Tetranuclear Gadolinium(III) Porphyrin Complex as a Theranostic Agent for Multimodal Imaging and Photodynamic Therapy

The Copper Reduction Potential Determines the Reductive Cytotoxicity: Relevance to the Design of Metal-Organic Antitumor Drugs

Copper-organic compounds have gained momentum as potent antitumor drug candidates largely due to their ability to generate an oxidative burst upon the transition of Cu2+ to Cu1+ triggered by the exogenous-reducing agents. We have reported the differential potencies of a series of Cu(II)-organic complexes that produce reactive oxygen species (ROS) and cell death after incubation with N-acetylcysteine (NAC). To get insight into the structural prerequisites for optimization of the organic ligands, we herein investigated the electrochemical properties and the cytotoxicity of Cu(II) complexes with pyridylmethylenethiohydantoins, pyridylbenzothiazole, pyridylbenzimidazole, thiosemicarbazones and porphyrins. We demonstrate that the ability of the complexes to kill cells in combination with NAC is determined by the potential of the Cu+2 → Cu+1 redox transition rather than by the spatial structure of the organic ligand. For cell sensitization to the copper-organic complex, the electrochemical potential of the metal reduction should be lower than the oxidation potential of the reducing agent. Generally, the structural optimization of copper-organic complexes for combinations with the reducing agents should include uncharged organic ligands that carry hard electronegative inorganic moieties.

Three in One: In Vitro and In Vivo Evaluation of Anticancer Activity of a Theranostic Agent that Combines Magnetic Resonance Imaging, Optical Bioimaging, and Photodynamic Therapy Capabilities

Cancer treatment is a crucial area of research and development, as current chemotherapeutic treatments can have severe side effects or poor outcomes. In the constant search for new strategies that are localized and minimally invasive and produce minimal side effects, photodynamic therapy (PDT) is an exciting therapeutic modality that has been gaining attention. The use of theranostics, which combine diagnostic and therapeutic capabilities, can further improve treatment monitoring through image guidance. This study explores the potential of a theranostic agent consisting of four Gd(III) DTTA complexes (DTTA: diethylenetriamine-N,N,N″,N″-tetraacetate) grafted to a meso-tetraphenylporphyrin core for PDT, fluorescence, and magnetic resonance imaging (MRI). The agent was first tested in vitro on both nonmalignant TIB-75 and MRC-5 and tumoral CT26 and HT-29 cell lines and subsequently evaluated in vivo in a preclinical colorectal tumor model. Advanced MRI and optical imaging techniques were employed with engineered quantitative in vivo molecular imaging based on dynamic acquisition sequences to track the biodistribution of agents in the body. With 3D quantitative volume computed by MRI and tumoral cell function assessed by bioluminescence imaging, we could demonstrate a significant impact of the molecular agent on tumor growth following light application. Further exhaustive histological analysis confirmed these promising results, making this theranostic agent a potential drug candidate for cancer.

Discovery and Feasibility Study of Medical Fluorophore 33 as a Novel Theranostic Agent

Fluorescent dyes have garnered significant attention as theranostic platforms owing to their inherent characteristics. In this study, we present the discovery of Medical Fluorophore 33 (MF33), a novel and potent theranostic agent with a phenaleno-isoquinolinium salt structure that can serve as a cancer therapeutic strategy. The synthesis of MF33 is readily achievable through a simple Rh(III)-catalyzed reaction. Moreover, MF33 displayed strong fluorescence signals, excellent microsomal stability, and high biocompatibility in vivo. It induces significant apoptosis in cancer cells via the p53/p21/caspase-3 signaling pathway, leading to selective cytotoxicity in various cancer cells. In vivo fluorescence imaging with MF33 enabled the visualization of sentinel lymph nodes in living mice. Notably, repeated intraperitoneal administration of MF33 resulted in antitumor activity in mice with colorectal cancer. Collectively, our findings suggest that phenaleno-isoquinolinium salt-based MF33 is a viable theranostic agent for biomedical imaging and cancer treatment.

