18F-Alanine Derivative Serves as an ASCT2 Marker for Cancer Imaging

Locally unlocks prodrugs by radiopharmaceutical in tumor for cancer therapy

Chemotherapy is the first-line treatment for cancer, but its systemic toxicity can be severe. Tumor-selective prodrug activation offers promising opportunities to reduce systemic toxicity. Here, we present a strategy for activating prodrugs using radiopharmaceuticals. This strategy enables the targeted release of chemotherapeutic agents due to the high tumor-targeting capability of radiopharmaceuticals. [18F]FDG (2-[18F]-fluoro-2-deoxy-D-glucose), one of the most widely used radiopharmaceuticals in clinics, can trigger Pt(IV) complex for controlled release of axial ligands in tumors, it might be mediated by hydrated electrons generated by water radiolysis resulting from the decay of radionuclide 18F. Its application offers the controlled release of fluorogenic probes and prodrugs in living cells and tumor-bearing mice. Of note, an OxaliPt(IV) linker is designed to construct an [18F]FDG-activated antibody-drug conjugate (Pt-ADC). Sequential injection of Pt-ADC and [18F]FDG efficiently releases the toxin in the tumor and remarkably suppresses the tumor growth. Radiotherapy is booming as a perturbing tool for prodrug activation, and we find that [18F]FDG is capable of deprotecting various radiotherapy-removable protecting groups (RPGs). Our results suggest that tumor-selective radiopharmaceutical may function as a trigger, for developing innovative prodrug activation strategies with enhanced tumor selectivity.

B-Glycine as a marker for β cell imaging and β cell mass evaluation

PURPOSE

β cell mass (BCM) and function are essential to the diagnosis and therapy of diabetes. Diabetic patients serve β cell loss is, and damage of β cells leads to severe insulin deficiency. Our understanding of the role of BCM in diabetes progression is extremely limited by lacking efficient methods to evaluate BCM in vivo. In vitro methods of labeling islets, including loading of contrast reagent or integration of exogenous biomarker, require artificial manipulation on islets, of which the clinical application is limited. Imaging methods targeting endogenous biomarkers may solve the above problems. However, traditional reagents targeting GLP-1R and VAMT2 result in a high background of adjacent tissues, complicating the identification of pancreatic signals. Here, we report a non-invasive and quantitative imaging technique by using radiolabeled glycine mimics ([18F]FBG, a boron-trifluoride derivative of glycine) to assay islet function and monitor BCM changes in living animals.

METHODS

Glycine derivatives, FBG, FBSa, 2Me-FBG, 3Me-FBG, were successfully synthesized and labeled with 18F. Specificity of glycine derivatives were characterized by in vitro experiment. PET imaging and biodistribution studies were performed in animal models carring GLYT over-expressed cells. In vivo evaluation of BCM with [18F]FBG were performed in STZ (streptozocin) induced T1D (type 1 diabetes) models.

RESULTS

GLYT responds to excess blood glycine levels and transports glycine into islet cells to maintain the activity of the glycine receptor (GLYR). Best PET imaging condition was 80 min after given a total of 240 ~ 250 nmol imaging reagent (a mixture of [18F]FBG and natural glycine) intravenously. [18F]FBG can detect both endogenous and exogenous islets clearly in vivo. When applied to STZ induced T1D mouse models, total uptake of [18F]FBG in the pancreas exhibited a linear correlation with survival BCM.

CONCLUSION

[18F]FBG targeting the endogenous glycine transporter (GLYT), which is highly expressed on islet cells, avoiding extra modification on islet cells. Meanwhile the highly restricted expression pattern of GLYT excluded the background in adjacent tissues. This [18F]FBG-based imaging technique provides a non-invasive method to quantify BCM in vivo, implying a new evaluation index for diabetic assessment.

