Pim kinase inhibitor, SGI-1776, induces apoptosis in chronic lymphocytic leukemia cells. Blood. 2009;114:4150-4157. [PMID: 19734450 DOI: 10.1182/blood-2009-03-212852]

PIM2 kinase is induced by cisplatin in ovarian cancer cells and limits drug efficacy

Platinum-based chemotherapy is widely used to treat various cancers, but many patients ultimately relapse due to drug resistance. We employed phosphoproteomic analysis and functional assays of the response of SK-OV-3 ovarian cancer cells to cisplatin as a strategy to identify kinases as candidate druggable targets to sensitize cells to platinum. A SILAC-based approach combined with TiO2-based phosphopeptide enrichment allowed the direct identification of ERK1/2, p90RSK, and ERBB2 as kinases whose phosphorylation is regulated by cisplatin. Bioinformatic analysis revealed enrichment in linear phosphorylation motifs predicted to be targets of p38MAPK, CDK2, and PIM2. All three PIM kinases were found expressed in a panel of 10 ovarian cancer cell lines, with the oncogenic PIM2 being the most commonly induced by cisplatin. Targeting PIM2 kinase by either biochemical inhibitors or RNA interference impaired cell growth, decreased cisplatin-triggered BAD phosphorylation, and sensitized ovarian cancer cells to drug-induced apoptosis. Overexpression of PIM2 triggered anchorage-independent growth and resulted in increased BAD phosphorylation and cell resistance to DNA damaging agents. The data show that the PIM2 kinase plays a role in the response of ovarian cancer cells to platinum drugs and suggest that PIM inhibitors may find clinical application as an adjunct to platinum-based therapies.

Pathophysiological roles of Pim-3 kinase in pancreatic cancer development and progression

Pim-3 is a member of the provirus integration site for Moloney murine leukemia virus (Pim) family proteins that exhibit serine/threonine kinase activity. Similar to the other Pim kinases (Pim-1 and Pim-2), Pim-3 is involved in many cellular processes, including cell proliferation, survival, and protein synthesis. Although Pim-3 is expressed in normal vital organs, it is overexpressed particularly in tumor tissues of endoderm-derived organs, including the liver, pancreas, and colon. Silencing of Pim-3 expression can retard in vitro cell proliferation of hepatocellular, pancreatic, and colon carcinoma cell lines by promoting cell apoptosis. Pim-3 lacks the regulatory domains similarly as Pim-1 and Pim-2 lack, and therefore, Pim-3 can exhibit its kinase activity once it is expressed. Pim-3 expression is regulated at transcriptional and post-transcriptional levels by transcription factors (e.g., Ets-1) and post-translational modifiers (e.g., translationally-controlled tumor protein), respectively. Pim-3 could promote growth and angiogenesis of human pancreatic cancer cells in vivo in an orthotopic nude mouse model. Furthermore, a Pim-3 kinase inhibitor inhibited cell proliferation when human pancreatic cancer cells were injected into nude mice, without inducing any major adverse effects. Thus, Pim-3 kinase may serve as a novel molecular target for developing targeting drugs against pancreatic and other types of cancer.

A small-molecule inhibitor of PIM kinases as a potential treatment for urothelial carcinomas

The proto-oncogene proviral integration site for moloney murine leukemia virus (PIM) kinases (PIM-1, PIM-2, and PIM-3) are serine/threonine kinases that are involved in a number of signaling pathways important to cancer cells. PIM kinases act in downstream effector functions as inhibitors of apoptosis and as positive regulators of G₁-S phase progression through the cell cycle. PIM kinases are upregulated in multiple cancer indications, including lymphoma, leukemia, multiple myeloma, and prostate, gastric, and head and neck cancers. Overexpression of one or more PIM family members in patient tumors frequently correlates with poor prognosis. The aim of this investigation was to evaluate PIM expression in low- and high-grade urothelial carcinoma and to assess the role PIM function in disease progression and their potential to serve as molecular targets for therapy. One hundred thirty-seven cases of urothelial carcinoma were included in this study of surgical biopsy and resection specimens. High levels of expression of all three PIM family members were observed in both noninvasive and invasive urothelial carcinomas. The second-generation PIM inhibitor, TP-3654, displays submicromolar activity in pharmacodynamic biomarker modulation, cell proliferation studies, and colony formation assays using the UM-UC-3 bladder cancer cell line. TP-3654 displays favorable human ether-à-go-go-related gene and cytochrome P450 inhibition profiles compared with the first-generation PIM inhibitor, SGI-1776, and exhibits oral bioavailability. In vivo xenograft studies using a bladder cancer cell line show that PIM kinase inhibition can reduce tumor growth, suggesting that PIM kinase inhibitors may be active in human urothelial carcinomas.

Pim1 serine/threonine kinase regulates the number and functions of murine hematopoietic stem cells

The genes and pathways that govern the functions and expansion of hematopoietic stem cells (HSC) are not completely understood. In this study, we investigated the roles of serine/threonine Pim kinases in hematopoiesis in mice. We generated PIM1 transgenic mice (Pim1-Tx) overexpressing human PIM1 driven by vav hematopoietic promoter/regulatory elements. Compared to wild-type littermates, Pim1-Tx mice showed enhanced hematopoiesis as demonstrated by increased numbers of Lin(-) Sca-1 (+) c-Kit (+) (LSK) hematopoietic stem/progenitor cells and cobblestone area forming cells, higher BrdU incorporation in long-term HSC population, and a better ability to reconstitute lethally irradiated mice. We then extended our study using Pim1(-/-), Pim2(-/-), Pim3(-/-) single knockout (KO) mice. HSCs from Pim1(-/-) KO mice showed impaired long-term hematopoietic repopulating capacity in secondary and competitive transplantations. Interestingly, these defects were not observed in HSCs from Pim2(-/-) or Pim3(-/-) KO mice. Limiting dilution competitive transplantation assay estimated that the frequency of LSKCD34(-) HSCs was reduced by approximately 28-fold in Pim1(-/-) KO mice compared to wild-type littermates. Mechanistic studies demonstrated an important role of Pim1 kinase in regulating HSC cell proliferation and survival. Finally, our polymerase chain reaction (PCR) array and confirmatory real-time PCR (RT-PCR) studies identified several genes including Lef-1, Pax5, and Gata1 in HSCs that were affected by Pim1 deletion. Our data provide the first direct evidence for the important role of Pim1 kinase in the regulation of HSCs. Our study also dissects out the relative role of individual Pim kinase in HSC functions and regulation.

