(Non-targeted) radioactive/fluorescent nanoparticles and their potential in combined pre- and intraoperative imaging during sentinel lymph node resection

19 F MRI Probes for Multimodal Imaging*

Magnetic resonance imaging (MRI) is one of the most powerful imaging tools today, capable of displaying superior soft-tissue contrast. This review discusses developments in the field of ¹⁹ F MRI multimodal probes in combination with optical fluorescence imaging (OFI), ¹ H MRI, chemical exchange saturation transfer (CEST) MRI, ultrasonography (USG), X-ray computed tomography (CT), single photon emission tomography (SPECT), positron emission tomography (PET), and photoacoustic imaging (PAI). In each case, multimodal ¹⁹ F MRI probes compensate for the deficiency of individual techniques and offer improved sensitivity or accuracy of detection over unimodal counterparts. Strategies for designing ¹⁹ F MRI multimodal probes are described with respect to their structure, physicochemical properties, biocompatibility, and the quality of images.

Contemporary update of SPECT tracers and novelties in radioguided surgery: a perspective based on urology

Recent technical advances and implementation of novel radiotracers have further increased the potential of radioguided surgery for a broad variety of malignancies. Indeed, the possibilities for future applications of novel radiotracers in diverse oncological strategies has become more promising than ever. This literature review aims to provide a contemporary update on a selected group of radiotracers and evaluates the usability of radioguided surgery and sentinel node procedures, focusing on most promising advances. For example, the impact of targeted radiotracers on prostate specific membrane antigen (PSMA), CD206 receptor-targeted agents (^99mTc-tilmanocept), and hybrid tracers adding fluorescence to radioguidance (ICG-^99mTc-nanocolloid) as well as targeting hypoxia-induced carbonic anhydrase IX (CAIX) will be covered. Furthermore, future outlooks on the implementation of gold nanoparticles (AuNP's), but also technical advances in improved radiotracer detection by hybrid gamma devices will be discussed.

Molecularly targeted nanoparticles: an emerging tool for evaluation of expression of the receptor for advanced glycation end products in a murine model of peripheral artery disease

Background

Molecular imaging with molecularly targeted probes is a powerful tool for studying the spatio-temporal interactions between complex biological processes. The pivotal role of the receptor for advanced glycation end products (RAGE), and its involvement in numerous pathological processes, aroused the demand for RAGE-targeted imaging in various diseases. In the present study, we evaluated the use of a diagnostic imaging agent for RAGE quantification in an animal model of peripheral artery disease, a multimodal dual-labeled probe targeted at RAGE (MMIA-CML).

Methods

PAMAM dendrimer was conjugated with Nε-carboxymethyl-lysine (CML) modified albumin to synthesize the RAGE-targeted probe. A control untargeted agent carried native non-modified human albumin (HSA). Bifunctional p-SCN-Bn-NOTA was used to conjugate the ⁶⁴Cu radioisotope. Surgical right femoral artery ligation was performed on C57BL/6 male mice. One week after femoral artery ligation, mice were injected with MMIA-CML or MMIA-HSA labeled with ⁶⁴Cu radioisotope and 60 min later in vivo microPET-CT imaging was performed. Immediately after PET imaging studies, the murine hindlimb muscle tissues were excised and prepared for gene and protein expression analysis. RAGE gene and protein expression was assessed using real-time qPCR and Western blot technique respectively. To visualize RAGE expression in excised tissues, microscopic fluorescence imaging was performed using RAGE-specific antibodies and RAGE-targeted and -control MMIA.

Results

Animals subjected to PET imaging exhibited greater MMIA-CML uptake in ischemic hindlimbs than non-ischemic hindlimbs. We observed a high correlation between fluorescent signal detection and radioactivity measurement. Significant RAGE gene and protein overexpression were observed in ischemic hindlimbs compared to non-ischemic hindlimbs at one week after surgical ligation. Fluorescence microscopic staining revealed significantly increased uptake of RAGE-targeted nanoparticles in both ischemic and non-ischemic muscle tissues compared to the control probe but at a higher level in ischemic hindlimbs. Ischemic tissue exhibited explicit RAGE dyeing following anti-RAGE antibody and high colocalization with the MMIA-CML targeted at RAGE.

Conclusions

The present results indicate increased expression of RAGE in the ischemic hindlimb and enable the use of multimodal nanoparticles in both in vitro and in vivo experimental models, creating the possibility for imaging structural and functional changes with a RAGE-targeted tracer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-021-00253-0.

