Application of Photoactive Compounds in Cancer Theranostics: Review on Recent Trends from Photoactive Chemistry to Artificial Intelligence

According to the World Health Organization (WHO) and the International Agency for Research on Cancer (IARC), the number of cancer cases and deaths worldwide is predicted to nearly double by 2030, reaching 21.7 million cases and 13 million fatalities. The increase in cancer mortality is due to limitations in the diagnosis and treatment options that are currently available. The close relationship between diagnostics and medicine has made it possible for cancer patients to receive precise diagnoses and individualized care. This article discusses newly developed compounds with potential for photodynamic therapy and diagnostic applications, as well as those already in use. In addition, it discusses the use of artificial intelligence in the analysis of diagnostic images obtained using, among other things, theranostic agents.

Photosensitizer-based small molecule theranostic agents for tumor-targeted monitoring and phototherapy

Small molecule theranostic agents for tumor treatment exhibited triadic properties in tumor targeting, imaging, and therapy, which have attracted increasing attention as a potential complement for, or improved to, classical small molecule antitumor drugs. Photosensitizer have dual functions of imaging and phototherapy, and have been widely used in the construction of small molecule theranostic agents over the last decade. In this review, we summarized representative agents that have been studied in the field of small molecule theranostic agents based on photosensitizer in the last decade, and highlighted their characteristics and application in tumor-targeted monitoring and phototherapy. The challenges and future perspectives of photosensitizers in building small molecule theranostic agents for diagnosis and therapy of tumors were also discussed.

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.

Recent progress in photosensitizers for overcoming the challenges of photodynamic therapy: from molecular design to application

Photodynamic therapy (PDT), a therapeutic mode involving light triggering, has been recognized as an attractive oncotherapy treatment. However, nonnegligible challenges remain for its further clinical use, including finite tumor suppression, poor tumor targeting, and limited therapeutic depth. The photosensitizer (PS), being the most important element of PDT, plays a decisive role in PDT treatment. This review summarizes recent progress made in the development of PSs for overcoming the above challenges. This progress has included PSs developed to display enhanced tolerance of the tumor microenvironment, improved tumor-specific selectivity, and feasibility of use in deep tissue. Based on their molecular photophysical properties and design directions, the PSs are classified by parent structures, which are discussed in detail from the molecular design to application. Finally, a brief summary of current strategies for designing PSs and future perspectives are also presented. We expect the information provided in this review to spur the further design of PSs and the clinical development of PDT-mediated cancer treatments.

Functional titanium dioxide nanoparticle conjugated with phthalocyanine and folic acid as a promising photosensitizer for targeted photodynamic therapy in vitro and in vivo

Photodynamic therapy (PDT) is a promising cancer treatment that can be implemented using various agents. The conventional photosensitizer Al (III) phthalocyanine chloride tetrasulfonic acid (Pc) has limitations of selectivity in tumor targeting, low affinity to cancer cells, and low two-photon absorption. This study presents a novel photosensitizer FA-TiO₂-Pc, which has the TiO₂ nanoparticle conjugated with a tumor targeting agent of folic acid (FA), and Pc. FA-TiO₂-Pc possessed high targeted photodynamic therapeutic activity and excellent biocompatibility. This promising photosensitizer showed high therapeutic drug efficiency in vitro at a low concentration dose and short incubation time under one-photon excitation (OPE). In vivo, when treated with a low dose of FA-TiO₂-Pc and low light irradiation, the tumor growth was depressed in mice bearing HeLa xenograft tumors with minimal side effects. In addition, the two-photon absorption of FA-TiO₂-Pc was also enhanced compared to Pc, proving that FA-TiO₂-Pc system has a great potential to be used for the therapy of the folate receptor positive cancer cells in both OPE-PDT and two-photon excitation (TPE)-PDT agents.

