Radiopharmaceutical therapy of patients with metastasized melanoma with the melanin-binding benzamide 131I-BA52

Melanin-Targeting Radiotracers and Their Preclinical, Translational, and Clinical Status: From Past to Future

Melanin is one of the representative biomarkers of malignant melanoma and a potential target for diagnosis and therapy. With advancements in chemistry and radiolabeling technologies, promising strides have been made to synthesize radiolabeled melanin-binding molecules for various applications. We present an overview of melanin-targeted radiolabeled molecules and compare their features reported in preclinical studies. Clinical practice and trials are also discussed to elaborate on the safety and validity of the probes, and expanded applications beyond melanoma are reviewed. Melanin-targeted imaging holds potential value in the diagnosis, staging, and prognostic assessment of melanoma and other applications. Melanin-targeted radionuclide therapy possesses immense potential but requires more clinical validation. Furthermore, an intriguing avenue for future research involves expanding the application scope of melanin-targeted probes and exploring their value.

[177Lu]Lu-PSMA-617 theranostic probe for hepatocellular carcinoma imaging and therapy

PURPOSE

This study aimed to explore the feasibility of using [177Lu]Lu-prostate-specific membrane antigen (PSMA)-617 and [177Lu]Lu-Evans blue (EB)-PSMA-617 for in vivo radioligand therapy by single-dose administration in a PSMA-positive hepatocellular carcinoma (HCC) xenograft mouse model.

METHODS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were prepared, and labelling efficiency and radiochemical purity were determined. A HepG2 human HCC subcutaneous xenograft mouse model was established. After intravenous injection of [177Lu]Lu-PSMA-617 or [177Lu]Lu-EB-PSMA-617 (37 MBq) into the mouse model, single-photon emission computed tomography/computed tomography (SPECT/CT) was performed. Biodistribution studies were conducted to verify targeting specificity and pharmacokinetics. In the radioligand therapy study, mice were randomized into 4 groups: 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, 7.4 MBq [177Lu]Lu-EB-PSMA-617, and saline (control). A single-dose administration was applied at the beginning of therapy studies. Tumor volume, body weight, and survival were monitored every 2 days. After the end of therapy, mice were euthanized. Tumors were then weighed, and systemic toxicity was evaluated via blood testing and histological examination of healthy organs.

RESULTS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were successfully prepared with high purity and stability. SPECT/CT and biodistribution showed that tumor uptake was higher and persisted longer for [177Lu]Lu-EB-PSMA-617 compared with [177Lu]Lu-PSMA-617. [177Lu]Lu-PSMA-617 was rapidly cleared from the blood, while [177Lu]Lu-EB-PSMA-617 persisted for significantly longer. In radioligand therapy studies, tumor growth was significantly suppressed in the 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, and 7.4 MBq [177Lu]Lu-EB-PSMA-617 groups compared to the saline group. Median survival was 40, 44, 43, and 30 days, respectively. No healthy organ toxicity was observed in safety and tolerability evaluation.

CONCLUSIONS

Radioligand therapy using [177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 significantly suppressed tumor growth and prolonged survival time in PSMA-positive HCC xenograft mice without obvious toxicity. These radioligands appear promising for clinical use in humans, and future studies are warranted.

Clinical Advances and Perspectives in Targeted Radionuclide Therapy

Targeted radionuclide therapy has become increasingly prominent as a nuclear medicine subspecialty. For many decades, treatment with radionuclides has been mainly restricted to the use of iodine-131 in thyroid disorders. Currently, radiopharmaceuticals, consisting of a radionuclide coupled to a vector that binds to a desired biological target with high specificity, are being developed. The objective is to be as selective as possible at the tumor level, while limiting the dose received at the healthy tissue level. In recent years, a better understanding of molecular mechanisms of cancer, as well as the appearance of innovative targeting agents (antibodies, peptides, and small molecules) and the availability of new radioisotopes, have enabled considerable advances in the field of vectorized internal radiotherapy with a better therapeutic efficacy, radiation safety and personalized treatments. For instance, targeting the tumor microenvironment, instead of the cancer cells, now appears particularly attractive. Several radiopharmaceuticals for therapeutic targeting have shown clinical value in several types of tumors and have been or will soon be approved and authorized for clinical use. Following their clinical and commercial success, research in that domain is particularly growing, with the clinical pipeline appearing as a promising target. This review aims to provide an overview of current research on targeting radionuclide therapy.

Synthesis and Preclinical Evaluation of a 68Ga-Labeled Pyridine-Based Benzamide Dimer for Malignant Melanoma Imaging

Benzamide (BZA), a small molecule that can freely cross cell membranes and bind to melanin, has served as an effective targeting group for melanoma theranostics. In this study, a novel pyridine-based BZA dimer (denoted as H-2) was labeled with ⁶⁸Ga ([⁶⁸Ga]Ga-H-2) for positron emission tomography (PET) imaging of malignant melanomas. [⁶⁸Ga]Ga-H-2 was obtained with high radiochemical yield (98.0 ± 2.0%) and satisfactory radiochemical purity (>95.0%). The specificity and affinity of [⁶⁸Ga]Ga-H-2 were confirmed in melanoma B16F10 cells and in vivo PET imaging of multiple tumor models (B16F10 tumors, A375 melanoma, and lung metastases). Monomeric [⁶⁸Ga]Ga-H-1 was prepared as a control radiotracer to verify the effects of the molecular structure on pharmacokinetics. The values of the lipid-water partition coefficient of [⁶⁸Ga]Ga-H-2 and [⁶⁸Ga]Ga-H-1 demonstrated hydrophilicity with log P = -2.37 ± 0.07 and -2.02 ± 0.09, respectively. PET imaging and biodistribution showed a higher uptake of [⁶⁸Ga]Ga-H-2 in B16F10 primary and metastatic melanomas than that in A375 melanomas. However, the relatively low uptake of monomeric [⁶⁸Ga]Ga-H-1 in B16F10 tumors and high accumulation in nontarget organs resulted in poor PET imaging quality. This study demonstrates the synthesis and preclinical evaluation of the novel pyridine-based BZA dimer [⁶⁸Ga]Ga-H-2 and indicates that the dimer tracer has promising applications in malignant melanoma-specific PET imaging because of its high uptake and long-time retention in malignant melanoma.

