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

Development and evaluation of 89Zr-trastuzumab for clinical applications

Objectives

Due to the suitable physical characteristics of ⁸⁹Zr as a PET radionuclide and affinity of Trastuzumab monoclonal antibody against HER2, [⁸⁹Zr]Zr-Trastuzumab was prepared and went through preclinical evaluations for ultimate human applications.

Methods

⁸⁹Zr was produced by using ⁸⁹Y(p,n)⁸⁹Zr reaction at a 30 MeV cyclotron (radionuclide purity>99.9%, specific activity of 17 GBq/µg). p-SCN-Bn-Deferoxamine (DFO); was conjugated to trastuzumab, followed by labeling with ⁸⁹Zr in oxalate form at optimized condition. Cell binding, internalization and, radioimmuno-activity assays were studied using HER2+ BT474 and HER2- CHO cell lines. Finally, the biodistribution of the radioimmunoconjugate was assessed in normal and HER2+ BT474 tumor-bearing mice using tissue counting and imaging at different intervals after injection. Also, a woman with HER2-positive metastatic breast cancer under treatment with Herceptin underwent both [⁸⁹Zr]Zr-Trastuzumab and, [¹⁸F]FDG PET/CTs.

Results

⁸⁹Zr was produced with high radionuclidic and radiochemical purities (>99%) and [⁸⁹Zr]Zr-DFO-Trastuzumab was prepared with radiochemical purity of >98% and specific activity of 9.85 GBq/µmol. The radioimmunoconjugate was stable both in PBS buffer and in human serum for at least 48 h. The radioimmunoactivity assay demonstrated about 70% of [⁸⁹Zr]Zr-DFO-Trastuzumab is bound to the BT474 cells at the number of 250×10⁶ cells. Cell binding studies showed that about 28% of radioimmunoconjugate is attached to BT474 cells after 90 min. Internalization studies showed that 50% of [⁸⁹Zr]Zr-Trastuzumab is internalized to BT474 cells only in 6 h. The biodistribution study of the labeled compound in normal mice demonstrated the same pattern of the monoclonal antibodies which is entirely different from the biodistribution of free ⁸⁹Zr. Biodistribution and imaging studies in tumor-bearing mice showed the significant uptake values of [⁸⁹Zr]Zr-Trastuzumab in tumor sites. [⁸⁹Zr]Zr-Trastuzumab PET/CT revealed metastatic lesions documented previously with [¹⁸F]FDG PET/CT scan in a woman with breast cancer who was under treatment with Herceptin. Although the [¹⁸F]FDG PET/CT scan had better quality images, the valuable and unique advantage of [⁸⁹Zr]Zr-Trastuzumab PET/CT is delineating HER2+ metastasis, which is essential in diagnosis and HER2-based treatments.

Conclusion

The prepared [⁸⁹Zr]Zr-Trastuzumab has a high potential radio-pharmaceutical for immune-PET imaging of the patients with HER2+ tumors.

Progress in the Surface Functionalization of Selenium Nanoparticles and Their Potential Application in Cancer Therapy

As an essential micronutrient, selenium participates in numerous life processes and plays a key role in human health. In the past decade, selenium nanoparticles (SeNPs) have attracted great attention due to their excellent functionality for potential applications in pharmaceuticals. However, the utilization of SeNPs has been restricted by their instability and low targeting ability. Since the existing reviews mainly focused on the applications of SeNPs, this review highlights the synthesis of SeNPs and the strategies to improve their stability and targeting ability through surface functionalization. In addition, the utilization of functionalized SeNPs for the single and co-delivery of drugs or genes to achieve the combination of therapy are also presented, with the emphasis on the potential mechanism. The current challenges and prospects of functionalized SeNPs are also summarized. This review may provide valuable information for the design of novel functionalized SeNPs and promote their future application in cancer therapy.

Fluorescent imaging for cancer therapy and cancer gene therapy

The translation of laboratory science into effective clinical cancer therapy is gaining momentum more rapidly than any other time in history. Understanding cancer cell-surface receptors, cancer cell growth, and cancer metabolic pathways has led to many promising molecular-targeted therapies and cancer gene therapies. These same targets may also be exploited for optical imaging of cancer. Theoretically, any antibody or small molecule targeting cancer can be labeled with bioluminescent or fluorescent agents. In the laboratory setting, fluorescence imaging (FI) and bioluminescence imaging (BLI) have long been used in preclinical research for quantification of tumor bulk, assessment of targeting of tumors by experimental agents, and discrimination between primary and secondary effects of cancer treatments. Many of these laboratory techniques are now moving to clinical trials. Imageable engineered fluorescent probes that are highly specific for cancer are being advanced. This will allow for the identification of tumors for staging, tracking novel therapeutic agents, assisting in adequate surgical resection, and allowing image-guided biopsies. The critical components of FI include (1) a fluorescent protein that is biologically safe, stable, and distinctly visible with a high target to background ratio and (2) highly sensitive optical detectors. This review will summarize the most promising optical imaging agents and detection devices for cancer clinical research and clinical care.

