Despite promising results in malaria-naïve individuals, whole sporozoite (SPZ) vaccine efficacy in malaria-endemic settings has been suboptimal. Vaccine hypo-responsiveness due to previous malaria... Show moreDespite promising results in malaria-naïve individuals, whole sporozoite (SPZ) vaccine efficacy in malaria-endemic settings has been suboptimal. Vaccine hypo-responsiveness due to previous malaria exposure has been posited as responsible, indicating the need for SPZ vaccines of increased immunogenicity. To this end, we here demonstrate a proof-of-concept for altering SPZ immunogenicity, where supramolecular chemistry enables chemical augmentation of the parasite surface with a TLR7 agonist-based adjuvant (SPZ-SAS(CL307)). In vitro, SPZ-SAS(CL307) remained well recognized by immune cells and induced a 35-fold increase in the production of pro-inflammatory IL-6 (p < 0.001). More promisingly, immunization of mice with SPZ-SAS(CL307) yielded improved SPZ-specific IFN-γ production in liver-derived NK cells (percentage IFN-γ+ cells 11.1 ± 1.8 vs. 9.4 ± 1.5%, p < 0.05), CD4+ T cells (4.7 ± 4.3 vs. 1.8 ± 0.7%, p < 0.05) and CD8+ T cells (3.6 ± 1.4 vs. 2.5 ± 0.9%, p < 0.05). These findings demonstrate the potential of using chemical augmentation strategies to enhance the immunogenicity of SPZ-based malaria vaccines. Show less
Background: The occurrence of accidental nerve damage during surgery and the increasing application of image guidance during head-and-neck surgery have highlighted the need for molecular targeted... Show moreBackground: The occurrence of accidental nerve damage during surgery and the increasing application of image guidance during head-and-neck surgery have highlighted the need for molecular targeted nerve-sparing interventions. The implementation of such interventions relies on the availability of nerve-specific tracers. In this paper, we describe the development of a truncated peptide that has an optimized affinity for protein zero (P0), the most abundant protein in myelin. Methods and Materials: Further C- and N-terminal truncation was performed on the lead peptide Cy5-P0(101-125). The resulting nine Cy5-labelled peptides were characterized based on their photophysical properties, P0 affinity, and in vitro staining. These characterizations were combined with evaluation of the crystal structure of P0, which resulted in the selection of the optimized tracer Cy5-P0(112-125). A near-infrared Cy7-functionalized derivative (Cy7-P0(112-125)) was used to perform an initial evaluation of fluorescence-guided surgery in a porcine model. Results: Methodological truncation of the 26-amino-acid lead compound Cy5-P0(101-125) resulted in a size reduction of 53.8% for the optimized peptide Cy5-P0(112-125). The peptide design and the 1.5-fold affinity gain obtained after truncation could be linked to interactions observed in the crystal structure of the extracellular portion of P0. The near-infrared analogue Cy7-P0(112-125) supported nerve illumination during fluorescence-guided surgery in the head-and-neck region in a porcine model. Conclusions: Methodological truncation yielded a second-generation P0-specific peptide. Initial surgical evaluation suggests that the peptide can support molecular targeted nerve imaging. Show less
Duszenko, N.; Willigen, D.M. van; Bunschoten, A.; Velders, A.H.; Roestenberg, M.; Leeuwen, F.W.B. van 2022
Many pathogens blunt immune responses because they lack immunogenic structural features, which typically results in disease. Here, we show evidence suggesting that pathogen immunogenicity can be... Show moreMany pathogens blunt immune responses because they lack immunogenic structural features, which typically results in disease. Here, we show evidence suggesting that pathogen immunogenicity can be chemically enhanced. Using supramolecular host-guest chemistry, we complexed onto the surface of a poorly immunogenic bacterium (Staphylococcus aureus) a TLR7 agonist-based adjuvant. "Adjuvanted" bacteria were readily recognized by macrophages and induced a more pro-inflammatory immunophenotype. Future applications of this concept could yield treatment modalities that bolster the immune system's response to pathogenic microbes. Show less
