Synthesis and biological assessment of a ruthenium(II) cyclopentadienyl complex in breast cancer cells and on the development of zebrafish embryos

Abstract

Ruthenium-based complexes currently attract great attention as they hold promise to replace platinum-based drugs as a first line cancer treatment. Whereas ruthenium arene complexes are some of the most studied species for their potential anticancer properties, other types of ruthenium complexes have been overlooked for this purpose. Here, we report the synthesis and characterization of Ru(II) cyclopentadienyl (Cp), Ru(II) cyclooctadienyl (COD) and Ru(III) complexes bearing anastrozole or letrozole ligands, third-generation aromatase inhibitors currently used to treat estrogen receptor-positive (ER+) breast cancer. Among these complexes, Ru(II)Cp 2 was the only species found to be stable in DMSO and in cell culture media and as a result, the only complex for which the in vitro and in vivo biological activities were investigated. Unlike anastrozole alone, complex 2 was considerably cytotoxic in vitro (IC50 values < 1μM) in human Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Cationic RuII Cyclopentadienyl Complexes with Antifungal Activity against Several Candida Species

“…RuÀ Cl, [Ru-ACN] + and [Ru-ATZ] + (Figure 2) were synthesized and purified according to previously reported procedures. [56,58,59] Due to the generally poor water-solubility of metal-based drug candidates, the preparation of stock solutions of these compounds in an organic solvent (usually DMSO), followed by their dilution in cell growth media, is routinely achieved prior to testing their biological activity. [60,61] Although DMSO is commonly used for this purpose, the solubility [61] and stability assessment of drug candidates in this solvent are often overlooked.…”

“…The three complexes were also found to be highly stable in DMSO, as no spectral alteration was observed by UV/Vis (at 0.8 mM) up to at least 30 minutes ( Figure S2). [56] The in vitro antifungal activity of the three complexes was evaluated against five different Candida species (albicans, glabrata, tropicalis, krusei and lusitanae). Their activity was also assessed against a Cryptococcus neoformans strain, an emerging pathogen, known as a cause of a meningitis with a high death rate partly due to its emerging resistance to antifungal drugs such as FCZ.…”

“…The study presented here was motivated i) by the fact that, although several organoruthenium complexes were previously studied for this purpose, [34,40,41,44,48] the antifungal activity of Ru IIcyclopentadienyl complexes has so far scarcely been examined, but also ii) by the unique features of a cationic Ru II -cyclopentadienyl complex of anastrozole (ATZ) we recently reported ([Ru-ATZ] + , Figure 2), which showed promising stability in biologically relevant conditions, in vitro anticancer activity against different human breast cancer cell lines and low systemic in vivo toxicity on the development of zebrafish embryos. [56] ATZ is a triazole-containing aromatase inhibitor that inhibits the activity of the human P450 enzyme CYP19, aromatase, by blocking the production of estrogen in postmenopausal women diagnosed with estrogen receptor-positive breast cancer. [56] Given the similarity between the anti-aromatase (CYP19) mode of action of ATZ and the anti-CYP51 mode of action of the azole-containing antifungal drugs such as FCZ, [19] both involving an interaction between a triazole nitrogen [57] and the iron of a P450 enzyme cofactor, we reasoned that the presence of a metal-uncoordinated triazole moiety in [Ru-ATZ] + could be a factor enhancing its antifungal activity.…”

“…[56] ATZ is a triazole-containing aromatase inhibitor that inhibits the activity of the human P450 enzyme CYP19, aromatase, by blocking the production of estrogen in postmenopausal women diagnosed with estrogen receptor-positive breast cancer. [56] Given the similarity between the anti-aromatase (CYP19) mode of action of ATZ and the anti-CYP51 mode of action of the azole-containing antifungal drugs such as FCZ, [19] both involving an interaction between a triazole nitrogen [57] and the iron of a P450 enzyme cofactor, we reasoned that the presence of a metal-uncoordinated triazole moiety in [Ru-ATZ] + could be a factor enhancing its antifungal activity. It is interesting to note that Turel et al previously reported a similar approach with Ru-cymene complexes bearing azole-containing antifungal agents for the treatment of a non-Candida fungal species, Curvularia lunata.…”

Rationally Designed Ruthenium Complexes for Breast Cancer Therapy

“…Notably, more than 50% of zebrafish embryos treated with cisplatin under the same conditions could not hatch after 96 h, a clear indication of the toxicity of this chemotherapeutic agent [40]. Importantly, Castonguay et al (2020) recently developed a novel ruthenium(II) cyclopentadiene (Cp) complex of anastrozole (3) ( Figure 1) with a high in vitro cytotoxicity not only in ER+ breast cancer cells (IC 50 = 0.50 ± 0.09 µM, MCF7; 0.32 ± 0.03 µM, T47D) but also in a TNBC cell line, MDA-MB-231 (IC 50 = 0.39 ± 0.09 µM) [51]. Although this species was also cytotoxic in a non-cancerous breast cell line, MCF-12A (IC 50 = 0.58 ± 0.02 µM), no apparent in vivo toxicity was observed on the development of zebrafish embryos at concentrations around its IC 50 values.…”