Efficacy of intravenous delta-aminolaevulinic acid photodynamic therapy on rabbit papillomas

Combined treatment with X-ray irradiation and 5-aminolevulinic acid elicits better transcriptomic response of cell cycle-related factors than X-ray irradiation alone

PURPOSE

5-Aminolevulinic acid (ALA) is a precursor of the photosensitizer protoporphyrin (PpIX) used in photodynamic therapy. In our previous work, PpIX enhanced the generation of reactive oxygen species by X-ray irradiation. In this study, we evaluated the potential of ALA as an endogenous sensitizer to X-ray irradiation.

METHODOLOGY

Tumor-bearing C57BL/6J mice implanted with B16-BL6 melanoma cells were subsequently treated with irradiation (3 Gy/day for 10 days; total, 30 Gy) plus local administration of 50 mg/kg ALA 24 hours prior to each irradiation (ALA-XT). Tumor-bearing mice without treatment (NT), those treated with ALA only (ALAT), and those treated with X-ray irradiation only (XT) were used as controls.

RESULTS

ALA potentiated tumor suppression by X-ray irradiation. In microarray analyses using tumor tissue collected after 10 sessions of fractional irradiation, functional analysis revealed that the majority of dysregulated genes in the XT and ALA-XT groups were related to cell-cycle arrest. Finally, the XT and ALA-XT groups differed in the strength of expression, but not in the pattern of expression.

CONCLUSIONS

mRNA analysis revealed that the combined use of ALA and X-ray irradiation sensitized tumors to X-ray treatment. Furthermore, the present results were consistent with ALA's tumor suppressive effects in vivo.

In vitro and Animal Models for Antiviral Therapy in Papillomavirus Infections

The need for antiviral therapies for papillomavirus infections is well recognized but the difficulties of reproducing the infectious cycle of papillomaviruses in vitro has hindered our understanding of virus-cell interactions and the regulation of viral gene expression during permissive growth. Recent advances in understanding the temporal expression and function of papillomavirus proteins has enabled consideration of a targeted approach to papillomavirus chemotherapy and in particular the inhibition of viral replication by targeting the E1 and E2 proteins. There are in vitro culture systems available for the screening of new chemotherapeutic agents, since significant advances have been made with culture systems which promote epithelial differentiation in vitro. However, to date, there are no published data which show that virions generated in vitro can infect keratinocytes and initiate another round of replication in vitro. In vivo animal models are therefore necessary to assess the efficacy of antivirals in preventing and treating viral infection, particularly for the low-risk genital viruses which are on the whole refractory to culture in vitro. Although papillomaviruses affect a wide variety of hosts in a species-specific manner, the animals most useful for modelling papillomavirus infections include the rabbit, ox, mouse, dog, horse, primate and sheep. The ideal animal model should be widely available, easy to house and handle, be large enough to allow for adequate tissue sampling, develop lesions on anatomical sites comparable with those in human diseases and these lesions should be readily accessible for monitoring and ideally should yield large amounts of infectious virus particles for use in both in vivo and in vitro studies. The relative merits of the various papillomavirus animal models available in relation to these criteria are discussed.

5-Aminolevulinic acid enhances cancer radiotherapy in a mouse tumor model

5-Aminolevulinic acid (ALA) is a photosensitizer used in photodynamic therapy (PDT) because it causes preferential accumulation of protoporphyrin IX (PpIX) in tumor cells, where it forms singlet oxygen upon light irradiation and kills the tumor cells. Our previous study demonstrated that PpIX enhances generation of reactive oxygen species by physicochemical interaction with X-rays. We investigated the effect of ALA administration with X-ray irradiation of mouse B16-BL6 melanoma cells in vitro and in vivo. ALA facilitates PpIX accumulation in tumor cells and enhances ROS generation in vitro. Tumor suppression significantly improved in animals treated with fractionated doses of radiation (3 Gy × 10; total, 30 Gy) with local administration of 50 mg/kg ALA at 24 h prior to fractional irradiation. These results suggest ALA may improve the efficacy of cancer radiotherapy by acting as a radiomediator.

Photodynamic therapy using 5-aminolaevulinic acid for the treatment of dysplasia in Barrett's oesophagus

BACKGROUND

5-Aminolaevulinic acid (ALA) is the naturally occurring metabolic precursor of an endogenously formed photosensitiser, protoporphyrin IX. It is used topically to treat benign and malignant skin disorders by a process called photodynamic therapy (PDT). Recently, data are emerging on its systemic use in the treatment of dysplasia in Barrett's oesophagus.

