Evaluation of 124I-JS001 for hPD1 immuno-PET imaging using sarcoma cell homografts in humanized mice

Demystifying the Role of Immuno PET-CT in Non-Small Cell Lung Cancer: Clinical Value and Research Trends

The management of Lung cancer, especially non-small cell lung cancer has undergone a paradigm shift recently with the advent of new treatment approaches including focused radiotherapy as well as evolution of a newer class of immunotherapy agents. Treatment efficacy and survival rates have improved and it is now even more important that patients are selected for appropriate interventions on the basis of a comprehensive assessment including a range of imaging as well as in-vitro tests such as immunohistochemistry. A new class of tracers targeting programmed cell death such as PD1 and PDL1 (broadly classed as Immuno PET) are being increasingly used in the molecular characterisation of patients deemed resistant to standard treatment approaches and being considered for additional interventions such as immunotherapy. In this review, we review the latest evidence in the field and propose a summary of clinical usefulness and provide a review of the research trends in this exciting and evolving field.

Development of selective ssDNA micro-probe for PD1 detection as a novel strategy for cancer imaging

Programmed death receptor 1, PD1, modulates the function of immune cells by providing inhibitory signals and constitutes the marker of immune exhaustion. Monitoring the level of PD1 promises a useful diagnostic approach in autoimmune diseases and cancer. Here we describe the development of an ssDNA aptamer-based molecular probe capable of specific recognition of human PD1 receptor. The aptamer was selected using SELEX, its sequence was further optimized, and the affinity and specificity were determined in biochemical assays. The aptamer was converted into a fluorescent probe and its potential in molecular imaging was demonstrated in a culture of human cells overexpressing PD1 and murine pancreatic organoids / immune cells mixed co-culture model. We conclude that the provided aptamers are suitable probes for imaging of PD1 expressing immune cells even in complex cellular models and may find future utility as diagnostic tools.

Next Generation of Solid Target Radionuclide Antibody Conjugates for Tumor Immuno-Therapy

Immune checkpoint therapy has emerged as an effective treatment option for various types of cancers. Key immune checkpoint molecules, such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and lymphocyte activation gene 3 (LAG-3), have become pivotal targets in cancer immunotherapy. Antibodies designed to inhibit these molecules have demonstrated significant clinical efficacy. Nevertheless, the ability to monitor changes in the immune status of tumors and predict treatment response remains limited. Conventional methods, such as assessing lymphocytes in peripheral blood or conducting tumor biopsies, are inadequate for providing real-time, spatial information about T-cell distributions within heterogeneous tumors. Positron emission tomography (PET) using T-cell specific probes represents a promising and noninvasive approach to monitor both systemic and intratumoral immune changes during treatment. This technique holds substantial clinical significance and potential utility. In this paper, we review the applications of PET probes that target immune cells in molecular imaging.

Construction of [89Zr]Zr-Labeled HuL13 for ImmunoPET Imaging of LAG-3 Checkpoint Expression on Tumor-Infiltrating T Cells

Lymphocyte activation gene 3 (LAG-3) has attracted much attention as a potentially valuable immune checkpoint. Individual identification of LAG-3 expression at screening and during treatment could improve the successful implementation of anti-LAG-3 therapies. HuL13 is a human IgG1 monoclonal antibody that binds to the LAG-3 receptor in T cells. Here, we used [89Zr]Zr-labeled HuL13 to delineate LAG-3+ T-cell infiltration into tumors via positron emission tomography (PET) imaging. A549/LAG-3 cells, which stably express LAG-3, were generated by infection with lentivirus. The uptake of [89Zr]Zr-DFO-HuL13 in A549/LAG-3 cells was greater than that in the negative control (A549/NC) cells at each time point. The equilibrium dissociation constant (Kd) of [89Zr]Zr-DFO-HuL13 for the LAG-3 receptor was 8.22 nM. PET imaging revealed significant uptake in the tumor areas of A549/LAG-3 tumor-bearing mice from 24 h after injection (SUVmax = 2.43 ± 0.06 at 24 h). As a proof of concept, PET imaging of the [89Zr]Zr-DFO-HuL13 tracer was further investigated in an MC38 tumor-bearing humanized LAG-3 mouse model. PET imaging revealed that the [89Zr]Zr-DFO-HuL13 tracer specifically targets human LAG-3 expressed on tumor-infiltrating lymphocytes (TILs). In addition to the tumors, the spleen was also noticeably visible. Tumor uptake of the [89Zr]Zr-DFO-HuL13 tracer was lower than its uptake in the spleen, but high uptake in the spleen could be reduced by coinjection of unlabeled antibodies. Coinjection of unlabeled antibodies increases tracer activity in the blood pool, thereby improving tumor uptake. Dosimetry evaluation of the healthy mouse models revealed that the highest absorbed radiation dose was in the spleen, followed by the liver and heart wall. In summary, these studies demonstrate the feasibility of using the [89Zr]Zr-DFO-HuL13 tracer for the detection of LAG-3 expression on TILs. Further clinical evaluation of the [89Zr]Zr-DFO-HuL13 tracer may be of significant help in the stratification and management of patients suitable for anti-LAG-3 therapy.

