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Background: The aim of this research is the synthesis and characterization of coumarin-palladium complex and the investigation of the cytotoxicity of both the ligand and the complex. Methods: The palladium( II) complex (CC) was obtained in the reaction between (E)-3-(1-((4-hydroxy-3-methoxyphenyl)amino)ethylidene)-2,4-dioxochroman-7-yl-acetate (CL) and potassium-tetrachloropalladate(II) and characterized using IR and NMR spectra, experimentally and theoretically. Cytotoxicity of CL and CC were determined for human cervical carcinoma HeLa, ovarian cancer A2780, hormone dependent breast cancer MCF7, and colorectal cancer HCT116 lines. The interaction of investigated compounds with HSA was followed by spectrofluorimetric method. The binding mechanism in the active pocket was assessed via molecular docking simulations. Results: A low mean absolute error between experimental and theoretical data proved that the optimized structure corresponded to the experimental one. Both compounds showed a satisfactory selectivity index towards neoplastic cells. The binding affinity of tested compounds to the HSA were confirmed. The molecular docking showed a much lower change in the Gibbs free energy of binding for CC compared to CL. Conclusions: The obtained results revealed that CL and CC exhibit significant effects on several cancer cell lines and good binding properties to HSA, while molecular docking discovered that CC has the most pronounced activity against alpha-fetoprotein.

In the original publication [...]

The luminal A-subtype of breast cancer, where the oestrogen receptor α (ERα) is overexpressed, is the most frequent one. The prodrug tamoxifen (1) is the clinically used agent, inhibiting the ERα activity via the formation of several active metabolites, such as 4-hydroxytamoxifen (2) or 4,4′-dihydroxytamoxifen (3). In this study, we present the tamoxifen derivative 4-[1,1-bis(4-methoxyphenyl)but-1-en-2-yl]-2,2′-bipyridine (4), which was combined with platinum or palladium dichloride, the former a well-known scaffold in anticancer treatment, to give [PtCl2(4-κ2N,N′)] (5) or [PdCl2(4-κ2N,N′] (6). To prevent fast exchange of weakly coordinating chlorido ligands in aqueous solution, a bulky, highly stable and hydrophobic nido-carborate(−2) ([C2B9H11]2−) was incorporated. The resulting complexes [3-(4-κ2N,N′)-3,1,2-PtC2B9H11] (7) and [3-(4-κ2N,N′)-3,1,2-PdC2B9H11] (8) exhibit a dramatic change in electronic and biological properties compared to 5 and 6. Thus, 8 is highly selective for triple-negative MDA-MB-231 cells (IC50 = 3.7 μM, MTT test), while 7 is completely inactive against this cell line. The observed cytotoxicity of compounds 4–6 and 8 against this triple-negative cell line suggests off-target mechanisms rather than only ERα inhibition, for which these compounds were originally designed. Spectroscopic properties and electronic structures of the metal complexes were investigated for possible explanations of the biological activities.

The ineffectiveness and failing of chemotherapeutic treatments are often associated with multidrug resistance (MDR). MDR is primarily linked to the overexpression of ATP-binding cassette (ABC) transporter proteins in cancer cells. ABCG2 (ATP-binding cassette subfamily G member 2, also known as the breast cancer resistance protein (BCRP)) mediates MDR by an increased drug efflux from the cancer cells. Therefore, the inhibition of ABCG2 activity during chemotherapy ought to improve the efficacy of the administered anti-cancer agents by reversing MDR or by enhancing the agents’ pharmacokinetic properties. Significant efforts have been made to develop novel, powerful, selective, and non-toxic inhibitors of BCRP. However, thus far the clinical relevance of BCRP-selective MDR-reversal has been unsuccessful, due to either adverse drug reactions or significant toxicities in vivo. We here report a facile access towards carboranyl quinazoline-based inhibitors of ABCG2. We determined the influence of different methoxy-substitution patterns on the 2-phenylquinazoline scaffold in combination with the beneficial properties of an incorporated inorganic carborane moiety. A series of eight compounds was synthesized and their inhibitory effect on the ABCG2-mediated Hoechst transport was evaluated. Molecular docking studies were performed to better understand the structure-protein interactions of the novel inhibitors, exhibiting putative binding modes within the inner binding site. Further, the most potent, non-toxic compounds were investigated for their potential to reverse ABCG2-mediated mitoxantrone (MXN) resistance. Of these five evaluated compounds, N-(closo-1,7-dicarbadodecaboran(12)-9-yl)-6,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-quinazolin-4-amine (DMQCd) exhibited the strongest inhibitory effect towards ABCG2 in the lower nanomolar ranges. Additionally, DMQCd was able to reverse BCRP-mediated MDR, making it a promising candidate for further research on hybrid inorganic-organic compounds.