Early inhibition of DNA synthesis in the developing rat cerebral cortex by the purine analogues olomoucine and roscovitine

Roscovitine has anti-proliferative and pro-apoptotic effects on glioblastoma cell lines: A pilot study

Purine analogue roscovitine, a cyclin-dependent kinase (CDK) inhibitor, has shown strong anti-proliferative and pro-apoptotic effects in solid and hematologic cancers such as non small-cell lung cancer and lymphomas. It targets CDK2, 7 and 9 preferentially, which are also overexpressed in glioblastoma. Τherefore, the biological effects of roscovitine in glioblastoma cell lines were investigated. Glioblastoma A172 and G28 cell lines were incubated with serial concentrations of roscovitine for 24-120 h. Proliferation was measured using the xCELLigence Real-Time Cell Analyzer, an impedance‑based cell viability system. Cell cycle distribution was assessed by flow cytometry and gene expression was quantified by quantitative RT-PCR and western blot analysis. Roscovitine exhibited a clear dose-dependent anti‑proliferative and pro‑apoptotic effect in the A172 cell line, while G28 cells showed a anti-proliferative effect only at 100 µM. The results of the flow cytometric (FACS) analysis revealed a dose-dependent increase of the G2/M and sub-G1 fractions in A172 cells, while G28 cells responded with an elevated sub-G1 fraction only at the highest concentration. Roscovitine led to a dose‑dependent decrease of transcripts of p53, CDK 7 and cyclins A and E and an increase of >4-fold of p21 in A172 cells. In G28 cells, a dose‑dependent induction of CDK2, p21 and cyclin D was observed between 10 and 50 µM roscovitine after 72 h, however, at the highest concentration of 100 µM, all investigated genes were downregulated. Roscovitine exerted clear dose-dependent anti-proliferative and pro-apoptotic effects in A172 cells and less distinct effects on G28 cells. In A172 cells, roscovitine led to G2/M arrest and induced apoptosis, an effect accompanied by induced p21 and a reduced expression of CDK2, 7 and 9 and cyclins A and E. These effects requre further studies on a larger scale to confirm whether roscovitine can be used as a therapeutic agent against glioblastoma.

CDK INHIBITORY NUCLEOSIDE ANALOGS PREVENT TRANSCRIPTION FROM VIRAL GENOMES

Targeting viral proteins has lead to many successful antivirals. Yet, such antivirals rapidly select for resistance, tend to be active against only a few related viruses, and require previous characterization of the target proteins. Alternatively, antivirals may be targeted to cellular proteins. Replication of many viruses requires cellular CDKs and pharmacological CDK inhibitors (PCIs), such as the purine-based roscovitine (Rosco), are proving safe in clinical trials against cancer. Rosco inhibits replication of wild-type or (multi-)drug resistant HIV, HCMV, EBV, VZV, and HSV-1 and 2. However, the antiviral mechanisms of purine PCIs remain unknown. Our objective is to characterize these mechanisms using HSV as a model We have shown that Rosco prevents initiation of transcription from viral, but not cellular, genomes. This inhibition is promoter independent, but genome dependent, and requires no viral proteins. This is a novel antiviral mechanism and a previously unknown activity for purine PCIs.

Strong inhibition of replicative DNA synthesis in the developing rat cerebral cortex and glioma cells by roscovitine

The effects of the cyclin-dependent kinase inhibitors roscovitine and olomoucine on DNA synthesis rate during normal rat brain development were studied by using short time (90 min) incubation. Both purine analogues at 100 microM concentration decreased the DNA synthesis of rat cerebral cortex in an age-dependent manner. The maximum inhibitory effect (approximately 90% for roscovitine, approximately 60% for olomoucine) occurred in rats of 2-13 days postnatal age. In adult rats (> 60 days postnatal age), the effect of both purine analogues was low. Roscovitine even at 200 microM concentration did not inhibit the fraction of DNA synthesis insensitive to hydroxyurea (unscheduled DNA synthesis (UDS)). In addition, in the RG2 rat glioma model, roscovitine produced a strong inhibition of DNA synthesis in glioma cells when compared to adult normal tissue. Since in adult rat brain more than 60% of DNA synthesis is related to DNA repair, usually measured as UDS, our results indicate that roscovitine strongly blocks ongoing DNA synthesis connected with replicative processes.

