PIM kinase inhibitors downregulate STAT3(Tyr705) phosphorylation

A review on structure-function mechanism and signaling pathway of serine/threonine protein PIM kinases as a therapeutic target

The proviral integration for the Moloney murine leukemia virus (PIM) kinases, belonging to serine/threonine kinase family, have been found to be overexpressed in various types of cancers, such as prostate, breast, colon, endometrial, gastric, and pancreatic cancer. The three isoforms PIM kinases i.e., PIM1, PIM2, and PIM3 share a high degree of sequence and structural similarity and phosphorylate substrates controlling tumorigenic phenotypes like proliferation and cell survival. Targeting short-lived PIM kinases presents an intriguing strategy as in vivo knock-down studies result in non-lethal phenotypes, indicating that clinical inhibition of PIM might have fewer adverse effects. The ATP binding site (hinge region) possesses distinctive attributes, which led to the development of novel small molecule scaffolds that target either one or all three PIM isoforms. Machine learning and structure-based approaches have been at the forefront of developing novel and effective chemical therapeutics against PIM in preclinical and clinical settings, and none have yet received approval for cancer treatment. The stability of PIM isoforms is maintained by PIM kinase activity, which leads to resistance against PIM inhibitors and chemotherapy; thus, to overcome such effects, PIM proteolysis targeting chimeras (PROTACs) are now being developed that specifically degrade PIM proteins. In this review, we recapitulate an overview of the oncogenic functions of PIM kinases, their structure, function, and crucial signaling network in different types of cancer, and the potential of pharmacological small-molecule inhibitors. Further, our comprehensive review also provides valuable insights for developing novel antitumor drugs that specifically target PIM kinases in the future. In conclusion, we provide insights into the benefits of degrading PIM kinases as opposed to blocking their catalytic activity to address the oncogenic potential of PIM kinases.

S100A8/A9 predicts response to PIM kinase and PD-1/PD-L1 inhibition in triple-negative breast cancer mouse models

BACKGROUND

Understanding why some triple-negative breast cancer (TNBC) patients respond poorly to existing therapies while others respond well remains a challenge. This study aims to understand the potential underlying mechanisms distinguishing early-stage TNBC tumors that respond to clinical intervention from non-responders, as well as to identify clinically viable therapeutic strategies, specifically for TNBC patients who may not benefit from existing therapies.

METHODS

We conducted retrospective bioinformatics analysis of historical gene expression datasets to identify a group of genes whose expression levels in early-stage tumors predict poor clinical outcomes in TNBC. In vitro small-molecule screening, genetic manipulation, and drug treatment in syngeneic mouse models of TNBC were utilized to investigate potential therapeutic strategies and elucidate mechanisms of drug action.

RESULTS

Our bioinformatics analysis reveals a robust association between increased expression of immunosuppressive cytokine S100A8/A9 in early-stage tumors and subsequent disease progression in TNBC. A targeted small-molecule screen identifies PIM kinase inhibitors as capable of decreasing S100A8/A9 expression in multiple cell types, including TNBC and immunosuppressive myeloid cells. Combining PIM inhibition and immune checkpoint blockade induces significant antitumor responses, especially in otherwise resistant S100A8/A9-high PD-1/PD-L1-positive tumors. Notably, serum S100A8/A9 levels mirror those of tumor S100A8/A9 in a syngeneic mouse model of TNBC.

CONCLUSIONS

Our data propose S100A8/A9 as a potential predictive and pharmacodynamic biomarker in clinical trials evaluating combination therapy targeting PIM and immune checkpoints in TNBC. This work encourages the development of S100A8/A9-based liquid biopsy tests for treatment guidance.

PIM3 Kinase: A Promising Novel Target in Solid Cancers

PIM3 (provirus-integrating Moloney site 3) is a serine/threonine kinase and belongs to the PIM family (PIM1, PIM2, and PIM3). PIM3 is a proto-oncogene that is frequently overexpressed in cancers originating from endoderm-derived tissues, such as the liver, pancreas, colon, stomach, prostate, and breast cancer. PIM3 plays a critical role in activating multiple oncogenic signaling pathways promoting cancer cell proliferation, survival, invasion, tumor growth, metastasis, and progression, as well as chemo- and radiation therapy resistance and immunosuppressive microenvironment. Genetic inhibition of PIM3 expression suppresses in vitro cell proliferation and in vivo tumor growth and metastasis in mice with solid cancers, indicating that PIM3 is a potential therapeutic target. Although several pan-PIM inhibitors entered phase I clinical trials in hematological cancers, there are currently no FDA-approved inhibitors for the treatment of patients. This review provides an overview of recent developments and insights into the role of PIM3 in various cancers and its potential as a novel molecular target for cancer therapy. We also discuss the current status of PIM-targeted therapies in clinical trials.

S100A8/A9 predicts triple-negative breast cancer response to PIM kinase and PD-1/PD-L1 inhibition

It remains elusive why some triple-negative breast cancer (TNBC) patients respond poorly to existing therapies while others respond well. Our retrospective analysis of historical gene expression datasets reveals that increased expression of immunosuppressive cytokine S100A8/A9 in early-stage tumors is robustly associated with subsequent disease progression in TNBC. Although it has recently gained recognition as a potential anticancer target, S100A8/A9 has not been integrated into clinical study designs evaluating molecularly targeted therapies. Our small molecule screen has identified PIM kinase inhibitors as capable of decreasing S100A8/A9 expression in multiple cell types, including TNBC and immunosuppressive myeloid cells. Furthermore, combining PIM inhibition and immune checkpoint blockade induces significant antitumor responses, especially in otherwise resistant S100A8/A9-high PD-1/PD-L1-positive tumors. Importantly, serum S100A8/A9 levels mirror those of tumor S100A8/A9 in a syngeneic mouse model of TNBC. Thus, our data suggest that S100A8/A9 could be a predictive and pharmacodynamic biomarker in clinical trials evaluating combination therapy targeting PIM and immune checkpoints in TNBC and encourage the development of S100A8/A9-based liquid biopsy tests.

