ZW800-PEG: A Renal Clearable Zwitterionic Near-Infrared Fluorophore for Potential Clinical Translation

Lessons learned in application driven imaging agent design for image-guided surgery

To meet the growing demand for intraoperative molecular imaging, the development of compatible imaging agents plays a crucial role. Given the unique requirements of surgical applications compared to diagnostics and therapy, maximizing translational potential necessitates distinctive imaging agent designs. For effective surgical guidance, exogenous signatures are essential and are achievable through a diverse range of imaging labels such as (radio)isotopes, fluorescent dyes, or combinations thereof. To achieve optimal in vivo utility a balanced molecular design of the tracer as a whole is required, which ensures a harmonious effect of the imaging label with the affinity and specificity (e.g., pharmacokinetics) of a pharmacophore/targeting moiety. This review outlines common design strategies and the effects of refinements in the molecular imaging agent design on the agent's pharmacological profile. This includes the optimization of affinity, pharmacokinetics (including serum binding and target mediated background), biological clearance route, the achievable signal intensity, and the effect of dosing hereon.

Fluorescence Imaging Using Deep-Red Indocyanine Blue, a Complementary Partner for Near-Infrared Indocyanine Green

Indocyanine Blue (ICB) is the deep-red pentamethine analogue of the widely used clinical near-infrared heptamethine cyanine dye Indocyanine Green (ICG). The two fluorophores have the same number of functional groups and molecular charge and vary only by a single vinylene unit in the polymethine chain, which produces a predictable difference in spectral and physicochemical properties. We find that the two dyes can be employed as a complementary pair in diverse types of fundamental and applied fluorescence imaging experiments. A fundamental fluorescence spectroscopy study used ICB and ICG to test a recently proposed Förster Resonance Energy Transfer (FRET) mechanism for enhanced fluorescence brightness in heavy water (D2O). The results support two important corollaries of the proposal: (a) the strategy of using heavy water to increase the brightness of fluorescent dyes for microscopy or imaging is most effective when the dye emission band is above 650 nm, and (b) the magnitude of the heavy water florescence enhancement effect for near-infrared ICG is substantially diminished when the ICG surface is dehydrated due to binding by albumin protein. Two applied fluorescence imaging studies demonstrated how deep-red ICB can be combined with a near-infrared fluorophore for paired agent imaging in the same living subject. One study used dual-channel mouse imaging to visualize increased blood flow in a model of inflamed tissue, and a second mouse tumor imaging study simultaneously visualized the vasculature and cancerous tissue in separate fluorescence channels. The results suggest that ICB and ICG can be incorporated within multicolor fluorescence imaging methods for perfusion imaging and hemodynamic characterization of a wide range of diseases.

Aggregation-enhanced photothermal therapy of organic dyes

Photothermal therapy (PTT) represents a groundbreaking approach to targeted disease treatment by harnessing the conversion of light into heat. The efficacy of PTT heavily relies on the capabilities of photothermal agents (PTAs). Among PTAs, those based on organic dyes exhibit notable characteristics such as adjustable light absorption wavelengths, high extinction coefficients, and high compatibility in biological systems. However, a challenge associated with organic dye-based PTAs lies in their efficiency in converting light into heat while maintaining stability. Manipulating dye aggregation is a key aspect in modulating non-radiative decay pathways, aiming to augment heat generation. This review delves into various strategies aimed at improving photothermal performance through constructing aggregation. These strategies including protecting dyes from photodegradation, inhibiting non-photothermal pathways, maintaining space within molecular aggregates, and introducing intermolecular photophysical processes. Overall, this review highlights the precision-driven assembly of organic dyes as a promising frontier in enhancing PTT-related applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Precise and safe pulmonary segmentectomy enabled by visualizing cancer margins with dual-channel near-infrared fluorescence

BACKGROUND

Segmentectomy is a type of limited resection surgery indicated for patients with very early-stage lung cancer or compromised function because it can improve quality of life with minimal removal of normal tissue. For segmentectomy, an accurate detection of the tumor with simultaneous identification of the lung intersegment plane is critical. However, it is not easy to identify both during surgery. Here, the authors report dual-channel image-guided lung cancer surgery using renally clearable and physiochemically stable targeted fluorophores to visualize the tumor and intersegmental plane distinctly with different colors; cRGD-ZW800 (800 nm channel) targets tumors specifically, and ZW700 (700 nm channel) simultaneously helps discriminate segmental planes.

METHODS

The near-infrared (NIR) fluorophores with 700 nm and with 800 nm channels were developed and evaluated the feasibility of dual-channel fluorescence imaging of lung tumors and intersegmental lines simultaneously in mouse, rabbit, and canine animal models. Expression levels of integrin αvβ3, which is targeted by cRGD-ZW800-PEG, were retrospectively studied in the lung tissue of 61 patients who underwent lung cancer surgery.

RESULTS

cRGD-ZW800-PEG has clinically useful optical properties and outperforms the FDA-approved NIR fluorophore indocyanine green and serum unstable cRGD-ZW800-1 in multiple animal models of lung cancer. Combined with the blood-pooling agent ZW700-1C, cRGD-ZW800-PEG permits dual-channel NIR fluorescence imaging for intraoperative identification of lung segment lines and tumor margins with different colors simultaneously and accurately.

CONCLUSION

This dual-channel image-guided surgery enables complete tumor resection with adequate negative margins that can reduce the recurrence rate and increase the survival rate of lung cancer patients.

