Purging leukemia remission marrows with alkyl-lysophospholipids, preclinical and clinical results

Alkyl-lysophospholipids are unique compounds which have selective anti-cancer activity with relative sparing of normal bone marrow stem cells. Thus, they would appear to be ideal candidates for marrow purging. In contrast to most anti-cancer drugs, these compounds act on the cell membrane resulting in inhibition of phosphatidylcholine biosynthesis. In addition, these compounds inhibit protein kinase C activity and may interfere with signal transmission. In low doses in in vitro systems, they have been shown to induce differentiation in leukemic cell lines. Lethally irradiated Balb/c mice were injected with normal bone marrow cells containing 1-2% leukemic cells (WEHI III-B) to simulate a remission marrow after the cells were incubated in vitro for 24 hours with 0-100 ug/ml of 1-0-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine (ALP). All the mice given cells not treated with ALP succumbed to leukemia, whereas there was a dose-response increase in survival in those given ALP treated cells. Similar results were observed when the cells were cryopreserved and thawed before injection. Very little effect of ALP was noted on stem cells as measured by the spleen colony assay. In vitro studies using human marrow progenitor assays (CFU-GEMM) were undertaken in which marrow was mixed with 0.1% HL60 cells and exposed for 1 or 4 hours to ALP at 0, 25 and 50 ug/ml. The cells were plated and assayed for CFU-GEMM and leukemic colonies. At 50 ug/ml, HL60 colonies were eliminated and there was no significant reduction in normal marrow progenitor cells. Clinical trials were initiated. Eleven patients with acute leukemia in remission who were candidates for autologous bone marrow transplantation had marrow harvested, incubated with 50 ug/ml of ALP and cryopreserved. CFU-GEMM assays before and after purging showed no differences. There was a similar significant reduction after cryopreservation regardless of whether marrows were purged. Two patients were transplanted with purged marrow, one in early relapse and one in a marrow remission, but had evidence of CNS leukemia. In both, ablative therapy consisted of cytosine arabinoside, 3 gm/m2 x 12 doses, followed by fractionated TBI to a total of 12 Gy prior to reinfusion of thawed marrow. The patient in early relapse had progression of leukemia by day 28. The patient in marrow remission is disease-free 9 months after transplantation. These studies indicate that purging marrow with ALP is a promising approach and further clinical studies are indicated.