The CXCR4 Antagonist AMD3100 Has Dual Effects, Initially Enhancing and Later Inhibiting Survival and Proliferation, in Myeloid Leukemia Cells in Vitro.

Abstract 1721

Poster Board I-747

AMD3100, a small bicyclam antagonist for chemokine receptor CXCR4, induces the peripheral mobilization of hematopoietic stem cells. It also induces the segregation of leukemia cells in the bone marrow microenvironment, which should enhance the chemosensitivity of the cells. Based on these observations, AMD3100 is being considered for clinical use. However, AMD3100 activates G-protein coupled with CXCR4 and acts as a partial CXCR4 agonist. In this study, we explored whether AMD3100 affects the proliferation and survival of myeloid leukemia cells. As demonstrated previously, both AMD3100 and T140, another CXCR4 antagonist, markedly inhibited stromal cell-derived factor-1 (SDF-1)-induced chemotaxis and induced the internalization of CXCR4 in myeloid leukemia cell lines (U937, HL-60, MO7e, KG1a, and K562 cells) and CD34+ primary human acute myeloid leukemia (AML) cells. SDF-1 alone did not stimulate the proliferation of these leukemia cells, nor did it rescue the cells from apoptosis induced by serum deprivation. By contrast, AMD3100, but not T140, stimulated the proliferation of all five leukemia cell lines and primary AML cells in a dose-dependent manner in serum-free conditions for up to 5 days (∼ 2-fold increases at a concentration of 10^-5M), which was abrogated by pretreating the cells with pertussis toxin. AMD3100 binds to CXCR7, another SDF-1 receptor, and all of the cells examined in this study expressed CXCR4 on the cell surface to some extent. The proliferation-enhancing effects of AMD3100 were not changed by knocking-down CXCR7 using the siRNA technique, whereas knocking-down CXCR4 significantly delayed the enhanced proliferation induced by AMD3100. Neither AMD3100 nor T140 induced the phosphorylation of Akt, Stat3, MAPK p44/p42, or MAPK p38, which are involved in SDF-1 signaling. In extended cultures of these cells for up to 14 days, AMD3100, but not T140, induced a marked decrease in the number of cells, compared to the control, after incubation for 5-7 days. Adding SDF-1 at the beginning and middle of the incubation did not affect the early increase or later decrease in the number of cells. AMD3100 reduced the apoptosis of these cells to a modest degree over the first 5-7 days and then markedly increased it. Consistent with the proliferation assay, AMD3100 increased the number of leukemia cell colonies during the early period of the assay, while it markedly decreased the number and size of the colonies in the later period of the assay. In conclusion, AMD3100 exerts dual effects, initially enhancing and subsequently inhibiting the survival and proliferation, in myeloid leukemia cells in vitro.