Specific Targeting of Somatostatin Receptor Subtype-2 for Fluorescence-Guided Surgery

eTFC-01: a dual-labeled chelate-bridged tracer for SSTR2-positive tumors

BACKGROUND

Integrating radioactive and optical imaging techniques can facilitate the prognosis and surgical guidance for cancer patients. Using a single dual-labeled tracer ensures consistency in both imaging modalities. However, developing such molecule is challenging due to the need to preserve the biochemical properties of the tracer while introducing bulky labeling moieties. In our study, we designed a trifunctional chelate that facilitates the coupling of the targeting vector and fluorescent dye at opposite sites to avoid undesired steric hindrance effects. The synthesis of the trifunctional chelate N3-Py-DOTAGA-(tBu)3 (7) involved a five-step synthetic route, followed by conjugation to the linear peptidyl-resin 8 through solid-phase synthesis. After deprotection and cyclization, the near-infrared fluorescent dye sulfo-Cy.5 was introduced using copper free click chemistry, resulting in eTFC-01. Subsequently, eTFC-01 was labeled with [111In]InCl3. In vitro assessments of eTFC-01 binding, uptake, and internalization were conducted in SSTR2-transfected U2OS cells. Ex-vivo biodistribution and fluorescence imaging were performed in H69-tumor bearing mice.

RESULTS

eTFC-01 demonstrated a two-fold higher IC50 value for SSTR2 compared to the gold standard DOTA-TATE. Labeling of eTFC-01 with [111In]InCl3 gave a high radiochemical yield and purity. The uptake of [111In]In-eTFC-01 in U2OS.SSTR2 cells was two-fold lower than the uptake of [111In]In-DOTA-TATE, consistent with the binding affinity. Tumor uptake in H69-xenografted mice was lower for [111In]In-eTFC-01 at all-time points compared to [111In]In-DOTA-TATE. Prolonged blood circulation led to increased accumulation of [111In]In-eTFC-01 in highly vascularized tissues, such as lungs, skin, and heart. Fluorescence measurements in different organs correlated with the radioactive signal distribution.

CONCLUSION

The successful synthesis and coupling of the trifunctional chelate to the peptide and fluorescent dye support the potential of this synthetic approach to generate dual labeled tracers. While promising in vitro, the in vivo results obtained with [111In]In-eTFC-01 suggest the need for adjustments to enhance tracer distribution.

Engineering peptide drug therapeutics through chemical conjugation and implication in clinics

The development of peptide drugs has made tremendous progress in the past few decades because of the advancements in modification chemistry and analytical technologies. The novel-designed peptide drugs have been modified through various biochemical methods with improved diagnostic, therapeutic, and drug-delivery strategies. Researchers found it a helping hand to overcome the inherent limitations of peptides and bring continued advancements in their applications. Furthermore, the emergence of peptide-drug conjugates (PDCs)-utilizes target-oriented peptide moieties as a vehicle for cytotoxic payloads via conjugation with cleavable chemical agents, resulting in the key foundation of the new era of targeted peptide drugs. This review summarizes the various classifications of peptide drugs, suitable chemical modification strategies to improve the ADME (adsorption, distribution, metabolism, and excretion) features of peptide drugs, and recent (2015-early 2024) progress/achievements in peptide-based drug delivery systems as well as their fruitful implication in preclinical and clinical studies. Furthermore, we also summarized the brief description of other types of PDCs, including peptide-MOF conjugates and peptide-UCNP conjugates. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development and progress toward a bright future of novel peptide drugs.

