Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment.

Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.

Discovery of dual PARP and CDK6 inhibitors for triple-negative breast cancer with wild-type BRCA.

Inhibition of PARP is synthetic lethal with defects in BRCA, which provide effective targeted therapy strategy for BRCA mutation type of TNBC patients. However, approximately 80% of TNBC patients do not have BRCA mutations. Recent studies have shown that CDK4/6 inhibitors can increase the sensitivity of wild-type BRCA cells to PARP inhibitors. We designed a series of dual PARP and CDK6 inhibitors, and the most promising compound, P4i, showed good inhibitory activity against PARP1 and CDK6 and good inhibitory effects on MDA-MB-231 (IC50 = 1.96 µM), MDA-MB-468 (IC50 = 2.81 µM) and BT-549 (IC50 = 2.37 µM) cells with wild-type BRCA. Compared with Olaparib, the inhibition capacity of the three BRCA wild-type (MDA-MB-231, MDA-MB-468 and BT-549) cells was about 10-20 times higher, and even better than the combination of Olaparib and Palbociclib. As a novel PARP multifunctional molecule, it is a potential compound for the treatment of BRCA wild-type TNBC.

Cadmium inhibits apoptosis of human esophageal epithelial cells by upregulating CDK6.

Cadmium (Cd) exposure in environment is associated with development of esophageal cancer. However, the mechanisms of Cd-induced carcinogenesis are still not been fully cleared, and the present study aimed to explore the possible etiological mechanism of Cd-induced esophageal cancer. Human esophageal epithelial cell lines (HET-1A and KYSE450) were treated with CdCl2 at 0.05 mg/l for 12, 24 h, and the then the apoptosis were detected using flow cytometry with annexin-V-FITC/PI staining. Results showed that apoptosis of treatment groups was significantly inhibited, and decreased reactive oxygen species (ROS) production played a key role in the inhibitory effects by upregulating Bcl-2 and downregulating Caspase-3/9. The relief of oxidative stress during Cd exposure was actively promoted by the increased nicotinamide adenine dinucleotide phosphoric acid and glutathione levels. To investigate the causes of enhanced intracellular antioxidant capacity, the activity of pyruvate kinase (PK), a key enzyme of glycolysis, was detected. Our results showed that PK activity was inhibited, suggesting that glycolysis process was blocked which promoted more intermediate metabolites of glycolysis to be used for reduced nicotinamide adenine dinucleotide phosphoric acid (NADPH) or other antioxidants synthesis. PK activity was closely correlated with phosphorylation of pyruvate kinase M2 (PKM2), and a highly negative correlation (correlation coefficients: -0.835, p < 0.05) between them was found. Western blotting showed the overphosphorylation of PKM2 in Cd-exposed cells, resulting from increased expression of cyclin-dependent kinases 6 (CDK6). These results suggested a possible mechanism of carcinogenic: Cd-induced upregulation of CDK6 in esophageal cell lines caused PKM2 overphosphorylation inhibiting PK activity, thereby shunting glucose-derived carbon into the pentose phosphate pathway and promoting the production of NADPH and reduced glutathione (GSH) to neutralize ROS, which finally results in the inhibited apoptosis.

MR-Based Radiomics Predicts CDK6 Expression and Prognostic Value in High-grade Glioma.

