title: Imaging primary mouse sarcomas after radiation therapy using cathepsin-activatable fluorescent imaging agents.
abstract: OBJECTIVE
  Cathepsin-activated fluorescent probes can detect tumors in mice and in canine patients. We previously showed that these probes can detect microscopic residual sarcoma in the tumor bed of mice during gross total resection. Many patients with soft tissue sarcoma (STS) and other tumors undergo radiation therapy (RT) before surgery. This study assesses the effect of RT on the ability of cathepsin-activated probes to differentiate between normal and cancerous tissue.
  
  
  METHODS
  A genetically engineered mouse model of STS was used to generate primary hind limb sarcomas that were treated with hypofractionated RT. Mice were injected intravenously with cathepsin-activated fluorescent probes, and various tissues, including the tumor, were imaged using a hand-held imaging device. Resected tumor and normal muscle samples were harvested to assess cathepsin expression by Western blot. Uptake of activated probe was analyzed by flow cytometry and confocal microscopy. Parallel in vitro studies using mouse sarcoma cells were performed.
  
  
  RESULTS
  RT of primary STS in mice and mouse sarcoma cell lines caused no change in probe activation or cathepsin protease expression. Increasing radiation dose resulted in an upward trend in probe activation. Flow cytometry and immunofluorescence showed that a substantial proportion of probe-labeled cells were CD11b-positive tumor-associated immune cells.
  
  
  CONCLUSIONS
  In this primary murine model of STS, RT did not affect the ability of cathepsin-activated probes to differentiate between tumor and normal muscle. Cathepsin-activated probes labeled tumor cells and tumor-associated macrophages. Our results suggest that it would be feasible to include patients who have received preoperative RT in clinical studies evaluating cathepsin-activated imaging probes.
authors: Department of Radiation Oncology, Duke University School of Medicine, Durham, North Carolina 27710, USA.
authors: Kyle C
authors: KC
authors: Cuneo
authors: Jeffrey K
authors: JK
authors: Mito
authors: Melodi P
authors: MP
authors: Javid
authors: Jorge M
authors: JM
authors: Ferrer
authors: Yongbaek
authors: Y
authors: Kim
authors: W David
authors: WD
authors: Lee
authors: Moungi G
authors: MG
authors: Bawendi
authors: Brian E
authors: BE
authors: Brigman
authors: David G
authors: DG
authors: Kirsch
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002403:Cathepsins / Q000378:metabolism*; D003937:Diagnosis, Differential; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism*; D006614:Hindlimb; D051379:Mice; D018613:Microscopy, Confocal; D018482:Muscle, Skeletal / Q000378:metabolism*; D012513:Sarcoma, Experimental / Q000175:diagnosis / Q000378:metabolism* / Q000532:radiotherapy*; D014018:Tissue Distribution; D014916:Whole-Body Irradiation / Q000379:methods
chemical_list: D005456:Fluorescent Dyes; D002403:Cathepsins
references: J Clin Oncol. 1996 May;14(5):1679-89
references: 8622088
references: PLoS One. 2009 Nov 30;4(11):e8075
references: 19956606
references: Cancer. 2012 Nov 1;118(21):5320-30
references: 22437667
references: Clin Orthop Relat Res. 2013 Mar;471(3):834-42
references: 22972654
references: PLoS One. 2012;7(3):e33060
references: 22427947
references: J Clin Oncol. 1996 Mar;14(3):859-68
references: 8622034
references: Radiother Oncol. 2005 Apr;75(1):48-53
references: 15948265
references: Lancet. 2002 Jun 29;359(9325):2235-41
references: 12103287
references: Proc Natl Acad Sci U S A. 2011 Jun 14;108(24):9945-50
references: 21628592
references: Int J Cancer. 2009 Apr 15;124(8):1794-801
references: 19101991
references: J Clin Oncol. 1998 Jan;16(1):197-203
references: 9440743
references: Nat Med. 2007 Aug;13(8):992-7
references: 17676052
references: Arch Surg. 1999 Feb;134(2):190-4
references: 10025462
references: Cancer. 2009 Jul 15;115(14):3254-61
references: 19472403