Chromatin state dynamics confers specific therapeutic strategies in enhancer subtypes of colorectal cancer.

OBJECTIVE: Enhancer aberrations are beginning to emerge as a key epigenetic feature of colorectal cancers (CRC), however, a comprehensive knowledge of chromatin state patterns in tumour progression, heterogeneity of these patterns and imparted therapeutic opportunities remain poorly described. DESIGN: We performed comprehensive epigenomic characterisation by mapping 222 chromatin profiles from 69 samples (33 colorectal adenocarcinomas, 4 adenomas, 21 matched normal tissues and 11 colon cancer cell lines) for six histone modification marks: H3K4me3 for Pol II-bound and CpG-rich promoters, H3K4me1 for poised enhancers, H3K27ac for enhancers and transcriptionally active promoters, H3K79me2 for transcribed regions, H3K27me3 for polycomb repressed regions and H3K9me3 for heterochromatin. RESULTS: We demonstrate that H3K27ac-marked active enhancer state could distinguish between different stages of CRC progression. By epigenomic editing, we present evidence that gains of tumour-specific enhancers for crucial oncogenes, such as ASCL2 and FZD10, was required for excessive proliferation. Consistently, combination of MEK plus bromodomain inhibition was found to have synergistic effects in CRC patient-derived xenograft models. Probing intertumour heterogeneity, we identified four distinct enhancer subtypes (EPIgenome-based Classification, EpiC), three of which correlate well with previously defined transcriptomic subtypes (consensus molecular subtypes, CMSs). Importantly, CMS2 can be divided into two EpiC subgroups with significant survival differences. Leveraging such correlation, we devised a combinatorial therapeutic strategy of enhancer-blocking bromodomain inhibitors with pathway-specific inhibitors (PARPi, EGFRi, TGFßi, mTORi and SRCi) for EpiC groups. CONCLUSION: Our data suggest that the dynamics of active enhancer underlies CRC progression and the patient-specific enhancer patterns can be leveraged for precision combination therapy.

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.

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.

Arenicolins: C-Glycosylated Depsides from Penicillium arenicola.

During investigation of the secondary metabolism of four strains of Penicillium arenicola, two new depsides, arenicolins A (1) and B (2), were isolated and characterized. Their structures were established mainly by analysis of NMR and HRMS data and by comparison with known compounds. These depsides incorporate intriguing structural features, including dual alkyl side chains and a C-glycosyl unit, with 1 also containing an acylated 2-hydroxymethyl-4,5,6-trihydroxycyclohexenone moiety. Although the arenicolins were produced by all strains tested, arenicolin A (1) was obtained using only one of five medium compositions employed, while arenicolin B (2) was produced in all media tested. Neither compound showed antibacterial or antifungal activity, but 1 exhibited cytotoxicity toward mammalian cell lines, including colorectal carcinoma (HCT-116), neuroblastoma (IMR-32), and ductal carcinoma (BT-474), with IC50 values of 7.3, 6.0, and 9.7 µM, respectively.

Application of Immuno-PET in Antibody-Drug Conjugate Development.

Targeted therapies hold great promise for cancer treatment and may exhibit even greater efficacy when combined with patient selection tools. The clinical impact of identifying likely responders includes reducing the number of unnecessary and ineffective therapies as well as more accurately determining drug effects. Positron emission tomography (PET) imaging using zirconium-89 radiolabeled monoclonal antibodies (mAbs), also referred to as zirconium-89 (89Zr)-immuno-PET, provides a potential biomarker to measure target expression and verify optimal delivery of targeted agents to tumors. Antibody-drug conjugates (ADCs) combine the high affinity and specificity of mAbs with the potency of cytotoxic drugs to target tumor-expressing antigen and destroy cancer cells. Thus, 89Zr-immuno-PET of whole-body biodistribution, pharmacokinetics, and tumor targeting of antibodies and ADCs to predict toxicity and efficacy could help guide individualized treatment. Here, we review how 89Zr-immuno-PET is being used as a companion diagnostic with the development of ADCs. Furthermore, we discuss how 89Zr-immuno-PET may be utilized in future clinical trials as an adjunct tool with novel ADCs to select cancer patients who have the greatest potential to benefit from treatment and improve ADC dosing regimens.

Evaluation of Anti-LGR5 Antibodies by ImmunoPET for Imaging Colorectal Tumors and Development of Antibody-Drug Conjugates.

