TETRAHEDRON Pergamon Tetrahedron 57 *2001) 9513±9547 Tetrahedron report number 591 Photobleaching of sensitisers used in photodynamic therapy Raymond Bonnettp and Gabriel MartõÂnez Department of Chemistry, Queen Mary, University of London, Mile End Road, London E1 4NS, UK Received 12 September 2001 Contents 1.Introduction: tumour phototherapy 9513 2.Photobleaching and PDT 9515 3.Photobleaching studies in solution 9518 3.1. Haematoporphyrin and related photosensitisers *HpD, Photofrinw) 9518 3.2. Protoporphyrin *d-ALA as a prodrug) 9521 3.3. Other b-polyalkylporphyrins 9523 3.4. meso-Tetraphenylporphyrin and its relatives 9524 3.5. Chlorins and bacteriochlorins 9528 3.5.1. 5,10,15,20-Tetrakis*m-hydroxyphenyl)chlorin, m-THPC 10 9528 3.5.2. Benzoporphyrin derivative monoacid A, BPDMA 11 9531 3.5.3. Monoaspartylchlorin e6,MACE13 9531 3.5.4. Purpurin derivatives 9531 3.5.5. Chlorophyll and related compounds 9532 3.6. Phthalocyanine and related compounds 9534 4.Photobleaching studies in cell cultures *in vitro) 9539 4.1. Haematoporphyrin derivative and related compounds 9539 4.2. Second generation photosensitisers 9540 5.Photobleaching studies in vivo 9541 5.1. First generation photosensitisers *Photofrinw) 9541 5.2. Second generation photosensitisers 9541 5.3. Dosimetry 9542 6.Summary and outlook 9543 1. Introduction: tumour phototherapy was a feature of the domestic architecture of the ancient Greeks and Romans and, in India, plant extracts containing The bene®cial and therapeutic properties of light either furocoumarins were administered orally followed by alone or in combination with a chemical agent have long sunlight exposure to treat vitiligo.1a,b In modern times, been recognised by mankind.The solarium, for example, Finsen's seminal work on phototherapy,2 and especially p Corresponding author.Fax: 144-20-7882-7794; e-mail: [email protected] Abbreviations:AAbsorbance; aqAqueous; ArAryl; BPD-MABenzoporphyrin derivative monoacid ring A; Brij 35Polyoxyethylene*23)lauryl ether; cConcentration; CPCCetyl pyridinium chloride; CTABCetyl trimethylammonium bromide; DABCODiazabicyclo[2.2.2]octane; d-ALAd-Amino- laevulinic acid; DDQ2,3-Dichloro-5,6-dicyano-1,4-benzoquinone; DMFDimethylformamide; DMSODimethylsulfoxide; DPPCDipalmitoyl-l-a- phosphatidylcholine; DTABDodecyl trimethylammonium bromide; EPRElectron paramagnetic resonance; FCSFoetal calf serum; hHour*s); HpHaematoporphyrin; HpDHaematoporphyrin derivative; HPLCHigh pressure liquid chromatography; HPMAN-*2-Hydroxypropyl)methacrylamide; HSAHuman serum albumin; kRate constant; MACEMono-l-aspartylchlorin e6; MALDIMatrix assisted laser desorption ionization; minMinute*s); m-THPBC5,10,15,20-Tetrakis*3-hydroxyphenyl)bacteriochlorin; m-THPC5,10,15,20-Tetrakis*3-hydroxyphenyl)chlorin; m-THPP5,10,15,20-Tetra- kis*3-hydroxyphenyl)porphyrin; m-TMeOPP5,10,15,20-Tetrakis*3-methoxyphenyl)porphyrin; MSMass spectrometry; MVMethyl viologen; PBS Phosphate buffered saline; Photofrinw, PhotosanwProprietary names for puri®ed HpD; PDTPhotodynamic therapy; rel.Relative; SDSSodium dodecyl sulfate; SODSuperoxide dismutase; tTime; TTemperature; TPPmeso-Tetraphenylporphyrin; TPPS45,10,15,20-Tetrakis*4-sulphonatophenyl)- porphyrin; UVUltra violet; UV±VisAbsorption spectroscopy; visVisible. 0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd.All rights reserved. PII: S0040-4020*01)00952-8 9514 R. Bonnett, G. MartõÂnez / Tetrahedron 57 .2001) 9513±9547 his successful treatment of lupus vulgaris *a tubercular condition of the skin), established the foundations for the use of light in contemporary medicine.Since then, photo- therapy has been successfully used in the treatment of vitamin D de®ciency, psoriasis, and neonatal hyper- bilirubinemia.1c Photodynamic therapy *PDT) is an emerging treatment for a variety of conditions, but particularly for cancer and for wet age-related macular degeneration.It requires a combination of oxygen, visible light and a drug *a photosensitiser), which causes damage to living tissue.The scienti®c basis for this treatment is the photodynamic effect, which was discovered a century ago by Raab.3 By 1913, Meyer Betz4 had demon- strated the photodynamic effect in the human body in a Figure 1. Modi®ed Jablonski diagram to show Type I and Type II mechan- celebrated *if foolhardy) experiment in which he injected isms *Pporphyrin photosensitiser). himself with a solution of 200 mg of haematoporphyrin 8: subsequent exposure to sunlight caused severe damage to result of energy transfer from the triplet exited state of the his hands and face.Several decades later, in 1942, Auler and photosensitiser to the triplet ground state of the dioxygen Banzer5 observed tumour ¯uorescence and necrosis under molecule *Fig.1). UV light after porphyrin administration in experimental