In vitro activity of cyclin-dependent kinase inhibitor CYC202 (Seliciclib, R-roscovitine) in mantle cell lymphomas

Design and Synthesis of a Novel 4-aryl-N-(2-alkoxythieno [2,3-b]pyrazine-3-yl)-4-arylpiperazine-1-carboxamide DGG200064 Showed Therapeutic Effect on Colon Cancer through G2/M Arrest

Cancer cells are characterized by an abnormal cell cycle. Therefore, the cell cycle has been a potential target for cancer therapeutic agents. We developed a new lead compound, DGG200064 (7c) with a 2-alkoxythieno [2,3-b]pyrazine-3-yl)-4-arylpiperazine-1-carboxamide core skeleton. To evaluate its properties, compound DGG200064 was tested in vivo through a xenograft mouse model of colorectal cancer using HCT116 cells. The in vivo results showed high cell growth inhibition efficacy. Our results confirmed that the newly synthesized DGG200064 inhibits the growth of colorectal cancer cells by inducing G2/M arrest. Unlike the known cell cycle inhibitors, DGG200064 (GI₅₀ = 12 nM in an HCT116 cell-based assay) induced G2/M arrest by selectively inhibiting the interaction of FBXW7 and c-Jun proteins. Additionally, the physicochemical properties of the lead compounds were analyzed. Based on the results of the study, we suggested further development of DGG200064 as a novel oral anti-colorectal cancer drug.

CDK9 Inhibitors in Cancer Research

Cyclin dependent kinase 9 (CDK9) played an essential role in regulating transcriptional elongation. Aberrations in CDK9 activity have been observed in various cancers, which made CDK9 was an attractive therapeutic...

Targeting DNA Repair, Cell Cycle, and Tumor Microenvironment in B Cell Lymphoma

The DNA double-strand break (DSB) is the most cytotoxic lesion and compromises genome stability. In an attempt to efficiently repair DSBs, cells activate ATM kinase, which orchestrates the DNA damage response (DDR) by activating cell cycle checkpoints and initiating DSB repair pathways. In physiological B cell development, however, programmed DSBs are generated as intermediates for effective immune responses and the maintenance of genomic integrity. Disturbances of these pathways are at the heart of B cell lymphomagenesis. Here, we review the role of DNA repair and cell cycle control on B cell development and lymphomagenesis. In addition, we highlight the intricate relationship between the DDR and the tumor microenvironment (TME). Lastly, we provide a clinical perspective by highlighting treatment possibilities of defective DDR signaling and the TME in mantle cell lymphoma, which serves as a blueprint for B cell lymphomas.

Roscovitine enhances All-trans retinoic acid (ATRA)-induced leukemia cell differentiation: Novel effects on signaling molecules for a putative Cdk2 inhibitor

All-trans retinoic acid (ATRA)-based differentiation therapy has been unsuccessful in treating t(15;17) negative acute myeloid leukemia (AML) patients, motivating interest in combination therapies using ATRA plus other agents. Using the t (15, 17) negative HL-60 human myeloblastic leukemia model, we find that the cyclin-dependent kinase (CDK) inhibitor, roscovitine, augments signaling by an ATRA-induced macromolecular signalsome that propels differentiation and enhances ATRA-induced differentiation. Roscovitine co-treatment enhanced ATRA-induced expression of pS259- pS289/296/301- pS621-c-Raf, pS217/221-Mek, Src Family Kinases (SFKs) Lyn and Fgr and SFK Y416 phosphorylation, adaptor proteins c-Cbl and SLP-76, Vav, and acetylated 14-3-3 in the signalsome. Roscovitine enhanced ATRA-induced c-Raf interaction with Lyn, Vav, and c-Cbl. Consistent with signalsome hyper-activation, roscovitine co-treatment enhanced ATRA-induced G1/0 arrest and expression of differentiation markers, CD11b, ROS and p47 Phox. Because roscovitine regulated Lyn expression, activation and partnering, a stably transfected Lyn knockdown was generated from wt-parental cells to investigate its function in ATRA-induced differentiation. Lyn-knockdown enhanced ATRA-induced up-regulation of key signalsome molecules, c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, Vav1, SLP-76, and Fgr, but with essentially total loss of pY416-SFK. Compared to ATRA-treated wt-parental cells, differentiation markers p47 phox, CD11b, G1/G0 arrest and ROS production were enhanced in ATRA-treated Lyn-knockdown stable transfectants, and addition of roscovitine further enhanced these ATRA-inducible markers. The Lyn-knockdown cells expressed slightly higher c-Raf, pS259-c-Raf, pS289/296/301-c-Raf, and SLP-76 than wt-parental cells, and this was associated with enhanced ATRA-induced upregulation of Fgr and cell differentiation, consistent with heightened signaling, suggesting that enhanced Fgr may have compensated for loss of Lyn to enhance differentiation in the Lyn-knockdown cells.

Mantle cell lymphoma in the era of precision medicine-diagnosis, biomarkers and therapeutic agents

Despite advances in the development of clinical agents for treating Mantle Cell Lymphoma (MCL), treatment of MCL remains a challenge due to complexity and frequent relapse associated with MCL. The incorporation of conventional and novel diagnostic approaches such as genomic sequencing have helped improve understanding of the pathogenesis of MCL, and have led to development of specific agents targeting signaling pathways that have recently been shown to be involved in MCL. In this review, we first provide a general overview of MCL and then discuss about the role of biomarkers in the pathogenesis, diagnosis, prognosis, and treatment for MCL. We attempt to discuss major biomarkers for MCL and highlight published and ongoing clinical trials in an effort to evaluate the dominant signaling pathways as drugable targets for treating MCL so as to determine the potential combination of drugs for both untreated and relapse/refractory cases. Our analysis indicates that incorporation of biomarkers is crucial for patient stratification and improve diagnosis and predictability of disease outcome thus help us in designing future precision therapies. The evidence indicates that a combination of conventional chemotherapeutic agents and novel drugs designed to target specific dysregulated signaling pathways can provide the effective therapeutic options for both untreated and relapse/refractory MCL.

