Abstract 3527: OTX015, a novel BET-bromodomain (BET-BRD) inhibitor, displays antitumoral effects in orthotopic and heterotopic models of human glioblastoma
Authors: Astorgues-xerri Lucile , Berenger Caroline , Cayol Mylène , Bekradda Mohamed , Odore Elodie , Rezai Keyvan , Cvitkovic Esteban , Riveiro Maria E. , Ouafik L'Houcine 
Published: August 2015

Background: BRD2 and BRD4, members of the BET family of bromodomains, were recently described to be significantly increased in glioblastoma multiforme (GBM), the most common primary adult brain cancer. OTX015 (OncoEthix SA, Switzerland), a novel BET-BRD2/3/4 inhibitor, is currently being evaluated in clinical Phase Ib studies in hematologic malignancies and solid tumors, including GBM. Here, we report the effects of OTX015 in vitro as a single agent and in combination with temozolomide (TMZ) in human U87MG cells, along with in vivo activity in heterotopic and orthotopic U87MG models.

Material and Methods: GI50s were determined in U87MG cells after 72 h with OTX015 or JQ1 with MTT assays. Combination indexes of simultaneous and sequential schedules of OTX015 with TMZ were determined using Chou & Talalay analysis. For orthotopic in vivo experiments, 105 U87MG cells were injected in the frontal lobe of nude mice and 5 days later mice were randomized. For the xenograft model, 5.106 U87MG cells were injected into the right lateral flank and mice were randomized when tumors reached 100 mm3. Treatment groups (n = 6) were: vehicle PBS, OTX015 50 mg/kg/BID and 100 mg/kg/daily, or TMZ 100 mg/kg/daily (ip, days 6-10). Median survival was determined in the orthotopic model by the Kaplan-Meier method. Tumor volume was evaluated 3 times weekly in the flank model. An independent in vivo experiment was done for the evaluation of OTX015 levels in tumor and normal tissues, animals were sacrificed after 7 days of treatment at 50 mg/kg/BID, using ultra performance liquid chromatography with tandem mass spectrometry.

Results: OTX015 displayed antiproliferative effects in U87MG cells with GI50 values of 0.9μM versus 2.1μM for JQ1. OTX015/TMZ combination studies revealed synergistic activity when TMZ was administered after OTX015. OTX015 significantly increased survival in mice bearing orthotopic U87MG cells, with median survival of 28 and 25 days for 50 and 100 mg/kg/daily OTX015, respectively vs 19.5 days in control mice. Furthermore, in the heterotopic model, OTX015 treatment at both doses, significantly decreased tumor growth at day 22. No major side effects were seen during in vivo OTX015 treatment. In orthotopic models, OTX015 plasmatic levels were 1365.3 (±481)ng/mL, while in tumor and peritumoral brain tissues OTX015 levels were 995.0(±549) and 62.97(±10.3)ng/g tissue, respectively. In the flank model, OTX015 tumor levels were about 1.2 times higher than in peripheral muscle tissue and plasma levels [848.1(±127)ng/mL] and about 7 times higher than in normal brain tissue.

Conclusion: We demonstrated the passage of OTX015 across the blood-brain barrier, as well as preferential binding of OTX015 to tumor tissue. Oral OTX015 treatment significantly enhanced survival and decreased tumor growth in GBM xenograft models, highlighting the therapeutic potential of OTX015 in GBM patients.

Citation Format: Lucile Astorgues-xerri, Caroline Berenger, Mylène Cayol, Mohamed Bekradda, Elodie Odore, Keyvan Rezai, Esteban Cvitkovic, Maria E. Riveiro, L'Houcine Ouafik. OTX015, a novel BET-bromodomain (BET-BRD) inhibitor, displays antitumoral effects in orthotopic and heterotopic models of human glioblastoma. [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 3527. doi:10.1158/1538-7445.AM2015-3527