Necrosis has long been recognized as a major form of cell death after cellular exposure to radiation. Necrosis is generally thought to be a passive form of cell death caused by exposure to stress that leads to initial swelling and eventual rupturing of cellular membrane. Thus it is traditionally considered to be an unregulated form of cell death, in contrast to apoptosis, where a defined cascade of molecular events leads to programmed cell death. The discovery of necroptosis, which involves the systematic activation of select molecular factors that leads to active permeabilization of cellular membrane, indicates that necrosis could be actively regulated, similar to apoptosis. However, despite a recent surge of studies on the molecular signaling events involved in necroptosis, its role in cancer radiotherapy remains unclear. In this project, we propose to examine in the counter-intuitive hypothesis that the necroptotic factors play key roles in sustaining tumor growth and mediating tumor resistance to radiotherapy. Our hypothesis is based on recent results in our laboratory that indicated genetic deficiencies in necroptotic genes led to weakened tumorigenic abilities and increased radiation sensitivities of cancer cells. We will use state-of-the-art genome editing technologies such as CRISPR to examine the role of the necriptotic genes in tumor growth and tumor resistance to radiotherapy (Aim 1). We will also conduct studies to unveil the mechanisms through which the necroptotic factors promote tumor growth and tumor resistance to radiation (Aim 2). Finally, we will evaluate the anti-tumor efficacy of the small molecule inhibitors of the necroptotic factors alone or in combination with radiotherapy (Aim 3). Upon completion of the project, we hope to obtain a clearer picture of the role of necroptotic factors in tumor growth and tumor response to radiation therapy.