The oncogenic PIM kinase family regulates drug resistance through multiple mechanisms

Identification of pyrrolo[2,3-g]indazoles as new Pim kinase inhibitors

The synthesis and Pim kinase inhibition potency of a new series of pyrrolo[2,3-g]indazole derivatives is described. The results obtained in this preliminary structure-activity relationship study pointed out that sub-micromolar Pim-1 and Pim-3 inhibitory potencies could be obtained in this series, more particularly for compounds 10 and 20, showing that pyrrolo[2,3-g]indazole scaffold could be used for the development of new potent Pim kinase inhibitors. Molecular modeling experiments were also performed to study the binding mode of these compounds in Pim-3 ATP-binding pocket.

Pim kinases in cancer: diagnostic, prognostic and treatment opportunities

PIM proteins belong to a family of ser/thr kinases composed of 3 members, PIM1, PIM2 and PIM3, with greatly overlapping functions. PIM kinases are mainly responsible for cell cycle regulation, antiapoptotic activity and the homing and migration of receptor tyrosine kinases mediated via the JAK/STAT pathway. PIM kinases have been found to be upregulated in many hematological malignancies and solid tumors. Although these kinases have been described as weak oncogenes, they are heavily targeted for anticancer drug discovery. The present review summarizes the discoveries made to date regarding PIM kinases as driving oncogenes in the process of tumorigenesis and their validation as drug targets.

Role of additional novel therapies in myeloproliferative neoplasms

The recent approval of ruxolitinib (INCB018424) for myelofibrosis and the preclinical/clinical development of several additional janus kinase (JAK)-targeted agents have ushered in an era of novel therapies for advanced myeloproliferative neoplasms (MPN), which are associated with constitutive activation of the JAK-signal transducer and activation of transcription (STAT) signaling pathway. Collectively, these novel therapeutic approaches could rapidly broaden the spectrum of available therapies, with potential for improved clinical outcome for patients with advanced MPN. This review covers the recent developments in the testing of novel therapeutic agents other than JAK inhibitors that target signaling pathways in addition to JAK/STAT, or target the deregulated epigenetic mechanisms in MPN.

PIM kinase isoform specific regulation of MIG6 expression and EGFR signaling in prostate cancer cells

The PIM family of oncogenic serine/threonine kinases regulates tumour cell proliferation. To identify proliferative signaling pathways that are regulated by PIM kinases we analyzed gene expression differences in DU-145 and PC3 prostate cancer derived cells induced by treatment with the recently developed highly selective PIM kinase inhibitor M-110. This identified 97 genes the expression of which is affected by M-110 in both cell lines. We then focused on the M-110 induced up regulation of the MIG6 gene that encodes a negative regulator of EGFR signaling. Here we show that M-110 and the structurally unrelated PIM kinase inhibitor SGI-1776 up regulate MIG6 in DU-145 and PC3 cells. Knockdown of PIM-1 but not of PIM-2 or PIM-3 also up regulates MIG6 expression, which identifies MIG6 as a PIM-1 regulated gene. In agreement with the role of MIG6 protein as a negative regulator of EGFR signaling we found that M-110 treatment inhibits EGF induced EGFR activation and the activation of the downstream ERK MAPkinase pathway. The biological significance of these findings are demonstrated by the fact that co-treatment of DU-145 or PC3 cells with the EGFR tyrosine kinase inhibitor Gefitinib and M-110 or SGI-1776 has synergistic inhibitory effects on cell proliferation. These experiments define a novel biological function of PIM-1 as a co-regulator of EGFR signaling and suggest that PIM inhibitors may be used in combination therapies to increase the efficacy of EGFR tyrosine kinase inhibitors.

Kinase inhibitory potencies and in vitro antiproliferative activities of N-10 substituted pyrrolo[2,3-a]carbazole derivatives

Development of potent and selective Pim kinase inhibitors has recently emerged as an important field for the design of new anti-cancer drugs. We report the synthesis of new N-10-substituted pyrrolo[2,3-a]carbazole derivatives and their evaluation as Pim kinase inhibitors. Moreover, in vitro antiproliferative activity of these compounds was evaluated toward a human fibroblast primary culture and three human solid cancer cell lines (PA1, PC3 and DU145). Compounds 3, 7 and 10 showed inhibitory potencies toward Pim-1 and Pim-3 in the nanomolar range. Additionally, dimethylamino analog 10 also demonstrated interesting sub-micromolar antiproliferative activities toward the cell lines tested.

Kynurenic acid in human renal cell carcinoma: its antiproliferative and antimigrative action on Caki-2 cells

Kidneys possess a complex enzyme system which plays a major role in tryptophan metabolism. Taking into account a considerably high concentration of one of the tryptophan metabolites, kynurenic acid (KYNA) in this organ and previously reported antiproliferative activity against colon cancer cells in vitro, we measured its content in human normal and tumour kidney tissue. KYNA concentration was considerably higher in normal renal tissue (379.7 ± 39.7 pmol/g wet weight) than in renal cell carcinomas (115.5 ± 20.8 pmol/g wet weight). In in vitro experiments, KYNA in higher micro- and millimolar concentrations significantly inhibited proliferation, DNA synthesis and migration of renal cancer Caki-2 cells. Our results suggest that KYNA may affect cell cycle regulators and signalling pathways through overexpression of p21 Waf1/Cip1 and inhibition of phosphorylation of Rb protein and p38 MAPK. In conclusion, KYNA may be suggested as an endogenous agent, controlling the growth of tumour, or a chemopreventive agent.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.