title: Long-circulating, pH-sensitive liposomes versus long-circulating, non-pH-sensitive liposomes as a delivery system for tumor identification.
abstract: Bombesin (BBN) is a tetradecapeptide that binds specifically to gastrin-releasing peptide receptors in humans. Several forms of cancer, including lung, prostate, breast, and colon over-express receptors for bombesin-like peptides. Therefore, radiolabeled bombesin analogs might be useful for tumor identification. Nevertheless, it is well known that higher tumor uptake can yield images in higher quality. Hence, drug delivery systems, such as liposomes, can be used to achieve a higher concentration of radiotracer in tumor site, and also improve the radiotracer stability, since peptides can suffer easily degradation in vivo by natural plasma and tissue peptides. In this paper, we prepared long-circulating, pH-sensitive liposomes and long-circulation, non-pH sensitive liposomes. Both formulations were able to encapsulate the radiolabeled bombesin derivative (99mTc-BBN(7_14)), and also showing high in vitro stability. Biodistribution studies were performed in Ehrlich tumor bearing-mice to compare the ability of pH-sensitive and non-pH sensitive liposomes to deliver 99mTc-BBN(7_14) to tumor site. Results showed higher tumor uptake (2-fold) when pH-sensitive liposomes were used, suggesting that these vesicles can facilitate the access to the tumor by releasing the diagnostic agent into the ideal area. As a result, tumor-to-muscle ratio achieved with pH-sensitive liposomes was higher than that obtained with non-pH-sensitive formulation. In addition, scintigraphic images for pH-sensitive liposomes showed evident tumor uptake, corroborating with biodistribution data. Therefore, the results presented in this paper suggest that pH-sensitive liposomes are able to deliver more efficiently the radiolabeled bombesin analog. This finding poses a new possibility to improve images quality, since the tumor-to-muscle ratio was strongly enhanced.
authors: Faculdade de Farmácia, Universidade Federal de Minas Gerais, Av. AntOnio Carlos, 6627, 31279-901, Belo Horizonte, Minas Gerais, Brazil.
authors: André Luís Branco
authors: AL
authors: de Barros
authors: Luciene das Graças
authors: Ld
authors: Mota
authors: Daniel Crístian Ferreira
authors: DC
authors: Soares
authors: Cristina Maria
authors: CM
authors: de Souza
authors: Geovanni Dantas
authors: GD
authors: Cassali
authors: Mônica Cristina
authors: MC
authors: Oliveira
authors: Valbert Nascimento
authors: VN
authors: Cardoso
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000000981:diagnostic imaging* / Q000378:metabolism*; D045744:Cell Line, Tumor; D003692:Delayed-Action Preparations; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000737:chemistry*; D008297:Male; D008422:Materials Testing; D008657:Metabolic Clearance Rate; D051379:Mice; D053769:Nanocapsules / Q000737:chemistry*; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000737:chemistry / Q000493:pharmacokinetics*; D010446:Peptide Fragments / Q000737:chemistry / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D003692:Delayed-Action Preparations; D008081:Liposomes; D053769:Nanocapsules; D015609:Organotechnetium Compounds; D010446:Peptide Fragments; D019275:Radiopharmaceuticals; C555232:technetium 99m HYNIC-bombesin (7-14)