Förster Resonance Energy Transfer-Based Dual-Modal Theranostic Nanoprobe for In Situ Visualization of Cancer Photothermal Therapy

Biosynthesis of NIR-II Ag2Se Quantum Dots with Bacterial Catalase for Photoacoustic Imaging and Alleviating-Hypoxia Photothermal Therapy

Developing the second near-infrared (NIR-II) photoacoustic (PA) agent is of great interest in bioimaging. Ag2Se quantum dots (QDs) are one kind of potential probe for applications in NIR-II photoacoustic imaging (PAI). However, the surfaces with excess anions of Ag2Se QDs, which increase the probability of nonradiative transitions of excitons benefiting PA imaging, are not conducive to binding electron donor ligands for potential biolabeling and imaging. In this study, Staphylococcus aureus (S. aureus) cells are driven for the biosynthesis of Ag2Se QDs with catalase (CAT). Biosynthesized Ag2Se (bio-Ag2Se-CAT) QDs are produced in Se-enriched environment of S. aureus and have a high Se-rich surface. The photothermal conversion efficiency of bio-Ag2Se-CAT QDs at 808 and 1064 nm is calculated as 75.3% and 51.7%, respectively. Additionally, the PA signal responsiveness of bio-Ag2Se-CAT QDs is ≈10 times that of the commercial PA contrast agent indocyanine green. In particular, the bacterial CAT is naturally attached to bio-Ag2Se-CAT QDs surface, which can effectively relieve tumor hypoxia. The bio-Ag2Se-CAT QDs can relieve heat-initiated oxidative stress while undergoing effective photothermal therapy (PTT). Such biosynthesis method of NIR-II bio-Ag2Se-CAT QDs opens a new avenue for developing multifunctional nanomaterials, showing great promise for PAI, hypoxia alleviation, and PTT.

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.

Imaging of Indocyanine Green-Human Serum Albumin (ICG-HSA) Complex in Secreted Protein Acidic and Rich in Cysteine (SPARC)-Expressing Glioblastoma

Glioblastoma is the most common and fatal primary glioma and has a severe prognosis. It is a challenge for neurosurgeons to remove brain tumor tissues completely by resection. Meanwhile, fluorescence-guided surgery (FGS) is a technique used in glioma surgery to enhance the visualization of tumor edges to clarify the extent of tumor resection. Indocyanine green (ICG) is the only FDA-approved NIR fluorescent agent. It non-covalently binds to human serum albumin (HSA). Secreted protein acidic and rich in cysteine (SPARC) is an extracellular glycoprotein expressed in gliomas and binds to albumin, suggesting that it plays an important role in tumor uptake of the ICG-HSA complex. Here we demonstrate the binding properties of HSA or SPARC to ICG using surface plasmon resonance and saturation binding assay. According to in vitro and in vivo studies, the results showed that the uptake of ICG-HSA complex was higher in SPARC-expressing glioblastoma cell line and tumor region compared with the uptake of free ICG. Here, we visualized the SPARC-dependent uptake of ICG and ICG-HSA complex in U87MG. Our results demonstrated that the ICG-HSA complex is likely to be used as an efficient imaging agent targeting SPARC-expressing tumors, especially glioblastoma.

New anti-cancer explorations based on metal ions

Due to the urgent demand for more anti-cancer methods, the new applications of metal ions in cancer have attracted increasing attention. Especially the three kinds of the new mode of cell death, including ferroptosis, calcicoptosis, and cuproptosis, are of great concern. Meanwhile, many metal ions have been found to induce cell death through different approaches, such as interfering with osmotic pressure, triggering biocatalysis, activating immune pathways, and generating the prooxidant effect. Therefore, varieties of new strategies based on the above approaches have been studied and applied for anti-cancer applications. Moreover, many contrast agents based on metal ions have gradually become the core components of the bioimaging technologies, such as MRI, CT, and fluorescence imaging, which exhibit guiding significance for cancer diagnosis. Besides, the new nano-theranostic platforms based on metal ions have experimentally shown efficient response to endogenous and exogenous stimuli, which realizes simultaneous cancer therapy and diagnosis through a more controlled nano-system. However, most metal-based agents have still been in the early stages, and controlled clinical trials are necessary to confirm or not the current expectations. This article will focus on these new explorations based on metal ions, hoping to provide some theoretical support for more anti-cancer ideas.

