Parent, Ephraim E.

Abstract Background: Fibroblast activation protein (FAP) is a type II integral membrane glycoprotein, highly expressed on the cell surface of cancer-associated fibroblasts (CAFs) present in the tumor microenvironment of most epithelial cancers and showing limited expression in normal tissues. Given this expression profile, FAP appears to be a promising target for radioligand therapy that has pan-cancer potential. [177Lu]Lu-NNS309 is a FAP-targeted radiopharmaceutical that shows improved tumor retention and demonstrates promising anti-tumor activity in translationally relevant preclinical models (e.g., PDAC, NSCLC) where FAP is expressed on CAFs. Methods: CFXX489A12101 (NCT06562192) is a first-in-human phase I, open-label, multi-center study of [177Lu]Lu-NNS309 in patients with pancreatic ductal adenocarcinoma (PDAC), non-small cell lung cancer (NSCLC), breast cancer (BC), and colorectal cancer (CRC). The study includes a dose escalation part followed by a dose expansion part. Key eligibility criteria include prior treatment for locally advanced unresectable or metastatic disease and having all measurable lesions (per RECIST 1.1) showing [68Ga]Ga-NNS309 uptake on positron emission tomography/computed tomography (PET/CT). Patients who are eligible for treatment receive one dose of [177Lu]Lu-NNS309 on day 1 of each cycle. A 6-week and a 4-week dosing schedule will be explored. Dosimetry data will be obtained from patients in the dose escalation part after the first dose and will be used to calculate the cumulative radiation exposure. Dose escalation will be guided by a Bayesian hierarchical logistic regression model with overdose control (EWOC) principle, and assessment of all relevant data available from all dose levels including safety, tolerability, clinical dosimetry, pharmacodynamics, and preliminary efficacy. Once the recommended dose(s) (RD) and schedule(s) of [177Lu]Lu-NNS309 are determined, the expansion part may open and will include patients with locally advanced or metastatic PDAC (n∼20), locally advanced or metastatic NSCLC (n∼20), HR+/HER2- ductal BC (n∼15), HR+/HER2- lobular BC (n∼15), and triple negative BC (; n∼24).The primary objectives of the study are to evaluate the safety and tolerability of [177Lu]Lu-NNS309 and to identify the RD(s) and regimen(s) of [177Lu]Lu-NNS309 for further clinical evaluation. Secondary objectives of the study are to evaluate the preliminary anti-tumor activity of [177Lu]Lu-NNS309, characterize the pharmacokinetics of [177Lu]Lu-NNS309 in blood and urine, the radiation dosimetry for organs and tumor lesions, and to evaluate the safety and imaging properties of [68Ga]Ga-NNS309. Conclusion: The study is currently enrolling in the dose escalation part. Citation Format: Ravit Geva, Daniel Juneau, Shadi Abdar Esfahani, Cristiano Ferrario, Farshad Moradi, Amir Iravani, Jordi Ahnert, Ivan Manuel Victoria Ruiz, Thibaud Koessler, Aitana Calvo Ferrandiz, Bernard Doger de Speville, Patrick Flamen, Albiruni Razak, Desiree Deandreis, Laure Al-Mansour, Niklaus Schaefer, James Nagarajah, Hilde Nienhuis, Marco Maccauro, Angelina Filice, Jonathan Goldman, Ken Herrmann, Matthias Eiber, Alexander Drzezga, Martin Heuschkel, Jonathan McConathy, Johnson Geoffrey, Ephraim Parent, Yasutoshi Kuboki, Shizuka Origuchi, Xuan Mai Couillebault, Elisa Garcia Garayoa, Jayarama Naidu Roopa, Christopher Straub, Dominik Hainzl, Xinyu Chen, Fang Yang, Eirini Pectasides, Brandon Mancini. Phase I open-label, multi-center study to evaluate the safety, tolerability, dosimetry, and preliminary activity of FXX489 ([177Lu]Lu-NNS309) in patients with pancreatic, lung, breast and colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr CT112.

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.

