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A series of new 3-(1H-benzimidazol-2-yl)quinolin-2(1H)-one derivatives (5a1−5d6) were designed and synthesized as antitumor agents. In vitro antitumor assay results showed that some compounds exhibited moderate to high inhibitory activity against HepG2, SK-OV-3, NCI-H460 and BEL-7404 tumor cell lines, and most compounds exhibited much lower cytotoxicity against the HL-7702 normal cell line compared to 5-FU and cisplatin. In vivo antitumor assay results demonstrated that 5a3 exhibited effective inhibition on tumor growth in the NCI-H460 xenograft mouse model and that 5d3 displayed excellent antiproliferative activity in the BEL-7402 xenograft model. These results suggested that both 5a3 and 5d3 could be used as anticancer drug candidates. Mechanistic studies suggested that compounds 5a3 and 5d3 exerted their antitumor activity by up-regulation of Bax, intracellular Ca2+ release, ROS generation, downregulation of Bcl-2, activation of caspase-9 and caspase-3 and subsequent cleavage of PARP, inhibition of CDK activity and activation of the p53 protein.

Two G-quadruplex ligands: [Co(H-La)2Cl2] (Co1) and [Co(Lb)2][CoCl4]⋅2H2O (Co2) have been synthesized and characterized. Two cobalt oxoisoaporphine complexes exhibited selective cytotoxicity to SK-OV-3/DDP cells than for HL-7702 cells. Cytotoxic mechanism studies indicated that both Co1 and Co2 were telomerase inhibitor targeting c-myc, telomere, and bcl-2 G4s, and triggering cell senescence and apoptosis, which caused S phase arrest. They also induced mitochondrial dysfunction. The better antitumor activity of Co2, which should be correlated with a moiety of 2-[5-(2-pyridinyl)-1H-pyrrol-2-yl]pyridine in the Lb. Importantly, Co2 at high doses showed at least the same level of tumor growth inhibition efficacy compared to that of cisplatin, and better in vivo safety profile.

[Pd(L)(DMSO)Cl2] (1) and [Pt(L)(DMSO)Cl2] (2) with 9-amino-oxoisoaporphine (L), were synthesized and characterized. 1 and 2 are more selectively cytotoxic to Hep-G2 cells versus normal liver cells (HL-7702). Various experiments showed that 2 acted as telomerase inhibitors targeting G4-DNA and triggered cell apoptosis by interacting with c-myc G4-DNA. Furthermore, 2 significantly induced cell cycle arrest at both G2/M and S phase, which leading to the down-regulation of cdc25 A, cyclin D, cyclin B, cyclin A and CDK2 and the up-regulation of p53, p27, p21,chk1 and chk2. In addition, 2 also caused mitochondrial dysfunction. Taken together, we found that 2 exerted its cytotoxic activity mainly via inhibiting telomerase by interaction with c-myc G4-DNA and disruption of mitochondrial function.

[Pt(Q)2] (1) and [Pt(MQ)2] (2) exhibited enhanced cytotoxicity against BEL-7404, Hep-G2, NCI-H460, T-24, A549 tumor cells but low cytotoxicity on normal HL-7702 cells. 1 and 2 could cause the cell cycle arrest in G2 and S phase, respectively. While pifithrin-α, a specific p53 inhibitor, induced cell cycle arrest in G1 phase. Although 1, 2 and pifithrin-α caused serious inhibition on p53, 1 and 2 significantly cause the loss of mitochondrial membrane potential and increase of the reactive oxygen species level, cytochrome c, apaf-1 and caspase-3/9 ratio in BEL-7404 cells. 1 and 2 may trigger the cell apoptosis through a mitochondrial dysfunction pathway whereas pifithrin-α does not. The interactions of 1 and 2 with DNA are most probably via an intercalation.