Effects Of Cyclin-dependent Kinase Inhibitors Research Articles

The Association between Proton Pump Inhibitors and the Effectiveness of CDK Inhibitors in HR+/HER- Advanced Breast Cancer Patients: A Systematic Review and Meta-Analysis.

There have been many clinical questions regarding whether the use of proton pump inhibitors (PPIs) could deteriorate the effects of cyclin-dependent kinase inhibitors (CDKIs) in HR+/HER2- advanced breast cancer patients. We performed a systematic review and meta-analysis of this clinical question, including studies enrolling HR+/HER2- metastatic breast cancer patients treated with CDKIs (Palbociclib or Ribociclib) and reporting at least one comparative survival outcome, either overall survival (OS) or progression-free survival (PFS), between concomitant PPI users and non-users. Eight studies met the eligibility criteria, with a total of 2584 patients included (PPI users: 830, PPI non-users: 1754), demonstrating that concomitant PPI use was associated with significantly higher risks of all-cause mortality (HR = 2.03; 95% CI, 1.49 to 2.77; I2 = 0%) and disease progression (HR = 1.75; 95% CI, 1.26 to 2.43; I2 = 59%) in breast cancer patients taking Palbociclib. In contrast, there were no significant survival impacts of PPIs on Ribociclib (HR = 1.46; 95% CI, 0.91 to 2.34; I2 = 36%). Additionally, there was no significant difference in the risk associated with CDKI dose reduction due to drug toxicity (RR = 1.12; 95% CI, 0.97 to 1.29). Therefore, when HR+/HER2- advanced breast cancer patients require the use of PPIs, it may be reasonable to consider using Ribociclib.

The Individual Effects of Cyclin-Dependent Kinase Inhibitors on Head and Neck Cancer Cells-A Systematic Analysis.

Simple SummaryThis study examined the therapeutic potential of a combined therapy approach, based on clinical approved drugs (5-FU, Cisplatin, cetuximab) and cyclin-dependent kinase inhibitors (CDKi, dinaciclib, palbociclib, THZ1). We identified individual effects on head and neck squamous cell carcinoma cells, including induction of apoptosis/necrosis, and senescence as well as reduced invasiveness. Besides, we describe the relevance of the sequential timing of each combination partner to achieve synergistic effects. Another interesting finding of our study is the upregulation of immunologically relevant molecules on the tumor cell surface under certain CDKi-drug combinations. Here, dinaciclib and palboclicb had highest impact on immunogenicity, which even exceeded effects of the standard drugs. Finally, a therapeutic in vivo approach partially confirmed cell line-based results. Here, effective tumor growth control was seen when cisplatin was combined with dinaciclib. However, antitumoral effects were highly individual and nicely confirm the heterogeneity of this tumor entity.Cyclin-dependent kinase inhibitors (CDKi´s) display cytotoxic activity against different malignancies, including head and neck squamous cell carcinomas (HNSCC). By coordinating the DNA damage response, these substances may be combined with cytostatics to enhance cytotoxicity. Here, we investigated the influence of different CDKi´s (palbociclib, dinaciclib, THZ1) on two HNSCC cell lines in monotherapy and combination therapy with clinically-approved drugs (5-FU, Cisplatin, cetuximab). Apoptosis/necrosis, cell cycle, invasiveness, senescence, radiation-induced γ-H2AX DNA double-strand breaks, and effects on the actin filament were studied. Furthermore, the potential to increase tumor immunogenicity was assessed by analyzing Calreticulin translocation and immune relevant surface markers. Finally, an in vivo mouse model was used to analyze the effect of dinaciclib and Cisplatin combination therapy. Dinaciclib, palbociclib, and THZ1 displayed anti-neoplastic activity after low-dose treatment, while the two latter substances slightly enhanced radiosensitivity. Dinaciclib decelerated wound healing, decreased invasiveness, and induced MHC-I, accompanied by high amounts of surface-bound Calreticulin. Numbers of early and late apoptotic cells increased initially (24 h), while necrosis dominated afterward. Antitumoral effects of the selective CDKi palbociclib were weaker, but combinations with 5-FU potentiated effects of the monotherapy. Additionally, CDKi and CDKi/chemotherapy combinations induced MHC I, indicative of enhanced immunogenicity. The in vivo studies revealed a cell line-specific response with best tumor growth control in the combination approach. Global acting CDKi’s should be further investigated as targeting agents for HNSCC, either individually or in combination with selected drugs. The ability of dinaciclib to increase the immunogenicity of tumor cells renders this substance a particularly interesting candidate for immune-based oncological treatment regimens.