Use of regulators and inhibitors of Pim-1, a serine/threonine kinase, for tumour therapy (review)

Pim-1 is a proto-oncogene that encodes a serine/threonine kinase that is overexpressed in a range of haematopoietic malignancies and solid cancers. Pim-1 expression is tightly regulated by multiple biomolecules at different levels. Several lines of evidence have indicated that dysregulation of Pim-1 can interfere with the cell cycle and apoptosis to promote malignant transformation of a number of types of tumour. Thus, investigation of Pim-1 regulation may provide important theoretical guidance for the development of molecular targeting therapies and drug treatments for Pim-1‑associated diseases. Regulators of Pim-1 expression, include microRNAs, oestrogen, inecalcitol, adenosine triphosphate (ATP) mimetic inhibitors and ATP competitive inhibitors of Pim-1. Combinations of inhibitors of Pim-1 expression and Pim-1‑specific inhibitors may provide novel therapies for cancer patients and directions for cancer treatment.

PI3K and cancer: lessons, challenges and opportunities

The central role of phosphoinositide 3-kinase (PI3K) activation in tumour cell biology has prompted a sizeable effort to target PI3K and/or downstream kinases such as AKT and mammalian target of rapamycin (mTOR) in cancer. However, emerging clinical data show limited single-agent activity of inhibitors targeting PI3K, AKT or mTOR at tolerated doses. One exception is the response to PI3Kδ inhibitors in chronic lymphocytic leukaemia, where a combination of cell-intrinsic and -extrinsic activities drive efficacy. Here, we review key challenges and opportunities for the clinical development of inhibitors targeting the PI3K-AKT-mTOR pathway. Through a greater focus on patient selection, increased understanding of immune modulation and strategic application of rational combinations, it should be possible to realize the potential of this promising class of targeted anticancer agents.

PIM kinases are essential for chronic lymphocytic leukemia cell survival (PIM2/3) and CXCR4-mediated microenvironmental interactions (PIM1)

Overexpression of the CXCR4 receptor is a hallmark of chronic lymphocytic leukemia (CLL) and is important for CLL cell survival, migration, and interaction with their protective microenvironment. In acute myelogenous leukemia (AML), PIM1 was shown to regulate the surface expression of the CXCR4 receptor. Here, we show that PIM (proviral integration site for Moloney murine leukemia virus) kinases 1-3 are overexpressed and that the CXCR4 receptor is hyperphosphorylated on Ser339 in CLL compared with normal lymphocytes. Furthermore, CXCR4 phosphorylation correlates with PIM1 protein expression and PIM1 transcript levels in CLL. PIM kinase inhibition with three different PIM kinase inhibitors induced apoptosis in CLL cells independent of the presence of protective stromal cells. In addition, PIM inhibition caused dephosphorylation of the CXCR4 receptor on Ser339, resulting in enhanced ligand-dependent CXCR4 internalization and reduced re-externalization after withdrawal of CXCL12. Furthermore, PIM inhibition in CLL cells blocked CXCR4 functions, such as migration toward CXCL12- or CXCL12-induced extracellular signal-regulated kinase (ERK) phosphorylation. In concordance, pretreatment of CLL cells with PIM kinase inhibitors strongly reduced homing of CLL cells toward the bone marrow and the spleen of Rag2(-/-)γc(-/-) mice in vivo. Interestingly, the knockdown of PIM kinases in CLL cells demonstrated diverging functions, with PIM1 regulating CXCR4 surface expression and PIM2 and PIM3 as important for the survival of CLL cells. Our results show that PIM kinase inhibitors are an effective therapeutic option for CLL, not only by impairing PIM2/3-mediated CLL cell survival, but also by blocking the PIM1/CXCR4-mediated interaction of CLL cells with their protective microenvironment.

A regulatory feedback loop between HIF-1α and PIM2 in HepG2 cells

To survive under hypoxic conditions, cancer cells remodel glucose metabolism to support tumor progression. HIF transcription factor is essential for cellular response to hypoxia. The underlying mechanism how HIF is constitutively activated in cancer cells remains elusive. In the present study, we characterized a regulatory feedback loop between HIF-1α and PIM2 in HepG2 cells. Serine/threonine kinase proto-oncogene PIM2 level was induced upon hypoxia in a HIF-1α-mediated manner in cancer cells. HIF-1α induced PIM2 expression via binding to the hypoxia-responsive elements (HREs) of the PIM2 promoter. In turn, PIM2 interacted with HIF-1α, especially a transactivation domain of HIF-1α. PIM2 as a co-factor but not an upstream kinase of HIF-1α, enhanced HIF-1α effect in response to hypoxia. The positive feedback loop between PIM2 and HIF-1α was correlated with glucose metabolism as well as cell survival in HepG2 cells. Such a regulatory mode may be important for the adaptive responses of cancer cells in antagonizing hypoxia during cancer progression.