ZAP70 Activation Compensates for Loss of Class IA PI3K Isoforms Through Activation of the JAK-STAT3 Pathway

BACKGROUND/AIM

Tyrosine kinases have crucial functions in cell signaling and proliferation. The phosphatidylinositol 3-kinase (PI3K) pathway is frequently deregulated in human cancer and is an essential regulator of cellular proliferation. We aimed to determine which tyrosine kinases contribute to resistance elicited by PI3K silencing and inhibition.

MATERIALS AND METHODS

To mimic catalytic inactivation of p110α/β, specific p110α (BYL719) and p110β (KIN193) inhibitors were used in addition to genetic knock-out in in vitro assays. Cell viability was assessed using crystal violet staining, whereas cellular transformation ability was analyzed by soft-agar growth assays.

RESULTS

Activated zeta chain of T-cell receptor-associated protein kinase 70 (ZAP70) generated resistance to PI3K inhibition. This resistance was via activation of the Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) axis. We demonstrated that activated ZAP70 has a high transforming capability associated with the formation of malignant phenotype in untransformed cells and has the potential to be a tumor-initiating factor in cancer cells.

CONCLUSION

ZAP70 may be a potent driver of proliferation and transformation in untransformed cells and is implicated in resistance to PI3K inhibitors in cancer cells.

Stomatin-like Protein 2 Promotes Tumor Cell Survival by Activating the JAK2-STAT3-PIM1 Pathway, Suggesting a Novel Therapy in CRC

Despite intensive efforts, a considerable proportion of colorectal cancer (CRC) patients develop local recurrence and distant metastasis. Stomatin-like protein 2 (SLP-2), a member of the highly conserved stomatin superfamily, is upregulated across cancer types. However, the biological and functional roles of SLP-2 remain elusive in CRC. Here, we report that high SLP-2 expression was found in CRC tissues and was linked to tumor progression and tumor cell differentiation. Additionally, high SLP-2 expression correlated with poor overall survival (OS) in CRC patients (p < 0.001). SLP-2 knockout (SLP-2KO), generated by CRISPR/Cas9, reduced cell growth, migration, and invasion; induced apoptosis in CRC cells; and reduced tumor xenograft growth in vivo. A 181-compound library screening showed that SLP-2KO produced resistance to JAK2 inhibitors (NVP-BSK805 and TG-101348) and a PIM1 inhibitor (SGI-1776), revealing that the JAK2-STAT3-PIM1 oncogenic pathway was potentially controlled by SLP-2 in CRC. In vitro and in vivo, TG-101348 combined with SGI-1776 was synergistic in CRC (combination index [CI] < 1). Overall, our findings suggest that SLP-2 controls the JAK2-STAT3-PIM1 oncogenic pathway, offering a rationale for a novel therapeutic strategy with combined SGI-1776 and TG-101348 in CRC. Additionally, SLP-2 may be a prognostic marker and biomarker for sensitivity to JAK2 and PIM1 inhibitors.

The kinase polypharmacology landscape of clinical PARP inhibitors

Polypharmacology plays an important role in defining response and adverse effects of drugs. For some mechanisms, experimentally mapping polypharmacology is commonplace, although this is typically done within the same protein class. Four PARP inhibitors have been approved by the FDA as cancer therapeutics, yet a precise mechanistic rationale to guide clinicians on which to choose for a particular patient is lacking. The four drugs have largely similar PARP family inhibition profiles, but several differences at the molecular and clinical level have been reported that remain poorly understood. Here, we report the first comprehensive characterization of the off-target kinase landscape of four FDA-approved PARP drugs. We demonstrate that all four PARP inhibitors have a unique polypharmacological profile across the kinome. Niraparib and rucaparib inhibit DYRK1s, CDK16 and PIM3 at clinically achievable, submicromolar concentrations. These kinases represent the most potently inhibited off-targets of PARP inhibitors identified to date and should be investigated further to clarify their potential implications for efficacy and safety in the clinic. Moreover, broad kinome profiling is recommended for the development of PARP inhibitors as PARP-kinase polypharmacology could potentially be exploited to modulate efficacy and side-effect profiles.

PIM kinase inhibition: co-targeted therapeutic approaches in prostate cancer

PIM kinases have been shown to play a role in prostate cancer development and progression, as well as in some of the hallmarks of cancer, especially proliferation and apoptosis. Their upregulation in prostate cancer has been correlated with decreased patient overall survival and therapy resistance. Initial efforts to inhibit PIM with monotherapies have been hampered by compensatory upregulation of other pathways and drug toxicity, and as such, it has been suggested that co-targeting PIM with other treatment approaches may permit lower doses and be a more viable option in the clinic. Here, we present the rationale and basis for co-targeting PIM with inhibitors of PI3K/mTOR/AKT, JAK/STAT, MYC, stemness, and RNA Polymerase I transcription, along with other therapies, including androgen deprivation, radiotherapy, chemotherapy, and immunotherapy. Such combined approaches could potentially be used as neoadjuvant therapies, limiting the development of resistance to treatments or sensitizing cells to other therapeutics. To determine which drugs should be combined with PIM inhibitors for each patient, it will be key to develop companion diagnostics that predict response to each co-targeted option, hopefully providing a personalized medicine pathway for subsets of prostate cancer patients in the future.

