Abstract
Lung cancer is the most common cancer to metastasize to the brain, with 50% of all brain metastases originating from lung primary tumors. Traditional therapy for lung cancer brain metastases includes surgical resection, radiation, and chemotherapy. Due to the presence of the blood-tumor barrier, penetration of therapeutics is significantly hindered. Even when used in combination, tumor recurrence and regrowth after initial chemoradiotherapy remain a significant issue. To recapitulate recurrent disease, we aim to characterize a radio-resistant preclinical model of brain metastasis to investigate its effect on growth, chemosensitivity, and drug permeation across the blood-tumor barrier. Herein, we have generated a human NSCLC cell line bearing EGFR exon 19 deletion (PC9) that has been serial passaged in mice to colonize brain (PC9-Br). PC9-Br cells were serially irradiated and allowed to proliferate for 10-14 days prior to re-irradiation. The total dose administered to PC9-Br cells was 60 Gy to generate a radioresistant population (PC9-Br-RR). Clonogenic, MTT, and SRB analysis indicates a significant increase in survival percentage of PC9-Br-RR compared to PC9-Br irradiation at 2, 4, 6, and 8 Gy. While PC9-Br-RR cells are more resistant to cisplatin than PC9-Br (IC50: 2.5 µM and 1.5 µM, respectively at 72 h), they are more sensitive to osimertinib in vitro (IC50: 6.9 nM and 33 nM, respectively at 72 h). In vivo, PC9-Br-RR tumors developed more rapidly in mice than PC9-Br and brain-to-body tumor burden analysis showed PC9-Br-RR cells have increased brain tropism. Collectively, this data supports the characterization of a radio-resistant brain metastasis model to investigate the role of acquired radio-resistance at the blood-tumor barrier.