Developing efficient and safe vectors is one of the main challenges in gene therapy. Multiple fatal incidences in applying virus have brought safety issues to the attention and called for developing non-viral vectors, entailing lipoplex and polyplex. The present dissertation mainly focuses on a polyplex system. Inverse microemulsion-derived nanogel features a hydrophilic matrix, rendering the delivery of genes more compatible. Nanogel was modified with acid-buffering weak base, redox-sensitive cleavable crosslinker, and folate targeting ligand. Two types of plasmid DNA (pDNA)-nanogel formulations were assessed for transfection efficiency. First, luciferase pDNA was added to the microemulsion prior to the polymerization. It was hypothesized that pDNA will spontaneously reside in the aqueous phase and be well compacted. The energetics involved was not, however, sufficient enough to produce a stable system. Protamine-condensed pDNA increased the entrapment efficiency. Unfortunately, addition of methanol to dissolve the disulfide crosslinker disturbed microemulsion, reducing entrapment efficiency. Second, pDNA was mixed with pre-made cationic nanogels containing folate targeting ligands. Although pDNA-nanogel complex did not surpass the conventional transfecting reagents, it increased transfection efficiency in the folate receptor-expressing KB cells compared to the naked pDNA. Targeted formulations represented superior transfection efficiency to the non-targeted counterparts. Disulfide-containing crosslinker was necessary for an enhanced transfection. Incorporation of weak base improved the transfection efficiency only in the formulation with low positive charges. Most importantly, the targeting capacity was able to overcome non-specific binding only when electrostatic interaction was minimal.

Comparing to the relatively well-established nanogels, PRINT particles are in the early stage of development as a potential drug/gene carrier, featuring an unprecedented monodispersity in various physicochemical properties. Better understanding of in vivo pharmacokinetics of PRINT particles would lead to optimizing pharmacodynamics as a gene carrier. [¹²⁵I]-PRINT particles following an IV injection into the healthy mice accumulated in liver and spleen. However, the relatively short blood circulation and the probable premature decomposition called for further investigation. Also a more sensitive and reproducible monitoring method is highly desirable. Due to its preliminary nature, the study results are placed in Appendix.