A review on the effects of current chemotherapy drugs and natural agents in treating non-small cell lung cancer

Lung cancer is the leading cause of cancer deaths worldwide, and this makes it an attractive disease to review and possibly improve therapeutic treatment options. Surgery, radiation, chemotherapy, targeted treatments, and immunotherapy separate or in combination are commonly used to treat lung cancer. However, these treatment types may cause different side effects, and chemotherapy-based regimens appear to have reached a therapeutic plateau. Hence, effective, better-tolerated treatments are needed to address and hopefully overcome this conundrum. Recent advances have enabled biologists to better investigate the potential use of natural compounds for the treatment or control of various cancerous diseases. For the past 30 years, natural compounds have been the pillar of chemotherapy. However, only a few compounds have been tested in cancerous patients and only partial evidence is available regarding their clinical effectiveness. Herein, we review the research on using current chemotherapy drugs and natural compounds (Wortmannin and Roscovitine, Cordyceps militaris, Resveratrol, OSU03013, Myricetin, Berberine, Antroquinonol) and the beneficial effects they have on various types of cancers including non-small cell lung cancer. Based on this literature review, we propose the use of these compounds along with chemotherapy drugs in patients with advanced and/or refractory solid tumours.

Molecular Pathways: Leveraging the BCL-2 Interactome to Kill Cancer Cells--Mitochondrial Outer Membrane Permeabilization and Beyond

The inhibition of apoptosis enables the survival and proliferation of tumors and contributes to resistance to conventional chemotherapy agents and is therefore a very promising avenue for the development of new agents that will enhance current cancer therapies. The BCL-2 family proteins orchestrate apoptosis at the mitochondria and endoplasmic reticulum and are involved in other processes such as autophagy and unfolded protein response (UPR) that lead to different types of cell death. Over the past decade, significant efforts have been made to restore apoptosis using small molecules that modulate the activity of BCL-2 family proteins. The small molecule ABT-199, which antagonizes the activity of BCL-2, is currently the furthest in clinical trials and shows promising activity in many lymphoid malignancies as a single agent and in combination with conventional chemotherapy agents. Here, we discuss strategies to improve the specificity of pharmacologically modulating various antiapoptotic BCL-2 family proteins, review additional BCL-2 family protein interactions that can be exploited for the improvement of conventional anticancer therapies, and highlight important points of consideration for assessing the activity of small-molecule BCL-2 family protein modulators.

The BET Bromodomain Inhibitor OTX015 Affects Pathogenetic Pathways in Preclinical B-cell Tumor Models and Synergizes with Targeted Drugs

PURPOSE

In cancer cells, the epigenome is often deregulated, and inhibition of the bromodomain and extra-terminal (BET) family of bromodomain-containing proteins is a novel epigenetic therapeutic approach. Preliminary results of an ongoing phase I trial have reported promising activity and tolerability with the new BET bromodomain inhibitor OTX015.

EXPERIMENTAL DESIGN

We assessed the preclinical activity of OTX015 as single agent and in combination in mature B-cell lymphoma models and performed in vitro and in vivo experiments to identify the mechanism of action and the genetic features associated with sensitivity to the compound.

RESULTS

OTX015 showed antiproliferative activity in a large panel of cell lines derived from mature B-cell lymphoid tumors with median IC50 of 240 nmol/L, without significant differences among the different histotypes. In vitro and in vivo experiments showed that OTX015 targeted NFKB/TLR/JAK/STAT signaling pathways, MYC- and E2F1-regulated genes, cell-cycle regulation, and chromatin structure. OTX015 presented in vitro synergism with several anticancer agents, especially with mTOR and BTK inhibitors. Gene expression signatures associated with different degrees of sensitivity to OTX015 were identified. Although OTX015 was mostly cytostatic, the compound induced apoptosis in a genetically defined subgroup of cells, derived from activated B-cell-like diffuse large B-cell lymphoma, bearing wtTP53, mutations in MYD88, and CD79B or CARD11.

CONCLUSIONS

Together with the data coming from the ongoing phase I study, the in vitro and in vivo data presented here provide the basis for further clinical investigation of OTX015 as single agent and in combination therapies.

Discovery and development of Seliciclib. How systems biology approaches can lead to better drug performance

Seliciclib (R-Roscovitine) was identified as an inhibitor of CDKs and has undergone drug development and clinical testing as an anticancer agent. In this review, the authors describe the discovery of Seliciclib and give a brief summary of the biology of the CDKs Seliciclib inhibits. An overview of the published in vitro and in vivo work supporting the development as an anti-cancer agent, from in vitro experiments to animal model studies ending with a summary of the clinical trial results and trials underway is presented. In addition some potential non-oncology applications are explored and the potential mode of action of Seliciclib in these areas is described. Finally the authors argue that optimisation of the therapeutic effects of kinase inhibitors such as Seliciclib could be enhanced using a systems biology approach involving mathematical modelling of the molecular pathways regulating cell growth and division.

DNA methylation profiling identifies two splenic marginal zone lymphoma subgroups with different clinical and genetic features

Splenic marginal zone lymphoma is a rare lymphoma. Loss of 7q31 and somatic mutations affecting the NOTCH2 and KLF2 genes are the commonest genomic aberrations. Epigenetic changes can be pharmacologically reverted; therefore, identification of groups of patients with specific epigenomic alterations might have therapeutic relevance. Here we integrated genome-wide DNA-promoter methylation profiling with gene expression profiling, and clinical and biological variables. An unsupervised clustering analysis of a test series of 98 samples identified 2 clusters with different degrees of promoter methylation. The cluster comprising samples with higher-promoter methylation (High-M) had a poorer overall survival compared with the lower (Low-M) cluster. The prognostic relevance of the High-M phenotype was confirmed in an independent validation set of 36 patients. In the whole series, the High-M phenotype was associated with IGHV1-02 usage, mutations of NOTCH2 gene, 7q31-32 loss, and histologic transformation. In the High-M set, a number of tumor-suppressor genes were methylated and repressed. PRC2 subunit genes and several prosurvival lymphoma genes were unmethylated and overexpressed. A model based on the methylation of 3 genes (CACNB2, HTRA1, KLF4) identified a poorer-outcome patient subset. Exposure of splenic marginal zone lymphoma cell lines to a demethylating agent caused partial reversion of the High-M phenotype and inhibition of proliferation.

