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Photosensitiser delivery for photodynamic therapy. Part 1: Topical carrier platforms
Ryan F Donnelly1, Paul A McCarron, Desmond I J Morrow
1School of Pharmacy, Medical Biology Centre, Queen's University Belfast, 97 Lisburn Road, Belfast, UK. r.donnelly@qub.ac.uk
Background:
Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitising drug and visible light causes destruction of selected cells. Due to the lack of true selectivity of preformed photosensitisers for neoplastic tissue and their high molecular weights, PDT of superficial skin lesions has traditionally been mediated by topical application of the porphyrin precursor 5-aminolevulinic acid (ALA).
Objective:
This article aims to review the traditional formulation-based approaches taken to topical delivery of ALA and discusses the more innovative strategies investigated for enhancement of PDT mediated by topical application of ALA and preformed photosensitisers.
Methods:
All of the available published print and online literature in this area was reviewed. As drug delivery of agents used in PDT is still something of an emerging field, it was not necessary to go beyond literature from the last 30 years.
Results/Conclusion:
PDT of neoplastic skin lesions is currently based almost exclusively on topical application of simple semisolid dosage forms containing ALA or its methyl ester. Until expiry of patents on the current market-leading products, there is unlikely to be a great incentive to engage in design and evaluation of innovative formulations for topical PDT, especially those containing the more difficult-to-deliver preformed photosensitisers.
Insights
Topical photodynamic therapy (PDT) for skin lesions primarily uses 5-aminolevulinic acid (ALA) in simple formulations. Innovative delivery strategies for ALA and photosensitizers are needed but face patent barriers.
Area of Science:
- Dermatology
- Photochemistry
- Drug Delivery
Background:
- Photodynamic therapy (PDT) utilizes photosensitizers and light to destroy targeted cells.
- Topical 5-aminolevulinic acid (ALA) is common for superficial skin lesions due to formulation challenges with preformed photosensitizers.
Purpose of the Study:
- Review traditional topical delivery methods for ALA in PDT.
- Discuss innovative strategies to enhance topical ALA and photosensitizer delivery for PDT.
Main Methods:
- Comprehensive literature review of published print and online studies.
- Focus on research within the last 30 years due to the emerging nature of PDT drug delivery.
Main Results:
- Current topical PDT for neoplastic skin lesions relies heavily on simple semi-solid formulations of ALA or its methyl ester.
- Development of novel formulations for topical PDT, particularly for complex photosensitizers, is limited.
Conclusions:
- Patent expirations are anticipated to drive innovation in topical PDT formulations.
- Further research into advanced drug delivery systems is crucial for improving PDT efficacy, especially for preformed photosensitizers.
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