ABSTRACT: The main drawbacks of radioimmunotherapy have been severe hematological toxicity and potential development of myelodysplastic syndrome and secondary leukemia. Activation of p53 follows a major pathway by which normal tissues respond to DNA-damaging agents, such as chemotherapy and radiation therapy, that result in injuries and pathological consequences. This pathway is separate from the tumor suppressor pathway of p53. We have previously reported that use of low-dose arsenic (LDA) temporarily and reversibly suppresses p53 activation, thereby ameliorating normal tissue toxicity from exposure to 5-fluorouracil and X rays. We have also demonstrated that LDA-mediated protection requires functional p53 and thus is selective to normal tissues, as essentially every cancer cell has dysfunctional p53. Here we tested the protective efficacy of LDA for bone marrow tissue against radioimmunotherapy through animal experiments.Mice were subjected to LDA pretreatment for 3 days, followed by treatment with Y-90 ibritumomab tiuxetan. Both dose course (10, 25, 50, 100, and 200 ?Ci) and time course (6, 24, and 72 hours and 1 and 2 weeks) experiments were performed. The response of bone marrow cells to LDA was determined by examining the expression of NF?B, Glut1, and Glut3. Staining with hematoxylin and eosin, ?-H2AX, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was used to examine morphology, DNA damage response, and apoptotic cell populations.Elevated levels of NF?B, Glut1, and Glut3 were observed in bone marrow cells after LDA treatment. Bone marrow damage levels induced by Y-90 ibritumomab tiuxetan were greatly reduced by LDA pretreatment. Consistent with this observation, significantly less DNA damage and fewer apoptotic cells were accumulated after Y-90 ibritumomab tiuxetan treatment in LDA-pretreated mice. Furthermore, in the mouse xenograft model implanted with human Karpas-422 lymphoma cells, LDA pretreatment did not have any detectable effect on either tumor growth or Y-90 ibritumomab tiuxetan (200 ?Ci)-induced tumor suppression.LDA pretreatment protected bone marrow without compromising tumor control caused by Y-90 ibritumomab tiuxetan.
