Promising clinical performance of pretargeted immuno-PET with anti-CEA bispecific antibody and gallium-68-labelled IMP-288 peptide for imaging colorectal cancer metastases: a pilot study

It takes Two: Advancing cancer treatment with two-step nanoparticle delivery

The rapid advancement of nanobiotechnology has resulted in the development of numerous targeted nanoformulations and sophisticated nanobiorobots for biomedical applications. Despite the potential of nanostructures to improve drug delivery and therapeutic efficacy, their clinical application is still constrained by insufficient accumulation in tumor tissues. Current methodologies result in only an average of 0.6 % of administered nanoparticles reaching tumors, prompting the development of innovative strategies to improve targeting and influence the pharmacokinetics and pharmacodynamics of drugs. One such approach is two-step targeting, which includes either the concept of tumor pre-targeting with specific recognizing elements or the stimuli-sensitive activation of nanostructures. This review critically evaluates advancements in two-step drug delivery systems utilizing nanobiotechnology for targeted cancer therapy. For instance, two-step delivery based on the pre-targeting concept involves an initial injection of targeting molecules that bind to tumor-specific antigens, followed by the administration of drug-loaded nanocarriers modified with complementary adaptors. This approach enhances nanoparticle accumulation in tumors and improves therapeutic outcomes by increasing interaction avidity and overcoming steric hindrances. We critically assess existing adaptor systems for two-step drug delivery and synthesize findings from various studies demonstrating their efficacy in both in vitro and in vivo settings, while addressing challenges in clinical translation. We also explore future directions for developing novel adaptor systems to enhance two-step delivery mechanisms. This review aims to contribute to optimizing nanobiotechnology in oncology for more effective cancer therapies.

Ultra-low dose immunoPET using 64Cu-rituximab tracer for a human CD20 mouse model

Antibodies (Abs) and their fragments can be labeled with PET radioisotope (immunoPET) for in vivo diagnostic imaging. Compared to the conventional FDG-PET, immunoPET can be designed to target in vivo cancer-specific antigen expression levels for various tumors and metastasis, which makes immunoPET (iPET) a powerful technique for molecular imaging and therapy monitoring. However, achieving the optimal dose to minimize radioisotope toxicity without compromising the visualization of the smallest tumor is challenging. To find an ultra-minimal tracer dose, we have developed a novel iPET with an intact rituximab Ab labeled with 64Cu to image human CD20 (hCD20) in a transgenic mouse model for non-Hodgkin's lymphoma (NHL) imaging. Using phantom and in vivo mouse models, we optimized the minimal dose that can be administered in a mouse using a high-specific iPET tracer prepared from 64Cu-rituximab. A phantom study was used to characterize the scanner capability and limit for imaging using low doses. An ultra-minimal dose administered in a mouse model showed good image quality with high signal-to-noise ratio without compromising quantitative accuracy. The phantom study with below 50 μCi dose level indicated a slight increase in variability due to reduced dose specifically for target regions with lower uptakes (<3:1 ratio) relative to the background. In vivo study performed with four groups of mice (n = 3), each group injected with ~90, ~50, ~25, and ~10 μCi showed a linear increase of tracer uptake measured as percentage injected dose per gram (%ID/g). This tracer has shown high specific uptake in the spleen, where most B-cells are engineered to express hCD20. The study demonstrated that the lowest dose threshold limit for 64Cu-antibody-based iPET was about 25 μCi while achieving a high-quality image and quantitative accuracy.

Diagnostic Advances and Novel Therapeutics in Peritoneal Metastasis

Appropriate assessment of disease burden in patients with peritoneal surface malignancy (PSM) is critical for treatment decision-making, and conventional cross-sectional imaging (computed tomography and/or MRI) often underestimates burden of disease. Advances in imaging for PSM include novel functional imaging modalities that target cells unique to the tumor microenvironment. Novel alternative methods of diagnosis and disease monitoring are also potentially applicable to management of PSM. These include forms of "liquid biopsy" targeting circulating tumor DNA. Novel regional therapies include both new therapeutic agents (immune-based and nanoparticle-based), as well as new methods of delivery such as pressurized intraperitoneal aerosolized chemotherapy.

