Genetic Modeling of PIM Proteins in Cancer: Proviral Tagging and Cooperation with Oncogenes, Tumor Suppressor Genes, and Carcinogens

Targeting Pim kinases in hematological cancers: molecular and clinical review

Decades of research has recognized a solid role for Pim kinases in lymphoproliferative disorders. Often up-regulated following JAK/STAT and tyrosine kinase receptor signaling, Pim kinases regulate cell proliferation, survival, metabolism, cellular trafficking and signaling. Targeting Pim kinases represents an interesting approach since knock-down of Pim kinases leads to non-fatal phenotypes in vivo suggesting clinical inhibition of Pim may have less side effects. In addition, the ATP binding site offers unique characteristics that can be used for the development of small inhibitors targeting one or all Pim isoforms. This review takes a closer look at Pim kinase expression and involvement in hematopoietic cancers. Current and past clinical trials and in vitro characterization of Pim kinase inhibitors are examined and future directions are discussed. Current studies suggest that Pim kinase inhibition may be most valuable when accompanied by multi-drug targeting therapy.

A serine/threonine protein PIM kinase as a biomarker of cancer and a target for anti-tumor therapy

The PIM Kinases belong to the family of a proto-oncogene that essentially phosphorylates the serine/threonine residues of the target proteins. They are primarily categorized into three types PIM-1, PIM-2, PIM-3 which plays an indispensable regulatory role in signal transduction cascades, by promoting cell survival, proliferation, and drug resistance. These kinases are overexpressed in several solid as well as hematopoietic tumors which supports in vitro and in vivo malignant cell growth along with survival by regulating cell cycle and inhibiting apoptosis. They lack regulatory domain which makes them constitutively active once transcribed. PIM kinases usually appear to be important downstream effectors of oncoproteins which overexpresses and helps in mediating drug resistance to available agents, such as rapamycin. Structural studies of PIM kinases revealed that they have unique hinge regions where two Proline resides and makes ATP binding unique, by offering a target for an increasing number of potent PIM kinase inhibitors. Preclinical studies of those inhibitory compounds in various cancers indicate that these novel agents show promising activity and some of them currently being under examination. In this review, we have outlined PIM kinases molecular mechanism and signaling pathways along with matriculation in various cancer and list of inhibitors often used.

Safety profiling of genetically engineered Pim-1 kinase overexpression for oncogenicity risk in human c-kit+ cardiac interstitial cells

Advancement of stem cell-based treatment will involve next-generation approaches to enhance therapeutic efficacy which is often modest, particularly in the context of myocardial regenerative therapy. Our group has previously demonstrated the beneficial effect of genetic modification of cardiac stem cells with Pim-1 kinase overexpression to rejuvenate aged cells as well as potentiate myocardial repair. Despite these encouraging findings, concerns were raised regarding potential for oncogenic risk associated with Pim-1 kinase overexpression. Testing of Pim-1 engineered c-kit+ cardiac interstitial cells (cCIC) derived from heart failure patient samples for indices of oncogenic risk was undertaken using multiple assessments including soft agar colony formation, micronucleation, gamma-Histone 2AX foci, and transcriptome profiling. Collectively, findings demonstrate comparable phenotypic and biological properties of cCIC following Pim-1 overexpression compared with using baseline control cells with no evidence for oncogenic phenotype. Using a highly selective and continuous sensor for quantitative assessment of PIM1 kinase activity revealed a sevenfold increase in Pim-1 engineered vs. control cells. Kinase activity profiling using a panel of sensors for other kinases demonstrates elevation of IKKs), AKT/SGK, CDK1-3, p38, and ERK1/2 in addition to Pim-1 consistent with heightened kinase activity correlating with Pim-1 overexpression that may contribute to Pim-1-mediated effects. Enhancement of cellular survival, proliferation, and other beneficial properties to augment stem cell-mediated repair without oncogenic risk is a feasible, logical, and safe approach to improve efficacy and overcome current limitations inherent to cellular adoptive transfer therapeutic interventions.

