title: Novel design principles enable specific targeting of imaging and therapeutic agents to necrotic domains in breast tumors.
abstract: BACKGROUND
  Necrosis at the tumor center is a common feature of aggressive breast cancers and has been associated with poor prognosis. It is commonly identified by means of invasive histopathology, which often correlates with morbidity and potential tumor cell dissemination, and limits the reconstruction of the whole necrotic domain. In this study we hypothesized that non covalent association to serum albumin (SA) and covalent binding to ligands for tumor-abundant cell receptors should synergistically drive selective accumulation and prolonged retention of imaging and therapeutic agents in breast tumor necrotic domains enabling in vivo identification, imaging and possibly treatment of such tumors.
  
  
  METHODS
  Cyclo-Arg-Gly-Asp-D-Phe-Lys (c(RGDfK)) were conjugated to bacteriochlorophyll-derivatives (Bchl-Ds), previously developed as photodynamic agents, fluorescent probes and metal chelators in our lab. The c(RGDfK) component drives ligation to alphaVbeta3 integrin receptors over-expressed by tumor cells and neo-vessels, and the Bchl-D component associates to SA in a non-covalent manner. STL-6014, a c(RGDfK)-Bchl-D representative, was i.v. injected to CD-1, nude female mice bearing necrotic and non-necrotic human MDA-MB-231-RFP breast cancer tumors. The fluorescence signals of the Bchl-Ds and RFP were monitored over days after treatment, by quantitative whole body imaging and excised tumor/tissue samples derived thereof. Complementary experiments included competitive inhibition of STL-6014 uptake by free c(RGDfK), comparative pharmacokinetics of nonconjugated c(RGDfK) Bchl-D (STL-7012) and of two human serum albumin (HSA) conjugates: HSA-STL-7012 and HSA-STL-6014.
  
  
  RESULTS
  STL-6014 and STL-7012 formed complexes with HSA (HSA/STL-6014, HSA/STL-7012). STL-6014, HSA-STL-7012 and HSA-STL-6014, selectively accumulated at similar rates, in tumor viable regions over the first 8 h post administration. They then migrated into the necrotic tumor domain and presented tumor half lifetimes (T1/2) in the range of days where T1/2 for HSA-STL-6014 > STL-6014 > HSA-STL-7012. No accumulation of STL-7012 was observed. Pre-injection of c(RGDfK) excess, prevented the uptake of STL-6014 in the small, but not in the large tumors.
  
  
  CONCLUSIONS
  Non-covalent association to SA and covalent binding to c(RGDfK), synergistically enable the accumulation and prolonged retention of Bchl-Ds in the necrotic regions of tumors. These findings provide novel guidelines and strategy for imaging and treatment of necrotic tumors.
authors.affiliation: Department of Plant Sciences, Weizmann Institute of Science, Herzel Street, Rehovot, Israel. liat.goldshaid@weizmann.ac.il
authors.forename: Liat
authors.initials: L
authors.lastname: Goldshaid
authors.forename: Efrat
authors.initials: E
authors.lastname: Rubinstein
authors.forename: Alexander
authors.initials: A
authors.lastname: Brandis
authors.forename: Dadi
authors.initials: D
authors.lastname: Segal
authors.forename: Noa
authors.initials: N
authors.lastname: Leshem
authors.forename: Ori
authors.initials: O
authors.lastname: Brenner
authors.forename: Vyacheslav
authors.initials: V
authors.lastname: Kalchenko
authors.forename: Doron
authors.initials: D
authors.lastname: Eren
authors.forename: Tamar
authors.initials: T
authors.lastname: Yecheskel
authors.forename: Yoseph
authors.initials: Y
authors.lastname: Salitra
authors.forename: Yoram
authors.initials: Y
authors.lastname: Salomon
authors.forename: Avigdor
authors.initials: A
authors.lastname: Scherz
mesh_terms: D000818:Animals; D001429:Bacteriochlorophylls / Q000737:chemistry; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000378:metabolism / Q000628:therapy*; D003952:Diagnostic Imaging; D015195:Drug Design; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009336:Necrosis; D009842:Oligopeptides / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D012709:Serum Albumin / Q000008:administration & dosage* / Q000627:therapeutic use; D014018:Tissue Distribution
chemical_list: D001429:Bacteriochlorophylls; D009842:Oligopeptides; D012709:Serum Albumin; C047981:arginyl-glycyl-aspartic acid