In simple terms, the study found that the natural peptide thymosin‑alpha‑1 can slow down the growth of human non‑small cell lung cancer cells in lab dishes and in mice, but its smaller pieces don’t work as well.

The effect of thymosin alpha 1 (THN alpha 1) and its NH2-terminal fragment (THN1-14) and COOH-terminal fragment (THN15-28) on non-small cell lung cancer (NSCLC) growth was evaluated. Using an anti-THN alpha 1 antibody, receptors were identified on NSCLC cells that were pretreated with 10(-6) M THN alpha 1. [3H]Arachidonic acid was readily taken up by NSCLC cells and THN alpha 1 significantly increased the rate of arachidonic acid release. THN1-15 slightly stimulated but THN15-28 and THN beta 4 did not alter arachidonic acid release from NCI-H1299 cells. In clonogenic growth assays in vitro, THN alpha 1 (10(-6) M) significantly decreased NSCLC colony number whereas THN1-14, THN15-28, and THN beta 4 were less potent. Using growth assays in vivo, THN alpha 1 (10 micrograms s.c./day) but not THN1-14, THN15-28, or THN beta 4 inhibited significantly NSCLC xenograft formation in nude mice. These data suggest that biologically active THN alpha 1 receptors are present on NSCLC cells and that native THN alpha 1 inhibits the growth of human NSCLC.