Collaboration of pim-1 and bcl-2 in lymphomagenesis

Mutational Profile and Clonal Evolution of Relapsed/Refractory Diffuse Large B-Cell Lymphoma

Primary refractory/relapsed diffuse large B-cell lymphoma (rrDLBCL) is an unresolved issue for DLBCL treatment and new treatments to overcome resistance is required. To explore the genetic mechanisms underlying treatment resistance in rrDLBCL and to identify candidate genes, we performed targeted deep sequencing of 430 lymphoma-related genes from 58 patients diagnosed with rrDLBCL. Genetic alterations found between the initial biopsy and biopsy at recurrence or refractory disease were investigated. The genes most frequently altered (> 20%) were (in decreasing order of frequency) CDKN2A, PIM1, CD79B, TP53, MYD88, MYC, BTG2, BTG1, CDKN2B, DTX1, CD58, ETV6, and IRF4. Genes mutation of which in pretreatment sample were associated with poor overall survival included NOTCH1, FGFR2, BCL7A, BCL10, SPEN and TP53 (P < 0.05). FGFR2, BCL2, BCL6, BCL10, and TP53 were associated with poor progression-free survival (P < 0.05). Most mutations were truncal and were maintained in both the initial biopsy and post-treatment biopsy with high dynamics of subclones. Immune-evasion genes showed increased overall mutation frequency (CD58, B2M) and variant allele fraction (CD58), and decreased copy number (B2M, CD70) at the post-treatment biopsy. Using the established mutational profiles and integrative analysis of mutational evolution, we identified information about candidate genes that may be useful for the development of future treatment strategies.

Targeted therapies in pancreatic cancer: Promises and failures

Pancreatic ductal adenocarcinoma (PDAC) is an incidence rate nearly equal to its mortality rate. The poor prognosis of the disease can be explained by the absence of effective biomarkers for screening and early detection, together with the aggressive behavior and resistance to the currently available chemotherapy. The therapeutic failure can also be attributed to the inter-/intratumor genetic heterogeneity and the abundance of tumor stroma that occupies the majority of the tumor mass. Gemcitabine is used in the treatment of PDAC; however, the response rate is less than 12%. A recent phase III trial revealed that the combination of oxaliplatin, irinotecan, fluorouracil, and leucovorin could be an option for the treatment of metastatic PDAC patients with good performance status, although these approaches can result in high toxicity level. Further investigations are required to develop innovative anticancer agents that either improve gemcitabine activity, within novel combinatorial approaches or acts with a better efficacy than gemcitabine. The aim of the current review is to give an overview of preclinical and clinical studies targeting key dysregulated signaling pathways in PDAC.

PIM1 induces cellular senescence through phosphorylation of UHRF1 at Ser311

PIM1 is a proto-oncogene, encoding a serine/threonine protein kinase that regulates cell proliferation, survival, differentiation and apoptosis. Previous reports suggest that overexpression of PIM1 can induce cellular senescence. However, the molecular mechanism underlying this process is not fully understood. Here we report that UHRF1 is a novel substrate of PIM1 kinase, which could be phosphorylated at Ser311 and therefore promoted to degradation. Our data demonstrates that PIM1 destabilizes UHRF1, leading to DNA hypomethylation, which consequently results in genomic instability, increased p16 expression and subsequent induction of cellular senescence. Taken together, our results suggest that down-regulation of UHRF1 is an important mechanism of PIM1-mediated cellular senescence.

Combination of Pim kinase inhibitors and Bcl-2 antagonists in chronic lymphocytic leukemia cells

The Pim proteins are Ser/Thr kinases over-expressed in several hematological malignancies such as chronic lymphocytic leukemia (CLL) and some solid cancers like prostate cancer. Several small molecules have been developed to inhibit these kinases. In prostate cancer cell lines, the Pim kinase inhibitor SMI-4a and the Bcl-2 antagonist ABT-737 resulted in synergistic cytotoxicity. Akin to prostate cancer cells, CLL lymphocytes over-express Pim and Bcl-2 proteins. It was hypothesized that similar cytotoxic interaction should be observed in CLL. This study evaluated the in vitro cytotoxic effect of three Pim kinase inhibitors (AZD1208, SGI-1776 and SMI-4a) combined with Bcl-2 antagonists (ABT-737 or ABT-199) in malignant CLL lymphocytes. Data indicated Pim kinase inhibitors in combination with ABT-737 or ABT-199 resulted mostly in additive cytotoxicity with a few synergistic responses; however, the extent of synergism was less robust than that observed previously in prostate cancer cell lines treated with SMI-4a and ABT-737.

