PIM1 kinase as a promise of targeted therapy in prostate cancer stem cells

FDA-approved drugs as PIM-1 kinase inhibitors: A drug repurposed approach for cancer therapy

PIM-1 kinase, a member of the Serine/Threonine kinase family, has emerged as a promising therapeutic target in various cancers due to its role in promoting tumor growth and resistance to conventional therapies. In this study, we employed a structure-based approach to screen 3800 FDA-approved drugs to discover potential inhibitors of PIM-1. After an initial selection of 50 candidates based on high docking scores, four drugs, stanozolol, alfaxalone, rifaximin, and telmisartan, were identified as strong PIM-1 binders, interacting with key residues in the ATP-binding pocket of the kinase. To assess the stability of these interactions, we conducted all-atom molecular dynamic simulations, confirming favorable dynamics. Experimental validation via a kinase inhibition assay on recombinant PIM-1 showed that rifaximin significantly inhibited PIM-1 activity, with an IC50 of ∼26 μM. Fluorescence binding assays further demonstrated a strong binding affinity for rifaximin, with a binding constant, corroborated by isothermal titration calorimetry studies. Our findings suggest that rifaximin may serve as a potential repurposed drug for targeting PIM-1 in cancer treatment. However, further validations are required in a clinical setting before the final therapeutic implications.

Assessment of structural and activity-related contributions of various PIM-1 kinase inhibitors in the treatment of leukemia and prostate cancer

One of the most perilous illnesses in the world is cancer. The cancer may be associated with the mutation of different genes inside the body. The PIM kinase, also known as the serine/threonine kinase, plays a critical role in the biology of different kinds of cancer. They are widely distributed and associated with several biological processes, including cell division, proliferation, and death. Aberration of PIM-1 kinase is found in varieties of cancer. Prostate cancer and leukemia can both be effectively treated with PIM-1 kinase inhibitors. There are several potent compounds that have been explored in this review based on heterocyclic compounds for the treatment of prostate cancer and leukemia that have strong effects on the suppression of PIM-1 kinase. The present review summarizes the PIM-1 kinase pathway, their inhibitors under clinical trial, related patents, and SAR studies of several monocyclic, bicyclic, and polycyclic compounds. The study related to their molecular interactions with receptors is also included in the present manuscript. The study may be beneficial to scientists for the development of novel compounds as PIM-1 inhibitors in the treatment of prostate cancer and leukemia.

The Myc Family and the Metastasis Suppressor NDRG1: Targeting Key Molecular Interactions with Innovative Therapeutics

Cancer is a leading cause of death worldwide, resulting in ∼10 million deaths in 2020. Major oncogenic effectors are the Myc proto-oncogene family, which consists of three members including c-Myc, N-Myc, and L-Myc. As a pertinent example of the role of the Myc family in tumorigenesis, amplification of MYCN in childhood neuroblastoma strongly correlates with poor patient prognosis. Complexes between Myc oncoproteins and their partners such as hypoxia-inducible factor-1α and Myc-associated protein X (MAX) result in proliferation arrest and pro-proliferative effects, respectively. Interactions with other proteins are also important for N-Myc activity. For instance, the enhancer of zest homolog 2 (EZH2) binds directly to N-Myc to stabilize it by acting as a competitor against the ubiquitin ligase, SCFFBXW7, which prevents proteasomal degradation. Heat shock protein 90 may also be involved in N-Myc stabilization since it binds to EZH2 and prevents its degradation. N-Myc downstream-regulated gene 1 (NDRG1) is downregulated by N-Myc and participates in the regulation of cellular proliferation via associating with other proteins, such as glycogen synthase kinase-3β and low-density lipoprotein receptor-related protein 6. These molecular interactions provide a better understanding of the biologic roles of N-Myc and NDRG1, which can be potentially used as therapeutic targets. In addition to directly targeting these proteins, disrupting their key interactions may also be a promising strategy for anti-cancer drug development. This review examines the interactions between the Myc proteins and other molecules, with a special focus on the relationship between N-Myc and NDRG1 and possible therapeutic interventions. SIGNIFICANCE STATEMENT: Neuroblastoma is one of the most common childhood solid tumors, with a dismal five-year survival rate. This problem makes it imperative to discover new and more effective therapeutics. The molecular interactions between major oncogenic drivers of the Myc family and other key proteins; for example, the metastasis suppressor, NDRG1, may potentially be used as targets for anti-neuroblastoma drug development. In addition to directly targeting these proteins, disrupting their key molecular interactions may also be promising for drug discovery.

