The effects of mono, duple and triple treatment with octreotide, galanin and serotonin on a human colon cancer cell line (SW 620) were investigated. The cancer cells were exposed to a dose corresponding to 20 µg/kg body weight/day, and to 50 and 25% of this dose (0.2, 0.1 and 0.05 µg/ml). The cells were observed at the intervals: 3, 6, 12, 24 and 48 h. MTT-assay was used to determine numbers of viable cells. Proliferation and apoptosis were detected by immunocytochemistry using the avidin-biotin complex (ABC) method. The antibodies used were anti-Ki-67, anti-poly (ADP-ribose) polymerase ‘PARP’ and anti-Bcl-x. Proliferative and apoptotic indices were determined by computerized image analysis. Almost all the mono and duple treatments of the bioactive substances succeeded in reducing the numbers of viable cells. With triple treatment, however, this decrease was greater and was evident at all observation times. The effect on proliferation varied between none, and an enhancing or inhibiting action, depending on the dose, combination and observation time. The effect on apoptosis of mono or duple exposure to the bioactive gut substances varies, depending on the concentration, combination and observation time. Triple combination at the effective dose increased the apoptotic index, with the two markers used, and appeared after 6 h, extending up to 48 h. The reduction in the number of viable cancer cells was greater and occurred earlier than the increase in apoptosis and was observed whether the bioactive substances were used alone or in combinations and at different concentrations. It is therefore conceivable that some other mechanism(s) than apoptosis is involved which inhibits cancer cell respiration. It is possible that some of the dramatic in vivo changes seen earlier, following triple treatment with octreotide, galanin and serotonin, may have been direct effects of these substances on cancer cells.

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