Pim-selective inhibitor DHPCC-9 reveals Pim kinases as potent stimulators of cancer cell migration and invasion

BACKGROUND

Pim family kinases are small constitutively active serine/threonine-specific kinases, elevated levels of which have been detected in human hematopoietic malignancies as well as in solid tumours. While we and others have previously shown that the oncogenic Pim kinases stimulate survival of hematopoietic cells, we now examined their putative role in regulating motility of adherent cancer cells. For this purpose, we inhibited Pim kinase activity using a small molecule compound, 1,10-dihydropyrrolo[2,3-a]carbazole-3-carbaldehyde (DHPCC-9), which we had recently identified as a potent and selective inhibitor for all Pim family members.

RESULTS

We now demonstrate that the Pim kinase inhibitor DHPCC-9 is very effective also in cell-based assays. DHPCC-9 impairs the anti-apoptotic effects of Pim-1 in cytokine-deprived myeloid cells and inhibits intracellular phosphorylation of Pim substrates such as Bad. Moreover, DHPCC-9 slows down migration and invasion of cancer cells derived from either prostate cancer or squamocellular carcinoma patients. Silencing of Pim expression reduces cell motility, while Pim overexpression enhances it, strongly suggesting that the observed effects of DHPCC-9 are dependent on Pim kinase activity. Interestingly, DHPCC-9 also abrogates NFATc-dependent migration of cancer cells, implying that NFATc factors mediate at least part of the pro-migratory effects of Pim kinases.

CONCLUSIONS

Altogether, our data indicate that DHPCC-9 is not only a powerful tool to investigate physiological effects of the oncogenic Pim family kinases, but also an attractive molecule for drug development to inhibit invasiveness of Pim-overexpressing cancer cells.

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

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

A small molecule inhibitor of Pim protein kinases blocks the growth of precursor T-cell lymphoblastic leukemia/lymphoma

The serine/threonine Pim kinases are up-regulated in specific hematologic neoplasms, and play an important role in key signal transduction pathways, including those regulated by MYC, MYCN, FLT3-ITD, BCR-ABL, HOXA9, and EWS fusions. We demonstrate that SMI-4a, a novel benzylidene-thiazolidine-2, 4-dione small molecule inhibitor of the Pim kinases, kills a wide range of both myeloid and lymphoid cell lines with precursor T-cell lymphoblastic leukemia/lymphoma (pre-T-LBL/T-ALL) being highly sensitive. Incubation of pre-T-LBL cells with SMI-4a induced G1 phase cell-cycle arrest secondary to a dose-dependent induction of p27(Kip1), apoptosis through the mitochondrial pathway, and inhibition of the mammalian target of rapamycin C1 (mTORC1) pathway based on decreases in phospho-p70 S6K and phospho-4E-BP1, 2 substrates of this enzyme. In addition, treatment of these cells with SMI-4a was found to induce phosphorylation of extracellular signal-related kinase1/2 (ERK1/2), and the combination of SMI-4a and a mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor was highly synergistic in killing pre-T-LBL cells. In immunodeficient mice carrying subcutaneous pre-T-LBL tumors, treatment twice daily with SMI-4a caused a significant delay in the tumor growth without any change in the weight, blood counts, or chemistries. Our data suggest that inhibition of the Pim protein kinases may be developed as a therapeutic strategy for the treatment of pre-T-LBL.

Pim-1 kinase expression predicts radiation response in squamocellular carcinoma of head and neck and is under the control of epidermal growth factor receptor

Pim-1 is an oncogenic serine/threonine kinase with poorly defined function in epithelial cancers. In this study, we determined 1) associations of Pim-1 expression with clinicopathological parameters including responsiveness to irradiation in squamocellular cancers of head and neck and 2) how Pim-1 expression is controlled subsequent to irradiation. Moderate to high expression of Pim-1 correlated to poor response to radiation therapy (P = .003). It is also associated to the expression of epidermal growth factor receptor (EGFR, P < .0001), which has been shown to be activated by irradiation. In radioresistant tumors, irradiation promoted nuclear translocation of Pim-1 (P < .005). When directly testing EGFR dependence of Pim-1 expression, up-regulation and nuclear translocation of Pim-1 could be induced through stimulation of EGFR with its ligands EGF or transforming growth factor alpha. Both ligand- and irradiation-induced changes in Pim-1 expression and localization could be inhibited by the monoclonal anti-EGFR antibody cetuximab and by the tyrosine kinase inhibitor gefitinib also targeting EGFR. These results suggest that irradiation-induced activation of EGFR upregulates Pim-1, and Pim-1 may be used as a novel predictive marker of radiation response in patients with squamocellular cancers of head and neck.

