Serum-free medium conditioned by activated cells of the acute monocytic leukemia line, THP-1, was examined for growth-inhibitory activity with several established human cell lines. Freefloating clusters of THP-1 cells were activated into adherent nonproliferating cells by a 24-hr exposure to 10-7m mezerein in Roswell Park Memorial Institute 1640 medium containing 1% fetal bovine serum. Adherent cells were incubated for an additional 24 hr in serum-free medium containing insulin (5 µg/ml). Dose-response studies revealed that a cervical carcinoma (HeLa), a melanoma (A375Ag5), and several mammary carcinoma cell lines (MCF-7, BT474, MDA-MB415, and T47D) were growth inhibited by this conditioned medium. We concluded, from the results of thymidine release assays and from experiments on reversibility, that inhibition was a cytostatic and not a cytolytic response. In contrast, THP-1 conditioned medium stimulated the growth of two mammary lines (ZR75-1 and HBL-100), a lung type II carcinoma (549), and a colon adenocarcinoma (SW48). Preliminary characterization showed that the inhibitory activity was stable to acid and urea treatment but was destroyed by trypsin and sodium dodecyl sulfate. Molecular sieve chromatography of acetic acid-extracted material separated the inhibitory and stimulatory components.


Supported by a Biomedical Research Grant from The Pennsylvania State University.

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