Targeted contrast agents for intraoperative imaging include amino acids and
peptides such as aminolevulinic acid, cyclic arginine-glycine-aspartate (cRGD),
folate, chlorotoxin, and specific antibodies against antigens such as CA19-9,
carcinoembryonic antigen (CEA), epithelial cell adhesion molecule (EPCAM),
PSMA, and epidermal growth factor receptor (EGFR) [28, 39]. In organic probes,
the NIR fluorophores are usually conjugated to a specific targeting ligand or monoclonal antibody. NIR agents target biomarkers expressed on certain types of cancers.
Antibodies for imaging increased expression of growth factor receptors such as
EGFR, Her2/neu receptor, or vascular endothelial growth factor (VEGF) receptor
are labeled with Cyanine 5.5 and Alexa Fluor 750 fluorophores. Fluorophores bound
to a specific ligand, e.g., VEGF or EGF, can be internalized, allowing uptake of the
tracer to be monitored [28].
For imaging tumor angiogenesis, alpha-v-beta-3 (α v β 3 ) integrin, a wellcharacterized adhesion molecule found at the sprouting ends of newly formed
blood vessels, can easily be targeted with molecular probes. For this reason, it has
been used to model targeting of agents to tumors. High expression of adhesion
receptors can be detected when targeting α v β 3 integrin with cRGD conjugated to
Cyanine 5.5 or IRdye800CW [28]. Previous studies demonstrated that integrin
α v β 3 or CD13 molecules, overexpressed specifically on the surfaces of endothelial
or tumor cells, can serve as imaging targets for early tumor detection and NIR
fluorescence-guided surgical navigation in glioblastomas [49, 57, 58].
Similar approaches using activatable fluorophores are followed when targeting
the upregulation of tumor-associated proteolytic enzymes such as cathepsins and
matrix metalloproteinases (MMP). This allows detection of proteases abundant in
malignant tissue, which can be associated with specific invasive, aggressive, or
metastatic characteristics of tumors. However, proteolytic enzymes are not specific
for molecules in cancer cells, because cathepsins and matrix metalloproteinases
are abundant in inflammatory tissue. NIR probes activated by proteases such as
Cathepsin B and MMP-2 were injected in an inactivated state (quenched), and
cleaved by enzymes that result in dequenching and increased fluorescence [28, 59].
Summary Integration of optical imaging in intraoperative guidance is necessary to
improve the surgical accuracy and outcomes of clinical cancer surgery.
4 Cerenkov Luminescence Imaging and Therapy
Cerenkov Luminescence Cerenkov luminescence (CL) or Cerenkov radiation is a
continuous spectrum of light peaking in the blue-to-ultraviolet spectrum. It is
produced by subatomic charged particles traveling faster than the speed of light
through a dielectric medium such as water or biological tissues. CL was discovered
in 1934, but it was first recognized for biomedical research applications in 2009 due
to advances in highly sensitive optical cameras [60, 61]. Since then, the applications
of CL from clinically relevant radionuclides have been expanding to biomedical
214
E. P. Stater et al.
peptides such as aminolevulinic acid, cyclic arginine-glycine-aspartate (cRGD),
folate, chlorotoxin, and specific antibodies against antigens such as CA19-9,
carcinoembryonic antigen (CEA), epithelial cell adhesion molecule (EPCAM),
PSMA, and epidermal growth factor receptor (EGFR) [28, 39]. In organic probes,
the NIR fluorophores are usually conjugated to a specific targeting ligand or monoclonal antibody. NIR agents target biomarkers expressed on certain types of cancers.
Antibodies for imaging increased expression of growth factor receptors such as
EGFR, Her2/neu receptor, or vascular endothelial growth factor (VEGF) receptor
are labeled with Cyanine 5.5 and Alexa Fluor 750 fluorophores. Fluorophores bound
to a specific ligand, e.g., VEGF or EGF, can be internalized, allowing uptake of the
tracer to be monitored [28].
For imaging tumor angiogenesis, alpha-v-beta-3 (α v β 3 ) integrin, a wellcharacterized adhesion molecule found at the sprouting ends of newly formed
blood vessels, can easily be targeted with molecular probes. For this reason, it has
been used to model targeting of agents to tumors. High expression of adhesion
receptors can be detected when targeting α v β 3 integrin with cRGD conjugated to
Cyanine 5.5 or IRdye800CW [28]. Previous studies demonstrated that integrin
α v β 3 or CD13 molecules, overexpressed specifically on the surfaces of endothelial
or tumor cells, can serve as imaging targets for early tumor detection and NIR
fluorescence-guided surgical navigation in glioblastomas [49, 57, 58].
Similar approaches using activatable fluorophores are followed when targeting
the upregulation of tumor-associated proteolytic enzymes such as cathepsins and
matrix metalloproteinases (MMP). This allows detection of proteases abundant in
malignant tissue, which can be associated with specific invasive, aggressive, or
metastatic characteristics of tumors. However, proteolytic enzymes are not specific
for molecules in cancer cells, because cathepsins and matrix metalloproteinases
are abundant in inflammatory tissue. NIR probes activated by proteases such as
Cathepsin B and MMP-2 were injected in an inactivated state (quenched), and
cleaved by enzymes that result in dequenching and increased fluorescence [28, 59].
Summary Integration of optical imaging in intraoperative guidance is necessary to
improve the surgical accuracy and outcomes of clinical cancer surgery.
4 Cerenkov Luminescence Imaging and Therapy
Cerenkov Luminescence Cerenkov luminescence (CL) or Cerenkov radiation is a
continuous spectrum of light peaking in the blue-to-ultraviolet spectrum. It is
produced by subatomic charged particles traveling faster than the speed of light
through a dielectric medium such as water or biological tissues. CL was discovered
in 1934, but it was first recognized for biomedical research applications in 2009 due
to advances in highly sensitive optical cameras [60, 61]. Since then, the applications
of CL from clinically relevant radionuclides have been expanding to biomedical
214
E. P. Stater et al.