Effects of CDK inhibitors on the maturation, transcription, and MPF activity of porcine oocytes

In mammals, cyclin-dependent kinases (CDKs) are involved in regulating both the cell cycle and transcription. Although CDK1 is known to act as the kinase subunit of maturation-promoting factor (MPF), the roles of the other CDKs in mammalian oocyte maturation are not yet understood. Here, we show that inhibition of various CDKs by small molecule inhibitors has different effects on the maturation and transcriptional activity of pig oocytes in vitro. Inhibition of CDK1 did not significantly affect cumulus cell expansion, but its kinase activity was necessary for germinal vesicle breakdown (GVBD). The inhibitions of CDK2, CDK4, or CDK6 had no effect on cumulus expansion or GVBD. The catalytic activity of CDK7 was crucial for GVBD but less important for cumulus expansion, whereas inhibition of CDK9 severely blocked both cumulus cell expansion and GVBD. CDK1, -2, -4, and -6 appeared to be dispensable for nuclear transcription, as their inhibitions did not affect nascent RNA production in oocytes. However, inhibition of CDK7 or CDK9 dramatically decreased the transcriptional activity in oocytes. Finally, we found that the GVBD arrest triggered by CDK9 inhibition was not due to altered MPF activity, but rather the inhibition of transcription. Overall, our results show that CDK7 and CDK9 are important for the nuclear maturation and transcriptional activity of pig oocytes.

GSK3β inhibition is involved in the neuroprotective effects of cyclin-dependent kinase inhibitors in neurons

In the present study, we evaluated the effects of roscovitine (Rosco) and flavopiridol (Flavo), both of which are classified as cyclin-dependent kinase (CDK) inhibitors, on apoptosis induced by the inhibition of PI3K/AKT pathway in cerebellar granule neurons (CGNs). Our results demonstrate that both CDK inhibitors prevented apoptosis induced by LY294002 (LY), as also occurs with SB415286 (SB4), a selective GSK3β inhibitor. Our findings also indicate that these CDK inhibitors inhibit GSK3β, representing a potential pharmacological mechanism involved in their neuroprotective properties. Thus, the increased activity of GSK3β induced by LY294002 and detected by dephosphorylation at Ser9 was prevented by both compounds. Likewise, GSK3β activity was measured by a radioactivity assay, revealing that CDK inhibitors and SB415286 prevented the increase in GSK3β activity induced by PI3K inhibition. In addition, we analysed c-Jun, which is also a mediator of PI3K inhibition-induced apoptosis. However, neither of the CDK inhibitors nor SB415286 prevented the increase in c-Jun phosphorylation induced by PI3K inhibition. Therefore, our data identify GSK3β as a crucial mediator of CGN apoptosis induced by PI3K inhibition and indicate that the antiapoptotic effects of CDKs are mediated by the inhibition of this pharmacological target.

Cell cycle inhibitor enhances the resolution of HSV-1-induced proinflammatory response in murine microglial cells

Background and Purpose: Herpes simplex encephalitis remains one of the most devastating intracranial infections despite available antiviral treatment, with sequelae secondary to a persistent inflammatory response. Recently, cyclin-dependent kinases (CDKs) have been found to act as cellular targets for antiviral drugs. However, the pharmacological effects of CDK inhibitors on glial cell function in herpes simplex encephalitis have not been elucidated. The aim of this work was to determine the influence of olomoucine on microglial activation during the inflammatory response after herpes simplex virus 1(HSV-1) infection.Methods: Microglial cells were treated with various concentrations of olomoucine after HSV-1 infection. The expression change of cyclin D1 and myeloid cell leukemia 1 (Mcl-1) in microglia were detected by Western blot analysis. Flow cytometry was used to assess the apoptosis ratio of microglial cells among the groups of control, HSV-1 infected and olomoucine treated with or without zVAD-fmk. ELISA was adopted to analyse cytokines in the supernatant. We used semiquantitative reverse transcription polymerase chain reaction to detect HSV glycoprotein D gene.Results: The following are the results of this work: (1) olomoucine reduced HSV-1-induced proliferation associated cyclin D1 expression; (2) olomoucine also induced microglial cells apoptosis early at 24 hours post-infection and inhibited the release of proinflammatory cytokine and chemokine, including tumor necrosis factor α and monocyte chemoattractant protein 1; and (3) olomoucine-induced apoptosis was caspase-dependent, and it also reduced the antiapoptotic protein Mcl-1.Discussion: Our conclusion is that microglial cells are targets for olomoucine and that modulation of glial response and inflammation may be an appendant mechanism of CDK inhibitor-mediated neuroprotection in HSV-1 encephalitis.

The effects of cyclin-dependent kinase inhibitors on adipogenic differentiation of human mesenchymal stem cells

The molecular mechanisms that couple growth arrest and cell differentiation were examined during adipogenesis. Here, to understand the cyclin-dependent kinase inhibitor (CKI) genes involved in the progression of adipogenic differentiation, we examined changes in the protein and mRNA expression levels of CKI genes in vitro. During the onset of growth arrest associated with adipogenic differentiation, two independent families of CKI genes, p27Kip1 and p18INK4c, were significantly increased. The expressions of p27Kip1 and p18INK4c, regulated at the level of protein and mRNA accumulation, were directly coupled to adipogenic differentiation. This finding was supported by the inhibition of adipogenic differentiation caused by short interfering RNA (siRNA). In this study, we investigated the regulatory effects of transforming growth factor beta-1 (TGFβ-1) on CKI genes involved in adipogenic differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs). Only the up-regulation of p18INK4c during adipogenic differentiation, and not that of the p27Kip1 gene was prevented by treatment with TGFβ-1, one of the factors that inhibit adipogenesis in vitro. This finding indicates a close correlation between adipogenic differentiation and p18INK4c induction in hMSCs. Thus, these data demonstrate a role for the differentiation-dependent cascade expression of cyclin-dependent kinase inhibitors in regulating adipogenic differentiation, thereby providing a molecular mechanism that couples growth arrest and differentiation.

