99mTc(CO)3-labeled 1-(2-Pyridyl)piperazine derivatives as radioligands for 5-HT7 receptors

BACKGROUND

The 5-hydroxytryptamine receptor (5-HTR) family includes seven classes of receptors. The 5-HT7R is the newest member of this family and contributes to different physiological and pathological processes. As a pathology, glioblastoma multiform (GBM) overexpresses 5-HT7R; hence, this study aims to develop radiolabeled aryl piperazine derivatives as 5-HT7R imaging agents.  METHODS: Compounds 6 and 7 as 1-(3-nitropyridin-2-yl)piperazine derivatives were radiolabeled with fac-[99mTc(CO)3(H2O)3]+ and 99mTc(CO)3-[6] and 99mTc(CO)3-[7] were obtained with high radiochemical purity (RCP > 94%). The stability of the radiotracers was evaluated in both saline and mouse serum. Specific binding on different cell lines including U-87 MG, MCF-7, SKBR3, and HT-29 was performed. The biodistribution of these radiotracers was evaluated in normal and U-87 MG Xenografted models. Finally, 99mTc(CO)3-[6] and 99mTc(CO)3-[7] were applied for in vivo imaging in U-87 MG Xenografted models.

RESULTS

Specific binding study indicates that 99mTc(CO)3-[6] and 99mTc(CO)3-[7] can recognize 5-HT7R of U87-MG cell line. The biodistribution study in normal mice indicates that the brain uptake of 99mTc(CO)3-[6] and 99mTc(CO)3-[7] is the highest at 30 min post-injection (0.8 ± 0.25 and 0.64 ± 0.18%ID/g, respectively). The data of the biodistribution study in the U87-MG xenograft model revealed that these radiotracers could accumulate in the tumor site, and the highest tumor uptake was observed at 60 min post-injection (3.38 ± 0.65 and 3.27 ± 0.5%ID/g, respectively). The injection of pimozide can block the tumor's radiotracer uptake, indicating the binding of these radiotracers to the 5-HT7R. The imaging study in the xenograft model also confirms the biodistribution data. The acquired images clearly show the tumor site, and the tumor-to-muscle ratio for 99mTc(CO)3-[6] and 99mTc(CO)3-[7] at 60 min was 3.33 and 3.88, respectively.  CONCLUSIONS: 99mTc(CO)3-[6] and 99mTc(CO)3-[7] can visualize tumor in the U87-MG xenograft model  due to their affinity toward 5-HT7R.

Engineering HEK293T cell line by lentivirus to produce miR34a-loaded exosomes

BACKGROUND

RNA (ribonucleic acid) antisense is developing as a possible treatment option. As an RNA, miR-34a is involved in P53 function and cancer cell apoptosis. Although the therapeutic applications of miRNAs have several limitations, such as structural instability and susceptibility to nucleases. To resolve these issues, this study aims to apply exosomes as a delivery vehicle for miR-34a.

AIMS

This study aims to create a cell factory to generate miR34a-enriched exosomes. The produced nanoparticles act as a delivery system and improve the structural stability of miR34a.

METHODS

First exosome specific sequences were inserted into miR34a. The resulting miR34a oligonucleotide was transduced HEK293T cells genome with a lentiviral system. In the structure of miR34a oligonucleotide, six nucleotides were substituted to increase its packaging rate into exosomes. To maintain the secondary structure, stability, and expression of the miRNA gene, changes to the miR34a oligonucleotide were made using PCR (polymerase chain reaction) Extension. The forward-34a (5-TGGGGAGAGGCAGGACAGG-3) and Reverse-34a primers (5-TCCGAAGTCCTGGCGTCTCC-3) were used for amplification of the miR34a gene from DNA.

RESULTS

The results confirmed that the changes in miR34a oligonucleotide do not affect its secondary structure. The energy level of the manipulated miR34a oligonucleotide was kept the same compared to the original one. Moreover, the loading of miR34a to the exosomes was increased.

