Photodynamic Therapy for Benign Cutaneous Neurofibromas Using Aminolevulinic Acid Topical Application and 633 nm Red Light Illumination

Abstract

<b><i>Background:</i></b> Neurofibromatosis type 1 (NF1) has no current effective treatments beyond surgery. Topical photodynamic therapy (PDT) has the potential to provide a less invasive treatment modality. <b><i>Objective:</i></b> Based on murine data, we hypothesized PDT could be used for the treatment of cutaneous neurofibromas (cNF). <b><i>Methods and results:</i></b> We conducted a phase I trial to examine absorption and conversion of topical aminolevulinic acid (ALA) in cNF and determine safety in a dose escalation study. ALA or control vehicle was applied to neurofibromas through microneedle-assisted delivery (<i>n</i> = 4) and excised specimens were examined 24 h later for protoporphyrin IX fluorescence. Fluorescence was detected in the tumors at 304 ± 94 U/μm², while adjacent paralesional normal skin and vehicle-treated tumors showed no fluorescence (<i>p</i> < 0.0001). Subsequently, neurofibromas (<i>n</i> = 27) were treated with ALA and irradiated with 633 nm red light 18 h later, at escalating dosages of 50 and 100 mJ/cm². Maximum tolerable dose was established at 100 mJ/cm². Light microscopy study of tumors biopsied 48 h after PDT (ALA <i>n</i> = 14 and vehicle <i>n</i> = 4) showed mixed inflammatory infiltrate in the ALA, but not in the vehicle-treated tumors or perilesional normal skin. TUNEL evaluation showed 42.5 ± 19.9 apoptotic cells per visual field for ALA-treated and 1.1 ± 1.4 for vehicle-treated tumors (<i>p</i> = 0.002). <b><i>Conclusions:</i></b> In the first reported clinical trial of PDT for NF1, PDT targeted neurofibromas specifically, and may offer a normal tissue-sparing treatment modality in the future. This study is registered at Clintrials.gov (NCT01682811).