Dynamic Contrast-Enhanced Magnet Resonance Imaging of Sunitinib-Induced Vascular Changes to Schedule Chemotherapy in Renal Cell Carcinoma Xenograft Tumors

In an attempt to develop better therapeutic approaches for metastatic renal cell carcinoma (RCC), the combination of the antiangiogenic drug sunitinib with gemcitabine was studied. Using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), we have previously determined that a sunitinib dosage of 20 mg/kg per day increased kidney tumor perfusion and decreased vascular permeability in a preclinical murine RCC model. This sunitinib dosage causing regularization of tumor vessels was selected to improve delivery of gemcitabine to the tumor. DCE-MRI was used to monitor regularization of vasculature with sunitinib in kidney tumors to schedule gemcitabine. We established an effective and nontoxic schedule of sunitinib combined with gemcitabine consisting of pretreatment with sunitinib for 3 days followed by four treatments of gemcitabine at 20 mg/kg given 3 days apart while continuing daily sunitinib treatment. This treatment caused significant tumor growth inhibition resulting in small residual tumor nodules exhibiting giant tumor cells with degenerative changes, which were observed both in kidney tumors and in spontaneous lung metastases, suggesting a systemic antitumor response. The combined therapy caused a significant increase in mouse survival. DCE-MRI monitoring of vascular changes induced by sunitinib, gemcitabine, and both combined showed increased tumor perfusion and decreased vascular permeability in kidney tumors. These findings, confirmed histologically by thinning of tumor blood vessels, suggest that both sunitinib and gemcitabine exert antiangiogenic effects in addition to cytotoxic antitumor activity. These studies show that DCE-MRI can be used to select the dose and schedule of antiangiogenic drugs to schedule chemotherapy and improve its efficacy.