Engineering Cyanine- and Hemicyanine-Based Probes for Optical Imaging of Kidney Diseases

Molecular optical probes play pivotal roles in in vivo imaging of biomarkers associated to kidney diseases. Relying on structural tunability and high fluorescence quantum yields, versatile optical probes have been constructed on cyanine or hemicyanine-based scaffold in recent years. This review summaries the recent progress on the development of optical probes for imaging of kidney diseases, particularly through near-infrared fluorescence, chemiluminescence and photoacoustic imaging modalities. The chemical design and sensing mechanisms are discussed along with applications in the detection of renal cell carcinoma and acute kidney injury. This progress provides insights and directions for the development of next generation kidney-targeted probes and for pushing their further applications in preclinical and clinical research.

Discovery of Near-Infrared Heptamethine Cyanine Probes for Imaging-Guided Surgery in Solid Tumors

Near-infrared (NIR) fluorescence imaging has attracted much attention in image-guided interventions with unique advantages. However, the clinical translation rate of fluorescence probes is extremely low, primarily due to weak lesion signal contrast and poor specificity. To address this dilemma, a series of small-molecule near-infrared fluorescence probes have been designed for tumor imaging. Among them, YQ-04-03 showed notable optical stability and remarkable sensitivity toward tumor targeting. Moreover, within a specific concentration and time range against oxidizing reducing agents and laser, it demonstrated better stability than ICG. The retention time of YQ-04-03 in tumors was significantly longer compared to other nonspecific uptake sites in the subjects, and its tumor-to-normal tissue ratio (TNR) outperformed ICG. Successful resection of in situ hepatocarcinoma and peritoneal carcinoma was achieved using probe imaging guidance, with the smallest visual lesion resected measuring approximately 1 mm3. Ultimately, this probe holds great potential for advancing tumor tracer.

NIR-II Protein-Escaping Dyes Enable High-Contrast and Long-Term Prognosis Evaluation of Flap Transplantation

Real-time vascular positioning, postoperative flap monitoring, and vascular reconstruction assessment are of great importance in flap transplantation. Cyanine dyes offer the advantage of high resolution in the Near-infrared-II (NIR-II) imaging window. However, the nonspecific binding of many cyanine dyes to endogenous albumin leads to high organ accumulation and skin absorption, resulting in low-quality imaging and poor reproducibility of contrast during long-term (e.g., 7 days) postoperative monitoring. Here, a novel strategy is proposed that can be widely applied to prevent protein binding for NIR-I/II Cl-containing cyanine dyes. This strategy produces protein-escaping dyes, ensuring high fluorescence enhancement in the blood with rapid clearance and no residual fluorescence, allowing for short-term repeatable injections for vascular imaging. This strategy in the perioperative monitoring of pedicle perforator flap models in mice and rats is successfully applied. Furthermore, leveraging the universality of this strategy, multiple nonoverlapping protein-escaping probes that achieve dual-excitation (808 and 1064 nm) interference-free imaging of nerve-vessel and tumor-vessel simultaneously are designed and synthesized. These protein-escaping dyes enable long-term repeatable dual-color imaging of tumor localization, resection, and tumor-vessel reconstruction at the wound site.

Molecular Engineering of Activatable NIR-II Hemicyanine Reporters for Early Diagnosis and Prognostic Assessment of Inflammatory Bowel Disease

Molecular imaging in the second near-infrared window (NIR-II) provides high-fidelity visualization of biopathological events in deep tissue. However, most NIR-II probes produce "always-on" output and demonstrate poor signal specificity toward biomarkers. Herein, we report a series of hemicyanine reporters (HBCs) with tunable emission to NIR-II window (715-1188 nm) and structurally amenable to constructing activatable probes. Such manipulation of emission wavelengths relies on rational molecular engineering by integrating benz[c,d]indolium, benzo[b]xanthonium, and thiophene moieties to a conventional hemicyanine skeleton. In particular, HBC4 and HBC5 possess bright and record long emission over 1050 nm, enabling improved tissue penetration depth and superior signal to background ratio for intestinal tract mapping than NIR-I fluorophore HC1. An activatable inflammatory reporter (AIR-PE) is further constructed for pH-triggered site-specific release in colon. Due to minimized background interference, oral gavage of AIR-PE allows clear delineation of irritated intestines and assessment of therapeutic responses in a mouse model of inflammatory bowel disease (IBD) through real-time NIRF-II imaging. Benefiting from its high fecal clearance efficiency (>90%), AIR-PE can also detect IBD and evaluate the effectiveness of colitis treatments via in vitro optical fecalysis, which outperforms typical clinical assays including fecal occult blood testing and histological examination. This study thus presents NIR-II molecular scaffolds that are not only applicable to developing versatile activatable probes for early diagnosis and prognostic monitoring of deeply seated diseases but also hold promise for future clinical translations.

Site-specific albumin tagging with NIR-II fluorogenic dye for high-performance and super-stable bioimaging

Synthetic near-infrared-II (NIR-II) dyes are promising for deep tissue imaging, yet they are generally difficult to target a given biomolecule with high specificity. Furthermore, the interaction mechanism between albumin and cyanine molecules, which is usually regarded as uncertain "complexes" such as crosslinked nanoparticles, remains poorly understood. Methods: Here, we propose a new class of NIR-II fluorogenic dyes capable of site-specific albumin tagging for in situ albumin seeking/targeting or constructing high-performance cyanine@albumin probes. We further investigate the interaction mechanism between NIR-II fluorogenic dyes and albumin. Results: We identify CO-1080 as an optimal dye structure that produces a stable/bright NIR-II cyanine@albumin probe. CO-1080 exhibits maximum supramolecular binding affinity to albumin while catalyzing their covalent attachment. The probe shows exact binding sites located on Cys476 and Cys101, as identified by proteomic analysis and docking modeling. Conclusion: Our cyanine@albumin probe substantially improves the pharmacokinetics of its free dye counterpart, enabling high-performance NIR-II angiography and lymphography. Importantly, the site-specific labeling tags between NIR-II fluorogenic dyes and albumin occur under mild conditions, offering a specific and straightforward synthesis strategy for NIR-II fluorophores in the fields of targeting bioimaging and imaging-guided surgery.