Background: With the rise of prostate-specific membrane antigen (PSMA) radioguided surgery, which is performed using a microdosing regime, demand for visual target confirmation via fluorescence... Show moreBackground: With the rise of prostate-specific membrane antigen (PSMA) radioguided surgery, which is performed using a microdosing regime, demand for visual target confirmation via fluorescence guidance is growing. While proven very effective for radiotracers, microdosing approaches the detection limit for fluorescence imaging. Thus, utility will be highly dependent on the tracer performance, the sensitivity of the fluorescence camera used, and the degree of background signal. Using a porcine model the ability to perform robot-assisted radical prostatectomy under fluorescence guidance using the bimodal or rather hybrid PSMA tracer (Tc-99m-EuK-(SO3)Cy5-mas(3)) was studied, while employing the tracer in a microdosing regime. This was followed by ex vivo evaluation in surgical specimens obtained from prostate cancer patients. Results: T-50% blood and T-50% urine were reached at 85 min and 390 min, in, respectively, blood and urine. Surgical fluorescence imaging allowed visualization of the prostate gland based on the basal PSMA-expression in porcine prostate. Together, in vivo visualization of the prostate and urinary excretion suggests at least an interval of > 7 h between tracer administration and surgery. Confocal microscopy of excised tissues confirmed tracer uptake in kidney and prostate, which was confirmed with PSMA IHC. No fluorescence was detected in other excised tissues. Tumor identification based on ex vivo fluorescence imaging of human prostate cancer specimens correlated with PSMA IHC. Conclusion: Intraoperative PSMA-mediated fluorescence imaging with a microdosing approach was shown to be feasible. Furthermore, EuK-(SO3)Cy5-mas(3) allowed tumor identification in human prostate samples, underlining the translational potential of this novel tracer. Trial registration Approval for use of biological material for research purposes was provided by the Translational Research Board of the Netherlands Cancer Institute-Antoni van Leeuwenhoek hospital (NKI-AvL) under reference IRBm19-273 (22/10/2019). Show less
Purpose Sentinel lymph node biopsy is a routine procedure for nodal staging in penile cancer. Most commonly, this procedure is guided by radioactive tracers, providing various forms of preoperative... Show morePurpose Sentinel lymph node biopsy is a routine procedure for nodal staging in penile cancer. Most commonly, this procedure is guided by radioactive tracers, providing various forms of preoperative and intraoperative guidance. This is further extended with fluorescence imaging using hybrid radioactive-fluorescence tracers. Alternatively, a magnetic-based approach has become available using superparamagnetic iron-oxide nanoparticles (SPIONs). This study investigates a novel freehand magnetic particle imaging and navigation modality (fhMPI) for intraoperative localization, along with a hybrid approach, combining magnetic and fluorescence guidance. Materials and methods The fhMPI set-up was built with a surgical navigation device, optical tracking system and magnetometer probe. A dedicated reconstruction software based on a look-up-table method was used to reconstruct a superficial 3D volume of the SPION distribution in tissue. For fluorescence guidance, indocyanine green (ICG) was added to the SPIONs. The fhMPI modality was characterized in phantoms, ex vivo human skin and in vivo porcine surgery. Results Phantom and human skin explants illustrated that the current fhMPI modality had a sensitivity of 2.2 x 10(-2) mg/mL SPIONs, a resolving power of at least 7 mm and a depth penetration up to 1.5 cm. Evaluation during porcine surgery showed that fhMPI allowed for an augmented reality image overlay of the tracer distribution in tissue, as well as 3D virtual navigation. Besides, using the hybrid approach, fluorescence imaging provided a visual confirmation of localized nodes. Conclusion fhMPI is feasible in vivo, providing 3D imaging and navigation for magnetic nanoparticles in the operating room, expanding the guidance possibilities during magnetic sentinel lymph node procedures. Furthermore, the integration of ICG provides the ability to visually refine and confirm correct localization. Further clinical evaluation should verify these findings in human patients as well. Show less
