The evaluation of NIR-absorbing porphyrin derivatives as contrast agents in photoacoustic imaging

Sex-specific outcomes in cancer therapy: the central role of hormones

Sex hormones play a pivotal role in modulating various physiological processes, with emerging evidence underscoring their influence on cancer progression and treatment outcomes. This review delves into the intricate relationship between sex hormones and cancer, elucidating the underlying biological mechanisms and their clinical implications. We explore the multifaceted roles of estrogen, androgens, and progesterone, highlighting their respective influence on specific cancers such as breast, ovarian, endometrial, and prostate. Special attention is given to estrogen receptor-positive (ER+) and estrogen receptor-negative (ER-) tumors, androgen receptor signaling, and the dual role of progesterone in both promoting and inhibiting cancer progression. Clinical observations reveal varied treatment responses contingent upon hormonal levels, with certain therapies like tamoxifen, aromatase inhibitors, and anti-androgens demonstrating notable success. However, disparities in treatment outcomes between males and females in hormone-sensitive cancers necessitate further exploration. Therapeutically, the utilization of hormone replacement therapy (HRT) during cancer treatments presents both potential risks and benefits. The promise of personalized therapies, tailored to an individual's hormonal profile, offers a novel approach to optimizing therapeutic outcomes. Concurrently, the burgeoning exploration of new drugs and interventions targeting hormonal pathways heralds a future of more effective and precise treatments for hormone-sensitive cancers. This review underscores the pressing need for a deeper understanding of sex hormones in cancer therapy and the ensuing implications for future therapeutic innovations.

Quest for the Most Aromatic Pathway in Charged Expanded Porphyrins

Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AV_min remains the best tool to determine the main conjugation pathway of expanded porphyrins.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

Recent Advances in Photosensitizers as Multifunctional Theranostic Agents for Imaging-Guided Photodynamic Therapy of Cancer

In recent years tremendous effort has been invested in the field of cancer diagnosis and treatment with an overall goal of improving cancer management, therapeutic outcome, patient survival, and quality of life. Photodynamic Therapy (PDT), which works on the principle of light-induced activation of photosensitizers (PS) leading to Reactive Oxygen Species (ROS) mediated cancer cell killing has received increased attention as a promising alternative to overcome several limitations of conventional cancer therapies. Compared to conventional therapies, PDT offers the advantages of selectivity, minimal invasiveness, localized treatment, and spatio-temporal control which minimizes the overall therapeutic side effects and can be repeated as needed without interfering with other treatments and inducing treatment resistance. Overall PDT efficacy requires proper planning of various parameters like localization and concentration of PS at the tumor site, light dose, oxygen concentration and heterogeneity of the tumor microenvironment, which can be achieved with advanced imaging techniques. Consequently, there has been tremendous interest in the rationale design of PS formulations to exploit their theranostic potential to unleash the imperative contribution of medical imaging in the context of successful PDT outcomes. Further, recent advances in PS formulations as activatable phototheranostic agents have shown promising potential for finely controlled imaging-guided PDT due to their propensity to specifically turning on diagnostic signals simultaneously with photodynamic effects in response to the tumor-specific stimuli. In this review, we have summarized the recent progress in the development of PS-based multifunctional theranostic agents for biomedical applications in multimodal imaging combined with PDT. We also present the role of different imaging modalities; magnetic resonance, optical, nuclear, acoustic, and photoacoustic in improving the pre-and post-PDT effects. We anticipate that the information presented in this review will encourage future development and design of PSs for improved image-guided PDT for cancer treatment.

Recent progress in near-infrared photoacoustic imaging

The emergence of the photoacoustic imaging (PAI) expands the application of biomolecules bioimaging in cells, various tissues, and living body to monitor multiple physiological processes in complex internal environments. The PAI possesses intriguing properties such as non-invasive, highly selective excitation, and weak signal attenuation. Especially, the near-infrared (NIR) PAI displays low optical absorption and scattering, good temporal or spatial resolution and deep penetration, holds great potential in biomedical applications. We briefly compare different imaging modalities to provide a comprehensive understanding of their characteristics and related applications, highlighting the feature of the PAI. The principle of PAI is then delineated and the emerging NIR-PAI is discussed. We then focus on elaboration of the recent achievement of typical NIR-PAI contrast and their biomedical applications, especially the strategies used to improve contrast rational design and PAI performance are summarized. The PAI-related multimodal imaging approaches for improving imaging accuracy are also covered in the review. Finally, the challenges and prospective are pointed out for attracting more researchers to accelerate the development of PAI.

Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques

Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions between porphyrinic compounds and macromolecules. Such interactions are of special interest in medical applications of porphyrinic photosensitizers that are mostly combined with macromolecular carrier systems. The macromolecular surrounding typically stabilizes the encapsulated drug and may also modify its physical properties. Moreover, the interaction with macromolecular physiological components needs to be explored to understand and control mechanisms of action and therapeutic efficacy. This review focuses on such non-covalent interactions of porphyrinic drugs with synthetic polymers as well as with biomolecules such as phospholipids or proteins. A brief introduction into various NMR spectroscopic techniques is given including chemical shift perturbation methods, NOE enhancement spectroscopy, relaxation time measurements and diffusion-ordered spectroscopy. How these NMR tools are used to address porphyrin-macromolecule interactions with respect to their function in biomedical applications is the central point of the current review.

880 nm NIR-Triggered Organic Small Molecular-Based Nanoparticles for Photothermal Therapy of Tumor

Photothermal therapy (PTT) has received constant attention as an efficient cancer therapy method due to locally selective treatment, which is not affected by the tumor microenvironment. In this study, a novel 880 nm near-infrared (NIR) laser-triggered photothermal agent (PTA), 3TT-IC-4Cl, was used for PTT of a tumor in deep tissue. Folic acid (FA) conjugated amphiphilic block copolymer (folic acid-polyethylene glycol-poly (β-benzyl-L-aspartate)₁₀, FA-PEG-PBLA₁₀) was employed to encapsulate 3TT-IC-4Cl by nano-precipitation to form stable nanoparticles (TNPs), and TNPs exhibit excellent photothermal stability and photothermal conversion efficiency. Furthermore, the in vitro results showed TNPs display excellent biocompatibility and significant phototoxicity. These results suggest that 880 nm triggered TNPs have great potential as effective PTAs for photothermal therapy of tumors in deep tissue.

Metalloporphyrins in Medicine: From History to Recent Trends

The history of metalloporphyrins dates back more than 200 years ago. Metalloporphyrins are excellent catalysts, capable of forming supramolecular systems, participate in oxygen photosynthesis, transport, and used as contrast agents or superoxide dismutase mimetics. Today, metalloporphyrins represent complexes of conjugated π-electron system and metals from the entire periodic system. However, the effect of these compounds on living systems has not been fully understood, and researchers are exploring the properties of metalloporphyrins thereby extending their further application. This review provides an overview of the variety of metalloporphyrins that are currently used in different medicine fields and how metalloporphyrins became the subject of scientists' interest. Currently, metalloporphyrins utilization has expanded significantly, which gave us an opprotunuty to summarize recent progress in metalloporphyrins derivatives and prospects of their application in the treatment and diagnosis of different diseases.

Design Strategies of Photoacoustic Molecular Probes

Photoacoustic (PA) probes have been developed very quickly and applied in broad areas in recent years. Most of them are constructed based on organic dyes with intrinsic near-infrared (NIR) absorption properties. To increase PA contrast and improve imaging resolution and the sensitivity of detection, various methods for the design of PA probes have been developed. This minireview mainly focuses on the development and design strategies of activatable small-molecule PA probes in four aspects: reaction-cleavage, metal ion chelation, photoswitch, and protonation-deprotonation. It highlights some key points of designing PA probes corresponding to their properties and applications. The challenges and perspectives for small-molecule PA probes are also discussed.

Photoacoustic Imaging Probes Based on Tetrapyrroles and Related Compounds

Photoacoustic imaging (PAI) is a rapidly evolving field in molecular imaging that enables imaging in the depths of ultrasound and with the sensitivity of optical modalities. PAI bases on the photoexcitation of a chromophore, which converts the absorbed light into thermal energy, causing an acoustic pressure wave that can be captured with ultrasound transducers, in generating an image. For in vivo imaging, chromophores strongly absorbing in the near-infrared range (NIR; > 680 nm) are required. As tetrapyrroles have a long history in biomedical applications, novel tetrapyrroles and inspired mimics have been pursued as potentially suitable contrast agents for PAI. The goal of this review is to summarize the current state of the art in PAI applications using tetrapyrroles and related macrocycles inspired by it, highlighting those compounds exhibiting strong NIR-absorption. Furthermore, we discuss the current developments of other absorbers for in vivo photoacoustic (PA) applications.

Synthesis and Self-Assembly Behavior of Chlorophyll Derivatives for Ratiometric Photoacoustic Signal Optimization

Self-assembly provides researchers powerful tools for creating ordered functional structures and complex architectures. Investigation of in vivo self-assembly reveals the assembly/aggregation-induced retention (AIR) effect and enhanced targeting effect, which can be applied to promising biomedical applications by enhancing molecular accumulation in the target region. These unique bioeffects inspire the interest of researchers in construction of self-assembled nanomaterials in biological systems. Although many efforts have been achieved, the in-depth analysis of the relationship between assemblies and functions is rarely reported. Here, we focus on the relationship of chlorophyll-derivative assemblies and their photoacoustic signals and attempt to establish a method for monitoring the aggregation efficiency in vivo based on photoacoustic signals. Three arginine-rich peptide-purpurin molecules were designed and synthesized. The assembled capabilities and assembly processes of these molecules were characterized and monitored by UV, fluorescence, and CD spectra images of gradually changing polarities in mixed solvents, and the morphologies of the assemblies were observed by TEM. Furthermore, the relationship between the aggregation ratios of the molecules and the ratiometric photoacoustic signals was systemically studied. We prospect that the fundamental research in revealing objective laws will be useful for future guidance in optimizing photoacoustic detection windows and assembled molecule design.

