Inhibition of angiogenesis induces chromaffin differentiation and apoptosis in neuroblastoma

Inhibition of angiogenesis has been shown to reduce tumor growth, metastasi s, and tumor microvascular density in experimental models. To these effects we would now like to add induction of differentiation, based on biological analysis of xenografted human neuroblastoma (SH-SY5Y, WAG rnu/rnu) treated with the angiogenesis inhibitor TNP-470. Treatment with TNP-470 (10 mg/kg s.c., n = 15) reduced the tumor growth by 66% and stereological vascular pa rameters (L-V, V-V, S-V) by 36-45%. The tumor cell apoptotic fraction incre ased more than threefold, resulting in a decrease in viable tumor cells by 33%. In contrast, the mean vascular diameter (29 mu m) and the mean tumor c ell proliferative index (49%) were unaffected. TNP-470-treated tumors exhib ited striking chromaffin differentiation of neuroblastoma cells, observed a s increased expression of insulin-like growth factor II gene (+ 88%), tyros ine hydroxylase (+ 96%), chromogranin A, and cellular processes. Statistica l analysis revealed an inverse correlation between differentiation and angi ogenesis. It is suggested that by inhibiting angiogenesis, TNP-470 induces metabolic stress, resulting in chromaffin differentiation and apoptosis in neuroblastoma. Such agonal differentiation may be the link between angiosta tic therapy and tumor cell apoptosis.