Background Surgically induced nerve damage is a common but debilitating side effect in oncological surgery. With the aim to use fluorescence guidance to enable nerve-sparing interventions in future... Show moreBackground Surgically induced nerve damage is a common but debilitating side effect in oncological surgery. With the aim to use fluorescence guidance to enable nerve-sparing interventions in future surgery, a fluorescent tracer was developed that specifically targets myelin protein zero (P0). Results Truncated homotypic P0 protein-based peptide sequences were C-terminally functionalized with the far-red cyanine dye Cy5. The lead compound Cy5-P0(101-125) was selected after initial solubility, (photo)physical and in vitro evaluation (including P0-blocking experiments). Cy5-P0(101-125) (K-D = 105 +/- 17 nM) allowed in vitro and ex vivo P0-related staining. Furthermore, Cy5-P0(101-125) enabled in vivo fluorescence imaging of the Sciatic nerve in mice after local intravenous (i.v.) administration and showed compatibility with a clinical fluorescence laparoscope during evaluation in a porcine model undergoing robot-assisted surgery. Biodistribution data revealed that i.v. administered [In-111]In-DTPA-P0(101-125) does not enter the central nervous system (CNS). Conclusion P0(101-125) has proven to be a potent nerve-specific agent that is able to target P0/myelin under in vitro, ex vivo, and in vivo conditions without posing a threat for CNS-related toxicity. Show less
Welling, M.M.; Duszenko, N.; Willigen, D.M. van; Smits, W.K.; Buckle, T.; Roestenberg, M.; Leeuwen, F.W.B. van 2021
Cyclodextrin (CD)-based host-guest interactions with adamantane (Ad) have demonstrated use for functionalizing living cells in vitro. The next step in this supramolecular functionalization approach... Show moreCyclodextrin (CD)-based host-guest interactions with adamantane (Ad) have demonstrated use for functionalizing living cells in vitro. The next step in this supramolecular functionalization approach is to explore the concept to deliver chemical cargo to living cells in vivo, e.g., inoculated bacteria, in order to study their dissemination. We validated this concept in two rodent Staphylococcus aureus models. Bacteria (1 X 10(8) viable S. aureus) were inoculated by (1) intramuscular injection or (2) intrasplenic injection followed by dissemination throughout the liver. The bacteria were prefunctionalized with Tc-99m-UBI29-41-Ad(2) (primary vector), which allowed us to both determine the bacterial load and create an in vivo target for the secondary host-vector (24 h post-inoculation). The secondary vector, i.e., chemical cargo delivery system, made use of a In-111-Cy5(0)(.5)CD(9)PIBMA(39 )polymer that was administered intravenously. Bacteria-specific cargo delivery as a result of vector complexation was evaluated by dual-isotope SPECT imaging and biodistribution studies (In-111), and by fluorescence (Cy5); these evaluations were performed 4 h post-injection of the secondary vector. Mice inoculated with nonfunctionalized S. aureus and mice without an infection served as controls. Dual-isotope SPECT imaging demonstrated that In-111-Cy5(0)(.5)CD(9)PIBMA(3)(9) colocalized with Tc-99m-UBI29-41-Ad(2)-labeled bacteria in both muscle and liver. In inoculated muscle, a 2-fold higher uptake level (3.2 +/- 1.0%ID/g) was noted compared to inoculation with nonfunctionalized bacteria (1.9 +/- 0.4%ID/g), and a 16-fold higher uptake level compared to noninfected muscle (0.2 +/- 0.1%ID/g). The hepatic accumulation of the host-vector was nearly 10-fold higher (27.1 +/- 11.1%ID/g) compared to the noninfected control (2.7 +/- 0.3%ID/g; p < 0.05). Fluorescence imaging of the secondary vector corroborated SPECT-imaging and biodistribution findings. We have demonstrated that supramolecular host-guest complexation can be harnessed to achieve an in vivo cargo delivery strategy, using two different bacterial models in soft tissue and liver. This proof-of-principle study paves a path toward developing innovative drug delivery concepts via cell functionalization techniques. Show less
Aim: Pre-targeting is a proven strategy for in vivo delivery of a diagnostic or therapeutic payload. The pre-targeting concept can be realized through various conjugation strategies, one of which... Show moreAim: Pre-targeting is a proven strategy for in vivo delivery of a diagnostic or therapeutic payload. The pre-targeting concept can be realized through various conjugation strategies, one of which is based on copper-free "click" chemistry. Copper-free click reactions have shown in vivo potential for imaging and radionuclide therapy, but this conjugation strategy has not yet been explored in combination with microspheres or unicellular organisms. This study aims to evaluate the