Opportunities in the Synthesis and Design of Radioactive Thin Films and Nanoparticles

Studies of radioactive isotopes at the liquid-solid or gas-solid interface are enabling a detailed mechanistic understanding of the effects of radioactive decay on physical, biological, and chemical systems. In recent years, there has been a burgeoning interest in using radioactive isotopes for both imaging and therapeutic purposes by attaching them to the surface of colloidal nanoparticles. By merging the field of nanomedicine with the more mature field of internal radiation therapy, researchers are discovering new ways to diagnose and treat cancer. In this Perspective, we discuss state-of-the-art radioactive thin films as applied to both well-defined surfaces and more complex nanoparticles. We highlight the design considerations that are unique to radioactive films, which originate from the damaging and potentially self-destructive emissions produced during radioactive decay, and highlight future opportunities in the largely underexplored area between radioisotope chemistry and nanoscience.

Hybrid Tracers Based on Cyanine Backbones Targeting Prostate-Specific Membrane Antigen: Tuning Pharmacokinetic Properties and Exploring Dye-Protein Interaction

Prostate cancer surgery is currently being revolutionized by the use of prostate-specific membrane antigen (PSMA)-targeted radiotracers, for example, ^99mTc-labeled PSMA tracer analogs for radioguided surgery. The purpose of this study was to develop a second-generation ^99mTc-labeled PSMA-targeted tracer incorporating a fluorescent dye. Methods: Several PSMA-targeted hybrid tracers were synthesized: glutamic acid-urea-lysine (EuK)-Cy5-mas₃, EuK-(SO₃)Cy5-mas₃, EuK-Cy5(SO₃)-mas₃, EuK-(Ar)Cy5-mas₃, and EuK-Cy5(Ar)-mas₃; the Cy5 dye acts as a functional backbone between the EuK targeting vector and the 2-mercaptoacetyl-seryl-seryl-seryl (mas₃) 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 ^99mTc, 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 × 10⁴ M^-1 × 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 (tumor-to-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, ^99mTc-EuK-(SO₃)Cy5-mas₃ 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 small-molecule tracers. In this design, having 1 sulfonate on the indole moiety adjacent to EuK (^99mTc-EuK-(SO₃)Cy5-mas₃) yielded the most promising tracer candidate for imaging of PSMA.

Design and Challenges of Radiopharmaceuticals

This review describes general concepts with regard to radiopharmaceuticals for diagnostic or therapeutic applications that help to understand the specific challenges encountered during the design, (radio)synthesis, in vitro and in vivo evaluation and clinical translation of novel radiopharmaceuticals. The design of a radiopharmaceutical requires upfront decisions with regard to combining a suitable vector molecule with an appropriate radionuclide, considering the type and location of the molecular target, the desired application, and the time constraints imposed by the relatively short half-life of radionuclides. Well-designed in vitro and in vivo experiments allow nonclinical validation of radiotracers. Ultimately, in combination with a limited toxicology package, the radiotracer becomes a radiopharmaceutical for clinical evaluation, produced in compliance with regulatory requirements for medicines for intravenous (IV) injection.

Trastuzumab-Modified Gold Nanoparticles Labeled with 211At as a Prospective Tool for Local Treatment of HER2-Positive Breast Cancer

Highly localized radiotherapy with radionuclides is a commonly used treatment modality for patients with unresectable solid tumors. Herein, we propose a novel α-nanobrachytherapy approach for selective therapy of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. This uses local intratumoral injection of 5-nm-diameter gold nanoparticles (AuNPs) labeled with an α-emitter (²¹¹At), modified with polyethylene glycol (PEG) chains and attached to HER2-specific monoclonal antibody (trastuzumab). The size, shape, morphology, and zeta potential of the 5 nm synthesized AuNPs were characterized by TEM (Transmission Electron Microscopy) and DLS (Dynamic Light Scattering) techniques. The gold nanoparticle surface was modified by PEG and subsequently used for antibody immobilization. Utilizing the high affinity of gold for heavy halogens, the bioconjugate was labelled with ²¹¹At obtained by α irradiation of the bismuth target. The labeling yield of ²¹¹At was greater than 99%. ²¹¹At bioconjugates were stable in human serum. Additionally, in vitro biological studies indicated that ²¹¹At-AuNP-PEG-trastuzumab exhibited higher affinity and cytotoxicity towards the HER2-overexpressing human ovarian SKOV-3 cell line than unmodified nanoparticles. Confocal and dark field microscopy studies revealed that ²¹¹At-AuNP-PEG-trastuzumab was effectively internalized and deposited near the nucleus. These findings show promising potential for the ²¹¹At-AuNP-PEG-trastuzumab radiobioconjugate as a perspective therapeutic agent in the treatment of unresectable solid cancers expressing HER2 receptors.