Leflunomide Synergizes with Gemcitabine in Growth Inhibition of PC Cells and Impairs c-Myc Signaling through PIM Kinase Targeting

The immunosuppressive agent leflunomide has been used in the treatment of over 300,000 patients with rheumatoid arthritis. Its active metabolite, teriflunomide (Ter), directly inhibits dihydroorotate dehydrogenase (DHODH), an enzyme involved in nucleoside synthesis. We report that Ter not only shows in vitro anti-proliferative activity in pancreatic cancer (PC) cells as a single agent but also synergizes with the chemotherapeutic gemcitabine (Gem) in growth inhibition of PC cells. The growth-inhibitory effects of Ter are not solely caused by inhibition of DHODH. Through a kinase screening approach, we identified the PIM-3 serine-threonine kinase as a novel direct target. Subsequent dose-response kinase assays showed that Ter directly inhibited all three PIM family members, with the highest activities against PIM-3 and -1. The PIM-3 kinase was the PIM family member most often associated with PC oncogenesis and was also the kinase inhibited the most by Ter among more than 600 kinases investigated. Ter in PC cells induced changes in phosphorylation and expression of PIM downstream targets, consistent with the effects achieved by overexpression or downregulation of PIM-3. Finally, pharmacological inhibition of PIM proteins not only diminished PC cell proliferation, but also small-molecule pan-PIM and PIM-3 inhibitors synergized with Gem in growth inhibition of PC cells.

AZD1208, a Pan-Pim Kinase Inhibitor, Has Anti-Growth Effect on 93T449 Human Liposarcoma Cells via Control of the Expression and Phosphorylation of Pim-3, mTOR, 4EBP-1, S6, STAT-3 and AMPK

Overexpression of Pim kinases has an oncogenic/pro-survival role in many hematological and solid cancers. AZD1208 is a pan-Pim kinase inhibitor that has anti-cancer and anti-adipogenic actions. Here, we investigated the effects of AZD1208 on the growth of 93T449 cells, a differentiated human liposarcoma cell line. At 20 µM, AZD1208 was cytotoxic (cytostatic) but not apoptotic, reducing cell survival without DNA fragmentation, caspase activation or increasing cells in the sub G1 phase; known apoptotic parameters. Notably, AZD1208 reduced phosphorylation of signal transducer and activator of transcription-3 (STAT-3) in 93T449 cells. STAT-3 inhibition by AG490, a JAK2/STAT-3 inhibitor similarly reduced cell survival. AZD1208 down-regulated phosphorylation of mammalian target of rapamycin (mTOR) and ribosomal S6 while up-regulated eukaryotic initiation factor-2α (eIF-2α). In addition, AZD1208 induced a LKB-1-independent AMPK activation, which was crucial for its cytostatic effect, as knock-down of AMPK greatly blocked AZD1208s ability to reduce cell survival. AZD1208 had no effect on expression of two members of Pim kinase family (Pim-1 and Pim-3) but inhibited phosphorylation of 4EBP-1, a downstream effector of Pim kinases. Importantly, a central role for Pim-3 in the actions of AZD1208 was confirmed by knock-down, which not only reduced 93T449 cell survival but also led to the inhibition of 4EBP-1, mTOR, eIF-2α and STAT-3, along with the activation of AMPK. In summary, this is the first report demonstrating that AZD1208 inhibits growth of liposarcoma cells and that this activity is mediated through Pim-3 kinase, STAT-3, mTOR, S6 and AMPK expression and phosphorylation pathways.

Identification and molecular characterization of the Pim1 serine/threonine kinase homolog in Litopenaeus vannamei

The Pim1 serine/threonine kinase is associated with multiple cellular functions including proliferation, survival, differentiation, apoptosis, tumorigenesis, immune regulation and inflammation in vertebrates. However, little is known about the role of Pim1 in invertebrate immunity. In this study, we identified and characterized for the first time, a Pim1 (LvPim1) gene in Litopenaeus vannamei, with a full-length cDNA of 2352 bp and a 1119 bp open reading frame (ORF) encoding a putative protein of 372 amino acids, which contains a typical serine/threonine kinase domain. Sequence and phylogenetic analysis revealed that LvPim1 shared a close evolutionary relationship with Pim1 from vertebrates. Real-time qPCR analysis showed that LvPim1 was widely expressed in all tissues tested; with its transcript level induced in hepatopancreas and hemocytes upon challenge with Vibrio parahaemolyticus, Streptoccocus iniae, lipopolysaccharide (LPS), and white spot syndrome virus (WSSV), thus, suggesting its probable involvement in shrimp immune response. Moreover, knockdown of LvPim1 resulted in increased hemocytes apoptosis; shown by high caspase3/7 activity, coupled with increase in pro-apoptotic LvCaspase3 and LvCytochrome C, and decrease in pro-survival LvBcl2, LvIAP1, and LvIAP2 mRNA expression in hemocytes. Finally, LvPim1 knockdown renders shrimps more susceptible to V. parahaemolyticus infection. Taken together, our present data strongly suggest that LvPim1 is involved in modulating shrimp resistance to pathogen infection, promote hemocytes survival, and therefore plays a role in shrimp immune response.

Pim-3 enhances melanoma cell migration and invasion by promoting STAT3 phosphorylation

Melanoma is the deadliest form of commonly encountered skin cancer, and has fast propagating and highly invasive characteristics. Pim-3, a highly expressed oncogene in melanoma, is a highly conserved serine/threonine kinase with various biological activities, such as proliferation-accelerating and anti-apoptosis effects on cancer progression. However, whether Pim-3 regulates melanoma metastasis has not been determined. Here, we constructed a Pim-3-silencing short hairpin RNA (sh-Pim-3), a TLR7-stimulating ssRNA and a dual-function vector containing a sh-Pim-3 and a ssRNA, and transfected them into the B16F10 melanoma cell line to investigate the effects of Pim-3 on migration and invasion in melanoma. We found that sh-Pim-3 inhibited B16F10 cell migration and invasion in vitro. In a tumor-bearing mouse model, sh-Pim-3 significantly downregulated pulmonary metastasis of B16F10 melanoma cell in vivo. Mechanistically, sh-Pim-3 inhibited metastasis by regulating the expression of genes related to epithelial-mesenchymal transition (EMT). Further study revealed that by promoting the phosphorylation of STAT3 (signal transducer and activator of transcription 3), Pim-3 induced the expression of Slug, Snail, and ZEB1, which enhanced EMT-related changes and induced melanoma migration and invasion. Our study suggests that Pim-3 is a potential effective target for melanoma therapy.

