Cai, Hancheng

Abstract Purpose The thyroid-stimulating hormone receptor (TSHR) is a cell-surface receptor predominantly expressed on benign and malignant thyroid cells, making it a viable target for developing radiotheranostics for metastatic thyroid cancer imaging and therapy. This study reports the radiosynthesis and preclinical evaluation of a 64Cu-labelled human antibody for positron emission tomography (PET) imaging of TSHR expression in thyroid cancer mouse models. Methods Human anti-TSHR recombinant antibody K1-70™ (TSHR-Ab) was conjugated with a bifunctional chelator, 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA), and then labelled with [64Cu]Cu2+, yielding radiotracer [64Cu]Cu-NOTA-TSHR-Ab. The specificity and binding affinity of the radiotracer to TSHR-positive (THJ529TTSHR(+)) or wild-type (THJ529TWT) cells were assessed in vitro. A series of immnuoPET imaging with [64Cu]Cu-NOTA-TSHR-Ab were conducted in mice bearing dual-flank tumors (THJ529TWT on the left and THJ529TTSHR(+) on the right) at multiple time points (1, 2, 4, 18, 24, and 48 h) post-injection (p.i.). Radiotracer co-injection studies with varying doses of unlabelled (cold) TSHR-Ab (100, 50, 25, 0 µg) were studied to assess its effect on radiotracer uptake in tumors and off-target organs. Biodistribution and immunohistochemistry (IHC) were performed to verify the immnuoPET imaging results. Results [64Cu]Cu-NOTA-TSHR-Ab was synthesised with a radiochemical yield of 46.89 ± 3.74%, radiochemical purity of 98.77 ± 0.89%, and specific activity >1.42 GBq/mg (n = 5). In vitro cell studies demonstrated [64Cu]Cu-NOTA-TSHR-Ab had high specificity and nanomolar affinity for THJ529TTSHR(+) cells, with a dissociation constant (Kd) of 4.74 nM and an inhibition constant (Ki) of 0.92 nM. The immnuoPET imaging studies showed that the radiotracer could reach tumor quickly and showed high uptake in TSHR-positive thyroid tumors (SUVmax: 3.63 ± 0.42, 3.82 ± 0.44, and 4.09 ± 0.56 at 18, 24, and 48 h p.i., respectively). Co-injection with cold TSHR-Ab at doses ranging from 25 to 100 µg effectively reduced background signals, especially in spleen, liver, and bone. Notably, a dose of 25 µg cold TSHR-Ab reduced off-target signals without affecting tumor uptake. The biodistribution and IHC analyses further supported PET imaging findings. Conclusion TSHR-targeted radiotracer [64Cu]Cu-NOTA-TSHR-Ab was synthesized with high radiochemical purity. Our preclinical evaluation results demonstrate it is a promising radiotracer for PET imaging of TSHR-positive thyroid cancer, which may guide and monitor TSHR-targeted therapies. High radiotracer uptake in tumor, prolonged retention time, and favourable pharmacokinetics with the support of cold antibody co-injection, pave the way for the development of paired radiotherapeutics to treat TSHR-positive thyroid cancers.

ABSTRACTMitochondrial membrane translocator protein 18 kDa (TSPO) expression is increased in activated microglia, established as a plausible target of neuroinflammation imaging. [11C]ER176, specifically binding to TSPO, has been developed as the third generation of radioligand for PET imaging of TSPO, which showed the potential in better quantifying neuroinflammation than its predecessors. In the current study, we developed an automated radiosynthesis with an improved HPLC purification method for [11C]ER176 clinical production. The improved HPLC separation was integrated into the automated production of [11C]ER176 using a reverse phase semi‐preparative HPLC column with an isocratic pump and the mixture of methanol and 50 mM ammonium acetate as the mobile phase. The fraction corresponding to [11C]ER176 was collected around 8.5–9.0 min without the risk of getting contaminations from nearby impurities. The automated production process took about 30 min after end of bombardment (EOB) and the quality of the final product [11C]ER176 met all specifications for clinical use based on current US Pharmacopeia and FDA CGMP requirements.

