX015 reduces cell proliferation and induces cell cycle arrest in NSCLC cell lines with or without the EML4-ALK translocation OTX015 displayed antiproliferative effects in EML4-ALK negative and positive NSCLC cell lines (Table ?(Table1,1, detailed in Supplementary Table S2). After 72 h exposure, two out five cell lines (HOP62, HOP92) displayed GI50 values below 0.5 M, whereas H2228 and H3122 cells offered GI50 values below 1.0 M (0.63 and 0.70 M, respectively). In addition, these four cell lines displayed Emax values from 35% to 58% after 72 h-exposure. On the other hand, A549 cells offered a GI50 > 6 M and an Emax of 82%. The OTX015-resistant A549 cell collection presents both KRAS and LKB1 mutated genes (Table ?(Table1).1). OTX015 was more potent than JQ1 following 72 h-exposure in all five cell lines. OTX015 inhibited cell proliferation in sensitive cell lines at concentrations that are achievable in plasma samples of patients treated with nontoxic OTX015 doses in an ongoing Phase I study in hematologic malignancies [23]. Table 1 Antiproliferative effects of the BET inhibitor OTX015 in NSCLC and SCLC cell lines fusion protein and and amplification. Red indicates mutation, blue is usually wild-type, Y = yes, and NE = not evaluated. To determine if OTX015 exerts cytostatic effects in NSCLC cells, as previously explained for other adult cancers [14, 17, SEL10 20] we evaluated cell cycle regulation after 500 nM OTX015 treatment in three OTX015-sensitive cell lines (HOP92, H2228 Olmutinib (HM71224) and H3122) and one resistant model (A549). After 24 h-treatment a decrease in cells in the S phase was seen in H2228 and H3122 cell lines, while then after 72 h of OTX015-exposure in HOP92 cells a significant increase in the percentage of cells in G1, along with a decrease in the percentage of cells in the S phase were seen (< 0.05) (Figure Olmutinib (HM71224) ?(Figure1A)1A) after 72 h-treatment. No modulation of cell cycle phases was observed at any time point for the OTX015-resistant cell collection A549. Similar results were obtained with JQ1 (data not shown). Open in a separate window Physique 1 (A) OTX015 induces cell cycle changes in OTX015-sensitive NSCLC cell lines. Effect of 500 nM OTX015 on cell cycle progression after 24 h in H2228 and H3122 and after 72 h in HOP92 Olmutinib (HM71224) and A549 cells, by FACScan, expressed as percent cells per cell cycle phase (*< 0.05 for G0/G1 cell cycle phase, and #< 0.05 for S phase). (B) OTX015 modulates MYC and MYCN mRNA levels in sensitive and resistant NSCLC cell lines. Effect of Olmutinib (HM71224) 500 nM OTX015 on MYC and MYCN mRNA levels after 4 and 24 h by qPCR, expressed as fluorescence intensity normalized to housekeeping genes. Results represent the imply SD of one representative experiment.