Gene therapy holds promise for treating many diseases. However, clinical translation of gene therapy has been limited by the lack of approach for efficient and safe delivery of genetic materials to disease locations. In current clinic, viral vectors are often used because of their high delivery efficiency. Unfortunately, long-term safety of viral vectors remains as a concern. To overcome this problem, development of non-viral vectors using synthetic nanoparticles (NPs) is promising. Compared to viral vectors, synthetic NPs have limited immunogenicity and considerable flexibility for surface engineering. The recent success in use of lipid NPs (LNPs) for delivery of COVID-19 mRNA vaccines highlights the potential of non-viral vectors. Nevertheless, LNPs are limited by thermal instability, inability to prolong gene expression, and high complexity with 4-5 components. For several years, our group has focused on development of simple formulation polymeric NPs for gene delivery. In a recent effort, we synthesized a family of poly(amine-co-ester) (PAE) NPs through polymerization of diethyl sebacate (DES) and N-methyldiethanolamine (MDEA) with lactones. This synthetic approach is unique in that it allows tuning four important parameters in one single molecule: positive charge, molecular weight, hydrophobicity, and solidity. We demonstrated that the gene delivery capacity of polymers is not solely determined by charge, but by a balance of positive charge, molecular weight, and hydrophobicity. As a result, we can design and synthesize polymers for gene delivery with high efficiency but limited toxicity. More recently, we further optimized the chemistry and synthesized a new generation of PAEs containing stimuli responsive components, which can form solid NPs. We demonstrate that, in addition to their high efficiency, the NPs have several major important features, including: 1) remarkable stability, allowing them to be stored as lyophilized powder without compromising efficiency; 2) capacity to produce sustained gene expression over a longer time than LNPs; and 3) simplicity, consisting of one polymer, in contrast to 4-5 components for LNPs. Those features make the new generation PAE NPs ideal for clinical translation.

• Discussion of synthesis and application of a new generation of polymeric nanoparticles that are optimal for gene delivery and clinical translation.