Novel CYP11B-ligand [123/131I]IMAZA as promising theranostic tool for adrenocortical tumors: comprehensive preclinical characterization and first clinical experience

Continuous flow-through steady state system for in vitro characterization of CYP11B2 inhibitors-Impact on enzyme kinetics of steroidogenesis

BACKGROUND

The homology of aldosterone- and cortisol-producing enzymes, aldosterone synthase (CYP11B2) and 11β-hydroxylase, complicates identification of selective CYP11B2 inhibitors required for antihypertensive treatment or for imaging approaches in patients with primary aldosteronism. To improve preclinical evaluation of novel CYP11B2-targeting compounds, we developed a flow-through cell culture system that provides insights into kinetics of steroidogenesis and inhibitory responses at CYP11B2 active sites.

METHODS

NCI-H295RA and HAC-15 cells were cultured in ibidi flow chambers under constant culture medium flow. Supernatants were collected hourly before and after treatment with (R)-1-[1-(4-iodophenyl)ethyl]-1H-imidazole-5-carboxylic acid azetidinylamide (IMAZA), a non-selective CYP11B1/B2 inhibitor, or the potential CYP11B2 inhibitors ID-69 and ID-191. Steroid profiles were analyzed by liquid chromatography-tandem mass spectrometry. Steady state approximation in steroidogenesis allowed mathematical modeling-based calculation of metabolic fluxes and relative rate constants of biocatalytic steps.

RESULTS

An optimized flow-through system is now available to characterize inhibitory responses at the three catalytic sites of CYP11B2 in two steroid-producing cell lines. IMAZA non-selectively inhibited CYP11B 11β-hydroxylase function, while ID-69 and ID-191 affected the CYP11B2-specific 18-hydroxylase active site with minor effects on catalytic activity of 11β-hydroxylase. ID-191 simultaneously impaired catalytic activity of cortisol production, whereas ID-69 was highly selective for CYP11B2 inhibition.

CONCLUSION

Our flow-through system provides insights into inhibitor-induced alterations of metabolic fluxes and enzymatic rate constants, and thus represents an improved preclinical model sytem for complex characterization of CYP11B2 inhibitors.

Targeting pediatric adrenocortical carcinoma: Molecular insights and emerging therapeutic strategies

Pediatric adrenocortical carcinoma (pACC) is an exceptionally rare and aggressive malignancy, accounting for only 0.2-0.3% of childhood cancers. Characterized by significant endocrine activity and often associated with genetic syndromes such as Li-Fraumeni syndrome, pACC exhibits distinct clinical and molecular profiles compared to adult adrenocortical carcinoma (ACC). Current treatment approaches, largely adapted from adult protocols, center on surgery and chemotherapy, including mitotane. However, the lack of pediatric-specific data and major clinical trials underscores a pressing need for tailored therapeutic strategies. Advances in molecular profiling have unveiled actionable targets, such as alterations in the Wnt/β-catenin and MAP/ERK pathways, overexpression of IGF2, and epigenetic dysregulation. Emerging therapies, including immune checkpoint inhibitors, CAR T-cell therapy, and radiopharmaceuticals, hold promise but remain largely untested in pediatric populations. Targeting metabolic vulnerabilities, such as steroidogenesis and lipid metabolism, offers additional avenues for therapeutic innovation. Furthermore, improved diagnostic tools like liquid biopsy and steroid profiling may enhance disease monitoring and early detection. Despite progress in understanding pACC biology, significant challenges remain in translating these insights into effective treatments. Collaborative efforts, such as the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT), and the development of pediatric-specific clinical trials are vital for advancing the field. Multidisciplinary care and international research initiatives will be pivotal in addressing the unmet needs of pACC patients. By leveraging molecular insights and fostering global collaboration, the field can move toward personalized medicine, improving outcomes and quality of life for children with this challenging disease. Expanding clinical trials, refining diagnostic tools, and integrating novel therapies into treatment regimens will be critical in bridging the gap between pediatric and adult ACC treatment success.

Radiopharmaceuticals for Treatment of Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) represents a rare tumor entity with limited treatment options and usually rapid tumor progression in case of metastatic disease. As further treatment options are needed and ACC metastases are sensitive to external beam radiation, novel theranostic approaches could complement established therapeutic concepts. Recent developments focus on targeting adrenal cortex-specific enzymes like the theranostic twin [123/131I]IMAZA that shows a good image quality and a promising therapeutic effect in selected patients. But other established molecular targets in nuclear medicine such as the C-X-C motif chemokine receptor 4 (CXCR4) could possibly enhance the therapeutic regimen as well in a subgroup of patients. The aims of this review are to give an overview of innovative radiopharmaceuticals for the treatment of ACC and to present the different molecular targets, as well as to show future perspectives for further developments since a radiopharmaceutical with a broad application range is still warranted.

Advances in the molecular imaging of primary aldosteronism

Primary aldosteronism (PA) is the most common cause of secondary hypertension. It predisposes to adverse outcomes such as nephrotoxicity and cardiovascular damage, which are mediated by direct harm from hypertension to the target organs. Accurate subtype diagnosis and localization are crucial elements in choosing the type of treatment for PA in clinical practice since the dominant side of aldosterone secretion in PA affects subsequent treatment options. The gold standard for diagnosing PA subtypes, adrenal venous sampling (AVS), requires specialized expertise, the invasive nature of the procedure and high costs, all of which delay the effective treatment of PA. Nuclide molecular imaging is non-invasive and has wider applications in the diagnosis and treatment of PA. This review aims to provide a summary of the application of radionuclide imaging in the diagnosis, treatment management and prognostic assessment of PA.