Bifunctional Tumor-Targeted Bioprobe for Phothotheranosis

Background: Near-infrared (NIR) phototheranostics provide promising noninvasive imaging and treatment for head and neck squamous cell carcinoma (HNSCC), capitalizing on its adjacency to skin or mucosal surfaces. Activated by laser irradiation, targeted NIR fluorophores can selectively eradicate cancer cells, harnessing the power of synergistic photodynamic therapy and photothermal therapy. However, there is a paucity of NIR bioprobes showing tumor-specific targeting and effective phototheranosis without hurting surrounding healthy tissues. Methods: We engineered a tumor-specific bifunctional NIR bioprobe designed to precisely target HNSCC and induce phototheranosis using bioconjugation of a cyclic arginine-glycine-aspartic acid (cRGD) motif and zwitterionic polymethine NIR fluorophore. The cytotoxic effects of cRGD-ZW800-PEG were measured by assessing heat and reactive oxygen species (ROS) generation upon an 808-nm laser irradiation. We then determined the in vivo efficacy of cRGD-ZW800-PEG in the FaDu xenograft mouse model of HNSCC, as well as its biodistribution and clearance, using a customized portable NIR imaging system. Results: Real-time NIR imaging revealed that intravenously administered cRGD-ZW800-PEG targeted tumors rapidly within 4 h postintravenous injection in tumor-bearing mice. Upon laser irradiation, cRGD-ZW800-PEG produced ROS and heat simultaneously and exhibited synergistic photothermal and photodynamic effects on the tumoral tissue without affecting the neighboring healthy tissues. Importantly, all unbound bioprobes were cleared through renal excretion. Conclusions: By harnessing phototheranosis in combination with tailored tumor selectivity, our targeted bioprobe ushers in a promising paradigm in cancer treatment. It promises safer and more efficacious therapeutic avenues against cancer, marking a substantial advancement in the field.

HSA-ZW800-PEG for Enhanced Optophysical Stability and Tumor Targeting

Small molecule fluorophores often face challenges such as short blood half-life, limited physicochemical and optical stability, and poor pharmacokinetics. To overcome these limitations, we conjugated the zwitterionic near-infrared fluorophore ZW800-PEG to human serum albumin (HSA), creating HSA-ZW800-PEG. This conjugation notably improves chemical, physical, and optical stability under physiological conditions, addressing issues commonly encountered with small molecules in biological applications. Additionally, the high molecular weight and extinction coefficient of HSA-ZW800-PEG enhances biodistribution and tumor targeting through the enhanced permeability and retention effect. The unique distribution and elimination dynamics, along with the significantly extended blood half-life of HSA-ZW800-PEG, contribute to improved tumor targetability in both subcutaneous and orthotopic xenograft tumor-bearing animal models. This modification not only influences the pharmacokinetic profile, affecting retention time and clearance patterns, but also enhances bioavailability for targeting tissues. Our study guides further development and optimization of targeted imaging agents and drug-delivery systems.

Tailored Zwitterionic Hemicyanine Reporters for Early Diagnosis and Prognostic Assessment of Acute Renal Failure

Drug-induced renal failure (DIRF) poses a serious medical complication with high mortality risk. However, early diagnosis or prognosis of DIRF remain challenging, as current methods rely on detecting late-stage biomarkers. Herein we present a library of zwitterionic unimolecular hemicyanines (ZCs) available for constructing activatable reporters to detect DIRF since its initial stage. Zwitterionic properties of these probes are achieved through interspersedly integrating alkyl sulfonates and quaternary ammonium cations onto hemicyanine skeleton, which result in record low plasma protein binding (<5 %) and remarkable renal clearance efficiencies (≈96 %). An activatable reporter ZCRR is further developed by masking the optimal candidate ZC6 with a tetrapeptide specifically cleavable by caspase-8, an initiating indicator of apoptosis. In living mice with cisplatin-induced DIRF, systematically administered ZCRR efficiently accumulates in kidneys and responds to elevated caspase-8 for near-infrared fluorescence signals 'turn-on', enabling sensitive detection of intrarenal apoptosis 60 h earlier than clinical methods, and precise evaluation of apoptosis remediation effects by different medications on DIRF mice. As it's urinary excretable, ZCRR also allows for remote detection of DIRF and predicting renoprotective efficacy through in vitro optical urinalysis. This study thus presents unimolecular renal clearable scaffolds that are applicable to developing versatile activatable reporters for renal diseases management.