animals.In 1961, Lipson and his colleages 6 reported clear Several sorts of biomolecules, such as unsaturated lipids evidence that a porphyrin preparation *haematoporphyrin *exempli®ed by 1), cholesterol, and side chains of certain derivative, HpD) was selectively taken up by tumours. a-amino acids, such as tryptophanyl 3, histidyl, and Another decade had to pass before Diamond and his methionyl 6 react readily with singlet oxygen, as illustrated coworkers7 proved that such sensitised tumours could be in Scheme 1.These components are essential constituents of destroyed by visible irradiation.In 1976, Kelly and Snell 8 various biological membranes, and it is therefore considered made the ®rst record of a clinical example *a single bladder likely that membrane damage is an important process lead- cancer case, brie¯y reported).Shortly afterwards, an exten- ing to both photonecrosis and vascular shutdown. sive and detailed clinical study was described by Dougherty and his colleagues9 which eventually led to the ®rst regula- In general, the photosensitisers employed in cancer photo- tory approval of a PDT sensitiser *Photofrinw).In 1993, therapy have been porphyrin-type materials: there is no Photofrinw was authorised for use against certain types of reason to suppose that the ®eld is restricted to this series, bladder tumour in Canada, and was later approved for the although some advantages are discernible amongst these treatment of various sorts of tumour in the USA, Japan, and compounds *aromatic stability, high singlet oxygen some European countries.By this time, much effort was quantum yields, apparent lack of dark toxicity, and absorp- being devoted to discover more ef®cient photosensitisers tion in the red region).HpD and its more puri®ed versions, *often referred to as `second generation' sensitisers). such as Photofrinw, Photosanw and Photohemw, were the ®rst photosensitisers employed in PDT and they are referred PDT essentially consists of the following steps: *i) a good to as ®rst generation.HpD is a mixture of porphyrin photosensitiser *and preferably a single substance with a monomers, dimers and oligomers which are formed from straightforward synthesis) is identi®ed which shows some haematoporphyrin 8 as shown in Scheme 2.1c,10 The anti- preferential accumulation in the tumour tissue; *ii) this tumour activity basically resides in the covalently-linked compound is administered and a certain time *the drug- oligomeric fraction, and therefore in the commercial light interval) is allowed to elapse in order to obtain the preparations the less active monomeric fraction is removed maximum differentiation in photonecrosis between normal using HPLC or gel permeation chromatography. and malignant tissue; and *iii) the tumour is irradiated with visible light in order to destroy the abnormal cells.The The ®rst generation photosensitisers, however, possess three photosensitiser is usually administered using an aqueous major drawbacks: their selectivity is low and, consequently, buffer solution or liposomes and the light source is often a skin photosensitivity is a major side effect; absorption in the laser since this can be ef®ciently connected to optical ®bres red region is weak, and so deep tumours are dif®cult to treat; to treat deep tumours with good precision.While the process and the photosensitisers are complex mixtures of active of photosensitiser localisation, which favours tumour components. accumulation, is not really understood, the process of tumour photonecrosis has received mechanistic In designing improved photosensitisers, a number of factors rationalisation. need to be considered in addition to their ease of synthesis.11 A photosensitiser should have: little or no toxicity in the Two oxidative mechanisms are considered to be principally dark; good pharmacokinetic behaviour, i.e. high selectivity involved in the photodestruction of tissue,1c namely Type I for tumour tissue and easy elimination from the body and Type II.In the Type I mechanism, the photosensitiser *amphiphilic character seems to be advantageous); a interacts with a biomolecule *or oxygen) with a resulting constant composition *preferably a single achiral hydrogen atom *or electron) transfer to produce radicals.In substance); a high triplet quantum yield and a triplet the Type II mechanism, singlet oxygen is generated as a energy .94 kJ mol21 with ef®cient energy transfer to R. Bonnett, G. MartõÂnez / Tetrahedron 57 .2001) 9513±9547 9515 Scheme 1. Reactions of singlet oxygen with some biomolecules. produce singlet oxygen; and red absorption to take administered, however, this regulatory mechanism is advantage of deep light penetration. bypassed, and the biosynthesis sequence is triggered, produc- ing mainly protoporphyrin 9 which