Abstract 5396: Characterization of small molecule inhibitors of the PIM kinases in in vitro models of hematological malignancies

The three members of the Pim kinase family, Pim-1, -2, and -3, are established oncogenes and are attractive targets in hematological malignancies. We have developed multiple potent and selective scaffolds of pan-Pim inhibitors with picomolar enzymatic potency and nanomolar cellular potency. Using these agents, we have observed that the abolishment of Pim activity impairs tumor cell viability in multiple settings, both in vitro and in vivo. We have developed numerous assays to measure Pim protein levels and activity, including Pim downstream markers p-PDCD4 and p-BAD, that might be broadly applicable to human tissues. These assays have allowed us to establish a correlation between Pim protein levels and sensitivity to Pim inhibition across multiple tumor settings, in vitro. We have observed that all tested multiple myeloma (MM) cell lines express high levels of Pim-2 protein and that pan-Pim inhibition impairs viability in 90% of these lines and induces apoptosis in a subset. In acute myelogenous leukemia (AML) cell lines, sensitivity to Pim inhibition significantly correlates with Pim-1 protein expression. Numerous diffuse, large B-cell lymphoma (DLBCL) cell lines have high Pim levels and many are sensitive to Pim inhibition. We have also assessed Pim expression and activity in human tumor and normal tissues. Studies performed with myeloma cells isolated from patient bone marrow aspirates have revealed elevated Pim-2 protein levels as well as sensitivity to ex vivo dosing with Pim inhibitors, as evidenced by inhibition of PDCD4 phosphorylation. Primary patient samples from numerous other hematological tumors have also been found to have high Pim-1 or Pim-2 protein levels. To expand the possible utility of Pim inhibitors in the clinic, we have combined our molecules with numerous clinical agents, including dexamethasone, carfilzomib, and PI3K inhibitors, across multiple settings, in vitro. In all indications surveyed, we have observed that the combination of Pim molecules and these agents can lead to synergistic effects on cell viability, apoptosis and pathway signaling. In some cases, cell lines that show mild or no response to either single agent alone are sensitive to combination treatment. Collectively, our data provide a rationale for the development of Pim kinase inhibitors for use either as monotherapy or in combination with other agents in diverse tumor settings. Citation Format: Christine E. Sastri, Nadia Guerrero, Dongyin Yu, Bethany Mattson, Ken