Effects of the Ruthenium (II) Arene Complexes with 1,3,5-Triaza-7-Phosphaadamantane Ligand (RAPTA) on the Human Breast Cancer Suppressor Gene BRCA1 and Its Encoded Protein

Abstract

The ruthenium(II) arene complexes with 1,3,5-triaza-7- phosphaadamantane ligand, namely RAPTA complexes (RAPTAs), have been reported to overcome drug resistance in cisplatin-resistant cancer cells. However, the exact mechanism of these complexes remains largely unknown. Here, we presented the effects of the RAPTAs on the human breast cancer suppressor gene BRCA1 and its encoded protein. The RAPTAS induced the conformational change of the plasmid DNA in similar pattern. RAPTA-C formed in vitro interstrand Ru-BRCA1 adducts more rapidly than carboRAPTA-C, preferentially attacked the base of A, C, and G (not T) in the order and consequently inhibited BRCA1 amplification. The in vitro interactions of the RAPTAS with the N-terminal region of the BRCA1 RING domain proteins have been performed. The binding of the ruthenium compounds to the BRCA1 proteins resulted in change in protein conformation, a release of Zn2+ ions in a dose- and time- dependent manner, as well as thermal alteration of ruthenated BRCA1 proteins, causing the inactivation of the BRCA1-mediated E3 ubiquitin ligase function, which plays an essential role in response to DNA damage repair. The D67Y BRCA1 reduced ubiquitination function and was more susceptible to RAPTAs treatment than the D67E BRCA1. In addition, other metal complexes including ruthenium(II) polypyridyl complexes (Ru-bpy and Ru-phen), and gold(III) complexes (Auphen and Auterpy) were used for comparison on metal-BRCA1 interaction. Surprisingly, Ru-bpy-, Ru- phen-, Auphen-, and Auterpy-treated BRCA1 showed strongly changes in protein conformation, the release of Zn2+ ions in a dose- and time-dependent manner, resulting in the inactivation of the BRCA1-mediated E3 ubiquitin ligase, equivalent to RAPTA- EA1-treated BRCA1. HCC1937 cells apperred to be more sensitive against the RAPTAS or ruthenium(II) polypyridyl complexes than MCF-7 or MDA-MB-231 cells. The combination treatment of RAPTA-EA1 and olaparib exhibited a synergistic effect and showed a higher ability of inhibiting cell proliferation than RAPTA-EA1 or olaparib alone, with a 5-fold higher ability to inhibit E3 ligase activity than RAPTA- EA1 alone. These findings could provide insights into the underlying molecular mechanism by which the RAPTAs exerted on the BRCA1 gene and its encoded protein. In addition, this could raise the possibility of utilizing the BRCA1, especially in mutant proteins, as a potentially molecular target for metal-based drugs in breast cancer chemotherapy.