Abstract 2533: Synergistic leukemic killing when combining a small molecule Pim protein kinase inhibitor and standard chemotherapeutic agents

Field: Pharmacology, Toxicology and Pharmaceutics (Life Sciences)

Abstract The serine/threonine Pim protein kinases, originally cloned from a M-MuLV integration site, are up-regulated and associated with poor outcomes in multiple human hematologic malignancies including chronic lymphocytic leukemia, myeloid leukemia, diffuse large B-cell lymphoma, and T-cell lymphoma. We have developed novel benzylidene-thiazolidine-2, 4-diones inhibitors of Pim kinases that kill a wide range of both myeloid and lymphoid cell lines and shown that one of those inhibitors, SMI-4a inhibits subcutaneous tumor growth of T-cell acute lymphoblastic leukemia (T-ALL) in nude mice by an average of 47.9% (p&lt; .05). These SMI-4a treated mice had no change in weight, blood counts, cell morphology, or blood chemistries. Treatment of these leukemic cells demonstrates that SMI-4a induced G1-phase cell cycle arrest secondary to an induction of p27Kip1, apoptosis through the mitochondrial pathway, and inhibition of mTORC1 pathway based on decreases in phosphorylation of p70 S6K and 4E-BP1. Since Pim kinases play an important role in cell survival and resistance to chemotherapy, we investigated the activity of combination treatment with SMI-4a and chemotherapeutic agents including daunorubicin (DNR), cytarabine (Ara-C), and 6-thioguanine (6-TG). Although DNR has been employed to treat both T-ALL and myeloid leukemias and is indispensable for the induction of complete remission, it is known to possess cardiotoxicity leading to cardiac failure, and thus drugs that decrease the dosage of DNR may be useful in therapy. We examined the combination of DNR and SMI-4a in T-ALL cell lines, myeloid leukemic cell lines and primary AML blasts from patients. Although this combination exhibits modest additive effect in T-ALL cells, the combination of 20 nM DNR and 40 μM SMI-4a killed 96% of the FLT3-ITD cell line MV4-11, while as single agents DNR and SMI-4a killed only 15 and 30% respectively. Evaluation of primary AML samples demonstrated that this combination significantly increased cell death compared to each agent alone. In addition to DNR, the combination of Ara-C and SMI-4a proved effective. We found significant killing effects when T-ALL cell lines, myeloid leukemic cell lines, and primary AML blasts were incubated with multiple doses of Ara-C in combination with SMI-4a. These changes were also seen when this inhibitor was combined with 6-TG. Since 6-TG induced hepatotoxicity and neutropenia often limit maintenance therapy, this combination therapy could allow a significant decrease in 6-TG dosing in humans. Thus, SMI-4a, a Pim kinase inhibitor with activity in animal models as a single agent with little overt toxicity, enhances the anti-leukemic effects of standard anti-leukemic drugs DNR, Ara-C, and 6-TG in vitro. If used in humans SMI-4a has the potential to limit the dose of these agents needed for treatment, decreasing their toxicity while maintaining anti-leukemic activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2533.