Update on radioguided surgery: from international consensus on sentinel node in head and neck cancer to the advances on gynaecological tumors and localization of non-palpable lesions

The aim of this review is to provide an updated perspective on different fields of radioguided surgery. With reference to the sentinel lymph node biopsy in oral squamous cell carcinoma, we present the results of the interactive debate held at the recent Congress of our specialty about the more relevant aspects of the London Consensus. Drainage peculiarities and indications according to the current guidelines on gynaecological tumours, endometrial and cervical cancer, are detailed and new scenarios for nuclear medicine physicians are presented; robotic surgery and hybrid tracers, for instance. Moreover, the notable growth in radioguided surgery indications for non-palpable lesions, widely used in mammary pathology, make it advisable to update two procedures which have shown satisfying results, such as the solitary pulmonary nodule and the osteoid osteoma.

Silver nanoparticles coupled to anti‑EGFR antibodies sensitize nasopharyngeal carcinoma cells to irradiation

Radiotherapy is the major form of treatment for head and neck carcinoma, a malignant tumour of epithelial origin. The identification of agents, which can be co‑administered in order to sensitize these tumours to radiotherapy, has become a major focus of investigations. In the present study, a novel 20 nm nanocomposite, Ag/C225, was constructed, which consisted of silver nanoparticles (AgNPs) conjugated to an epidermal growth factor receptor‑specific antibody (C225). Physical characterization demonstrated that the Ag/C225 nanoparticles were spherical and dispersed well in water. Enzyme‑linked immunosorbent assays showed that the activity of C225 was preserved in the Ag/C225 nanoparticles. The results of 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide analysis revealed that AgNPs and Ag/C225 inhibited the proliferation of nasopharyngeal carcinoma epithelial (CNE) cells in a dose‑ and time‑dependent manner. Flow cytometry revealed that AgNPs and Ag/C225 induced the apoptosis of CNEs, and abrogated G2 arrest; the latter effect was more marked with Ag/C225 than with AgNPs. Clonogenic assays indicated that AgNPs and Ag/C225 increased the sensitivity of CNEs to irradiation. The sensitizer enhancement ratios were 1.610±0.012 and 1.405±0.033 Gy for AgNPs and Ag/C225, respectively. Western blot analysis revealed that combining X‑ray irradiation with either AgNPs or Ag/C225 reduced the expression levels of DNA damage/repair proteins Ku‑70, Ku‑80 and Rad51; Ag/C225 was also more effective than AgNPs in this context. These results indicated that AgNPs and Ag/C225 effectively enhanced CNE cell radiosensitivity in vitro. Therefore, these potent agents may be considered for use as radiosensitizers during the treatment of human nasopharyngeal carcinoma.

Role of ICG-99mTc-nanocolloid for sentinel lymph node detection in cervical cancer: a pilot study

PURPOSE

Sentinel lymph node biopsy (SLNB) can be used for nodal staging in early cervical cancer. For this purpose, the tracers most commonly used are radiotracers based on technetium. For the last decade, indocyanine green (ICG) has been used as a tracer for SLNB in other malignancies with excellent results and, more recently, a combination of ICG and a radiotracer has been shown to have the advantages of both tracers. The aim of this study was to evaluate the role of ICG-^99mTc-nanocolloid in SLN detection in patients with cervical cancer.

METHODS

This prospective study included 16 patients with cervical cancer. The hybrid tracer was injected the day (19-21 h) before surgery for planar and SPECT/CT lymphoscintigraphy. Blue dye was administered periorificially in 14 patients. SLNs were removed according to their distribution on lymphoscintigraphy and when radioactive, fluorescent and/or stained with blue dye. Nodal specimens were pathologically analysed for metastases including by immunochemistry.

RESULTS

Lymphoscintigraphy and SPECT/CT showed drainage in all patients. A total of 69 SLNs were removed, of which 66 were detected by their radioactivity signal and 67 by their fluorescence signal. Blue dye identified only 35 SLNs in 12 of the 14 patients (85.7%). All patients showed bilateral pelvic drainage. Micrometastases were diagnosed in two patients, and were the only lymphatic nodes involved.

CONCLUSIONS

SLNB with ICG-^99mTc-nanocolloid is feasible and safe in patients with early cervical cancer. This hybrid tracer provided bilateral SLN detection in all patients and a higher detection rate than blue dye, so it could become an alternative to the combined technique.