Nano-Radiopharmaceuticals in Colon Cancer: Current Applications, Challenges, and Future Directions

Colon cancer remains a significant global health challenge; however, the treatment outcome for colon patients can be improved through early detection and effective treatment. Nano-radiopharmaceuticals, combining nanotechnology with radiopharmaceuticals, are emerging as a revolutionary approach in both colon cancer diagnostic imaging and therapy, playing a significant role in the management of colon cancer patients. This review examines the use of nano-radiopharmaceuticals in the diagnosis and treatment of colon cancer, highlighting current applications, challenges, and future directions. Nanocarriers of radionuclides have shown potential in improving cancer treatment, including liposomes, microparticles, nanoparticles, micelles, dendrimers, and hydrogels, which are approved by the FDA. These nanocarriers can deliver targeted drugs into malignant cells without affecting normal cells, reducing side effects. Antibody-guided systemic radionuclide-targeted therapy has shown potential for treating cancer. Novel cancer nanomedicines, like Hensify and 32P BioSilicon, are under clinical development for targeted radiation delivery in percutaneous intratumoral injections. Although using nano-radiopharmaceuticals is a superior technique for diagnosing and treating colon cancer, there are limitations and challenges, such as the unintentional accumulation of nanoparticles in healthy tissues, which leads to toxicity due to biodistribution issues, as well as high manufacturing costs that limit their availability for patients. However, the future direction is moving toward providing more precise radiopharmaceuticals, which is crucial for enhancing the diagnosis and treatment of colon cancer and reducing production costs.

Pharmacokinetic Positron Emission Tomography Imaging of an Optimized CD38-Targeted 68Ga-Labeled Peptide in Multiple Myeloma: A Pilot Study

Multiple myeloma (MM) is an incurable disease characterized by its clinical and prognostic heterogeneity. Despite conventional chemotherapy and autologous hematopoietic stem cell transplantation, the management of relapsed and refractory MM disease poses significant challenges, both medically and socioeconomically. CD38, highly expressed on the surface of MM cells, serves as a distinct tumor biological target in MM. Peptides offer advantages over antibodies, enabling precise tumor imaging and facilitating early tumor diagnosis and dynamic immunotherapy monitoring. In this study, we developed PF381, a CD38-targeted peptide, and investigated its role in diagnosis, biodistribution, and dosimetry through 68Ga-labeling for preclinical evaluation in tumor-bearing models. We screened a microchip-based combinatorial chemistry peptide library to obtain the amino acid sequence of PF381. Affinity for human CD38 was evaluated by SPRi. PF381 was conjugated with DOTA for radiolabeling with 68Ga, and the complex was characterized by HPLC. PET imaging was performed in murine tumor models after the administration of [68Ga]Ga-DOTA-PF381. Biodistribution analysis compared CD38-positive H929 and CD38-negative U266 tumors, and human radiation dosimetry was estimated. Tumor sections were stained for CD38 expression. SPRi showed that PF381 had a high affinity for CD38 with a KD of 2.49 × 10-8 M. HPLC measured a radiolabeling efficiency of 78.45 ± 7.91% for [68Ga]Ga-DOTA-PF381, with >98% radiochemical purity. PET imaging revealed rapid and persistent accumulation of radioactivity in CD38-positive H929 tumors, contrasting with negligible uptake in CD38-negative U266 tumors. Biodistribution confirmed higher uptake in H929 tumors (0.75 ± 0.03%ID/g) vs U266 (0.26 ± 0.08%ID/g, P < 0.001). The kidney received the highest radiation dose (3.57 × 10-02 mSv/MBq), with an effective dose of 1.41 × 10-02 mSv/MBq. Immunofluorescence imaging supported PET and biodistribution findings. We developed a novel peptide targeting CD38 and proved that 68Ga-labeled PF381 had rapid targeting and good tumor penetration capabilities. Therefore, 68Ga-labeled PF381 could achieve high sensitivity in vivo imaging for CD38-positive hematological malignancies.

