Synthesis and antitumor mechanism of a new iron(iii) complex with 5,7-dichloro-2-methyl-8-quinolinol as ligands

Abstract

A new iron(iii) complex with 5,7-dichloro-2-methyl-8-quinolinol (HClMQ) as ligands, i.e., [Fe(ClMQ)₂Cl] (1), was synthesized and evaluated for its anticancer activity. Compared to the HClMQ ligand, complex 1 showed a higher cytotoxicity towards a series of tumor cell lines, including Hep-G2, BEL-7404, NCI-H460, A549, and T-24, with IC₅₀ values in the range of 5.04-14.35 μM. Notably, the Hep-G2 cell line was the most sensitive to complex 1. Mechanistic studies indicated that complex 1 is a telomerase inhibitor targeting c-myc G-quadruplex DNA and can trigger cell apoptosis via inducing cell cycle arrest and DNA damage.

Scheme 1. Synthetic route of complex 1.

Fig. 1. Crystal structure of complex 1 with atom labeling.

Fig. 2. Cellular uptake and distribution of complex 1 (5 μM) and cisplatin (10 μM) by Hep-G2 cells in 24 h at 37 °C. The metal contents in the whole cell (A) and in different cellular fractions (B) were measured using ICP-MS. The control cells were treated with a vehicle (TBS buffer with 1% DMSO). The data are presented as “mean ± SD” from three independent measurements.

Fig. 3. qRT-PCR analysis of the expression levels of hTERT and c-myc in the Hep-G2 cells treated with complex 1. The Hep-G2 cells (5 × 10⁵) were treated with complex 1 (5 μM) for 24 h. The total RNA in the cells was extracted and subjected to reverse transcription, followed by PCR for hTERT, c-myc and GAPDH (control).

Fig. 4. Western blot analysis of the expression of hTERT and c-myc bcl-2 in the Hep-G2 cells treated with complex 1 (5 μM) for 24 h. (A) Gel image. (B) Densitometric analysis of the protein bands of hTERT and c-myc (normalized with the β-actin band). The relative expression level of each band is calculated as follows: the density of each band/the density of the β-actin band. Mean ± SD was calculated from three independent measurements.

Fig. 5. Transfection of the EGFP (A) and c-myc (B) plasmid vectors in the Hep-G2 cells. The EGFP-carrying plasmid vector (2 μg) and the c-myc-carrying plasmid vector (2 μg) were transfected into the Hep-G2 cells using Lipofectamine 2000 (Invitrogen, Grand Island, NY, USA). Complex 1 (5 μM) was then added into the medium 6 h after the transfection. After a 24 h incubation, the cells were imaged using a Nikon TE2000 (Japan) scanning fluorescence microscope (A) and examined using a multimode plate reader and a luciferase reporter gene assay kit (B).

Fig. 6. Cell cycle arrest induced by complex 1 (5 μM) in the Hep-G2 cells.

Fig. 7. Complex 1-induced DNA damage in the Hep-G2 cells. The cells were treated with complex 1 (5 μM, B) and 1% DMSO solution (control, A) for 24 h and then analyzed by the comet assay. The length of the tail reflects the degree of DNA damage in cells.

Fig. 8. Apoptosis effect on the Hep-G2 cells treated with complex 1 (5 μM) for 24 h.