In vivo imaging using surface enhanced spatially offset raman spectroscopy (SESORS): balancing sampling frequency to improve overall image acquisition

In the field of optical imaging, the ability to image tumors at depth with high selectivity and specificity remains a challenge. Surface enhanced resonance Raman scattering (SERRS) nanoparticles (NPs) can be employed as image contrast agents to specifically target cells in vivo; however, this technique typically requires time-intensive point-by-point acquisition of Raman spectra. Here, we combine the use of "spatially offset Raman spectroscopy" (SORS) with that of SERRS in a technique known as "surface enhanced spatially offset resonance Raman spectroscopy" (SESORRS) to image deep-seated tumors in vivo. Additionally, by accounting for the laser spot size, we report an experimental approach for detecting both the bulk tumor, subsequent delineation of tumor margins at high speed, and the identification of a deeper secondary region of interest with fewer measurements than are typically applied. To enhance light collection efficiency, four modifications were made to a previously described custom-built SORS system. Specifically, the following parameters were increased: (i) the numerical aperture (NA) of the lens, from 0.2 to 0.34; (ii) the working distance of the probe, from 9 mm to 40 mm; (iii) the NA of the fiber, from 0.2 to 0.34; and (iv) the fiber diameter, from 100 μm to 400 μm. To calculate the sampling frequency, which refers to the number of data point spectra obtained for each image, we considered the laser spot size of the elliptical beam (6 × 4 mm). Using SERRS contrast agents, we performed in vivo SESORRS imaging on a GL261-Luc mouse model of glioblastoma at four distinct sampling frequencies: par-sampling frequency (12 data points collected), and over-frequency sampling by factors of 2 (35 data points collected), 5 (176 data points collected), and 10 (651 data points collected). In comparison to the previously reported SORS system, the modified SORS instrument showed a 300% improvement in signal-to-noise ratios (SNR). The results demonstrate the ability to acquire distinct Raman spectra from deep-seated glioblastomas in mice through the skull using a low power density (6.5 mW/mm2) and 30-times shorter integration times than a previous report (0.5 s versus 15 s). The ability to map the whole head of the mouse and determine a specific region of interest using as few as 12 spectra (6 s total acquisition time) is achieved. Subsequent use of a higher sampling frequency demonstrates it is possible to delineate the tumor margins in the region of interest with greater certainty. In addition, SESORRS images indicate the emergence of a secondary tumor region deeper within the brain in agreement with MRI and H&E staining. In comparison to traditional Raman imaging approaches, this approach enables improvements in the detection of deep-seated tumors in vivo through depths of several millimeters due to improvements in SNR, spectral resolution, and depth acquisition. This approach offers an opportunity to navigate larger areas of tissues in shorter time frames than previously reported, identify regions of interest, and then image the same area with greater resolution using a higher sampling frequency. Moreover, using a SESORRS approach, we demonstrate that it is possible to detect secondary, deeper-seated lesions through the intact skull.

Somatostatin Receptor Subtype-2 Targeting System for Specific Delivery of Temozolomide

Temozolomide (TMZ) is a DNA alkylating agent that produces objective responses in patients with neuroendocrine tumors (NETs) when the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is inactivated. At high doses, TMZ therapy exhausts MGMT activity but also produces dose-limiting toxicities. To reduce off-target effects, we converted the clinically approved radiotracer 68Ga-DOTA-TOC into a peptide-drug conjugate (PDC) for targeted delivery of TMZ to somatostatin receptor subtype-2 (SSTR2)-positive tumor cells. We used an integrated radiolabeling strategy for direct quantitative assessment of receptor binding, pharmacokinetics, and tissue biodistribution. In vitro studies revealed selective binding to SSTR2-positive cells with high affinity (5.98 ± 0.96 nmol/L), internalization, receptor-dependent DNA damage, cytotoxicity, and MGMT depletion. Imaging and biodistribution analysis showed preferential accumulation of the PDC in receptor-positive tumors and high renal clearance. This study identified a trackable SSTR2-targeting system for TMZ delivery and utilizes a modular design that could be broadly applied in PDC development.