Construction and preclinical evaluation of a 124I-labelled bispecific antibody targeting PD-L1 and PD-L2

PURPOSE

NB12 is a bispecific antibody that consists of two anti-programmed cell death-ligand 1 (PD-L1) nanobodies and two anti-programmed cell death-ligand 2 (PD-L2) nanobodies. The aim of this study was to design a novel tracer, [124I]I-NB12, targeting PD-L1/2 and perform preclinical evaluations to dynamically monitor PD-L1/2 expression for determining cancer patient responsiveness to ICI therapy.

METHODS

NB12 was labelled with the radionuclide 124I at room temperature (RT). An in vitro binding assay was performed to assess the affinity of [124I]I-NB12 for PD-L1 and PD-L2. Cellular uptake, pharmacokinetic, and biodistribution experiments were performed to evaluate the biological properties. Micro-PET/CT imaging with [124I]I-NB12 was conducted at different time points. Immunohistochemical and haematoxylin and eosin (HE) staining experiments were carried out using tumour tissues. Routine blood, biochemical indices and major organ pathology were used to evaluate the biosafety of the tracers.

RESULTS

The radiochemical yield of [124I]I-NB12 was 84.62 ± 3.90%, and the radiochemical purity (RCP) was greater than 99%. [124I]I-NB12 had a high affinity for the PD-L1 (Kd = 19.82 nM) and PD-L2 (Kd = 2.93 nM). Cellular uptake experiments confirmed that the uptake of [124I]I-NB12 by A549-PDL1/2 cells was greater than that by A549 cells. The half-lives of the distribution phase and elimination phase were 0.26 h and 4.08 h, respectively. Micro-PET/CT showed significant [124I]I-NB12 uptake in the tumour region of A549-PDL1/2 tumour-bearing mice compared with A549 tumour-bearing mice 24 h postinjection. Immunohistochemical and HE staining experiments confirmed that tumour-bearing mice was successfully constructed.

CONCLUSION

We constructed a bispecific antibody that targets PD-L1 and PD-L2, namely, [124I]I-NB12. Biological evaluation revealed its specificity and affinity for PD-L1/2, and micro-PET/CT confirmed the feasibility of visualizing tumour PD-L1/2 in vivo. Using [124I]I-NB12 may be a promising strategy for identifying cancer patients that can potentially benefit from ICI therapy.

Clinical Progresses and Challenges of Bispecific Antibodies for the Treatment of Solid Tumors

In recent years, bispecific antibodies (BsAbs) have emerged as a promising therapeutic strategy against tumors. BsAbs can recruit and activate immune cells, block multiple signaling pathways, and deliver therapeutic payloads directly to tumor sites. This review provides a comprehensive overview of the recent advances in the development and clinical application of BsAbs for the treatment of solid tumors. We discuss the different formats, the unique mechanisms of action, and the clinical outcomes of the most advanced BsAbs in solid tumor therapy. Several studies have also analyzed the clinical progress of bispecific antibodies. However, this review distinguishes itself by exploring the challenges associated with bispecific antibodies and proposing potential solutions. As the field progresses, BsAbs hold promise to redefine cancer treatment paradigms and offer new hope to patients with solid tumors.

Nuclear Imaging of Bispecific Antibodies on the Rise

Bispecific antibodies (bsAbs) are engineered to target 2 different epitopes simultaneously. About 75% of the 16 clinically approved bsAbs have entered the clinic internationally since 2022. Hence, research on biomedical imaging of various radiolabeled bsAb scaffolds may serve to improve patient selection for bsAb therapy. Here, we provide a comprehensive overview of recent advances in radiolabeled bsAbs for imaging via PET or SPECT. We compare direct targeting and pretargeting approaches in preclinical and clinical studies in oncologic research. Furthermore, we show preclinical applications of imaging bsAbs in neurodegenerative diseases. Finally, we offer perspectives on the future directions of imaging bsAbs based on their challenges and opportunities.

