Evaluation of 68Ga-labeled MG7 antibody: a targeted probe for PET/CT imaging of gastric cancer

Targeting Patient-Derived Orthotopic Gastric Cancers with a Fluorescent Humanized Anti-CEA Antibody

BACKGROUND

Gastric cancer poses a major diagnostic and therapeutic challenge as surgical resection provides the only opportunity for a cure. Specific labeling of gastric cancer could distinguish resectable and nonresectable disease and facilitate an R0 resection, which could improve survival.

METHODS

Two patient-derived gastric cancer lines, KG8 and KG10, were established from surgical specimens of two patients who underwent gastrectomy for gastric adenocarcinoma. Harvested tumor fragments were implanted into the greater curvature of the stomach to establish patient-derived orthotopic xenograft (PDOX) models. M5A (humanized anti-CEA antibody) or IgG control antibodies were conjugated with the near-infrared dye IRDye800CW. Mice received 50 µg of M5A-IR800 or 50 µg of IgG-IR800 intravenously and were imaged after 72 hr. Fluorescence imaging was performed by using the LI-COR Pearl Imaging System. A tumor-to-background ratio (TBR) was calculated by dividing the mean fluorescence intensity of the tumor versus adjacent stomach tissue.

RESULTS

M5A-IR800 administration resulted in bright labeling of both KG8 and K10 tumors. In the KG8 PDOX models, the TBR for M5A-IR800 was 5.85 (SE ± 1.64) compared with IgG-IR800 at 0.70 (SE ± 0.17). The K10 PDOX models had a TBR of 3.71 (SE ± 0.73) for M5A-IR800 compared with 0.66 (SE ± 0.12) for IgG-IR800.

CONCLUSIONS

Humanized anti-CEA (M5A) antibodies conjugated to fluorescent dyes provide bright and specific labeling of gastric cancer PDOX models. This tumor-specific fluorescent antibody is a promising potential clinical tool to detect the extent of disease for the determination of resectability as well as to visualize tumor margins during gastric cancer resection.

Development and Biodistribution of a Nerve Growth Factor Radioactive Conjugate for PET Imaging

PURPOSE

The purpose of these studies was to develop a nerve growth factor (NGF) radiometal-chelator conjugate to determine the biodistribution and brain uptake of NGF by positron emission tomography/computerized tomography (PET-CT).

PROCEDURES

Purified NGF from llama seminal plasma was conjugated with FITC, and the chelator NOTA or DFO. NGF conjugates were evaluated for bioactivity. NOTA- and DFO-conjugated NGF were radiolabeled with gallium-68 or zirconium-89 ([68 Ga]GaCl3, half-life = 68 min; [89Zr]Zr(oxalate)4, half-life = 3.3 days). [89Zr]Zr-NGF was evaluated for biodistribution (0.5, 1, or 24 h), PET imaging (60 min), and brain autoradiography in mice.

RESULTS

Cell-based in vitro assays confirmed that the NGF conjugates maintained NGF receptor-binding and biological activity. Zirconium-89 and gallium-68 radiolabeling showed a high efficiency; however, only[89Zr]Zr-NGF was stable in vitro. Biodistribution studies showed that, as with most small proteins < 70 kDa, [89Zr]Zr-NGF uptake was predominantly in the kidney and was cleared rapidly with almost complete elimination of NGF at 24 h. Dynamic PET imaging from 0-60 min showed a similar pattern to ex vivo biodistribution with some transient liver uptake. Interestingly, although absolute brain uptake was very low, at 24 h after treatment, cerebral cortex uptake was higher than any other brain area examined and blood.