Water-Soluble Gd(III)-Porphyrin Complexes Capable of Both Photosensitization and Relaxation Enhancement

With the aim of developing more stable Gd(III)-porphyrin complexes, two types of ligands 1 and 2 with carboxylic acid anchors were synthesized. Due to the N-substituted pyridyl cation attached to the porphyrin core, these porphyrin ligands were highly water-soluble and formed the corresponding Gd(III) chelates, Gd-1 and Gd-2. Gd-1 was sufficiently stable in neutral buffer, presumably due to the preferred conformation of the carboxylate-terminated anchors connected to nitrogen in the meta position of the pyridyl group helping to stabilize Gd(III) complexation by the porphyrin center. ¹H NMRD (nuclear magnetic relaxation dispersion) measurements on Gd-1 revealed high longitudinal water proton relaxivity (r₁ = 21.2 mM^-1 s^-1 at 60 MHz and 25 °C), which originates from slow rotational motion resulting from aggregation in aqueous solution. Under visible light irradiation, Gd-1 showed extensive photoinduced DNA cleavage in line with efficient photoinduced singlet oxygen generation. Cell-based assays revealed no significant dark cytotoxicity of Gd-1, while it showed sufficient photocytotoxicity on cancer cell lines under visible light irradiation. These results indicate the potential of this Gd(III)-porphyrin complex (Gd-1) as a core for the development of bifunctional systems acting as an efficient photodynamic therapy photosensitizer (PDT-PS) with magnetic resonance imaging (MRI) detection capabilities.

Luminescent Lanthanide Complexes for Effective Oxygen-Sensing and Singlet Oxygen Generation

Oxygen quantification using luminescence has attracted considerable attention in various fields, including environmental monitoring and clinical analysis. Among the reported luminophores, trivalent lanthanide complexes have displayed characteristic narrow emission bands with high brightness. This bright emission is based on photo-sensitized energy transfer via organic triplet states. The organic triplet states in lanthanide complexes effectively react with the triplet oxygen, enabling oxygen quantification by lanthanide luminescence. Some Tb^III and Eu^III complexes with slow deactivation processes have also formed the excited state equilibrium, thus resulting in the emission-lifetime based oxygen sensing property. The combination of Tb^III /Eu^III emission, Eu^III /Sm^III emission, Eu^III /ligand phosphorescence, and ligand fluorescence/ligand phosphorescence provide the ratiometric oxygen-sensing properties. Moreover, the reaction generates singlet oxygen species which exhibit numerous applications in the photo-medical field. The ligands with large π-conjugated aromatic systems, such as porphyrin, phthalocyanine, and polyaromatic compounds, induces highly efficient oxygen generation. The combination of effective luminescence with singlet-oxygen generation by the lanthanide complexes render them suitable for photo-driven theranostics. This review summarizes the research progress of lanthanide complexes with efficient oxygen-sensing and singlet-oxygen generation properties.

Platinum(II)-Metallaclip-Based Theranostics for Cell Imaging and Synergetic Chemotherapy-Photodynamic Therapy

Supramolecular coordination complexes formed by coordination-induced assembly not only avoid the loss of activity of precursors but also provide an efficient way for controlled release, which can be further used in various fields of biology such as drug delivery, cell imaging, and tumor treatment. In this work, a Pt^II metallaclip (4) was prepared from 4-[4-(1,2,2-triphenylvinyl)phenyl]pyridine (1), 5,10,15-triphenyl-20-(pyridin-4-yl)porphyrin (2), 90^o Pt, and glycol-chain-modified isophthalic acid (3) in an acetone/water mixture through the "coordination-driven self-assembly" method. ³¹P and ¹H NMR spectroscopy and high-resolution mass spectrometry were used to characterize the obtained metallaclip 4. 4 can self-assemble into fluorescent nanostructures in aqueous solution because of the tetraphenylethylene unit and its amphiphilic nature. Importantly, the fluorescent nanoparticles not only can be employed for cell imaging but also can generate singlet oxygen (¹O₂) under 660 nm laser irradiation and the release of Pt drug in the tumor issue for cancer therapy. The work may provide a new way for scientists to construct functional biomaterials with multiple applications via molecular self-assembly.