Engineered Antibodies as Cancer Radiotheranostics

Radiotheranostics is a rapidly growing approach in personalized medicine, merging diagnostic imaging and targeted radiotherapy to allow for the precise detection and treatment of diseases, notably cancer. Radiolabeled antibodies have become indispensable tools in the field of cancer theranostics due to their high specificity and affinity for cancer-associated antigens, which allows for accurate targeting with minimal impact on surrounding healthy tissues, enhancing therapeutic efficacy while reducing side effects, immune-modulating ability, and versatility and flexibility in engineering and conjugation. However, there are inherent limitations in using antibodies as a platform for radiopharmaceuticals due to their natural activities within the immune system, large size preventing effective tumor penetration, and relatively long half-life with concerns for prolonged radioactivity exposure. Antibody engineering can solve these challenges while preserving the many advantages of the immunoglobulin framework. In this review, the goal is to give a general overview of antibody engineering and design for tumor radiotheranostics. Particularly, the four ways that antibody engineering is applied to enhance radioimmunoconjugates: pharmacokinetics optimization, site-specific bioconjugation, modulation of Fc interactions, and bispecific construct creation are discussed. The radionuclide choices for designed antibody radionuclide conjugates and conjugation techniques and future directions for antibody radionuclide conjugate innovation and advancement are also discussed.

Approaches to Reducing Normal Tissue Radiation from Radiolabeled Antibodies

Radiolabeled antibodies are powerful tools for both imaging and therapy in the field of nuclear medicine. Radiolabeling methods that do not release radionuclides from parent antibodies are essential for radiolabeling antibodies, and practical radiolabeling protocols that provide high in vivo stability have been established for many radionuclides, with a few exceptions. However, several limitations remain, including undesirable side effects on the biodistribution profiles of antibodies. This review summarizes the numerous efforts made to tackle this problem and the recent advances, mainly in preclinical studies. These include pretargeting approaches, engineered antibody fragments and constructs, the secondary injection of clearing agents, and the insertion of metabolizable linkages. Finally, we discuss the potential of these approaches and their prospects for further clinical application.

Revolutionizing cancer immunotherapy: unleashing the potential of bispecific antibodies for targeted treatment

Recent progressions in immunotherapy have transformed cancer treatment, providing a promising strategy that activates the immune system of the patient to find and eliminate cancerous cells. Bispecific antibodies, which engage two separate antigens or one antigen with two distinct epitopes, are of tremendous concern in immunotherapy. The bi-targeting idea enabled by bispecific antibodies (BsAbs) is especially attractive from a medical standpoint since most diseases are complex, involving several receptors, ligands, and signaling pathways. Several research look into the processes in which BsAbs identify different cancer targets such angiogenesis, reproduction, metastasis, and immune regulation. By rerouting cells or altering other pathways, the bispecific proteins perform effector activities in addition to those of natural antibodies. This opens up a wide range of clinical applications and helps patients with resistant tumors respond better to medication. Yet, further study is necessary to identify the best conditions where to use these medications for treating tumor, their appropriate combination partners, and methods to reduce toxicity. In this review, we provide insights into the BsAb format classification based on their composition and symmetry, as well as the delivery mode, focus on the action mechanism of the molecule, and discuss the challenges and future perspectives in BsAb development.

Immuno-PET of colorectal cancer with a CEA-targeted [68 Ga]Ga-nanobody: from bench to bedside

PURPOSE

An accurate diagnosis of colorectal carcinoma (CRC) can assist physicians in developing reasonable therapeutic regimens, thereby significantly improving the patient's prognosis. Carcinoembryonic antigen (CEA)-targeted PET imaging shows great potential for this purpose. Despite showing remarkable abilities to detect primary and metastatic CRC, previously reported CEA-specific antibody radiotracers or pretargeted imaging are not suitable for clinical use due to poor pharmacokinetics and complicated imaging procedures. In contrast, radiolabeled nanobodies exhibit ideal characteristics for PET imaging, for instance, rapid clearance rates and excellent distribution profiles, allowing same-day imaging with sufficient contrast. In this study, we developed a novel CEA-targeted nanobody radiotracer, [68 Ga]Ga-HNI01, and assessed its tumor imaging ability and biodistribution profile in preclinical xenografts and patients with primary and metastatic CRC.