Bcl2 family proteins in carcinogenesis and the treatment of cancer

Deregulation of Bcl2 family members is a frequent feature of human malignant diseases and causal for therapy resistance. A number of studies have recently shed light onto the role of pro- and anti-apoptotic Bcl2 family members in tumour-pathogenesis and in mediating the effects of classical as well as novel front-line anticancer agents, allowing the development of more efficient and more precisely targeted treatment regimens. Most excitingly, recent progress in our understanding of how Bcl2-like proteins maintain or perturb mitochondrial integrity has finally enabled the development of rational-design based anticancer therapies that directly target Bcl2 regulated events at the level of mitochondria. This review aims to give an overview on the most recent findings on the role of the Bcl2 family in tumour development in model systems of cancer, to relate these findings with observations made in human pathologies and drug-action.

Pim-1 kinase phosphorylates RUNX family transcription factors and enhances their activity

Background

The pim family genes encode oncogenic serine/threonine kinases which in hematopoietic cells have been implicated in cytokine-dependent signaling as well as in lymphomagenesis, especially in cooperation with other oncogenes such as myc, bcl-2 or Runx family genes. The Runx genes encode α-subunits of heterodimeric transcription factors which regulate cell proliferation and differentiation in various tissues during development and which can become leukemogenic upon aberrant expression.

Results

Here we have identified novel protein-protein interactions between the Pim-1 kinase and the RUNX family transcription factors. Using the yeast two-hybrid system, we were able to show that the C-terminal part of human RUNX3 associates with Pim-1. This result was confirmed in cell culture, where full-length murine Runx1 and Runx3 both coprecipitated and colocalized with Pim-1. Furthermore, catalytically active Pim-1 kinase was able to phosphorylate Runx1 and Runx3 proteins and enhance the transactivation activity of Runx1 in a dose-dependent fashion.

Conclusion

Altogether, our results suggest that mammalian RUNX family transcription factors are novel binding partners and substrates for the Pim-1 kinase, which may be able to regulate their activities during normal hematopoiesis as well as in leukemogenesis.

Cryptic promoter activity in the DNA sequence corresponding to the pim-1 5'-UTR

The serine/threonine kinase pim-1 mRNA contains a long and G/C rich 5'-untranslated region (5'-UTR). Previous work suggested that the pim-1 5'-UTR harbors an internal ribosomal entry site (IRES) allowing for internal initiation of translation. However, several previously reported eukaryotic IRES elements actually contain cryptic promoter activity. To test whether an IRES or a cryptic promoter is present in the pim-1 5'-UTR, the 5'-UTR was re-examined using stringent test procedures. Our results show the presence of strong promoter activity in the DNA sequence corresponding to the pim-1 5'-UTR. Both promoterless dicistronic test and northern blot analysis show transcripts being derived from the cryptic promoter in the pim-1 5'-UTR sequence. This cryptic promoter is active in all cell types tested, including Cos-7, NIH3T3, HEK293, Jurkat and K562 cells. When a dicistronic mRNA containing the pim-1 5'-UTR was translated in vitro or in vivo, no IRES activity could be detected. However, the control IRESs from both human rhinovirus and encephalomyocarditis virus exhibited strong IRES activities. In addition, both the RNase protection assay and the 5'-RACE assay detected endogenous pim-1 transcripts with shorter 5'-UTRs. Our data strongly suggest that the IRES activity reported earlier for the pim-1 5'-UTR sequence is due to cryptic promoter activity.

FLT3 Inhibitors

The area of molecularly-targeted cancer therapeutics is generating tremendous interest and excitement. While clinical investigation of these agents has been largely limited to adults, clinical trials for paediatric cancer patients with many of these agents are now underway. This paper reviews the current status of molecularly-targeted therapies for paediatric malignancies, with special attention given to one class of agents, inhibitors of the FLT3 receptor tyrosine kinase. FLT3 is expressed and activated in many human leukemias, including a significant percentage of pediatric AML and infant and childhood ALL, especially in the setting of MLL gene rearrangement. Activating mutations of FLT3 portend a poor prognosis in pediatric AML. Activated FLT3 can be effectively and selectively targeted by small molecule inhibitors, and these agents have shown promise in early phase clinical trials in adults with AML. Limited preclinical data with FLT3 inhibitors in MLL-rearranged ALL have also been reported. Challenges and future directions for the use of FLT3 inhibitors and other targeted agents in paediatric cancer are discussed.

