Interstitial Photodynamic Therapy in the CanineProstate With Disulfonated AluminumPhthalocyanine and 5-Aminolevulinic

Acid-Induced Protoporphyrin IX

Shi-Chung Chang,1,2* Giovanni A. Buonaccorsi,1 Alexander J. MacRobert,1 andStephen G. Bown1

1National Medical Laser Center, Department of Surgery, University College London MedicalSchool, London, UK

2Department of Urology, Tzu-Chi General Hospital and College of Medicine,Hua-Lien, Taiwan

BACKGROUND. Photodynamic therapy (PDT) is an experimental approach for treatingprostate cancer localized to the gland that does not involve surgery or irradiation. Second-generation photosensitizers 5-aminolevulinic acid (ALA) and aluminum disulfonated phtha-locyanine (AlS2Pc) were studied in the normal canine prostate.METHODS. Tissue biodistribution of photosensitizers on serial biopsies was examined usingfluorescence microscopy. Photodynamic therapy was done by delivering red light intersti-tially 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 PDTlesions were up to 12 mm in diameter using AlS2Pc, but only 1–2 mm with ALA. Light at 300mW caused thermal lesions. At 28 days, damaged glands remained atrophic, but the inter-lobular supporting stroma was well-preserved. Urethral lesions healed by 28 days withoutfunctional impairment.CONCLUSIONS. Although the results with ALA were disappointing, PDT using AlS2Pclooks like a promising modality for treatment of localized prostate cancer. Prostate 32:89–98,1997. © 1997 Wiley-Liss, Inc.

KEY WORDS: fluorescence microscopy; photodynamic therapy; 5-aminolevulinic acid;phthalocyanine; prostate

INTRODUCTION

There is considerable interest in developing newmodalities for treating prostate cancer, but little workhas yet been done on one of the most promising tech-niques, photodynamic therapy (PDT). PDT is a tech-nique which combines the administration of photosen-sitizing agents with subsequent illumination of thetarget organ with light of an appropriate wavelengthto be absorbed by the photosensitizer. This causes lo-calized tissue necrosis by photochemical mechanisms.A few studies concerning the optical properties of theprostate and the effectiveness of PDT in prostate tissuehave been reported in vitro [1] and ex vivo [2,3]. Pan-

telides et al. [2] reported that the prostate was a favor-able organ for interstitial PDT, as the delivered lightwas predominantly scattered rather than absorbedwithin the gland, making it feasible to treat the entiregland with a relatively small number of fiber sites. Inan ex vivo human prostate model, Chen et al. [4]found no measurable difference in optical propertiesbetween normal and cancer tissue of the human pros-tate.

*Correspondence to: Dr. Shi-Chung Chang, Department of Urology,Tzu-Chi General Hospital and College of Medicine, 501, Section 3,Chaeng-Yang Rd, Hua-Lien, Taiwan, China.Received 22 February 1996; Accepted 30 April 1996

The Prostate 32:89–98 (1997)

© 1997 Wiley-Liss, Inc.

Canine prostate is the most frequently used modelfor PDT studies, as there is insufficient prostate tissuein smaller animals or even in minipigs. Previously,lesions in canine prostate as large as 1.7 cm in diam-eter were produced by PDT using dihematoporphyrinester/ether (Photofrin) [4,5], but the skin photosensi-tization caused by this particular photosensitizer,which lasted 4–6 weeks, was a major concern [6]. PDTwith the newer photosensitizer Tin(II) etiopurpurinwas able to produce hemorrhagic necrosis up to 1 cmfrom the urethra in canine prostate after transurethrallight illumination [7]. This paper looks at the effects ofPDT in the same animal model with two further pho-tosensitizers, 5-aminolevulinic acid (ALA)-inducedprotoporphyrin IX (PpIX) and aluminum disulfonatedphthalocyanine (AlS2Pc) [8,9]. These photosensitizershave the major advantage of causing less skin photo-sensitivity, ALA because it is cleared from the bodywithin 1–2 days, and AlS2Pc because it only absorbs inthe red and very little at other wavelengths in the solarspectrum (apart from some absorption in the ultravio-let) [10].

ALA is a photosensitizer precursor currently underextensive experimental and clinical assessment [8,11–14]. It is an endogenous intermediate in the biosyn-thetic pathway for heme in living cells. Through aseries of chain reactions, ALA is metabolized to pro-toporphyrin IX (PpIX) before being converted to pho-toinactive heme [15]. As the conversion of photoactivePpIX to heme is the rate-limiting step in this reaction,excess exogenous ALA will result in temporary accu-mulation of PpIX for tissue photosensitization. Asheme-containing enzymes are essential for mitochon-drial energy production, cells of different biologicalactivities have different demands and so build up dif-ferent levels of PpIX in situ when excess ALA is given.