METHODS

The novel nanobody HNI01 was acquired by immunizing the llama with CEA proteins. [68 Ga]Ga-HNI01 was synthesized by site-specifically conjugating [68 Ga]Ga with tris(hydroxypyridinone) (THP). Small-animal PET imaging and biodistribution studies were performed in CEA-overexpressed LS174T and CEA-low-expressed HT-29 tumor models. Following successful preclinical assessment, a phase I study was conducted on 9 patients with primary and metastatic CRC. Study participants received 151.21 ± 25.25 MBq of intravenous [68 Ga]Ga-HNI01 and underwent PET/CT scans at 1 h and 2 h post injection. Patients 01-03 also underwent whole-body dynamic PET imaging within 0-40 min p.i. All patients underwent [18F]F-FDG PET/CT imaging within 1 week after [68 Ga]Ga-HNI01 imaging. Tracer distribution, pharmacokinetics, and radiation dosimetry were calculated.

RESULTS

[68 Ga]Ga-HNI01 was successfully synthesized within 10 min under mild conditions, and the radiochemical purity was more than 98% without purification. Micro-PET imaging with [68 Ga]Ga-HNI01 revealed clear visualization of LS174T tumors, while signals from HT-29 tumors were significantly lower. Biodistribution studies indicated that uptake of [68 Ga]Ga-HNI01 in LS174T and HT-29 was 8.83 ± 3.02%ID/g and 1.81 ± 0.87%ID/g, respectively, at 2 h p.i. No adverse events occurred in all clinical participants after the injection of [68 Ga]Ga-HNI01. A fast blood clearance and low background uptake were observed, and CRC lesions could be visualized with high contrast as early as 30 min after injection. [68 Ga]Ga-HNI01 PET could clearly detect metastatic lesions in the liver, lung, and pancreas and showed superior ability in detecting small metastases. A significant accumulation of radioactivity was observed in the kidney, and normal tissues physiologically expressing CEA receptors showed slight uptakes of [68 Ga]Ga-HNI01. An interesting finding was that strong uptake of [68 Ga]Ga-HNI01 was found in non-malignant colorectal tissues adjacent to the primary tumor in some patients, suggesting abnormal CEA expression in these healthy tissues.

CONCLUSION

[68 Ga]Ga-HNI01 is a novel CEA-targeted PET imaging radiotracer with excellent pharmacokinetics and favorable dosimetry profiles. [68 Ga]Ga-HNI01 PET is an effective and convenient imaging tool for detecting CRC lesions, particularly for identifying small metastases. Furthermore, its high specificity for CEA in vivo makes it an ideal tool for selecting patients for anti-CEA therapy.

PET/CT in Patients with Breast Cancer Treated with Immunotherapy

Significant advances in breast cancer (BC) treatment have been made in the last decade, including the use of immunotherapy and, in particular, immune checkpoint inhibitors that have been shown to improve the survival of patients with triple negative BC. This narrative review summarizes the studies supporting the use of immunotherapy in BC. Furthermore, the usefulness of 2-deoxy-2-[¹⁸F]fluoro-D-glucose (2-[¹⁸F]FDG) positron emission/computerized tomography (PET/CT) to image the tumor heterogeneity and to assess treatment response is explored, including the different criteria to interpret 2-[¹⁸F]FDG PET/CT imaging. The concept of immuno-PET is also described, by explaining the advantages of mapping treatment targets with a non-invasive and whole-body tool. Several radiopharmaceuticals in the preclinical phase are referred too, and, considering their promising results, translation to human studies is needed to support their use in clinical practice. Overall, this is an evolving field in BC treatment, despite PET imaging developments, the future trends also include expanding immunotherapy to early-stage BC and using other biomarkers.