PIM activity in tumours: A key node of therapy resistance

The PIM kinases are proto-oncogenes which have been shown to facilitate cell survival and proliferation to drive malignancy and resistance post-therapy. They are able to suppress cell death signals, sustain PI3K/AKT/mTORC1 pathway activity and regulate the MYC oncogenic program. Recent work has revealed PIM kinase essentiality for advanced tumour maintenance and described tumour sensitivity to small molecule inhibitors targeting PIM kinase in multiple malignancies.

STAT3 and STAT5A are potential therapeutic targets in castration-resistant prostate cancer

Mechanisms of castration-resistant prostate cancer (CRPC) are not well understood, thus hindering rational-based drug design. Activation of STAT3/5A, key components of the JAK/STAT pathway, is implicated in aggressive PC, yet their clinical relevance in CRPC remains elusive. Here, we evaluated the possible role of STAT3/5A in CRPC using immunological, quantitative mRNA expression profiling, and pharmacological methods. We observed a strong nuclear immunoreactivity for STAT3 and STAT5A in 93% (n=14/15) and 80% (n=12/15) of CRPC cases, respectively, compared with benign prostatic hyperplasia (BPH). We demonstrated that PC cells express varying levels of STAT3 and STAT5A transcripts. In addition, we demonstrate that pimozide, a psychotropic drug and an indirect inhibitor of STAT5, attenuated PC cells growth, and induced apoptosis in a dose-dependent manner. Furthermore, our analysis of the PC public data revealed that the STAT3/5A genes were frequently amplified in metastatic CRPC. These findings suggest that STAT3/5A potentially serves as a predictive biomarker to evaluate the therapeutic efficacy of a cancer drug targeting the JAK/STAT pathway. Since the JAK/STAT and AR pathways are suggested to be functionally synergistic, inhibition of the JAK/STAT signaling alone or together with AR may lead to a novel treatment modality for patients with advanced PC.

Ubenimex suppresses Pim-3 kinase expression by targeting CD13 to reverse MDR in HCC cells

Hepatocellular carcinoma (HCC) is one of the most serious cancers, with rapid progression and high mortality. However, chemotherapy of HCC is hindered by multi-drug resistance (MDR). It is urgent, therefore, to explore new approaches for overcoming MDR of HCC cells. Ubenimex, an inhibitor of CD13, has been used as an immuno-enhancer for treating hematological neoplasms and other solid tumors. Here, we demonstrate that Ubenimex can also reverse MDR in the HCC cell lines HepG2/5-FU and Bel7402/5-FU. Ubenimex inhibits the expression of the proto-oncogene, Pim-3, which is accompanied by decreased expression of BCL-2 and BCL-XL, decreased phosphorylation of Bad, and increased tumor apoptosis.

Moreover, Ubenimex decreases expression of the MDR-associated proteins P-gp, MRP3 and MRP2 to enhance intracellular accumulation of Cisplatin, for which down-regulation of Pim-3 is essential. Our results reveal a previously uncharacterized function of Ubenimex in mediating drug resistance in HCC, which suggests that Ubenimex may provide a new strategy to reverse MDR and improve HCC sensitivity to chemotherapeutic drugs via its effects on Pim-3.

PIM kinases 1, 2 and 3 in intracellular LIF signaling, proliferation and apoptosis in trophoblastic cells

Proviral insertion in murine (PIM) lymphoma proteins are mainly regulated by the Janus Kinase/Signal Transducer Activator of Transcription (JAK/STAT) signaling pathway, which can be activated by members of the Interleukin-6 (IL-6) family, including Leukemia Inhibitory Factor (LIF). Aim of the study was to compare PIM1, PIM2 and PIM3 expression and potential cellular functions in human first and third trimester trophoblast cells, the immortalized first trimester extravillous trophoblast cell line HTR8/SVneo and the choriocarcinoma cell line JEG-3. Expression was analyzed by qPCR and immunochemical staining. Functions were evaluated by PIM inhibition followed by analysis of kinetics of cell viability as assessed by MTS assay, proliferation by BrdU assay, and apoptosis by Western blotting for BAD, BCL-XL, (cleaved) PARP, CASP3 and c-MYC. Apoptosis and necrosis were tested by flow cytometry (annexin V/propidium iodide staining). All analyzed PIM kinases are expressed in primary trophoblast cells and both cell lines and are regulated upon stimulation with LIF. Inhibition of PIM kinases significantly reduces viability and proliferation and induces apoptosis. Simultaneously, phosphorylation of c-MYC was reduced. These results demonstrate the involvement of PIM kinases in LIF-induced regulation in different trophoblastic cell lines which may indicate similar functions in primary cells.

Expression of PIM kinases in Reed-Sternberg cells fosters immune privilege and tumor cell survival in Hodgkin lymphoma

Reed-Sternberg (RS) cells of classical Hodgkin lymphoma (cHL) express multiple immunoregulatory proteins that shape the cHL microenvironment and allow tumor cells to evade immune surveillance. Expression of certain immunoregulatory proteins is modulated by prosurvival transcription factors, such as NFκB and STATs. Because these factors also induce expression of the oncogenic PIM1/2/3 serine/threonine kinases, and as PIMs modulate transcriptional activity of NFκB and STATs, we hypothesized that these kinases support RS cell survival and foster their immune privilege. Here, we investigated PIM1/2/3 expression in cHL and assessed their role in developing RS cell immune privilege and survival. PIM1/2/3 were ubiquitously expressed in primary and cultured RS cells, and their expression was driven by JAK-STAT and NFκB activity. Genetic or chemical PIM inhibition with a newly developed pan-PIM inhibitor, SEL24-B489, induced RS cell apoptosis. PIM inhibition decreased cap-dependent protein translation, blocked JAK-STAT signaling, and markedly attenuated NFκB-dependent gene expression. In a cHL xenograft model, SEL24-B489 delayed tumor growth by 95.8% (P = .0002). Furthermore, SEL24-B489 decreased the expression of multiple molecules engaged in developing the immunosuppressive microenvironment, including galectin-1 and PD-L1/2. In coculture experiments, T cells incubated with SEL24-B489-treated RS cells exhibited higher expression of activation markers than T cells coincubated with control RS cells. Taken together, our data indicate that PIM kinases in cHL exhibit pleiotropic effects, orchestrating tumor immune escape and supporting RS cell survival. Inhibition of PIM kinases decreases RS cell viability and disrupts signaling circuits that link these cells with their niches. Thus, PIM kinases are promising therapeutic targets in cHL.