Superoxide Anion-Mediated Afterglow Mechanism-Based Water-Soluble Zwitterion Dye Achieving Renal-Failure Mice Detection

Afterglow materials-based biological imaging has promising application prospects, due to negligible background. However, currently available afterglow materials mainly include inorganic materials as well as some organic nanoparticles, which are difficult to translate to the clinic, resulting from non-negligible metabolic toxicity and even leakage risk of inorganic heavy metals. Although building small organic molecules could solve such obstacles, organic small molecules with afterglow ability are extremely scarce, especially with a sufficient renal metabolic capacity. To address these issues, herein, we designed water-soluble zwitterion Cy5-NF with renal metabolic capacity and afterglow luminescence, which relied on an intramolecular cascade reaction between superoxide anion (O2•-, instead of 1O2) and Cy5-NF to release afterglow luminescence. Of note, compared with different reference contrast agents, zwitterion Cy5-NF not only had excellent afterglow properties but also had a rapid renal metabolism rate (half-life period, t1/2, around 10 min) and good biocompatibility. Unlike prior afterglow nanosystems possessing a large size, for the first time, zwitterion Cy5-NF has achieved the construction of water-soluble renal metabolic afterglow contrast agents, which showed higher sensitivity and signal-to-background ratio in afterglow imaging than fluorescence imaging for the kidney. Moreover, zwitterion Cy5-NF had a longer kidney retention time in renal-failure mice (t1/2 more than 15 min). More importantly, zwitterion Cy5-NF can be metabolized very quickly even in severe renal-failure mice (t1/2 around 25-30 min), which greatly improved biosecurity. Therefore, we are optimistic that the O2•--mediated afterglow mechanism-based water-soluble zwitterion Cy5-NF is very promising for clinical application, especially rapid detection of kidney failure.

Ultra-Bright Heptamethine Dye Clusters Based on a Self-Adaptive Co-Assembly Strategy for NIR-IIb Biomedical Imaging

Despite the wide range of applications of bright NIR-II polymethine scaffolds in biomedical imaging, their solvatochromism and aggregation-caused quenching (ACQ) effects in aqueous solutions limit their inherent brightness using traditional encapsulation methods, and effective hydrophilization strategies are still scarce. Here, a new set of Flav dyes is synthesized and PEGylated, followed by manufacturing DSPE@FlavP2000 nanoparticles using a self-adaptive co-assembly strategy to overcome these limitations. FlavP2000 can autonomously adjust its conformation when co-assembled with DSPE-PEG2000 , resulting in high-efficiency luminescence (≈44.9% fluorescence of Flav in DMSO). DSPE@FlavP2000 enables NIR-IIb (>1500 nm) angiography with high signal-to-noise ratios. Notably, this co-assembly can occur in situ between FlavP2000 with proteins in the living body based on a novel mechanism of brightness activation induced by disassembly (BAD), achieving consistent brightness as DSPE@FlavP2000 in blood or serum. The self-adaptive co-assembly strategy can be enhanced by incorporating an IPA moiety, which dynamically binds to albumin to prolong the dye's blood circulation time. Thus, the "enhanced" BAD is successfully applied to long-term vascular imaging and sciatic nerve imaging. Both the self-adaptive co-assembly strategy and BAD phenomenon improve the selectivity and availability of the hydrophilization methods, paving the way for efficient biological applications of polymethine dyes.

H-Dot Mediated Nanotherapeutics Mitigate Systemic Toxicity of Platinum-Based Anticancer Drugs

Platinum-based anticancer agents have revolutionized oncological treatments globally. However, their therapeutic efficacy is often accompanied by systemic toxicity. Carboplatin, recognized for its relatively lower toxicity profile than cisplatin, still presents off-target toxicities, including dose-dependent cardiotoxicity, neurotoxicity, and myelosuppression. In this study, we demonstrate a delivery strategy of carboplatin to mitigate its off-target toxicity by leveraging the potential of zwitterionic nanocarrier, H-dot. The designed carboplatin/H-dot complex (Car/H-dot) exhibits rapid drug release kinetics and notable accumulation in proximity to tumor sites, indicative of amplified tumor targeting precision. Intriguingly, the Car/H-dot shows remarkable efficacy in eliminating tumors across insulinoma animal models. Encouragingly, concerns linked to carboplatin-induced cardiotoxicity are effectively alleviated by adopting the Car/H-dot nanotherapeutic approach. This pioneering investigation not only underscores the viability of H-dot as an organic nanocarrier for platinum drugs but also emphasizes its pivotal role in ameliorating associated toxicities. Thus, this study heralds a promising advancement in refining the therapeutic landscape of platinum-based chemotherapy.

Ultralow Background Near-Infrared Fluorophores with Dual-Channel Intraoperative Imaging Capability

Two of the most pressing challenges facing bioimaging are nonspecific uptake of intravenously administered contrast agents and incomplete elimination of unbound targeted agents from the body. Designing a targeted contrast agent that shows fast clearance from background tissues and eventually the body after complete targeting is key to the success of image-guided interventions. Here, this work describes the development of renally clearable near-infrared contrast agents and their potential use for dual-channel image-guided tumor targeting. cRGD-ZW800-PEG (800 nm channel) and ZW700-PEG (700 nm channel) are able to visualize tumor margins and tumor vasculature simultaneously and respectively. These targeted agents show rapid elimination from the bloodstream, followed by renal clearance, which together significantly lower off-target background signals and potential toxicity. To demonstrate its applicability, this multispectral imaging is performed in various tumor-bearing animal models including lung cancer, pancreatic neuroendocrine tumors, breast, and ovarian cancer.

Membrane-tethered activation design of a photosensitizer boosts systemic antitumor immunity via pyroptosis

Pyroptotic immunogenic cell death presents an emerging targeting pathway for cancer immunotherapy. We report a novel membrane-tethered activation design of a photosensitizer (PS) that boosts systemic anti-tumor immunity to primary and distant tumors via pyroptosis induction. The membrane-tethered PS is designed by installing a new phenylbenzopyrylium PS with zwitterionic lipid anchors and a target-cleavable caging moiety. This design affords excellent membrane tethering and enzymatic activation of the PS, exerting specific phototoxicity to cancer cells and inducing effective pyroptosis. Our design demonstrates prolonged circulation, long-lasting fluorogenic imaging and persistent photodynamic therapy of immunogenic 'cold' tumors in vivo, eliciting potent immunity toward local and abscopal tumors via promoted maturation of dendritic cells and recruitment of cytotoxic T lymphocytes. This design affords a promising approach for enhancing systemic antitumor immunity for cancer immunotherapy.

