Abstract 3271: BRD4 inhibition enhances the acalabrutinib tumor response by modulating PAX5 and interferon signaling in ABC-DLBCL
Authors: Oien Derek B. , Sharma Samanta , Xu Ye , Hattersley Maureen , DuPont Michelle , Burke Kathleen , Criscione Steven W. , Prickett Laura , Zhang Jingwen , Chan Ho Man , Drew Lisa , Yao Yi 
Published: June 2022

Abstract
AZD5153 is a bivalent bromodomain and extraterminal (BET) inhibitor that simultaneously engages the two bromodomains of bromodomain-containing protein 4 (BRD4). Here, we initially tested AZD5153 in combination with acalabrutinib, a Bruton tyrosine kinase (BTK) inhibitor, in a panel of diffuse large B-cell lymphoma (DLBCL) cell lines. The ABC type DLBCL cells responded to the AZD5153 and acalabrutinib combination at lower drug concentrations compared to other DLBCL cell lines. Many of these lower concentrations were below the clinical equivalent dose for each drug. Similar results were achieved in DLBCL patient-derived xenografts, with most ABC-DLBCL tumors having more growth inhibition than the other B-cell lymphoma tumors after combination dosing at fixed concentrations. To delineate the mechanism of ABC-subtype preference for combination therapy, we performed RNA sequencing on ABC-DLBCL tumor samples treated with AZD5153, acalabrutinib, and the combination of AZD5153 and acalabrutinib. Pathway meta-analyses identified significant alterations of PAX5 signaling and interferon pathways in combination-treated tumors compared to monotherapy-treated samples. PAX5 is a key gene for B-cell activation and is associated with lymphoma pathogenesis. Protein levels of PAX5 and corresponding downstream transcription targets were also decreased by the combination of AZD5153 and acalabrutinib in ABC-DLBCL cell lines. In addition, STAT proteins related to PAX5 activation, the alternative RelB-NFκB pathway, and toll-like receptors in the interferon type I pathway were also modulated at the protein level by this drug combination in ABC-DLBCL cell lines. We hypothesized the AZD5153 and acalabrutinib combination induces changes to interferon signaling that impacts PAX5 activation. This mechanism is supported by evidence of AZD5153 and acalabrutinib combination-induced downregulation of interferons alpha and beta, as well as interferon gamma and IP-10 in vivo. In summary, our results demonstrate AZD5153 enhances the efficacy of acalabrutinib, and our in vitro data suggest adding AZD5153 to acalabrutinib concentrations much lower than the clinical equivalent dose results in a similar biomarker response. We show that this drug combination attenuates interferon signaling, which supports the mechanism of AZD5153 and acalabrutinib inhibiting PAX5 signaling in ABC-DLBCL.
Citation Format: Derek B. Oien, Samanta Sharma, Ye Xu, Maureen Hattersley, Michelle DuPont, Kathleen Burke, Steven W. Criscione, Laura Prickett, Jingwen Zhang, Ho Man Chan, Lisa Drew, Yi Yao. BRD4 inhibition enhances the acalabrutinib tumor response by modulating PAX5 and interferon signaling in ABC-DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3271.