Navigating the landscape of PD-1/PD-L1 imaging tracers: from challenges to opportunities

Immunotherapy targeted to immune checkpoint inhibitors, such as the program cell death receptor (PD-1) and its ligand (PD-L1), has revolutionized cancer treatment. However, it is now well-known that PD-1/PD-L1 immunotherapy response is inconsistent among patients. The current challenge is to customize treatment regimens per patient, which could be possible if the PD-1/PD-L1 expression and dynamic landscape are known. With positron emission tomography (PET) imaging, it is possible to image these immune targets non-invasively and system-wide during therapy. A successful PET imaging tracer should meet specific criteria concerning target affinity, specificity, clearance rate and target-specific uptake, to name a few. The structural profile of such a tracer will define its properties and can be used to optimize tracers in development and design new ones. Currently, a range of PD-1/PD-L1-targeting PET tracers are available from different molecular categories that have shown impressive preclinical and clinical results, each with its own advantages and disadvantages. This review will provide an overview of current PET tracers targeting the PD-1/PD-L1 axis. Antibody, peptide, and antibody fragment tracers will be discussed with respect to their molecular characteristics and binding properties and ways to optimize them.

Preclinical imaging evaluation of a bispecific antibody targeting hPD1/CTLA4 using humanized mice

BACKGROUND

The lack of an efficient way to screen patients who are responsive to immunotherapy challenges PD1/CTLA4-targeting cancer treatment. Immunotherapeutic efficacy cannot be clearly determined by peripheral blood analyses, tissue gene markers or CT/MR value. Here, we used a radionuclide and imaging techniques to investigate the novel dual targeted antibody cadonilimab (AK104) in PD1/CTLA4-positive cells in vivo.

METHODS

First, humanized PD1/CTLA4 mice were purchased from Biocytogen Pharmaceuticals (Beijing) Co., Ltd. to express hPD1/CTLA4 in T-cells. Then, mouse colon cancer MC38-hPD-L1 cell xenografts were established in humanized mice. A bispecific antibody targeting PD1/CTLA4 (AK104) was labeled with radio-nuclide iodine isotopes. Immuno-PET/CT imaging was performed using a bispecific monoclonal antibody (mAb) probe 124I-AK104, developed in-house, to locate PD1+/CTLA4+ tumor-infiltrating T cells and monitor their distribution in mice to evaluate the therapeutic effect.

RESULTS

The 124I-AK104 dual-antibody was successfully constructed with ideal radiochemical characteristics, in vitro stability and specificity. The results of immuno-PET showed that 124I-AK104 revealed strong hPD1/CTLA4-positive responses with high specificity in humanized mice. High uptake of 124I-AK104 was observed not only at the tumor site but also in the spleen. Compared with PD1- or CTLA4-targeting mAb imaging, 124I-AK104 imaging had excellent standard uptake values at the tumor site and higher tumor to nontumor (T/NT) ratios.

CONCLUSIONS

The results demonstrated the potential of translating 124I-AK104 into a method for screening patients who benefit from immunotherapy and the efficacy, as well as the feasibility, of this method was verified by immuno-PET imaging of humanized mice.

