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

Dissecting the regulatory network of transcription factors in T cell phenotype/functioning during GVHD and GVT

Transcription factors play a major role in regulation and orchestration of immune responses. The immunological context of the response can alter the regulatory networks required for proper functioning. While these networks have been well-studied in canonical immune contexts like infection, the transcription factor landscape during alloactivation remains unclear. This review addresses how transcription factors contribute to the functioning of mature alloactivated T cells. This review will also examine how these factors form a regulatory network to control alloresponses, with a focus specifically on those factors expressed by and controlling activity of T cells of the various subsets involved in graft-versus-host disease (GVHD) and graft-versus-tumor (GVT) responses.

Tozasertib Attenuates Neuropathic Pain by Interfering with Aurora Kinase and KIF11 Mediated Nociception

Kinesins are the motor proteins that transport excitatory receptors to the synaptic membrane by forming a complex with receptor cargo leading to central sensitization causing neuropathic pain. Many regulatory proteins govern the transit of receptors by activating kinesin, and Aurora kinases are one of them. In this study, we have performed in silico molecular dynamics simulation to delineate the dynamic interaction of Aurora kinase A with its pharmacological inhibitor, tozasertib. The results from the molecular dynamics study shows that tozasertib-Aurora kinase A complex is stabilized through hydrogen bonding, polar interactions, and water bridges. Findings from the in vitro studies suggest that tozasertib treatment significantly attenuates lipopolysaccharide (LPS)-induced increase in oxidonitrosative stress and kif11 overexpression in C6 glial cell lines. Further, we investigated the regulation of kif11 and its modulation by tozasertib in an animal model of neuropathic pain. Two weeks post-CCI surgery we observed a significant increase in pain hypersensitivity and kif11 overexpression in DRG and spinal cord of nerve-injured rats. Tozasertib treatment significantly attenuates enhanced pain hypersensitivity along with the restoration of kif11 expression in DRG and spinal cord and oxidonitrosative stress in the sciatic nerve of injured rats. Our findings demonstrate the potential role of tozasertib for the management of neuropathic pain.

Cellular and Molecular Mechanisms of R/S-Roscovitine and CDKs Related Inhibition under Both Focal and Global Cerebral Ischemia: A Focus on Neurovascular Unit and Immune Cells

Ischemic stroke is the second leading cause of death worldwide. Following ischemic stroke, Neurovascular Unit (NVU) inflammation and peripheral leucocytes infiltration are major contributors to the extension of brain lesions. For a long time restricted to neurons, the 10 past years have shown the emergence of an increasing number of studies focusing on the role of Cyclin-Dependent Kinases (CDKs) on the other cells of NVU, as well as on the leucocytes. The most widely used CDKs inhibitor, (R)-roscovitine, and its (S) isomer both decreased brain lesions in models of global and focal cerebral ischemia. We previously showed that (S)-roscovitine acted, at least, by modulating NVU response to ischemia. Interestingly, roscovitine was shown to decrease leucocytes-mediated inflammation in several inflammatory models. Specific inhibition of roscovitine majors target CDK 1, 2, 5, 7, and 9 showed that these CDKs played key roles in inflammatory processes of NVU cells and leucocytes after brain lesions, including ischemic stroke. The data summarized here support the investigation of roscovitine as a potential therapeutic agent for the treatment of ischemic stroke, and provide an overview of CDK 1, 2, 5, 7, and 9 functions in brain cells and leucocytes during cerebral ischemia.

Immunomodulatory Roles of Cell Cycle Regulators

Core cell cycle regulators, including cyclin-dependent kinases (CDKs), cyclins, and cyclin-dependent kinase inhibitors (CKIs), are known for their well-characterized roles in cell division. Several recent studies have shed light on the roles of these proteins in immune modulation. The development and activation of cells in the immune system take place not only during embryonic development but throughout the life of a multicellular organism. Cell cycle regulators are involved in the development of immune cells, partly as the machinery controlling the expansion and differentiation of the populations of immune cells. In addition, these proteins serve non-cell cycle functions. In this review, we summarize the emerging roles of cell cycle regulators in modulating functions of the immune system and discuss how they may be exploited as therapeutic targets.

