Imaging and biodistribution of Her2/neu expression in non-small cell lung cancer xenografts with Cu-labeled trastuzumab PET

The diagnostic value of 68Ga-NOTA-MAL-Cys-MZHER2:342 PET/CT imaging for HER2-positive lung adenocarcinoma

Background

The human epidermal growth factor receptor 2 gene (HER2) has been identified as a potential therapeutic target in lung adenocarcinoma (LUAD). Non-invasive positron emission tomography (PET) imaging provides a reliable strategy for in vivo determination of HER2 expression through whole-body detection of abnormalities. The PET tracer 68Ga-NOTA-MAL-Cys-MZHER2:342 has shown promising results for HER2-positive breast and gastric cancers. This study aims to evaluate the performance of 68Ga-NOTA-MAL-Cys-MZHER2:342 in vitro and in vivo models and in clinical patients with HER2-positive LUAD.

Methods

NOTA-MAL-Cys-MZHER2:342 was synthesized and labeled with 68Ga. Cell uptake, cell binding ability, and stability studies of 68Ga-NOTA-MAL-Cys-MZHER2:342 were assessed both in the Calu-3 lung cancer (LC) cell line and normal mice. In vivo assessment in tumor-bearing mice was conducted using microPET imaging and biodistribution experiments. Additionally, preliminary PET/CT imaging analysis was performed on HER2-positive LC patients.

Results

68Ga-NOTA-MAL-Cys-MZHER2:342 was prepared with a radiochemical purity (RCP) exceeding 95%. The tracer demonstrated high cell uptake in HER2-overexpressing Calu-3 cells, with an IC50 of 158.9, an adequate 1.73 nM. Good stability was exhibited both in vitro and in vivo. MicroPET imaging of Calu-3-bearing mice revealed high tumor uptake and notable tumor-to-background ratios. Positive outcomes were also observed in two HER2-positive LUAD patients.

Conclusion

68Ga-NOTA-MAL-Cys-MZHER2:342 demonstrated satisfactory stability, sensitivity, and specificity. These findings suggest that 68Ga-NOTA-MAL-Cys-MZHER2:342 PET/CT imaging provides a novel tool for non-invasive visual assessment of HER2 expression in LUAD patients.

Reduction of the hepatic radioactivity levels of [111In]In-DOTA-labeled antibodies via cleavage of a linkage metabolized in lysosomes

INTRODUCTION

Radiolabeled antibodies are promising tools for cancer diagnosis using nuclear medicine. A DOTA-chelating system is useful for preparing immuno-positron emission tomography and immuno-single-photon emission computed tomography probes with various radiometals. Radiolabeled antibodies are generally metabolized in the reticuloendothelial system, producing radiometabolites after proteolysis in hepatic lysosomes. Because of the bulkiness and extremely high hydrophilicity of DOTA, radiometabolites containing a radiometal-DOTA complex typically exhibit high and persistent localization in hepatic lysosomes. Radioactivity in the liver impairs the accurate diagnosis of cancer surrounding the liver and liver metastasis, and a high tumor/liver ratio is desirable. In this study, we reduced the hepatic radioactivity of radiometal-labeled antibodies containing a DOTA-chelating system. A cleavable linkage was inserted to liberate the radiometabolite, which exhibited a short residence time in hepatocytes.

METHODS

Using indium-111 (111In)-labeled antibodies, we prepared 111In-labeled galactosyl-neoglycoalbumins (NGAs) because they are useful for evaluating the residence time of radiometabolites in the liver. An 111In-labeled NGA with a cleavable linkage ([111In]In-DO3AiBu-Bn-FGK-NGA) was administered to normal mice, and biodistribution studies and metabolic analyses of urinary and fecal samples were performed with comparison to an 111In-labeled NGA prepared by a conventional method ([111In]In-DOTA-Bn-SCN-NGA). Then, 111In-labeled antibodies ([111In]In-DO3AiBu-Bn-FGK-IgG and [111In]In-DOTA-Bn-SCN-IgG) were prepared using a procedure similar to that for 111In-labeled NGAs. In vitro plasma stability and biodistribution were investigated for both 111In-labeled antibodies in U87MG tumor-bearing mice.

RESULTS

Through the liberation of radiometabolites including [111In]In-DO3AiBu-Bn-F, [111In]In-DO3AiBu-Bn-FGK-NGA was cleared more rapidly from the liver than [111In]In-DOTA-Bn-SCN-NGA (4.07 ± 1.54%ID VS 71.68 ± 3.03%ID at 6 h postinjection). [111In]In-DO3AiBu-Bn-FGK-IgG exhibited lower tumor accumulation (8.83 ± 1.48%ID/g) but a significantly higher tumor/liver ratio (2.21 ± 0.53) than [111In]In-DOTA-Bn-SCN-IgG (11.65 ± 2.17%ID/g in the tumor and a tumor/liver ratio of 0.85 ± 0.18) at 72 h after injection.

CONCLUSION

A molecular design that reduces the high and persistent hepatic radioactivity of radiolabeled antibodies by liberating radiometabolites with a short hepatic residence time in lysosomes would be applicable for radiometal-labeled antibodies using a DOTA-chelating system.

PET Imaging of Lung Cancers in Precision Medicine: Current Landscape and Future Perspective

Despite the recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Immunotherapies using immune checkpoint inhibitors (ICIs) achieved substantial efficacy in nonsmall cell lung cancer (NSCLC). Currently, most ICIs are still a monoclonal antibody (mAb). Using mAbs or antibody derivatives labeled with radionuclide as the tracers, immunopositron emission tomography (immunoPET) possesses multiple advantages over traditional ¹⁸F-FDG PET in imaging lung cancers. ImmunoPET presents excellent potential in detecting, diagnosing, staging, risk stratification, treatment guidance, and recurrence monitoring of lung cancers. By using radiolabeled mAbs, immunoPET can visualize the biodistribution and uptake of ICIs, providing a noninvasive modality for patient stratification and response evaluation. Some novel targets and associated tracers for immunoPET have been discovered and investigated. This Review introduces the value of immunoPET in imaging lung cancers by summarizing both preclinical and clinical evidence. We also emphasize the value of immunoPET in optimizing immunotherapy in NSCLC. Lastly, immunoPET probes developed for imaging small cell lung cancer (SCLC) will also be discussed. Although the major focus is to summarize the immunoPET tracers for lung cancers, we also highlighted several small-molecule PET tracers to give readers a balanced view of the development status.

