Complement system activation contributes to the ependymal damage induced by microbial neuraminidase.

BACKGROUND: In the rat brain, a single intracerebroventricular injection of neuraminidase from Clostridium perfringens induces ependymal detachment and death. This injury occurs before the infiltration of inflammatory blood cells; some reports implicate the complement system as a cause of these injuries. Here, we set out to test the role of complement. METHODS: The assembly of the complement membrane attack complex on the ependymal epithelium of rats injected with neuraminidase was analyzed by immunohistochemistry. Complement activation, triggered by neuraminidase, and the participation of different activation pathways were analyzed by Western blot. In vitro studies used primary cultures of ependymal cells and explants of the septal ventricular wall. In these models, ependymal cells were exposed to neuraminidase in the presence or absence of complement, and their viability was assessed by observing beating of cilia or by trypan blue staining. The role of complement in ependymal damage induced by neuraminidase was analyzed in vivo in two rat models of complement blockade: systemic inhibition of C5 by using a function blocking antibody and testing in C6-deficient rats. RESULTS: The complement membrane attack complex immunolocalized on the ependymal surface in rats injected intracerebroventricularly with neuraminidase. C3 activation fragments were found in serum and cerebrospinal fluid of rats treated with neuraminidase, suggesting that neuraminidase itself activates complement. In ventricular wall explants and isolated ependymal cells, treatment with neuraminidase alone induced ependymal cell death; however, the addition of complement caused increased cell death and disorganization of the ependymal epithelium. In rats treated with anti-C5 and in C6-deficient rats, intracerebroventricular injection of neuraminidase provoked reduced ependymal alterations compared to non-treated or control rats. Immunohistochemistry confirmed the absence of membrane attack complex on the ependymal surfaces of neuraminidase-exposed rats treated with anti-C5 or deficient in C6. CONCLUSIONS: These results demonstrate that the complement system contributes to ependymal damage and death caused by neuraminidase. However, neuraminidase alone can induce moderate ependymal damage without the aid of complement.

Therapeutic mechanism and efficacy of the antibody-drug conjugate BAY 79-4620 targeting human carbonic anhydrase 9.

Carbonic anhydrase IX (CAIX) is a cell surface glycoprotein that is expressed in many different tumors and yet restricted in normal tissues to the gastrointestinal tract. It is upregulated by hypoxia and correlates with tumor grade and poor survival in several tumor indications. Monoclonal antibodies (mAb) with single digit nanomolar binding affinity for CAIX were derived by panning with the recombinant ectodomain of CAIX against the MorphoSys HUCAL Gold library of human Fabs. Highest affinity Fabs were converted to full-length IgGs and subjected to further characterization based upon their avidity and selectivity for CAIX, their capacity to undergo internalization in CAIX-expressing cell lines, and their selective localization to CAIX-positive human xenografted tumors when administered to mice as fluorescent conjugates. Through this selection process, the 3ee9 mAb was identified, which upon conjugation to monomethyl auristatin E through a self-immolative enzyme-cleavable linker yielded the potent and selective CAIX antibody-drug conjugate CAIX-ADC (BAY 79-4620). In preclinical human xenograft models in mice representing several tumor indications, BAY 79-4620 showed potent antitumor efficacy and in some models showed partial and complete tumor shrinkage even following a single dose. The mechanism of action was shown by histology to involve the sequelae of events typical of antitubulin agents. Efficacy in murine preclinical models correlated semiquantitatively, with CAIX expression levels as determined by immunohistochemistry and ELISA. These preclinical data collectively support the development of BAY 79-4620 for the treatment of cancer patients with CAIX overexpressing tumors.