Coactivation of the MDR1 and MYCN genes in human neuroblastoma cells during the metastatic process in the nude mouse.

In metastatic human neuroblastoma, MYCN amplification and MDR1 overexpression are frequently observed. No in vivo model is yet available for the study of the regulation of these two genes during the metastatic process of this disease. Culture of an involved bone marrow of a patient with stage IV neuroblastoma gave rise to an established in vitro neuroblastoma cell line, IGR-N-91, and a subsequent s.c. xenograft model in nude mice. When cultured in vitro, blood cells, bone marrow, and the myocardium of mice bearing s.c. tumor xenograft reproducibly yielded cells with morphological and molecular features of neuroblastoma cells, including consistent MYCN amplification (60 copies/haploid genome). Compared to the neuroblastoma cells of the primitive s.c. tumor xenograft, metastatic cells showed a significant increase in the MYCN gene transcript levels associated with an overexpression of the MDR1 gene mRNA levels leading to a P-glycoprotein capable of extruding Adriamycin. This study offers compelling evidence that (a) IGR-N-91 is a human neuroblastoma xenograft model able to induce metastasis in nude mice, (b) an increase in MYCN and MDR1 transcripts levels is associated with the metastatic process, and (c) IGR-N-91 provides a biological tool for the study of gene activations during tumor dissemination in neuroblastoma.