CONCLUSIONS

We conclude that conjugation of DFO to NGF through a thiourea linkage allows effective radiolabeling with zirconium-89 while maintaining NGF bioactivity. Following intravenous administration, the radiolabeled NGF targets non-neuronal tissues (e.g., kidney, liver), and although absolute brain uptake was very low, the brain uptake that was observed was restricted to the cortex.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

State of the Art in Radiolabeling of Antibodies with Common and Uncommon Radiometals for Preclinical and Clinical Immuno-PET

Inert and stable radiolabeling of monoclonal antibodies (mAb), antibody fragments, or antibody mimetics with radiometals is a prerequisite for immuno-PET. While radiolabeling is preferably fast, mild, efficient, and reproducible, especially when applied for human use in a current Good Manufacturing Practice compliant way, it is crucial that the obtained radioimmunoconjugate is stable and shows preserved immunoreactivity and in vivo behavior. Radiometals and chelators have extensively been evaluated to come to the most ideal radiometal–chelator pair for each type of antibody derivative. Although PET imaging of antibodies is a relatively recent tool, applications with ⁸⁹Zr, ⁶⁴Cu, and ⁶⁸Ga have greatly increased in recent years, especially in the clinical setting, while other less common radionuclides such as ⁵²Mn, ⁸⁶Y, ⁶⁶Ga, and ⁴⁴Sc, but also ¹⁸F as in [¹⁸F]AlF are emerging promising candidates for the radiolabeling of antibodies. This review presents a state of the art overview of the practical aspects of radiolabeling of antibodies, ranging from fast kinetic affibodies and nanobodies to slow kinetic intact mAbs. Herein, we focus on the most common approach which consists of first modification of the antibody with a chelator, and after eventual storage of the premodified molecule, radiolabeling as a second step. Other approaches are possible but have been excluded from this review. The review includes recent and representative examples from the literature highlighting which radiometal–chelator–antibody combinations are the most successful for in vivo application.

Antibody-Targeted Imaging of Gastric Cancer

The specificity of antibodies for antigens overexpressed or uniquely expressed in tumor cells makes them ideal candidates in the development of bioconjugates for tumor imaging. Molecular imaging can aid clinicians in the diagnosis of gastric tumors and in selecting patients for therapies targeting receptors with a heterogeneous intratumoral or intertumoral expression. Antibodies labeled with an imaging radiometal can be used to detect primary tumors and metastases using whole-body positron emission tomography (PET) or single photon emission computed tomography (SPECT), both during diagnosis and monitoring disease response. Conjugated with fluorescent dyes, antibodies can image tumors by targeted optical imaging. This review provides an overview of the most recent advances in the use of antibodies labeled with radiometals or conjugated with fluorescent dyes for gastric cancer imaging.

Reactive oxygen species and enzyme dual-responsive biocompatible drug delivery system for targeted tumor therapy

Spurred by newly developed drug delivery systems (DDSs), side effects of cancer chemotherapy could be reduced by using multifunctional nanoplatforms. However, the facile synthesis of effective DDSs remains a challenge. Here, a six-arginine-tailed anti-epidermal growth factor receptor (EGFR) affibody was employed to easily synthesize the highly reactive oxygen species (hROS)- and trypsin-responsive 11-mercaptoundecanoic acid-modified gold nanoclusters (MUA-Au NCs) for tumor-targeted drug delivery. The polyarginine moiety of affibody sealed methotrexate (MTX)-loaded MUA-Au NCs through charge effect, as well as leaving the rest targeting fragment of the affibody to specifically bind tumor overexpressed EGFR. As the shell of MUA-Au NCs-MTX-Affibody (MAMA), polyarginine chains of affibody could be digested by trypsin, helping to release MTX from MAMA. The released MTX accelerated destroying MUA-Au NCs through inducing the generation of hROS. Specifically targeting EGFR-overexpressed tumors, quickly delivering a sufficient amount of drug to the tumor, subsequently increasing the local MTX and hROS levels, and safely eliminating the biocompatible structure from kidney, endowed MAMA greater treatment effectiveness and lower side effect than chemotherapy, especially in pancreatic cancer due to its high trypsin level. This simply fabricated DDS may find applications in high effective cancer therapy, especially for tumors with high trypsin activity.