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.

Pre-Clinical Study of the [18F]AlF-Labeled HER2 Affibody for Non-Invasive HER2 Detection in Gastric Cancer

Human epidermal growth factor receptor 2 (HER2) is an important biomarker in gastric cancer (GC) and directly influences the therapeutic effect. Fluorine is firmly bound to Al³⁺ forming [¹⁸F]AlF-1,4,7-triazacyclononanetriacetic acid (NOTA)-HER2 affibody is a promising radiolabeled tracer that can monitor the changes of HER2 expression combining the advantages of simple preparation and the properties of ¹⁸F. The aim of this study was to develop a quick method for the synthesis of [¹⁸F]AlF-NOTA-HER2 affibody and evaluate its utility for HER2+ GC imaging in mouse models. Moreover, ⁶⁸Ga-NOTA-HER2 affibody imaging was also performed to highlight the superiority of [¹⁸F]AlF-NOTA-HER2 affibody imaging in resolution. The HER2 affibody was conjugated with NOTA and labeled using ¹⁸F based on the complexation of [¹⁸F]AlF by NOTA. Its quality control and stability were performed by high-pressure liquid chromatography (HPLC). The molecular specificity and binding affinity of the novel radiotracer were evaluated in the GC cell line with HER2 overexpression (NCI-N87) and negative expression (MKN74). Distribution studies and PET/CT imaging were performed in mouse models. ⁶⁸Ga-NOTA-HER2 affibody PET/CT imaging was also performed. [¹⁸F]AlF-NOTA-HER2 affibody was efficiently prepared within 30 min with a non-decay-corrected maximum yield of 32.69% and a radiochemical purity of more than 98%. [¹⁸F]AlF-NOTA-HER2 affibody was highly stable in incubation medium for 4 h in vitro and in the blood of nude mice at 30 min post-injection (p.i.). In vitro studies revealed specific binding and high binding affinity of the probe in NCI-N87 cells, while no binding was seen in MKN74 cells. PET imaging showed that NCI-N87 xenografts were differentiated from MKN74 xenografts with excellent contrast and low abdominal background, which was confirmed by the distribution results. High-level accumulation of the [¹⁸F]AlF-NOTA-HER2 affibody in HER2+ tumors was blocked by excess unlabeled NOTA-HER2 affibody. [¹⁸F]AlF-NOTA-HER2 affibody has a higher image resolution than that of ⁶⁸Ga-NOTA-HER2 affibody. [¹⁸F]AlF-NOTA-HER2 affibody could be produced facilely with high radiochemical yield and may serve as a novel molecular probe with tremendous clinical potential for the non-invasive whole-body detection of the HER2 status in GC with good image contrast and resolution. This method could provide an in vivo understanding of GC biology that will ultimately guide the accurate diagnosis and treatment of GC.

Targeted alpha immunotherapy of CD20-positive B-cell lymphoma model: dosimetry estimate of 225Ac-DOTA-rituximab using 64Cu-DOTA-rituximab

OBJECTIVE

The aim of this study was to evaluate the radiation dosimetry of alpha-emitter 225Ac-DOTA-rituximab using Monte Carlo simulation of 64Cu-DOTA-rituximab.

METHODS

CD20 expression was evaluated in lymphoma cell lines (Jurkat and Raji). DOTA-rituximab was conjugated and then chelated by 64Cu. Tumor xenograft models were established in BALB/c-nu mice. Animal PET/CT imaging was obtained after tail vein injection with and without a pre-dose of 2 mg of cold rituximab. Specific binding of tumors was evaluated by an organ distribution assay and autoradiography. CD20 expression in tumor tissues was evaluated by immunohistochemistry. The residence time was calculated using 64Cu-DOTA-rituximab PET/CT acquisition data using OLINDA/EXM software. 225Ac-DOTA-rituximab tumor dosimetry was performed using Monte Carlo simulation with 64Cu-DOTA-rituximab PET/CT images.

RESULTS

Specific binding of Raji cells (CD20 positive) was 90 times that of Jurkat cells (CD20 negative) (p < 0.0001). Immunoreactivity was more than 75%. PET/CT imaging with 64Cu-DOTA-rituximab was specifically observed in tumors. The radioactivity of the tumor was much higher than that of other organs, and tumor uptake was related to CD20 expression. The predicted human dose for the administration of 64Cu-DOTA-rituximab was measured as the effective dose (1.07E-02 mSv/MBq). In the tumor region, equivalent doses of 225Ac-DOTA-rituximab (14 SvRBE5/MBq) were much higher (74-fold) than those of 64Cu-DOTA-rituximab (0.19 SvRBE5/MBq) (p < 0.01).

CONCLUSION

Tumor dosimetry of 225Ac-DOTA-rituximab can be estimated via the Monte Carlo simulation of 64Cu-DOTA-rituximab. 225Ac-DOTA-rituximab can be employed for lymphoma as targeted alpha therapy.

PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology

The human epidermal growth factor receptor family (EGFR-family, other designations: HER family, RTK Class I) is strongly linked to oncogenic transformation. Its members are frequently overexpressed in cancer and have become attractive targets for cancer therapy. To ensure effective patient care, potential responders to HER-targeted therapy need to be identified. Radionuclide molecular imaging can be a key asset for the detection of overexpression of EGFR-family members. It meets the need for repeatable whole-body assessment of the molecular disease profile, solving problems of heterogeneity and expression alterations over time. Tracer development is a multifactorial process. The optimal tracer design depends on the application and the particular challenges of the molecular target (target expression in tumors, endogenous expression in healthy tissue, accessibility). We have herein summarized the recent preclinical and clinical data on agents for Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) imaging of EGFR-family receptors in oncology. Antibody-based tracers are still extensively investigated. However, their dominance starts to be challenged by a number of tracers based on different classes of targeting proteins. Among these, engineered scaffold proteins (ESP) and single domain antibodies (sdAb) show highly encouraging results in clinical studies marking a noticeable trend towards the use of smaller sized agents for HER imaging.

