Treatment of metastatic
renal cell cancer (RCC) with
antiangiogenic agents that block
vascular endothelial growth factor (
VEGF) receptor 2 signaling produces
tumor regression in a substantial fraction of patients; however, resistance typically develops within 6 to 12 months. The purpose of this study was to identify molecular pathways involved in resistance. Treatment of mice bearing either 786-0 or A498 human RCC xenografts with
sorafenib or
sunitinib produced
tumor growth stabilization followed by regrowth despite continued
drug administration analogous to the clinical experience.
Tumors and plasma were harvested at day 3 of
therapy and at the time of resistance to assess pathways that may be involved in resistance. Serial perfusion imaging, and plasma and
tumor collections were obtained in mice treated with either placebo or
sunitinib alone or in combination with intratumoral
injections of the angiostatic
chemokine CXCL9.
Sunitinib administration led to an early downmodulation of IFNγ levels as well as reduction of IFNγ receptor and downstream angiostatic
chemokines CXCL9 to 11 within the
tumor. Intratumoral injection of CXCL9, although producing minimal effects by itself, when combined with
sunitinib resulted in delayed resistance in vivo accompanied by a prolonged reduction of microvascular density and
tumor perfusion as measured by perfusion imaging relative to
sunitinib alone. These results provide evidence that resistance to
VEGF receptor therapy is due at least in part to resumption of angiogenesis in association with reduction of IFNγ-related angiostatic
chemokines, and that this resistance can be delayed by concomitant administration of CXCL9.