About this Research Topic
Photodynamic therapy (PDT) is an effective treatment against pathogenic bacteria and cancer cells. In recent years, a lot of work has been carried out on PDT that makes use of a photosensitizer (PS) which generates reactive oxygen species (ROS) upon photoactivation. There are two mechanisms that operate in PDT. Type-I produces active oxygen like superoxide anion radicals (O2−•C), hydroxyl radicals (•OH), and other oxygen-containing radicals by electron transfer reaction. Type-II is related to the energy transfer reaction between the triplet state excited PS and oxygen, which eventually generates singlet state oxygen (1O2). Where this therapy is commonly practiced in the treatment of a number of cancers, including lungs, bladder, and skin and in the treatment of age-related, macular degeneration, psoriasis, atherosclerosis, and herpes. PDT offers advantages to the patient because this treatment requires a delicate surgery with minimal disfigurement or scar formation.
PDT, however, is associated with drawbacks such as poor solubility of the photosensitizer, high cost, and possible photosensitization of skin tissue. One of the key features that are associated with PS to work in PDT, apart from ROS generation ability, includes a large absorptivity within the 600−900 nm range. The most used PSs belonged to the class of porphyrin and Photofrin which was used for a long time in clinical PDT. However, their poor solubility and poor absorptivity required the need for a second-generation which along with many derivatives of porphyrins has metallated porphyrins. Here, diamagnetic or paramagnetic metals are coordinated to the tetrapyrrole ring which increases the absorptivity coefficient and also increased the phototherapeutic window. However, porphyrin derivatives also had limitations such as their tendency to self-aggregate in physiological conditions which reduces their bioavailability. As a consequence, a higher amount of PS was required to obtain satisfactory effects which result in increased side-effects.
To overcome the drawbacks associated with second-generation PS, 3rd generation focused on the conjugation of PS with biomolecules, organic nanoparticles, and inorganic nanoparticles. Attempts have been made to generate peptide and protein-based nanomaterials, to make amphiphilic PS, hydrophilic PS-vitamin B conjugates. Use of nanoparticles which either encapsulated the PS, physically adsorbed PS, or covalently linked the PS to the nanoparticles surface, still suffered from disadvantages like self-quenching of PS or large ROS diffusion length that results in the decrease in the cytotoxic effects, thus reducing the PDT activity. The current research in PDT i.e. 4th generation is focusing on Metal-Organic Framework nanoparticles which look to overcome the current limitations producing new and effective materials to be utilized within PDT.
In this Research Topic, we are looking forward towards the utility of various aspects of nanotechnology that can be used with regard to PDT. We accept Original Research, Reviews, and Mini-reviews on, but not restricted to, the following research areas:
• Role of metallic nanoparticles in enhancing PDT
• The use of MOFs in PDT
• The utilization of organic nanoparticles in PDT
• Role of nanoparticles as photosensitizers and their use in PDT
• Analysis of bimetallic or hybrid nanoparticles for their use in PDT
Keywords: Nanotechnology, Photodynamic therapy, metallic nanoparticles, Metal-organic frameworks, organic nanoparticles, PDT, photosensitizer, hybrid nanoparticles
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