Species-dependent variability of ADAMTS13-mediated proteolysis of human recombinant von Willebrand factor

BACKGROUND

von Willebrand factor (VWF) is composed of a series of multimers, the sizes of which are regulated by the plasma metalloprotease ADAMTS13.

OBJECTIVE

Proteolysis of human recombinant VWF (rVWF) by ADAMTS13 present in the plasma of different species typically used as preclinical animal models was investigated to evaluate the efficacy and safety of rVWF.

METHODS

Degradation of rVWF was studied in vitro under moderate denaturing conditions and was monitored by multimer analysis, residual collagen binding, and immunoblot analysis. In vivo cleavage was determined by administration of rVWF to cynomolgus monkeys, rabbits and VWF-deficient mice and subsequent analysis of plasma samples by immunoblot. Plasma ADAMTS13 levels were determined with a synthetic human VWF peptide (FRETS-VWF73).

RESULTS

From the animals tested, only rabbit plasma was as efficient as human plasma in proteolysing rVWF in vitro. Mouse plasma virtually failed to cleave rVWF. Administration of human rVWF resulted in ADAMTS13-specific cleavage products in rabbits and, to a lesser extent, in cynomolgus monkeys at various doses of rVWF. Virtually no cleavage occurred in mice. ADAMTS13 activity levels in rabbit and monkey plasma were similar to those in human plasma and were not significantly altered upon infusion of rVWF up to very high doses, indicating that rVWF did not lead to an exhaustion of endogenous ADAMTS13 in both species.

CONCLUSIONS

The differences in susceptibility to cleavage of rVWF by different species need to be considered when interpreting the physiology of human rVWF from results of tests in animal models.

Local gene therapy of solid tumors with GM-CSF and B7-1 eradicates both treated and distal tumors

Gene therapy-induced expression of immunostimulatory molecules at tumor cell level may evoke antitumor immune mechanisms by recruiting and enhancing viability of antigen-processing cells and specific tumoricidal lymphocytes. The antitumor efficacy of a plasmid, coding for granulocyte-macrophage colony-stimulating factor (GM-CSF) and the B7-1 costimulatory immune molecule, delivered into growing solid tumors by electroporation was investigated. Murine fibrosarcomas (JBS) growing in Balb/C mice (<or=100 mm3) were transfected with GM-CSF/B7-1-expressing plasmid. Complete tumor regression occurred in greater than 60% of treated animals. This response was systemic, durable and tumor specific, with all responding animals resistant to repeat tumor challenge. Using a liver metastatic model, effective cure of distal metastases was achieved following treatment of the primary subcutaneous tumor. This treatment strategy could be applicable in the clinical setting for effective elimination of both primary tumors and associated metastatic disease.

Expression and dimerization of the rat activin subunits betaC and betaE: evidence for the ormation of novel activin dimers

Activins are cytokines of the transforming growth factor beta family, which plays a central role in the determination of cell fate and the regulation of tissue balance. Family members are composed of two subunits and this dimerization is critical for liganding their cognate receptors and execution of proper functions. In the current study we focused on the localization of activin betaA, betaB, betaC and betaE subunits in the adult rat and analyzed the composition of putative activin beta dimers. By dissecting tissue distribution of various activins, we found that the liver, in particular the hepatocytes, is the major source for activin betaC and betaE transcripts, since other tissues almost failed to express these isoforms. In sharp contrast, the emergence of activin betaA and betaB appeared ubiquitous. Using a highly selective proteome approach, we were able to identify homo- as well as heterodimers of individual activin subunits, indicating a high redundancy of ligand composition. Certainly, this broad potential to homo- and heterodimerize has to be considered in future studies on activin function.