Early detection and longitudinal monitoring of experimental primary and disseminated melanoma using [18F]ICF01006, a highly promising melanoma PET tracer

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.

Translating Molecules into Imaging—The Development of New PET Tracers for Patients with Melanoma

Melanoma is a deadly disease that often exhibits relentless progression and can have both early and late metastases. Recent advances in immunotherapy and targeted therapy have dramatically increased patient survival for patients with melanoma. Similar advances in molecular targeted PET imaging can identify molecular pathways that promote disease progression and therefore offer physiological information. Thus, they can be used to assess prognosis, tumor heterogeneity, and identify instances of treatment failure. Numerous agents tested preclinically and clinically demonstrate promising results with high tumor-to-background ratios in both primary and metastatic melanoma tumors. Here, we detail the development and testing of multiple molecular targeted PET-imaging agents, including agents for general oncological imaging and those specifically for PET imaging of melanoma. Of the numerous radiopharmaceuticals evaluated for this purpose, several have made it to clinical trials and showed promising results. Ultimately, these agents may become the standard of care for melanoma imaging if they are able to demonstrate micrometastatic disease and thus provide more accurate information for staging. Furthermore, these agents provide a more accurate way to monitor response to therapy. Patients will be able to receive treatment based on tumor uptake characteristics and may be able to be treated earlier for lesions that with traditional imaging would be subclinical, overall leading to improved outcomes for patients.

Ultrasensitive detection of malignant melanoma using PET molecular imaging probes

With the emergence of new therapeutic modalities, the diagnosis of melanoma at the earliest practicable stage has become more important for improving the survival of patients. We developed a positron emission tomography (PET) imaging probe, N-(2-(dimethylamino)ethyl)-5-[¹⁸F]fluoropicolinamide ([¹⁸F]DMPY2) and evaluated diagnostic performance in animal models. [¹⁸F]DMPY2 PET exhibited excellent performance in detecting primary and metastatic melanomas, demonstrating strong/prolonged tumoral uptake and rapid background clearance. This suggests that this radiotracer could be used as a novel PET imaging agent to obtain outstanding image quality in the diagnosis of melanoma. This is the pioneering report of pyridine-based benzamide derivative with reduced alkyl chains in the amine residue and ultrasensitive detection of melanoma lesions in living subjects compared to conventional PET imaging agents.

Malignant melanoma has one of the highest mortality rates of any cancer because of its aggressive nature and high metastatic potential. Clinical staging of the disease at the time of diagnosis is very important for the prognosis and outcome of melanoma treatment. In this study, we designed and synthesized the ¹⁸F-labeled pyridine-based benzamide derivatives N-(2-(dimethylamino)ethyl)-5-[¹⁸F]fluoropicolinamide ([¹⁸F]DMPY2) and N-(2-(dimethylamino)ethyl)-6-[¹⁸F]fluoronicotinamide ([¹⁸F]DMPY3) to detect primary and metastatic melanoma at an early stage and evaluated their performance in this task. [¹⁸F]DMPY2 and [¹⁸F]DMPY3 were synthesized by direct radiofluorination of the bromo precursor, and radiochemical yields were ∼15–20%. Cell uptakes of [¹⁸F]DMPY2 and [¹⁸F]DMPY3 were >103-fold and 18-fold higher, respectively, in B16F10 (mouse melanoma) cells than in negative control cells. Biodistribution studies revealed strong tumor uptake and retention of [¹⁸F]DMPY2 (24.8% injected dose per gram of tissue [ID/g] at 60 min) and [¹⁸F]DMPY3 (11.7%ID/g at 60 min) in B16F10 xenografts. MicroPET imaging of both agents demonstrated strong tumoral uptake/retention and rapid washout, resulting in excellent tumor-to-background contrast in B16F10 xenografts. In particular, [¹⁸F]DMPY2 clearly visualized almost all metastatic lesions in lung and lymph nodes, with excellent image quality. [¹⁸F]DMPY2 demonstrated a significantly higher tumor-to-liver ratio than [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) and the previously reported benzamide tracers N-[2-(diethylamino)-ethyl]-5-[¹⁸F]fluoropicolinamide ([¹⁸F]P3BZA) and N-[2-(diethylamino)-ethyl]-4-[¹⁸F]fluorobenzamide ([¹⁸F]FBZA) in B16F10-bearing or SK-MEL-3 (human melanoma)-bearing mice. In conclusion, [¹⁸F]DMPY2 might have strong potential for the diagnosis of early stage primary and metastatic melanoma using positron emission tomography (PET).