Abstract Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive malignancy with poor outcomes. To investigate novel therapeutic strategies, we characterized three new metastatic prostate cancer patient derived-tumor xenograft (PDTX) models and developed 3D spheroids from each to investigate molecular targeted therapy combinations including CDK4/6 inhibitors (CDK4/6i) with AKT inhibitors (ATKi). Metastatic prostate cancer tissue was collected and three PDTX models were established and characterized using whole-exome sequencing. PDTX 3D spheroids were developed from these three PDTXs to show resistance patterns and test novel molecular-targeted therapies. CDK4/6i's were combined with AKTi's to assess synergistic antitumor response to prove our hypothesis that blockade of AKT overcomes drug resistance to CDK4/6i. This combination was evaluated in PDTX three-dimensional (3D) spheroids and in vivo experiments with responses measured by tumor volumes, PSA, and Ga-68 PSMA-11 PET-CT imaging. We demonstrated CDK4/6i's with AKTi's possess synergistic antitumor activity in three mCRPC PDTX models. These models have multiple unique pathogenic and deleterious genomic alterations with resistance to single-agent CDK4/6i's. Despite this, combination therapy with AKTi's was able to overcome resistance mechanisms. The IHC and Western blot analysis confirmed on target effects, whereas tumor volume, serum PSA ELISA, and radionuclide imaging demonstrated response to therapy with statistically significant SUV differences seen with Ga-68 PSMA-11 PET-CT. These preclinical data demonstrating antitumor synergy by overcoming single-agent CDK 4/6i as well as AKTi drug resistance provide the rational for a clinical trial combining a CDK4/6i with an AKTi in patients with mCRPC whose tumor expresses wild-type retinoblastoma 1.

The radiotracer 1‐(2‐[18F]fluoroethyl)‐L‐tryptophan (L‐[18F]FETrp or [18F]FETrp) is a substrate of indoleamine 2,3‐dioxygenase, the initial and key enzyme of the kynurenine pathway associated with tumoral immune resistance. In preclinical positron emission tomography studies, [18F]FETrp is highly accumulated in a wide range of primary and metastatic cancers, such as lung cancer, prostate cancer, and gliomas. However, the clinical translation of this radiotracer into the first‐in‐human trial has not been reported, partially due to its racemization during radiofluorination which renders the purification of the final product challenging. However, efficient purification is essential for human studies in order to assure radiochemical and enantiomeric purity. In this work, we report a fully automated radiosynthesis of [18F]FETrp on a Synthra RNPlus research module, including a one‐pot two steps radiosynthesis, dual independent chiral and reverse‐phase semipreparative high‐performance liquid chromatography purifications, and solid‐phase extraction‐assisted formulation. The presented approach has led to its Investigational New Drug application and approval that allows the testing of this tracer in humans.

Conventional imaging has been the standard imaging modality for assessing prostate cancer recurrence and is utilized to determine treatment response to therapy. Molecular imaging with PSMA PET–CT has proven to be more accurate, sensitive, and specific at identifying pelvic or distant metastatic disease, resulting in earlier diagnosis of advanced disease. Since advanced disease may not be seen on conventional imaging, due to its lower sensitivity, but can be identified by molecular imaging, this reveals that metastatic prostate cancer occurs on a continuum from negative PSMA PET–CT and negative conventional imaging to positive PSMA PET–CT and positive conventional imaging. Understanding this continuum, the accuracy of these modalities, and treatment related outcomes based on imaging, will allow the clinician to counsel patients on management. This review will highlight the differences in conventional and molecular imaging in prostate cancer and how PSMA PET–CT can be used for the management of prostate cancer patients in different clinical scenarios, while providing cautionary notes for overtreatment.