The Small-Molecule VEGF-Receptor Inhibitor Pazopanib (GW786034B) Targets Both Tumor and Endothelial Cells in Multiple Myeloma.

A critical role for vascular endothelial factor (VEGF) has been demonstrated in multiple myeloma (MM) pathogenesis. Here we characterized the effect of the novel and potent small-molecule VEGF-receptor inhibitor pazopanib on MM cells in the bone marrow milieu. Pazopanib inhibits VEGF-triggered signaling pathways in both tumor and endothelial cells, thereby blocking in vitro MM cell growth, survival, and migration; and inhibits VEGF-induced upregulation of adhesion molecules on both endothelial and tumor cells, thereby abrogating endothelial cell-MM cell binding and associated cell proliferation. We show that pazopanib is the first-in-class VEGF-receptor inhibitor to inhibit in vivo tumor cell growth associated with increased MM cell apoptosis, decreased angiogenesis, and prolonged survival in a mouse xenograft model of human MM. Low-dose pazopanib demonstrates synergistic cytotoxicity with conventional (melphalan) and novel (bortezomib, immunomodulatory drugs) therapies. Finally, gene expression and signaling network analysis show transcriptional changes of several cancer-related genes, in particular cMyc. Using siRNA, we confirm the role of cMyc in VEGF-production and -secretion, as well as angiogenesis. These preclinical studies provide the rationale for clinical evaluation of pazopanib, alone and in combination with conventional and novel therapies, to increase efficacy, overcome drug resistance, reduce toxicity, and improve patient outcome in MM.