Human neuroblastoma (NB) is the second most frequent solid tumor of childhood and represents a highly heterogeneous disease at clinical and biologic levels. Little progress has been made to improve the poor prognosis of patients with high-stage NB. Tumor progression and metastatic dissemination still represent major obstacles to the successful treatment of advanced stage disease. In order to develop and evaluate new, targeted, therapeutic strategies, fully defined and biologically relevant in vivo models of NB are strongly needed. We have developed an orthotopic model of metastatic human NB in the nude mouse, using 2 well-characterized NB cell lines. Tumor growth, vascular properties and metastatic patterns were investigated using a sensitive and newly developed in vivo echographic technology in addition to immunohistochemistry and PCR analyses. Results show that implantation of low numbers of NB cells directly into the adrenal gland of nude mice resulted in rapid and homogeneous tumor growth without tumor morbidity. Nude mice were shown to rapidly develop highly vascularized adrenal tumors that selectively metastasized to the liver and bone marrow. In addition, the newly formed mouse vessels in orthotopic but not in heterotopic tumors, were found to express the highly angiogenic ␣v3 Human neuroblastoma (NB) is one of the most frequent solid tumors of childhood and represents a highly heterogeneous tumor at clinical and biologic levels. 1,2 Spontaneous regressions are common in children under 1 year of age and in low-stage tumors, while NB is extremely aggressive in older children with high-risk and metastatic disease, which are often associated with genetic lesions such as MYCN oncogene amplification or 1p deletions. 3 Little progress has been made toward improving the poor prognosis of patients with high-stage NB. Tumor progression and metastatic dissemination still represent major obstacles in the successful treatment of advanced stage NB, despite intensive multimodal treatments. In order to investigate the in vivo metastatic process and to develop and evaluate new, targeted, therapeutic strategies, well-defined in vivo models of tumor cell growth and dissemination are strongly needed. The outcome of the metastatic process depends on multiple and complex interactions between malignant cells and the host microenvironment. 4 In particular, neovascularization has been shown to be a major prerequisite for tumor growth and dissemination. 5-9 Indeed, angiogenesis in NB tumors correlates with metastatic disease, MYCN amplification and poor outcome. 10 Ectopic transplanted tumor models, e.g., subcutaneously growing tumors, allow rapid screening of potentially active compounds. Transgenic models offer opportunities to study early cellular and molecular events in tumor progression and metastasis, but are rather difficult to use for therapeutic experiments. Orthotopic transplantation of tumor cells represents a favorable condition for the analysis of metastasis-related processes and the study of organspecific determina...