CONCLUSION

Our findings revealed that normal HEK293T did not express miR34a. However, lentiviral transduced miR34a oligonucleotide induced the loading of miR34a into the exosome. Moreover, replacing six nucleic acids in the 3' end of miR34a increased the loading of miR34a to exosome.

The preclinical study of 177Lu-DOTA-LTVSPWY as a potential therapeutic agent against HER2 overexpressed cancer

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) has evolved in cancer therapy and diagnosis. LTVSPWY, as a peptide, can target HER2 receptor; on the other hand, ¹⁷⁷Lu emits β^- which is helpful for cancer therapy. The radiolabeling of LTVSPWY with ¹⁷⁷Lu results in a therapeutic agent (¹⁷⁷Lu-DOTA-LTVSPWY) capable of cancer treatment.

METHODS

¹⁷⁷Lu-DOTA-LTVSPWY was prepared with high radiochemical purity (RCP). The stability was investigated in saline and human serum. The radiotracer affinity toward the SKOV-3 cell line with overexpression of the HER2 receptor was evaluated. Then the impact of the radiotracer on the colony formation of the SKOV-3 cell line was investigated with colony assay. Moreover, the biodistribution of this radiotracer in SKOV-3 xenograft tumor-bearing nude mice were also studied to determine the radiotracer accumulation in the tumor site. The mice were treated with ¹⁷⁷Lu-DOTA-LTVSPWY and subjected to histopathological evaluation.

RESULTS

The RCP of ¹⁷⁷Lu-DOTA-LTVSPWY after radiolabeling and stability tests was more than 97.7%. The radiotracer displayed high affinity toward the SKOV-3 cell line (K_D = 6.6 ± 3.2 nM). Treatment of the SKOV-3 cell line with the radiotracer reduces the SKOV-3 colony survival to less than 3% for 5 MBq of the radiotracer. Tumor-to-muscle (T/M) ratio is the highest at 48 h and 1 h post-injection (2.3 and 4.75, respectively). The histopathological study also confirms the cellular damage to the tumor tissue.

CONCLUSIONS

¹⁷⁷Lu-DOTA-LTVSPWY can recognize HER2 receptors in vivo and in vitro; hence, it can serve as a therapeutic agent.

Synthesis and evaluation of 99mTc-labeled 1-(2-Pyridyl)piperazine derivatives as radioligands for 5HT7 receptors

Glioblastoma multiform (GBM) is one of the most aggressive tumors of the central nervous system in humans. GBM overexpresses serotonin-7 receptors (5-HT₇Rs); hence, this study aims to develop 5-HT₇R targeted radiotracers. Aryl piperazine derivatives can act as ligands for 5-HT₇R. Therefore, compounds 6 and 7 as 1-(3-nitropyridin-2-yl)piperazine derivatives were synthesized and radiolabeled with ^99mTcN²⁺ core. Radiolabeled 6 and 7 (^99mTcN-[6] and ^99mTcN-[7]) were prepared with high radiochemical purity (RCP > 96%). They displayed high affinity toward U-87 MG cell line 5-HT₇R. The calculated K_i for ^99mTcN-[7] was lower than that of ^99mTcN-[6] (14.85 ± 0.32 vs 22.57 ± 0.73 nM) which indicates the higher affinity of ^99mTcN-[7] toward 5-HT₇R. A molecular docking study also confirmed the binding of these radiotracers to 5-HT₇R. The biodistribution study in normal mice revealed that ^99mTcN-[7] has the highest brain accumulation at 30 min post-injection (0.54 ± 0.12 %ID/g) while the uptake of ^99mTcN-[6] is much lower (0.14 ± 0.02 %ID/g). The biodistribution study in the xenograft model confirms that the radiotracers recognize the tumor site. ^99mTcN-[6], and ^99mTcN-[7] showed the highest tumor uptake at 1-hour post-injection (5.44 ± 0.58 vs 4.94 ± 1.65 %ID/g) and tumor-to-muscle ratios were (4.61 vs. 5.61). The injection of pimozide blocks the receptors and significantly reduces the tumor-to-muscle ratios at 1-hour post-injection to 0.81 and 0.31, respectively. In correlation with in vitro study, ^99mTcN-[6] and ^99mTcN-[7] visualize the tumor site in U-87 MG glioma xenografted nude mice and display the tumor-to-muscle ratios of 7.05 and 6.03.

