GNRH1 and colon carcinoma: Among these conjugates, [4Lys(Bu)]-GnRH-III(Dau=Aoa) containing butyric acid (Bu) acylated at the 4Lys residue was proved to be the most potent one in all different assays (enzymatic stability, cellular uptake, and in vitro antitumor activity) on HT-29 colon carcinoma cell lines [19].