Inhibition of oncogenic Pim-3 kinase modulates transformed growth and chemosensitizes pancreatic cancer cells to gemcitabine

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer with a 5-year survival rate of only 6%. Although the cytosine analog gemcitabine is the drug commonly used to treat PDAC, chemoresistance unfortunately renders the drug ineffective. Thus, strategies that can decrease this resistance will be essential for improving the dismal outcome of patients suffering from this disease. We previously observed that oncogenic Pim-1 kinase was aberrantly expressed in PDAC tissues and cell lines and was responsible for radioresistance. Furthermore, members of the Pim family have been shown to reduce the efficacy of chemotherapeutic drugs in cancer. Therefore, we attempted to evaluate the role of Pim-3 in chemoresistance of PDAC cells. We were able to confirm upregulation of the Pim-3 oncogene in PDAC tissues and cell lines versus normal samples. Biological consequences of inhibiting Pim-3 expression with shRNA-mediated suppression included decreases in anchorage-dependent growth, invasion through Matrigel and chemoresistance to gemcitabine as measured by caspase-3 activity. Additionally, we were able to demonstrate that Pim-1 and Pim-3 play overlapping but non-identical roles as it relates to gemcitabine sensitivity of pancreatic cancer cells. To further support the role of Pim-3 suppression in sensitizing PDAC cells to gemcitabine, we used the pharmacological Pim kinase inhibitor SGI-1776. Treatment of PDAC cells with SGI-1776 resulted in decreased phosphorylation of the proapoptotic protein Bad and cell cycle changes. When SGI-1776 was combined with gemcitabine, there was a greater decrease in cell viability in the PDAC cells versus cells treated with either of the drugs separately. These results suggest combining drug therapies that inhibit Pim kinases, such as Pim-3, with chemotherapeutic agents, to aid in decreasing chemoresistance in pancreatic cancer.

Combination of Pim kinase inhibitor SGI-1776 and bendamustine in B-cell lymphoma

BACKGROUND

SGI-1776 is a small-molecule Pim kinase inhibitor that primarily targets c-MYC-driven transcription and cap-dependent translation in mantle cell lymphoma (MCL) cells. Bendamustine is an alkylating chemotherapeutic agent approved for use in B-cell lymphoma that is known to induce DNA damage and initiate response to repair.

MATERIALS AND METHODS

Our studies were conducted in MCL cell lines JeKo-1 and Mino, as well as primary B-cell lymphoma samples of MCL and splenic marginal zone lymphoma (SMZL), where we treated cells with SGI-1776 and bendamustine. We measured levels of cellular apoptosis, macromolecule synthesis inhibition, and DNA damage induced by drug treatments.

RESULTS

Both SGI-1776 and bendamustine effectively induced apoptosis as single agents, and when used in combination, an additive effect in cell killing was observed in MCL cell lines JeKo-1 and Mino, as well as in MCL and SMZL primary cells. As expected, SGI-1776 was effective in inducing a decrease of global RNA and protein synthesis, and bendamustine significantly inhibited DNA synthesis and generated a DNA damage response. When used in combination, the effects were intensified in DNA, RNA, and protein synthesis inhibition compared with single-agent treatments.

CONCLUSION

These data provide a foundation and suggest the feasibility of using Pim kinase inhibitors in combination with chemotherapeutic agents such as bendamustine in B-cell lymphoma.

Biological effects of the Pim kinase inhibitor, SGI-1776, in multiple myeloma

BACKGROUND

Pim kinases are constitutively active serine/threonine/tyrosine kinases that are overexpressed in hematological malignancies such as multiple myeloma. Pim kinase substrates are involved in transcription, protein translation, cell proliferation, and apoptosis. SGI-1776 is a potent Pim kinase inhibitor that has proven to be cytotoxic to leukemia and lymphoma cells. Based on this background, we hypothesized that SGI-1776 treatment would result in myeloma cytotoxicity.

MATERIALS AND METHODS

To test this, myeloma cell lines and primary CD138(+) cells from myeloma patients were treated with SGI-1776 in a dose- and time-dependent manner, and effect on cell death and proliferation, induction of autophagy, and changes in cell cycle profile were measured.

RESULTS

SGI-1776 treatment resulted in limited apoptosis in cell lines (mean 30%) and CD138(+) cells (< 10%) assessed using Annexin-V/propidium iodide. Limited effect was observed in cell cycle profile or growth in cell lines. However, DNA synthesis was decreased by 70% at 3 μM (all time points) in U266 though this was not observed in MM.1S. In accordance, immunoblot analyses revealed no change in transcription (c-Myc and H3), or apoptotic (Bad) proteins that are substrates of Pim kinases. In contrast, autophagy, assessed using acridine orange staining, was induced with SGI-1776 treatment in both cell lines (U266, 25%-70%; MM.1S, 8%-52%) and CD138(+) cells (19%-21%). Immunoblot analyses of the autophagy LC3b marker and translation initiation proteins (phospho-p70S6K and 4E-BP1) corroborated autophagy induction.

CONCLUSION

These data indicate that SGI-1776 treatment in myeloma cell lines and CD138(+) myeloma cells elicits its deleterious effects through inhibition of translation and induction of autophagy.

Identification of 1,6-dihydropyrazolo[4,3-c]carbazoles and 3,6-dihydropyrazolo[3,4-c]carbazoles as new Pim kinase inhibitors

New 1,6-dihydropyrazolo[4,3-c]carbazoles and 3,6-dihydropyrazolo[3,4-c]carbazoles were prepared and evaluated for their Pim kinase inhibitory potencies as well as their antiproliferative activities toward two prostatic cancer cell lines. Pyrazolocarbazole 15a was found to be a potent Pim kinase modulator with inhibitory potency toward the three isoforms. Compound 6c strongly inhibited Pim-3 with weaker effect toward Pim-1 and Pim-2, and thus could be used as an interesting molecular tool to study Pim-3 biological functions.

Chronic lymphocytic leukaemia--the role of the microenvironment pathogenesis and therapy

Chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL) is one of the more common forms of B cell malignancy. Although the condition has a variable clinical course, the trend is towards eventual relapse and the disease is considered incurable. Whilst the majority of the circulating CD5-positive neoplastic B cells are arrested in the G0 phase of the cell cycle, those in the bone marrow and lymphoid tissues proliferate at a rate of 0·1-1% of the entire clone per day. This proliferation is supported by the tissue microenvironment, which has been shown to induce upregulation of anti-apoptotic proteins and enhance the survival of the neoplastic cells. Microenvironmental factors are also thought to be important in tumour relapse and resistance to therapy. This review outlines the main signalling pathways involved in these tumour cell-stromal interactions, and includes potential therapeutic strategies based on the manipulation of key components within the CLL microenvironment.