OBJECTIVE

To investigate the use of ALA-PDT for the treatment of dysplasia and early cancer in Barrett's oesophagus.

METHODS

A systematic literature review and synopsis is given.

CONCLUSION

ALA is an attractive alternative to the currently approved photosensitiser (porfimer sodium) due to its oral route of administration, shorter generalised skin photosensitivity period and lower rate of stricture formation. The studies presented demonstrate that ALA-PDT is both safe and effective for the treatment of dysplasia and early cancer in Barrett's oesophagus.

Pharmacokinetics of a tri-glucoconjugated 5,10,15-(meta)-trihydroxyphenyl-20-phenyl porphyrin photosensitizer for PDT. A single dose study in the rat

Photodynamic therapy (PDT) involves a non invasive treatment of small and superficial cancers using a photosensitive drug and light to kill tumoral cells. 5,10,15-meso-tri-(meta-O-beta-D-glucosyloxyphenyl)-20-phenylporphyrin [m-TPP(glu)3] is a new photosensitizer (PS) with more enhanced photocytotoxicity relative to 5,10,15,20-meso-tetra-(meta-hydroxyphenyl) chlorin [m-THPC] (Foscan). It was injected intravenously once to healthy rats at three different doses (0.25, 0.5 and 1 mg kg(-1)) and compared to m-THPC (0.3 mg kg(-1)). Pharmacokinetic parameters for both photosensitizers were derived from plasma concentration-time data using a non-compartmental analysis and a two-compartment pharmacokinetic model. m-TPP(glu)3 is more rapidly eliminated throughout the organism than m-THPC. Its mean plasma clearance is 19 mL h(-1) kg(-1) (6 mL h(-1) kg(-1) for m-THPC), and its mean residence time is 5h (20 h for m-THPC). The area under curve (AUC) and initial mean serum concentration (C0) were found to be proportional to the dose. As for Foscan, no metabolite of m-TPP(glu)3 was detected in plasma. The biodistribution study demonstrates that the most significant amount of m-TPP(glu)3 was concentrated in organs such as lung, liver and spleen which are rich in reticulo-endothelial cells. Maximum concentrations were reached in organs 14 h after IV administration. At 48 h, the photosensitizer was essentially eliminated from all organs. Because of its shorter elimination time, m-TPP(glu)3 is more attractive than m-THPC as a PDT agent since secondary side effects of shorter duration could be expected.

In vivo fluorescence kinetics and photodynamic therapy in condylomata acuminata

BACKGROUND

Topical application of 5-aminolaevulinic acid (ALA) to condylomata acuminata leads to accumulation of protoporphyrin IX (PpIX); therefore ALA-induced photodynamic therapy (ALA-PDT) appears to be a potential treatment.

OBJECTIVES

To investigate in vivo the PpIX fluorescence time course after topical application of ALA in order to determine the optimal time for irradiation, and to assess the efficacy of subsequently performed ALA-PDT.

METHODS

Fluorescence kinetics was studied in 12 male patients with condylomata acuminata. Confirmation of diagnosis was established with conventional histology and polymerase chain reaction. Lesions were treated with 20% ALA and irradiated at the optimal time with a dose of 70 J cm-2 or 100 J cm-2 light. An additional session with 100 J cm-2 was administered 1 week later to lesions that persisted.

RESULTS

The in vivo study of fluorescence kinetics indicated that the optimal time for irradiation varied among patients from 6 to 11 h. The overall cure rate was 72.9%, 12 months after treatment.

CONCLUSIONS

Topical ALA-PDT is a potentially effective treatment for condylomata acuminata.

Quantitative model calculation of the time-dependent protoporphyrin IX concentration in normal human epidermis after delivery of ALA by passive topical application or lontophoresis