Development of novel cyanopyridines as PIM-1 kinase inhibitors with potent anti-prostate cancer activity: Synthesis, biological evaluation, nanoparticles formulation and molecular dynamics simulation

Recently, inhibition of PIM-1 enzyme is found as an effective route in the fight against proliferation of cancer. Herein, new cyano pyridines that target PIM-1 kinase were designed, synthesized, and biologically evaluated. Two prostate cell lines were used to examine each of the new compounds in vitro for anticancer activity, namely, PC-3 and DU-145. The cyanopyridine derivatives 2b, 3b, 4b, and 5b with an N,N-dimethyl phenyl group at the pyridine ring's 4-position showed considerable antitumor effect on the tested cell lines. Additionally, the high selectivity index revealed that these compounds were less cytotoxic to normal WI-38 cells. Furthermore, they exhibited strong inhibitory effect on PIM-1 having IC₅₀ = 0.248, 0.13, 0.326 and 0.245 μM, respectively. The most powerful derivatives2b, 3b, 4b, and 5b, were chosen for further examination of their inhibitory potential on both kinases (PIM-2 and PIM-3). Interestingly, upon loading compound 3b in a cubosomes formulation with nanometric size, improvements in cytotoxicity and inhibitory effect on PIM-1 kinase were observed. In silico ADME parameters study revealed that compound 3b is orally bioavailable without penetration to the blood-brain barrier. Further, the docking simulations revealed the ability of our potent compounds to well accommodate the PIM-1 kinase active site forming stable complexes. In a 150 ns MD simulation, the most powerful PIM-1 inhibitor 3b produced stable complex with the PIM-1 enzyme (RMSD = 1.76). Furthermore, the 3b-PIM-1 complex has the low binding free energy (-242.2 kJ/mol) according to the MM-PBSA calculations.

The Role of PIM Kinases in Pediatric Solid Tumors

PIM kinases have been identified as potential therapeutic targets in several malignancies. Here, we provide an in-depth review of PIM kinases, including their structure, expression, activity, regulation, and role in pediatric carcinogenesis. Also included is a brief summary of the currently available pharmaceutical agents targeting PIM kinases and existing clinical trials.

PIM1 Inhibition Affects Glioblastoma Stem Cell Behavior and Kills Glioblastoma Stem-like Cells

Despite comprehensive therapy and extensive research, glioblastoma (GBM) still represents the most aggressive brain tumor in adults. Glioma stem cells (GSCs) are thought to play a major role in tumor progression and resistance of GBM cells to radiochemotherapy. The PIM1 kinase has become a focus in cancer research. We have previously demonstrated that PIM1 is involved in survival of GBM cells and in GBM growth in a mouse model. However, little is known about the importance of PIM1 in cancer stem cells. Here, we report on the role of PIM1 in GBM stem cell behavior and killing. PIM1 inhibition negatively regulates the protein expression of the stem cell markers CD133 and Nestin in GBM cells (LN-18, U-87 MG). In contrast, CD44 and the astrocytic differentiation marker GFAP were up-regulated. Furthermore, PIM1 expression was increased in neurospheres as a model of GBM stem-like cells. Treatment of neurospheres with PIM1 inhibitors (TCS PIM1-1, Quercetagetin, and LY294002) diminished the cell viability associated with reduced DNA synthesis rate, increased caspase 3 activity, decreased PCNA protein expression, and reduced neurosphere formation. Our results indicate that PIM1 affects the glioblastoma stem cell behavior, and its inhibition kills glioblastoma stem-like cells, pointing to PIM1 targeting as a potential anti-glioblastoma therapy.