Selective bisubstrate inhibitors with sub-nanomolar affinity for protein kinase Pim-1

Potent and selective: The unique nature of the ATP binding pocket structure of Pim family protein kinases (PKs) was used for the development of bisubstrate inhibitors and a fluorescent probe with sub-nanomolar affinity. Conjugates of arginine-rich peptides with two ATP mimetic scaffolds were synthesized and tested as inhibitors of Pim-1. Against a panel of 124 protein kinases, a novel ARC-PIM conjugate selectively inhibited PKs of the Pim family.

A new target for an old drug: identifying mitoxantrone as a nanomolar inhibitor of PIM1 kinase via kinome-wide selectivity modeling

The rational design of selective kinase inhibitors remains a great challenge. Here we describe a physics-based approach to computationally modeling the kinase inhibitor selectivity profile. We retrospectively assessed this protocol by computing the binding profiles of 17 well-known kinase inhibitors against 143 kinases. Next, we predicted the binding profile of the chemotherapy drug mitoxantrone, and chose the predicted top five kinase targets for in vitro kinase assays. Remarkably, mitoxantrone was shown to possess low nanomolar inhibitory activity against PIM1 kinase and to inhibit the PIM1-mediated phosphorylation in cancer cells. We further determined the crystal complex structure of PIM1 bound with mitoxantrone, which reveals the structural and mechanistic basis for a novel mode of PIM1 inhibition. Although mitoxantrone's mechanism of action had been originally thought to act through DNA intercalation and type II topoisomerase inhibition, we hypothesize that PIM1 kinase inhibition might also contribute to mitoxantrone's therapeutic efficacy and specificity.

The Pim kinase inhibitor SGI-1776 decreases cell surface expression of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) and drug transport by Pim-1-dependent and -independent mechanisms

Overexpression of the ATP-binding cassette (ABC) drug efflux proteins P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) on malignant cells is associated with inferior chemotherapy outcomes. Both, ABCB1 and ABCG2, are substrates of the serine/threonine kinase Pim-1; Pim-1 knockdown decreases their cell surface expression, but SGI-1776, the first clinically tested Pim inhibitor, was shown to reverse drug resistance by directly inhibiting ABCB1-mediated transport. We sought to characterize Pim-1-dependent and -independent effects of SGI-1776 on drug resistance. SGI-1776 at the Pim-1-inhibitory and non-cytotoxic concentration of 1 μM decreased the IC(50)s of the ABCG2 and ABCB1 substrate drugs in cytotoxicity assays in resistant cells, with no effect on the IC(50) of non-substrate drug, nor in parental cells. SGI-1776 also increased apoptosis of cells overexpressing ABCG2 or ABCB1 exposed to substrate chemotherapy drugs and decreased their colony formation in the presence of substrate, but not non-substrate, drugs, with no effect on parental cells. SGI-1776 decreased ABCB1 and ABCG2 surface expression on K562/ABCB1 and K562/ABCG2 cells, respectively, with Pim-1 overexpression, but not HL60/VCR and 8226/MR20 cells, with lower-level Pim-1 expression. Finally, SGI-1776 inhibited uptake of ABCG2 and ABCB1 substrates in a concentration-dependent manner irrespective of Pim-1 expression, inhibited ABCB1 and ABCG2 photoaffinity labeling with the transport substrate [(125)I]iodoarylazidoprazosin ([(125)I]IAAP) and stimulated ABCB1 and ABCG2 ATPase activity. Thus SGI-1776 decreases cell surface expression of ABCB1 and ABCG2 and inhibits drug transport by Pim-1-dependent and -independent mechanisms, respectively. Decrease in ABCB1 and ABCG2 cell surface expression mediated by Pim-1 inhibition represents a novel mechanism of chemosensitization.

PIM1 kinase inhibitors induce radiosensitization in non-small cell lung cancer cells

Radiotherapy plays a critical role in the treatment of non-small cell lung cancer (NSCLC). However, radioresistance is a major barrier against increasing the efficiency of radiotherapy for NSCLC. To understand the mechanisms underlying NSCLC radioresistance, we previously focused on the potential involvement of PIM1, PRAS40, FOXO3a, 14-3-3, and protein phosphatases. Among these proteins, PIM1 functioned as an oncogene and was found to act as a crucial mediator in radioresistant NSCLC cells. Therefore, we investigated the use of PIM1-specific inhibitors as novel therapeutic drugs to regulate radiosensitivity in NSCLC. After structure-based drug selection, SGI-1776, ETP-45299, and tryptanthrin were selected as candidates of PIM1 inhibitors that act as radiosensitizers. With irradiation, these drugs inhibited only PIM1 kinase activity without affecting PIM1 mRNA/protein levels or cellular localization. When PIM1 kinase activity was suppressed by these inhibitors, PRAS40 was not phosphorylated. Consequently, unphosphorylated PRAS40 did not form trimeric complexes with 14-3-3 and FOXO3a, leading to increased nuclear localization of FOXO3a. Nuclear FOXO3a promoted the expression of pro-apoptotic proteins such as Bim and FasL, resulting in a radiosensitizing effect on radioresistant NSCLC cells. Moreover, an in vivo xenograft mouse model confirmed this radiosensitizing effect induced by PIM1 inhibitors. In these model systems, tumor volume was significantly reduced by a combinational treatment with irradiation and PIM1 inhibitors compared to irradiation alone. Taken together, our findings provided evidence that PIM1-specific inhibitors, SGI-1776, ETP-45299, and tryptanthrin, can act as novel radiosensitizers to enhance the efficacy of radiotherapy by inhibiting irradiation-induced signaling pathway associated with radioresistance.

