The biological effects of the growth-inhibiting epidermal pentapeptide, pyroGlu-Glu-Asp-Ser-GlyOH (EPP), were studied at cell and gene level. After treatment with high doses of EPP (1,000 ng/ml 2 nanomol/ml), 3H-TdR incorporation was reduced in both non-transformed (NC3H10) and transformed (TC3H10) cells. These findings were corroborated by flow cytometry DNA distributions that revealed that the fraction of cells with G1 DNA content was increased while the fraction of cells with S phase DNA content was reduced in both cell lines. In addition, a site-selective analogue of cyclic AMP (cAMP), 8-Br-cAMP, was found to inhibit proliferation of the two fibroblast cell lines, but the transformed cells were more sensitive to this agent. When both EPP and 8-Br-cAMP were given together to cultures of NC3H10 or TC3H10 cells the transformed TC3H10 cells were inhibited whilst there was no obvious effect on NC3H10 cell proliferation. The results of Northern blots showed that RNA expression of c-fos, ki-ras, and neu genes in TC3H10 cells decreased following treatment with EPP. The results could indicate that N-substituted growth-inhibiting oligopeptides may have an anti-tumor effect when combined with 8-Br-cAMP.

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