Nuclear medicine and biology最新文献

Direct fluorination of a tosylate or mesylate precursor has been a wide-spread and reliable way for radio-fluorination. This approach can be difficult to achieve when the precursor cannot be easily obtained or is chemically unstable. A possible alternative method is to radiolabel ethylene ditosylate or 1,3-propanediol di-p-tosylate to form a radiofluorinated synthon. Here we present the automation of a simplified and reliable approach for the two-step fluorination using [¹⁸F]FP-TMP, an analog of antibacterial agent trimethoprim. We demonstrate the feasibility of purifying the fluorinated synthon via filtration, and one final HPLC purification on a commercially available Trasis AllinOne module. The overall reaction time for the two-step reaction is around 90 min andthe decay-corrected yield for more than fifty preparations of [¹⁸F]FP-TMP is 22 ± 5 % with high radiochemical purity (≥ 90 %) and specific activities (147 ± 107 GBq/μmol). All batches passed pre-established quality control specifications, demonstrating the utility of using this method in tracer syntheses that meet good manufacturing practice (GMP) requirement. This method can be adopted to the syntheses of other radiotracers, such as [¹⁸F]FE-TMP, (+)-[¹⁸F]F-PHNO and [¹⁸F]FFMZ.

Radiometals play an important role in nuclear medicine, both for imaging and therapy. Binding studies represent an important step in the development of new radiolabeled ligands, as valuable insights into the binding properties can be gained. However, this technique requires high radiochemical purity, otherwise results may lead to wrong assumptions or misinterpretations of affinities or uptake rates.

Therefore, this in vitro study aimed at investigating the cell binding and internalization characteristics of different radiometal chlorides ([¹¹¹In]InCl₃, [⁶⁸Ga]GaCl₃ and [¹⁷⁷Lu]LuCl₃) commonly applied in nuclear medicine, as well as the clinically applied [¹⁷⁷Lu]Lu-PSMA-I&T in comparison, by using prostate cancer cells. PC-3 and LNCaP cells were incubated with 100 kBq of the respective radiometal chloride or [¹⁷⁷Lu]Lu-PSMA-I&T for 1 h. For [¹⁷⁷Lu]LuCl₃, nuclei isolations and colloid determinations in saline and cell medium were also performed.

Results showed that [¹¹¹In]InCl₃ and [⁶⁸Ga]GaCl₃ bind and are internalized up to 3 % to PC-3 and LNCaP cells, whereas [¹⁷⁷Lu]LuCl₃ showed cell binding of up to 25 %, internalization up to 2.5 % and a nuclear uptake below 0.3 %. In comparison, [¹⁷⁷Lu]Lu-PSMA-I&T showed only 3 % total cell binding to LNCaP cells. Further analysis of [¹⁷⁷Lu]LuCl₃ stability in NaCl and cell medium showed only low amounts of colloids, which are not increasing over time, and negligible unspecific binding to the used cell culture plates.

In conclusion, the results demonstrate the importance of high radiochemical purity, especially with regard to Lu-177 labeled compounds. Even if radiopharmaceuticals comply with common release-criteria, significant uptake can be derived from [¹⁷⁷Lu]LuCl₃ impurities and lead to wrong estimations of a compound's uptake behavior. Assuming an experimental result of 2 % membrane binding of the applied product, and 5 % residual [¹⁷⁷Lu]LuCl₃ in the final product (thereof 25 % membrane binding, as described above), would lead to 1.25 % membrane binding resulting from [¹⁷⁷Lu]LuCl₃ and only 0.75 % from the radiopharmaceutical.

Introduction

Astatine-211 has attained significant interest in the recent times as a promising radioisotope for targeted alpha therapy (TAT) of cancer. In this study, we report the production of ²¹¹At via ²⁰⁹Bi (α, 2n) ²¹¹At reaction in a cyclotron and development of a facile radiochemical separation procedure to isolate ²¹¹At for formulation of nanoradiopharmaceuticals.