Targeting Melanin in Melanoma with Radionuclide Therapy

Nearly 100,000 individuals are expected to be diagnosed with melanoma in the United States in 2022. Treatment options for late-stage metastatic disease up until the 2010s were few and offered only slight improvement to the overall survival. The introduction of B-RAF inhibitors and anti-CTLA4 and anti-PD-1/PD-L1 immunotherapies into standard of care brought measurable increases in the overall survival across all stages of melanoma. Despite the improvement in the survival statistics, patients treated with targeted therapies and immunotherapies are subject to very serious side effects, the development of drug resistance, and the high costs of treatment. This leaves room for the development of novel approaches as well as for the exploration of novel combination therapies for the treatment of metastatic melanoma. One such approach is targeting melanin pigment with radionuclide therapy. Advances in melanin-targeting radionuclide therapy of melanoma can be viewed from two spheres: (1) radioimmunotherapy (RIT) and (2) radiolabeled small molecules. The investigation of mechanisms of the action and efficacy of targeting melanin in melanoma treatment by RIT points to the involvement of the immune system such as complement dependent cytotoxicity. The combination of RIT with immunotherapy presents synergistic killing in mouse melanoma models. The field of radiolabeled small molecules is focused on radioiodinated compounds that have the ability to cross the cellular membranes to access intracellular melanin and can be applied in both therapy and imaging as theranostics. Clinical applications of targeting melanin with radionuclide therapies have produced encouraging results and clinical work is on-going. Continued work on targeting melanin with radionuclide therapy as a monotherapy, or possibly in combination with standard of care agents, has the potential to strengthen the current treatment options for melanoma patients.

Phase I study of [131I] ICF01012, a targeted radionuclide therapy, in metastatic melanoma: MELRIV-1 protocol

Background

Benzamide-based radioligands targeting melanin were first developed for imaging melanoma and then for therapeutic purpose with targeted radionuclide therapy (TRT).

[¹³¹I]ICF01012 presents a highly favorable pharmacokinetics profile in vivo for therapy. Tumour growth reduction and increase survival have been established in preclinical models of melanoma. According the these preclinical results, we initiate a first-in-human study aimed to determine the recommended dose of [¹³¹I]ICF01012 to administer for the treatment of patients with pigmented metastatic melanoma.

Methods

The MELRIV-1 trial is an open-label, multicentric, dose-escalation phase I trial. The study is divided in 2 steps, a selection part with an IV injection of low activity of [¹³¹I]ICF01012 (185 MBq at D0) to select patients who might benefit from [¹³¹I]ICF01012 TRT in therapeutic part, i.e. patient presenting at least one tumour lesion with [¹³¹I]ICF01012 uptake and an acceptable personalized dosimetry to critical organs (liver, kidney, lung and retina). According to dose escalation scheme driven by a Continual Reassessment Method (CRM) design, a single therapeutic injection of 800 MBq/m², or 1600 MBq/m², or 2700 MBq/m² or 4000 MBq/m² of [¹³¹I]ICF01012 will be administered at D11 (± 4 days). The primary endpoint is the recommended therapeutic dose of [¹³¹I]ICF01012, with DLT defined as any grade 3-4 NCI-CT toxicity during the 6 weeks following therapeutic dose. Safety, pharmacokinetic, biodistribution (using planar whole body and SPECT-CT acquisitions), sensitivity / specificity of [¹³¹I]ICF01012, and therapeutic efficacy will be assessed as secondary objectives. Patients who received therapeutic injection will be followed until 3 months after TRT. Since 6 to 18 patients are needed for the therapeutic part, up to 36 patients will be enrolled in the selection part.

Discussion

This study is a first-in-human trial evaluating the [¹³¹I]ICF01012 TRT in metastatic malignant melanomas with a diagnostic dose of the [¹³¹I]ICF01012 to select the patients who may benefit from a therapeutic dose of [¹³¹I]ICF01012, with at least one tumor lesion with [¹³¹I]ICF01012 uptake and an acceptable AD to healthy organ.

Trial registration

Clinicaltrials.gov: NCT03784625. Registered on December 24, 2018.

Identifier in French National Agency for the Safety of Medicines and Health Products (ANSM): N°EudraCT 2016-002444-17.

Theranostics – present and future

Theragnostics in nuclear medicine constitute an essential element of precision medicine. This notion integrates radionuclide diagnostics procedures and radionuclide therapies using appropriate radiopharmaceutics and treatment targeting specific biological pathways or receptors. The term theragnostics should also include another aspect of treatment: not only whether a given radioisotopic drug can be used, but also in what dose it ought to be used. Theragnostic procedures also allow predicting the effects of treatment based on the assessment of specific receptor density or the metabolic profile of neoplastic cells. The future of theragnostics depends not only on the use of new radiopharmaceuticals, but also on new gamma cameras. Modern theragnostics already require unambiguous pharmacokinetic and pharmacodynamic measurements based on absolute values. Only dynamic studies provide such a possibility. The introduction of the dynamic total-body PET-CT will enable this type of measurements characterizing metabolic processes and receptor expression on the basis of Patlak plot.

Efficacy of Targeted Radionuclide Therapy Using [131I]ICF01012 in 3D Pigmented BRAF- and NRAS-Mutant Melanoma Models and In Vivo NRAS-Mutant Melanoma

Simple Summary

Targeted radionuclide therapy (TRT) aims to selectively deliver radioactive molecules to tumor cells. For this purpose, we deliver iodine-131 ([¹³¹I]) to melanoma cells by using our laboratory-developed melanin specific radiotracer, the ICF01012. Approximately 50% and 20%–30% of human melanomas have activating mutation in BRAF or NRAS genes, respectively. These mutations lead to a constitutive activation of the MAPK/ERK pathway, which is known to be involved in tumor cells’ radioresistance. In this work, we showed using 3D in vitro tumor models, an additive efficiency of combining [¹³¹I]ICF01012-TRT and MAPK/ERK inhibitors in BRAF- and NRAS-mutant melanoma cells. In mice bearing NRAS^Q61K-mutated melanoma, TRT induced an impressive decrease in tumor growth, as well as a highly extended survival. Additionally, we showed that TRT reduces the metastatic capacity of melanoma, especially through lymph-node dissemination. These results are therefore of great interest, especially for patients with NRAS-mutant metastatic melanoma who currently lack specific efficient therapies.