Pim-1 kinase inhibits STAT5-dependent transcription via its interactions with SOCS1 and SOCS3

Signal transducer and activator of transcription 5 (STAT5) plays a critical role in cytokine-induced survival of hematopoietic cells. One of the STAT5 target genes is pim-1, which encodes an oncogenic serine/threonine kinase. Here we demonstrate that Pim-1 inhibits STAT5-dependent transcription in cells responsive to interleukin-3, prolactin, or erythropoietin. Ectopic expression of Pim-1 in cytokine-dependent FDCP1 myeloid cells results in reduced tyrosine phosphorylation and DNA binding of STAT5, indicating that Pim-1 interferes already with the initial steps of STAT5 activation. However, the Pim-1 kinase does not directly phosphorylate or bind to STAT5. By contrast, Pim-1 interacts with suppressor of cytokine signaling 1 (SOCS1) and SOCS3 and potentiates their inhibitory effects on STAT5, most likely via phosphorylation-mediated stabilization of the SOCS proteins. Thus, both Pim and SOCS family proteins may be components of a negative feedback mechanism that allows STAT5 to attenuate its own activity.

Developmental expression of pim kinases suggests functions also outside of the hematopoietic system

We have cloned a novel quail cDNA with strong homology to the pim family of proto-oncogenes. The deduced amino acid (aa) sequence of the cDNA, named qpim, is more closely related to Xenopus Pim and to the recently identified rat Pim-3 than to human or rodent Pim-1 or Pim-2. The protein encoded by the qpim cDNA can autophosphorylate itself and share substrates with murine Pim-1, suggesting functional redundancy to other Pim family serine/threonine kinases. We have compared the expression of qpim in avian embryos to mouse pim-1, -2 and -3 by in situ hybridization. qpim shows a highly dynamic expression pattern, particularly at early developmental stages. Surprisingly, its expression pattern is not identical to any of the murine pim genes, which show complementary and/or partially overlapping expression sites both in- and outside of the hematopoietic system. Altogether, our results suggest novel functions for Pim family kinases during embryonic development, in particular in epithelia and in the central nervous system.

The PIM-1 serine kinase prolongs survival and inhibits apoptosis-related mitochondrial dysfunction in part through a bcl-2-dependent pathway

We have examined potential mechanisms by which the Pim-1 kinase acts as a hematopoietic cell survival factor. Enforced expression of the wild type 33 kd (FD/hpim33) and 44 kd (FD/mpim44) Pim-1 proteins in murine factor-dependent FDCP1 cells prolonged survival after withdrawal of IL-3, while expression of a dominant negative Pim-1 protein (FD/pimNT81) shortened survival. Following removal of IL-3 FDCP1 cells exhibited loss of mitochondrial transmembrane potential and production of reactive oxygen species, as determined by flow cytometry analysis. The wild type Pim-1 proteins decreased these changes while the dominant negative protein enhanced mitochondrial dysfunction. The antiapoptotic activity of the kinases could not be attributed to modulation of glutathione, catalase, or superoxide dismutase activities. Both the FD/hpim33 and FD/mpim44 cells maintained expression of bcl-2 mRNA following cytokine removal, while a substantial decrease was seen in FD/neo cells. To modulate Bcl-2 protein levels, a bcl-2 antisense RNA construct was coexpressed with the wild type pim-1 cDNAs. FD/hpim33 cells with low cellular Bcl-2 protein levels had shortened cytokine-independent survival compared with FD/hpim33 clones with high Bcl-2 expression. However survival of FD/mpim44 cells after IL-3 withdrawal was substantially independent of cellular Bcl-2 protein levels. The 33 kd protein delayed, and the 44 kd protein completely prevented enhanced cell death associated with enforced expression of human Bax protein however. Our results suggest that the 33 kd Pim-1 kinase may enhance cell survival through cooperation with and regulation of bcl-2. In addition the 44 kd kinase may regulate the expression or activity of other pro- and anti-apoptotic members of the bcl-2 family.

Dr. Josef Steiner Cancer Research Prize Lecture: the role of physiological cell death in neoplastic transformation and in anti-cancer therapy

Cell death is a physiological process which is required for normal development and existence of multi-cellular organisms. Physiological cell death, or apoptosis, is controlled by an evolutionarily conserved mechanism. Abnormalities in this process are implicated as a cause or contributing factor in a variety of diseases. Inhibition of apoptosis can promote neoplastic transformation, particularly in combination with dysregulated cell-cycle control, and can influence the response of tumour cells to anti-cancer therapy. Molecular biological and biochemical approaches are used to find missing cell-death regulators and to define signalling cascades, while experiments in genetically modified mice will identify the essential function of these molecules. Discoveries from cell death research should provide clues for designing therapies for a variety of diseases, including degenerative disorders, auto-immunity and cancer.