Immuno-PET: Design options and clinical proof-of-concept

Radioimmunoconjugates have been used for over 30 years in nuclear medicine applications. In the last few years, advances in cancer biology knowledge have led to the identification of new molecular targets specific to certain patient subgroups. The use of these targets in targeted therapies approaches has allowed the developments of specifically tailored therapeutics for patients. As consequence of the PET-imaging progresses, nuclear medicine has developed powerful imaging tools, based on monoclonal antibodies, to in vivo characterization of these tumor biomarkers. This imaging modality known as immuno-positron emission tomography (immuno-PET) is currently in fastest-growing and its medical value lies in its ability to give a non-invasive method to assess the in vivo target expression and distribution and provide key-information on the tumor targeting. Currently, immuno-PET presents promising probes for different nuclear medicine topics as staging/stratification tool, theranostic approaches or predictive/prognostic biomarkers. To develop a radiopharmaceutical drug that can be used in immuno-PET approach, it is necessary to find the best compromise between the isotope choice and the immunologic structure (full monoclonal antibody or derivatives). Through some clinical applications, this paper review aims to discuss the most important aspects of the isotope choice and the usable proteic structure that can be used to meet the clinical needs.

Antibody Engineering for Nuclear Imaging and Radioimmunotherapy

Radiolabeled antibodies have become indispensable tools in nuclear medicine. However, the natural roles of antibodies within the immune system mean that they have several intrinsic limitations as a platform for radiopharmaceuticals. In recent years, the field has increasingly turned to antibody engineering to circumvent these issues while retaining the manifold benefits of the immunoglobulin framework. In this "Focus on Molecular Imaging" review, we cover recent advances in the application of antibody engineering to immunoPET, immunoSPECT, and radioimmunotherapy. Specifically, we address how antibody engineering has been used to improve radioimmunoconjugates on four fronts: optimizing pharmacokinetics, facilitating site-specific bioconjugation, modulating Fc interactions, and creating bispecific constructs.

Pretargeting: A Path Forward for Radioimmunotherapy

Pretargeted radioimmunodiagnosis and radioimmunotherapy aim to efficiently combine antitumor antibodies and medicinal radioisotopes for high-contrast imaging and high-therapeutic-index (TI) tumor targeting, respectively. As opposed to conventional radioimmunoconjugates, pretargeted approaches separate the tumor-targeting step from the payload step, thereby amplifying tumor uptake while reducing normal-tissue exposure. Alongside contrast and TI, critical parameters include antibody immunogenicity and specificity, availability of radioisotopes, and ease of use in the clinic. Each of the steps can be optimized separately; as modular systems, they can find broad applications irrespective of tumor target, tumor type, or radioisotopes. Although this versatility presents enormous opportunity, pretargeting is complex and presents unique challenges for clinical translation and optimal use in patients. The purpose of this article is to provide a brief historical perspective on the origins and development of pretargeting strategies in nuclear medicine, emphasizing 2 protein delivery systems that have been extensively evaluated (i.e., biotin-streptavidin and hapten-bispecific monoclonal antibodies), as well as radiohaptens and radioisotopes. We also highlight recent innovations, including pretargeting with bioorthogonal chemistry and novel protein vectors (such as self-assembling and disassembling proteins and Affibody molecules). We caution the reader that this is by no means a comprehensive review of the past 3 decades of pretargeted radioimmunodiagnosis and pretargeted radioimmunotherapy. But we do aim to highlight major developmental milestones and to identify benchmarks for success with regard to TI and toxicity in preclinical models and clinically. We believe this approach will lead to the identification of key obstacles to clinical success, revive interest in the utility of radiotheranostics applications, and guide development of the next generation of pretargeted theranostics.

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.

Imaging immunity in patients with cancer using positron emission tomography

Immune checkpoint inhibitors and related molecules can achieve tumour regression, and even prolonged survival, for a subset of cancer patients with an otherwise dire prognosis. However, it remains unclear why some patients respond to immunotherapy and others do not. PET imaging has the potential to characterise the spatial and temporal heterogeneity of both immunotherapy target molecules and the tumor immune microenvironment, suggesting a tantalising vision of personally-adapted immunomodulatory treatment regimens. Personalised combinations of immunotherapy with local therapies and other systemic therapies, would be informed by immune imaging and subsequently modified in accordance with therapeutically induced immune environmental changes. An ideal PET imaging biomarker would facilitate the choice of initial therapy and would permit sequential imaging in time-frames that could provide actionable information to guide subsequent therapy. Such imaging should provide either prognostic or predictive measures of responsiveness relevant to key immunotherapy types but, most importantly, guide key decisions on initiation, continuation, change or cessation of treatment to reduce the cost and morbidity of treatment while enhancing survival outcomes. We survey the current literature, focusing on clinically relevant immune checkpoint immunotherapies, for which novel PET tracers are being developed, and discuss what steps are needed to make this vision a reality.

