Necroptosis is a novel mechanism of radiation-induced cell death in anaplastic thyroid and adrenocortical cancers

Background. Necroptosis is a recently described mechanism of programmed cellular death. We hypothesize that necroptosis plays an important role in radiation-induced cell death in endocrine cancers. Methods. Thyroid and adrenocortical carcinoma cell lines were exposed to increasing doses of radiation in the presence of necroptosis inhibitor Nec-1 and/or apoptosis-inhibitor zVAD. H295R cells deficient in receptor interacting protein 1 (RIP1), an essential kinase for necroptosis, were used as controls. Survival curves were generated at increasing doses of radiation. Results. Nec-1 and zVAD increased cellular survival with increasing doses of radiotherapy in 8505c, TPC-1, and SW13. Both inhibitors used together had an additive effect. At 6 Gy, 8505c, TPC-1, and SW13 cell survival was significantly increased compared to controls by 40%; 33%, and 31% with Nec-1 treatment, by 53%, 47%, and 44% with zVAD treatment, and by 80%, 70%, and 65% with both compounds, respectively (P < .05). H295R showed no change in survival with Nec-1 treatment. The radiobiologic parameter quasithreshold dose was significantly increased in 8505c, TPC-1, and SW13 cells when both Nec-1 and WAD were used in combination to inhibit necroptosis and apoptosis together, revealing resistance to standard doses of fractionated therapeutic radiation. Conclusion. Necroptosis contributes to radiation-induced cell death. Future studies should investigate ways to promote the activation of necroptosis to improve radiosensitivity. (Surgery 2011;150:1032-9.)