Simulated Stereotactic Body Radiation Therapy (SBRT) of Patient-derived Non-small Cell Lung Cancer (NSCLC) Cultured by Conditional Reprogramming: Radiobiological Comparison with Established Cell Lines

Abstract

Methods to predict individual patient tumor control by radiation therapy may lead to improved treatment outcomes in NSCLC. We used conditional reprogramming culture (CRC) to measure primary culture radiosensitivity parameters for large single and multiple radiation fractions employed in SBRT. Corresponding measurements were made in 4 established NSCLC lines. With IRB approval, resected tumor samples (n = 4; 2/4 proliferated) within 4 h of surgical excision were minced, enzymatically dissociated, and plated in CRC medium. Epithelial and mesenchymal phenotypes suggested by dual morphology were confirmed by Western blot for vimentin and β-catenin biomarkers. E and M populations were separated by differential trypsinization and plated for monolayer clonogenic assay in 96-well plates. Irradiation was by 137Cs irradiator at 0.6 Gy/min. Plates were stained and scored within 4 weeks of plating and clonogenic survivals were fitted to the linear-quadratic (LQ) model. Spheroid cultures were established in ultralow-attachment plates. Monolayer LQ parameters based on single-fraction survival curves (2-16 Gy) are shown in Table 1. Both α/β ratios and single-fraction sensitivities ranged widely, with SF (16 Gy) differing by 800-fold across tested cell lines. Notably, some surviving colonies of irradiated E cells developed M morphology. Effective survival measurements (5 or 10 fx of 2 Gy, 2-4 fx of 6 Gy, 2-3 fx of 8 Gy, 2 fx of 10 Gy) at 1 or 2 d intervals often differed from the effective survival fraction (ESF) predicted from the standard radiobiological assumption of equal effect per fraction. Primary L343E/M cells from one patient were intermediate in the spectrum of radiosensitivities for established NSCLC lines. Effective survivals for multiple conventional and SBRT fractions differed from those predicted by the time-independent biologically effect dose (BED), despite use of the measured α/β value rather than assuming α/β = 10. Reasons could include repopulation for conventional fractionation and incomplete repair of sublethal damage for large (≥ 6 Gy) fractions used for SBRT. Primary culture by the CRC method can be used to measure patient NSCLC radiosensitivity parameters and might, after clinical validation, provide an alternative to genomic personalization of radiation therapy.Abstract 3182; Table 1NSCLC Cellsα ± SEMβ±SEMα/βRESF* (2 Gy x 10)RESF (6 Gy x 3)L343M (1°)0.17 ± 0.030.020 ± 0.0098.518.30.39L343E (1°)0.12 ± 0.020.024 ± 0.0085.04.20.20A5490.06 ± 0.010.018 ± 0.0062.60.430.49H19750.30 ± 0.060.025 ± 0.01019.49.610.98 (8Gyx2)*RESF = Relative Effective Survival Fraction = (ESFmeas / ESFpred), where ESFpred = [SF(d)]n Open table in a new tab