Evaluation of 177Lu[Lu]-CHX-A″-DTPA-6A10 Fab as a radioimmunotherapy agent targeting carbonic anhydrase XII

Radiotheranostic landscape: A review of clinical and preclinical development

BACKGROUND

Radiotheranostics combines diagnostic imaging with targeted radionuclide therapy, representing a transformative approach in precision oncology. Landmark approvals of Lutathera® and Pluvicto® have catalyzed significant advancements in this field, driving research into novel radionuclides, targeting strategies, and clinical applications. This review evaluates the evolving clinical and preclinical landscape of radiotheranostics, highlighting advancements, emerging trends, and persistent challenges in radionuclide therapy.

METHODS

A comprehensive analysis was performed, encompassing active clinical trials as of December 2024, sourced from ClinicalTrials.gov and TheranosticTrials.org. Preclinical developments were evaluated through a review of recent literature, focusing on innovations in radionuclide production, targeting molecules, and radiochemistry.

RESULTS

In reviewing the clinical landscape, agents targeting somatostatin receptors (SSTR) and prostate-specific membrane antigen (PSMA) still dominate the field, but new targets such as fibroblast activation protein (FAP), integrins, and gastrin-releasing peptide receptors (GRPR) are gaining traction in both clinical and preclinical development. While small molecules and peptides remain the most common radionuclide carriers, antibody-based carriers including bispecific antibodies, immunoglobin-derived antigen-binding fragments, and antibody-mimetic proteins are on the rise due to their specificity and adaptability. Innovations in radioligand design are driving a shift from agonists to antagonists, accompanied by the development of modified peptides with enhanced pharmacokinetics and tumor-targeting properties. Next-generation therapeutic radionuclides, such as the beta-emitter terbium-161 and alpha-emitters actinium-225 and lead-212, are under investigation to complement or replace lutetium-177, addressing the need for improved efficacy and reduced toxicity. Paired isotopic radionuclides are gaining popularity for their ability to optimize imaging and therapeutic dosimetry as they offer near-identical specificity, biodistribution, and metabolism. Additionally, radiohybrid systems represent an innovative approach to chelating chemically distinct radionuclide pairs within a single molecule, further enhancing flexibility in radiotheranostic design.

CONCLUSION

Radiotheranostics has transformed cancer care through its precision and adaptability, but challenges in radionuclide production, regulatory frameworks, and workforce training hinder broader adoption. Advances in isotopic pairing, next-generation radionuclides, and radiohybrid systems in preclinical and clinical settings hold promise to overcome these barriers. Collaborative efforts among academia, industry, and regulatory bodies are critical to accelerating innovation and optimizing clinical outcomes.

PET imaging of gliomas: Status quo and quo vadis?

PET imaging, particularly using amino acid tracers, has become a valuable adjunct to anatomical MRI in the clinical management of patients with glioma. Collaborative international efforts have led to the development of clinical and technical guidelines for PET imaging in gliomas. The increasing readiness of statutory health insurance agencies, especially in European countries, to reimburse amino acid PET underscores its growing importance in clinical practice. Integrating artificial intelligence and radiomics in PET imaging of patients with glioma may significantly improve tumor detection, segmentation, and response assessment. Efforts are ongoing to facilitate the clinical translation of these techniques. Considerable progress in computer technology developments (eg quantum computers) may be helpful to accelerate these efforts. Next-generation PET scanners, such as long-axial field-of-view PET/CT scanners, have improved image quality and body coverage and therefore expanded the spectrum of indications for PET imaging in Neuro-Oncology (eg PET imaging of the whole spine). Encouraging results of clinical trials in patients with glioma have prompted the development of PET tracers directing therapeutically relevant targets (eg the mutant isocitrate dehydrogenase) for novel anticancer agents in gliomas to improve response assessment. In addition, the success of theranostics for the treatment of extracranial neoplasms such as neuroendocrine tumors and prostate cancer has currently prompted efforts to translate this approach to patients with glioma. These advancements highlight the evolving role of PET imaging in Neuro-Oncology, offering insights into tumor biology and treatment response, thereby informing personalized patient care. Nevertheless, these innovations warrant further validation in the near future.

