History of Photodynamic Therapy

The treatment of superficial nonmelanoma skin cancers and actinic keratoses (AKs) with lasers and light sources has recently entered a new era in dermatology with the advent of 20% 5-aminolevulinic acid (ALA), a potent photosen-sitizer. This photosensitizer has demonstrated an effective ability to interact with lasers and light sources of appropriate wavelengths to selectively destroy the lesions in question. The term photodynamic therapy, or PDT, is now a phrase which is not foreign to laser physicians and has, over the past several years, become an integral part of their therapeutic armamentarium. A review of what PDT is, its history and how it is being incorporated into dermatologist's offices today will follow.

PDT is a treatment modality which involves the use of a photosensitizer, a light source which fits the absorption spectrum of the pho-tosensitizer, and molecular oxygen, which when stimulated will destroy a specific target tissue. To be effective in the process, the photosensi-tizer must be able to preferentially penetrate more into the targeted tissue than the surrounding skin. ALA has been shown to be absorbed very well by actinically damaged skin, skin cancer cells, and by the pilosebaceous glands of the skin. The photosensitizer may be given exogenously or formed endogenously during normal biochemical pathways found within certain disease state pathways. An appropriate light source must be employed to activate the photosensitizer and the wavelength of that light must be within the appropriate absorption spectrum of the photosensitizer. Various lasers and light are being utilized by dermatologists for PDT. These devices have different wavelengths of light and thus different penetration depths into tissues.

5-ALA, the most common drug used in dermatology for PDT, occurs naturally in cells as an intermediate product formed during the endogenous porphyrin synthesis process. 5-ALA acts as a "prodrug" and has been demonstrated to effectively penetrate the stratum corneum and to localize in the target tissues already mentioned. Once localized into the appropriate cells within the target tissues, the 5-ALA is transformed into a highly photoactive

Protoporphyrin absorption spectrum

In vivo excitation of PplX (ALA inj, mouse, j,EM = 707nm, peaks at 409,509,544,584,634 nm)

In vivo excitation of PplX (ALA inj, mouse, j,EM = 707nm, peaks at 409,509,544,584,634 nm)

In vivo emission of PplX (human psoriatic skin lesion after topical ALA application, peaks at 636 and 708 nm)

Protoporphyrin absorption spectrum

Pictures Ofphotodynamic Therapy

350 400 450 500 550 600 650 Wavelength [nm]

How To Prevent Skin Cancer

How To Prevent Skin Cancer

Complete Guide to Preventing Skin Cancer. We all know enough to fear the name, just as we do the words tumor and malignant. But apart from that, most of us know very little at all about cancer, especially skin cancer in itself. If I were to ask you to tell me about skin cancer right now, what would you say? Apart from the fact that its a cancer on the skin, that is.

Get My Free Ebook


Post a comment