Abstract

Purpose: To assess the efficiency of targeted radionuclide therapy (TRT), alone or in combination with MEK inhibitors (MEKi), in melanomas harboring constitutive MAPK/ERK activation responsible for tumor radioresistance. Methods: For TRT, we used a melanin radiotracer ([¹³¹I]ICF01012) currently in phase 1 clinical trial (NCT03784625). TRT alone or combined with MEKi was evaluated in three-dimensional melanoma spheroid models of human BRAF^V600E SK-MEL-3, murine NRAS^Q61K 1007, and WT B16F10 melanomas. TRT in vivo biodistribution, dosimetry, efficiency, and molecular mechanisms were studied using the C57BL/6J-NRAS^Q61K 1007 syngeneic model. Results: TRT cooperated with MEKi to increase apoptosis in both BRAF- and NRAS-mutant spheroids. NRAS^Q61K spheroids were highly radiosensitive towards [¹³¹I]ICF01012-TRT. In mice bearing NRAS^Q61K 1007 melanoma, [¹³¹I]ICF01012 induced a significant extended survival (92 vs. 44 days, p < 0.0001), associated with a 93-Gy tumor deposit, and reduced lymph-node metastases. Comparative transcriptomic analyses confirmed a decrease in mitosis, proliferation, and metastasis signatures in TRT-treated vs. control tumors and suggest that TRT acts through an increase in oxidation and inflammation and P53 activation. Conclusion: Our data suggest that [¹³¹I]ICF01012-TRT and MEKi combination could be of benefit for advanced pigmented BRAF-mutant melanoma care and that [¹³¹I]ICF01012 alone could constitute a new potential NRAS-mutant melanoma treatment.

Benzamide derivative radiotracers targeting melanin for melanoma imaging and therapy: Preclinical/clinical development and combination with other treatments

Cutaneous melanoma arises from proliferating melanocytes, cells specialized in the production of melanin. This property means melanin can be considered as a target for monitoring melanoma patients using nuclear imaging or targeted radionuclide therapy (TRT). Since the 1970s, many researchers have shown that specific molecules can interfere with melanin. This paper reviews some such molecules: benzamide structures improved to increase their pharmacokinetics for imaging or TRT. We first describe the characteristics and biosynthesis of melanin, and the main features of melanin tracers. The second part summarizes the preclinical and corresponding clinical studies on imaging. The last section presents TRT results from ongoing protocols and discusses combinations with other therapies as an opportunity for melanoma non-responders or patients resistant to treatments.

Renal outcomes of radioligand therapy: experience of 177lutetium-prostate-specific membrane antigen ligand therapy in metastatic castrate-resistant prostate cancer

BACKGROUND

Radioligand therapy (RLT) with 177lutetium (Lu)-labelled prostate-specific membrane antigen (PSMA) ligands has been increasingly used in recent years for therapy of metastatic castrate-resistant prostate cancer (mCRPC). Studies have revealed that 177Lu-PSMA ligand therapy is well tolerated and appears to cause fewer adverse effects than current standard of care third-line treatments. Notably, since 177Lu-PSMA agents are predominantly excreted by kidneys, there are concerns relating to their potential nephrotoxicity and renal outcomes. Although many recent studies have focused on mostly nephrotoxic adverse reactions at up to 3-month follow-up, assessment of renal outcomes after 177Lu-PSMA RLT in longer term follow-up is lacking. The aim of this study was to assess the influence of 177Lu-PSMA RLT on renal function in patients treated for mCRPC at >3 months post-therapy.

METHODS

In this retrospective cohort study, we assessed 195 men with progressive mCRPC who had received therapy with 177Lu-PSMA as second- or third-line after standard therapeutic interventions. Patients underwent investigations with 68Ga-PSMA-ligand positron emission tomography/computed tomography scan to confirm PSMA-expressing mCRPC. Eligible patients were required to have estimated glomerular filtration rate (eGFR) >30 mL/min/1.73 m2, an Eastern Cooperative Oncology Group performance status score <3, no severe liver injury (as characterized by liver function tests) and no significant bone marrow dysfunction. Enrolled patients received two to five cycles of intravenous 177Lu-PSMA I&T or 177Lu-PSMA-617, at 6- to 10-week intervals. Renal outcomes were assessed according to Kidney Disease: Improving Global Outcomes guidelines as incidence of acute kidney injury (AKI), acute kidney disease (AKD) or chronic kidney disease (CKD). All assessments and tests were undertaken between therapy cycles and at follow-up of at least 3 months.

RESULTS

Of 195 assessed men with mCRPC, 110 patients aged [mean ± SD (range)] 70 ± 8 (53-92) years were recruited into this study with median follow-up of 8 (interquartile range 5-12, minimum 3, maximum 29) months and mean baseline eGFR 81 ± 13 mL/min/1.73 m2. Pre-existing CKD was identified in 12% of patients. None of the patients experienced an AKI during RLT. Two AKD and three CKD G3a cases were identified. Analysis of possible impact of prior CKD and major risk factors (hypertension, diabetes, history of AKI) on incidence of AKD or CKD demonstrated relative risk 4.2 [95% confidence interval (CI) 1.23-14.29] and 1.91 (95% CI 1.14-3.12), respectively. However, Fisher's exact test did not reveal statistical significance of the impact of both conditions.

CONCLUSIONS

Current Lu-PSMA RLT protocols appear to carry a mild nephrotoxic risk with the rate of about 4.5%. Prior CKD is potentially the most significant risk factor of post-RLT renal dysfunction.

