Angiogenesis-dependent tumor spread in reinforced fibrin clot culture

To investigate the role played by developing microvessels in the spread of tumors, segments of rat aorta were cultured with aggregates of NBT-II-81, a cell line derived from squamous cell carcinoma of rat bladder. Aortic rings cultured in plasma clot gave rise to microvascular networks composed of branching endothelial channels. Aggregates of carcinoma in contract with fibrin clot alone grew slowly and by expansion. When the proliferating branching endothelial sprouts and channels contacted the tumor aggregates, the pattern of neoplastic growth changes abruptly, as carcinoma cells infiltrated the fibrin clot, migrating and proliferating in periendothelial location. Some vascular channels were disrupted and permeated by cords of invading tumor cells. Ultrastructural studies revealed intimate associated between invading epithelial cells and endothelial cells. Focal fusion of the endothelial basal lamina with the basal lamina of the tumor cells was observed. Our results demonstrate that angiogenesis in vitro, ie., in absence of active circulation, markedly enhanced the spread of a carcinoma in plasma clot and modified its pattern of growth. This indicates that other vascular-related factors beside nutritional gradients from the circulation attract tumor cells along endothelial paths.