Methods

Natural bismuth oxide target in pelletized form wrapped in Al foil was irradiated with 30 MeV α-beam in an AVF cyclotron. The irradiated target was dissolved in 2 M HNO₃ followed by selective precipitation of Bi as Bi(OH)₃ under alkaline condition. The radiochemically separated ²¹¹At was used for labeling cyclic RGD peptide conjugated gold nanoparticles (Au-RGD NPs) by surface adsorption. The radiochemical stability of ²¹¹At-Au-RGD NPs was evaluated in phosphate buffered saline (PBS) and human serum media.

Results

The batch yield of ²¹¹At at the end of irradiation was ∼6 MBq.μA⁻¹.h⁻¹. After radiochemical separation, ∼80 % of ²¹¹At could be retrieved with >99.9 % radionuclidic purity. Au-RGD NPs (particle size 8.4±0.8 nm) could be labeled with ²¹¹At with >99 % radiolabeling yield. The radiolabeled nanoparticles retained their integrity in PBS and human serum media over a period of 21 h.

Conclusions

The present strategy simplifies ²¹¹At production in terms of purification and would increase affordable access to this radioisotope for TAT of cancer.

Positron emission tomography (PET) can provide information about tumor-associated macrophage (TAM) infiltration, as long as a suitable tracer is available. This study aimed to evaluate the radiolabeled peptide [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC as a potential PET tracer for imaging of the CD163 receptor, which is expressed on M2-type tumor-associated macrophages. The conjugated peptide NODA-MP-C6-CTHRSSVVC was labeled with aluminum [¹⁸F]fluoride. Tracer binding and its biodistribution were evaluated in an in vitro binding assay and in healthy BALB/c mice, respectively. In addition, different treatments with cyclophosphamide in tumor-bearing mice were used to assess whether the tracer could detect differences in CD163 expression caused by differential TAM infiltration. After 7 days of treatment, animals were injected with [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC, and a 60-min dynamic PET scan was performed, followed by an ex vivo biodistribution study. [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC was prepared in 23 ± 6 % radiochemical yield and showed approximately 50 % of specific receptor-mediated binding in an in vitro binding assay on human CD163-expressing tissue homogenates. No CD163-mediated binding of [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC was detected by PET under normal physiological conditions in healthy BALB/c mice. On the other hand, CD163-positive xenograft tumors were clearly visualized with PET and a positive correlation was found between CD163 levels and the [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC tumor-to-muscle ratio (TMR) obtained from the PET images (Pearson r = 0.76, p = 0.002). No significant differences in the CD163 protein level and in the tracer uptake between treatment groups were found in the tumors. Taken together, [¹⁸F]AlF-NODA-MP-C6-CTHRSSVVC appears a promising candidate PET tracer for M2-type TAM, as it binds specifically to CD163 in vitro and its tumor uptake correlates well with CD163 expression in vivo.

Introduction

Prostate-specific membrane antigen (PSMA) is a promising target for treating metastatic castration-resistant prostate cancer. Our previous report presented ¹¹¹In- or ²²⁵Ac-labeled PSMA-NAT-DA1 (PNT-DA1) as a PSMA-targeted ligand. To improve its therapeutic efficiency, PNT-DA1 contains 4-(p-iodophenyl)butyric acid (IPBA), which is known as an albumin binder (ALB) moiety. However, few reports have examined the relationship between the chemical modification of the ALB moiety and pharmacokinetics of PSMA-targeted radioligands. To assess this relationship, we designed, synthesized, and evaluated four [¹¹¹In]In-PNT-DA1 analogues with ALB moieties different from IPBA.

Methods

The [¹¹¹In]In-PNT-DA1 analogues were synthesized from their corresponding precursors through ligand substitution reaction. The stability of [¹¹¹In]In-PNT-DA1 analogues in mouse plasma, their affinity for human serum albumin (HSA), their binding to mouse plasma proteins, and their affinity for PSMA were evaluated in vitro. The tissue distribution profile of the radioligands was assessed in biodistribution studies using LNCaP tumor-bearing nude mice.