Pim-3 Regulates Stemness of Pancreatic Cancer Cells via Activating STAT3 Signaling Pathway

Due to its aggressiveness and unusual resistance to conventional therapies, pancreatic cancer is a highly lethal gastrointestinal malignancy with poor prognosis. According to the cancer stem cell hypothesis, there exists a fraction of cancer cells, that is, cancer stem cells, responsible for tumor maintenance and therapeutic failure. Herein we investigated the involvement of proto-oncogene Pim-3 in driving the stemness properties in pancreatic cancer. Expression levels of several stemness-associated markers were examined in several pancreatic cancer cell lines. The double positive (CD24+ESA+) and double negative (CD24-ESA-) pancreatic cancer cells were isolated from PANC-1 and L3.6pl, and their self-renewal ability, tumorigenicity as well as sensitivity to gemcitabine were then evaluated. Results showed that there existed heterogeneity in expression levels of stemness-associated surface markers among pancreatic cancer cell lines. CD24+ESA+ pancreatic cancer cells exhibited increased tumorigenicity and decreased chemosensitivity to gemcitabine as compared to CD24-ESA- cells. Besides, the double positive (CD24+ESA+) subpopulation also exhibited greater expression level of Pim-3 when compared with the double negative (CD24-ESA-) ones. Furthermore, silencing of Pim-3 in pancreatic cancer cells leads to decreased proportions of both single positive (CD24+ and ESA+) and double positive (CD24+ESA+) pancreatic cancer cells. Overexpression of Pim-3 was associated with increased levels of some stemness-associated transcription factors (STAT3, etc.). Moreover, the phosphorylation level and transcriptional activity of STAT3 were decreased in Pim-3 silenced pancreatic cancer cells and restoration of its activity results in restitution of stem cell-like phenotypes. Therefore, Pim-3 maintains stemness of pancreatic cancer cells via activating STAT3 signaling pathway and might be used as a novel therapeutic target in pancreatic cancer.

MicroRNA-33a-mediated downregulation of Pim-3 kinase expression renders human pancreatic cancer cells sensitivity to gemcitabine

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, with less than 5% of patients surviving 5 years beyond diagnosis. Systemic therapies, particularly gemcitabine, have a modest clinical benefit, but chemoresistance limits their efficacy. Here, we demonstrate that plasma miR-33a levels positively correlated with miR-33a levels in tumor tissues of patients with PDAC and are a good prognostic indicator of overall survival. Overexpression of miR-33a inhibited tumor cell proliferation and increased the chemosensitivity to gemcitabine both in vitro and in vivo. Moreover, miR-33a targets Pim-3 directly in PDAC. Pim-3 expression was a prognostic indicator related to poor survival in pancreatic cancer patients. Plasma miR-33a levels were significantly lower in pancreatic cancer patients with high Pim-3 protein expression than in healthy controls. Furthermore, overexpression of miR-33a in pancreatic cancer cell lines suppressed Pim-3 expression, leading to downregulation of the AKT/Gsk-3β/β-catenin pathway. Overall, these results indicate that miR-33a functions as a tumor suppressor that downregulates Pim-3 kinase expression to inhibit both pancreatic tumor growth and gemcitabine resistance via the AKT/β-catenin pathway. Hence, detection of plasma miR-33a may be a simple and convenient method of predicting therapeutic responses.

Overexpression of pim-3 and protective role in lipopolysaccharide-stimulated hepatic stellate cells

AIM: To investigate pim-3 expression in hepatic stellate cells (HSCs) stimulated by lipopolysaccharide (LPS), and its protective effect on HSCs.

METHODS: Rat HSC-T6 cells were stimulated by LPS. The effect of LPS on proliferation and apoptosis of HSC-T6 cells was investigated by methyl thiazoyltetrazolium (MTT) assay and flow cytometry after annexin V-fluorescein isothiocyanate/propidium iodide double staining. pim-3 mRNA and protein were detected by reverse transcriptase polymerase chain reaction and Western blotting at 48 h when HSC-T6 cells were stimulated with 1 μg/mL LPS for 0, 3, 6, 12, 24 and 48 h. The cells without stimulation served as controls. To study the effect of pim-3 kinase on HSC-T6 cells, si-pim3 (siRNA against pim-3) was transfected into HSC-T6 cells. HSC-T6 cells were subjected to different treatments, including LPS, si-pim3, or si-pim3 plus LPS, and control cells were untreated. Protein expression of pim-3 was detected at 48 h after treatment, and cell proliferation at 24 and 48 h by MTT assay. Apoptosis was detected by flow cytometry, and confirmed with caspase-3 activity assay.