Toxic warhead-armed antibody for targeted treatment of glioblastoma

Glioblastoma is a fatal intracranial tumor with a poor prognosis, exhibiting uninterrupted malignant progression, widespread invasion throughout the brain leading to the destruction of normal brain tissue and inevitable death. Monoclonal antibodies alone or conjugated with cytotoxic payloads to treat patients with different solid tumors showed effective. This treatment strategy is being explored for patients with glioblastoma (GBM) to obtain meaningful clinical responses and offer new drug options for the treatment of this devastating disease. In this review, we summarize clinical data (from pubmed.gov database and clinicaltrial.gov database) on the efficacy and toxicity of naked antibodies and antibody-drug conjugates (ADCs) against multiple targets on GBM, elucidate the mechanisms that ADCs act at the site of GBM lesions. Finally, we discuss the potential strategies for ADC therapies currently used to treat GBM patients.

On the Use of Artificial Intelligence for Dosimetry of Radiopharmaceutical Therapies

Routine clinical dosimetry along with radiopharmaceutical therapies is key for future treatment personalization. However, dosimetry is considered complex and time-consuming with various challenges amongst the required steps within the dosimetry workflow. The general workflow for image-based dosimetry consists of quantitative imaging, the segmentation of organs and tumors, fitting of the time-activity-curves, and the conversion to absorbed dose. This work reviews the potential and advantages of the use of artificial intelligence to improve speed and accuracy of every single step of the dosimetry workflow.

Targeting carbonic anhydrases for the management of hypoxic metastatic tumors

INTRODUCTION

Several isoforms of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) are connected with tumorigenesis. Hypoxic tumors overexpress CA IX and XII as a consequence of HIF activation cascade, being involved in pH regulation, metabolism, and metastases formation. Other isoforms (CA I, II, III, IV) were also reported to be present in some tumors.

AREAS COVERED

Some CA isoforms are biomarkers for disease progression or response to therapy. Inhibitors, antibodies, and other procedures for targeting these enzymes for the treatment of tumors/metastases are discussed. Sulfonamides and coumarins represent the most investigated classes of inhibitors, but carboxylates, selenium, and tellurium-containing inhibitors were also investigated. Hybrid drugs of CA inhibitors with other antitumor agents for multitargeted therapy were reported.

EXPERT OPINION

Targeting CAs present in solid or hematological tumors with selective, targeted inhibitors is a validated approach, which has been consolidated in the last years. A host of new preclinical data and several clinical trials of antibodies and small-molecule inhibitors are ongoing, which connected with the large number of new chemotypes/procedures discovered to be effective, may lead to a breakthrough in this therapeutic area. The scientific/patent literature has been searched for on PubMed, ScienceDirect, Espacenet, and PatentGuru, from 2018 to 2023.

First clinical experience with fractionated intracavitary radioimmunotherapy using [177Lu]Lu-6A10-Fab fragments in patients with glioblastoma: a pilot study

BACKGROUND

Following resection and standard adjuvant radio- and chemotherapy, approved maintenance therapies for glioblastoma are lacking. Intracavitary radioimmunotherapy (iRIT) with 177Lu-labeled 6A10-Fab fragments targeting tumor-associated carbonic anhydrase XII and injected into the resection cavity offers a novel and promising strategy for improved tumor control.

METHODS

Three glioblastoma patients underwent tumor resection followed by standard radio- and chemotherapy. These patients with stable disease following completion of standard therapy underwent iRIT on compassionate grounds. After surgical implantation of a subcutaneous injection reservoir with a catheter into the resection cavity, a leakage test with [99mTc]Tc-DTPA was performed to rule out leakage into other cerebral compartments. IRIT comprised three consecutive applications over three months for each patient, with 25%, 50%, 25% of the total activity injected. A dosimetry protocol was included with blood sampling and SPECT/CT of the abdomen to calculate doses for the bone marrow and kidneys as potential organs at risk.

