Abstract 1036: Cbl-independent degradation of Met: Ways to avoid agonism of bivalent Met targeting antibody.

The Met receptor tyrosine kinase, found to be constitutively activated in many tumors, has become a leading target for cancer therapy. Disruptions in Met down-regulation have been associated with aggressive tumor progression with several therapeutic strategies addressing this aspect of Met biology. Cbl E3 ligase-mediated degradation, which attenuates Met signaling via ligand-dependent Met internalization, is a major negative regulator of Met expression. It is believed that one of the mechanisms by which the therapeutic anti-Met antibodies induce cancer cell death in Met over-expressing tumors is via internalization and subsequent degradation of Met from the cell surface. However, a previously reported Met targeting antibody demonstrated intrinsic agonistic activity while capable of inducing Cbl-mediated degradation of Met, suggesting that Cbl-mediated degradation requires receptor activation and impedes therapeutic application. We have developed a potent and selective bivalent Met targeting antibody (SAIT301) that invokes Met degradation using an alternative regulator LRIG1. In this report, we demonstrate that LRIG1 mediates degradation of Met by SAIT301 and this degradation does not require Met activation. Furthermore, SAIT301 was able to down-regulate Met and dramatically inhibit growth of tumors with low or no Cbl expression, as well as tumors with Met exon 14 deletion that prevents Met binding to Cbl. In summary, we demonstrate the enhanced therapeutic potential of a novel tumor-inhibiting anti-Met antibody, SAIT301, which utilizes a Cbl-independent, LRIG1-mediated Met degradation pathway and thereby avoids the agonism that limits the effectiveness of previously reported anti-Met antibodies. Citation Format: Ji Min Lee, Bogyou Kim, Kyung-Ah Kim. Cbl-independent degradation of Met: Ways to avoid agonism of bivalent Met targeting antibody. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1036. doi:10.1158/1538-7445.AM2013-1036