With the exceptionof 6-Cl derivatives, in cellular systems, all compounds showed notableantitumor activity in COX-I/II against tumor cells HT-29 (IC50 = 1.5–2.7 μM),MDA-MB-231 (IC50 = 5.2–8.0μM), but less active against MCF-7 breast cancer cell line (IC50 = 15.2–22.9 μM).Hence, these results demonstrated that the interference with the COX-I/IIcascade contributes to the anticancer effects of the cobalt alkynecomplexes (Figure 44). Here, MT-CO1 is linked to breast cancer.