Synthesis and Biological Evaluation of Fluorine-18 and Deuterium Labeled l-Fluoroalanines as Positron Emission Tomography Imaging Agents for Cancer Detection

To fully explore the potential of 18F-labeled l-fluoroalanine for imaging cancer and other chronic diseases, a simple and mild radiosynthesis method has been established to produce optically pure l-3-[18F]fluoroalanine (l-[18F]FAla), using a serine-derivatized, five-membered-ring sulfamidate as the radiofluorination precursor. A deuterated analogue, l-3-[18F]fluoroalanine-d3 (l-[18F]FAla-d3), was also prepared to improve metabolic stability. Both l-[18F]FAla and l-[18F]FAla-d3 were rapidly taken up by 9L/lacZ, MIA PaCa-2, and U87MG cells and were shown to be substrates for the alanine-serine-cysteine (ASC) amino acid transporter. The ability of l-[18F]FAla, l-[18F]FAla-d3, and the d-enantiomer, d-[18F]FAla-d3, to image tumors was evaluated in U87MG tumor-bearing mice. Despite the significant bone uptake was observed for both l-[18F]FAla and l-[18F]FAla-d3, the latter had enhanced tumor uptake compared to l-[18F]FAla, and d-[18F]FAla-d3 was not specifically taken up by the tumors. The enhanced tumor uptake of l-[18F]FAla-d3 compared with its nondeuterated counterpart, l-[18F]FAla, warranted the further biological investigation of this radiotracer as a potential cancer imaging agent.

Recent Advances in 18F-Labeled Amino Acids Synthesis and Application

Radiolabeled amino acids are an important class of agents for positron emission tomography imaging that target amino acid transporters in many tumor types. Traditional ¹⁸F-labeled amino acid synthesis strategies are always based on nucleophilic aromatic substitution reactions with multistep radiosynthesis and low radiochemical yields. In recent years, new ¹⁸F-labeling methodologies such as metal-catalyzed radiofluorination and heteroatom (B, P, S, Si, etc.)-¹⁸F bond formation are being effectively used to synthesize radiopharmaceuticals. This review focuses on recent advances in the synthesis, radiolabeling, and application of a series of ¹⁸F-labeled amino acid analogs using new ¹⁸F-labeling strategies.

MRI measurement of alanine uptake in a mouse xenograft model of U-87 MG glioblastoma

The potential use of alanine as an MRI contrast agent was investigated. The relaxation properties of alanine solutions were measured at 9.4 T. The T₂ relaxivity caused by the chemical exchange (R_2ex) between amine protons and water protons was 0.10 mM^-1 s^-1 at 37 °C. As a demonstration, alanine uptake in a mouse xenograft model of U-87 MG glioblastoma was measured using MRI, and was compared with immunohistochemistry staining of ASCT2, a transporter that imports amino acids into cancer cells. Statistically significant (p = 0.0079) differences in ASCT2 distribution were found between regions that show strong and weak alanine uptake in MRI. To better understand the influence of perfusion, the effect of ASCT2 inhibition on the alanine uptake in MRI was investigated, and dynamic contrast enhanced MRI was compared with alanine MRI.

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.

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.

Recent developments in ligands and chemical probes targeting solute carrier transporters

Solute carrier (SLC) membrane transporters remain a largely unexploited target class, despite their central roles in cell identity and metabolism. This gap is reflected in the lack of high-quality chemical ligands or probes and in the small number of compounds that have progressed toward clinical development. In this review, we discuss recent advancements in SLC ligand discovery as well as new candidates that have been added to the investigational toolkit, with a particular focus on first-in-class ligands and the cognate discovery strategies. The availability of new probes expands the opportunity to elucidate the functions of SLCs and their relevance in physiology and explores any future potential of SLC druggability.

18F-Boramino acid PET/CT in healthy volunteers and glioma patients

PURPOSE

In this work, the safety, biodistribution, and radiation dosimetry of large neutral amino acid transporter type-1 (LAT-1) targeting PET tracer ¹⁸F-trifluorobborate-derived tyrosine (denoted as ¹⁸F-FBY) has been investigated. It is designed as a first-in-human study in healthy volunteers and to assay LAT-1 expression level in glioma patients.