Synthesis of N-(6-[18F]Fluoropyridin-3-yl)glycine as a potential renal PET agent

OBJECTIVE

Given the requirements of high sensitivity and spatial resolution, the development of new positron emission tomography (PET) agents is required for PET renography. The objective of this study was to investigate a new fluorine-18 labeled hippurate analogue of picolinamide, N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine, as a new renal PET agent for evaluating renal function.

METHODS

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was prepared via a two-step reaction, including the nucleophilic substitution reaction of Br with ¹⁸F using methyl 2-(6-bromonicotinamido)acetate as a precursor followed the hydrolysis with sodium hydroxide and purification by preparative-HPLC. The in vitro and in vivo stability were determined using HPLC, and the plasma protein binding (PPB) and erythrocyte uptake of N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine were determined using blood collected from healthy rats at 5 min post-injection. Biodistribution and dynamic micro-PET/CT imaging studies were conducted in healthy rats.

RESULTS

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was prepared within 45 min with an uncorrected radiochemical yield of 24.5 ± 6.7% (n = 6, based on [¹⁸F]F^-) and a radiochemical purity of >98%. N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine demonstrated good stability both in vitro and in vivo. The results of the biodistribution and dynamic micro-PET/CT imaging studies in normal rats indicated that N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine was rapidly and exclusively excreted via the renal-urinary pathway.

CONCLUSION

N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine is has been shown to be a promising renal PET agent and warrants further evaluation of renal function.

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.

Rapid radiosynthesis of two [18F]-labeled nicotinamide derivatives for malignant melanoma imaging

The rapid synthesis of two radiofluoronicotinamide derivatives, namely, [¹⁸F]MEL050 and [¹⁸F]MEL-2F has been simply performed starting from commercial materials. [¹⁸F]MEL-2F is a new, potential analogue PET-probe for melanoma imaging. [¹⁸F]MEL050 is already an excellent PET imaging probe for early specific diagnosis. The synthesis involves coupling step to obtain the precursor followed by radiofluorination. During the synthesis of the precursors different coupling reagents, such as HBTU, TFFH, HOBT, COMU and PyCIU have been applied. PyClU was found the best to reduce the coupling period to < 1h. The labeled compounds were isolated and purified by HPLC. In the in-vitro study three kinds of cells, namely, Melur (melanin free), KB-3 carcinoma cell line (non-melanoma) and B16-F10 melanoma cell line were used to evaluate the uptake of the radiotracers.

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.

[18F]MEL050 as a melanin-targeted PET tracer: Fully automated radiosynthesis and comparison to 18F-FDG for the detection of pigmented melanoma in mice primary subcutaneous tumors and pulmonary metastases

INTRODUCTION

Melanoma is a highly malignant cutaneous tumor of melanin-producing cells. MEL050 is a synthetic benzamide-derived molecule that specifically binds to melanin with high affinity. Our aim was to implement a fully automated radiosynthesis of [¹⁸F]MEL050, using for the first time, the AllInOne™ synthesis module (Trasis), and to evaluate the potential of [¹⁸F]MEL050 for the detection of pigmented melanoma in mice primary subcutaneous tumors and pulmonary metastases, and to compare it with that of [¹⁸F]FDG.

