Abstract 2215: Pharmacogenomic investigation of Bruton's tyrosine kinase (BTK) inhibitor ibrutinib (PCI-32765): drug sensitivity in diffuse large B-cell lymphoma (DLBCL) within a tumor microenvironment-aligned high-throughput screen.
Authors: Cuc Davis, Tineke Casneuf, Willem Lightenberg, Richard Rickles, Winnie Tam, Matthias Versele, Steven McClue, Sriram Balasubramanian, Joseph Buggy, Kate Sasser, Brett Hall
Journal: Cancer Research (2013)

Abstract Ibrutinib (PCI-32765) is an orally administered small molecule that covalently binds to Cys-481 of Bruton's tyrosine kinase (BTK). Ibrutinib has demonstrated promise across several types of B-cell malignancies and is currently in Phase 2/3 clinical testing. Preclinical studies have established three key mechanisms following blunting of proximal B cell receptor (BCR) signaling through BTK inhibition: (1) suppression of pro-survival pathways, (2) diminished integrin activation and (3) attenuation of chemotactic response. Single agent ibrutinib Phase 1/2 clinical trials have revealed high clinical response rates in both naïve and relapsed or refractory chronic lymphocytic leukemia (CLL), as well as, relapsed or refractory mantle cell lymphoma (MCL) patients (Byrd, et al. 2012 ASH; Wang, et al. 2012 ASH; Advani, et al. 2010 JCO). Response rates in a phase 2 diffuse large B cell lymphoma (DLBCL) clinical trial appeared to be more prevalent in “activated B-cell” (ABC) over “germinal center B-cell like” (GCB) DLBCL patients (Staudt et al., ASH 2012). To gain a further understanding of ibrutinib response and inform optimal therapeutic combinations in DLBCL, we established a combination high throughput pharmacology screen (cHTS) with ibrutinib. Ibrutinib was evaluated alone and in combination with 99 targeted compounds, across 17 (12 GCB; 5 ABC) DLBCL cell lines. To better align with human biology, DLBCL cell lines were screened in the presence of human marrow stromal cell conditioned media (hMSC-CM) and B-cell receptor stimulation via anti-IgG/anti-IgM antibodies. Interestingly, 8/17 (47%) DLBCL cell lines were intolerant to any external BCR stimulation, so those lines were screened in hMSC-CM without exogenous BCR stimulation. Under our experimental conditions, 11/17 (65%) cell lines displayed some sensitivity (IC50 &amp;lt; 10 M) to ibrutinib at 72 hours based on ATPliteTM measurements [breakdown: 4/17 (24%) highly sensitive (IC50 &amp;lt; 200 nM), 2/17 (12%) sensitive (IC50 200 nM &amp;lt; x &amp;lt; 1 M), 5/17 (29%) modestly sensitive (IC50 1 M &amp;lt; x &amp;lt; 10 M), and 6/17(35%) resistant (IC50 &amp;gt; 10 M)]. Consistent with DLBCL clinical responses, the highly sensitive (IC50 &amp;lt; 200 nM) DLBCL models, which better reflect clinically attainable drug concentrations, demonstrated approximately a two-fold enrichment in ABC (40%; 2/5) versus GCB (17%; 2/12) response with single agent ibrutinib. However, selective drug combinations were found to drive greater sensitivity across both ABC and GCB subtypes. Ongoing work is focused on mapping pathways that contribute to combination drug sensitivity by comparing pharmacologic synergy of targeted agents against mutational (Exome-Seq) and whole genome gene expression profiling (GEP). Together, these data will help to inform optimal ibrutinib combination strategies in DLBCL. Citation Format: Cuc Davis, Tineke Casneuf, Willem Lightenberg, Richard Rickles, Winnie Tam, Matthias Versele, Steven McClue, Sriram Balasubramanian, Joseph Buggy, Kate Sasser, Brett Hall. Pharmacogenomic investigation of Bruton's tyrosine kinase (BTK) inhibitor ibrutinib (PCI-32765): drug sensitivity in diffuse large B-cell lymphoma (DLBCL) within a tumor microenvironment-aligned high-throughput screen. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2215. doi:10.1158/1538-7445.AM2013-2215