FINITE PROLIFERATIVE LIFE-SPAN IN-VITRO OF A HUMAN BREAST-CANCER CELLSTRAIN ISOLATED FROM A METASTATIC LYMPH-NODE

We recently described culture conditions that allow proliferation of m etastatic human breast cancer cells from biopsy specimens of certain p atient samples. These conditions resulted in the development of an imm ortalized cell strain designated SUM-44PE. These same culture conditio ns were used to isolate a human breast cancer cell strain from a metas tatic lymph node of a separate breast cancer patient. The SUM-16LN hum an breast cancer cells isolated from this specimen were cultured eithe r in serum-free medium or serum-containing medium supplemented with in sulin and hydrocortisone. Unlike the SUM-44PE cells that have prolifer ated in culture continuously for over two years, SUM-16LN cells prolif erated in culture for approximately 200 days and underwent 15 to 20 po pulation doublings before undergoing cell senescence. No cells of this strain proliferated beyond passage 8. SUM-16LN cells were keratin-19 positive and had an aneuploid karyotype. These cells overexpressed p53 protein and had an amplified epidermal growth factor (EGF) receptor g ene that resulted in high level expression of tyrosine phosphorylated EGF receptor protein. Despite the presence of high levels of tyrosine phosphorylated EGF receptor in these cells, they proliferated in serum -free, EGF-free medium and did not secrete detectable levels of EGF-li ke mitogenic growth factor. In addition, these cells were potently gro wth inhibited by all concentrations of exogenous EGF tested and by the neutralizing EGF receptor antibody Mab 425. These results suggest tha t the high level of tyrosine phosphorylated EGF receptor present in th ese cells is the direct result of receptor overexpression and not the result of the presence of a simulatory ligand. Thus, SUM-16LN represen ts a human breast cancer cell strain that exhibited genetic and cellul ar characteristics of advanced human breast cancer cells. Nevertheless , these cells exhibited a finite proliferative lifespan in culture, su ggesting that cellular immortalization is not a phenotype expressed by all human breast cancer cells.