Methods in which targeted SEPHS2 disruption/inhibition and/or administration of selenite are used, e.g., in cancers that express SLC7A11.

Disclosed is a method for forming selenoneine or analogs thereof. The method may include phosphorylating sodium selenide to a selenophosphate, using adenosine triphosphate (ATP) and at least a first protein, generating a selenosugar by converting the selenophosphate using at least a second protein in the presence of a common sugar donor, and forming selenoneine or an analog thereof by combining the selenosugar with N,N,N-trimethyl-L-histidine or analogs thereof using at least a third protein. The method may include combining SenA, SenB, and SenC in an aqueous buffer at neutral pH and ambient temperature, and allowing SenA, SenB, and SenC to form selenoneine or an analog thereof in the presence of ATP, a common sugar donor, and sodium selenide.