Therapeutic targeting of PIM KINASE signaling in cancer therapy: Structural and clinical prospects

BACKGROUND

PIM kinases are well-studied drug targets for cancer, belonging to Serine/Threonine kinases family. They are the downstream target of various signaling pathways, and their up/down-regulation affects various physiological processes. PIM family comprises three isoforms, namely, PIM-1, PIM-2, and PIM-3, on alternative initiation of translation and they have different levels of expression in different types of cancers. Its structure shows a unique ATP-binding site in the hinge region which makes it unique among other kinases.

SCOPE OF REVIEW

PIM kinases are widely reported in hematological malignancies along with prostate and breast cancers. Currently, many drugs are used as inhibitors of PIM kinases. In this review, we highlighted the physiological significance of PIM kinases in the context of disease progression and therapeutic targeting. We comprehensively reviewed the PIM kinases in terms of their expression and regulation of different physiological roles. We further predicted functional partners of PIM kinases to elucidate their role in the cellular physiology of different cancer and mapped their interaction network.

MAJOR CONCLUSIONS

A deeper mechanistic insight into the PIM signaling involved in regulating different cellular processes, including transcription, apoptosis, cell cycle regulation, cell proliferation, cell migration and senescence, is provided. Furthermore, structural features of PIM have been dissected to understand the mechanism of inhibition and subsequent implication of designed inhibitors towards therapeutic management of prostate, breast and other cancers.

GENERAL SIGNIFICANCE

Being a potential drug target for cancer therapy, available drugs and PIM inhibitors at different stages of clinical trials are discussed in detail.

Breast Cancer Resistance Protein: A Potential Therapeutic Target for Cancer

Breast Cancer Resistance Protein (BCRP) is an efflux transporter responsible for causing multidrug resistance (MDR). It is known to expel many potent antineoplastic drugs, owing to its efflux function. Efflux of chemotherapeutics because of BCRP develops resistance to many drugs, leading to failure in cancer treatment. BCRP plays an important role in physiology by protecting the organism from xenobiotics and other toxins. It is a half-transporter affiliated to the ATP- binding cassette (ABC) superfamily of transporters, encoded by the gene ABCG2 and functions in response to adenosine triphosphate (ATP). Regulation of BCRP expression is critically controlled at molecular levels, which help in maintaining the balance of xenobiotics and nutrients inside the body. Expression of BCRP can be found in brain, liver, lung cancers and acute myeloid leukemia (AML). Moreover, it is also expressed at high levels in stem cells and many cell lines. This frequent expression of BCRP has an impact on the treatment procedures and, if not scrutinized, may lead to the failure of many cancer therapies.

New cyanopyridine-based scaffold as PIM-1 inhibitors and apoptotic inducers: Synthesis and SARs study

Two novel series of 6-(4-benzamido-/4-phthalimido)-3-cyanopyridine derivatives were designed and synthesized as inhibitors of PIM-1 kinase. Based on cytotoxicity results via MTT assay against prostate carcinoma PC3, human hepatocellular carcinoma HepG2 and breast adenocarcinoma MCF-7 cell lines, the most potent cytotoxic cyanopyridine hits, 6, 7, 8, 12 and 13 were 1.5-3.3 times more inhibitor of cell proliferation than the reference standard, 5-FU. Selectivity profile of the latter compounds on normal human cells (WI-38), was executed, indicating that they are highly selective (IC₅₀ > 145 μM) in their cytotoxic effect. The promising compounds were further evaluated as PIM-1 kinase inhibitors. These compounds elicited remarkable inhibition of PIM-1 kinase (76.43-53.33%). Extensive studies on apoptosis were conducted for these compounds; they enhanced caspase-3 and boosted the Bax/Bcl-2 ratio 27-folds in comparison to the control. Molecular docking study of the most potent compound, 13 in PIM-1 kinase active site was consistent with the in vitro activity. Finally, prediction of chemo-informatic properties released compound 13 as the most promising ligand.

