Expression of transfected recombinant oncogenes increases radiation resistance of clonal hematopoietic and fibroblast cell lines selectively at clinical low dose rate.

To determine the effect of oncogene expression on gamma radiation sensitivity of hematopoietic compared to fibroblastic cells, we selected clonal sublines of an interleukin-3 (IL-3)-dependent hematopoietic progenitor cell line 32D cl 3 and NIH/3T3 embryo fibroblastic cells following transfection with each oncogene linked to the mycophenolic acid resistance gene. Each mycophenolic acid-resistant subclone demonstrated high levels of specific poly(A)+ mRNA for each oncogene. The parent line 32D cl 3 demonstrated similar radiosensitivity at 116 cGy/min (D0 126, n 1.17) compared to 5 cGy/min (D0 123, n 1.65). This pattern was not altered in subclones of 32D cl 3 cells transfected with the epidermal growth factor (EGF) receptor gene and grown in EGF (at 116 cGy/min D0 104, n 0.998, at 5 cGy/min D0 115, n 1.09), or in 32D cl 3 cells expressing the v-sis oncogene (at 116 cGy/min D0 122.4, n 1.79, at 5 cGy/min D0 135, n 1.43). In contrast, expression of the transfected oncogenes v-erb-B, v-abl, or v-src conferred significant radioresistance at 5 cGy/min dose rate (D0 194, n 1.77; D0 165.5, n 1.56; D0 171, n 1.28, respectively). With the exception of v-sis, oncogene expression resulted in nonautocrine factor independence of 32D cl 3 subclones, and production of donor origin tumors in syngeneic new-born or adult mice. Two rare spontaneous factor-independent subclones of 32D cl 3 were also tested. Nonautocrine clone 32D cl 2 demonstrated significantly increased radioresistance at low dose rate (D0 186, n 1.63), while autocrine (IL-3 producing) subclone 32D cl 4 revealed no significant increase in radioresistance at 5 cGy/min. The parent fibroblast cell line NIH/3T3 showed an intrinsic relative radioresistance at low dose rate (at 5 cGy/min D0 157.3, n 1.81, compared to 116 cGy/min D0 134.3, n 1.57). Expression in NIH/3T3 of transfected oncogenes v-abl, v-fms, v-fos, or H-ras increased radioresistance at low dose rate (D0 208.6, n 1.61; D0 206.6, n 1.51; D0 167.5, n 1.85; and D0 206.8, n 1.08, respectively). Thus expression of each of several oncogenes induces resistance to gamma irradiation at 5 cGy/min in hematopoietic and fibroblast cell lines. These data may help explain the clinical recurrence of oncogene-expressing leukemia and lymphoma cells after marrow stem cell ablative doses of low-dose-rate total-body irradiation.