Development of Small HN Linked Radionuclide Iodine-125 for Nanocarrier Image Tracing in Mouse Model

Background

Radionuclides have important roles in clinical tumor radiotherapy as they are used to kill tumor cells or as imaging agents for drug tracing. The application of radionuclides has been developing as an increasing number of nanomaterials are used to deliver radionuclides to tumor areas to kill tumor cells. However, promoting the efficient combination of radionuclides and nanocarriers (NCs), enhancing radionuclide loading efficiency, and avoiding environmental pollution caused by radionuclide overuse are important challenges that hinder their further development.

Methods

In the present study, a new small molecule compound (3-[[(2S)-2-hydroxy-3-(4-hydroxyphenyl)-1-carbonyl] amino]-alanine, abbreviation: HN, molecular formula: C12H16N2O5) was synthesized as a linker between radionuclide iodine-125 (125I) and NCs to enable a more efficient binding between NCs and radionuclides.

Results

In vitro evidence indicated that the linker was able to bind 125I with higher efficiency (labeling efficiency >80%) than that of tyrosine, as well as various NCs, such as cellulose nanofibers, metal oxide NCs, and graphene oxide. Single-photon emission computed tomography/computed tomography imaging demonstrated the biological distribution of 125I-labeled NCs in different organs/tissues after administration in mice.

Conclusion

These results showed an improvement in radionuclide labeling efficiency for nanocarriers and provided an approach for nanocarrier image tracing.

An iodine‑labelled Antibody-drug conjugate PET probe for noninvasive monitoring of Nectin-4 expression in urothelial carcinoma

BACKGROUND AND PURPOSE

Some kinds of antibody-drug conjugate (ADC) with high affinity to Nectin-4 have demonstrated breakthrough progress in the third-line setting for bladder cancer. However, many patients are still difficult to benefit from treatment based on the heterogeneity of tumour. As the most advanced auxiliary treatment technology, treatment visualization can most intuitively predict the effectiveness of drug treatment, and timely detect the occurrence of drug resistance. Among them, nuclear medicine molecular probes play an important role in this field.

METHODS

124/125I-EV was prepared by labelling Enfortumad Vedetin (EV), an ADC drugs widely used in clinic targeted Nectin-4, with Na124/125I using N-bromine succinimide as oxidant. The radiochemical purity was analyzed via radio-TLC and bioactivity was measured by enzyme-linked immunosorbent assay. Cell uptake assay and small-animal PET imaging were performed to verified the specificity and targeting.

KEY RESULTS

124/125I-EV was prepared with high labeling yield and radiochemical purity. ELISA assays demonstrated that 124I-EV maintained the same high bioactivity as EV with significantly higher uptake in SW780 cells (Nectin-4 positive, 4.05 ± 0.32 %IA/5 × 105 cells at 8 h) than that in T24 cells (Nectin-4 negative, 1.34 ± 0.18 %IA/5 × 105 cells, p < 0.001). In PET imaging, 124I-EV had a significantly higher accumulation in SW780 tumour than that in T24 tumour and the uptake in SW780 tumour could be specifically blocked when co-injected with cold EV. The signal-to-noise ratio at the tumour site gradually increased with time, and peaked at 72 h.

CONCLUSION AND IMPLICATIONS

124I-EV was successfully prepared with high specificity and binding affinity of Nectin-4. This radioactive probe completely simulates the internal circulation of ADC drugs and tumour uptake and retention, which will greatly improve the clinical application of ADC therapy.

124I-labeled anti-CD147 antibody for noninvasive detection of CD147-positive pan-cancers: construction and preclinical studies

