Mol Imaging Biol (2016)DOI: 10.1007/s11307-016-0956-7* World Molecular Imaging Society, 2016
A Clinical Wide-Field Fluorescence EndoscopicDevice for Molecular Imaging DemonstratingCathepsin Protease Activity in Colon CancerSteven Sensarn,1,2,3 Cristina L. Zavaleta,1,3 Ehud Segal,4 Stephan Rogalla,2
Wansik Lee,1,5 Sanjiv S. Gambhir,1,3,6,7 Matthew Bogyo,4 Christopher H. Contag1,2,3,8,9
1Department of Radiology, Stanford University, James H. Clark Center for Biomedical Engineering & Sciences, Stanford, CA, 94305, USA2Department of Pediatrics, Stanford University, James H. Clark Center for Biomedical Engineering & Sciences, Stanford, CA, 94305, USA3Molecular Imaging Program at Stanford (MIPS), Stanford University, Stanford, CA, 94305, USA4Department of Pathology, Stanford University, Stanford, CA, 94305, USA5Department of Internal Medicine, Chonnam National University Medical School, Gwangju, Republic of Korea6Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA7Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA8Department of Microbiology & Immunology, Stanford University, Stanford, CA, 94305, USA9Stanford University, 318 Campus Drive, Stanford, CA, 94305-5427, USA
AbstractPurpose: Early and effective detection of cancers of the gastrointestinal tract will require novelmolecular probes and advances in instrumentation that can reveal functional changes in dysplasticandmalignant tissues. Here, we describe adaptation of a wide-field clinical fiberscope to performwide-field fluorescence imaging while preserving its white-light capability for the purpose of providing wide-field fluorescence imaging capability to point-of-care microscopes.Procedures: Wedeveloped and used a fluorescent fiberscope to detect signals fromaquenched probe,BMV109, that becomes fluorescent when cleaved by, and covalently bound to, active cathepsinproteases. Cathepsins are expressed in inflammation- and tumor-associated macrophages as well asdirectly from tumor cells and are a promising target for cancer imaging. The fiberscope has a 1-mmouterdiameter enabling validation via endoscopic exams inmice, and therefore we evaluated topically appliedBMV109 for the ability to detect colon polyps in an azoxymethane-induced colon tumor model in mice.Results: This wide-field endoscopic imaging device revealed consistent and clear fluorescencesignals from BMV109 that specifically localized to the polypoid regions as opposed to the normaladjacent colon tissue (p G0.004) in the murine colon carcinoma model.Conclusions: The sensitivity of detection of BMV109 with the fluorescence fiberscope suggestedutility of these tools for early detection at hard-to-reach sites. The fiberscope was designed to beused in conjunction with miniature, endoscope-compatible fluorescence microscopes for dualwide-field and microscopic cancer detection.
Key words: Optical imaging, Optical probes, Endoscopy, Fluorescence, Imaging systems,Medical imaging, Fiber optics, Biomedical optics
Steven Sensarn and Cristina L. Zavaleta contributed equally to this work.Electronic supplementary material The online version of this article(doi:10.1007/s11307-016-0956-7) contains supplementary material, whichis available to authorized users.
Correspondence to: Christopher Contag; e-mail: email@example.com
IntroductionCancer remains the second most common cause of death inthe USA, with over 1.6 million new cancer cases estimatedthis year according to the American Cancer Society .Even more alarming is the 585,000 cancer-related deathsexpected this year in the US alone. Diagnostic tools thatenable early detection, including endoscopy as a screeningprocedure for colon cancer, have been shown to reducecancer mortality . However, many of the imaging toolsavailable for clinical screening, including endoscopy, arelimited by the use of white light revealing gross structuralabnormalities based on visual inspection. As such, white-light endoscopy has miss rates of up to 25 % . Therefore,the development of point-of-care diagnostic tools that offeradditional molecular information with sufficient sensitivityand specificity for early cancer detection is critical foreffective early detection and early intervention. Toward thisend, fluorescence endoscopy has the potential for sensitivemolecular analyses through the use of fluorescent molecularprobes that have specificity for dysplastic or malignanttissues . To effectively detect such functional probes,new accessories that image over a range of scales frommacro- to microscopic levels and are compatible withclinical endoscopes need to be developed. Effective opticaltools with a breadth of capabilities would facilitate cancerdetection and have the potential to significantly impact thesurvival rates of patients.