METHODS

Six healthy volunteers (3 M, 3 F) underwent whole-body PET acquisitions at multiple time points after bolus injection of ¹⁸F-FBY. Regions of interest (ROIs) were mapped manually on major organs, and then the time-activity curves (TACs) were obtained. Dosimetry was calculated with the OLINDA/EXM software. Thirteen patients who were suspected of glioma were scanned with PET/CT at 30 min after ¹⁸F-FBY injection. Within 7 days after PET/CT, the tumor was removed surgically, and LAT-1 immunohistochemical staining for LAT-1 was performed on tumor samples and correlated with ¹⁸F-FBY PET imaging.

RESULTS

¹⁸F-FBY was well tolerated by all healthy volunteers, and no adverse symptoms were observed or reported. ¹⁸F-FBY is rapidly cleared from the blood circulation and excreted mainly through the kidneys and urinary tract. The effective dose (ED) was 0.0039 ± 0.0006 mSv/MBq. In 14 surgical confirmed gliomas (one of the patiens had two gliomas), ¹⁸F-FBY uptake increased consistently with tumor grade, with maximum standard uptake values (SUV_max) of 0.28 ± 0.14 and 2.84 ± 0.46 and tumor-to-normal contralateral activity (T/N) ratio of 2.30 ± 1.26 and 24.56 ± 6.32 in low- and high-grade tumors, respectively. In addition to the significant difference in the uptakes between low- and high-grade gliomas (P < 0.001), the immunohistochemical staining confirmed the positive correlations between the SUV_max, LAT-1 expression (r² = 0.80, P < 0.001), and Ki-67 labeling index (r² = 0.79, P < 0.001).

CONCLUSION

¹⁸F-FBY is a PET tracer with favorable dosimetry profile and pharmacokinetics. It has the potential to assay LAT-1 expression in glioma patients and may provide imaging guidance for further boron neutron capture therapy of gliomas.

TRIAL REGISTRATION

clinicaltrials.gov (NCT03980431).

Amino Acid Transporters on the Guard of Cell Genome and Epigenome

Tumorigenesis is driven by metabolic reprogramming. Oncogenic mutations and epigenetic alterations that cause metabolic rewiring may also upregulate the reactive oxygen species (ROS). Precise regulation of the intracellular ROS levels is critical for tumor cell growth and survival. High ROS production leads to the damage of vital macromolecules, such as DNA, proteins, and lipids, causing genomic instability and further tumor evolution. One of the hallmarks of cancer metabolism is deregulated amino acid uptake. In fast-growing tumors, amino acids are not only the source of energy and building intermediates but also critical regulators of redox homeostasis. Amino acid uptake regulates the intracellular glutathione (GSH) levels, endoplasmic reticulum stress, unfolded protein response signaling, mTOR-mediated antioxidant defense, and epigenetic adaptations of tumor cells to oxidative stress. This review summarizes the role of amino acid transporters as the defender of tumor antioxidant system and genome integrity and discusses them as promising therapeutic targets and tumor imaging tools.

PET imaging facilitates antibody screening for synergistic radioimmunotherapy with a 177Lu-labeled αPD-L1 antibody

Rationale: The low response rate of immunotherapy, such as anti-PD-L1/PD-1 and anti-CTLA4, has limited its application to a wider population of cancer patients. One widely accepted view is that inflammation within the tumor microenvironment is low or ineffective for inducing the sufficient infiltration and/or activation of lymphocytes. Here, a highly tumor-selective anti-PD-L1 (αPD-L1) antibody was developed through PET imaging screening, and it was radiolabeled with Lu-177 for PD-L1-targeted radioimmunotherapy (RIT) and radiation-synergized immunotherapy. Methods: A series of αPD-L1 antibodies were radiolabeled with zirconium-89 for PET imaging to screen the most suitable antibodies for RIT. Mice were divided into an immunotherapy group, a RIT group and a radiation-synergized immunotherapy group to evaluate the therapeutic effect. Alterations in the tumor microenvironment after treatment were assessed using flow cytometry and immunofluorescence microscopy. Results: Radiation-synergistic RIT can achieve a significantly better therapeutic effect than immunotherapy or RIT alone. The dosages of the radiopharmaceuticals and αPD-L1 antibodies were reduced, the infiltration of CD4⁺ and CD8⁺ T cells in the tumor microenvironment was increased, and no side effects were observed. This radiation-synergistic RIT strategy successfully showed a strong synergistic effect with αPD-L1 checkpoint blockade therapy, at least in the mouse model. Conclusions: PET imaging of ⁸⁹Zr-labeled antibodies is an effective method for antibody screening. RIT with a ¹⁷⁷Lu-labeled αPD-L1 antibody could successfully upregulate antitumor immunity in the tumor microenvironment and turn "cold" tumors "hot" for immunotherapy.