RESULTS

All three patients presented without relevant leakage after application of [99mTc]Tc-DTPA. Two patients underwent three full cycles of iRIT (592 MBq and 1228 MBq total activity). One patient showed histologically proven tumor progression after the second cycle (526 MBq total activity). No relevant therapy-associated toxicities or adverse events were observed. Dosimetry did not reveal absorbed doses above upper dose limits for organs at risk.

CONCLUSIONS

In first individual cases, iRIT with [177Lu]Lu-6A10-Fab appears to be feasible and safe, without therapy-related side effects. A confirmatory multicenter phase-I-trial was recently opened and is currently recruiting.

An International Study of Factors Affecting Variability of Dosimetry Calculations, Part 2: Overall Variabilities in Absorbed Dose

Dosimetry for personalized radiopharmaceutical therapy has gained considerable attention. Many methods, tools, and workflows have been developed to estimate absorbed dose (AD). However, standardization is still required to reduce variability of AD estimates across centers. One effort for standardization is the Society of Nuclear Medicine and Molecular Imaging 177Lu Dosimetry Challenge, which comprised 5 tasks (T1-T5) designed to assess dose estimate variability associated with the imaging protocol (T1 vs. T2 vs. T3), segmentation (T1 vs. T4), time integration (T4 vs. T5), and dose calculation (T5) steps of the dosimetry workflow. The aim of this work was to assess the overall variability in AD calculations for the different tasks. Methods: Anonymized datasets consisting of serial planar and quantitative SPECT/CT scans, organ and lesion contours, and time-integrated activity maps of 2 patients treated with 177Lu-DOTATATE were made available globally for participants to perform dosimetry calculations and submit their results in standardized submission spreadsheets. The data were carefully curated for formal mistakes and methodologic errors. General descriptive statistics for ADs were calculated, and statistical analysis was performed to compare the results of different tasks. Variability in ADs was measured using the quartile coefficient of dispersion. Results: ADs to organs estimated from planar imaging protocols (T2) were lower by about 60% than those from pure SPECT/CT (T1), and the differences were statistically significant. Importantly, the average differences in dose estimates when at least 1 SPECT/CT acquisition was available (T1, T3, T4, T5) were within ±10%, and the differences with respect to T1 were not statistically significant for most organs and lesions. When serial SPECT/CT images were used, the quartile coefficients of dispersion of ADs for organs and lesions were on average less than 20% and 26%, respectively, for T1; 20% and 18%, respectively, for T4 (segmentations provided); and 10% and 5%, respectively, for T5 (segmentation and time-integrated activity images provided). Conclusion: Variability in ADs was reduced as segmentation and time-integration data were provided to participants. Our results suggest that SPECT/CT-based imaging protocols generate more consistent and less variable results than planar imaging methods. Effort at standardizing segmentation and fitting should be made, as this may substantially reduce variability in ADs.

Carbonic anhydrase inhibitors: an update on experimental agents for the treatment and imaging of hypoxic tumors

INTRODUCTION

Hypoxic tumors, unlike normal tissues, overexpress proteins involved in oxygen sensing, metabolism, pH regulation, angiogenesis, immunological response, and other survival mechanisms, which are under investigation as antitumor drug targets.

AREAS COVERED

Carbonic anhydrase (CA) isoforms CA IX and XII are among these validated antitumor/antimetastatic drug targets, with several of their inhibitors undergoing preclinical or clinical-stage investigations. Alone or in combination with other chemotherapeutic agents or radiotherapy, CA IX/XII inhibitors, such as SLC-0111, SLC-149, S4, 6A10, etc., were shown to inhibit the growth of the primary tumor, metastases, and invasiveness of many tumor types, being also amenable for the development of imaging agents.

EXPERT OPINION

SLC-0111 is the most investigated agent, being in Phase Ib/II clinical trials. In addition to its interference with extracellular acidifications, it has been shown to promote ferroptosis in cancer cells, another antitumor mechanism of this compound and the entire class. A large number sulfonamide and non-sulfonamide inhibitors have been developed using SLC-0111 as lead in the last three years, together with hybrid agents incorporating CA inhibitors and other anticancer chemotypes, including cytotoxins, telomerase, thioredoxin or P-glycoprotein inhibitors, adenosine A₂A receptor antagonists, pyrophosphatase/phosphodiesterase-3 inhibitors or antimetabolites. All of them showed significant antitumor activity.

