Photodetection of early human bladder cancer based on the fluorescence of 5-aminolaevulinic acid hexylester-induced protoporphyrin IX: a pilot study

Abstract

Fluorescence photodetection (PD) and photodynamic therapy (PDT) are techniques currently under clinical assessment for both visualization and local destruction of malignant tumours and premalignant lesions. One drawback of these methods found with some photosensitizers is a more or less long-term cutaneous photosensitivity (Wagnières et al, 1998;Dougherty et al, 1990). A more recent strategy for administering photosensitizers involves the application of 5-aminolaevulinic acid (ALA) in order to stimulate the formation of protoporphyrin IX (PpIX) in situ. The exogenous ALA bypasses the negative feedback control from haem to ALA synthase that catalyses the condensation of glycine and succinyl-coenzyme A (CoA). Given in excess, exogenous ALA thus can result in a temporary accumulation of PpIX, in particular, in cells with higher metabolic turnover. Since PPIX has fairly good photosensitizing properties (Cox et al, 1982;Kennedy et al, 1990) proposed ALA as a possible photodynamic agent. Following this pioneering work, this treatment modality has been widely studied for various cancers (Kennedy et al, 1992;Peng et al, 1992;Svanberg et al, 1994).As well as for the PDT of malignant or premalignant lesions, ALA-induced PpIX is now being used for the detection of such lesions. This technique has been shown to work, among other applications, in urology, where easy instillation in the bladder, combined with the fact that this organ is readily accessible endoscopically, makes it an ideal object. Alongside classical techniques such as cytology or white light examination, fluorescence PD by ALA-induced PpIX provides some advantages (Leveckis et al, 1994;Kriegmair et al, 1996;Jichlinski et al, 1997). This inspection modality allows an exact mapping which pinpoints, with a high level of sensitivity and specificity, the locations of carcinoma in situ (CIS) as well as early stages of cancer-like dysplasias, which are normally difficult to recognize under white light examination.However, when using topically instilled ALA for the PDT of CIS and precancerous lesions, this modality appears to be limited by the amount of ALA that enter the target cells or by the tissue penetration and the distribution of the resulting PpIX in the targeted tissue. Almost all of these possible disadvantages accompanying the use of ALA can be ascribed to the physical-chemical properties of the molecule itself. Applied under physiological conditions, ALA is a zwitterion (Novo et al, 1996). Because the lipid bilayer of biological membranes is relatively impermeable to charged molecules, the cellular uptake of ALA is shallow. Consequently, in order to increase the transport across cellular membranes, fairly high drug doses and increased administration times have to be used. This deficiency results in a low penetration depth (Warloe et al, 1992;Loh et al, 1993;Peng et al, 1995) and an ALA-induced PpIX distribution, which is not optimized for the PDT of the deep layers of nodular lesions in the urothelium (Iinuma et al, 1995;Chang et al, 1996) after topical A...

Porphyrin accumulation induced by 5-aminolaevulinic acid esters in tumour cells growing in vitro and in vivo

“…This suggests that at least some murine tissues have Experimental Therapeutics the capacity to utilise certain ALA-esters for porphyrin synthesis, and that the results obtained in tumour tissue are not a reflection of murine metabolism per se. Previous work in vitro has suggested that a number of ALAesters, including hexyl-ALA, are most effective when used at much lower doses than ALA (Kloek et al, 1998;Lange et al, 1999;Uehlinger et al, 2000). Here, we found that reducing the dose of i.v.…”

“…Clinical and animal studies do not yet provide a consistent answer with regard to the efficacy of ALA-esters (Peng et al, 1996;Lange et al, 1999;Fritsch et al, 1998;van den Akker et al, 2000). Here, we have found that several esters are less effective than ALA at inducing porphyrin accumulation in a s.c. mouse tumour.…”

“…As a result, esterified derivatives of ALA, which are less hydrophilic than the parent compound (Uehlinger et al, 2000), are under investigation as possible alternatives to ALA. Work in vitro has demonstrated that a number of cell lines have the ability to take-up and metabolise certain ALA-esters into PpIX at a faster rate, and at lower concentrations, than ALA (Kloek and Beijersbergen van Henegouwen, 1996;Peng et al, 1996). A number of in vivo studies have suggested that topical application of some ALA esters can result in greater PpIX accumulation than similar concentrations of ALA (Peng et al, 1996;Lange et al, 1999;van den Akker et al, 2000). In contrast, however, clinical work with human solar keratoses showed methyl-ALA to induce less PpIX than ALA (Fritsch et al, 1998).…”

Photodynamic diagnosis of ovarian cancer using hexaminolaevulinate: a preclinical study

“…The synthesis of HAL is described elsewhere (Kloek et al, 1998;Lange et al, 1999). In all, 2 ml of solution (4 -12 mM HAL in PBS titrated with HCl to pH 7.4, 8 mM ALA) was injected intraperitoneally into each rat.…”

Hexyl‐aminolevulinate‐mediated photodynamic therapy: How to spare normal urothelium. An in vitro approach

“…Topically administered, these derivatives have an excellent specificity for epithelia such as urothelium with a pronounced affinity for tumor tissue. ALA or HAL-based fluorescence cystoscopy clearly improves the detection of carcinomas in situ, which are precisely the lesions on which PDT is assumed to be effective [5][6][7].…”