A translational blueprint for developing intraoperative imaging agents via radiopharmaceutical-guided drug design

Cancer imaging is a rapidly evolving field due to the discovery of novel molecular targets and the availability of corresponding techniques to detect them with high precision, accuracy, and sensitivity. Nuclear medicine is the most widely used molecular imaging modality and has a growing toolkit of clinically used radiopharmaceuticals that enable whole-body tumor visualization, staging, and treatment monitoring for a variety of tumors in a non-invasive manner. The need for similar imaging capabilities in the operating room has led to the emergence of fluorescence-guided surgery (FGS) as a powerful technique that gives surgeons unprecedented ability to distinguish tumors from healthy tissues. While a variety of strategies have been used to develop contrast agents for FGS, the use of radiopharmaceuticals as models brings exceptional translational potential and has increasingly been explored. Here, we review strategies used to convert clinically used radiopharmaceuticals into fluorescent and multimodal counterparts. Unique preclinical and clinical capabilities stemming from radiopharmaceutical-based agent design are also discussed to illustrate the advantages of this approach.

High-Contrast Detection of Somatostatin Receptor Subtype-2 for Fluorescence-Guided Surgery

Dye design can influence the ability of fluorescently labeled imaging agents to generate tumor contrast and has become an area of significant interest in the field of fluorescence-guided surgery (FGS). Here, we show that the charge-balanced near-infrared fluorescent (NIRF) dye FNIR-Tag enhances the imaging properties of a fluorescently labeled somatostatin analogue. In vitro studies showed that the optimized fluorescent conjugate MMC(FNIR-Tag)-TOC bound primarily via somatostatin receptor subtype-2 (SSTR2), whereas its negatively charged counterpart with IRDye 800CW had higher off-target binding. NIRF imaging in cell line- and patient-derived xenograft models revealed markedly higher tumor contrast with MMC(FNIR-Tag)-TOC, which was attributed to increased tumor specificity. Ex vivo staining of surgical biospecimens from primary and metastatic tumors, as well as involved lymph nodes, demonstrated binding to human tumors. Finally, in an orthotopic tumor model, a simulated clinical workflow highlighted our unique ability to use standard preoperative nuclear imaging for selecting patients likely to benefit from SSTR2-targeted FGS. Our findings demonstrate the translational potential of MMC(FNIR-Tag)-TOC for intraoperative imaging and suggest broad utility for using FNIR-Tag in fluorescent probe development.

Peptide-Drug Conjugates: A New Hope for Cancer Management

Cancer remains the leading cause of death worldwide despite advances in treatment options for patients. As such, safe and effective therapeutics are required. Short peptides provide advantages to be used in cancer management due to their unique properties, amazing versatility, and progress in biotechnology to overcome peptide limitations. Several appealing peptide-based therapeutic strategies have been developed. Here, we provide an overview of peptide conjugates, the better equivalents of antibody-drug conjugates, as the next generation of drugs for required precise targeting, enhanced cellular permeability, improved drug selectivity, and reduced toxicity for the efficient treatment of cancers. We discuss the basic components of drug conjugates and their release action, including the release of cytotoxins from the linker. We also present peptide-drug conjugates under different stages of clinical development as well as regulatory and other challenges.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Establishment of Novel Neuroendocrine Carcinoma Patient-Derived Xenograft Models for Receptor Peptide-Targeted Therapy

Simple Summary

Gastroenteropancreatic neuroendocrine neoplasms (GEP NENs) are a family of rare cancers with rising incidence in recent years. GEP NEN tumor cells are difficult to propagate, and few cellular and patient-derived xenograft (PDX) models are available for testing new therapies and studying the heterogeneous nature of these cancers. Here, we described the establishment and characterization of two novel NEC cellular and PDX models (NEC913 and NEC1452). NEC913 PDX tumors express somatostatin receptor 2 (SSTR2), whereas NEC1452 PDX tumors are SSTR2 negative. As a proof-of-concept study, we demonstrated how these PDX models can be used for peptide imaging experiments targeting SSTR2 using fluorescently labelled octreotide. The NEC913 and NEC1452 PDX lines represent valuable new tools for accelerating the process of drug discovery for GEP NENs.

