Ciguatera, a global issue, lacks adequate capacity for ciguatoxin analysis in most affected countries. The Caribbean region, known for its endemic ciguatera and being home to a majority of the global small island developing states, particularly needs established methods for ciguatoxin detection in seafood and the environment. The radioligand receptor binding assay (r-RBA) is among the in vitro bioassays currently used for ciguatoxin analysis; however, similarly to the other chemical-based or bioassays that have been developed, it faces challenges due to limited standards and interlaboratory comparisons. This work presents a single laboratory validation of an r-RBA developed in a Cuban laboratory while characterizing the performance of the liquid scintillation counter instrument as a key external parameter. The results obtained show the assay is precise, accurate and robust, confirming its potential as a routine screening method for the detection and quantification of ciguatoxins. The new method will aid in identifying high-risk ciguatoxic fish in Cuba and the Caribbean region, supporting monitoring and scientific management of ciguatera and the development of early warning systems to enhance food safety and food security, and promote fair trade fisheries.

Background: Real-time quantification of radioligand binding to cells under in vivo-like conditions improves evaluation of clinical potential. Materials and Methods: SKOV-3 tumor cells were grown in a monolayer on a thin glass plate placed in a sealable shallow chamber with a continuous flow of 125I-trastuzumab solution. The time-dependent cell binding was measured using a NaI detector, and the binding parameters were derived by computational analysis. Results: The detection efficiency of 125I was 65 cps/kBq for radioligand bound to the cells. Experiments were analyzed to find the values of kon and koff. The resulting kon was 3.2-7.9 × 104 M-1 s-1 and koff was 0.11-4.2 × 10-5 s-1. Conclusions: Radioligands can be rapidly evaluated by binding to living cells for selection and optimization of radioconjugates for diagnostic and therapeutic purposes.

The structure-activity relationships (SAR) of alkylxanthine derivatives as antagonists at the recombinant human adenosine receptors were explored in order to identify selective antagonists of A2B receptors. The effects of lengthening alkyl substituents from methyl to butyl at 1- and 3-positions and additional substitution at the 7- and 8-positions were probed. Ki values, determined in competition binding in membranes of HEK-293 cells expressing A2B receptors using 125I-ABOPX (125I-3-(4-amino-3-iodobenzyl)-8-(phenyl-4-oxyacetate)-1-propylxanthine), were approximately 10 to 100 nM for 8-phenylxanthine functionalized congeners. Xanthines containing 8-aryl, 8-alkyl, and 8-cycloalkyl substituents, derivatives of XCC (8-[4-[[[carboxy]methyl]oxy]phenyl]-1,3-dipropylxanthine) and XAC (8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl]-oxy]phenyl]-1,3-dipropylxanthine), containing various ester and amide groups, including L- and D-amino acid conjugates, were included. Enprofylline was 2-fold more potent than theophylline in A2B receptor binding, and the 2-thio modification was not tolerated. Among the most potent derivatives examined were XCC, its hydrazide and aminoethyl and fluoroethyl amide derivatives, XAC, N-hydroxyethyl-XAC, and the L-citrulline and D-p-aminophenylalanine conjugates of XAC. An N-hydroxysuccinimide ester of XCC (XCC-NHS, MRS 1204) bound to A2B receptors with a Ki of 9.75 nM and was the most selective (at least 20-fold) in this series. In a functional assay of recombinant human A2B receptors, four of these potent xanthines were shown to fully antagonize the effects of NECA-induced stimulation of cyclic AMP accumulation.

Prostate-specific membrane antigen (PSMA) represents a promising target for PSMA-overexpressing diseases, especially prostate cancer-a common type of cancer among men worldwide. In response to the challenges in tackling prostate cancers, several promising PSMA inhibitors from a variety of molecular scaffolds (e.g., phosphorous-, thiol-, and urea-based molecules) have been developed. In addition, PSMA inhibitors bearing macrocyclic chelators have attracted interest due to their favorable pharmacokinetic properties. Recently, conjugating a small PSMA molecule inhibitor-bearing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator, as exemplified by [177Lu]Lu-PSMA-617 could serve as a molecular imaging probe and targeted radioligand therapy (TRT) of metastatic castration resistant prostate cancer (mCRPC). Hence, studies related to mCRPC have drawn global attention. In this review, the recent development of PSMA ligand-617-labeled with 177Lu for the management of mCRPC is presented. Its molecular mechanism of action, safety, efficacy, and future direction are also described.

Estrogen receptors (ERs) play a multitude of roles in brain function and are implicated in various brain disorders. The use of positron emission tomography (PET) tracers for the visualization of ERs\' intricate landscape has shown promise in oncology but remains limited in the context of brain disorders. Despite recent progress in the identification and development of more selective ligands for various ERs subtypes, further optimization is necessary to enable the reliable and efficient imaging of these receptors. In this perspective, we briefly touch upon the significance of estrogen signaling in the brain and raise the setbacks associated with the development of PET tracers for identification of specific ERs subtypes in the brain. We then propose avenues for developing efficient PET tracers to non-invasively study the dynamics of ERs in the brain, as well as neuropsychiatric diseases associated with their malfunction in a longitudinal manner. This perspective puts several potential candidates on the table and highlights the unmet needs and areas requiring further research to unlock the full potential of PET tracers for ERs imaging, ultimately aiding in deepening our understanding of ERs and forging new avenues for potential therapeutic strategies.

