Aneuploid primary cancers metastasize as diploid cancer stem cells

The standard cancer treatment modalities have focused on destroying daughter cancer cells while having minimal effect on Cancer Stem Cells (CSCs). The details of the underlying mechanism by which CSCs metastasize in our sarcoma model are presented. To understand the fundamental process of metastatic disease, we used a chemically induced cancer model by painting the shaved distal thigh musculature of DBA/6J mice with 1.0% 3-methylcholanthrene in sesame oil. Approximately 90% of the mice developed an intramuscular tumor in situ within six months. The original chemically induced cancer cells were enzymatically dissociated into single cells, and 5 × 10 4 sarcoma cells in 0.1 ml were injected intramuscularly into new mice. Using our DAPI-Nuclear Isolation Medium and our high-resolution DNA flow cytometry, we generated DNA histograms of the tumor cell populations. When the primary tumors reached 2.0 cm in diameter, metastatic nodes in the lungs were detected using an India ink contrast stain after dissecting about 10 small 1.0 mm metastatic nodules and enzymatically dissociating the metastatic cancer cells into viable populations, as described above. The metastatic tumors were almost exclusively diploid, showing a normal total DNA content. When diploid metastatic tumors were transplanted intramuscularly, they grew as an aneuploid population containing both diploid cancer stem cells and aneuploid daughter cancer cells, with the same DNA Index, which served as a fingerprint of each original tumor. We could repeat this process many times. Our early observations revealed that the diploid population of an aneuploid cancer was the most virulent to metastasis. The diploid metastatic CSCs with their low S-phase would have a good chance of escaping the immune system, as their cell surfaces would appear normal. They would also be less affected by chemotherapy or radiation therapy because of their low S-phase. All excised lung metastases between 2 and 8mm in diameter maintained their diploid DNA histogram pattern, with only 1% aneuploidy. These diploid metastases, after enzymatic single-cell preparations, were either transplanted into the flank of a new mouse or placed in cell culture. Aneuploid cells began to emerge from the diploid cell populations, resulting in a DNA index equivalent to that of the original chemically induced sarcoma. These data indicate that cancer stem cells (CSCs) originate in the diploid portion of the primary aneuploid sarcoma, as only these diploid cells can evade the immune system and establish diploid lung metastases. The diploid CSCs still retained the capacity to transform into daughter aneuploid cells.