Abstract

Gastroenteropancreatic neuroendocrine neoplasms (GEP NENs) are rare cancers consisting of neuroendocrine carcinomas (NECs) and neuroendocrine tumors (NETs), which have been increasing in incidence in recent years. Few cell lines and pre-clinical models exist for studying GEP NECs and NETs, limiting the ability to discover novel imaging and treatment modalities. To address this gap, we isolated tumor cells from cryopreserved patient GEP NECs and NETs and injected them into the flanks of immunocompromised mice to establish patient-derived xenograft (PDX) models. Two of six mice developed tumors (NEC913 and NEC1452). Over 80% of NEC913 and NEC1452 tumor cells stained positive for Ki67. NEC913 PDX tumors expressed neuroendocrine markers such as chromogranin A (CgA), synaptophysin (SYP), and somatostatin receptor-2 (SSTR2), whereas NEC1452 PDX tumors did not express SSTR2. Exome sequencing revealed loss of TP53 and RB1 in both NEC tumors. To demonstrate an application of these novel NEC PDX models for SSTR2-targeted peptide imaging, the NEC913 and NEC1452 cells were bilaterally injected into mice. Near infrared-labelled octreotide was administered and the fluorescent signal was specifically observed for the NEC913 SSTR2 positive tumors. These 2 GEP NEC PDX models serve as a valuable resource for GEP NEN therapy testing.

Targeted Dual-Modal PET/SPECT-NIR Imaging: From Building Blocks and Construction Strategies to Applications

Molecular imaging is an emerging non-invasive method to qualitatively and quantitively visualize and characterize biological processes. Among the imaging modalities, PET/SPECT and near-infrared (NIR) imaging provide synergistic properties that result in deep tissue penetration and up to cell-level resolution. Dual-modal PET/SPECT-NIR agents are commonly combined with a targeting ligand (e.g., antibody or small molecule) to engage biomolecules overexpressed in cancer, thereby enabling selective multimodal visualization of primary and metastatic tumors. The use of such agents for (i) preoperative patient selection and surgical planning and (ii) intraoperative FGS could improve surgical workflow and patient outcomes. However, the development of targeted dual-modal agents is a chemical challenge and a topic of ongoing research. In this review, we define key design considerations of targeted dual-modal imaging from a topological perspective, list targeted dual-modal probes disclosed in the last decade, review recent progress in the field of NIR fluorescent probe development, and highlight future directions in this rapidly developing field.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

Characterization of Peptides Targeting Metastatic Tumor Cells as Probes for Cancer Detection and Vehicles for Therapy Delivery

Metastasis is the leading cause of cancer-related deaths, and metastatic cancers remain largely incurable due to chemoresistance. Biomarkers of metastatic cells are lacking, and probes that could be used to detect and target metastases would be highly valuable. Here we hypothesize that metastatic cancer cells express cell-surface receptors that can be harnessed for identification of molecules homing to metastases. Screening a combinatorial library in a mouse mammary tumor model of spontaneous metastasis identified cyclic peptides with tropism for cancer cells disseminated to the lungs. Two lead peptides, CLRHSSKIC and CRAGVGRGC, bound murine and human cells derived from breast carcinoma and melanoma in culture and were selective for metastatic cells in vivo. In mice, peptide CRAGVGRGC radiolabeled with ⁶⁷Ga for biodistribution analysis demonstrated selective probe homing to lung metastases. Moreover, systemic administration of ⁶⁸Ga-labeled CRAGVGRGC enabled noninvasive imaging of lung metastases in mice by PET. A CRAGVGRGC-derived peptide induced apoptosis upon cell internalization in vitro and suppressed metastatic burden in vivo. Colocalization of CLRHSSKIC and CRAGVGRGC with N-cadherin⁺/E-cadherin^- cells indicated that both peptides are selective for cancer cells that have undergone the epithelial-to-mesenchymal transition. We conclude that CRAGVGRGC is useful as a probe to facilitate the development of imaging modalities and therapies targeting metastases. SIGNIFICANCE: This study identifies new molecules that bind metastatic cells and demonstrates their application as noninvasive imaging probes and vehicles for cytotoxic therapy delivery in preclinical cancer models.

