Biochemical Manipulation via Iron Chelation to Enhance Porphyrin Production from Porphyrin Precursors

Abstract

Topical protoporphyrin IX (PPIX) induced photodynamic therapy (PDT) of basal cell carcinoma (BCC) produces good clinical outcomes with excellent cosmesis as long as the disease remains superficial. Efficacy for nodular BCC, however, appears inferior to standard treatment unless repeat treatments are performed. Enhancement is therefore required and may be possible by employing iron chelating agents to temporarily increase PPIX accumulation above the levels normally obtained using aminolaevulinic acid (ALA) or the methyl ester of ALA (MAL) alone. In vitro studies investigated the efficacies of the novel iron chelator, CP94 (1,2-diethyl-3-hydroxypyridin-4-one hydrochloride), and the established iron chelator, desferrioxamine (DFO), at increasing PPIX fluorescence in cultured human lung fibroblasts and squamous carcinoma cells incubated with ALA/MAL. CP94 was found to produce greater PPIX fluorescence when administered with ALA/MAL than either congener could produce alone. CP94 was also found to be superior to DFO in the enhancement of PPIX fluorescence and could be employed to accumulate the same levels of PPIX within a shorter time period. Clinical utilization of CP94 to enhance ALA/MAL-PDT could potentially result in greater PPIX accumulation or alternatively could be employed to reduce the length of the required drug-light interval. Clinical investigation of this is currently underway.

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

“…With regard to PpIX-based photodynamic cell killing, it has previously been shown that ALA-induced, mitochondria-localised PpIX was far more efficacious than exogenous, ubiquitously-distributed PpIX when compared at equivalent concentrations [40] . 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] .…”

Improving in vitro photodynamic therapy through the development of a novel iron chelating aminolaevulinic acid prodrug

“…The level of PpIX (the light sensitive photosensitiser produced from the prodrugs administered in this form of PDT) accumulation was monitored using a well-established, previously validated, fluorescence based assay employed within our laboratory [11,43,44,67]. Briefly, cells were seeded at 2 × 10 4 cells per well in a 96 well plate and left to adhere overnight.…”

“…To evaluate the ability of AP2-18 to cause PpIX accumulation within cells, a series of concentrations were prepared (250 μM; 500 μM; 1000 μM), which reflect the range previously employed by our group during similar experimentation with PpIX precursors and iron chelating agents [11,43,44,67]. These were tested alongside equimolar concentrations of ALA and CP94 (the components of AP2-18) and methyl aminolevulinate (MAL) (the licenced prodrug currently widely employed in dermatological PDT in the UK), with all test compounds being investigated in both human dermal fibroblasts (84BR; Fig.…”

“…Direct comparison of CP94 and desferrioxamine (DFO; Desferal; an established iron chelator administered clinically by long infusion for the treatment of iron overload) in cultured human lung fibroblasts and epidermal carcinoma cells has previously established [42] that CP94 is a better enhancer of ALA/MAL-induced PpIX fluorescence than DFO (and it is already known that DFO is a better enhancer of PpIX-PDT than EDTA [40]), probably as a result of its lower molecular weight, greater lipophilicity and neutral charge enabling it to access intracellular iron pools more rapidly [43]. Further in vitro experimentation has also indicated that CP94 is also a better enhancer of ALA/MAL/HAL-PDT than the already clinically established iron chelator dexrazoxane (a bisdioxopiperazine iron chelating agent similar to EDTA, which can administered clinically as an injection alongside doxorubicin to act as a cardioprotective agent in women receiving treatment for metastatic breast cancer) [44] and works in a number of different human cell types [45].…”

Pretreatment to Enhance Protoporphyrin IX Accumulation in Photodynamic Therapy

“…CP94 produced higher PpIX fluorescence when administered with ALA/MAL than either congener could produce alone. CP94 was superior to DFO in the enhancement of PpIX fluorescence within a shorter time period [33]. The same author investigated CP94 administration and light dose fractionation in colonic rat tumors.…”