Targeting TRAIL Death Receptor 4 with Trivalent DR4 Atrimer Complexes

Abstract

TRAIL is a trimeric protein that potently induces apoptosis in cancer cells by binding to the trimeric death receptors (DR4 or DR5). Death receptors are attractive therapeutic targets through both the recombinant TRAIL ligand as well as receptor agonist monoclonal antibodies. Although efficacy of the ligand is hampered by its short half-life, agonistic antibodies have a much longer half-life and have shown some clinical efficacy as antitumor agents. However, the efficacy of these antibodies may be limited by their bivalent nature that does not optimally mimic the trimeric ligand. To overcome limitations of currently used death receptor-targeting agents, we engineered trimeric proteins called Atrimer complexes that selectively bind DR4 and potently induce apoptosis in a variety of cancer cells. Atrimer complexes are based on human tetranectin, a trimeric plasma protein of approximately 60 kDa. Loop regions within the tetranectin C-type lectin domains (CTLD) were randomized to create a large phage display library that was used to select DR4-binding complexes. A panel of unique and potent agonist DR4 Atrimer complexes with subnanomolar affinity to DR4 and no detectable binding to DR5 or the decoy receptors was identified. Mechanism of action studies with a selected Atrimer complex, 1G 2 , showed that Atrimer complexes induce caspase-dependent and DR4-specific apoptosis in cancer cells while sparing normal human fibroblasts and, importantly, hepatocytes. This proof-of-principle study supports the use of alternative proteins engineered to overcome limitations of therapeutically desirable molecules such as TRAIL. Mol Cancer Ther; 11(10); 2087-95. Ó2012 AACR.

RG7386, a Novel Tetravalent FAP-DR5 Antibody, Effectively Triggers FAP-Dependent, Avidity-Driven DR5 Hyperclustering and Tumor Cell Apoptosis

“…In addition to full-length antibodies, different scaffolds such as atrimers (31) or multivalent monobodies (32,33) are under evaluation to target DRs. However, the lack of clinical efficacy observed with untargeted DR5 agonistic antibodies illustrates that the activity of these molecules in vitro may not necessarily translate into clinical efficacy.…”

The Design and Characterization of Receptor-selective APRIL Variants

“…Directed evolution methods employing phage display were also used to generate receptorselective TRAIL variants (37), a receptor-selective TNF␣ antagonist (38), and a LIGHT/LT␤ variant that does not bind DcR3 (39). In addition, selective receptor activation can also be achieved by the use of receptor-specific agonistic antibodies (40,41) or other binding scaffolds (42). Although these approaches can be equally useful, factors such as stoichiometry of receptor activation (40) and prolonged activation due to a longer half-life must be taken into account.…”

ONC201 induces cell death in pediatric non-Hodgkin's lymphoma cells

“…The limited clinical activity of these TRAIL-based agents has been ascribed to intrinsic tumor cell attributes such as O-glycosylation enzymes, 17,18 the tumor microenvironment, 19,20 and limitations of the therapeutic agents themselves such as suboptimal death receptor clustering and poor chemical characteristics. 21 Nonetheless, TRAIL possesses ideal therapeutic properties as an endogenous, natural, anti-cancer protein that was evolved as part of the immune system. 5 The power of the immune system in general and TRAIL pathway in particular in cancer suppression motivated our effort to identify small molecules that harness the therapeutic potential of the endogenous death receptor pathway without the limitations of exogenous protein mimetics.…”