BCR‐ABL influences the antileukaemic efficacy of alkylphosphocholines

We have compared the antileukaemic efficacy of a series of new i.v. injectable alkylphosphocholines (APC) with their clinically used congeners miltefosine and perifosine. The test system consisted of four leukaemic cell lines carrying the bcr‐abl rearrangement (K‐562, LAMA‐84, CML‐T1 and BV‐173) and two other leukaemic cell lines (HL‐60 and SKW‐3) without this genetic alteration. The prototype of i.v. injectable APC, erucylphosphocholine, was more active against BCR‐ABL‐positive cell lines than the two reference APC. It induced programmed cell death in HL‐60 and SKW‐3 cells after exposure for 24 h, and in bcr‐abl expressing cells after a prolonged incubation period (48 h). LAMA‐84 cells responded to i.v. injectable APC with increased conversion to an adherent, fibroblast‐like phenotype. Experiments with a cell‐free system showed that the target structures of APC are localized within the cytoplasmic compartment. Blockade of ceramide synthase by fumonisin B1 was insufficient to prevent oligonucleosomal DNA fragmentation. Using RT‐PCR we confirmed that K‐562 and LAMA‐84 cells carry the b3a2 fusion type, and CML‐T1 and BV‐173 the b2a2 variant. BV‐173 cells had the lowest level of bcr‐abl mRNA which correlated with their increased sensitivity. Transfection of K‐562 cells with antisense oligonucleotides directed against bcr‐abl caused a specific suppression of K‐562 clonogenicity. Our data indicated that i.v. injectable alkylphosphocholines are potent inducers of apoptosis and display increased antileukaemic efficacy against BCR‐ABL‐positive blasts as compared with miltefosine and perifosine. The expression of BCR‐ABL cannot prevent apoptosis but delays erucylphosphocholine‐induced programmed cell death. Transfection with bcr‐abl directed antisense oligonucleotides reduces the clonogenicity of K‐562 cells.