DNA-Triggered Enhancement of Singlet Oxygen Production by Pyridinium Alkynylanthracenes

There is an ongoing interest in ¹ O₂ sensitizers, whose activity is selectively controlled by their interaction with DNA. To this end, we synthesized three isomeric pyridinium alkynylanthracenes 2 o-p and a water-soluble trapping reagent for ¹ O₂ . In water and in the absence of DNA, these dyes show a poor efficiency to sensitize the photooxygenation of the trapping reagent as they decompose due to electron transfer processes. In contrast, in the presence of DNA ¹ O₂ is generated from the excited DNA-bound ligand. The interactions of 2 o-p with DNA were investigated by thermal DNA melting studies, UV/vis and fluorescence spectroscopy, and linear and circular dichroism spectroscopy. Our studies revealed an intercalative binding with an orientation of the long pyridyl-alkynyl axis parallel to the main axis of the DNA base pairs. In the presence of poly(dA : dT), all three isomers show an enhanced formation of singlet oxygen, as indicated by the reaction of the latter with the trapping reagent. With green light irradiation of isomer 2 o in poly(dA : dT), the conversion rate of the trapping reagent is enhanced by a factor >10. The formation of ¹ O₂ was confirmed by control experiments under anaerobic conditions, in deuterated solvents, or by addition of ¹ O₂ quenchers. When bound to poly(dG : dC), the opposite effect was observed only for isomers 2 o and 2 m, namely the trapping reagent reacted significantly slower. Overall, we showed that pyridinium alkynylanthracenes are very useful intercalators, that exhibit an enhanced photochemical ¹ O₂ generation in the DNA-bound state.

Metformin-Templated Nanoporous ZnO and Covalent Organic Framework Heterojunction Photoanode for Photoelectrochemical Water Oxidation

Photoelectrochemical water-splitting offers unique opportunity in the utilization of abundant solar light energy and water resources to produce hydrogen (renewable energy) and oxygen (clean environment) in the presence of a semiconductor photoanode. Zinc oxide (ZnO), a wide bandgap semiconductor is found to crystallize predominantly in the hexagonal wurtzite phase. Herein, we first report a new crystalline triclinic phase of ZnO by using N-rich antidiabetic drug metformin as a template via hydrothermal synthesis with self-assembled nanorod-like particle morphology. We have fabricated a heterojunction nanocomposite charge carrier photoanode by coupling this porous ZnO with a covalent organic framework, which displayed highly enhanced photocurrent density of 0.62 mA/cm² at 0.2 V vs. RHE in photoelectrochemical water oxidation and excellent photon-to-current conversion efficiency at near-neutral pH vis-à-vis bulk ZnO. This enhancement of the photocurrent for the porous ZnO/COF nanocomposite material over the corresponding bulk ZnO could be attributed to the visible light energy absorption by COF and subsequent efficient charge-carrier mobility via porous ZnO surface.

Self-Assembly of Mitochondria-Targeted Photosensitizer to Increase Photostability and Photodynamic Therapeutic Efficacy in Hypoxia

The development of photosensitizers for cancer photodynamic therapy has been challenging due to their low photostability and therapeutic inefficacy in hypoxic tumor microenvironments. To overcome these issues, we have developed a mitochondria-targeted photosensitizer consisting of an indocyanine moiety with triphenylphosphonium arms, which can self-assemble into spherical micelles directed to mitochondria. Self-assembly of the photosensitizer resulted in a higher photostability by preventing free rotation of the indoline ring of the indocyanine moiety. The mitochondria targeting capability of the photosensitizer allowed it to utilize intramitochondrial oxygen. We found that the mitochondria-targeted photosensitizer localized to mitochondria and induced apoptosis of cancer cells both normoxic and hypoxic conditions through generation of ROS. The micellar self-assemblies of the photosensitizer were further confirmed to selectively localize to tumor tissues in a xenograft tumor mouse model through passive targeting and showed efficient tumor growth inhibition.

