In Vivo Tracking of Long Circulating Bimodal PEGylated Au@SiO₂ Nanoparticles (NPs) Combining Near Infrared (NIR) Optical Imaging (OI) and μ-Computed Tomography (µCT)

When and Where

Nov 29, 2022
4:15pm - 4:30pm

Hynes, Level 1, Room 104

Presenter

Megi Bejko

Clement Vecco-Garda

Coralie Genevois

Nestor Pallares-Lupon

Richard Walton

Franck Couillaud

Olivier Sandre

Stéphane Mornet

Co-Author(s)

Megi Bejko^1,2,Clement Vecco-Garda²,Coralie Genevois³,Nestor Pallares-Lupon⁴,Richard Walton⁴,Franck Couillaud³,Olivier Sandre¹,Stéphane Mornet²

Laboratoire de Chimie des Polymères Organiques¹,Institut de Chimie de la Matière Condensée de Bordeaux²,Bordeaux Research Institute On Cancer³,L'institut de Rythmologie et Modélisation Cardiaque⁴

Abstract

Megi Bejko^1,2,Clement Vecco-Garda²,Coralie Genevois³,Nestor Pallares-Lupon⁴,Richard Walton⁴,Franck Couillaud³,Olivier Sandre¹,Stéphane Mornet²

Thanks to their physicochemical features, Au NPs present a broad scope for innovative treatments in oncology with applications ranging from imaging to drug delivery, and photo-induced therapy.1 One of the particularities of this element is the high atomic number and thus high X-ray absorption coefficient, endowing them with substantial contrast enhancement in X-Ray CT scans. These properties combined with the biocompatibility and tunable surface chemistry, has encouraged the use of Au NPs for µCT imaging in vascular, cardiac and cancer fields.2 The high spatial resolution (1 µm) afforded by µCT imaging, allows non-invasive quantification of local accumulated Au in zones of interest. This enables robust full body evaluation of the in vivo fate of Au NPs in rodents, which is beneficial in a preclinical setting. However, studies regarding the in vivo fate of Au NPs for µCT imaging rely on injecting large amounts (up to 1.1 g Au/kg) to promote sufficient local concentration, necessary to enhance contrast of tumors at high-resolution.3 This is done to counteract the poor pharmacokinetics (PK) of the NP as well as the low sensitivity of µCT. Herein, we propose to combine two complementary imaging techniques: µCT with classic NIR OI. Thereby, bimodal core-shell NPs with an Au core and fluorescent SiO2 shell is designed to associate high spatial resolution and non-invasive quantitative analysis of µCT with the high sensitivity of NIR OI. Combining these two imaging modalities enables full tracking of the in vivo fate of the NPs. In addition, physicochemical features of the NPs are adjusted to promote long blood circulation times and prevent injection of clinically irrelevant doses. For this, fluorescent SiO2 is grown on 15 nm Au NPs following known sol-gel protocols.4 The SiO2 shell reduces the high attraction potential of the Au surface, which has a Hamaker constant 50x higher than amorphous SiO2.5,6 This surface modification is a first step towards long circulating NPs by minimizing plasma protein adsorption. The second step consists on the covalent grafting of polyethylene glycol (PEG) (Mw=4 kDa) on to the SiO2 shell in a dense brush conformational regime giving an RF/D (RF: Flory radius, D: distance between two anchoring sites) value of 5. This value is higher than the threshold RF/D = 4.0, above which NPs possess prolonged blood circulation times as reported for SiO2 NPs by our team.7 A final neutral NP surface charge (+3 mV, pH=7.4) is purposely generated as reports show better PK when compared to their positive counterparts.8 A low quantity of Au (0.06 g Au/kg) is then i.v. injected in mice (N=9) possessing subcutaneous prostate cancer (RM1), genetically modified to overexpress the luciferase firefly enzyme. The PK of the NPs is evaluated by OI where the maximal tumor accumulation is observed 24h post injection and NP circulation persisted up to 72h post-injection. µCT imaging is then acquired on anesthetized mice (N=6) 24h post-injection. The images reveal micro-distributions of Au in organs of interest (i.e. liver, spleen) and tumor periphery at a higher spatial resolution than OI. Thanks to prior calibration of µCT signal, the 3D distribution and quantity of accumulated Au with respect to the quantity of NPs injected is determined in peripheral tumors and key organs. In conclusion, two complementary imaging techniques are combined, allowing a full non-invasive tracking of bimodal NPs using realistic administered doses (reduced by a factor 20): OI provided PK and biodistribution of circulating NPs and µCT quantitatively evaluated 3D distribution within organs and tumors. References: 1.Bansal, S. A. et al., Nanoscale Adv.2020 2.Ashton, J. R. et al., Front. Pharmacol.2015 3.Hainfeld, J. F. et al., Br.J.Radiol.2011 4.Fernández-López,C. et al., Langmuir 2009 5.Bergstrom, L., Adv.Colloid Interface Sci.1997 6.Biggs, S. et al., J.Chem.Phys.1994 7.Adumeau, L. et al., Biochim.Biophys.Acta BBA.2017 8.Sakulkhu, U. et al., Nanoscale 2014