Mouse models are typically used for development ofmolecular probes, and a number of instruments have beendescribed that enable molecular detection of colon cancer inmice . Endoscope design options for colonoscopy inmice are limited to a device diameter less than approxi-mately 3.5 mm . Rigid borescopes yield beautiful, high-resolution  rodent endoscopic images but have limitedlength and cannot navigate beyond the distal colon, restrict-ing their utility. Fiber bundle-based endoscopesfibersco-pesmay have poorer resolution than rigid scopes but havea much smaller cross section (1 mm), ease of sterilization,and simplicity of manufacture, and may serve as an adjunctmodality for other high-resolution imaging tools. Fiber-scopes are particularly well suited for fluorescence imagingsince they can be made very small, use extremely sensitivedetectors, such as intensified or electron-multiplying cam-eras, and can detect weak fluorescence signals through theworking channels of existing clinical endoscopes . Also,when used in conjunction with targeted molecular probes,the resolution of a fiberscope is less prohibitive and canreveal the presence of fluorescence signalsrather thanrelying on high-resolution morphological detail, and may besufficient to guide further inspection with more high-resolution devices that have smaller fields of view, or toguide biopsy. Fluorescence-enabled fiberscopes would haveutility in animal models, and would also be suitable for usewith clinical devices for early detection, guided microscopyand image-guided biopsy.
Here, we describe modifications to a commerciallyavailable white-light fiberscope for use as a wide-fieldfluorescence endoscope, and demonstrate its use in mousemodels. The fiberscope is currently approved by the Foodand Drug Administration (FDA) for white-light imaging ofbile ducts and can be sterilized and reused, making it apromising candidate for adding small-footprint fluorescenceimaging to endoscopic devices in the clinic and forincorporation into other devices to create multifunctionalinstruments that operate over a range of scales using severaldifferent modes. In addition to its clear clinical applications,this device also has potential for use as a preclinical imagingdevice to assess the tumor-targeting efficiency of newlydeveloped optical probes, in preparation for clinicaltranslation.
We have adapted the 1-mm fiberscope to perform dualwhite-light and fluorescence imaging, and demonstrated itsuse in the distal colon of mice where we were able toevaluate the location, shape, and size of polyps. This isparticularly useful when planning experiments in expensivetransgenic mouse models and time-intensive carcinogen-induced models. No other preclinical imaging techniquecurrently exists to assess tumor progression in orthotopiccolon cancer models in real time, and therefore time andmaterials are often wasted in the testing of new drugs ortumor-targeting agents. We demonstrate functional imagingusing BMV109, a fluorescent probe designed to target activecathepsin proteases expressed by inflammation- and tumor-associated macrophages and certain tumor cells themselves. The probe has similar pan-cathepsin-targeting activityas the previously described MV151  but utilizes aquencher that is cleaved upon activation, such that the probeis activated at the tumor site. Used in conjunction with anazoxymethane-induced (AOM) mouse model of coloncancer, the device and molecular probe demonstratedsensitive and specific targeting of colorectal tumors. Werevealed that the combination of the wide-field fluorescencefiberscope and the cathepsin-activated probe reliablydetected small polyps in relevant rodent models indicatingutility in early detection of human disease.
Material and MethodsSmall Animal Fluorescence Endoscope
The core component of the endoscope used in this study is theSpyGlass fiber-optic probe from Boston Scientific. The device isFDA-approved for white-light cholangiography and consists of a6600-fiber imaging bundle surrounded by 225 wide-angle illumi-nation fibers. The probe has an outer diameter of less than 1 mmand images a 70-degree field of view. We have adapted thefiberscope to perform dual white-light and fluorescence imagingutilizing a dual-illumination setup with a laser and light-emittingdiode (LED), as well as a removable mirror detection scheme.
For illumination, a 660-nm fiber-coupled diode laser (CoherentCUBE) was coupled into the SpyGlass light guide port using a 60
S. Sensarn et al.: Fluorescence Endoscope and Targeted Probe for Colon Cancer