Spontaneous Transfer of Indocyanine Green from Liposomes to Albumin Is Inhibited by the Antioxidant α-Tocopherol

Indocyanine Green (ICG) is a clinically approved organic dye with near-infrared absorption and fluorescence. Over the years, many efforts to improve the photophysical and pharmacokinetic properties of ICG have investigated numerous nanoparticle formulations, especially liposomes with membrane-embedded ICG. A series of systematic absorption and fluorescence experiments, including FRET experiments using ICG as a fluorescence energy acceptor, found that ICG transfers spontaneously from liposomes to albumin protein residing in the external solution with a half-life of ∼10 min at 37 °C. Moreover, transfer of ICG from liposome membranes to external albumin reduces light-activated leakage from thermosensitive liposomes with membrane-embedded ICG. A survey of lipophilic liposome additives discovered that the presence of clinically approved antioxidant, α-tocopherol, greatly increases ICG retention in the liposomes (presumably by forming favorable aromatic stacking interactions), inhibits ICG photobleaching and prevents albumin-induced reduction of light-triggered liposome leakage. This new insight will help researchers with the specific task of optimizing ICG-containing liposomes for fluorescence imaging or phototherapeutics. More broadly, the results suggest a broader design concept concerning light triggered liposome leakage, that is, proximity of the light absorbing dye to the bilayer membrane is a critical design feature that impacts the extent of liposome leakage.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

γ-Glutamyl transpeptidase-activatable near-infrared nanoassembly for tumor fluorescence imaging-guided photothermal therapy

Rationale: Precise treatment of tumors is attracting increasing attention. Molecular probes simultaneously demonstrating the diagnostic signal and pharmacological effect in response to tumor microenvironment are highly desired. γ-glutamyl transpeptidase (GGT) is a biomarker with significantly up-regulated expression in the tumor area. We developed a GGT responsive near-infrared (NIR) nanoassembly for tumor-specific fluorescence imaging-guided photothermal therapy. Methods: The GGT responsive NIR probe was constructed by conjugating GGT-specific substrate γ-glutamic acid (γ-Glu) with cyanine fluorophore (NRh-NH2) via amide reaction. The resulting NRh-G spontaneously assembled into nanoparticles (NRh-G-NPs) around 50 nm. The NPs were characterized and the properties evaluated in the presence or absence of GGT. Subsequently, we studied fluorescence imaging and photothermal therapy of NRh-G-NPs in vitro and in vivo. Results: NRh-G-NPs, upon specific reaction with GGT, turned into NRh-NH2-NPs, showing a ~180-fold fluorescence enhancement and excellent photothermal effect recovery. NRh-G-NPs could selectively light up U87MG tumor cells while their fluorescence was weak in L02 human normal liver cells. The NPs also showed excellent tumor cell ablation upon laser irradiation. After intravenous injection into tumor-bearing mice, NRh-G-NPs could arrive in the tumor area and specifically light up the tumor. Following laser irradiation, the tumor could be completely erased with no tumor reoccurrence for up to 40 days. Conclusions: NRh-G-NPs were specifically responsive to GGT overexpressed in U87MG tumor cells and selectively lit up the tumor for imaging-guided therapy. Besides, the recovery of photothermal property in the tumor area could improve cancer therapy precision and decreased side effects in normal tissues.

Albumin-based fluorescence resonance energy transfer nanoprobes for multileveled tumor tissue imaging and dye release imaging

Tumor tissue imaging and drug release imaging are both crucial for tumor imaging and image-guided drug delivery. It is urgent to develop a multileveled tumor imaging platform to realize the multiple imaging applications. In this work, we synthesized an albumin-based fluorescence resonance energy transfer (FRET) probe Cy5/7@HSA NPs containing two near-infrared cyanine dyes (CyBI5 and CyBI7) with high FRET efficiency (97 %). Excellent brightness and efficient FRET inside Cy5/7@HSA NPs enabled high-sensitive cell imaging and tumor imaging. This unique nanoprobe imaged 4T1 tumor-bearing mice with high sensitivity (TBR = 5.2) at 24 h post-injection and the dyes penetrated the tumor interior around 4 h post-injection. The release of dyes from nanoprobes was also tracked. This result shows the strong potential of this albumin-based FRET nanoprobe as multileveled tumor imaging platform for in vivo tumor imaging, drug delivery and image-guided surgery.

