AMD3100, an antagonist of the chemokine receptor CXCR4, is about to be used clinically for the peripheral mobilization of hematopoietic stem cells, especially in patients with lymphoma and multiple myeloma. However, AMD3100 has been shown to activate a G protein coupled with CXCR4 and thus acts as a partial CXCR4 agonist in vitro. Although stromal cell-derived factor-1 (SDF-1) alone has minimal or negligible effects on the growth and survival of myeloma cells in vitro, many reports are consistent with the SDF-1/CXCR4 axis being involved in the progression of myeloma. Therefore, it is necessary to address the question of whether AMD3100 functions as a partial agonist for CXCR4 in myeloma cells, before it is released for wide clinical application. In this study, we explored whether AMD3100 affects the proliferation and survival of myeloma cells in vitro. As demonstrated previously, AMD3100 markedly inhibited the SDF-1 induced chemotaxis of myeloma cells, including three cell lines (RPMI8226, U266, and ARH77 cells), and CD138+ primary human myeloma cells. AMD3100 also induced internalization of CXCR4. SDF-1 alone did not stimulate the proliferation of these myeloma cells, nor did it rescue the cells from apoptosis induced by serum deprivation. By contrast, AMD3100 at 10−5M enhanced the proliferation of all three myeloma cell lines in serum-free condition by up to 2-folds in 3-day cultures, which was abrogated by pretreating the cells with pertussis toxin (PTX). This phenomenon was also observed with CD138+ primary human myeloma cells. In addition, AMD3100 enhanced the proliferation of U266 and ARH77 cells induced by interleukin-6 (IL-6). AMD3100 partially inhibited the apoptosis induced by serum deprivation, and the anti-apoptotic effect of AMD3100 was further enhanced in the presence of IL-6. AMD3100 on its own induced the phosphorylation of Akt and ERK1/2 but not Stat3 and p38/MAPK in RPMI8226 and U266 cells. The phosphorylation was also inhibited by pretreating the cells with PTX. The signal blocking agents wortmannin, PD98056, SB203580, and rapamycin did not affect the AMD3100-induced proliferation of RPMI8226 cells. LY294002 at concentrations not inhibiting spontaneous proliferation (5 μM or less) did not affect AMD3100-induced proliferation of the cells. AG490 inhibited spontaneous proliferation and AMD3100-induced proliferation of the cells in a dose-dependent manner. Accordingly, the signal-blocking effects were unclear. However, these results show that AMD3100 partially overcame the strong growth inhibition of myeloma cells induced by AG490. Our results indicate that AMD3100 can induce the phosphorylation of signaling molecules and stimulate the proliferation of myeloma cells, through signaling via G-protein pathway.

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