Discovery of novel triazolo[4,3-b]pyridazin-3-yl-quinoline derivatives as PIM inhibitors

PIM kinase family (PIM-1, PIM-2 and PIM-3) is an appealing target for the discovery and development of selective inhibitors, useful in various disease conditions in which these proteins are highly expressed, such as cancer. The significant effort put, in the recent years, towards the development of small molecules exhibiting inhibitory activity against this protein family has ended up with several molecules entering clinical trials. As part of our ongoing exploration for potential drug candidates that exhibit affinity towards this protein family, we have generated a novel chemical series of triazolo[4,3-b]pyridazine based tricycles by applying a scaffold hopping strategy over our previously reported potent pan-PIM inhibitor ETP-47453 (compound 2). The structure-activity relationship studies presented herein demonstrate a rather selective PIM-1/PIM-3 biochemical profile for this novel series of tricycles, although pan-PIM and PIM-1 inhibitors have also been identified. Selected examples show significant inhibition of the phosphorylation of BAD protein in a cell-based assay. Moreover, optimized and highly selective compounds, such as 42, did not show significant hERG inhibition at 20 μM concentration, and proved its antiproliferative activity and utility in combination with particular antitumoral agents in several tumor cell lines.

miR-486 inhibited osteosarcoma cells invasion and epithelial-mesenchymal transition by targeting PIM1

OBJECTIVE

Osteosarcoma is the most common malignant tumor of bone with high recurrent rate. miR-486 was downregulated and acted as a tumor suppressor in plenty of tumors. The purpose of this study was to explore how miR-486 worked in osteosarcoma on cell invasion and EMT.

RESULTS

miR-486 was low expressed in osteosarcoma while PIM1 was overexpressed, and it had negative correlation between miR-486 and PIM1. miR-486 upregulation or PIM1 downregulation could inhibit osteosarcoma cell invasion and EMT. Meanwhile, miR-486 mediated PIM1 expression through binding to PIM1 mRNA 3'-UTR. PIM1 could reveal partial function of miR-486 on osteosarcoma invasion. In addition, miR-486 low expression or PIM1 overexpression predicted poor prognosis of osteosarcoma patients.

CONCLUSION

miR-486 regulated osteosarcoma cell invasion and EMT through targeting to PIM1. miR-486 low expression or PIM1 overexpression predicted poor prognosis of osteosarcoma patients. The newly identified miR-486/PIM1 axis provides novel insight into the pathogenesis of osteosarcoma.

PARP1 activation increases expression of modified tumor suppressors and pathways underlying development of aggressive hepatoblastoma

Hepatoblastoma (HBL) is a pediatric liver cancer that affects children under the age of three. Reduction of tumor suppressor proteins (TSPs) is commonly seen in liver cancer. However, in our studies we find that aggressive, chemo-resistant HBLs exhibit an elevation of TSPs. HBL patients with a classic phenotype have reduced TSP levels, but patients with aggressive HBL express elevated TSPs that undergo posttranslational modifications, eliminating their tumor suppression activities. Here we identify unique aggressive liver cancer domains (ALCDs) that are activated in aggressive HBL by PARP1-mediated chromatin remodeling leading to elevation of modified TSPs and activation of additional cancer pathways: WNT signaling and β-catenin. Inhibition of PARP1 blocks activation of ALCDs and normalizes expression of corresponding genes, therefore reducing cell proliferation. Our studies reveal PARP1 activation as a mechanism for the development of aggressive HBL, further suggesting FDA-approved PARP1 inhibitors might be used for treatment of patients with aggressive HBL.

Leila Valanejad et al. report increased expression of modified tumor suppressor proteins (TSPs) with loss of tumor suppressor activity in aggressive, chemotherapy-resistant hepatoblastoma. They find that TSP upregulation occurs via PARP1-mediated chromatin remodeling, leading to activation of multiple cancer-associated pathways.

C/EBPα-dependent preneoplastic tumor foci are the origin of hepatocellular carcinoma and aggressive pediatric liver cancer

Recent publications show that classic hepatoblastoma (HBL) is the result of failure of hepatic stem cells to differentiate into hepatocytes, while hepatocellular carcinoma (HCC) is caused by the dedifferentiation of hepatocytes into cancer stem cells. However, the mechanisms of aggressive HBL and the mechanisms that cause dedifferentiation of hepatocytes into cancer stem cells are unknown. We found that, similar to HCC but opposite to classic HBL, aggressive HBL is the result of dedifferentiation of hepatocytes into cancer stem cells. In both cases of liver cancer, the dephosphorylation of tumor suppressor protein CCAAT/enhancer binding protein α (C/EBPα) at Ser193 (Ser190 in human protein) or mutation of Ser193 to Ala results in a modified protein with oncogenic activities. We have investigated liver cancer in a mouse model C/EBPα-S193A, in a large cohort of human HBL samples, and in Pten/p53 double knockout mice and found that these cancers are characterized by elevation of C/EBPα that is dephosphorylated at Ser190/193. We found that dephosphorylated C/EBPα creates preneoplastic foci with cancer stem cells that give rise to HCC and aggressive HBL. C/EBPα-dependent dedifferentiation of hepatocytes into cancer stem cells includes increased proliferation of hepatocytes, followed by generation of multinucleated hepatocytes and subsequent appearance of hepatocytes with delta-like 1 homolog-positive intranuclear inclusions. We further isolated C/EBPα-dependent multinucleated hepatocytes and found that they possess characteristics of tumor-initiating cells, including elevation of stem cell markers. C/EBPα-dependent cancer stem cells are observed in patients with aggressive HBL and in patients with a predisposition for liver cancer.