Integrating SWATH-MS Proteomics and Transcriptome Analysis Identifies CHI3L1 as a Plasma Biomarker for Early Gastric Cancer

Early diagnosis of gastric cancer (GC) provides patients opportunities for minimally invasive endoscopic resection. Here, we developed a new strategy integrated the state-of-the-art sequential windowed acquisition of all theoretical fragment ion (SWATH) mass spectra (MS) with multi-dataset joint analysis to screen for the stage-I GC plasma biomarker. In SWATH-MS assays, we identified 37 upregulated and 21 downregulated proteins in GC plasma. In the mRNA database analysis, 633 genes were identified as differentially expressed genes in at least 4 out of 5 datasets, but there were only 94 genes identified as upregulated. Only 1 gene, CHI3L1, was characterized as upregulated in both the dataset consensus list and the SWATH-MS list. Then, we detected the CHI3L1 level in the plasma of a large cohort consisting of 200 participants. The area under the ROC curve (AUC) of CHI3L1 in distinguishing GC from others was 0.788. Integrating the plasma CHI3L1 level with clinical factors further boosted the AUC to 0.887. In conclusion, we provide a novel strategy for biomarker screening, combining recent MS techniques with public database analysis, and identified plasma CHI3L1 as a potential biomarker for patients with endoscopically resectable GC.

Characterization of drug responses of mini patient-derived xenografts in mice for predicting cancer patient clinical therapeutic response

Background

Patient-derived organoids and xenografts (PDXs) have emerged as powerful models in functional diagnostics with high predictive power for anticancer drug response. However, limitations such as engraftment failure and time-consuming for establishing and expanding PDX models followed by testing drug efficacy, and inability to subject to systemic drug administration for ex vivo organoid culture hinder realistic and fast decision-making in selecting the right therapeutics in the clinic. The present study aimed to develop an advanced PDX model, namely MiniPDX, for rapidly testing drug efficacy to strengthen its value in personalized cancer treatment.

Methods

We developed a rapid in vivo drug sensitivity assay, OncoVee^® MiniPDX, for screening clinically relevant regimens for cancer. In this model, patient-derived tumor cells were arrayed within hollow fiber capsules, implanted subcutaneously into mice and cultured for 7 days. The cellular activity morphology and pharmacokinetics were systematically evaluated. MiniPDX performance (sensitivity, specificity, positive and negative predictive values) was examined using PDX as the reference. Drug responses were examined by tumor cell growth inhibition rate and tumor growth inhibition rate in PDX models and MiniPDX assays respectively. The results from MiniPDX were also used to evaluate its predictive power for clinical outcomes.

Results

Morphological and histopathological features of tumor cells within the MiniPDX capsules matched those both in PDX models and in original tumors. Drug responses in the PDX tumor graft assays correlated well with those in the corresponding MiniPDX assays using 26 PDX models generated from patients, including 14 gastric cancer, 10 lung cancer and 2 pancreatic cancer. The positive predictive value of MiniPDX was 92%, and the negative predictive value was 81% with a sensitivity of 80% and a specificity of 93%. Through expanding to clinical tumor samples, MiniPDX assay showed potential of wide clinical application.

Conclusions

Fast in vivo MiniPDX assay based on capsule implantation was developed-to assess drug responses of both PDX tumor grafts and clinical cancer specimens. The high correlation between drug responses of paired MiniPDX and PDX tumor graft assay, as well as translational data suggest that MiniPDX assay is an advanced tool for personalized cancer treatment.

PET Imaging of VCAM-1 Expression and Monitoring Therapy Response in Tumor with a 68Ga-Labeled Single Chain Variable Fragment