Physicochemical characterisation of novel tetrabutylammonium aryltrifluoroborate ionic liquids

While there have been many studies on the physicochemical characterisation of ILs, little work has previously been reported on the properties unique to the trifluoroborate anion. Here we have characterised the thermal properties, viscosity, liquid nanostructure and intramolecular interactions of 15 novel aryltrifluoroborate ILs. These ILs all contained a tetrabutylammonium cation paired with either meta- or para-substituted aryltrifluoroborate anions, or di-anionic substituted aryltrifluroborate anions. It was found that of the 15 samples analysed, 4 would technically be considered molten salts as they have melting points greater than 100 °C. Overall the structure-property relationship trends of these samples are similar to those previously reported for alkyl and perfluoroalkyltrifluoroborate ILs which contained K+ or Cs+ cations, with the big difference being the ILs in this study having considerably lower melting points.

Radiosynthesis, in vitro and preliminary biological evaluation of [18 F]2-amino-4-((2-((3-fluorobenzyl)oxy)benzyl)(2-((3-(fluoromethyl)benzyl)oxy)benzyl)amino)butanoic acid, a novel alanine serine cysteine transporter 2 inhibitor-based positron emission tomography tracer

The metabolic alterations in tumors make it possible to visualize the latter by means of positron emission tomography, enabling diagnosis and providing metabolic information. The alanine serine cysteine transporter-2 (ASCT-2) is the main transporter of glutamine and is upregulated in several tumors. Therefore, a good positron emission tracer targeting this transport protein would have substantial value. Hence, the aim of this study is to develop a fluorine-18-labeled version of a V-9302 analogue, one of the most potent inhibitors of ASCT-2. The precursor was labeled with fluorine-18 via a nucleophilic substitution of the corresponding benzylic bromide. The cold reference product was subjected to in vitro assays with [3 H]glutamine in a PC-3 and F98 cell line to determine the affinity for both the human and rat ASCT-2. To evaluate the tracer potential dynamic μPET, images were acquired in a mouse xenograft model for prostate cancer. The tracer could be synthesized with an overall nondecay corrected yield of 3.66 ± 1.90%. in vitro experiments show inhibitor constants Ki of 90 and 125 μM for the PC-3 and F98 cells, respectively. The experiments in the PC-3 xenograft demonstrate a low uptake in the tumor tissue. We have successfully synthesized the radiotracer [18 F]2-amino-4-((2-((3-fluorobenzyl)oxy)benzyl)(2-((3-(fluoromethyl)benzyl)oxy)benzyl)amino)butanoic acid. in vitro experiments show a good affinity for both the human and rat ASCT-2. However, the tracer suffers from poor in vivo tumor uptake in the PC-3 model. Briefly, we present the first fluorine-18-labeled derivative of compound V-9302, a promising novel ASCT-2 blocker used for inhibition of tumor growth.

Side Chain Optimization Remarkably Enhances the in Vivo Stability of 18F-Labeled Glutamine for Tumor Imaging

