Cellular and molecular effects of beta radiation from I-131 on human tumor cells: a comparison with gamma radiation.

To study the comparative effects of beta radiation emitted from Na(131)I with equivalent dose of (60)Co γ- radiation across a range of tumor types and underlying mechanism of cytotoxicity. Different tumor cell lines of various tissue origin viz. Raji, U937, A431 and MCF-7 were irradiated with beta radiation emitted from Na(131)I and equivalent dose of (60)Co γ- radiation (0.4 Gy). Cellular toxicity and apoptosis study were carried out in four cell lines and the effects were compared. Gene expression studies of P21, RAD51 and BAX genes were analyzed by q-PCR after β- and γ-irradiation. Cell viability (trypan blue assay) and apoptosis (DNA fragmentation and cleavage of PARP assays) studies for both types of radiation showed that among the four cell lines, A431 is most radio-resistant while MCF-7 and U937 are moderately radiation resistant and Raji cells showed maximum radiosensitivity. However, irradiation of cells with beta radiation from I-131 resulted in enhanced toxicity and apoptosis in tumor cells compared to equivalent dose of γ- rays. Gene expression studies in Raji cells showed difference in magnitude and kinetics of RAD51 and P21 expression after β- and γ-irradiation. Our results showed higher efficacy of beta radiation in induction of tumor cell cytotoxicity and apoptosis compared to an equivalent dose of γ-radiation, which may be associated with differential DNA damage and subsequent repair kinetics in tumor cells after these radiations.