Successful Application of CuAAC Click Reaction in Constructing 64Cu-Labeled Antibody Conjugates for Immuno-PET Imaging

Immuno-positron emission tomography (immuno-PET) is a rapidly growing imaging technique in which antibodies are radiolabeled to monitor their in vivo behavior in real time. However, effecting the controlled conjugation of a chelate-bearing radioactive atom to a bulky antibody without affecting its immunoreactivity at a specific site is always challenging. The in vivo stability of the radiolabeled chelate is also a key issue for successful tumor imaging. To address these points, a facile ultra-stable radiolabeling platform is developed by using the propylene cross-bridged chelator (PCB-TE2A-alkyne), which can be instantly functionalized with various groups via the click reaction, thus enabling specific conjugation with antibodies as per choice. The PCB-TE2A-tetrazine derivative is selected to demonstrate the proposed strategy. The antibody trastuzumab is functionalized with the trans-cyclooctene (TCO) moiety in the presence or absence of the PEG linker. The complementary ⁶⁴Cu-PCB-TE2A-tetrazine is synthesized via the click reaction and radiolabeled with ⁶⁴Cu ions, which then reacts with the aforementioned TCO-modified antibody via a rapid biorthogonal ligation. The ⁶⁴Cu-PCB-TE2A-trastuzumab conjugate is shown to exhibit excellent in vivo stability and to maintain a higher binding affinity toward HER2-positive cells. The tumor targeting feasibility of the radiolabeled antibody is evaluated in tumor models. Both ⁶⁴Cu-PCB-TE2A-trastuzumab conjugates show high tumor uptakes in biodistribution studies and enable unambiguous tumor visualization with minimum background noise in PET imaging. Interestingly, the ⁶⁴Cu-PCB-TE2A-PEG₄-trastuzumab containing an additional PEG linker displays a much faster body clearance compared to its counterpart with less PEG linker, thus affording vivid tumor imaging with an unprecedentedly high tumor-to-background ratio.

Radiochemistry, Production Processes, Labeling Methods, and ImmunoPET Imaging Pharmaceuticals of Iodine-124

Target-specific biomolecules, monoclonal antibodies (mAb), proteins, and protein fragments are known to have high specificity and affinity for receptors associated with tumors and other pathological conditions. However, the large biomolecules have relatively intermediate to long circulation half-lives (>day) and tumor localization times. Combining superior target specificity of mAbs and high sensitivity and resolution of the PET (Positron Emission Tomography) imaging technique has created a paradigm-shifting imaging modality, ImmunoPET. In addition to metallic PET radionuclides, 124I is an attractive radionuclide for radiolabeling of mAbs as potential immunoPET imaging pharmaceuticals due to its physical properties (decay characteristics and half-life), easy and routine production by cyclotrons, and well-established methodologies for radioiodination. The objective of this report is to provide a comprehensive review of the physical properties of iodine and iodine radionuclides, production processes of 124I, various 124I-labeling methodologies for large biomolecules, mAbs, and the development of 124I-labeled immunoPET imaging pharmaceuticals for various cancer targets in preclinical and clinical environments. A summary of several production processes, including 123Te(d,n)124I, 124Te(d,2n)124I, 121Sb(α,n)124I, 123Sb(α,3n)124I, 123Sb(3He,2n)124I, natSb(α, xn)124I, natSb(3He,n)124I reactions, a detailed overview of the 124Te(p,n)124I reaction (including target selection, preparation, processing, and recovery of 124I), and a fully automated process that can be scaled up for GMP (Good Manufacturing Practices) production of large quantities of 124I is provided. Direct, using inorganic and organic oxidizing agents and enzyme catalysis, and indirect, using prosthetic groups, 124I-labeling techniques have been discussed. Significant research has been conducted, in more than the last two decades, in the development of 124I-labeled immunoPET imaging pharmaceuticals for target-specific cancer detection. Details of preclinical and clinical evaluations of the potential 124I-labeled immunoPET imaging pharmaceuticals are described here.

Observations on the Effects of Residualization and Dehalogenation on the Utility of N-Succinimidyl Ester Acylation Agents for Radioiodination of the Internalizing Antibody Trastuzumab

Trastuzumab is an antibody used for the treatment of human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancers. Since trastuzumab is an internalizing antibody, two factors could play an important role in achieving high uptake and prolonged retention of radioactivity in HER2-positive tumors after radioiodination-residualizing capacity after receptor-mediated internalization and susceptibility to dehalogenation. To evaluate the contribution of these two factors, trastuzumab was radiolabeled using the residualizing reagent N-succinimidyl 4-guanidinomethyl-3-[*I]iodobenzoate ([*I]SGMIB) and the nonresidualizing reagent N-succinimidyl-3-[*I]iodobenzoate ([*I]SIB), both of which are highly dehalogenation-resistant. Paired-label uptake and intracellular retention of [¹²⁵I]SGMIB-trastuzumab and [¹³¹I]SIB-trastuzumab was compared on HER2-expressing BT474 human breast carcinoma cells. Tumor uptake and normal tissue distribution characteristics for the two labeled conjugates were assessed in mice bearing BT474M1 xenografts. The internalization and intracellular retention of initially-bound radioactivity in BT474 cells was similar for the two labeled conjugates up to 4 h, but were significantly higher for [¹²⁵I]SGMIB-trastuzumab at 6 and 24 h. Similarly, [*I]SGMIB labeling resulted in significantly higher uptake and retention of radioactivity in BT474M1 xenografts at all studied time points. Moreover, tumor-to-tissue ratios for [¹²⁵I]SGMIB-trastuzumab were consistently higher than those for [¹³¹I]SIB-trastuzumab starting at 12 h postinjection. Thus, optimal targeting of HER2-positive breast cancers with a radioiodinated trastuzumab conjugate requires an acylation agent that imparts residualizing capacity in addition to high stability towards dehalogenation in vivo.