CONCLUSION

The earliest steps of adult HCC and aggressive pediatric liver cancer have identical features that include conversion of the tumor suppressor C/EBPα into an oncogenic isoform, which further creates preneoplastic foci where hepatocytes dedifferentiate into cancer cells, giving rise to liver cancer. (Hepatology 2018;67:1857-1871).

FXR-Gankyrin axis is involved in development of pediatric liver cancer

The development of hepatoblastoma (HBL) is associated with failure of hepatic stem cells (HSC) to differentiate into hepatocytes. Despite intensive investigations, mechanisms of the failure of HSC to differentiate are not known. We found that oncogene Gankyrin (Gank) is involved in the inhibition of differentiation of HSC via triggering degradation of tumor suppressor proteins (TSPs) Rb, p53, C/EBPα and HNF4α. Our data show that the activation of a repressor of Gank, farnesoid X receptor, FXR, after initiation of liver cancer by Diethylnitrosamine (DEN) prevents the development of liver cancer by inhibiting Gank and rescuing tumor suppressor proteins. We next analyzed FXR-Gank-Tumor suppressor pathways in a large cohort of HBL patients which include 6 controls and 53 HBL samples. Systemic analysis of these samples and RNA-Seq approach revealed that the FXR-Gank axis is activated; markers of hepatic stem cells are dramatically elevated and hepatocyte markers are reduced in HBL samples. In the course of these studies, we found that RNA binding protein CUGBP1 is a new tumor suppressor protein which is reduced in all HBL samples. Therefore, we generated CUGBP1 KO mice and examined HBL signatures in the liver of these mice. Micro-array studies revealed that the HBL-specific molecular signature is developed in livers of CUGBP1 KO mice at very early ages. Thus, we conclude that FXR-Gank-TSPs-Stem cells pathway is a key determinant of liver cancer in animal models and in pediatric liver cancer. Our data provide a strong basis for development of FXR-Gank-based therapy for treatment of patients with hepatoblastoma.

Chromosome 19q13 disruption alters expressions of CYP2A7, MIA and MIA-RAB4B lncRNA and contributes to FAP-like phenotype in APC mutation-negative familial colorectal cancer patients

Familial adenomatous polyposis (FAP) is an autosomal-dominantly inherited form of colorectal cancer (CRC) caused by mutation in the adenomatous polyposis coli (APC) gene. Our ability to exhaustively screen for APC mutations identify microsatellite-stable and APC-mutation negative familial CRC patients, enabling us to search for novel genes. We performed genome-wide scan on two affected siblings of one family and 88 ethnicity- and gender-matched healthy controls to identify deletions shared by the siblings. Combined loss of heterozygosity, copy number and allelic-specific copy number analysis uncovered 5 shared deletions. Long-range polymerase chain reaction (PCR) confirmed chromosome 19q13 deletion, which was subsequently found in one other family. The 32 kb deleted region harbors the CYP2A7 gene and was enriched with enhancer, repressor and insulator sites. The wildtype allele was lost in the polyps of the proband. Further, real-time RT-PCR assays showed that expressions of MIA and MIA-RAB4B located 35 kb upstream of the deletion, were up-regulated in the polyps compared to the matched mucosa of the proband. MIA-RAB4B, the read-through long non-coding RNA (lncRNA), RAB4B, PIM2 and TAOK1 share common binding site of a microRNA, miR-24, in their 3'UTRs. PIM2 and TAOK1, two target oncogenes of miR-24, were co-ordinately up-regulated with MIA-RAB4B in the polyps, suggesting that MIA-RAB4B could function as competitive endogenous RNA to titrate miR-24 away from its other targets. The data suggest that the 19.13 deletion disrupted chromatin boundary, leading to altered expression of several genes and lncRNA, could contribute to colorectal cancer via novel genetic and epigenetic mechanisms.