Targeting RNA transcription and translation in ovarian cancer cells with pharmacological inhibitor CDKI-73

Dysregulation of cellular transcription and translation is a fundamental hallmark of cancer. As CDK9 and Mnks play pivotal roles in the regulation of RNA transcription and protein synthesis, respectively, they are important targets for drug development. We herein report the cellular mechanism of a novel CDK9 inhibitor CDKI-73 in an ovarian cancer cell line (A2780). We also used shRNA-mediated CDK9 knockdown to investigate the importance of CDK9 in the maintenance of A2780 cells. This study revealed that CDKI-73 rapidly inhibited cellular CDK9 kinase activity and down-regulated the RNAPII phosphorylation. This subsequently caused a decrease in the eIF4E phosphorylation by blocking Mnk1 kinase activity. Consistently, CDK9 shRNA was also found to down-regulate the Mnk1 expression. Both CDKI-73 and CDK9 shRNA decreased anti-apoptotic proteins Mcl-1 and Bcl-2 and induced apoptosis. The study confirmed that CDK9 is required for cell survival and that ovarian cancer may be susceptible to CDK9 inhibition strategy. The data also implied a role of CDK9 in eIF4E-mediated translational control, suggesting that CDK9 may have important implication in the Mnk-eIF4E axis, the key determinants of PI3K/Akt/mTOR- and Ras/Raf/MAPK-mediated tumorigenic activity. As such, CDK9 inhibitor drug candidate CDKI-73 should have a major impact on these pathways in human cancers.

Cyclin-dependent kinase modulators and cancer therapy

The cell cycle of eukaryotic cells varies greatly from species to species and tissue to tissue. Since an erroneous control of the cell cycle can have disastrous consequences for cellular life, there are genetically programmed signals, so-called cell cycle checkpoints, which ensure that all events of each stage are completed before beginning the next phase. Among the numerous molecules involved in this process, the most important are the cyclin-dependent kinases (CDKs), proteins that are activated only when bound to cyclins (regulatory proteins with fluctuating concentrations). In general, more CDKs are overexpressed in cancer cells than in normal cells, which explains why cancer cells divide uncontrollably. Succeeding in modulating CDK activity with pharmacological agents could result in decreasing the abnormal proliferation rate of cancer cells. This review offers an overview of CDK-cyclin complexes in relation to different cell cycle phases, an analysis of CDK activation and inhibition of molecular mechanisms, and an extensive report, including clinical trials, regarding four new drugs acting as CDK modulators: alvocidib, P276-00, SNS-032 and seliciclib.

Cyclin-dependent kinase modulators and cancer therapy

The cell cycle of eukaryotic cells varies greatly from species to species and tissue to tissue. Since an erroneous control of the cell cycle can have disastrous consequences for cellular life, there are genetically programmed signals, so-called cell cycle checkpoints, which ensure that all events of each stage are completed before beginning the next phase. Among the numerous molecules involved in this process, the most important are the cyclin-dependent kinases (CDKs), proteins that are activated only when bound to cyclins (regulatory proteins with fluctuating concentrations). In general, more CDKs are overexpressed in cancer cells than in normal cells, which explains why cancer cells divide uncontrollably. Succeeding in modulating CDK activity with pharmacological agents could result in decreasing the abnormal proliferation rate of cancer cells. This review offers an overview of CDK-cyclin complexes in relation to different cell cycle phases, an analysis of CDK activation and inhibition of molecular mechanisms, and an extensive report, including clinical trials, regarding four new drugs acting as CDK modulators: alvocidib, P276-00, SNS-032 and seliciclib.

Targeting cell cycle kinases and kinesins in anticancer drug development

The cell cycle is regulated by kinases such as the cyclin-dependent kinases (CDKs) and non-CDKs, which include Aurora and polo-like kinases, as well as checkpoint proteins. Mitotic kinesins are involved in the establishment of the mitotic spindle formation and function, and also play a role in cell cycle control. The disruption of the cell cycle is a hallmark of malignancy. Genetic or epigenetic events result in the upregulation of these kinases and mitotic kinesins in a myriad of tumour types, suggesting that their inhibition could result in preferential targeting of malignant cells. Such findings make the development of these inhibitors a rational and attractive new area for cancer therapeutics. Although challenges of potency and non-specificity have hampered their progress through the clinic, several novel compounds are presently in various phases of clinical trial evaluation.

Substituted 4-(thiazol-5-yl)-2-(phenylamino)pyrimidines are highly active CDK9 inhibitors: synthesis, X-ray crystal structures, structure-activity relationship, and anticancer activities

Cancer cells often have a high demand for antiapoptotic proteins in order to resist programmed cell death. CDK9 inhibition selectively targets survival proteins and reinstates apoptosis in cancer cells. We designed a series of 4-thiazol-2-anilinopyrimidine derivatives with functional groups attached to the C5-position of the pyrimidine or to the C4-thiazol moiety and investigated their effects on CDK9 potency and selectivity. One of the most selective compounds, 12u inhibits CDK9 with IC(50) = 7 nM and shows over 80-fold selectivity for CDK9 versus CDK2. X-ray crystal structures of 12u bound to CDK9 and CDK2 provide insights into the binding modes. This work, together with crystal structures of selected inhibitors in complex with both enzymes described in a companion paper, (34) provides a rationale for the observed SAR. 12u demonstrates potent anticancer activity against primary chronic lymphocytic leukemia cells with a therapeutic window 31- and 107-fold over those of normal B- and T-cells.

