Antibody-Based Imaging and Therapy for Precision Medicine

Dual-Functional Nanobody Optical Probes for In Vivo Fluorescence Imaging and Photodynamic Therapy

Nanobodies have gained significant attention as promising tools for cancer diagnostics and treatment due to their unique ability to precisely target specific cancer cells. However, a major challenge lies in the site-specific incorporation of multifunctional molecules into nanobodies, as it is essential to link these molecules in a manner that preserves the nanobody's function and stability while retaining the desired therapeutic or diagnostic properties. This study outlines the development of dual-functional nanobody optical probes for enhanced cancer diagnostics and therapeutic interventions. We designed a dual-functional clickable linker that enables site-specific functionalization of the nanobody, facilitating the simultaneous conjugation of two dyes: indocyanine green for imaging and chlorin e6 for photodynamic therapy. In vitro cellular assays confirmed the successful labeling of the dual-functional dyes, with the nanobody probe exhibiting high cellular binding specificity. In vivo imaging of mice bearing Hep3B tumors revealed clear visualization with a high signal-to-noise ratio. Furthermore, PEGylated probes significantly improved tumor retention, enhancing both imaging contrast and photodynamic therapy efficacy as compared to free chlorin e6. These dual-functional nanobody probes show great promise for the precise diagnosis and treatment of malignant tumors.

Production of site-specific antibody conjugates using metabolic glycoengineering and novel Fc glycovariants

Molecular conjugation to antibodies has emerged as a growing strategy to combine the mechanistic activities of the attached molecule with the specificity of antibodies. A variety of technologies have been applied for molecular conjugation; however, these approaches face several limitations, including disruption of antibody structure, destabilization of the antibody, and/or heterogeneous conjugation patterns. Collectively, these challenges lead to reduced yield, purity, and function of conjugated antibodies. While glycoengineering strategies have largely been applied to study protein glycosylation and manipulate cellular metabolism, these approaches also harbor great potential to enhance the production and performance of protein therapeutics. Here, we devise a novel glycoengineering workflow for the development of site-specific antibody conjugates. This approach combines metabolic glycoengineering using azido-sugar analogs with newly installed N-linked glycosylation sites in the antibody constant domain to achieve specific conjugation to the antibody via the introduced N-glycans. Our technique allows facile and efficient manufacturing of well-defined antibody conjugates without the need for complex or destructive chemistries. Moreover, the introduction of conjugation sites in the antibody fragment crystallizable (Fc) domain renders this approach widely applicable and target agnostic. Our platform can accommodate up to three conjugation sites in tandem, and the extent of conjugation can be tuned through the use of different sugar analogs or production in different cell lines. We demonstrated that our platform is compatible with various use-cases, including fluorescent labeling, antibody-drug conjugation, and targeted gene delivery. Overall, this study introduces a versatile and effective yet strikingly simple approach to producing antibody conjugates for research, industrial, and medical applications.

Application of Microfluidic Devices for Automated Two-Step Radiolabeling of Antibodies

Radioimmunoconjugates (RICs) composed of tumor-targeting monoclonal antibodies and radionuclides have been developed for diagnostic and therapeutic application. A new radiolabeling method using microfluidic devices is expected to facilitate simpler and more rapid synthesis of RICs. In the microfluidic method, microfluidic chips can promote the reaction between reactants by mixing them efficiently, and pumping systems enable automated synthesis. In this study, we synthesized RICs by the pre-labeling method, in which the radiometal is coordinated to the chelator and then the radiolabeled chelator is incorporated into the antibodies, using microfluidic devices for the first time. As a result of examining the reaction parameters including the material of mixing units, reaction temperature, and flow rate, RICs with radiochemical purity (RCP) exceeding 90% were obtained. These high-purity RICs were successfully synthesized without any purification simply by pumping three solutions of a chelating agent, radiometal, and antibody into microfluidic devices. Under the same conditions, the RCP of RICs labeled by conventional methods was below 50%. These findings indicate the utility of microfluidic devices for automatic and rapid synthesis of high-quality RICs.

