Growth suppression of transformed cells by a human placental extract not related to transforming growth factor beta

We have examined whether human placental extracts contain tumour-growth-inhibitory factors. One fraction (EAP) from such extracts inhibited growth, in soft agar, of Ha-ras-transformed BALB/c 3T3 cells and human squamous lung carcinoma A-2182 cells. However, this fraction had no effect on the anchorage-dependent growth of these cells, although there was a slight mitogenic activity on nontransformed cells. These data together with those on plating efficiency indicated no significant cytotoxicity of EAP on transformed cell lines. Although this fraction contained transforming growth factor beta (TGF beta), this cannot account for its inhibitory activity, since (a) pure TGF beta does not inhibit anchorage-dependent growth of Ha-ras-transformed BALB/c 3T3 cells, (b) EAP retains its inhibitory activity in the presence of antibodies against TGF beta and (c) the inhibitory activity did not copurify with TGF beta. Partial characterization of our inhibitory factor suggests that the inhibitory factor is a new tumour-growth-inhibitory factor.