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.

In Search of Advanced Tumor Diagnostics and Treatment: Achievements and Perspectives of Carbonic Anhydrase IX Targeted Delivery

The research of how cells sense and adapt the oxygen deficiency has been recognized as worth winning a Nobel Prize in 2019. Understanding hypoxia-driven molecular machinery paved a path for novel strategies in fighting hypoxia-related diseases including cancer. The oxygen depletion inside the tumor provokes HIF-1 dependent gene and protein expression which helps the tumor to survive. For this reason, tumor related molecules are in the spotlight for scientists developing anticancer agents. One such target is carbonic anhydrase IX (CA IX)-a protein located on the outer cell membrane of most hypoxic tumor cells. This offers the opportunity to exploit it as a target for delivery of cytotoxic drugs, dyes, or radioisotopes to cancer cells. Therefore, researchers investigate CA IX specific small molecules and antibodies as tumor-targeting moieties in nanosystems and conjugates which are expected to overcome the limitations of some existing diagnostic and treatment strategies. This review covers the vast majority of CA IX-targeted systems (nanoparticle and conjugate based) for both therapeutic and imaging purposes published up to now. Furthermore, it shows their stage of development and gives an assessment of their clinical translation possibilities.

Recombinant-fully-human-antibody decorated highly-stable far-red AIEdots for in vivo HER-2 receptor-targeted imaging

We developed highly bright and stable far-red emissive AIEdots by using a new kind of click-functional PEG grafted amphiphilic polymer to coat hydrophobic AIE-active polymers (PDFDP). Furthermore, an anti-HER2 recombinant fully human antibody was produced and conjugated on the AIEdots via metal-free click chemistry to fabricate in vivo tumor-targeting nanoprobes.

A Switchable Site-Specific Antibody Conjugate

Genetic incorporation of unnatural amino acids (UAAs) provides a unique approach to the synthesis of site-specific antibody conjugates that are homogeneous and better defined constructs than random conjugates. Yet, the yield varies for every antibody, and the process is costly and time-consuming. We have developed a switchable αGCN4-Fab conjugate that incorporates UAA p-acetylphenylalanine. The GCN4 peptide is used as a switch, and antibodies fused by GCN4 can direct the αGCN4-Fab conjugate to target different cancer cells for diagnosis, imaging, or therapeutic treatment. More importantly, this switchable conjugate demonstrated an impressive potential for pretargeted imaging in vivo. This approach illustrates the utility of an orthogonal switch as a general strategy to endow versatility to a single antibody conjugate, which should facilitate the application of UAA-based site-specific conjugates for a host of biomedical uses in the future.

CD4+ levels control the odds of induction of humoral immune responses to tracer doses of therapeutic antibodies

Rapidly increasing number of therapeutic antibodies are being repurposed to imaging probes for noninvasive diagnosis, as well as monitoring during treatment or disease recurrence. Though antibody-based imaging involves tracer doses (~3 log lower than therapeutic doses), and immune responses are severely reduced in patients with impaired immunity, formation of anti-tracer antibodies (ATA) has been observed hampering further diagnostic monitoring. Here, we explored the potential to develop humoral responses to intravenously administered tracer dose of a monoclonal antibody F(ab΄)2 fragment, and associated with host related immune measures in 49 rhesus macaques categorized into healthy (uninfected controls), SIV-progressors, SIV non-progressors, or total body irradiated (TBI). Antibody fragment administered in tracer amount (~100μg) induced immune responses with significantly lower odds in SIV-progressors or TBI macaques (P<0.005) as compared to healthy animals. Peripheral blood (PB) CD4+ cell counts, but not CD20+ cell levels, were associated with significantly higher risk of developing a humoral response (P<0.001). Doubling the PB CD4+ counts is associated with an odds ratio of developing an immune response of 1.73. Among SIV-infected animals, CD4+ cell count was a stronger predictor of immune response than plasma SIV-RNA levels. Both SIV-progressors and TBI macaques showed higher odds of responses with increasing CD4+ counts, however when compared to healthy or SIV non-progressors with similar CD4+ count, they were still functionally incompetent in generating a response (P<0.01). Moreover, presence of ATA in systemic circulation altered the in vivo biodistribution by increasing hepatic uptake and decreasing plasma radiotracer clearance, with minimal to no binding detected in targeted tissues.