Adrenal functional imaging - which marker for which indication?

PURPOSE OF REVIEW

In recent years, a broad spectrum of molecular image biomarkers for assessment of adrenal functional imaging have penetrated the clinical arena. Those include positron emission tomography and single photon emission computed tomography radiotracers, which either target glucose transporter, CYP11B enzymes, C-X-C motif chemokine receptor 4, norepinephrine transporter or somatostatin receptors. We will provide an overview of key radiopharmaceuticals and determine their most relevant clinical applications, thereby providing a roadmap for the right image biomarker at the right time for the right patient.

RECENT FINDINGS

Numerous radiotracers for assessment of adrenal incidentalomas ([18F]FDG; [123I]IMTO/IMAZA), ACC ([123I]IMTO/IMAZA; [18F]FDG; [68Ga]PentixaFor), pheochromocytomas and paragangliomas ([123I]mIBG; [18F]flubrobenguane; [18F]AF78; [68Ga]DOTATOC/-TATE), or primary aldosteronism ([11C]MTO, [68Ga]PentixaFor) are currently available and have been extensively investigated in recent years. In addition, the field is currently evolving from adrenal functional imaging to a patient-centered adrenal theranostics approach, as some of those radiotracers can also be labeled with ß-emitters for therapeutic purposes.

SUMMARY

The herein reviewed functional image biomarkers may not only allow to increase diagnostic accuracy for adrenal gland diseases but may also enable for achieving substantial antitumor effects in patients with adrenocortical carcinoma, pheochromocytoma or paraganglioma.

Adrenal functional imaging

Given the more widespread use of conventional imaging techniques such as magnetic resonance imaging or computed tomography, recent years have witnessed an increased rate of incidental findings in the adrenal gland and those adrenal masses can be either of benign or malignant origin. In this regard, routinely conducted morphological imaging cannot always reliably distinguish between cancerous and noncancerous lesions. As such, those incidental adrenal masses trigger further diagnostic work-up, including molecular functional imaging providing a non-invasive read-out on a sub-cellular level. For instance, [¹⁸F]FDG positron emission tomography (PET) as a marker of glucose consumption has been widely utilized to distinguish between malignant vs benign adrenal lesions. In addition, more adrenal cortex-targeted radiotracers for PET or single photon emission computed tomography have entered the clinical arena, e.g., Iodometomidate or IMAZA, which are targeting CYP11B enzymes, or Pentixafor identifying CXCR4 in adrenal tissue. All these tracers are used for diagnosing tumors deriving from the adrenal cortex. Furthermore, radiolabeled MIBG, DOPA, and DOTATOC/-TATE are radiotracers that are quite helpful in detecting pheochromocytomas originating from the adrenal medulla. Of note, after having quantified the retention capacities of the target in-vivo, such radiotracers have the potential to be used as anti-cancer therapeutics by using their therapeutic equivalents in a theranostic setting. The present review will summarize the current advent of established and recently introduced molecular image biomarkers for investigating adrenal masses and highlight its transformation beyond providing functional status towards image-guided therapeutic approaches, in particular in patients afflicted with adrenocortical carcinoma.

Targeting 11-Beta Hydroxylase With [131I]IMAZA: A Novel Approach for the Treatment of Advanced Adrenocortical Carcinoma

CONTEXT

Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with limited treatment options. Theranostic approaches with adrenal specific radiotracers hold promise for improved diagnostics and treatment.

OBJECTIVE

Here, we report a new theranostic approach to advanced ACC applying (R)-1-[1-(4-[123I]iodophenyl)ethyl]-1H-imidazole-5-carboxylic acid azetidinyl amide ([123I]IMAZA) for diagnostic imaging and [131I]IMAZA for radionuclide therapy.

METHODS

Sixty-nine patients with nonresectable, metastatic ACCs were screened using a diagnostic [123I]IMAZA scan. Patients with significant uptake in all tumoral lesions were offered treatment with [131I]IMAZA. Tumor response was assessed according to Response Evaluation Criteria in Solid Tumors (RECIST version 1.1), and adverse effects were assessed by Common Toxicity Criteria (version 5.0).

RESULTS

After screening, 13 patients were treated with a median of 25.7 GBq [131I]IMAZA (range 18.1-30.7 GBq). Five individuals received a second treatment course. Best response was a decrease in the RECIST target lesions of -26% in 2 patients. Five patients with disease stabilization experienced a median progression-free survival of 14.3 months (range 8.3-21.9). Median overall survival in all patients was 14.1 months (4.0-56.5) after therapy. Treatment was well tolerated, in other words no severe toxicities (CTCAE grade ≥3) were observed.

CONCLUSION

In patients with advanced ACC refractory to standard therapeutic regimens, [131I]IMAZA treatment was associated with disease stabilization and nonsignificant tumor size reduction in a significant patient fraction and only limited toxicities. High [131I]IMAZA-uptake in tumor lesions was observed in 38.5% of patients with advanced ACC, rendering [131I] IMAZA a potential treatment option in a limited, well-defined patient fraction. Further clinical trials will be necessary to evaluate the full potential of this novel theranostic approach.