Abstract
Photodynamic therapy (PDT) employs non-toxic dyes called photosensitizers (PSs), which absorb visible light to give the excited singlet state, followed by the long-lived triplet state that can undergo photochemistry. In the presence of ambient oxygen, reactive oxygen species (ROS), such as singlet oxygen and hydroxyl radicals are formed that are able to kill cancer cells, inactivate microbial pathogens and destroy unwanted tissue. Although there are already several clinically approved PSs for various disease indications, many studies around the world are using animal models to investigate the further utility of PDT. The present review will cover the main groups of animal models that have been described in the literature. Cancer comprises the single biggest group of models including syngeneic mouse/rat tumours that can either be subcutaneous or orthotopic and allow the study of anti-tumour immune response; human tumours that need to be implanted in immunosuppressed hosts; carcinogen-induced tumours; and mice that have been genetically engineered to develop cancer (often by pathways similar to those in patients). Infections are the second biggest class of animal models and the anatomical sites include wounds, burns, oral cavity, ears, eyes, nose etc. Responsible pathogens can include Gram-positive and Gram-negative bacteria, fungi, viruses and parasites. A smaller and diverse group of miscellaneous animal models have been reported that allow PDT to be tested in ophthalmology, atherosclerosis, atrial fibrillation, dermatology and wound healing. Successful studies using animal models of PDT are blazing the trail for tomorrow's clinical approvals.
Highlights
Photodynamic therapy (PDT) employs non-toxic dyes called photosensitizers (PSs), which absorb visible light of the correct wavelength to first give the excited singlet state, followed by a transition to the long-lived excited triplet state that can undergo photochemistry [1]
In the presence of molecular oxygen, the photochemical reactions produce a variety of reactive oxygen species (ROS) including singlet oxygen and hydroxyl radicals
These ROS cause oxidative damage to proteins, lipids and nucleic acids and leading to cell death by necrosis and/or apoptosis (Figure 1), PDT was originally developed as a cancer treatment, but has subsequently been investigated as a treatment for choroidal neovascularization secondary to age-related macular degeneration, for a range of localized infections and for disorders related to dermatology and immunology
Summary
Photodynamic therapy (PDT) employs non-toxic dyes called photosensitizers (PSs), which absorb visible light of the correct wavelength to first give the excited singlet state, followed by a transition to the long-lived excited triplet state that can undergo photochemistry [1]. Individual laboratory mouse strains (Mus musculus) have particular combinations of major histocompatibility complexes (MHCs; MHC class I such as H2B and MHC class II such as Ia) and the tumour cells should have the same combination of MHC molecules as the host mouse to allow them to grow without instant rejection This syngeneic mouse tumour approach is often used because the mice have intact immune systems and, immunology and antitumour immunity effects after PDT can be studied. PDT of subcutaneous mouse tumours is usually carried out by IV injection of the PS (often in the tail vein) followed after a certain period of time by light delivery to the tumour including a certain amount of surrounding normal tissue. Due to the increased susceptibility of these mice to infections, the cell
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