Nanoparticles Yield Increased Drug Uptake and Therapeutic Efficacy upon Sequential Near-Infrared Irradiation

Nanoparticles offer great opportunities for precision medicine. However, the use of nanoparticles as smart photosensitizers that target tumor biomarkers and are responsive to the tumor microenvironment has yet to be explored. Herein, prostate cancer (PCa)-selective theranostic gold nanoparticles (AuNPs) for precise cancer imaging and therapy are developed. Silicon phthalocyanine, Pc158, was synthesized and deactivated by conjugating it to AuNPs via a biocleavable linker. In vitro and in vivo, the targeted AuNPs show excellent selectivity for PSMA-positive tumor cells. Triggered release of the therapeutic, Pc158, followed by sequential photodynamic therapy (PDT) results in significant inhibition of tumor growth. Further, we demonstrate that multiple sequential PDT greatly enhances nanoparticle uptake and therapeutic efficacy. PSMA is highly expressed in the neovasculature of most other solid tumors in humans, as well as PCa, making this approach of great practical interest for precision PDT in a wide range of cancers.

Tumour-targeting photosensitisers for one- and two-photon activated photodynamic therapy

Efficient receptor-mediated delivery of a folate-targeted photosensitiser to kill cancer cells following two-photon excitation in the near-infrared is demonstrated.

Molecular photosensitisers for two-photon photodynamic therapy

Two-photon excitation has attracted the attention of biologists, especially after the development of two-photon excited microscopy in the nineties. Since then, new applications have rapidly emerged such as the release of biologically active molecules and photodynamic therapy (PDT) using two-photon excitation. PDT, which requires a light-activated drug (photosensitiser), is a clinically approved and minimally invasive treatment for cancer and for non-malignant diseases. This feature article focuses on the engineering of molecular two-photon photosensitisers for PDT, which should bring important benefits to the treatment, increase the treatment penetration depth with near-infrared light excitation, improve the spatial selectivity and reduce the photodamage to healthy tissues. After an overview of the two-photon absorption phenomenon and the methods to evaluate two-photon induced phototoxicity on cell cultures, the different classes of photosensitisers described in the literature are discussed. The two-photon PDT performed with historical one-photon sensitisers are briefly presented, followed by specifically engineered cyclic tetrapyrrole photosensitisers, purely organic photosensitisers and transition metal complexes. Finally, targeted two-photon photosensitisers and theranostic agents that should enhance the selectivity and efficiency of the treatment are discussed.

Conjugate of biotin with silicon(IV) phthalocyanine for tumor-targeting photodynamic therapy

In order to improve the efficacy of photodynamic therapy (PDT), biotin was axially conjugated with silicon(IV) phthalocyanine (SiPc) skeleton to develop a new tumor-targeting photosensitizer SiPc-biotin. The target compound SiPc-biotin showed much higher binding affinity toward BR-positive (biotin receptor overexpressed) HeLa human cervical carcinoma cells than its precursor SiPc-pip. However, when the biotin receptors of HeLa cells were blocked by free biotin, >50% uptake of SiPc-biotin was suppressed, demonstrating that SiPc-biotin could selectively accumulate in BR-positive cancer cells via the BR-mediated internalization. The confocal fluorescence images further confirmed the target binding ability of SiPc-biotin. As a consequence of specificity of SiPc-biotin toward BR-positive HeLa cells, the photodynamic effect was also largely dependent on the BR expression level of HeLa cells. The photodynamic activities of SiPc-biotin against HeLa cells were dramatically reduced when the biotin receptors were blocked by the free biotin (IC₅₀: 0.18μM vs. 0.46μM). It is concluded that SiPc-biotin can selectively damage BR-positive cancer cells under irradiation. Furthermore, the dark toxicity of SiPc-biotin toward human normal liver cell lines LO2 was much lower than that of its precursor SiPc-pip. The targeting photodynamic activity and low dark toxicity suggest that SiPc-biotin is a promising photosensitizer for tumor-targeting photodynamic therapy.

