Synthesis and biodistribution of a new oxo-technetium-99m bis(aminothiol) complex as a potential melanoma tracer

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.

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.

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).

Mild and selective silicon-mediated access to enantioenriched 1,2-mercaptoamines and β-amino arylchalcogenides

Metal-free ring opening reactions of activated and unactivated aziridines with different silyl chalcogenides are described.

N-(2-(Dimethylamino)Ethyl)-4-18F-Fluorobenzamide: A Novel Molecular Probe for High-Contrast PET Imaging of Malignant Melanoma

Malignant melanoma is an aggressive and serious form of skin cancer, with prognosis and treatment outcome depending heavily on the clinical stage of the disease at the time of diagnosis. Here, we synthesized a novel ¹⁸F-labeled benzamide derivative to target melanoma and then evaluated its biologic characteristics in small-animal models. Methods: N-(2-(dimethylamino)ethyl)-4-¹⁸F-fluorobenzamide (¹⁸F-DMFB) was synthesized by reaction of N-succinimidyl 4-¹⁸F-fluorobenzoate with N,N-dimethylethylenediamine. The binding affinity of ¹⁸F-DMFB was measured in B16F10 (mouse melanoma) cells with or without l-tyrosine. Small-animal PET imaging with ¹⁸F-DMFB was performed on B16F10 xenograft and metastasis mouse models. Results: The overall non-decay-corrected radiochemical yield of ¹⁸F-DMFB was approximately 10%-15%. Uptake of ¹⁸F-DMFB was melanin-specific, as cellular uptake in B16F10 increased more than 18-fold in the presence of l-tyrosine. Biodistribution studies revealed that ¹⁸F-DMFB accumulated, and was retained, in B16F10 xenografts for 120 min (10, 30, 60, and 120 min: 9.24, 10.80, 13.0, and 10.59 percentage injected dose/g, respectively) after radiotracer injection. Liver uptake of ¹⁸F-DMFB decreased from 10 to 120 min and showed fast clearance (10, 30, 60, and 120 min: 11.19, 5.7, 2.47, and 0.4 percentage injected dose/g). Furthermore, ¹⁸F-DMFB allowed visualization of metastatic lesions immediately after injection and was retained in lesions for over 60 min, with a high tumor-to-background ratio. Conclusion: ¹⁸F-DMFB demonstrated a high melanin-targeting ability and tumor-specific tumor uptake in both primary and metastatic lesions in animal models bearing malignant melanoma. ¹⁸F-DMFB may be a potential PET imaging agent for melanoma.

[99mTcOAADT]-(CH2)2-NEt2: a potential small-molecule single-photon emission computed tomography probe for imaging metastatic melanoma

Evaluation of [99mTc]oxotechnetium(V) complexes of the amine-amide-dithiol (AADT) chelates containing tertiary amine substituents as small-molecule probes for the diagnostic imaging of metastatic melanoma has shown that technetium-99m-labeled AADT-(CH2)2-NEt2 (99mTc-1) has the highest tumor uptake and other favorable biological properties. We have, therefore, assessed this agent in a more realistic metastatic melanoma model in which, after i.v. tail injection, a highly invasive melanoma cell line, B16F10, forms pulmonary tumor nodules in normal C57BL6 mice. Small melanotic lesions develop in the lungs and, on histologic examination, appear as small black melanoma colonies, increasing in size and number with time after tumor cell injection. Groups of mice received tumor cell inocula of 2 x 10(5), 4 x 10(5), or 8 x 10(5) B16F10 cells; 14 days later, 2 hours after 99mTc-1 administration, lung uptake of 2.83 +/- 0.21%, 3.63 +/- 1.07%, and 4.92 +/- 1.61% injected dose per gram of tissue (% ID/g), respectively, was observed, compared with normal lung uptake of 2.13 +/- 0.2% ID/g (P < 0.05). Additionally, a higher level of 99mTc-1 accumulation was seen 17 days after tumor cell inoculation as the lung lesions grew. These in vivo studies coupled with additional in vitro and ex vivo assessment show that 99mTc-1 has high and specific uptake in melanoma metastases in lungs and can potentially follow the temporal growth of these tumors.

Synthesis and characterization of novel 99gTc(V) and Re(V) complexes with water-soluble tetraaza diamido dipyridino ligands: single-crystal X-ray structural investigations of mono- and dinuclear complexes

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N(4)) water-soluble ligands (2-C(5)H(4)NCH(2)NHCO)(2)CH(2), 1 (L(1)H2), (2-C(5)H(4)NNHNHCO)(2)CH(2), 2, and [2-C(5)H(4)N(+)(O)(-)CH(2)NHCO](2)CH(2), 3, were synthesized. Reaction of L(1)H2 with ReOCl(3)(PPh(3))(2) resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(L(1))(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex mu-oxo [ReO(L(1))](2)O. Reaction of 1 with [n-Bu(4)N][ReOCl(4)] resulted in the neutral complex 6, trans-[ReO(L(1))]Cl. Similarly, when ligand 1 was reacted with [n-Bu(4)N][(99g)TcOCl(4)], the neutral trans-[(99)TcO(L(1))]Cl complex 7 was formed, which upon dissolution transformed into a cationic complex 8, trans-[(99)TcO(L(1))(OH(2))](+)Cl(-). The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear mu-oxo [TcO(L(1))](2)O, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.

Melanoma uptake of (99m)Tc complexes containing the N-(2-diethylaminoethyl)benzamide structural element

On the basis of the avid uptake of radioiodinated benzamides by melanoma cells, (99m)Tc complexes containing the structural elements of N-(dialkylaminoalkyl)benzamide pharmacophores have been synthesized and evaluated in vitro and in vivo for melanoma uptake. One of the complexes Tc-12 containing the ligand 4-(S-benzoyl-2-thioacetyl-glycyl-glycylamido)-N-(2-diethylaminoethyl)benzamide (11) displayed the highest melanoma uptake. The 1-h melanoma uptake values and the corresponding blood counts indicate an interdependence of tumor uptake and bioavailability of the (99m)Tc complexes.