Tissue distribution, pharmacokinetics and identification of roscovitine metabolites in rat

The pharmacokinetics, biodistribution and the metabolic pathway of roscovitine were investigated in Sprague-Dawley rats after a single intravenous dose of 25 mg/kg. Blood, lungs, kidney, liver, testis, adipose tissue, spleen and brain were removed at different time-points. Plasma and tissue samples were analyzed using high performance liquid chromatography. The metabolites were identified using liquid chromatography/tandem mass spectrometry and nuclear magnetic resonance spectroscopy. Roscovitine (MW=354) was cleared rapidly from circulation and highly distributed to the tissues. The elimination half-life of roscovitine in plasma and tissues was short (<30 min). A major metabolite (M1) was observed mainly in plasma and in lower levels in all other tissues. M1 was identified as conversion of the hydroxyl-group at C2 to carboxylic acid (MW=368). A second metabolite (M2) was observed mainly in liver and kidney and identified as a hydroxylation product of the C8 of the purine-ring (MW=370). A third metabolite (M3) was found in several organs and corresponded to N-dealkylation of the N9-isopropyl side-chain (MW=312). Roscovitine concentrations in the brain were 30% of that observed in plasma, however no metabolites were detected in brain. In this investigation, three major metabolites of roscovitine were isolated and identified. Also, it was shown that roscovitine eliminates rapidly from both blood and tissues.

Analysis of roscovitine using novel high performance liquid chromatography and UV-detection method: pharmacokinetics of roscovitine in rat

Roscovitine (2-(R)-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine, is a potent and selective inhibitor of cyclin-dependent kinases (CDKs). It inhibits cdc2, cdk2, cdk5 and erk 1 and 2 by competing for the ATP binding domain of the kinases. It inhibits cell proliferation; induces DNA fragmentation and causes cell cycle arrest in S phase. Its stability and toxicity are not fully known. A liquid chromatography method was developed to measure roscovitine in human and rat plasma. The lower limit of quantitation (LLOQ) was 100ng/ml; the intra- and inter-day precision was below 10% at all control levels. Likewise, the accuracy between and within days was lower than 6% at all levels. The drug was stable at room temperature. Twenty-four hours at room temperature has result in a decrease of only 9% of the drug. The recovery of roscovitine from plasma was 84% at 750ng/ml. The present method was used to study the pharmacokinetics of the drug in a rat model. The present investigation, to the authors' knowledge, is the first analytical method reported and the first pharmacokinetics investigation of roscovitine in rat. Roscovitine was administered as a bolus injection (25mg/kg body weight). The pharmacokinetic analysis showed that roscovitine is fitted to a two-compartment open-mode with a biphasic elimination half-life (6 and 26min, respectively). The distribution volume was determined to 3.5l/kg and the clearance (Cl) was 29.5ml/min.

In vitro and in vivo antitumor properties of the cyclin dependent kinase inhibitor CYC202 (R-roscovitine)

CDK2 inhibitors have been proposed as effective anti-cancer therapeutics. We show here that CYC202 (R-roscovitine) is a potent inhibitor of recombinant CDK2/cyclin E kinase activity (IC(50) = 0.10 microM) with an average cytotoxic IC(50) of 15.2 microM in a panel of 19 human tumour cell lines, and we also demonstrate selectivity for rapidly proliferating cells over non-proliferating cells. A study of the cell cycle effects of CYC202 in Lovo colorectal carcinoma cells showed that the major effect was not the predicted arrest in one part of the cycle, but rather an induction of cell death from all compartments of the cell cycle. The maximum tolerated dose given intravenously to mice was in excess of 20 mg/kg. Doses up to 2,000 mg/kg were tolerated when administered orally in mice. Following repeated intraperitoneal administration (3 times daily for 5 days) of 100 mg/kg to nude mice bearing the Lovo human colorectal tumour, CYC202 induced a significant antitumour effect with a 45% reduction in tumour growth compared to controls. A second experiment using the human uterine xenograft MESSA-DX5 treated with orally administered CYC202 (500 mg/kg 3 times daily for 4 days) also exhibited a significant reduction in the rate of growth of the tumour (62%). These data, showing enzyme and cellular potency together with antitumour activity, confirm the potential of CDK2 inhibitors such as CYC202 as anticancer drugs.