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is highly expressed in colorectal tumors and marks colon cancer stem cells that drive tumor growth and metastasis. Recently, we showed that LGR5 is a promising target for antibody-drug conjugate (ADC) therapy. However, it is important to identify LGR5-positive tumors that would respond to ADC treatment. Prior to drug conjugation, we evaluated two different anti-LGR5 monoclonal antibodies (mAbs), 8F2 and 9G5, using 89Zr-immunoPET to select the optimal mAb for ADC development and tumor imaging. Binding, specificity, and internalization were compared, and mAbs were prescreened as ADC candidates against colon cancer cells using secondary ADCs. Both mAbs demonstrated strong, specific binding in 293T-LGR5 cells but not 293T-vector cells. In DLD-1 colorectal cancer cells, which express high levels of LGR5, the mAbs rapidly internalized into lysosomes and promoted ADC-induced cytotoxicity, with 8F2 exhibiting slightly higher potency. No binding was detected in DLD-1-shLGR5 (LGR5 knockdown) cells. 89Zr-DFO-LGR5 mAbs were generated and shown to retain high affinity and LGR5-dependent uptake in vitro. PET/CT imaging of DLD-1 tumors was performed 5 days postinjection of 89Zr-DFO-LGR5 mAbs, and findings were consistent with biodistribution data, which showed significantly higher tumor uptake (%ID/g) for 89Zr-DFO-8F2 (17.9 ± 2.2) compared to 89Zr-DFO-9G5 (5.5 ± 1.2) and 89Zr-DFO-IgG (3.8 ± 1.0). No significant uptake was observed in DLD-1-shLGR5 tumors. This study identifies 8F2 as the optimal candidate for ADC development and provides initial evidence that 89Zr-DFO-LGR5 mAbs may be utilized to stratify tumors which would respond best to LGR5-targeted ADC therapy.

Targeting pili in enterococcal pathogenesis.

Passive protection, the administration of antibodies to prevent infection, has garnered significant interest in recent years as a potential prophylactic countermeasure to decrease the prevalence of hospital-acquired infections. Pili, polymerized protein structures covalently anchored to the peptidoglycan wall of many Gram-positive pathogens, are ideal targets for antibody intervention, given their importance in establishing infection and their accessibility to antibody interactions. In this work, we demonstrated that a monoclonal antibody to the major component of Enterococcus faecalis pili, EbpC, labels polymerized pilus structures, diminishes biofilm formation, and significantly prevents the establishment of a rat endocarditis infection. The effectiveness of this anti-EbpC monoclonal provides strong evidence in support of its potential as a preventative. In addition, after radiolabeling, this monoclonal identified the site of enterococcal infection, providing a rare example of molecularly specific imaging of an established bacterial infection and demonstrating the versatility of this agent for use in future diagnostic and therapeutic applications.

A simple and rapid in vitro assay for identification of direct inhibitors of O6-methylguanine-DNA methyltransferase.

O6-Methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that is overexpressed in certain tumors and is associated with resistance to the DNA alkylating agent temozolomide. MGMT inhibitors show potential in combating temozolomide resistance, but current assays for MGMT enzyme activity and inhibition, primarily oligonucleotide-based and fluorescent probe-based, are laborious and costly. The clinical relevance of temozolomide therapy calls for more convenient methodologies to study MGMT inhibition. Here, we extended the application of SNAP-Capture magnetic beads to develop a novel MGMT inhibition assay that demonstrated efficacy not only with known MGMT inhibitors, but also with the aldehyde dehydrogenase inhibitor, disulfiram. The assay uses standard fluorescence microscopy as a simple and reliable detection method, and is translationally applicable in drug discovery programs.

A cell line expressing MGMT-GFP fusion protein was generated. After harvesting the cells, the cell lysate was prepared and combined with SNAP-Capture magnetic beads and incubated at room temperature. Successful immobilization of MGMT-GFP on SNAP-Capture magnetic beads was verified by fluorescence microscopy. For the MGMT inhibition assay, the cell lysate underwent pre-treatment with established MGMT inhibitors before interaction with SNAP-capture magnetic beads and then underwent immobilization and fluorescence microscopy.

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.

Combined multiphoton microscopy and somatostatin receptor type 2 imaging of pancreatic neuroendocrine tumors.

