Abstract 793: The novel Bruton's tyrosine kinase inhibitor ARQ531 disrupts survival signaling and triggers apoptosis in AML cells
Authors: debora soncini , orecchioni stefania , cagnetta antonia , retali veronica , ruberti samantha , minetto paola , contini paola , nencioni alessio , monacelli fiammetta , Hall Terence , gobbi marco , eathiraj sudharshan , schwartz briam , bertolini francesco , lemoli roberto , cea michele 
Published: August 2018

Abstract
Introduction: Currently available therapeutics against Acute Myeloid Leukemia (AML) have improved patient outcome. However, resistance develops even to novel therapies and patient overall survival remains low, especially for patients who are not eligible for allogeneic bone marrow transplantation. Therefore, there is an urgent need to overcome the biologic mechanisms underlying drug resistance in AML, to both enhance the efficacy of existing treatments and to facilitate the design of novel approaches. The Bruton's tyrosine kinase (BTK) is emerging as new therapeutic target in a wide range of hematologic malignancies including AML, especially those carrying FLT3-ITD mutation. ARQ 531 is an ATP competitive, orally bioavailable, potent inhibitor of BTK and other relevant kinases. Herein we present preclinical data with ARQ 531 in AML and its efficacy compared with the standard BTK inhibitor Ibrutinib.
Methods: Inhibitory effects of ARQ531 on cell viability were investigated in a panel of AML cell lines as well as primary tumor cells. The effect of ARQ531 on BCR signaling was investigated by western blot. Specific transcriptomic profiling of ARQ531 treated AML cells was performed by RNA-Seq. NSG mice engrafted with primary AML cells were used to determine anti-AML activity of ARQ531 in vivo.
Results: ARQ531 blocked phosphorylation of BTK and downstream protein PLCγ in a panel of AML cell line regardless of their genetic background. ARQ531 also inhibited cell viability of AML cell lines (n=11) and primary AML cells (n=12) with IC50 values lower than reference compound (0.9±1 µM compared with 19±0.6 µM of Ibrutinib). Moreover, ARQ531 effects were not reduced in presence of normal or leukemic mesenchymal stromal cells (MSCs) and, more importantly such treatment showed greater therapeutic window than standard: IC50 value on CD34+ cells from healthy donors was &gt;10µM and ±3 µM after ARQ531or ibrutinib, respectively. A transcriptome profiling analysis revealed a reversion of the oncogenic MYC-driven transcriptional program as specific event triggered by ARQ531. As result, Myc-targets inhibition was observed in AML cells treated with ARQ531 compared with ibrutinib. Finally, the anti-tumor activity of ARQ 531 was determined in AML-PDX model. At 31st day after cell transfer, flow cytometry evaluation of the circulating human CD45+ cells in the murine PB revealed a significant lower leukemia burden after ARQ531 treatment compared with Ibrutinib (10 ± 0.1% and 40 ± 0.01%, respectively; p=0.006)
Conclusion: The novel BTK inhibitor ARQ 531 is a highly potent kinase inhibitor with promising activity against AML in preclinical models.
Citation Format: soncini debora, stefania orecchioni, antonia cagnetta, veronica retali, samantha ruberti, paola minetto, paola contini, alessio nencioni, fiammetta monacelli, Terence Hall, marco gobbi, sudharshan eathiraj, briam schwartz, francesco bertolini, roberto lemoli, michele cea. The novel Bruton's tyrosine kinase inhibitor ARQ531 disrupts survival signaling and triggers apoptosis in AML cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 793.