Stuart L. Marcus

Photodynamic therapy (PDT) is a form of photochemotherapy requiring the simultaneous presence of a photosensitiser, activating light of the proper wavelength and molecular oxygen in order to produce a localised therapeutic effect thought to be due to high-energy singlet oxygen generation. Neither drug nor light alone are effective as therapeutic agents and thus PDT treatment methods should be looked upon as true, necessary, drug and device combinations (‘systems’). Selectivity of treatment is imparted by a combination of factors, including accumulation of photosensitiser by the target lesion and targeted application of activating light. The most common systemic side effect of systemically administered photosensitisers is cutaneous photosensitivity of varying periods of time. Local toxicities depend on the area of treatment. Sources of light which have been used in PDT include lasers, arc lamps, light-emitting diodes and fluorescent lamps. PDT has been used for a wide variety of clinical applications. In 1...

5-Aminolevulinic acid (ALA) is a precursor of protoporphyrin IX (PpIX) that is being evaluated for use in photodiagnosis and phototherapy of malignant and nonmalignant disorders. Previous clinical studies using topical, oral, and intravesical administration have been conducted in attempts to determine the optimal route of administration for ALA. The purpose of these studies was to examine the systemic pharmacokinetics and elimination of ALA, the bioavailability of ALA after oral and intravesical doses, and the factors that affect ALA concentrations in the bladder during intravesical treatment. The disposition of ALA was evaluated in six healthy volunteers receiving single intravenous and oral doses (100 mg) and eight patients at high risk for recurrent bladder cancer receiving an intravesical dose (1.328 g) of ALA. The mean (±S.D.) plasma area under the plasma concentration-time curve from time 0 to infinity of PpIX (0.20 ± 0.11 μg · h/ml) after intravenous administration of ALA was not significantly different from that observed after oral administration of ALA (0.15 ± 0.11 μg∗h/ml;P = 0.49). ALA terminal half-life was approximately 45 min after intravenous or oral administration. The oral bioavailability of ALA was approximately 60%. After intravesical administration, urine production was largely responsible for decreases in ALA concentration in the bladder, with less than 1% being absorbed into the systemic circulation. In summary, oral and intravenous administration of ALA at these doses results in modest plasma levels of PpIX. Regional administration (i.e., intravesical) of ALA resulted in a significant pharmacokinetic advantage, with urinary bladder being exposed to concentrations approximately 20,000-fold higher than systemic circulation.

BACKGROUND AND AIMS: Photodynamic therapy (PDT) is a treatment in which cell damage is achieved by the action of light on a photosensitising agent. We have assessed the potential use of PDT in the ablation of Barrett's oesophagus. METHODS: Thirty six patients with dysplastic Barrett's oesophagus receiving acid suppression medication with omeprazole were randomised to receive oral 5-aminolaevulinic acid (ALA) 30 mg/kg or placebo, followed four hours later by laser endoscopy. Follow up endoscopy was performed at one, six, 12, and 24 months. RESULTS: Of 18 patients in the ALA group, a response was seen in 16 (median decrease in area in the treated region 30%; range 0–60%). In the placebo group, a decrease in area of 10% was observed in two patients with no change in 16 (median 0%; range 0–10%; treatment v placebo, p<0.001). No dysplasia was seen in the columnar epithelium within the treatment area of any patient in the PDT group. However, in the placebo group, persistent low grade dysplasia was found in 12 patients (p<0.001). There were no short or long term major side effects. The effects of treatment were maintained for up to 24 months. CONCLUSIONS: This is the first randomised controlled trial of PDT for Barrett's oesophagus. It demonstrates that ALA induced PDT can provide safe and effective ablation of low grade dysplastic epithelium.

