Title : Rational optimization of antibody–cyanine bioconjugates for targeted theranostic drug delivery and photo/sono activation
Abstract:
Photodynamic therapy (PDT) is a well-established treatment modality; however, its clinical translation is limited by poor light penetration in deep tissues. Sonodynamic therapy (SDT), which utilizes ultrasound as an external trigger, offers a promising alternative due to its ability penetrate deeper biological tissues with minimal scattering. Despite this advantage, the development of efficient sonosensitizer systems with controlled structure–property relationships remain limited.
Cyanine dyes are attractive candidates for theranostic applications owing to their strong near-infrared (NIR) absorption and fluorescence properties. Incorporation of heavy atoms, such as iodine, enhances intersystem crossing and promotes reactive oxygen species (ROS) generation, which is critical for both PDT and SDT. However, conjugation of such dyes to antibodies for targeted delivery introduces challenges related to dye aggregation. Aggregation significantly reduces fluorescence intensity, thereby compromising diagnostic imaging capability and limiting the theranostic efficiency of antibody–dye conjugates.
In this work, we focus on the optimization of trastuzumab (Herceptin)-based 2ICy7 conjugates by systematically varying dye equivalence and reaction conditions to obtain controlled dye–antibody ratios (DAR). Aggregation-corrected analysis indicates that intermediate DAR values provide a balance between sufficient dye loading and preservation of optical properties, whereas higher DAR leads to aggregation-induced fluorescence quenching, reducing imaging reliability.
To understand therapeutic performance from a chemical perspective, ROS generation under both photo- and ultrasound irradiation was evaluated using H₂DCFDA and coumarin-based assays. These studies highlight the importance of assessing ROS generation efficiency prior to in vivo experiments, as it directly governs therapeutic outcome and enables rational selection of optimal conjugate design.
Preliminary in vivo studies in a HER2-positive breast cancer mouse model demonstrate effective tumor accumulation of the optimized conjugate and reveal differences in therapeutic response between PDT and SDT, with SDT showing improved tumor suppression under the tested conditions.
This work is currently at a preliminary stage and aims to establish a correlation between DAR, aggregation behavior, and ROS generation efficiency for improved theranostic design. Future studies will extend this strategy to other targeting antibodies, such as cetuximab, for targeted drug delivery in colorectal and other cancers.
