Inhibition of human breast cancer cell (MCF-7) growth in vitro by the somatostatin analog SMS 201-995: effects on cell cycle parameters and apoptotic cell death.

Somatostatin (SS) and SS analogs have been shown to exert an antiproliferative effect on several transplantable tumors in animals and to reduce the growth of pancreatic, pituitary, and mammary tumor cells in vitro. We evaluated the effects that the SS analog SMS 201-995 exerts on growth, cell-cycle parameters, and suicidal cell death (apoptosis) of human breast cancer cells (MCF-7) in vitro. SMS 201-995 significantly reduced the MCF-7 cell growth induced by serum, estradiol, insulin, and insulin-like growth Factor-I in both short term and long term experiments. The effect was maximal when 10 nM estradiol was used as mitogen in long term cultures. SMS 201-995 treatment produced a slight but transient accumulation of cells in the G2/M phase but did not cause any noteworthy reduction in the percentage of proliferating cells. There was, instead, a time-related increase in the number of cells with the flow-cytometric characteristics of apoptosis in the cultures treated with the SS analog, which correlated well with its growth-inhibiting activity. It would, therefore, seem that SMS 201-995 exerts its inhibitory effect on MCF-7 cell growth in vitro mainly by enhancing the rate of programmed (or suicidal) cell death in the culture.