Indocyanine Green Guided Pelvic Lymph Node Dissection: An Efficient Technique to Classify the Lymph Node Status of Patients with Prostate Cancer Who Underwent Radical Prostatectomy

PURPOSE

We evaluated the effectiveness of indocyanine green guided pelvic lymph node dissection for the optimal staging of prostate cancer and analyzed whether the technique could replace extended pelvic lymph node dissection.

MATERIALS AND METHODS

A solution of 25 mg indocyanine green in 5 ml sterile water was transperineally injected. Pelvic lymph node dissection was started with the indocyanine green stained nodes followed by extended pelvic lymph node dissection. Primary outcome measures were sensitivity, specificity, predictive value and likelihood ratio of a negative test of indocyanine green guided pelvic lymph node dissection.

RESULTS

A total of 84 patients with a median age of 63.55 years and a median prostate specific antigen of 8.48 ng/ml were included in the study. Of these patients 60.7% had intermediate risk disease and 25% had high or very high risk disease. A median of 7 indocyanine green stained nodes per patient was detected (range 2 to 18) with a median of 22 nodes excised during extended pelvic lymph node dissection. Lymph node metastasis was identified in 25 patients, 23 of whom had disease properly classified by indocyanine green guided pelvic lymph node dissection. The most frequent location of indocyanine green stained nodes was the proximal internal iliac artery followed by the fossa of Marcille. The negative predictive value was 96.7% and the likelihood ratio of a negative test was 8%. Overall 1,856 nodes were removed and 603 were stained indocyanine green. Pathological examination revealed 82 metastatic nodes, of which 60% were indocyanine green stained. The negative predictive value was 97.4% but the likelihood ratio of a negative test was 58.5%.

CONCLUSIONS

Indocyanine green guided pelvic lymph node dissection correctly staged 97% of cases. However, according to our data it cannot replace extended pelvic lymph node dissection. Nevertheless, its high negative predictive value could allow us to avoid extended pelvic lymph node dissection if we had an accurate intraoperative lymph fluorescent analysis.

Hybrid surgical guidance based on the integration of radionuclear and optical technologies

With the evolution of imaging technologies and tracers, the applications for nuclear molecular imaging are growing rapidly. For example, nuclear medicine is increasingly being used to guide surgical resections in complex anatomical locations. Here, a future workflow is envisioned that uses a combination of pre-operative diagnostics, navigation and intraoperative guidance. Radioguidance can provide means for pre-operative and intraoperative identification of "hot" lesions, forming the basis of a virtual data set that can be used for navigation. Luminescence guidance has shown great potential in the intraoperative setting by providing optical feedback, in some cases even in real time. Both of these techniques have distinct drawbacks, which include inaccuracy in areas that contain a background signal (radioactivity) or a limited degree of signal penetration (luminescence). We, and others, have reasoned that hybrid/multimodal approaches that integrate the use of these complementary modalities may help overcome their individual weaknesses. Ultimately, this will lead to advancement of the field of interventional molecular imaging/image-guided surgery. In this review, an overview of clinically applied hybrid surgical guidance technologies is given, whereby the focus is placed on tracers and hardware.

Multimodal theranostic assemblies: double encapsulation of protoporphyrine-IX/Gd3+in niosomes

Theranostically engineered protoporphyrin IX/Gd³⁺encapsulated niosomes were prepared and used as multimodal theranostic agent.

Applications of nanoparticles in cancer medicine and beyond: optical and multimodal in vivo imaging, tissue targeting and drug delivery

INTRODUCTION

Nanotechnology has opened up the way to the engineering of new organized materials endowed with improved performances. In the past decade, engineered nanoparticles (NPs) have been progressively implemented by exploiting synthetic strategies that yield complex materials capable of performing functions with applications also in medicine. Indeed, in the field of 'nanomedicine' it has been explored the possibility to design multifunctional nanosystems, characterized by high analytical performances and stability, low toxicity and specificity towards a given cell target.

AREA COVERED

In this review article, we summarize the advances in the engineering of NPs for biomedical applications, from optical imaging (OI) to multimodal OI and targeted drug delivery. For this purpose, we will provide some examples of how investigations in nanomedicine can support preclinical and clinical research generating innovative diagnostic and therapeutic strategies in oncology.

EXPERT OPINION

The progressive breakthroughs in nanomedicine have supported the development of multifunctional and multimodal NPs. In particular, NPs are significantly impacting the diagnostic and therapeutic strategies since they allow the development of: NP-based OI probes containing more than one modality-specific contrast agent; surface functionalized NPs for specific 'molecular recognition'. Therefore, the design and characterization of innovative NP-based systems/devices have great applicative potential into the medical field.