Lanthanide porphyrinoids as molecular theranostics

In recent years, lanthanide (Ln) porphyrinoids have received increasing attention as theranostics. Broadly speaking, the term 'theranostics' refers to agents designed to allow both disease diagnosis and therapeutic intervention. This Review summarises the history and the 'state-of-the-art' development of Ln porphyrinoids as theranostic agents. The emphasis is on the progress made within the past decade. Applications of Ln porphyrinoids in near-infrared (NIR, 650-1700 nm) fluorescence imaging (FL), magnetic resonance imaging (MRI), radiotherapy, and chemotherapy will be discussed. The use of Ln porphyrinoids as photo-activated agents ('phototheranostics') will also be highlighted in the context of three promising strategies for regulation of porphyrinic triplet energy dissipation pathways, namely: regioisomeric effects, metal regulation, and the use of expanded porphyrinoids. The goal of this Review is to showcase some of the ongoing efforts being made to optimise Ln porphyrinoids as theranostics and as phototheranostics, in order to provide a platform for understanding likely future developments in the area, including those associated with structure-based innovations, functional improvements, and emerging biological activation strategies.

Smart nanocomposite assemblies for multimodal cancer theranostics

Despite great strides in anticancer research, performance statistics of current treatment modalities remain dismal, highlighting the need for safe, efficacious strategies for tumour mitigation. Non-invasive fusion technology platforms combining photodynamic, photothermal and hyperthermia therapies have emerged as alternate strategies with potential to meet many of the unmet clinical demands in the domain of cancer. These therapies make use of metallic and magnetic nanoparticles with light absorbing properties, which are manipulated to generate either reactive cytotoxic oxygen species or heat for tumour ablation. Combination therapies integrating light, heat and magnetism-mediated nanoplatforms with the conventional approaches of chemotherapy, radiotherapy and surgery are emerging as precision medicine for targeted interventions against cancer. This article aims to compile recent developments of advanced nanocomposite assemblies that integrate multimodal therapeutics for cancer treatment. Amalgamation of various effective, non-invasive technological platforms such as photodynamic therapy (PDT), photothermal therapy (PTT), magnetic hyperthermia (MHT), and chemodynamic therapy (CDT) have tremendous potential in presenting safe and efficacious solutions to the formidable challenges in cancer therapeutics.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Application of phototherapeutic-based nanoparticles in colorectal cancer

Colorectal cancer (CRC) is the third most commonly diagnosed malignancy and the second leading cause of cancer death, which accounts for approximately 10% of all new cancer cases worldwide. Surgery is the main method for treatment of early-stage CRC. However, it is not effective for most metastatic tumors, and new treatment and diagnosis strategies need to be developed. Photosensitizers (PSs) play an important role in the treatment of CRC. Phototherapy also has a broad prospect in the treatment of CRC because of its low invasiveness and low toxicity. However, most PSs are associated with limitations including poor solubility, poor selectivity and high toxicity. The application of nanomaterials in PSs has added many advantages, including increased solubility, bioavailability, targeting, stability and low toxicity. In this review, based on phototherapy, we discuss the characteristics and development progress of PSs, the targeting of PSs at organ, cell and molecular levels, and the current methods of optimizing PSs, especially the application of nanoparticles as carriers in CRC. We introduce the photosensitizer (PS) targeting process in photodynamic therapy (PDT), the damage mechanism of PDT, and the application of classic PS in CRC. The action process and damage mechanism of photothermal therapy (PTT) and the types of ablation agents. In addition, we present the imaging examination and the application of PDT / PTT in tumor, including (fluorescence imaging, photoacoustic imaging, nuclear magnetic resonance imaging, nuclear imaging) to provide the basis for the early diagnosis of CRC. Notably, single phototherapy has several limitations in vivo, especially for deep tumors. Here, we discuss the advantages of the combination therapy of PDT and PTT compared with the single therapy. At the same time, this review summarizes the clinical application of PS in CRC. Although a variety of nanomaterials are in the research and development stage, few of them are actually on the market, they will show great advantages in the treatment of CRC in the near future.

