Calcium influx-mediated translocation of m-calpain induces Ku80 cleavage and enhances the Ku80-related DNA repair pathway.

Proteomic analysis of ionomycin-treated and untreated mammary epithelial MCF10A cells elucidated differences in Ku80 cleavage. Ku80, a subunit of the Ku protein complex, is an initiator of the non-homologous, end-joining (NHEJ), double-strand breaks (DSBs) repair pathway. The nuclear Ku80 was cleaved in a calcium concentration-dependent manner by m-calpain but not by m-calpain. The cleavage of nuclear Ku80 at its α/ß domain was validated by Western blotting analysis using flag-tagged expression vectors of truncated versions of Ku80 and a flag antibody and was confirmed in m-calpain knock-down cells and in vitro cell-free evaluation with recombinant proteins of calpains, Ku70, and Ku80. In addition, the cleaved Ku80 still formed a Ku heterodimer and promoted DNA DSB repair activity. Taken together, these findings indicate that translocated m-calpain enhances the NHEJ pathway through the cleavage of Ku80. Based on the present study, m-calpain in DNA repair pathways might be a novel anticancer drug target, or its mechanism might be a possible route for resistance acquisition of DNA damage-inducing chemotherapeutics.

Synthesis and investigation of dihydroxychalcones as calpain and cathepsin inhibitors.

In order to identify potential calpain and cathepsin inhibitors we prepared 12 dihydroxychalcone analogues and tested their ability to inhibit µ-calpain, m-calpain, cathepsins B and L. In the calpain inhibition test, compound 10 exhibited the most active inhibitory activity against m-calpain with an IC50 value of 25.25±0.901µM. With respect to inhibition of cathepsins B and L, compound 13 exhibited the most potent inhibitory activity on cathepsin L and moderate inhibitory activity on cathepsin B with IC50 values of 2.80±0.100 and 11.47±0.087µM, respectively. Our results suggest the possibility of developing dual calpain and cathepsin inhibitors by properly modulating structures and/or combining the essential aspects of the functional group effective for specific calpain and cathepsin inhibition.

Chalcones, inhibitors for topoisomerase I and cathepsin B and L, as potential anti-cancer agents.

In order to diversify the pharmacological activity of chalcones and extend the scaffold of topoisomerase and cathepsins B and L inhibitors, we have designed and synthesized total 18 chalcone compounds and tested their biological activity. In the topoisomerase inhibition test, most analogues in group III and IV except compound 11 exhibited more efficient topoisomerase I inhibitory activity than camptothecin at 20 µM. Compounds 15, 16 and 18 in group IV showed significant cathepsin B and L inhibitory activity. Among the compounds, compound 15 was most active with IC50 values of 1.81±0.05 µM on cathepsin B and 3.15±0.07 µM on cathepsin L, respectively. Compound 15 also showed most potent cytotoxic activity against T47D and SNU638 cells with IC50 values of 1.37±0.05 µM and 0.62±0.01 µM, respectively. Overall, although more compounds should be tested and analyzed for clear SAR against topoisomerase I and cathepsin B and L, compound 15 showed consistent inhibitory ability on the tested assays, which can implicate the cytotoxic activity of compound 15 on topoisomerase I and cathepsin B and L inhibitory pathways.

Effect of conjugated linoleic acid, µ-calpain inhibitor, on pathogenesis of Alzheimer's disease.

µ-Calpain is a calcium-dependent cysteine protease, which is activated by µM concentration of calcium in vitro. Disrupted intracellular calcium homeostasis leads to hyper-activation of µ-calpain. Hyper-activated µ-calpain enhances the accumulation of ß-amyloid peptide by increasing the expression level of ß-secretase (BACE1) and induces hyper-phosphorylation of tau along with the formation of neurofibrillary tangle by mediating p35 cleavage into p25, both of which are the major mechanisms of neurodegeneration in Alzheimer's disease (AD). Hence, inhibition of µ-calpain activity is very important in the treatment and prevention of AD. In this study, conjugated linoleic acid (CLA), an eighteen-carbon unsaturated fatty acid, was discovered as a µ-calpain-specific inhibitor. CLA showed neuroprotective effects against neurotoxins such as H2O2 and Aß1-42 in SH-SY5Y cells, and inhibited Aß oligomerization/fibrillation and Aß-induced Zona Occludens-1 degradation. In addition, CLA decreased the levels of proapoptotic proteins, p35 conversion to p25 and tau phosphorylation. These findings implicate CLA as a new core structure for selective µ-calpain inhibitors with neuroprotective effects. CLA should be further evaluated for its potential use as an AD therapeutic agent.