A Potential Therapeutic Strategy for Chronic Lymphocytic Leukemia by Combining GS-1101, a PI3 kinase Delta (PI3Kδ) Inhibitor and a Novel Highly Selective Spleen Tyrosine Kinase (Syk) Inhibitor, GS-9973

• Published in: Blood 2012-11, Vol.120 (21), p.3876-3876
• Main Authors: Burke, Russell T, Clarke, Astrid, Meadows, Sarah A, Loriaux, Marc M, Dunlap, Jennifer B, Fan, Guang, Maciejewski, Patricia, Di Paolo, Julie, Lannutti, Brian J., Druker, Brian J., Spurgeon, Stephen E
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V120.21.3876.3876

Abstract 3876 Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western World and remains incurable with standard therapies. Despite significant advances, novel treatments are essential to improve outcomes. A number of therapeutic agents have recently been developed including some that have shown significant activity and tolerability in clinical trials. Among these drugs, are small molecule kinase inhibitors that inhibit B-cell receptor (BCR)-mediated signaling pathways and disrupt essential CLL cell-microenvironment interactions. Specifically, when primary CLL cells are treated with GS-1101, a PI3 kinase delta-specific isoform (PI3Kδ) inhibitor, Bruton’s tyrosine kinase (Btk) inhibitors or spleen tyrosine kinase (Syk) inhibitors, inhibition of signaling pathways downstream of the BCR, cell killing, and disruption of chemokine-mediated CLL cell migration are observed. Although significant clinical activity has been observed in patients treated with single agents that target these critical pathways, very little is known about the effects of inhibiting multiple nodes in the BCR pathway. Simultaneous inhibition of multiple pathways downstream of the BCR has the potential to result in a synergistic response that may overcome the resistance observed with single compound use. These considerations prompted us to assess the effects of PI3Kd and Syk inhibition and to determine if dual inhibition might enhance antitumor effects in CLL. CLL patient samples were assessed for growth inhibition, chemokine release, and pathway activation status using a tetrazolium-based MTS assay, ELISA, and flow cytometry, respectively. PBMCs were isolated from primary patient samples using a Ficoll-Paque gradient. GS-1101, a PI3Kδ inhibitor, and GS-9973, a novel Syk inhibitor, were plated either alone in concentrations known to span their IC50 (.6nM to 10uM), or in combination using equimolar concentrations of each drug (.6nM to 10uM) in 96-well plates. 5×105 primary cells were cultured in triplicate in HS-5 stromal cell conditioned media and growth inhibition was determined after 72 hours. To explore potential additive, synergistic, or antagonistic interactions between GS-1101 and GS-9973, dose response and interaction indices were calculated using R (Lee et al. 2007). Given the importance of microenvironmental signals in the ability of malignant cells to survive, proliferate, and resist standard therapies, we investigated the effect of combining PI3Kd and Syk inhi