Serum-free growth of human mammary epithelial cells: rapid clonal growth in defined medium and extended serial passage with pituitary extract.

A serum-free medium with bovine pituitary extract as the only undefined supplement has been developed for long-term culture of human mammary epithelial cells. This medium supports serial subculture of normal cells for 10-20 passages (1:10 splits) without conditioning or special substrates, and it supports rapid clonal growth with plating efficiencies up to 35%. It consists of an optimized basal nutrient medium, MCDB 170, supplemented with insulin, hydrocortisone, epidermal growth factor, ethanolamine, phosphoethanolamine, and bovine pituitary extract. Replacement of pituitary extract with prostaglandin E1 and ovine prolactin yields a defined medium that supports rapid clonal growth and serial subculture for three or four passages. Cultures initiated in these media from normal reduction mammoplasty tissue remain diploid and maintain normal epithelial morphology, distribution of cell-associated fibronectin, expression of keratin fibrils, and a low level of expression of milk fat globule antigen. Large cell populations can now be generated and stored frozen, permitting multiple experiments over a period of time with cells from a single donor. These media greatly extend the range of experiments that can be performed both conveniently and reproducibly with cultured normal and tumor-derived human mammary epithelial cells.