Radioimmunotherapy of glioblastoma multiforme - Current status and future prospects

Glioblastoma multiforme (GBM) or grade IV astrocytoma is the most diagnosed form of primary brain tumours in adults. Radioimmunotherapy (RIT), mostly in combination with conventional therapies, is presented in the current review as a therapeutic strategy of high potential in the management of GBM. A systematic literature search was performed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) to identify clinical studies that employed a form of radioimmunotherapy using alpha- or beta-emitting radioisotopes. The available literature on RIT in GBM and high-grade gliomas is presented and discussed. The results suggest that this promising treatment approach merits further investigation in future clinical studies.

Current State of Targeted Radiometal-Based Constructs for the Detection and Treatment of Disease in the Brain

The continual development of radiopharmaceutical agents for the field of nuclear medicine is integral to promoting the necessity of personalized medicine. One way to greatly expand the selection of radiopharmaceuticals available is to broaden the range of radionuclides employed in such agents. Widening the scope of development to include radiometals with their variety of physical decay characteristics and chemical properties opens up a myriad of possibilities for new actively targeted molecules and bioconjugates. This is especially true to further advance the imaging and treatment of disease in the brain. Over the past few decades, imaging of disease in the brain has heavily relied on agents which exploit metabolic uptake. However, through utilizing the broad range of physical characteristics that radiometals offer, the ability to target other processes has become more available. The varied chemistries of radiometals also allows for them to incorporated into specifically designed diverse constructs. A major limitation to efficient treatment of disease in the brain is the ability for relevant agents to penetrate the blood-brain barrier. Thus, along with efficient disease targeting, there must be intentional thought put into overcoming this challenge. Here, we review the current field of radiometal-based agents aimed at either imaging or therapy of brain disease that have been evaluated through at least in vivo studies.

Carbonic Anhydrase XII is a Clinically Significant, Molecular Tumor-Subtype Specific Therapeutic Target in Glioma with the Potential to Combat Invasion of Brain Tumor Cells

Background

The metabolic enzyme carbonic anhydrase 12 (CA12/CAXII) emerges as a promising cancer therapeutic target with drug development projects underway. Previous reports proposed the relevance of CA12 in the context of glioma but are limited in patient data quantity, ignore ethnic diversity of patients or rely on semi-quantitative, thereby out of date, methodology. Moreover, little is known on the association of CA12 to brain tumor stemness or on the effect of anti-CAXII-directed monotherapies on glioma stem cells (GSCs), in particular their response regarding mesenchymal differentiation status.

Methods

We performed in silico analysis on three independent, large-scale patient datasets interrogating state of the art molecular diagnostics alongside clinical outcomes. We analyzed CAXII abundance on a collection of GSCs and functionally tested their response to exposure to CAXII blocking antibody 6A10.

Results

CA12 is highly expressed in glial tumors compared with normal tissue and predicts for poor clinical course of tumor patients. CA12 expression in glioblastoma significantly correlates with clinically established, molecular markers of IDH1^WT DNA, WHO grade IV or absence of 1p/19q chromosome arm co-deletion. Furthermore, tumors with elevated CA12 cluster into the mesenchymal transcription subclass of the disease. CAXII abundance in different GSCs ranges from almost absent to high levels and does not correlate to stem cell marker CD133/AC133 cell surface expression. Moreover, aiming to pharmacologically block CAXII in our cells with antibody 6A10 caused significant functional response only in one of the tested GSCs models, featuring suppression of cell invasion accompanied by reduction of ZEB1 protein and other stem cell markers.

Conclusion

CA12 represents a clinically relevant and molecular brain tumor-subtype specific therapeutic target. Our correlative data from experimental and clinical samples does not support CA12/CAXII to be GSC specific. 6A10 possesses promising potential to impede the invasive capacity of glioma cells and supports the emerging concept that CAXII interacts with cancer EMT programs. However, further mechanistic studies are required to comprehensively assess the therapeutic potential of 6A10 and to identify different resistance mechanisms of GSCs.

