title: Development of a bone-targeted pH-sensitive liposomal formulation containing doxorubicin: physicochemical characterization, cytotoxicity, and biodistribution evaluation in a mouse model of bone metastasis.
abstract: BACKGROUND
  Despite recent advances in cancer therapy, the treatment of bone tumors remains a major challenge. A possible underlying hypothesis, limitation, and unmet need may be the inability of therapeutics to penetrate into dense bone mineral, which can lead to poor efficacy and high toxicity, due to drug uptake in healthy organs. The development of nanostructured formulations with high affinity for bone could be an interesting approach to overcome these challenges.
  
  
  OBJECTIVE
  To develop a liposomal formulation with high affinity for hydroxyapatite and the ability to release doxorubicin (DOX) in an acidic environment for future application as a tool for treatment of bone metastases.
  
  
  METHODS
  Liposomes were prepared by thin-film lipid hydration, followed by extrusion and the sulfate gradient-encapsulation method. Liposomes were characterized by average diameter, ζ-potential, encapsulation percentage, X-ray diffraction, and differential scanning calorimetry. Release studies in buffer (pH 7.4 or 5), plasma, and serum, as well as hydroxyapatite-affinity in vitro analysis were performed. Cytotoxicity was evaluated by MTT assay against the MDA-MB-231 cell line, and biodistribution was assessed in bone metastasis-bearing animals.
  
  
  RESULTS
  Liposomes presented suitable diameter (~170 nm), DOX encapsulation (~2 mg/mL), controlled release, and good plasma and serum stability. The existence of interactions between DOX and the lipid bilayer was proved through differential scanning calorimetry and small-angle X-ray scattering. DOX release was faster when the pH was in the range of a tumor than at physiological pH. The bone-targeted formulation showed a strong affinity for hydroxyapatite. The encapsulation of DOX did not interfere in its intrinsic cytotoxicity against the MDA-MB-231 cell line. Biodistribution studies demonstrated high affinity of this formulation for tumors and reduction of uptake in the heart.
  
  
  CONCLUSIONS
  These results suggest that bone-targeted pH-sensitive liposomes containing DOX can be an interesting strategy for selectively delivering this drug into bone-tumor sites, increasing its activity, and reducing DOX-related toxicity.
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil; Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors: Diêgo Dos Santos
authors: Ddos S
authors: Ferreira
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Samilla Dornelas
authors: SD
authors: Faria
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Sávia Caldeira de Araújo
authors: SC
authors: Lopes
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Cláudia Salviano
authors: CS
authors: Teixeira
authors: Department of Physics.
authors: Angelo
authors: A
authors: Malachias
authors: Department of Physics.
authors: Rogério
authors: R
authors: Magalhães-Paniago
authors: Department of Chemistry, Institute of Exact Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
authors: José Dias
authors: JD
authors: de Souza Filho
authors: Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors: Bruno Luis de Jesus Pinto
authors: BL
authors: Oliveira
authors: Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors: Alexander Ramos
authors: AR
authors: Guimarães
authors: Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors: Peter
authors: P
authors: Caravan
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Lucas Antônio Miranda
authors: LA
authors: Ferreira
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Ricardo José
authors: RJ
authors: Alves
authors: Department of Pharmaceutical Products, Faculty of Pharmacy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors: Mônica Cristina
authors: MC
authors: Oliveira
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000737:chemistry; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000556:secondary*; D001842:Bone and Bones / Q000187:drug effects*; D002021:Buffers; D002152:Calorimetry, Differential Scanning; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D055598:Chemical Phenomena; D002626:Chemistry, Pharmaceutical; D004195:Disease Models, Animal; D004317:Doxorubicin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D017886:Durapatite / Q000737:chemistry; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D049329:Nanostructures / Q000737:chemistry; D011092:Polyethylene Glycols / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use; D053838:Scattering, Small Angle; D044967:Serum; D014018:Tissue Distribution / Q000187:drug effects; D014961:X-Ray Diffraction
chemical_list: D000903:Antibiotics, Antineoplastic; D002021:Buffers; C506643:liposomal doxorubicin; D011092:Polyethylene Glycols; D004317:Doxorubicin; D017886:Durapatite
keywords: bisphosphonates; bone-tumor treatment; hydroxyapatite-targeted formulations; pH-responsive nanostructures