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

Recent Advances in Preclinical Studies of the Theranostic Agent [64Cu]CuCl2

64Cu is gaining recognition not only for its diagnostic capabilities in nuclear medical imaging but also for its therapeutic and theranostic potential. The simultaneous β- and Auger emissions of 64Cu can be utilized to induce a therapeutic effect on cancerous lesions. The finding of the exceptional biodistribution characteristics of the radionuclide 64Cu, when administered as basic copper ions, has highlighted its potential therapeutic application in cancer treatment. Preclinical and clinical research on the effectiveness of [64Cu]CuCl2 as a theranostic radiopharmaceutical has commenced only in the past decade. Current clinical studies are increasingly demonstrating the high specificity and uptake of [64Cu]Cu2+ by malignant tissues during early cancer progression, indicating its potential for early cancer diagnosis across various organs. This short review aims to present the latest preclinical studies involving [64Cu]CuCl2, offering valuable insights for researchers planning new in vitro and in vivo studies to explore the theranostic potential of [64Cu]Cu2+.

CAXII inhibitors: Potential sensitizers for immune checkpoint inhibitors in HCC treatment

Hepatocellular carcinoma (HCC) is a lethal malignancy with a lack of effective treatments particularly for the disease at an advanced stage. Even though immune checkpoint inhibitors (ICIs) have made great progress in the treatment of HCC, durable and ideal clinical benefits still cannot be achieved in plenty of patients with HCC. Therefore, novel and refined ICI-based combination therapies are still needed to enhance the therapeutic effect. The latest study has reported that the carbonic anhydrase XII inhibitor (CAXIIi), a novel type of anticancer drug, can modify the tumor immunosuppression microenvironment by affecting hypoxic/acidic metabolism and alter the functions of monocytes and macrophages by regulating the expression of C-C motif chemokine ligand 8 (CCL8). These observations shine a light on improving programmed cell death protein 1 (PD-1)/programmed cell death ligand-1 (PD-L1) immunotherapy in combination with CAXIIis. This mini-review aims to ignite enthusiasm to explore the potential application of CAXIIis in combination with immunotherapy for HCC.

Evaluation of Betulinic Acid Derivatives as PET Tracers for Hypoxia-Induced Carbonic Anhydrase IX (CA IX) Expression

Non-invasive visualisation of the expression of hypoxia-related proteins, such as carbonic anhydrase IX (CA IX), by positron emission tomography (PET) could provide important information on the oxygenation status of tumours. Since betulinic acid derivatives bind specifically to CA IX the aim of the study was the development betulinic acid-based 68Ga-labelled PET tracers and to evaluate the hypoxia detecting properties in vitro and in vivo. The binding of betulinic acid (B-DOTA) and betulinyl-3-sulfamate (BS-DOTA) was assessed in two rat tumour cell lines (AT1 prostate and Walker-256 mammary carcinomas). AT1 cells express CA IX in a hypoxia-dependent manner whereas Walker-256 cells, expressing almost no CA IX in wildtype, were transfected with the rat Car9 gene. In vivo measurements were carried out in a small animal PET/CT in AT1 tumours in rats breathing room air, 8% or 100% O2. In AT1 cells hypoxia-induced overexpression of CA IX led to a stronger binding of BS-DOTA but not of B-DOTA. The BS-DOTA binding correlated linearly with the CA IX protein expression and could be blocked by an excess of unlabelled tracer. In the transfected Walker-256 cells no specific binding of either of the tracers was seen. In vivo the intratumoral accumulation of BS-DOTA was increased in animals kept under inspiratory hypoxia and reduced by hyperoxia. Therefore, betulinyl-3-sulfamate could be used as a PET tracer of CA IX expression in tumours and to provide information about the oxygenation status. However, accumulation data indicated that binding not only depends on hypoxia-induce CA IX expression but also on the tumour-line-specific basal expression and on the initial oxygenation status of the tumour.

