Inhibition of hormone and growth factor responsive and resistant human breast cancer cells by CeReS-18, a cell regulatory sialoglycopeptide

We have previously documented that CeReS-18, a cellregulatory sialoglycopeptide, inhibits the cellular proliferation of normaland transformed cell types from a diverse rangeof species. Most cell types studies exhibit asimilar sensitivity to the reversible but growth inhibitoryeffects of CeReS-18 at 7 × 10^-8 Mconcentration, while at higher concentrations CeReS-18 can elicitcytotoxicity. The present study was conducted to examinethe effect of CeReS-18 on the proliferation ofhuman mammary epithelial carcinoma cells. MCF-7 cells, whichare estrogen receptor positive (ER⁺), and BT-20 cells,which are estrogen receptor negative (ER^-), were utilized.Both cell lines show equal sensitivity to growthinhibition elicited by CeReS-18. Complete cessation of cellcycling was achieved with 7 × 10^-8 MCeReS-18, and the arrest was shown to becompletely reversible. Flow cytometric analysis, performed on CeReS-18treated cells from both cell types, revealed thatthe majority of these cells were arrested inthe G1 phase of the cell cycle. Whencells were treated simultaneously with inhibitor and stimulatoryconcentrations of mitogens such as epidermal growth factor(EGF), basic fibroblast growth factor (b-FGF), estrogen, insulin-likegrowth factors I and II (IGFI and IGFII),no alteration of the inhibitory activity of CeReS-18was observed. CeReS-18 clearly abrogated the mitogenic activitythat these growth factors elicited with human mammarycarcinoma cells.