Enhanced Tumor Uptake and Retention of Cyanine Dye-Albumin Complex for Tumor-Targeted Imaging and Phototherapy

Heptamethine cyanine dyes are widely used for in vivo near-infrared (NIR) fluorescence imaging and NIR laser-induced cancer phototherapy due to their good optical properties. Since most of heptamethine cyanine dyes available commercially are highly hydrophobic, they can usually be used for in vivo applications after formation of complexes with blood plasma proteins, especially serum albumin, to increase aqueous solubility. The complex formation between cyanine dyes and albumin improves the chemical stability and optical property of the hydrophobic cyanine dyes, which is the bottom of their practical use. In this study, the complexes between three different heptamethine cyanine dyes, namely clinically available indocyanine green (ICG), commercially available IR-786 and zwitterionic ZW800-Cl, and bovine serum albumin (BSA), were prepared to explore the effect of cyanine dyes on their tumor uptake and retention. Among the three complexes, IR-786©BSA exhibited increased tumor accumulation with prolonged tumor retention, compared to other complexes. Moreover, IR-786 bound to BSA played an important role in tumor growth suppression due to its cytotoxicity. To achieve complete tumor ablation, the tumor targeted by IR-786©BSA was further exposed to 808 nm laser irradiation for effective photothermal cancer treatment.

Molecular Tuning of IR-786 for Improved Tumor Imaging and Photothermal Therapy

A tumor-targeted near-infrared (NIR) fluorophore CA800Cl was developed based on commercially available IR-786 by modulating its physicochemical properties. IR-786, a hydrophobic cationic heptamethine cyanine fluorophore, was previously recognized as a mitochondria-targeting NIR agent with excellent optical properties. Owing to the poor tumor specificity of IR-786 itself, in vivo studies on tumor-targeted imaging have not yet been investigated. A chloro-cyclohexene ring and indolium side groups on the heptamethine chain are key structural features that improve tumor targetability, owing to better biodistribution and clearance. Thus, IR-786 should be designed to be more soluble in aqueous solutions so that it can preferentially accumulate in the tumor based on the structure-inherent targeting strategy. In this study, we developed a bifunctional NIR fluorophore CA800Cl by incorporating carboxylate moieties in the basic structure of IR-786. This improved its tumor targetability and water solubility, thereby enabling the use of CA800Cl for enhanced photothermal cancer therapy.

Heptamethine Cyanine–Based Application for Cancer Theranostics

Cancer is the most common life-threatening malignant disease. The future of personalized cancer treatments relies on the development of functional agents that have tumor-targeted anticancer activities and can be detected in tumors through imaging. Cyanines, especially heptamethine cyanine (Cy7), have prospective application because of their excellent tumor-targeting capacity, high quantum yield, low tissue autofluorescence, long absorption wavelength, and low background interference. In this review, the application of Cy7 and its derivatives in tumors is comprehensively explored. Cy7 is enormously acknowledged in the field of non-invasive therapy that can “detect” and “kill” tumor cells via near-infrared fluorescence (NIRF) imaging, photothermal therapy (PTT), and photodynamic therapy (PDT). Furthermore, Cy7 is more available and has excellent properties in cancer theranostics by the presence of multifunctional nanoparticles via fulfilling multimodal imaging and combination therapy simultaneously. This review provides a comprehensive scope of Cy7’s application for cancer NIRF imaging, phototherapy, nanoprobe-based combination therapy in recent years. A deeper understanding of the application of imaging and treatment underlying Cy7 in cancer may provide new strategies for drug development based on cyanine. Thus, the review will lead the way to new types with optical properties and practical transformation to clinical practice.

Discovery of novel phenaleno isoquinolinium-based fluorescence imaging agents for sentinel lymph node mapping

Fluorescence imaging agents have recently received huge attention due to their important role in disease diagnostics. However, the intrinsic problems of these probes, such as complex synthetic routes and high molecular weight, remain challenging. Here, we developed novel phenaleno isoquinolinium-based fluorescent agents, Medical Fluorophores 37-41 (MF37-41), applicable to the quantitative and sensitive detection of sentinel lymph nodes (SLNs). These imaging agents showed no adverse effects on the proliferation of immune and normal cells and did not induce in vivo toxicity. In vivo fluorescence lifetime imaging demonstrated the accumulation of phenaleno isoquinolinium salts in the SLNs of nude mice within 15 min postinjection, consistent with our biodistribution findings. These results suggest that phenaleno isoquinolinium salts are feasible fluorescence imaging agents that can be used as potential lymphatic tracers.

