CDK/CK1 inhibitors roscovitine and CR8 downregulate amplified MYCN in neuroblastoma cells.

To understand the mechanisms of action of (R)-roscovitine and (S)-CR8, two related pharmacological inhibitors of cyclin-dependent kinases (CDKs), we applied a variety of '-omics' techniques to the human neuroblastoma SH-SY5Y and IMR32 cell lines: (1) kinase interaction assays, (2) affinity competition on immobilized broad-spectrum kinase inhibitors, (3) affinity chromatography on immobilized (R)-roscovitine and (S)-CR8, (4) whole genome transcriptomics analysis and specific quantitative PCR studies, (5) global quantitative proteomics approach and western blot analysis of selected proteins. Altogether, the results show that the major direct targets of these two molecules belong to the CDKs (1,2,5,7,9,12), DYRKs, CLKs and CK1s families. By inhibiting CDK7, CDK9 and CDK12, these inhibitors transiently reduce RNA polymerase 2 activity, which results in downregulation of a large set of genes. Global transcriptomics and proteomics analysis converge to a central role of MYC transcription factors downregulation. Indeed, CDK inhibitors trigger rapid and massive downregulation of MYCN expression in MYCN-amplified neuroblastoma cells as well as in nude mice xenografted IMR32 cells. Inhibition of casein kinase 1 may also contribute to the antitumoral activity of (R)-roscovitine and (S)-CR8. This dual mechanism of action may be crucial in the use of these kinase inhibitors for the treatment of MYC-dependent cancers, in particular neuroblastoma where MYCN amplification is a strong predictor factor for high-risk disease.

Uniaxial pressure setup for piezoresistance and magnetoresistance measurements in Heusler materials.

We report on a new uniaxial pressure experimental setup for electrical resistivity measurements working in a 77 K-500 K temperature range and in a magnetic field up to 8 T. Such a continuous uniaxial pressure device enables the study of the piezoresistance and the pressure induced change in electrical properties of bulk samples. Strong influence of uniaxial pressure on transport properties is shown for Ni-Co-Mn-In Heusler single crystal material. A shift of the martensite-austenite first order transformation temperature is measured with an applied uniaxial pressure leading to an electrical resistance changed by up to 120%.

Short-term cytogenetic assays of nine cancer chemotherapeutic drugs with metabolic activation.

Nine anticancer drugs were analyzed in cell cultures with respect to their cytogenetic effects with or without the addition of liver fraction S9 as an in vitro metabolic system. Among them, vincristine was the only drug which induced a significant accumulation of mitosis with or without S9. Adriamycin and neocarzinostatin were most potent in induction of chromosome breakage, but their clastogenic activities were reduced after metabolic conversion. On the other hand, cyclophosphamide had a dose-dependent activation of clastogenic effect by S9. The activity of bleomycin was enhanced by S9. S9 had no effect on the activities of actinomycin D, cytosine arabinoside, mitomycin C, and methotrexate. Vincristine showed no clastogenic property in our short-term assay system with or without S9. The activities of these anticancer drugs observed from our assay were compatible with those from other assay systems. The incorporation of S9 or other metabolic systems in routine clastogen assays should allow us to improve our understanding of the genetic toxicity of chemical agents.