Vascular cell adhesion molecule-1 (VCAM-1) is a transmembrane glycoprotein closely related to tumorigenicity as well as tumor metastasis. It is also a well-known candidate for detecting tumors. LY2409881, an IKKβ inhibitor, could induce apoptosis of VCAM-1 positive cells. Our purpose is to prepare a novel tracer to evaluate its feasibility of detecting VCAM-1 expression and monitoring LY2409881 tumor curative effect. The tracer was prepared by conjugating the single chain variable fragment (scFv) of VCAM-1 and NOTA-NHS-ester and then labeled with ⁶⁸Ga. ⁶⁸Ga-NOTA-VCAM-1_scFv was successfully prepared with high radiochemical yield. VCAM-1 overexpression and underexpression melanoma cell lines, B16F10 and A375m, were used in this study. The results of microPET/CT imaging in small animals indicated that the uptake of ⁶⁸Ga-NOTA-VCAM-1_scFv in B16F10 tumor was much higher than that of A375m, which was also confirmed by the biodistribution and autoradiography results. LY2409881 inhibits the growth of B16F10 melanoma in vivo by inducing dose- and time-dependent growth inhibition and apoptosis of the cells. The LY2409881 treated group and DMSO control group were established and imaged by microPET/CT. In the LY2409881 group, uptake of the tracer in tumor was decreased at the first week, and then gradually recovered to the initial level. In DMSO control, the uptake of the tracer remained at the same level during the whole time. The results suggested that LY2409881 inhibits the expression of VCAM-1 and suppresses tumor growth. ⁶⁸Ga-NOTA-VCAM-1_scFv, an easily synthesized probe, has a potential clinical application in the visual monitoring of IKKβ inhibitor intervention on VCAM-1 positive tumors.

Multimodality Imaging of Angiogenesis in a Rabbit Atherosclerotic Model by GEBP11 Peptide Targeted Nanoparticles

Background and Aims: Angiogenesis is an important pathological process during progression of plaque formation, which can result in plaque hemorrhage and vulnerability. This study aims to explore non-invasive imaging of angiogenesis in atherosclerotic plaque through magnetic resonance imaging (MRI) and positron emission tomography (PET) by using GEBP11 peptide targeted magnetic iron oxide nanoparticles in a rabbit model of atherosclerosis.

Methods: The dual-modality imaging probe was constructed by coupling 2, 3-dimercaptosuccinnic acid-coated paramagnetic nanoparticles (DMSA-MNPs) and the PET ⁶⁸Ga chelator 1,4,7-triazacyclononane-N, N', N''-triacetic acid (NOTA) to GEBP11 peptide. The atherosclerosis model was induced in New Zealand white rabbits by abdominal aorta balloon de-endothelialization and atherogenic diet for 12 weeks. The plaque areas in abdominal artery were detected by ultrasound imaging and Oil Red O staining. Immunofluorescence staining and Prussian blue staining were applied respectively to investigate the affinity of GEBP11 peptide. MTT and flow cytometric analysis were performed to detect the effects of NGD-MNPs on cell proliferation, cell cycle and apoptosis in Human umbilical vein endothelial cells (HUVECs). In vivo MRI and PET imaging of atherosclerotic plaque were carried out at different time points after intravenous injection of nanoparticles.

Results: The NGD-MNPs with hydrodynamic diameter of 130.8 nm ± 7.1 nm exhibited good imaging properties, high stability, low immunogenicity and little cytotoxicity. In vivo PET/MR imaging revealed that ⁶⁸Ga-NGD-MNPs were successfully applied to visualize atherosclerotic plaque angiogenesis in the rabbit abdominal aorta. Prussian blue and CD31 immunohistochemical staining confirmed that NGD-MNPs were well co-localized within the blood vessels' plaques.

Conclusion:⁶⁸Ga-NGD-MNPs might be a promising MR and PET dual imaging probe for visualizing the vulnerable plaques.

Development of 68Ga-SCN-DOTA-Capsaicin as an Imaging Agent Targeting Apoptosis and Cell Cycle Arrest in Breast Cancer

