A small molecular weight growth inhibitory factor in tissue culture supernatants

A small molecule in tissue culture supernatants has growth inhibitory effects on the parent and other cells. Supernatants from stationary phase cultures of a human normal lymphoid cell line (No. 802) inhibited the growth of the parent cells even when the latter were in optimal concentrations. The inhibitory activity was associated with small molecular weight fractions prepared by filtration. Fractions with materials smaller than 5000 daltons were the most active. Growth inhibition was observed also with fractions smaller than 2000 and 1000 daltons. Similar growth inhibition of parent cells was observed with the small molecular weight fractions of supernatants from the human acute lymphoblastic leukemia cell line CCRF-SB, the human lung Ca cell line A-549 and from a mouse leukemia L1210 line. The latter were inhibited only in the absence of serum. The fractions from all 3 human cell lines inhibited the cells from all human lines indicating a lack of tissue specificity. The fractions from the human 802 line and the mouse L1210 line did not inhibit the cell growth of each other. Species specificity, however, cannot as yet be considered established.