Analogues of the tetrahydroisoquinoline family of antitumor antibiotics, 3-epi-jorumycin (3) and 3-epi-renieramycin G (4), in addition to their respective parent natural products (-)-jorumycin (1) and (-)-renieramycin G (2) were evaluated against both human colon (HCT-116) and human lung (A549) cancer cell lines. (-)-Jorumycin (1) displayed potent growth inhibition with GI50 values in the low nanomolar range (1.9-24.3 nM), while compounds 2-4 were found to be substantially less cytotoxic (GI50 0.6-14.0 microM).