Karen Cromie

Multivalent nanobodies targeting death receptor 5 elicit superior tumor cell killing through efficient caspase induction

Multiple therapeutic agonists of death receptor 5 (DR5) have been developed and are under clinical evaluation. Although these agonists demonstrate significant anti-tumor activity in preclinical models, the clinical efficacy in human cancer patients has been notably disappointing. One possible explanation might be that the current classes of therapeutic molecules are not sufficiently potent to elicit significant response in patients, particularly for dimeric antibody agonists that require secondary cross-linking via Fcγ receptors expressed on immune cells to achieve optimal clustering of DR5. To overcome this limitation, a novel multivalent Nanobody approach was taken with the goal of generating a significantly more potent DR5 agonist. In the present study, we show that trivalent DR5 targeting Nanobodies mimic the activity of natural ligand, and furthermore, increasing the valency of domains to tetramer and pentamer markedly increased potency of cell killing on tumor cells, with pentamers being more potent than tetramers in vitro. Increased potency was attributed to faster kinetics of death-inducing signaling complex assembly and caspase-8 and caspase-3 activation. In vivo, multivalent Nanobody molecules elicited superior anti-tumor activity compared to a conventional DR5 agonist antibody, including the ability to induce tumor regression in an insensitive patient-derived primary pancreatic tumor model. Furthermore, complete responses to Nanobody treatment were obtained in up to 50% of patient-derived primary pancreatic and colon tumor models, suggesting that multivalent DR5 Nanobodies may represent a significant new therapeutic modality for targeting death receptor signaling.

Potent and Efficacious Inhibition of CXCR2 Signaling by Biparatopic Nanobodies Combining Two Distinct Modes of Action

Chemokines and chemokine receptors are key modulators in inflammatory diseases and malignancies. Here, we describe the identification and pharmacologic characterization of nanobodies selectively blocking CXCR2, the most promiscuous of all chemokine receptors. Two classes of selective monovalent nanobodies were identified, and detailed epitope mapping showed that these bind to distinct, nonoverlapping epitopes on the CXCR2 receptor. The N-terminal–binding or class 1 monovalent nanobodies possessed potencies in the single-digit nanomolar range but lacked complete efficacy at high agonist concentrations. In contrast, the extracellular loop-binding or class 2 monovalent nanobodies were of lower potency but were more efficacious and competitively inhibited the CXCR2-mediated functional response in both recombinant and neutrophil in vitro assays. In addition to blocking CXCR2 signaling mediated by CXCL1 (growth-related oncogene α) and CXCL8 (interleukin-8), both classes of nanobodies displayed inverse agonist behavior. Bivalent and biparatopic nanobodies were generated, respectively combining nanobodies from the same or different classes via glycine/serine linkers. Interestingly, receptor mutation and competition studies demonstrated that the biparatopic nanobodies were able to avidly bind epitopes within one or across two CXCR2 receptor molecules. Most importantly, the biparatopic nanobodies were superior over their monovalent and bivalent counterparts in terms of potency and efficacy.

Abstract 3853: TAS266, a novel tetrameric nanobody agonist targeting death receptor 5 (DR5), elicits superior antitumor efficacy than conventional DR5-targeted approaches

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