In vitro and In silico studies on the anticancer and antimicrobial activity of Cu(II), Ni(II) and Co(II) complexes with bis (pyrazolyl) borate derivative ligand

A bidentate N-donor pyrazole-based ligand abbreviated as K[H2B(Pz )2] and corresponding complexes with Cu(II), Ni(II) and Co(II) were synthesized and characterized, where Pz=3,5-dimethylpyrazole. The synthesized ligand and complexes were evaluated for anticancer activities against (MDA-MB-231) human breast cell line. Their Antibacterial activity against gram-positive and gram-negative bacteria was investigated. Also, their molecular docking with YmaH (PDB ID: 3HSB), ecKAS III (PDB ID: 1HNJ) protein and DNA dodecamer (PDB ID: 1BNA) as the possible targets was performed. In silico molecular docking along with the experimental MTT assay and antibacterial studies, indicated the metal complexes are more bioactive than free uncoordinated ligand and can be excellent candidates for further evaluations in the biological area.


Introduction
Since the first reportage of poly(pyrazolyl)borates and in especially bis(pyrazolyl)borates by Trofimenko, these compounds have been developed in the inorganic coordination chemistry area and widely employed in various transition metal coordination complexes as anionic Ndonor ligands. [1][2][3][4][5] In these type of the ligands, by controlling the number of pyrazolate rings and the substituents of different derivatives, their structure can be modified for the design and synthesis of the ligands with special properties to formation of stable complexes. [6][7][8] On the other hand, the excellent therapeutic properties of pyrazole-based drugs have attracted the attention of pharmaceutical chemists for the synthesis, development and investigation of various new chemotherapy drugs. [9][10][11][12] Development of the pyrazole-based coordination compounds is greatly enhanced due to the identification of their structure as anti-cancer, antifungal, anti-bacterial, anti-viral and anti-inflammatory agents. [13][14][15][16][17] On the other hand, Docking simulation can help us to understand the environment around compounds in the active site and allowing medicinal chemists to design and modify compounds. Keeping in view therapeutic and biological activities of pyrazoles based compounds and the potential of transition metals such as copper, cobalt, and nickel in the antimicrobial application area, we find it vital to join the chemistry of both moieties in designing and developing biometal compounds which could aggressively work against various bacterial species and cancer cells. [18][19][20][21][22] In this work, we report the synthesis and characterization of copper (II), nickel (II) and cobalt (II) complexes of dihydrobis(pyrazolyl)borate ligands. Also, antibacterial activities, MTT assay and molecular docking of these compounds were investigated. As we previously reported, the synthesized 3, 5 dimethyl pyrazole, 21,24 (0.19 g, 2 mmol) and KBH4 (0.05 g, 1 mmol) were heated to 100˚C under nitrogen atmosphere and hydrogen evolution started at this point. The temperature is raised to 130˚C gradually and was controlled evolution of hydrogen, after the production of (2 mmol) of hydrogen, the reaction was finished and the resulting white precipitate washed with the mixture of THF (20 mL) and n-hexane (10 mL

Antibacterial activity
The synthesized compounds (1-4) were evaluated for their antibacterial activity against  Table 2).

Molecular docking
Based on the literature and due to the fact that these proteins (YmaH, ecKAS III) and DNA have significant inhibition against the studied bacteria and investigated cell line, respectively.
So these macromolecules are shown to be the possible targets for anticancer and antibacterial agents. 30

FT-IR spectral studies
In

Antibacterial studies
The synthesized compounds, positive and negative controls, were screened separately to evaluate their antibacterial activity against Gram-positive (B. subtilis), and Gram-negative (S. enterica). The results were summarized in Table 1.   Table 2). The results showed that the IC50 value of  complexes (3,4), also this complex showed almost the same activity with the Paclitaxel as a drug against the investigated cell line. Generally, the coordination compounds have high cytotoxicity compared with free organic compounds and it can be explained by chelation theory which is the reason for the high cytotoxic character of the inorganic compounds. 44,45 Our experimental findings, along with molecular docking studies, suggest that the copper complex could be an excellent candidate for further anticancer studies.

Molecular docking analysis
In silico Molecular docking studies were carried out by AutoDock software for a synthesized ligand and their Cu(II), Ni(II), and Co(II) complexes with the DNA and two selected proteins (YmaH and ecKAS III). The predicted binding energy and other results are summarized in Tables (3-5). According to the obtained results of these studies, the investigated receptors showed better interactions with most of the synthesized metal complexes compared to the free ligands. As can be seen in (Tables 3),