Quinoline-annulated porphyrin platinum complexes as NIR emitters

The platinum(II) complexes of known quinoline-annulated porphyrins were prepared and spectroscopically characterized. Their optical properties (UV-vis absorption and phosphorescence spectra and phosphorescence lifetimes) were recorded and contrasted against their 2,3-dioxoporphyrin precursor platinum(II) complex. The absorbance and emission spectra (in EtOH glass at 77 K) of the quinoline-annulated porphyrins fall within the NIR optical window of tissue, ranging, depending on the derivative, between [Formula: see text]950 and 1200 nm. The much red-shifted optical spectra, when compared to their non-quinoline-annulated precursors, are attributed to the [Formula: see text]-extension and conformational non-planarity that the annulation causes. The emission yields of the mono-quinoline-annulated derivatives are too low and their lifetimes too short to be practical emitters, but the bis-annulated derivative possesses a practical lifetime and emission yield, suggesting its further exploration, particularly since the methodology toward the solubilization of the quinoline-annulated porphyrins in biological media through derivatization is known.

In Situ Fluorescent and Photoacoustic Imaging of Golgi pH to Elucidate the Function of Transmembrane Protein 165

Golgi pH homeostasis affects many different biological processes, including glycosylation. Recent studies have demonstrated that transmembrane protein 165 (TMEM165) deficiency leads to Golgi glycosylation abnormalities by disturbing Golgi pH homeostasis. However, due to the lack of specific tools to measure Golgi pH in situ, evidence for TMEM165 involvement in H⁺ transport in the Golgi apparatus is still absent. Herein, the photoacoustic and fluorescent dual-mode probe CPH was developed for ratiometric detection of Golgi pH. CPH was proved to accumulate in the Golgi apparatus and reversibly image Golgi pH in real-time with high sensitivity in cells. Furthermore, we found that the absence of TMEM165 influenced H⁺ equilibrium and caused Golgi apparatus acidification. Our work provides strong evidence that TMEM165 regulates Golgi pH homeostasis. Moreover, we believe that CPH has the potential to be a practical tool to monitor Golgi pH in various biological processes.

Multifunctional materials conjugated with near-infrared fluorescent organic molecules and their targeted cancer bioimaging potentialities

Near-infrared fluorescent dyes based on small organic molecules are believed to have a great influence on cancer diagnosis at large and targeted cancer cell bioimaging, in particular. NIR dyes-based organic molecules have notable characteristics features, such as high tissue penetration and low tissue autofluorescence in the NIR spectral region. Cancer targeted bioimaging relies significantly on the synthesis of highly specific molecular probes with excellent stability. Recently, NIR dyes have emerged as unique fluorescent probes for cancer bioimaging. These current advancements have overcome many limitations of conventional NIR probes e.g., poor photostability and hydrophilicity, insufficient stability and low quantum yield. The further potential lies in NIR dyes or NIR dyes-coated nanocarriers conjugated with cancer-specific ligand (e.g., peptides, antibodies, proteins or other small molecules). Multifunctional NIR dyes have synthesized, which efficiently accumulate in cancer cells without requiring chemical conjugation and also these dyes have presented novel photophysical and pharmaceutical properties for in vivo imaging. This review highlights the recently developed NIR dyes with novel applications in cancer bioimaging. We believe that these novel fluorophores will enhance our understanding of cancer imaging and pave a new road in cancer diagnosis and treatment.

Improving the High-Frequency Response of PEI-Based Earphone with Sodium Copper Chlorophyllin

The polyetherimide diaphragm, sodium copper chlorophyllin (SCC), and copper ion coating composite used on earphones were observed to improve the high-frequency (10k–14k Hz) performance. This reinforcement phenomenon was expected to make the sound experience brighter and more diverse. By SEM observation, the mixed coating of SCC/Cu²⁺ on the polyethylenimine (PEI) diaphragm exhibited a planar blocky structure and was tightly bonded to the surface of the PEI polymer without the aid of colloids. The endothermic process of SCC and metal ion complexation was analyzed by isothermal titration calorimetry. The association ratios of SCC/Cu²⁺ and SCC/Ni²⁺ were 4/1 and 6/1, respectively, and the SCC/Cu²⁺ association yielded a stronger binding constant and more free energy. It was expected that the SCC/Cu²⁺(4/1) mixed liquid would be immobilized on the PEI polymer by multivalent interaction, including hydrogen-bonding networks between carboxyl groups of SCC and amine groups of PEI, and cross-linking of bridging copper ions. We used dimethylethylenediamine (DME) monomer instead of PEI polymer to analyze this multivalent interaction and observed a two-stage exothermic association of SCC/Cu²⁺(4/1) and DME with a total Gibbs free energy of 15.15 kcal/mol. We observed that the binding energy could be used to explain that the SCC/Cu²⁺ mixed formulation could be fixed on the surface of the PEI polymer and could enhance the strength of the PEI film. Compared with graphene films, which can continuously improve the performance of high and ultrasonic frequencies, this study was devoted to and was initiated for the purpose of applying porphyrin compounds to improve music performance.