⁶⁸Ga-labeled capsaicin using a DOTA (1,4,7,10-tetraazocyclododecane-N,N',N″,N'″-tetraacetic acid) derivative [⁶⁸Ga-SCN-Benzyl(Bn)-DOTA-capsaicin] was studied for the diagnosis of breast cancers, such as MCF-7 and SK-BR-3. The standard compound, ⁶⁹Ga-SCN-Bn-DOTA-capsaicin, was also prepared and characterized by spectroscopic analysis. The binding affinity of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was evaluated by using breast cancer cell lines (MCF-7, SK-BR-3) and colon cancer cell (CT-26); the biodistribution was carried out by using MCF-7-bearing nude mice, after which the positron emission tomography (PET) images were obtained at different time intervals (15-120 minutes). ⁶⁸Ga-SCN-Bn-DOTA-capsaicin showed a cellular uptake of 0.93% Injected Dose (ID) after 30 minutes of incubation, whereas ⁶⁸Ga-SCN-Bn-DOTA showed a lower uptake of 0.25% ID. The tumor-to-blood ID/g% ratios increased and were found to be 0.49, 0.22, and 0.77 for 15, 30, and 60 minutes, respectively. The small-animal PET study showed that the uptake of ⁶⁸Ga-SCN-Bn-DOTA-capsaicin was higher in the tumor regions even at 30 minutes after injection. These results suggest that ⁶⁸Ga-SCN-Bn-DOTA-capsaicin is a potential targeting agent for PET imaging of MCF-7.

Weight Multispectral Reconstruction Strategy for Enhanced Reconstruction Accuracy and Stability With Cerenkov Luminescence Tomography

Cerenkov luminescence tomography (CLT) provides a novel technique for 3-D noninvasive detection of radiopharmaceuticals in living subjects. However, because of the severe scattering of Cerenkov light, the reconstruction accuracy and stability of CLT is still unsatisfied. In this paper, a modified weight multispectral CLT (wmCLT) reconstruction strategy was developed which split the Cerenkov radiation spectrum into several sub-spectral bands and weighted the sub-spectral results to obtain the final result. To better evaluate the property of the wmCLT reconstruction strategy in terms of accuracy, stability and practicability, several numerical simulation experiments and in vivo experiments were conducted and the results obtained were compared with the traditional multispectral CLT (mCLT) and hybrid-spectral CLT (hCLT) reconstruction strategies. The numerical simulation results indicated that wmCLT strategy significantly improved the accuracy of Cerenkov source localization and intensity quantitation and exhibited good stability in suppressing noise in numerical simulation experiments. And the comparison of the results achieved from different in vivo experiments further indicated significant improvement of the wmCLT strategy in terms of the shape recovery of the bladder and the spatial resolution of imaging xenograft tumors. Overall the strategy reported here will facilitate the development of nuclear and optical molecular tomography in theoretical study.

64Cu-PSMA-617: A novel PSMA-targeted radio-tracer for PET imaging in gastric adenocarcinoma xenografted mice model

Here, we report that it's feasible for imaging gastric adenocarcinoma mice model with prostate-specific membrane antigen (PSMA) targeting imaging agents, which could potentially provide an alternate and readily translational tool for managing gastric adenocarcinoma. DKFZ-PSMA-617, a PSMA targeting ligand reported recently, was chosen to be radio-labeled with nuclide ⁶⁴Cu. ⁶⁴Cu-PSMA-617 was radio-synthesized in high radio-chemical yield and specific activity up to 19.3 GBq/µmol. It showed good stability in vitro. The specificity of ⁶⁴Cu-PSMA-617 was confirmed by cell uptake experiments in PSMA (+) LNCaP cell and PSMA (-) PC-3 and gastric adenocarcinoma BGC-823 cells. Micro-PET imaging in BGC-823 and PC-3 xenografts nude mice was evaluated (n = 4). And the tumors were visualized and better tumor-to-background achieved till 24 h. Co-administration of N- [[[(1S)-1-Carboxy-3-methylbutyl]amino]-carbonyl]-L-glutamic acid (ZJ-43) can substantially block the uptake in those tumors. Dissected tumor tissues were analyzed by auto-radiography and immunohistochemistry, and these results confirmed the PSMA expression in neo-vasculature which explained the target molecular imaging of ⁶⁴Cu-PSMA-617. All those results suggested ⁶⁴Cu-PSMA-617 may serve as a novel radio-tracer for tumor imaging more than prostate cancer.

