[(186)Re]Liposomal doxorubicin (Doxil): in vitro stability, pharmacokinetics, imaging and biodistribution in a head and neck squamous cell carcinoma xenograft model

Abstract

The purpose of this study was to determine the feasibility of radiolabeling liposomal doxorubicin (Doxil) for cancer chemoradionuclide therapy by directly loading the therapeutic radionuclide rhenium-186 ((186)Re) into the liposome interior. The pharmacokinetics, imaging and biodistribution of [(186)Re]Doxil (555 MBq/kg) and control [(186)Re]polyethylene glycol (PEG) liposomes (555 MBq/kg) were determined after intravenous administration in a head and neck cancer xenograft model in nude rats. [(186)Re]Doxil and [(186)Re]PEG liposomes were radiolabeled using [(186)Re]N,N-bis(2-mercaptoethyl)-N',N'-diethylethylenediamine. (186)Re labeling efficiency was 76.1+/-8.3% with Doxil. The in vitro serum stability of [(186)Re]Doxil at 37 degrees C was 38.06+/-12.13% at 24 h. Pharmacokinetic studies revealed that [(186)Re]Doxil had a two-phase blood clearance with half clearance times of 0.8 and 28.2 h. Images acquired over 120 h showed that [(186)Re]Doxil had slow blood clearance, low liver accumulation and increasing spleen accumulation. The biodistribution study at 120 h indicated that the percentage of injected dose (%ID) in the blood and tumor for [(186)Re]Doxil was 20-fold higher than that of [(186)Re]PEG liposomes. The %ID values in the kidney and liver were not significantly different between [(186)Re]Doxil and [(186)Re]PEG liposomes. These results suggest that the long circulation and prolonged bioavailability of [(186)Re]Doxil could potentially deliver high concentrations of both doxorubicin and (186)Re to tumor when encapsulated in the same liposome vehicle.

Figure 1

In vitro stability of ¹⁸⁶Re-Doxil and ¹⁸⁶Re-PEG liposomes at different times after incubation in FBS at 37°C (A) or in PBS, pH 7.4 at 25°C (B) (mean ± SD, n=3).

Figure 1

In vitro stability of ¹⁸⁶Re-Doxil and ¹⁸⁶Re-PEG liposomes at different times after incubation in FBS at 37°C (A) or in PBS, pH 7.4 at 25°C (B) (mean ± SD, n=3).

Figure 2

Blood clearance curves of ¹⁸⁶Re-Doxil and ¹⁸⁶Re-PEG-liposomes after iv administration in HNSCC tumor bearing rats. Data represented as mean %ID ± SD. (n=7 at each time point for each group).

Figure 3

MicroSPECT/CT images acquired at 20 h post administration of ¹⁸⁶Re-Doxil using MPH collimator. Three dimensional (3D) volume rendered SPECT image of ¹⁸⁶Re-Doxil overlaid with CT isosurface displayed in bone window shows the accumulation in Tumor (T), liver (L), spleen (S) and circulation through heart (H).

Figure 4

Lateral planar scintigraphic images depicting the distribution of ¹⁸⁶Re-Doxil (upper panel) and ¹⁸⁶Re-PEG-liposomes (lower panel) at various time points after injection. The slow clearance of ¹⁸⁶Re-Doxil, low accumulation in liver and high accumulation in tumor is seen. (H-Heart, L-Liver, S-Spleen, K-Kidney, T-Tumor, STD-Standard).

Figure 5

The distribution of ¹⁸⁶Re-Doxil (A) and ¹⁸⁶Re-PEG-liposomes (B) at various time points determined from planar image analysis. The %ID/g in blood, tumor and spleen are significantly higher for ¹⁸⁶Re-Doxil. Data represented as mean ± SD. (n=4 at each time point and for each group).

Figure 5

The distribution of ¹⁸⁶Re-Doxil (A) and ¹⁸⁶Re-PEG-liposomes (B) at various time points determined from planar image analysis. The %ID/g in blood, tumor and spleen are significantly higher for ¹⁸⁶Re-Doxil. Data represented as mean ± SD. (n=4 at each time point and for each group).

Figure 6

Comparison of H&E stained paraffin sections and autoradiographic images to determine the microdistribution of ¹⁸⁶Re in the tumor at 120 h post administration of ¹⁸⁶Re-Doxil (A) and ¹⁸⁶Re-PEG-liposomes (B). ¹⁸⁶Re is in the periphery of both tumor specimens. ¹⁸⁶Re-Doxil accumulation was increased in tumor compared to ¹⁸⁶Re-PEG-liposomes. (Scale bar: 3 mm).