T-18, a stemonamide synthetic intermediate inhibits Pim kinase activity and induces cell apoptosis, acting as a potent anticancer drug

Pim-3 kinase has been shown to be aberrantly expressed in premalignant and malignant lesions of endoderm-derived organs such as the liver, pancreas, colon and stomach. Pim-3 kinase inactivates the Bad protein, a proapoptotic molecule, and improves the expression of Bcl-xL, an antiapoptotic molecule, to promote cell proliferation. Thus, blocking Pim-3 kinase activity may be a new strategy for the treatment of pancreatic cancer. In this study, we screened low molecular compounds and observed that the stemonamide synthetic intermediate, T-18, potently inhibited Pim kinase activity. Moreover, T-18 inhibited the proliferation of human pancreatic, as well as that of hepatocellular and colon cancer cells in vitro. It also induced the apoptosis of human pancreatic carcinoma cells in vitro by decreasing the levels of phospho-Ser112-Bad; the levels of Pim-3 kinase and total Bad protein were not altered. Furthermore, T-18 inhibited the growth of human pancreatic cancer cells in nude mice without apparent adverse effects when the tumor was palpable. These observations indicate that stemonamide synthetic intermediates may be novel drugs for the treatment of gastrointestinal cancers, particularly pancreatic cancer.

Fragment-hopping-based discovery of a novel chemical series of proto-oncogene PIM-1 kinase inhibitors

A new chemical series, triazolo[4,5-b]pyridines, has been identified as an inhibitor of PIM-1 by a chemotype hopping strategy based on a chemically feasible fragment database. In this case, structure-based virtual screening and in silico chemogenomics provide added value to the previously reported strategy of prioritizing among proposed novel scaffolds. Pairwise comparison between compound 3, recently discontinued from Phase I clinical trials, and molecule 8, bearing the selected novel scaffold, shows that the primary activities are similar (IC(50) in the 20 to 150 nM range). At the same time, some ADME properties (for example, an increase of more than 45% in metabolic stability in human liver microsomes) and the off-target selectivity (for example, an increase of more than 2 log units in IC(50)vs. FLT3) are improved, and the intellectual property (IP) position is enhanced. The discovery of a reliable starting point that fulfills critical criteria for a plausible medicinal chemistry project is demonstrated in this prospective study.

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.

Mechanisms of apoptosis induction by simultaneous inhibition of PI3K and FLT3-ITD in AML cells in the hypoxic bone marrow microenvironment

We investigated the antileukemia effects and molecular mechanisms of apoptosis induction by simultaneous blockade of PI3K and mutant FLT3 in AML cells grown under hypoxia in co-cultures with bone marrow stromal cells. Combined treatment with selective class I PI3K inhibitor GDC-0941 and sorafenib reversed the protective effects of bone marrow stromal cells on FLT3-mutant AML cells in hypoxia, which was associated with downregulation of Pim-1 and Mcl-1 expression levels. These findings suggest that combined inhibition of PI3K and FLT3-ITD may constitute a targeted approach to eradicating chemoresistant AML cells sequestered in hypoxic bone marrow niches.

Multifaceted actions of 8-amino-adenosine kill BCR-ABL positive cells

Survival of chronic myelogenous leukemia (CML) cells is dependent on BCR-ABL kinase, the activity of which is contingent on the level of BCR-ABL protein and the availability of adenosine triphosphate (ATP). We hypothesized that 8-amino-adenosine (8-amino-Ado)-mediated reduction in cellular ATP level and inhibition of mRNA synthesis leading to a decrease in protein level would result in a multifaceted targeting of BCR-ABL. Using K562 cells, we demonstrated that there was a dose- and time-dependent increase in 8-amino-ATP accompanied by a > 95% decline in the endogenous ATP pool. In parallel, 8-amino-Ado inhibited RNA synthesis and resulted in a depletion of BCR-ABL transcript. Consistent with this, BCR-ABL and ABL protein levels were also decreased. These effects were associated with the initiation of cell death as visualized by poly(ADP-ribose) polymerase (PARP) cleavage, decreased clonogenicity and greater than additive interaction with imatinib. In imatinib-sensitive and -resistant KBM5 cells, 8-amino-Ado treatment augmented the imatinib effect on growth inhibition.

Initial testing (stage 1) of SGI-1776, a PIM1 kinase inhibitor, by the pediatric preclinical testing program

The PIM kinase inhibitor, SGI-1776, was tested against the PPTP in vitro (1.0 nM-10 µM) and in vivo panels (148 mg/kg daily × 5 days for 3 weeks). SGI-1776 exhibited cytotoxic activity in vitro with a median relative IC(50) of 3.1 µM. SGI-1776 induced significant differences in EFS distribution in vivo in 9 of 31 solid tumor xenografts and in 1 of 8 of the evaluable ALL xenografts. SGI-1776 induced tumor growth inhibition meeting criteria for intermediate EFS T/C activity in 1 of 39 evaluable models. In contrast, SGI-1776 induced complete responses of subcutaneous MV4;11 (B myeloid leukemia).

Investigational agent MLN9708/2238 targets tumor-suppressor miR33b in MM cells

miRs play a critical role in tumor pathogenesis as either oncogenes or tumor-suppressor genes. However, the role of miRs and their regulation in response to proteasome inhibitors in multiple myeloma (MM) is unclear. In the current study, miR profiling in proteasome inhibitor MLN2238-treated MM.1S MM cells shows up-regulation of miR33b. Mechanistic studies indicate that the induction of miR33b is predominantly via transcriptional regulation. Examination of miR33b in patient MM cells showed a constitutively low expression. Overexpression of miR33b decreased MM cell viability, migration, colony formation, and increased apoptosis and sensitivity of MM cells to MLN2238 treatment. In addition, overexpression of miR33b or MLN2238 exposure negatively regulated oncogene PIM-1 and blocked PIM-1 wild-type, but not PIM-1 mutant, luciferase activity. Moreover, PIM-1 overexpression led to significant abrogation of miR33b- or MLN2238-induced cell death. SGI-1776, a biochemical inhibitor of PIM-1, triggered apoptosis in MM. Finally, overexpression of miR33b inhibited tumor growth and prolonged survival in both subcutaneous and disseminated human MM xenograft models. Our results show that miR33b is a tumor suppressor that plays a role during MLN2238-induced apoptotic signaling in MM cells, and these data provide the basis for novel therapeutic strategies targeting miR33b in MM.

