Inhibition of Kallikrein-Related Peptidases 7 and 5 by Grafting Serpin Reactive-Center Loop Sequences onto Sunflower Trypsin Inhibitor-1 (SFTI-1).

Serpin proteins irreversibly inhibit serine proteases, but only a small part of the serpin reactive-center loop (RCL) is responsible for the initial protein-protein interaction (PPI). To develop peptidic protease inhibitors, kallikrein-related peptidases 7 (KLK7) and 5 (KLK5) were chosen. Firstly, we demonstrated that short peptides derived from RCL sequences can be cleaved by KLK7 in a substrate-like manner. Next, these substrates were grafted onto the protease-binding loop of sunflower trypsin inhibitor-1 (SFTI-1). Peptides based on kallistatin, α1 -antichymotrypsin, and protein C inhibitor (PCI) inhibited KLK7 with Ki =0.4, 0.5, and 0.7 µm, respectively. In contrast, the trypsin-like KLK5 was only blocked by the peptide derived from PCI (Ki =0.6 µm). Thus, serpin function can be mimicked by introducing its PPI site into the rigid structure of the SFTI-1 scaffold. This approach might be applicable not only to KLKs but also to other serine protease members, thus opening up new therapeutic fields.

Dexrazoxane may prevent doxorubicin-induced DNA damage via depleting both topoisomerase II isoforms.

BACKGROUND: The bisdioxopiperazine dexrazoxane (DRZ) prevents anthracycline-induced heart failure, but its clinical use is limited by uncertain cardioprotective mechanism and by concerns of interference with cancer response to anthracyclines and of long-term safety. METHODS: We investigated the effects of DRZ on the stability of topoisomerases IIα (TOP2A) and IIß (TOP2B) and on the DNA damage generated by poisoning these enzymes by the anthracycline doxorubicin (DOX). RESULTS: DRZ given i.p. transiently depleted in mice the predominant cardiac isoform Top2b. The depletion was also seen in H9C2 cardiomyocytes and it was attenuated by mutating the bisdioxopiperazine binding site of TOP2B. Consistently, the accumulation of DOX-induced DNA double strand breaks (DSB) by wild-type, although not by mutant TOP2B, was reduced by DRZ. In contrast, the DRZ analogue ICRF-161, which is capable of iron chelation but not of TOP2B binding and cardiac protection, did not deplete TOP2B and did not prevent the accumulation of DOX-induced DSB. TOP2A, re-expressed in cultured cardiomyocytes by fresh serum, was depleted by DRZ along with TOP2B. DRZ depleted TOP2A also from fibrosarcoma-derived cells, but not from lung cancer-derived and human embryo-derived cells. DRZ-mediated TOP2A depletion reduced the accumulation of DOX-induced DSB. CONCLUSIONS: Taken together, our data support a model of anthracycline-induced heart failure caused by TOP2B-mediated DSB and of its prevention by DRZ via TOP2B degradation rather than via iron chelation. The depletion of TOP2B and TOP2A suggests an explanation for the reported DRZ interference with cancer response to anthracyclines and for DRZ side-effects.