Roscovitine sensitizes leukemia and lymphoma cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a death ligand with selective antitumor activity. However, many primary tumors are TRAIL resistant. Previous studies reported that roscovitine, a cyclin-dependent kinase inhibitor, sensitized various solid cancer cells to TRAIL. We show that roscovitine and TRAIL demonstrate synergistic cytotoxicity in hematologic malignant cell lines and primary cells. Pretreatment of TRAIL-resistant leukemia cells with roscovitine induced enhanced cleavage of death-inducing signaling complex-bound proximal caspases after exposure to TRAIL. We observed increased levels of both pro- and antiapoptotic BCL-2 proteins at the mitochondria following exposure to roscovitine. These results suggest that roscovitine induces priming of cancer cells for death by binding antiapoptotic BCL-2 proteins to proapoptotic BH3-only proteins at the mitochondria, thereby decreasing the threshold for diverse proapoptotic stimuli. We propose that the mitochondrial priming and enhanced processing of apical caspases represent major molecular mechanisms of roscovitine-induced sensitization to TRAIL in leukemia/lymphoma cells.

Fascaplysin as a specific inhibitor for CDK4: insights from molecular modelling

Cyclin-dependent kinases (CDKs) play a key role in the cell cycle and are important anti-cancer drug targets. The natural product fascaplysin inhibits CDK4 with surprising selectivity (IC(50) = 0.4 µM) compared to the close homolog CDK2 (IC(50) = 500 µM). Free energy calculations of the positively charged fascaplysin and an uncharged iso-electronic derivative in the CDK2 and CDK4 inhibitor complexes indicate that the positive charge of fascaplysin is crucial for selectivity. This finding will guide further improvements in the design of fascaplysin-based selective inhibitors for CDK4.

The impact of CDK inhibition in human malignancies associated with pronounced defects in apoptosis: advantages of multi-targeting small molecules

Malignant cells in chronic lymphocytic leukemia (CLL) and related diseases are heterogeneous and consist primarily of long-lived resting cells in the periphery and a minor subset of dividing cells in proliferating centers. Both cell populations have different molecular signatures that play a major role in determining their sensitivity to therapy. Contemporary approaches to treating CLL are heavily reliant on cytotoxic chemotherapeutics. However, none of the current treatment regimens can be considered curative. Pharmacological CDK inhibitors have extended the repertoire of potential drugs for CLL. Multi-targeted CDK inhibitors affect CDKs involved in regulating both cell cycle progression and transcription. Their interference with transcriptional elongation represses anti-apoptotic proteins and, thus, promotes the induction of apoptosis. Importantly, there is evidence that treatment with CDK inhibitors can overcome resistance to therapy. The pharmacological CDK inhibitors have great potential for use in combination with other therapeutics and represent promising tools for the development of new curative treatments for CLL.

Selective CDK4/6 inhibition with tumor responses by PD0332991 in patients with mantle cell lymphoma

Mantle cell lymphoma (MCL) carries an unfavorable prognosis and requires new treatment strategies. The associated t(11:14) translocation results in enhanced cyclin D1 expression and cyclin D1-dependent kinase activity to promote cell-cycle progression. A pharmacodynamic study of the selective CDK4/6 inhibitor PD0332991 was conducted in 17 patients with relapsed disease, using 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) and 3-deoxy-3[(18)F]fluorothymidine (FLT) positron emission tomography (PET) to study tumor metabolism and proliferation, respectively, in concert with pre- and on-treatment lymph node biopsies to assess retinoblastoma protein (Rb) phosphorylation and markers of proliferation and apoptosis. Substantial reductions in the summed FLT-PET maximal standard uptake value (SUV(max)), as well as in Rb phosphorylation and Ki-67 expression, occurred after 3 weeks in most patients, with significant correlations among these end points. Five patients achieved progression-free survival time of > 1 year (range, 14.9-30.1+ months), with 1 complete and 2 partial responses (18% objective response rate; 90% confidence interval, 5%-40%). These patients demonstrated > 70%, > 90%, and ≥ 87.5% reductions in summed FLT SUV(max) and expression of phospho-Rb and Ki67, respectively, parameters necessary but not sufficient for long-term disease control. The results of the present study confirm CDK4/6 inhibition by PD0332991 at a well-tolerated dose and schedule and suggest clinical benefit in a subset of MCL patients. This study is registered at www.clinicaltrials.gov under identifier NCT00420056.

The impact of multi-targeted cyclin-dependent kinase inhibition in breast cancer cells: clinical implications

INTRODUCTION

The progression of the mammalian cell cycle is driven by the transient activation of complexes consisting of cyclins and cyclin-dependent kinases (CDKs). Loss of control over the cell cycle results in accelerated cell division and malignant transformation and can be caused by the upregulation of cyclins, the aberrant activation of CDKs or the inactivation of cellular CDK inhibitors. For these reasons, cell cycle regulators are regarded as very promising therapeutic targets for the treatment of human malignancies.

AREAS COVERED

This review covers the structures and anti-breast cancer activity of selected pharmacological pan-specific CDK inhibitors. Multi-targeted CDK inhibitors affect CDKs involved in the regulation of both cell cycle progression and transcriptional control. The inhibition of CDK7/CDK9 has a serious impact on the activity of RNA polymerase II; when its carboxy-terminal domain is unphosphorylated, it is unable to recruit the cofactors required for transcriptional elongation, resulting in a global transcriptional block. Multi-targeted inhibition of CDKs represses anti-apoptotic proteins and thus promotes the induction of apoptosis. Moreover, the inhibition of CDK7 in estrogen receptor (ER)-positive breast cancer cells prevents activating phosphorylation of ER-α.

EXPERT OPINION

These diverse modes of action make multi-targeted CDK inhibitors promising drugs for the treatment of breast cancers.

