We have established a set of technologies called Tunable Drug Conjugates (TDCs) that will differentiate from other DCs via a rapid payload release/rapid systemic clearance approach intended to quickly drive high toxic “payload” concentrations within tumor cells while minimizing toxicities to patients. TDCs use proprietary Silicon-based linker chemistries (SiLinkers) in novel Payload Cassettes (PCs) that enable the rapid and uniform release of multiple and/or mixed payloads both in the endosome after internalization and within the necrotic microenvironment of tumors. PCs can incorporate multiple copies of the same payload or optimal ratios of different therapeutic agents that work together synergistically to kill cancer cells. A second technology - a Dual variable Domain-Fab (DVD-Fab) targeting capability provides a proprietary means of specifically targeting a broad array of cell surface proteins. DVD-Fab containing TDCs should be cleared from the body within hours, enabling better management of side-effects. Our Silinker system is differentiated by the exquisite and tunable sensitivity of the linkers to cleavage under the modestly acidic conditions encountered in the endosomal and lysosomal compartments of a cell, and in the microenvironment of solid tumors. Good stability at physiological pH (and in human plasma) compares to rapid cleavage at relevant lower pHs as demonstrated using model systems. SiLinkers exhibit good stability at 37°C in pH7.4 buffer (and plasma) and show rapid hydrolysis at pH ~5.5 to 6.5 (t1/2 = 15 - 120 min). Confocal microscopy studies with imaging constructs demonstrate the translation of the in vitro data to cellular systems. We assembled SiLinker based prototype TDCs to target the folate receptor α (FAR) with folic acid as the targeting ligand and vinblastine analogs as the payload(s). We used single and PC drug conjugates to show cellular and in vivo proof-of-concept. We tested our TDCs in cell lines overexpressing FAR and showed that cytotoxicity was blocked by excess folic acid. Subsequent in vivo studies, using a nude mouse xenograft model, showed good antitumor activity for these prototype TDCs. BB-01 (a single payload construct) showed a clear dose response and had cures in 3 out of 5 mice after 24 days on a 3 μmol/kg TIW schedule. BB-03 (a triple PC construct) shows essentially complete tumor regression compared to modest inhibition by BB-01 at doses that deliver equivalent amounts of payload, demonstrating the synergistic potential of the PC concept to enhance the activity. We have also synthesized DVD-Fab TDCs. DVD-Fabs contain a reactive chemical group for seamless connection with our SiLinkers and PCs. We will describe conjugation chemistries and present cellular and in vivo Xenograft data for prototype DVD-Fab TDCs.

Citation Format: Sara C. Hickey, Alex R. Nanna, Hanh N. Nguyen, Leslie Ofori, Christoph Rader, Michael K. Rood, Jutta Wanner, Doug S. Werner. Tunable Drug Conjugates: a differentiated drug conjugate (DC) platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5153. doi:10.1158/1538-7445.AM2017-5153