The phthalocyanines (PC) are synthetic azaporphy-rin derivatives which chemically mimic naturally oc-curring porphyrins in many respects. With the incor-poration of a diamagnetic aluminum ion in the struc-ture and with various degrees of sulfonation, thealuminum sulfonated phthalocyanines (AlSPc) havesome of the physical, chemical, and biological charac-teristics of an ideal photosensitizer [9]. Apart from thelower risk of skin photosensitivity [10], the strong ab-sorption of red light at 675–700 nm is superior to thatof Photofrin at 630 nm in terms of tissue penetration(50% deeper) and extinction coefficient (50 timeshigher) [16]. Among the various aluminum sulfonatedderivatives, the disulfonated one has been shown to bethe best for PDT [17].

In this study, we examined the in vivo efficacy ofPDT using ALA-induced PpIX and AlS2Pc on the nor-mal dog prostate. The objective was to understand the

biodistribution of these photosensitizers after drug ad-ministration, and the nature and extent of PDT effectsafter interstitial light delivery.

MATERIALS AND METHODS

Animals and Anesthesia

Eleven mature beagles were used for this study (6–7years old, 12–16 kg). The animals were premedicatedwith fentanyl/fluanisone (Hypnorm, Janssen, Oxford,UK), 0.1–0.2 ml/kg by intramuscular injection. Afterintubation they were maintained under inhalation an-esthesia using halothane 1–2% and nitrous oxide as a50:50 or 60:40 mixture with oxygen on a Magills an-esthetic circuit. Stable anesthesia was maintainedthroughout the procedures and recovery was unevent-ful in all cases. Postoperatively, all animals received a3-day course of prophylactic antibiotics (2.5% enro-floxacin, 0.2 ml/kg) and a single dose of nonsteroidalantiinflammatory analgesic (flunixin meglumine, 1mg/kg) by subcutaneous injection, and they werekept in a dimly lighted area. They were carefully ob-served for any sign of urinary problems or generalphysical distress.

Photosensitizers

5-aminolevulinic acid in the form of powder (ALA-HCl 98%) was obtained from DUSA Pharmaceuticals,Inc. (New York, NY), dissolved in normal saline, andtitrated with saturated sodium bicarbonate solution topH 4, giving a final concentration of 10% (100 mg/ml).AlS2Pc was supplied by the Department of Chemistry,Imperial College, London, and dissolved in 0.1 M so-dium hydroxide before being buffered to pH 7.4 withNaH2PO4. The photosensitizing agents were giventhrough a 0.2-micrometer filter into an antecubitalvein. Four animals received 200 mg/kg ALA, and 4received 1 mg/kg AlS2Pc (1 for pharmacokinetics and3 for PDT for each drug). An additional 2 animalsreceived 100 mg/kg ALA for PDT in an attempt toreproduce the results of Johnson et al. [18].

Transrectal Ultrasound-Guided Prostate Biopsy

After shaving and cleaning the perineal area withchlorhexidine, a biplaner transrectal ultrasound probe(Model UST 664, 5/7.5 MHz; Aloka, San Jose, CA),which allowed for longitudinal and transverse pros-tate scanning, was inserted into the anus. The tip ofthe probe was placed 7–8 cm above the anal verge toguide the percutaneous advance of an 18-gauge bi-opsy needle which was mounted on a spring operat-ing device. Following photosensitizer injection, biop-

90 Chang et al.

sies were taken from the prostate at 15 and 30 min andat 1, 3, 5, and 24 hr for ALA, and at 1, 3, 5, 24, and 48hr and 7 days for AlS2Pc. Biopsies in the first 5 hr weretaken under the initial anesthetic, while those at sub-sequent times were obtained under separate heavy se-dation with intramuscular fentanyl/fluanisone 0.1–0.2ml/kg (Hypnorm) with a supplementary oxygenmask. Two or three biopsies were taken from eachprostate at each time point. The time needed to takethree biopsies was about 5–10 min. The specimenswere placed on a sheet of paper and immersed in pre-cooled isopentane (BDH Chemicals Ltd., Poole, UK)before being stored in liquid nitrogen for subsequentpreparation of cryosections.