We present a mathematical layer model to quantitatively calculate the diffusion of 5-aminolevulinic acid (ALA) in the skin in vivo, its uptake into the cells and its conversion to protoporphyrin IX (PpIX) and subsequently to heme. The model is a modification and extension of a recently presented three-compartment model. The diffusion of ALA in the skin (epidermis, dermis) is described by the time-dependent diffusion equation, and the sink in this equation accounts for ALA uptake in the cells. As boundary conditions, we use the ALA flux across the human stratum corneum (SC) in vitro during passive or iontophoretic ALA delivery as measured in vitro. Besides the diffusion equation, the model includes three additional equations, similar in form to those of the three-compartment model but with a different interpretation. Our additional equations are supposed to describe, respectively, the conversion of ALA in the cytoplasm to some intermediate compound in the mitochondria and the conversion of the latter to PpIX and of PpIX to heme. The first conversion is a process of the Michaelis-Menten type, the other two are first-order rate processes. When fitted to the published data of PpIX fluorescence from normal human skin following iontophoresis of ALA, the model yields the tissue concentration of PpIX as a function of time after ALA application. The computed concentrations are in good agreement with the published phototoxic concentrations of PpIX in the tissues obtained from extraction. The model parameters obtained from the fit are subsequently used to compute the PpIX concentration in normal human skin after 4 h topical application of 10, 20 and 40% ALA. This again yields the PpIX concentrations in tissue, in good agreement with the published values. The saturation of the PpIX concentration as a function of applied ALA concentration is calculated and agrees with clinical observations on the effectiveness of photodynamic therapy. Photobleaching is simulated, with subsequent resynthesis of PpIX in qualitative agreement with experiment. Finally, the model predicts that only 2.5-3.5% of the ALA entering the skin after passing the SC is converted to PpIX. The layered model is a considerable simplification of real skin, but its successful qualitative and quantitative reproduction of experimental data may encourage further studies to test and refine the model to improve our understanding of the kinetics of ALA and the synthesis of PpIX in the skin.

In vivo anti-papillomavirus activity of nucleoside analogues including cidofovir on CRPV-induced rabbit papillomas

A series of nucleoside analogues were tested for in vivo anti-papillomavirus activity using the cottontail rabbit papillomavirus (CRPV) domestic rabbit model. Compounds were delivered either topically, injected into growing papillomas, or delivered subcutaneously at a site remote from the papillomas. Compounds tested included cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine] (HPMPC); cyclic HPMPC (cHPMPC); cyclopentenylcytosine (CPE-C); lobucavir [1R(1alpha,2beta,3alpha)]-9-[2, 3-bis(hydroxymethyl)cyclobutyl]guanine; 9-((2-phosphonylmethoxy)propyl)adenine (PMPA); adefovir 9-((2-phosphonylmethoxy)ethyl)adenine(PMEA) and cyclopropyl 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (cyclopropylPMEDAP). Dose response curves and time-course treatments were included for most compounds tested. Strong anti-viral activity was detected using cidofovir and cHPMPC when delivered either topically or by the intralesional route. Complete cures were obtained using 1% (w/v) topical cidofovir at dosing schedules of twice daily for 8 weeks beginning at 4 weeks after CRPV infection, which represents a time when papillomas were clearly visible. Complete cures of large established papillomas were obtained by intralesional injection of 1% cidofovir three times per week for 8 weeks. Topical treatments with adefovir had strong anti-viral activity, cyclopropyl PMEDAP had moderate anti-viral activity, and CPE-C, PMPA and lobucavir showed no effects. These data indicate that certain nucleoside analogues have strong in vivo anti-papillomavirus activity and that the CRPV/rabbit model is a good model for assessing clinical responses of anti-viral treatments for patients with HPV disease.

Comparative biodistribution of meta-Tetra(Hydroxyphenyl) chlorin in multiple species: clinical implications for photodynamic therapy

BACKGROUND AND OBJECTIVE

To optimize photodynamic therapy, it is necessary to know the distribution of photosensitizer in normal tissue as well as tumors and to know how well animal models match human. This study measured the biodistribution of meta-Tetra(Hydroxyphenyl) Chlorin (mTHPC) in three species of animals and in humans.

STUDY DESIGN/MATERIALS AND METHODS

mTHPC was injected intravenously into dogs, rabbits, and humans, and drug levels in various tissues were determined 6 days later. One dog was perfused with 3 L of saline to remove blood trapped within organs.

RESULTS

Absolute and relative concentrations of drug in specific tissues varied between species and between individuals. There was a general pattern of distribution. Highly vascularized tissues had the highest levels of mTHPC, not simply due to trapping of blood. mTHPC did not localize in bone and did not cross the blood-brain barrier. Humans had much higher levels of drug in their plasma and tissues than did animals.