Potent anti-leukemic activity of a specific cyclin-dependent kinase 9 inhibitor in mouse models of chronic lymphocytic leukemia

Onset of progression even during therapy with novel drugs remains an issue in chronic lymphocytic leukemia (CLL). Thus, there is ongoing demand for novel agents. Approaches targeting cyclin-dependent kinases (CDK) have reached the clinical trial stage. CDK9 mediating RNA transcriptional elongation is the evolving pivotal CLL CDK inhibitor target. However, more CDK9 selective compounds are desirable. Here, we describe the CDK9 inhibitor LDC526 displaying a low nanomolar biochemical activity against CDK9 and an at least 50-fold selectivity against other CDKs. After demonstrating in vitro MEC-1 cell line and primary human CLL cell cytotoxicity we evaluated the LDC526 in vivo effect on human CLL cells transplanted into NOD/scid/γc^null (NSG) mice. LDC526 administration (75 mg/kg) for 5 days resulted in a 77% reduction of human CLL cells in NSG spleens compared to carrier control treatment. Next, we longitudinally studied the LDC526 impact on circulating CLL cells in the TCL1 transgenic mouse model. LDC526 (50 mg/kg) administration for two days led to a 16-fold reduction of blood CLL cell numbers. Remarkably, residual CLL cells exhibited significantly increased intracellular BCL-2 levels. However, the LDC526 cytotoxic effect was not restricted to CLL cells as also declining numbers of normal B and T lymphocytes were observed in LDC526 treated TCL1 mice. Taken together, our in vivo data provide a strong rational for continued LDC526 development in CLL therapy and argue for the combination with BCL-2 inhibitors.

Dinaciclib induces immunogenic cell death and enhances anti-PD1-mediated tumor suppression

Blockade of the checkpoint inhibitor programmed death 1 (PD1) has demonstrated remarkable success in the clinic for the treatment of cancer; however, a majority of tumors are resistant to anti-PD1 monotherapy. Numerous ongoing clinical combination therapy studies will likely reveal additional therapeutics that complement anti-PD1 blockade. Recent studies found that immunogenic cell death (ICD) improves T cell responses against different tumors, thus indicating that ICD may further augment antitumor immunity elicited by anti-PD1. Here, we observed antitumor activity following combinatorial therapy with anti-PD1 Ab and the cyclin-dependent kinase inhibitor dinaciclib in immunocompetent mouse tumor models. Dinaciclib induced a type I IFN gene signature within the tumor, leading us to hypothesize that dinaciclib potentiates the effects of anti-PD1 by eliciting ICD. Indeed, tumor cells treated with dinaciclib showed the hallmarks of ICD including surface calreticulin expression and release of high mobility group box 1 (HMGB1) and ATP. Mice treated with both anti-PD1 and dinaciclib showed increased T cell infiltration and DC activation within the tumor, indicating that this combination improves the overall quality of the immune response generated. These findings identify a potential mechanism for the observed benefit of combining dinaciclib and anti-PD1, in which dinaciclib induces ICD, thereby converting the tumor cell into an endogenous vaccine and boosting the effects of anti-PD1.

Cyclin-dependent kinase 5 activity is required for allogeneic T-cell responses after hematopoietic cell transplantation in mice

Molecular intermediates in T-cell activation pathways are crucial targets for the therapy and prevention of graft-versus-host disease (GVHD) following allogeneic hematopoietic cell transplantation (allo-HCT). We recently identified an essential role for cyclin-dependent kinase 5 (Cdk5) in T-cell activation and effector function, but the contribution of Cdk5 activity to the development of GVHD has not been explored. Using an established, preclinical, murine, GVHD model, we reveal that Cdk5 activity is increased in key target organs early after allo-HCT. We then generated chimeric mice (Cdk5^+/+C or Cdk5^-/-C) using hematopoietic progenitors from either embryonic day 16.5 Cdk5^+/+ or Cdk5^-/- embryos to enable analyses of the role of Cdk5 in GVHD, as germ line Cdk5 gene deletion is embryonically lethal. The immunophenotype of adult Cdk5^-/-C mice is identical to control Cdk5^+/+C mice. However, transplantation of donor Cdk5^-/-C bone marrow and T cells dramatically reduced the severity of systemic and target organ GVHD. This phenotype is attributed to decreased T-cell migration to secondary lymphoid organs (SLOs), reduced in vivo proliferation within these organs, and fewer cytokine-producing donor T cells during GVHD development. Moreover, these defects in Cdk5^-/- T-cell function are associated with altered CCR7 signaling following ligation by CCL19, a receptor:ligand interaction critical for T-cell migration into SLOs. Although Cdk5 activity in donor T cells contributed to graft-versus-tumor effects, pharmacologic inhibition of Cdk5 preserved leukemia-free survival. Collectively, our data implicate Cdk5 in allogeneic T-cell responses after HCT and as an important new target for therapeutic intervention.

