RARα-Specific Retinoid Am-80 Prevents SDF-1-Mediated Chemotaxis in CXCR4 Expressing Tumor Cells.

Chemokine (C-X-C motif) receptor 4 (CXCR4) plays an important role on hematogenous metastasis of tumor cells to the organs comprising constitutively stromal cell-derived facter-1 (SDF-1). Retinoids have been utilized as a drug for treatment of acute promyelocytic leukemia (APL), in which tumor cells give rise to differentiation and cell death by activation of retinoic acid receptors (RARs). However, the effects of retinoid on chemokine-mediated cell motility are totally unknown. In this study, we examined the effects of retinoids, including all-trans retinoic acid (ATRA) and RARα-specific retinoid Am-80, on CXCR4-mediated chemotactic activity using five myeloid and lymphoid leukemia cells (HL-60, K562, MOLT-3, Jurkat, and U266B1). When cells were incubated with ATRA or Am-80 at doses up to 10 mM for 3 days, comparable effects were found; cytotoxic effect occurred only in HL-60, and growth inhibition was albeit detected in all of other cells. The extents of cell surface CXCR4 in all of the cells detected by flow cytometric analysis tended to be correlated with SDF-1-induced migration activity. Cell surface CXCR4 was slightly decreased by ATRA treatment, while it was significantly decreased by Am-80 treatment, and the alterations were in time- and dose-dependent fashions. In terms of CXCR4 expression, Jurkat was the most sensitive cells. Cell migration in response to SDF-1, was monitored by a modified Boyden chamber method. SDF-1 induced significant chemotaxis in HL-60, MOLT-3 and Jurkat cells, but did not in K562 and U266B1 cells. After treatment with the retinoids, HL-60 was only a cell type increasing random cell motility, however in retinoids-pretreated MOLT-3 and Jurkat cells, no such effect was found, and therefore suggesting that up-regulation of the motility in HL-60 is maybe due to a response by dyeing cells. However, in a case of pretreatment with not ATRA but Am-80, SDF-1-induced chemotaxis of MOLT-3 and Jurkat cells was dose-dependently repressed in accordance with decrease in cell surface CXCR4 expression. This was also confirmed by a time-laps horizontal migration system, indicated that pseudopodia formation accompanied with F-actin rearrangement by SDF-1 was strongly inhibited by Am-80-pretreatment. These results indicate that RARα-specific retinoid Am-80 may induce not only growth inhibition, but also prevention of SDF-1/CXCR4-mediated hematogenous metastasis in CXCR4 expressing tumor cells.