Dual-imaging model of SQUID biosusceptometry for locating tumors targeted using magnetic nanoparticles

BACKGROUND

For intraoperative imaging in operating theaters or preoperative imaging in clinics, compact and economic integration rather than large and expensive equipment is required to coregister structural and functional imaging. However, current technologies, such as those integrating optical and gamma cameras or infrared and fluorescence imaging, involve certain drawbacks, including the radioactive biorisks of nuclear medicine indicators and the inconvenience of conducting measurements in dark environments.

METHODS

To specifically and magnetically label liver tumors, an anti-alpha-fetoprotein (AFP) reagent was synthesized from biosafe iron oxide magnetic nanoparticles (MNPs) coated with anti-AFP antibody and solved in a phosphate buffered saline solution. In addition, a novel dual-imaging model system integrating an optical camera and magnetic scanning superconducting-quantum-interference device (SQUID) biosusceptometry (SSB) was proposed. The simultaneous coregistration of low-field magnetic images of MNP distributions and optical images of anatomical regions enabled the tumor distribution to be determined easily and in real time. To simulate targeted MNPs within animals, fewer reagents than the injected dose were contained in a microtube as a sample for the phantom test. The phantom test was conducted to examine the system characteristics and the analysis method of dual images. Furthermore, the animal tests were classified into two types, with liver tumors implanted either on the backs or livers of rats. The tumors on the backs were to visually confirm the imaging results of the phantom test, and the tumors on the livers were to simulate real cases in hepatocellular carcinoma people.

RESULTS

A phantom test was conducted using the proposed analysis method; favorable contour agreement was shown between the MNP distribution in optical and magnetic images. Consequently, the positioning and discrimination of liver tumors implanted on the backs and livers of rats were verified by conducting in vivo and ex vivo tests. The results of tissue staining verified the feasibility of using this method to determine the distribution of liver tumors.

CONCLUSION

The results of this study indicate the clinical potential of using anti-AFP-mediated MNPs and the dual-imaging model SSB for discriminating and locating tumors.

Evaluation of the novel near-infrared fluorescence tracers pullulan polymer nanogel and indocyanine green/γ-glutamic acid complex for sentinel lymph node navigation surgery in large animal models

BACKGROUND

This study aimed to examine tracers designed to overcome the disadvantages of indocyanine green (ICG), which disperses quickly to multiple lymph nodes, using a near-infrared (NIR) imaging system in animal models.

METHODS

Diluted ICG, ICG/poly-γ-glutamic acid (PGA) complex, and IRDye900-conjugated pullulan-cholesterol nanoprobe "near-infrared polynagogel" (NIR-PNG) were injected into the stomachs of dogs and pigs, and the patterns of dispersion were observed using an NIR imaging system. To compare retention times, fluorescence signals were evaluated in the stomach and small bowel of animals 1 week after injection.

RESULTS

A diluted concentration (~0.1 mg/ml) of ICG was optimal for NIR imaging compared with the conventional concentration (5 mg/ml) for visual inspection. When injected into the stomach, the signals of ICG and ICG/PGA complex were relatively large at the injection site, and signals were detected at multiple sentinel nodes and lymph nodes beyond them. The NIR-PNG signal intensity was relatively small at the injection site and limited to only one sentinel node with no additional node. When evaluated 1 week after injection, only the NIR-PNG signal was detected in the canine stomach, and the signal intensity at the lymph nodes of the porcine small bowel was the highest with NIR-PNG, followed by ICG/PGA complex and finally ICG.

CONCLUSION

NIR-PNG showed the best characteristics of less dispersion and longer retention in the sentinel nodes, and ICG/PGA complex remained longer than diluted ICG. These tracers could potentially be used as optimal tracers for sentinel node navigation surgery in gastric cancer.

U-SPECT-BioFluo: an integrated radionuclide, bioluminescence, and fluorescence imaging platform

Background

In vivo bioluminescence, fluorescence, and single-photon emission computed tomography (SPECT) imaging provide complementary information about biological processes. However, to date these signatures are evaluated separately on individual preclinical systems. In this paper, we introduce a fully integrated bioluminescence-fluorescence-SPECT platform. Next to an optimization in logistics and image fusion, this integration can help improve understanding of the optical imaging (OI) results.

Methods

An OI module was developed for a preclinical SPECT system (U-SPECT, MILabs, Utrecht, the Netherlands). The applicability of the module for bioluminescence and fluorescence imaging was evaluated in both a phantom and in an in vivo setting using mice implanted with a 4 T1-luc + tumor. A combination of a fluorescent dye and radioactive moiety was used to directly relate the optical images of the module to the SPECT findings. Bioluminescence imaging (BLI) was compared to the localization of the fluorescence signal in the tumors.

