Regional emergence of metastatic heterogeneity in a growing tumor.

Clones and subcloned cell lines of the murine B16 melanoma tumor were used to address the question of whether in vivo and in vitro growing tumors exhibit zonal metastatic heterogeneity. Cell clones were recloned in a semi-solid medium or injected subcutaneously into C57BL/6 mice, sublines of the parental colonies were established in culture from defined colonies that grew in suspension in the same agarose plate and from different regions of an in vivo growing tumor. Induction of experimental lung metastases after intravenous inoculation of 5 X 10(4) viable cells from these cell lines revealed that, both in vivo and in vitro zonal growth may induce the emergence of tumor cells exhibiting metastatic heterogeneity. Furthermore, metastatic diversity in the B16 melanoma clones occurred at a higher frequency during in vivo growth as compared to in vitro cultivation. All the cloned cell lines were found to be aneuploid with unstable chromosome number.