Abstract 2577: In vitro and in vivo efficacy of the anti-MN immunoconjugate BAY 79-4620, MN-IC, in MN (CAIX) expressing preclinical tumor models
Authors: Petrul Heike , Ranges Gerald , Bouret Elizabeth , Chang Yong , Voznesensky Andrei , Schatz Christoph , Kopitz Charlotte , Tamburini Paul , Ziegelbauer Karl 
Published: February 2011

Abstract
BAY 79-4620 is a novel immunoconjugate consisting of a fully human monoclonal antibody directed against MN (carbonic anhydrase IX; CAIX) conjugated with the auristatin derivative MMAE currently in Phase I testing. CAIX is overexpressed in a range of tumor types, such as gastric cancer, non-small cell lung cancer, pancreatic cancer or colorectal cancer. CAIX expression is regulated by HIF-1α, making this protein a marker associated with tumor hypoxia. Expression of this protein has been linked to higher aggressiveness of tumors and is predictive of poor prognosis in several cancers.
We report on the pharmacological profile of a novel immunoconjugate directed against MN (CAIX) conjugated with the auristatin derivative MMAE to a fully human anti-MN (CAIX) monoclonal antibody (BAY 79-4620). In vitro studies showed the specific binding and internalization of BAY 79-4620 into CAIX-expressing tumor cells. Intracellular release of the tubulin-inhibiting toxophore MMAE led to mitotic arrest and specific cell kill of tumor cells, with EC50s in the low nanomolar range in most CAIX-positive tumor cell lines tested. In CAIX-negative tumor cell lines, a cytotoxic effect of BAY 79-4620 was seen at only very high doses. Cytotoxicity of this immunoconjugate depends on both CAIX expression and sensitivity of tumor cells to tubulin inhibitors. In vivo activity of the CAIX targeted Mab-MMAE conjugate resulted in higher efficacy (minimum effective dose (MED) of 0.625mg/kg in the HeLa-MaTu model, Q4Dx3 dosing schedule) compared to the systemic administration of either free MMAE toxophore (MED not achieved) or unconjugated anti-CAIX antibody which lacked efficacy in all models tested. Tumor regressions (in 80% of the animals) were achieved at doses of immunoconjugate as low as 1.25mg/kg while higher doses up to 10 mg/kg resulted in complete tumor eradication (in 90% of the animals treated). Efficacy in the HT29 model tested was schedule independent when comparing single dose, Q7Dx2 and Q4Dx3 schedules. The in vivo mode of action of the immunoconjugate was confirmed by tubulin staining in the tumor sections. Treatment with the immunoconjugate was found to be less toxic than that with free MMAE. The maximum tolerated dose of BAY 79-4620 in mice was 60mg/kg, which in terms of toxophore delivered exceeds the LD50 of MMAE (1mg/kg).
In summary, these results demonstrate that targeted delivery of MMAE resulted in higher efficacy of BAY 79-4620 in tumor models with high CAIX expression. The immunoconjugate BAY 79-4620 currently in Phase I testing is a promising novel agent for the treatment of gastric, non-small cell lung, pancreatic, colorectal and other MN (CAIX)-positive tumors.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2577.