Development of 64Cu-NOTA-Trastuzumab for HER2 Targeting: A Radiopharmaceutical with Improved Pharmacokinetics for Human Studies

The purpose of this study was to develop ⁶⁴Cu-labeled trastuzumab with improved pharmacokinetics for human epidermal growth factor receptor 2 (HER2). Methods: Trastuzumab was conjugated with SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu. Serum stability and immunoreactivity of ⁶⁴Cu-NOTA-trastuzumab were tested. Small-animal PET imaging and biodistribution studies were performed in a HER2-positive breast cancer xenograft model (BT-474). The internal dosimetry for experimental animals was determined using the image-based approach with the Monte Carlo N-particle code. Results: ⁶⁴Cu-NOTA-trastuzumab was prepared with high radiolabeling yield and radiochemical purity (>98%) and showed high stability in serum and good immunoreactivity. Uptake of ⁶⁴Cu-NOTA-trastuzumab was highest at 48 h after injection as determined by PET imaging and biodistribution results in BT-474 tumors. The blood radioactivity concentrations of ⁶⁴Cu-NOTA-trastuzumab decreased biexponentially with time in both mice with and mice without BT-474 tumor xenografts. The calculated absorbed dose of ⁶⁴Cu-NOTA-trastuzumab was 0.048 mGy/MBq for the heart, 0.079 mGy/MBq for the liver, and 0.047 mGy/MBq for the spleen. Conclusion: ⁶⁴Cu-NOTA-trastuzumab was effectively targeted to the HER2-expressing tumor in vitro and in vivo, and it exhibited a relatively low absorbed dose due to a short residence time. Therefore, ⁶⁴Cu-NOTA-trastuzumab could be applied to select the right patients and right timing for HER2 therapy, to monitor the treatment response after HER2-targeted therapy, and to detect distal or metastatic spread.

18F-AlF Labeled Peptide and Protein Conjugates as Positron Emission Tomography Imaging Pharmaceuticals

The clinical applications of positron emission tomography (PET) imaging pharmaceuticals have increased tremendously over the past several years since the approval of ¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) by the Food and Drug Administration (FDA). Numerous ¹⁸F-labeled target-specific potential imaging pharmaceuticals, based on small and large molecules, have been evaluated in preclinical and clinical settings. ¹⁸F-labeling of organic moieties involves the introduction of the radioisotope by C-¹⁸F bond formation via a nucleophilic or an electrophilic substitution reaction. However, biomolecules, such as peptides, proteins, and oligonucleotides, cannot be radiolabeled via a C-¹⁸F bond formation as these reactions involve harsh conditions, including organic solvents, high temperature, and nonphysiological conditions. Several approaches, including ¹⁸F-labeled prosthetic groups, silicon, boron, and aluminum fluoride acceptor chemistry, and click chemistry have been developed, in the past, for ¹⁸F labeling of biomolecules. Linear and macrocyclic polyaminocarboxylates and their analogs and derivatives form thermodynamically stable and kinetically inert aluminum chelates. Hence, macrocyclic polyaminocarboxylates have been used for conjugation with biomolecules, such as folate, peptides, affibodies, and protein fragments, followed by ¹⁸F-AlF chelation, and evaluation of their targeting abilities in preclinical and clinical environments. The goal of this report is to provide an overview of the ¹⁸F radiochemistry and ¹⁸F-labeling methodologies for small molecules and target-specific biomolecules, a comprehensive review of coordination chemistry of Al³⁺, ¹⁸F-AlF labeling of peptide and protein conjugates, and evaluation of ¹⁸F-labeled biomolecule conjugates as potential imaging pharmaceuticals.

[(64) Cu]-labelled trastuzumab: optimisation of labelling by DOTA and NODAGA conjugation and initial evaluation in mice

The human epidermal growth factor receptor‐2 (HER2) is overexpressed in 20–30% of all breast cancer cases, leading to increased cell proliferation, growth and migration. The monoclonal antibody, trastuzumab, binds to HER2 and is used for treatment of HER2‐positive breast cancer. Trastuzumab has previously been labelled with copper‐64 by conjugation of a 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) chelator. The aim of this study was to optimise the ⁶⁴Cu‐labelling of DOTA‐trastuzumab and as the first to produce and compare with its 1,4,7‐triazacyclononane, 1‐glutaric acid‐5,7 acetic acid (NODAGA) analogue in a preliminary HER2 tumour mouse model. The chelators were conjugated to trastuzumab using the activated esters DOTA mono‐N‐hydroxysuccinimide (NHS) and NODAGA‐NHS. ⁶⁴Cu‐labelling of DOTA‐trastuzumab was studied by varying the amount of DOTA‐trastuzumab used, reaction temperature and time. Full ⁶⁴Cu incorporation could be achieved using a minimum of 10‐µg DOTA‐trastuzumab, but the fastest labelling was obtained after 15 min at room temperature using 25 µg of DOTA‐trastuzumab. In comparison, 80% incorporation was achieved for ⁶⁴Cu‐labelling of NODAGA‐trastuzumab. Both [⁶⁴Cu]DOTA‐trastuzumab and [⁶⁴Cu]NODAGA‐trastuzumab were produced after purification with radiochemical purities of >97%. The tracers were injected into mice with HER2 expressing tumours. The mice were imaged by positron emission tomography and showed high tumour uptake of 3–9% ID/g for both tracers.

New bifunctional chelator for 64Cu-immuno-positron emission tomography

A new tetraazamacrocyclic bifunctional chelator, TE2A-Bn-NCS, was synthesized in high overall yield from cyclam. An extra functional group (NCS) was introduced to the N-atom of TE2A for specific conjugation with antibody. The Cu complex of TE2A-Bn-NCS showed high kinetic stability in acidic decomplexation and cyclic voltammetry studies. X-ray structure determination of the Cu-TE2A-Bn-NH2 complex confirmed octahedral geometry, in which copper atom is strongly coordinated by four macrocyclic nitrogens in equatorial positions and two carboxylate oxygen atoms occupy the elongated axial positions. Trastuzumab was conjugated with TE2A-Bn-NCS and then radiolabeled with 64Cu quantitatively at room temperature within 10 min. Biodistribution studies showed that the 64Cu-labeled TE2A-Bn-NCS-trastuzumab conjugates maintain high stability in physiological conditions, and NIH3T6.7 tumors were clearly visualized up to 3 days by 64Cu-immuno-positron emission tomography imaging in animal models.

