Abstract 2464: DART® molecules with enhanced DR5 agonistic activity for improved cancer cell cytotoxicity

Introduction: Death Receptor 5 (DR5) belongs to the tumor necrosis factor receptor superfamily. The target and its associated signaling pathway are preferentially active on cancer cells. DR5 elicits pro-apoptotic signal through receptor oligomerization upon binding of TRAIL or an agonistic mAb. Chemotherapy and radiation also can synergize with the DR5 pathway. Various therapeutics targeting DR5 have been generated but clinical outcomes have been generally disappointing. Here we describe optimization of the agonistic activity of anti-DR5 mAbs by enabling multivalent target engagement via engineering into DARTs; covalently-linked Fv-based diabodies optimized for manufacturability and stability (1) whose modular nature facilitates tailoring avidity and PK properties to the specific needs of the application. Methods: Anti-DR5 mAbs were selected from a panel of mAbs generated from cancer cell immunizations and characterized for binding properties. DARTs with varying anti-DR5 specificities, valency and incorporation of either a wild type IgG1 Fc or an Fc mutated to eliminate FcγR binding, were expressed in CHO cells and purified to homogeneity. DR5 DARTs and mAbs were characterized across a panel of cell lines including those derived from colorectal, lung, pancreatic, breast and prostate cancer and by IHC on normal and tumor tissue specimens. Results: mAbs from whole cancer cell immunizations displaying differential expression on both normal and cancer tissues were subjected to antigen identification and identified a subset with reactivity to DR5. Binding analyses revealed DR5 mAbs recognizing non-overlapping epitopes that do not block the TRAIL-DR5 interaction. Upon secondary cross-linking or when combined, the DR5 mAbs induced apoptosis across multiple cancer cell lines. Further potency enhancement independent of secondary cross-linking was obtained by the engineered multivalent DR5-targeting DARTs. Dose-dependent growth inhibition assay demonstrated that the DR5-targeting DARTs delivered significantly greater potency than TRAIL (≥100-fold) across a broad range of cancer cell lines. Furthermore, the DR5-targeting DARTs maintained the exquisite tumor/normal differential reactivity displayed by the parental DR5 mAbs from which they were derived. Combination of an HDAC inhibitor with DR5-targeting DARTs revealed maintenance of synergistic activity and potential to overcome pathway resistance. Conclusion: Whole cancer cell immunizations yielded DR5 mAb candidates with desirable binding and functional properties. Through incorporation of the anti-DR5 mAb specificities into multivalent DART molecules, we have generated a new class of therapeutics that may overcome the limitations of existing DR5-based therapeutics. The data support the use of DR5-targeting DARTs to target this apoptotic pathway in multiple cancer cells. Reference: (1) Johnson et al. 2010. J Mol Bio. 399:436-49 Citation Format: Jonathan C. Li, Kalpana Shah, Jill Rillema, Francine Chen, Doug Smith, Steve Burke, Valentina Ciccarone, Sergey Gorlatov, Ralph Alderson, James Tamura, Ezio Bonvini, Syd Johnson, Paul A. Moore. DART® molecules with enhanced DR5 agonistic activity for improved cancer cell cytotoxicity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2464. doi:10.1158/1538-7445.AM2015-2464