Enhancing Protoporphyrin IX induced Photodynamic Therapy with a Topical Iron Chelating Agent in a Normal Skin Model

Abstract

Protoporphyrin IX (PpIX)-induced photodynamic therapy (PDT) is being utilised within dermatological practice as a topical method of localised ablation of nonmelanoma skin cancer/precancer. Standardised protocols have been implemented to good effect when the disease remains superficial but improvement is required to widen the application of this light activated drug therapy to treat thicker or acrally located conditions. As innate haem biosynthesis is exploited to accumulate the light sensitive PpIX from a topically applied inert prodrug (aminolaevulinic acid; ALA), this pathway can be further manipulated through the concurrent administration of an iron chelating agent to hyper-accumulate PpIX by temporarily reducing its iron dependent conversion to haem.A topical preparation of ALA was applied to normal rat skin with or without the hydroxypyridinone iron chelator, CP94. Image analysis quantification of tissue fluorescence following excision indicated that ALA plus CP94 produced 29.0% more fluorescence than ALA alone (p < 0.09), peaking at 5 hours. Furthermore, fluorescence spectroscopy of frozen skin samples from each treatment group were characteristic of PpIX (maxima 636 +/-2 nm), indicating that topical CP94 administration elevated PpIX levels without significantly producing any other fluorescent species. When PDT efficacy was considered post irradiation, a substantial three-fold increase in effect was observed 4 days after treatment when the iron chelator CP94 was co-administered topically with the prodrug (p < 0.07).It has therefore been established that the hydroxypyridinone CP94, is topically active within normal rat skin, effectively chelating iron to elevate PpIX accumulation and thus improve PDT efficacy.4

The hydroxypyridinone iron chelator CP94 increases methyl-aminolevulinate-based photodynamic cell killing by increasing the generation of reactive oxygen species

“…We have previously demonstrated that CP94 significantly increases the efficacy of MAL-based photodynamic cell killing in a range of human cultured cell types, more effectively than the more established iron chelator desferrioxamine [41] , [42] and is effective with all PpIX congeners (ALA, MAL and HAL (hexaminolevulinate)) and oxygen concentrations (5%, 20% and 40%) investigated to date [43] . Furthermore these experimental findings have translated into greater reductions in tumour thickness when applied to skin cancers clinically [30] , [31] as CP94 is effective as a topical formulation [44] . Here, we have shown that, following treatment with 0.5 mM MAL and irradiation (25 J/cm 2 ), A431 cells died primarily by necrosis at each time point measured, with little more than “background” apoptosis.…”

An experimental investigation of a novel iron chelating protoporphyrin IX prodrug for the enhancement of photodynamic therapy

“…It is closely related to the clinically established oral iron chelating agent Deferiprone (1,2‐dimethyl‐3‐hydroxypyridin‐4‐one hydrochloride (CP20); Ferriprox, Swedish Orphan Biovitrum Ltd, Sweden) but CP94 was found to be superior to CP20 for this particular application (PpIX‐PDT enhancement) in previous animal studies . CP94 is particularly effective at chelating intracellular iron and has a lower molecular weight and higher lipophilicity than either DFO or EDTA and is well suited to augmenting dermatological PDT as it can be applied topically . CP94 has already been demonstrated to enhance ALA‐induced PpIX fluorescence and to also produce greater tumor necrosis within animal models .…”

Photodynamic therapy for skin cancer: How to enhance drug penetration?

“…PpIX accumulation and caused a better clearance rate as presented in Table2 [71]. DFO was also used, but Curnow et al Have recently reported that CP94 was a more efficient enhancer of PpIX-induced PDT in vitro than DFO [1].…”

“…Protoporphyrin IX-induced PDT has been widely used in dermatological practice such as treatment of skin cancers [1].…”

“…[10,11] For most clinical trials [12][13][14][15], 5-ALA was administrated at a high dose (≈80mg) as a cream on the lesion to promote PpIX accumulation [16]. After an incubation period 1 , lesions were illuminated with a special wavelength (usually 635 nm) appropriate for tissue transmission and able to stimulate the PS [1,3]. Stimulated PS (PS*) follow the process presented in Fig.2 and PDT occurs.…”