Fluorescent imaging of cancerous tissues for targeted surgery

Abstract

To maximize tumor excision and minimize collateral damage are the primary goals of cancer surgery. Emerging molecular imaging techniques have made "image-guided surgery" developed into "molecular imaging-guided surgery", which is termed as "targeted surgery" in this review. Consequently, the precision of surgery can be advanced from tissue-scale to molecule-scale, enabling "targeted surgery" to be a component of "targeted therapy". Evidence from numerous experimental and clinical studies has demonstrated significant benefits of fluorescent imaging in targeted surgery with preoperative molecular diagnostic screening. Fluorescent imaging can help to improve intraoperative staging and enable more radical cytoreduction, detect obscure tumor lesions in special organs, highlight tumor margins, better map lymph node metastases, and identify important normal structures intraoperatively. Though limited tissue penetration of fluorescent imaging and tumor heterogeneity are two major hurdles for current targeted surgery, multimodality imaging and multiplex imaging may provide potential solutions to overcome these issues, respectively. Moreover, though many fluorescent imaging techniques and probes have been investigated, targeted surgery remains at a proof-of-principle stage. The impact of fluorescent imaging on cancer surgery will likely be realized through persistent interdisciplinary amalgamation of research in diverse fields.

Keywords: Fluorescent imaging; Image-guided surgery; Molecular imaging; Multimodality imaging; Multiplex imaging; System molecular imaging; Targeted surgery; Targeted therapy.

Figure 1

Representative fluorescent materials for molecular imaging. (modified from ref [32], [205, 206])

Figure 2

The first clinical trial of fluorescent molecular imaging-guided surgery in ovarian cancer by folate receptor-α targeting. (A): Schematic of folate-FITC (molecular weight: 917 kDa). Folate-FITC was synthesized by conjugating folate to FITC through an ethylenediamine spacer. (B): Color image of a representative area in the abdominal cavity. (C): The corresponding tumor-specific fluorescence image with A in the same area in the abdominal cavity, which demonstrated that the biggest benefit of intraoperative tumor-specific fluorescence imaging would be improved intraoperative staging as well as more radical cytoreductive surgery. Reprinted with permission from[81]. Copyright 2011, Nature medicine.

Figure 3

Representative experimental results manifest the potential breakthroughs that may result from fluorescent molecular imaging-guided surgery. (A): Colorectal liver and peritoneal metastases can be clearly demarcated during surgery using an integrinαvβ3 targeted NIRF probeIntegriSense®680. A1:Intraoperative NIRF image of a colorectal liver metastasis lesion in a rat 24 h after injection of IntegriSense®680. A2–4: Shown are a color image (A2), a NIR fluorescence image (A3), and a pseudo-colored green merge of the two images (A4) of a part of the jejunum and adjacent mesentery of a rat bearing multiple mesenteric metastases, which were all acquired intraoperatively. (B): Cy5-labeled free activatable cell-penetrating peptides (ACPPs) delineated tumor at the margin of resection. B1: White light image of a MDA-MB-435 xenograft following skin incision and tumor (large arrow) exposure. B2: Fluorescence image of GFP-labeled tumor cells from the same animal as in A. B3: Fluorescence image 6 h following i.v. administration of Cy5-labeled free ACPPs showing increased uptake by the tumor (large arrow) compared to surrounding tissue. B4: Overlay fluorescence image showing co-localization of the Cy5 free ACPP with the GFP-labeled tumor. Following gross tumor excision by standard (unguided) technique, the tumor bed (*) seen with white light. (C) Nerve-highlighting fluorescent imaging for image-guided surgery. C1: After i.p. injection, BMB stains the cerebellar white matter. C2–4: Cy5-NP41 (acetyl-SHSNTQTLAKAPEHTGC-(Cy5)-amide) labeling of the sciatic nerve in Thy1-YFP transgenic mice. C2: Low-power bright field view of left exposed sciatic nerve. Inset shows magnified view of central boxed region. C3: Same nerve as in C2 with YFP fluorescence (pseudocolored yellow) superimposed on the bright field image, showing transgenic expression of YFP in axons. C4: Same nerve as in a and C2 viewed with Cy5 fluorescence(pseudocolored cyan for maximal contrast during live surgery) superimposed on the bright field image, showing nerve labeling with Cy5-NP41. Arrows in C3 and C4 point to thin buried nerve branches that are better revealed by the long-wavelength Cy5 fluorescence than by bright field reflectance or shorter wavelength YFP fluorescence. There is some nonspecific labeling of skin(asterisk) and cut edges of muscle (arrowhead) by Cy5-NP41. Fortunately, such nonspecific labeling hardly ever has the filamentous appearance of nerves, so an experienced surgeon can usually distinguish nonspecific from specific targets. Reprinted with permission from [85, 143, 145, 147]. Copyright 2011, the journal of the European Society of Surgical Oncology and the British Association of Surgical Oncology; Copyright 2010, Proceedings of the National Academy of Sciences of the United States of America; Copyright 2011, Nature biotechnology; Copyright 2006, Proceedings of the National Academy of Sciences of the United States of America.