METHODS

Automated radiosynthesis of [¹⁸F]MEL050, including HPLC purification and formulation, were performed on an AllInOne™ synthesis module. [¹⁸F]MEL050 was synthesized using a one-step bromine-for-fluorine nucleophilic heteroaromatic substitution. Melanoma models were induced by subcutaneous (primary tumor) or intravenous (pulmonary metastases) injection of B16-F10-luc2 cells in NMRI mice. The maximum percentage of [¹⁸F]MEL050 Injected Dose per g of lung tissue (%ID/g Max) was determined on PET images, compared to [¹⁸F]FDG and correlated to in vivo bioluminescence imaging.

RESULTS

The automated radiosynthesis of [¹⁸F]MEL050 required an overall radiosynthesis time of 48min, with a yield of 13-18% (not-decay corrected) and radiochemical purity higher than 99%. [¹⁸F]MEL050 PET/CT images were concordant with bioluminescence imaging, showing increased radiotracer uptake in all primary subcutaneous tumors and pulmonary metastases of mice. PET quantification of radiotracers uptake in tumors and muscles demonstrated similar tumor-to-background ratio (TBR) with [¹⁸F]MEL050 and [¹⁸F]FDG in subcutaneous tumors and higher TBR with [¹⁸F]MEL050 than with [¹⁸F]FDG in pulmonary metastases.

CONCLUSION

We successfully implemented the radiosynthesis of [¹⁸F]MEL050 using the AllInOne™ module, including HPLC purification and formulation. In vivo PET/CT validation of [¹⁸F]MEL050 was obtained in mouse models of pigmented melanoma, where higher [¹⁸F]MEL050 uptake was observed in sub-millimetric pulmonary metastases, comparatively to [¹⁸F]FDG.

Risk Factors for Positive Deep Pelvic Nodal Involvement in Patients with Palpable Groin Melanoma Metastases: Can the Extent of Surgery be Safely Minimized? : A Retrospective, Multicenter Cohort Study

Background

Patients with palpable melanoma groin metastases have a poor prognosis. There is debate whether a combined superficial and deep groin dissection (CGD) is necessary or if superficial groin dissection (SGD) alone is sufficient.

Aim

The aim of this study was to analyze risk factors for deep pelvic nodal involvement in a retrospective, multicenter cohort of palpable groin melanoma metastases. This could aid in the development of an algorithm for selective surgery in the future.

Methods

This study related to 209 therapeutic CGDs from four tertiary centers in The Netherlands (1992–2013), selected based on complete preoperative imaging and pathology reports. Analyzed risk factors included baseline and primary tumor characteristics, total and positive number of inguinal nodes, inguinal lymph node ratio (LNR) and positive deep pelvic nodes on imaging (computed tomography [CT] ± positron emission tomography [PET], or PET − low-dose CT).

Results

Median age was 57 years, 54 % of patients were female, and median follow-up was 21 months (interquartile range [IQR] 11–46 months). Median Breslow thickness was 2.10 mm (IQR 1.40–3.40 mm), and 26 % of all primary melanomas were ulcerated. Positive deep pelvic nodes occurred in 35 % of CGDs. Significantly fewer inguinal nodes were positive in case of negative deep pelvic nodes (median 1 [IQR 1–2] vs. 3 [IQR 1–4] for positive deep pelvic nodes; p < 0.001), and LNR was significantly lower for negative versus positive deep pelvic nodes [median 0.15 (IQR 0.10–0.25) vs. 0.33 (IQR 0.14–0.54); p < 0.001]. A combination of negative imaging, low LNR, low number of positive inguinal nodes, and no extracapsular extension (ECE) could accurately predict the absence of pelvic nodal involvement in 84 % of patients.

Conclusions

Patients with negative imaging, few positive inguinal nodes, no ECE, and low LNR have a low risk of positive deep pelvic nodes and may safely undergo SGD alone.

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.