Results

All [¹¹¹In]In-PNT-DA1 analogues were obtained at a high radiochemical yield and purity. These analogues were highly stable in mouse plasma after 24 h. The binding affinity for HSA significantly varied among the different ALB moieties. Moreover, high affinity for mouse plasma proteins was observed for all [¹¹¹In]In-PNT-DA1 analogues compared with their counterparts without an ALB moiety. The affinity for PSMA was comparable for all radioligands. In the biodistribution assay, the pharmacokinetics of [¹¹¹In]In-PNT-DA1 analogues varied markedly depending on the type of ALB moiety. In particular, tumor area under the curve (AUC) values were increased for radioligands with higher blood retention, while some previous studies reported that compounds with moderate blood retention exhibited the highest tumor AUC values.

Conclusion

The introduction of an appropriate ALB moiety into the ligand may lead to the development of more useful PSMA-targeted radioligands with higher tumor accumulation.

Background

Targeted alpha therapy (TAT) of somatostatin receptor-2 (SSTR2) positive neuroendocrine tumors (NETs) involving Ac-225 ([²²⁵Ac]Ac-DOTA-TATE) has previously demonstrated improved therapeutic efficacy over conventional beta particle-emitting peptide receptor radionuclide therapy agents. DOTA-TATE requires harsh radiolabeling conditions for chelation of [²²⁵Ac]Ac³⁺, which can limit the achievable molar activities and thus therapeutic efficacy of such TAT treatments. Macropa-TATE was recently highlighted as a potential alternative to DOTA-TATE, owing to the mild radiolabeling conditions and high affinity toward [²²⁵Ac]Ac³⁺; however, elevated liver and kidney uptake were noted as a major limitation and a suitable imaging radionuclide is yet to be reported, which will be required for patient dosimetry studies and assessment of therapeutic benefit. Previously, [¹⁵⁵Tb]Tb-crown-TATE has shown highly effective imaging of NETs in preclinical SPECT/CT studies, with high tumor uptake and low non-target accumulation; these favourable properties and the versatile coordination behavior of the crown chelator may therefore show promise for combination with Ac-225 for TAT.

Methods

Crown-TATE was labeled with Ac-225, and radiochemical yield was analyzed as the function of crown-TATE concentration. LogD_7.4 was measured as the indication of hydrophilicity. Free [²²⁵Ac]Ac³⁺ release from [²²⁵Ac]Ac-crown-TATE in human serum was studied. Biodistribution studies of [²²⁵Ac]Ac-crown-TATE in mice bearing AR42J tumors was evaluated at 1, 4, 24, 48, and 120 h, and the absorbed dose to major organs calculated. Therapy-monitoring studies with AR42J tumor bearing mice were undertaken using 30 kBq and 55 kBq doses of [²²⁵Ac]Ac-crown-TATE and compared to controls treated with PBS or crown-TATE.

Results

[²²⁵Ac]Ac-crown-TATE was successfully prepared with high molar activity (640 kBq/nmol), and characterized as a moderately hydrophilic radioligand (LogD_7.4 = −1.355 ± 0.135). No release of bound Ac-225 was observed over 9 days in human serum. Biodistribution studies of [²²⁵Ac]Ac-crown-TATE showed good initial tumor uptake (11.1 ± 1.7% IA/g at 4 h) which was sustained up to 120 h p.i. (6.92 ± 2.03% IA/g). Dosimetry calculations showed the highest absorbed dose was delivered to the tumors. Therapy monitoring studies demonstrated significant (log-rank test, P < 0.005) improved survival in both treatment groups compared to controls.

Conclusions

This preclinical study demonstrated the therapeutic efficacy of [²²⁵Ac]Ac-crown-TATE for treatment of NETs, and highlights the potential of using crown chelator for stable chelation of Ac-225 under mild conditions.

Background

[¹⁸F]F13640 is a new PET radiopharmaceutical for brain molecular imaging of serotonin 5-HT_1A receptors. Since we intend to use this radiopharmaceutical in psychiatric studies, it is crucial to establish possible sensitivity modification of 5-HT_1A receptors availability during an acute stress exposure. In this study, we first assessed the cerebrometabolic effects of a new animal model of stress with [¹⁸F]FDG and then proceeded to test for effects of this model on the cerebral binding of [¹⁸F]F13640, a 5-HT_1A receptors PET radiopharmaceutical.