CONCLUSIONS

First, drug retention varies from one tissue to another. Second, there is significant variability from one individual to another, whether animal or human. Third, current models cannot accurately predict from animal studies the optimum dose for humans. Measurement of photosensitizer level in plasma at time of treatment would allow optimal photodynamic dosing.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Photodynamic therapy in women with cervical intraepithelial neoplasia using topically applied 5-aminolevulinic acid

Photodynamic therapy (PDT) is a novel treatment modality that produces local tissue necrosis with laser light after prior administration of a photosensitizing agent. We performed a study of topically applied 5-aminolevulinic acid (5-ALA) in the photodynamic treatment of women with high-grade cervical intraepithelial neoplasia (CIN) using fixed 5-ALA doses and application protocols derived from previous in vitro and in vivo results. Three to 5 hr prior to PDT, 10 ml of a 20% solution of 5-ALA was topically applied using a cervical cap. PDT was performed with irradiation of 100 J/cm2 at an irradiance of 100-150 mW/cm2 with an argon-ion-pumped dye laser at 635 nm. For the endocervix, a specifically designed cylindrical applicator was used. Ten treatment cycles of PDT using 5-ALA were performed in 7 patients with high-grade CIN. Non-thermal laser treatment with 100-150 mW/cm2 was well tolerated. Local toxicity was minor as several patients reported burning sensations and vaginal discharge, but no necrosis, sloughing or scarring occurred. After 3 months, a significant reduction in the size of the ectocervical CIN lesions was noted in only 3 patients, who underwent a second PDT cycle. However, no significant improvement in CIN lesions was noted since cold knife conization revealed persistent CIN in all 7 cases. Therefore, PDT after topical application of 5-ALA using an irradiation of 100 J/cm2 produces only minimal side effects. However, it does not appear to be effective in treating CIN.

Systemic application of photosensitizers in the chick chorioallantoic membrane (CAM) model: photodynamic response of CAM vessels and 5-aminolevulinic acid uptake kinetics by transplantable tumors

The aim of this study is to modify the chick chorioallantoic membrane (CAM) model into a whole-animal tumor model for photodynamic therapy (PDT). By using intraperitoneal (i.p.) photosensitizer injection of the chick embryo, use of the CAM for PDT has been extended to include systemic delivery as well as topical application of photosensitizers. The model has been tested for its capability to mimic an animal tumor model and to serve for PDT studies by measuring drug fluorescence and PDT-induced effects. Three second-generation photosensitizers have been tested for their ability to produce photodynamic response in the chick embryo/CAM system when delivered by i.p. injection: 5-aminolevulinic acid (ALA), benzoporphyrin derivative monoacid ring A (BPD-MA), and Lutetium-texaphyrin (Lu-Tex). Exposure of the CAM vasculature to the appropriate laser light results in light-dose-dependent vascular damage with all three compounds. Localization of ALA following i.p. injections in embryos, whose CAMs have been implanted with rat ovarian cancer cells to produce nodules, is determined in real time by fluorescence of the photoactive metabolite protoporphyrin IX (PpIX). Dose-dependent fluorescence in the normal CAM vasculature and the tumor implants confirms the uptake of ALA from the peritoneum, systemic circulation of the drug, and its conversion to PpIX.

5-Aminolaevulinic acid-induced protoporphyrin IX accumulation in tissues: pharmacokinetics after oral or intravenous administration

In this study, the biodistribution of 5-aminolaevulinic acid (ALA) and accumulation of protoporphyrin IX (PpIX) in rats have been examined. Two groups of 21 WAG/Rij rats are given 200 mg/kg ALA orally or intravenously. Six rats serve as controls. At 1, 2, 3, 4, 6, 12 and 24 h after ALA administration, ALA and porphyrin concentrations are measured in 18 tissues and fluids. Liver enzymes and renal-function tests are measured to determine ALA toxicity. In both groups ALA concentration is highest in kidney, bladder and urine. After oral administration, high concentrations are also found in duodenal aspirate and jejunum. Mild, short-lasting elevation of creatinine is seen in both treatment groups. Porphyrins, especially PpIX, accumulate mainly in duodenal aspirate, jejunum, liver and kidney (> 10 nmol/g tissue), less in oesophagus, stomach, colon, spleen, bladder, heart, lung and nerve (2-10 nmol/g tissue), and only slightly in plasma, muscle, fat, skin and brain (< 2 nmol/g tissue). In situ synthesis of porphyrins rather than enterohepatic circulation contributes to the PpIX accumulation. Confocal laser scanning microscopy shows selective porphyrin fluorescence in epithelial layers. Peak levels and total production of porphyrins are equal after oral and intravenous ALA administration.