Supramolecular cancer nanotheranostics

Among the many challenges in medicine, the treatment and cure of cancer remains an outstanding goal given the complexity and diversity of the disease. Nanotheranostics, the integration of therapy and diagnosis in nanoformulations, is the next generation of personalized medicine to meet the challenges in precise cancer diagnosis, rational management and effective therapy, aiming to significantly increase the survival rate and improve the life quality of cancer patients. Different from most conventional platforms with unsatisfactory theranostic capabilities, supramolecular cancer nanotheranostics have unparalleled advantages in early-stage diagnosis and personal therapy, showing promising potential in clinical translations and applications. In this review, we summarize the progress of supramolecular cancer nanotheranostics and provide guidance for designing new targeted supramolecular theranostic agents. Based on extensive state-of-the-art research, our review will provide the existing and new researchers a foundation from which to advance supramolecular cancer nanotheranostics and promote translationally clinical applications.

Gadolinium theranostics for the diagnosis and treatment of cancer

Combining therapeutic and diagnostic tools into a single ‘theranostic’ platform lies at the forefront of cancer research. Some of the most promising theranostics exploit the unique nuclear and electronic properties of the lanthanoid metal gadolinium.

Conjugated Photosensitizers for Imaging and PDT in Cancer Research

Early cancer detection and perfect understanding of the disease are imperative toward efficient treatments. It is straightforward that, for choosing a specific cancer treatment methodology, diagnostic agents undertake a critical role. Imaging is an extremely intriguing tool since it assumes a follow up to treatments to survey the accomplishment of the treatment and to recognize any conceivable repeating injuries. It also permits analysis of the disease, as well as to pursue treatment and monitor the possible changes that happen on the tumor. Likewise, it allows screening the adequacy of treatment and visualizing the state of the tumor. Additionally, when the treatment is finished, observing the patient is imperative to evaluate the treatment methodology and adjust the treatment if necessary. The goal of this review is to present an overview of conjugated photosensitizers for imaging and therapy.

Synthesis and In Vitro Studies of a Gd(DOTA)-Porphyrin Conjugate for Combined MRI and Photodynamic Treatment

With the aim of developing new molecular theranostic agents, a π-extended Zn(II) porphyrin as photosensitizer for photodynamic therapy (PDT) linked to two GdDOTA-type complexes for magnetic resonance imaging (MRI) detection was synthesized. The relaxivity studies revealed a much higher relaxivity value per Gd ion for this medium sized molecule (19.32 mM^-1 s^-1 at 20 MHz and 298 K) compared to clinical contrast agents-a value which strongly increases in the presence of bovine serum albumin, reaching 25.22 mM^-1 s^-1. Moreover, the photophysical studies showed the strong ability of the molecule to absorb light in the deep red (670 nm, ε ≈ 60000 M^-1 cm^-1) and in the near-infrared following two-photon excitation (920 nm, σ₂ ≈ 650 GM). The conjugate is also able to generate singlet oxygen, with a quantum yield of 0.58 in DMSO. Promising results were obtained in cellular studies, demonstrating that the conjugate is internalized in HeLa cells at micromolar concentration and leads to 70% of cell death following 30 min irradiation at 660 nm. These results confirm the potential of the designed molecule as an imaging and therapeutic agent.

Functional gadolinium-based nanoscale systems for cancer theranostics

Cancer theranostics is a new strategy for combating cancer that integrates cancer imaging and treatment through theranostic agents to provide an efficient and safe way to improve cancer prognosis. Design and synthesis of these cancer theranostic agents are crucial since these agents are required to be biocompatible, tumor-specific, imaging distinguishable and therapeutically efficacious. In this regard, several types of gadolinium (Gd)-based nanomaterials have been introduced to combine different therapeutic agents with Gd to enhance the efficacy of therapeutic agents. At the same time, the entire treatment procedure could be monitored via imaging tools due to incorporation of Gd ions, Gd chelates and Gd/other imaging probes in the theranostic agents. This review aims to overview recent advances in the Gd-based nanomaterials for cancer theranostics and perspectives for Gd nanomaterial-based cancer theranostics are provided.

