Dendrigraft Poly-L-lysine (d-PLL) Coated Gold Nanoparticles in Water for siRNA Delivery to Prostate Cancer Cells

K. Rahme, G. Minassian, E. Ghanem, E. Souaid, J. Guo, C.M. O’Driscoll, J.D. Holmes
Notre Dame University-Louaize,

Keywords: gold nanoparticles, dendrigraft polymers,targeting ligands, polyethyleneglycol, receptor-mediated internalization, non-viral siRNA delivery, prostate cancer, gene therapy


In this study we used dendrigraft poly-L-lysine (d-PLL) as a stabilising ligand for gold nanoparticles (AuNPs) in water. The d-PLL generation two (P2) with narrow molecular weight distribution of about 7 KD was obtained by a previously reported method [1]. AuNPs-d-PLL with diameters ranging between 50–120 nm have been synthesised via chemical reduction of HAuCl4.3H2O by ascorbic acid in the presence of d-PLL stabiliser. The AuNPs-d-PLL diameters were found to strongly depend on the HAuCl4.3H2O and d-PLL concentrations, while the concentration of ascorbic acid showed a lower effect on the final AuNPs sizes. UV-visible spectroscopy showed that the AuNPs-d-PLL exhibit a surface plasmon resonance red shift (longer wavelengths) and a decreased absorbance, that were found to correlate with their size increase as demonstrated by Dynamic Light scattering (DLS) analysis. Furthermore, thiolated polyethylene glycol folate (SH-PEG5000-FA) was synthesised by coupling of SH-PEG-NH2 (Mn 5,000) and Folate N-hydroxysuccinimidyl ester, the later was obtained by activation of folic acid via N-hydroxysuccinimide (NHS) dicyclohexylcarbodiimide (DCC) coupling [2]. The obtained SH-PEG5000-FA was characterised by FTIR and used to conjugate the positively charged AuNPs-d-PLL, the PEGylated AuNPs-d-PLL ability to complex fluorescent siRNA (Mw 13,800 g mol-1) was also tested. DLS measurements showed that the AuNPs-d-PLL size increased by about 30 nm after conjugation with SH-PEG5000-FA, while the corresponding AuNPs-d-PLL-SH-PG5000-FA increased by about 50 nm after 1 hour soaking with siRNA, while conserving their polydispersity index (PDI 0.18  0.03) [3, 4]. Furthermore, the zeta-potential of the colloidal solution decreased from 35  6 mV to +18 mV after PEG attachment and to about -16 mV after soaking with siRNA indicating the successful PEG attachment and AuNPs-d-PLL-SH-PG5000-FA.siRNA complexes formation. Furthermore, AuNPs.siRNA complexes formation was also demonstrated by gel electrophoresis (data not shown) [5]. Finally, cellular uptakes were also performed using PC3-PSMA cancer cells. Fluorescence-activated cell sorting (FACS) results following 24 hours incubation indicated that AuNPs-d-PLL-SH-PG5000-FA.siRNA achieved significantly higher fluorescein-positive cells relative to AuNPs-d-PLL.siRNA and AuNPs-d-PLL-SH-PG5000-OCH3.siRNA respectively (data not shown), suggesting their potential use to deliver specifically siRNA into prostate cancer cells. Acknowledgments: We acknowledge financial support from the National Council for Scientific Research Lebanon (CNRS-L-GRP2015-3538). References [1] H. Collet and E. Souaid et al. Chem. Eur. J., 2010, 16, 2309–2316 [2] J. Song et al. Nanoscale, 2013, 5, 5816-5824 [3] K. Rahme et al. RSC Adv., 2013, 3, 6085–6094 [4] K. Rahme et al. RSC Adv., 2015, 5, 17862–17871 [5] J. Guo et al. Int. J. Pharm., 2016, 509, 16–27