Discovery, affinity maturation and multimerization of small molecule ligands against human tyrosinase and tyrosinase-related protein 1

Human tyrosinase (hTYR) and tyrosinase-related protein 1 (hTYRP1) are closely-related enzymes involved in the synthesis of melanin, which are selectively expressed in melanocytes and, in a pathological context, in melanoma lesions. We used a previously described tyrosinase inhibitor (Thiamidol™) and DNA-encoded library technology for the discovery of novel hTYR and hTYRP1 ligands, that could be used as vehicles for melanoma targeting. Performing de novo selections with DNA-encoded libraries, we discovered novel ligands capable of binding to both hTYR and hTYRP1. More potent ligands were obtained by multimerizing Thiamidol™ moieties, leading to homotetrameric structures that avidly bound to melanoma cells, as revealed by flow cytometry. These findings suggest that melanoma lesions may, in the future, be targeted not only by monoclonal antibody reagents but also by small organic ligands.

A series of different strategies were oriented toward the discovery of small molecule ligands binding to the human version of tyrosinase (hTYR) and tyrosinase-related protein 1 (hTYRP1), which may represent the basis for novel treatments of melanoma.

Neutron-activated theranostic radionuclides for nuclear medicine

Theranostics in nuclear medicine refers to personalized patient management that involves targeted therapy and diagnostic imaging using a single or combination of radionuclide (s). The radionuclides emit both alpha (α) or beta (β-) particles and gamma (γ) rays which possess therapeutic and diagnostic capabilities, respectively. However, the production of these radionuclides often faces difficulties due to high cost, complexity of preparation methods and that the products are often sourced far from the healthcare facilities, hence losing activity due to radioactive decay during transportation. Subject to the availability of a nuclear reactor within an accessible distance from healthcare facilities, neutron activation is the most practical and cost-effective route to produce radionuclides suitable for theranostic purposes. Holmium-166 (166Ho), Lutetium-177 (177Lu), Rhenium-186 (186Re), Rhenium-188 (188Re) and Samarium-153 (153Sm) are some of the most promising neutron-activated radionuclides that are currently in clinical practice and undergoing clinical research for theranostic applications. The aim of this paper is to review the physical characteristics, current clinical applications and future prospects of these neutron activated radionuclides in theranostics. The production, physical properties, validated clinical applications and clinical studies for each neutron-activated radionuclide suitable for theranostic use in nuclear medicine are reviewed in this paper.

64Cu-labeled melanin nanoparticles for PET/CT and radionuclide therapy of tumor

Melanin is a group of natural pigments found in living organism. It can be used for positron emission tomography (PET) imaging due to its inherent chelating ability to radioactive cupric ion. This study was to prepare ⁶⁴Cu-labeled PEGylated melanin nanoparticles (⁶⁴Cu-PEG-MNPs), and to further take advantage of the enhanced permeability and retention (EPR) effect of radiolabeled nanoparticles to realize the integration of tumor diagnosis and treatment. We successfully synthesized PEG-MNPs. Saline and serum stability experiments demonstrated good stability. PET/CT showed high tumor aggregation. Moreover, ⁶⁴Cu-PEG-MNPs resulted in a therapeutic effect on the A431 tumor-bearing mice in the treatment group. The pathological results further confirmed that the therapeutic doses of ⁶⁴Cu-PEG-MNPs cause pathological changes of tumor tissues while showing minimal toxicity to normal tissues. Our data successfully demonstrate the good imaging performance of ⁶⁴Cu-PEG-MNPs on A431 tumors and further proved its therapeutic effect, highlighting a great potential in targeted radionuclide therapy.

Targeted melanoma radiotherapy using ultrasmall 177Lu-labeled α-melanocyte stimulating hormone-functionalized core-shell silica nanoparticles

Lutetium-177 (¹⁷⁷Lu) radiolabeled ultrasmall (~6 nm dia.) fluorescent core-shell silica nanoparticles (Cornell prime dots or C' dots) were developed for improving efficacy of targeted radiotherapy in melanoma models. PEGylated C' dots were surface engineered to display 10-15 alpha melanocyte stimulating hormone (αMSH) cyclic peptide analogs for targeting the melanocortin-1 receptor (MC1-R) over-expressed on melanoma tumor cells. The ¹⁷⁷Lu-DOTA-αMSH-PEG-C' dot product was radiochemically stable, biologically active, and exhibited high affinity cellular binding properties and internalization. Selective tumor uptake and favorable biodistribution properties were also demonstrated, in addition to bulk renal clearance, in syngeneic B16F10 and human M21 xenografted models. Prolonged survival was observed in the treated cohorts relative to controls. Dosimetric analysis showed no excessively high absorbed dose among normal organs. Correlative histopathology of ex vivo treated tumor specimens revealed expected necrotic changes; no acute pathologic findings were noted in the liver or kidneys. Collectively, these results demonstrated that ¹⁷⁷Lu-DOTA-αMSH-PEG-C' dot targeted melanoma therapy overcame the unfavorable biological properties and dose-limiting toxicities associated with existing mono-molecular treatments. The unique and tunable surface chemistries of this targeted ultrasmall radiotherapeutic, coupled with its favorable pharmacokinetic properties, substantially improved treatment efficacy and demonstrated a clear survival benefit in melanoma models, which supports its further clinical translation.

Advances in GLP-1 receptor targeting radiolabeled agent development and prospective of theranostics

In the light of theranostics/radiotheranostics and prospective of personalized medicine in diabetes and oncology, this review presents prior and current advances in the development of radiolabeled imaging and radiotherapeutic exendin-based agents targeting glucagon-like peptide-1 receptor. The review covers chemistry, preclinical, and clinical evaluation. Such critical aspects as structure-activity-relationship, stability, physiological potency, kidney uptake, and dosimetry are discussed.

Targeted Radionuclide Therapy Decreases Melanoma Lung Invasion by Modifying Epithelial-Mesenchymal Transition-Like Mechanisms

Melanin-radiolabeled molecules for targeted radionuclide therapy (TRT) provide a promising approach for the treatment of pigmented melanoma. Among these radiolabeled molecules, the iodinated melanin-specific binding molecule ([¹³¹I]ICF01012) has shown a significant antitumor effect on metastatic melanoma preclinical models. We report herein that [¹³¹I]ICF01012 decreases the epithelial-mesenshymal transition-like (EMT-like) markers in both in vivo and in vitro three-dimensional (3D) melanoma spheroid models. [¹³¹I]ICF01012 spheroids irradiation resulted in reduced clonogenic capacity of all pigmented spheroids accompanied by increased protein expression levels of phosphorylated H2A.X, p53 and its downstream target p21. In addition, [¹³¹I]ICF01012 treatment leads to a significant increase of cell pigmentation as demonstrated in SK-MEL3 human xenograft model. We also showed that [¹³¹I]ICF01012 decreases the size and the number of melanoma lung colonies in the syngeneic murine B16BL6 in vivo model assessing its potentiality to kill circulating tumor cells. Taken together, these results indicate that [¹³¹I]ICF01012 reduces metastatic capacity of melanoma cells presumably through EMT-like reduction and cell differentiation induction.