Self-Assembly of Porphyrin-Containing Metalla-Assemblies and Cancer Photodynamic Therapy

In this report, we describe the synthesis of two porphyrin-containing Pt(II) supramolecular assemblies via coordination-driven self-assembly. X-ray crystallographic analysis on one assembly reveals that the metalla-assembly formation imposes large interchromophore distances, leading to a higher 1O2 generation efficiency, relative to the corresponding small molecular precursors. The metalla-assemblies were examined as photosensitizers for photodynamic therapy as the potential reduction of the unfavorable self-aggregation phenomenon. In vivo and in vitro investigations demonstrate that the metalla-assemblies exhibit enhanced anticancer activity with minimal dose requirement and side effects comparable to the small molecule precursors. Thus, our work demonstrates that self-assembly provides a promising methodology for enhancing the therapeutic effectiveness of anticancer agents.

Novel water-soluble Cu(ii) complexes based on acylhydrazone porphyrin ligands for DNA binding and in vitro anticancer activity as potential therapeutic targeting candidates

Three novel water-soluble Cu(ii) complexes featuring miscellaneous acylhydrazone tricationic porphyrin ligands (named Cu-Por1, Cu-Por2 and Cu-Por3) were successfully prepared and isolated.

Unsymmetrical nonplanar 'push-pull' β-octasubstituted porphyrins: facile synthesis, structural, photophysical and electrochemical redox properties

Mixed substitution at the β-position of porphyrins influences their photophysical and electrochemical redox properties. Two new series of asymmetrically mixed β-octasubstituted porphyrins viz. MTPP(Ph)2Br5X (X = NO2 or Br and M = 2H, Co(ii), Ni(ii), Cu(ii), and Zn(ii)) have been synthesized and characterized by various spectroscopic techniques. The single crystal X-ray structure of H2TPP(NO2)(Ph)2Br5 showed a nonplanar saddle shape conformation of the macrocyclic core. Furthermore, the fully optimized geometries confirmed the saddle shape conformation of H2TPP(Ph)2Br5X (X = NO2 or Br). Electronic spectra revealed a significant bathochromic shift by appending both electron donor and acceptor substituents at the β-position of the meso-tetraphenylporphyrin skeleton, which reflects the following order H2TPP < H2TPP(NO2) < H2TPP(NO2)(Ph)2 < H2TPP(Ph)2Br6 < H2TPP(NO2)(Ph)2Br5. H2TPP(Ph)2Br5X (X = NO2 or Br) exhibited a significant bathochromic shift (Δλmax = 53-61 nm) in the Soret band and (Δλmax = 90-95 nm) in the longest wavelength Qx(0,0) band as compared to H2TPP. Nonplanar conformations and electron withdrawing β-substituents induce higher protonation and deprotonation constants for H2TPP(NO2)(Ph)2Br5 and H2TPP(Ph)2Br6 as compared to precursor porphyrins viz. H2TPP, H2TPP(NO2) and H2TPP(NO2)(Ph)2. The electronic spectral properties and redox potentials of MTPP(Ph)2Br5X (X = NO2 or Br and M = 2H, Co, Ni, Cu and Zn) are affected by β-substituents at the periphery of the porphyrin core. Redox tunability was achieved by appending push-pull substituents at the β-position of the MTPP (M = 2H, CoII, NiII, CuII, and ZnII) skeleton of the macrocycle. CuTPP(Ph)2Br6 and CuTPP(NO2)(Ph)2Br5 exhibited a dramatically reduced HOMO-LUMO gap with a difference of 0.55 V and 0.62 V, respectively as compared to CuTPP due to the push-pull effect of β-substituents and nonplanarity of the porphyrin core.