Similar to glycolysis, glutaminolysis acts as a vital energy source in tumor cells, providing building blocks for the metabolic needs of tumor cells. To capture glutaminolysis in tumors, ¹⁸F-(2S,4R)4-fluoroglutamine ([¹⁸F]FGln) and ¹⁸F-fluoroboronoglutamine ([¹⁸F]FBQ) have been successfully developed for positron emission tomography (PET) imaging, but these two molecules lack stability, resulting in undesired yet significant bone uptake. In this study, we found that [¹⁸F]FBQ-C₂ is a stable Gln PET tracer by adding two more methylene groups to the side chain of [¹⁸F]FBQ. [¹⁸F]FBQ-C₂ was synthesized with a good radiochemical yield of 35% and over 98% radiochemical purity. [¹⁸F]FBQ-C₂ showed extreme stability in vitro, and no defluorination was observed after 2 h in phosphate buffered saline at 37 °C. The competitive inhibition assay results indicated that [¹⁸F]FBQ-C₂ enters cells via the system ASC and N, similar to natural glutamine, and can be transported by tumor-overexpressed ASCT2. PET imaging and biodistribution results indicated that [¹⁸F]FBQ-C₂ is stable in vivo with low bone uptake (0.81 ± 0.20% ID/g) and can be cleared rapidly from most tissues. Dynamic scan and pharmacokinetic studies using BGC823-xenograft-bearing mice revealed that [¹⁸F]FBQ-C₂ accumulates specifically in tumors, with a longer half-life (101.18 ± 6.50 min) in tumor tissues than in other tissues (52.70 ± 12.44 min in muscle). Biodistribution exhibits a high tumor-to-normal tissue ratio (4.8 ± 1.7 for the muscle, 2.5 ± 1.0 for the stomach, 2.2 ± 0.9 for the liver, and 17.8 ± 8.4 for the brain). In conclusion, [¹⁸F]FBQ-C₂ can be used to perform high-contrast Gln imaging of tumors and can serve as a PET tracer for clinical research.

A Metabolically Stable Boron-Derived Tyrosine Serves as a Theranostic Agent for Positron Emission Tomography Guided Boron Neutron Capture Therapy

Boronophenylalanine (BPA) is the dominant boron delivery agent for boron neutron capture therapy (BNCT), and [¹⁸F]FBPA has been developed to assist the treatment planning for BPA-BNCT. However, the clinical application of BNCT has been limited by its inadequate tumor specificity due to the metabolic instability. In addition, the distinctive molecular structures between [¹⁸F]FBPA and BPA can be of concern as [¹⁸F]FBPA cannot quantitate boron concentration of BPA in a real-time manner. In this study, a metabolically stable boron-derived tyrosine (denoted as fluoroboronotyrosine, FBY) was developed as a theranostic agent for both boron delivery and cancer diagnosis, leading to PET imaging-guided BNCT of cancer. [¹⁸F]FBY was synthesized in high radiochemical yield (50%) and high radiochemical purity (98%). FBY showed high similarity with natural tyrosine. As shown in in vitro assays, the uptake of FBY in murine melanoma B16-F10 cells was L-type amino acid transporter (LAT-1) dependent and reached up to 128 μg/10⁶ cells. FBY displayed high stability in PBS solution. [¹⁸F]FBY PET showed up to 6 %ID/g in B16-F10 tumor and notably low normal tissue uptake (tumor/muscle = 3.16 ± 0.48; tumor/blood = 3.13 ± 0.50; tumor/brain = 14.25 ± 1.54). Moreover, administration of [¹⁸F]FBY tracer along with a therapeutic dose of FBY showed high accumulation in B16-F10 tumor and low normal tissue uptake. Correlation between PET-image and boron biodistribution was established, indicating the possibility of estimating boron concentration via a noninvasive approach. At last, with thermal neutron irradiation, B16-F10 tumor-bearing mice injected with FBY showed significantly prolonged median survival without exhibiting obvious systemic toxicity. In conclusion, FBY holds great potential as an efficient theranostic agent for imaging-guided BNCT by offering a possible solution of measuring local boron concentration through PET imaging.

