Disclosed herein are compounds of formula I and/or a stereoisomer, stable isotopologue, and/or pharmaceutically acceptable salts thereof; and therapeutic uses of these compounds, which are inhibitors of tryptophan 2, 3-dioxygenase 2 (TDO2) and/or indoleamine 2, 3-dioxygenase 1 (IDO1), potentially useful in the treatment of diseases treatable, such as cancers.