Synthesis and Evaluation of a Cathepsin B-Recognizing Trifunctional Chelating Agent to Improve Tumor Retention of Radioimmunoconjugates

Cathepsin B (CTSB) is a lysosomal protease that is overexpressed in tumor cells. Radioimmunoconjugates (RICs) composed of CTSB-recognizing chelating agents are expected to increase the molecular weights of their radiometabolites by forming conjugates with CTSB in cells, resulting in their improved retention in tumor cells. We designed a novel CTSB-recognizing trifunctional chelating agent, azide-[111In]In-DOTA-CTSB-substrate ([111In]In-ADCS), to synthesize a RIC, trastuzumab-[111In]In-ADCS ([111In]In-TADCS), and evaluated its utility to improve tumor retention of the RIC. [111In]In-ADCS and [111In]In-TADCS were synthesized with satisfactory yield and purity. [111In]In-ADCS was markedly stable in murine plasma until 96 h postincubation. [111In]In-ADCS showed binding to CTSB in vitro, and the conjugation was blocked by the addition of CTSB inhibitor. In the internalization assay, [111In]In-TADCS exhibited high-level retention in SK-OV-3 cells, indicating the in vitro utility of the CTSB-recognizing unit. In the biodistribution assay, [111In]In-TADCS showed high-level tumor accumulation, but the retention was hardly improved. In the first attempt to combine a CTSB-recognizing unit and RIC, these findings show the fundamental properties of the CTSB-recognizing trifunctional chelating agent to improve tumor retention of RICs.

Site-Specific Modification of Single Domain Antibodies by Enzyme-Immobilized Magnetic Beads

Nanobodies as imaging agents and drug conjugates have shown great potential for cancer diagnostics and therapeutics. However, site-specific modification of a nanobody with microbial transglutaminase (mTGase) encounters problems in protein separation and purification. Here, we describe a facile yet reliable strategy of immobilizing mTGase onto magnetic beads for site-specific nanobody modification. The mTGase immobilized on magnetic beads (MB-mTGase) exhibits catalytic activity nearly equivalent to that of the free mTGase, with good reusability and universality. Magnetic separation simplifies the protein purification step and reduces the loss of nanobody bioconjugates more effectively than size exclusion chromatography. Using MB-mTGase, we demonstrate site-specific conjugation of nanobodies with fluorescent dyes and polyethylene glycol molecules, enabling targeted immunofluorescence imaging and improved circulation dynamics and tumor accumulation in vivo. The combined advantages of MB-mTGase method, including high conjugation efficiency, quick purification, less protein loss, and recycling use, are promising for site-specific nanobody functionalization and biomedical applications.

18F-5-FPN: A Specific Probe for Monitoring Photothermal Therapy Response in Malignant Melanoma

Previously, we successfully synthesized a ¹⁸F-labeled positron-emission tomography (PET) tracer, termed ¹⁸F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide (¹⁸F-5-FPN), with high specificity for melanin. In this study, we sought to investigate the value of ¹⁸F-5-FPN in assessing the response to photothermal therapy (PTT) in melanoma via comparison with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) to reveal an early response, recognize early recurrence, and distinguish the inflammatory response during the treatment. B16F10, inflammatory, and MDA-MB-231 models were subjected to ¹⁸F-FDG PET and ¹⁸F-5-FPN PET static acquisitions. We compared quantitative data to assess the specificity of different agents for different diseases. B16F10 and MDA-MB-231subcutaneous tumor models were irradiated with an 808 nm laser for PTT. Their survival was documented to observe the efficacy of and response to PTT, using ¹⁸F-5-FPN and ¹⁸F-FDG PET. ¹⁸F-5-FPN accumulated in B16F10 cell xenografts only, whereas ¹⁸F-FDG accumulated in all three models. Melanin in B16F10 cell xenografts successfully transformed the optical energy into heat. Hematoxylin and eosin (H&E) staining at 24 h revealed destruction and extensive necrosis of tumor tissue. PTT rapidly inhibited the growth of B16F10 cell xenografts and prolonged the median survival. The mean tumor uptakes of ¹⁸F-5-FPN on day 2 (7.52 ± 3.65 %ID/g) and day 6 (10.22 ± 6.00 %ID/g) were much lower than that before treatment (18.33 ± 4.98 %ID/g, p < 0.01). However, a significant difference in ¹⁸F-FDG uptakes was not found between day 1 after PTT and before treatment. Compared with ¹⁸F-FDG, ¹⁸F-5-FPN PET could estimate PTT efficacy in melanoma, monitor minimal recurrence, and distinguish melanoma from inflammation and other carcinoma types, thanks to its high affinity to melanin. ¹⁸F-5-FPN may provide a new approach for precise and accurate evaluation of response, timely management of therapeutic regimens, and sensitive follow-up.