in vivo efficacy of strain-promoted azide-alkyne cycloaddition (SPAAC) reactions to achieve imaging and targeting of azide-functionalized macro-aggregated albumin (MAA) microspheres and Staphylococcus aureus bacteria. Methods: MAA microspheres (diameter 10-90 mu m) were functionalized with a biorthogonal Cy5 fluorophore, bearing an azide functionality (N-3), to generate MAA-Cy5-N-3. S. aureus (diameter similar to 1 mu m) were functionalized with Tc-99m-UBI29-41-Cy5-N-3, generating S. aureus-Tc-99m-UBI29-41-Cy5-N-3. In situ and in vitro click conjugation on the -N-3 moieties was studied for 20 h using a radioactivity-based assay and fluorescence microscopy. For in vivo validation, both primary entities, radiolabeled with Tc-99m, were deposited into the microvasculature of the liver via intrasplenic injections. Secondary targeting was realized following the intravenous administration of indium-111-radiolabeled diethylenetriaminepentaacetic acid-dibenzocyclooctyne (In-111-DTPA-DBCO). To assess click reaction efficiency in vivo, Tc-99m and In-111-biodistributions were measured (SPECT and %ID g(-1)). Use of In-111-DTPA-DBCO in mice without MAA deposits or mice infected with non-functionalized S. aureus served as controls. Ex vivo confocal fluorescence imaging was carried out in excised tissues to confirm the presence of functionalized MAA and bacteria. Results: In vitro data confirmed effective click reactions on both the MAA particles and the bacterial membrane. SPECT imaging and biodistribution studies revealed significantly (p < 0.05) increased accumulation of In-111-DTPA-DBCO at the sites where MAA-Cy5-N-3 (7.5 +/- 1.5%ID g(-1)vs. 3.5 +/- 0.5%ID g(-1) in control mice) and S. aureus-Tc-99m-UBI29-41-Cy5-N-3 (9.3 +/- 1.3%ID g(-1)vs. 6.0 +/- 0.5%ID g(-1) in control mice) resided. Ex vivo fluorescence imaging confirmed the presence of either functionalized MAA or S. aureus in excised spleens and livers of mice. Conclusion: Copper-free click chemistry between a DBCO moiety and Cy5-N-3-functionalized microspheres or bacterial entities in the liver can be used to realize in vivo imaging and targeting. Show less
Pentamethine cyanine (Cy5) fluomphores have proven to be versatile imaging agents (i.e., tracers) for a range of micro- and macroscopic imaging applications, including image-guided surgery. In this... Show morePentamethine cyanine (Cy5) fluomphores have proven to be versatile imaging agents (i.e., tracers) for a range of micro- and macroscopic imaging applications, including image-guided surgery. In this study the relationship between the structure of asymmetric Cy5 fluorophores and their photophysical properties was studied. To this end, seven Cy5 analogues, bearing orthogonal N-indole substituents (H, SC3-, or benzene), were synthesised and evaluated. In-depth analysis revealed that introduction of sulfonates enhanced the fluorescence brightness and photostability, while reducing the lipophilicity, serum binding and stacking tendency. The addition of benzene moieties induced a bathochromic shift of 10-20 nm, increased the lipophilicity (LogP = -1.56-1.23) and serum binding (67.3-93.8% bound), as well as negatively impacted the brightness (0.74-42.9 . 10(3) M-1 cm(-1)), photostability (24.4-90.6% remaining), and stacking tendency. Chemical stability was uninfluenced by the substitution pattern. Additionally, the generation of a c[RGDyK]-based hybrid tracer based on one of these fluomphores in combination with a diethylenetriaminepentaacetic acid (DTPA) chelate and an In-111-isotope was reported. This compound was evaluated in vitro using alpha(v)beta(3)-overexpressing Ge beta 3 cells and in vivo using a 4T1 mouse tumour model. Overall, the presented results imply that alterations of the asymmetrical orthogonal Cy5 fluomphore structure have impact on the (photo)physical properties. Furthermore, the orthogonal Cy5 fluorophore framework can readily be applied in tracer development. Show less
Meershoek, P.; Kleinjan, G.H.; Willigen, D.M. van; Bauwens, K.P.; Spa, S.J.; Beurden, F. van; ... ; Oosterom, M.N. van 2020
