Effect of cryopreservation on purging of leukemic marrow with alkyl-lysophospholipids

Alkyl-lysophospholipids (ALP) are reported to be selectively cytotoxic to neoplastic cells and have been demonstrated to be an effective purging agent for autologous marrow transplantation in a murine model, WEHI-3B. We studied the effect of in vitro treatment of normal bone marrow cells with ALP and of cryopreservation on spleen colony-forming units (CFU-s) in irradiated, syngeneic Balb/c mice. We found that exposure of cells to doses of ALP of 5 or 20 micrograms/ml followed by cryopreservation had no effect on CFU-s, but that a dose of 100 micrograms/ml was toxic. A simulated remission marrow was prepared by mixing normal murine bone marrow cells with WEHI-3B myelomonocytic leukemic cells to give a 1%-2% concentration of leukemic cells. These were exposed to 0- to 100-micrograms/ml concentrations of ALP for 24 h, cryopreserved, thawed, and injected into the tail veins of lethally irradiated syngeneic mice, and survival measured. It was found that concentrations of ALP from 10 to 50 micrograms/ml resulted in long-term disease-free survivors. These results established the fact that cryopreservation did not alter the effectiveness of ALP in purging marrows of residual leukemic cells.