A new tubulin polymerization inhibitor, auristatin PE, induces tumor regression in a human Waldenstrom's macroglobulinemia xenograft model.

Waldenstrom's macroglobulinemia (WM) is an uncommon lymphoproliferative disease which remains incurable with current treatment protocols. We have previously established a permanent WM cell line, WSU-WM, which grows as a xenograft in severe combined immune deficient (SCID) mice. In this study, we investigated the anti-tumor effects of auristatin PE (a structural modification of the marine, shell-less mollusk peptide constituent dolastatin 10). WSU-WM cells were cultured in RPMI-1640 at a concentration of 2x10(5) cells/ml using 24-well plates. Auristatin PE or dolastatin 10 were added to triplicate wells and cell count and viability were assessed after 24, 48 and 72 h. Results showed that both agents were active against WSU-WM, and were able to induce complete growth inhibition at 100 pg/ml. The efficacy of these agents in vivo was evaluated using the WSU-WM SCID mouse xenograft model. Auristatin PE and dolastatin 10 were given i.v. via tail vein at 2.0 mg/kg and 0.2 mg/kg, respectively. The agents were given every second day for three injections which represent the maximum tolerated doses. Tumor growth inhibition (T/C), tumor growth delay (T-C), and log10 kill for auristatin PE and dolastatin 10 were 0%, 18 days, 2.83 and 67%, 2 days, 0.06, respectively. Based on these animal results, dolastatin 10 was inactive while auristatin PE was highly active. We therefore focused further investigation on auristatin PE to understand some of its mechanisms of action. Using two flow cytometry assays, propidium iodide for cell cycle analysis and 7-amino actinomycin D (7AAD) to detect apoptosis, we were able to demonstrate that auristatin PE at 10 pg/ml after 24 h arrested 50% of WSU-MW cells in G2M. Concomitantly, 31% of auristatin PE-treated cells entered apoptosis. By 72 h, greater than 75% of the cells became apoptotic. The activity of auristatin PE should be evaluated in other tumor types and in clinical trials.