Research advances in integrated theranostic probes for tumor fluorescence visualization and treatment

At present, cancer is obviously a major threat to human health worldwide. Accurate diagnosis and treatment are in great demand and have become an effective method to alleviate the development of cancer and improve the survival rate of patients. A large number of theranostic probes that combine diagnosis and treatment methods have been developed as promising tools for tumor precision medicine. Among them, fluorescent theranostic probes have developed rapidly in the frontier research field of precision medicine with their real time, low toxicity, and high-resolution merit. Therefore, this review focuses on recent advances in the development of fluorescent theranostic probes, as well as their applications for cancer diagnosis and treatment. Initially, small-molecule fluorescent theranostic probes mainly including tumor microenvironment-responsive fluorescent prodrugs and phototherapeutic probes were introduced. Subsequently, nanocomposite probes are expounded based on four types of nano-fluorescent particles combining different therapies (chemotherapy, photothermal therapy, photodynamic therapy, gene therapy, etc.). Then, the capsule-type "all in one" probes, which occupy an important position in theranostic probes, are summarized according to the surface carrier type. This review aims to present a comprehensive guide for researchers in the field of tumor-related theranostic probe design and development.

Active-Targeting NIR-II Phototheranostics in Multiple Tumor Models Using Platelet-Camouflaged Nanoprobes

Cancer phototheranostics in the second near-infrared window (NIR-II, 1000-1700 nm) has recently attracted much attention owing to its high efficacy and good safety compared with that in the first near-infrared window (NIR-I, 650-950 nm). However, the lack of theranostic nanoagents with active-targeting features limits its further application in cancer precision therapies. Herein, we constructed platelet-camouflaged nanoprobes with active-targeting characteristics for NIR-II cancer phototheranostics. The as-prepared biomimetic nanoprobes can not only escape phagocytosis by macrophages but also specifically bind to CD44 on the surface of most cancer cells. We evaluated the active-targeting performance of biomimetic nanoprobes in pancreatic cancer, breast cancer, and glioma mouse models and achieved NIR-II photoacoustic imaging with a high signal-to-background ratio and photothermal treatment with excellent tumor growth inhibition. Our results show the great potential of platelet-camouflaged nanoprobes with NIR-II active-targeting features for cancer precision diagnosis and efficient therapies.

Europium-Diethylenetriaminepentaacetic Acid Loaded Radioluminescence Liposome Nanoplatform for Effective Radioisotope-Mediated Photodynamic Therapy

Photodynamic therapy (PDT) is an effective anticancer strategy with a higher selectivity and fewer adverse effects than conventional therapies; however, shallow tissue penetration depth of light has hampered the clinical utility of PDT. Recently, reports have indicated that Cerenkov luminescence-induced PDT may overcome the tissue penetration limitation of conventional PDT. However, the effectiveness of this method is controversial because of its low luminescence intensity. Herein, we developed a radiolabeled diethylenetriaminepentaacetic acid chelated Eu³⁺ (Eu-DTPA)/photosensitizer (PS) loaded liposome (Eu/PS-lipo) that utilizes ionizing radiation from radioisotopes for effective in vivo imaging and radioluminescence-induced PDT. We utilized Victoria blue-BO (VBBO) as a PS and observed an efficient luminescence resonance energy transfer between Eu-DTPA and VBBO. Furthermore, ⁶⁴Cu-labeled Eu lipo demonstrated a strong radioluminescence with a 2-fold higher intensity than Cerenkov luminescence from free ⁶⁴Cu. In our radioluminescence liposome, radioluminescence energy transfer showed a 6-fold higher energy transfer efficiency to VBBO than Cerenkov luminescence energy transfer (CLET). ⁶⁴Cu-labeled Eu/VBBO lipo (⁶⁴Cu-Eu/VBBO lipo) showed a substantial tumor uptake of up to 19.3%ID/g by enhanced permeability and retention effects, as revealed by in vivo positron emission tomography. Finally, the PDT using ⁶⁴Cu-Eu/VBBO lipo demonstrated significantly higher in vitro and in vivo therapeutic effects than Cerenkov luminescence-induced PDT using ⁶⁴Cu-VBBO lipo. This study envisions a great opportunity for clinical PDT application by establishing the radioluminescence liposome which has high tumor targeting and efficient energy transfer capability from radioisotopes.