Methods and techniques for in vitro subcellular localization of radiopharmaceuticals and radionuclides

In oncology, the holy grail of radiotherapy is specific radiation dose deposition in tumours with minimal healthy tissue toxicity. If used appropriately, injectable, systemic radionuclide therapies could meet these criteria, even for treatment of micrometastases and single circulating tumour cells. The clinical use of α and β- particle-emitting molecular radionuclide therapies is rising, however clinical translation of Auger electron-emitting radionuclides is hampered by uncertainty around their exact subcellular localisation, which in turn affects the accuracy of dosimetry. This review aims to discuss and compare the advantages and disadvantages of various subcellular localisation methods available to localise radiopharmaceuticals and radionuclides for in vitro investigations.

Receptor-Targeted Fluorescence-Guided Surgery With Low Molecular Weight Agents

Cancer surgery remains the primary treatment option for most solid tumors and can be curative if all malignant cells are removed. Surgeons have historically relied on visual and tactile cues to maximize tumor resection, but clinical data suggest that relapse occurs partially due to incomplete cancer removal. As a result, the introduction of technologies that enhance the ability to visualize tumors in the operating room represents a pressing need. Such technologies have the potential to revolutionize the surgical standard-of-care by enabling real-time detection of surgical margins, subclinical residual disease, lymph node metastases and synchronous/metachronous tumors. Fluorescence-guided surgery (FGS) in the near-infrared (NIRF) spectrum has shown tremendous promise as an intraoperative imaging modality. An increasing number of clinical studies have demonstrated that tumor-selective FGS agents can improve the predictive value of fluorescence over non-targeted dyes. Whereas NIRF-labeled macromolecules (i.e., antibodies) spearheaded the widespread clinical translation of tumor-selective FGS drugs, peptides and small-molecules are emerging as valuable alternatives. Here, we first review the state-of-the-art of promising low molecular weight agents that are in clinical development for FGS; we then discuss the significance, application and constraints of emerging tumor-selective FGS technologies.

A Cyanine-Bridged Somatostatin Hybrid Probe for Multimodal SSTR2 Imaging in Vitro and in Vivo: Synthesis and Evaluation

Multimodal imaging probes have attracted the interest of ongoing research, for example, for the surgical removal of tumors. Modular synthesis approaches allow the construction of hybrid probes consisting of a radiotracer, a fluorophore and a targeting unit. We present the synthesis of a new asymmetric bifunctional cyanine dye that can be used as a structural and functional linker for the construction of such hybrid probes. 68 Ga-DOTATATE, a well-characterized radiopeptide targeting the overexpressed somatostatin receptor subtype 2 (SSTR2) in neuroendocrine tumors, was labeled with our cyanine dye, thus providing additional information along with the data obtained from the radiotracer. We tested the SSTR2-targeting and imaging properties of the resulting probe 68 Ga-DOTA-ICC-TATE in vitro and in a tumor xenograft mouse model. Despite the close proximity between dye and pharmacophore, we observed a high binding affinity towards SSTR2 as well as elevated uptake in SSTR2-overexpressing tumors in the positron emission tomography (PET) scan and histological examination.

Not so innocent: Impact of fluorophore chemistry on the in vivo properties of bioconjugates

The combination of targeting ligands and fluorescent dyes is a powerful strategy to observe cell types and tissues of interest. Conjugates of peptides, proteins, and, in particular, monoclonal antibodies (mAbs) exhibit excellent tumor targeting in various contexts. This approach has been translated to a clinical setting to provide real-time molecular insights during the surgical resection of solid tumors. A critical element of this approach is the generation of highly fluorescent bioconjugates that maintain the properties of the parent targeting ligand. A number of studies have found that fluorophores can dramatically impact the pharmacokinetic and tumor-targeting properties of the bioconjugates they are meant to only innocently observe. In this review, we summarize several examples of these effects and highlight strategies that have been used to mitigate them. These include the application of site-specific labeling chemistries, modulating label density, and altering the structure of the fluorescent probe itself. In particular, we point out the significant potential of fluorophores with hydrophilic but net-neutral structures. Overall, this review highlights recent progress in refining the in vivo properties of fluorescent bioconjugates, and we hope, will inform future efforts in this area.