Small interfering RNAs targeting cyclin D1 and cyclin D2 enhance the cytotoxicity of chemotherapeutic agents in mantle cell lymphoma cell lines

Cyclin D1 (CCND1) is a known cell cycle regulator whose overexpression is a hallmark of mantle cell lymphoma (MCL). Although molecular techniques have unified the diagnostic approach to MCL, no therapeutic advances have been made to target this particular pathway. The significance of CCND1 in the pathogenesis and treatment of MCL has yet to be defined. We have taken advantage of RNA interference (RNAi) to down-regulate CCND1 expression in two MCL cell lines (Granta-519 and Jeko-1) to investigate the cytotoxic effect of combining RNAi with conventional chemotherapeutic agents. We designed four small interfering RNAs (siRNAs) specific to CCND1, one specific to CCND2, and one dual-targeting siRNA that simultaneously down-regulates CCND1 and CCND2. Etoposide and doxorubicin were used as chemotherapeutics in combination with the siRNAs. The transfected siRNAs in MCL cell lines triggered 40-60% reduction in target mRNA and protein levels. Importantly, the siRNA-mediated reduction in cyclins resulted in decreased IC(50) (50% inhibitory concentration) values for both doxorubicin and etoposide. The combination of siRNA-mediated inhibition of the cyclins along with chemotherapeutic agents could potentially be used to lower the effective doses of the chemotherapeutic agents and reduce drug-related toxicities.

Responses in mantle cell lymphoma cells to SNS-032 depend on the biological context of each cell line

SNS-032 is a potent inhibitor of cyclin-dependent kinases (Cdk) 2, 7, and 9 that regulate the cell cycle and transcription. Our studies in indolent primary chronic lymphocytic leukemia cells showed that SNS-032 inhibited transcription, diminished the antiapoptotic protein Mcl-1, and induced apoptosis. The present study focuses on evaluating this compound in four proliferating mantle cell lymphoma lines (Jeko-1, Granta 519, Mino, and SP-53). Consistent with its action against Cdk9 and Cdk7, SNS-032 inhibited the phosphorylation of RNA pol II in all four lines and blocked RNA synthesis. The transcripts and protein levels of short-lived proteins decreased, including cyclin D1 and Mcl-1. Cell growth was inhibited in a concentration-dependent manner in all lines. Apoptosis was induced in JeKo-1, Mino, and SP-53 cells without disrupting cell cycle distribution. However, apoptosis was limited in Granta cells; rather, there was a significant reduction of clonogenic survival. Small interfering RNA was used to specifically knock down Mcl-1 and cyclin D1 in JeKo-1 and Granta cells. Knocking down Mcl-1 induced significant apoptosis in Jeko-1 cells but not Granta cells. Reducing cyclin D1, rather than Mcl-1, was associated with loss of clonogenic survival in Granta cells. Thus, these results indicated that mantle cell lymphoma cell lines have distinct mechanisms sustaining their survival, and the mechanism of action of SNS-032 is dependent on the biological context of an individual line.

Seliciclib in malignancies

Cyclins and cyclin-dependent kinases (CDK) form a key part of the regulatory proteins that govern the cell cycle. Aberrancy in their function can lead to uncontrolled growth and proliferation of the cells which forms the basis of many human diseases, especially cancers. Seliciclib (CYC202, R-roscovitine) is a second-generation CDK inhibitor that competes for ATP binding sites on these kinases, reducing tumor growth and inducing cell death. It is a direct inhibitor of cyclin E/CDK2 and also has inhibitory effects on cyclin H/CDK7 and cyclin T/CDK9. Seliciclib leads to growth arrest and apoptosis of cell lines through activation of the p53 gene, inhibition of RNA processing and blockage of the RNA polymerase II-dependent transcription, and reduction of anti-apoptotic proteins. Seliciclib has good oral bioavailability, although its absorption is slowed by food. It is distributed rapidly to the body tissues and metabolized rapidly to a carboxylated derivative that is excreted by the kidneys. The major adverse effects of seliciclib are electrolyte disturbances (hypokalemia, hyponatremia), gastrointestinal side effects (nausea, emesis, anorexia), fatigue, transient hyperglycemia, elevation of liver enzymes and reversible elevation of serum creatinine. At present, it is in Phase II trials for non-small cell lung cancer and nasopharyngeal carcinoma.

8-Amino-adenosine inhibits multiple mechanisms of transcription

Roscovitine and flavopiridol suppress cyclin-dependent kinase 7 (CDK7) and CDK9 activity resulting in transcription inhibition, thus providing an alternative mechanism to traditional genotoxic chemotherapy. These agents have been effective in slow or nonreplicative cell types. 8-Amino-adenosine is a transcription inhibitor that has proved very effective in multiple myeloma cell lines and primary indolent leukemia cells. The objective of the current work was to define mechanisms of action that lead to transcription inhibition by 8-amino-adenosine. 8-Amino-adenosine is metabolized into the active triphosphate (8-amino-ATP) in cells. This accumulation resulted in a simultaneous decrease of intracellular ATP and RNA synthesis. When the effects of established ATP synthesis inhibitors and transcription inhibitors on intracellular ATP concentrations and RNA synthesis were studied, there was a strong correlation between ATP decline and RNA synthesis. This correlation substantiated the hypothesis that the loss of ATP in 8-amino-adenosine-treated cells contributes to the decrease in transcription due to the lack of substrate needed for mRNA body and polyadenylation tail synthesis. RNA polymerase II COOH terminal domain phosphorylation declined sharply in 8-amino-adenosine-treated cells, which may have been due to the lack of an ATP phosphate donor or competitive inhibition with 8-amino-ATP at CDK7 and CDK9. Furthermore, 8-amino-ATP was incorporated into nascent RNA in a dose-dependent manner at the 3'-end resulting in transcription termination. Finally, in vitro transcription assays showed that 8-amino-ATP competes with ATP for incorporation into mRNA. Collectively, we have concluded that 8-amino-adenosine elicits effects on multiple mechanisms of transcription, providing a new class of transcription inhibitors.

Novel potent pharmacological cyclin-dependent kinase inhibitors

Progression of the cell cycle is controlled by various activating and inhibiting cellular factors. The subtle balance between these counteracting regulators in normal cells ensures proper cell cycle progression and facilitates cellular responses to a variety of stress stimuli. Key activators include cyclin-dependent kinases (CDKs) and, consequently, loss or inactivation of CDK inhibitors contributes to the escape of cancer cells from cell cycle control and hyperactivation of CDKs occurs in various neurodegenerative disorders. However, these adverse effects may be compensated by pharmacological counterparts. Inhibitors of CDKs representing various classes of compounds with diverse CDK inhibitory patterns have been developed, but inhibitors that have high selectivity and offer highly targeted activity against both cell cycle and transcriptional CDKs are of particular interest. This review focuses on pharmacological CDK inhibitors that have entered clinical trials and some compounds that have been evaluated preclinically. Recent discoveries in cell cycle regulation have provided rationales for clinical applications of CDK inhibitors in both monotherapeutic and combined therapeutic regimens.

