The role of CDK8 in mesenchymal stem cells in controlling osteoclastogenesis and bone homeostasis.

Bone marrow mesenchymal stem cells (MSCs) are critical regulators of postnatal bone homeostasis. Osteoporosis is characterized by bone volume and strength deterioration, partly due to MSC dysfunction. Cyclin-dependent kinase 8 (CDK8) belongs to the transcription-related CDK family. Here, CDK8 in MSCs was identified as important for bone homeostasis. CDK8 level was increased in aged MSCs along with the association with aging-related signals. Mouse genetic studies revealed that CDK8 in MSCs plays a crucial role in bone resorption and homeostasis. Mechanistically, CDK8 in MSCs extrinsically controls osteoclastogenesis through the signal transducer and transcription 1 (STAT1)-receptor activator of the nuclear factor κ Β ligand (RANKL) axis. Moreover, aged MSCs have high osteoclastogenesis-supporting activity, partly through a CDK8-dependent manner. Finally, pharmacological inhibition of CDK8 effectively repressed MSC-dependent osteoclastogenesis and prevented ovariectomy-induced osteoclastic activation and bone loss. These findings highlight that the CDK8-STAT1-RANKL axis in MSCs could play a crucial role in bone resorption and homeostasis.

Pharmacokinetic model analysis of interaction between phenytoin and capecitabine.

OBJECTIVE: Recent reports have shbown an increase in serum phenytoin levels resulting in phenytoin toxicity after initiation of luoropyrimidine chemotherapy. To prevent phenytoin intoxication, phenytoin dosage must be adjusted. We sought to develop a pharmacokinetic model of the interaction between phenytoin and capecitabine. METHODS: We developed the phenytoin-capecitabine interaction model on the assumption that fluorouracil (5-FU) inhibits cytochrome P450 (CYP) 2C9 synthesis in a concentration- dependent manner. The plasma 5-FU concentration after oral administration of capecitabine was estimated using a conventional compartment model. Nonlinear pharmacokinetics of phenytoin was modeled by incorporating the Michaelis-Menten equation to represent the saturation of phenytoin metabolism. The resulting model was fitted to data from our previously-reported cases. RESULTS: The developed phenytoincapecitabine interaction model successfully described the profiles of serum phenytoin concentration in patients who received phenytoin and capecitabine concomitantly. The 50% inhibitory 5-FU concentration for CYP2C9 synthesis and the degradation rate constant of CYP2C9 were estimated to be 0.00310 ng/mL and 0.0768 day-1, respectively. This model and these parameters allow us to predict the appropriate phenytoin dosage schedule when capecitabine is administered concomitantly. CONCLUSIONS: This newly-developed model accurately describes changes in phenytoin concentration during concomitant capecitabine chemotherapy, and it may be clinically useful for predicting appropriate phenytoin dosage adjustments for maintaining serum phenytoin levels within the therapeutic range.

[A case of toxicity caused by drug interaction between capecitabine and phenytoin in patient with colorectal cancer].

We present a case of toxicity caused by a drug interaction between capecitabine and phenytoin (PHT). The drug combination elevated the plasma level of PHT in a patient on chemotherapy with capecitabine for colorectal cancer. Our patient was a 44-year-old woman diagnosed with epilepsy in her 20's, being treated with valproic acid (VPA) and PHT. Adjuvant chemotherapy with capecitabine began following surgery for colorectal cancer. Seven weeks later, she developed numbness, dizziness, dysarthria and difficulty walking, and was hospitalized for investigation. Her serum PHT level was elevated at 35. 1 µg/ mL. This case suggests that when capecitabine and PHT are coadministered, PHT levels should be monitored frequently, and that PHT dosage should be adjusted accordingly if it cannot be replaced by an alternative anticonvulsant.

Synthesis and biological activity of optically active NCL-1, a lysine-specific demethylase 1 selective inhibitor.

Optically active (1S,2R)-NCL-1 and (1R,2S)-NCL-1 were synthesized and evaluated for their lysine-specific demethylase 1 inhibitory activity and cell growth inhibitory activity. In enzyme assays, the (1S,2R)-isomer was approximately four times more potent than the (1R,2S)-isomer. In cell growth inhibition assays, the two isomers showed similar activity in HEK293 cells and SH-SY5Y cells, whereas the (1S,2R)-isomer showed approximately four times more potent activity than the (1R,2S)-isomer in HeLa cells.

Identification of cell-active lysine specific demethylase 1-selective inhibitors.

Lysine specific demethylase 1 (LSD1) plays a key role in the regulation of gene expression by removing the methyl groups from methylated Lys4 of histone H3 (H3K4). Here we report the identification of the first small-molecule LSD1-selective inhibitors. These inhibitors show in vivo H3K4-methylating activity and antiproliferative activity and should be useful as lead structures for anticancer drugs and as tools for studying the biological roles of LSD1.

Inhibition of human sirtuins by in situ generation of an acetylated lysine-ADP-ribose conjugate.

A new type of small-molecular sirtuin inhibitor was designed on the basis of the proposed catalytic mechanism for deacetylation of acetylated lysine substrates by sirtuins. Among the compounds thus designed and synthesized, we found that 2k, which contains an ethoxycarbonyl group at the alpha position to the acetamide of acetylated lysine substrate analogue 1, showed potent inhibitory activity in an in vitro assay using recombinant SIRT1, with high selectivity over SIRT2 and SIRT3. Mechanistic study by means of kinetic analysis, mass spectroscopy, and computation indicated that the enol form of compound 2k nucleophilically attacks NAD(+) in the active site of SIRTs to afford the stable compound 2k-ADP-ribose conjugate 5, leading to inhibition of the enzyme activity. Compound 2k also caused a dose-dependent increase of p53 acetylation in human colon cancer HCT116 cells, indicating inhibition of SIRT1 in the cells. These results have implications for the development of selective sirtuin inhibitors by means of mechanism-based drug design.

Insulinomimetic zinc(II) complexes with natural products: in vitro evaluation and blood glucose lowering effect in KK-Ay mice with type 2 diabetes mellitus.

In vitro insulinomimetic activities of Zn(II) complexes with three natural products, betaine, L-lactic acid, and D-(-)-quinic acid (qui), were found in rat adipocytes treated with epinephrine in terms of the inhibition of free fatty acid release. Based on the results, the blood glucose lowering effect in KK-A(y) mice with type 2 diabetes mellitus was observed by daily i.p. injections of a monomeric zinc(II) complex, Zn(qui)(2), for 13 d.