The most potent and efficient bioconjugate which has been evaluated in in vitro cytostatic effect measurements on human breast cancer cells (MCF7) and human colon cancer cells (HT-29), is GnRH-III–[4Lys(Bu), 8Lys(Dau=Aoa)] (K2). This evidence concerns the gene GNRH1 and malignant colon neoplasm.