Ionizing Irradiation Protection and Mitigation by Carbamazepine Is p53 and Autophagy Independent,

Carbamazepine (CBZ), an established sodium channel blocker, used in treatment of epilepsy and trigeminal neuralgia, induces autophagy. CBZ has recently been demonstrated to be an ionizing radiation mitigator and protector (Kim,H.et. al IJRB-in press). CBZ protected C57BL/6NHsd female mice from irradiation if given 24 hr before total body irradiation (TBI) and mitigated if given 12 hours after irradiation.

Materials and Methods: To elucidate the mechanism of CBZ action, autophagy incompetent (ATG5−/−) and competent (ATG5+/+) mouse embryo fibroblasts (MEF), p53−/− and p53+/+ bone marrow stromal cells and 32D cl 3 murine IL-3 dependent hematopoietic progenitor cells were tested for CBZ mediated radiation protection and mitigation in clonagenic irradiation survival curves. We also measured CBZ effect on irradiation-induced apoptosis, and depletion of antioxidant stores in vitro and after (TBI) in vivo in control mice and in hind limb irradiated mice with orthotopic tumors.

CBZ was a significant radiation protector and mitigator for both ATG5−/− and ATG5 +/+ cell lines by an increased ñ (a measurement of the shoulder on the clonogenic survival curve). CBZ treated ATG5 +/+ cells has an increased ñ of 11.1 +/− 0.2 or 8.8 +/− 0.2 for CBZ added before or after irradiation respectively compared to 5.4 +/− 0.9 for irradiation control cells (p = 0.0287 or 0.0119,respectively). ATG −/− cells were also protected and mitigated by CBZ (ñ of 16.1 +/− 2.6 as a radioprotector or 9.8 +/− 1.5 as a mitigator compared to 4.6 +/− 0.7 for irradiated control cells (p = 0.0002 or 0.0037, respectively). Thus, CBZ functions independent of autophagy. Incubation of p53 +/+ and p53−/− cell lines in 10 μM CBZ for one hour before irradiation protected (ñ of 5.6 +/− 0.9 compared to 1.9 +/− 0.5 for control irradiated p53 +/+ cells (p = 0.0126) and 3.7 +/− 1.9 compared to 1.8 +/− 0.4 for irradiated control p53 −/− cells (p = 0.0018). Thus, CBZ functions in a p53 independent manner. Other pro-autophagy drugs, Valproic Acid and Lithium Carbonate, were ineffective radiation protectors or mitigators. CBZ treatment of 32D cl 3 cells for one hour before or immediately following irradiation had no effect on mitochondrial membrane depolarization, apoptosis or viability but was protective and mitigative in clonagenic survival curve assays. Irradiation initially decreased antioxidant stores in both ATG5+/+ and ATG5−/− cells 10 to 30 min following irradiation. However, cells treated with CBZ had a faster recovery of antioxidant stores to pre-irradiation levels by 90 min compared to 120 min for control irradiated cells. To determine if CBZ protected both normal tissues and tumors in vivo mice with 3LL Lewis Lung carcinoma hind limb xenografts were treated with 10 mg/kg CBZ before or after 20 Gy limb irradiation. There was no significant difference in tumor growth inhibition by 20 Gy in mice treated with CBZ before or after irradiation (p = 0.2431 or 0.5439, respectively).

Thus, CBZ is an effective radiation protector and mitigator of normal but not tumor tissues by a novel mechanism independent of autophagy, p53 and apoptosis.

This project was supported by U191A168021–06.

No relevant conflicts of interest to declare.