Introduction: CAR-T (chimeric antigen receptor T-cell) therapy is known to be associated with immune-mediated toxicities including cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). [18F]-Flurodeoxyglucose-positron emission tomography (FDG-PET) is frequently utilized for cancer staging before and after CAR-T therapy. Case series have demonstrated cerebral glucose hypometabolism (CGHM) on FDG-PET imaging in patients who developed CRS and ICANS. In this study, we aim to further characterize CART-CGHM. Methods: Patients who received CAR-T therapy at our institution from October 2019 to December 2023 were included. Clinical data was collected from retrospective review of the electronic medical record including patient age, sex, diagnosis, cancer stage, development of CRS or ICANS, and survival outcome. Standard of care whole body FDG-PET scans obtained before and approximately 30 days post CAR-T therapy were utilized. FDG-PET images of the brain were sub-selected and processed with dedicated imaging software (GE AW server 3.2 with Cortex ID, MIM Neuro, version 7.2.7). To identify CART-CGHM, visual and statistical comparison was made between the pre-CAR-T FDG-PET and the post-CAR-T FDG-PET using the age and gender matched normal cohort in the database as controls. Z-score changes > 1.5 were considered significant. Baseline variables were reported as frequency (%) and compared between patients with and without CGHM using Chi-squared test. Kaplan-Meier method was used to estimate the overall survival rate (OS) at different time points and log rank test was used to compare survival rates between the groups with and without CGHM. Multivariable Cox regression model was performed to evaluate the association between CGHM and OS with adjustment for ICANS. All tests were two-sided with p<0.05 considered statistically significant. Results: In total, 84 patients (41 women, 49%) were included. The median age at time of CAR-T therapy was 66 (33-85) years old. The most common diagnosis was multiple myeloma (n=39, 46%) followed by diffuse large B-cell lymphoma (n=33, 39%), follicular lymphoma (n=7, 8%), mantle cell lymphoma (n=3, 4%), and B-cell acute lymphoblastic leukemia (n=2, 2%). CART-CGHM was identified in 27 patients (32%). The pattern of CGHM was either global (n=15, 56%) or focal (n=12, 44%) with the prefrontal cortex predominantly affected. Of these 27 patients with CART-CGHM, 17 patients (63%) experienced ICANS and 23 patients (85%) experienced CRS. The diagnosis of lymphoma and development of ICANS were significantly associated with CGHM (p- 0.038 and <0.001 respectively). On univariate analysis, CGHM and ICANS were associated with negative impact on OS. The post-CAR-T 12-month OS for patients with CGHM was 76% versus 84% without CGHM (p-0.016), and 12-month OS for patients with ICANS was 64% versus 91% without ICANS (p-0.001). The post-CAR-T median OS for patients with CGHM, patients with ICANS, and patients with both CGHM and ICANS were 17.1 months, 13.5 months, and 12.6 months, respectively. On multivariate analysis, after adjusting for ICANS, CGHM alone did not have an impact on OS [HR 1.76 (0.71, 4.37); p-0.2250] but ICANS continued to have a negative impact on OS [HR 3.03 (1.21, 7.57); p-0.0178]. Conclusions: Our study represents the largest study to date on CART-CGHM. CART-CGHM was seen in 32% of CAR-T patients and had a strong association with ICANS and lymphoma patients. ICANS was found in 63% of CART-CGHM patients. ICANS alone or CGHM with ICANS were associated with a negative impact on OS. Although the underlying biological mechanism of CART-CGHM is not clear, it likely represents a significant immune-mediated reduction in cerebral glucose uptake. We suggest that CGHM represents a novel metabolic complication of CAR-T therapy and significantly contributes to CAR-T therapy associated neuro-cognitive toxicity. Although CART-CGHM can resolve completely, our study also showed patients with persistent CGHM on post-CART follow up FDG-PET scans. As such, CART-CGHM can potentially result in chronic neuro-cognitive complications. The current therapeutic interventions for CRS and ICANS do not appear to be adequately effective for CART-CGHM. Further research, involving multiple institutions, is urgently needed for better understanding of CART-CGHM and to develop specific therapeutic interventions.

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.