Melanoma and nuclear medicine

Supported by a large body of published work, the contribution of nuclear medicine technologies to the assessment of melanoma has been increasing in recent years. Lymphoscintigraphy-assisted sentinel lymph node biopsy and PET are in continuous evolution with the aid of technological imaging advances, making it possible to fuse functional and anatomic images (e.g., with SPECT/CT, PET/CT and 3D rendering systems). The development of hybrid fluorescent-radioactive tracers that enable high-quality preoperative lymphoscintigraphy and SPECT/CT, and the optimization of modern intraoperative portable imaging technologies, such as free-hand SPECT and portable γ-cameras, are important innovations that have improved sentinel lymph node identification in complex anatomical areas, such as the pelvis and head and neck. Concurrently, ¹⁸F-fluorodeoxyglucose-PET has proved its usefulness in the clinical staging and treatment decision-making process, and there is also emerging evidence regarding its utility in the evaluation of therapeutic response. The potential uses of other novel PET radiotracers could open up a new field of use for this technique. In this article, we review the current and future role of nuclear medicine in the management of melanoma.

Synthesis and preclinical characterization of [18F]FPBZA: a novel PET probe for melanoma

INTRODUCTION

Benzamide can specifically bind to melanoma cells. A 18F-labeled benzamide derivative, [18F]N-(2-diethylaminoethyl)-4-[2-(2-(2-fluoroethoxy) ethoxy)ethoxy]benzamide ([18F]FPBZA), was developed as a promising PET probe for primary and metastatic melanoma.

METHODS

[18F]FPBZA was synthesized via a one-step radiofluorination in this study. The specific uptake of [18F]FPBZA was studied in B16F0 melanoma cells, A375 amelanotic melanoma cells, and NB-DNJ-pretreated B16F0 melanoma cells. The biological characterization of [18F]FPBZA was performed on mice bearing B16F0 melanoma, A375 amelanotic melanoma, or inflammation lesion.

RESULTS

[18F]FPBZA can be prepared efficiently with a yield of 40-50%. The uptake of [18F]FPBZA by B16F0 melanoma cells was significantly higher than those by A375 tumor cells and NB-DNJ-pretreated B16F0 melanoma cells. B16F0 melanoma displayed prominent uptake of [18F]FPBZA at 2 h (7.81±0.82%ID/g), compared with A375 tumor and inflammation lesion (3.00±0.71 and 1.67±0.56%ID/g, resp.). [18F]FPBZA microPET scan clearly delineated B16F0 melanoma but not A375 tumor and inflammation lesion. In mice bearing pulmonary metastases, the lung radioactivity reached 4.77±0.36%ID/g at 2 h (versus 1.16±0.23%ID/g in normal mice).

CONCLUSIONS

Our results suggested that [18F]FPBZA PET would provide a promising and specific approach for the detection of primary and metastatic melanoma lesions.

Deep lymph node metastases in the groin significantly affects prognosis, particularly in sentinel node-positive melanoma patients

BACKGROUND

In order to define patients eligible for only a superficial groin dissection or a combined superficial and deep groin dissection, this study aimed to determine the incidence of deep lymph node metastases (LNM) in patients with melanoma metastasized to the groin, to identify patient and melanoma factors that predict deep nodal involvement, and to analyze the impact of deep nodal involvement on survival and recurrence.

METHODS

Patients who underwent a combined superficial (inguinal) and deep (iliac and obturator) complete (CLND) or therapeutic lymph node dissection (TLND) of the groin between 1994 and 2012 were analyzed.

RESULTS

QueryDeep LNM were found in 8 of 62 CLND patients (13 %) and in 21 of 67 TLND patients (31 %). More than three superficial LNM was the only independent predictor for deep LNM in both CLND and TLND patients. The 5-year melanoma-specific survival (MSS) for CLND and TLND patients with deep LNM was 14.3 and 16.6 %, respectively, and was significantly worse (hazard ratio [HR] 3.39, 95 % CI 1.34-8.58, p = 0.010; and HR 2.01, 95 % CI 1.04-3.88, p = 0.039) compared with CLND and TLND patients without deep LNM (5-year MSS: 54.1 and 37.2 %, respectively). Distant recurrence was significantly associated with deep LNM in CLND patients (p = 0.032).