Near-infrared fluorescence lifetime imaging of amyloid-β aggregates and tau fibrils through the intact skull of mice

Non-invasive methods for the in vivo detection of hallmarks of Alzheimer's disease can facilitate the study of the progression of the disease in mouse models and may enable its earlier diagnosis in humans. Here we show that the zwitterionic heptamethine fluorophore ZW800-1C, which has peak excitation and emission wavelengths in the near-infrared optical window, binds in vivo and at high contrast to amyloid-β deposits and to neurofibrillary tangles, and allows for the microscopic imaging of amyloid-β and tau aggregates through the intact skull of mice. In transgenic mouse models of Alzheimer's disease, we compare the performance of ZW800-1C with that of the two spectrally similar heptamethine fluorophores ZW800-1A and indocyanine green, and show that ZW800-1C undergoes a longer fluorescence-lifetime shift when bound to amyloid-β and tau aggregates than when circulating in blood vessels. ZW800-1C may prove advantageous for tracking the proteinic aggregates in rodent models of amyloid-β and tau pathologies.

A Water-Soluble AIEgen for Noninvasive Diagnosis of Kidney Fibrosis via SWIR Fluorescence and Photoacoustic Imaging

Early diagnosis of renal fibrosis is crucially significant on account of its worldwide prevalent tendency. Optical imaging in the near-infrared window has been recognized as an appealing technique for the timely detection of renal dysfunction. However, formulating a contrast agent that allows early monitoring of renal fibrosis and concurrently renally clearable in a normal group is still challenging. Herein, a nanosized fluorophore with aggregation-induced emission (AIE) features, namely AIE-4PEG550 NPs, is well-tailored and amenable to longitudinal visualization of the fibrosis progression specifically in the early-stage via short-wave infrared (SWIR, 900-1700 nm) fluorescence and photoacoustic bimodal imaging. The small size (≈26 nm), renally filtrable molecular weight (3.3 kDa), high renal clearance efficiency (93.1 ± 1.7% excretion through the kidneys within 24 h), outstanding imaging performance, and good biocompatibility, together make AIE-4PEG550 NPs remarkably impressive and far superior to clinical diagnostic assays. The finding in this study would provide a blueprint for the next generation of diagnostic agents for the extent of renal fibrosis.

In situ detection of alkaline phosphatase in a cisplatin-induced acute kidney injury model with a fluorescent/photoacoustic bimodal molecular probe

Kidneys play an important part in drug metabolism and excretion. High local concentration of drugs or drug allergies often cause acute kidney injury (AKI). Identification of effective biomarkers of initial stage AKI and constructing activable molecular probes with excellent detection properties for early evaluation of AKI are necessary, yet remain significant challenges. Alkaline phosphatase (ALP), a key hydrolyzing protease, exists in the epithelial cells of the kidney and is discharged into the urine following kidney injury. However, no studies have revealed its level in drug-induced AKI. Existing ALP fluorescent molecular probes are not suitable for testing and imaging of ALP in the AKI model. Drug-induced AKI is accompanied by oxidative stress, and many studies have indicated that a large increase in reactive oxygen species (ROS) occur in the AKI model. Thus, the probe used for imaging of AKI must be chemically stable in the presence of ROS. However, most existing near-infrared fluorescent (NIRF) ALP probes are not stable in the presence of ROS in the AKI model. Hence, we built a chemically stable molecular sensor (CS-ALP) to map ALP level in cisplatin-induced AKI. This novel probe is not destroyed by ROS generated in the AKI model, thus allowing high-fidelity imaging. In the presence of ALP, the CS-ALP probe generates a new absorbance peak at 685 nm and a fluorescent emission peak at 716 nm that could be used to "turn on" photoacoustic (PA) and NIRF imaging of ALP in AKI. Levels of CS-ALP build up rapidly in the kidney, and CS-ALP has been successfully applied in NIRF/PA bimodal in vivo imaging. Through the NIRF/PA bimodal imaging results, we demonstrate that upregulated expression of ALP occurs in the early stages of AKI and continues with injury progression.

P800SO3-PEG: a renal clearable bone-targeted fluorophore for theranostic imaging

BACKGROUND

Due to the deep tissue penetration and reduced scattering, NIR-II fluorescence imaging is advantageous over conventional visible and NIR-I fluorescence imaging for the detection of bone growth, metabolism, metastasis, and other bone-related diseases.

METHODS

Bone-targeted heptamethine cyanine fluorophores were synthesized by substituting the meso-carbon with a sulfur atom, resulting in a bathochromic shift and increased fluorescence intensity. The physicochemical, optical, and thermal stability of newly synthesized bone-targeted NIR fluorophores was performed in aqueous solvents. Calcium binding, bone-specific targeting, biodistribution, pharmacokinetics, and 2D and 3D NIR imaging were performed in animal models.

