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Bone marrow (BM)-derived mesenchymal stem cells (MSCs) have been shown to favor tumor growth, suggesting the relevance of pharmaceutical inhibition of MSCs for the treatment of malignancies. We tested the effect of PTK787/ZK 222584 (PTK) on the outgrowth of MSCs from human bone marrow-derived mononuclear cells (MNCs) and the migration and tube formation capacity of MSCs in vitro. PTK dose-dependently inhibited the outgrowth of BM-MSCs from BM-MNCs (LC50 1.12 microM PTK), while hematopoietic colony formation (HCF) was only slightly hampered (13 +/- 19% at 1 microM PTK, and stable at approximately 50% at higher concentrations of PTK). Addition of 10 microM PTK inhibited proliferation of MSCs by 74 +/- 6.6% compared to control (p < 0.0001) and increased apoptosis of MSCs by 63 +/- 7.7% (p < 0.01). In addition, upon addition of PTK, BM-MSCs showed impaired tube formation as well as reduced migration (52 +/- 19%, p = 0.006) compared to control. Pepchip array analysis revealed that PTK effectively inhibits activity of kinases involved in cell cycling (WEE1 and several cyclin dependent kinases), and migratory processes (including Rho kinase). In conclusion, we show that PTK impairs outgrowth, proliferation, migration and tube formation of human BM-MSCs. In addition, we show the usability of Pepchip array analysis as a powerful tool for kinase activity profiling in functional studies since the effect of PTK on the kinome profile of MSCs corresponds with the observed functional effects of PTK on proliferation and migration. Inhibition of BM-MSCs and their contribution to tumor growth may be an additional strategy for treatment of cancer in the future.

Acute myeloid leukemia (AML) is a disease with a poor prognosis. It has been demonstrated that AML cells express the vascular endothelial growth factors, VEGFA and VEGFC, as well as kinase insert domain-containing receptor (VEGFR2), the main receptor for downstream effects, resulting in an autocrine pathway for cell survival. This study investigates the role of the VEGFR inhibitor PTK787/ZK 222584 in leukemic cell death, and the possibility of an additional effect on cell death by a chemotherapeutic drug, amsacrine. In three AML cell lines and 33 pediatric AML patient samples, we performed total cell-kill assays to determine the percentages of cell death achieved by PTK787/ZK 222584 and/or amsacrine. Both drugs induced AML cell death. Using a response surface analysis, we could show that, in cell lines as well as in primary AML blasts, an equal magnitude of leukemic cell death could be obtained when lower doses of the more toxic amsacrine were combined with low dosages of the less toxic VEGFR inhibitor. This study shows that PTK787/ZK 222584 might have more clinical potential in AML when combined with a chemotherapeutic drug such as amsacrine. In future, it will be interesting to study whether the complications and the long-term effects of chemotherapy can be reduced by lowering the dosages of amsacrine, and by replacing it with other drugs with lower toxicity profiles, such as PTK787/ZK 222584.