Fluorescence Microscopy

An inverted phase-contrast epifluorescence micro-scope (Olympus IMT-2; Olympus, Hamburg, Ger-many) attached to an 8 mW helium neon laser (632.8nm) was used for examination of fluorescence fromthe biopsy specimens. The laser output was passedthrough a 10-nm band-pass filter and then directedonto the cryosection with a liquid light guide and di-chroic mirror. The emitted fluorescence was detectedbetween 665–710 nm (with maximum response at 690nm), using a combination of band-pass and long-pass(Omega Optical Inc., Brattleboro VT) filters, and im-aged through a high-resolution (385 × 578 pixels)slow-scan charge-coupled device (CCD) camera(Model 1, Wright Instruments Ltd., Cambridge, UK)fitted to the microscope. Image processing and cameraoperation were carried out by an IBM personal com-puter which converted the fluorescence signals (incounts per pixel) into a falsely color-coded image. Thesoftware also enabled fluorescence signals in each tis-sue block to be quantified digitally by averaging overspecific areas. The quantification of fluorescence inten-sity at each time point was done by taking the averageof results calculated from at least five different sec-tions. After fluorescence imaging, the sections werefixed in formalin and stained with hematoxylin andeosin for histological study.

Laser and Light-Delivery Systems

Red light at wavelengths of 630 and 675 nm (forALA and AlS2Pc, respectively) was supplied by a KTP(Potassium Titanyl Phosphate) laser pumping a DyeLaser Model 630 (Laserscope, San Jose, CA). For PDT,a biopsy needle was positioned transperineally undertransrectal ultrasound guidance, and a 600-mm bare-tip fiber inserted through it until the tip was 8–10 mmbeyond the bevel (Fig. 1). Exposure time for AlS2Pc-sensitized beagles was 1,000 sec at 100 mW, giving a

total energy of 100 J for each treatment. For ALA andAlS2Pc, drug and light doses are shown in Table I. Thelaser power was checked before and after each treat-ment.

PDT Treatment

Two animals were treated at the wavelength of 630nm, and at a power of 100 or 300 mW to a total doseof 100–1,080 J without prior photosensitization, as con-trols. From the fluorescence study results, the timebetween sensitization and light delivery chosen forALA was 3 hr, as this was the time at which the high-est levels of PpIX were found, but in view of the find-ings of Johnson et al. [18], 2 further animals weretreated with a time interval of 8 hr. For AlS2Pc, thetime interval chosen was 24 hr as peak tissue levelswere seen at this time. One or two sites were treated ineach animal, one near the prostate capsule and theother near the urethra. Details are given in Table I.After treatment, the animals were kept in a dimlylighted chamber for careful further observation. Theywere killed with expiral (pentobarbitone 120 mg/kgbody weight), 3, 7, and 28 days after PDT, and blad-ders and prostates were removed en bloc. For grossinspection, specimens were sectioned serially from thebladder neck to the apical region at intervals of 3–5mm according to the extent of the lesion. The maxi-mum diameter of each zone of PDT-induced necrosiswas measured macroscopically on these blocks. Blocksof interest were then fixed and sent for histologicalassessment with H & E and Van Gieson’s stains.

RESULTS

Pharmacokinetic Studies

In the control animal that received no photosensi-tizer, no PpIX or AlS2Pc fluorescence was detectable.In the animal given ALA, significant levels of PpIX

Fig. 1. Transrectal ultrasound, showing a laser fiber in the pros-tate (arrowhead).

PDT of the Prostate 91

were not seen until 1 hr after administration with apeak at 3 hr, returning to background levels by 24 hr(Fig. 2). In the animal given AlS2Pc, the fluorescenceintensity showed a steady increase in the first 5 hr andthen maintained a plateau to 48 hr before starting tofall. AlS2Pc was still detectable at 7 days at about thesame level as that found at 3 hr (Fig. 3). Fluorescencemicroscopy 24 hr after AlS2Pc showed accumulationof the photosensitizer in both the stroma and glandu-lar tissue (Fig. 4).

Photodynamic Effects

Macroscopic findings. No lesion was seen in controlanimals receiving 100 or 300 J at 100 mW, but a large

lesion (10 × 9 × 9 mm) was seen in the control animalreceiving 1080 J at 300 mW (Fig. 5A). With ALA, onlytiny hemorrhagic lesions 1–2 mm in diameter werefound 3 days after PDT with the laser power at 100mW (360 J), but a much larger lesion with central cavi-tation (9 × 9 × 9 mm) was created using 300 mW (1,080J) 8 hr after ALA (Fig. 5B). In contrast, PDT withAlS2Pc produced lesions up to 12 mm in diameterwith laser power and exposure times that had no ef-fect in unsensitized animals. The 3-day lesion was awell-circumscribed hemorrhagic necrotic area withoutcavitation, measuring 12 × 10 × 10 mm (Fig. 6). Thestructures overlying the prostate were intact, althoughthe lesion did not quite reach the capsule. Lesions at 7days were slightly smaller (10 × 9 × 9 and 9 × 9 × 8

TABLE I. Treatment Parameters and Macroscopic Results

Animalno.

