Inhibition of cellular proliferation by drug targeting of cyclin-dependent kinases

Influence of Pi3-K and PKC activity on 99mTc-(V)-DMSA uptake: correlation with tumour aggressiveness in an in vitro malignant glioblastoma cell line model

PURPOSE

Intensive proliferation and a high degree of migration and invasion are characteristic features of malignant glioblastomas, associated with a poor prognosis. Phosphatidylinositol-3-kinase (Pi3-K) and protein kinase C (PKC) are two phosphorylated proteins involved in glioblastoma cell progression. Phosphorylated focal adhesion protein kinase (FAK) has also been reported to be involved in tumour progression. In a recent study, we demonstrated a correlation between phosphorylated FAK, proliferation rate and 99mTc-(V)-dimercaptosuccinate [(V)-DMSA] uptake. We hypothesised that 99mTc-(V)-DMSA could be a potential imaging agent to evaluate glioblastoma aggressiveness. The aim of the present study was to assess the relationship between 99mTc-(V)-DMSA incorporation rate and modulation of Pi3-K and PKC activity.

METHODS

Proliferation, migration and invasion capacities in the presence of protein kinase modulators-staurosporine (PKC inhibitor), 4-phorbol 12-myristate 13-acetate (PMA; PKC activator) and LY294002 (Pi3-K inhibitor)-were correlated with 99mTc-(V)-DMSA cell accumulation in an in vitro model of several malignant glioma cells: G111 (grade II), U-87-MG (grade III) and G152 (grade IV).

RESULTS

In all cell lines tested, LY294002 and staurosporine treatment inhibited cell proliferation, migration and invasion. In contrast, treatment with PMA stimulated tumour aggressiveness. 99mTc-(V)-DMSA uptake was strongly correlated with the % of cellular proliferation (r=0.8462) and the % of cellular migration (r=0.9081), and to a lesser extent with the % of cellular invasion (r=0.7761).

CONCLUSION

Our results clearly demonstrated that 99mTc-(V)-DMSA reflects Pi3-K and PKC activity and is correlated with tumour aggressiveness. 99mTc-(V)-DMSA could be a reliable in vivo marker providing additional information on the biological status of malignant glioblastoma.

Imidazole-4,5-dicarboxamide derivatives with antiproliferative activity against HL-60 cells

A series of N,N'-disubstituted imidazole-4,5-dicarboxamides (I45DCs) were prepared and tested in order to determine their antiproliferative activity against HL-60 cells. The design of the I45DCs was based in part on the structures of trisubstituted purines complexed with cyclin dependent kinase 2 (cdk2), a protein important in regulating the G1/S transition in the cell cycle, and the intramolecular hydrogen bond in I45DCs that predisposes the conformation to one that mimics substituted adenosines. A majority of the I45DCs in this study inhibit proliferation of HL-60 cells as measured by an MTS mitochondrial functional assay with IC50's in the 2.5-25 microM range. The SAR of the I45DCs is consistent with anticipated hydrogen bonding interactions in the ATP-binding site of cdk2. Thus, the I45DCs represent a useful scaffold for anticancer lead discovery that is both readily accessible and easily diversified.

Nuclear transcription factors in the hippocampus

In the mammalian hippocampus, there is a trisynaptic loop that has been often referred to in studies on learning and memory mechanisms and their physiological correlate, the long-term potentiation (LTP). The three sets of synapses are formed by the fibers of perforant pathway terminating on granule cells and by the mossy fibers and Schaeffer collaterals making connections with the pyramidal cells. Each of the three types of synapses can develop LTP. LTP is accompanied by changes in gene expression and it is the nuclear transcription, involving specific transcription factors, that is the starting point for the series of biological amplifications and consolidations both necessary for such sustained changes. The transcription factors are proteins that control gene expression, development and functional formation in every eukaryotic cell. Two categories of transcription factors have been defined to date: general factors that comprise at least 20 proteins to form multiple preinitiation complex at the TATA box (TATA rich sequence) or regulatory factors that bind to promoter or enhancer regions at specific sites on the DNA close to, or distant from, the TATA box. Transcription factors have been divided into five different major classes according to unique protein motifs. These include basic domain, zinc-finger, helix-turn-helix, beta-Scaffold factors with minor groove contacts and other transcription factors not specifically classified. Much evidence has been accumulating in favor of the participation of several transcription factors in the consolidation of memory in the mammalian hippocampus following a spatial memory task. It is, therefore, of great importance that the involvement of transcription factors in de novo protein synthesis relevant to the synaptic mechanisms that mediate the formation of long-term memory should be summarized and discussed. No specific correlation between transduction of extracellular signals and expression of nuclear transcription factors, however, has been demonstrated to date.

Role of cyclins in epithelial response to oxidants

Oxidants are involved in a large variety of pulmonary diseases. Among the various cell types that compose the respiratory system, the epithelial cells appear to be a major target for oxidative stress. When cells are exposed to DNA-damaging agents such as oxidants, a feedback control is activated that acts as a brake on the cell cycle to inhibit entry into the S phase until DNA repair is completed. Progression through the G1 phase and the G1-S transition involves sequential assembly and activation of key regulators of the cell cycle machinery, the cyclin-dependent kinases (CDKs). Activity of the CDKs is regulated by several mechanisms, which include the CDK inhibitors (CKIs). The CKI p21(CIP1) appears to play an important role in the response of epithelial cells to oxidants.