Modulating Innate and Adaptive Immunity by (R)-Roscovitine: Potential Therapeutic Opportunity in Cystic Fibrosis

(R)-Roscovitine, a pharmacological inhibitor of kinases, is currently in phase II clinical trial as a drug candidate for the treatment of cancers, Cushing's disease and rheumatoid arthritis. We here review the data that support the investigation of (R)-roscovitine as a potential therapeutic agent for the treatment of cystic fibrosis (CF). (R)-Roscovitine displays four independent properties that may favorably combine against CF: (1) it partially protects F508del-CFTR from proteolytic degradation and favors its trafficking to the plasma membrane; (2) by increasing membrane targeting of the TRPC6 ion channel, it rescues acidification in phagolysosomes of CF alveolar macrophages (which show abnormally high pH) and consequently restores their bactericidal activity; (3) its effects on neutrophils (induction of apoptosis), eosinophils (inhibition of degranulation/induction of apoptosis) and lymphocytes (modification of the Th17/Treg balance in favor of the differentiation of anti-inflammatory lymphocytes and reduced production of various interleukins, notably IL-17A) contribute to the resolution of inflammation and restoration of innate immunity, and (4) roscovitine displays analgesic properties in animal pain models. The fact that (R)-roscovitine has undergone extensive preclinical safety/pharmacology studies, and phase I and II clinical trials in cancer patients, encourages its repurposing as a CF drug candidate.

Roscovitine in cancer and other diseases

Roscovitine [CY-202, (R)-Roscovitine, Seliciclib] is a small molecule that inhibits cyclin-dependent kinases (CDKs) through direct competition at the ATP-binding site. It is a broad-range purine inhibitor, which inhibits CDK1, CDK2, CDK5 and CDK7, but is a poor inhibitor for CDK4 and CDK6. Roscovitine is widely used as a biological tool in cell cycle, cancer, apoptosis and neurobiology studies. Moreover, it is currently evaluated as a potential drug to treat cancers, neurodegenerative diseases, inflammation, viral infections, polycystic kidney disease and glomerulonephritis. This review focuses on the use of roscovitine in the disease model as well as clinical model research.

Cyclin-dependent kinase 9 may as a novel target in downregulating the atherosclerosis inflammation (Review)

Inflammation is a key component of atherosclerosis. Genes coding for inflammatory or anti-inflammatory molecules are considered good candidates for estimating the risk of developing atherosclerosis. Cyclin-dependent kinase 9 (CDK9), the kinase of positive transcription elongation factor b (P-TEFb), is crucial in the cell cycle and apoptosis. Previous studies have focused on its inhibition of immune cells for the resolution of inflammation. Considering the effects of inflammation in the pathogenicity of atherosclerosis, decreasing inflammation through the inhibition of CDK9 may be useful for the prognosis of atherosclerosis. The aim of this review was to examine whether inhibition of the CDK9 monocyte may affect the process of inflammation by acting on the cytokine secretion and interacting with endothelial cells (ECs). Thus, CDK9 may be a novel target for the diagnosis and therapy of atherosclerosis.

The cyclin dependent kinase inhibitor (R)-roscovitine mediates selective suppression of alloreactive human T cells but preserves pathogen-specific and leukemia-specific effectors

Graft versus host disease (GvHD), mediated by donor T cells, remains the primary cause of non-relapse mortality after allogeneic hematopoietic stem cell transplantation and novel therapeutic approaches are required. Cdk2 is a critical node of signal integration and programming of T cell responses towards immunity versus anergy but is dispensable for hematopoiesis and thymocyte development. We examined the effects of pharmacologic Cdk2 inhibition on alloreactive human T cells. Inhibition of Cdk2 blocked expansion of alloreactive T cells upon culture with HLA-mismatched dendritic cells and prevented generation of IFN-γ-producing alloantigen-specific effectors. In contrast, Cdk2 inhibition preserved effectors specific for Wilms' tumor 1 (WT1) leukemia antigen and for CMV as determined by WT1-specific and CMV-specific pentamers. Cdk2 inhibition preserved Treg cells, which have the ability to prevent GvHD while maintaining GvL. Thus, Cdk inhibitors may improve allogeneic HSCT by reducing alloreactivity and GvHD without loss of pathogen-specific and leukemia-specific immunity.

