Synthesis and evaluation of (18)F-labeled tertiary benzenesulfonamides for imaging carbonic anhydrase IX expression in tumours with positron emission tomography

Preclinical and pilot clinical evaluation of a small-molecule carbonic anhydrase IX targeting PET tracer in clear cell renal cell carcinoma

PURPOSE

Clear cell renal cell carcinoma (ccRCC) highly expresses carbonic anhydrase IX (CAIX). The purpose of this study was to evaluate 68Ga-NY104, a small-molecule CAIX-targeting PET agent, in tumor models of ccRCC and patients diagnosed with confirmed, or suspicious, ccRCC.

METHODS

The in vivo and ex vivo biodistribution of 68Ga-NY104 was investigated in CAIX-positive OS-RC-2 xenograft-bearing models. The binding of the tracer was further validated using autoradiography for human ccRCC samples. In addition, three patients with confirmed or suspicious ccRCC were studied.

RESULTS

NY104 can be labeled with high radiochemical yield and purity. It quickly cleared through kidney with α-half-life of 0.15 h. Discernible uptake is noted in the heart, lung, liver, stomach, and kidney. The OS-RC-2 xenograft demonstrated intense uptake 5 min after injection and gradually increased until 3 h after injection with ID%/g of 29.29 ± 6.82. Significant binding was detected using autoradiography on sections of human ccRCC tumor. In the three patients studied, 68Ga-NY104 was well-tolerated and no adverse events were reported. Substantial accumulation was observed in both primary and metastatic lesions in patient 1 and 2 with SUVmax of 42.3. Uptake in the stomach, pancreas, intestine, and choroid plexus was noted. The lesion in third patient was correctly diagnosed as non-metastatic for negative 68Ga-NY104 uptake.

CONCLUSION

68Ga-NY104 can efficiently and specifically bind to CAIX. Given the pilot nature of our study, future clinical studies are warranted to evaluate 68Ga-NY104 for detection of CAIX-positive lesions in patients with ccRCC.

TRIAL REGISTRATION

The clinical evaluation part of this study was retrospectively registered at ClinicalTrial.gov (NCT05728515) as NYPILOT on 6 Feb, 2023.

PET radiotracers and fluorescent probes for imaging human carbonic anhydrase IX and XII in hypoxic tumors

Positron emission tomography (PET) and fluorescent imaging play a pivotal role in medical diagnosis, biomedical oncologic research, and drug development process, which include identification of target location, target engagement, but also prove on mechanism of action or pharmacokinetics of new drug candidates. PET estimates physiological changes at the molecular level using specific radiotracers containing a short-lived positron emitting radionuclide such as fluorine-18 or carbon-11, whereas fluorescent imaging techniques use fluorescent probes labeled with suitable drug candidates for detection at the molecular level. The human carbonic anhydrase (hCA) isoforms IX and XII are overexpressed in hypoxic cancer cells, promoting tumor growth by regulating extra/intracellular pH, ferroptosis, and metabolism, being recognized as promising targets for anticancer theranostic agents. In this review, we have focused on PET radiotracers as well as fluorescent probes for diagnosis and treatment of tumors expressing hCA IX and hCA XII.

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.

Comparative evaluation of affibody- and antibody fragments-based CAIX imaging probes in mice bearing renal cell carcinoma xenografts

Carbonic anhydrase IX (CAIX) is a cancer-associated molecular target for several classes of therapeutics. CAIX is overexpressed in a large fraction of renal cell carcinomas (RCC). Radionuclide molecular imaging of CAIX-expression might offer a non-invasive methodology for stratification of patients with disseminated RCC for CAIX-targeting therapeutics. Radiolabeled monoclonal antibodies and their fragments are actively investigated for imaging of CAIX expression. Promising alternatives are small non-immunoglobulin scaffold proteins, such as affibody molecules. A CAIX-targeting affibody ZCAIX:2 was re-designed with the aim to decrease off-target interactions and increase imaging contrast. The new tracer, DOTA-HE₃-ZCAIX:2, was labeled with ¹¹¹In and characterized in vitro. Tumor-targeting properties of [¹¹¹In]In-DOTA-HE₃-ZCAIX:2 were compared head-to-head with properties of the parental variant, [^99mTc]Tc(CO)₃-HE₃-ZCAIX:2, and the most promising antibody fragment-based tracer, [¹¹¹In]In-DTPA-G250(Fab’)₂, in the same batch of nude mice bearing CAIX-expressing RCC xenografts. Compared to the ^99mTc-labeled parental variant, [¹¹¹In]In-DOTA-HE₃-ZCAIX:2 provides significantly higher tumor-to-lung, tumor-to-bone and tumor-to-liver ratios, which is essential for imaging of CAIX expression in the major metastatic sites of RCC. [¹¹¹In]In-DOTA-HE₃-ZCAIX:2 offers significantly higher tumor-to-organ ratios compared with [¹¹¹In]In-G250(Fab’)₂. In conclusion, [¹¹¹In]In-DOTA-HE₃-ZCAIX:2 can be considered as a highly promising tracer for imaging of CAIX expression in RCC metastases based on our results and literature data.

