Disclosed are DNA elements and constructs useful for obtaining tumor-selective gene expression in tumors having a mutated .beta.-catenin/APC pathway. In particular, the use of these constructs to express genes encoding therapeutic proteins in colorectal cancer cells is described. The constructs comprise multiple repeats of a TCF-binding element operably linked to a promoter. By means of such a construct, tumor cell-specific expression of a prodrug-converting enzyme such as nitroreductase may be achieved. Coupled with systemic administration of a suitable prodrug, such as CB1954, selective killing of such tumor cells can be demonstrated.