Radioprotective gene therapy through retroviral expression of manganese superoxide dismutase.
BACKGROUND
Radiotherapy for the control of cancer, either alone or in conjunction with chemotherapy, is often limited by normal tissue toxicity including haematopoietic toxicity. Exposure of cells to ionizing radiation leads to the formation of reactive oxygen species that are associated with radiation-induced cytotoxicity. The antioxidant enzyme manganese superoxide dismutase (SOD2) catalyzes the dismutation of the superoxide anions into hydrogen peroxide.


METHODS
We have investigated the potential of SOD2 overexpression, through retroviral gene transfer using a retrovirus optimized for transcription in early haematopoietic cells, to enhance the radioresistance of a human erythroleukaemic cell line and primary murine bone marrow. Using these as in vitro models we have investigated whether SOD2 gene therapy may be suitable for the protection of the haematopoietic compartment from the effects of ionizing radiation.


RESULTS
Here we demonstrate using both biological and physical assays that overexpression of SOD2 protects haematopoietic cells from ionizing radiation injury. Our results show that an increase in the levels of SOD2 enzymatic activity within K562 cells (from 160.7 +/- 23.6 to 321.8 +/- 45.2 U/mg protein) or primary murine haematopoietic progenitor cells leads to both a significant decrease in DNA fragmentation and a significant increase in clonogenic survival, as evident by a significant increase in Dbar (from 2.66 to 3.42Gy), SF2 (from 0.52 to 0.73) values, and a significant decrease in the alpha value (from 0.3040 +/- 0.037 to 0.0630 +/- 0.037 Gy(-1)) when compared either to cells transduced with a retroviral vector encoding eGFP alone or to the parental line.


CONCLUSIONS
The results presented suggest that retroviral radioprotective gene therapy may be applicable to the haematopoietic compartment, enabling radiation dose escalation in cancer therapy.
Southgate
Thomas D
TD
Cancer Research UK Gene Therapy Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 4BX, UK. Tsouthgate@picr.man.ac.uk
Sheard
Victoria
V
Milsom
Michael D
MD
Ward
Timothy H
TH
Mairs
Robert J
RJ
Boyd
Marie
M
Fairbairn
Leslie J
LJ
D000818:Animals; D003114:Colony-Forming Units Assay; D004249:DNA Damage; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000201:enzymology; D006801:Humans; D066298:In Vitro Techniques; D020014:K562 Cells; D051379:Mice; D011835:Radiation Protection; D012190:Retroviridae / Q000235:genetics; D013482:Superoxide Dismutase / Q000235:genetics*; D000099156:Superoxide Dismutase 2
D049452:Green Fluorescent Proteins; D013482:Superoxide Dismutase; D000099156:Superoxide Dismutase 2; C485184:enhanced green fluorescent protein