Thiazolidine derivatives as potent and selective inhibitors of the PIM kinase family

The PIM family of serine/threonine kinases have become an attractive target for anti-cancer drug development, particularly for certain hematological malignancies. Here, we describe the discovery of a series of inhibitors of the PIM kinase family using a high throughput screening strategy. Through a combination of molecular modeling and optimization studies, the intrinsic potencies and molecular properties of this series of compounds was significantly improved. An excellent pan-PIM isoform inhibition profile was observed across the series, while optimized examples show good selectivity over other kinases. Two PIM-expressing leukemic cancer cell lines, MV4-11 and K562, were employed to evaluate the in vitro anti-proliferative effects of selected inhibitors. Encouraging activities were observed for many examples, with the best example (44) giving an IC₅₀ of 0.75μM against the K562 cell line. These data provide a promising starting point for further development of this series as a new cancer therapy through PIM kinase inhibition.

Up-regulation of Pim-3 in Chronic Obstructive Pulmonary Disease (COPD) patients and its potential therapeutic role in COPD rat modeling

BACKGROUND

Pim-3 belongs to the PIM kinase family and plays an important role in promoting inflammation, which is essential in the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD).

METHODS

Immunohistochemistry (IHC), western blot, and RT-PCR analyses were performed to assess the expression of Pim-3 in both COPD and healthy lung tissue samples. SMA (Smooth Muscle Actin) and Cyclin D1 expression were detected by IHC. We also constructed animal models for the control, COPD, and Pim-3 inhibition groups, in order to analyze the effects of Pim-3 inhibition on COPD, and the role of Pim-3 in the p38 pathway.

RESULTS

Compared with normal lung tissue, Pim-3 mRNA and protein were up-regulated in COPD tissue. Expression of Cyclin D1 and SMA were also up-regulated in the COPD group. In the animal model experiment, we found that suppression of Pim-3 decreased Pim-3, Cyclin D1, and SMA expression, as well as ameliorated lung damage in COPD patients. The inhibition of Pim-3 also resulted in the suppression of the p38 pathway.

CONCLUSION

Our study suggests that up-regulation of Pim-3 successfully accelerated COPD development, and aggravated lung damage. The molecular mechanism of Pim-3 in COPD might be related to the p38 pathway, and is correlated with Cyclin D1 and SMA expression.

The Novel PIM1 Inhibitor NMS-P645 Reverses PIM1-Dependent Effects on TMPRSS2/ERG Positive Prostate Cancer Cells And Shows Anti-Proliferative Activity in Combination with PI3K Inhibition

PIM1 is over-expressed in multiple tumors, including prostate cancer (PCa). PIM1 upregulation is mediated by direct binding of the ERG transcription factor to its promoter. About 50% of PCa cases are characterized by the presence of the TMPRSS2/ERG fusion, leading to ERG over-expression and thus to PIM1 transcriptional activation. PIM kinases are considered as weak oncogenes, but when combined with additional genetic alterations can induce strong transforming effects. Here we show anti-proliferative activity of the newly described PIM1 inhibitor NMS-P645 in combination with the PI3K inhibitor GDC-0941 in TMPRSS2/ERG positive and negative PCa cells. Treatment with NMS-P645 alone can reverse PIM1-mediated pro-survival signals in prostate cells, such as activation of STAT3 through Tyr705 phosphorylation and resistance to taxane-based treatments, but does not exert a strong anti-tumoral effect. However, the simultaneous treatment with NMS-P645 and GDC-0941 induces a significant anti-proliferative response in PCa cells. These results support the use of combination strategies with PIM and PI3K inhibitors as effective treatment for PCa cases.

hGBP-1 Expression Predicts Shorter Progression-Free Survival in Ovarian Cancers, While Contributing to Paclitaxel Resistance

Ovarian cancer is the gynecological cancer with the poorest prognosis. One significant reason is the development of resistance to the chemotherapeutic drugs used in its treatment. The large GTPase, hGBP-1, has been implicated in paclitaxel resistance in ovarian cell lines. Forced expression of hGBP-1 in SKOV3 ovarian cancer cells protects them from paclitaxel-induced cell death. However, prior to this study, nothing was known about whether hGBP-1 was expressed in ovarian tumors and whether its expression correlated with paclitaxel resistance. hGBP-1 is expressed in 17% of ovarian tumors from patients that have not yet received treatment. However, at least 80% of the ovarian tumors that recurred after therapies that included a tax-ane, either paclitaxel or docetaxel, were positive for hGBP-1. In addition, hGBP-1 expression predicts a significantly shorter progression-free survival in ovarian cancers. Based on these studies, hGBP-1 could prove to be a potential biomarker for paclitaxel resistance in ovarian cancer.

