ABSTRACT
Small molecule chaperones are a promising therapeutic approach for the Lysosomal Storage Disorders (LSDs). Here, we report the discovery of a new series of non-iminosugar glucocerebrosidase inhibitors with chaperone capacity, and describe their structure activity relationship (SAR), selectivity, cell activity phamacokinetics.
ABSTRACT
Cells that suffer substantial inhibition of DNA replication halt their cell cycle via a checkpoint response mediated by the PI3 kinases ATM and ATR. It is unclear how cells cope with milder replication insults, which are under the threshold for ATM and ATR activation. A third PI3 kinase, DNA-dependent protein kinase (DNA-PK), is also activated following replication inhibition, but the role DNA-PK might play in response to perturbed replication is unclear, since this kinase does not activate the signaling cascades involved in the S-phase checkpoint. Here we report that mild, transient drug-induced perturbation of DNA replication rapidly induced DNA breaks that promptly disappeared in cells that contained a functional DNA-PK whereas such breaks persisted in cells that were deficient in DNA-PK activity. After the initial transient burst of DNA breaks, cells with a functional DNA-PK did not halt replication and continued to synthesize DNA at a slow pace in the presence of replication inhibitors. In contrast, DNA-PK deficient cells subject to low levels of replication inhibition halted cell cycle progression via an ATR-mediated S-phase checkpoint. The ATM kinase was dispensable for the induction of the initial DNA breaks. These observations suggest that DNA-PK is involved in setting a high threshold for the ATR-Chk1-mediated S-phase checkpoint by promptly repairing DNA breaks that appear immediately following inhibition of DNA replication.
Subject(s)
DNA Breaks, Double-Stranded , DNA Repair/physiology , DNA-Activated Protein Kinase/metabolism , Animals , Aphidicolin/pharmacology , Cell Line , Cricetinae , DNA Replication/drug effects , DNA-Activated Protein Kinase/chemistry , Histones/metabolism , Humans , Phosphorylation , Protein Subunits , S PhaseABSTRACT
Intracellular calcium (Ca2+) is involved in the regulation of a variety of biological functions in cancer cells, including growth inhibition, tumor invasiveness, and drug resistance. To gain insight into the possible role played by Ca2+ in the development of drug resistance in breast cancer, we performed a comparative high-content analysis of the intracellular Ca2+ dynamics in drug-sensitive human breast cancer MCF-7 cells and five drug-resistant, MCF-7-derived clonal cell lines. Fura-2 single cell ratiometric fluorescence microscopy was used to monitor real-time quantitative changes in cytosolic-free Ca2+ concentration ( [Ca2+]i ) upon addition of phosphoinositol-coupled receptor agonists. While the magnitude and the onset kinetics of the [Ca2+]i rise were similar in drug-sensitive and drug-resistant cell lines, the decay kinetics of the [Ca2+]i increase was found to be consistently slower in drug-resistant than drug-sensitive cells. Such a delay in reestablishing homeostatic [Ca2+]i persisted in the absence of extracellular Ca2+ and was independent of the expression or function of specific drug efflux pumps associated with drug resistance. Moreover, intracellular Ca2+ pools releasable by phosphoinositol-coupled receptor agonists or thapsigargin appeared to be differentially shared in drug-sensitive and drug-resistant cells. In light of the clinical relevance that drug resistance has in the treatment of cancer, the molecular and biochemical relationship between alterations in Ca2+ dynamics and drug resistance demands to be further investigated and tested in a wider array of cell types. Automated microscopy will help greatly in this pursuit by facilitating both sample imaging and data analysis, thus allowing high-content as well as high-throughput screening of large sample sets. A protocol for studying [Ca2+]i kinetics with a commercially available automated imaging platform is described.