Selective inhibition of CDK4/6: A safe and effective strategy for developing anticancer drugs.

The sustained cell proliferation resulting from dysregulation of the cell cycle and activation of cyclin-dependent kinases (CDKs) is a hallmark of cancer. The inhibition of CDKs is a highly promising and attractive strategy for the development of anticancer drugs. In particular, third-generation CDK inhibitors can selectively inhibit CDK4/6 and regulate the cell cycle by suppressing the G1 to S phase transition, exhibiting a perfect balance between anticancer efficacy and general toxicity. To date, three selective CDK4/6 inhibitors have received approval from the U.S. Food and Drug Administration (FDA), and 15 CDK4/6 inhibitors are in clinical trials for the treatment of cancers. In this perspective, we discuss the crucial roles of CDK4/6 in regulating the cell cycle and cancer cells, analyze the rationale for selectively inhibiting CDK4/6 for cancer treatment, review the latest advances in highly selective CDK4/6 inhibitors with different chemical scaffolds, explain the mechanisms associated with CDK4/6 inhibitor resistance and describe solutions to overcome this issue, and briefly introduce proteolysis targeting chimera (PROTAC), a new and revolutionary technique used to degrade CDK4/6.

Rapid membrane effect of estrogens on stimulation of corticotropin-releasing hormone.

BACKGROUND: Classic nuclear-initiated estrogen signaling stimulates corticotropin-releasing hormone (CRH) gene expression as a transcription factor. However, the possible mechanism by which membrane-initiated estrogen signaling (MIES) influences CRH expression remains unclear. There are indications that MIES may upregulate nitric oxide (NO) production through the phosphatidylinositol 3-hydroxy kinase (PI3K) and potentially through the mitogen-activated protein kinase (MAPK) pathway. OBJECTIVES: We investigated the effect of MIES-mediated kinase pathways on CRH expression with or without NO synthesis. METHOD: In SK-N-SH cell culture, estradiol-bovine serum albumin (E2-BSA) was used as the specific membrane estrogen receptor activator, with a specific NO donor, and/or inhibitors for NO synthase (NOS), PI3K, MAPK, protein kinase A (PKA), and protein kinase C (PKC). RESULTS: E2-BSA significantly increased NO and CRH levels in the medium and NOS1-mRNA levels in the cells. In addition, NO donor up-regulated CRH expression, while NOS-inhibitor down-regulated it. When the inhibitor of MAPK and/or the inhibitor of PI3K was added to the medium, only the latter appeared to significantly block the stimulating effect of E2-BSA on NO synthesis, and this was accompanied by an increased CRH expression in the medium. We further studied the effect of the MIES-PKC-mediated pathway on CRH expression, with or without NOS-inhibitor, while the MIES-PKA(-PI3K) pathway served as a control. We found that MIES-PKC upregulated CRH expression independent of NO synthesis. CONCLUSION: MIES can efficiently upregulate CRH expression via various intracellular kinase pathways and may thus be a crucial component in the stress response.

Silibinin ameliorates hepatic lipid accumulation and oxidative stress in mice with non-alcoholic steatohepatitis by regulating CFLAR-JNK pathway.

Non-alcoholic steatohepatitis (NASH) is a chronic metabolic syndrome and the CFLAR-JNK pathway can reverse the process of NASH. Although silibinin is used for the treatment of NASH in clinical, its effect on CFLAR-JNK pathway in NASH remains unclear. This study aimed to investigate the effect of silibinin on CFLAR-JNK pathway in NASH models both in vivo and in vitro. The in vivo study was performed using male C57BL/6 mice fed with methionine- choline-deficient diet and simultaneously treated with silibinin for 6 weeks. The in vitro study was performed by using mouse NCTC-1469 cells which were respectively pretreated with oleic acid plus palmitic acid, and adenovirus-down Cflar for 24 h, then treated with silibinin for 24 h. After the drug treatment, the key indicators involved in CFLAR-JNK pathway including hepatic injury, lipid metabolism and oxidative stress were determined. Silibinin significantly activated CFLAR and inhibited the phosphorylation of JNK, up-regulated the mRNA expression of Pparα, Fabp5, Cpt1α, Acox, Scd-1, Gpat and Mttp, reduced the activities of serum ALT and AST and the contents of hepatic TG, TC and MDA, increased the expression of NRF2 and the activities of CAT, GSH-Px and HO-1, and decreased the activities and expression of CYP2E1 and CYP4A in vivo. These effects were confirmed by the in vitro experiments. Silibinin prevented NASH by regulating CFLAR-JNK pathway, and thereby on one hand promoting the ß-oxidation and efflux of fatty acids in liver to relieve lipid accumulation, and on the other hand inducing antioxidase activity (CAT, GSH-Px and HO-1) and inhibiting pro-oxidase activity (CYP2E1 and CYP4A) to relieve oxidative stress.

MicroRNA-126 Targeting PIK3R2 Inhibits NSCLC A549 Cell Proliferation, Migration, and Invasion by Regulation of PTEN/PI3K/AKT Pathway.

BACKGROUND: Our study explored whether the microRNA-126 (miR-126)-mediated PTEN/PI3K/AKT (phosphatase and tensin homology deleted on chromosome 10/phosphatidylinositol 3-kinase regulatory subunit-ß/AKT) signaling pathway by targeting PIK3R2 affects the proliferation, migration, and invasion of non-small-cell lung cancer (NSCLC) A549 cells. MATERIALS AND METHODS: Quantitative real-time polymerase chain reaction was used to measure the expression of miR-126 in A549 cells. The MTT (methyl thiazolyl tetrazolium) assay, cell scratch test, Transwell assay, and Western blot were used to detect the proliferation, migration, and invasion of A549 cells and protein expression in A549 cells, respectively. RESULTS: The expression of miR-126 decreased and the expression of PIK3R2 increased in A549 cells (P < .05, for both). Upregulation of miR-126 resulted in the decrease of the proliferation, migration, and invasive abilities of A549 cells, the downregulation of the expression of PIK3R2, PI3K, and phosphorylated Akt (p-Akt) protein, and the upregulation of PTEN expression (P < .05 for all). Also, these abilities of A549 cells increased, and the expression of these 3 proteins was upregulated with downregulation of miR-126 (P < .05 for all). The results of the dual luciferase reporter gene assay showed that PIK3R2 was the target gene of miR-126. PIK3R2, PI3K, and p-Akt proteins were downregulated, but PTEN protein was upregulated as PIK3R2 was silenced or the inhibitor of the PTEN/PI3K/AKT signaling pathway increased. Also, downregulation of miR-126 with silencing of PIK3R2 or increasing the inhibitor of the pathway caused increased PI3K and p-Akt protein expression and increased active proliferation, migration, and invasive abilities of A549 cells (P < .05 for all). CONCLUSION: The upregulation of miR-126 in NSCLC A549 cells can reduce the expression of the target gene PIK3R2 and influence the PTEN/PI3K/AKT signaling pathway, suppressing the proliferation, migration, and invasive abilities of A549 cells.