Bromodomain and extraterminal (BET) bromodomain (BRD) proteins are epigenetic readers that bind to acetylated lysine residues on chromatin, acting as co-activators or co-repressors of gene expression. BRD2 and BRD4, members of the BET family, are significantly increased in glioblastoma multiforme (GBM), the most common primary adult brain cancer. OTX015 (MK-8628), a novel BRD2/3/4 inhibitor, is under evaluation in dose-finding studies in solid tumors, including GBM. We investigated the pharmacologic characteristics of OTX015 as a single agent and combined with targeted therapy or conventional chemotherapies in glioblastoma cell lines. OTX015 displayed higher antiproliferative effects compared to its analog JQ1, with GI 50 values of approximately 0.2 mM. In addition, C-MYC and CDKN1A mRNA levels increased transiently after 4 h-exposure to OTX015, while BRD2, SESN3, HEXIM-1, HIST2H2BE, and HIST1H2BK were rapidly upregulated and sustained after 24 h. Studies in three additional GBM cell lines supported the antiproliferative effects of OTX015. In U87MG cells, OTX015 showed synergistic to additive activity when administered concomitant to or before SN38, temozolomide or everolimus. Single agent oral OTX015 significantly increased survival in mice bearing orthotopic or heterotopic U87MG xenografts. OTX015 combined simultaneously with temozolomide improved mice survival over either single agent. The passage of OTX015 across the blood-brain barrier was demonstrated with OTX015 tumor levels 7 to 15-fold higher than in normal tissues, along with preferential binding of OTX015 to tumor tissue. The significant antitumor effects seen with OTX015 in GBM xenograft models highlight its therapeutic potential in GBM patients, alone or combined with conventional chemotherapies.Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumor in humans, accounting for 52% of all functional tissue brain tumors and 20% of all intracranial tumors. 1,2 Standard of care is typically surgery followed by radiotherapy with the DNA alkylating agent temozolomide. 3 Median survival after diagnosis is only 15 months, leaving a large unmet medical need. 4 Alternative therapeutic approaches have focused on targeted therapies against processes known to play a major role in GBM development, such as blocking angiogenesis with the anti-VEGF agent, bevacizumab. 5 The topoisomerase inhibitor irinotecan which blocks DNA replication causing cell death has also shown hints of activity against malignant glioma in the clinical setting. 6,7 Key words: BET inhibitor, OTX015 (MK-8628), glioblastoma, blood brain barrier, combination studies. Abbreviations: 95% CI: 95% confidence interval; BET: bromodomain and extraterminal; BID: bi-daily; BRD: bromodomain; CI: combination index; E max : drug efficacy as percent cell proliferation inhibition at the highest dose; GBM: glioblastoma multiforme; GI 50 : drug concentration at which cell proliferation is reduced by half; IP: intraperitoneal; MTX: methotrexate; po: per orally; VEGF: vascula...

Triple-negative breast cancer (TNBC) is an aggressive and heterogeneous subgroup of breast tumors clinically defined by the lack of estrogen, progesterone and HER2 receptors, limiting the use of the targeted therapies employed in other breast malignancies. Recent evidence indicates that c-MYC is a key driver of TNBC. The BET-bromodomain inhibitor OTX015 (MK-8628) has potent antiproliferative activity accompanied by c-MYC down-regulation in several tumor types, and has demonstrated synergism with the mTOR inhibitor everolimus in different models. The aim of this study was to evaluate the anti-tumor activity of OTX015 as single agent and in combination with everolimus in TNBC models. OTX015 was assayed in three human TNBC-derived cell lines, HCC1937, MDA-MB-231 and MDA-MB-468, all showing antiproliferative activity after 72 h (GI50 = 75–650 nM). This was accompanied by cell cycle arrest and decreased expression of cancer stem cells markers. However, c-MYC protein and mRNA levels were only down-regulated in MDA-MB-468 cells. Gene set enrichment analysis showed up-regulation of genes involved in epigenetic control of transcription, chromatin and the cell cycle, and down-regulation of stemness-related genes. In vitro, combination with everolimus was additive in HCC1937 and MDA-MB-231 cells, but antagonistic in MDA-MB-468 cells. In MDA-MB-231 murine xenografts, tumor mass was significantly (p < 0.05) reduced by OTX015 with respect to vehicle-treated animals (best T/C = 40.7%). Although everolimus alone was not active, the combination was more effective than OTX015 alone (best T/C = 20.7%). This work supports current clinical trials with OTX015 in TNBC (NCT02259114).

The pharmacokinetics of oral OTX015 in patients with haematologic malignancies can be described with a one-compartment model. Population pharmacokinetic modelling of OTX015 plasma concentrations showed that LBM influences V and CL. These findings do not suggest the need for dose adjustment.