RESULTS

The newly synthesized S-substituted heptamethine fluorophores demonstrated a high affinity for hydroxyapatite and calcium phosphate, which improved bone-specific targeting with signal-background ratios > 3.5. Particularly, P800SO3-PEG showed minimum nonspecific uptake, and most unbound molecules were excreted into the urinary bladder. Histological analyses demonstrated that P800SO3-PEG remained stable in the bone for over two weeks and was incorporated into bone matrices. Interestingly, the flexible thiol ethylene glycol linker on P800SO3-PEG induced a promising photothermal effect upon NIR laser irradiation, demonstrating potential theranostic imaging.

CONCLUSIONS

P800SO3-PEG shows a high affinity for bone tissues, deeper tissue imaging capabilities, minimum nonspecific uptake in the major organs, and photothermal effect upon laser irradiation, making it optimal for bone-targeted theranostic imaging.

Phototheranostics for multifunctional treatment of cancer with fluorescence imaging

Phototheranostics stem from the recent advances in nanomedicines and bioimaging to diagnose and treat human diseases. Since tumors' diversity, heterogeneity, and instability limit the clinical application of traditional diagnostics and therapeutics, phototheranostics, which combine light-induced therapeutic and diagnostic modalities in a single platform, have been widely investigated. Numerous efforts have been made to develop phototheranostics for efficient light-induced antitumor therapeutics with minimal side effects. Herein, we review the fundamentals of phototheranostic nanomedicines with their biomedical applications. Furthermore, the progress of near-infrared fluorescence imaging and cancer treatments, including photodynamic therapy and photothermal therapy, along with chemotherapy, immunotherapy, and gene therapy, are summarized. This review also discusses the opportunities and challenges associated with the clinical translation of phototheranostics in pan-cancer research. Phototheranostics can pave the way for future research, improve the quality of life, and prolong cancer patients' survival times.

Rationally Designed Heptamethine Cyanine Photosensitizers that Amplify Tumor-Specific Endoplasmic Reticulum Stress and Boost Antitumor Immunity

Cancer phototherapy activates immunogenic cell death (ICD) and elicits a systemic antitumor immune response, which is an emerging approach for tumor treatment. Most available photosensitizers require a combination of immune adjuvants or checkpoint inhibitors to trigger antitumor immunity because of the immunosuppressive tumor microenvironment and the limited phototherapeutic effect. A class of tumor-targeting heptamethine cyanine photosensitizers modified with an endoplasmic reticulum (ER)-targeting group (benzenesulfonamide) are synthesized. Phototherapy of tumor cells markedly amplifies ER stress and promotes tumor antigen release, as the ER is required for protein synthesis, secretion, and transport. More importantly, different electron-donating or -withdrawing substitutions are introduced into benzenesulfonamide to modulate the nonradiative decay pathways through intramolecular charge transfer, including singlet-triplet intersystem crossing (photodynamic effect) and internal thermal conversion (photothermal effect). Thus, a heptamethine cyanine photosensitizer containing a binitro-substituted benzenesulfonamide (ER-Cy-poNO₂ ) is identified that preferentially accumulates in the ER of tumor cells. It significantly enhances the phototherapeutic effect by inducing excessive ER stress and robust ICD. Consequently, this small molecular photosensitizer triggers a sufficient antitumor immune response and effectively suppresses the growth of both primary and distant metastatic tumors, whereas no apparent toxicity is observed. This heptamethine cyanine photosensitizer has the potential to enhance cancer-targeted immunotherapy.

A novel active mitochondrion-selective fluorescent probe for the NIR fluorescence imaging and targeted photodynamic therapy of gastric cancer

The annual morbidity and mortality due to gastric cancer are still high across the world, posing a serious threat to public health. Improving the diagnosis rate of gastric cancer and exploring new treatments are urgent issues in the clinical field. In recent years, photosensitizer (PS)-based photodynamic therapy (PDT) has proven to be an effective cancer treatment strategy and can be used to treat a variety of cancers. Developing PSs with tumor-targeting ability and high singlet oxygen yield (Φ(¹O₂)) is the key to improving the PDT effect. Herein, we developed a novel diagnosis and treatment system (Cy₁₃₉₅-NPs). Our active thio-photosensitizer is based on the sulfur substitution strategy as it can reduce the S1-T1 energy gap, which can promote the process of intersystem crossing (ISC), thus resulting in high ROS generation efficiency. Cy₁₃₉₅-NPs exhibited stable spectral characteristics, satisfactory biocompatibility and high ¹O₂ yield under laser irradiation due to the introduction of the sulfur atom. In cellular studies, Cy₁₃₉₅-NPs could specifically target MKN45 cells via integrin α_vβ₃-mediated cRGD endocytosis and selectively aggregate in the mitochondria. Cy₁₃₉₅-NPs had no obvious cytotoxicity for MKN45 cells and exerted obvious phototoxicity due to the production of ¹O₂ under laser irradiation. The in vivo results showed that the fluorescence signal from the tumor site was obviously enhanced in 16-48 h, and Cy₁₃₉₅-NPs could selectively target solid tumors with a retention time of about 32 h. Under laser irradiation, Cy₁₃₉₅-NPs significantly inhibited tumor growth and led to significant tumor suppression and apoptosis. In summary, the developed Cy₁₃₉₅-NPs could actively target tumors and exert mitochondrial selectivity, showing an excellent fluorescence imaging effect. Under the irradiation of an 808 nm laser, Cy₁₃₉₅-NPs achieved good inhibition of gastric cancer cells both in vitro and in vivo, thus displaying the functions of tumor targeting, mitochondrial selectivity, fluorescence imaging and tumor inhibition. Our strategy provides a new diagnostic and treatment method for gastric cancers in clinical settings.

