CX-4945, an Orally Bioavailable Selective Inhibitor of Casein Kinase 2 (CK2), Exhibits Anti-Tumor Activity in Chronic Lymphocytic Leukemia and Exhibits Synergy When Combined with the PI3K-Δ Inhibitor GS-1101 or Fludarabine

• Published in: Blood 2012-11, Vol.120 (21), p.2471-2471
• Main Authors: Prins, Renee C, Burke, Russell T, Loriaux, Marc M, Druker, Brian J., Spurgeon, Stephen E
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V120.21.2471.2471

Abstract 2471 Casein kinase 2 (CK2) is a highly conserved and constitutively active serine-threonine protein kinase that plays a fundamental role in maintaining cell survival through pro-proliferative, anti-apoptotic and pro-angiogenic signaling. CK2 promotes malignant cell viability by regulating critical downstream signaling pathways including PI3K/AKT, and overexpression and hyperactivation of this kinase has been well described in B-cell malignancies including chronic lymphocytic leukemia (CLL) and multiple myeloma (MM). In B-cell malignancies, the B-cell receptor (BCR) represents another key survival pathway. BCR activation results in downstream signaling of multiple pro-survival kinases including PI3K and AKT. Drugs that inhibit the transmission of signals through the BCR have been shown to reduce cell survival. Given that BCR-mediated kinase signaling relies on the convergence of many regulatory inputs, we hypothesize that inhibiting this pathway at more than one site would be most effective at killing cells. CX-4945 is the first orally bioavailable small molecule inhibitor of CK2 to progress to human clinical trials. CX-4945 has been found to be highly selective for CK2 and has been shown to inhibit AKT phosphorylation. We have previously reported pre-clinical single agent activity of CX-4945 across a broad range of primary hematologic malignancy samples including CLL. Many of the samples sensitive to CX-4945 were also sensitive to other inhibitors of the BCR pathway. Here we present our findings combining CX-4945 with GS-1101, the isoform selective inhibitor of PI3KΔ, or fludarabine in CLL. Fresh peripheral blood mononuclear cells from CLL patients were purified using a Ficoll-Paque gradient. Purified cells were then added to wells (5 × 104 per well) containing HS-5 stromal cell conditioned media and serial dilutions (ranging from 4.5 nM to 10 μM) of CX-4945 alone and in combination with serial dilutions of GS-1101 and fludarabine (both ranging from 4.5 nM to 10 μM). Cells were cultured for 72 hours and a tetrazolium-based MTS assay was performed to measure cell viability. Synergy analysis was performed using R or CalcuSyn. Ramos, a Burkitt's lymphoma cell line, and primary patient samples were treated with increasing concentrations of CX-4945 alone and in combination with GS-1101, and phosphorylation of the BCR pathway including AKT and ERK were evaluated by immunoblotting. Synergy was observed between CX-4945 and GS-1101 in all samples tested (9