Sensitizer (mg/kg)Sensitization

time (hr)Power(mW)

Illuminationtime (sec)

Lightdose (J)

Animalkilled (day)

Lesionsize (mm)ALA AlS2Pc

1 100 1,000 100 3 Nil300 3,600 1,080 3 10 × 9 × 9

2 100 3,600 360 3 Nil3 100 8 100 1,000 100 3 2 × 2 × 24 100 8 300 3,600 1,080 3 9 × 9 × 9

100 8 100 3,600 360 3 2 × 1 × 15 200 3 100 1,000 100 3 2 × 1 × 16 200 3 100 1,000 100 7 Nil7 200 3 100 1,000 100 28 Nil8 1 24 100 1,000 100 3 12 × 10 × 109 1 24 100 1,000 100 7 10 × 9 × 9

1 24 100 1,000 100 7 9 × 9 × 810 1 24 100 1,000 100 28 10 × 8 × 8

1 24 100 1,000 100 28 6 × 5 × 5

Fig. 2. Plot of protoporphyrin IX fluorescence in prostateagainst time after intravenous administration of ALA. Data shownare the means from 10–20 blocks (50 × 50 pixels) from threebiopsies at each time point. The single point in an animal given 100mg/kg was from an experiment designed to reproduce the resultsof Johnson et al. [18].

Fig. 3. Plot of AlS2Pc fluorescence in prostate against time afterintravenous administration of 1 mg/kg AlS2Pc. Data shown are themeans from 10–12 blocks (50 × 50 pixels) from three biopsies ateach time point.

92 Chang et al.

mm) and less hemorrhagic than those seen at 3 days(Fig. 7). Four weeks after PDT, wedge-shaped fibroticscars measuring 10 × 8 × 8 and 6 × 5 × 5 mm wereformed beneath the prostate capsule (Fig. 8), but noevidence of deformity of the gland as a whole wasseen.

Histology. The control prostates treated at lower laserpower (100 mW) had no detectable lesions, macro-scopically or microscopically. However, at the higherpower of 300 mW, peripheral coagulation necrosis andcentral cavitation were found around the fiber site 3days after treatment, typical of a thermal effect (Fig.5A). The tiny lesions seen after PDT with ALA at lowlaser power showed hemorrhagic necrosis, but thelarger lesion seen after treatment at 300 mW (Fig. 5B)had microscopic features similar to those of the controlanimal treated with 300 mW, strongly suggesting thatit was produced by a thermal and not a PDT effect. Incontrast, the lesion seen 3 days after PDT with AlS2Pcshowed extensive hemorrhagic necrosis of the glandu-lar epithelium, with relative sparing of interlobularcollagenous fibrils. The demarcation between the ne-crosed zone and normal glandular areas was sharplydefined (Fig. 9). By 7 days there was marked infiltra-tion of inflammatory cells. Glands were still atrophicat 28 days. There was damage to the acinar collagen,but the collagen and other connective tissues in theinterlobular stroma were well-preserved through thefollow-up period (Fig. 10). The lesion studied at 3 daysdid not include the urethra, but one of the lesions at 7days showed suburethral edema, congestion, fibro-blast infiltration, and early urethral reepithelializationwithout definite hemorrhagic necrosis. By day 28, theepithelial lining of the prostatic urethra appeared nor-mal in the treated area, but the periurethral tissueshowed evidence of inflammatory cell and fibroblastinfiltration consistent with safe healing in this area.

Perioperative responses. No animal had any adverseeffects associated with the laser procedures duringthis study. One animal developed a urinary tract in-fection with mild hematuria 5 days after prostate bi-opsy, which was successfully treated with 2.5% enro-floxacin (0.2 ml/kg) for 3 days, but no others had anymacroscopic hematuria, difficulty in urination, or signof any general physical distress.

DISCUSSION

Programs for screening for prostate cancer remaincontroversial, but with more widespread use of serumprostate-specific antigen (PSA), it is likely that moreearly cases will be detected [19,20]. The American Uro-logical Association recommends measurement of se-rum PSA, with or without digital rectal examination

(DRE), as a means for detecting clinically significantearly cancers [21]. Inevitably, these patients will seekeffective treatments which carry a low morbidity [22].However, so far, the only effective modalities for con-trolling organ-confined prostate cancers are radicalprostatectomy or radical radiotherapy, both of whichare associated with a significant incidence of compli-cations [23]. PDT, with its collagen-sparing effect,could provide an alternative with the potential for lo-cal eradication while maintaining the integrity of theanatomical structures of the prostatic region aftertreatment. Encouraged by the preliminary results re-ported by Windahl et al. [24], we investigated PDTeffects on the canine prostate to evaluate the feasibilityand effectiveness of interstitial laser illumination us-ing the photosensitizing agents ALA and AlS2Pc. Inorgans other than the prostate, both have been studiedextensively in animal models [10–14,25] and prelimi-nary reports using ALA clinically are now appearing[8,26,27]