592 Background: The introduction of peptide receptor radionuclide therapy (PRRT) using Lutetium-177 (177Lu) DOTATATE has led to a paradigm shift in the treatment of neuroendocrine tumors (NETs). Hematological toxicity is a well-recognized adverse effect (AE) of 177Lu DOTATATE. Most cytopenias are transient, with an estimated incidence of 10-25%, typically mild to moderate in severity (grade G1-2). The most dreaded AE of PRRT is therapy-related myeloid neoplasm (t-MN), with an estimated 2-8% incidence and a higher incidence reported in patients who also received prior chemotherapy. We sought to evaluate the hematological safety of 177Lu PRRT in the setting of NETs with extensive (i.e., innumerable) bone metastases. Methods: We retrospectively reviewed the medical records of all Mayo Clinic patients (pts) with extensive/innumerable osseous metastases, defined as >50% skeletal involvement by positron emission tomography (PET) DOTATATE, who were treated with 177Lu DOTATATE. Pts characteristics and laboratory results were collected before, during, and after 177Lu DOTATATE treatment. Hematotoxicity was graded according to the NCI-CTCAE v5. Results: Out of 27 pts, 13(48%) developed cytopenia(s) of any grade after treatment with one or more cycles of 177Lu DOTATATE. In total, there were 13(48%) pts with anemia, 13(48%) with thrombocytopenia, and 6(22%) with neutropenia. Six (22%) pts had severe hematological toxicity (G3-4). Twelve months post-PRRT, 7(26%) pts continued to experience cytopenia(s) of any grade, of whom 4(15%) had G3-4 hematotoxicity. One pt developed t-MN, and two pts had myelophthisis on bone marrow biopsy from infiltrating NET. 16(59%) pts received cytotoxic chemotherapy before PRRT, and 7(25.9%) developed subsequent cytopenia(s). Overall, 15(55%) pts completed four cycles, while 3 pts didn’t complete four cycles of 177Lu DOTATATE due to hematotoxicity. Conclusions: Pts with advanced NETs and extensive/innumerable bone metastases treated with PRRT could be at higher risk for myelosuppression than historical controls. Our study highlights the importance of carefully monitoring and assessing hematological parameters in pts being considered for 177Lu DOTATATE with extensive/innumerable bone metastasis. [Table: see text]

Abstract BACKGROUND Differentiating radiation necrosis from tumour progression after radiation therapy (RT) for brain metastases (BM) remains clinically challenging, and accurate imaging is crucial to prevent unnecessary surgery or unwarranted changes in therapy. 18F-Fluciclovine is a PET radiopharmaceutical with low background uptake in the brain and increased uptake in BM. The PURSUE study (NCT04410367) aimed to establish image interpretation criteria (IIC) for detecting suspected recurrent BM after RT using 18F-fluciclovine PET, based on several measures of lesion uptake. MATERIAL AND METHODS Across 7 US sites, 23 patients with solid tumour BM and a previously irradiated ‘reference’ lesion equivocal for recurrence on MRI who were scheduled for craniotomy underwent 18F-fluciclovine PET (185 MBq) <42 days post-MRI and 1-21 days pre-craniotomy. Three independent, blinded readers qualitatively rated lesion 18F-fluciclovine uptake as ‘mild’ (up to blood pool), ‘moderate’ (above blood pool to parotid gland), or ‘marked’ (above parotid gland). The primary endpoint was the diagnostic performance of different thresholds of lesion uptake on qualitative (visual) reads vs central histopathology. Secondary endpoints included diagnostic performance, based on different thresholds, of quantitative (e.g., lesion standardized uptake value [SUV]), and dynamic measures. A committee, including two independent imaging physicians, reviewed all data to establish the IIC, which were subsequently used to evaluate the diagnostic performance of 18F-fluciclovine. RESULTS All 23 reference lesions underwent histopathological analysis, with 10 (43%) being pathologically confirmed BM recurrence. The highest performing qualitative measure of 18F-fluciclovine lesion uptake was ‘marked’, rendering 92-100% and variable (40-80%) across readers. SUVmax was a reader-independent, high-performing quantitative metric (AUC 0.87, SUVmax threshold 4.8, 80% sensitivity, 85% specificity). Dynamic measures did not add diagnostic value. Thus, the committee established IIC as: "Lesions with 18F-fluciclovine uptake of a SUVmax equal to or greater than 4.8, or visually greater than the parotid gland, should be considered suspicious for recurrence. Otherwise, recurrence should be considered unlikely." Application of these IIC resulted in 80% sensitivity, 77-85% specificity, 73-80% positive predictive value, and 83-85% negative predictive value across readers. CONCLUSION PURSUE is the first prospective, multicentre study to define IIC for 18F-fluciclovine PET for accurate identification of suspected recurrent BM after RT, verified by histopathology. In this initial cohort, the IIC convey excellent diagnostic performance for 18F-fluciclovine and will help evaluate 18F-fluciclovine PET in future studies. This study was sponsored by Blue Earth Diagnostics Ltd.

