G-quadruplex (G4) DNA is often observed as a DNA secondary structure in guanine-rich sequences, and is thought to be relevant to pharmacological and biological events. Therefore, G4 ligands have attracted great attention as potential anticancer therapies or in molecular probe applications. Here, we designed cyclic imidazole/lysine polyamide (cIKP) as a new class of G4 ligand. It was readily synthesized without time-consuming column chromatography. cIKP selectively recognized particular G4 structures with low nanomolar affinity. Moreover, cIKP exhibited the ability to induce G4 formation of the promoter of G4-containing DNA in the context of stable double-stranded DNA (dsDNA) under molecular crowding conditions. This cIKP might be applicable as a molecular probe for the detection of potential G4-forming sequences in dsDNA.

Mutation of KRAS is a key step in many cancers. Mutations occur most frequently at codon 12, but the targeting of KRAS is notoriously difficult. We recently demonstrated selective reduction in the volume of tumors harboring the KRAS codon 12 mutation in a mouse model by using an alkylating hairpin N-methylpyrrole–N-methylimidazole polyamide seco-1,2,9,9a-tetrahydrocyclopropa[1,2-c]benz[1,2-e]indol-4-one conjugate (conjugate 4) designed to target the KRAS codon 12 mutation sequence. Herein, we have compared the alkylating activity of 4 against three other conjugates that were also designed to target the KRAS codon 12 mutation sequence. Conjugate 4 displayed greater affinity for the G12D mutation sequence than for the G12V sequence. A computer-minimized model suggested that conjugate 4 could bind more efficiently to the G12D match sequence than to a one-base-pair mismatch sequence. Conjugate 4 was modified for next-generation sequencing. Bind-n-Seq analysis supported the evidence showing that conjugate 4 could target the G12D mutation sequence with exceptionally high affinity and the G12V mutation sequence with much higher affinity than that for the wild-type sequence.

Pyrrole–imidazole (PI) polyamides bind to the minor groove of the DNA duplex in a sequence-specific manner and thus have the potential to regulate gene expression. To date, various types of PI polyamides have been designed as sequence-specific DNA binding ligands. One of these, cysteine cyclic PI polyamides containing two β-alanine molecules, were designed to recognize a 7 bp DNA sequence with high binding affinity. In this study, an efficient cyclization reaction between a cysteine and a chloroacetyl residue was used for dimerization in the synthesis of a unit that recognizes symmetrical DNA sequences. To evaluate specific DNA binding properties, dimeric PI polyamide binding was measured by using a surface plasmon resonance (SPR) method. Extending this molecular design, we synthesized a large dimeric PI polyamide that can recognize a 14 bp region in duplex DNA.

A synthetic transcriptional activator encompassing both sequence-specific pyrrole–imidazole polyamides (PIPs) and an epigenetic activator (suberoylanilide hydroxamic acid) was recently shown to induce the endogenous expression of core pluripotency genes in mouse embryonic fibroblasts (MEFs). Microarray data analysis suggested Oct-3/4 as the probable target pathway of the activator. However, the expression levels in MEFs treated with the activator were relatively lower than those in mouse embryonic stem cells. Herein, we report studies carried out to improve the efficacy of the activator and show that the biological activity was significantly (p<0.05) improved against the core pluripotency genes after the incorporation of an isophthalic acid (IPA) at the C terminus. The resultant IPA conjugate dramatically induced Oct-3/4 and demonstrated a new chemical strategy for developing PIP conjugates as next-generation genetic switches.

Tandem N-methylpyrroleN-methylimidazole (PyIm) polyamides with good sequence-specific DNA-alkylating activities have been designed and synthesized. Three alkylating tandem PyIm polyamides with different linkers, which each contained the same moiety for the recognition of a 10 bp DNA sequence, were evaluated for their reactivity and selectivity by DNA alkylation, using high-resolution denaturing gel electrophoresis. All three conjugates displayed high reactivities for the target sequence. In particular, polyamide 1, which contained a β-alanine linker, displayed the most-selective sequence-specific alkylation towards the target 10 bp DNA sequence. The tandem PyIm polyamide conjugates displayed greater sequence-specific DNA alkylation than conventional hairpin PyIm polyamide conjugates (4 and 5). For further research, the design of tandem PyIm polyamide conjugates could play an important role in targeting specific gene sequences.