Targeted radiotherapy of pigmented melanoma with 131I-5-IPN

Purpose

There has been no satisfactory treatment for advanced melanoma until now. Targeted radionuclide therapy (TRNT) may be a promising option for this heretofore lethal disease. Our goal in this study was to synthesize ¹³¹I-N-(2-(diethylamino)ethyl)-5-(iodo-131I)picolinamide (¹³¹I-5-IPN) and evaluate its therapeutic ability and toxicity as a radioiodinated melanin-targeting therapeutic agent.

Methods

The trimethylstannyl precursor was synthesized and labeled with ¹³¹I to obtain ¹³¹I-5-IPN. The pharmacokinetics of ¹³¹I-5-IPN was evaluated through SPECT imaging, and its biodistribution was assessed in B16F10 tumor models and in A375 human-to-mouse xenografts. For TRNT, B16F10 melanoma-bearing mice were randomly allocated to receive one of five treatments (n = 10 per group): group A (the control group) received 0.1 mL saline; group B was treated with an equimolar dose of unlabeled precursor; group C received 18.5 MBq of [¹³¹I]NaI; group D and E received one or two dose of 18.5 MBq ¹³¹I-5-IPN, respectively. TRNT efficacy was evaluated through tumor volume measurement and biology study. The toxic effects of ¹³¹I-5-IPN on vital organs were assessed with laboratory tests and histopathological examination. The radiation absorbed dose to vital organs was estimated based on biodistribution data.

Results

¹³¹I-5-IPN was successfully prepared with a good radiochemistry yield (55% ± 5%, n = 5), and it exhibited a high uptake ratio in melanin-positive B16F10 cells which indicating high specificity. SPECT imaging and biodistribution of ¹³¹I-5-IPN showed lasting high tumor uptake in pigmented B16F10 models for 72 h. TRNT with ¹³¹I-5-IPN led to a significant anti-tumor effect and Groups D and E displayed an extended median survival compared to groups A, B, and C. The highest absorbed dose to a vital organ was 0.25 mSv/MBq to the liver; no obvious injury to the liver or kidneys was observed during treatment. ¹³¹I-5-IPN treatment was associated with reduction of expression of proliferating cell nuclear antigen (PCNA) and Ki67 and cell cycle blockage in G2/M phase in tumor tissues. Decreased vascular endothelial growth factor and CD31 expression, implying reduced tumor growth, was noted after TRNT.

Conclusion

We successfully synthesized ¹³¹I-5-IPN, which presents long-time retention in melanotic melanoma. TRNT with ¹³¹I-5-IPN has the potential to be a safe and effective strategy for management of pigmented melanoma.

Radioiodination and biodistribution of newly synthesized 3-benzyl-2-([3-methoxybenzyl]thio)benzo[g]quinazolin-4-(3H)-one in tumor bearing mice

3-Benzyl-2-((3-methoxybenzyl)thio)benzo[g]quinazolin-4(3H)-one was previously synthesized and proved by physicochemical analyses (HRMS, 1H and 13C NMR). The target compound was examined for its radioactivity and the results showed that benzo[g]quinazoline was successfully labeled with radioactive iodine using NBS via an electrophilic substitution reaction. The reaction parameters that affected the labeling yield such as concentration, pH and time were studied to optimize the labeling conditions. The radiochemical yield was 91.2 ± 1.22% and the in vitro studies showed that the target compound was stable for up to 24 h. The thyroid was among the other organs in which the uptake of 125I-benzoquinazoline has increased significantly over the time up to 4.1%. The tumor uptake was 6.95%. Radiochemical and metabolic stability of the benzoquinazoline in vivo/in vitro and biodistribution studies provide some insights about the requirements for developing more potent radiopharmaceutical for targeting the tumor cells.

PSMA Theranostics: Current Status and Future Directions

Prostate-specific membrane antigen (PSMA) is a promising target for imaging diagnostics and targeted radionuclide therapy (theranostics) of prostate cancer and its metastases. There is increasing evidence of encouraging response rates and a low toxicity profile of radioligand therapy (RLT) of metastatic castration-resistant prostate cancer using ¹⁷⁷Lu-labeled PSMA ligands. In this article, we review the current status of diagnostics and therapy using radiolabeled PSMA ligands. We also suggest protocols for patient selection criteria and conduct of PSMA-based RLT. Challenges and opportunities of PSMA theranostics are discussed.

Combined external beam radiotherapy with carbon ions and tumor targeting endoradiotherapy

External beam radiotherapy (EBRT) with carbon ions and endoradiotherapy using radiolabeled tumor targeting agents are emerging concepts in precision cancer therapy. We report on combination effects of these two promising strategies.

Tumor targeting ¹³¹I-labelled anti-EGFR-antibody (Cetuximab) was used in the prototypic EGFR-expressing A431 human squamous cell carcinoma xenograft model. A ¹³¹I-labelled melanin-binding benzamide derivative was utilized targeting B16F10 melanoma in an orthotopic syngeneic C57bl6 model. Fractionated EBRT was performed using carbon ions in direct comparison with conventional photon irradiation.