The role of PIM1/PIM2 kinases in tumors of the male reproductive system

The PIM family of serine/threonine kinases has three highly conserved isoforms (PIM1, PIM2 and PIM3). PIM proteins are regulated through transcription and stability by JAK/STAT pathways and are overexpressed in hematological malignancies and solid tumors. The PIM kinases possess weak oncogenic abilities, but enhance other genes or chemical carcinogens to induce tumors. We generated conditional transgenic mice that overexpress PIM1 or PIM2 in male reproductive organs and analyzed their contribution to tumorigenesis. We found an increase in alterations of sexual organs and hyperplasia in the transgenic mice correlating with inflammation. We also found that PIM1/2 are overexpressed in a subset of human male germ cells and prostate tumors correlating with inflammatory features and stem cell markers. Our data suggest that PIM1/2 kinase overexpression is a common feature of male reproductive organs tumors, which provoke tissue alterations and a large inflammatory response that may act synergistically during the process of tumorigenesis. There is also a correlation with markers of cancer stem cells, which may contribute to the therapy resistance found in tumors overexpressing PIM kinases.

Pim-3 is a Critical Risk Factor in Development and Prognosis of Prostate Cancer

BACKGROUND Pim-3 kinase is a highly homologous serine/threonine kinase that is overexpressed in hematological malignancies and solid tumors. Few studies have been conducted to define the role of Pim-3 in solid tumors, especially in prostate cancer. The aim of this study was to define the role of Pim-3 in development and prognosis of prostate cancer. MATERIAL AND METHODS We collected specimens from 160 patients with prostate cancer, as well as 100 patients with benign prostatic hyperplasia. Realtime polymerase chain reaction was used for the assessment of Pim-3 expression at the RNA level and Western blot was used to quantify the Pim-3 protein synthesis in 3 different cell lines. RESULTS We found that Pim-3 mRNA expression in prostate cancer tissue was significantly higher than that in benign prostatic hyperplasia tissue (p<0.05). Accordingly, the protein level expression of Pim-3 in prostate cancer cell lines was also significantly higher than that in control cells. In addition, the expression status of Pim-3 mRNA was significantly associated with pathological parameters such as pre-surgery prostate specific antigen, Gleason score, pathological stage, and lymphoid metastasis. High expression of Pim-3 also significantly decreased the survival rate of patients after surgery. CONCLUSIONS Pim-3 expression is an important risk factor for prostate cancer; we are the first team to report Pim-3 as a valuable biomarker in Chinese.

Expression and function of PIM kinases in osteosarcoma

The provirus integrating site Moloney murine leukemia virus (PIM) family of serine/threonine protein kinases is composed of three members, PIM1, PIM2 and PIM3, which have been identified as oncoproteins in various malignancies. However, their role in osteosarcoma (OS) remains largely unknown. This study aimed to examine the expression patterns and the clinical significance of PIM kinases in human OS and their biological effects in human OS cell lines. Immunohistochemical staining was used to detect PIM kinases in archived pathologic material from 43 patients with primary OS; in addition, the effects of PIM knockdown and overexpression on the proliferation, migration and invasion of OS cell lines were determined. We observed that all three PIM kinases were frequently expressed in OS, but only PIM1 positive expression was associated with poorer prognosis regarding overall survival of OS patients. In addition, knockdown of PIM kinases notably inhibited OS cell proliferation, migration and invasiveness, whereas overexpression of PIM kinases resulted in increased OS cell growth and motility. This study suggests that PIM1 could be a valuable prognostic marker in patients with OS, and the biological functions of PIM kinase family in the osteosarcoma cell lines indicate that they could serve as potential therapeutic targets for OS.

