Time–dose relationships in radiation-enhanced integration

Abstract

Purpose: We have shown that ionizing radiation increases recombination, as manifested by increased stable transduction of both plasmid and adenoviral vectors. This paper reports the duration of increased recombination after irradiation. Materials and methods: A549 or NIH/3T3 cells were transfected at various times after irradiation. Cells were also irradiated with several fractionation schemes and then transfected. Results: Enhanced integration (EI) is a very long-lived process, lasting at least 2-3 days after single radiation fractions. The duration of EI activation is radiation dose-dependent. The efficiency of EI is dependent on radiation dose and independent of fractionation, such that low dose-rate, fractionated and single radiation doses result in similar levels of EI when corrected for diverences in cytotoxicity. Conclusions: Radiation, given with fraction sizes and dose-rates used in clinical radiation therapy, induces a long-lived hyper-recombination state. Since radiotherapy is already a component of treatment for many malignancies and is integrated into radiation-gene therapy trials, an understanding of recombination events that improve gene delivery is important and timely.