Pancreatic neuroendocrine tumors (PNETs) are a rare but increasingly more prevalent cancer with heterogeneous clinical and pathological presentation. Surgery is the preferred treatment for all hormone-expressing PNETs and any PNET greater than 2 cm, but difficulties arise when tumors are multifocal, metastatic, or small in size due to lack of effective surgical localization. Existing techniques such as intraoperative ultrasound provide poor contrast and resolution, resulting in low sensitivity for such tumors. Somatostatin receptor type 2 (SSTR2) is commonly overexpressed in PNETs and presents an avenue for targeted tumor localization. SSTR2 is often used for pre-operative imaging and therapeutic treatment, with recent studies demonstrating that somatostatin receptor imaging (SRI) can be applied in radioguided surgery to aid in removal of metastatic lymph nodes and achieving negative surgical margins. However not all PNETs express SSTR2, indicating labeled SRI could benefit from using a supplemental label-free technique such as multiphoton microscopy (MPM), which has proven useful in improving the accuracy of diagnosing more common exocrine pancreatic cancers. Our work tests the suitability of combined SRI and MPM for localizing PNETs by imaging and comparing samples of PNETs and normal pancreatic tissue. Specimens were labeled with a novel SSTR2-targeted contrast agent and imaged using fluorescence microscopy, and subsequently imaged using MPM to collect four autofluorescent channels and second harmonic generation. Our results show that a combination of both SRI and MPM provides enhanced contrast and sensitivity for localizing diseased tissue, suggesting that this approach could be a valuable clinical tool for surgical localization and treatment of PNETs.

Imaging prostate cancer lymph node metastases with a multimodality contrast agent.

BACKGROUND: Methods to detect lymph node (LN) metastases in prostate cancer (PCa) are limited. Pelvic LN dissection is commonly performed during prostatectomy, but often followed by morbid complications. More refined methods for detecting LN invasion are needed. METHODS: We developed a dual-labeled targeting agent having a near-infrared (NIR) fluorophore for intraoperative guidance, and a conventional radiotracer for detection of LN metastasis. Nu/Nu mice were orthotopically implanted with DsRed-expressing human PCa (PC3) cells. Antibody (Ab) specific for epithelial cell adhesion molecule was conjugated to DOTA, IRDye 800CW, and radiolabeled with (64) Cu. Dual-labeled Ab was administered intravenously at 10-12 weeks post-implantation, and positron emission tomography/computed tomography (PET/CT) and fluorescence imaging were performed within 18-24 hr. RESULTS: Metastasis to lumbar LNs was detected by DsRed fluorescence imaging, as well as pathology, in 75% of mice having pathology-confirmed primary prostate tumors. These metastases were also detected by NIR fluorescence imaging. In some cases, metastases to sciatic, medial, renal, and axillary nodes were also detected. For all LNs examined, no significant differences were found between the percentages of metastases detected by NIR imaging (63%) and µPET/CT (64%) (P = 0.93), or between those detected by DsRed imaging (25%) and pathological examination (19%) (P = 0.12). CONCLUSION: This study demonstrates that a multimodality contrast agent is useful for early detection of metastatic disease, and has applications for intraoperative PCa treatment. Further agent optimization is necessary to enhance specificity, and provide validation for prostate and other LN metastasizing epithelial cancers.

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.

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

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.

Characterization of chemical, radiochemical and optical properties of a dual-labeled MMP-9 targeting peptide.

Optical imaging possesses similar sensitivity to nuclear imaging and has led to the emergence of multimodal approaches with dual-labeled nuclear/near-infrared (NIR) agents. The growing impact of (68)Ga (t(1/2)=68 min) labeled peptides on preclinical and clinical research offers a promising opportunity to merge the high spatial resolution of NIR imaging with the clinically-accepted positron emission tomography (PET). Previously, dual-labeled agents have been prepared with longer-lived radiometals and showed no detrimental effects on optical properties as a result of radiolabeling. In this study, we selected a peptide (M(2)) that targets MMP-2/9 and is dual-labeled with IRDye 800 CW and (68)Ga. Since (68)Ga chelation typically requires low pH (3.5-4) and elevated heating temperatures (95 °C), we sought to evaluate the impact of (68)Ga labeling on the optical properties of M(2). An efficient method for preparation of (68)Ga-M(2) was developed and reaction conditions were optimized. Stability studies in PBS, DTPA, and serum were performed and high levels of intact agent were evident under each condition. The addition of multiple reporters to a targeting agent adds further complexity to the characterization and validation and thus requires not only testing to ensure the agent is stable chemically and radiochemically, but also optically. Therefore, fluorescence properties were evaluated using a spectrofluorometer as well as by fluorescence detection via HPLC. It was determined that (68)Ga-labeling conditions did not impair the fluorescent properties of the agent. The agent was then used for in vivo imaging in a mouse model of heterotopic ossification (HO) with activated MMP-9 expression as an early biomarker which precedes mineralization. Although (68)Ga-complexation greatly reduced binding affinity of the peptide and negated tracer uptake on PET, NIR imaging showed consistent fluorescent signal that correlated to MMP-9 expression. This attests to the feasibility of using (68)Ga/NIR for dual-labeling of other peptides or small molecules for multimodality molecular imaging.

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.

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.

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.

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.