Functional p53 in cells contributes to the anticancer effect of the cyclin-dependent kinase inhibitor roscovitine

Inhibitors of cyclin-dependent kinases (CDKs) undergoing clinical trials as anticancer agents usually target several CDKs in cells. Some of them are also able to increase cellular levels of p53 protein and to activate p53-regulated transcription. To define the role of p53 in the anticancer effect of selective CDK inhibitors, two related compounds roscovitine and olomoucine II were studied. Roscovitine differs functionally from its congener olomoucine II only in the selectivity towards transcriptional CDK9. Action of both compounds on proliferation, cell-cycle progression, and apoptosis was examined in RPMI-8226 cells expressing the temperature-sensitive mutant of p53 and in MCF-7 cells with wild-type p53. Both compounds blocked proliferation, decreased phosphorylation of RNA polymerase II, downregulated antiapoptotic protein Mcl-1 in both cell lines in a dose-dependent manner, and also activated p53 in MCF-7 cells. Moreover, we showed that the anticancer efficiency of CDK inhibitors was enhanced by active p53 in RPMI-8226 cells kept at permissive temperature, where downregulation of Mcl-1, fragmentation of PARP-1, and increased caspase-3 activity was detected with lower doses of the compounds. The results confirm that functional p53 protein may enhance the anticancer activity of roscovitine that could be beneficial for anticancer therapy.

Preclinical activity of 8-chloroadenosine with mantle cell lymphoma: roles of energy depletion and inhibition of DNA and RNA synthesis

8-Chloroadenosine (8-Cl-Ado), an RNA-directed nucleoside analogue, is currently under evaluation in phase I clinical trials for treatment of chronic lymphocytic leukaemia. In the current study, the efficacy of 8-Cl-Ado was evaluated using mantle cell lymphoma (MCL) cell lines: Granta 519, JeKo, Mino, and SP-53. After continuous exposure to 10 mumol/l 8-Cl-Ado for 24 h, loss of mitochondrial transmembrane potential and poly [adenosine diphosphate (ADP)-ribose] polymerase (PARP) cleavage were detected in three of four cell lines. Reduced ATP levels (30-60% reduction) and concurrent 8-Cl-ATP accumulation were highly associated with cell death (P < 0.01). The intracellular 8-Cl-ATP concentrations were also highly correlated with inhibition of global transcription (50-90%, r(2) = 0.90, P < 0.01). However, the inhibition of transcription only accounted for 30-40% of cell death as determined by equivalent inhibition with actinomycin D. Likewise, short-lived mRNAs, those encoding cyclin D1 and Mcl-1, were not consistently reduced after treatment. Unique to MCL as compared to other haematological malignancies, 8-Cl-Ado inhibited the rates of DNA synthesis and selectively depleted dATP pools (50-80%). We conclude that the DNA and RNA directed actions of 8-Cl-Ado in combination with depleted energetics may promote cell death and inhibit growth of MCL cell lines.

The cyclin dependent kinase inhibitor (R)-roscovitine prevents alloreactive T cell clonal expansion and protects against acute GvHD

Cell cycle re-entry of quiescent T lymphocytes regulated by cdk2 is required for antigen-specific clonal expansion and generation of productive T cell responses. Recently, we determined that induction of antigen-specific T cell tolerance results in impaired cdk2 activity leading to enhanced Smad3 transactivation, upregulation of p15 and blockade of cell cycle progression. Here we report that pharmacologic inhibition of cdk2 with (R)-roscovitine blocked expansion of alloreactive T cells in vitro and in vivo and protected from lethal acute GvHD. In addition to inhibiting alloreactive T cell responses, (R)-roscovitine prevented TNF-alpha-mediated activation of NF-kappa B pathway, which is involved in the inflammatory process leading to the development of GvHD. The combined anti-proliferative and anti-inflammatory properties of (R)-roscovitine make it an attractive treatment modality toward control of GvHD.

Wortmannin potentiates roscovitine-induced growth inhibition in human solid tumor cells by repressing PI3K/Akt pathway

Roscovitine has been reported to have anti-tumor effects in some cancer cell lines. The phosphatidylinositol-3-kinase (PI3K) signaling, which activates protein kinase B (PKB)/Akt, is known to mediate cell survival. The current study examined the role of wortmannin, a PI3K inhibitor, as a chemosensitizer for roscovitine and its proposed mechanism of action. The results showed that wortmannin significantly chemosensitized three human tumor cell lines (A549, HCT116 and HeLa cells). In A549 cells, wortmannin increased roscovitine-induced apoptosis in a dose-dependent manner, which was correlated with the inhibition of phosphorylated PKB/Akt level. Wortmannin enhanced the effects of roscovitine by causing pronounced reduction of mitochondrial transmembrane potential (MMP) and increases of cytochrome c release and active caspase-3, as well as enhanced activation of Bax and Bad, including Bax oligomerization and mitochondrial translocation of Bax and Bad. Taken together, these results provide evidence for the potential application of roscovitine/wormannin combination in clinical treatment for solid tumors.