CONCLUSIONS

The present study showed that LNM in the deep area of the groin are fairly common in both CLND and TLND patients and significantly affect prognosis, especially in CLND patients. The number of superficial LNM is the only factor that was found to predict a finding of deep nodal metastases.

18F-labelled intermediates for radiosynthesis by modular build-up reactions: newer developments

This brief review gives an overview of newer developments in (18)F-chemistry with the focus on small (18)F-labelled molecules as intermediates for modular build-up syntheses. The short half-life (<2 h) of the radionuclide requires efficient syntheses of these intermediates considering that multistep syntheses are often time consuming and characterized by a loss of yield in each reaction step. Recent examples of improved synthesis of (18)F-labelled intermediates show new possibilities for no-carrier-added ring-fluorinated arenes, novel intermediates for tri[(18)F]fluoromethylation reactions, and (18)F-fluorovinylation methods.

(123)I-BZA2 as a melanin-targeted radiotracer for the identification of melanoma metastases: results and perspectives of a multicenter phase III clinical trial

Our group has developed a new radiopharmaceutical, (123)I - N-(2-diethylaminoethyl)-2-iodobenzamide ((123)I-BZA2), a benzamide derivative able to bind to melanin pigment in melanoma cells. In a prospective and multicentric phase III clinical study, the value of (18)F-FDG PET/CT and (123)I-BZA2 scintigraphy was compared for melanoma staging.

METHODS

Patients with a past history of cutaneous or ocular melanoma were included from 8 hospitals. (18)F-FDG imaging was performed according to a standard PET protocol. Whole-body, static planar, and SPECT/CT (if available) images were acquired 4 h after injection of a 2 MBq/kg dose of (123)I-BZA2. (18)F-FDG and (123)I-BZA2 sensitivity and specificity for the diagnosis of melanoma metastasis were calculated and compared on both a lesion basis and a patient basis. True-positive and true-negative lesion status was determined after 6 mo of clinical follow-up or according to lesion biopsies (if available). Melanin content in biopsies was evaluated with the standard Fontana-Masson silver method and was correlated with (123)I-BZA2 uptake. Based on statistical analysis, the number of inclusions was estimated at 186.

RESULTS

In all, 87 patients were enrolled from 2008 to 2010. Of these, 45 (52%) had metastases. A total of 338 imaging abnormalities were analyzed; 86 lesions were considered metastases, and 20 of 25 lesion biopsies found melanoma metastases. In a patient-based analysis, the sensitivity of (18)F-FDG for diagnosis of melanoma metastases was higher than that of (123)I-BZA2, at 87% and 39%, respectively (P < 0.05). For specificity, (18)F-FDG and (123)I-BZA2 were not statistically different, at 78% and 94%, respectively. In a lesion-based analysis, the sensitivity of (18)F-FDG was statistically higher than that of (123)I-BZA2 (80% vs. 23%, P < 0.05). The specificity of (18)F-FDG was lower than that of (123)I-BZA2 (54% vs. 86%, P < 0.05). According to biopsy analysis, only 9 of 20 metastatic lesions (45%) were pigmented with high melanin content. (123)I-BZA2 imaging was positive for 6 of 8 melanin-positive lesions, fairly positive for 3 of 10 melanin-negative lesions, and negative for 7 of 10 melanin-negative lesions. The sensitivity and specificity of (123)I-BZA2 for the diagnosis of melanin-positive lesions were 75% and 70%, respectively. Because of a low (123)I-BZA2 sensitivity, this clinical trial was prematurely closed after 87 patients had been included.

CONCLUSION

This study confirms the value of (18)F-FDG PET/CT for melanoma staging and strengthens the high accuracy of (123)I-BZA2 for diagnosis of melanin-positive metastatic melanoma. Moreover, benzamide derivatives radiolabeled with therapeutic radionuclide may offer a new strategy for the treatment of metastatic melanoma patients harboring melanin-positive metastases.