|399. Schallon, A.; Synatschke, C.V.; Pergushov, D.V.; Jérôme, V.; Müller, A.H.E.; Freitag, R.: DNA Melting Temperature Assay for Assessing the Stability of DNA Polyplexes Intended for Nonviral Gene Delivery, Langmuir 27(19), 12042 (2011) -- DOI: 10.1021/la201803c|
Many synthetic polycations have the ability to form complexes with the polyanion DNA, yet only a few, most notably poly(ethylene imine) (PEI), are efficient gene delivery vehicles. While a common explanation for this observation relies on the buffering capacity of the polycation, the intracellular stability of the complex may also play a role and should not be neglected. Assays typically used to follow complex formation, however, often do not provide the required information on stability. In this contribution, we propose the change in the DNA melting temperature observable after complex formation as a significant indicator for complex stability. For a given DNA/polycation charge ratio, changes in the melting temperature are shown to depend on the polycation chemistry, but not on the DNA topology or the polycation architecture. Effects of changes in the DNA/polycation (N/P) ratio as well as the effect of polycation quaternization can be interpreted using the melting temperature assay. Finally, the assay was used to follow the displacement of the DNA from the complexes by poly(methacrylic acid) or short single-stranded DNA sequences as competing polyanions.