Photosensitizers for Photodynamic Therapy

As an emerging clinical modality for cancer treatment, photodynamic therapy (PDT) takes advantage of the cytotoxic activity of reactive oxygen species (ROS) that are generated by light irradiating photosensitizers (PSs) in the presence of oxygen (O₂ ). However, further advancements including tumor selectivity and ROS generation efficiency are still required. Substantial efforts are devoted to design and synthesize smart PSs with optimized properties for achieving a desirable therapeutic efficacy. This review summarizes the recent progress in developing intelligent PSs for efficient PDT, ranging from single molecules to delicate nanomaterials. The strategies to improve ROS generation through optimizing photoinduced electron transfer and energy transfer processes of PSs are highlighted. Moreover, the approaches that combine PDT with other therapeutics (e.g., chemotherapy, photothermal therapy, and radiotherapy) and the targeted delivery in cancer cells or tumor tissue are introduced. The main challenges for the clinical application of PSs are also discussed.

ZnII Complexes for Bioimaging and Correlated Applications

Zinc is a biocompatible element that exists as the second most abundant transition metal ion and an indispensable trace element in the human body. Compared to traditional metal-organic complexes systems, d¹⁰ metal Zn^II complexes not only exhibit a large Stokes shift and good photon stability but also possess strong emission and low cytotoxicity with a relatively small molecular weight. The use of Zn^II complexes has emerged in the last decade as a versatile and convenient tool for numerous biological applications, including bioimaging, molecular and protein recognition, as well as photodynamic therapy. Herein, we review recent developments involving Zn^II metal complexes applied as specific subcellular compartment imaging probes and their correlated utilizations.

Molecular Theranostic Agents for Photodynamic Therapy (PDT) and Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is a powerful non-invasive diagnostic tool that can provide important insights for medical treatment monitoring and optimization. Photodynamic therapy (PDT), a minimally invasive treatment for various types of tumors, is drawing increasing interest thanks to its temporal and spatial selectivity. The combination of MRI and PDT offers real-time monitoring of treatment and can give significant information for drug-uptake and light-delivery parameters optimization. In this review we will give an overview of molecular theranostic agents that have been designed for their potential application in MRI and PDT.

Surfactant-Stripped Pheophytin Micelles for Multimodal Tumor Imaging and Photodynamic Therapy

Porphyrin-based nanomaterials can inherently integrate multiple contrast imaging functionalities with phototherapeutic capabilities. We dispersed pheophytin (Pheo) into Pluronic F127 and carried out low-temperature surfactant-stripping to remove the bulk surfactant. Surfactant-stripped Pheo (ss-Pheo) micelles exhibited a similar size, but higher near-infrared fluorescence, compared to two other nanomaterials also with high porphyrin density (surfactant-stripped chlorophyll micelles and porphysomes). Singlet oxygen generation, which was higher for ss-Pheo, enabled photodynamic therapy (PDT). ss-Pheo provided contrast for photoacoustic and fluorescence imaging, and following seamless labeling with ⁶⁴Cu, was used for positron emission tomography. ss-Pheo had a long blood circulation and favorable accumulation in an orthotopic murine mammary tumor model. Trimodal tumor imaging was demonstrated, and PDT resulted in delayed tumor growth.

Emerging Applications of Porphyrins and Metalloporphyrins in Biomedicine and Diagnostic Magnetic Resonance Imaging

In recent years, scientific advancements have constantly increased at a significant rate in the field of biomedical science. Keeping this in view, the application of porphyrins and metalloporphyrins in the field of biomedical science is gaining substantial importance. Porphyrins are the most widely studied tetrapyrrole-based compounds because of their important roles in vital biological processes. The cavity of porphyrins containing four pyrrolic nitrogens is well suited for the binding majority of metal ions to form metalloporphyrins. Porphyrins and metalloporphyrins possess peculiar photochemical, photophysical, and photoredox properties which are tunable through structural modifications. Their beneficial photophysical properties, such as the long wavelength of emission and absorption, high singlet oxygen quantum yield, and low in vivo toxicity, have drawn scientists' interest to discover new dimensions in the biomedical field. Applications of porphyrins and metalloporphyrins have been pursued in the perspective of contrast agents for magnetic resonance imaging (MRI), photodynamic therapy (PDT) of cancer, bio-imaging, and other biomedical applications. This review discusses photophysics and the photochemistry of porphyrins and their metal complexes. Secondly, it explains the current developments and mode of action for contrast agents for MRI. Moreover, the application of porphyrin and metalloporphyrin-based molecules as a photosensitizer in PDT of cancer, the mechanism of the generation of reactive oxygen species (ROS), factors that determine the efficiency of PDT, and the developments to improve this technology are delineated. The last part explores the most recent research and developments on metalloporphyrin-based materials in bio-imaging, drug delivery, and the determination of ferrochelatase in bone marrow indicating their prospective clinical applications.

