Improved detection of ovarian cancer metastases by intraoperative quantitative fluorescence protease imaging in a pre-clinical model
Introduction
Cytoreductive surgery in metastatic ovarian cancer has been shown to have a significant beneficial effect on patient outcome and represents an important cornerstone in the treatment of this disease [1], [2], [3]. Current guidelines define an “optimal” debulking procedure as one in which the surgeon leaves the abdomen with less than 1 cubic cm of residual tumor; additional evidence suggests that greater improvements in clinical outcome can be achieved by setting even lower thresholds for residual tumor [4]. There is an unmet clinical need for an intraoperative imaging modality to assist the surgeon in identifying tumor foci. Improved intraoperative tumor detection has the potential to yield both more accurate staging as well as decreased residual metastatic disease.
A variety of imaging modalities have been applied towards more sensitive detection of diffuse peritoneal carcinomatosis, with near infrared (NIR) optical imaging showing particular promise. The advent of fluorescent molecular probes with a propensity for differentially illuminating tumor foci against normal background tissue has allowed for the application of optical imaging towards a number of cancer models [5], [6], including ovarian cancer [7], [8], [9]. Our laboratory has developed a novel class of “smart” probes that are administered in an optically silent state, but in the presence of specific proteases, are cleaved and thus activated, resulting in up to a hundred-fold signal amplification [10], [11]. Protease, particularly cathepsin B, up-regulation has been shown to occur in a variety of disease states, including ovarian cancer[12], and thus these probes represent highly sensitive molecular beacons that may be applied for the detection of metastatic disease [13].
One commonly cited drawback to intravital optical imaging is the inability to quantify fluorescent signal. The collected signal varies dramatically as the distance between the tissue under investigation and the imaging apparatus changes during an operative procedure; this variability precludes quantitative analysis of the molecular probe's signal intensity, thus severely limiting the applicability of optical imaging to reliable minimally invasive tumor detection. To account for this distance dependence, we have recently developed methods that allow for the intravital and real-time quantification of NIR fluorescence [6], [14]. In this study, we demonstrate the ability of NIR “smart” probes to detect ovarian cancer metastases with high TBRs, as well as to improve upon the sensitivity for the visualization of cancer foci adherent to and within abdominal structures, versus standard white light (WL) evaluation. Finally, we apply a distance dependence correction algorithm to allow fluorescence imaging in a quantitative manner during in vivo laparoscopic procedures.
Section snippets
NIR activatable probe
The imaging probe used for this study is a commercially available protease-activatable NIR fluorescent probe, Prosense750 (VisEn Medical, Woburn, MA). The probe's structure consists of a synthetic graft polymer composed of poly-l-lysine that is sterically protected by multiple methoxypolyethylene glycol side chains. Conjugated onto this lysine backbone are multiple NIR fluorochromes whose fluorescence is quenched by their proximity to one another in a phenomenon similar to fluorescence
Ex vivo imaging of metastatic ovarian cancer with conventional WL and ProSense750
To evaluate the ability of ProSense750 to detect ovarian cancer metastases, explanted abdominal and pelvic organs from a peritoneal carcinomatosis animal model were imaged under both conventional WL and NIR fluorescence; the results of this study are summarized in Fig. 1 by images of representative tissue samples with tumor foci. Fig. 1A demonstrates a section of omentum with a large, fixed, and irregular mass visible in WL that fluoresces vividly under NIR interrogation; histologic analysis
Discussion
Optical imaging with molecularly targeted probes has numerous advantages compared to other detection methods for evaluation of potential residual disease. The approach focally highlights disease, lacks ionizing radiation, and has a low barrier to incorporation in the operating room. Near infrared protease imaging in particular offers a number of distinct advantages in the detection of ovarian cancer peritoneal metastases, by targeting an enzyme class widely present across most ovarian cancers
Conflict of interest statement
RW is a shareholder and member of the Board of Directors for VisEn Medical. All other authors have no conflicts of interest to declare.
Acknowledgments
This research was supported in part by NIH grant R01-EB001872 and U24-CA92782.
References (17)
- et al.
Survival and prognostic factors in patients with ovarian cancer
Obstet. Gynecol.
(2003) - et al.
Symptoms of ovarian cancer
Obstet. Gynecol.
(2001) - et al.
What is the optimal goal of primary cytoreductive surgery for bulky stage IIIC epithelial ovarian carcinoma (EOC)?
Gynecol. Oncol.
(2006) - et al.
The role of cathepsin B and cystatin C in the mechanisms of invasion by ovarian cancer
Gynecol. Oncol.
(2004) - et al.
Cancer statistics
CA: Cancer J. Clinic.
(2007) - et al.
Near infrared thoracoscopy of tumoral protease activity for improved detection of peripheral lung cancer
Int. J Cancer
(2006) - et al.
Miniaturized multichannel near infrared endoscope for mouse imaging
Mol. Imaging
(2003) - et al.
Catheter-based in vivo imaging of enzyme activity and gene expression: feasibility study in mice
Radiology
(2004)
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