Extracellular matrix metalloproteinase inducer CD147 is a glycoprotein on the cell surface. There is minimal expression of CD147 in normal epithelial and fetal tissues, but it is highly expressed in a number of aggressive tumors. CD147 has been implicated in pan-cancer immunity and progression. With the development of CD147-targeting therapeutic strategy, accurate detection of CD147 expression in tumors and its changes during the therapy is necessary. In this study we constructed a novel radiotracer by labeling the anti-CD147 mAb with radionuclide 124/125I (124/125I-anti-CD147) for noninvasive detection of CD147 expression in pan-cancers, and characterized its physicochemical properties, affinity, metabolic characteristics, biodistribution and immunoPET imaging with 124I-IgG and 18F-FDG as controls. By examining the expression of CD147 in cancer cell lines, we found high CD147 expression in colon cancer cells LS174T, FADU human pharyngeal squamous cancer cells and 22RV1 human prostate cancer cells, and low expression of CD147 in human pancreatic cancer cells ASPC1 and human gastric cancer cells BGC823. 124/125I-anti-CD147 was prepared using N-bromine succinimide (NBS) as oxidant and purified by PD-10 column. Its radiochemical purity (RCP) was over 99% and maintained over 85% in saline or 5% human serum albumin (HSA) for more than 7 d; the RCP of 125I-anti-CD147 in blood was over 90% at 3 h post injection (p.i.) in healthy mice. The Kd value of 125I-anti-CD147 to CD147 protein was 6.344 nM, while that of 125I-IgG was over 100 nM. 125I-anti-CD147 showed much greater uptake in CD147 high-expression cancer cells compared to CD147 low-expression cancer cells. After intravenous injection in healthy mice, 125I-anti-CD147 showed high initial uptake in blood pool and liver, the uptake was decreased with time. The biological half-life of distribution and clearance phases in healthy mice were 0.63 h and 19.60 h, respectively. The effective dose of 124I-anti-CD147 was estimated as 0.104 mSv/MBq. We conducted immunoPET imaging in tumor-bearing mice, and demonstrated a significantly higher tumor-to-muscle ratio of 124I-anti-CD147 compared to that of 124I-IgG and 18F-FDG in CD147 (+) tumors. The expression levels of CD147 in cells and tumors were positively correlated with the maximum standardized uptake value (SUVmax) (P < 0.01). In conclusion, 124/125I-anti-CD147 displays high affinity to CD147, and represents potential for the imaging of CD147-positive tumors. The development of 124I-anti-CD147 may provide new insights into the regulation of tumor microenvironment and formulation of precision diagnosis and treatment programs for tumors.

Construction and Preclinical Evaluation of a 124/125I-Labeled Specific Antibody Targeting PD-L2 in Lung Cancer

Programmed cell death-ligand 2 (PD-L2) is an important emerging molecule of the immune checkpoint, which is closely related to the prognosis of patients with immune checkpoint inhibitor (ICI) therapy. The quantification of PD-L2 can provide a potential reference for patients who benefit from ICI treatment. In this study, we used iodine isotope (^nat/124/125I)-labeled PD-L2 antibody (ATL2) to noninvasively detect PD-L2 expression in mice with human lung adenocarcinoma A549 cell lines. The radiochemical yields of ¹²⁵I-ATL2 and ¹²⁴I-ATL2 were 73.56 ± 3.72% and 69.46 ± 2.05%, respectively. The radiochemical purity (RCP) of the tracers was more than 99%. The positive cell line A549-PDL2 was constructed by lentivirus. Western blot, immunofluorescence, and flow cytometry indicated that the A549-PDL2 cells showed a higher PD-L2 protein level than the A549 cells. The dissociation constant of ¹²⁵I-ATL2 binding to the PD-L2 protein was 7.25 nM. Cellular uptake experiments confirmed that the uptake of ¹²⁵I-ATL2 in A549-PDL2 cells was higher than that in A549 cells at each time point (P < 0.0001). Micro-PET/CT showed significant uptake in the tumor region of A549-PDL2 tumor-bearing mice 24 h postinjection of ¹²⁴I-ATL2 compared with that of other groups (SUV_max = 0.75 ± 0.06, 0.19 ± 0.07, and 0.27 ± 0.05, respectively). Consistently, the biodistribution of the tracers at 24 h postinjection showed a higher tumor uptake in A549-PDL2 mice (7.11 ± 0.38 %ID/g for ¹²⁴I-ATL2 in A549-PDL2 mice vs 2.72 ± 0.15 %ID/g for ¹²⁴I-ATL2 in A549 mice vs 3.89 ± 0.65 %ID/g for ¹²⁴I-IgG in A549-PDL2 mice). The dosimetry estimation by using Olinda software showed that the effective dose of ¹²⁴I-ATL2 was 3.62 × 10^-2 mSv/MBq, which is within the range of acceptable doses. Immunohistochemical results further confirmed that the expression of PD-L2 in the tumor tissues of A549-PDL2-bearing mice was higher than that of the A549 model mice. In conclusion, the development of ^124/125I-ATL2 provides the first noninvasive quantification of PD-L2 expression in lung cancer by molecular imaging, which provides a new reference for screening potential beneficiaries of ICI therapy.