The field of fluorescence-guided surgery builds on colored fluorescent tracers that have become available for different clinical applications. Combined use of complementary fluorescent emissions... Show moreThe field of fluorescence-guided surgery builds on colored fluorescent tracers that have become available for different clinical applications. Combined use of complementary fluorescent emissions can allow visualization of different anatomical structures (e.g. tumor, lymphatics and nerves) in the same patient. With the aim to assess the requirements for multi-color fluorescence guidance under in vivo conditions, we thoroughly characterized two FDA-approved laparoscopic Firefly camera systems available on the da Vinci Si or da Vinci Xi surgical robot. In this process, we studied the cameras' performance with respect to the photophysical properties of the FDA-approved dyes Fluorescein and ICG. Our findings indicate that multi-wavelength fluorescence imaging of Fluorescein and ICG is possible using clinical-grade fluorescence laparoscopes, but critical factors for success include the photophysical dye properties, imaging system performance and the amount of accumulated dye. When comparing the camera performance, the Xi system provided more effective excitation (adaptions in the light source) and higher detection sensitivity (chip-on-a-tip and/or enhanced image processing) for both Fluorescein and ICG. Both systems can readily be used for multi-wavelength fluorescence imaging of Fluorescein and ICG under clinically relevant conditions. With that, another step has been made towards the routine implementation of multi-wavelength image-guided surgery concepts. Show less
Beurden, F. van; Willigen, D.M. van; Vojnovic, B.; Oosterom, M.N. van; Brouwer, O.R.; Poel, H.G. van der; ... ; Buckle, T. 2020
With the rise of fluorescence-guided surgery, it has become evident that different types of fluorescence signals can provide value in the surgical setting. Hereby a different range of targets have... Show moreWith the rise of fluorescence-guided surgery, it has become evident that different types of fluorescence signals can provide value in the surgical setting. Hereby a different range of targets have been pursued in a great variety of surgical indications. One of the future challenges lies in combining complementary fluorescent readouts during one and the same surgical procedure, so-called multi-wavelength fluorescence guidance. In this review we summarize the current clinical state-of-the-art in multi-wavelength fluorescence guidance, basic technical concepts, possible future extensions of existing clinical indications and impact that the technology can bring to clinical care. Show less
Duszenko, N.; Willigen, D.M. van; Welling, M.M.; Korne, C.M. de; Schuijlenburg, R. van; Winkel, B.M.F.; ... ; Roestenberg, M. 2020
In an era of antimicrobial resistance, a better understanding of the interaction between bacteria and the sentinel immune system is needed to discover new therapeutic targets for combating... Show moreIn an era of antimicrobial resistance, a better understanding of the interaction between bacteria and the sentinel immune system is needed to discover new therapeutic targets for combating bacterial infectious disease. Sentinel immune cells such as macrophages phagocytose intact bacteria and thereby initiate ensuing immune responses. The bacterial surface composition is a key element that determines the macrophage signaling. To study the role of the bacterial cell surface composition in immune recognition, we developed a platform technology for altering bacterial surfaces in a controlled manner with versatile chemical scaffolds. We show that these scaffolds are efficiently loaded onto both Gram-positive and -negative bacteria and that their presence does not impair the capacity of monocyte-derived macrophages to phagocytose bacteria and subsequently signal to other components of the immune system. We believe this technology thus presents a useful tool to study the role of bacterial cell surface composition in disease etiology and potentially in novel interventions utilizing intact bacteria for vaccination. Show less
Hensbergen, A.W.; Willigen, D.M. van; Beurden, F. van; Leeuwen, P.J. van; Buckle, T.; Schottelius, M.; ... ; Leeuwen, F.W.B. van 2020
Expressed on virtually all prostate cancers and their metastases, the transmembrane protein prostate-specific membrane antigen (PSMA) provides a valuable target for the imaging of prostate cancer.... Show moreExpressed on virtually all prostate cancers and their metastases, the transmembrane protein prostate-specific membrane antigen (PSMA) provides a valuable target for the imaging of prostate cancer. Not only does PSMA provide a target for noninvasive diagnostic imaging, e.g., PSMA-positron emission tomography (PSMA PET), it can also be used to guide surgical resections of PSMA-positive lesions. The latter characteristic has led to the development of a plethora of PSMA-targeted tracers, i.e., radiolabeled, fluorescent, or hybrid. With image-guided surgery applications in mind, this review discusses these compounds based on clinical need. Here, the focus is on the chemical aspects (e.g., imaging label, spacer moiety, and targeting vector) and their impact on in vitro and in vivo tracer characteristics (e.g., affinity, tumor uptake, and clearance pattern). Show less