IN CONCLUSION

administration of 200 mg/kg ALA results in accumulation of photosensitive concentrations of PpIX, 1 to 6 h after ALA administration, in all tissues except muscle, fat, skin and brain. Knowledge of the time-concentration relationship should be helpful in selecting dosages, routes of administration and timing of ALA photodynamic therapy.

Protoporphyrin IX fluorescence induced in basal cell carcinoma by oral delta-aminolevulinic acid

Limited depth of penetration significantly limits photodynamic therapy of nodular basal cell carcinoma (BCC) using topical delta (5)-aminolevulinic acid (ALA). To demonstrate safety and efficacy of orally administered ALA in inducing endogenous protoporphyrin IX (PpIX) production in BCC, 13 patients with BCC ingested ALA in a dose-escalation protocol. All dose ranges (10, 20 or 40 mg/kg single doses) resulted in formation of PpIX in human skin and BCC, measurable by in vivo fluorescence spectrophotometry. The PpIX fluorescence peaked in tumors before normal adjacent skin from 1 to 3 h after ALA ingestion. Gross fluorescence imaging of ex vivo specimens revealed greater PpIX fluorescence in tumor than normal skin only at the 40 mg/kg dose. Fluorescence microscopy confirmed this finding by showing distinct, full-thickness PpIX fluorescence in all subtypes of BCC only after ALA given at 40 mg/kg. Side effects were dose dependent and self limited. Photosensitivity lasting less than 24 h and nausea coinciding with peak skin PpIX fluorescence occurred at 20 and 40 mg/kg doses. After 40 mg/kg ALA, serum hepatic enzyme levels rose to a maximum within 24 h, then resolved over 1-3 weeks. Transient bilirubinuria occurred in two patients.

Interstitial photodynamic therapy in the canine prostate with disulfonated aluminum phthalocyanine and 5-aminolevulinic acid-induced protoporphyrin IX

BACKGROUND

Photodynamic therapy (PDT) is an experimental approach for treating prostate cancer localized to the gland that does not involve surgery or irradiation. Second-generation photosensitizers 5-aminolevulinic acid (ALA) and aluminum disulfonated phthalocyanine (AlS2Pc) were studied in the normal canine prostate.

METHODS

Tissue biodistribution of photosensitizers on serial biopsies was examined using fluorescence microscopy. Photodynamic therapy was done by delivering red light interstitially at 100 mW through fibers placed under transrectal ultrasound guidance.

RESULTS

Peak levels of AlS2Pc appeared at 5-24 hr and at 3 hr for ALA. Macroscopic PDT lesions were up to 12 mm in diameter using AlS2Pc, but only 1-2 mm with ALA. Light at 300 mW caused thermal lesions. At 28 days, damaged glands remained atrophic, but the interlobular supporting stroma was well-preserved. Urethral lesions healed by 28 days without functional impairment.

CONCLUSIONS

Although the results with ALA were disappointing, PDT using AlS2Pc looks like a promising modality for treatment of localized prostate cancer.

5-Aminolevulinic acid-based photodynamic therapy. Clinical research and future challenges

BACKGROUND

Photodynamic therapy (PDT) for cancer patients has developed into an important new clinical treatment modality in the past 25-years. PDT involves administration of a tumor-localizing photosensitizer or photosensitizer prodrug (5-aminolevulinic acid [ALA], a precursor in the heme biosynthetic pathway) and the subsequent activation of the photosensitizer by light. Although several photosensitizers other than ALA-derived protoprophyrin IX (PpIX) have been used in clinical PDT, ALA-based PDT has been the most active area of clinical PDT research during the past 5 years. Studies have shown that a higher accumulation of ALA-derived PpIX in rapidly proliferating cells may provide a biologic rationale for clinical use of ALA-based PDT and diagnosis. However, no review updating the clinical data has appeared so far.

METHODS

A review of recently published data on clinical ALA-based PDT and diagnosis was conducted.