Here, we introduce the third release of Kalium database (http://kaliumdb.org/), a manually curated comprehensive depository that accumulates data on polypeptide ligands of potassium channels. The major goal of this amplitudinous update is to summarize findings for natural polypeptide ligands of K+ channels, as well as data for the artificial derivatives of these substances obtained over the decades of exploration. We manually analyzed more than 700 original manuscripts and systematized the information on mutagenesis, production of radio- and fluorescently labeled derivatives, and the molecular pharmacology of K+ channel ligands. As a result, data on more than 1200 substances were processed and added enriching the database content fivefold. We also included the electrophysiological data obtained on the understudied and neglected K+ channels including the heteromeric and concatenated channels. We associated target channels in Kalium with corresponding entries in the official database of the International Union of Basic and Clinical Pharmacology. Kalium was supplemented with an adaptive Statistics page, where users are able to obtain actual data output. Several other improvements were introduced, such as a color code to distinguish the range of ligand activity concentrations and advanced tools for filtration and sorting. Kalium is a fully open-access database, crosslinked to other databases of interest. It can be utilized as a convenient resource containing ample up-to-date information about polypeptide ligands of K+ channels.

The radioligand binding assay is a powerful method to study the interaction of a ligand with its target. This technique allows not only to determine different pharmacological key parameters such as the affinity and the association and dissociation constants but also to estimate the amount of target expressed in recombinant or endogenous cells or tissues. The current detailed protocols describe the different binding assays (saturation, kinetic, and competition) that can be performed on melatonin receptors using their most commonly used and validated radioligands 2-[125I]-iodomelatonin (2-[125I]-MLT) and [3H]-melatonin ([3H]-MLT).

Peroxisome proliferator-activated receptors (PPARs) have been exploited as drug targets for combating multiple diseases. Several activators with different selectivity for the PPAR α, γ, and δ subtypes have been introduced into the market or have reached advanced clinical trials. Binding assays are of utmost importance for the discovery and profiling of such PPAR ligands. Binding assays are often based on radioligands, in particular, tritiated molecules are applied. We developed synthetic procedures for tritiating various PPAR agonists and applied these radioligands for setting up a scintillation proximity assay (SPA) for PPAR α, γ, and δ. These SPAs allow to assess the binding affinities of PPAR α, γ, and δ ligands, along with their respective subtype selectivity profiles. Therefore, SPA is an important tool for hit discovery and lead optimization campaigns aimed at identifying next-generation PPAR ligands.

Due to its overexpression on the surface of prostate cancer cells, prostate-specific membrane antigen (PSMA) is a relatively novel effective target for molecular imaging and radioligand therapy (RLT) in prostate cancer. Recent studies reported that PSMA is expressed in the neovasculature of various types of cancer and regulates tumour cell invasion as well as tumour angiogenesis. Several authors explored the role of diagnostic and therapeutic PSMA radioligands in various malignancies. In this narrative review, we describe the current status of the literature on PSMA radioligands\' application in solid tumours other than prostate cancer to explore their potential role as diagnostic or therapeutic agents, with particular regard to the relevance of PSMA radioligand uptake as neoangiogenetic biomarker. Hence, a comprehensive review of the literature was performed to find relevant articles on the applications of PSMA radioligands in non-prostate solid tumours. Data on the general, methodological and clinical aspects of all included studies were collected. Forty full-text papers were selected for final review, 8 of which explored PSMA radioligand PET/CT performances in gliomas, 3 in salivary gland malignancies, 6 in thyroid cancer, 2 in breast cancer, 16 in renal cell carcinoma and 5 in hepatocellular carcinoma. In the included studies, PSMA radioligand PET showed promising performance in patients with non-prostate solid tumours. Further studies are needed to better define its potential role in oncological patients management, especially in those undergoing antineoangiogenic therapies, and to assess the efficacy of PSMA-RLT in this clinical context.

The structure-activity relationships (SAR) of 8-phenyl-1,3-dipropylxanthine derivatives in binding to recombinant human A2B adenosine receptors were explored, in order to identify selective antagonists. Based on the finding of receptor selectivity in MRS 1204, containing an N-hydroxysuccinimide ester attached through the p-position of the 8-phenyl substituent [Jacobson et al. (1999): Drug Dev. Res., 47:45-53], a hydrazide and its more stable imide derivatives were synthesized. The hydrazide of XCC (8-[4-[[[carboxy]methyl]oxy]phenyl]-1,3-dipropylxanthine) was acylated with a variety of mono- and dicarboxylic acids. Ki values were determined in the adenosine receptor binding assays. At recombinant human A2B receptors expressed in membranes of HEK-293 cells, antagonist radioligands used were the xanthine 125I-ABOPX (125I-3-(4-amino-3-iodobenzyl)-8-oxyacetate-1-propyl-xanthine) and the nonxanthine antagonist [3H]ZM 241385 ([3H]4-(2-[7-amino-2-{furyl}{1,2,4}triazolo{2,3-a}{1,3,5}triazin-5-ylamino-ethyl)phenol). The initial screening utilized rat A1/A2A receptors and human A3 receptors, and selected compounds were examined at the human A1/A2A subtypes. A 1,2-dimethylmaleimide derivative, 14 (MRS 1595), bound to human A2B receptors with a Ki of 19 nM and proved to be selective vs. human A1/A2A/A3 receptors by 160-, 100-, and 35-fold, respectively. Enprofylline (3-propylxanthine) is slightly selective for A2B receptors, suggesting removal of the 1-propyl group; however, combination of the 1-H-3-Pr and 8-phenyl substituents eliminated the selectivity. Other potent and moderately selective A2B antagonists were a tetrahydrophthaloyl derivative 18b (MRS 1614, Ki value 10 nM) and amino acid conjugates of the XCC-hydrazide, i.e., the glutarimide 24b (MRS 1626, Ki value 13 nM), and protected dipeptide 27 (MRS 1615, Ki value 11 nM). Drug Dev. Res. 47:178-188, 1999.