Structure-Based Optimization of 10-DEBC Derivatives as Potent and Selective Pim-1 Kinase Inhibitors

Pim-1 kinase has been widely regarded as an attractive target for anticancer drugs. Here, we reported our continued efforts in structure-based optimization of compound 10-DEBC, a previously identified micromolar Pim-1 inhibitor. Guided by the Site Identification by Ligand Competitive Saturation (SILCS) method, we quickly obtained a series of 10-DEBC derivatives with significantly improved activity and selectivity. In particular, compound 26 exhibited an IC₅₀ value of 0.9 nM, as well as 220- and 8-fold selectivity over Pim-2 and Pim-3 kinases, respectively.

PIM protein kinases regulate the level of the long noncoding RNA H19 to control stem cell gene transcription and modulate tumor growth

The proviral integration site for Moloney murine leukemia virus (PIM) serine/threonine kinases have an oncogenic and prosurvival role in hematological and solid cancers. However, the mechanism by which these kinases drive tumor growth has not been completely elucidated. To determine the genes controlled by these protein kinases, we carried out a microarray analysis in T-cell acute lymphoblastic leukemia (T-ALL) comparing early progenitor (ETP-ALL) cell lines whose growth is driven by PIM kinases to more mature T-ALL cells that have low PIM levels. This analysis demonstrated that the long noncoding RNA (lncRNA) H19 was associated with increased PIM levels in ETP-ALL. Overexpression or knockdown of PIM in these T-ALL cell lines controlled the level of H19 and regulated the methylation of the H19 promoter, suggesting a mechanism by which PIM controls H19 transcription. In these T-ALL cells, the expression of PIM1 induced stem cell gene expression (SOX2, OCT-4, and NANOG) through H19. Identical results were found in prostate cancer (PCa) cell lines where PIM kinases drive cancer growth, and both H19 and stem cell gene levels. Small molecule pan-PIM inhibitors (PIM-i) currently in clinical trials reduced H19 expression in both of these tumor types. Importantly, the knockdown of H19 blocked the ability of PIM to induce stem cell genes in T-ALL cells, suggesting a novel signal transduction cascade. In PCa, increases in SOX2 levels have been shown to cause both resistance to the androgen deprivation therapy (ADT) and the induction of neuroendocrine PCa, a highly metastatic form of this disease. Treatment of PCa cells with a small molecule pan-PIM-i reduced stem cell gene transcription and enhanced ADT, while overexpression of H19 suppressed the ability of pan-PIM-i to regulate hormone blockade. Together, these results demonstrate that the PIM kinases control the level of lncRNA H19, which in turn modifies stem cell gene transcription regulating tumor growth.

miR24-2 accelerates progression of liver cancer cells by activating Pim1 through tri-methylation of Histone H3 on the ninth lysine

Several microRNAs are associated with carcinogenesis and tumour progression. Herein, our observations suggest both miR24‐2 and Pim1 are up‐regulated in human liver cancers, and miR24‐2 accelerates growth of liver cancer cells in vitro and in vivo. Mechanistically, miR24‐2 increases the expression of N6‐adenosine‐methyltransferase METTL3 and thereafter promotes the expression of miR6079 via RNA methylation modification. Furthermore, miR6079 targets JMJD2A and then increased the tri‐methylation of histone H3 on the ninth lysine (H3K9me3). Therefore, miR24‐2 inhibits JMJD2A by increasing miR6079 and then increases H3K9me3. Strikingly, miR24‐2 increases the expression of Pim1 dependent on H3K9me3 and METTL3. Notably, our findings suggest that miR24‐2 alters several related genes (pHistone H3, SUZ12, SUV39H1, Nanog, MEKK4, pTyr) and accelerates progression of liver cancer cells through Pim1 activation. In particular, Pim1 is required for the oncogenic action of miR24‐2 in liver cancer. This study elucidates a novel mechanism for miR24‐2 in liver cancer and suggests that miR24‐2 may be used as novel therapeutic targets of liver cancer.

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.