Initial preclinical evaluation of 68 Ga-DOTA-(Ser) 3 -LTVSPWY peptide as a PET radiotracer for glioblastoma targeting and imaging

PURPOSE

Imaging of glioblastoma multiform (GBM) tumor using 68 -Galium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaceticacid-Ser-Ser-Ser-Leu-Thr-Val-Ser-Pro-Trp-Tyr ( 68 Ga-DOTA-(Ser)3-LTVSPWY) as a PET radiotracer for HER2 receptor due to fact that this receptor plays a pivotal role in the tumorigenesis and tumor progression in a wide range of cancer.

METHODS

68 Ga-DOTA-(Ser) 3 -LTVSPWY was produced with high radiochemical purity. The affinity and specificity of this radiotracer toward HER2 receptor on the surface of glioma glioblastoma (U-87 MG) cell line were evaluated. Furthermore, the biodistribution and PET imaging of this radiolabeled peptide were investigated on xenografted U-87 MG tumor-bearing mice.

RESULTS

The in-vitro specific binding study revealed that the 68 Ga-DOTA-(Ser) 3 -LTVSPWY binds to different cell lines with respect to their level of HER2 expression. The calculated K D and B max of radiolabeled peptide toward U-87 MG cell line were 5.5 ± 2.4 nmol/l and (2.4 ± 0.3) × 10 5 receptors per cell, respectively. The highest tumor uptake was observed at 30-min postinjection, whereas the tumor-to-muscle ratio was about four-fold. The acquired PET images distinctively show tumor site, which was blocked with excess nonlabeled peptide that revealed specific in-vivo targeting of 68 Ga-DOTA-(Ser) 3 -LTVSPWY for glioma.

CONCLUSION

68 Ga-DOTA-(Ser) 3 -LTVSPWY specifically recognizes HER2 receptors and could be a potential candidate for GBM imaging.

The influence of kidneys ion transport inhibitors on the pharmacokinetic and tumor uptake behaviors of a HER2-targeted small size radiolabeled peptide

BACKGROUND

HER2 over-expression plays a crucial role in the cancer treatment protocol. This study evaluates the effectiveness of kidney organic anion and cation transport inhibitors on the tumor uptake of 99mTc-HYNIC-(Ser)3-LTVPWY radiotracer in SKOV-3 tumor-bearing nude mice.

METHODS

Before the injection of the radiolabeled peptide, SKOV-3 tumor-bearing nude mice were treated with furosemide, cimetidine, para-amino hippuric acid, and saline. The inhibition effects of the organic anion and cation transport inhibitors were compared with the control group. In both treatment and control groups, the tumor and renal accumulation of radiopeptide in mice bearing SKOV-3 tumors were assessed in biodistribution and SPECT imaging studies.

RESULTS

The biodistribution and imaging results suggested that all treated groups showed a higher tumor and higher normal tissue radioactivity compared to the control group. According to the tumor imaging study, the furosemide-treated group had slightly better tumor uptake and a higher tumor to muscle uptake ratio than the other treatment groups.

CONCLUSIONS

Administration of furosemide (an OAT inhibitor) increased radioactivity accumulation in the kidneys and blood and improved tumor radioactivity uptake. PAH (an anion transporter substrate) and cimetidine (an OCT inhibitor) have a minor effect on the accumulation of radioactivity in the kidneys and the acquired images.

The Radiolabeled HER3 Targeting Molecules for Tumor Imaging

The human epidermal growth factor receptor (HER) family plays pivotal roles in physiologic and pathologic conditions (such as tumor growth, proliferation, and progression in multiple epithelial malignancies). All the family members are considered tyrosine kinase, while HER3 as a member of this family shows no intrinsic tyrosine kinase. HER3 is called ‘pseudokinase’ because it undergoes heterodimerization and forms dimers such as HER2-HER3 and HER1 (EGFR)-HER3. The exact role of HER3 in cancer is still unclear; however, the overexpression of this receptor is involved in the poor prognosis of malignancies. To that end, different studies investigated the development of radiotracers for imaging of HER3. The main focus of this review is to gather all the studies on developing new radiotracers for imaging of HER3.

