Highly-efficient and versatile fluorous-tagged Cu(I)-catalyzed azide-alkyne cycloaddition ligand for preparing bioconjugates

The use of a uPAR-targeted probe for photothermal cancer therapy prolongs survival in a xenograft mouse model of glioblastoma

The development of tumor-targeted probes that can efficiently reach cancerous tissue is an important focus of preclinical research. Photothermal cancer therapy (PTT) relies on light-absorbing molecules, which are directed towards tumor tissue and irradiated with an external source of light. This light is transformed into heat, causing localized hyperthermia and tumor death. The fluorescent probe indocyanine green (ICG) is already used as an imaging agent both preclinically and in clinical settings, but its use for PTT is yet to be fully exploited due to its short retention time and non-specific tumor targeting. Therefore, increasing ICG tumor uptake is necessary to improve treatment outcome. The urokinase-type plasminogen activator receptor, uPAR, is overexpressed in multiple tumor types. ICG-Glu-Glu-AE105, consisting of the uPAR-targeting peptide AE105 conjugated to ICG, has shown great potential for fluorescence-guided surgery. In this study, ICG-Glu-Glu-AE105 was evaluated as photothermal agent in a subcutaneous mouse model of human glioblastoma. We observed that the photothermal abilities of ICG-Glu-Glu-AE105 triggered high temperatures in the tumor during PTT, leading to tumor death and prolonged survival. This confirms the potential of ICG-Glu-Glu-AE105 as photothermal agent and indicates that it could be used as an add-on to the application of the probe for fluorescence-guided surgery.

An Overview of Antibody Conjugated Polymeric Nanoparticles for Breast Cancer Therapy

Nanoparticles (NPs) are promising drug delivery systems (DDS) for identifying and treating cancer. Active targeting NPs can be generated by conjugation with ligands that bind overexpressed or mutant cell surface receptors on target cells that are poorly or not even expressed on normal cells. Receptor-mediated endocytosis of the NPs occurs and the drug is released inside the cell or in the surrounding tissue due to the bystander effect. Antibodies are the most frequently used ligands to actively target tumor cells. In this context, antibody-based therapies have been extensively used in HER2+ breast cancer. However, some patients inherently display resistance and in advanced stages, almost all eventually progress. Functionalized NPs through conjugation with antibodies appear to be a promising strategy to optimize targeted therapies due to properties related to biocompatibility, suitable delivery control and efficiency of functionalization. This review is focused on the different strategies to conjugate antibodies into polymeric NPs. Recent antibody conjugation approaches applied to the improvement of breast cancer therapy are highlighted in this review.

Photo-Click-Facilitated Screening Platform for the Development of Hetero-Bivalent Agents with High Potency

A novel photo-click-based platform has been developed for rapid screening and affinity optimization of heterobivalent agents. This method allows for the efficient selection of high-affinity dual receptor-targeting agents via streamlining tedious organic synthesis and biological evaluation procedures required by traditional approaches. The high-avidity heterobivalent agents targeting both integrin α_vβ₃ and urokinase-type plasminogen activator receptors have been developed using this photo-click-facilitated screening platform. The affinity screening results were further validated by traditional in vitro and in vivo evaluation techniques, reaffirming the reliability of the method. The convenience, rapidity, universality, and robustness of the screening platform, discussed in this report, can greatly facilitate the development of new heterobivalent agents for research and/or clinical applications.

Functionalizing nanoparticles with cancer-targeting antibodies: A comparison of strategies

Standard cancer therapies sometimes fail to deliver chemotherapeutic drugs to tumor cells in a safe and effective manner. Nanotechnology takes the lead in providing new therapeutic options for cancer due to major potential for selective targeting and controlled drug release. Antibodies and antibody fragments are attracting much attention as a source of targeting ligands to bind specific receptors that are overexpressed on cancer cells. Therefore, researchers are devoting time and effort to develop targeting strategies based on nanoparticles functionalized with antibodies, which hold great promise to enhance therapeutic efficacy and circumvent severe side effects. Several methods have been described to immobilize antibodies on the surface of nanoparticles. However, selecting the most appropriate for each application is challenging but also imperative to preserve antigen binding ability and yield stable antibody-conjugated nanoparticles. From this perspective, we aim to provide considerable knowledge on the most widely used methods of functionalization that can be helpful for decision-making and design of conjugation protocols as well. This review summarizes adsorption, covalent conjugation (carbodiimide, maleimide and "click" chemistries) and biotin-avidin interaction, while discussing the advantages, limitations and relevant therapeutic approaches currently under investigation.

Facile Cu(ii)-mediated conjugation of thioesters and thioacids to peptides and proteins under mild conditions

The bioconjugation of peptide derivatives such as polypeptides, peptide-based probes and proteins is a vibrant area in many scientific fields. However, reports on metal-mediated chemical methods towards native peptides especially non-engineering protein modification under mild conditions are still limited. Herein, we describe a novel Cu(ii)-mediated strategy for the conjugation of thioesters/thioacids to peptides under mild conditions with high functional group tolerance. Based on this strategy, polypeptides, even peptide-based fluorescent probes, can be efficiently constructed. Finally, the selective modification of lysine residues of native Ub with thioesters could be realized and complete conjugation of Ub could be achieved even under equivalent Cu(ii). These promising results could greatly expand Cu(ii)-mediated reaction strategies on chemical biology and molecular imaging.

A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry

The copper-catalyzed cycloaddition of organic azides and alkynes (CuAAC) is one of the most popular reactions for rapid assembly of multifunctional molecular frameworks from commercially available building blocks. It is also attractive for synthesis of conjugates of multidentate chelate ligands (chelators) with molecular targeting vectors, such as peptides or proteins, which serve as precursors for labeling with metal radionuclides or are useful as MRI contrast agents after Gd(III) complexation. However, applicability of CuAAC for such purposes is complicated by formation of unwanted copper chelates. The alternative use of copper-free click chemistry, for example, the strain-promoted alkyne-azide cycloaddition (SPAAC) or the Diels-Alder reaction of tetrazines and strained alkenes, entails other specific challenges: Introduction of large, isomerically non-homogeneous and hydrophobic linker groups affects product homogeneity and can severely change pharmacokinetic profiles. Against this background, this review elucidates scope and applicability of both Cu-catalyzed and Cu-free alkyne-azide cycloadditions pertinent to the elaboration of radiometal chelates and MRI contrast agents, with an emphasis on strategies to tackle the problem of copper complexation during CuAAC.

Novel Strategy for Preparing Dual-Modality Optical/PET Imaging Probes via Photo-Click Chemistry

Preparation of small molecule based dual-modality probes remains a challenging task due to the complicated synthetic procedure. In this study, a novel concise and generic strategy for preparing dual-modality optical/PET imaging probes via photo-click chemistry was developed, in which the diazole photo-click linker functioned not only as a bridge between the targeting-ligand and the PET imaging moiety, but also as the fluorophore for optical imaging. A dual-modality AE105 peptidic probe was successfully generated via this strategy and subsequently applied in the fluorescent staining of U87MG cells and the (68)Ga based PET imaging of mice bearing U87MG xenograft. In addition, dual-modality monoclonal antibody cetuximab has also been generated via this strategy and labeled with (64)Cu for PET imaging studies, broadening the application of this strategy to include the preparation of macromolecule based imaging probes.