New insight into formation of DNA-containing microparticles during PCR: the scaffolding role of magnesium pyrophosphate crystals

Sustained Release of Minor-Groove-Binding Antibiotic Netropsin from Calcium-Coated Groove-Rich DNA Particles

Control of the release properties of drugs has been considered a key factor in the development of drug delivery systems (DDSs). However, drug delivery has limitations including cytotoxicity, low loading efficiency, and burst release. To overcome these challenges, nano or micro-particles have been suggested as carrier systems to deliver chemical drugs. Herein, nano-sized DNA particles (DNAp) were manufactured to deliver netropsin, which is known to bind to DNA minor grooves. The rationally designed particles with exposed rich minor grooves were prepared by DNAp synthesis via rolling circle amplification (RCA). DNAp could load large quantities of netropsin in its minor grooves. An analytical method was also developed for the quantification of netropsin binding to DNAp by UV–visible spectrometry. Moreover, controlled release of netropsin was achieved by forming a layer of Ca²⁺ on the DNAp (CaDNAp). As a proof of concept, the sustained release of netropsin by CaDNAp highlights the potential of the DNAp-based delivery approach.

Structural variability of DNA-containing Mg-pyrophosphate microparticles: optimized conditions to produce particles with desired size and morphology

Our previous studies demonstrated the formation of structurally diverse DNA-containing microparticles (DNA MPs) in PCR with Mg-pyrophosphate (MgPPi) as the structure-forming component. These DNA MPs were referred to major structural types: microdisks (2D MPs) with nanometer thickness and 3D MPs with sophisticated morphology and constructed from intersecting disks and their segments. Little is known about factors that influence both the morphology and size of DNA MPs, and the present study was aimed at fulfilling this gap. We showed that the addition of Mn²⁺ cations to PCR mixtures caused the profound changes in MPs morphology, depending on DNA polymerase used (KlenTaq or Taq). Asymmetric PCR with 20-fold decrease in the concentration of one of two primers facilitated the predominant formation of microdisks with unusual structure. The addition of 1 mM Na-pyrophosphate to PCR mixtures with synthesized DNA and subsequent thermal cycling (10-15 cycles) were optimal to produce microdisks or nanometer 3D particles. Using electron microscopy, we studied also the structure of inorganic micro- and nanoparticles from MgPPi, formed during multiple heating and cooling cycles of a mixture of Mg²⁺ and Na-pyrophosphate in various regimes. Also, we found the conditions to yield planar (Mg·Mn)PPi nanocrystals (diameter ~100 nm and thickness ~10 nm) which efficiently adsorbed exogenous DNA. These inorganic nanoparticles are promising for DNA delivery in transfection studies. Mechanisms to be involved in structural modifications of MPs and perspectives of their practical application are discussed.