Preliminary studies of (99m)Tc-memantine derivatives for NMDA receptor imaging

Design and development of microemulsion systems of a new antineoplaston A10 analog for enhanced intravenous antitumor activity: In vitro characterization, molecular docking, 125I-radiolabeling and in vivo biodistribution studies

A10, (3-phenylacetylamino-2,6-piperidinedione), is a natural peptide with broad antineoplastic activity. Recently, in vitro antitumor effect of a new A10 analog [3-(4-methoxybenzoylamino)-2,6-piperidinedione] (MPD) has been verified. However, poor aqueous solubility represents an obstacle towards intravenous formulation of MPD and impedes successful in vivo antitumor activity. To surmount such limitation, MPD microemulsion (MPDME) was developed. A 3¹2² full factorial design using Design-Expert® software was adopted to study the influence of different parameters and select the optimum formulation (MPDME1). Transmission electron microscopy (TEM) displayed spherical droplets of MPDME1. The cytotoxicity of MPDME1 in Michigan Cancer Foundation 7 (MCF-7) breast cancer cell line exceeded that of MPD solution (MPDS) and tamoxifen. Compatibility with injectable diluents, in vitro hemolytic studies and in vivo histopathological examination confirmed the safety of parenteral application of MPDME1. Molecular docking results showed almost same binding affinity of A10, MPD and ¹²⁵I-MPD with histone deacetylase 8 (HDAC8) receptor. Accordingly, radioiodination of MPDME1 and MPDS was done via direct electrophilic substitution reaction. Biodistribution of ¹²⁵I-MPDME1 and ¹²⁵I-MPDS in normal and tumor (ascites and solid) bearing mice showed high accumulation of ¹²⁵I-MPDME1 in tumor tissues. Overall, the results proved that MPDME represents promising parenteral delivery system capable of improving antineoplastic activity of MPD.

Synthesis, preclinical, and pharmacokinetic evaluation of a new zoledronate derivative as a promising antiosteoporotic candidate using radiolabeling technique

A novel zoledronic acid (ZL) derivative, 3-(2-ethyl-4-methyi-1H-imidazole-1-yl)-1-hydroxy-1-phosphonopropyl phosphonic acid (EMIHPBP), was synthesized, characterized, and successfully radiolabeled with ^99m Tc. The in vivo biodistribution of ^99m Tc-EMIHPBP was investigated and compared with the previously reported zoledronate derivatives aiming to formulate a novel zoledronate derivative with a high-potential uptake to bone as a promising antiosteoporotic candidate. To further evaluate the bone uptake efficiency, the pharmacokinetics of ^99m Tc-EMIHPBP was investigated and showed that maximum concentration in bone (C_max ) was 31.60 ± 0.15%ID/gram after 60 minutes (t_max ). Cumulative residence of ^99m Tc-EMIHPBP in the bone [AUC _(0-∞) (%ID∙min/gram bone)] was 3685.23, mean residence time was 384.354 minutes, and the calculated bone bioavailability was 15.831%. Finally, the time needed for half of the ^99m Tc-EMIHPBP formulation to be eliminated from bone (t_1/2 ) was 263.914 minutes. Excellent bone uptake can be obtained 1-hour postinjection with high bone/blood ratio of 23.76 detected with gamma counter. The biodistribution and kinetic studies could recommend EMIHPBP as a promising antiosteoporotic candidate with high selectivity to the skeletal system and rapid clearance from soft tissues.

Selected PET Radioligands for Ion Channel Linked Neuroreceptor Imaging: Focus on GABA, NMDA and nACh Receptors

Positron emission tomography (PET) neuroimaging of ion channel linked receptors is a developing area of preclinical and clinical research. The present review focuses on recent advances with radiochemistry, preclinical and clinical PET imaging studies of three receptors that are actively pursued in neuropsychiatric drug discovery: namely the γ-aminobutyric acid-benzodiazapine (GABA) receptor, nicotinic acetylcholine receptor (nAChR), and N-methyl-D-aspartate (NMDA) receptor. Recent efforts to develop new PET radioligands for these targets with improved brain uptake, selectivity, stability and pharmacokinetics are highlighted.