RPS6KA6 and esophageal squamous cell carcinoma: In response to these findings, we designed and synthesized, for the first time, a series of 1,4-dihydro-2 H-pyrimido[4,5-d] [1, 3]oxazin-2-ones derivatives, which are novel RSK4 inhibitors that could become effective therapeutic agents for improving the radiosensitivity of ESCC in the future [12].