Action of resveratrol alone or in combination with roscovitine, a CDK inhibitor, on cell cycle progression in human HL-60 leukemia cells

Results of a number of epidemiological and experimental studies indicate that polyphenols (e.g. resveratrol (RES), epicatechins etc.), antioxidant agents and abundant micronutrients in our food could have strong anti-mitotic as well as pro-apoptotic effects. In this study we raised the question whether roscovitine (ROSC), an inhibitor of cyclin-dependent kinases (CDKs) with increased selectivity towards CDK2, could be able to affect human leukemia HL-60 cells in which the p53 gene is inactivated and whether ROSC-induced effects could be additionally modulated by compounds of natural origin, especially by polyphenols e.g. RES. Exposure of HL-60 cells to ROSC for 24 h inhibited their proliferation. Flow cytometric analyses revealed that unlike MCF-7 cells, HL-60 cells were arrested in G(1) upon ROSC treatment. Furthermore, ROSC also induced apoptosis in HL-60 cells. After treatment with 40 microM ROSC for 24 h the frequency of hypoploid cells representing cells undergoing apoptosis reached approximately 50%. In the next step the action of RES alone or in combination with ROSC was examined. Interestingly, synergistic effects were observed after combined treatment for 24 h and sequential post-incubation for 48 h in the presence of RES. Such combined treatment resulted in a marked reduction of the frequency of the S- and G(2)/M-phase cells and simultaneously increased the G(1) cell population up to 80% at a fourfold lower ROSC dose. Further analyses revealed that the combined treatment strongly activated caspase-3. These results clearly evidence that RES strongly potentiates ROSC-induced apoptosis.

Functionally associated targets in mantle cell lymphoma as defined by DNA microarrays and RNA interference

Mantle cell lymphoma (MCL) is a non-Hodgkin lymphoma with poor prognosis. Its hallmark is the translocation t(11:14)q (13;32), leading to overexpression of cyclin D1, a positive regulator of the cell cycle. As cyclin D1 up-regulation is not sufficient for inducing malignant transformation, we combined DNA microarray and RNA interference (RNAi) approaches to identify novel deregulated genes involved in the progression of MCL. DNA microarray analysis identified 46 genes specifically up-regulated in MCL compared with normal B cells; 20 of these were chosen for further studies based on their cellular functions, such as growth and proliferation. The Granta 519 cell line was selected as an MCL in vitro model, to set up the RNAi protocol. To confirm the functionality of overexpression of the 20 disease-associated genes, they were knocked down using small interfering RNAs (siRNAs). In particular, knockdown of 3 genes, encoding the hepatoma-derived growth factor related protein 3 (HDGFRP3), the frizzled homolog 2 (FZD2), and the dual specificity phosphatase 5 (DUSP5), induced proliferative arrest in Granta 519 MCL cells. These genes emerged as functionally associated in MCL, in relation to growth and survival, and interfering with their function would increase insight into lymphoma growth regulation, potentially leading to novel clinical intervention modalities.

Genetic and molecular pathogenesis of mantle cell lymphoma: perspectives for new targeted therapeutics

Mantle cell lymphoma (MCL) is a well-defined lymphoid malignancy characterized by a rapid clinical evolution and poor response to current therapeutic protocols. The genetic and molecular mechanisms involved in its pathogenesis combine the dysregulation of cell proliferation and survival pathways with a high level of chromosome instability that seems related to the disruption of the DNA damage response pathway. Understanding these mechanisms and how they affect tumour behaviour is providing the rationale for the identification of reliable predictors of clinical evolution and the design of innovative therapeutic strategies that could open new avenues for the treatment of patients with MCL.

Novel therapeutic targets in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterised by cell cycle dysregulation and a defective DNA damage response pathway. An evolving understanding of these processes has provided the rationale for development of novel agents targeting various steps that appear to be involved in lymphomagenesis and disease progression. Cyclin D1, overexpressed in nearly 100% of MCL, and the cyclin-dependent kinases were among the first rational targets identified. Therapies focusing on the PI3K/Akt pathway, the tumour microenvironment, and cell surface markers are also in various stages of exploration. Here, the authors discuss the rationale for developing targeted therapies and discuss future challenges in combining some of these agents.

Cyclin-dependent kinase inhibition limits glomerulonephritis and extends lifespan of mice with systemic lupus

OBJECTIVE

To examine whether the cyclin-dependent kinase (CDK) inhibitor seliciclib ameliorates autoimmune nephritis in (NZB x NZW)F(1) mice.

METHODS

In experiment 1, NZB x NZW mice received seliciclib (100 mg/kg or 200 mg/kg) or vehicle by gavage, beginning at age 2 months and ending at 8 months of age. In experiment 2, seliciclib (200 mg/kg) was administered alone or combined with low-dose methylprednisolone, starting at age 5 months, when immune complex deposition in the kidney had already occurred. Animals were followed up until all vehicle-treated mice died. In 2 additional groups of NZB x NZW mice treated with seliciclib or vehicle from 2 months of age until 5 months of age, splenocytes were isolated and tested ex vivo for T cell and B cell activity.

RESULTS

Seliciclib, given at an early phase of disease, prolonged survival, delayed the onset of proteinuria and renal function impairment, and protected the kidney against glomerular hypercellularity, tubulointerstitial damage, and inflammation. Combining seliciclib with low-dose methylprednisolone in mice with established disease extended the lifespan and limited proteinuria and renal damage more than treatment with either agent alone. Seliciclib limited immunologic signs of disease, reducing glomerular IgG and C3 deposits and levels of serum anti-DNA antibodies. Moreover, it inhibited ex vivo T cell and B cell proliferative responses to polyclonal stimuli. T cell production of interferon-gamma and interleukin-10 and B cell release of IgG2a were reduced by treatment with seliciclib.

CONCLUSION

These findings suggest that CDK activity may be a useful target in the treatment of systemic lupus erythematosus. A direct immunomodulatory action of seliciclib on T cells and B cells may be one of the mechanisms underlying the beneficial effects.

Cyclin-dependent kinase inhibitor seliciclib shows in vitro activity in diffuse large B-cell lymphomas

Despite recent improvements in treatment, a significant fraction of patients with diffuse large B-cell lymphoma (DLBCL) still fail therapy. Therefore, new therapeutic modalities are needed to advance the cure rate. Seliciclib (CYC202, R-roscovitine) is a purine analog developed as an inhibitor of CDK2/cyclin E CDK7/cyclin H and CDK9/cyclin T. Seliciclib has been shown to be active in B-cell neoplasms, such as mantle cell lymphoma, chronic lymphocytic leukemia and in multiple myeloma in vitro. The aim of this study was to assess the in vitro activity of seliciclib in DLBCL. The anti-proliferative activity of seliciclib was tested in nine human DLBCL cell lines and six DLBCL primary cell cultures. The effects of seliciclib on the cell cycle and on apoptosis, as well as on transcription-related proteins were assessed. The cell viability of all DLBCL cell lines and primary cells was reduced by seliciclib treatment. The IC50 for the cell lines ranged from 13 - 36 microm. The effect of seliciclib was independent of the genetic aberrations characterizing the cell lines. After seliciclib exposure cells accumulated in G2/M or in G1 phase, with most of the cells showing signs of apoptosis. Despite the clear cytotoxic effect and induction of apoptosis, this study could not identify a unique mechanism of action. The in vitro data suggest that seliciclib is an active agent in DLBCL. Its efficacy is apparently independent of the underlying chromosomal translocations characteristic of DLBCL. The drug might represent a new therapeutic agent in this lymphoma sub-type.