Antibody-based imaging of HER-2: moving into the clinic

Human epidermal growth factor receptor-2 (HER-2) mediates a number of important cellular activities, and is up-regulated in a diverse set of cancer cell lines, especially breast cancer. Accordingly, HER-2 has been regarded as a common drug target in cancer therapy. Antibodies can serve as ideal candidates for targeted tumor imaging and drug delivery, due to their inherent affinity and specificity. Advanced by the development of a wide variety of imaging techniques, antibody-based imaging of HER-2 can allow for early detection and localization of tumors, as well as monitoring of drug delivery and tissue's response to drug treatment. In this review article, antibody-based imaging of HER-2 are summarized and discussed, with an emphasis on the involved imaging methods.

Detection of vascular endothelial growth factor in colon cancer xenografts using bevacizumab based near infrared fluorophore conjugate

Background

The aim of this study was to develop the near infrared fluorescence (NIRF)-based imaging agent for the visualization of vascular endothelial growth factor (VEGF) in colon cancer. AlexaFluor 750 conjugating with bevacizumab, and injected intravenously into nude mice bearing VEGF over-expressing HT29 human colorectal cancer. Optical imaging was performed at 15 min, 24 h and 48 h post injection. Immunofluorescences staining of the tumor sections were performed. HT29 colorectal cancer xenografts were clearly visualized with bevacizumab-AlexaFluor 750.

Results

Ex vivo analysis showed 2.1 ± 0.4%, 37.6 ± 6.3% and 38.5 ± 6.2% injected dose/g accumulated in the tumors at 15 min, 24 h and 48 h respectively. Tumor uptake was significantly decreased in pretreated with excess of bevacizumab (p = 0.002). Immunofluorescence analysis showed strong staining of anti-CD 31 antibody around the blood vessels. Anti-VEGF-A and bevacizumab showed heterogeneous expression throughout the tumor.

Conclusions

Current study successfully detected the VEGF expression in HT29 colorectal cancer xenografts, signifying as a potential agent for non-invasive imaging of VEGF expression, which may be applied in clinical practice.

Controlled administration of penicillamine reduces radiation exposure in critical organs during 64Cu-ATSM internal radiotherapy: a novel strategy for liver protection

Purpose

⁶⁴Cu-diacetyl-bis (N⁴-methylthiosemicarbazone) (⁶⁴Cu-ATSM) is a promising theranostic agent that targets hypoxic regions in tumors related to malignant characteristics. Its diagnostic usefulness has been recognized in clinical studies. Internal radiotherapy (IRT) with ⁶⁴Cu-ATSM is reportedly effective in preclinical studies; however, for clinical applications, improvements to reduce radiation exposure in non-target organs, particularly the liver, are required. We developed a strategy to reduce radiation doses to critical organs while preserving tumor radiation doses by controlled administration of copper chelator penicillamine during ⁶⁴Cu-ATSM IRT.

Methods

Biodistribution was evaluated in HT-29 tumor-bearing mice injected with ⁶⁴Cu-ATSM (185 kBq) with or without oral penicillamine administration. The appropriate injection interval between ⁶⁴Cu-ATSM and penicillamine was determined. Then, the optimal penicillamine administration schedule was selected from single (100, 300, and 500 mg/kg) and fractionated doses (100 mg/kg×3 at 1- or 2-h intervals from 1 h after ⁶⁴Cu-ATSM injection). PET imaging was performed to confirm the effect of penicillamine with a therapeutic ⁶⁴Cu-ATSM dose (37 MBq). Dosimetry analysis was performed to estimate human absorbed doses.

Results

Penicillamine reduced ⁶⁴Cu accumulation in the liver and small intestine. Tumor uptake was not affected by penicillamine administration at 1 h after ⁶⁴Cu-ATSM injection, when radioactivity was almost cleared from the blood and tumor uptake had plateaued. Of the single doses, 300 mg/kg was most effective. Fractionated administration at 2-h intervals further decreased liver accumulation at later time points. PET indicated that penicillamine acts similarly with the therapeutic ⁶⁴Cu-ATSM dose. Dosimetry demonstrated that appropriately scheduled penicillamine administration reduced radiation doses to critical organs (liver, ovaries, and red marrow) below tolerance levels. Laxatives reduced radiation doses to the large intestine.

Conclusions

We developed a novel strategy to reduce radiation exposure in critical organs during ⁶⁴Cu-ATSM IRT, thus promoting its clinical applications. This method could be beneficial for other ⁶⁴Cu-labeled compounds.

Interrogating tumor metabolism and tumor microenvironments using molecular positron emission tomography imaging. Theranostic approaches to improve therapeutics

Positron emission tomography (PET) is a noninvasive molecular imaging technology that is becoming increasingly important for the measurement of physiologic, biochemical, and pharmacological functions at cellular and molecular levels in patients with cancer. Formation, development, and aggressiveness of tumor involve a number of molecular pathways, including intrinsic tumor cell mutations and extrinsic interaction between tumor cells and the microenvironment. Currently, evaluation of these processes is mainly through biopsy, which is invasive and limited to the site of biopsy. Ongoing research on specific target molecules of the tumor and its microenvironment for PET imaging is showing great potential. To date, the use of PET for diagnosing local recurrence and metastatic sites of various cancers and evaluation of treatment response is mainly based on [(18)F]fluorodeoxyglucose ([(18)F]FDG), which measures glucose metabolism. However, [(18)F]FDG is not a target-specific PET tracer and does not give enough insight into tumor biology and/or its vulnerability to potential treatments. Hence, there is an increasing need for the development of selective biologic radiotracers that will yield specific biochemical information and allow for noninvasive molecular imaging. The possibility of cancer-associated targets for imaging will provide the opportunity to use PET for diagnosis and therapy response monitoring (theranostics) and thus personalized medicine. This article will focus on the review of non-[(18)F]FDG PET tracers for specific tumor biology processes and their preclinical and clinical applications.

