Tumor xenograft studies

For subcutaneous xenograft tumor models, female athymic nude/beige mice (Charles River Laboratories, Wilmington, MA) were housed and maintained in laminar flow cabinets under specific pathogen-free conditions. All experiments were approved by the Institutional Animal Care and Use Committee at Beth Israel Deaconess Medical Center. To establish RCC tumor xenografts, 786-O and A498 tumor cells were injected subcutaneously (10⁷ cells) into the flanks of 6–8 week old nude beige mice (~20 g on average). When tumors reached 12 mm length along the long axis (~500 mm³ in volume), mice were randomized into treatment groups (5–8 mice per group). The person performing tumor measurements was different from the person treating the animals so the measurements were performed in a blinded fashion. Our prior studies showed that VEGFR TKI treatment consistently and markedly decreases tumor vasculature and tumor blood flow (measured by perfusion MRI at day 3–10 of therapy). There followed, however, significant recovery of MRI-measured tumor perfusion despite continued treatment, a marker of development of resistance to VEGFR TKI therapy¹³. Treatment was continued until tumors reached 20 mm length along the long axis or until 50 days after treatment initiation.