Propiolactone

β-Propiolactone is a direct-acting alkylating agent that exerts its biological effects through covalent modification of cellular macromolecules. Using quantum chemical computational methods, the mechanism of β-propiolactone reaction with nucleobases and glutathione was investigated. Among all nucleobases, guanine most readily forms adducts with β-propiolactone through an SN2 reaction mechanism, with activation free energies of 23.6 kcal/mol for alkylation at the N7 position of guanine and 25.3 kcal/mol for acylation at the exocyclic amino group. Alkylation represents an energetically more favorable reaction than acylation for all nucleobases. Comparison of activation free energies revealed that glutathione reacts with β-propiolactone with an activation barrier of 21.0 kcal/mol for alkylation and 22.5 kcal/mol for acylation, both lower than the guanine alkylation barrier. This indicates that glutathione may act as an efficient natural scavenger of β-propiolactone, providing cellular protection against DNA damage. The carboxyethyl group from β-propiolactone forms a stable covalent adduct at the N7 position of guanine, which can lead to depurination mutations and A to T transversions.

Fig. 1 Acylation Reaction between β-Propiolactone and Methylguanine. (Španinger E, Bren U. 2020)

Beta-propiolactone was employed as a zwitterionic modification agent to improve the performance of polyethylenimine (PEI) as a siRNA delivery carrier. The ring-opening addition reaction of beta-propiolactone with primary amines in hydrophobically modified PEI introduced N-carboxyethyl groups, creating a zwitterionic surface. This modification significantly reduced non-specific protein adsorption and cytotoxicity of the resulting nanoparticles, while enhancing their stability against nuclease degradation. The optimized PEI derivative, formulated as siRNA nanoparticles, achieved high gene silencing efficiency (>70%) with nearly 100% cell viability in cancer cell lines. This study demonstrates that beta-propiolactone is a valuable tool for the chemical modification of polymeric drug delivery systems for nucleic acid therapeutics.

Fig. 2 Characterizations of H-zPEI/siRNA NPs prepared at a polymer/siRNA mass ratio of 30:1. (Liu F.; et al. 2022)