Tumor uptake of ¹³¹I-Cetuximab and ¹³¹I-Benzamide was enhanced by fractionated EBRT as determined by biodistribution studies. This effect was independent of radiation quality and significant for the small molecule ¹³¹I-Benzamide, i.e., >30% more uptake in irradiated vs. non-irradiated melanoma was found (p<0.05). Compared to each monotherapy, dual combination with ¹³¹I-Cetuximab and EBRT was most effective in inhibiting A431 tumor growth. A similar trend was seen for ¹³¹I-Benzamide and EBRT in B16F10 melanoma model. Addition of ¹³¹I-Benzamide endoradiotherapy to EBRT altered expression of genes related to DNA-repair, cell cycle and cell death. In contrast, immune-response related pathways such as type 1 interferon response genes (ISG15, MX1) were predominantly upregulated after combined ¹³¹I-Cetuximab and EBRT. The beneficial effects of combined 131I-Cetuximab and EBRT was further attributed to a reduced microvascular density (CD31) and decreased proliferation index (Ki-67).

Fractionated EBRT could be favorably combined with endoradiotherapy. ¹³¹I-Benzamide endoradiotherapy accelerated EBRT induced cytotoxic effects. Activation of immune-response by carbon ions markedly enhanced anti-EGFR based endoradiotherapy suggesting further evaluation of this novel and promising radioimmunotherapy concept.

It is time to move forward into the era of Theranostics

Radionuclide therapy, which until 15 years ago included only a few approved therapies, is gaining importance in the treatment of various malignancies. The future of oncology will not be limited to surgery, chemo-, antibody therapies or external radiation; it will include targeted therapy with radionuclides, which will become the standard of care for a variety of malignant diseases in combination or as an alternative to other therapies. Therefore there is a need to train Nuclear Oncologists, who are able to approach oncological diseases, promote development of radiopharmacy, understand the biology of radionuclide treatment, apply radionuclide treatments and be able to use molecular imaging such as PET/CT and SPECT/CT for treatment planning and dosimetry.

PET and SPECT imaging of melanoma: the state of the art

Melanoma represents the most aggressive form of skin cancer, and its incidence continues to rise worldwide. 18F-FDG PET imaging has transformed diagnostic nuclear medicine and has become an essential component in the management of melanoma, but still has its drawbacks. With the rapid growth in the field of nuclear medicine and molecular imaging, a variety of promising probes that enable early diagnosis and detection of melanoma have been developed. The substantial preclinical success of melanin- and peptide-based probes has recently resulted in the translation of several radiotracers to clinical settings for noninvasive imaging and treatment of melanoma in humans. In this review, we focus on the latest developments in radiolabeled molecular imaging probes for melanoma in preclinical and clinical settings, and discuss the challenges and opportunities for future development.

Targeting DNA repair by coDbait enhances melanoma targeted radionuclide therapy

Radiolabelled melanin ligands offer an interesting strategy for the treatment of disseminated pigmented melanoma. One of these molecules, ICF01012 labelled with iodine 131, induced a significant slowing of melanoma growth. Here, we have explored the combination of [¹³¹I]ICF01012 with coDbait, a DNA repair inhibitor, to overcome melanoma radioresistance and increase targeted radionuclide therapy (TRT) efficacy. In human SK-Mel 3 melanoma xenograft, the addition of coDbait had a synergistic effect on tumor growth and median survival. The anti-tumor effect was additive in murine syngeneic B16Bl6 model whereas coDbait combination with [¹³¹I]ICF01012 did not increase TRT side effects in secondary pigmented tissues (e.g. hair follicles, eyes). Our results confirm that DNA lesions induced by TRT were not enhanced with coDbait association but, the presence of micronuclei and cell cycle blockade in tumor shows that coDbait acts by interrupting or delaying DNA repair. In this study, we demonstrate for the first time, the usefulness of DNA repair traps in the context of targeted radionuclide therapy.

Theranostics in nuclear medicine practice

The importance of personalized medicine has been growing, mainly due to a more urgent need to avoid unnecessary and expensive treatments. In nuclear medicine, the theranostic approach is an established tool for specific molecular targeting, both for diagnostics and therapy. The visualization of potential targets can help predict if a patient will benefit from a particular treatment. Thanks to the quick development of radiopharmaceuticals and diagnostic techniques, the use of theranostic agents has been continually increasing. In this article, important milestones of nuclear therapies and diagnostics in the context of theranostics are highlighted. It begins with a well-known radioiodine therapy in patients with thyroid cancer and then progresses through various approaches for the treatment of advanced cancer with targeted therapies. The aim of this review was to provide a summary of background knowledge and current applications, and to identify the advantages of targeted therapies and imaging in nuclear medicine practices.

Dual addressing of thymidine synthesis pathways for effective targeting of proliferating melanoma

Here, we examined the potential of blocking the thymidine de novo synthesis pathways for sensitizing melanoma cells to the nucleoside salvage pathway targeting endogenous DNA irradiation. Expression of key nucleotide synthesis and proliferation enzymes thymidylate synthase (TS) and thymidine kinase 1 (TK1) was evaluated in differentiated (MITF^high [microphthalmia‐associated transcription factor] IGR1) and invasive (MITF^mediumIGR37) melanoma cells. For inhibition of de novo pathways cells were incubated either with an irreversible TS inhibitor 5‐fluoro‐2′‐deoxyuridine (FdUrd) or with a competitive dihydrofolate‐reductase (DHFR) inhibitor methotrexate (MTX). Salvage pathway was addressed by irradiation‐emitting thymidine analog [^123/125I]‐5‐iodo‐4′‐thio‐2′‐deoxyuridine (^123/125I‐ITdU). The in vivo targeting efficiency was visualized by single‐photon emission computed tomography. Pretreatment with FdUrd strongly increased the cellular uptake and the DNA incorporation of ¹²⁵I‐ITdU into the mitotically active IGR37 cells. This effect was less pronounced in the differentiated IGR1 cells. In vivo, inhibition of TS led to a high and preferential accumulation of ¹²³I‐ITdU in tumor tissue. This preclinical study presents profound rationale for development of therapeutic approach by highly efficient and selective radioactive targeting one of the crucial salvage pathways in melanomas.