New roles for cyclin-dependent kinases in T cell biology: linking cell division and differentiation

The proliferation of a few antigen-reactive lymphocytes into a large population of effector cells is a fundamental property of adaptive immunity. The cell division that fuels this process is driven by signals from antigen, co-stimulatory molecules and growth factor receptors, and is controlled by the cyclin-dependent kinase (CDK) cascade. In this Opinion article, we discuss how the CDK cascade provides one potential link between cell division and differentiation through the phosphorylation of immunologically relevant transcription factors, and how components of this pathway might ultimately participate in the decision between tolerance and immunity.

Utilizing glycogen synthase kinase-3β as a marker for the diagnosis of graft-versus-host disease

INTRODUCTION

Graft-versus-host disease (GVHD) is a deadly complication of allogeneic hematopoietic stem cell transplantation. Timely diagnosis is critical, because mortality rates for GVHD are high, increasing with disease severity. A diagnostic tool to predict GVHD before the onset of clinical symptoms could save many lives. On the cellular level, GVHD occurs when T cells from the transplant attack the tissues of the host, after perceiving them to be foreign. T-cell proliferation occurs even before clinical symptoms appear. Glycogen synthase kinase (GSK)-3β is a protein which regulates proliferation in many cell types including T-cells. GSK-3β has never been directly connected with GVHD and we applied GSK-3β as a novel marker for GVHD prediction, seeking herein to determine whether GSK-3β can be utilized as a marker for the early diagnosis of GVHD.

METHODS

For the mouse model of acute GVHD, irradiated mice underwent allogeneic splenocyte transplantation and GSK-3β expression levels and phosphorylation states were monitored in harvested spleens by western blot. FACS analysis was used to measure the number of T cells within the harvested spleens.

RESULTS

Mice developed observable GVHD symptoms by day 5 post-transplantation, with severe symptoms on day 6 requiring mice to be killed for humane reasons. A significantly increased number of T cells in the allogeneic mice correlated with GVHD development. GSK-3β protein expression levels and phosphorylation levels were significantly lower in allogeneic (GVHD) mice compared with negative (untreated) and positive (syngeneic transplant; non-GVHD) controls over time.

CONCLUSION

GSK-3β was directly connected with the onset and progression of GVHD. Therefore, it can be utilized as a marker for GVHD diagnosis in animals and potentially in humans.

Foxp3 protein stability is regulated by cyclin-dependent kinase 2

Foxp3 is a transcription factor required for the development of regulatory T cells (Treg). Mice and humans with a loss of Foxp3 function suffer from uncontrolled autoimmunity and inflammatory disease. Expression of Foxp3 is necessary for the anti-inflammatory capacity of Treg, but whether Foxp3 activity is further subject to regulation by extracellular signals is unclear. The primary structure of Foxp3 contains four cyclin-dependent kinase (CDK) motifs (Ser/Thr-Pro) within the N-terminal repressor domain, and we show that CDK2 can partner with cyclin E to phosphorylate Foxp3 at these sites. Consistent with our previous demonstration that CDK2 negatively regulates Treg function, we find that mutation of the serine or threonine at each CDK motif to alanine (S/T→A) results in enhanced Foxp3 protein stability in CD4(+) T cells. T cells expressing the S/T→A mutant of Foxp3 showed enhanced induction (e.g. CD25) and repression (e.g. IL2) of canonical Foxp3-responsive genes, exhibited an increased capacity to suppress conventional T cell proliferation in vitro, and were highly effective at ameliorating colitis in an in vivo model of inflammatory bowel disease. These results indicate that CDK2 negatively regulates the stability and activity of Foxp3 and implicate CDK-coupled receptor signal transduction in the control of regulatory T cell function and stability.

Cyclin-dependent kinase inhibitor therapy for hematologic malignancies

INTRODUCTION

Cyclin-dependent kinases (CDKs) regulate cell cycle progression. Certain CDKs (e.g., CDK7, CDK9) also control cellular transcription. Consequently, CDKs represent attractive targets for anticancer drug development, as their aberrant expression is common in diverse malignancies, and CDK inhibition can trigger apoptosis. CDK inhibition may be particularly successful in hematologic malignancies, which are more sensitive to inhibition of cell cycling and apoptosis induction.

AREAS COVERED

A number of CDK inhibitors, ranging from pan-CDK inhibitors such as flavopiridol (alvocidib) to highly selective inhibitors of specific CDKs (e.g., CDK4/6), such as PD0332991, that are currently in various phases of development, are profiled in this review. Flavopiridol induces cell cycle arrest, and globally represses transcription via CDK9 inhibition. The latter may represent its major mechanism of action via down-regulation of multiple short-lived proteins. In early phase trials, flavopiridol has shown encouraging efficacy across a wide spectrum of hematologic malignancies. Early results with dinaciclib and PD0332991 also appear promising.

