Pyrrole–Imidazole Polyamides – A Frontrunner in Nucleic Acid‐Based Small Molecule Drugs

The remarkable success of messenger RNA vaccines against the ongoing coronavirus-2019 (COVID-19) pandemic renews attention toward nucleic acid therapeutics. While nucleic acid therapy using unmodified DNA or RNA is the primary focus in disease treatment, there is growing need to develop nucleic acid-based small molecules owing to their potential clinical benefits as drugs in terms of cost and scalability. While small molecules targeting protein–protein interactions are known to alter the transcriptional status of a cell, they can result in a transient effect and variation of bio-efficacy among patients. Small molecules targeting DNA and/or RNA are in demand in the precision medicine approach as they have consistent bioactivity among patients. This review details the progress of sequence-specific DNA-binding pyrrole–imidazole polyamides (PIPs) in modulating the transcriptional status of target gene(s) without altering the underlying DNA sequence. Here, the different versions of PIPs are listed, and also, how conjugating them with DNA alkylating agents, epigenetic modulators, and other drugs can improve their clinical utility as targeted transcription therapeutics. Owing to their specificity, functional diversity, and limited toxicity, PIP technology holds enormous promise as frontrunner in small-molecule-based nucleic acid drugs to precisely regulate therapeutically important genes on demand and treat intractable diseases.