Protoporphyrin IX Radio- and Sono-dynamic Therapy in an in Vitro Lung Cancer Brain Metastasis Model

Introduction: More than half of all intracranial tumors are a result of metastatic lung cancer. While traditional approaches of surgery and stereotactic radiosurgery have advanced outcomes over the past decades, novel treatment strategies, such as development of photo- and radio-sensitizers, may translate to therapies for CNS metastases, including lung cancer brain metastasis (LCBM).

Methods: A novel LCBM line was generated using A549 lung adenocarcinoma cells (A549-N) via six serial intracardiac injections in Nu/Nu athymic mice and subsequent explantation (A549-Br). Cultures of A549-N and A549-Br were treated with 5-aminolevulinic acid (5-ALA) at non-toxic doses of 150mg/L or 300mg/L and allowed to incubate for 6h at 5% CO2 and 37°C. Fluorescent intensities were recorded and cells were treated with either single fraction 8Gy X-ray radiation (200kV, 13.0mA) or low-intensity focused ultrasound (LIFU, 10-30W) and maintained in culture for 5 days, with viability indirectly assayed based on ATP levels.

Results: A549-Br cells exhibited a 3.5- (150mg/L) and 4.0-fold (300mg/L) increase in relative fluorescent intensity whereas the A549-N cells plateaued at a 1.9-fold increase over both doses, when compared to their respective baselines. When treated with a single fraction of 8Gy X-ray radiation, A549-Br 5-ALA treated cells had 51% (150mg/L) and 73% (300mg/L) reduction in cell survival as compared to radiation alone. There were no differences observed in cell viability between irradiated A549-N and A549-N 5-ALA treated groups. A549-Br 5-ALA treated cells expressed a 23% reduction in cell survival after LIFU. No cytotoxicity was observed in the A549-Br LIFU alone group (5-day, p< 0.05).

Conclusion : Novel LCBM cell lines revealed increased functional metabolism of 5-ALA and a higher radio-biological effect (RBE) when compared to their parental cell line. When treated with LIFU, cell survival was uninfluenced without prior administration of 5-ALA. Ultimately, radio- and sono-sensitization of LCBM may be achieved using 5-ALA as a combinative therapy.