Selective inhibition of ADAM metalloproteases blocks HER-2 extracellular domain (ECD) cleavage and potentiates the anti-tumor effects of trastuzumab

Abstract

13021 Background: HER-2, a member of ErbB family of receptor tyrosine kinases, is an important regulator of cell proliferation and survival, and is a clinically validated target of therapeutic intervention in HER-2 positive metastatic breast cancer patients. In HER-2 overexpressing cells, the extracellular domain (ECD) is frequently cleaved, rendering the remaining transmembrane portion of HER-2 (p95) constitutively active. The presence of both serum ECD and cellular p95 protein have been linked to poor clinical outcome as well as reduced effectiveness of some therapeutic treatments, suggesting that signaling via p95 is clinically relevant and may represent an attractive target for therapeutic intervention. Methods: Through medicinal chemistry efforts, we have identified a series of potent, selective small molecule inhibitors of ADAM metalloproteases, exemplified here by INCB7839. These compounds were tested both in vitro and in vivo for inhibition of HER-2 ECD cleavage and anti-tumor activity in the HER-2 overexpressing BT-474 cell line. Inhibition of circulating HER-2 ECD levels was monitored in a phase I multiple dose escalation study in healthy volunteers. Results: We demonstrate that these inhibitors effectively blocked HER-2 cleavage in HER-2 overexpressing human breast cancer cell lines. When used in combination, INCB7839 dramatically enhanced the antiproliferative activity of suboptimal doses of the anti-HER-2 antibody, trastuzumab, in HER-2 overexpressing/shedding breast cancer cell lines, accompanied by reduced ERK and AKT phosphorylation. Consistent with these in vitro data, INCB7839 reduced serum ECD levels in tumor-bearing mice and enhanced the antitumor effect of trastuzumab in a xenograft tumor model derived from the HER-2 overexpressing BT-474 breast cancer cell line. In a phase I clinical trial, INCB7839 demonstrated a dose-dependent decrease in the circulating levels of HER-2 ECD present in healthy volunteers. Conclusions: Collectively, these findings suggest that blocking HER-2 cleavage with selective ADAM inhibitors, especially in combination with anti-HER-2 antibody therapy, may represent a novel approach for treating HER-2 overexpressing breast cancer patients. [Table: see text]