EXPERT OPINION

In general, the antitumor efficacy of CDK inhibitor monotherapy is modest, and rational combinations are being explored, including those involving other targeted agents. While selective CDK4/6 inhibition might be effective against certain malignancies, broad-spectrum CDK inhibition will likely be required for most cancers.

Cyclin-dependent kinase 2 controls peripheral immune tolerance

Adaptive immunity requires signals from both the TCR and the costimulatory molecule CD28. These receptors activate multiple signaling pathways, including the cyclin-dependent kinase (CDK) cascade, and antigenic signals in the absence of costimulation result in a tolerant state that is enforced by the CDK inhibitory protein p27kip1. We find that CDK2, the major target of p27kip1, is highly active in T cells that infiltrate and reject cardiac allografts. We used mice genetically deficient for CDK2 to determine whether CDK2 is required for T cell alloimmunity. Blockade of CD28 costimulation alone was unable to inhibit the rejection of cardiac allografts by wild-type recipients. However, targeting this pathway in CDK2-deficient recipients led to long-term allograft survival. CDK2-deficient CD4(+) T cells proliferated normally in response to stimulation in vitro and in vivo, however, genetic, short hairpin RNA, or small molecule-mediated antagonism of CDK2 resulted in decreased production of IL-2 and IFN-γ. In addition, surviving grafts from CDK2-deficient recipients showed increased infiltration of Foxp3(+) regulatory T cells (Treg), and Treg from CDK2-deficient mice exhibited increased suppressive activity in vitro and in an in vivo model of inflammatory bowel disease. These data suggest that p27kip1 promotes peripheral tolerance through its ability to inhibit CDK2, which otherwise acts to promote conventional T cell differentiation and restrict Treg function.

Roscovitine blocks leukocyte extravasation by inhibition of cyclin-dependent kinases 5 and 9

BACKGROUND AND PURPOSE

Roscovitine, a cyclin-dependent kinase (CDK) inhibitor that induces tumour cell death, is under evaluation as an anti-cancer drug. By triggering leukocyte apoptosis, roscovitine can also enhance the resolution of inflammation. Beyond death-inducing properties, we tested whether roscovitine affects leukocyte-endothelial cell interaction, a vital step in the onset of inflammation.

EXPERIMENTAL APPROACH

Leukocyte-endothelial cell interactions were evaluated in venules of mouse cremaster muscle, using intravital microscopy. In primary human endothelial cells, we studied the influence of roscovitine on adhesion molecules and on the nuclear factor-κB (NF-κB) pathway. A cellular kinome array, in vitro CDK profiling and RNAi methods were used to identify targets of roscovitine.

KEY RESULTS

In vivo, roscovitine attenuated the tumour necrosis factor-α (TNF-α)-induced leukocyte adherence to and transmigration through, the endothelium. In vitro, roscovitine strongly inhibited TNF-α-evoked expression of endothelial adhesion molecules (E-selectin, intercellular cell adhesion molecule, vascular cell adhesion molecule). Roscovitine blocked NF-κB-dependent gene transcription, but not the NF-κB activation cascade [inhibitor of κB (IκB) kinase activity, IκB-α degradation, p65 translocation]. Using a cellular kinome array and an in vitro CDK panel, we found that roscovitine inhibited protein kinase A, ribosomal S6 kinase and CDKs 2, 5, 7 and 9. Experiments using kinase inhibitors and siRNA showed that the decreased endothelial activation was due solely to blockade of CDK5 and CDK9 by roscovitine.

CONCLUSIONS AND IMPLICATIONS

Our study highlights a novel mode of action for roscovitine, preventing endothelial activation and leukocyte-endothelial cell interaction by inhibition of CDK5 and 9. This might expand its usage as a promising anti-inflammatory compound.

Treatment with a cyclin-dependent kinase inhibitor, seliciclib, is effective in reducing glomerular macrophage numbers and the severity of established experimental glomerulonephritis

AIM

The cyclin-dependent kinase inhibitor, seliciclib (R-roscovitine, CYC202), has anti-proliferative activity through its inhibition of cyclin-dependent kinase 2. We hypothesized that treatment with seliciclib would reduce glomerular macrophage numbers and glomerular crescent formation in experimental crescentic glomerulonephritis even when treatment is started after onset of disease.