RESULTS: LPS promoted HSC-T6 cell proliferation and protected against apoptosis. Significantly delayed upregulation of pim-3 expression induced by LPS occurred at 24 and 48 h for mRNA expression (pim-3/β-actin RNA, 24 or 48 h vs 0 h, 0.81 ± 0.20 or 0.78 ± 0.21 vs 0.42 ± 0.13, P < 0.05), and occurred at 12 h and peaked at 24 and 48 h for protein expression (pim-3/GAPDH protein, 12, or 24 or 48 h vs 0 h, 0.68 ± 0.12, 1.47 ± 0.25 or 1.51 ± 0.23 vs 0.34 ± 0.04, P < 0.01). pim-3 protein was ablated by si-pim3 and upregulated by LPS in HSC-T6 cells at 48 h after treatment (pim-3/GAPDH: si-pim3, si-pim3 plus LPS or LPS vs control, 0.11 ± 0.05, 0.12 ± 0.05 or 1.08 ± 0.02 vs 0.39 ± 0.03, P < 0.01). Ablation of pim-3 by si-pim3 in HSC-T6 cells partly abolished proliferation (OD at 24 h, si-pim3 group or si-pim3 plus LPS vs control, 0.2987 ± 0.050 or 0.4063 ± 0.051 vs 0.5267 ± 0.030, P < 0.01; at 48 h 0.4634 ± 0.056 or 0.5433 ± 0.031 vs 0.8435 ± 0.028, P < 0.01; si-pim3 group vs si-pim3 plus LPS, P < 0.01 at 24 h and P < 0.05 at 48 h), and overexpression of pim-3 in the LPS group increased cell proliferation (OD: LPS vs control, at 24 h, 0.7435 ± 0.028 vs 0.5267 ± 0.030, P < 0.01; at 48 h, 1.2136 ± 0.048 vs 0.8435 ± 0.028, P < 0.01). Ablation of pim3 with si-pim3 in HSC-T6 cells aggravated apoptosis (si-pim3 or si-pim3 plus LPS vs control, 42.3% ±1.1% or 40.6% ± 1.3% vs 16.8% ± 3.3%, P < 0.01; si-pim3 vs si-pim3 plus LPS, P > 0.05), and overexpression of pim-3 in the LPS group attenuated apoptosis (LPS vs control, 7.32% ± 2.1% vs 16.8% ± 3.3%, P < 0.05). These results were confirmed by caspase-3 activity assay.

CONCLUSION: Overexpression of pim-3 plays a protective role in LPS-stimulated HSC-T6 cells.

PIM kinases: an overview in tumors and recent advances in pancreatic cancer

The PIM kinases represent a family of serine/threonine kinases, which is composed of three different members (PIM1, PIM2 and PIM3). Aberrant expression of PIM kinases is observed in variety of tumors, including pancreatic cancer. The PIM kinases play pivotal roles in the regulation of cell cycle, apoptosis, properties of stem cells, metabolism, autophagy, drug resistance and targeted therapy. The roles of PIM kinases in pancreatic cancer include the regulation of proliferation, apoptosis, cell cycle, formation, angiogenesis and prediction prognosis. Blocking the activities of PIM kinases could prevent pancreatic cancer development. PIM kinases may be a novel target for cancer therapy.

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.

Pim-3 promotes human pancreatic cancer growth by regulating tumor vasculogenesis

Pim-3, a proto-oncogene with serine/threonine kinase activity, is aberrantly expressed in malignant lesions, but not in normal pancreatic tissues. To assess the role of Pim-3 in human pancreatic carcinogenesis in vivo and to determine the underlying Pim-3 signaling regulatory mechanisms, we established MiaPaca-2 cells overexpressing wild-type Pim-3 or Pim-3 kinase dead mutants (K69M-Pim-3) as well as PCI55 cells stably expressing Pim-3 shRNA or scrambled shRNA in a tetracycline-inducible manner. In addition, we conducted studies utilizing a nude mouse tumor xenograft model. Our results demonstrated that cells stably overexpressing wild-type Pim-3 exhibited functionally enhanced phosphorylation of Bad at Ser112 and increased proliferation. In contrast, the stable inactivation of Pim-3 by K69M-Pim-3 or silencing of Pim-3 expression by Pim-3 shRNA resulted in functionally decreased phosphorylation of Bad at Ser112 and higher apoptotic cells. Following subcutaneous injection of these stable cell lines, nude mice injected with Pim-3 overexpressing cells developed 100% subcutaneous tumors, together with increased PCNA-positive cells and enhanced intratumoral CD31-positive vascular areas. On the other hand, intratumoral neovascularization and tumor cell proliferation was attenuated in mice injected with Pim-3 kinase inactive cells, eventually reducing tumorigenicity in these mice to 46.6%. Moreover, Pim-3 overexpression upregulated the intratumoral levels of pSTAT3Try705, pSurvivinThr34, HGF, EGF, FGF-2 and VEGF, while the increases were markedly diminished on Pim-3 kinase inactivation. Collectively, the Pim-3 kinase emerges as being involved in accelerating human pancreatic cancer development and in promoting tumor neovascularization and subsequent tumor growth. Targeting Pim-3 may play a dual role in halting tumor progression, by promoting tumor cell death and blocking angiogenesis.

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.

Functional role and therapeutic potential of the pim-1 kinase in colon carcinoma

PURPOSE

The provirus integration site for Moloney murine leukemia virus 1 (Pim-1) kinase is overexpressed in various tumors and has been linked to poor prognosis. Its role as proto-oncogene is based on several Pim-1 target proteins involved in pivotal cellular processes. Here, we explore the functional relevance of Pim-1 in colon carcinoma.

EXPERIMENTAL DESIGN

RNAi-based knockdown approaches, as well as a specific small molecule inhibitor, were used to inhibit Pim-1 in colon carcinoma cells. The effects were analyzed regarding proliferation, apoptosis, sensitization toward cytostatic treatment, and overall antitumor effect in vitro and in mouse tumor models in vivo.

RESULTS

We demonstrate antiproliferative, proapoptotic, and overall antitumor effects of Pim-1 inhibition. The sensitization to 5-fluorouracil (5-FU) treatment upon Pim-1 knockdown offers new possibilities for combinatorial treatment approaches. Importantly, this also antagonizes a 5-FU-triggered Pim-1 up-regulation, which is mediated by decreased levels of miR-15b, a microRNA we newly identify to regulate Pim-1. The analysis of the molecular effects of Pim-1 inhibition reveals a complex regulatory network, with therapeutic Pim-1 repression leading to major changes in oncogenic signal transduction with regard to p21(Cip1/WAF1), STAT3, c-jun-N-terminal kinase (JNK), c-Myc, and survivin and in the levels of apoptosis-related proteins Puma, Bax, and Bcl-xL.