Porphyrinoid-based photosensitizers for diagnostic and therapeutic applications: An update

Porphyrin-based molecules are actively studied as dual function theranostics: fluorescence-based imaging for diagnostics and fluorescence-guided therapeutic treatment of cancers. The intrinsic fluorescent and photodynamic properties of the bimodal molecules allows for these theranostic approaches. Several porphyrinoids bearing both hydrophilic and/or hydrophobic units at their periphery have been developed for the aforementioned applications, but better tumor selectivity and high efficacy to destroy tumor cells is always a key setback for their use. Another issue related to their effective clinical use is that, most of these chromophores form aggregates under physiological conditions. Nanomaterials that are known to possess incredible properties that cannot be achieved from their bulk systems can serve as carriers for these chromophores. Porphyrinoids, when conjugated with nanomaterials, can be enabled to perform as multifunctional nanomedicine devices. The integrated properties of these porphyrinoid-nanomaterial conjugated systems make them useful for selective drug delivery, theranostic capabilities, and multimodal bioimaging. This review highlights the use of porphyrins, chlorins, bacteriochlorins, phthalocyanines and naphthalocyanines as well as their multifunctional nanodevices in various biomedical theranostic platforms.

Metalloporphyrin Nanoparticles: Coordinating Diverse Theranostic Functions

Metalloporphyrins serve key roles in natural biological processes and also have demonstrated utility for biomedical applications. They can be encapsulated or grafted in conventional nanoparticles or can self-assemble themselves at the nanoscale. A wide range of metals can be stably chelated either before or after porphyrin nanoparticle formation, without the necessity of any additional chelator chemistry. The addition of metals can substantially alter a range of behaviors such as modulating phototherapeutic efficacy; conferring responsiveness to biological stimuli; or providing contrast for magnetic resonance, positron emission or surface enhanced Raman imaging. Chelated metals can also provide a convenient handle for bioconjugation with other molecules via axial coordination. This review provides an overview of some recent biomedical, nanoparticulate approaches involving gain-of-function metalloporphyrins and related molecules.

Acoustogenic Probes: A New Frontier in Photoacoustic Imaging

Photoacoustic imaging (PAI) is a powerful imaging modality capable of mapping the absorption of light in biological tissue via the PA effect. When chromophores are optically excited, subsequent energy loss in the form of heat generates local thermoelastic expansion. Repeated excitation from a pulsed laser induces pressure fluctuations that propagate through tissue and can be detected as ultrasound waves. By combining ultrasonic detection with optical excitation, PAI enables high-resolution image acquisition at centimeter depths. PAI is also relatively inexpensive and relies on safe, nonionizing excitation light in the near-infrared window, making it an attractive alternative to other common biomedical imaging modalities. Research in our group is aimed at developing small-molecule activatable probes that can be used for analyte detection in deep tissue via PAI. These probes contain reactive triggers that undergo a selective chemical reaction in the presence of specific stimuli to produce a spectral change that can be observed via PAI. Chemically tuning the absorbance profile of the probe and the reacted product such that they are both within the PA imaging window enables ratiometric imaging when each species is irradiated at a specific wavelength. Ratiometric imaging is an important design feature of these probes as it minimizes error associated with tissue-dependent signal fluctuations and instrumental variation. In this Account, we discuss key properties for designing small-molecule PA probes that can be applied for in vivo studies and the challenges associated with this area of probe development. We also highlight examples from our group including probes capable of detecting metal ions (Cu(II)), reactive nitrogen species (NO), and oxygen tension (hypoxia). Each of these targets can be sensed using a modular design strategy based on influencing the electronic and spectral properties of a NIR-absorbing dye platform. We demonstrate that ideal small-molecule PA probes have high molar absorptivity, low fluorescence quantum yields, and selective triggers that can reliably report on a single analyte in a complex biological setting. Probes must also be highly chemo- and photostable to enable long-term imaging studies. We show that these PA probes react rapidly and selectively and can be utilized for deep-tissue imaging in mouse models of various diseases. Overall, these examples represent a new class of biomedical imaging tools that seek to enable high-resolution molecular imaging capable of improving diagnostic methods and elucidating new biological discoveries. We anticipate that the combination of small-molecule PA probes with new PAI technology will enable noninvasive detection of analytes relevant to disease progression and mapping of tissue microenvironments.