Antagonizing somatostatin receptor subtype 2 and 5 reduces blood glucose in a gut- and GLP-1R-dependent manner

Somatostatin (SS) inhibits glucagon-like peptide-1 (GLP-1) secretion in a paracrine manner. We hypothesized that blocking somatostatin subtype receptor 2 (SSTR2) and 5 (SSTR5) would improve glycemia by enhancing GLP-1 secretion. In the perfused mouse small intestine, the selective SSTR5 antagonist (SSTR5a) stimulated glucose-induced GLP-1 secretion to a larger degree than the SSTR2 antagonist (SSTR2a). In parallel, mice lacking the SSTR5R showed increased glucose-induced GLP-1 secretion. Both antagonists improved glycemia in vivo in a GLP-1 receptor-dependent (GLP-1R-dependent) manner, as the glycemic improvements were absent in mice with impaired GLP-1R signaling and in mice treated with a GLP-1R-specific antagonist. SSTR5a had no direct effect on insulin secretion in the perfused pancreas, whereas SSTR2a increased insulin secretion in a GLP-1R-independent manner. Adding a dipeptidyl peptidase 4 inhibitor (DPP-4i) in vivo resulted in additive effects on glycemia. However, when glucose was administered intraperitoneally, the antagonist was incapable of lowering blood glucose. Oral administration of SSTR5a, but not SSTR2a, lowered blood glucose in diet-induced obese mice. In summary, we demonstrate that selective SSTR antagonists can improve glucose control primarily through the intestinal GLP-1 system in mice.

Somatostatin Receptor as a Molecular Imaging Target in Human and Canine Cushing Disease

OBJECTIVES

Fluorescence-guided surgery may improve completeness of resection in transsphenoidal surgery for Cushing disease (CD) by enabling visualization of residual tumor tissue at the margins. In this review we discuss somatostatin receptors (SSTRs) as targets for fluorescence-guided surgery and overview existing SSTR-specific imaging agents. We also compare SSTR expression in normal pituitary and corticotrophinoma tissues from human and canine CD patients to assess canines as a translational model for CD.

METHODS

A PubMed literature search was conducted for publications containing the terms canine, somatostatin receptor, Cushing's disease, and corticotroph adenoma. SSTR expression data from each study was documented as the presence or absence of expression or, when possible, the number of tumors expressing a given SSTR subtype within a group of tumors being studied. Studies that used reverse transcription polymerase chain reaction to quantify SSTR expression were selected for additional comparative analysis.

RESULTS

SSTR5 is strongly expressed in human corticotroph adenomas and weakly expressed in surrounding pituitary parenchyma, a pattern not conclusively observed in canine patients. SSTR2 mRNA expression is similar in human normal pituitary and corticotrophinoma cells but may be significantly higher in canine normal pituitary tissue than in corticotroph tumoral tissue. Limited data were available on SSTR subtypes 1, 3, and 4.

CONCLUSIONS

Further studies must fill the knowledge gaps related to species-specific SSTR expression, so using canine CD as a translational model may be premature. We do conclude that the expression profile of SSTR5 (i.e., high local expression in pituitary adenomas relative to normal surrounding tissues) makes SSTR5 a promising molecular target for FGS.

Comparison of HER2-Targeted Antibodies for Fluorescence-Guided Surgery in Breast Cancer

Background

Although therapeutic advances have led to enhanced survival in patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer, detection of residual disease remains challenging. Here, we examine two approved anti-HER2 monoclonal antibodies (mAbs), trastuzumab and pertuzumab, as potential candidates for the development of immunoconjugates for fluorescence-guided surgery (FGS).

Methods

mAbs were conjugated to the near-infrared fluorescent (NIRF) dye, IRDye800, and for quantitative in vitro assessment, to the radiometal chelator, desferrioxamine, to enable dual labeling with ⁸⁹Zr. In vitro binding was evaluated in HER2-overexpressing (BT474, SKBR3) and HER2-negative (MCF7) cell lines. BT474 and MCF7 xenografts were used for in vivo and ex vivo fluorescence imaging.