Our results of ALA-mediated PDT in the canineprostate are disappointing. The only lesion >1–2 mmin diameter was the one produced with the high laserpower of 300 mW, and an essentially identical lesionwas seen in a control animal treated with the samelaser power and treatment time but without ALA,strongly suggesting that the lesion in the sensitizedanimal was a thermal rather than a PDT effect. Thiswas confirmed by the histological findings. Johnson etal. [18] recently reported hemorrhagic necrosis up to10 mm in depth in a normal canine prostate 1 weekafter PDT (8 hr after 100 mg/kg ALA given intrave-nously), using a 2-cm diffuser fiber transurethrallywith a high light dose (650 mW for 45 min, 1755 J). Nolesion was seen in an unsensitized animal treated withthe same light dose. These findings are inconsistentwith our present results. They used a different lightdelivery system (diffuser transurethrally vs. bare fiberinterstitially), with a higher laser power and longersensitization time (8 vs. 3 hr), but the striking differ-ence which cannot be explained by these factors is thatthey saw no lesion in their control animal, whereas wedid in the one treated at 300 mW, even though we onlyused an energy of 1,080 J compared with their 1,755 J.Further experiments are required to resolve this dis-crepancy.

The depth of PDT effect may relate to the dose androute of administration of ALA as well as to the organbeing treated. The maximum dose that can be toler-ated clinically is 60 mg/kg orally (equivalent to 30mg/kg intravenously), and with this it only appearspossible to get necrosis up to 1–2 mm in depth ingastrointestinal tumors [27]. In contrast, lesions up to8 mm deep (comparable to the depth of effect reportedby Johnson et al. [18] have been reported using 200

PDT of the Prostate 93

mg/kg intravenously in papillomas in rabbits [28] and400 mg/kg orally (equivalent to 200 mg/kg intrave-nously) in cancers transplanted into the hamster pan-creas [11]. We could only get 1–2 mm of necrosis in theprostate using 200 mg/kg. It is possible that higherlevels of PpIX will be found in prostate cancers than inthe normal gland, but the first report on treatment oforal cancers using systemic ALA [29] showed that

even if there is more PpIX in the cancer, both cancerand normal tissue are necrosed if both are exposed tothe therapeutic light, so that there is unlikely to be anymore necrosis in a prostate cancer than we found innormal prostate. Giving ALA intravesically to rats(200 mg/kg), urothelial levels of PpIX are comparableto those seen in the prostate in the present work, andwith appropriate light doses, these levels can destroy

Fig. 4 Fluores-cence microscopy,showing accumula-tion of AlS2Pc in thestroma and glands(G1) 24 hr aftersensitization. Highconcentration, blue;low concentration,orange/black (abso-lute intensity in arbi-trary units).

Fig. 5. a: Control prostate at 300 mW, 1,080 J, but without ALA. b: After PDT with ALA (100 mg/kg). Right: 300 mW, 1,080 J (blackarrow). Left: 100 mw, 360 J (white arrow). All lesions shown 3 days after PDT.

94 Chang et al.

Fig. 6. Prostate lesion 3 days after PDT, withAlS2Pc at a light dose of 100 J (100 mW for 1,000sec) delivered interstitially through a single fiber.

Fig. 7. Prostate lesion near urethra 7 days after PDT, withAlS2Pc at a light dose of 100 J (100 mW for 1,000 sec) deliveredinterstitially through a single fiber.

Fig. 8. Subcapsular prostate lesion 28 days after PDT, withAlS2Pc at a light dose of 100 J (100 mw for 1,000 sec) deliveredinterstitially through a single fiber. There is no change in basic sizeand shape of the gland.

Fig. 9. Hemorrhagic necrosis in the prostate 3days after PDT, with AlS2Pc. There is clear de-marcation between the necrosed and undamagedareas (×40, H&E stain). The fiber was placed be-neath the capsule, and the lesion did not extendas far as the urethra.

the urothelium without damaging the underlyingmuscle [13]. However, the thickness of the rat bladderwall is <1 mm, so that the absolute depth of effect is nogreater than what we found in the prostate. ALA lookspromising for treating superficial lesions with PDT,but more questionable when a greater depth of effectis required, as in management of prostate cancer.From our results, PDT with ALA is not likely to be ofvalue for treating the prostate unless ways are foundto markedly increase the depth of necrosis produced.Just increasing the light dose seems unlikely to do this,although there could be some benefit from fractionat-ing the light [30].