Molecular Photoacoustic Contrast Agents: Design Principles & Applications

Photoacoustic imaging (PAI) is a rapidly growing field which offers high spatial resolution and high contrast for deep-tissue imaging in vivo. PAI is nonionizing and noninvasive and combines the optical resolution of fluorescence imaging with the spatial resolution of ultrasound imaging. In particular, the development of exogenous PA contrast agents has gained significant momentum of late with a vastly expanding complexity of dye materials under investigation ranging from small molecules to macromolecular proteins, polymeric and inorganic nanoparticles. The goal of this review is to survey the current state of the art in molecular photoacoustic contrast agents (MPACs) for applications in biomedical imaging. The fundamental design principles of MPACs are presented and a review of prior reports spanning from early-to-current literature is put forth.

Organic Dye Based Nanoparticles for Cancer Phototheranostics

Phototheranostics, which simultaneously combines photodynamic and/or photothermal therapy with deep-tissue diagnostic imaging, is a promising strategy for the diagnosis and treatment of cancers. Organic dyes with the merits of strong near-infrared absorbance, high photo-to-radical and/or photothermal conversion efficiency, great biocompatibility, ready chemical structure fine-tuning capability, and easy metabolism, have been demonstrated as attractive candidates for clinical phototheranostics. These organic dyes can be further designed and fabricated into nanoparticles (NPs) using various strategies. Compared to free molecules, these NPs can be equipped with multiple synergistic functions and show longer lifetime in blood circulation and passive tumor-targeting property via the enhanced permeability and retention effect. In this article, the recent progress of organic dye-based NPs for cancer phototheranostic applications is summarized, which extends the anticancer arsenal and holds promise for clinical uses in the near future.

Embedding heteroatoms: an effective approach to create porphyrin-based functional materials

Incorporation of planarized heteroatom(s) onto the porphyrin periphery is an effective approach to create porphyrin-based functional materials. In the last three decades, such an "embedding heteroatom" strategy has been actively explored in order to realize attractive electronic, optical, and electrochemical properties. This review aims to cover a variety of synthetic methodologies that have been developed for the construction of heteroatom-embedded porphyrins. Moreover, we also summarize their structure-property relationships as well as possible applications in various research fields including artificial photosynthesis, molecular engineering, organic electronics, and bioimaging.

Feasibility of photoacoustic-guided teleoperated hysterectomies

Hysterectomies (i.e., surgical removal of the uterus) are the prevailing solution to treat medical conditions such as uterine cancer, endometriosis, and uterine prolapse. One complication of hysterectomies is accidental injury to the ureters located within millimeters of the uterine arteries that are severed and cauterized to hinder blood flow and enable full uterus removal. This work explores the feasibility of using photoacoustic imaging to visualize the uterine arteries (and potentially the ureter) when this imaging method is uniquely combined with a da Vinci^® surgical robot that enables teleoperated hysterectomies. We developed a specialized light delivery system to surround a da Vinci^® curved scissor tool, and an ultrasound probe was placed externally, representing a transvaginal approach, to receive the acoustic signals. Photoacoustic images were acquired while sweeping the tool across our custom 3-D uterine vessel model covered in ex vivo bovine tissue that was placed between the 3-D model and the fiber, as well as between the ultrasound probe and the 3-D model. Four tool orientations were explored, and the robot kinematics were used to provide tool position and orientation information simultaneously with each photoacoustic image acquisition. The optimal tool orientation produced images with contrast >10  dB and background signal-to-noise ratios (SNRs) >1.7, indicating minimal acoustic clutter from the tool tip. We achieved similar contrast and SNR measurements with four unique wrist orientations explored with the scissor tool in open and closed configurations. Results indicate that photoacoustic imaging is a promising approach to enable visualization of the uterine arteries to guide hysterectomies (and other gynecological surgeries). These results are additionally applicable to other da Vinci^® surgeries and other surgical instruments with similar tip geometry.

Switching of inter-valence charge transfer in stimuli-responsive bis(ferrocenyl)porphyrin

Stimuli-responsive 5,15-bis(ferrocenyl)-10,20-bis(mesityl)porphyrin (BFP) was synthesized and used to demonstrate the ON/OFF switching of inter-valence charge transfer (IVCT) between ferrocene terminals.

