Overexpression and constitutive activation of CYCLIN D1 and Casein Kinase 2 are common features of many hematologic malignancies, including mantle cell lymphoma (MCL) and leukemias such as T-cell acute lymphoblastic leukemia (T-ALL). Although both CK2 and CDK4 inhibitors have shown promising results against these tumor types, none of these agents have achieved objective responses in the clinic as monotherapies. Because both proteins play key roles in these and other hematological malignancies, we have analyzed the therapeutic potential of ON108110, a novel dual specificity ATP-competitive inhibitor of protein kinase CK2 as well as CDK4/6 in MCL and T-ALL. We show that in cell growth inhibition assays, MCL and T-ALL cell lines exhibited increased sensitivity to ON108110 when compared to other tumor types. Treatment with ON108110 reduced the level of phosphorylated RB-family proteins. In addition, ON108110 treatment resulted in concentration dependent inhibition of PTEN phosphorylation and a concomitant decrease in PI3K-AKT signaling mediated by CK2. Accordingly, cells treated with ON108110 rapidly accumulated in the G0/G1 stage of the cell cycle as a function of increasing concentration followed by rapid onset of apoptosis. Together, these results indicate that dual inhibition of CK2 and CDK4/6 may be an efficient treatment of MCL and T-ALLs displaying upregulation of CK2/PI3K and CDK4 signaling pathways.

Triple negative breast cancer (TNBC) remains clinically challenging as patients have heterogeneous responses to current standard of care therapies. Chemotherapy sensitivity is a strong predictor of long-term outcomes for patients, and incomplete response of early stage disease to chemotherapy treatment is associated with a much higher risk of disease relapse and metastatic progression, often occurring within a short time from initial diagnosis. Therefore, treatment strategies that target chemotherapy-resistant TNBC and/or enhance chemosensitivity would improve outcomes for these high-risk patients. Breast cancer stem cell-like cells (BCSC) have been proposed to represent a chemotherapy-resistant subpopulation within the tumor which are also responsible for tumor initiation, progression and metastases. Targeting this population could lead to improved TNBC disease control. We have identified a novel multi-kinase inhibitor 108600 from a screen for inhibitors of this TNBC BCSC population. 108600 treatment suppresses growth, colony and mammosphere forming capacity of the BCSC population. Treatment with 108600 induces G2M arrest and eventual apoptosis of TNBC cells in vitro and of TNBC xenografts in vivo, and overcomes chemotherapy (paclitaxel) resistance of triple negative patient-derived xenografts (PDX). Finally, treatment with 108600 and chemotherapy suppressed the growth of already established TNBC metastases, providing additional support for the clinical translation of this agent to clinical trials.

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