Neuroimaging Modalities in Alzheimer’s Disease: Diagnosis and Clinical Features

Alzheimer’s disease (AD) is a neurodegenerative disease causing progressive cognitive decline until eventual death. AD affects millions of individuals worldwide in the absence of effective treatment options, and its clinical causes are still uncertain. The onset of dementia symptoms indicates severe neurodegeneration has already taken place. Therefore, AD diagnosis at an early stage is essential as it results in more effective therapy to slow its progression. The current clinical diagnosis of AD relies on mental examinations and brain imaging to determine whether patients meet diagnostic criteria, and biomedical research focuses on finding associated biomarkers by using neuroimaging techniques. Multiple clinical brain imaging modalities emerged as potential techniques to study AD, showing a range of capacity in their preciseness to identify the disease. This review presents the advantages and limitations of brain imaging modalities for AD diagnosis and discusses their clinical value.

Synthesis, Renal Clearance, and Photothermal Therapy Based on the Self-Assembly of a Nanomedicine Consisting of Quaterrylene Bisimide and Glycocluster Conjugates

Renal-clearable nanomedicines are considered the next generation of nanomedicines, and show potential application for future clinical translations. However, it is important to determine whether self-assembly can form large aggregates that accrue in tumors and then tailor the size of these assemblies to be excreted renally. In this paper, a renal-clearable nanomedicine based on quanterrylene bisimide-mannose conjugates (QDI-Man) was developed. QDI-Man showed a high renal clearance efficiency of 80.31 ± 2.85% in mice. We confirmed that the self-assembly of QDI-Man exhibited a dynamic adjustment process through the renal filtration thresholds, that is, "aggregation → self-regulating the aggregate size through the renal filtration thresholds → reaggregating into aggregates". Benefiting from the modification of mannose-based glycoclusters, QDI-Man showed selective photothermal therapy because of the mannose receptors overexpressed in breast cancer cells, and showed good photothermal therapy in mice. This paper developed a dynamic adjustment theory for effective renal clearance based on organic self-assembly.

Fast and Durable Intraoperative Near-infrared Imaging of Ovarian Cancer Using Ultrabright Squaraine Fluorophores

The residual tumor after surgery is the most significant prognostic factor of patients with epithelial ovarian cancer. Near-infrared (NIR) fluorescence-guided surgery is actively utilized for tumor localization and complete resection during surgery. However, currently available contrast-enhancing agents display low on-target binding, unfavorable pharmacokinetics, and toxicity, thus not ideal for clinical use. Here we report ultrabright and stable squaraine fluorophores with optimal pharmacokinetics by introducing an asymmetric molecular conformation and surface charges for rapid transporter-mediated cellular uptake. Among the tested, OCTL14 shows low serum binding and rapid distribution into cancer tissue via organic cation transporters (OCTs). Additionally, the charged squaraine fluorophores are retained in lysosomes, providing durable intraoperative imaging in a preclinical murine model of ovarian cancer up to 24 h post-injection. OCTL14 represents a significant departure from the current bioconjugation approach of using a non-targeted fluorophore and would provide surgeons with an indispensable tool to achieve optimal resection.

Targeted Fluorogenic Cyanine Carbamates Enable In Vivo Analysis of Antibody-Drug Conjugate Linker Chemistry

Antibody-drug conjugates (ADCs) are a rapidly emerging therapeutic platform. The chemical linker between the antibody and the drug payload plays an essential role in the efficacy and tolerability of these agents. New methods that quantitatively assess the cleavage efficiency in complex tissue settings could provide valuable insights into the ADC design process. Here we report the development of a near-infrared (NIR) optical imaging approach that measures the site and extent of linker cleavage in mouse models. This approach is enabled by a superior variant of our recently devised cyanine carbamate (CyBam) platform. We identify a novel tertiary amine-containing norcyanine, the product of CyBam cleavage, that exhibits a dramatically increased cellular signal due to an improved cellular permeability and lysosomal accumulation. The resulting cyanine lysosome-targeting carbamates (CyLBams) are ∼50× brighter in cells, and we find this strategy is essential for high-contrast in vivo targeted imaging. Finally, we compare a panel of several common ADC linkers across two antibodies and tumor models. These studies indicate that cathepsin-cleavable linkers provide dramatically higher tumor activation relative to hindered or nonhindered disulfides, an observation that is only apparent with in vivo imaging. This strategy enables quantitative comparisons of cleavable linker chemistries in complex tissue settings with implications across the drug delivery landscape.

A Bright, Renal-Clearable NIR-II Brush Macromolecular Probe with Long Blood Circulation Time for Kidney Disease Bioimaging

Early detection of kidney disease is of vital importance due to its current prevalence worldwide. Fluorescence imaging, especially in the second near-infrared window (NIR-II) has been regarded as a promising technique for the early diagnosis of kidney disease due to the superior resolution and sensitivity. However, the reported NIR-II organic renal-clearable probes are hampered by their low brightness (ϵ_max Φ_f>1000 nm <10 M^-1  cm^-1 ) and limited blood circulation time (t_1/2 <2 h), which impede the targeted imaging performance. Herein, we develop the aza-boron-dipyrromethene (aza-BODIPY) brush macromolecular probes (Fudan BDIPY Probes (FBP 912)) with high brightness (ϵ_max Φ_f>1000 nm ≈60 M^-1  cm^-1 ), which is about 10-fold higher than that of previously reported NIR-II renal-clearable organic probes. FBP 912 exhibits an average diameter of ≈4 nm and high renal clearance efficiency (≈65 % excretion through the kidney within 12 h), showing superior performance for non-invasively diagnosis of renal ischemia-reperfusion injury (RIR) earlier than clinical serum-based protocols. Additionally, the high molecular weight polymer brush enables FBP 912 with prolonged circulation time (t_1/2 ≈6.1 h) and higher brightness than traditional PEGylated renal-clearable control fluorophores (t_1/2 <2 h), facilitating for 4T1 tumor passive targeted imaging and renal cell carcinoma active targeted imaging with higher signal-to-noise ratio and extended retention time.