The situation with AlS2Pc is much more promising.The lesions produced in the prostate were well-circumscribed and up to 12 × 10 × 10 mm. They healedwithout disruption of the basic connective tissue ar-chitecture of the organ, as has been shown in otherorgans [31]. This is of particular importance for treat-ing prostate cancer, since preservation of anatomicalalignment between the bladder neck and external ure-thral sphincter is the best way to avoid the major com-plications that may arise from radical surgery. It isalso likely to make it safe to treat large areas of thegland, which is important as the disease is often mul-tifocal and occurs in the peripheral zone close to sur-rounding vital structures such as the neurovascularbundle, rectum, and urethral sphincter. The prostatecapsule seems unlikely to be significantly affected byPDT, but if PDT effects do extend to the rectum ormajor blood vessels, using AlS2Pc, it is well-documented that the resultant lesions heal withoutany unacceptable effects on their structure or function[31,32]. There are no good experimental studies on theeffect of PDT using AlS2Pc (or indeed any other pho-

tosensitizer) on peripheral nerves, although our ownfluorescence microscopy data suggest that very littleAlS2Pc is taken up in nerve bundles (unpublisheddata). It is one of the greatest attractions of PDT that itis possible to treat not only the target organ, but alsoadjacent normal tissues, in the knowledge that if le-sions are produced in these other tissues, they arelikely to heal by regeneration without serious sequel-ae. Thus it should be feasible to treat the entire pros-tate and a margin of surrounding tissues safely. Theone tissue that may be at risk is the sphincteric com-plex. Muscle heals better after PDT than after thermalinjury, but there may be significant impairment offunction [33]. No studies have yet looked at the effectof PDT on sphincter function, but it should normallybe possible to treat the entire prostate without signifi-cant light doses reaching the sphincter region if thelight can be properly applied interstitially or througha well-designed transuretheral balloon catheter. Ourresults suggest that although the prostatic urethramay be damaged, it heals satisfactorily without steno-sis at any time after treatment, although to be sure ofthis it would be necessary to undertake further experi-ments producing larger PDT lesions in the immediatevicinity of the urethra. Another concern is urinary re-tention due to edema, which is likely if a large volumeof tissue is destroyed around the urethra. This maycause problems in experimental animals, but is un-likely to pose a particular hazard in clinical practice asit can be managed by temporary catheterization.

PDT initially attracted so much interest because ofthe selectivity of uptake of photosensitizers betweenmalignant tumors and the adjacent normal tissue inwhich the tumor arose. This aspect, however, has beenconsiderably overemphasized, as it is difficult to turn

Fig. 10. Prostate 28 days after PDT, withAlS2Pc showing atrophic glands with preservationof collagen fibrils in the stroma (×60, HVG stain).Open arrows, atrophic glands; short arrows, stroma;long arrows, unaffected gland.

96 Chang et al.

selectivity of uptake of a photosensitizer (typically inthe range of 2–3:1) into selective tumor necrosis whenboth are exposed to the same light dose, as will inevi-tably be the case when treating the region where tu-mor meets normal tissue. Nevertheless, it is logical tochoose the time interval between photosensitizationand light delivery to be that at which the ratio of pho-tosensitizer between tumor and normal tissue is great-est. There are no data on this for the prostate, but in arat colon cancer model, the best ratio (2:1) was found48 hr after giving AlSPc (a mixture of mono-, di-, tri-,and tetrasulfonated derivatives), although there wasno great difference between 24 and 48 hr [25]. In thepresent experiments, the tissue level of AlS2Pc in theprostate was roughly constant between 5–48 hr afterphotosensitization, so it was decided to use the middleof this range at 24 hr for the PDT study. Peak levels ofAlS2Pc at these times contrast with the results of Chat-lani et al. [17], who reported a maximum level ofAlS2Pc in the mucosa of normal rat colon 1 hr afteradministration. Similarly, Pope et al. [33] found thehighest levels of AlSPc (not AlS2Pc) in all layers ofnormal rat bladder 1 hr after photosensitization, butby 24 hr there was more in the mucosa than in theunderlying muscle, although the absolute levels werelower in both layers than at 1 hr. With different bio-logical structures in various species, further study isneeded to look at the distribution of AlS2Pc in patientswith prostate cancer to define the relative concentra-tion of photosensitizer in normal and malignant tis-sues, but it is most unlikely that there will be less inthe tumor than in normal tissue. Published data onadenocarcinomas of the colon and pancreas showedthat there was 2–3 times as much AlSPc in the canceras in the normal tissue from which they arose [25]. Thepresent study did not look at skin photosensitivity,but one of the greatest potential advantages of AlS2Pcover Photofrin is the likely lack of serious skin photo-sensitivity [10].

