sphingosine-1-phosphate and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

FTY720 is an immunosuppressant developed to prevent organ transplant rejection. Recent studies indicate an additional role for FTY720 in inducing cell apoptosis. We demonstrate here that FTY720 mediates toxic effects in cell lines representing different B-cell malignancies and primary B cells from patients with chronic lymphocytic leukemia (CLL). In contrast to previous reports in T-cell lines, FTY720-induced toxicity in the Raji cell line and primary CLL B cells is independent of activation of caspases or poly(ADP-ribose) polymerase processing. Further, pancaspase inhibitor Z-VAD-fmk failed to rescue these cells from apoptosis mediated by FTY720. FTY720 induced down-regulation of Mcl-1 but not Bcl-2 in CLL B cells. Overexpression of Bcl-2 failed to protect transformed B cells from FTY720-induced apoptosis, suggesting a Bcl-2-independent mechanism. Interestingly, FTY720 induced protein phosphatase 2a (PP2a) activation and downstream dephosphorylation of ERK1/2, whereas okadaic acid at concentrations that inhibited the FTY720-induced PP2a activation also resulted in inhibition of FTY720-mediated apoptosis and restoration of baseline ERK1/2 phosphorylation in primary CLL cells, indicating a role for PP2a activation in FTY720-induced cytotoxicity. Further, FTY720 treatment resulted in significant prolonged survival in a xenograft severe combined immunodeficiency (SCID) mouse model of disseminated B-cell lymphoma/leukemia. These results provide the first evidence for the potential use of FTY720 as a therapeutic agent in a variety of B-cell malignancies, including CLL.

Topics: Animals; Apoptosis; B-Lymphocytes; Caspases; Cell Line; Cysteine Endopeptidases; Down-Regulation; Fingolimod Hydrochloride; Humans; Immunosuppressive Agents; Leukemia, Lymphocytic, Chronic, B-Cell; Lysophospholipids; Mice; Mice, SCID; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Propylene Glycols; Protein Phosphatase 2; Proto-Oncogene Proteins c-bcl-2; Signal Transduction; Sphingosine; Xenograft Model Antitumor Assays

Sphingosine has been shown to inhibit cell growth in many cell lines although the mechanism of this effect remains obscure. More recently, D-erythro-sphingosine has been shown to act as an early inducer of dephosphorylation of the retinoblastoma gene product (pRb) in the lymphoblastic leukemia cell line MOLT-4 [Chao, R., Khan, W., & Hannun, Y.A. (1992) J. Biol. Chem., 267, 23459-23462]. In the current study, the role of the natural D-erythro-sphingosine in regulation of cell growth and pRb dephosphorylation was evaluated using chemically synthesized pure isomers of sphingosine. Of the four possible stereoisomers of sphingosine, D-erythro-sphingosine was most active in inducing dephosphorylation of pRb protein with an EC50% of 0.6 microM whereas its enantiomer L-erythro-sphingosine was 8-fold less potent with an EC50% of 5 microM. The dose responses for inhibition of cell growth were nearly identical to the EC50% for pRb dephosphorylation with D-erythro-sphingosine causing 50% inhibition at 0.6 microM whereas L-erythro-sphingosine was 5-6-fold less potent. All of the stereoisomers were taken up by the cells, and the greater potency of D-erythro-sphingosine was not due to differences in cellular uptake. The metabolism of D-erythro-sphingosine was also studied to evaluate the possible role of sphingosine metabolites on regulation of retinoblastoma protein. Evidence is provided against a role for ceramide or sphingosine 1-phosphate as mediators of the effects of sphingosine on pRb dephosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Cell Death; Cell Division; Drug Synergism; Fumonisins; Kinetics; Lysophospholipids; Mycotoxins; Phosphorylation; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Retinoblastoma Protein; Sphingosine; Stereoisomerism; Tumor Cells, Cultured