Pim kinase inhibitors: a survey of the patent literature

PIM kinases are progression markers and emerging therapeutic targets in diffuse large B-cell lymphoma

Background:

PIM serine/threonine kinases are often highly expressed in haematological malignancies. We have shown that PIM inhibitors reduced the survival and migration of leukaemic cells. Here, we investigated PIM kinases in diffuse large B-cell lymphoma (DLBCL) biopsy samples and DLBCL cell lines.

Methods:

Immunohistochemical staining for PIM kinases and CXCR4 was performed on tissue microarrays from a cohort of 101 DLBCL cases, and the effects of PIM inhibitors on the survival and migration of DLBCL cell lines were determined.

Results:

PIM1 expression significantly correlated with the activation of signal transducer and activator of transcription (STAT) 3 and 5, P-glycoprotein expression, CXCR4-S339 phosphorylation, and cell proliferation. Whereas most cases exhibited cytoplasmic or cytoplasmic and nuclear PIM1 and PIM2 expression, 12 cases (10 of the non-germinal centre DLBCL type) expressed PIM1 predominately in the nucleus. Interestingly, nuclear expression of PIM1 significantly correlated with disease stage. Exposure of DLBCL cell lines to PIM inhibitors modestly impaired cellular proliferation and CXCR4-mediated migration.

Conclusion:

This work demonstrates that PIM expression in DLBCL is associated with activation of the JAK/STAT signalling pathway and with the proliferative activity. The correlation of nuclear PIM1 expression with disease stage and the modest response to small-molecule inhibitors suggests that PIM kinases are progression markers rather than primary therapeutic targets in DLBCL.

Discovery of CX-6258. A Potent, Selective, and Orally Efficacious pan-Pim Kinases Inhibitor

Structure-activity relationship analysis in a series of 3-(5-((2-oxoindolin-3-ylidene)methyl)furan-2-yl)amides identified compound 13, a pan-Pim kinases inhibitor with excellent biochemical potency and kinase selectivity. Compound 13 exhibited in vitro synergy with chemotherapeutics and robust in vivo efficacy in two Pim kinases driven tumor models.

Targeting the PI3K/AKT/mTOR pathway in non-Hodgkin's lymphoma: results, biology, and development strategies

Signaling by the PI3K/AKT/mTOR pathway is frequently deregulated in non-Hodgkin's lymphoma (NHL), prompting evaluation of the rapamycin-analog (rapalog) mTOR inhibitors in multiple clinical trials. The drugs show activity as single agents, and the rapalog temsirolimus is now accepted as a therapeutic option in relapsed/refractory mantle cell lymphoma. Response rates, however, are typically below 50%, resulting in remissions that are neither complete nor durable. Results of preclinical studies shed important new light on resistance mechanisms that may explain results. Looking ahead, it is likely PI3K/AKT/mTOR inhibition will find expanded roles in NHL therapy due to 1) assessments of the rapalogs in combination with other therapies and in less heavily pretreated patients, 2) the development and evaluation of multiple novel inhibitors of the pathway that may increase specificity and potency, 3) alternative treatment strategies able to bypass particular resistance mechanisms, and 4) increased efforts to identify biomarkers for better pretreatment patient stratification.

PIM2 inhibition as a rational therapeutic approach in B-cell lymphoma

PIM serine/threonine kinases are overexpressed, translocated, or amplified in multiple B-cell lymphoma types. We have explored the frequency and relevance of PIM expression in different B-cell lymphoma types and investigated whether PIM inhibition could be a rational therapeutic approach. Increased expression of PIM2 was detected in subsets of mantle cell lymphoma, diffuse large B-cell lymphoma (DLBLC), follicular lymphoma, marginal zone lymphoma-mucosa–associated lymphoid tissue type, chronic lymphocytic leukemia, and nodal marginal zone lymphoma cases. Increased PIM2 protein expression was associated with an aggressive clinical course in activated B-like-DLBCL patients. Pharmacologic and genetic inhibition of PIM2 revealed p4E-BP1(Thr37/46) and p4E-BP1(Ser65) as molecular biomarkers characteristic of PIM2 activity and indicated the involvement of PIM2 kinase in regulating mammalian target of rapamycin complex 1. The simultaneous genetic inhibition of all 3 PIM kinases induced changes in apoptosis and cell cycle. In conclusion, we show that PIM2 kinase inhibition is a rational approach in DLBCL treatment, identify appropriate biomarkers for pharmacodynamic studies, and provide a new marker for patient stratification.

Discovery of novel 3,5-disubstituted indole derivatives as potent inhibitors of Pim-1, Pim-2, and Pim-3 protein kinases

A series of novel 3,5-disubstituted indole derivatives as potent and selective inhibitors of all three members of the Pim kinase family is described. High throughput screen identified a pan-Pim kinase inhibitor with a promiscuous scaffold. Guided by structure-based drug design, SAR of the series afforded a highly selective indole chemotype that was further developed into a potent set of compounds against Pim-1, 2, and 3 (Pim-1 and Pim-3: IC(50)≤2nM and Pim-2: IC(50)≤100nM).