Near-Infrared Fluorescence Imaging of Carotid Plaques in an Atherosclerotic Murine Model

Successful imaging of atherosclerosis, one of the leading global causes of death, is crucial for diagnosis and intervention. Near-infrared fluorescence (NIRF) imaging has been widely adopted along with multimodal/hybrid imaging systems for plaque detection. We evaluate two macrophage-targeting fluorescent tracers for NIRF imaging (TLR4-ZW800-1C and Feraheme-Alexa Fluor 750) in an atherosclerotic murine cohort, where the left carotid artery (LCA) is ligated to cause stenosis, and the right carotid artery (RCA) is used as a control. Imaging performed on dissected tissues revealed that both tracers had high uptake in the diseased vessel compared to the control, which was readily visible even at short exposure times. In addition, ZW800-1C's renal clearance ability and Feraheme's FDA approval puts these two tracers in line with other NIRF tracers such as ICG. Continued investigation with these tracers using intravascular NIRF imaging and larger animal models is warranted for clinical translation.

Comparison of cRGDfK Peptide Probes with Appended Shielded Heptamethine Cyanine Dye () for Near Infrared Fluorescence Imaging of Cancer

Previous work has shown that the sterically shielded near-infrared (NIR) fluorescent heptamethine cyanine dye, s775z, with a reactive carboxyl group produces fluorescent bioconjugates with an unsurpassed combination of high photostability and fluorescence brightness. This present contribution reports two new reactive homologues of s775z with either a maleimide group for reaction with a thiol or a strained alkyne group for reaction with an azide. Three cancer-targeting NIR fluorescent probes were synthesized, each with an appended cRGDfK peptide to provide selective affinity for integrin receptors that are overexpressed on the surface of many cancer cells including the A549 lung adenocarcinoma cells used in this study. A set of cancer cell microscopy and mouse tumor imaging experiments showed that all three probes were very effective at targeting cancer cells and tumors; however, the change in the linker structure produced a statistically significant difference in some aspects of the mouse biodistribution. The mouse studies included a mock surgical procedure that excised the subcutaneous tumors. A paired-agent fluorescence imaging experiment co-injected a binary mixture of targeted probe with 850 nm emission, an untargeted probe with 710 nm emission and determined the targeted probe's binding potential in the tumor tissue. A comparison of pixelated maps of binding potential for each excised tumor indicated a tumor-to-tumor variation of integrin expression levels, and a heterogeneous spatial distribution of integrin receptors within each tumor.

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.

Shielding Unit Engineering of NIR-II Molecular Fluorophores for Improved Fluorescence Performance and Renal Excretion Ability

Molecular fluorophores emitting in the second near-infrared (NIR-II) window with good renal excretion ability are favorable for in vivo bio-imaging and clinical applications. So far, renally excretable fluorophores are still less studied. Understanding the influences of molecular structure on optical properties and renal excretion abilities are vital for fluorophore optimization. Herein, a series of shielding unit-donor-acceptor-donor-shielding unit (S-D-A-D-S) NIR-II molecular fluorophores are designed and synthesized with dialkoxy chains substituted benzene as the S unit. The anchoring positions of dialkoxy chains on benzene are tuned as meso-2,6, para-2,5, or ortho-3,4 to afford three fluorophores: BGM6P, BGP6P and BGO6P, respectively. Experimental and calculation results reveal that alkoxy side chains anchored closer to the conjugated backbone can provide better protection from water molecules and PEG chains, affording higher fluorescence quantum yield (QY) in aqueous solutions. Further, these side chains can enable good encapsulation of backbone, resulting in decreased binding with albumin and improved renal excretion. Thus, fluorophore BGM6P with meso-2,6-dialkoxy chains exhibits the highest quantum yield and fastest renal excretion. This work emphasizes the important roles of side chain patterns on optimizing NIR-II fluorophores with high brightness and renal excretion ability.

Rapid Tumor Targeting of Renal-Clearable ZW800-1 Conjugate for Efficient Photothermal Cancer Therapy

The combination of near-infrared (NIR) fluorophores and photothermal therapy (PTT) provides a new opportunity for safe and effective cancer treatment. However, the precise molecular design of functional NIR fluorophores with desired properties, such as high tumor targetability and low nonspecific uptake, remains challenging. In this study, a renal-clearable NIR fluorophore conjugate with high tumor targetability was developed for efficient photothermal cancer therapy. The isoniazid (INH)–ZW800-1 conjugate (INH–ZW) was synthesized by conjugating an antibiotic drug, INH, with a well-known zwitterionic NIR fluorophore, ZW800-1, to improve in vivo performance and fluorescence-guided cancer phototherapy. INH–ZW not only showed rapid tumor accumulation without nonspecific tissue/organ uptake within 1 h after the injection but also generated thermal energy to induce cancer cell death under NIR laser irradiation. Compared with previously reported ZW800-1 conjugates, INH–ZW preserved the ideal biodistribution of ZW800-1 and facilitated improved tumor targeting and PTT. Together, these results demonstrate that the INH–ZW conjugate has great potential to serve as an effective PTT agent capable of rapid tumor targeting and high renal clearance, with excellent photothermal efficacy.