Hensbergen, A.W.; Buckle, T.; Willigen, D.M. van; Schottelius, M.; Welling, M.M.; Wijk, F.A. van der; ... ; Leeuwen, F.W.B. van 2020
Prostate cancer surgery is currently being revolutionized by the use of prostate-specific membrane antigen (PSMA)-targeted radiotracers, for example, (99)mTc-labeled PSMA tracer analogs for... Show moreProstate cancer surgery is currently being revolutionized by the use of prostate-specific membrane antigen (PSMA)-targeted radiotracers, for example, (99)mTc-labeled PSMA tracer analogs for radioguided surgery. The purpose of this study was to develop a second-generation (99)mTc-labeled PSMA-targeted tracer incorporating a fluorescent dye. Methods: Several PSMA-targeted hybrid tracers were synthesized: glutamic acid- urea-lysine (EuK)-Cy5-mas(3), EuK-(SO3)Cy5-mas(3), EuK-Cy5(SO3)-mas(3), EuK-(Ar)Cy5-mas(3), and EuK-Cy5(Ar)-mas(3); the Cy5 dye acts as a functional backbone between the EuK targeting vector and the 2-mercaptoacetyl-seryl-seryl-seryl (mas(3)) chelate to study the dye's interaction with PSMA's amphipathic entrance funnel. The compounds were evaluated for their photophysical and chemical properties and PSMA affinity. After radiolabeling with (99)mTc, we performed in vivo SPECT imaging, biodistribution, and fluorescence imaging on BALB/c nude mice with orthotopically transplanted PC346C tumors. Results: The dye composition influenced the photophysical properties (brightness range 0.3-1.5 x 10(4) M-1 x cm(-1)), plasma protein interactions (range 85.0% +/- 2.3%-90.7%+/- 1.3% bound to serum, range 76%+/- 0%-89%+/- 6% stability in serum), PSMA affinity (half-maximal inhibitory concentration [IC50] range 19.2 +/- 5.8-175.3 +/- 61.1 nM) and in vivo characteristics (tumorto-prostate and tumor-to-muscle ratios range 0.02 +/- 0.00-154.73 +/- 28.48 and 0.46 +/- 0.28-5,157.50 +/- 949.17, respectively; renal, splenic, and salivary retention). Even though all tracer analogs allowed tumor identification with SPECT and fluorescence imaging, (99)mTc-EuK(SO3)Cy5-mas(3) had the most promising properties (e.g., half-maximal inhibitory concentration, 19.2 +/- 5.8, tumor-to-muscle ratio, 5,157.50 +/- 949.17). Conclusion: Our findings demonstrate the intrinsic integration of a fluorophore in the pharmacophore in PSMA-targeted smallmolecule tracers. In this design, having 1 sulfonate on the indole moiety adjacent to EuK ((99)mTc-EuK-(SO3)Cy5-mas(3)) yielded the most promising tracer candidate for imaging of PSMA. Show less
Debie, P.; Lafont, C.; Defrise, M.; Hansen, I.; Willigen, D.M. van; Leeuwen, F.W.B. van; ... ; Hernot, S. 2020
A compound's intratumoural distribution is an important determinant for the effectiveness of molecular therapy or imaging. Antibodies (Abs), though often used in the design of targeted compounds,... Show moreA compound's intratumoural distribution is an important determinant for the effectiveness of molecular therapy or imaging. Antibodies (Abs), though often used in the design of targeted compounds, struggle to achieve a homogenous distribution due to their large size and bivalent binding mechanism. In contrast, smaller compounds like nanobodies (Nbs) are expected to distribute more homogenously, though this has yet to be demonstrated in vivo at the microscopic level. We propose an intravital approach to evaluate the intratumoural distribution of different fluorescently labeled monomeric and dimeric Nb tracers and compare this with a monoclonal antibody (mAb).Monomeric and dimeric formats of the anti-HER2 (2Rb17c and 2Rb17c-2Rb17c) and control (R3B23 and R3B23-R3B23) Nb, as well as the dimeric monovalent Nb 2Rbl7c-R3B23 were generated and fluorescently labeled with a Cy5 fluorophore. The mAb trastuzumab-Cy5 was also prepared. Whole-body biodistribution of all constructs was investigated in mice bearing subcutaneous xenografts (HER2 + SKOV3) using in vivo epi-fluorescence imaging. Next, for intravital experiments, GFP-expressing SKOV3 cells were grown under dorsal window chambers on athymic nude mice (n = 3/group), and imaged under a fluorescence stereo microscope immediately after intravenous injection of the tracers. Consecutive fluorescence images within the tumour were acquired over the initial 20 min after injection and later, single images were taken at 1, 3 and 24 h post-injection. Additionally, two-photon microscopy was used to investigate the colocalization of GFP (tumour cells) and Cy5 fluorescence (tracers) at higher resolution.Whole-body images showed rapid renal clearance of all Nbs, and fast tumour targeting for the specific Nbs. Specific tumour uptake of the mAb could only be clearly distinguished from background after several hours. Intravital imaging revealed that monomeric Nb tracers accumulated rapidly and distributed homogenously in the tumour mere minutes after intravenous injection. The dimeric compounds initially achieved lower fluorescence intensities than the monomeric. Furthermore, whereas the HER2-specific dimeric bivalent compound remained closely associated to the blood vessels over 24 h, the HER2-specific dimeric monovalent tracer achieved a more homogenous tumour distribution from 1 h post-injection onwards. Non-specific tracers were not retained in the tumour. Trastuzumab had the most heterogenous intratumoural distribution of all evaluated compounds, while -due to the long blood retention- achieving the highest overall tumour uptake at 24 h post-injection.In conclusion, monomeric Nbs very quickly and homogenously distribute through tumour tissue, at a rate significantly greater than dimeric Nbs and mAbs. This underlines the potential of monomeric Nb tracers and therapeutics in molecular imaging and targeted therapies. Show less
Buckle, T.; Wal, S. van der; Willigen, D.M. van; Aalderink, G.; KleinJan, G.H.; Leeuwen, F.W.B. van 2020
Introduction: Adequate signal to background ratios are critical for the implementation of fluorescence-guided surgery technologies. While local tracer administrations help to reduce the chance of... Show moreIntroduction: Adequate signal to background ratios are critical for the implementation of fluorescence-guided surgery technologies. While local tracer administrations help to reduce the chance of systemic side effects, reduced spatial migration and non-specific tracer diffusion can impair the discrimination between the tissue of interest and the background. To combat background signals associated with local tracer administration, we explored a pretargeting concept aimed at quenching non-specific fluorescence signals. The efficacy of this concept was evaluated in an in vivo neuronal tracing set-up.Methods: Neuronal tracing was achieved using a wheat germ agglutinin (WGA) lectin. functionalized with an azide-containing Cy5 dye (N-3-Cy5-WGA). A Cy7 quencher dye (Cy7-DBCO) was subsequently used to yield Cy7-Cy5-WGA, a compound wherein the Cy5 emission is quenched by Forster resonance energy transfer to Cy7. The photophysical properties of N-3-Cy5-WGA and Cy7-Cy5-WGA were evaluated together with deactivation kinetics in situ, in vitro (Schwannoma cell culture), ex vivo (muscle tissue from mice; used for dose optimization), and in vivo (nervus ischiadicus in THY-1 YFP mice).Results: In situ, conjugation of Cy7-DBCO to N-3-Cy5-WGA resulted in >90% reduction of the Cy5 fluorescence signal intensity at 30 minutes after addition of the quencher. In cells, pretargeting with the N-3-Cy5-WGA lectin yielded membranous staining, which could efficiently be deactivated by Cy7-DBCO over the course of 30 minutes (91% Cy5 signal decrease). In ex vivo muscle tissue, administration of Cy7-DBCO at the site where N-3-Cy5-WGA was injected induced 80-90% quenching of the Cy5-related signal after 10-20 minutes, while the Cy7-related signal remained stable over time. In vivo, Cy7-DBCO effectively quenched the non-specific background signal up to 73% within 5 minutes, resulting in a 50% increase in the signal-to-background ratio between the nerve and injection site.Conclusion: The presented pretargeted fluorescence-quenching technology allowed fast and effective reduction of the background signal at the injection site, while preserving in vivo nerve visualization. While this proof-of-principle study was focused on imaging of nerves using a fluorescent WGA-lectin, the same concept could in the future also apply to applications such as sentinel node imaging. Show less
Acker, T. van; Buckle, T.; Malderen, S.J.M. van; Willigen, D.M. van; Unen, V. van; Leeuwen, F.W.B. van; Vanhaecke, F. 2019