METHOD

Nephrotoxic nephritis (NTN) was induced in Wistar Kyoto rats. In experiment 1, seliciclib (150 mg/kg per day) was given by oral gavage from 1 h before induction of NTN and continued to day 14. In experiment 2, treatment was started on day 4 of NTN and continued to day 14 in order to examine the effect of seliciclib in established glomerulonephritis.

RESULTS

In experiment 1, seliciclib reduced proteinuria (119.5 ± 13.9 vs 191.4 ± 18.8 mg/day, P < 0.01), serum creatinine (54.0 ± 3.0 vs 81.0 ± 2.5 µmol/L, P < 0.005) and glomerular crescent score (23.9 ± 2.1 vs 44.6 ± 2.2, P < 0.005) in comparison with controls. In experiment 2, seliciclib ameliorated established glomerulonephritis, with reduction in proteinuria (58 ± 16 vs 165 ± 13 mg/day, P < 0.005), serum creatinine (39 ± 3 vs 62 ± 5 µmol/L, P < 0.05), glomerular macrophage numbers (6.8 ± 2.5 vs 18.5 ± 1.2 ED1+ cells per glomerular cross section, P < 0.05), glomerular cell proliferation (1.2 ± 0.37 vs 4.2 ± 0.80 bromodeoxyuridine (BrdU)+ cells per glomerular section, P < 0.05) and crescent score (10.8 ± 1.6 vs 43.9 ± 1.4, P < 0.05), in comparison with the controls.

CONCLUSION

Seliciclib is effective in both prevention and treatment of established crescentic glomerulonephritis in Wistar Kyoto rats, in association with a reduction in the number of glomerular macrophages. We suggest that seliciclib, or other cyclin-dependent kinase inhibitors, may represent a novel therapeutic approach for patients with proliferative glomerulonephritis.

Twice switched at birth: cell cycle-independent roles of the "neuron-specific" cyclin-dependent kinase 5 (Cdk5) in non-neuronal cells

Cdk5 (cyclin-dependent kinase 5 or initially NCLK for neuronal CDC2-like kinase) was switched twice at its birth nearly twenty years ago: first it was thought to be cyclin-dependent, second it was assumed to be primarily of importance in neuronal cells-both turned out not to be the case. In this review we want to discuss issues of pharmacological inhibition, to highlight the versatile roles, and to summarize the growing evidence for the functional importance of Cdk5 in non-neuronal tissues, such as blood cells, tumor cells, epithelial cells, the vascular endothelium, testis, adipose and endocrine tissues. The organizing principles we follow are apoptosis/cell death, migration/motility, aspects of inflammation, and, finally, secretion/metabolism.

The Role of Pharmacokinetics and Pharmacodynamics in Early Drug Development with reference to the Cyclin-dependent Kinase (Cdk) Inhibitor - Roscovitine

Pharmacokinetics, pharmacodynamics and pharmacogenetics play an important role in drug discovery and contribute to treatment success. This is an essential issue in cancer treatment due to its high toxicity. During the last decade, cyclin-dependent kinase inhibitors were recognised as a new class of compounds that was introduced for the treatment of several diseases including cancer. Cyclin-dependent kinases (Cdks) play a key role in the regulation of cell cycle progression and ribonucleic acid transcription. Deregulation of Cdks has been associated with several malignancies, neurodegenerative disorders, viral and protozoa infections, glomerulonephritis and inflammatory diseases. (R)-roscovitine is a synthetic tri-substituted purine that inhibits selectively Cdk1, 2, 5, 7 and 9. Roscovitine has shown promising cytotoxicity in cell lines and tumor xenografts. In this paper, we present several aspects of pharmacokinetics (PK) and pharmacodynamics (PD) of roscovitine. We present also some of our investigations including bioanalysis, haematotoxicity, age dependent kinetics, PK and effects on Cdks in the brain. Unfavourable kinetic parameters in combination with poor distribution to the bone marrow compartment could explain the absence of myelosuppression in vivo despite the efficacy in vitro. Higher plasma and brain exposure and longer elimination half-life found in rat pups compared to adult rats may indicate that roscovitine can be a potential candidate for the treatment of brain tumours in children. Cdk5 inhibition and Erk1/2 activation that was detected in brain of rat pups may suggest the use of roscovitine in neurodegenerative diseases. Early pharmacokinetic/pharmacodynamic studies are important issues in drug discovery and may affect further development of promising drug candidates.