Determining efficacy of breast cancer therapy by PET imaging of HER2 mRNA

INTRODUCTION

Monitoring the effectiveness of therapy early and accurately continues to be challenging. We hypothesize that determination of Human Epidermal Growth Factor Receptor 2 (HER2) mRNA in malignant breast cancer (BC) cells by positron emission tomography (PET) imaging, before and after treatment, would reflect therapeutic efficacy.

METHOD

WT4340, a peptide nucleic acid (PNA) 12-mer complementary to HER2 mRNA was synthesized together with -CSKC, a cyclic peptide, which facilitated internalization of the PNA via IGFR expressed on BC cells, and DOTA that chelated Cu-64. Mice (n = 8) with BT474 ER+/HER2+ human BC received doxorubicin (DOX, 1.5mg/kg) i.p. once a week for six weeks. Mice (n = 8) without DOX served as controls. All mice were PET imaged with F-18-FDG and 48 h later with Cu-64-WT4340. PET imaging were performed before and 72 h after each treatment. Standardized uptake values (SUVs) were determined and percent change calculated. Animal body weight (BW) and tumor volume (TV) were measured.

RESULTS

SUVs for Cu-64-WT4340 after DOX treatment declined by 54% ± 17% after the second dose, 41% ± 15% after the fourth dose, and 29% ± 7% after the sixth dose, compared with 42% ± 22%, 31% ± 18%, and 13% ± 9% (p<0.05) for F-18-FDG. In untreated mice, the corresponding percent SUVs for Cu-64-WT4340 were 145% ± 82%, 165% ± 39%, and 212% ± 105% of pretreatment SUV, compared with 108% ± 28%, 151% ± 8%, and 152% ± 35.5%, (p<0.08) for F-18-FDG. TV in mice after second dose was 114.15% ± 61.83%, compared with 144.7% ± 64.4% for control mice. BW of DOX-treated mice was 103.4% ± 7.6% of pretreatment, vs. 100.1% ± 4.3% for control mice.

CONCLUSION

Therapeutic efficacy was apparent sooner by molecular PET imaging than by determination of reduction in TV.

Imaging EGFR and HER2 by PET and SPECT: a review

In an effort to discover a noninvasive method for predicting which cancer patients will benefit from therapy targeting the EGFR and HER2 proteins, a large body of the research has been conducted toward the development of PET and SPECT imaging agents, which selectively target these receptors. We provide a general overview of the advances made toward imaging EGFR and HER2, detailing the investigation of PET and SPECT imaging agents ranging in size from small molecules to monoclonal antibodies.

PET imaging with ⁸⁹Zr: from radiochemistry to the clinic

The advent of antibody-based cancer therapeutics has led to the concomitant rise in the development of companion diagnostics for these therapies, particularly nuclear imaging agents. A number of radioisotopes have been employed for antibody-based PET and SPECT imaging, notably ⁶⁴Cu, ¹²⁴I, ¹¹¹In, and (99m)Tc; in recent years, however, the field has increasingly focused on ⁸⁹Zr, a radiometal with near ideal physical and chemical properties for immunoPET imaging. In the review at hand, we seek to provide a comprehensive portrait of the current state of ⁸⁹Zr radiochemical and imaging research, including work into the production and purification of the isotope, the synthesis of new chelators, the development of new bioconjugation strategies, the creation of novel ⁸⁹Zr-based agents for preclinical imaging studies, and the translation of ⁸⁹Zr-labeled radiopharmaceuticals to the clinic. Particular attention will also be dedicated to emerging trends in the field, ⁸⁹Zr-based imaging applications using vectors other than antibodies, the comparative advantages and limitations of ⁸⁹Zr-based imaging compared to that with other isotopes, and areas that would benefit from more extensive investigation. At bottom, it is hoped that this review will provide both the experienced investigator and new scientist with a full and critical overview of this exciting and fast-developing field.

Comparison of (64)Cu-complexing bifunctional chelators for radioimmunoconjugation: labeling efficiency, specific activity, and in vitro/in vivo stability

High radiolabeling efficiency, preferably to high specific activity, and good stability of the radioimmunoconjugate are essential features for a successful immunoconjugate for imaging or therapy. In this study, the radiolabeling efficiency, in vitro stability, and biodistribution of immunoconjugates with eight different bifunctional chelators labeled with (64)Cu were compared. The anti-CD20 antibody, rituximab, was conjugated to four macrocyclic bifunctional chelators (p-SCN-Bn-DOTA, p-SCN-Bn-Oxo-DO3A, p-SCN-NOTA, and p-SCN-PCTA), three DTPA derivatives (p-SCN-Bn-DTPA, p-SCN-CHX-A″-DTPA, and ITC-2B3M-DTPA), and a macrobicyclic hexamine (sarcophagine) chelator (sar-CO2H) = (1-NH2-8-NHCO(CH2)3CO2H)sar where sar = sarcophagine = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane). Radiolabeling efficiency under various conditions, in vitro stability in serum at 37 °C, and in vivo biodistribution and imaging in normal mice over 48 h were studied. All chelators except sar-CO2H were conjugated to rituximab by thiourea bond formation with an average of 4.9 ± 0.9 chelators per antibody molecule. Sar-CO2H was conjugated to rituximab by amide bond formation with 0.5 chelators per antibody molecule. Efficiencies of (64)Cu radiolabeling were dependent on the concentration of immunoconjugate. Notably, the (64)Cu-NOTA-rituximab conjugate demonstrated the highest radiochemical yield (95%) under very dilute conditions (31 nM NOTA-rituximab conjugate). Similarly, sar-CO-rituximab, containing 1/10th the number of chelators per antibody compared to that of other conjugates, retained high labeling efficiency (98%) at an antibody concentration of 250 nM. In contrast to the radioimmunoconjugates containing DTPA derivatives, which demonstrated poor serum stability, all macrocyclic radioimmunoconjugates were very stable in serum with <6% dissociation of (64)Cu over 48 h. In vivo biodistribution profiles in normal female Balb/C mice were similar for all the macrocyclic radioimmunoconjugates with most of the activity remaining in the blood pool up to 48 h. While all the macrocyclic bifunctional chelators are suitable for molecular imaging using (64)Cu-labeled antibody conjugates, NOTA and sar-CO2H show significant advantages over the others in that they can be radiolabeled rapidly at room temperature, under dilute conditions, resulting in high specific activity.