CONCLUSIONS

We demonstrate that Pim-1 plays a pivotal role in several tumor-relevant signaling pathways and establish the functional relevance of Pim-1 in colon carcinoma. Our results also substantiate the RNAi-mediated Pim-1 knockdown based on polymeric polyethylenimine/small interfering RNA nanoparticles as a promising therapeutic approach.

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.

Pim-3 promotes the growth of human pancreatic cancer in the orthotopic nude mouse model through vascular endothelium growth factor

BACKGROUND

As one of the most lethal cancers, pancreatic cancer presents poor prognosis with an overall 5-y survival of less than 5%. We previously reported that Pim-3, a member of the proto-oncogene Pim family that encodes serine/threonine kinases, is aberrantly expressed in human pancreatic cancer lesions. In the current study, we investigated the role of Pim-3 in promoting tumor growth and angiogenesis in an orthotopic nude mouse model of human pancreatic cancer.

METHODS

We constructed retroviral vectors for human Pim-3 and a kinase-dead mutant of human Pim-3 (K69M); the retroviral supernatants generated from these vectors were then used to infect the human pancreatic cancer cell line MiaPaCa-2 to establish stable cell lines. We assessed cell proliferation using CCK-8, tumor growth, and angiogenesis in vivo in an orthotopic mouse model of pancreatic cancer. While tumor size was measured using magnetic resonance imaging, the tumor tissues were excised for protein extraction and histological analysis to detect vascular endothelium growth factor (VEGF) expression and vessel density.

RESULTS

We established an orthotopic nude mouse model of human pancreatic cancer. We observed that Pim-3 promoted the proliferation of human pancreatic cancer cells, both in vitro and in vivo. Moreover, Pim-3 is required for vasculogenesis of primary human pancreatic tumors in vivo and promotion of angiogenesis through the induction of VEGF expression.

CONCLUSIONS

Pim-3 can promote tumor growth and angiogenesis by stimulating the VEGF pathway.

Small molecule inhibitors of PIM1 kinase: July 2009 to February 2013 patent update

INTRODUCTION

The proviral insertion in murine (PIM) lymphoma proteins for which three isoforms, PIM1, PIM2 and PIM3 have been identified, belonging to the family of serine/threonine kinases has emerged recently as an important therapeutic target for the development of selective inhibitors as the new drugs for treating hematological malignancies and solid tumors. The small molecules developed by academia and the pharmaceutical industry have steadily increased in the last few years. Several drug discovery groups focus on treating disorders, such as cancer mediated by PIM kinase, have provided preclinical evidence suggesting that PIM inhibitor provides anti-apoptotic activity, inhibit cell survival and cell proliferation.

AREAS COVERED

This article discloses recent reviews on research and advances published in the patent literature and scientific publications from July 2009 to February 2013, highlighting discoveries on PIM1 kinase.

EXPERT OPINION

Several PIM1 kinase small molecule inhibitors are now at the pre-clinical research stage, development and testing. Though nearly 40 patents emerged in the last 3 years, greater efforts towards additional designs and medicinal chemistry continues for developing clinically efficacious PIM1 inhibitors, due to the significance of the target for cancer and the potential for novel and diverse inhibitors as drug candidates.

The over-expression of Pim-2 promote the tumorigenesis of prostatic carcinoma through phosphorylating eIF4B

BACKGROUND

Cell experiments have found Pim-2 may take part in the tumorigenesis of prostatic carcinoma (PCA). More direct evidences are needed, and the detailed anti-apoptotic mechanism of Pim-2 in PCA cells is still unknown.

METHODS

Pim-2 expression levels were compared between benign prostatic hyperplasia (BPH) tissues and PCA tissues using real time PCR and Western blot, respectively. Then Pim-2 expression levels were detected in PCA cell lines DU-145 and LNCaP, as well as in nontumorous prostatic epithelial cell lines RWPE-1 and PNT1a, using real time PCR and Western blot, respectively. The co-expression of Pim-2 and eukaryotic initiation factor 4B (eIF4B) was examined by immunofluorescence cytochemistry using laser scanning confocal microscope. Finally, Pim-2 SiRNA was transfected into DU-145 cells and Pim-2 was transfected into RWPE-1 cells, and the level of Pim-2 and phosphorylated eukaryotic initiation factor 4B (p-eIF4B) were detected, as well as the apoptosis rate.

RESULTS

The Pim-2 mRNA and protein level were significantly higher in PCA tissues than those in BPH tissues. The Pim-2 mRNA and protein level in DU-145 and LNCaP cells were significantly higher than those in RWPE-1 and PNT1a cells. Pim-2 and eIF4B could co-express in DU-145 cells. Pim-2 level determined the phosphorylation level of eIF4B and the apoptosis rate of prostatic cells. The higher Pim-2 expressed, the more eIF4B phosphorylated, then the less cell got apoptosis, and vice versa.

CONCLUSION

Pim-2 was over-expressed in PCA cell lines and tissues. It may inhibit the apoptosis of PCA cells through phosphorylating eIF4B, thus promote the tumorigenesis of PCA.

Unveiling the association of STAT3 and HO-1 in prostate cancer: role beyond heme degradation

Activation of the androgen receptor (AR) is a key step in the development of prostate cancer (PCa). Several mechanisms have been identified in AR activation, among them signal transducer and activator of transcription 3 (STAT3) signaling. Disruption of STAT3 activity has been associated to cancer progression. Recent studies suggest that heme oxygenase 1 (HO-1) may play a key role in PCa that may be independent of its catalytic function. We sought to explore whether HO-1 operates on AR transcriptional activity through the STAT3 axis. Our results display that HO-1 induction in PCa cells represses AR activation by decreasing the prostate-specific antigen (PSA) promoter activity and mRNA levels. Strikingly, this is the first report to show by chromatin immunoprecipitation analysis that HO-1 associates to gene promoters, revealing a novel function for HO-1 in the nucleus. Furthermore, HO-1 and STAT3 directly interact as determined by co-immunoprecipitation studies. Forced expression of HO-1 increases STAT3 cytoplasmic retention. When PCa cells were transfected with a constitutively active STAT3 mutant, PSA and STAT3 downstream target genes were abrogated under hemin treatment. Additionally, a significant decrease in pSTAT3 protein levels was detected in the nuclear fraction of these cells. Confocal microscopy images exhibit a decreased rate of AR/STAT3 nuclear co-localization under hemin treatment. In vivo studies confirmed that STAT3 nuclear delimitation was significantly decreased in PC3 tumors overexpressing HO-1 grown as xenografts in nude mice. These results provide a novel function for HO-1 down-modulating AR transcriptional activity in PCa, interfering with STAT3 signaling, evidencing its role beyond heme degradation.