Positron emission tomography molecular imaging to monitor anti-tumor systemic response for immune checkpoint inhibitor therapy

Immune checkpoint inhibitors (ICIs) achieve a milestone in cancer treatment. Despite the great success of ICI, ICI therapy still faces a big challenge due to heterogeneity of tumor, and therapeutic response is complicated by possible immune-related adverse events (irAEs). Therefore, it is critical to assess the systemic immune response elicited by ICI therapy to guide subsequent treatment regimens. Positron emission tomography (PET) molecular imaging is an optimal approach in cancer diagnosis, treatment effect evaluation, follow-up, and prognosis prediction. PET imaging can monitor metabolic changes of immunocytes and specifically identify immuno-biomarkers to reflect systemic immune responses. Here, we briefly review the application of PET molecular imaging to date of systemic immune responses following ICI therapy and the associated rationale.

Imaging Hallmarks of Sarcoma Progression Via X-ray Computed Tomography: Beholding the Flower of Evil

Simple Summary

Sarcomas represent the largest group of rare solid tumors that arise from mesenchymal stem cells and are a leading cause of cancer death in individuals younger than 20 years of age. There is an immediate need for the development of an algorithm for the early accurate diagnosis of sarcomas due to the high rate of diagnostic inaccuracy, which reaches up to 30%. X-ray computed tomography is a non-invasive imaging technique used to obtain detailed internal images of the human or animal body in clinical practice and preclinical studies. We summarized the main imaging features of soft tissue and bone sarcomas, and noted the development of new molecular markers to reach tumor type-specific imaging. Also, we demonstrated the possibility of the use X-ray computed microtomography for non-destructive 3D visualization of sarcoma progression in preclinical studies. Finding correlations between X-ray computed tomography modalities and the results of the histopathological specimen examination may significantly increase the accuracy of diagnostics, which leads to the initiation of appropriate management in a timely manner and, consequently, to improved outcomes.

Abstract

Sarcomas are a leading cause of cancer death in individuals younger than 20 years of age and represent the largest group of rare solid tumors. To date, more than 100 morphological subtypes of sarcomas have been described, among which epidemiology, clinical features, management, and prognosis differ significantly. Delays and errors in the diagnosis of sarcomas limit the number of effective therapeutic modalities and catastrophically worsen the prognosis. Therefore, the development of an algorithm for the early accurate diagnosis of sarcomas seems to be as important as the development of novel therapeutic advances. This literature review aims to summarize the results of recent investigations regarding the imaging of sarcoma progression based on the use of X-ray computed tomography (CT) in preclinical studies and in current clinical practice through the lens of cancer hallmarks. We attempted to summarize the main CT imaging features of soft-tissue and bone sarcomas. We noted the development of new molecular markers with high specificity to antibodies and chemokines, which are expressed in particular sarcoma subtypes to reach tumor type-specific imaging. We demonstrate the possibility of the use of X-ray computed microtomography (micro-CT) for non-destructive 3D visualization of solid tumors by increasing the visibility of soft tissues with X-ray scattering agents. Based on the results of recent studies, we hypothesize that micro-CT enables the visualization of neovascularization and stroma formation in sarcomas at high-resolution in vivo and ex vivo, including the novel techniques of whole-block and whole-tissue imaging. Finding correlations between CT, PET/CT, and micro-CT imaging features, the results of the histopathological specimen examination and clinical outcomes may significantly increase the accuracy of soft-tissue and bone tumor diagnostics, which leads to the initiation of appropriate histotype-specific management in a timely manner and, consequently, to improved outcomes.

Virtual Biopsy in Soft Tissue Sarcoma. How Close Are We?