Peripherally Metalated Porphyrins with Applications in Catalysis, Molecular Electronics and Biomedicine

Porphyrins are conjugated, stable chromophores with a central core that binds a variety of metal ions and an easily functionalized peripheral framework. By combining the catalytic, electronic or cytotoxic properties of selected transition metal complexes with the binding and electronic properties of porphyrins, enhanced characteristics of the ensemble are generated. This review article focuses on porphyrins bearing one or more peripheral transition metal complexes and discusses their potential applications in catalysis or biomedicine. Modulation of the electronic properties and intramolecular communication through coordination bond linkages in bis-porphyrin scaffolds is also presented.

Assessing Photosensitizer Targeting Using Meso-Tetra(Carboxyphenyl) Porphyrin

Mesotetra(4-carboxyphenyl)porphyrin (mTCPP) is a commercially available small molecule fluorophore and photosensitizer with four free carboxylic acid groups. mTCPP can readily be conjugated with amines for facile attachment of functional groups. In this work, we synthesized and assessed tetravalent, lysine-conjugated mTCPP, for its potential applications in targeted imaging and photodynamic therapy. Fmoc-protected d-lysine or l-lysine was conjugated to mTCPP via amide coupling with the epsilon amine group of lysine, followed by Fmoc deprotection. The resulting compounds did not dissolve well in aqueous solvent, but could be solubilized with the assistance of surfactants, including cholic acid. The l-amino acid transporter (LAT1) can uptake diverse neutral l-amino acids. In vitro studies with U87 cells revealed a non-specific uptake of the hydrophobic Fmoc-protected lysine-conjugated mTCPP precursors, but not d- or l-lysine mTCPP. Likewise, only the Fmoc-protected compounds induced substantial phototoxicty in cells following incubation and irradiation with blue light. These experimental results do not provide evidence to suggest that lysine-mTCPP is able to specifically target cancer cells. However, they do highlight mTCPP as a convenient and accessible framework for assessing molecular targeting of photosensitizers.

DNA binding and in vitro anticarcinogenic activity of a series of newfashioned Cu(II)-complexes based on tricationic metalloporphyrin salicyloylhydrazone ligands

Four novel water-soluble Cu(II) derivatives based on the meso-10, 15, 20-Tris (N-methyl-X-pyridyl)-5-(4'-salicyloylhydrazone) metalloporphyrin ligands (X=4, M=Zn(1) Co(2); X=2, M=Zn(3), Co(4)), have been prepared and isolated. Various physicochemical techniques indicate that complex 2 interacts with calf thymus DNA stronger than the others through partial intercalation, suggesting that Co(II) has no axial ligands at porphyrin core plays a crucial role, interestingly, 2 exhibits higher DNA binding affinity compared to 4, which could be ascribed to the influences of peripheral electronic effect of porphyrin ring. Cytotoxicity studies manifest all conjugates possess superior cytotoxicity towards non-small cell lung cancer (A549) and liver hepatocellular carcinoma (HepG2) but weak toxicity for human normal breast cells (Hs 578Bst) boiled down to the tumor selectivity of porphyrin. In addition, the IC₅₀ value of 1 is lower than its analogues against HepG2 cells when cultivated 72h, thus the effects of representative complex 1 on cell morphological and cell cycle have been tailed.