Fluoroenesulphonamides: N-sulphonylurea isosteres showing nanomolar selective cancer-related transmembrane human carbonic anhydrase inhibition

After hydrofluorination of ynesulphonamides in superacid or in the presence of hydrofluoric acid/base reagents, a series of α-fluoroenamides has been synthesised and tested for the inhibition of carbonic anhydrase (CA, EC 4.2.1.1) isoforms. This study reveals a new, highly selective family of cancer-related transmembrane human (h) CA IX/XII inhibitors. These original fluorinated ureido isosters do not inhibit the widespread cytosolic isoforms hCA I and II and selectively inhibit the transmembrane cancer-related hCA IX and XII, offering interesting new leads for future studies.

Evaluation of 99mTc-sulfonamide and sulfocoumarin derivatives for imaging carbonic anhydrase IX expression

With the aim to prepare hypoxia tumor imaging agents, technetium(I) and rhenium(I) tricarbonyl complexes with dipyridylamine (L1 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazol-4-yl]methyl}-N-(2-pyridinylmethyl)-2-pyridinemethanamine; L3 = N-{[1-[N-(4-aminosulfonylphenyl)]-1H-1,2,3-triazol-4-yl]methyl}-N-(2-pyridinyl-methyl)-2-pyridinemethanamine), and iminodiacetate (H₂L2 = N-{[1-(2,2-dioxido-1,2-benzoxathiin-6-yl)-1H-1,2,3-triazole-4-yl]methyl}-N-(carboxy-methyl)-glycine; H₂L4 = N-{[1-[N-(4-aminosulfonylphenyl)]-1H-1,2,3-triazole-4-yl]methyl}-N-(carboxymethyl)-glycine) ligands appended to sulfonamide or sulfocoumarin carbonic anhydrase inhibitors were synthesized. The Re(I) complexes were characterized using ¹H/¹³C NMR, MS, EA, and in one case the X-ray structure of [Et₃NH][Re(CO)₃(L2)] was obtained. As expected, the Re coordination geometry is distorted octahedral, with a tridentate iminodiacetate ligand in a fac arrangement dictated by the three strong-field CO ligands. Inhibition studies of human carbonic anhydrases (hCAs) showed that the Re sulfocoumarin derivatives were inactive against hCA-I, -II and -IV, but had moderate affinity for hCA-IX. The Re sulfonamides showed improved affinity against all tested hCAs, with [Re(CO)₃(L4)]^- being the most active and selective for the hCA-IX isoform. The corresponding ^99mTc complexes were synthesized from fac-[^99mTc(CO)₃(H₂O)₃]⁺, purified by HPLC, and obtained with average 41-76% decay-corrected radiochemical yields and with >99% radiochemical purity. Uptake in HT-29 tumors at 1 h post-injection was highest for [^99mTc(CO)₃(L4)]^- (0.14 ± 0.10%ID/g) in comparison to [^99mTc(CO)₃(L1)]⁺ (0.06 ± 0.01%ID/g), [^99mTc(CO)₃(L2)]^- (0.03 ± 0.00%ID/g), and [^99mTc(CO)₃(L3)]⁺ (0.07 ± 0.03%ID/g). The uptake in tumors was further reduced at 4 h post-injection. For potential imaging application with single photon emission computed tomography, further optimization is needed to improve the affinity to hCA-IX and uptake in hCA-IX expressing tumors.

Past, Present, and Future: Development of Theranostic Agents Targeting Carbonic Anhydrase IX

Theranostics is the integration of diagnostic information with pharmaceuticals to increase effectiveness and safety of cancer treatments. Nuclear medicine provides a non-invasive means to visualize drug target expression across primary and metastatic sites, and assess pharmacokinetics and efficacy of companion therapeutic agents. This is significant given the increasing recognition of the importance of clonal heterogeneity in treatment response and resistance. Carbonic anhydrase IX (CA-IX) has been advocated as an attractive diagnostic and therapeutic biomarker for targeting hypoxia in solid malignancies. CA-IX confers cancer cell survival under low oxygen tension, and is associated with increased propensity for metastasis. As such, CA-IX is overexpressed in a broad spectrum of cancers. Different classes of antigen recognition molecules targeting CA-IX including monoclonal antibodies, peptides, small molecule inhibitors, and antibody mimetics have been radiolabeled for imaging and therapeutic applications. cG250, a chimeric monoclonal antibody, has been labeled with an assortment of radionuclides (¹²⁴I, ¹¹¹In, ⁸⁹Zr, ¹³¹I, ⁹⁰Y, and ¹⁷⁷Lu) and is the most extensively investigated CA-IX radiopharmaceutical. In recent years, there have been tremendous advancements made by the research community in developing alternatives to cG250. Although still in preclinical settings, several small molecule inhibitors and antibody mimetics hold great promise in improving the management of aggressive and resistant cancers.