A shift in radiology to a data-driven specialty has been unlocked by synergistic developments in imaging biomarkers (IB) and computational science. This is advancing the capability to deliver "virtual biopsies" within oncology. The ability to non-invasively probe tumour biology both spatially and temporally would fulfil the potential of imaging to inform management of complex tumours; improving diagnostic accuracy, providing new insights into inter- and intra-tumoral heterogeneity and individualised treatment planning and monitoring. Soft tissue sarcomas (STS) are rare tumours of mesenchymal origin with over 150 histological subtypes and notorious heterogeneity. The combination of inter- and intra-tumoural heterogeneity and the rarity of the disease remain major barriers to effective treatments. We provide an overview of the process of successful IB development, the key imaging and computational advancements in STS including quantitative magnetic resonance imaging, radiomics and artificial intelligence, and the studies to date that have explored the potential biological surrogates to imaging metrics. We discuss the promising future directions of IBs in STS and illustrate how the routine clinical implementation of a virtual biopsy has the potential to revolutionise the management of this group of complex cancers and improve clinical outcomes.

124I Radiolabeled Basiliximab for CD25-Targeted Immuno-PET Imaging of Activated T Cells

Activated T cells played critical roles in immunotherapy and adoptive T cell therapy, and a non-invasive imaging strategy can provide us useful information concerning the transportation, accumulation, and homing of T cells in vivo. In this paper, by utilizing the long half-life radionuclide iodine-124 (¹²⁴I) and CD25 specific monoclonal antibody Basiliximab, we have fabricated a novel probe, namely, ¹²⁴I-Basiliximab, which was highly promising in the immuno-PET imaging of T cells. In vitro, ¹²⁴I-Basiliximab had superior affinity to CD25 protein (Kd = 5.31 nM) and exhibited much higher accumulation in CD25 high-expression lymphoma cell line Karpas299 than that in CD25-negative cell line Daudi. In vivo, ¹²⁴I-Basiliximab was excreted slowly from the body of mice, rendering it a relatively high effective dose (0.393 mSv/MBq) when applied in the immuno-PET imaging. In Karpas299 tumor xenograft, ¹²⁴I-Basiliximab probe was observed to accumulate in the tumor quickly after tracer administration, with the optimal image acquired at 24 h post-injection. More importantly, PHA-activated hPBMC had much higher uptake of ¹²⁴I-Basiliximab, indicating the potential utility of ¹²⁴I-Basiliximab to discriminate activated hPBMC from its non-activated status. In summary, ¹²⁴I-Basiliximab was fabricated for the first time, which can be applied in CD25-targeted immuno-PET imaging of activated T cells in vivo.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [18F]-FDG and NA [18F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of 11C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

China’s radiopharmaceuticals on expressway: 2014–2021

This review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Toripalimab: the First Domestic Anti-Tumor PD-1 Antibody in China

Toripalimab (Tuoyi™) is a selective, recombinant, humanized monoclonal antibody against programmed death protein 1 (PD-1) developed by Shanghai Junshi Bioscience Co., Ltd. Toripalimab is able to bind to PD-1 and block the interaction with its ligands. The binding of toripalimab to PD-1 is mainly attributed to the heavy chain of the former and the FG loop of the latter. Toripalimab received a conditional approval in China for the treatment of melanoma (second-line) in December, 2018. It has also received approvals to treat nasopharyngeal carcinoma (first-line and third-line) and urothelial carcinoma (second-line) in 2021. Additionally, several orphan drug designations were granted to toripalimab by the US Food and Drug Administration. Toripalimab has exhibited primary anti-tumor effects in tumors such as melanoma, lung cancer, digestive tract tumors, hepatobiliary and pancreatic tumors, neuroendocrine neoplasms, nasopharyngeal carcinoma and urothelial carcinoma. It showed a satisfactory anti-tumor effect and long-term survival benefits in Chinese melanoma patients, while the combination of axitinib with toripalimab exhibited an impressive result in metastatic mucosal melanoma. As a checkpoint inhibitor, toripalimab was generally well-tolerated in the enrolled patients. Due to different study populations, comparisons could not be made directly between toripalimab and other drugs in most cases. Nevertheless, the introduction of toripalimab may offer a valuable choice for decision-making in the treatment of tumors in the future.

