On the Role of Iron and one of its Chelating Agents in the Production of Protoporphyrin IX Generated by 5‐Aminolevulinic Acid and its Hexyl Ester Derivative Tested on an Epidermal Equivalent of Human Skin

Abstract

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) or its derivatives as precursors of protoporphyrin IX (PPIX) is routinely used in dermatology for the treatment of various pathologies. However, this methodology suffers to some extent from a limited efficacy. Therefore, the main goal of this study was to investigate the modulation and pharmacokinetics of PPIX buildup after a 5 h incubation with ALA (1.5 mM) and one of its derivatives, the hexyl ester of ALA (h-ALA) (1.5 mM), on the human epidermal equivalent Epidex. PPIX production was modulated with (L+) ascorbic acid iron (II) salt (LAI) or the iron (II)-specific chelating agent deferoxamine (DFO). PPIX fluorescence from the Epidex layers was measured up to 150 h after the precursor administration using a microspectrofluorometer (lambda(ex): 400 +/- 20 nm; lambda(det): 635 nm). The maximum PPIX fluorescence intensity induced by h-ALA was about 1.7 x larger than that induced by ALA. The addition of DFO resulted in a more than 50% increase in PPIX fluorescence for both precursors. The decay half life measured for PPIX fluorescence is 30 and 42.5 h, respectively, for ALA and h-ALA. These half lives are doubled when the samples contain DFO. In the samples with the highest fluorescence intensity, a modified fluorescence spectrum was observed after 10 h, with the emergence of a peak at 590 nm, which is attributed to zinc protoporphyrin IX (Zn PPIX).

A comparative study on the enhancement efficacy of specific and non-specific iron chelators for protoporphyrin IX production and photosensitization in HaCat cells

“…However, the iron chelator DFO has even higher affinity and can bind iron with a large preference over other metal ions. It was found that the combined incubation of ALA and DFO could enhance the accumulation of PpⅨ on an epidermal equivalent of human skin [24] . Moreover, DFO itself generates PpⅨ in absence of ALA, and DFO in combination with light could photo-kill the cancer cells in vitro, at high concentration of 1.0 mmol/L or more [25] .…”

Pretreatment to Enhance Protoporphyrin IX Accumulation in Photodynamic Therapy

“…In their publication, Uehlinger et al [31 ]addressed the question of the quantitative improvement in PpIX production using iron chelation in a very suitable model which is skin equivalent. They tested the role of iron and one of its chelating agents in the production of PpIX generated by ALA and its hexyl ester derivative on an epidermal equivalent of human skin, Epidex.…”

The importance of iron chelation and iron availability during PpIX-induced photodynamic therapy

“…Many adaptations to standard treatment have been considered to improve efficacy including skin pre-treatment with the malignant cell differentiation potentiator dimethyl sulfoxide [20], skin stripping with tape [21], light dose fractionation [22,23], low fluence rate light administration [24] as well as combinations with other techniques such as low-dose Photofrin ® [25], hyperthermia [26,27], iontophoresis [28] and bioreductive drugs [29]. Concurrent administration of an iron chelator, such as ethylenediamine tetraacetic acid (EDTA) [30][31][32][33], desferrioxamine (DFO) [30,[34][35][36][37] or the novel hydroxypyridinone iron chelator 1,2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94) [38][39][40][41][42][43], during PpIX-PDT has also been demonstrated to increase cellular accumulation of PpIX by reducing its bioconversion to haem by ferrochelatase (an iron dependent process) thus increasing cell kill on subsequent irradiation. This method of enhancement is attractive because simply increasing the precursor dose or application time doesn't appear to produce cost efficacy or practical substantial improvements [44].…”