Results

Both the phantom and in vivo mouse studies showed that superficial fluorescence signals could be imaged accurately. The SPECT and bioluminescence images could be used to place the fluorescence findings in perspective, e.g. by showing tracer accumulation in non-target organs such as the liver and kidneys (SPECT) and giving a semi-quantitative read-out for tumor spread (bioluminescence).

Conclusions

We developed a fully integrated multimodal platform that provides complementary registered imaging of bioluminescent, fluorescent, and SPECT signatures in a single scanning session with a single dose of anesthesia. In our view, integration of these modalities helps to improve data interpretation of optical findings in relation to radionuclide images.

Imaging preclinical tumour models: improving translational power

Recent developments and improvements of multimodal imaging methods for use in animal research have substantially strengthened the options of in vivo visualization of cancer-related processes over time. Moreover, technological developments in probe synthesis and labelling have resulted in imaging probes with the potential for basic research, as well as for translational and clinical applications. In addition, more sophisticated cancer models are available to address cancer-related research questions. This Review gives an overview of developments in these three fields, with a focus on imaging approaches in animal cancer models and how these can help the translation of new therapies into the clinic.

Bimodal imaging probes for combined PET and OI: recent developments and future directions for hybrid agent development

Molecular imaging—and especially positron emission tomography (PET)—has gained increasing importance for diagnosis of various diseases and thus experiences an increasing dissemination. Therefore, there is also a growing demand for highly affine PET tracers specifically accumulating and visualizing target structures in the human body. Beyond the development of agents suitable for PET alone, recent tendencies aim at the synthesis of bimodal imaging probes applicable in PET as well as optical imaging (OI), as this combination of modalities can provide clinical advantages. PET, due to the high tissue penetration of the γ-radiation emitted by PET nuclides, allows a quantitative imaging able to identify and visualize tumors and metastases in the whole body. OI on the contrary visualizes photons exhibiting only a limited tissue penetration but enables the identification of tumor margins and infected lymph nodes during surgery without bearing a radiation burden for the surgeon. Thus, there is an emerging interest in bimodal agents for PET and OI in order to exploit the potential of both imaging techniques for the imaging and treatment of tumor diseases. This short review summarizes the available hybrid probes developed for dual PET and OI and discusses future directions for hybrid agent development.

Surface chemistry architecture of silica nanoparticles determine the efficiency of in vivo fluorescence lymph node mapping

Near-infrared (NIR) imaging of the lymphatic system offers a sensitive, versatile, and accurate lymph node mapping to locate the first, potentially metastatic, draining nodes in the operating room. Many luminescent nanoprobes have received great attention in this field, and the design of nontoxic and bright nanosystems is of crucial importance. Fluorescent NIR-emitting dye doped silica nanoparticles represent valuable platforms to fulfill these scopes, providing sufficient brightness, resistance to photobleaching, and hydrophilic nontoxic materials. Here, we synthesized these highly stable core-shell nanoparticles with a programmable surface charge positioning and determined the effect of these physicochemical properties on their in vivo behavior. In addition, we characterized their fluorescence kinetic profile in the right axillary lymph node (RALN) mapping. We found that nanoparticles with negative charges hidden by a PEG shell are more appropriate than those with external negative charges in the mapping of lymph nodes. We also demonstrated the efficient excretion of these nanostructures by the hepatobiliary route and their nontoxicity in mice up to 3 months postinjection. These results indicate the potential future development of these fluorescent nanosystems for LN mapping.

Multimodal chelation platform for near-infrared fluorescence/nuclear imaging

Dual-labeled compounds containing nuclear and near-infrared fluorescence contrast have the potential to molecularly guide surgical resection of cancer by extending whole-body diagnostic imaging findings into the surgical suite. To simplify the dual labeling process for antibody-based agents, we designed a multimodality chelation (MMC) scaffold which combined a radiometal chelating agent and fluorescent dye into a single moiety. Three dye-derivatized MMC compounds were synthesized and radiolabeled. The IRDye 800CW conjugate, 4, had favorable optical properties and showed rapid clearance in vivo. Using 4, an epithelial cell adhesion molecule (EpCAM) targeting MMC-immunoconjugate was prepared and dual-labeled with (64)Cu. In vitro binding activity was confirmed after MMC conjugation. Multimodal imaging studies showed higher tumor accumulation of (64)Cu-7 compared to nontargeted (64)Cu-4 in a prostate cancer model. Further evaluation in different EpCAM-expressing cell lines is warranted as well as application of the MMC dual labeling approach with other monoclonal antibodies.