Tumor-Targeted ZW800-1 Analog for Enhanced Tumor Imaging and Photothermal Therapy

ZW800-1, a representative zwitterionic near-infrared (NIR) fluorophore, can minimize background tissue uptake owing to its balanced surface charges, and therefore, is widely used for improved NIR fluorescence imaging. As ZW800-1 has no tumor targetability, tumor imaging is highly dependent on the ability of the molecules conjugated to the ZW800-1. To enable tumor targeting using ZW800-1 without additional conjugation, we developed a tumor-targetable and renal-clearable ZW800-1 analog (ZW800-AM) based on the structural modification of ZW800-1. Specifically, an amine group on the center linker of the ZW800-1 indocyanine backbone was modified by replacing phenoxypropionic acid with tyramine linkage on the meso-chlorine atom. This modification improved the tumor targeting ability, which is known as the structure-inherent targeting strategy. More importantly, ZW800-AM not only showed sufficient tumor accumulation without nonspecific uptake but also produced a photothermal effect, killing tumor cells under 808 nm NIR laser irradiation. In addition, ZW800-AM exhibited rapid renal elimination from the body within 4 h of injection, similar to ZW800-1. Overall, the discovery of ZW800-AM as a bifunctional phototherapeutic agent may provide an ideal alternative for tumor-targeted imaging and phototherapy.

Fluorescence Guided Surgery

Fluorescence guided surgery (FGS) is an imaging technique that allows the surgeon to visualise different structures and types of tissue during a surgical procedure that may not be as visible under white light conditions. Due to the many potential advantages of fluorescence guided surgery compared to more traditional clinical imaging techniques such as its higher contrast and sensitivity, less subjective use, and ease of instrument operation, the research interest in fluorescence guided surgery continues to grow over various key aspects such as fluorescent probe development and surgical system development as well as its potential clinical applications. This review looks to summarise some of the emerging opportunities and developments that have already been made in fluorescence guided surgery in recent years while highlighting its advantages as well as limitations that need to be overcome in order to utilise the full potential of fluorescence within the surgical environment.

Membrane engineering of cell membrane biomimetic nanoparticles for nanoscale therapeutics

In recent years, cell membrane camouflaging technology has emerged as an important strategy of nanomedicine, and the modification on the membranes is also a promising approach to enhance the properties of the nanoparticles, such as cancer targeting, immune evasion, and phototherapy sensitivity. Indeed, diversified approaches have been exploited to re-engineer the membranes of nanoparticles in several studies. In this review, first we discuss direct modification strategy of cell membrane camouflaged nanoparticles (CM-NP) via noncovalent, covalent, and enzyme-involved methods. Second, we explore how the membranes of CM-NPs can be re-engineered at the cellular level using strategies such as genetic engineering and membranes fusion. Due to the innate biological properties and excellent biocompatibility, the functionalized cell membrane-camouflaged nanoparticles have been widely applied in the fields of drug delivery, imaging, detoxification, detection, and photoactivatable therapy.

Indocyanine Green and Methyl-β-Cyclodextrin Complex for Enhanced Photothermal Cancer Therapy

A feasible and biocompatible supramolecular complex self-assembled from indocyanine green (ICG) and methyl-β-cyclodextrin (Mβ-CD) was developed for targeted cancer imaging, which enhanced fluorescence-guided photothermal cancer therapy. This study confirmed that the formation of an inclusion complex of the heterocyclic ICG moiety and Mβ-CD inner cavity could result in improved tumor targetability compared with free ICG. The ICG-CD complex could be used as a bifunctional phototherapeutic agent for targeted cancer phototherapy due to the high tumor targetability of the Mβ-CD moiety and effective photothermal performance of the near-infrared (NIR) ICG moiety. Upon NIR laser irradiation, the photothermal effect exerted by the ICG-CD complex significantly enhanced the temperature at the tumor site by 56.2 °C within 5 min. Targeting HT-29 tumors using the ICG-CD complex resulted in an apparent reduction in tumor volumes over the 9 days after photothermal treatment. Moreover, no tumor recurrence or body weight loss were observed after administering a single dose of ICG-CD complex with NIR laser irradiation. Therefore, the administration of the biocompatible ICG-CD complex in combination with NIR laser treatment can be safely explored as a potential strategy for future clinical applications.

Hybrid Multimodal Imaging Synthons for Chemoselective and Efficient Biomolecule Modification with Chelator and Near-Infrared Fluorescent Cyanine Dye

The development of hybrid multimodal imaging synthons (MIS), carrying in addition to a chelator for radiometal labeling also a near-infrared (NIR) fluorescent cyanine dye was the aim of this work. The MIS should be introducible into biomolecules of choice via an efficient and chemoselective click chemistry reaction. After chemical optimization, a successful synthetic strategy towards such hybrid MIS was developed, based on solid phase-based synthesis techniques and applying different near-infrared fluorescent cyanine dyes. The developed hybrid agents were shown to be easily introducible into a model homobivalent peptidic gastrin-releasing peptide receptor- (GRPR)-specific carrier without forming any side products and the MIS as well as their bioconjugates were radiolabeled with the positron-emitter ⁶⁸Ga³⁺. The hybrid multimodal agents were characterized with regard to their log_Ds, GRPR target affinities and photophysical characteristics. It could be shown that the properties of the bioconjugates were not per se affected by the introduction of the MIS but that the cyanine dye used and specifically the number of comprised negative charges per dye molecule can have a considerable influence on target receptor binding. Thus, the molecular toolbox described here enables the synthesis of tailored hybrid multimodal imaging synthons for biomolecule modification, meeting the specific need and envisioned application of the combined imaging agent.