Removal of breast cancer cells from bone marrow by in vitro purging with ether lipids and cryopreservation

Four cell lines from human breast cancer (HTB 19, HTB 133, IZB B, and MCF 7M) were investigated for in vitro growth before and after incubation with the ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) for 4 h and at increasing concentrations (25, 50, 75, and 100 micrograms/ml), as well as with and without cryopreservation. When measured with the human tumor cloning assay in agar or methyl-cellulose the surviving fraction showed an inverse correlation with the concentrations of ET-18-OCH3. After a 4-h exposure with 75 micrograms/ml ET-18-OCH3 at a cell density of 2 x 10(5)/ml the number of colonies of HTB 19 decreased from 75 +/- 10/10(3) cells (100%) to 1 +/- 0/10(3) cells (1%), and after subsequent cryopreservation no remaining colonies were found. In order to simulate the situation in autologous bone marrow transplantation we contaminated normal human bone marrow cells with malignant HTB 19 breast cancer cells at a ratio of 100:1. After incubation with 75 micrograms/ml ET-18-OCH3 for 4 h and subsequent cryopreservation there was a considerable reduction of HTB 19 colonies whereas the majority of normal human hematopoietic progenitors recovered. We conclude that ET-18-OCH3, in combination with cryopreservation, can remove breast cancer cells from bone marrow by up to 1 log and may be useful for purging bone marrow for autologous bone marrow transplantation not only in acute leukemia and non-Hodgkin's lymphoma but also in breast cancer.