Avidin Biotin Liposomes Method For Intrapleural and Mediastinal Lymph Node Drug Delivery

Our group has investigated the avidin/biotin-liposome system as a method to prolong drug delivery and increase liposomal drug retention in the pleural cavity and the mediastinal nodes that receive drainage from this cavity using a rat model (4,41). The avidin/biotin-liposome system can greatly prolong the retention of liposomes in the pleural space and also greatly increase liposome trapping in the mediastinal nodes (4). Mediastinal nodes are important therapeutic targets. Mediastinal nodes are involved as centers of incubation and dissemination in several diseases including lung cancer, tuberculosis, and anthrax (56-58). Treatment and control of these diseases is hard to accomplish because of the limited access of drugs to mediastinal nodes using common pathways of drug delivery. Also, the anatomical location of mediastinal nodes represents a difficult target for external beam irradiation due to its close proximity to major vessels and the heart.

Methodology

99mTc-biotin liposomes containing blue dye were prepared as previously described for the intraperitoneal studies in Section on "Preparation of Biotin-Liposomes Containing Blue Dye.'' These liposomes were injected into the pleural space using the following technique. Anesthetized rats were shaved in the lateral left chest. An incision of approximately 8 mm was made through the skin, then the fascia was dissected away and a small incision was made through the external oblique muscle layer, the latissimus dorsi and the serratus layers. Using fine scissors a nick was made in the intercostal layers. The intercostal layers were punctured using a flat tipped needle stub (19 gauge ~ 4.5 mm in length). To confirm penetration and to prevent damage to the underlying lungs, a 1 mL tuberculin syringe was fitted to the 19 gauge luer hub and 0.1 mL of air was injected into the pleural space. When successfully placed, the air will enter the pleural space without resistance. If resistance was encountered, the 19 gauge stub was removed and reintroduced again. The material was then injected using a flat tipped 23 gauge needle stub (~20 mm in length) inserted through the 19 gauge needle stub.

Study with Intrapleural Avidin/Biotin-Liposomes

Studies were performed by injecting 99mTc-biotin-liposomes containing blue dye into the pleural space followed two hours later by an injection of avidin. This approach was the reverse of the sequence used with the intraperitoneal studies in which avidin was injected after the biotin-liposomes (6,48).

By 22 hours after injection, good retention (15.7% ID/mediastinal nodes; 515 % ID/g) of liposomes was achieved in the mediastinal nodes with the avidin/biotin-liposome system. The scintigraphic images that visually demonstrate the mediastinal node uptake are shown in Figure 2. The images demonstrate the high uptake of liposomes in the mediastinal nodes. In the absence of avidin, liposomes were minimally retained in the nodes (<1.0% ID/organ; 36% ID/g). The specific targeting of a liposome-encapsulated drug to mediastinal lymph nodes could result in a prolonged targeted sustained depot-like delivery of high drug concentrations to these nodes while the liposomes are slowly degraded and metabolized by phago-cytic cells located within these nodes. In the study by Medina et al., evidence of prolonged retention and sustained release of liposome-encapsulated agent in the mediastinal lymph nodes is provided by the continued blue staining of lymph nodes for 22 hours (4). The very high retention of liposomes in

Mediastinal Lymph Node Mice

Figure 2 Scintigraphic images at 22 hours following intrapleural administration of 99mTc-biotin liposomes. The rat in the left panel received intrapleural avidin two hours before administration of the liposomes while the rat in the right panel did not receive avidin. Note the high accumulation of liposomes in the mediastinal nodes in the rat the received the prior injection of avidin. The control rat had a biodistribution of liposomes that resembled an intravenous administration.

Figure 2 Scintigraphic images at 22 hours following intrapleural administration of 99mTc-biotin liposomes. The rat in the left panel received intrapleural avidin two hours before administration of the liposomes while the rat in the right panel did not receive avidin. Note the high accumulation of liposomes in the mediastinal nodes in the rat the received the prior injection of avidin. The control rat had a biodistribution of liposomes that resembled an intravenous administration.

the pleural space and in the mediastinal lymph nodes suggests that this delivery methodology could be used for treatment of disease processes that involve this space or affect the mediastinal lymph nodes. Future experiments using intrapleural injection of the avidin/biotin-liposome system to target drugs to mediastinal nodes should be pursued.

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  • kristiina eskelinen
    Where are lymph glands located in rat?
    8 years ago

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