Subcutaneous (SC) administration of monoclonal antibodies (mAbs) enhances patient compliance and therapeutic efficacy but remains challenging for antibody-drug conjugates (ADCs) due to formulation instability, delivery constraints, and immunogenicity risks. Conventional SC formulations require cold-chain storage and often display variable bioavailability. Here, we introduce a zwitterionic chitosan-based hydrogel that enables controlled release and prolonged stability of mAbs and ADCs at ambient temperature, offering a scalable alternative for clinical translation.

Zwitterionic chitosan-based hydrogels were designed for the sustained release of trastuzumab, rituximab, trastuzumab/pertuzumab, and trastuzumab-emtansine (T-DM1). Comprehensive characterization was performed, including rheology, injectability, stability, and in vitro release kinetics. Two lead formulations were developed: chitosan@DOTAGA:chitosan for mAbs and a zwitterionic chitosan-only hydrogel optimized for ADCs to ensure cGMP compliance. Pharmacokinetic (PK) studies in murine and nonhuman primate (NHP) models compared these formulations to standard-of-care therapies (Herceptin® SC and Kadcyla® IV, respectively). Tolerability was assessed using ex vivo human skin explants, while therapeutic efficacy was evaluated in HER2+ xenograft models with multidose (trastuzumab) and monodose (T-DM1) administration.

The chitosan@DOTAGA:chitosan-mAb hydrogel preserved the structural integrity of trastuzumab for up to 15 days at ambient temperature. Functional stability was confirmed via SECnMS and peptide mapping. In vivo, the hydrogel underwent complete biodegradation in both murine and NHP models, with no detectable immune activation. PK studies in NHPs revealed comparable systemic exposure profiles to SC formulations utilizing rHuPH20. For the zwitterionic chitosan-only hydrogel encapsulating T-DM1, ADC integrity was preserved for over one month at ambient temperature, with no inflammatory response detected in patient skin explants. In murine models, SC administration of the hydrogel resulted in a prolonged systemic exposure duration (9.5 vs. 5.6 mg·day/mL) compared to IV administration. In a HER2+ xenograft tumor model, therapeutic efficacy studies confirmed that tumor growth inhibition following hydrogel-mediated ADC delivery was comparable to clinically approved IV T-DM1, underscoring the potential for sustained SC drug delivery.

Our zwitterionic chitosan-based hydrogel formulations overcome key barriers in SC biologic delivery, providing extended stability and precise drug release while eliminating cold-chain constraints. By ensuring prolonged bioavailability and therapeutic efficacy, this platform offers a clinically viable strategy for next-generation SC biosimilars and ADC therapies.