dinaciclib and Glioma

In the present study, we investigated the effect of CDK inhibitors (ribociclib, palbociclib, seliciclib, AZD5438, and dinaciclib) on malignant human glioma cells for cell viability, apoptosis, oxidative stress, and mitochondrial function using various assays. None of the CDK inhibitors induced cell death at a clinically relevant concentration. However, low nanomolar concentrations of dinaciclib showed higher cytotoxic activity against Bcl-xL silenced cells in a time- and concentration-dependent manner. This effect was not seen with other CDK inhibitors. The apoptosis-inducing capability of dinaciclib in Bcl-xL silenced cells was evidenced by cell shrinkage, mitochondrial dysfunction, DNA damage, and increased phosphatidylserine externalization. Dinaciclib was found to disrupt mitochondrial membrane potential, resulting in the release of cytochrome c, AIF, and smac/DIABLO into the cytoplasm. This was accompanied by the downregulation of cyclin-D1, D3, and total Rb. Dinaciclib caused cell cycle arrest in a time- and concentration-dependent manner and with accumulation of cells in the sub-G1 phase. Our results also revealed that dinaciclib, but not ribociclib or palbociclib or seliciclib or AZD5438 induced intrinsic apoptosis via upregulation of the levels of pro-apoptotic proteins (Bax and Bak), resulting in the activation of caspases and cleavage of PARP. We also found an additional mechanism for the dinaciclib-induced augmentation of apoptosis due to abrogation RAD51-cyclin D1 interaction, specifically proteolysis of the DNA repair proteins RAD51 and Ku80. Our results suggest that successfully interfering with Bcl-xL function may restore sensitivity to dinaciclib and could hold the promise for an effective combination therapeutic strategy.

Topics: Apoptosis; Apoptosis Regulatory Proteins; bcl-X Protein; Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Cyclic N-Oxides; Cyclin-Dependent Kinases; Glioma; Humans; Indolizines; Ku Autoantigen; Membrane Potential, Mitochondrial; Mitochondria; Protein Kinase Inhibitors; Proteolysis; Pyridinium Compounds; Rad51 Recombinase; RNA Interference; Up-Regulation

The prognosis for malignant glioma, the most common brain tumor, is still poor, underscoring the need to develop novel treatment strategies. Because glioma cells commonly exhibit genomic alterations involving genes that regulate cell-cycle control, there is a strong rationale for examining the potential efficacy of strategies to counteract this process. In this study, we examined the antiproliferative effects of the cyclin-dependent kinase inhibitor dinaciclib in malignant human glioma cell lines, with intact, deleted, or mutated p53 or phosphatase and tensin homolog on chromosome 10; intact or deleted or p14ARF or wild-type or amplified epidermal growth factor receptor. Dinaciclib inhibited cell proliferation and induced cell-cycle arrest at the G2/M checkpoint, independent of p53 mutational status. In a standard 72-hour 3-[4,5-dimethylthiazol- 2yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H, tetrazolium (MTS) assay, at clinically relevant concentrations, dose-dependent antiproliferative effects were observed, but cell death was not induced. Moreover, the combination of conventional chemotherapeutic agents and various growth-signaling inhibitors with dinaciclib did not yield synergistic cytotoxicity. In contrast, combination of the Bcl-2/Bcl-xL inhibitors ABT-263 (4-[4-[[2-(4-chlorophenyl)-5,5-dimethylcyclohexen-1-yl]methyl]piperazin-1-yl]-N-[4-[[(2R)-4-morpholin-4-yl-1-phenylsulfanylbutan-2-yl]amino]-3-(trifluoromethylsulfonyl)phenyl]sulfonylbenzamide) or ABT-737 (4-[4-[[2-(4-chlorophenyl)phenyl]methyl]piperazin-1-yl]-N-[4-[[(2R)-4-(dimethylamino)-1-phenylsulfanylbutan-2-yl]amino]-3-nitrophenyl]sulfonylbenzamide) with dinaciclib potentiated the apoptotic response induced by each single drug. The synergistic killing by ABT-737 with dinaciclib led to cell death accompanied by the hallmarks of apoptosis, including an early loss of the mitochondrial transmembrane potential; the release of cytochrome c, smac/DIABLO, and apoptosis-inducing factor; phosphatidylserine exposure on the plasma membrane surface and activation of caspases and poly ADP-ribose polymerase. Mechanistic studies revealed that dinaciclib promoted proteasomal degradation of Mcl-1. These observations may have important clinical implications for the design of experimental treatment protocols for malignant human glioma.

Topics: Biphenyl Compounds; Bridged Bicyclo Compounds, Heterocyclic; Cell Death; Cell Line, Tumor; Cell Proliferation; Cyclic N-Oxides; Cyclin-Dependent Kinases; Dose-Response Relationship, Drug; Drug Synergism; Glioma; Humans; Indolizines; Myeloid Cell Leukemia Sequence 1 Protein; Nitrophenols; Piperazines; Proteasome Endopeptidase Complex; Pyridinium Compounds; Sulfonamides