Inhibitory Monoclonal Antibodies and Their Recombinant Derivatives Targeting Surface-Exposed Carbonic Anhydrase XII on Cancer Cells

Monoclonal and recombinant antibodies are widely used for the diagnostics and therapy of cancer. They are generated to interact with cell surface proteins which are usually involved in the development and progression of cancer. Carbonic anhydrase XII (CA XII) contributes to the survival of tumors under hypoxic conditions thus is considered a candidate target for antibody-based therapy. In this study, we have generated a novel collection of monoclonal antibodies (MAbs) against the recombinant extracellular domain of CA XII produced in HEK-293 cells. Eighteen out of 24 MAbs were reactive with cellular CA XII on the surface of live kidney and lung cancer cells as determined by flow cytometry. One MAb 14D6 also inhibited the enzymatic activity of recombinant CA XII as measured by the stopped-flow assay. MAb 14D6 showed the migrastatic effect on human lung carcinoma A549 and renal carcinoma A498 cell lines in a ‘wound healing’ assay. It did not reduce the growth of multicellular lung and renal cancer spheroids but reduced the cell viability by the ATP Bioluminescence assay. Epitope mapping revealed the surface-exposed amino acid sequence (35-FGPDGENS-42) close to the catalytic center of CA XII recognized by the MAb 14D6. The variable regions of the heavy and light chains of MAb 14D6 were sequenced and their complementarity-determining regions were defined. The obtained variable sequences were used to generate recombinant antibodies in two formats: single-chain fragment variable (scFv) expressed in E. coli and scFv fused to human IgG1 Fc fragment (scFv-Fc) expressed in Chinese Hamster Ovary (CHO) cells. Both recombinant antibodies maintained the same specificity for CA XII as the parental MAb 14D6. The novel antibodies may represent promising tools for CA XII-related cancer research and immunotherapy.

Mapping actionable pathways and mutations in brain tumours using targeted RNA next generation sequencing

Many biology-based precision drugs are available that neutralize aberrant molecular pathways in cancer. Molecular heterogeneity and the lack of reliable companion diagnostic biomarkers for many drugs makes targeted treatment of cancer inaccurate for many individuals. Identifying actionable hyperactive biological pathways in individual cancers may improve this situation.

To achieve this we applied a novel targeted RNA next generation sequencing (t/RNA-NGS) technique to surgically obtained glioma tissues. The test combines mutation detection with analysis of biological pathway activities that are involved in tumour behavior in many cancer types (e.g. tyrosine kinase signaling, angiogenesis signaling, immune response, metabolism), via quantitative measurement of transcript levels and splice variants of hundreds of genes. We here present proof of concept that the technique, which uses molecular inversion probes, generates a histology-independent molecular diagnosis and identifies classifiers that are strongly associated with conventional histopathology diagnoses and even with patient prognosis. The test not only confirmed known glioma-associated molecular aberrations but also identified aberrant expression levels of actionable genes and mutations that have so far been considered not to be associated with glioma, opening up the possibility of drug repurposing for individual patients. Its cost-effectiveness makes t/RNA-NGS to an attractive instrument to aid oncologists in therapy decision making.

