Growing interest in i-motif DNA as a transcriptional regulatory element motivates development of synthetic molecules capable of targeting these structures. In this study, we designed unmodified peptide nucleic acid (PNA) and gamma-modified PNA (γPNA) oligomers complementary to an i-motif forming sequence derived from the promoter of the KRAS oncogene. Biophysical techniques such as circular dichroism (CD) spectroscopy, CD melting, and fluorescence spectroscopy demonstrated the successful invasion of the i-motif by PNA and γPNA. Both PNA and γPNA showed very strong binding to the target sequence with high thermal stability of the resulting heteroduplexes. Interestingly fluorescence and CD experiments indicated formation of an intermolecular i-motif structure via the overhangs of target-probe heteroduplexes formed by PNA/γPNA invasion of the intramolecular i-motif. Targeting promoter i-motif forming sequences with high-affinity oligonucleotide mimics like γPNAs may represent a new approach for inhibiting KRAS transcription, thereby representing a potentially useful anti-cancer strategy.

中文翻译：

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通过未修饰和 γ 修饰的肽核酸寡聚体靶向 KRAS i-motif 形成序列

人们对 i-motif DNA 作为转录调控元件的兴趣日益浓厚，这推动了能够靶向这些结构的合成分子的开发。在这项研究中，我们设计了未修饰的肽核酸 (PNA) 和伽马修饰的 PNA (γPNA) 寡聚体，这些寡聚体与源自 KRAS 启动子的 i-motif 形成序列互补致癌基因。圆二色性 (CD) 光谱、CD 熔解和荧光光谱等生物物理技术证明了 PNA 和 γPNA 成功侵入了 i-motif。PNA 和 γPNA 均显示与目标序列的结合非常强，所产生的异源双链体具有高热稳定性。有趣的是，荧光和 CD 实验表明，通过 PNA/γPNA 入侵分子内 i-motif 形成的靶标-探针异源双链体的突出端形成了分子间 i-motif 结构。使用高亲和力寡核苷酸模拟物（如 γPNA）靶向启动子 i-motif 形成序列可能代表一种抑制KRAS转录的新方法，从而代表一种潜在有用的抗癌策略。