Comparison of three remote radiolabelling methods for long-circulating liposomes

Area of Science:

• Nanomedicine
• Radiopharmaceutical Chemistry
• Drug Delivery Systems

Background:

• Long-circulating liposomes (LCL) are crucial drug carriers, often radiolabeled for in vivo tracking.
• Traditional methods involve encapsulating DTPA in LCL (DTPA-LCL) for Indium-111 labeling with Indium-111 oxine.
• An alternative approach uses DTPA-conjugated DSPE incorporated into the lipid bilayer (DTPA-DSPE LCL) for labeling with Indium-111 chloride.

Purpose of the Study:

• To compare the in vitro and in vivo properties of DTPA-DSPE LCL with conventional DTPA-LCL.
• To evaluate the efficiency, stability, and targeting of liposomes labeled with different methods.

Main Methods:

• DTPA-DSPE LCL were labeled with (111)InCl3, while DTPA-LCL and empty LCL were labeled with (111)In-oxine.
• In vitro stability was assessed in human serum at 37°C.
• In vivo studies in mice with Staphylococcus aureus thigh infections involved imaging, blood sampling, and biodistribution analyses.

Main Results:

• DTPA-DSPE LCL achieved significantly higher labeling efficiency at greater specific activity compared to DTPA-LCL and empty LCL.
• (111)In-labeled DTPA-DSPE LCL and DTPA-LCL demonstrated excellent stability in human serum (>98% radiolabel retention after 48h).
• In vivo abscess targeting by (111)In-DTPA-DSPE LCL was comparable to (111)In-DTPA LCL.

Conclusions:

• Labeling DTPA-DSPE LCL with (111)InCl3 is a robust, rapid, and efficient method.
• This technique is advantageous over the more complex conventional DTPA-LCL labeling with (111)In-oxine.
• DTPA-DSPE LCL offers a preferred approach for radiolabeling liposomes for in vivo tracking and drug delivery studies.