4-tert-butylphenoxy substituted phthalocyanine with RGD motif as highly selective one-photon and two-photon imaging probe for mitochondria and cancer cell

An unsymmetrical phthalocyanine based one- and two-photon fluorescence imaging probe that substituted with 4-tert-butylphenoxy and RDGyK moieties was developed and characterized by UV-vis and high-resolution MALDI-TOF/MS. The conjugate is non-aggregated in [Formula: see text],[Formula: see text]-dimethylformamide, with relatively weak fluorescence emission ([Formula: see text] 0.023) and high singlet oxygen quantum yield ([Formula: see text] 0.55). Conjugation of the cyclic peptide sequence c(RGDyK) can enhance the cellular uptake towards the DU145 and PC3 cells. While the fluorescence is greatly enhanced in mitochondria, the conjugate is non-cytotoxicity either in dark or upon exposure to red-light with dose up to 12 J.cm[Formula: see text]. The results suggest that this conjugate is a promising multifunctional imaging probe for mitochondria and cancer.

Highly water-soluble and tumor-targeted photosensitizers for photodynamic therapy

Biological uses of photosensitizers in photodynamic therapy (PDT) often suffer from a lack of tumor selectivity; a strategy based on molecule-targeted cancer therapies could provide a promising solution. To synthesize new water-soluble phthalocyanines (Pcs) for bio-conjugation with peptides or antibodies, we developed a method to synthesize asymmetrically substituted Pcs with both high water solubility and one monoamino group for conjugation with biological agents for tumor homing, using folic acid as the ligand model to direct the modified Pcs into target cells. Here, we report studies on the syntheses and characterization of these Pcs. In vitro and in vivo assays prove that the high solubility characteristic can greatly increase the tumor targeting capability of Pcs by reducing non-specific uptake. This newly designed photosensitizer accumulated almost completely in tumor regions, with a negligible signal found in other tissues in the xenograft tumor model. These initial data provide strong evidence of the high specificity tumor targeting of Pcs with folate and tri-glycerol substitutions. Theoretically, the synthesized Pcs could be conveniently conjugated to many other ligands, endorsing the broad applicability of this method for tumor-targeted PDT.

Phthalocyanine-cRGD conjugate: synthesis, photophysical properties and in vitro biological activity for targeting photodynamic therapy

Phthalocyanine-RGD conjugate was synthesized and examined for its two-photon absorption cross section (TPACS), cellular uptake, and photocytotoxicity.

Non-covalent complexes of folic acid and oleic acid conjugated polyethylenimine: An efficient vehicle for antisense oligonucleotide delivery

Polyethylenimine (PEI) was conjugated to oleic acid (PEI-OA) and evaluated as a delivery agent for LOR-2501, an antisense oligonucleotide against ribonucleotide reductase R1 subunit. PEI-OA/LOR-2501 complexes were further coated with folic acid (FA/PEI-OA/LOR-2501) and evaluated in tumor cells. The level of cellular uptake of FA/PEI-OA/LOR-2501 was more than double that of PEI/LOR-2501 complexes, and was not affected by the expression level of folate receptor (FR) on the cell surface. Efficient delivery was seen in several cell lines. Furthermore, pathway specific cellular internalization inhibitors and markers were used to reveal the principal mechanism of cellular uptake. FA/PEI-OA/LOR-2501 significantly induced the downregulation of R1 mRNA and R1 protein. This novel formulation of FA/PEI-OA provides a reliable and highly efficient method for delivery of oligonucleotide and warrants further investigation.

Conducting polymer nanoparticles for targeted cancer therapy

Functionalized conducting polymer nanoparticles allow for targeted delivery, tracking by fluorescence bioimaging, and therapeutics through formation of reactive oxygen species.

The synthesis of an octasubstituted monohydroxylated phthalocyanine designed to investigate the effect of the presence of active moieties

Filling a lack: monofunctionalized octasubstitution, the missing substitution pattern of phthalocyanines.

Smart dual-functional warhead for folate receptor-specific activatable imaging and photodynamic therapy

Folic acid as a bi-functional warhead to develop smart dual-targeted theranostic agents.