Abstract 3853: TAS266, a novel tetrameric nanobody agonist targeting death receptor 5 (DR5), elicits superior antitumor efficacy than conventional DR5-targeted approaches
Authors: Huet Heather , Schuller Alwin , Li Jing , Johnson Jennifer , Dombrecht Bruno , Meerschaert Kris , Cromie Karen , Bilic Sanela , Li Sharon , Garner Andrew , Nunes Sandra , Chopra Rajiv , Clark Kirk , Yao Megan , Fawell Stephen , Stover David , Sellers William R. , Ettenberg Seth 
Published: August 2012

Abstract
Preferential induction of apoptosis in cancer cells has been the objective of therapeutic strategies targeting apoptotic pathways. To this end, multiple therapeutic agonists of Death Receptors 4 and 5 (DR4, DR5), have been developed and are under clinical evaluation. Although these agonists, including antibodies and soluble ligand TRAIL, demonstrate significant anti-tumor activity in preclinical models, the clinical efficacy in human cancer patients has been notably disappointing. One possible explanation for the discrepant pre-clinical and clinical results is that DR5 may play a more prominent role in in vitro model systems as opposed to cancers in humans. Alternatively, these results might indicate that the current classes of therapeutic molecules are not sufficiently potent to elicit significant response in patients. In particular, naturally dimeric antibody agonists require secondary cross-linking via Fcα receptors expressed on immune cells present in the tumor microenvironment to achieve optimal clustering of DR5 into a ternary active state. Because immune cell content in the tumor can be heterogeneous, reliance on this secondary mechanism for activity may limit the potency of these antibodies. To overcome this limitation, a novel nanobody approach was taken to eliminate the need for cross-linking and improve receptor activation with the goal of generating a significantly more potent DR5 agonist. Nanobodies are a class of therapeutic proteins based on single, high affinity heavy chain domain (VHH) antibodies that naturally occur in camelid species, and these VHH domains can be linked to form multivalent structures (di-, tri-, tetra-, etc). This approach led to the development of a tetrameric DR5 targeted agonist, TAS266, with significantly greater avidity for DR5 binding. TAS266 activates downstream caspases with more rapid kinetics and is up to 1000-fold more potent in cell death assays when compared to a cross-linked DR5 antibody or TRAIL. In vivo, TAS266 elicits single dose tumor regressions in multiple tumor xenograft models and sustained tumor regressions after treatment cessation. TAS266 showed superior anti-tumor activity compared to a DR5 agonist antibody and TRAIL, including the ability to induce tumor regression in a patient-derived primary pancreatic tumor model that is insensitive to the agonist antibody. Thus, TAS266 has the potential for superior clinical activity in settings insensitive to the conventional therapeutic approaches to DR5. First-in-man trials are expected to begin in 2012.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3853. doi:1538-7445.AM2012-3853