(6aR,12aR,12bS)-1,3,4,4a,5,6,6a,12,12a,12b-Decahydro-10-hydroxy-4,4,6a,12b-tetramethyl-2H-benzo[a]xanthene-8,11-dione is an analog of (4aS,6aS,12aR,12bS)-1,3,4,4a,5,6,6a,12,12a,12b-Decahydro-9-(hydroxymethyl)-4,4,6a,12b-tetramethyl-2H-benzo[a]xanthene-8,11-dione (BE 40644) which is a new human thioredoxin system inhibitor. Be 40644 shows the ability to inhibit the growth of several cancer cell lines.