Roscovitine inhibits ongoing DNA synthesis in human cervical cancer

The effect of roscovitine, a purine analogue and cyclin dependent kinase inhibitor, on DNA synthesis rate in tissue mini-units obtained from human cervical cancers was investigated. Roscovitine (100 microM) gave a DNA synthesis rate inhibition by 61% (P<0.0001; range 23-93%) within 30 min of incubation. This inhibitory effect was concentration-dependent. The results suggest that the inhibition of tumor DNA synthesis rate is due to a direct effect on the DNA synthesis machinery via presently unknown mechanisms. In addition, the potential application of CDKs inhibitors as preventive agents is discussed.

Synthesis and in vitro evaluation of novel 2,6,9-trisubstituted purines acting as cyclin-dependent kinase inhibitors

Novel C-2, C-6, N-9 trisubstituted purines derived from the olomoucine/roscovitine lead structure were synthesized and evaluated for their ability to inhibit starfish oocyte CDK1/cyclin B, neuronal CDK5/p35 and erk1 kinases in purified extracts. Structure activity relationship studies showed that increased steric bulk at N-9 reduces the inhibitory potential whereas substitution of the aminoethanol C-2 side chain by various groups of different size (methyl, propyl, butyl, phenyl, benzyl) only slightly decreases the activity when compared to (R)-roscovitine. Optimal inhibitory activity against CDK5, CDK1 and CDK2, with IC50 values of 0.16, 0.45 and 0.65 microM, respectively, was obtained with compound 21 containing a (2R)-pyrrolidin-2-yl-methanol substituent at the C-2 and a 3-iodobenzylamino group at the C-6 of the purine. Compound 21 proved cytotoxic against human tumor HeLa cells (LD50-6.7 microM versus 42.7 microM for olomoucine, 24-h contact). Furthermore, unlike olomoucine, compound 21 was effective upon short exposure (LD50= 25.3 microM, 2-h contact). The available data suggest that the affinity for CDKs and the cytotoxic potential of the drugs are inter-related. However, no straightforward cell cycle phase specificity of the cytotoxic response to 21 was observed in synchronized HeLa cells. With the noticeable exception of pronounced lengthening of the S-phase transit by 21 applied during early-S in synchronized HeLa cells, and in striking contrast with earlier reports on studies using plant or echinoderm cells. olomoucilnc and compound 21 were unable to reversibly arrest cell cycle progression in asynchronous growing HeLa cells. Some irreversible hlock in GI and G2 phase occurred at high olomoucine concentration, correlated with induced cell death. Moreover, chmronic exposure to lethal doses of compound 21 resulted in massive nuclear fragmentation, evocative of mitotic catastrophe with minour amounts of apoptosis only. It was also found that olomoucine and compound 21 reversibly block the intracellular uptake of nuicleosides with high efficiency.

Transient hypoxia may lead to neuronal proliferation in the developing mammalian brain: from apoptosis to cell cycle completion

Cerebral hypoxia/ischemia was shown to induce delayed, apoptotic neuronal death occurring through biochemical pathways potentially sharing common events with cell proliferation. This study was designed to test the hypothesis that a sublethal hypoxia may promote mitotic activity in developing central neurons. After six days in vitro, cultured neurons from the forebrain of 14-day-old rat embryos were exposed to hypoxia (95% N2/5% CO2) for 3 h and re-oxygenated for up to 96 h. Controls were kept in normoxia. As a function of time, cell viability was measured by diphenyltetrazolium bromide, and rates of DNA and protein synthesis were monitored using [3H]thymidine and [3H]leucine, respectively. Morphological features of apoptosis, necrosis and mitosis were scored under fluorescence microscopy after nuclear staining with 4,6-diamidino-2-phenylindole, and the expression profile of proliferating cell nuclear antigen, a cofactor for DNA polymerase, was analysed by immunohistochemistry. Data were compared to those obtained after transient hypoxia for 6 h followed by re-oxygenation for 96 h and which was shown to induce apoptosis. Whereas a 6-h insult reduced cell viability, with 23% of the neurons exhibiting apoptosis by the end of re-oxygenation, a 3-h hypoxia led to a cycloheximide-sensitive increase in the final number of living neurons compared to controls (13%, P < 0.01), with no signs of apoptosis, significantly increased thymidine incorporation into acid-precipitable fraction, and persistent over-expression of proliferating cell nuclear antigen. Accordingly, final score of mitotic nuclei was significantly enhanced. In addition, the cell cycle inhibitor olomoucine (50 microM) prevented apoptosis consecutive to a 6-h hypoxia, but impaired the stimulatory effects of a 3-h insult. These findings support the conclusion that some neurons exposed to sublethal hypoxia may dodge apoptotic death by fully achieving the cell cycle.