Structure-based design of novel quinoxaline-2-carboxylic acids and analogues as Pim-1 inhibitors

We identified a new series of quinoxaline-2-carboxylic acid derivatives, targeting the human proviral integration site for Moloney murine leukemia virus-1 (HsPim-1) kinase. Seventeen analogues were synthesized providing useful insight into structure-activity relationships studied. Docking studies realized in the ATP pocket of HsPim-1 are consistent with an unclassical binding mode of these inhibitors. The lead compound 1 was able to block HsPim-1 enzymatic activity at nanomolar concentrations (IC₅₀ of 74 nM), with a good selectivity profile against a panel of mammalian protein kinases. In vitro studies on the human chronic myeloid leukemia cell line KU812 showed an antitumor activity at micromolar concentrations. As a result, compound 1 represents a promising lead for the design of novel anticancer targeted therapies.

Synthesis of new pyridothienopyrimidinone and pyridothienotriazolopyrimidine derivatives as pim-1 inhibitors

Three series of 2-arylpyridothieno[3,2-d]pyrimidin-4-ones 3a–j, pyridothienotriazolopyrimidines 6–8 and 4-imino-pyridothieno[3,2-d]pyrimidines 9a,b were prepared to improve the pim-1 inhibitory activity of the previously reported 2-arylpyridothieno[3,2-d]pyrimidin-4-ones. All the test compounds showed highly potent pim-1 inhibition with IC₅₀ in the range of 0.06–1.76 µM. No significant difference was detected between the pim-1 inhibitory activity of the 4-pyrimidinone and the 4-imino (=NH) or the cyclised triazolopyrimidine derivatives. The most active compounds were tested for their cytotoxic activity on MCF7 and HCT116 and showed potent activity on both the cell lines.

Thyroid hormone inhibits growth of hepatoma cells through induction of miR-214

Thyroid hormone (TH) plays a role in regulating the metabolic rate, heart functions, muscle control and maintenance of bones. 3,3′5-tri-iodo-L-thyronine (T₃) displays high affinity to nuclear thyroid hormone receptors (TRs), which mediate most TH actions. Recent studies have shown hypothyroidism in patients with an increased risk of hepatocellular carcinoma (HCC). MicroRNAs (miRNAs), a class of non-protein-coding RNA, are suggested to control tumor growth by interacting with target genes. However, the clinical significance of T₃/TR-regulated miRNAs in tumors has yet to be established. In the current study, miRNA expression profile screening was performed using SYBR Green-Based qRT-PCR array in TR-overexpressing HepG2 cells. miR-214-3p, which is expressed at low levels in HCC, was stimulated upon T₃ application. The 3′UTR luciferase reporter assay confirmed that the proto-oncogene serine/threonine-protein kinase, PIM-1, is a miR-214-3p target. PIM-1 was decreased upon treatment with miR-214-3p or T₃ stimulation. PIM-1 was highly expressed in HCC, and the effect of PIM-1 on cell proliferation might be mediated by the inhibition of p21. Furthermore, the T₃-induced suppression of cell proliferation was partially rescued upon miR-214-3p knockdown. Our data demonstrate that T₃ induces miR-214-3p expression and suppresses cell proliferation through PIM-1, thus contributing to the inhibition of HCC tumor formation.

PIM-1 kinase inhibitor SMI-4a exerts antitumor effects in chronic myeloid leukemia cells by enhancing the activity of glycogen synthase kinase 3β

The development of targeted tyrosine kinase inhibitors (TKIs) has succeeded in altering the course of chronic myeloid leukemia (CML). However, a number of patients have failed to respond or experienced disease relapse following TKI treatment. Proviral integration site for moloney murine leukemia virus-1 (PIM-1) is a serine/threonine kinase that participates in regulating apoptosis, cell cycle, signal transduction and transcriptional pathways, which are associated with tumor progression, and poor prognosis. SMI-4a is a selective PIM-1 kinase inhibitor that inhibits PIM-1 kinase activity in vivo and in vitro. The present study aimed to explore the mechanism underlying the antitumor effect of SMI-4a in K562 and imatinib-resistant K562 (K562/G) cell lines. It was demonstrated that SMI-4a inhibited the proliferation of K562 and K562/G cells using a WST-8 assay. The Annexin V-propidium iodide assay demonstrated that SMI-4a induced apoptosis of K562 and K562/G cells in a dose-, and time-dependent manner. Furthermore, Hoechst 33342 staining was used to verify the apoptosis rate. The clone formation assay revealed that SMI-4a significantly inhibited the colony formation capacity of K562 and K562/G cells. Western blot analysis demonstrated that SMI-4a decreased phosphorylated (p)-Ser9-glycogen synthase kinase (GSK) 3β/pGSK3β and inhibited the translocation of β-catenin. In addition, the downstream gene expression of apoptosis regulator Bax and poly(ADP-ribose) polymerase-1 was upregulated, and apoptosis regulator Bcl-2 and Myc proto-oncogene protein expression levels were downregulated. Immunofluorescence results demonstrated changes in the expression level of β-catenin in the plasma and nucleus. The results of the present study suggest that SMI-4a is an effective drug to use in combination with current chemotherapeutics for the treatment of imatinib-resistant CML.