Theranostic Approach for Metastatic Pigmented Melanoma Using ICF15002, a Multimodal Radiotracer for Both PET Imaging and Targeted Radionuclide Therapy

PURPOSE: This work reports, in melanoma models, the theranostic potential of ICF15002 as a single fluorinated and iodinated melanin-targeting compound. METHODS: Studies were conducted in the murine syngeneic B16BL6 model and in the A375 and SK-MEL-3 human xenografts. ICF15002 was radiolabeled with fluorine-18 for positron emission tomography (PET) imaging and biodistribution, with iodine-125 for metabolism study, and iodine-131 for targeted radionuclide therapy (TRT). TRT efficacy was assessed by tumor volume measurement, with mechanistics and dosimetry parameters being determined in the B16BL6 model. Intracellular localization of ICF15002 was characterized by secondary ion mass spectrometry (SIMS). RESULTS: PET imaging with [¹⁸F]ICF15002 evidenced tumoral uptake of 14.33 ± 2.11%ID/g and 4.87 ± 0.93%ID/g in pigmented B16BL6 and SK-MEL-3 models, respectively, at 1 hour post inoculation. No accumulation was observed in the unpigmented A375 melanoma. SIMS demonstrated colocalization of ICF15002 signal with melanin polymers in melanosomes of the B16BL6 tumors. TRT with two doses of 20 MBq [¹³¹I]ICF15002 delivered an absorbed dose of 102.3 Gy to B16BL6 tumors, leading to a significant tumor growth inhibition [doubling time (DT) of 2.9 ± 0.5 days in treated vs 1.8 ± 0.3 in controls] and a prolonged median survival (27 days vs 21 in controls). P53S15 phosphorylation and P21 induction were associated with a G2/M blockage, suggesting mitotic catastrophe. In the human SK-MEL-3 model, three doses of 25 MBq led also to a DT increase (26.5 ± 7.8 days vs 11.0 ± 3.8 in controls) and improved median survival (111 days vs 74 in controls). CONCLUSION: Results demonstrate that ICF15002 fulfills suitable properties for bimodal imaging/TRT management of patients with pigmented melanoma.

Synthesis, radiolabelling, and biodistribution studies of triazole derivatives for targeting melanoma

Molecular probes that target specific markers expressed in solid tumours are in demand for cancer imaging and radionuclide therapy applications. The synthesis, characterization, and in vivo evaluation of radioiodinated triazoles designed as probes to target melanoma are described here. Compounds were prepared using a thermal click reaction between ethynylstannane and methyl 2-azidoacetate, resulting in preferential formation of the corresponding 1,4-tin triazole. The primary amine of various targeting vectors was then coupled to the resulting tin triazole methyl ester. These precursors were labelled with no carrier added 123I or 125I and purified by high performance liquid chromatography to give isolated radiochemical yields between 6% and 51% and radiochemical purities of >95% in all cases. Among the evaluated compounds, N-(2-diethylamino-ethyl)-2-(4-iodo-[1,2,3]triazol-1-yl)acetamide (7a) and N-(1-benzylpiperidin-4-yl)-2-(4-iodo-1H-1,2,3-triazol-1-yl)acetamide (7d) showed the most promising in vivo data, and their 123I-labelled forms were used in single photon emission computed tomography computed tomography (SPECT–CT) imaging studies. The imaging data showed excellent tumour visualization with a very high signal to noise ratio.

Preparation and characterization of a novel Al(18)F-NOTA-BZA conjugate for melanin-targeted imaging of malignant melanoma

Melanin is an attractive target for the diagnosis and treatment of malignant melanoma. Previous studies have demonstrated the specific binding ability of benzamide moiety to melanin. In this study, we developed a novel (18)F-labeled NOTA-benzamide conjugate, Al(18)F-NOTA-BZA, which can be synthesized in 30min with a radiochemical yield of 20-35% and a radiochemical purity of >95%. Al(18)F-NOTA-BZA is highly hydrophilic (logP=-1.96) and shows good in vitro stability. Intravenous administration of Al(18)F-NOTA-BZA in two melanoma-bearing mouse models revealed highly specific uptake in B16F0 melanotic melanoma (6.67±0.91 and 1.50±0.26%ID/g at 15 and 120min p.i., respectively), but not in A375 amelanotic melanoma (0.87±0.21 and 0.24±0.09%ID/g at 15 and 120min p.i., respectively). The clearance from most normal tissues was fast. A microPET scan of Al(18)F-NOTA-BZA-injected mice also displayed high-contrast tumor images as compared with normal organs. Owing to the favorable in vivo distribution of Al(18)F-NOTA-BZA after intravenous administration, the estimated absorption dose was low in all normal organs and tissues. The melanin-specific binding ability, sustained tumor retention, fast normal tissues clearance and thelow projected human dosimetry supported that Al(18)F-NOTA-BZA is a very promising melanin-specific PET probe for melanin-positive melanoma.

Synthesis and characterization of a novel radioiodinated phenylacetamide and its homolog as theranostic agents for malignant melanoma

Melanin is an attractive target for the diagnosis and treatment of malignant melanoma. This study reports the preparation and biological characterizations of N-(2-(diethylamino)ethyl)-2-(3-(123/131)I-iodo-4- hydroxyphenyl)acetamide and N-(2-(diethylamino)ethyl)-3-(3-(123/131)I-iodo-4-hydroxyphenyl)propanamide (123/131)I-IHPA and 123/131I-IHPP) as novel melanin-specific theranostic agents. These two tracers were hydrophilic, exhibited good serum stability and high binding affinity to melanin. In vitro and in vivo studies revealed rapid, high and tenacious uptakes of both 131I-IHPA and 131I-IHPP in melanotic B16F0 cell line and in C57BL/6 mice bearing B16F0 melanoma, but not in amelanonic A375 cell line and tumors. Small-animal SPECT imaging also clearly delineate B16F0 melanoma since 1 h postinjection of 123I-IHPA and 123I-IHPP in tumor-bearing mice. Owing to the favorable biodistribution of 131I-IHPA and 131I-IHPP after intravenous administration, the estimated absorption dose was low in most normal organs and relatively high in melanotic tumor. The melanin-specific binding ability, sustained tumor retention, fast normal tissues clearance and acceptable projected human dosimetry supported that these two tracers are promising theranostic agents for melanin-positive melanoma.