Novel Nanocrystal Injection of Insoluble Drug Anlotinib and Its Antitumor Effects on Hepatocellular Carcinoma

The molecularly targeted agent anlotinib offers a novel therapeutic strategy against advanced hepatocellular carcinoma (HCC). With this study, we aimed to solve the technical problem of anlotinib being insoluble in injectable solutions; we also aimed to assess the antitumor activity of anlotinib on hepatocellular carcinoma cells. We prepared an anlotinib nanocrystal injection by wet grinding, and we optimized the prescription process using a transmission electron microscope (TEM) and a laser particle size analyzer (LPSA). The release of anlotinib from the injected nanocrystals was evaluated using LC-MS/MS in vitro, and the drug’s anti-tumor effects were assessed in a nude mice tumor model. The anlotinib nanocrystals had a uniform particle size distribution (the average nanoparticle size was ~200 nm). The preparation of anlotinib into nanocrystals did not change the original crystal structure. The intravenous injection of anlotinib nanocrystals achieved anti-tumor activity at very low doses compared to those required for oral administration of an anlotinib suspension: anlotinib nanocrystals at a dose of 50 μg/kg inhibited the subcutaneous growth of the HCC cell line MHCC97-H; whereas the dose of anlotinib suspension required for an equivalent effect was 1 mg/kg. Therefore, our novel anlotinib nanocrystal injection preparation provides an option for achieving a safe and effective molecularly targeted therapy against advanced HCC.

Knockdown of FBI-1 Inhibits the Warburg Effect and Enhances the Sensitivity of Hepatocellular Carcinoma Cells to Molecular Targeted Agents via miR-3692/HIF-1α

The transcription suppressor factor FBI-1 (the factor that binds to inducer of short transcripts-1) is an important regulator of hepatocellular carcinoma (HCC). In this work, the results showed that FBI-1 promoted the Warburg effect and enhances the resistance of hepatocellular carcinoma cells to molecular targeted agents. Knockdown of FBI-1 via its small-interfering RNA (siRNA) inhibited the ATP level, lactate productions, glucose uptake or lactate dehydrogenase (LDH) activation of HCC cells. Transfection of siFBI-1 also decreased the expression of the Warburg-effect-related factors: hypoxia-inducible factor-1 alpha (HIF-1α), lactate dehydrogenase A (LDHA), or GLUT1, and the epithelial-mesenchymal transition-related factors, Vimentin or N-cadherin. The positive correlation between the expression of FBI-1 with HIF-1α, LDHA, or GLUT1 was confirmed in HCC tissues. Mechanistically, the miR-30c repressed the expression of HIF-1α by binding to the 3'-untranslated region (3'-UTR) of HIF-1α in a sequence-specific manner, and FBI-1 enhanced the expression of HIF-1α and HIF-1α pathway's activation by repressing the expression of miR. By modulating the miR-30c/HIF-1α, FBI-1 promoted the Warburg effect or the epithelial-mesenchymal transition of HCC cells and promoted the resistance of HCC cells to molecular targeted agents.

Current status and future perspective of radiopharmaceuticals in China

Radiopharmaceuticals are essential components of nuclear medicine and serve as one of the cornerstones of molecular imaging and precision medicine. They provide new means and approaches for early diagnosis and treatment of diseases. After decades of development and hard efforts, a relatively matured radiopharmaceutical production and management system has been established in China with high-quality facilities. This review provides an overview of the current status of radiopharmaceuticals on production and distribution, clinical application, and regulatory supervision and also describes some important advances in research and development and clinical translation of radiopharmaceuticals in the past 10 years. Moreover, some prospects of research and development of radiopharmaceuticals in the near future are discussed.

PET imaging of immune checkpoint proteins in oncology

Despite the remarkable clinical successes of immune checkpoint inhibitors (ICIs) in various advanced cancers, response is still limited to a subset of patients that generally exhibit tumoral expression of immune checkpoint (IC) proteins. Development of biomarkers assessing the expression of such ICs is therefore a major challenge nowadays to refine patient selection and improve therapeutic benefits. Positron emission tomography (PET) imaging using IC-targeted radiolabeled monoclonal antibodies (immunoPET) provides a non-invasive and whole-body visualization of in vivo IC biodistribution. As such, PET imaging of ICs may serve as a robust biomarker to predict and monitor responses to ICIs, complementing the existing immunohistochemical techniques. Besides monoclonal antibodies, other PET radioligand formats, ranging from antibody-derived fragments to small proteins, have gained increasing interest owing to their faster pharmacokinetics and enhanced imaging characteristics. We provide an overview of the various strategies investigated so far for PET imaging of ICs in preclinical and clinical studies, emphasizing their benefits and limitations. Moreover, we discuss various parameters to consider for designing optimized and best-suited PET radioligands.