Concomitant radio- and fluorescence-guided sentinel lymph node biopsy in squamous cell carcinoma of the oral cavity using ICG-(99m)Tc-nanocolloid

PURPOSE

For oral cavity malignancies, sentinel lymph node (SLN) mapping is performed by injecting a radiocolloid around the primary tumour followed by lymphoscintigraphy. Surgically, SLNs can then be localized using a handheld gamma ray detection probe. The aim of this study was to evaluate the added value of intraoperative fluorescence imaging to the conventional radioguided procedure. For this we used indocyanine green (ICG)-(99m)Tc-nanocolloid, a hybrid tracer that is both radioactive and fluorescent.

METHODS

Fourteen patients with oral cavity squamous cell carcinoma were peritumourally injected with ICG-(99m)Tc-nanocolloid. SLNs were preoperatively identified with lymphoscintigraphy followed by single photon emission computed tomography (SPECT)/CT for anatomical localization. During surgery, SLNs were detected with a handheld gamma ray detection probe and a handheld near-infrared fluorescence camera. Pre-incision and post-excision imaging with a portable gamma camera was performed to confirm complete removal of all SLNs.

RESULTS

SLNs were preoperatively identified using the radioactive signature of ICG-(99m)Tc-nanocolloid. Intraoperatively, 43 SLNs could be localized and excised with combined radio- and fluorescence guidance. Additionally, in four patients, an SLN located close to the primary injection site (in three patients this SLN was located in level I) could only be intraoperatively localized using fluorescence imaging. Pathological analysis of the SLNs revealed a metastasis in one patient.

CONCLUSION

Combined preoperative SLN identification and intraoperative radio- and fluorescence guidance during SLN biopsies for oral cavity cancer proved feasible using ICG-(99m)Tc-nanocolloid. The addition of fluorescence imaging was shown to be of particular value when SLNs were located in close proximity to the primary tumour.

Multimodal interventional molecular imaging of tumor margins and distant metastases by targeting αvβ3 integrin

α(v)β(3) integrin is involved in (tumor-induced) angiogenesis and is a promising candidate for the specific visualization of both primary tumors and of their distant metastases. Combination of radioactive and fluorescent imaging labels in a single multimodal, or rather hybrid, RGD-based imaging agent enables integration of pre-, intra-, and postoperative angiogenesis imaging. A hybrid imaging agent targeting the α(v)β(3) integrin--(111)In-MSAP-RGD (MSAP = multifunctional single-attachment-point reagent), which contains a targeting moiety, a pentetic acid (DTPA) chelate, and a cyanine dye--was evaluated for its potential value in combined lesion detection and interventional molecular imaging in a 4T1 mouse breast cancer model. SPECT/CT and fluorescence imaging were used to visualize the tumor in vivo. Tracer distribution was evaluated ex vivo down to the microscopic level. The properties of (111)In-MSAP-RGD were compared with those of (111)In-DTPA-RGD. Biodistribution studies revealed a prolonged retention and increased tumor accumulation of (111)In-MSAP-RGD relative to (111)In-DTPA-RGD. With (111)In-MSAP-RGD, identical features could be visualized preoperatively (SPECT/CT) and intraoperatively (fluorescence imaging). As well as the primary tumor, (111)In-MSAP-RGD also enabled detection and accurate excision of distant metastases in the head and neck region of the mice. Therefore, the hybrid RGD derivative (111)In-MSAP-RGD shows potential in preoperative planning and fluorescence-based surgical intervention.

Hybrid peptide dendrimers for imaging of chemokine receptor 4 (CXCR4) expression

The chemokine receptor 4 (CXCR4), which is overexpressed in many types of cancer, is an emerging target in the field of molecular imaging and therapeutics. The CXCR4 binding of several peptides, including the cyclic Ac-TZ14011, has already been validated. In this study mono-, di- and tetrameric Ac-TZ14011-containing dendrimers were prepared and functionalized with a multimodal (hybrid) label, consisting of a Cy5.5-like fluorophore and a DTPA chelate. Confocal microscopy revealed that all three dendrimers were membrane bound at 4 °C, consistent with CXCR4 binding in vitro. The unlabeled dimer and tetramer had a somewhat lower affinity for CXCR4 than the unlabeled monomer. However, when labeled with the multimodal label the CXCR4 affinity of the dimer and tetramer was considerably higher compared to that of the labeled monomer. On top of that, biodistribution studies revealed that the additional peptides in the dimer and tetramer reduced nonspecific muscle uptake. Thus, multimerization of the cyclic Ac-TZ14011 peptide reduces the negative influence of the multimodal label on the receptor affinity and the biodistribution.

