Abstract B228: Discovery of 6-Methyl-3-aryl-7,8-dihydro-6H-9-oxa-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalen-5-ylamine compounds as Pim kinase inhibitors with potent activity in tumoral cell lines and special binding mode

Proviral integration site for Moloney murine leukemia virus (PIM) kinases are potent oncogens. Pim-1, 2 and 3 are highly conserved kinases that have unique structural properties, and are characterized by a constitutive serine/threonine activity that does not depend on post-translational modifications for activation. Pim kinases activity supports in vitro and in vivo tumor cell growth and survival through modification of an increasing number of common as well as isoform-specific substrates including c-myc and Histone H3, which drive transcription, eukaryotic elongation factor 4E-BP-1 that regulates transcription and Bad that activates cell survival. Furthermore, cell cycle protein activation by Pim kinases is involved with proliferation, and through regulation of AMPK activity Pim kinases mediated control of energy metabolism. Pim kinases are overexpressed in a range of haematopoietic malignancies and solid cancers, and its overexpression is associated with drug resistance. Inhibition of PIM kinase activity may be an attractive therapeutic strategy with possible favourable toxicity profiles due to minimal phenotype of mice mutant for all Pim family members.

Knowledge of the three-dimensional structure of Pim1 is especially important for understanding the design of potent and selective Pim1 inhibitors as novel therapeutic agents. Using a rational strategy we have generated a novel chemical series, by introduction of a morpholine cycle in the C-7, C-8 position of the triazolopyridazine ring. Morpholine ring can be accommodated in the catalytic site due to a change in the conformation of the P-loop on the crystal structure to afford very potent and selective tricyclic compounds against PIM kinases. Depending on the amine C-6 substitution fragment we have observed different isoforms profiles. Here, we describe the exploration and biological characterization of C-6 tricyclic series, reporting its SAR/SPR (ADME).

We identified lead compounds with potency in the low nanomolar range vs. PIM1, 2 and 3 and high selectivity versus a panel of 24 protein kinases. The compounds display cellular activity by blocking PIM signaling, S112 P-Bad in H1299 Pim1 cells, in the low nanomolar range. The combination of the PI3K inhibitor GDC-0941 with Pim inhibitors was strongly synergistic in vitro in non solid and solid tumoral cell lines.

Finally, we assessed the effect of Pim kinase inhibition on Pim signaling in vivo in a mouse subcutaeneous tumor xenograft model employing a human mantle cell lymphoma cell line, Jeko-1. Results demonstrated that ETP-652 inhibited phosphorylation of S112 P-Bad in vivo.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B228.