The PI3K/AKT/mTOR signaling pathway inhibitors enhance radiosensitivity in cancer cell lines

INTRODUCTION

Radiotherapy is one of the most common types of cancer treatment modalities. Radiation can affect both cancer and normal tissues, which limits the whole delivered dose. It is well documented that radiation activates phosphatidylinositol 3-kinase (PI3K) and AKT signaling pathway; hence, the inhibition of this pathway enhances the radiosensitivity of tumor cells. The mammalian target of rapamycin (mTOR) is a regulator that is involved in autophagy, cell growth, proliferation, and survival.

CONCLUSION

The inhibition of mTOR as a downstream mediator of the PI3K/AKT signaling pathway represents a vital option for more effective cancer treatments. The combination of PI3K/AKT/mTOR inhibitors with radiation can increase the radiosensitivity of malignant cells to radiation by autophagy activation. Therefore, this review aims to discuss the impact of such inhibitors on the cell response to radiation.

Synthesis and Biological Evaluation of 99mTc-Labeled Phenylpiperazine Derivatives as Selective Serotonin-7 Receptor Ligands for Brain Tumor Imaging

With a poor prognosis, glioblastoma multiforme is the most aggressive tumor of the central nervous system in humans. The aim of this study was to develop novel tracers for the tumor targeting and imaging of overexpressed serotonin-7 receptors (5-HT₇Rs) in U-87 MG glioma xenografted nude mice. Two phenylpiperazine derivatives named as PHH and MPHH were designed, and the corresponding radiotracers ^99mTc-PHH and ^99mTc-MPHH were synthesized in high radiochemical purity (>95%). ^99mTc-MPHH showed a higher affinity to 5-HT₇Rs on U-87 MG cells compared to ^99mTc-PHH. In biodistribution studies, the radiocomplexes showed good brain uptake at 15 min combined with good radioactivity retention in the brain for 240 min. Regional rabbit brain studies indicated a higher radioactivity concentration in the hippocampus and diencephalon than in the cerebellum. Compared to ^99mTc-MPHH, the ^99mTc-PHH exhibited a significantly increased tumor uptake at 15 and 60 min, but the rapid blood clearance of ^99mTc-MPHH led to enhanced tumor-to-muscle ratios at 240 min. A significant reduction in tumor uptake 60 min after an injection of pimozide (5-HT₇ receptor antagonist) confirms the tumor uptake was receptor-mediated specifically. The tumor-to-contralateral muscle tissue ratio of ^99mTc-PHH and ^99mTc-MPHH in nude mice with U-87 MG xenograft was measured (5.25 and 4.65) at 60 min as well as (6.25 and 6.76) at 240 min, respectively.

The effects of pharmacological interventions, exercise, and dietary supplements on extra-cardiac radioactivity in myocardial perfusion single-photon emission computed tomography imaging

Myocardial perfusion imaging (MPI) as an imaging modality plays a key role in the monitoring of patients with cardiovascular disease. MPI enables the assessment of cardiovascular disease, the effectiveness of therapy, and viable myocardial tissue. However, MPI suffers from some downfalls and limitations, which can influence its clinical applications. These limitations can arise from the patient's condition, equipment, or the actions of the technologist. In this review, we mainly focused on the different effective parameters on radioactivity uptake of organs including liver, intestines, stomach, and gall bladder and how they affect the quality of the acquired images in nuclear medicine. More importantly, we cover how different suggested medicines, foods and exercise alleviative this problem.