There is no convenient model of prostate cancer inthe dog, but from the literature on other organs, we donot consider this a major problem. If normal prostatecan be necrosed by PDT, it is highly likely that cancerwill respond at least as well, which was the case in ourprevious studies on the colon [14] and pancreas [11].

In conclusion, PDT with ALA does not look prom-ising in the management of prostate cancer, but usingAlS2Pc, it is possible to necrose zones up to 12 mm indiameter around each treatment site with safe healing.Although there are many questions concerning long-term effects of PDT on prostate cancer, and concerningits safety as regards the urethra and sphincter, itwould now appear reasonable to consider pilot clini-cal studies in a few carefully selected patients withsmall cancers localized to the prostate. A suitable

group would be those with localized recurrence afterradical radiotherapy who are considered unsuitablefor salvage surgery.

ACKNOWLEDGMENTS

We are grateful to Dr. D. Rickards, Consultant Ra-diologist at Middlesex Hospital, London, for loan ofthe transrectal ultrasound scanner, and to LaserScope(CA) for loan of the KTP pumped dye laser system.Dr. Shi-Chung Chang is funded by the CompassionRelief of Tsu-Chi Foundation in Taiwan.

REFERENCES

1. Camps JL Jr, Powers SK, Beckman WC Jr, Brown JT, WeissmanRM: Photodynamic therapy of prostate cancer: An in vitrostudy. J Urol 134:1222–1226, 1985.

2. Pantelides ML, Whitehurst C, Moore JV, King TA, Blacklock NJ:Photodynamic therapy for localized prostatic cancer: Light pen-etration in human prostate gland. J Urol 143:398–401, 1990.

3. Whitehurst C, Pantelides ML, Moore JV, Blacklock NJ: Optimi-zation of multifiber light delivery for the photodynamic therapyof localized prostate cancer. Photochem Photobiol 58:589–593,1993.

4. Chen Q, Shetty SD, Heads L, Bolin F, Wilson B, Patterson M,Sirls LT, Schultz D, Cerny JC, Hetzel FW: Photodynamictherapy in prostate cancer: Optical dosimetry and response ofnormal tissue. SPIE 1881:231–235, 1993.

5. Shetty SD, Chen Q, Schultz D, Wilson B, Patterson M, HetzelFW, Cerny JC: Evaluation of prostatic optical properties andtissue response to photodynamic therapy in a canine model.SPIE 2078:416–421, 1994.

6. Dougherty TJ: Photodynamic therapy. Photochem Photobiol 58:895–900, 1993.

7. Selman SH, Keck RW: The effect of transurethral light on thecanine prostate after sensitization with the photosensitizerTin(II) etiopurpurin dichloride: A pilot study. J Urol 152:2129–2132, 1994.

8. Kennedy JC, Pottier RH, Pross DC: Photodynamic therapy withendogenous protoporphyrin IX: Basic principles and presentclinical experience. J Photochem Photobiol [B] 6:143–148, 1990.

9. Ben-Hur E: Basic photobiology and mechanisms of action ofphthalocyanines. In Henderson BW, Dougherty TJ (eds.): ‘‘Pho-todynamic Therapy.’’ New York: Marcel Dekker, 1992, pp 63–77.

10. Tralau CJ, Young AR, Walker NPJ, Vernon DI, MacRobert AJ,Brown SB, Bown SG: Mouse skin photosensitivity with dihema-toporphyrin ether (DHE) and aluminum sulphonated phthalo-cyanine (AlSPc): A comparative study. Photochem Photobiol49:305–312, 1989.

11. Regula J, Ravi B, Bedwell J, MacRobert AJ, Bown SG: Photody-namic therapy using 5-aminolaevulinic acid for experimentalpancreatic cancer-prolonged animal survival. Br J Cancer 70:248–254, 1994.

12. Loh CS, MacRobert AJ, Bedwell J, Regula J, Krasner N, BownSG: Oral versus intravenous administration of 5-aminolevulinicacid for photodynamic therapy. Br J Cancer 68:41–51, 1993.

13. Chang SC, MacRobert AJ, Bown SG: Photodynamic therapy onrat urinary bladder with intravesical instillation of 5-aminolevu-linic acid: Light diffusion and histological changes. J Urol155:1749–1753, 1996.

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14. Bedwell J, MacRobert AJ, Phillips D, Bown SG: Fluorescencedistribution and photodynamic effect of ALA-induced PpIX inthe DMH rat colonic tumor model. Br J Cancer 65:818–824, 1992.

