Probing in vivo trafficking of polymer/DNA micellar nanoparticles using SPECT/CT imaging

Abstract

Successful translation of nonviral gene delivery to therapeutic applications requires detailed understanding of in vivo trafficking of the vehicles. This report compares the pharmacokinetic and biodistribution profiles of polyethylene glycol-b-polyphosphoramidate (PEG-b-PPA)/DNA micellar nanoparticles after administration through intravenous infusion, intrabiliary infusion, and hydrodynamic injection using single photon emission computed tomography/computed tomography (SPECT/CT) imaging. Nanoparticles were labeled with (111)In using an optimized protocol to retain their favorable physicochemical properties. Quantitative imaging analysis revealed different in vivo trafficking kinetics for PEG-b-PPA/DNA nanoparticles after different routes of administration. The intrabiliary infusion resulted in the highest liver uptake of micelles compared with the other two routes. Analysis of intrabiliary infusion by the two-compartment pharmacokinetic modeling revealed efficient retention of micelles in the liver and minimal micelle leakage from the liver to the blood stream. This study demonstrates the utility of SPECT/CT as an effective noninvasive imaging modality for the characterization of nanoparticle trafficking in vivo and confirms that intrabiliary infusion is an effective route for liver-targeted delivery of DNA-containing nanoparticles.

Figure 1

Optimization of radiolabeling of polyethylene glycol-b-polyphosphoramidate (PEG-b-PPA). (a) Effect of DTPA-grafting degree on radiolabeling efficiency of the polymer (mean ± SD of mean, n = 3, *P < 0.01. The DTPA-grafting degree was analyzed by ¹H-NMR. (b) The stability of radiolabeled PEG-b-PPA in water and 10% fetal serum albumin-containing medium at 37 °C for 4 and 24 hours, respectively. The radiolabeling stability was estimated using thin-layer chromatography. The freshly prepared radiolabeled polymer was used as the control.

Figure 2

Effect of radiolabeling on size, morphology, and stability of PEG-b-PPA/DNA micellar nanoparticles. TEM images of (a) unlabeled micelles and (b) ¹¹¹In-labeled micelles (Bars = 200 nm). (c) Stabilities of unlabeled and labeled micelles in 0.15 mol/l NaCl or 10% fetal bovine serum (FBS) by gel retardation assay. Lane 1: plasmid DNA; lane 2: unlabeled micelles; lane 3: radiolabeled micelles; lanes 4 and 5: unlabeled and labeled micelles, respectively, after incubation in 0.15 mol/l NaCl solution for 1 hour at 37 °C; lanes 6 and 7: unlabeled and labeled micelles, respectively, after incubation in 10% FBS-containing medium for 1 hour at 37 °C.

Figure 3

In vivo trafficking of radiolabeled micelles following intravenous infusion. (a) Pharmacokinetic profiles and (b) biodistribution profiles of radiolabeled micelles administered through intravenous infusion obtained by single photon emission computed tomography/computed tomography (SPECT/CT) and gamma-counting (mean ± SD of mean, n = 4). (c) Time intensity curves in different organs by SPECT/CT quantification of micelles infused by intravenous infusion in rats (mean ± SD of mean, n = 4). (d) Whole-body images (gray scale: CT, pseudo-color map: SPECT) of a rat at 2 hours postinfusion. The rendered 3-D images can be accessed in Supplementary Video S1.

Figure 4

In vivo trafficking of radiolabeled micelles following hydrodynamic injection and intrabiliary infusion. Whole-body images [a and d, gray scale, CT images; pseudo-color, single photon emission computed tomography (SPECT) images], (b, e) time intensity curves and (c, f) biodistribution profiles of labeled micelles in different organs (mean ± s.e. of mean, n = 3) of a rat at 2.02 hours and 2 hours after administration through (a–c) hydrodynamic injection and (d–f) intrabiliary infusion, respectively. Same color schemes were used for all SPECT imaging analysis. The compassed appearance of the liver in (d) was due to the use of cotton balls to push the liver backwards for the ease of visualization and infusion into the common bile duct. The rendered 3-D images can be accessed in Supplementary Videos S2 and S3.

Figure 5

Comparison of time courses of DNA micelle deposition in the liver after three different routes of administration determined by single photon emission computed tomography/computed tomography (SPECT/CT) quantification (mean ± s.e. of mean, n = 3).

Figure 6

Analysis of micelle concentration in the liver by the two-compartment pharmacokinetics model constructed for intrabiliary infusion of DNA micelles. (a) Description of the compartments. (b) Model fit of liver concentration profile from Figure 5 and data generated by the two-compartment model analysis.