Functionalization of Ruthenium(II) Terpyridine Complexes with Cyclic RGD Peptides To Target Integrin Receptors in Cancer Cells

The lack of selectivity for cancer cells and the resulting negative impact on healthy tissue is a severe drawback of actual cancer chemotherapy. Tethering of cytotoxic drugs to targeting vectors such as peptides, which recognize receptors overexpressed on the surface of tumor cells, is one possible strategy to overcome such a problem. The pentapeptide cyc(RGDfK) targets the integrin receptor α_vβ₃, important for tumor growth and metastasis formation. In this work, two terpyridine-based Ru^II complexes were prepared and for the first time conjugated to cyc(RGDfK) through amide bond formation, which resulted in a monomeric and a dimeric bioconjugate. Both Ru^II complexes were found to bind strongly and selectively to integrin α_vβ₃, and the dimeric molecule displayed a 20-fold higher affinity to the receptor than the monomeric one. However, the cytotoxicity of the complexes and related bioconjugates against human A549 and SKOV-3 cell lines is still not sufficient for application as anticancer agents. Nevertheless, considering the high selectivity for integrin receptor α_vβ₃, the synthesis of Ru-based bioconjugates with cyc(RGDfK) paves a promising way towards the design of effective targeted anticancer agents.