The novel combination of dual mTOR inhibitor AZD2014 and pan-PIM inhibitor AZD1208 inhibits growth in acute myeloid leukemia via HSF pathway suppression

Mammalian target of rapamycin (mTOR) signaling is a critical pathway in the biology of acute myeloid leukemia (AML). Proviral integration site for moloney murine leukemia virus (PIM) serine/threonine kinase signaling takes part in various pathways exerting tumorigenic properties. We hypothesized that the combination of a PIM kinase inhibitor with an mTOR inhibitor might have complementary growth-inhibitory effects against AML. The simultaneous inhibition of the PIM kinase by pan-PIM inhibitor AZD1208 and of mTOR by selective mTORC1/2 dual inhibitor AZD2014 exerted anticancer properties in AML cell lines and in cells derived from primary AML samples with or without supportive stromal cell co-culture, leading to suppressed proliferation and increased apoptosis. The combination of AZD1208 and AZD2014 rapidly activated AMPKα, a negative regulator of translation machinery through mTORC1/2 signaling in AML cells; profoundly inhibited AKT and 4EBP1 activation; and suppressed polysome formation. Inhibition of both mTOR and PIM counteracted induction of heat-shock family proteins, uncovering the master negative regulation of heat shock factor 1 (HSF1), the dominant transcription factor controlling cellular stress responses. The novel combination of the dual mTOR inhibitor and pan-PIM inhibitor synergistically inhibited AML growth by effectively reducing protein synthesis through heat shock factor pathway suppression.

Guanylate-Binding Protein-1 protects ovarian cancer cell lines but not breast cancer cell lines from killing by paclitaxel

Forced expression of the cytokine-induced large GTPase, human Guanylate-Binding Protein-1 (hGBP-1), in ovarian cancer cell lines increases resistance to paclitaxel. Elevated hGBP-1 RNA in ovarian tumors correlates with shorter recurrence-free survival. In contract, hGBP-1 is part of a gene signature predicting improved prognosis in all subtypes of breast cancers. hGBP-1 does not confer paclitaxel resistance on MCF-7 and TMX2-28 breast cancer cells. Expression of the isotype of the hGBP-1-interacting protein, PIM1, which may contribute to paclitaxel resistance when associated with hGBP-1, is different in breast and ovarian cancer cell lines. Breast cancer cell lines express the 44 kDa isoform of PIM-1, and ovarian cancer cell lines express the 33 kDa isoform.

Protein profiling identifies mTOR pathway modulation and cytostatic effects of Pim kinase inhibitor, AZD1208, in acute myeloid leukemia

Pim kinases phosphorylate and regulate a number of key acute myeloid leukemia (AML) cell survival proteins, and Pim inhibitors have recently entered clinical trial for hematological malignancies. AZD1208 is a small molecule pan-Pim kinase inhibitor and AZD1208 treatment resulted in growth inhibition and cell size reduction in AML cell lines including FLT3-WT (OCI-AML-3, KG-1a, and MOLM-16) and FLT3-ITD mutated (MOLM-13 and MV-4-11). There was limited apoptosis induction (<10% increase) in the AML cell lines evaluated with up to 3 μM AZD1208 for 24 h, suggesting that growth inhibition is not through apoptosis induction. Using reverse phase protein array (RPPA) and immunoblot analysis, we identified that AZD1208 resulted in suppression of mTOR signaling, including inhibition of protein phosphorylation of mTOR (Ser2448), p70S6K (Thr389), S6 (Ser235/236), and 4E-BP1 (Ser65). Consistent with mTOR inhibition, there was also a reduction in protein synthesis that correlated with cell size reduction and growth inhibition with AZD1208; our study provides insights into the mechanism of AZD1208.

The PIM family of oncoproteins: small kinases with huge implications in myeloid leukemogenesis and as therapeutic targets

PIM kinases are a family of serine/threonine kinases involved in cell survival and proliferation. There is significant structural similarity between the three PIM kinases (PIM1, PIM2 and PIM3) and few amino acid differences. Although, several studies have specifically monitored the role of PIM1 in tumorigenesis, much less is known about PIM2 and PIM3. Therefore, in this study we have used in vitro cell culture models and in vivo bone marrow infection/transplantation to assess the comparative signaling and oncogenic potential of each of the three PIM kinases. All three PIM kinases were able to protect FL5.12 cells from IL-3 withdrawal induced death. Interestingly, the downstream signaling cascades were indistinguishable between the three kinases. Transplantation of murine bone marrow co-expressing MYC and PIM1, PIM2 or PIM3 caused rapid and uniformly lethal myeloid leukemia. De-induction of MYC 18 days following transplantation significantly increased the survival of mice, even with continual expression of PIM kinases. Alternatively, mice treated at the pre-leukemic stage with a PIM kinase inhibitor increased the lifespan of the mice, even with continual expression of the MYC transgene. These data demonstrate the role of PIM kinases in driving myeloid leukemia, and as candidate molecules for therapy against human malignancies.