Synergistic Effects in PtII -Porphyrinoid Dyes as Candidates for a Dual-Action Anticancer Therapy: A Theoretical Exploration

The combination of a photosensitizer (PS) with a cisplatin-like unit represents a challenging strategy to increase the effectiveness of photodynamic therapy and to afford a dual-action anticancer treatment. Recently, new tetra-Pt^II -porphyrin conjugates have been proposed as promising multitarget agents. To reveal the effect of the Pt^II center on the chemical and physical properties of the PS and to explore the effect of the PS on the activation mechanism of Pt^II ligand before reaching its biological target, we carried out a first-principle investigation on these tetra-Pt^II -porphyrin conjugates. To propose a further advance in this novel field and to gain useful insights for the design of new, more efficient Pt^II -PS conjugates, we introduced structural modifications into the porphyrin dye, which involved the synthesis of the tetra-Pt^II -chlorin and tetra-Pt^II -bacteriochlorin derivatives. Results showed that the designed dyes better met the criteria to be successful in a dual-action therapy, as they displayed improved optical properties and reduced the hydrolysis rate of the Pt^II moiety, the latter being a desirable feature to avoid many side reactions of the conjugate during their transport to the biological target.

Control of the DNA-Binding and Antiproliferative Properties of Hydroxybenzo[b]quinolizinium Derivatives with pH and Light

The interactions of 8-hydroxybenzo[b]quinolizinium and 9-hydroxybenzo[b]quinolizinium with DNA are investigated in detail. Specifically, spectrophotometric and spectrofluorimetric titrations, thermal DNA-denaturation experiments as well as CD- and LD-spectroscopic analysis show that a pH shift by just one or two orders of magnitude has a significant impact on the interactions of the acidic ligands with the nucleic acid. Both ligands bind with high affinity to DNA at pH 6 (K_b ≈10⁵  m^-1 ). At pH 7 or 8, however, the binding interactions are much weaker because of the formation of the corresponding charge-neutral conjugate bases, the affinity to DNA of which is reduced because of the resulting lack of a positive charge. Notably, the variation of DNA affinity occurs in a range that corresponds to the fluctuations of pH values under physiological conditions, so that these ligands may be employed to target DNA in tissue with particular pH values, especially, cancer cells. The antiproliferative activity of the title compounds under different conditions is also investigated. In the absence of irradiation, both compounds show only a modest cytotoxicity toward cancer cells. However, upon irradiation, even at low UV-A doses, a significant reduction of cell viability of tumor cell lines is induced by the ligands.

Light-Harvesting Photosensitizers for Photodynamic Inactivation of Bacteria under Both Visible and Near-Infrared Excitations

We report a hybrid singlet oxygen production system, where strong resonance coupling between plasmonic nanoparticles and photosensitizing molecules results in exceptionally high singlet oxygen production under both visible light and near-infrared light excitation, even for the photosensitizing molecules without near-infrared absorption. The light-harvesting property of the plasmon-photosensitizer hybrids leads to an enhanced, broad-spectrum photodynamic inactivation of bacteria under a wide range of excitations, including that with near-infrared light.

Nanocomposite-Based Photodynamic Therapy Strategies for Deep Tumor Treatment

Photodynamic therapy (PDT), as an emerging clinically approved modality, has been used for treatment of various cancer diseases. Conventional PDT strategies are mainly focused on superficial lesions because the wavelength of illumination light of most clinically approved photosensitizers (PSs) is located in the UV/VIS range that possesses limited tissue penetration ability, leading to ineffective therapeutic response for deep-seated tumors. The combination of PDT and nanotechnology is becoming a promising approach to fight against deep tumors. Here, the rapid development of new PDT modalities based on various smartly designed nanocomposites integrating with conventionally used PSs for deep tumor treatments is introduced. Until now many types of multifunctional nanoparticles have been studied, and according to the source of excitation energy they can be classified into three major groups: near infrared (NIR) light excited nanomaterials, X-ray excited scintillating/afterglow nanoparticles, and internal light emission excited nanocarriers. The in vitro and in vivo applications of these newly developed PDT modalities are further summarized here, which highlights their potential use as promising nano-agents for deep tumor therapy.