Design, synthesis and evaluation of 18F-labeled cationic carbonic anhydrase IX inhibitors for PET imaging

Carbonic anhydrase IX (CA-IX) is a marker for tumor hypoxia, and its expression is negatively correlated with patient survival. CA-IX represents a potential target for eliminating hypoxic cancers. We synthesized fluorinated cationic sulfonamide inhibitors 1-3 designed to target CA-IX. The binding affinity for CA-IX ranged from 0.22 to 0.96 μM. We evaluated compound 2 as a diagnostic PET imaging agent. Compound 2 was radiolabeled with ¹⁸F in 10 ± 4% decay-corrected radiochemical yield with 85.1 ± 70.3 GBq/μmol specific activity and >98% radiochemical purity. ¹⁸F-labeled 2 was stable in mouse plasma at 37 °C after 1 h incubation. PET/CT imaging was conducted at 1 h post-injection in a human colorectal cancer xenograft model. ¹⁸F-labeled 2 cleared through hepatobiliary and renal pathways. Tumor uptake was approximately 0.41 ± 0.06% ID/g, with a tumor-to-muscle ratio of 1.99 ± 0.25. Subsequently, tumor xenografts were visualized with moderate contrast. This study demonstrates the use of a cationic motif for conferring isoform selectively for CA-IX imaging agents.

Comparative Evaluation of Affibody Molecules for Radionuclide Imaging of in Vivo Expression of Carbonic Anhydrase IX

Overexpression of the enzyme carbonic anhydrase IX (CAIX) is documented for chronically hypoxic malignant tumors as well as for normoxic renal cell carcinoma. Radionuclide molecular imaging of CAIX would be useful for detection of hypoxic areas in malignant tumors, for patients' stratification for CAIX-targeted therapies, and for discrimination of primary malignant and benign renal tumors. Earlier, we have reported feasibility of in vivo radionuclide based imaging of CAIX expressing tumors using Affibody molecules, small affinity proteins based on a nonimmunoglobulin scaffold. In this study, we compared imaging properties of several anti-CAIX Affibody molecules having identical scaffold parts and competing for the same epitope on CAIX, but having different binding paratopes. Four variants were labeled using residualizing ^99mTc and nonresidualizing ¹²⁵I labels. All radiolabeled variants demonstrated high-affinity detection of CAIX-expressing cell line SK-RC-52 in vitro and specific accumulation in SK-RC-52 xenografts in vivo. ¹²⁵I-labeled conjugates demonstrated much lower radioactivity uptake in kidneys but higher radioactivity concentration in blood compared with ^99mTc-labeled counterparts. Although all variants cleared rapidly from blood and nonspecific compartments, there was noticeable difference in their biodistribution. The best variant for imaging of expression of CAIX in disseminated cancer was ^99mTc-(HE)₃-ZCAIX:2 providing tumor uptake of 16.3 ± 0.9% ID/g and tumor-to-blood ratio of 44 ± 7 at 4 h after injection. For primary renal cell carcinoma, the most promising imaging candidate was ¹²⁵I-ZCAIX:4 providing tumor-kidney ratio of 2.1 ± 0.5. In conclusion, several clones of scaffold proteins should be evaluated to select the best variant for development of an imaging probe with optimal sensitivity for the intended application.

Evaluation of Nonpeptidic Ligand Conjugates for SPECT Imaging of Hypoxic and Carbonic Anhydrase IX-Expressing Cancers

As tumors grow, vasculature is often deficient or malformed, resulting in many localized areas of hypoxia. Cells located in these hypoxic regions exhibit an altered gene expression pattern that can significantly alter resistance to conventional anticancer treatments such as ionizing radiation and chemotherapeutic drugs. A priori knowledge of the level of hypoxia within a tumor may better guide clinical care. In an effort to create a hypoxia specific imaging agent, a ligand for the tissue hypoxia marker, carbonic anhydrase IX (CA IX), was synthesized and used as a targeting ligand to deliver an attached (99m)Tc-chelating agent. Binding of the resulting conjugates to hypoxic cancer cells was first characterized in vitro. Whole animal imaging and biodistribution studies then were performed to determine tumor specificity in vivo. Several conjugates were found to bind selectively to CA IX expressing tumors in a receptor-dependent manner. We suggest that such conjugates could prove useful in identifying hypoxic cancers and/or quantitating the level of hypoxia within a tumor.

Synthesis of sulfonamide conjugates of Cu(ii), Ga(iii), In(iii), Re(v) and Zn(ii) complexes: carbonic anhydrase inhibition studies and cellular imaging investigations

New sulfonamides and their metal complexes are reported, with a focus on porphyrin derivatives for simultaneous cellular optical imaging, radiolabelling and Carbonic Anhydrase inhibition capabilities.

Fluorinated pyrrolidines and piperidines incorporating tertiary benzenesulfonamide moieties are selective carbonic anhydrase II inhibitors

A series of substituted pyrrolidines and piperidines were synthesized using superacid HF/SbF5 chemistry. Investigated as inhibitors of several human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, i.e. the cytosolic hCA I and II as well as the tumor-associated transmembrane isoforms hCA IX and XII, these compounds showed a never yet reported selectivity toward the human carbonic anhydrase hCA II. In the tertiary benzenesulfonamide family, this class of inhibitors points out a new mechanism of action for human carbonic anhydrase II inhibition.