Increased expression of calponin 2 is a positive prognostic factor in pancreatic ductal adenocarcinoma

Calponin 2 plays an important role in regulating actin cytoskeleton, which is critical for cell division and migration. Previous studies have demonstrated that calponin 2 inhibits prostate cancer cell proliferation and metastasis. However, the role of calponin 2 in pancreatic tumor growth, metastasis and patient survival remains unclear. Here, we demonstrate that the level of calponin 2 is a positive prognostic factor for patients with pancreatic ductal adenocarcinoma (PDAC). Patients with high calponin 2 expression in the tumor presented less lymph node metastasis and longer survival. Knockdown of calponin 2 facilitated pancreatic cancer cell proliferation and metastasis. Further experiments suggested that PI3K/AKT, NF-κB, Vimentin, Fibronectin, Snail and Slug were upregulated and E-cadherin was downregulated after calponin 2 was knocked down, implicating altered functions in PDAC proliferation and metastasis. In addition, we verified that calponin 2 functioned through inhibiting PI3K/AKT and NF-κB pathways. Our study suggests that the upregulation of calponin 2 in PDAC correlates to lower malignancy and presents a novel target for the development of new treatment.

Secreted frizzled-related protein 1 overexpression in gastric cancer: Relationship with radiological findings of dual-energy spectral CT and PET-CT

We explored the role of secreted frizzled-related protein 1 (sFRP1) overexpression in gastric cancer and its relationship with radiological findings from dual-energy spectral CT(DEsCT) and positron emission tomography/computed tomography (PET/CT). We established mouse metastatic models using the SGC-7901/sFRP1 gastric cancer cell line. A control group was established using the SGC-7901/vector cell line. The models were then scanned with dual-energy spectral CT and PET-CT. Subsequent analysis, including immunohistochemistry and Transferase-mediated deoxyuridine triphosphate-biotin nick end labelling (TUNEL), was performed to confirm the role of sFRP1. Transwell chamber and angiogenesis assays were conducted to verify the effect of sFRP1 in vitro. We found that the control group showed negative radiological performance with successful implantation. Concurrently, the treated group showed visible lesions, a higher FDG uptake and increasing enhancement. The immunological and histological analysis confirmed the positive radiological performance with larger size, increasing proliferation, more microvessels and less apoptosis. The angiogenic up-regulation of sFRP1 overexpression were further verified with in vitro cell models. This preliminary study demonstrates that sFRP1 overexpression in gastric cancer cells leads to increased cell proliferation and angiogenesis, which may, in turn, contribute to positive PET/CT and CT performances.

Noninvasive detection of gastric cancer

Gastric cancer (GC) is the fifth most common cancer and the third common cause of cancer death worldwide. Endoscopy is the most effective method for GC screening, but its application is limited by the invasion. Therefore, continuous efforts have been made to develop noninvasive methods for GC detection and promising results have been reported. Here, we review the advances in GC detection by protein and nucleic acid tumor markers, circulating tumor cells, and tumor-associated autoantibodies in peripheral blood. Some potential new noninvasive methods for GC detection are also reviewed, including exhaled breath analysis, blood spectroscopy analysis and molecular imaging.

Identification of CEACAM5 as a Biomarker for Prewarning and Prognosis in Gastric Cancer

MGd1, a monoclonal antibody raised against gastric cancer cells, possesses a high degree of specificity for gastric cancer (GC). Here we identified that the antigen of MGd1 is CEACAM5, and used MGd1 to investigate the expression of CEACAM5 in non-GC and GC tissues (N=643), as a biomarker for prewarning and prognosis. The expression of CEACAM5 was detected by immunohistochemistry in numerous tissues; its clinicopathological correlation was statistically analyzed. CEACAM5 expression was increased progressively from normal gastric mucosa to chronic atrophic gastritis, intestinal metaplasia, dysplasia and finally to GC (p<0.05). In gastric precancerous lesions (intestinal metaplasia and dysplasia), CEACAM5-positive patients had a higher risk of developing GC as compared with CEACAM5-negative patients (OR = 12.68, p<0.001). Besides, CEACAM5 was found positively correlated with invasion depth of gastric adenocarcinoma (p<0.001). In survival analysis, CEACAM5 was demonstrated to be an independent prognostic predictor for patients with GC of clinical stage IIIA/IV (p=0.033). Our results demonstrate that CEACAM5 is a promising biomarker for GC prewarning and prognostic evaluation.