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

Exogenous administration of 5-aminolaevulinic acid (ALA) is becoming widely used to enhance the endogenous synthesis of protoporphyrin IX (PpIX) in ph otodynamic therapy (PDT) and fluorescence photodetection (PD). Recently, re sults have shown that the chemical modification of ALA into its more lipoph ilic esters circumvents limitations of ALA-induced PpIX like shallow penetr ation depth into deep tissue layers and inhomogeneous biodistribution and e nhances the total PpIX formation. The present clinical pilot study assesses the feasibility and the advantages of a topical ALA ester-based fluorescen ce photodetection in the human bladder. In this preliminary study 5-aminola evulinic acid hexylester (h-ALA) solutions, containing concentrations rangi ng from 4 to 16 mM, were applied intravesically to 25 patients. Effects of time and drug dose on the resulting PpIX fluorescence level were determined in vivo with an optical fibre-based spectrofluorometer. Neither local nor systemic side-effects were observed for the applied conditions. All conditi ons used yielded a preferential PpIX accumulation in the neoplastic tissue. Our clinical investigations indicate that with h-ALA a twofold increase of PpIX fluorescence intensity can be observed using 20-fold lower concentrat ions as compared to ALA.