Predicting cetuximab accumulation in KRAS wild-type and KRAS mutant colorectal cancer using 64Cu-labeled cetuximab positron emission tomography

Overexpression of epidermal growth factor receptor (EGFR) is common in colorectal cancer. However, cetuximab as an EGFR-targeting drug is useful only for a subset of patients and currently no single predictor other than V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation status has been established. In the present study, we investigated cetuximab accumulation in colorectal tumors and major organs using (111)In-DOTA-cetuximab. We also evaluated the potential of positron emission tomography (PET) imaging of (64)Cu-DOTA-cetuximab. Colorectal tumor xenografts with a different EGFR expression level and KRAS mutation status were subjected to in vivo biodistribution study and PET imaging at 48 h post-injection of radiolabeled cetuximab. The EGFR expression levels on colorectal tumors were determined by ex vivo immunoblotting and ELISA. We found that KRAS wild-type tumors had significantly higher (111)In-DOTA-cetuximab accumulation than KRAS mutant tumors (P < 0.001). Based on KRAS mutation status, a strong correlation was found between (111)In-DOTA-cetuximab tumor uptake and EGFR expression level (KRAS wild type: r = 0.988; KRAS mutant: r = 0.829), and between (64)Cu-DOTA-cetuximab tumor uptake with EGFR expression level (KRAS wild type: r = 0.838; KRAS mutant: r = 0.927). Significant correlation was also found between tumor uptake of (111)In-DOTA-cetuximab and (64)Cu-DOTA-cetuximab (r = 0.920). PET imaging with (64)Cu-DOTA-cetuximab allowed clear visualization of tumors. Both radiolabeled cetuximab had effectively visualized cetuximab accumulation in colorectal tumors with a wide variety of EGFR expression levels and different KRAS mutation status as commonly encountered in the clinical setting. Our findings suggest that this radioimmunoimaging therefore can be clinically translated as an in vivo tool to predict cetuximab accumulation in colorectal cancer patients prior to cetuximab therapy.

Imaging of human epidermal growth factor receptor type 2 expression with 18F-labeled affibody molecule ZHER2:2395 in a mouse model for ovarian cancer

Affibody molecules are small (7 kDa) proteins with subnanomolar targeting affinity. Previous SPECT studies in xenografts have shown that the Affibody molecule (111)In-DOTA-Z(HER2)(:2395) can discriminate between high and low human epidermal growth factor receptor type 2 (HER2)-expressing tumors, indicating that radiolabeled Affibody molecules have potential for patient selection for HER2-targeted therapy. Compared with SPECT, PET with positron-emitting radionuclides, such as (18)F, may improve imaging of HER2 expression because of higher sensitivity and improved quantification of PET. The aim of the present study was to determine whether the (18)F-labeled NOTA-conjugated Affibody molecule Z(HER2)(:2395) is a suitable agent for imaging of HER2 expression. The tumor-targeting properties of (18)F-labeled Z(HER2)(:2395) were compared with (111)In- and (68)Ga-labeled Z(HER2)(:2395) in mice with HER2-expressing SK-OV-3 xenografts.

METHODS

Z(HER2)(:2395) was conjugated with NOTA and radiolabeled with (18)F, (68)Ga, and (111)In. Radiolabeling with (18)F was based on the complexation of Al(18)F by NOTA. The 50% inhibitory concentration values for NOTA-Z(HER2)(:2395) labeled with (19)F, (69)Ga, and (115)In were determined in a competitive cell-binding assay using SK-OV-3 cells. Mice bearing subcutaneous SK-OV-3 xenografts were injected intravenously with radiolabeled NOTA-Z(HER2)(:2395). One and 4 h after injection, PET/CT or SPECT/CT images were acquired, and the biodistribution was determined by ex vivo measurement.

RESULTS

The 50% inhibitory concentration values for (19)F-, (69)Ga-, and (115)In-NOTA-Z(HER2)(:2395) were 5.0, 6.3, and 5.3 nM, respectively. One hour after injection, tumor uptake was 4.4 ± 0.8 percentage injected dose per gram (%ID/g), 5.6 ± 1.6 %ID/g, and 7.1 ± 1.4 %ID/g for (18)F-, (68)Ga-, and (111)In-NOTA-Z(HER2)(:2395), respectively, and the respective tumor-to-blood ratios were 7.4 ± 1.8, 8.0 ± 1.3, and 4.8 ± 1.3. Tumor uptake was specific, because uptake could be blocked efficiently by coinjection of an excess of unlabeled Z(HER2)(:2395). PET/CT and SPECT/CT images clearly visualized HER2-expressing SK-OV-3 xenografts.

CONCLUSION

This study showed that (18)F-NOTA-Z(HER2)(:2395) is a promising new imaging agent for HER2 expression in tumors. Affibody molecules were successfully labeled with (18)F within 30 min, based on the complexation of Al(18)F by NOTA. Further research is needed to determine whether this technique can be used for patient selection for HER2-targeted therapy.