Transcription and translation are primary targets of Pim kinase inhibitor SGI-1776 in mantle cell lymphoma

Proviral integration site for Moloney murine leukemia virus (Pim) kinases are serine/threonine/tyrosine kinases and oncoproteins that promote tumor progression. Three isoforms of Pim kinases have been identified and are known to phosphorylate numerous substrates, with regulatory functions in transcription, translation, cell cycle, and survival pathways. These kinases are involved in production, proliferation, and survival of normal B cells and are overexpressed in B-cell malignancies such as mantle cell lymphoma (MCL). SGI-1776 is a small molecule and Pim kinase inhibitor with selectivity for Pim-1. We hypothesize that Pim kinase function can be inhibited by SGI-1776 in MCL and that inhibition of phosphorylation of downstream substrates will disrupt transcriptional, translational, and cell cycle processes and promote cell death. SGI-1776 treatment in 4 MCL cell lines resulted in apoptosis induction. Phosphorylation of transcription (c-Myc) and translation targets (4E-BP1), tested in Jeko-1 and Mino, was declined. Consistent with these data, Mcl-1 and cyclin D1 protein levels were decreased. Importantly, similar to cell line data, MCL primary cells but not normal cells showed similar inhibition of substrate phosphorylation and cytotoxicity from SGI-1776 treatment. Genetic knockdown of Pim-1/Pim-2 affected similar proteins in MCL cell lines. Collectively these data demonstrate Pim kinases as therapeutic targets in MCL.

Inhibition of Pim-1 kinase ameliorates dextran sodium sulfate-induced colitis in mice

BACKGROUND

Pim-1 kinase is involved in the control of cell growth, differentiation and apoptosis. Recent evidence suggests that Pim kinases play a role in immune regulation and inflammation. However, the role of Pim-1 kinase in inflammatory bowel diseases (IBD) remains unclear.

AIMS

The aims of this study were to explore the role of Pim-1 kinase in the pathology of IBD and to assess whether inhibiting Pim-1 kinase may be of therapeutic benefit as a treatment regimen for IBD.

METHODS

Colitic mouse model was established by the induction of dextran sodium sulfate. The expression of Pim-1 in the colonic samples of control and colitic mice was examined. Furthermore, the mice were treated with Pim-1inhibitor (PIM-Inh), then the body weight and colon inflammation were evaluated, and the production of cytokines including IFN-γ, IL-4, TGF-β and IL-17 in colon tissues was determined by ELISA. The expression of T cell master transcription factors T-bet, ROR-γt, GATA-3 and Foxp3 and Nuclear factor κB (NF-κB) and inducible nitric oxide synthase in colon tissues was detected by real-time PCR and western blot. Finally, the effect of LPS on Pim-1 expression and the effects of PIM-Inh on LPS-induced upregualtion of p65 and TNF-α in RAW264.7 cells were examined by real-time PCR and western blot.

RESULTS

Pim-1 expression was correlated with the degree of mucosal inflammation in vivo, and it was significantly induced by LPS in vitro. PIM-Inh had protective effects on acute colitis in vivo. Mechanistically, PIM-Inh reduced the proinflammatory immune response through the inhibition of the overactivation of macrophages and the down-regulation of excessive Th1- and Th17-type immune responses. Furthermore, PIM-Inh could skew T cell differentiation towards a Treg phenotype.

CONCLUSIONS

Pim-1 kinase is involved in mucosal injury/inflammation and Pim-1 kinase inhibitor may provide a novel therapeutic approach for IBD.

Activation of cell cycle arrest and apoptosis by the proto-oncogene Pim-2

Potent survival effects have been ascribed to the serine/threonine kinase proto-oncogene PIM-2. Elevated levels of PIM-2 are associated with various malignancies. In human cells, a single Pim-2 transcript gives rise mainly to two protein isoforms (34, 41 kDa) that share an identical catalytic site but differ at their N-terminus, due to in-frame alternative translation initiation sites. In this study we observed that the 34 kDa PIM-2 isoform has differential nuclear and cytoplasmic forms in all tested cell lines, suggesting a possible role for the balance between these forms for PIM-2's function. To further study the cellular role of the 34 kDa isoform of PIM-2, an N-terminally HA-tagged form of this isoform was transiently expressed in HeLa cells. Surprisingly, this resulted in increased level of G1 arrested cells, as well as of apoptotic cells. These effects could not be obtained by a Flag-tagged form of the 41 kDa isoform. The G1 arrest and apoptotic effects were associated with an increase in T14/Y15 phosphorylation of CDK2 and proteasom-dependent down-regulation of CDC25A, as well as with up-regulation of p57, E2F-1, and p73. No such effects were obtained upon over-expression of a kinase-dead form of the HA-tagged 34 kDa PIM-2. By either using a dominant negative form of p73, or by over-expressing the 34 kDa PIM-2 in p73-silenced cells, we demonstrated that these effects were p73-dependent. These results demonstrate that while PIM-2 can function as a potent survival factor, it can, under certain circumstances, exhibit pro-apoptotic effects as well.

Targeting diverse signaling interaction sites allows the rapid generation of bivalent kinase inhibitors

The identification of potent and selective modulators of protein kinase function remains a challenge, and new strategies are needed for generating these useful ligands. Here, we describe the generation of bivalent inhibitors of three unrelated protein kinases: the CAMK family kinase Pim1, the mitogen-activated protein kinase (MAPK) p38α, and the receptor tyrosine kinase (RTK) epidermal growth factor receptor (EGFR). These bivalent inhibitors consist of an ATP-competitive inhibitor that is covalently tethered to an engineered form of the self-labeling protein O(6)-alkylguanine-DNA alkyltransferase (SNAP-tag). In each example, SNAP-tag is fused to a peptide ligand that binds to a signaling interaction site of the kinase being targeted. These interactions increase the overall selectivity and potency of the bivalent inhibitors that were generated. The ability to exploit disparate binding sites in diverse kinases points to the generality of the method described. Finally, we demonstrate that ATP-competitive inhibitors that are conjugated to the bio-orthogonal tag O(4)-benzyl-2-chloro-6-aminopyrimidine (CLP) are cell-permeable. The selective labeling of SNAP-tag with CLP conjugates allows the rapid assembly of bivalent inhibitors in living cells.