Tracing Boron with Fluorescence and Positron Emission Tomography Imaging of Boronated Porphyrin Nanocomplex for Imaging-Guided Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) induces high-energy radiation within cancer cells while avoiding damage to normal cells without uptake of BNCT drugs, which is holding great promise to provide excellent control over locally invasive malignant tumors. However, lack of quantitative imaging technique to determine local boron concentration has been a great challenge for nuclear physicians to apply accurate neutron irradiation during the treatment, which is a key factor that has limited BNCT's application in clinics. To meet this challenge, this study describes coating boronated porphyrins with a biocompatible poly(lactide- co-glycolide)-monomethoxy-poly(polyethylene-glycol) (PLGA-mPEG) micelle for selective tumor accumulation and reduced toxicity comparing with the previously reported boronated porphyrin drugs. Fluorescence imaging and positron emission tomography (PET) imaging were performed, unveiling the potential imaging properties of this boronated porphyrin nanocomplex (BPN) to locate tumor region and to determine tissue-localized boron concentration which facilitates treatment planning. By studying the pharmacokinetics of BPN with Cu-64 PET imaging, the treatment plan was adjusted from single bolus injection to multiple times of injections of smaller doses. As expected, high tumor uptake of boron (125.17 ± 13.54 ppm) was achieved with an extraordinarily high tumor to normal tissue ratio: tumors to liver, muscle, fat, and blood were 3.24 ± 0.22, 61.46 ± 20.26, 31.55 ± 10.30, and 33.85 ± 5.73, respectively. At last, neutron irradiation with BPN showed almost complete tumor suppression, demonstrating that BPN holds a great potential for being an efficient boron delivery agent for imaging-guided BNCT.

Preclinical Study of a Fully Human Anti-PD-L1 Antibody as a Theranostic Agent for Cancer Immunotherapy

Recently, inhibiting the PD-1/PD-L1 checkpoint pathway utilizing anti-PD-1 or anti-PD-L1 antibodies has achieved great clinical success in cancer treatment. However, anti-PD-1 immunotherapy cannot be applied to all cancer patients, no more than 25% showed a positive response. Immunohistochemistry (IHC) is the gold standard to determine the PD-L1 expression level in malignant lesions, but a noninvasive imaging-meditated strategy is urgently required for clinical diagnosis to cover the shortcomings of invasive techniques. MX001, which is an anti-PD-L1 antibody, was labeled with Cu-64 ( t_1/2 = 12.7 h) and purified by PD-10 chromatography. Comprehensive studies including positron emission tomography (PET), ex vivo biodistribution, IHC, and immunotherapy have been performed in mice bearing MC38 (PD-L1 positive (+)) and 4T1 (PD-L1 negative (-)) xenografts. PET imaging of [¹⁸F]FDG was taken before and after therapy to monitor the therapeutic efficacy. [⁶⁴Cu]Cu-NOTA-MX001 exhibited 2.3 ± 1.2, 5.6 ± 2.1, 5.6 ± 1.2, 6.1 ± 1.1, 6.1 ± 0.5, and 10.2 ± 1.7%ID/g uptake in MC38 xenografts at 0.5, 12, 24, 36, 48, and 62 h post-injection (p.i.), respectively. Meanwhile, the uptake in the liver and muscle at corresponding time points was 17.5 ± 2.2, 8.4 ± 2.4, 11.3 ± 3.2, 7.2 ± 2.1, 7.9.1 ± 3.5, and 3.8 ± 1.8%ID/g, and 1.2 ± 0.5, 1.3 ± 0.4, 1.5 ± 0.5, 0.7 ± 0.1, 0.6 ± 0.2, and 0.2 ± 0.1%ID/g, respectively. The uptake of [¹⁸F]FDG in MC38 and 4T1 xenografts at 1-h p.i. was 5.3 ± 0.4 and 6.4 ± 0.6%ID/g, while the uptake of [⁶⁴Cu]Cu-NOTA-MX001 was 5.6 ± 0.3 and 1.3 ± 0.4%ID/g at 12-h p.i. IHC analysis confirmed that the MC38 tumor exhibited high PD-L1 expression, and the 4T1 tumor, liver, and muscle exhibited low PD-L1 expression. In addition, MC38 xenografts were suppressed by MX001 about 88% in the immunotherapy study. MX001 was successfully developed as a fully human anti-PD-L1 antibody with a high binding affinity in mouse, monkey, and human. The in vivo pharmacokinetics of MX001 was evaluated with PET imaging after being radiolabeled with Cu-64. The uptake of [⁶⁴Cu]Cu-NOTA-MX001 was clearly correlated to the PD-L1 expression on various types of cancer. Subsequent immunotherapy studies demonstrated that MX001 could effectively suppress tumor growth with positive PD-L1 expression, but had poor antitumor efficacy on tumors which exhibited low PD-L1 expression. Together with the above results, MX001 has the potential to be further developed as an antibody theranostic agent for both PET imaging and immunotherapy of cancers in clinics.