TYR as a multifunctional reporter gene regulated by the Tet-on system for multimodality imaging: an in vitro study

The human tyrosinase gene TYR is a multifunctional reporter gene with potential use in photoacoustic imaging (PAI), positron emission tomography (PET), and magnetic resonance imaging (MRI). We sought to establish and evaluate a reporter gene system using TYR under the control of the Tet-on gene expression system (gene expression induced by doxycycline [Dox]) as a multimodality imaging agent. We transfected TYR into human breast cancer cells (MDA-MB-231), naming the resulting cell line 231-TYR. Using non-transfected MDA-MB-231 cells as a control, we verified successful expression of TYR by 231-TYR after incubation with Dox using western blot, cellular tyrosinase activity, Masson-Fontana silver staining, and a cell immunofluorescence study, while the control cells and 231-TYR cells without Dox exposure revealed no TYR expression. Detected by its absorbance at 405 nm, increasing concentrations of melanin correlated positively with Dox concentration and incubation time. TYR expression by Dox-induced transfected cells shortened MRI T1 and T2 relaxation times. Photoacoustic signals were easily detected in these cells. (18)F-5-fluoro-N-(2-[diethylamino]ethyl)picolinamide ((18)F-5-FPN), which targets melanin, quickly accumulated in Dox-induced 231-TYR cells. These show that TYR induction of melanin production is regulated by the Tet-on system, and TYR-containing indicator cells may have utility in multimodality imaging.

Early side effects and first results of radioligand therapy with (177)Lu-DKFZ-617 PSMA of castrate-resistant metastatic prostate cancer: a two-centre study

Background

Radioligand therapy (RLT) with ¹⁷⁷Lu-DKFZ-617 PSMA (Lu-PSMA) (prostate-specific membrane antigen) is a novel targeted therapy of metastatic prostate cancer. We analysed retrospectively the early side effects and the response rate in the first patients, who received a therapy with Lu-PSMA in our departments.

Methods

RLT was performed in ten hormone- and/or chemo-refractory patients with distant metastases and progressive disease (mean age 73.5 years). ⁶⁸Ga-PSMA HBED-CC PET/CT was performed in all patients prior to RLT. The median PSA level prior to the therapy was 298.5 ng/ml (range 5–853 ng/ml). All patients received CBC, renal and liver function tests the day before and 2 days after application (mean administered activity 5.6 GBq, range 4.1–6.1 GBq), followed by further tests every 2 weeks. All patients were contacted by telephone every week regarding side effects or any positive and negative changes.

Results

Eight weeks after the therapy, seven patients (70 %) experienced a PSA decline, of whom six experienced more than 30 % and five more than 50 %. Three patients showed a progressive disease according to the PSA increase. No patient experienced any side effects immediately after injection of Lu-PSMA. Relevant hematotoxicity (grade 3 or 4) occurred 7 weeks after the administration in just one patient. The same patient showed a leucopenia grade 2. Two patients showed a disturbance of only 1 hematologic cell line, whereas one patient showed a reduction of grades 1 and 2 in leucocytes and thrombocytes, respectively. Six patients did not show any hematotoxicity during the 8 weeks after therapy. There was no relevant nephrotoxicity (grade 3 or 4).

Conclusions

Our initial results indicate that RLT with Lu-PSMA is safe and seems to have low early side-effect profile. A relevant PSA decline was detected in 70 % of patients.

Synthesis and evaluation of ¹²³/¹³¹I-Iochlonicotinamide as a novel SPECT probe for malignant melanoma

Malignant melanoma expresses a highly aggressive metastasis. Early diagnosis of malignant melanoma is important for patient survival. Radiolabeled benzamides and nicotinamides have been reported to be attractive candidates for malignant melanoma diagnosis as they bind to melanin, a characteristic substance that displays in malignant melanoma, and show high tumor accumulation and retention. Herein, we designed and synthesized a novel (123/131)I-labeled nicotinamide derivative that specifically binds to melanin. (123/131)I-Iochlonicotinamide was prepared with good radiochemical yield (50-70%, decay corrected) and high specific radioactivity (50-80 GBq/μmol). (131)I-Iochlonicotinamide exhibited good in vitro stability (radiochemical purity >95% after a 24-h incubation) in human serum. High uptake of (123/131)I-Iochlonicotinamide in B16F0 melanoma cells compared to that in A375 amelanotic cells demonstrated its selective binding to melanin. Intravenous administration of (123/131)I-Iochlonicotinamide in a melanoma-bearing mouse model revealed high uptake in melanotic melanoma and high tumor-to-muscle ratio. MicroSPECT scan of (123/131)I-Iochlonicotinamide injected mice also displayed high contrast tumor imaging as compared with normal organs. The radiation-absorbed dose projection for the administration of (131)I-Iochlonicotinamide to human was based on the results of biodistribution study. The effective dose appears to be approximately 0.44 mSv/MBq(-1). The specific binding of (123/131)I-Iochlonicotinamide to melanin along with a prolonged tumor retention and acceptable projected human dosimetry suggest that it may be a promising theranostic agent for treating malignant melanoma.

Radiolabeled dendritic probes as tools for high in vivo tumor targeting: application to melanoma

A small-sized and bifunctional¹¹¹In-radiolabeled dendron shows highin vivotargeting efficiency towards an intracellular target in a murine melanoma model.

The study of external dose rate and retained body activity of patients receiving 131I therapy for differentiated thyroid carcinoma

Radiation safety is an integral part of targeted radionuclide therapy. The aim of this work was to study the external dose rate and retained body activity as functions of time in differentiated thyroid carcinoma patients receiving ¹³¹I therapy. Seventy patients were stratified into two groups: the ablation group (A) and the follow-up group (FU). The patients’ external dose rate was measured, and simultaneously, their retained body radiation activity was monitored at various time points. The equations of the external dose rate and the retained body activity, described as a function of hours post administration, were fitted. Additionally, the release time for patients was calculated. The reduction in activity in the group receiving a second or subsequent treatment was more rapid than the group receiving only the initial treatment. Most important, an expeditious method was established to indirectly evaluate the retained body activity of patients by measuring the external dose rate with a portable radiation survey meter. By this method, the calculated external dose rate limits are 19.2, 8.85, 5.08 and 2.32 μSv·h⁻¹ at 1, 1.5, 2 and 3 m, respectively, according to a patient’s released threshold level of retained body activity <400 MBq. This study is beneficial for radiation safety decision-making.