Protein kinases: emerging therapeutic targets in chronic lymphocytic leukemia

INTRODUCTION

Although protein kinases are primary targets for inhibition in hematological malignancies, until recently their contribution to chronic lymphocytic leukemia (CLL) was poorly understood. Insights into B-cell receptor signaling and its role in regulating key cellular functions have shed light on candidate protein kinases that are aberrantly activated in CLL. In this regard, protein kinases are now considered as potential drug targets in CLL.

AREA COVERED

This review has covered signaling pathways and associated protein kinases in CLL and the kinase inhibitors currently available in preclinical and clinical investigations. Individual protein kinases that are abnormally active in CLL and the functional consequences of their inhibition are discussed.

EXPERT OPINION

A growing body of evidence suggests that protein kinases are druggable targets for patients with CLL. The emergence of novel and bio-available kinase inhibitors and their promising clinical activity in CLL underscore the oncogenic role of kinases in leukemogenesis. Further investigations directed towards their role as single agents or in combinations may provide insight into understanding the substantial role of kinase-mediated signal transduction pathways and their inhibition in B- CLL.

PIM1 kinase as a target for cancer therapy

INTRODUCTION

Inhibition of protein kinases has become a standard of modern clinical oncology. PIM1 belongs to a novel class of serine/threonine kinases with distinct molecular and biochemical features regulating various oncogenic pathways, for example hypoxia response, cell cycle progression and apoptosis resistance. PIM1 is overexpressed in human cancer diseases and has been associated with metastasis and overall treatment response; in experimental models, inhibition of PIM1 suppressed cell proliferation and migration, induced apoptotic cell death and synergized with other chemotherapeutic agents.

AREAS COVERED

A PubMed literature search was performed to review the currently available data on PIM1 expression, regulation and targets; its implication in different types of cancer and its impact on prognosis are described. We present ATP-competitive PIM1 inhibitors and the state of the art of PIM1 inhibitor design. Finally, we highlight the development of the unusual class of highly selective and potent organometallic PIM1 inhibitors.

EXPERT OPINION

As PIM1 possesses oncogenic functions and is overexpressed in various kinds of cancer diseases, its inhibition provides a new option in cancer therapy. Based on the ability of highly selective organometallic PIM1 inhibitors, promising in vivo applicability is expected.

Targeting JAK2 in the therapy of myeloproliferative neoplasms

INTRODUCTION

Myeloproliferative neoplasms (MPNs) are a group of stem cell diseases, including polycythemia vera, essential thrombocythemia and primary myelofibrosis. Currently, there is no curative therapy for these diseases other than bone marrow transplant; therefore there is an apparent need for palliative treatment. MPNs are frequently associated with activating mutations in JAK2; small-molecule drugs targeting this molecule have entered clinical trials.

AREAS COVERED

In this review novel JAK2 inhibitors are discussed and alternative approaches to inhibiting their transforming potential are highlighted. Current clinical approaches do not only aim at blocking JAK2 activity, but also at reducing its stability and expression are highlighted, including inhibition of heat shock protein 90 (HSP90) and deacetylases (DAC) have the potential to significantly enhance the efficacy of JAK2 inhibitors.

EXPERT OPINION

Preliminary results from clinical trials indicate the feasibility and efficacy of JAK2-targeted approaches. However, JAK2 inhibitor treatment is limited by dose-dependent toxicity and combination treatment might be required. The discovery of JAK2 mutations that cause secondary resistance in vitro would further highlight the need for the development of next-generation JAK2 inhibitors and novel synergistic approaches.

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.

Identification of a phenanthrene derivative as a potent anticancer drug with Pim kinase inhibitory activity

Pim-3, a proto-oncogene with serine/threonine kinase activity, is aberrantly expressed in malignant lesions, but not in normal tissues, of endoderm-derived organs, including the pancreas, liver, colon, and stomach. Furthermore, the development of hepatocellular carcinoma is accelerated in mice expressing Pim-3 transgene selectively in the liver when these mice are treated with a hepatocarcinogen. These observations suggest that a chemical targeting Pim-3 kinase may be a novel type of anticancer drug. In the present study, we screened low molecular weight chemicals and observed that the phenanthrene derivative T26 potently inhibited Pim-3 and Pim-1, but only weakly inhibited Pim-2. Moreover, T26 markedly inhibited the in vitro growth of human pancreatic cancer cell lines by inducing apoptosis and G(2) /M arrest. The growth inhibitory effects of T26 were reversed by overexpression of Pim-3 cDNA in human pancreatic cancer cells, indicating that T26 acts primarily on Pim-3. Furthermore, T26 inhibited the growth of a human pancreatic cancer cell line in nude mice without causing apparent adverse effects when it was administered after tumor formation was evident. These observations imply that the chemical and its related compounds may be effective for the treatment of cancers in which there is aberrant Pim-3 expression.

Inhibition of Pim1 kinase activation attenuates allergen-induced airway hyperresponsiveness and inflammation

Pim kinases are a family of serine/threonine kinases whose activity can be induced by cytokines involved in allergy and asthma. These kinases play a role in cell survival and proliferation, but have not been examined, to the best of our knowledge, in the development of allergic disease. This study sought to determine the role of Pim1 kinase in the development of allergic airway responses. Mice were sensitized and challenged with antigen (primary challenge), or were sensitized, challenged, and rechallenged with allergen in a secondary model. To assess the role of Pim1 kinase, a small molecule inhibitor was administered orally after sensitization and during the challenge phase. Airway responsiveness to inhaled methacholine, airway and lung inflammation, cell composition, and cytokine concentrations were assessed. Lung Pim1 kinase concentrations were increased after ovalbumin sensitization and challenge. In the primary allergen challenge model, treatment with the Pim1 kinase inhibitor after sensitization and during airway challenges prevented the development of airway hyperresponsiveness, eosinophilic airway inflammation, and goblet cell metaplasia, and increased Th2 cytokine concentrations in bronchoalveolar fluid in a dose-dependent manner. These effects were also demonstrated after a secondary allergen challenge, where lung allergic disease was established before treatment. After treatment with the inhibitor, a significant reduction was evident in the number of CD4(+) and CD8(+) T cells and concentrations of cytokines in the airways. The inhibition of Pim1 kinase was effective in preventing the development of airway hyperresponsiveness, airway inflammation, and cytokine production in allergen-sensitized and allergen-challenged mice. These data identify the important role of Pim1 kinase in the full development of allergen-induced airway responses.