Transparent Low Molecular Weight Poly(Ethylene Glycol) Diacrylate-Based Hydrogels as Film Media for Photoswitchable Drugs

Hydrogels have shown a great potential as materials for drug delivery systems thanks to their usually excellent bio-compatibility and their ability to trap water-soluble organic molecules in a porous network. In this study, poly(ethylene glycol)-based hydrogels containing a model dye were synthesized by ultraviolet (UV-A) photopolymerization of low-molecular weight macro-monomers and the material properties (dye release ability, transparency, morphology, and polymerization kinetics) were studied. Real-time infrared measurements revealed that the photopolymerization of the materials was strongly limited when the dye was added to the uncured formulation. Consequently, the procedure was adapted to allow for the formation of sufficiently cured gels that are able to capture and later on to release dye molecules in phosphate-buffered saline solution within a few hours. Due to the transparency of the materials in the 400⁻800 nm range, the hydrogels are suitable for the loading and excitation of photoactive molecules. These can be uptaken by and released from the polymer matrix. Therefore, such materials may find applications as cheap and tailored materials in photodynamic therapy (i.e., light-induced treatment of skin infections by bacteria, fungi, and viruses using photoactive drugs).

Quinone-fused porphyrins as contrast agents for photoacoustic imaging

Photoacoustic (PA) imaging is an emerging non-invasive diagnostic modality with many potential clinical applications in oncology, rheumatology and the cardiovascular field. For this purpose, there is a high demand for exogenous contrast agents with high absorption coefficients in the optical window for tissue imaging, i.e. the near infrared (NIR) range between 680 and 950 nm. We herein report the photoacoustic properties of quinone-fused porphyrins inserted with different transition metals as new highly promising candidates. These dyes exhibit intense NIR absorption, a lack of fluorescence emission, and PA sensitivity in concentrations below 3 nmol mL-1. In this context, the highest PA signal was obtained with a Zn(ii) inserted dye. Furthermore, this dye was stable in blood serum and free thiol solution and exhibited negligible cell toxicity. Additionally, the Zn(ii) probe could be detected with an up to 3.2 fold higher PA intensity compared to the clinically most commonly used PA agent, ICG. Thus, further exploration of the 'quinone-fusing' approach to other chromophores may be an efficient way to generate highly potent PA agents that do not fluoresce and shift their absorption into the NIR range.

Tumor-associated macrophages, nanomedicine and imaging: the axis of success in the future of cancer immunotherapy

The success of any given cancer immunotherapy relies on several key factors. In particular, success hinges on the ability to stimulate the immune system in a controlled and precise fashion, select the best treatment options and appropriate therapeutic agents, and use highly effective tools to accurately and efficiently assess the outcome of the immunotherapeutic intervention. Furthermore, a deep understanding and effective utilization of tumor-associated macrophages (TAMs), nanomedicine and biomedical imaging must be harmonized to improve treatment efficacy. Additionally, a keen appreciation of the dynamic interplay that occurs between immune cells and the tumor microenvironment (TME) is also essential. New advances toward the modulation of the immune TME have led to many novel translational research approaches focusing on the targeting of TAMs, enhanced drug and nucleic acid delivery, and the development of theranostic probes and nanoparticles for clinical trials. In this review, we discuss the key cogitations that influence TME, TAM modulations and immunotherapy in solid tumors as well as the methods and resources of tracking the tumor response. The vast array of current nanomedicine technologies can be readily modified to modulate immune function, target specific cell types, deliver therapeutic payloads and be monitored using several different imaging modalities. This allows for the development of more effective treatments, which can be specifically designed for particular types of cancer or on an individual basis. Our current capacities have allowed for greater use of theranostic probes and multimodal imaging strategies that have led to better image contrast, real-time imaging capabilities leveraging targeting moieties, tracer kinetics and enabling more detailed response profiles at the cellular and molecular levels. These novel capabilities along with new discoveries in cancer biology should drive innovation for improved biomarkers for efficient and individualized cancer therapy.

Near-infrared autofluorescence induced by intraplaque hemorrhage and heme degradation as marker for high-risk atherosclerotic plaques

Atherosclerosis is a major cause of mortality and morbidity, which is mainly driven by complications such as myocardial infarction and stroke. These complications are caused by thrombotic arterial occlusion localized at the site of high-risk atherosclerotic plaques, of which early detection and therapeutic stabilization are urgently needed. Here we show that near-infrared autofluorescence is associated with the presence of intraplaque hemorrhage and heme degradation products, particularly bilirubin by using our recently created mouse model, which uniquely reflects plaque instability as seen in humans, and human carotid endarterectomy samples. Fluorescence emission computed tomography detecting near-infrared autofluorescence allows in vivo monitoring of intraplaque hemorrhage, establishing a preclinical technology to assess and monitor plaque instability and thereby test potential plaque-stabilizing drugs. We suggest that near-infrared autofluorescence imaging is a novel technology that allows identification of atherosclerotic plaques with intraplaque hemorrhage and ultimately holds promise for detection of high-risk plaques in patients.

Atherosclerosis diagnosis relies primarily on imaging and early detection of high-risk atherosclerotic plaques is important for risk stratification of patients and stabilization therapies. Here Htun et al. demonstrate that vulnerable atherosclerotic plaques generate near-infrared autofluorescence that can be detected via emission computed tomography.

