Abstract 3526: OTX015 effects in triple-negative breast cancer (TNBC) models are independent of hypoxia conditions and synergistic with other anticancer agents
Authors: Vázquez Ramiro , Astorgues-Xerri Lucile , Riveiro María E. , Beltrame Luca , Marchini Sergio , Bertoni Francesco , Kwee Ivo , Mohamed Mohamed , Cvitkovic Esteban , Frapolli Roberta , D'Incalci Maurizio 
Published: August 2015

Background: TNBC is an aggressive and heterogeneous subtype group of breast cancers clinically defined by the lack of estrogen and progesterone receptors, as well as the human epidermal growth factor receptor 2 (HER2). Few therapeutic options have shown clinical benefit beyond cytotoxic chemotherapy. Clinical studies have demonstrated that more than 50% of human breast cancers present a much lower median O2 partial pressure than normal breast tissue, correlating with chemo- and radio-resistance. We previously reported the in vivo effects of the BET-bromodomain inhibitor OTX015 (OncoEthix SA, Switzerland) in TNBC models (Vázquez et al.; EORTC-ENA 2014; #580). The aim of this work was to evaluate the in vitro antitumor activity of OTX015 both in normoxic and hypoxic environments, as well as in combination with antitumor agents. Materials and Methods: OTX015 growth inhibition concentrations 50% (GI50) values were determined in HCC197, MDA-MB-231 and MDA-MB-468 human-derived TNBC cell lines after 48 and 72 h in normoxia and hypoxia (0.1% atmospheric O2), employing the MTT assay and cell counting. RT-PCR was performed with Fast SYBR Green Master Mix on a StepOnePlus Real-Time PCR System at baseline, and after 24, 48 and 72 h of OTX015 treatments. OTX015 was combined with docetaxel or the mTOR inhibitor, everolimus, and the combination index (CI) determined by the Chou-Talalay method (CI &lt; 0.9 synergy; CI = 0.9-1.1, additivity; CI &gt; 1.1, antagonism).

Results: OTX015 showed antiproliferative activity in the 3 cell lines after 48- and 72-h treatments in normoxia and hypoxia. MDA-MB-231 was the most sensitive in both conditions. Hypoxia significantly (p &lt; 0.05) increased the antiproliferative activity of OTX015 in MDA-MB-468 cells. In addition, the antitumor effect of OTX015 was accompanied - in these cells only - with a marked (p &lt; 0.05) reduction in the expression levels of c-MYC and n-MYC. The three cell lines presented a substantial increase in p21 expression following OTX015 exposure, correlating with G1 cell cycle arrest. Everolimus had an additive effect when simultaneously combined with OTX015 in HCC1937 and MDA-MB-231 cells (CI = 1.02 and 0.94, respectively), and was antagonistic in MDA-MB-468 cells (CI = 1.60). Likewise, docetaxel also had an additive effect when simultaneously combined with OTX015 in HCC1937 and MDA-MB-231 cells (CI = 1.03 and 0.95 respectively), and showed a slight synergism in MDA-MB-468 cells (CI = 0.87). Conclusion: These preclinical data support the further development OTX015 in the clinical setting for TNBC, alone or in combination with mTOR inhibitors. A single agent Phase Ib study in solid tumor patients including TNBC is underway.

Citation Format: Ramiro Vázquez, Lucile Astorgues-Xerri, María E. Riveiro, Luca Beltrame, Sergio Marchini, Francesco Bertoni, Ivo Kwee, Mohamed Mohamed, Esteban Cvitkovic, Roberta Frapolli, Maurizio D'Incalci. OTX015 effects in triple-negative breast cancer (TNBC) models are independent of hypoxia conditions and synergistic with other anticancer agents. [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 3526. doi:10.1158/1538-7445.AM2015-3526