VEGF inhibition and cytotoxic effect of aplidin in leukemia cell lines and cells from acute myeloid leukemia

Background: Aplidine (APL) is a marine depsipeptide isolated from the Mediterranean tunicate Aplidium albicans that is under clinical phase II development. In contrast to the lack of bone marrow toxicity reported in phase I/II studies, it has been shown to induce cytotoxicity at very low concentration against lymphoblastic leukemia blast, as well as having an impact in the vascular endothelial growth factor (VEGF)/VEGF receptor 1 loop. Patients and methods: To confirm these findings we investigated APL-related VEGF inhibition and its cytotoxic effect on myeloid leukemic cells lines (K-562, HEL and HL60) and fresh leukemia blasts derived from 30 patients with acute myeloid leukemia (AML). The conventional active 4-demetoxidaunorubicin (idarubicin; IDA) was included as a positive control. Results: APL was found to be significantly (P < 0.001) more active than IDA in obtaining 50% growth-inhibition in K-562, HEL and HL60 cell lines. Results obtained with AML blast cells were superimposible. ID50 ranged from 0.024 to 0.610 mu M for IDA (0.200 +/- 0.176) and from 0.001 to 0.108 mu M for APL (0.020 +/- 0.031). Annexin V tests and cell cycle analysis performed on cell lines confirmed the stronger citotoxic capability of APL as apoptotic inducer and as a G, blocker. The inhibitory effects of APL on VEGF release and secretion have been confirmed by ELISA tests performed on HEL: the VEGF concentration in cell surnatant was reduced from 169 to 36 pg/ml after 24 h of exposure to a pharmacological concentration of APL. Conclusions: APL harbors a strong in vitro antileukemic activity at a concentration achievable in patients at non-myelotoxic doses. Our data also support the notion of an impact on VEGF secretion. Clinical studies with this new marine-derived compound in relapsed/resistant leukemia are underway.