Tagged tumor cells reveal regulatory steps during earliest stages of tumor progression and micrometastasis

Histochemical marker genes were used to "tag" mouse fibrosarcoma or human neuroblastoma cells, providing a better understanding of their subsequent progression and metastasis mechanisms in nude mice. Micrometastases in the lung were initiated from clusters of 2-6 cells rather than single cells in most cases; tumor cells were also visualized binding to the endothelium of small blood vessels to initiate these micrometastases. Shortterm, these mechanisms relied heavily on fluidity of cell surface proteins, rather than nuclear events. Micrometastases in some organs were transient and never became established. Angiogenesis was visualized in both primary tumor systems via "fixation" of the animal's circulation; very small microvessels were growing toward the primary tumor as soon as 48-72 hours post-injection. Marker genes were also valuable for quantitating genetic instability of specific tumor cell populations and potential gene regulatory mechanisms operating in specific organ sites. These latter studies have direct relevance to the significance of N-myc oncogene amplification in neuroblastoma during progression and CD44 gene plasticity of expression in fibrosarcoma during metastasis. Marker gene-tagged single tumor cells can now be analyzed for gene regulatory events in virtually any organ and in combination with laser capture microdissection and other high-resolution methodologies, providing insight into the very earliest gene-regulatory events during micrometastasis