The PIM family of serine/threonine kinases in cancer

The proviral insertion site in Moloney murine leukemia virus, or PIM proteins, are a family of serine/threonine kinases composed of three different isoforms (PIM1, PIM2, and PIM3) that are highly evolutionarily conserved. These proteins are regulated primarily by transcription and stability through pathways that are controlled by Janus kinase/Signal transducer and activator of transcription, JAK/STAT, transcription factors. The PIM family proteins have been found to be overexpressed in hematological malignancies and solid tumors, and their roles in these tumors were confirmed in mouse tumor models. Furthermore, the PIM family proteins have been implicated in the regulation of apoptosis, metabolism, cell cycle, and homing and migration, which has led to the postulation of these proteins as interesting targets for anticancer drug discovery. In the present work, we review the importance of PIM kinases in tumor growth and as drug targets.

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.

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.

ZFP36 expression impairs glioblastoma cell lines viability and invasiveness by targeting multiple signal transduction pathways

RNA binding proteins belonging to the TIS11/TTP gene family regulate the stability of multiple targets. Their inactivation or deregulated expression has recently been related to cancer, and it has been suggested that they are capable of displaying tumor suppressor activities. Here we describe three new targets of ZFP36 (PIM-1, PIM-3 and XIAP) and show by different approaches that its ectopic expression is capable of impairing glioblastoma cell lines viability and invasiveness by interfering with different transduction pathways. Moreover, we provide evidence that compounds capable of inducing the expression of TIS11/TTP genes determine a comparable biological effect on the same cell contexts.

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.

Cell-based proteome profiling of potential dasatinib targets by use of affinity-based probes

Protein kinases (PKs) play an important role in the development and progression of cancer by regulating cell growth, survival, invasion, metastasis, and angiogenesis. Dasatinib (BMS-354825), a dual Src/Abl inhibitor, is a promising therapeutic agent with oral bioavailability. It has been used for the treatment of imatinib-resistant chronic myelogenous leukemia (CML). Most kinase inhibitors, including Dasatinib, inhibit multiple cellular targets and do not possess exquisite cellular specificity. Recent efforts in kinase research thus focus on the development of large-scale, proteome-wide chemical profiling methods capable of rapid identification of potential cellular (on- and off-) targets of kinase inhibitors. Most existing approaches, however, are still problematic and in many cases not compatible with live-cell studies. In this work, we have successfully developed a cell-permeable kinase probe (DA-2) capable of proteome-wide profiling of potential cellular targets of Dasatinib. In this way, highly regulated, compartmentalized kinase-drug interactions were maintained. By comparing results obtained from different proteomic setups (live cells, cell lysates, and immobilized affinity matrix), we found DA-2 was able to identify significantly more putative kinase targets. In addition to Abl and Src family tyrosine kinases, a number of previously unknown Dasatinib targets have been identified, including several serine/threonine kinases (PCTK3, STK25, eIF-2A, PIM-3, PKA C-α, and PKN2). They were further validated by pull-down/immunoblotting experiments as well as kinase inhibition assays. Further studies are needed to better understand the exact relevance of Dasatinib and its pharmacological effects in relation to these newly identified cellular targets. The approach developed herein should be amenable to the study of many of the existing reversible drugs/drug candidates.

Wnt inhibitor screen reveals iron dependence of β-catenin signaling in cancers

Excessive signaling from the Wnt pathway is associated with numerous human cancers. Using a high throughput screen designed to detect inhibitors of Wnt/β-catenin signaling, we identified a series of acyl hydrazones that act downstream of the β-catenin destruction complex to inhibit both Wnt-induced and cancer-associated constitutive Wnt signaling via destabilization of β-catenin. We found that these acyl hydrazones bind iron in vitro and in intact cells and that chelating activity is required to abrogate Wnt signaling and block the growth of colorectal cancer cell lines with constitutive Wnt signaling. In addition, we found that multiple iron chelators, desferrioxamine, deferasirox, and ciclopirox olamine similarly blocked Wnt signaling and cell growth. Moreover, in patients with AML administered ciclopirox olamine, we observed decreased expression of the Wnt target gene AXIN2 in leukemic cells. The novel class of acyl hydrazones would thus be prime candidates for further development as chemotherapeutic agents. Taken together, our results reveal a critical requirement for iron in Wnt signaling and they show that iron chelation serves as an effective mechanism to inhibit Wnt signaling in humans.

High-throughput kinase profiling: a more efficient approach toward the discovery of new kinase inhibitors

Selective protein kinase inhibitors have only been developed against a small number of kinase targets. Here we demonstrate that "high-throughput kinase profiling" is an efficient method for the discovery of lead compounds for established as well as unexplored kinase targets. We screened a library of 118 compounds constituting two distinct scaffolds (furan-thiazolidinediones and pyrimido-diazepines) against a panel of 353 kinases. A distinct kinase selectivity profile was observed for each scaffold. Selective inhibitors were identified with submicromolar cellular activity against PIM1, ERK5, ACK1, MPS1, PLK1-3, and Aurora A,B kinases. In addition, we identified potent inhibitors for so far unexplored kinases such as DRAK1, HIPK2, and DCAMKL1 that await further evaluation. This inhibitor-centric approach permits comprehensive assessment of a scaffold of interest and represents an efficient and general strategy for identifying new selective kinase inhibitors.