Effect of the Cdk-inhibitor roscovitine on mouse hematopoietic progenitors in vivo and in vitro

Myelosuppression is one the most frequent side effects of chemotherapy. New agents that more selectively target cancer cells have been developed in attempt to improve the effects and to decrease the side effects of cancer treatment. Roscovitine is a purine analogue and cyclin-dependent kinase inhibitor. Several studies have shown its cytotoxic effect in cancer cell lines in vitro and in xenograft models in vivo. In this study, we investigated the effect of roscovitine on hematopoietic progenitors in vitro and in vivo in mice. The clonogenic capacity of hematopoietic progenitors was studied using burst-forming unit-erythroid (BFU-E), colony-forming unit granulocyte, macrophage (CFU-GM) and colony-forming unit granulocyte, erythroid, macrophage, megakaryocyte (CFU-GEMM). In vitro, bone marrow cells were exposed to roscovitine (25-250 microM) in Iscove's modified Dulbecco's media for 4 h or to roscovitine (1-100 microM) in MethoCult media for 12 days. No effect on colony formation was observed after exposure to roscovitine for 4 h; however, concentration- and cell type-dependent effects were observed after 12 days. Roscovitine in concentration of 100 microM inhibited the growth of all types of colonies, while lower concentrations have shown differential effect on hematopoietic progenitors. The most sensitive were CFU-GEMM, followed by BFU-E and then CFU-GM. In vivo, mice were treated with single dose of roscovitine (50, 100 or 250 mg/kg) and the effect on bone marrow was studied on day 1, 3, 6, 9 or 12 after the treatment. In the second part of experiment, the mice were treated with roscovitine 350 mg/kg/day divided into two daily doses for 4 days. The bone marrow was examined on day 1 and 5 after the last dose of roscovitine. On day 1, BFU-E decreased to less than 50% of the controls (P = 0.019). No decrease in BFU-E formation was observed on day 5. No significant effect was observed on CFU-GM and CFU-GEMM growth after the treatment with multiple doses of roscovitine. Single doses of roscovitine or dimethylsulfoxide did not affect the colony formation. We also studied the distribution of roscovitine to the bone marrow after a dose of 50 mg/kg was administered intraperitoneally. Only 1.5% of the drug was detected in the bone marrow. Thus, the roscovitine effect on hematopoietic progenitors in bone marrow in vivo is only transient. One reason may be that only a small fraction of roscovitine reaches the bone marrow. Another explanation may be the short half-life observed for roscovitine that might not allow enough cell exposure to the drug. However, the toxicity of roscovitine to hematopoietic progenitors in vitro is within the same exposure range as cytotoxicity to cancer cells. Thus, precaution should be taken in clinical trials, especially when combinations with myelosuppressive cytostatics are used.

4-arylazo-3,5-diamino-1H-pyrazole CDK inhibitors: SAR study, crystal structure in complex with CDK2, selectivity, and cellular effects

In a routine screening of our small-molecule compound collection we recently identified 4-arylazo-3,5-diamino-1H-pyrazoles as a novel group of ATP antagonists with moderate potency against CDK2-cyclin E. A preliminary SAR study based on 35 analogues suggests ways in which the pharmacophore could be further optimized, for example, via substitutions in the 4-aryl ring. Enzyme kinetics studies with the lead compound and X-ray crystallography of an inhibitor-CDK2 complex demonstrated that its mode of inhibition is competitive. Functional kinase assays confirmed the selectivity toward CDKs, with a preference for CDK9-cyclin T1. The most potent inhibitor, 4-[(3,5-diamino-1H-pyrazol-4-yl)diazenyl]phenol 31b (CAN508), reduced the frequency of S-phase cells of the cancer cell line HT-29 in antiproliferation assays. Further observed cellular effects included decreased phosphorylation of the retinoblastoma protein and the C-terminal domain of RNA polymerase II, inhibition of mRNA synthesis, and induction of the tumor suppressor protein p53, all of which are consistent with inhibition of CDK9.

Pathogenesis and therapy of cutaneous lymphomas--progress or impasse?

The cutaneous environment hosts a number of hematopoietic neoplasms that are dominated by primary cutaneous (PC) T-cell lymphomas. Recent progress in molecular biology and immunology has provided tools to investigate the pathogenesis and the biology of these neoplasms. This review highlights newest findings concerning the immune biology of CD4+ CD56+ hematodermic neoplasms, and PC T-cell and B-cell lymphomas, speculating how these can be translated into more sophisticated, biology-based treatment approaches in the near future.

Update on the molecular biology of mantle cell lymphoma

Mantle cell lymphoma (MCL) accounts for 5-10% of non-Hodgkin's lymphomas and it bears the worst prognosis among B cell lymphomas. Even more than in the other lymphomas, new insights in MCL biology are needed. In this review we will discuss the most recent published data. Immunoglobulin sequencing data suggest that the MCL cell of origin is a mature B cell which might have undergone an extra-follicular T-cell independent antigen maturation. The main aberrations that affect cell cycle and DNA repair pathways in MCL are summarized, also discussing the need of the t(11;14)(q13;q32) to make diagnosis of MCL. After the gene expression studies of the last years, now the research focus has moved towards the new opportunities provided by arrayCGH technique for gene discovery and for identification of therapeutic targets. Examples of genes identified because deleted or amplified at DNA level and that might be relevant for MCL pathogenesis are presented.