Recently, a subset of N-phenyl-N'-(2-chloroethyl)ureas (CEU) was found abrogating the nuclear translocation of thioredoxin-1 and arresting the cell cycle in G(0)/G(1) phase. Several derivatives were prepared to assess their effect on cell cycle progression and on the intracellular location of Trx-1. Compounds 1-20, 21-40, and 41-60 exhibited GI(50) between 1 and 80 microM. Immunocytochemistry analysis showed compounds 4, 6, 8, 10, 11, 23, 24, 26-31, 34, 37, 41, 44, 46-51, 53, 56, and 57 inhibiting the nuclear translocation of Trx-1. Our results suggest that increasing the electrophilic character of these molecules might enhance the antiproliferative activity at the expense of the selectivity toward thioredoxin-1 and the G(0)/G(1) phase arrest.