Positron Emission Tomography Imaging of Programmed Death 1 Expression in Cancer Patients Using 124I-Labeled Toripalimab: A Pilot Clinical Translation Study

PURPOSE

Although anti-programmed cell death molecule-1 (PD-1)/PD-1 ligand therapy has achieved remarkable success in oncology field, the low response rate and lack of accurate prognostic biomarker identifying benefiting patients remain unresolved challenges. This study developed a PD-1 targeting radiotracer 124I-labeled toripalimab (124I-JS001) for clinical PET imaging and evaluated its biodistribution, safety, and dosimetry in human.

METHODS

Patients with melanoma or urologic cancer confirmed by pathology were enrolled. 124I-JS001 PET/CT and PET/MR were performed with or without coinjection of 5 mg unlabeled JS001, and 18F-FDG PET was undertaken within 1 week.

RESULTS

Eight melanoma and 3 urologic cancer patients were enrolled. No adverse events were noticed during the whole examination after the injection of 124I-JS001 and an acceptable dosimetry of 0.236 mSv/MBq was found. 124I-JS001 PET/CT showed high uptake in spleen and liver and slight uptake in bone marrow and lung. All primary and metastatic tumor lesions in 11 patients demonstrated different levels of uptake of 124I-JS001 with SUVmax ranging from 0.2 to 4.7. With coinjection of unlabeled JS001, the uptake in spleen was reduced significantly (P < 0.05), whereas tumor uptake and tumor background ratio increased significantly (P < 0.05). Four patients undertook regional 124I-JS001 PET/MR. All tumor lesions were detected effectively with abnormal MR signal on PET/MR, whereas PET/MR detected liver lesions more sensitively than PET/CT.

CONCLUSIONS

The first-in-human study demonstrated 124I-JS001 was a safe tracer for PET with acceptable dosimetry, and the PET/CT results showed a favorable biodistribution. PET/MR could detect liver lesions more sensitively than PET/CT.

Recent developments on PET radiotracers for TSPO and their applications in neuroimaging

The 18 kDa translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, is predominately localized to the outer mitochondrial membrane in steroidogenic cells. Brain TSPO expression is relatively low under physiological conditions, but is upregulated in response to glial cell activation. As the primary index of neuroinflammation, TSPO is implicated in the pathogenesis and progression of numerous neuropsychiatric disorders and neurodegenerative diseases, including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), multiple sclerosis (MS), major depressive disorder (MDD) and obsessive compulsive disorder (OCD). In this context, numerous TSPO-targeted positron emission tomography (PET) tracers have been developed. Among them, several radioligands have advanced to clinical research studies. In this review, we will overview the recent development of TSPO PET tracers, focusing on the radioligand design, radioisotope labeling, pharmacokinetics, and PET imaging evaluation. Additionally, we will consider current limitations, as well as translational potential for future application of TSPO radiopharmaceuticals. This review aims to not only present the challenges in current TSPO PET imaging, but to also provide a new perspective on TSPO targeted PET tracer discovery efforts. Addressing these challenges will facilitate the translation of TSPO in clinical studies of neuroinflammation associated with central nervous system diseases.

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.

Harnessing the PD-L1 interface peptide for positron emission tomography imaging of the PD-1 immune checkpoint

Interface peptides that mediate protein-protein interactions (PPI) are a class of important lead compounds for designing PPI inhibitors. However, their potential as precursors for radiotracers has never been exploited. Here we report that the interface peptides from programmed death-ligand 1 (PD-L1) can be used in positron emission tomography (PET) imaging of programmed cell death 1 (PD-1) with high accuracy and sensitivity. Moreover, the performance differentiation between murine PD-L1 derived interface peptide (mPep-1) and human PD-L1 derived interface peptide (hPep-1) as PET tracers for PD-1 unveiled an unprecedented role of a non-critical residue in target binding, highlighting the significance of PET imaging as a companion diagnostic in drug development. Collectively, this study not only provided a first-of-its-kind peptide-based PET tracer for PD-1 but also conveyed a unique paradigm for developing imaging agents for highly challenging protein targets, which could be used to identify other protein biomarkers involved in the PPI networks.