An activatable liposomal fluorescence probe based on fluorescence resonance energy transfer and aggregation induced emission effect for sensitive tumor imaging

Liposomes are of great interest and importance in tumor imaging, since they can greatly improve the imaging sensitivity and specificity by increasing the accumulation of contrast agents. Still, most liposome-based probes have high background signals during blood circulation, which limits enhancement of S/B ratio and tumor imaging sensitivity. To enhance the S/B ratio of tumor imaging, we construct a fluorescence resonance energy transfer (FRET) and aggregation induced emission (AIE) based liposomal fluorescence probe TPE/BHQ-lipo with excellent FRET effect (99 %) and great fluorescence enhancement upon liposome rupture (120-fold) as well as efficient fluorescence recovery in tumor cell imaging. Finally, we used the TPE/BHQ-lipo to image 4T1 tumor upon intravenous injection of liposomes and the group showed enhanced signal to background ratio of 4.1, compared to 1.8 from control AIE-based liposomal group (TPE-lipo). Our work offers an excellent FRET and AIE-based liposomal probe for high-sensitive tumor imaging.

Nanococktail Based on AIEgens and Semiconducting Polymers: A Single Laser Excited Image-Guided Dual Photothermal Therapy

Semiconducting polymers (SPs)-based dual photothermal therapy (PTT) obtained better therapeutic effect than single PTT due to its higher photothermal conversion efficiency. However, most dual PTT need to use two lasers for heat generation, which brings about inconvenience and limitation to the experimental operations. Herein, we report the development of "nanococktail" nanomaterials (DTPR) with 808 nm-activated image-guided dual photothermal properties for optimized cancer therapy. Methods: In this work, we co-encapsulated AIEgens (TPA-BDTO, T) and SPs (PDPPP, P) by using maleimide terminated amphiphilic polymer (DSPE-PEG2000-Mal, D), then further conjugated the targeting ligands (RGD, R) through "click" reaction. Finally, such dual PTT nanococktail (termed as DTPR) was constructed. Results: Once DTPR upon irradiation with 808 nm laser, near-infrared fluorescence from T could be partially converted into thermal energy through fluorescence resonance energy transfer (FRET) between T and P, coupling with the original heat energy generated by the photothermal agent P itself, thus resulting in image-guided dual PTT. The photothermal conversion efficiency of DTPR reached 60.3% (dual PTT), much higher as compared to its inherent photothermal effect of only 31.5% (single PTT), which was further proved by the more severe photothermal ablation in vitro and in vivo upon 808 nm laser irradiation. Conclusion: Such smart "nanococktail" nanomaterials could be recognized as a promising photothermal nanotheranostics for image-guided cancer treatment.

Single-molecular phosphorus phthalocyanine-based near-infrared-II nanoagent for photothermal antitumor therapy

As one of the noninvasive cancer treatments, photothermal therapy (PTT) has drawn intense attention recently. In this context, an important task is to explore novel and versatile nanoscale photothermal agents (PTAs), especially those with strong NIR-II light absorption, high photothermal conversion efficiency, good photostability and biocompatibility. Phthalocyanines (Pcs), as the second-generation photosensitizers, are a promising class of candidates for PTT due to their strong NIR absorption and high photothermal conversion efficiency. However, the poor water solubility severely limited their application as PTAs in tumor treatment. Herein, we report a molecular phosphorus phthalocyanine (P-Pc)-based nanoagent via incorporation of human serum albumin (HSA) under mild conditions. The obtained nanoscale P-Pc-HSA possesses excellent photothermal conversion efficiency (64.7%) upon 1064 nm light irradiation, furthermore, it can be a highly efficient NIR-II antitumor nanoagent via photothermal treatment (PTT), which is fully evidenced by the in vitro and in vivo experiments.

A molecular phosphorus phthalocyanine (P-Pc)-based nanoagent P-Pc-HSA, which can be a highly efficient NIR-II antitumor agent, is reported.