99mTc-radiolabeled HER2 targeted exosome for tumor imaging

Exosomes represent unique features including nontoxicity, non-immunogenicity, biodegradability, and targeting ability that make them suitable candidates for clinical applications. Therefore, in this study, ^99mTc-radiolabel HER2 targeted exosomes (^99mTc-exosomes) were provided for tumor imaging. These exomes are obtained from genetically engineered cells and possessed DARPin G3 as a ligand for HER2 receptors. These exosomes were radiolabeled using fac-[^99mTc(CO)₃(H₂O)₃]⁺ synthon. The quality control showed high radiochemical purity (RCP) for ^99mTc-exosomes (>96%). ^99mTc-exosomes displayed a higher affinity toward SKOV-3 cells (higher HER2 expression) in comparison with MCF-7, HT29, U87-MG, A549 cell lines at different levels of HER2 expression. Trastuzumab (an antibody with a high affinity toward HER2) inhibited the binding of ^99mTc-exosomes to SKOV-3 cells up to 40%. Biodistribution study in SKOV-3 tumor bearing nude mice confirmed the ability of ^99mTc-exosomes for accumulation in the tumor. ^99mTc-exosomes can visualize tumor in SKOV-3 tumor-bearing nude mouse. The blockage of HER2 receptors using trastuzumab (excessive amount) suggests the ^99mTc-exosomes binding to the receptors and reduced the accumulation of ^99mTc-exosomes in the tumor site. This suggest that ^99mTc-exosomes interact with HER2 receptors and act through specific targeting.

Preclinical pharmacokinetic, biodistribution, radiation dosimetry, and toxicity studies of 99mTc-HYNIC-(Ser)3-LTVPWY: A novel HER2-targeted peptide radiotracer

Accurate assessment of the HER2 expression is an essential issue for predicting response to anti-HER2 therapy in breast cancer patients. The aim of this study was to evaluate ^99mTc-HYNIC-(Ser)₃-LTVPWY (^99mTc-HYNIC-LY) peptide as a novel HER2-targeted radiolabeled peptide in healthy mice to examine the applicability of this imaging agent in a first-in-human clinical trial. To this end, pharmacokinetic and dosimetry studies were performed according to the ICH guideline M3 (R2) with ^99mTc-HYNIC-LY. To estimate the radiation-absorbed doses in humans, the accumulated activity in each mouse organ was calculated based on biodistribution data. In addition, toxicology assessment was performed based on mortality events, body weights, and serum biochemical, hematological, and histopathological assays. The pharmacokinetic study showed rapid blood clearance. Based on the results of biodistribution study, the highest radioactivity was observed in the kidneys. The projected absorbed doses to the kidneys, liver, lungs, stomach, and spleen were obtained as 1.70E-02, 1.42E-02, 1.02E-02, 8.62E-03, and 8.34E-03 mSv/MBq, respectively. The results also revealed that serum biochemical and hematological parameters were in the normal range. No significant morphologic alterations were observed in the liver, kidneys, and spleen tissues. Consequently, the results were indicative of the suitability of ^99mTc-HYNIC-LY peptide for advancement to a first-in-human clinical trial.

Pharmacokinetic Evaluation of 99mTc-radiolabeled Solid Lipid Nanoparticles and Chitosan Coated Solid Lipid Nanoparticles

BACKGROUND

Solid Lipid Nanoparticles (SLNs) possess unique in vivo features such as high resistivity, bioavailability, and habitation at the target site. Coating nanoparticles with polymers such as chitosan greatly affects their pharmacokinetic behavior, stability, tissue uptake, and controlled drug delivery. The aim of this study was to prepare and evaluate the biodistribution of 99mTc-labeled SLNs and chitosan modified SLNs in mice.

METHODS

99mTc-oxine was prepared and utilized to radiolabel pre-papered SLNs or chitosan coated SLNs. After purification of radiolabeled SLNs (99mTc-SLNs) and radiolabeled chitosan-coated SLNs (99mTc-Chi-SLNs) using Amicon filter, they were injected into BALB/c mice to evaluate their biodistribution patterns. In addition, nanoparticles were characterized using Transmission Electron Microscopy (TEM), Fourier-transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Powder Diffraction (XRD) and Dynamic Light Scattering (DLS).