Accumulation of p53 and Reductions in XIAP Abundance Promote the Apoptosis of Prostate Cancer Cells

Toward the goal of developing effective treatments for prostate cancers, we examined the effects of cyclin-dependent kinase inhibitors on the survival of prostate cancer cells. We show that roscovitine, R-roscovitine, and CGP74514A (collectively referred to as CKIs) induce the apoptosis of LNCaP and LNCaP-Rf cells, both of which express wild-type p53. Apoptosis required caspase-9 and caspase-3 activity, and cytochrome c accumulated in the cytosol of CKI-treated cells. Amounts of p53 increased substantially in CKI-treated cells, whereas amounts of the endogenous caspase inhibitor XIAP decreased. CKIs did not appreciably induce the apoptosis of LNCaP cells treated with pifithrin-alpha, which prevents p53 accumulation, or of prostate cancer cells that lack p53 function (PC3 and DU145). Ectopic expression of p53 in PC3 cells for 44 hours did not reduce XIAP abundance or induce apoptosis. However, p53-expressing PC3 cells readily apoptosed when exposed to CKIs or when depleted of XIAP by RNA interference. These findings show that CKIs induce the mitochondria-mediated apoptosis of prostate cancer cells by a dual mechanism: p53 accumulation and XIAP depletion. They suggest that these events in combination may prove useful in the treatment of advanced prostate cancers.

The expression of retinoblastoma and Sp1 is increased by low concentrations of cyclin-dependent kinase inhibitors.

We examined the effect of suboptimal concentrations of cyclin-dependent kinase inhibitors, which do not interfere with cell proliferation, on retinoblastoma expression in hamster (Chinese hamster ovary K1) and human (K562 and HeLa) cells. To achieve this, we used the chemical inhibitors roscovitine and olomoucine (which inhibit CDK2 preferentially), UCN-01 (which also inhibits CDK4/6) and p21 (as an intrinsic inhibitor). All chemical inhibitors and overexpression of p21 strongly induced retinoblastoma protein expression. UCN-01-mediated retinoblastoma expression was caused by an increase in both the levels of retinoblastoma mRNA and the stability of the protein. The expression of the transcription factor Sp1, a retinoblastoma-interacting protein, was also enhanced by all the cyclin-dependent kinase inhibitors tested. However, Sp1 expression was caused by an increase in the levels of Sp1 mRNA without modification in the stability of the protein. By using luciferase experiments, the transcriptional activation of both retinoblastoma and Sp1 promoters by UCN-01 was confirmed. Bisindolylmaleimide I, at concentrations causing a similar or higher inhibition of protein kinase C than UCN-01, provoked a lower activation of retinoblastoma and Sp1 expression. Finally, the effects of cyclin-dependent kinase inhibitors on dihydrofolate reductase gene expression were evaluated. Treatment with UCN-01 increased cellular dihydrofolate reductase mRNA levels, and dihydrofolate reductase enzymatic activity was enhanced by UCN-01, roscovitine, olomoucine and p21, in transient transfection experiments. These results support a mechanism for the self-regulation of retinoblastoma expression, and point to the need to establish the appropriate dose of cyclin-dependent kinase inhibitors as antiproliferative agents in anticancer treatments.

Effects of cyclin-dependent kinase inhibitors on transcription and ocular circadian rhythm of Aplysia.

Cyclin-dependent kinases (CDKs) mediate cell-cycle phase transitions. Recently, CDKs have been associated with non-cell-cycle roles such as DNA repair, transcription, and phosphate metabolism in yeast. The cyclical processes, circadian rhythms and the eukaryotic cell cycle, are similar in many respects. It is possible that a kinase like CDK is involved in the control of circadian rhythms. In this study, the effects of CDK inhibitors (olomoucine, roscovitine, and butyrolactone I) on the Aplysia ocular circadian rhythm were investigated. Continuous treatments with olomoucine (10 microM) lengthened the free-running period of the rhythm, and pulse treatments of olomoucine (6 h, 100 microM) delayed the rhythm. The effects of olomoucine on the rhythm were qualitatively similar to those of a reversible inhibitor of transcription, 5,6-dichloro-beta-1-ribobenzimidazole. Subsequently, olomoucine was found to inhibit RNA synthesis in the eye of Aplysia and Bulla. All of the other CDK inhibitors used in this study also inhibited transcription in the eye of Aplysia, and their effects on transcription correlated with their effects on the circadian rhythm. This study adds substantial evidence to that previously obtained by using 5,6-dichloro-beta-1-ribobenzimidazole for a role of transcription in the mechanism responsible for circadian rhythmicity in the eye of Aplysia. Also, these results indicate that caution is warranted in interpreting results obtained by using CDK inhibitors, because these drugs appear to inhibit transcription as well as CDKs.