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 dermatologic 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.

Photodynamic therapy (PDT) has been developed over the past decade into a useful treatment for several types of solid cancers in man. This unique therapy requires a photosensitiser accumulated in tumours and local activation by visible light generally delivered from lasers and delivered to the patient through various types of fibers and endoscopes. PDT appears to be most effective in treating certain superficial, difficult to treat cancers such as carcinoma in situ of the urinary bladder (here complete control is the intent), but also is effectively used in bulkier tumours obstructing bronchi or the oesophagus where palliation can be achieved. The primary mechanism of action is the in situ generation of an active form of molecular oxygen (singlet oxygen) which causes the rapid, local onset of vascular stasis and eventual vascular haemorrhage and tumour wall destruction. This process appears to be mediated through various cytokines such as prostaglandin, lymphokines and thromboxanes. The ultimate clinical value of PDT will be seen over the next few years following health agency approval worldwide.

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 eVects. The eVects 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 eVective ablation of low grade dysplastic epithelium. (Gut 2000;47:612-617)

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 (ϮS.D.) plasma area under the plasma concentration-time curve from time 0 to infinity of PpIX (0.20 Ϯ 0.11 g ⅐ h/ml) after intravenous administration of ALA was not significantly different from that observed after oral administration of ALA (0.15 Ϯ 0.11 g‫ء‬h/ml; P ϭ 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.

Full-length (35S) genomic RNA from murine mammary tumor virus (MuMTV) was translated in vitro, using a reticulocyte lysate system, into proteins of 105,000, 75,000, 65,000, 35,000, and 27,000 daltons. These proteins were all immunoprecipitable with a monospecific antiserum to the major viral core protein, p27, but not with antiserum to the major viral envelope glycoprotein, gp47. In the case of type C viruses, it has also been established that viral 35S genomic RNA contains information for the synthesis of the major proteins constituting the virus, namely, the core proteins, the glycoproteins, and the reverse transcriptase (5). The avian sarcoma viral RNA also codes for a src protein responsible for the transformation of fibroblasts in vitro and for the induction of sarcoma in vivo. However, when the full-size virion RNA or intracellular viral specific RNA of similar size is translated in an exogenous Xenopus oocyte system or an in vitro cell-free protein-synthesizing system, only the gag proteins and a gag-pol polyprotein are synthesized. It has been reported that virion RNA of smaller size classes can be translated into the src protein product (5). The env proteins are translated only from a virus-specific intracellular mRNA of about 21 S in size. For MuMTV no information is available regarding the identity of the mRNAs for different viral proteins.We report here the translation in vitro of MuMTV virion RNAs. By hybridization with a representative MuMTV cDNA probe, we have identified at least three size classes of MuMTV-specific intracellular RNAs. Intracellular RNA of 35S size class was translated into MuMTV core proteins, while 24S size class RNA was translated into MuMTV envelope proteins. MATERIALS AND METHODSCell Culture. MuMTV-producing GR cells (8) were grown in monolayer culture in Eagle's minimal essential medium supplemented with 10% calf serum. Confluent cultures were treated with dexamethasone at 1 /ig/ml for the production of MuMTV. The cells were grown in the presence of [3H]uridine at 50 ,uCi/ml (1 Ci = 3.7 X 1010 becquerels) for preparing RNA-labeled MuMTV.Virus Purification. Virus was purified from the culture fluid by using the following method. The culture fluid was first clarified by centrifugation at 10,000 X g for 10 min. The supernatant was then layered on a cushion of 60% sucrose in TNE buffer (10 mM Tris-HCI, pH 7.5/100 mM NaCl/1 mM EDTA) and centrifuged at 100,000 X g for 90 min. The virus layer at the top of the cushion was removed and layered onto a preformed linear gradient of 25% to 60% sucrose in TNE buffer. This was centrifuged at 100,000 X g for 3 hr. The virus banding at a density of 1.17 g/ml was removed and stored at 0C.Isolation of Viral and Cellular RNAs. RNA was extracted from the virus by incubation with self-digested Pronase and phenol/chloroform extraction (9). Total cytoplasmic RNA was extracted from cells that had been treated with dexamethasone for 18 hr, following published procedures (10). Poly(A)-containing RNA was selected from this total RNA by two cons...