ENGINEERING FUNCTIONALIZED DIAMOND NANOPARTICLES FOR GENE DELIVERY: BIODISTRIBUTION STUDIES

Abstract

Purpose: To understand the biodistribution of lysine and lysyl-histidine functionalized NDs (collectively ‘fND’) employed as gene carriers. MicroPET imaging and biodistribution studies will elucidate their fate at the organ level. Method: lysine and lysine histidine fNDs were synthesized via covalent conjugation using a 3-carbon chain linker. 1HNMR was used to confirm synthesis of amino acid conjugates after every step. Method development was carried out to optimize a synthetic approach for designing radiolabeled fNDs. A chelating agent desferoxamine (DFO) was conjugated to fNDs to allow labeling with a radionuclide, Zirconium 89 (89Zr). Thermograms of fNDs were used to quantify the percentage of DFO conjugation on ND surface. DFO was conjugated at 8%, 6%, 3% and 1% and characterized to maintain size and positive surface without compromising optimum radiolabeling efficiency. Pharmacokinetic and biodistribution studies of 89Zr-labeled fNDs were performed in naive Balb/c mice using microPET/CT imaging and ex vivo biodistribution Results: Among all conjugation ratios, 3% coverage of DFO to fNDs maintained the optimal size of under 200 nm and positive surface charge of +19.4±4.1 mV. The conjugates formed diamoplexes (DFO conjugated fNDs/siRNA complexes) at biocompatible mass ratios. Radiolabeling method was developed and optimized with respect time and temperature achieving more than 90% radiochemical yield (RCY). The 89Zr ND complexes were stable in phosphate buffer saline and mouse blood serum for over 96 h (97 ± 2%). Biodistribution assays revealed high accumulation of fNDs in liver after 6 h (6.11 ± 4.06) and 72 h (2.32 ± 2.09) followed by spleen (0.17 ± 2.71 at 6 h and 1.66 ± 1.31 at 72 h). PET images further confirmed the finding of biodistribution assays. Conclusion: This study establishes an understanding of in vivo behavior of fNDs for future design, optimization and application of these novel carriers for targeted gene therapy.