Methods

Four groups of male Sprague-Dawley were used to identify the optimal model: “stressed group” (n = 10), “post-traumatic stress disorder (PTSD) group” (n = 9) and “restraint group” (n = 8), compared with a control group (n = 8). All rats performed neuroimaging [¹⁸F]FDG μPET-CT to decipher which model was the most appropriate to test effects of stress on radiotracer binding. Subsequently, a group of rats (n = 10) underwent two PET imaging acquisitions (baseline and PTSD condition) using the PET radiopharmaceutical [¹⁸F]F13640 to assess influence of stress on its binding. Voxel-based analysis was performed to assess [¹⁸F]FDG or [¹⁸F]F13640 changes.

Results

In [¹⁸F]FDG experiments, the PTSD group showed a pattern of cerebrometabolic activation in various brain regions previously implicated in stress (amygdala, perirhinal cortex, olfactory bulb and caudate). [¹⁸F]F13640 PET scans showed increased radiotracer binding in the PTSD condition in caudate nucleus and brainstem.

Conclusions

The present study demonstrated stress-induced cerebrometabolic activation or inhibition of various brain regions involved in stress model. Applying this model to our radiotracer, [¹⁸F]F13640 showed few influence of stress on its binding. This will enable to rule out any confounding effect of stress during imaging studies.

Background

Prostate cancer affects 1 in 6 men, and it is the second‑leading cause of cancer-related death in American men. Surgery is one of the main treatment modalities for prostate cancer, but it often results in incomplete resection margins or complete resection that leads to nerve damage and undesirable side effects. In the present work, we have developed a new bimodal tracer, NODAGA-sCy7.5 PSMAi (prostate-specific membrane antigen inhibitor), labeled with the true matched theranostic pair ⁶⁴Cu/⁶⁷Cu and a near-infrared fluorescent dye. This agent could potentially be used for concomitant PET imaging, optical surgical navigation, and targeted radiopharmaceutical therapy.

Methods

A prostate-specific membrane antigen (PSMA)-targeting urea derivative was conjugated to NODAGA for copper radiolabeling and to the near-infrared fluorophore sulfo-Cy7.5 (sCy7.5). Binding studies were performed in PSMA-positive PC-3 PIP cells, as well as uptake and internalization assays in PC-3 PIP cells and PSMA-negative PC-3 wild type cells. Biodistribution studies of the ⁶⁴Cu-labeled compound were performed in PC-3 PIP- and PC-3 tumor-bearing mice, and ⁶⁷Cu biodistributions of the agent were obtained in PC-3 PIP tumor-carrying mice. PET imaging and fluorescence imaging were also performed, using the same molar doses, in the two mouse models.

Results

The PSMA conjugate bound with high affinity to PSMA-positive prostate cancer cells, as opposed to cells that were PSMA-negative. Uptake and internalization were rapid and PSMA-mediated in PC-3 PIP cells, while only minimal non-specific uptake was observed in PC-3 cells. Biodistribution studies showed specific uptake in PC-3 PIP tumors, while accumulation in PC-3 tumor-bearing mice was low. Furthermore, tumor uptake of the ⁶⁷Cu-labeled agent in the PC-3 PIP model was statistically equivalent to that of ⁶⁴Cu. PET and fluorescence imaging at 0.5 nmol per mouse also demonstrated that PC-3 PIP tumors could be clearly detected, while PC-3 tumors showed no tumor accumulation.

Conclusions

NODAGA-sCy7.5-PSMAi was specific and selective in detecting PSMA-positive, as opposed to PSMA-negative, tumors in mouse models of prostate cancer. This bioconjugate could potentially be used for PET staging with ⁶⁴Cu, targeted radiopharmaceutical therapy with ⁶⁷Cu, and/or image-guided surgery with sCy7.5.