Photodynamic Molecular Beacons Triggered by MMP-2 and MMP-9: Influence of the Distance Between Photosensitizer and Quencher onto Photophysical Properties and Enzymatic Activation

Enzyme-responsive design combined with photodynamic therapy for cancer treatment

Photodynamic therapy (PDT) is a noninvasive cancer treatment that has garnered significant attention in recent years. However, its application is still hampered by certain limitations, such as the hydrophobicity and low targeting of photosensitizers (PSs) and the hypoxia of the tumor microenvironment. Nevertheless, the fusion of enzyme-responsive drugs with PDT offers novel solutions to overcome these challenges. Utilizing the attributes of enzyme-responsive drugs, PDT can deliver PSs to the target site and selectively release them, thereby enhancing therapeutic outcomes. In this review, we spotlight recent advances in enzyme-responsive materials for cancer treatment and primarily delineate their application in combination with PDT.

Controllable Photodynamic Therapy Implemented by Regulating Singlet Oxygen Efficiency

With singlet oxygen (1O2) as the active agent, photodynamic therapy (PDT) is a promising technique for the treatment of various tumors and cancers. But it is hampered by the poor selectivity of most traditional photosensitizers (PS). In this review, we present a summary of controllable PDT implemented by regulating singlet oxygen efficiency. Herein, various controllable PDT strategies based on different initiating conditions (such as pH, light, H2O2 and so on) have been summarized and introduced. More importantly, the action mechanisms of controllable PDT strategies, such as photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), intramolecular charge transfer (ICT) and some physical/chemical means (e.g. captivity and release), are described as a key point in the article. This review provide a general overview of designing novel PS or strategies for effective and controllable PDT.

Extraction, Identification and Photo-Physical Characterization of Persimmon (Diospyros kaki L.) Carotenoids

Carotenoid pigments were extracted and purified from persimmon fruits using accelerated solvent extraction (ASE). Eleven pigments were isolated and five of them were clearly identified as all-trans-violaxanthine, all-trans-lutein, all-trans-zeaxanthin all-trans-cryptoxanthin and all-trans-β-carotene. Absorption and fluorescence spectra were recorded. To evaluate the potential of ¹O₂ quenching of the purified carotenoids, we used a monocarboxylic porphyrin (P1COOH) as the photosensitizer to produce ¹O₂. The rate constants of singlet oxygen quenching (Kq) were determined by monitoring the near-infrared (1270 nm) luminescence of ¹O₂ produced by photosensitizer excitation. The lifetime of singlet oxygen was measured in the presence of increasing concentrations of carotenoids in hexane. Recorded Kq values show that all-trans-β-cryptoxanthin, all-trans-β-carotene, all-trans-lycopene and all-trans-zeaxanthin quench singlet oxygen in hexane efficiently (associated Kq values of 1.6 × 10⁸, 1.3 × 10⁸, 1.1 × 10⁸ and 1.1 × 10⁸ M^-1·s^-1, respectively). The efficiency of singlet oxygen quenching of β-cryptoxanthin can thus change the consideration that β-carotene and lycopene are the most efficient singlet oxygen quenchers acting as catalysts for deactivation of the harmful ¹O₂.

Peptide-substituted phthalocyanine photosensitizers: design, synthesis, photophysicochemical and photobiological studies

Activatable molecular beacons were synthesized bearing phthalocyanine, peptide sequence and fluorophore groups. The phototoxicity and cytotoxicity of the systems were studied against the cervical cancer cell line named HeLa for evaluation of their suitability for photodynamic therapy.

A dual activatable photosensitizer toward targeted photodynamic therapy

An unsymmetrical bisferrocenyl silicon(IV) phthalocyanine has been prepared in which the disulfide and hydrazone linkers can be cleaved by dithiothreitol and acid, respectively. The separation of the ferrocenyl quenchers and the phthalocyanine core greatly enhances the fluorescence emission, singlet oxygen production, intracellular fluorescence intensity, and in vitro photocytotoxicity. The results have been compared with those for the two symmetrical analogues which contain either the disulfide or hydrazone linker and therefore can only be activated by one of these stimuli. For the dual activatable agent, the greatest enhancement can be attained under a slightly acidic environment (pH = 4.5-6.8) and in the presence of dithiothreitol (in millimolar range), which can roughly mimic the acidic and reducing environment of tumor tissues. This compound can also be activated in tumor-bearing nude mice. It exhibits an increase in fluorescence intensity in the tumor over the first 10 h after intratumoral injection and can effectively inhibit the growth of tumor upon illumination.