Targeting cap-dependent translation blocks converging survival signals by AKT and PIM kinases in lymphoma

New anticancer drugs that target oncogenic signaling molecules have greatly improved the treatment of certain cancers. However, resistance to targeted therapeutics is a major clinical problem and the redundancy of oncogenic signaling pathways provides back-up mechanisms that allow cancer cells to escape. For example, the AKT and PIM kinases produce parallel oncogenic signals and share many molecular targets, including activators of cap-dependent translation. Here, we show that PIM kinase expression can affect the clinical outcome of lymphoma chemotherapy. We observe the same in animal lymphoma models. Whereas chemoresistance caused by AKT is readily reversed with rapamycin, PIM-mediated resistance is refractory to mTORC1 inhibition. However, both PIM- and AKT-expressing lymphomas depend on cap-dependent translation, and genetic or pharmacological blockade of the translation initiation complex is highly effective against these tumors. The therapeutic effect of blocking cap-dependent translation is mediated, at least in part, by decreased production of short-lived oncoproteins including c-MYC, Cyclin D1, MCL1, and the PIM1/2 kinases themselves. Hence, targeting the convergence of oncogenic survival signals on translation initiation is an effective alternative to combinations of kinase inhibitors.

For better or for worse: the role of Pim oncogenes in tumorigenesis

Pim oncogenes are overexpressed in a wide range of tumours from a haematological and epithelial origin. Pim genes encode serine/threonine kinases that have been shown to counteract the increased sensitivity to apoptosis induction that is associated with MYC-driven tumorigenesis. Recently, considerable progress has been made in characterizing the pathways of PIM-mediated survival signalling. Given the unique structure of their active site and the minimal phenotype of mice mutant for all Pim family members, these oncogenes might be promising targets for highly specific and selective drugs with favourable toxicity profiles. In this Review, we discuss the physiological functions and oncogenic activities of Pim kinases.

Inflammation and survival pathways: chronic lymphocytic leukemia as a model system

A primary response to inflammation is an increased survival of the target cell. Several pathways have been identified that promote maintenance of the cell. The principal mechanism for the extended survival is through induction of anti-apoptotic Bcl-2 family proteins. Bcl-2 was the founding member of this family with five additional members, Bcl-X(L), Bcl-W, Bcl-B, Bfl-1, and Mcl-1, discovered mostly in hematological malignancies. Another mechanism that could add to cell survival is the Pim kinase pathway. This family of enzymes is associated with Myc-driven transcription, cell cycle regulation, degradation of pro-apoptotic proteins, and protein translation. Chronic lymphocytic leukemia serves as an optimal model to understand the mechanism by which these two protein families provide survival advantage to cells. In addition, since this malignancy is known to be maintained by microenvironment milieu, this further adds advantage to investigate mechanisms by which these pro-survival proteins are induced in the presence of stromal support. Multiple mechanisms exists that result in increase in transcript and protein level of anti-apoptotic Bcl-2 family members. Following these inductions, post-translational modifications occur resulting in increased stability of pro-survival proteins, while Pim-mediated phosphorylation inhibits pro-apoptotic protein activity. Furthermore, there is a cross-talk between these two (Bcl-2 family proteins and Pim family proteins) pathways that co-operate with each other for CLL cell survival and maintenance. Vigorous efforts are being made to create small molecules that affect these proteins directly or indirectly. Several of these pharmacological inhibitors are in early clinical trials for patients with hematological malignancies.

p53-dependent induction of prostate cancer cell senescence by the PIM1 protein kinase

The PIM family of serine threonine protein kinases plays an important role in regulating both the growth and transformation of malignant cells. However, in a cell line-dependent manner, overexpression of PIM1 can inhibit cell and tumor growth. In 22Rv1 human prostate cells, but not in Du145 or RWPE-2, PIM1 overexpression was associated with marked increases in cellular senescence, as shown by changes in the levels of beta-galactosidase (SA-beta-Gal), p21, interleukin (IL)-6 and IL-8 mRNA and protein. During early cell passages, PIM1 induced cellular polyploidy. As the passage number increased, markers of DNA damage, including the level of gammaH2AX and CHK2 phosphorylation, were seen. Coincident with these DNA damage markers, the level of p53 protein and genes transcriptionally activated by p53, such as p21, TP53INP1, and DDIT4, increased. In these 22Rv1 cells, the induction of p53 protein was associated not only with senescence but also with a significant level of apoptosis. The importance of the p53 pathway to PIM1-driven cellular senescence was further shown by the observation that expression of dominant-negative p53 or shRNA targeting p21 blocked the PIM1-induced changes in the DNA damage response and increases in SA-beta-Gal activity. Likewise, in a subcutaneous tumor model, PIM1-induced senescence was rescued when the p53-p21 pathways are inactivated. Based on these results, PIM1 will have its most profound effects on tumorigenesis in situations where the senescence response is inactivated.