Inflammation and stem markers association to PIM1/PIM2 kinase-induced tumors in breast and uterus

The PIM family of Ser/Thr kinase proteins has been implicated in tumorigenesis at different levels. PIM proteins are overexpressed in several tumor types and have been associated with chemoresistance. However, their role in hormone-dependent female tissues has not been explored, especially in the uterus, breast and ovary. We generated conditional transgenic mice with confined expression of human PIM1 or PIM2 genes in these tissues. We characterized the tumoral response to these genetic alterations corroborating their role as oncogenes since they induce hyperproliferation in all tissues and tumors in mammary gland and uterus. Furthermore, we observed a high degree of inflammatory infiltration in these tissues of transgenic mice accompanied by NFAT and mTOR activation and IL6 expression. Moreover, PIM1/2 were overexpressed in human breast, uterine and ovarian tumors, correlating with inflammatory features and stem cell markers. Our data suggest that PIM1/2 kinase overexpression provoke tissue alterations and a large IL6-dependent inflammatory response that may act synergistically during the process of tumorigenesis. The possible end-point is an increased percentage of cancer stem cells, which may be partly responsible for the therapy resistance found in tumors overexpressing PIM kinases.

Synthesis of new pyridothienopyrimidinone derivatives as Pim-1 inhibitors

Four series of pyridothienopyrimidin-4-one derivatives were designed and prepared to improve the pim-1 inhibitory activity of the previously reported thieno[2,3-b]pyridines. Significant improvement in the pim-1 inhibition and cytotoxic activity was achieved using structure rigidification strategy via ring closure. Six compounds (6c, 7a, 7c, 7d, 8b and 9) showed highly potent pim-1 inhibitory activity with IC₅₀ of 4.62, 1.18, 1.38, 1.97, 8.83 and 4.18 μM, respectively. Four other compounds (6b, 6d, 7b and 8a) showed moderate pim-1 inhibition. The most active compounds were tested for their cytotoxic activity on three cell lines [MCF7, HCT116 and PC3]. Compounds 7a [the 2-(2-chlorophenyl)-2,3-dihydro derivative] and 7d [the 2-(2-(trifluoromethyl)-phenyl)-2,3-dihydro derivative] displayed the most potent cytotoxic effect on the three cell lines tested consistent with their highest estimated pim-1 IC₅₀ values.

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-1 kinase as cancer drug target: An update

Proviral integration site for Moloney murine leukemia virus-1 (Pim-1) is a serine/threonine kinase that regulates multiple cellular functions such as cell cycle, cell survival, drug resistance. Aberrant elevation of Pim-1 kinase is associated with numerous types of cancer. Two distinct isoforms of Pim-1 (Pim-1S and Pim-1L) show distinct cellular functions. Pim-1S predominately localizes to the nucleus and Pim-1L localizes to plasma membrane for drug resistance. Recent studies show that mitochondrial Pim-1 maintains mitochondrial integrity. Pim-1 is emerging as a cancer drug target, particularly in prostate cancer. Recently the potent new functions of Pim-1 in immunotherapy, senescence bypass, metastasis and epigenetic dynamics have been found. The aim of the present updated review is to provide brief information regarding networks of Pim-1 kinase and focus on its recent advances as a novel drug target.