Abstract 2676: The MEK-inhibitor pimasertib is synergistic with PI3K-delta and BTK inhibitors in lymphoma models
Authors: Gaudio Eugenio , Tarantelli Chiara , Barassi Chiara , Bernasconi Elena , Kwee Ivo , Cascione Luciano , Ponzoni Maurilio , Rinaldi Andrea , Stathis Anastasios , Goodstal Samantha , Zucca Emanuele , Bertoni Francesco 
Published: August 2015

Abstract
Pimasertib (AS-703026) is a potent and highly selective ATP noncompetitive MEK1/2 inhibitor that has shown anti-tumor activity in different pre-clinical models. We have previously reported pimasertib activity as single agent in lymphoma models and preliminary combinations results (Gaudio et al, AACR 2014). Here, we report detailed data on combinations of pimasertib with the PI3K-delta inhibitor idelalisib and with the BTK-inhibitor ibrutinib.
Methods. Cell lines derived from activated B-cell like (ABC) diffuse large B-cell lymphoma (DLBCL) (OCI-Ly10, TMD8), germinal center B-cell like (GCB) DLBCL (DOHH2, RCK8) and from mantle cell lymphoma (REC1, JEKO1) were exposed to increasing doses of pimasertib alone and in combination with idelalisib and ibrutinib. Synergy was assessed by Chou-Talalay combination index (CI). ERK phosphorylation level and PARP cleavage were detected by western blotting in cell treated with single agents or combination of pimasertib with idelalisib or ibrutinib. NOD-Scid (NOD.CB17-Prkdcscid/NCrHsd) mice were subcutaneously inoculated with OCI-Ly-10 (10 x106) DLBCL cell line. Mice developed palpable tumors (100 mm3) and were randomized to receive pimasertib, orally once per day (30 mg/kg), ibrutinib (5 mg/Kg), the combination of the two, or control vehicle alone. Tumor size was measured two times per week using a digital caliper [tumor volume (mm3) = (I x W x W)/2].
Results. Strong synergism was observed with pimasertib combined with the PI3K inhibitor idelalisib in the ABC-DLBCL OCI-Ly10 (median CI = 0.026) and TMD8 (CI = 0.25), whereas synergistic/additive effects were detected in GCB-DLBCL (DOHH2, RCK8) and MCL (REC1, JEKO1). Synergism was observed with the BTK-inhibitor ibrutinib in all the cell lines: OCI-Ly10 (CI = 0.32), TMD8 (CI = 0.63), DOHH2 (CI = 0.66), RCK8 (CI = 0.87), REC1 and JEKO1 (CI = 0.2). Thirty minutes of exposure time with pimasertib were sufficient to knock-down phospho-ERK1/2 proteins in the mentioned ABC-DLBCL and MCL cell lines stimulated with anti-IgM (20μg/mL) for 20 minutes. Stronger down-regulation of phospho-ERK1/2 was seen in ABC-DLBCL and MCL cell lines treated with combination of pimasertib with idelalisib or pimasertib with ibrutinib rather than single agent treatment conditions. Notably, apoptosis and PARP cleavage was observed in cell lines treated with pimasertib in combination with ibrutinib or idelalisib.
OCI-Ly10 xenograft tumors that received a combination of pimasertib (30mg/Kg) and ibrutinib (5mg/Kg) for 14 days, showed a five-fold reduction of both tumor volume and weight as compared to the control and single compound groups.
Conclusions. Pimasertib-containing combinations with PI3K-delta and BTK inhibitors show very promising activity in preclinical models of mature lymphomas.
Citation Format: Eugenio Gaudio, Chiara Tarantelli, Chiara Barassi, Elena Bernasconi, Ivo Kwee, Luciano Cascione, Maurilio Ponzoni, Andrea Rinaldi, Anastasios Stathis, Samantha Goodstal, Emanuele Zucca, Francesco Bertoni. The MEK-inhibitor pimasertib is synergistic with PI3K-delta and BTK inhibitors in lymphoma models. [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 2676. doi:10.1158/1538-7445.AM2015-2676