Results

In vitro findings demonstrated HER2-mediated binding for both fluorescent immunoconjugates and were in agreement with radioligand assays using dual-labeled immunoconjugates. In vivo and ex vivo studies showed preferential accumulation of the fluorescently-labeled mAbs in tumors and similar tumor-to-background ratios. In vivo HER2 specificity was confirmed by immunohistochemical staining of resected tumors and normal tissues.

Conclusions

We showed for the first time that fluorescent trastuzumab and pertuzumab immunoconjugates have similar NIRF imaging performance and demonstrated the possibility of performing HER2-targeted FGS with agents that possess distinct epitope specificity.

Versatile Functions of Somatostatin and Somatostatin Receptors in the Gastrointestinal System

Somatostatin (SST) and somatostatin receptors (SSTRs) play an important role in the brain and gastrointestinal (GI) system. SST is produced in various organs and cells, and the inhibitory function of somatostatin-containing cells is involved in a range of physiological functions and pathological modifications. The GI system is the largest endocrine organ for digestion and absorption, SST-endocrine cells and neurons in the GI system are a critical effecter to maintain homeostasis via SSTRs 1-5 and co-receptors, while SST-SSTRs are involved in chemo-sensory, mucus, and hormone secretion, motility, inflammation response, itch, and pain via the autocrine, paracrine, endocrine, and exoendocrine pathways. It is also a power inhibitor for tumor cell proliferation, severe inflammation, and post-operation complications, and is a first-line anti-cancer drug in clinical practice. This mini review focuses on the current function of producing SST endocrine cells and local neurons SST-SSTRs in the GI system, discusses new development prognostic markers, phosphate-specific antibodies, and molecular imaging emerging in diagnostics and therapy, and summarizes the mechanism of the SST family in basic research and clinical practice. Understanding of endocrines and neuroendocrines in SST-SSTRs in GI will provide an insight into advanced medicine in basic and clinical research.

Development of a drug-device combination for fluorescence-guided surgery in neuroendocrine tumors

SIGNIFICANCE

The use of cancer-targeted contrast agents in fluorescence-guided surgery (FGS) has the potential to improve intraoperative visualization of tumors and surgical margins. However, evaluation of their translational potential is challenging.

AIM

We examined the utility of a somatostatin receptor subtype-2 (SSTR2)-targeted fluorescent agent in combination with a benchtop near-infrared fluorescence (NIRF) imaging system to visualize mouse xenografts under conditions that simulate the clinical FGS workflow for open surgical procedures.

APPROACH

The dual-labeled somatostatin analog, Ga67-MMC(IR800)-TOC, was injected into mice (n  =  24) implanted with SSTR2-expressing tumors and imaged with the customized OnLume NIRF imaging system (Madison, Wisconsin). In vivo and ex vivo imaging were performed under ambient light. The optimal dose (0.2, 0.5, and 2 nmol) and imaging time point (3, 24, 48, and 72 h) were determined using contrast-to-noise ratio (CNR) as the image quality parameter. Video captures of tumor resections were obtained to provide an FGS readout that is representative of clinical utility. Finally, a log-transformed linear regression model was fitted to assess congruence between fluorescence readouts and the underlying drug distribution.

RESULTS

The drug-device combination provided high in vivo and ex vivo contrast (CNRs  >  3, except lung at 3 h) at all time points with the optimal dose of 2 nmol. The optimal imaging time point was 24-h post-injection, where CNRs  >  6.5 were achieved in tissues of interest (i.e., pancreas, small intestine, stomach, and lung). Intraoperative FGS showed excellent utility for examination of the tumor cavity pre- and post-resection. The relationship between fluorescence readouts and gamma counts was linear and strongly correlated (n  =  334, R2  =  0.71; r  =  0.84; P  <  0.0001).

CONCLUSION

The innovative OnLume NIRF imaging system enhanced the evaluation of Ga67-MMC(IR800)-TOC in tumor models. These components comprise a promising drug-device combination for FGS in patients with SSTR2-expressing tumors.