Objective:To test the effectiveness of 5-aminolevulinic acid (ALA)-induced photodynamic endometrial ablation in the rhesus monkey under varying conditions of light delivery (fractionated versus continuous) and steroid priming. Methods:Photodynamic endometrial ablation was carried out in 17 rhesus monkeys that were either postmenopausal or in the early proliferative phase. Four hours after intralumental injection of ALA (250 mg in 1 mL hyskon), a quartz fiber with a diffusing tip was inserted. A KTP tunable dyye laser delivered 300 mW of light (635 nm) for 60 minutes in either continuous or fractionated fashion (20 minutes on, 5 minutes off, and 40 minutes on). In some experiments, thermistors were used to monitor temperature in the lumen and myometrium during light treatment. Hysterectomy was performed 3 or 4 days after treatment, and endometrial damage was assessed histologically. Two additional monkeys (one rhesus and one cynomolgus monkey) were exposed to the same protocol, except hyskon was substituted for ALA to control for potential ablative effects due to light treatment alone. Results:Endometrial ablation was evident in all ALA-photosensitized specimens. The degree of ablation around the light fiber ranged from moderate to complete. The depth of ablation ranged from 1.14 ± 0.54 to 2.15 ± 1.62 mm (mean ± standard deviation). Ablation was most complete in uteri of menopausal monkeys. Light treatment after ALA increased leumenal temperature from 36C to 50C, whereas temperature was not significantly increased by light treatment in the controls. Conclusion:This is the first report of endometrial destruction in the primate using a photodynamic approach. Whereas clinical application of photodynamic therapy (PDT) requires complete endometrial ablation to produce long-lasting amenorrhea, our results suggest that PDT may offer a simple office-based approach to endometrial ablation.

5-Aminolevulinic acid (ALA), when added to many tissues, results in the accumulation of sufficient quantities of the endogenous photosensitizer protoporphyrin IX (PpIX) via the heme biosynthetic pathway, to produce a photodynamic effect when exposed to activating light. Therefore, ALA is the only photodynamic therapy (PDT) agent in current clinical development that is a biochemical precursor of a photosensitizer. Topical ALA application, followed by exposure to activating light (ALA PDT), has been reported effective for the treatment of a variety of dermatologie diseases including cutaneous superficial and nodular basal cell carcinoma, Bowen's disease, and actinic (solar) keratoses. Local internal application of ALA has also been used for selective endometrial ablation in animal model systems and in human clinical studies has shown selective formation of PpIX within the endometrium. PpIX induced by ALA application has also been used as a fluorescence detection marker for photodiagnosis (PD) of cancer and dysplastic conditions of the urinary bladder and other organs. Systemic, oral administration of ALA has been used for ALA PDT of superficial head and neck cancer, various gastrointestinal cancers, and the condition known as Barrett's esophagus. The current state of knowledge of the mechanisms of endogenous topical and systemic photosensitization using ALA, the results of published clinical trials, and possible methods of increasing the efficacy of endogenous photosensitization for ALA PDT are reviewed in this paper.

Exogenous provision of ALA to many tissues results in the accumulation of sufficient quantities of the endogenous photosensitizer protoporphyrin IX, (PpIX), to produce a photodynamic effect. Therefore, ALA may be considered the only current PDT agent in clinical development which is a biochemical precursor of a photosensitizer. Topical ALA application, followed by exposure to activating light (ALA PDT), has been reported effective for the treatment of a variety of dermatologic diseases including cutaneous T-cell lymphoma, superficial basal cell carcinoma, Bowen's disease, and actinic (solar) keratoses, and is also being examined for treatment of acne and hirsutism. PpIX induced by ALA application also may serve as a fluorescence detection marker for photodiagnosis (PD) of malignant and pre- malignant conditions of the urinary bladder and other organs. Local internal application of ALA has also been used for selective endometrial ablation in animal model systems and is beginning to be examined in human clinical studies. Systemic, oral administration of ALA has been used for ALA PDT of superficial head and neck cancer, various gastrointestinal cancers, and the condition known as Barrett's esophagus. This brief paper reviews the current clinical and development status of ALA PDT.

Exogenous provision of 5-aminolevulinic acid (ALA) to many tissues results in the accumulation of sufficient quantities of the endogenous photosensitizer protoporphyrin IX (PpIX) via the heme biosynthetic pathway, to produce a photodynamic effect when exposed to activating light. Therefore, ALA may be considered the only current photodynamic therapy (PDT) agent in clinical development that is a biochemical precursor of a photosensitizer. Topical ALA application, followed by exposure to activating light (ALA PDT), has been reported effective for the treatment of a variety of dermatologic diseases including cutaneous superficial and nodular basal cell carcinoma, Bowen's disease, actinic (solar) keratoses, and T cell lymphoma. Local internal application of ALA has also been used for selective endometrial ablation in animal model systems and, in human clinical studies, it has shown selective formation of PpIX within the endometrium. PpIX induced by ALA application has also been used as a fluorescence detection marker for photodiagnosis (PD) of cancer and dysplastic conditions of the urinary bladder and other organs. Systemic, oral administration of ALA has been used for ALA PDT of superficial head and neck cancer, various gastrointestinal cancers, and the condition known as Barrett's esophagus. This paper reviews the current clinical and development status of ALA PDT and PD.