Dynamic assessment of angiogenesis in renal cell carcinoma spheroids by intravital microscopy

Renal cell cancer represents a suitable tumor model for in vivo observation of neo-angiogenesis. We used intravital microscopy and the well established dorsal skin fold chamber model to characterize neo-angiogenesis in freely implanted renal cell cancer spheroids.

Tumor spheroids were implanted into dorsal skin fold chambers of 8 nude mice. At days 3, 6, 10 and 14 after implantation the newly vascularized spheroid area, density of perfused microvessels in the spheroid versus the periphery, capillary center erythrocyte velocity and capillary diameter were recorded by intravital microscopy. Video images were analyzed by a computer assisted image analysis device. After the experiments the chambers were analyzed morphologically.

The model enabled quantitative analysis of microcirculation and angiogenesis in the renal cell cancer spheroids during 14 days of observation. Mean spheroid center perfused microvessel density +/- SEM increased from 3 +/- 2 to 269 +/- 21 cm.-1 on days 3 to 10 and subsequently decreased to 189 +/- 38 cm.-1 on day 14. Spheroid periphery perfused microvessel density was significantly higher throughout the experiments, attaining a mean maximum of 522 +/- 34 cm. on day 14. Mean capillary diameter decreased continuously from 14.2 +/- 0.9 to 8.4 +/- 0.4 microm. on days 3 to 14. In contrast, mean capillary center erythrocyte velocity significantly increased during 14 days of observation from 0.09 + 0.02 mm. per second on day 3 to 0.24 +/- 0.08 mm. per second on day 14. Histological analysis after 14 days revealed the spheroids as cell clusters in the upper layers of the dorsal skin fold chamber.

The model is suitable for the analysis of renal cell cancer angiogenesis. Although it is heterotopic, angiogenesis in renal cell cancer spheroids mimics important characteristics of human renal cell cancer.