Targeting PIM kinase enhances the activity of sunitinib in renal cell carcinoma

Background:

Upregulation of PIM kinase expression has been reported in many malignancies, suggesting that inhibition of PIM kinase activity may be an attractive therapeutic strategy. We hypothesised that inhibition of PIM kinase activity with SGI-1776, a novel small molecule inhibitor of PIM kinase activity, would reduce the viability of renal cell carcinoma (RCC) cells and enhance the activity of sunitinib.

Methods:

Immunoblotting, qRT–PCR, and gene expression arrays were carried out to identify genes modulated by SGI-1776 treatment. The anticancer activity of SGI-1776 and sunitinib was determined by viability and apoptosis assays and in tumour xenografts in vivo.

Results:

Treatment with SGI-1776 led to a decrease in phosphorylated and total c-Myc levels, which resulted in the modulation of c-Myc target genes. SGI-1776 in combination with sunitinib induced a further reduction in c-Myc levels, which was associated with enhanced anticancer activity. siRNA-mediated knockdown of c-Myc demonstrated that its expression has a key role in regulating the sensitivity to the combination of SGI-1776 and sunitinib. Importantly, the combination significantly reduced tumour burden in two RCC xenograft models compared with single-agent therapy and was very well tolerated.

Conclusion:

These data indicate that targeting PIM kinase signalling is a promising treatment strategy for RCC.

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.

Pim1 kinase is required to maintain tumorigenicity in MYC-expressing prostate cancer cells

PIM1 kinase and MYC are commonly co-expressed in human prostate cancer and synergize to induce rapidly progressing prostate cancer in mouse models. Deficiency of the Pim kinase genes is well tolerated in vivo, suggesting that PIM1 inhibition might offer an attractive therapeutic modality for prostate cancer, particularly for MYC-expressing tumors. Here we examine the molecular consequences of Pim1 and MYC over-expression in the prostate as well as the effects of depleting Pim1 in prostate carcinoma cells with high levels of MYC. Over-expression of Pim1 in the mouse prostate induces several pro-tumorigenic genetic programs including cell cycle genes and Myc-regulated genes prior to the induction of any discernible pathology. Pim1 depletion by RNA interference in mouse and human prostate cancer cells decreased cellular proliferation, survival, Erk signaling, and tumorigenicity even when MYC levels were not significantly altered. These results indicate that PIM1 may be necessary to maintain tumorigenicity, and further support efforts aimed at developing PIM1 inhibitors for prostate cancer therapy.

Mechanisms of cytotoxicity to Pim kinase inhibitor, SGI-1776, in acute myeloid leukemia

Pim kinases are Ser/Thr kinases with multiple substrates that affect survival pathways. These proteins are overexpressed in acute myeloid leukemia (AML) blasts and we hypothesized that Pim kinase inhibition would affect AML cell survival. Imidazo[1,2-b]pyridazine compound, SGI-1776 inhibits Pim-1, Pim-2 and Pim-3, and was evaluated in AML-cell line, -xenograft model, and -primary blasts. Treatment of AML cells with SGI-1776 results in a concentration-dependent induction of apoptosis and we investigated its effect on Pim kinase functions. Phosphorylation of traditional Pim kinase targets, c-Myc(Ser62) and 4E-BP1 (Thr36/Thr47), were both decreased in actively cycling AML cell lines MV-4-11, MOLM-13 and OCI-AML-3. Levels of antiapoptotic proteins Bcl-2, Bcl-x(L), XIAP, and proapoptotic Bak and Bax were unchanged; however, a significant reduction in Mcl-1 was observed. This was correlated with inhibition of global RNA and protein synthesis and MCL-1 transcript decline after SGI-1776 treatment. These data suggest that SGI-1776 mechanism in AML involves Mcl-1 protein reduction. Consistent with cell line data, xenograft model studies with mice bearing MV-4-11 tumors showed efficacy with SGI-1776. Importantly, SGI-1776 was also cytotoxic in AML primary cells, irrespective of FLT3 mutation status and resulted in Mcl-1 protein decline. Pim kinase inhibition may be a new strategy for AML treatment.

Roles of Pim-3, a novel survival kinase, in tumorigenesis

Pim-3 is a member of the Provirus integrating site Moloney murine leukemia virus (Pim) family, which belongs to the Ca(2+) /calmodulin-dependent protein kinase (CaMK) group and exhibits serine/threonine kinase activity. Similar to other members of the Pim family (i.e. Pim-1 and Pim-2), Pim-3 can prevent apoptosis and promote cell survival and protein translation, thereby enhancing cell proliferation of normal and malignant cells. Pim-3 is expressed in vital organs, such as the heart, lung, and brain. However, minimal phenotypic changes in Pim-3-deficient mice suggest that Pim-3 may be physiologically dispensable. Pim-3 expression is enhanced in several cancer tissues, particularly those of endoderm-derived organs, including the liver, pancreas, colon, and stomach. The development of hepatocellular carcinoma is accelerated in mice expressing the Pim-3 gene selectively in the liver only when these mice are treated with a hepatocarcinogen, indicating that Pim-3 can act as a promoter but not as an initiator. Moreover, inhibition of Pim-3 expression can retard in vitro cell proliferation of hepatocellular, pancreatic, and colon carcinoma cell lines by promoting cell apoptosis. Furthermore, a Pim-3 kinase inhibitor has been reported to inhibit cell proliferation in an in vivo xenograft model using a human pancreatic cancer cell line without inducing any major adverse effects. Thus, Pim-3 kinase may be a candidate molecule for the development of molecular targeting drugs against cancer.