RESULTS

Several individual studies in which patients with primary nonmelanoma cutaneous tumors received topical ALA-based PDT have reported promising results, including outstanding cosmetic results. However, the modality with present protocols does not in general, appear to be superior to conventional therapies with respect to initial complete response rates and long term recurrence rates, particularly in the treatment of nodular skin tumors. Topical ALA-PDT does have the following advantages over conventional treatments: it is noninvasive; it produces excellent cosmetic results; it is well tolerated by patients; it can be used to treat multiple superficial lesions in short treatment sessions; it can be applied to patients who refuse surgery or have pacemakers and bleeding tendency; it can be used to treat lesions in specific locations, such as the oral mucosa or the genital area; it can be used as a palliative treatment; and it can be applied repeatedly without cumulative toxicity. Topical ALA-PDT also has potential as a treatment for nonneoplastic skin diseases. Systemic administration of ALA does not seem to be severely toxic, but the advantage of using this approach for PDT of superficial lesions of internal hollow organs is still uncertain. The ALA-derived porphyrin fluorescence technique would be useful in the diagnosis of superficial lesions of internal hollow organs.

CONCLUSIONS

Promising results of ALA-based clinical PDT and diagnosis have been obtained. The modality has advantages over conventional treatments. However, some improvements need to be made, such as optimization of parameters of ALA-based PDT and diagnosis; increased tumor selectivity of ALA-derived PpIX; better understanding of light distribution in tissue: improvement of light dosimetry procedure; and development of simpler, cheaper, and more efficient light delivery systems.

Photodynamic therapy using 5-aminolevulinic acid for premalignant and malignant lesions of the oral cavity

BACKGROUND

Premalignant changes in the mouth, which are often widespread, are frequently excised or vaporized, whereas cancers are treated by excision or radiotherapy, both of which have cumulative morbidity. Photodynamic therapy (PDT) is another option that produces local tissue necrosis with light after prior administration of a photosensitizing agent. This heals with remarkably little scarring and no cumulative toxicity. This article describes the use of PDT with the photosensitizing agent 5-aminolevulinic acid (ALA) for premalignant and malignant lesions of the mouth.

METHODS

Eighteen patients with histologically proven premalignant and malignant lesions of the mouth were sensitized with 60 mg/kg ALA by mouth and treated with laser light at 628 nanometers (100 or 200 Joules/cm2). The results were assessed macroscopically and microscopically. Biopsies were taken immediately prior to PDT for fluorescence studies, a few days after PDT to assess the depth of necrosis, when healing was complete, and up to 88 weeks later.

RESULTS

The depth of necrosis varied from 0.1 to 1.3 mm, but complete epithelial necrosis was present in all cases. All 12 patients with dysplasia showed improvement (repeat biopsy was normal or less dysplastic) and the treated areas healed without scarring. Some benefit was observed in five of six patients with squamous cell carcinoma, but only two became tumor free (one with persistent mild dysplasia). No patient had cutaneous photosensitivity for longer than 2 days.

CONCLUSIONS

PDT using ALA for dysplasia of the mouth produces consistent epithelial necrosis with excellent healing and is a simple and effective way to manage these patients. Results in invasive cancers are less satisfactory, mainly because the PDT effect is too superficial with current treatment regimens using ALA as the photosensitizing agent.

Photodynamic therapy on the normal rabbit larynx with phthalocyanine and 5-aminolaevulinic acid induced protoporphyrin IX photosensitisation

Photodynamic therapy (PDT) is a promising technique for the treatment of small tumours in organs where it is essential to minimise damage to immediately adjacent normal tissue as PDT damage to many tissues heals by regeneration rather than scarring. As preservation of function is one of the main aims of treating laryngeal tumours, this project studied the effects of PDT on the normal rabbit larynx with two photosensitisers, endogenous protoporphyrin IX (PPIX) induced by the administration of 5-aminolaevulinic acid (ALA) and disulphonated aluminium phthalocyanine (AIS2Pc). The main aims of the study were to examine the distribution of protoporphyrin IX and AIS2Pc by fluorescence microscopy in the different regions of the larnyx and to assess the nature and subsequent healing of PDT damage. Peak levels of PPIX were found 0.5-4 h after administration of ALA (depending on dose) with highest levels in the epithelium of the mucosa. With 100 mg kg-1, PDT necrosis was limited to the mucosa, whereas with 200 mg kg-1 necrosis extended to the muscle. With 1 mg kg-1 AIS2Pc, 1 h after administration, the drug was mainly in the submucosa and muscle, whereas after 24 h, it was predominantly in the mucosa. PDT at 1 h caused deep necrosis whereas at 24 h it was limited to the mucosa. All mucosal necrosis healed by regeneration whereas deeper effects left some fibrosis. No damage to cartilage was seen in any of the animals studied. The results of this study have shown that both photosensitisers are suitable for treating mucosal lesions of the larynx, but that for both it is important to optimise the drug dose and time interval between drug and light to avoid unacceptable changes in normal areas.