In vivo photoacoustic tumor tomography using a quinoline-annulated porphyrin as NIR molecular contrast agent

The synthesis and photophysical properties of a tetra-PEG-modified and freely water-soluble quinoline-annulated porphyrin are described. We previously demonstrated the ability of quinoline-annulated porphyrins to act as an in vitro NIR photoacoustic imaging (PAI) contrast agent. The solubility of the quinoline-annulated porphyrin derivative in serum now allowed the assessment of the efficacy of the PEGylated derivative as an in vivo NIR contrast agent for the PAI of an implanted tumor in a mouse model. A multi-fold contrast enhancement when compared to the benchmark dye ICG could be shown, a finding that could be traced to its photophysical properties (short triplet lifetimes, low fluorescence and singlet oxygen sensitization quantum yields). A NIR excitation wavelength of 790 nm could be used, fully taking advantage of the optical window of tissue. Rapid renal clearance of the dye was observed. Its straight-forward synthesis, optical properties with the possibility for further optical fine-tuning, nontoxicity, favorable elimination rates, and contrast enhancement make this a promising PAI contrast agent. The ability to conjugate the PAI chromophore with a fluorescent tag using a facile and general conjugation strategy was also demonstrated.

Push–pull type meso-ester substituted BODIPY near-infrared dyes as contrast agents for photoacoustic imaging

Push–pull meso-ester BODIPYs with intense NIR absorption and good photo-stability were used for in vitro and in vivo photoacoustic imaging.

Synthesis and characterization of an HSP27-targeted nanoprobe for in vivo photoacoustic imaging of early nerve injury

Imaging is routinely used for clinical and diagnostic purposes, but techniques capable of high specificity and resolution for the early detection of nerve injury are still limited. In this study, we found that heat shock protein 27 (HSP27) becomes highly upregulated within 3 to 7 days of nerve injury. Taking advantage of this expression pattern, we conjugated gold nanorods (GNRs) to HSP27-specific antibodies to generate a nanoprobe (GNR-HSP27Abs) that could be targeted to the site of nerve injury and detected by near-infrared photoacoustic imaging. Notably, photoacoustic images acquired 12hours after local administration of GNR-HSP27Abs demonstrated that the nanoprobe can distinguish between injured and uninjured nerves in rats. Taken together, these findings expand the application of nanoprobe-targeted photoacoustic imaging to the detection of injured nerves, and prompt further development of this novel imaging platform for clinical application.

Quinoline-annulated chlorins and chlorin-analogs

The OsO4-mediated dihydroxylation of quinoline-annulated porphyrin generates a quinoline-annulated dihydroxychlorin in a regioselective fashion. Its dihydroxypyrroline moiety, located at the opposite of the annulated pyrrole, is susceptible to the same functional group interconversions we previously demonstrated for non-annulated dihydroxychlorins: oxidations to the corresponding dione, lactone, and dialkoxymorpholine derivatives. The quinoline-annulated chlorin and derivatives are all characterized by absorption spectra that are much broadened and between 130 and 220 nm red-shifted compared to their non-annulated analogs. Absorbance maxima in the NIR up to well above 800 nm were recorded. We attribute the bathochromic shift to their extended [Formula: see text]-systems and inferred non-planarity, highlighting that quinoline-annulation is a particularly effective and simple strategy to red-shift the absorption spectra of chlorins and chlorin analogs.

Engineering Lysosome-Targeting BODIPY Nanoparticles for Photoacoustic Imaging and Photodynamic Therapy under Near-Infrared Light

Developing lysosome-targeting organic nanoparticles combined with photoacoustic imaging (PAI) and photodynamic therapy (PDT) functions toward personalized medicine are highly desired yet challenging. Here, for the first time, lysosome-targeting BODIPY nanoparticles were engineered by encapsulating near-infrared (NIR) absorbed BODIPY dye within amphiphilic DSPE-mPEG5000 for high-performing lysosomal PAI and acid-activatable PDT against cancer cells under NIR light.

Panchromatic π-Extended Porphyrins from Conjugation with Quinones

Typical porphyrins are coloured compounds due to their characteristic wavelength-selective visible light absorptions. An exceptional "blackened" Zn^II -porphyrin was recently obtained from fusing the β,β'-positions of the porphyrin core with four quinone units. Here, studies with metal-free and Ni^II -containing analogues are reported. These quinone-fused porphyrins were prepared from the corresponding β,β'-tetrasulfolenoporphyrins via thermally generated porphyrindienes, which were trapped by [4+2] cycloaddition as benzoquinone cycloadducts, which were subsequently oxidised. By using this strategy, metal-free and Ni^II -containing porphyrins with one, two, three or four conjugated naphthoquinone moieties were prepared efficiently. The presence of the π-conjugated naphthoquinone moieties changed the porphyrin chromophores profoundly, giving broadly absorbing "blackened" pigments. The influence of coordinated Ni^II ions, or of the absence of a metal ion in the modified porphyrin core, on their structural and spectroscopic properties was explored. Blackened quinone-conjugated porphyrins might be pigments suitable for solar energy conversion. With their unique peripheral functional groups they are also a set of porphyrins "programmed" for further covalent extension. Thus, they are building blocks for the preparation of supra-porphyrinoid assemblies that might be useful in optoelectronics and in the nanosciences.