15. Divaris XG, Kennedy JC, Pottier RH: Phototoxic damage to se-baceous gland and hair follicles of mice after systemic admin-istration of 5-aminolaevulinic acid correlates with localized pro-toporphyrin IX fluorescence. Am J Pathol 136:891–897, 1990.

16. Ben-Hur E, Rosenthal I: Action spectrum (600–700 nm) for chlo-roaluminum phthalocyanine-induced phototoxicity in Chinesehamster cells. Lasers Life Sci 1:79–86, 1986.

17. Chatlani PT, Bedwell J, MacRobert AJ, Barr H, Boulos PB, Kras-ner N, Phillips D, Bown SG: Comparison of distribution andphotodynamic effects of di- and tetra-sulphonated aluminumphthalocyanines in normal rat colon. Photochem Photobiol 53:745–751, 1991.

18. Johnson S, Motamedi M, Egger N, Pow-Sang M, Orihuela E,Anderson K, Warren MM: Photosensitizing the canine prostatewith 5-aminolevulinic acid: A new laser prostatectomy? J Urol[Suppl] 153:298 (abstract), 1995.

19. Chodak GW: Questioning the value of screening for prostatecancer in asymptomatic men. Urology 42:116–118, 1993.

20. Partin AW, Oesterling JE: The clinical usefulness of prostaticspecific antigen: Update 1994. J Urol 152:1358–1368, 1994.

21. Catalona WJ, Richie JP, Ahamman FR, Hudson MA, ScardinoPT, Flanigan RC, de Kernion JB, Ratliff TL, Kavoussi LR, DalkinBL, Water WB, MacFarlane MT, Southwick PC: Comparison ofdigital rectal examination and serum prostate specific antigen inthe early detection of prostate cancer—Results of a multicenterclinical trial of 6,630 men. J Urol 151:1283–1290, 1994.

22. Catalona WJ: Screening for prostate cancer: Enthusiasm. Urol-ogy 42:113–115, 1993.

23. Walsh PC, Lepor H: The role of radical prostatectomy in themanagement of prostate cancer. Cancer 60:526–537, 1987.

24. Windahl T, Andersson SO, Lofgren L: Photodynamic therapy oflocalised prostatic cancer. Lancet 336:1139, 1990.

25. Tralau CJ, Barr H, Sandeman DR, Barton T, Lewin MR, BownSG: Aluminum sulfonated phthalocyanine distribution in ro-dent tumors of the colon, brain and pancreas. Photochem Pho-tobiol 46:777–781, 1987.

26. Cairnduff F, Stringer MR, Hudson EJ, Ash DV, Brown SB: Su-perficial photodynamic therapy with topical 5-aminolaevulinicacid for superficial primary and secondary skin cancer. Br JCancer 69:605–608, 1994.

27. Regula J, MacRobert AJ, Gorchein A, Buonaccorsi GA, ThorpeSM, Spencer GM, Hatfield ARW, Bown SG: Photosensitisationand photodynamic therapy of oesophageal, duodenal, and co-lorectal tumours using 5-aminolaevulinic acid induced proto-porphyrin IX—A pilot study. Gut 36:67–75, 1995.

28. Lofgren LA, Ronn AM, Nouri M, Lee CJ, Yoo D, Steinberg BM:Efficacy of intravenous d-aminolaevulinic acid photodynamictherapy on rabbit papillomas. Br J Cancer 72:857–864, 1995.

29. Grant WE, Hopper C, MacRobert AJ, Speight PM, Bown SG:Photodynamic therapy of oral cancer: Photosensitisation withsystemic aminolaevulinic acid. Lancet 342:147–148, 1993.

30. Messmann H, Mlkvy P, Buonaccorsi G, Davies C, MacRobert AJ,Bown SG: Enhancement of photodynamic therapy with 5-ami-nolaevulinic acid induced porphyrin photosensitisation in nor-mal rat colon by threshold and light fractionation studies. Br JCancer 72:589–594, 1995.

31. Barr H, Tralau CJ, Boulos PB, MacRobert AJ, Tilly R, Bown SG:The contrasting mechanisms of colonic collagen damage be-tween photodynamic therapy and thermal injury. PhotochemPhotobiol 46:795–800, 1987.

32. Grant WE, Speight PM, MacRobert AJ, Hopper C, Bown SG:Photodynamic therapy of normal rat arteries after photosensi-tisation using desulphonated aluminum phthalocyanine and5-aminolaevulinic acid. Br J Cancer 70:72–78, 1994.

33. Pope AJ, Bown SG: The morphological and functional changesin rat bladder following photodynamic therapy with phthalo-cyanine photosensitisation. J Urol 145:1064–1070, 1991.

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