BACKGROUND Dolastatins 10 and 15 are small peptides isolated from the marine sea hare Dolabella auricularia. In vitro studies of these peptides have demonstrated antimitotic and antiproliferative activity and growth inhibition in hematopoietic progenitor cells. OBJECTIVE The purpose of our in vitro study was to determine the biological effects of these marine peptides on growth of human lymphoma cell lines and to investigate mechanisms by which the dolastatins may act. METHODS Cell lines DB, HT, RL, and SR were grown from the ascites or pleural effusion of four patients with lymphoma. The DB, HT, and RL cell lines are of B-cell origin, and the SR cell line appears to be a less differentiated lymphoid cell type. Cells from these lines were cultured in the presence of vincristine or dolastatin 10 or 15. [3H]Thymidine-uptake assays were used to measure effects on DNA synthesis. Cell cycle analysis using propidium iodide was performed to measure drug-induced cell-cycle arrest. DNA fragmentation was used as an assay for drug-induced apoptosis and was measured by agarose gel electrophoresis. RESULTS In the three B cell lines, dolastatin 10 was more effective than dolastatin 15. Values for concentrations required for inhibition of proliferation by 50% (IC50) were .00013-.0013 nM for dolastatin 10 in each cell line; values for dolastatin 15 were approximately .13 nM in DB and HT cells and .0013-.013 nM in RL cells. SR cells were more sensitive to dolastatin 15 than to dolastatin 10 (IC50 = .00013-.0013 nM versus .0013-.013 nM). Both dolastatins arrested more than 70% of cells in mitosis in all cell lines. This effect was reversed if the drug was removed by 4 hours, but by 8 hours of exposure, reversal was not possible. Both dolastatins 10 and 15 produced apoptosis in DB and HT cells but not in the other two cell lines. CONCLUSIONS We have demonstrated that dolastatins 10 and 15 have a profound antiproliferative effect on four different human lymphoma cell lines and that the dolastatins are approximately 3-4 logarithms more effective as antiproliferative compounds, on a molar basis, than vincristine--a clinically useful, antiproliferative agent. These data support the hypothesis that apoptosis, as measured by DNA fragmentation, appears to be a cell-specific response and may not be directly related to the antimitotic effect of the dolostatins. CONCLUSIONS Our results suggest that these compounds may be good candidates for development as antineoplastic agents.