Phthalocyanine photosensitizers as contrast agents for in vivo photoacoustic tumor imaging

There is a need for contrast agents for non-invasive diagnostic imaging of tumors. Herein, Multispectral Optoacoustic Tomography (MSOT) was employed to evaluate phthalocyanines commonly used in photodynamic therapy as photoacoustic contrast agents. We studied the photoacoustic activity of three water-soluble phthalocyanine photosensitizers: phthalocyanine tetrasulfonic acid (PcS4), Zn(II) phthalocyanine tetrasulfonic acid (ZnPcS4) and Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS4) in phantom and in tumor-bearing mice to investigate the biodistribution and fate of the phthalocyanines in the biological tissues. PcS4 was observed to grant good contrast between the different reticuloendothelial organs and accumulate in the tumor within an hour of post-administration. ZnPcS4 and AlPcS4 offered little contrast in photoacoustic signals between the organs. PcS4 is a promising photoacoustic contrast agent and can be exploited as a photodiagnostic agent.

Mono- and Bisquinoline-Annulated Porphyrins from Porphyrin β,β'-Dione Oximes

An acid-induced reaction of meso-tetraphenyl-2-hydroxyimino-3-oxoporphyrin leads, with concomitant loss of water, to a formal electrophilic aromatic substitution of the ortho-position of the phenyl group adjacent to the oxime, forming a quinoline moiety. Owing in part to the presence of a π-extended chromophore, the resulting meso-triphenylmonoquinoline-annulated porphyrin (λmax = 750 nm) possesses a much altered optical spectrum from that of the starting oxime (λmax = 667 nm). An oxidative DDQ-induced ring-closure process is also possible, generating the corresponding meso-triphenylmonoquinoline-annulated porphyrin quinoline N-oxide, possessing a slightly shifted and sharpened UV-vis spectrum (λmax = 737 nm). The connectivity of the chromophores was conclusively shown by NMR spectroscopy. Both ketone functionalities in meso-tetraphenyl-2,3-dioxoporphyrin can be converted, via the oxime and using the acid- or oxidant-induced reaction pathways, either in one step or in a stepwise fashion, to bisquinoline-annulated porphyrin (λmax = 775 nm) and its N-oxide (λmax = 779 nm), respectively. This process is complementary to a previously established pathway toward bisquinoline-annulated porphyrins. Their zinc(II), nickel(II), and palladium(II) complexes are also described. Several examples of the quinoline-annulated porphyrins were crystallographically characterized, proving their connectivity and showing their conformations that are extremely distorted from planarity. The work presents a full account on the synthesis, structure, and spectroscopic properties of these classes of NIR-absorbing dyes.

Shining light on the dark side of imaging: excited state absorption enhancement of a bis-styryl BODIPY photoacoustic contrast agent

A first approach toward understanding the targeted design of molecular photoacoustic contrast agents (MPACs) is presented. Optical and photoacoustic Z-scan spectroscopy was used to identify how nonlinear (excited-state) absorption contributes to enhancing the photoacoustic emission of the curcuminBF2 and bis-styryl (MeOPh)2BODIPY dyes relative to Cy3.

Multifunctional photosensitizer-based contrast agents for photoacoustic imaging

Photoacoustic imaging is a novel hybrid imaging modality combining the high spatial resolution of optical imaging with the high penetration depth of ultrasound imaging. Here, for the first time, we evaluate the efficacy of various photosensitizers that are widely used as photodynamic therapeutic (PDT) agents as photoacoustic contrast agents. Photoacoustic imaging of photosensitizers exhibits advantages over fluorescence imaging, which is prone to photobleaching and autofluorescence interference. In this work, we examined the photoacoustic activity of 5 photosensitizers: zinc phthalocyanine, protoporphyrin IX, 2,4-bis [4-(N,N-dibenzylamino)-2,6-dihydroxyphenyl] squaraine, chlorin e6 and methylene blue in phantoms, among which zinc phthalocyanine showed the highest photoacoustic activity. Subsequently, we evaluated its tumor localization efficiency and biodistribution at multiple time points in a murine model using photoacoustic imaging. We observed that the probe localized at the tumor within 10 minutes post injection, reaching peak accumulation around 1 hour and was cleared within 24 hours, thus, demonstrating the potential of photosensitizers as photoacoustic imaging contrast agents in vivo. This means that the known advantages of photosensitizers such as preferential tumor uptake and PDT efficacy can be combined with photoacoustic imaging capabilities to achieve longitudinal monitoring of cancer progression and therapy in vivo.