BackgroundA guanine-rich strand within the promoter of the KRAS gene can fold into an intra-molecular G-quadruplex structure (G4), which has an important role in the regulation of KRAS transcription. We have previously identified indolo[3,2-b]quinolines with a 7-carboxylate group and three alkylamine side chains (IQ3A) as effective G4 stabilizers and promising selective anticancer leads. Herein we investigated the anticancer mechanism of action of these compounds, which we hypothesized due to stabilization of the G4 sequence in the KRAS promoter and subsequent down-regulation of gene expression.Methodology/Principal FindingsIQ3A compounds showed greater stabilization of G4 compared to duplex DNA structures and reduced KRAS promoter activity in a dual luciferase reporter assay. Moreover, IQ3A compounds showed high anti-proliferative activity in HCT116 and SW620 colon cancer cells (IC50 < 2.69 μM), without eliciting cell death in non-malignant HEK293T human embryonic kidney, and human colon fibroblasts CCD18co. IQ3A compounds significantly reduced KRAS mRNA and protein steady-state levels at IC50 concentrations, and increased p53 protein steady-state levels and cell death by apoptosis in HCT116 cells (mut KRAS, wt p53). Furthermore, KRAS silencing in HCT116 p53 wild-type (p53(+/+)) and null (p53(-/-)) isogenic cell lines induced a higher level of cell death, and a higher IQ3A-induced cell death in HCT116 p53(+/+) compared to HCT116 p53(-/-).ConclusionsHerein we provide evidence that G4 ligands such as IQ3A compounds can target G4 motifs present in KRAS promoter, down-regulate the expression of the mutant KRAS gene through inhibition of transcription and translation, and induce cell death by apoptosis in colon cancer cell lines. Thus, targeting KRAS at the genomic level with G4 ligands may be a new anticancer therapy strategy for colon cancer.

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ABSTRACT. We examined the expression of anti-apoptotic genes and apoptotic genes (cytochrome c, caspase-9, Apaf-1) in tissue samples of patients with superficial bladder cancer. Thirtytwo bladder cancer tissue samples (8 papillary urothelial neoplasm of low malignant potential, 10 low-grade, and 14 high-grade) and 8 normal bladder tissue samples from necropsy were used for the study of gene expression by real-time PCR analysis. Analysis of the expression of apoptotic gene constituents of an apoptosome demonstrated an increase in Apaf-1 expression in the three tumor grades when compared with the control (P < 0.01, P < 0.05, and P < 0.01), low expression of caspase-9 in all groups (P < 0.05), and an increase in cytochrome c expression in Intrinsic pathways of apoptosis in bladder cancer all tumor grades in relation to the control, although without statistically significant difference. The expression of anti-apoptotic genes revealed an increase in XIAP expression in all tumor grades in relation to the control, although without statistically significant difference, and low expression of Bcl-2 in all tumor grades and the control (P < 0.05). The results proved that there is low evidence of apoptotic activity by the intrinsic pathway, demonstrated by the low expression of caspase-9 and considerable increase in XIAP expression, which may render these genes potential therapeutic targets in bladder cancer treatment.