Erufosine: a membrane targeting antineoplastic agent with signal transduction modulating effects

The ether lipid analog erufosine (erucylphospho-N,N,N,-trimethylpropylammonium, ErPC3) has high activity against leukemic cells without affecting the normal hematopoiesis. It belongs to the group of alkylphosphocholines (APC) that are inhibitors of protein kinase C and phospholipase C. However, the mechanism of action of erufosine remains rather unclear. We focused on combination effects with the tyrosine kinase inhibitor imatinib mesylate (gleevec, former STI-571 or CGP-57148) against two chronic myeloid leukemia (CML)-derived cell lines (K-562 and BV-173). The influence of erufosine on proteins involved in the phosphatidylinositol-3-phosphate pathway and on expression of the retinoblastoma protein Rb was studied, the latter being a key component for cell cycle entry and progression in mammalian cells. The consecutive treatment of K-562 and BV-173 cells with erufosine (2.5, 5, 15, 30 microM) and imatinib mesylate (0.05, 0.1 microM) led to synergism as measured by the MTT-dye reduction assay and this is reason to hypothesize that such combinations could be beneficial for relapsed patients with drug-resistant disease. Whole cell lysates from K-562 and BV-173 were investigated for the expression of Rb, PKB/Akt, pAkt, and p27 by Western blot. Erufosine caused decreases of pAkt and CML fusion protein p210 (BCR-ABL) protein expression, but induced the Rb protein expression in K-562 cells. A parallel increase in p27 level was observed after 24 and 48 h treatment. These alterations in signal transduction could be an explanation for the drug interaction found. Furthermore, Rb is a substrate of caspases and is cleaved during apoptosis as already evidenced for BV-173 cells. Our experimental findings suggest that erufosine acts through induction of changes in protein signaling and especially through Rb induction. This unique mode of action makes it an attractive partner for combination therapies, for example, in combination with imatinib mesylate for treatment of CML.