Figure 4

Intraoperative metastases and sentinel node identification in clinical settings with the hybrid radioactive and fluorescent tracer indocyanine green (ICG)-^99mTc-nanocolloid. (A) Preoperative detection of metastases in sentinel lymph nodes. A1: Lymphoscintigraphy showing the injection site (IS) with three sentinel lymph nodes on the right side and one sentinel lymph node on the left side. A2: Three-dimensional volume-rendered single-proton emission computed tomography supplemented with computed tomography image revealing that the most caudal sentinel lymph node on the right side is located in an inferior Daseler zone. A3: Axial fused SPECT/CT images depicting both radioactive SNs. (B) Intraoperative identification of metastases in sentinel lymph nodes. B1–2: a color image (B1) and the corresponding NIR image (B2) showed that a radioactive, non-blue sentinel lymph node is clearly seen using fluorescence imaging. B3: The portable gamma camera provides an overview image of the sentinel lymph nodes that can be used to verify complete SN removal after excision (figure inlay). (C)Post-excision confirmation of complete sentinel node (SN) removal using a portable gamma camera. C1: Blocking the injection site using the Sentinella suite software visualizes the three SNs on the right side. C2: Post-excision image after removal of three radioactive/fluorescent nodes (as shown in A2) shows that the most caudal SN is still in situ. C3: After excision of the remaining SN, which proved to be tumor positive at histopathology, complete SN removal is verified. BL = blocked injection site using Sentinella Suite software; HE = higher echelon nodes. Reprinted with permission from [157]. Copyright 2014, European urology.

Figure 5

Cerenkov luminescence imaging in clinical settings and for providing guidance in experimental targeted cancer surgery. A: Representative CL images of ¹⁸F-FDG–positive axillary lymph node (left axillae). B: White-light photograph from left axilla, overlaid with significant CL signal (A). C: PET/CT images of ¹⁸F-FDG–positive left axillae lymph node. This signal colocalized with CL finding. D: Mouse bearing C6 glioma after tail-vein administration of 37 MBq (1 mCi) of ¹⁸F-FDGwas imaged by commercially available optical IVIS system. E–G: Mouse was imaged by IVIS optical system (E) and fiber-based system (F) after surgery to remove tumor tissues. Ambient-light images are on left, luminescent images are in middle, and fused images are on right (G). Reprinted with permission from[168, 169]. Copyright 2012 and 2014, Journal of nuclear medicine.

Figure 6

Dual modality imaging of SKOV3 tumor bearing mice by hybrid MRI and NIR imaging. (A) Optical imaging revealed strong signals in the primary tumor in the tumor bearing mice following NIR-830-Z_HER2:342-IONP administration. T2-weighted MRI also showed marked signal decrease (16%) in a large primary tumor (pink arrow). (B) MRI of SKOV3 tumor bearing mice after NIR-830-BSA-IONP injection. There was no contrast change in pre- and post-MR images of the tumor. Reprinted with permission from[181]. Copyright 2014, Small.