Preclinical Development of CD38-Targeted [89Zr]Zr-DFO-Daratumumab for Imaging Multiple Myeloma

Multiple myeloma (MM) is a plasma B-cell hematologic cancer that causes significant skeletal morbidity. Despite improvements in survival, heterogeneity in response remains a major challenge in MM. Cluster of differentiation 38 (CD38) is a type II transmembrane glycoprotein overexpressed in myeloma cells and is implicated in MM cell signaling. Daratumumab is a U.S. Food and Drug Administration-approved high-affinity monoclonal antibody targeting CD38 that is clinically benefiting refractory MM patients. Here, we evaluated [⁸⁹Zr]Zr-desferrioxamine (DFO)-daratumumab PET/CT imaging in MM tumor models. Methods: Daratumumab was conjugated to DFO-p-benzyl-isothiocyanate (DFO-Bz-NCS) for radiolabeling with ⁸⁹Zr. Chelator conjugation was confirmed by electrospray ionization-mass spectrometry, and radiolabeling was monitored by instant thin-layer chromatography. Daratumumab was conjugated to Cyanine5 (Cy5) dye for cell microscopy. In vitro and in vivo evaluation of [⁸⁹Zr]Zr-DFO-daratumumab was performed using CD38⁺ human myeloma MM1.S-luciferase (MM1.S) cells. Cellular studies determined the affinity, immunoreactivity, and specificity of [⁸⁹Zr]Zr-DFO-daratumumab. A 5TGM1-luciferase (5TGM1)/KaLwRij MM mouse model served as control for imaging background noise. [⁸⁹Zr]Zr-DFO-daratumumab PET/CT small-animal imaging was performed in severe combined immunodeficient mice bearing solid and disseminated MM tumors. Tissue biodistribution (7 d after tracer administration, 1.11 MBq/animal, n = 4-6/group) was performed in wild-type and MM1.S tumor-bearing mice. Results: A specific activity of 55.5 MBq/nmol (0.37 MBq/μg) was reproducibly obtained with [⁸⁹Zr]Zr-daratumumab-DFO. Flow cytometry confirmed CD38 expression (>99%) on the surface of MM1.S cells. Confocal microscopy with daratumumab-Cy5 demonstrated specific cell binding. Dissociation constant, 3.3 nM (±0.58), and receptor density, 10.1 fmol/mg (±0.64), was obtained with a saturation binding assay. [⁸⁹Zr]Zr-DFO-daratumumab/PET demonstrated specificity and sensitivity for detecting CD38⁺ myeloma tumors of variable sizes (8.5-128 mm³) with standardized uptake values ranging from 2.1 to 9.3. Discrete medullar lesions, confirmed by bioluminescence images, were efficiently imaged with [⁸⁹Zr]Zr-DFO-daratumumab/PET. Biodistribution at 7 d after administration of [⁸⁹Zr]Zr-DFO-daratumumab showed prominent tumor uptake (27.7 ± 7.6 percentage injected dose per gram). In vivo blocking was achieved with a 200-fold excess of unlabeled daratumumab. Conclusion: [⁸⁹Zr]Zr-DFO- and Cy5-daratumumab demonstrated superb binding to CD38⁺ human MM cells and significantly low binding to CD38^low cells. Daratumumab bioconjugates are being evaluated for image-guided delivery of therapeutic radionuclides.

Alternative reagents to antibodies in imaging applications

Antibodies have been indispensable tools in molecular biology, biochemistry and medical research. However, a number of issues surrounding validation, specificity and batch variation of commercially available antibodies have prompted research groups to develop novel non-antibody binding reagents. The ability to select highly specific monoclonal non-antibody binding proteins without the need for animals, the ease of production and the ability to site-directly label has enabled a wide variety of applications to be tested, including imaging. In this review, we discuss the success of a number of non-antibody reagents in imaging applications, including the recently reported Affimer.

Nanomedicine

Nanomedicine, an offshoot of nanotechnology, is considered as one of the most promising technologies of the 21st century. Due to their minute size, nanomedicines can easily target difficult-to-reach sites with improved solubility and bioavailability and reduced adverse effects. They also act as versatile delivery systems, carrying both chemotherapeutics and imaging agents to targeted sites. Hence, nanomedicine can be used to achieve the same therapeutic effect at smaller doses than their conventional counterparts and can offer impressive resolutions for various life-threatening diseases. Although certain issues have been raised about the potential toxicities of nanomaterials, it is anticipated that the advances in nanomedicine will furnish clarifications to many of modern medicine's unsolved problems. This chapter aims to provide a comprehensive and contemporary survey of various nanomedicine products along with the major risks and side effects associated with the nanoparticles.

Image-Guided Tumor Resection

Each year, millions of individuals undergo cancer surgery that is intended to be curative or at least a necessary component of a curative regimen. Particularly for those patients whose cancer harbors cells that are resistant to chemotherapy or radiation, the extent of surgery often defines whether they will be a survivor or casualty of the disease. For many solid tumor types, the difference in survival between patients who undergo gross total resection and those who have residual bulky disease is often profound. With surgery being central to cancer survivorship, it is stunning how few resources have been invested in improving surgical outcomes, particularly in comparison to chemotherapeutic research and discovery. This article reviews recent advances related to developing targeted fluorescent agents to guide surgeons during cancer removal. The goal of these drugs and devices is to clearly distinguish cancer from normal tissue to improve surgical outcome for cancer patients.