Potential for Nuclear Medicine Therapy for Glioblastoma Treatment

Glioblastoma is the most common malignant adult brain tumor and has a very poor patient prognosis. The mean survival for highly proliferative glioblastoma is only 10 to 14 months despite an aggressive current therapeutic approach known as Stupp's protocol, which consists of debulking surgery followed by radiotherapy and chemotherapy. Despite several clinical trials using anti-angiogenic targeted therapies, glioblastoma medical care remains without major progress in the last decade. Recent progress in nuclear medicine, has been mainly driven by advances in biotechnologies such as radioimmunotherapy, radiopeptide therapy, and radionanoparticles, and these bring a new promising arsenal for glioblastoma therapy. For therapeutic purposes, nuclear medicine practitioners classically use β^- particle emitters like ¹³¹I, ⁹⁰Y, ^186/188Re, or ¹⁷⁷Lu. In the glioblastoma field, these radioisotopes are coupled with nanoparticles, monoclonal antibodies, or peptides. These radiopharmaceutical compounds have resulted in a stabilization and/or improvement of the neurological status with only transient side effects. In nuclear medicine, the glioblastoma-localized and targeted internal radiotherapy proof-of-concept stage has been successfully demonstrated using β^- emitting isotopes. Similarly, α particle emitters like ²¹³Bi, ²¹¹At, or ²²⁵Ac appear to be an innovative and interesting alternative. Indeed, α particles deliver a high proportion of their energy inside or at close proximity to the targeted cells (within a few micrometers from the emission point versus several millimeters for β^- particles). This physical property is based on particle-matter interaction differences and results in α particles being highly efficient in killing tumor cells with minimal irradiation of healthy tissues and permits targeting of isolated tumor cells. The first clinical trials confirmed this idea and showed good therapeutic efficacy and less side effects, thus opening a new and promising era for glioblastoma medical care using α therapy. The objective of this literature review is focused on the developing field of nuclear medicine and aims to describe the various parameters such as targets, vectors, isotopes, or injection route (systemic and local) in relation to the clinical and preclinical results in glioblastoma pathology.

Intracavitary radioimmunotherapy of high-grade gliomas: present status and future developments

There is a distinct need for new and second-line therapies to delay or prevent local tumor regrowth after current standard of care therapy. Intracavitary radioimmunotherapy, in combination with radiotherapy, is discussed in the present review as a therapeutic strategy of high potential. We performed a systematic literature search following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The available body of literature on intracavitary radioimmunotherapy (iRIT) in glioblastoma and anaplastic astrocytomas is presented. Several past and current phase I and II clinical trials, using mostly an anti-tenascin monoclonal antibody labeled with I-131, have shown median overall survival of 19-25 months in glioblastoma, while adverse events remain low. Tenascin, followed by EGFR and variants, or smaller peptides have been used as targets, and most clinical studies were performed with I-131 or Y-90 as radionuclides while only recently Re-188, I-125, and Bi-213 were applied. The pharmacokinetics of iRIT, as well as the challenges encountered with this therapy, is comprehensively discussed. This promising approach deserves further exploration in future studies by incorporating several innovative modifications.

Preparation of 177Lu-Trastuzumab injection for treatment of breast cancer

The objective of this study was the facile preparation of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab injection for breast cancer therapy. Trastuzumab conjugated with CHX-A''-DTPA-NCS was radiolabeled with ¹⁷⁷Lu in >95% radiochemical purity. In vitro studies in SKBR3 and MDA-MB-453 cells confirmed specificity of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab to HER2 positive cells. The radioimmunoconjugate showed good immunoreactivity, in vitro stability in saline and K_d of 1.01 ± 0.13 nM in SKBR3 cells. Clearance of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab in Swiss mice was predominantly through the hepatobiliary route with minimal bone uptake.

Fully Automated Production and Characterization of 64 Cu and Proof-of-Principle Small-Animal PET Imaging Using 64 Cu-Labelled CA XII Targeting 6A10 Fab

⁶⁴ Cu is a cyclotron-produced radionuclide which offers, thanks to its characteristic decay scheme, the possibility of combining positron emission tomography (PET) investigations with radiotherapy. We evaluated the Alceo system from Comecer SpA to automatically produce ⁶⁴ Cu for radiolabelling purposes. We established a ⁶⁴ Cu production routine with high yields and radionuclide purity in combination with excellent operator radiation protection. The carbonic anhydrase XII targeting 6A10 antibody Fab fragment was successfully radiolabelled with the produced ⁶⁴ Cu, and proof-of-principle small-animal PET experiments on mice bearing glioma xenografts were performed. We obtained a high tumor-to-contralateral muscle ratio, which encourages further in vivo investigations of the radioconjugate regarding a possible application in diagnostic tumor imaging.