A series of poly[N-(2-hydroxypropyl)methacrylamide] copolymers with anthracene-derived fluorophores showing aggregation-induced emission properties for bioimaging

A series of new poly[N-(2-hydroxypropyl)methacrylamide]-based amphiphilic copolymers were synthesized through a radical copolymerization of a monomeric/hydrophobic fluorophore possessing aggregation-induced emission (AIE) property with N-(2-hydroxypropyl)methacrylamide. Photophysical properties were investigated using UV-Vis absorbance and fluorescence spectrophotometry. Influences of the polymer structures with different molar ratios of the AIE fluorophores on their photophysical properties were studied. Results show that the AIE fluorophores aggregate in the cores of the micelles formed from the amphiphilic random copolymers and polymers with more hydrophobic AIE fluorophores facilitate stronger aggregations of the AIE segments to obtain higher quantum efficiencies. The polymers reported herein have good water solubility, enabling the application of hydrophobic AIE materials in biological conditions. The polymers were endocytosed by two experimental cell lines, human brain glioblastoma U87MG cells and human esophagus premalignant CP-A, with a distribution into the cytoplasm. The polymers are non-cytotoxic to the two cell lines at a polymer concentration of 1 mg/mL.

Functionalized radioactive gold nanoparticles in tumor therapy

The development of new treatment modalities that offer clinicians the ability to reduce sizes of tumor prior to surgical resection or to achieve complete ablation without surgery would be a significant medical breakthrough in the overall care and treatment of prostate cancer patients. The goal of our investigation is aimed at validating the hypothesis that Gum Arabic-functionalized radioactive gold nanoparticles (GA-(198) AuNP) have high affinity toward tumor vasculature. We hypothesized further that intratumoral delivery of the GA-(198) AuNP agent within prostate tumor will allow optimal therapeutic payload that will significantly or completely ablate tumor without side effects, in patients with hormone refractory prostate cancer. In order to evaluate the therapeutic efficacy of this new nanoceutical, GA-(198) AuNP was produced by stabilization of radioactive gold nanoparticles ((198) Au) with the FDA-approved glycoprotein, GA. This review will describe basic and clinical translation studies toward realization of the therapeutic potential and myriad of clinical applications of GA-(198) AuNP agent in treating prostate and various solid tumors in human cancer patients.

Intraoperative laparoscopic fluorescence guidance to the sentinel lymph node in prostate cancer patients: clinical proof of concept of an integrated functional imaging approach using a multimodal tracer

BACKGROUND

Integration of molecular imaging and in particular intraoperative image guidance is expected to improve the surgical accuracy of laparoscopic lymph node (LN) dissection.

OBJECTIVE

To show the applicability of combining preoperative, intraoperative, and postoperative sentinel node imaging using an integrated diagnostic approach based on an imaging agent that is both radioactive and fluorescent.

DESIGN, SETTING, AND PARTICIPANTS

Before surgery, multimodal indocyanine green (ICG)-(99m)Tc-NanoColl was injected into the prostate. Subsequent lymphoscintigraphy and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging of pelvic nodes was performed to determine the location of the sentinel lymph nodes (SLNs) preoperatively. During the surgical procedure a fluorescence laparoscope, optimized for detection in the near infrared range, was used to visualize the nodes identified on SPECT/CT. Eleven patients scheduled for robot-assisted laparoscopic prostatectomy (RALP) with an increased risk of nodal metastasis, based on Memorial Sloan-Kettering Cancer Center/Kattan nomogram estimation, participated in a pilot assessment (N09IGF).

SURGICAL PROCEDURE

Patients underwent RALP with LN dissection for prostate cancer.

MEASUREMENTS

Radioactive and fluorescent signals were monitored using different modalities, and the correlation between the two types of signals was studied. The location of preoperatively detected SLNs was documented.

RESULTS AND LIMITATIONS

Preoperatively, SLNs were identified by SPECT/CT, and the multimodal nature of the imaging agent also enabled intraoperative detection via fluorescence imaging. Fluorescence particularly improved surgical guidance in areas with a high radioactive background signal such as the injection site. Ex vivo analysis revealed a strong correlation between the radioactive and fluorescent content in the excised LNs. Fluorescence detection is limited by the severe tissue attenuation of the signal. Therefore, radio guidance to the areas of interest is still desirable.

CONCLUSIONS

Initial data indicate that multimodal ICG-(99m)Tc-NanoColloid, in combination with a laparoscopic fluorescence laparoscope, can be used to facilitate and optimize dissection of SLNs during RALP procedures.