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.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

State of the Art in Radiolabeling of Antibodies with Common and Uncommon Radiometals for Preclinical and Clinical Immuno-PET

Inert and stable radiolabeling of monoclonal antibodies (mAb), antibody fragments, or antibody mimetics with radiometals is a prerequisite for immuno-PET. While radiolabeling is preferably fast, mild, efficient, and reproducible, especially when applied for human use in a current Good Manufacturing Practice compliant way, it is crucial that the obtained radioimmunoconjugate is stable and shows preserved immunoreactivity and in vivo behavior. Radiometals and chelators have extensively been evaluated to come to the most ideal radiometal–chelator pair for each type of antibody derivative. Although PET imaging of antibodies is a relatively recent tool, applications with ⁸⁹Zr, ⁶⁴Cu, and ⁶⁸Ga have greatly increased in recent years, especially in the clinical setting, while other less common radionuclides such as ⁵²Mn, ⁸⁶Y, ⁶⁶Ga, and ⁴⁴Sc, but also ¹⁸F as in [¹⁸F]AlF are emerging promising candidates for the radiolabeling of antibodies. This review presents a state of the art overview of the practical aspects of radiolabeling of antibodies, ranging from fast kinetic affibodies and nanobodies to slow kinetic intact mAbs. Herein, we focus on the most common approach which consists of first modification of the antibody with a chelator, and after eventual storage of the premodified molecule, radiolabeling as a second step. Other approaches are possible but have been excluded from this review. The review includes recent and representative examples from the literature highlighting which radiometal–chelator–antibody combinations are the most successful for in vivo application.

Electrochemical deposition of nickel targets from aqueous electrolytes for medical radioisotope production in accelerators: a review

This paper reviews reported methods of the electrochemical deposition of nickel layers which are used as target materials for accelerator production of medical radioisotopes. The review focuses on the electrodeposition carried out from aqueous electrolytes. It describes the main challenges related to the preparation of suitable Ni target layers, such as work with limited amounts of expensive isotopically enriched nickel; electrodeposition of sufficiently thick, smooth and free of cracks layers; and recovery of unreacted Ni isotopes from the irradiated targets and from used electrolytic baths.

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.

Radiotracers for positron emission tomography (PET) targeting tumour-associated carbonic anhydrase isoforms

The tumour-associated, cell membrane-bound isoforms IX and XII of human carbonic anhydrase (CA, EC 4.2.1.1) are overexpressed in cancer cells contributing to the hypoxic tumour pH/metabolism regulating machinery and as thus, can serve as markers of malignant neoplastic tissue. Inhibitors of CAs can be employed both for the treatment of hypoxic tumours and in the design of radiotracers for positron emission tomography and imaging of such cancers. The present review provides a comprehensive summary of the progress achieved to-date in the field of developing PET-tracers based on monoclonal antibodies, biomolecules, and small-molecule ligands of CA IX and XII.

Copper-64-immunoPET imaging: bench to bedside

Positron emission tomography (PET) is a growing non-invasive diagnostic and molecular imaging tool in nuclear medicine, that is used to identify several diseases including cancer. The immunoPET probe is made up of monoclonal antibodies (mAbs) or its fragments or similar molecules that tagged with positron radioisotopes (⁶⁸Ga, ⁶⁴Cu, ⁸⁹Zr) bound together by a bifunctional chelator (BFC). This probe is designed to identify a specific disease. Currently, several immunoPET probes are being developed for preclinical as well as for clinical applications. These studies are showing promising results, both in preclinical and patients, using mostly ⁶⁴Cu, ⁸⁹Zr isotopes. This review elucidates the ⁶⁴Cu based immunoPET applications, their pipelines and the emerging scope of this technique within the nuclear medicine and molecular imaging clinics from bench to bedside. Recently, immunoPET research have sharply increased especially after a big surge in approval of oncology antibodies by the FDA for immune checkpoint-blockade cancer immunotherapies. Currently, preclinical to clinical translations of immunoPET has several challenges, including designing probes, choice of radioisotopes, selection of stable BFC, and size of antibody and its tracer kinetics. All these obstacles will be addressed eventually by improving PET scanner sensitivity, designing appropriate size of imaging probe, and combining immunoPET with specific targeting antibodies. These improvements should contribute to the immunoPET becoming more applicable in clinics, which, in turn, will provide critical information for correct patient selection, for right dosing, and for the right time/staging of treatment.