Modular strategy for the construction of radiometalated antibodies for positron emission tomography based on inverse electron demand Diels-Alder click chemistry

A modular system for the construction of radiometalated antibodies was developed based on the bioorthogonal cycloaddition reaction between 3-(4-benzylamino)-1,2,4,5-tetrazine and the strained dienophile norbornene. The well-characterized, HER2-specific antibody trastuzumab and the positron emitting radioisotopes ⁶⁴Cu and ⁸⁹Zr were employed as a model system. The antibody was first covalently coupled to norbornene, and this stock of norbornene-modified antibody was then reacted with tetrazines bearing the chelators 1,4,7,10-tetraazacyclo-dodecane-1,4,7,10-tetraacetic acid (DOTA) or desferrioxamine (DFO) and subsequently radiometalated with ⁶⁴Cu and ⁸⁹Zr, respectively. The modification strategy is simple and robust, and the resultant radiometalated constructs were obtained in high specific activity (2.7–5.3 mCi/mg). For a given initial stoichiometric ratio of norbornene to antibody, the ⁶⁴Cu-DOTA- and ⁸⁹Zr-DFO-based probes were shown to be nearly identical in terms of stability, the number of chelates per antibody, and immunoreactivity (>93% in all cases). In vivo PET imaging and acute biodistribution experiments revealed significant, specific uptake of the ⁶⁴Cu- and ⁸⁹Zr-trastuzumab bioconjugates in HER2-positive BT-474 xenografts, with little background uptake in HER2-negative MDA-MB-468 xenografts or other tissues. This modular system—one in which the divergent point is a single covalently modified antibody stock that can be reacted selectively with various chelators—will allow for both greater versatility and more facile cross-comparisons in the development of antibody-based radiopharmaceuticals.

A practical guide to the construction of radiometallated bioconjugates for positron emission tomography

Positron emission tomography (PET) has become a vital imaging modality in the diagnosis and treatment of disease, most notably cancer. A wide array of small molecule PET radiotracers have been developed that employ the short half-life radionuclides (11)C, (13)N, (15)O, and (18)F. However, PET radiopharmaceuticals based on biomolecular targeting vectors have been the subject of dramatically increased research in both the laboratory and the clinic. Typically based on antibodies, oligopeptides, or oligonucleotides, these tracers have longer biological half-lives than their small molecule counterparts and thus require labeling with radionuclides with longer, complementary radioactive half-lives, such as the metallic isotopes (64)Cu, (68)Ga, (86)Y, and (89)Zr. Each bioconjugate radiopharmaceutical has four component parts: biomolecular vector, radiometal, chelator, and covalent link between chelator and biomolecule. With the exception of the radiometal, a tremendous variety of choices exists for each of these pieces, and a plethora of different chelation, conjugation, and radiometallation strategies have been utilized to create agents ranging from (68)Ga-labeled pentapeptides to (89)Zr-labeled monoclonal antibodies. Herein, the authors present a practical guide to the construction of radiometal-based PET bioconjugates, in which the design choices and synthetic details of a wide range of biomolecular tracers from the literature are collected in a single reference. In assembling this information, the authors hope both to illuminate the diverse methods employed in the synthesis of these agents and also to create a useful reference for molecular imaging researchers both experienced and new to the field.

Challenges in inhaled product development and opportunities for open innovation

Dosimetry, safety and the efficacy of drugs in the lungs are critical factors in the development of inhaled medicines. This article considers the challenges in each of these areas with reference to current industry practices for developing inhaled products, and suggests collaborative scientific approaches to address these challenges. The portfolio of molecules requiring delivery by inhalation has expanded rapidly to include novel drugs for lung disease, combination therapies, biopharmaceuticals and candidates for systemic delivery via the lung. For these drugs to be developed as inhaled medicines, a better understanding of their fate in the lungs and how this might be modified is required. Harmonized approaches based on 'best practice' are advocated for dosimetry and safety studies; this would provide coherent data to help product developers and regulatory agencies differentiate new inhaled drug products. To date, there are limited reports describing full temporal relationships between pharmacokinetic (PK) and pharmacodynamic (PD) measurements. A better understanding of pulmonary PK and PK/PD relationships would help mitigate the risk of not engaging successfully or persistently with the drug target as well as identifying the potential for drug accumulation in the lung or excessive systemic exposure. Recommendations are made for (i) better industry-academia-regulatory co-operation, (ii) sharing of pre-competitive data, and (iii) open innovation through collaborative research in key topics such as lung deposition, drug solubility and dissolution in lung fluid, adaptive responses in safety studies, biomarker development and validation, the role of transporters in pulmonary drug disposition, target localisation within the lung and the determinants of local efficacy following inhaled drug administration.

Positron emission tomography imaging and biodistribution of vascular endothelial growth factor with 64Cu-labeled bevacizumab in colorectal cancer xenografts

Vascular endothelial growth factor (VEGF) is considered to be a major angiogenic factor responsible for the development of tumor vasculature. The aim of this study was to image VEGF expression with (64)Cu-labeled anti-VEGF antibody (bevacizumab) non-invasively, and to see whether or not the expression was correlated with tumor accumulation in colorectal cancer xenografts. Bevacizumab was conjugated with the bifunctional chelator 1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid (DOTA) and radiolabeled with (64)Cu. In vivo biodistribution studies and positron emission tomography (PET) imaging were performed on mice bearing human colorectal cancer (HT29) xenografts after injection of (64)Cu-DOTA-bevacizumab, which showed clear accumulation of (64)Cu-DOTA-bevacizumab in the tumor (22.7 ± 1.0 %ID/g, 24 ± 0.2 %ID/g, 19.0 ± 2.5 %ID/g at 24, 48 and 72 h, respectively). Tumor accumulation of (64)Cu-DOTA-bevacizumab was significantly correlated with VEGF expression as measured by western blot (ρ = 0.81, P = 0.004). Vascular endothelial growth factor blocking with unlabeled bevacizumab significantly reduced tumor accumulation of (64) Cu-DOTA- bevacizumab (9.7 ± 1.2 %ID/g, P < 0.001) at 48 h. Interestingly, the blood concentration of VEGF in the mice treated with excess fold of bevacizumab was significantly higher than those without at 48 h (25.5 ± 4.6 %ID/g vs 6.5 ± 2.1 %ID/g, P = 0.0016). Liver uptake decreased from 24 h (17.2 ± 1.7 %ID/g) to 48 h (13.0 ± 4.2 %ID/g) and 72 h (10.6 ± 1.5 %ID/g) due to hepatic clearance of the tracer. The present study successfully showed (64) Cu-DOTA-bevacizumab as a potential PET tracer for non-invasive imaging of VEGF expression in colorectal cancer xenografts.