Abstract A179: The BRD4 degrader MZ1 exhibits potent antitumoral activity in diffuse large B cell lymphoma of the activated B cell-like type
Authors: Tarantelli Chiara , Ekeh Hillarie , Moscatello Carmelo , Gaudio Eugenio , Testa Andrea , Zucca Emanuele , Stathis Anastasios , Ciulli Alessio , Bertoni Francesco 
Published: August 2018

Abstract
Background: Bromodomain and Extra-Terminal domain (BET) proteins are epigenetic readers that play a fundamental role in transcription regulation. Preclinical and early clinical evidences sustain BET targeting as a promising novel approach for cancer treatment. BET degraders are chimeric compounds merging a BET inhibitor, which allows the binding to BET bromodomains, linked to an additional small molecule, which mediates the binding to an E3 ubiquitin ligase complex, triggering BET proteins degradation via the proteasome. These compounds are based on the concept of the PROTAC (Proteolysis targeting Chimera) (Sakamoto et al, PNAS 2001). MZ1 is a potent BRD4 degrader that exploits JQ1 for BET bromodomain binding and the von Hippel Lindau-containing complex for protein degradation (Zengerle et al, ACS Chem Biol 2015; Gadd et al., Nat Chem Biol 2017). MZ1 showed potent antiproliferative activity in AML cell lines (Chan et al. J Med Chem 2017). Here, we present data on the antitumor activity of MZ1 in diffuse large B cell lymphoma of the activated B cell like (ABC DLBCL). Materials and Methods: Established lymphoma cell lines were exposed for 72 hours to increasing doses of the compounds. Cell proliferation was evaluated by using MTT assay. FACS analysis was performed to measure apoptotic activation (Annexin V, threshold of 1.5 fold) after 72 hours of treatment. Results: The antitumor activity of the BET degrader MZ1, of its negative control epimer cisMZ1 and, as comparison, of the BET inhibitor OTX015/MK-8628 was assessed in seven cell lines derived from diffuse large B cell lymphoma of the activated B cell like (ABC DLBCL). MZ1 was very active with a median IC50 of 50nM (range, 5-150 nM). No activity was seen with cisMZ1. BET degrader was more active in vitro than the BET inhibitor, which presented a median IC50 of 125 nM (range, 80-400 nM) (P=0.024). Importantly, MZ1 (500nM, 72 h) induced apoptosis in all the seven ABC DLBCL cell lines, while, in accordance with previous data (Boi et al, Clin Cancer Res 2015), OTX015 (500nM, 72 h) was cytotoxic only in 2/7 cell lines (P=0.021). No apoptosis was observed with cisMZ1 (500nM, 72 h). Conclusion: The BRD4 degrader MZ1 had a strong cytotoxic activity in all the ABC-DLBCL cell lines we tested, and, at least in vitro, it elicited more profound effects than BET inhibitors, and encourages further investigations.
Citation Format: Chiara Tarantelli, Hillarie Ekeh, Carmelo Moscatello, Eugenio Gaudio, Andrea Testa, Emanuele Zucca, Anastasios Stathis, Alessio Ciulli, Francesco Bertoni. The BRD4 degrader MZ1 exhibits potent antitumoral activity in diffuse large B cell lymphoma of the activated B cell-like type [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A179.