RATIONALE AND OBJECTIVES: This study aims to assess the prognostic value of Cyclin-dependent kinases 6 (CDK6) expression levels and establish a machine learning-based radiomics model for predicting the expression levels of CDK6 in high-grade gliomas (HGG). MATERIALS AND METHODS: Clinical parameters and genomic data were extracted from 310 HGG patients in the Cancer Genome Atlas (TCGA) database and 27 patients in the Repository of Molecular Brain Neoplasia Data (REMBRANDT) database. Univariate and multivariate Cox regression, as well as Kaplan-Meier analysis, were performed for prognosis analysis. The correlation between immune cell Infiltration with CDK6 was assessed using spearman correlation analysis. Radiomic features were extracted from contrast-enhanced magnetic resonance imaging (CE-MRI) in the Cancer Imaging Archive (TCIA) database (n = 82) and REMBRANDT database (n = 27). Logistic regression (LR) and support vector machine (SVM) were employed to establish the radiomics model for predicting CDK6 expression. Receiver operating characteristic curve (ROC), calibration curve, and decision curve analysis (DCA) were utilized to assess the predictive performance of the radiomics model. Generate radiomic scores (RS) based on the LR model. An RS-based nomogram was constructed to predict the prognosis of HGG. RESULTS: CDK6 was significantly overexpressed in HGG tissues and was related to lower overall survival. A significant elevation in infiltrating M0 macrophages was observed in the CDK6 high group (P < 0.001). The LR radiomics model for the prediction of CDK6 expression levels (AUC=0.810 in the training cohort, AUC = 0.784 after cross-validation, AUC=0.750 in the testing cohort) was established utilizing three radiomic features. The predictive efficiencies of the RS-based nomogram, as measured by AUC, were 0.769 for 1-year, 0.815 for 3-year, and 0.780 for 5-year, respectively. CONCLUSION: The expression level of CDK6 can impact the prognosis of patients with HGG. The expression level of HGG can be noninvasively prognosticated utilizing a radiomics model.

Inhibition of the JAK2/STAT3 pathway and cell cycle re-entry contribute to the protective effect of remote ischemic pre-conditioning of rat hindlimbs on cerebral ischemia/reperfusion injury.

AIMS: Remote ischemic pre-conditioning (RIPC) protects against ischemia/reperfusion (I/R) injury. However, the mechanisms underlying this protection remain unclear. In the present study, we investigated the role of Janus-activated kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway and cell cycle arrest, and their relationship with neuronal apoptosis following RIPC. METHODS: A rat cerebral I/R injury model was induced by middle cerebral artery occlusion (MCAO), and AG490 was used to investigate the mechanisms of RIPC. p-JAK2-, p-STAT3-, cyclin D1-, and cyclin-dependent kinase 6 (CDK6) expression was assessed by Western blotting and immunofluorescence staining. RESULTS: RIPC reduced the infarct volume, improved neurological function, and increased neuronal survival. Furthermore, p-JAK2 and p-STAT3 were detected during the initial phase of reperfusion; the expression levels were significantly increased at 3 and 24 h after reperfusion and were suppressed by RIPC. Additionally, the MCAO-induced upregulation of the cell cycle regulators cyclin D1 and CDK6 was ameliorated by RIPC. Meanwhile, cyclin D1 and CDK6 were colocalized with p-STAT3 in the ischemic brain. CONCLUSION: RIPC ameliorates the induction of the JAK2/STAT3 pathway and cell cycle regulators cyclin D1 and CDK6 by MCAO, and this net inhibition of cell cycle re-entry by RIPC is associated with downregulation of STAT3 phosphorylation.

The role of PD0332991 in clonogenicity of mantle cell lymphoma cells / 中国肿瘤临床

Objective:To investigate the function and mechanism of cyclin-dependent kinase 4/6 (CDK4/6) inhibitor PD0332991 on clo-nogenicity of mantle cell lymphoma (MCL) cells. Methods:The effect of PD0332991 on MCL cell cycle distribution was assessed by flow cytometry;Western blot was used to test expression level of Rb protein and phosphorylated Rb protein in MCL after treatment with PD0332991;colony forming assay was performed to test the role of PD0332991 and mitoxantrone and their combination on colo-ny forming activity in MCL. Results:Flow cytometry revealed that PD0332991 can increase G0/G1 phase MCL cells and significantly de-crease S phase cells, leading to G0/G1 cell arrest. Western blot confirmed that PD0332991 exerted no effect on Rb protein expression but suppressed levels of phosphorylated Rb protein. Colony forming assay showed that PD0332991 significantly suppressed colony for-mation and enhanced the effect of mitoxantrone on colony forming activity in MCL. Conclusion:This study revealed that CDK4/6 inhib-itor PD0332991 induced G0/G1 cell arrest and increased the effect of mitoxantrone on MCL clonogenicity by suppressing levels of phosphorylated Rb protein.