In vivo multimodal tumor imaging and photodynamic therapy with novel theranostic agents based on the porphyrazine framework-chelated gadolinium (III) cation

BACKGROUND

A promising strategy for cancer diagnosis and therapy is the development of an agent for multimodal imaging and treatment. In the present paper we report on two novel multifunctional agents prepared on the porphyrazine pigment platform using a gadolinium (III) cation chelated by red-fluorescent tetrapyrrole macrocycles (GdPz1 and GdPz2).

METHODS

Spectral and magnetic properties of the compounds were analyzed. Monitoring of GdPz1 and GdPz2 accumulation in the murine colon carcinoma CT26 was performed in vivo using fluorescence imaging and MRI. The photobleaching of GdPz1 or GdPz2 and tumor growth rate after photodynamic therapy (PDT) were assessed.

RESULTS

GdPz1 and GdPz2 demonstrated the selective accumulation in tumor that was indicated by higher fluorescence intensity in the tumor area in comparison with the normal tissues. The results of MRI in vivo showed that GdPz1 or GdPz2 provided significant contrast enhancement of the tumor in T1 MR images. PDT with GdPz2 resulted in ~20% decrease in fluorescence intensity of the compound and the inhibition of tumor growth.

CONCLUSIONS

We assessed the efficiency of two innovative Gd(III) cation-porphyrazine chelates as bimodal MR and fluorescent probes and photosensitizers for PDT and showed their potentials for tumor diagnostics and treatment.

GENERAL SIGNIFICANCE

Water-soluble structures simple in preparation and administration into the body represent special interest for theranostics of tumors. Novel porphyrazine macrocycles chelating a central gadolinium cation demonstrated a good prospect as effective multimodal agents, representing a new approach to MRI and fluorescence imaging guided PDT.

Modifications of Porphyrins and Hydroporphyrins for Their Solubilization in Aqueous Media

The increasing popularity of porphyrins and hydroporphyrins for use in a variety of biomedical (photodynamic therapy, fluorescence tagging and imaging, photoacoustic imaging) and technical (chemosensing, catalysis, light harvesting) applications is also associated with the growing number of methodologies that enable their solubilization in aqueous media. Natively, the vast majority of synthetic porphyrinic compounds are not water-soluble. Moreover, any water-solubility imposes several restrictions on the synthetic chemist on when to install solubilizing groups in the synthetic sequence, and how to isolate and purify these compounds. This review summarizes the chemical modifications to render synthetic porphyrins water-soluble, with a focus on the work disclosed since 2000. Where available, practical data such as solubility, indicators for the degree of aggregation, and special notes for the practitioner are listed. We hope that this review will guide synthetic chemists through the many strategies known to make porphyrins and hydroporphyrins water soluble.

Facile Conversion of Ni(II) Cyclopropylchlorins into Novel β-Substituted Porphyrins through Acid-Catalyzed Ring-Opening Reaction

The conversion of cyclopropylchlorins into porphyrins represents a key step in the synthetic manipulation of macrocycles with tunable physical and chemical properties. Herein, we report a facile method for the synthesis of novel β-substituted porphyrins from cyclopropylchlorins. A series of Ni(II) cyclopropylchlorins was converted into the corresponding Ni(II) and free base porphyrins using TFA and H₂SO₄ under mild reaction conditions in good yields (75-86%). The new chlorins and porphyrins were characterized by various spectroscopic techniques and the single-crystal X-ray diffraction method. The reaction proceeds very fast (<5 min.) with complete conversion of chlorin into porphyrin with distinct color change. Facile conversion, shorter reaction time scale, and good yield (75-86%) without any side products are the significant features of this new protocol. These porphyrinoids exhibited red-shifted electronic spectral features with varying degrees nonplanar conformation, tunable redox properties, and porphyrin core basicity.

MRI-guided tumor chemo-photodynamic therapy with Gd/Pt bifunctionalized porphyrin

Gd/Pt bifunctionalized porphyrin derivative was synthesized for MRI-guided highly synergetic chemo-photodynamic therapy of cancer.