Recently, several small molecule drugs were approved for treatment of chronic lymphocytic leukemia (CLL), significantly improving patient management. However, knowledge about how to combine these therapies for optimal effects and what patients will best benefit from them is lacking. Here, we show that drug synergies can be identified by single cell signaling analyses. We investigated the effects of idelalisib, ibrutinib, and venetoclax on 35 protein epitopes by phospho flow in CLL cells. The activity of proteins in the B-cell receptor signalosome and the phosphatidylinositol 3-kinase pathway were altered upon drug exposure. Combined treatment with ibrutinib and venetoclax give promising results in clinical studies and we show that this combination exerted synergistic inhibitory effects on cell signaling and cell viability. Cell viability was monitored by flow cytometry and with independent drug sensitivity screens. Our analyses indicate that the standard dosages of ibrutinib and venetoclax can be lowered without loss of efficacy, potentially reducing drug costs, and toxicities. Observed correlation between signaling and viability indicates that signaling molecules could serve as biomarkers to predict response to therapy. We suggest that phospho flow should be considered as a novel approach for dose and synergy prediction in a precision medicine setting for CLL.
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The authors are grateful to all the study participants without whom this study would not have been possible. We thank Martine Schrøder, Marianne Enger, and Gladys M. Tjørhom for expert technical assistance. We are grateful to Alexandra Gade, Johannes Landskron, and Eirin Solberg at the High-Throughput Chemical Biology Screening Platform at Centre for Molecular Medicine Norway, University of Oslo, for assistance with drug sensitivity screens. This work was supported by the Norwegian Cancer Society, the Regional Health Authority for South-Eastern Norway, the Research Council of Norway and Stiftelsen Kristian Gerhard Jebsen (grant number SKGJ-MED-019). SSS was funded by a Career Development Research Fellowship from the Norwegian Cancer Society.
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Skånland, S.S., Cremaschi, A., Bendiksen, H. et al. An in vitro assay for biomarker discovery and dose prediction applied to ibrutinib plus venetoclax treatment of CLL. Leukemia 34, 478–487 (2020). https://doi.org/10.1038/s41375-019-0569-7
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