RESULTS

99mTc-oxine with high radiochemical purity (RCP~100%) and stability (RCP > 97% at 24 h) was used to provide 99mTc-SLNs and 99mTc-Chi-SLNs with high initial RCP (100%). TEM image and DLS data suggest 99mTc- SLNs susceptibility to aggregation. To that end, the main portion of 99mTc-SLNs radioactivity accumulates in the liver and intestines, while 99mTc-Chi-SLNs sequesters in the liver, intestines and kidneys. The blood radioactivity of 99mTc-Chi-SLNs was higher than that of 99mTc-SLNs by 7.5, 3.17 and 3.5 folds at 1, 4 and 8 h post-injection. 99mTc- Chi-SLNs uptake in the kidneys in comparison with 99mTc-SLNs was higher by 37.48, 5.84 and 11 folds at 1, 4 and 8h.

CONCLUSION

The chitosan layer on the surface of 99mTc-Chi-SLNs reduces lipophilicity in comparison with 99mTc- SLNs. Therefore, 99mTc-Chi-SLNs are less susceptible to aggregation, which leads to their lower liver uptake and higher kidney uptake and blood concentration.

99mTc-labeled Small Molecules for Diagnosis of Alzheimer’s Disease: Past, Recent and Future Perspectives

Background:

Alzheimer’s disease (AD) is an age-related progressive neurodegenerative disease. Its prominent hallmarks are extracellular deposition of β-amyloids (amyloid plaques), intracellular neurofibrillary tangles (NTFs), neurodegeneration and finally loss of cognitive function. Hence, AD diagnosis in the early stage and monitoring of the disease are of great importance.

Methods:

In this review article, we have reviewed recent efforts for design, synthesis and evaluation of 99mTc labeled small molecule for AD imaging purposes.

Results:

These small molecules include derivatives of Congo red, benzothiazole, benzofuran, benzoxazole, naphthalene, biphenyl, chalcone, flavone, aurone, stilbene, curcumin, dibenzylideneacetone, quinoxaline, etc. The different aspects of 99mTc-labeled small molecules including chemical structure, their affinity toward amyloid plaques, BBB permeation and in vivo/vitro stability will be discussed.

Conclusion:

The findings of this review confirm the importance of 99mTc-labeled small molecules for AD imaging. Future studies based on the pharmacophore of these designed compounds are needed for improvement of these molecules for clinical application.

Fundamental concepts of radiopharmaceuticals quality controls

Quality control (QC) procedures should always be performed following radiopharmaceutical preparation and prior to patient administration. The main aim of QC is to ensure optimal radiopharmaceutical product properties except for some short half-life tracers such as some positron emission tomography (PET) imaging probs. by dispensing a radiopharmaceutical of the highest quality the risk of having to repeat a nuclear medicine study due to poorly performing radiopharmaceuticals will be reduced. The existence of radiochemical impurity or impurities in radiopharmaceutical cause unnecessary radiation burden to the patient or undesirable high background without adding to the diagnostic information or improving treatment. Therefore, radiopharmaceuticals quality control is crucial and involves two different aspects including pharmaceutical parameters (such as sterility, bacterial endotoxins/ pyrogens, bioaffinity and biodistribution studies) and radioactive parameters (such as radionuclide and radiochemical purity) and chemical impurity which will be focused on here.

Basic and practical concepts of radiopharmaceutical purification methods

The presence of radiochemical impurities in a radiopharmaceutical contributes to an unnecessary radiation burden for the patients or to an undesirable high radioactivity background, which reduces the imaging contrast or therapeutic efficacy. Therefore, if the radiolabeling process results in unsatisfactory radiochemical purity, a purification step is unavoidable. A successful purification process requires a profound knowledge about the radiopharmaceuticals of interest ranging from structural features to susceptibility to different conditions. Most radiopharmaceutical purification methods are based on solid-phase extraction (SPE), high-performance liquid chromatography (HPLC), size exclusion chromatography (SEC), ion-exchange chromatography (IEC), and liquid-liquid extraction (LLE). Here, we discuss the basic and applied concepts of these purifications methods as well as their advantages and limitations.