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Advances in Radiotherapy
& Nuclear Medicine Radionuclide-carrying liposomes

can be combined with other imaging methods such The injection method utilizes a mixture of phospholipids
as computerized tomography or magnetic resonance dissolved in ethanol. Once the solution is injected into a
imaging to generate images of the body that provide water or phosphate buffer, it begins forming liposomal
precise anatomic localizations, highlighting regions where membranes. After precipitation, these membranes proceed
administered radionuclides are present. Encapsulated to continue forming and create lipid capsules.
positron emitting or single photon emitting radionuclides Reverse-phase evaporation utilizes a mixture of
within liposomes can be used to track their distribution phospholipids. An organic solvent is added to the flask
in the body, to assess the efficacy of liposome-based drug of a rotary evaporator, and rotary evaporation is used
delivery, and to monitor therapeutic radionuclides that to evaporate the solvent. The remaining lipids are then
emit beta particles for cancer therapy. 9 dissolved again in an organic solvent, leading to the
Liposome-delivered chemotherapy is an effective creation of capsule-like structures. The substance that is to
adjuvant treatment to radiotherapy. A study by Hagtvet be encapsulated is added to this mixture, and the resulting
et al. compared the therapeutic effects of radiotherapy on solution is sonicated in a nitrogen environment. 12
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the volume of hypoxic tumors to the effects of radiotherapy For the majority of biomedical applications, it is
along with doxorubicin carried within liposomes. The important to precisely control the size and homogeneity of
hypoxic tumors treated with both radiotherapy and the liposomes. Post-formation processing of liposomes is
liposomal doxorubicin showed a more significant decrease required to convert initially large multilamellar liposome
in tumor volume compared to tumors that received vesicles into small unilamellar liposomes with greater
radiotherapy alone. Liposomal doxorubicin has also homogeneity. This is generally performed by sonication,
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been shown to have increased accumulation in cancerous high-pressure homogenization, or extrusion through a
tumors when combined with certain other modalities. set of filters of decreasing size. The most common size for
For example, intravenously administered liposomal intravenously administered liposomes is 90 – 130 nm.
doxorubicin which was radiolabeled with technetium-
99m ( Tc), had ~3-fold greater accumulation in solid Microfluidic and supercritical techniques are commonly
99m
tumors when combined with simultaneous radiofrequency used in liposome creation. Microfluidic techniques can be
ablation of the tumor as compared with the same used in the injection method to control the mixing of the
radiolabeled liposomal doxorubicin that did not receive lipid and aqueous solutions. Supercritical methods include
radiofrequency ablation (p <0.0001). 11 dissolving lipids in an organic solvent, pressurizing the
mixture by introducing carbon dioxide and injecting the
3. Methods of creating liposomes resulting mixture into an aqueous medium.

Liposomes can be adapted for many applications including Potential problems associated with these techniques
modifications for drug delivery, diagnostic imaging, include a lack of ability to control the size of the liposomes,
and specific targeting (Figure 1). They can be made by the necessity for expensive and specialized equipment, and
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various methods that create products of differing qualities difficulty in removing liposomes from solvent solutions.
including size, stability, half-life, and permeability. These The variety of techniques used in creating liposomes,
methods include thin-film hydration, spray drying, however, gives scientists many options to optimize them
injection, reverse phase evaporation, microfluidic, and for their intended use.
supercritical methods. Shan et al. recently described a new method of
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Thin film hydration involves dissolving lipids in a creating liposomes using a microfluidic mixing device to
solvent solution within a flask, evaporating the solvent, and manufacture an aptamer-targeted liposome containing
then adding a substance that will be encapsulated by the indocyanine green with a high encapsulation efficiency
liposomes. When the flask is agitated, liposomes of varying of 89.9% and a mean size of 129 ± 5.5 nm. The liposomes
sizes form with the majority having multiple lipid bilayers are targeted to tumors for fluorescent imaging and
known as multilamellar liposome vesicles. photothermal therapy. 13
When spray-drying methods are used, phospholipids 4. Advantages of liposomes for drug
are dissolved in an organic mixture and mixed using a
magnetic stir bar and stir plate. The compound that will delivery
be encapsulated by the liposomes is added to this mixture, Using liposomes for drug delivery offers many advantages.
and the resulting solution is sonicated into spheres. These One major advantage is that liposomes are composed
spheres are spray-dried at high temperatures and then of naturally occurring lipids in the human body, which
hydrated, yielding larger-sized liposomes (300 – 600 nm). have natural pathways of degradation after they have

Volume 2 Issue 4 (2024) 3 doi: 10.36922/arnm.4373