Abstract C158: Tumor-specific inhibition of jagged-dependent notch signaling using a Probody™ therapeutic.
Authors: Sagert Jason , West James , Vasiljeva Olga , Richardson Jennifer , Desnoyers Luc , Liu Shouchun , Yang Annie , Wong Chihunt , Menendez Elizabeth , Polu Krishna , Lowman Henry 
Published: August 2014

Abstract
Probodies represent a unique class of antibody-based therapeutics that specifically target activity to diseased tissues including cancer. Probodies are designed to be inactive in circulation and in healthy tissue and activated only within the tumor microenvironment by dysregulated protease activity. The Probody approach enables promising therapeutic targets not druggable with conventional antibodies due to toxicity. Inhibition of Notch signaling has revealed the therapeutic potential of targeting this pathway in cancer; however, systemic inhibition results in severe toxicities (e.g. gastrointestinal and cardiac) in preclinical and clinical studies limiting the development of Notch-targeting therapeutics. We have developed a fully human IgG1 monoclonal antibody that binds and inhibits the activity of both human and mouse Jagged1 and Jagged2 (Jagged1/2). In vitro cell based assays and in vivo ectopic xenograft mouse tumor models (BxPC3 and H292) show dose-dependent inhibition of Notch signaling and anti-tumor activity, respectively. However, the antibody also shows profound toxicities in mice, including weight loss, alopecia, hyperkeratosis, and athymia, due to on-target inhibition of Jagged1/2 in healthy tissue. To address these toxicities, we developed a fully recombinant anti-Jagged1/2 Probody, CTX-033, comprised of the same antibody but with a unique peptide mask that blocks the antigen binding site linked to the light chain of the antibody by a linker containing a substrate that is cleavable by one or more proteases upregulated in cancer. CTX-033 had similar anti-tumor activity in the mouse xenograft models as compared to the antibody. However, despite a two-fold higher systemic exposure to CTX-033 as compared to the antibody, Probody treated mice did not exhibit the toxicities associated with the antibody treatment. Furthermore, CTX-033 shows additive anti-tumor efficacy when combined with gemcitabine in the BxPC3 model. Notably, the Probody plus gemcitabine combination lacks the significant toxicity associated with the antibody plus gemcitabine combination treatment. To validate both Jagged expression and protease activity in patient tumor samples, we used a novel in situ assay, immunofluorescent Probody zymography. The results reveal broad expression of the Jagged ligands and specific activation and binding of CTX-033 in patient pancreatic adenocarcinoma tissue samples. The data described here with the anti-Jagged Probody, CTX-033, demonstrates (1) the potential of the Probody platform to enable the safe targeting of two key ligands in the Notch signaling pathway not possible with a traditional antibody format and (2) the presence of both Jagged1/2 and proteases capable of activating CTX-033 in patient tumor samples.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C158.
Citation Format: Jason Sagert, James West, Olga Vasiljeva, Jennifer Richardson, Luc Desnoyers, Shouchun Liu, Annie Yang, Chihunt Wong, Elizabeth Menendez, Krishna Polu, Henry Lowman. Tumor-specific inhibition of jagged-dependent notch signaling using a Probody™ therapeutic. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C158.