Besides new efforts in the treatment with tyrosine-kinase-inhibitors like imatinib were made, Chronic myelogenous leukemia (CML) still remains chronic with a progression of the disease by time. New ways of treatment have to be found to eradicate the malignant clone in the bone marrow.

In our study we are evaluating whether an inhibition of the SDF-1-CXCR4-axis by the selective CXCR4 receptor antagonist AMD3100 results in increased cell kill of the BCR-ABL+ cell line BV-173 when combined with treatment with imatinib. AMD3100 significantly blocks binding of the FACS-anti-CXCR4-Mab to its corresponding receptor. Furthermore, AMD3100 significantly inhibits SDF-1 mediated chemotaxis towards 500ng/ml SDF-1 to 0.71±0.15 of spontaneous transmigration at the highest concentration (100μM) of AMD3100 whilst SDF-1 500ng/ml leads to 1.4±0.06 fold spontaneous transmigration (n=3). Even lower concentrations (10μM and 1μM) still significantly reduce transmigration to a level lower than spontaneous transmigration. Also migration into the SDF-1 producing stromal-cell line FBMD-1 was dose-dependently significantly reduced to 56.7% ± 8.6% migration of untreated controls at 100μM AMD3100 (n=4). Lower concentrations also significantly reduced migratory activity of BV-173. In a stroma-dependent co-culture AMD3100 dose-dependently increased susceptibility of BV-173 towards simultaneous treatment with Imatinib at a dose of 1.6μM. We saw 23% ± 8% PI+ cells in the control without AMD3100 vs. 40% ± 12% PI+ cells al 100μM AMD3100 (n=3; p=0.06). Incubation with 10μM and 1μM AMD3100 only resulted in a slight increase of PI+ cells to 28% ± 13% at 1μM and 29% ± 3 at 10μM respectively.

The same assays on the AML-cell line HL-60 and on the BCR-ABL+ cell line SD-1 led to a significant reduction in SDF-1 dependent chemotaxis and stromal-dependent migration especially at the 100μM concentration but on a level with higher transmigration rates. Interestingly, for these cell lines we found lower CXCR4 surface expression (MFI: 478 ± 71 for the BV-173 vs. 29 ± 8 for the HL-60 and 17 ± 1.5 for the SD-1) going hand in hand with lower effects on migration rates following incubation with AMD3100 than we could show for the CML cell line BV-173.

We conclude that co-treatment with AMD3100 and Imatinib leads to a sensitization of BCR-ABL+ leukaemia cells which is dependent on the baseline CXCR4 expression. This is a promising strategy to reduce residual BCR-ABL+ leukaemia cell load in CML patients.

Disclosures: Mr. Fruehauf is a memeber of the scientific advisory board of AnorMED.

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