Immunotherapy for Colorectal Cancer: Mechanisms and Predictive Biomarkers

Simple Summary

Late-stage colorectal cancer treatment often involves chemotherapy and radiation that can cause dose-limiting toxicity, and therefore there is great interest in developing targeted therapies for this disease. Immunotherapy is a targeted therapy that uses peptides, cells, antibodies, viruses, or small molecules to engage or train the immune system to kill cancer. Here, we discuss the preclinical and clinical development of immunotherapy for treatment of colorectal cancer and provide an overview of predictive biomarkers for such treatments. We also consider open questions including optimal combination treatments and sensitization of colorectal cancer patients with proficient mismatch repair enzymes.

Abstract

Though early-stage colorectal cancer has a high 5 year survival rate of 65–92% depending on the specific stage, this probability drops to 13% after the cancer metastasizes. Frontline treatments for colorectal cancer such as chemotherapy and radiation often produce dose-limiting toxicities in patients and acquired resistance in cancer cells. Additional targeted treatments are needed to improve patient outcomes and quality of life. Immunotherapy involves treatment with peptides, cells, antibodies, viruses, or small molecules to engage or train the immune system to kill cancer cells. Preclinical and clinical investigations of immunotherapy for treatment of colorectal cancer including immune checkpoint blockade, adoptive cell therapy, monoclonal antibodies, oncolytic viruses, anti-cancer vaccines, and immune system modulators have been promising, but demonstrate limitations for patients with proficient mismatch repair enzymes. In this review, we discuss preclinical and clinical studies investigating immunotherapy for treatment of colorectal cancer and predictive biomarkers for response to these treatments. We also consider open questions including optimal combination treatments to maximize efficacy, minimize toxicity, and prevent acquired resistance and approaches to sensitize mismatch repair-proficient patients to immunotherapy.

Current Landscape in Clinical Pretargeted Radioimmunoimaging and Therapy

The principle of pretargeted radioimmunoimaging and therapy has been investigated over the past 30 y in preclinical and clinical settings with the aim of reducing the radiation burden of healthy tissue for antibody-based nuclear medicine techniques. In the past few decades, 4 pretargeting methodologies have been proposed, and 2 of them-the bispecific antibody-hapten and the streptavidin-biotin platforms-have been evaluated in humans in phase 1 and 2 studies. With this review article, we aim to survey clinical pretargeting studies in order to understand the challenges that these platforms have faced in human studies and to provide an overview of how the clinical approval of the pretargeting system has proceeded in the past several decades. Additionally, we will discuss the successes of the pretargeting human studies and compare and highlight the pretargeting approaches and conditions that will advance clinical translation of the pretargeting platform in the future.

Synthesis and Characterization of Radiogallium-Labeled Cationic Amphiphilic Peptides as Tumor Imaging Agents

