[Photodynamic therapy: non-oncologic indications]

Photodynamic Therapy-Current Limitations and Novel Approaches

Photodynamic therapy (PDT) mostly relies on the generation of singlet oxygen, via the excitation of a photosensitizer, so that target tumor cells can be destroyed. PDT can be applied in the settings of several malignant diseases. In fact, the earliest preclinical applications date back to 1900’s. Dougherty reported the treatment of skin tumors by PDT in 1978. Several further studies around 1980 demonstrated the effectiveness of PDT. Thus, the technique has attracted the attention of numerous researchers since then. Hematoporphyrin derivative received the FDA approval as a clinical application of PDT in 1995. We have indeed witnessed a considerable progress in the field over the last century. Given the fact that PDT has a favorable adverse event profile and can enhance anti-tumor immune responses as well as demonstrating minimally invasive characteristics, it is disappointing that PDT is not broadly utilized in the clinical setting for the treatment of malignant and/or non-malignant diseases. Several issues still hinder the development of PDT, such as those related with light, tissue oxygenation and inherent properties of the photosensitizers. Various photosensitizers have been designed/synthesized in order to overcome the limitations. In this Review, we provide a general overview of the mechanisms of action in terms of PDT in cancer, including the effects on immune system and vasculature as well as mechanisms related with tumor cell destruction. We will also briefly mention the application of PDT for non-malignant diseases. The current limitations of PDT utilization in cancer will be reviewed, since identifying problems associated with design/synthesis of photosensitizers as well as application of light and tissue oxygenation might pave the way for more effective PDT approaches. Furthermore, novel promising approaches to improve outcome in PDT such as selectivity, bioengineering, subcellular/organelle targeting, etc. will also be discussed in detail, since the potential of pioneering and exceptional approaches that aim to overcome the limitations and reveal the full potential of PDT in terms of clinical translation are undoubtedly exciting. A better understanding of novel concepts in the field (e.g. enhanced, two-stage, fractional PDT) will most likely prove to be very useful for pursuing and improving effective PDT strategies.

Photodynamic therapy in dermatology

Photodynamic therapy (PDT) is a modern therapy modality, based upon the application of a photosensitizing agent like aminolevulinic acid, a physiological precursor of porphyrins, onto the tissue followed by illumination with light of the visible wavelength spectrum. During this oxygen-dependent reaction, reactive oxygen species (ROS) are generated that have immunomodulatory or cytotoxic effects. PDT shows excellent cosmetic results especially for its key indication in dermatology - the treatment of non-melanoma skin cancer. The associated pain and the low tissue penetration are the most frequent limiting factors of PDT. We review basic principles and recent developments in photosensitizers and light sources. Key oncological and non-oncological indications are presented as well.

Photodynamic therapy in dermatology--an update 2008

SUMMARY

Photodynamic therapy (PDT) is used for the prevention and treatment of non-melanoma skin cancer. Until recently, clinically approved indications have been restricted to actinic keratoses, nodular and superficial basal cell carcinoma, and--since 2006--Bowen disease. However, the range of indications has been expanding continuously. PDT is also used for the treatment of non-malignant conditions such as acne vulgaris and leishmaniasis, as well as for treating premature skin aging due to sun exposure. Here, PDT is used for the stimulation of immunomodulatory effects in contrast to the induction of necrosis and apoptosis as produced in the treatment of skin tumors. The porphyrin precursor 5-aminolevulinic acid (ALA) or its methyl ester (MAL, so far the only approved formulation in Europe) is applied topically as photosensitizer to exclude systemic reactions. Possible light sources include lasers as well as incoherent light sources; irradiation with incoherent light sources is cheaper and more appropriate for large treatment areas. The main advantages of PDT in comparison to other treatment modalities are its excellent cosmetic results and its high remission rates despite low invasiveness.This article provides up-to-date information about PDT with focus on recently published studies.