In Situ Fabrication of Intelligent Photothermal Indocyanine Green-Alginate Hydrogel for Localized Tumor Ablation

Simplifying synthesis and administration process, improving photothermal agents' accumulation in tumors, and ensuring excellent biocompatibility and biodegradability are keys to promoting the clinical application of photothermal therapy. However, current photothermal agents have great difficulties in meeting the requirements of clinic drugs from synthesis to administration. Herein, we reported the in situ formation of a Ca²⁺/Mg²⁺ stimuli-responsive ICG-alginate hydrogel in vivo for localized tumor photothermal therapy. An ICG-alginate hydrogel can form by the simple introduction of Ca²⁺/Mg²⁺ into ICG-alginate solution in vitro, and the widely distributed divalent cations in organization in vivo enabled the in situ fabrication of the ICG-alginate hydrogel without the leakage of any agents by simple injection of ICG-alginate solution into the body of mice. The as-prepared ICG-alginate hydrogel not only owns good photothermal therapy efficacy and excellent biocompatibility but also exhibits strong ICG fixation ability, greatly benefiting the high photothermal agents' accumulation and minimizing the potential side effects induced by the diffusion of ICG to surrounding tissues. The in situ-fabricated ICG-alginate hydrogel was applied successfully in highly efficient PTT in vivo without obvious side effects. Besides, the precursor of the hydrogel, ICG and alginate, can be stored in a stable solid form, and only simple mixing and noninvasive injection are needed to achieve PTT in vivo. The proposed in situ gelation strategy using biocompatible components lays down a simple and mild way for the fabrication of high-performance PTT agents with the superiors in the aspects of synthesis, storage, transportation, and clinic administration.

Photothermal cancer immunotherapy by erythrocyte membrane-coated black phosphorus formulation

Basal-like breast cancer exhibits a triple-negative phenotype and has a poor prognosis, even with traditional chemical and anti-human epidermal growth factor receptor (HER) treatments. However, the high mutation rate of this obstinate cancer type renders it suitable for immunotherapy. Photothermal therapy (PTT) is a high-efficiency method for inducing tumor neoantigen release in situ, which has great potential for use in cancer immunotherapy. Here, we prepared a biomimetic black phosphorus quantum dot (BPQDs) formulation to induce breast cancer cell apoptosis in situ by near-infrared (NIR) laser irradiation to mobilize the immune system to eliminate the residual and metastatic cancer cells. Erythrocyte membranes (RMs) were used to coat the BPQDs, forming a BPQD-RM nanovesicle (BPQD-RMNV) biomimetic formulation that exhibited a long circulation time and tumor accumulation in vivo. The basal-like 4T1 breast tumor underwent apoptosis and necrosis with the irradiation and recruited dendritic cells (DCs) to capture the tumor antigens in vivo. Furthermore, programmed cell death protein 1 (PD-1) antibody (aPD-1) was employed to prevent the CD8⁺ T cells from exhaustion. Notably, BPQD-RMNV-mediated PTT combined with aPD-1 treatment significantly delayed residual and metastatic tumor growth in vivo. Hence, BPQD-RMNV-mediated PTT combined with immune checkpoint blockade antibody increased the infiltration and activity of CD8⁺ T cells in the tumor, which directly restrained basal-like breast tumor growth in vivo.

Phototheranostics: Active Targeting of Orthotopic Glioma Using Biomimetic Proteolipid Nanoparticles

Advances in phototheranostics revolutionized glioma intraoperative fluorescence imaging and phototherapy. However, the lack of desired active targeting agents for crossing the blood-brain barrier (BBB) significantly compromises the theranostic efficacy. In this study, biomimetic proteolipid nanoparticles (NPs) with U.S. Food and Drug Administration (FDA)-approved indocyanine green (ICG) were constructed to allow fluorescence imaging, tumor margin detection, and phototherapy of orthotopic glioma in mice. By embedding glioma cell membrane proteins into NPs, the obtained biomimetic ICG-loaded liposome (BLIPO-ICG) NPs could cross BBB and actively reach glioma at the early stage thanks to their specific binding to glioma cells due to their excellent homotypic targeting and immune escaping characteristics. High accumulation in the brain tumor with a signal to background ratio of 8.4 was obtained at 12 h post-injection. At this time point, the glioma and its margin were clearly visualized by near-infrared fluorescence imaging. Under the imaging guidance, the glioma tissue could be completely removed as a proof of concept. In addition, after NIR laser irradiation (1 W/cm², 5 min), the photothermal effect exerted by BLIPO-ICG NPs efficiently suppressed glioma cell proliferation with a 94.2% tumor growth inhibition. No photothermal damages of normal brain tissue and treatment-induced side effects were observed. These results suggest that the biomimetic proteolipid NP is a promising phototheranostic nanoplatform for brain-tumor-specific imaging and therapy.