SVS-1 is a cationic amphiphilic peptide (CAP) that exhibits a preferential cytotoxicity towards cancer cells over normal cells. In this study, we developed radiogallium-labeled SVS-1 (⁶⁷Ga-NOTA-KV6), as well as two SVS-1 derivatives, with the repeating KV residues replaced by RV or HV (⁶⁷Ga-NOTA-RV6 and ⁶⁷Ga-NOTA-HV6). All three peptides showed high accumulation in epidermoid carcinoma KB cells (53-143% uptake/mg protein). Though ⁶⁷Ga-NOTA-RV6 showed the highest uptake among the three CAPs, its uptake in 3T3-L1 fibroblasts was just as high, indicating a low selectivity. In contrast, the uptake of ⁶⁷Ga-NOTA-KV6 and ⁶⁷Ga-NOTA-HV6 into 3T3-L1 cells was significantly lower than that in KB cells. An endocytosis inhibition study suggested that the three ⁶⁷Ga-NOTA-CAPs follow distinct pathways for internalization. In the biodistribution study, the tumor uptakes were found to be 4.46%, 4.76%, and 3.18% injected dose/g of tissue (% ID/g) for ⁶⁷Ga-NOTA-KV6, ⁶⁷Ga-NOTA-RV6, and ⁶⁷Ga-NOTA-HV6, respectively, 30 min after administration. Though the radioactivity of these peptides in tumor tissue decreased gradually, ⁶⁷Ga-NOTA-KV6, ⁶⁷Ga-NOTA-RV6, and ⁶⁷Ga-NOTA-HV6 reached high tumor/blood ratios (7.7, 8.0, and 3.8, respectively) and tumor/muscle ratios (5.0, 3.3, and 4.0, respectively) 120 min after administration. ⁶⁷Ga-NOTA-HV6 showed a lower tumor uptake than the two other tracers, but it exhibited very low levels of uptake into peripheral organs. Overall, the replacement of lysine in SVS-1 with other basic amino acids significantly influenced its binding and internalization into cancer cells, as well as its in vivo pharmacokinetic profile. The high accessibility of these peptides to tumors and their ability to target the surface membranes of cancer cells make radiolabeled CAPs excellent candidates for use in tumor theranostics.

Bispecific Antibodies: From Research to Clinical Application

Bispecific antibodies (BsAbs) are antibodies with two binding sites directed at two different antigens or two different epitopes on the same antigen. The clinical therapeutic effects of BsAbs are superior to those of monoclonal antibodies (MoAbs), with broad applications for tumor immunotherapy as well as for the treatment of other diseases. Recently, with progress in antibody or protein engineering and recombinant DNA technology, various platforms for generating different types of BsAbs based on novel strategies, for various uses, have been established. More than 30 mature commercial technology platforms have been used to create and develop BsAbs based on the heterologous recombination of heavy chains and matching of light chains. The detailed mechanisms of clinical/therapeutic action have been demonstrated with these different types of BsAbs. Three kinds of BsAbs have received market approval, and more than 110 types of BsAbs are at various stages of clinical trials. In this paper, we elaborate on the classic platforms, mechanisms, and applications of BsAbs. We hope that this review can stimulate new ideas for the development of BsAbs and improve current clinical strategies.

Targeting Stereotactic Body Radiotherapy on Metabolic PET- and Immuno-PET-Positive Vertebral Metastases

(1) Background: Stereotactic body radiotherapy (SBRT) for vertebral metastases (VM) allows the delivery of high radiation doses to tumors while sparing the spinal cord. We report a new approach to clinical target volume (CTV) delineation based on anti-carcinoembryonic antigen (CEA) positron emission tomography (pretargeted immuno-PET; “iPET”) in patients with metastatic breast cancer (BC) or medullary thyroid cancer (MTC). (2) Methods: All patients underwent iPET, spine magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT) using ¹⁸F-deoxyglucose (FDG) for BC or ¹⁸F-dihydroxy-phenylalanine (F-DOPA) for MTC. Vertebrae locations and vertebral segments of lesions were recorded and the impact on CTV delineation was evaluated. (3) Results: Forty-six VM eligible for SBRT following iPET were evaluated in eight patients (five BC, three MTC). Eighty-one vertebral segments were detected using MRI, 26 with FDG or F-DOPA PET/CT, and 70 using iPET. iPET was able to detect more lesions than MRI for vertebral bodies (44 vs. 34). iPET-based delineation modified MRI-based CTV in 70% (32/46) of cases. (4) Conclusion: iPET allows a precise mapping of affected VM segments, and adds complementary information to MRI in the definition of candidate volumes for VM SBRT. iPET may facilitate determining target volumes for treatment with stereotactic body radiotherapy in metastatic vertebral disease.