Contrast-Enhanced Multispectral Photoacoustic Imaging for Irregular Hepatectomy Navigation: A Pilot Study

Irregular hepatectomy plays a prominent role in the treatment of small hepatocellular carcinoma (HCC) patients with severe cirrhosis and localized liver metastasis. In clinical practices, intraoperative tumor boundaries delineation facilitates to accomplish tumor resection with negative margin, remarkably decreasing the recurrence rates. Currently, ultrasound (US) and ICG fluorescence-guided surgery has been used for intraoperative navigation in irregular hepatectomy, but insufficient specificity results in a limited prevalence. Inspired by the high resolution of photoacoustic (PA) imaging and established clinical efficacy of ¹⁸F-Alfatide that is specific for integrin α_vβ₃-overexpressed tumors, we herein developed a fluorescent analogue IR820-E[c(RGDfK)]₂, and a proof-of-concept intraoperative multispectral PA imaging navigation for precise irregular hepatectomy using hand-held PA/US imaging system. An integrin α_vβ₃-targeted fluorescent contrast agent IR820-E[c(RGDfK)]₂ was designed, synthesized, and characterized. In vitro studies were performed to determine optical and PA properties, affinity and specificity and biocompatibility. Multispectral PA imaging, the optimal imaging time point and contrast, multispectral PA imaging-guided irregular hepatectomy, pharmacokinetics, and safety profile were evaluated in subcutaneous and orthotopic HCC tumor models. Ex vivo macroscopic three-dimensions (3D) PA imaging with IR820-E[c(RGDfK)]₂ staining was also performed in surgical biospecimens from patients with HCC. IR820-E[c(RGDfK)]₂ has a simple synthetic method at gram scale, high affinity, and specificity for integrin α_vβ₃, excellent pharmacokinetic and safety profile can effectively differentiate tumor from normal liver tissues in animal models and surgical biospecimens from HCC patients. Preoperative tumor localization, intraoperative tumor boundaries delineation, and tumor excision, and postoperative negative margin assessment were successfully achieved during irregular hepatectomy. This initial attempt allows one to preoperatively detect tumor lesions, intraoperatively delineate tumor boundaries and guide tumor resection, and postoperatively evaluate tumor margin status during irregular hepatectomy. IR820-E[c(RGDfK)]₂ has the potential to be an investigational new drug for clinical use in multispectral photoacoustic imaging-guided irregular hepatectomy.

A proof-of-concept methodology to validate the in situ visualization of residual disease using cancer-targeted molecular agents in fluorescence-guided surgery

Introduction

The clinical need for improved intraoperative tumor visualization has led to the development of targeted contrast agents for fluorescence-guided surgery (FGS). A key characteristic of these agents is their high tumor specificity, which could enable detection of residual lesions that would likely be missed by visual inspection. Here, we examine the utility of a promising somatostatin receptor subtype-2 (SSTR2)-targeted fluorescent agent for detecting residual disease in mouse xenografts using FGS and post-operative histopathological validation.

Methods

Mice (n=2) implanted with SSTR2 overexpressing tumors were injected with 2 nmol of the dual-labeled somatostatin analog, ⁶⁷Ga-MMC(IR800)-TOC, and tumors were resected 48 h post-injection using traditional white light reflectance and palpation. Tumors underwent gamma counting and histopathology analysis. The wide-field FGS imaging platform (OnLume) was used to evaluate residual disease in situ under ambient light representative of an operating room.

Results

The tumor was resected with grossly negative margins using conventional inspection and palpation; however, additional in situ residual disease was found in the tumor cavity using FGS imaging. In situ fluorescent tumor contrast-to-noise ratios (CNRs) were 3.0 and 5.2. Agent accumulation was 7.72 and 8.20 %ID/g in tumors and 0.27 and 0.20 %ID/g in muscle. Fluorescence pixel values and gamma counts were highly correlated (r = 0.95, P < 0.048). H&E and IHC staining confirmed cancer positivity and SSTR2-overexpression, respectively.

Conclusion

Our findings demonstrate that the use of clinically relevant fluorescence imaging instrumentation enhances the evaluation of promising FGS agents for in situ visualization of residual disease.