Abstract BACKGROUND After radiation therapy (RT) for brain metastases (BM), differentiating radiation necrosis from tumor recurrence remains challenging. PURSUE (NCT04410367) evaluated various measures of lesion 18F-fluciclovine uptake to establish image interpretation criteria (IIC) for 18F-fluciclovine-PET to accurately diagnose recurrent BM. METHODS Patients with solid tumor BM and a previously irradiated ‘reference’ lesion equivocal for recurrence on MRI who were scheduled for craniotomy underwent 18F-fluciclovine-PET (185 MBq) <42 days post-MRI and 1-21 days pre-craniotomy. Lesion 18F-fluciclovine uptake was qualitatively rated as ‘mild’ (up to blood pool), ‘moderate’ (above blood pool to parotid gland), or ‘marked’ (above parotid gland) by three independent blinded readers. The primary endpoint was diagnostic performance of different uptake thresholds on qualitative reads vs central histopathology. Secondary endpoints included diagnostic performance, based on different thresholds, of quantitative (e.g., lesion standardized uptake value [SUV]) and dynamic measures. IIC were determined by committee and subsequently used to assess the diagnostic performance of 18F-fluciclovine. RESULTS All 23 reference lesions from 23 enrolled patients underwent histopathological analysis; 10 (43%) were pathologically-confirmed BM recurrence. The highest performing qualitative measure was ‘marked’, rendering 92-100% sensitivity and 40-80% specificity across readers. SUVmax was a reader-independent, high-performing quantitative metric (AUC 0.87, SUVmax threshold 4.8, 80% sensitivity, 85% specificity). Dynamic measures did not add diagnostic value. Thus, IIC was established as: “Lesions with 18F-fluciclovine uptake of SUVmax equal to or greater than 4.8, or visually greater than the parotid gland, should be considered suspicious for recurrence. Otherwise, recurrence should be considered unlikely.” Application of the IIC resulted in 80% sensitivity, 77-85% specificity, 73-80% PPV, and 83-85% NPV across the readers. CONCLUSIONS PURSUE is the first prospective, multicenter trial to establish IIC for 18F-fluciclovine-PET for suspected recurrent BM after RT, verified by histopathology. Finalized IIC demonstrated excellent diagnostic performance for 18F-fluciclovine and will help evaluate 18F-fluciclovine-PET in future studies.

2001 Background: Differentiating radiation necrosis from tumor progression remains one of the most commonly encountered and clinically challenging scenarios after radiation therapy (RT) for brain metastases (BM). PURSUE (NCT04410367) evaluated the diagnostic performance of 18F-fluciclovine, an amino acid PET radiopharmaceutical, based on various lesion metrics, to establish image interpretation criteria (IIC) for suspected recurrent BM after RT. Methods: Patients with solid tumor BM were enrolled across 7 US sites if they had a previously irradiated ‘reference’ lesion equivocal on MRI for recurrence and were planned for craniotomy. 18F-Fluciclovine PET (185 MBq) took place <42 days post-MRI and 1-21 days pre-craniotomy. The primary endpoint was the diagnostic performance (sensitivity, specificity, positive-, and negative-predictive value [PPV/NPV]) of different thresholds of lesion 18F-fluciclovine uptake on qualitative, visual reads vs central histopathological analysis. Lesion 18F-fluciclovine uptake was assessed qualitatively by 3 independent blinded readers who visually rated the uptake as ‘mild’ (up to blood pool), ‘moderate’ (above blood pool to parotid), or ‘marked’ (above parotid). Secondary endpoints included the diagnostic performance based on different thresholds of quantitative (e.g., lesion SUV) and dynamic measures of uptake. A committee, including 2 expert imaging physicians independent to PURSUE, reviewed all data in round-table meetings to establish the IIC, which were subsequently used to assess diagnostic performance. Results: All 23 reference lesions in 23 subjects underwent histopathological analysis, with 10 (43%) confirmed as recurrent tumor. The highest performing qualitative measure was ‘marked’, rendering a sensitivity of 92-100%, with variable specificity of 40-80% across readers. SUVmax was a reader-independent, high-performing quantitative metric on ROC analysis (AUC 0.87, SUVmax threshold 4.8 conferring a sensitivity of 80% and specificity of 85%). Dynamic measures did not provide added diagnostic value. After analyzing these metrics, the committee established IIC as: Lesions with 18F-fluciclovine uptake of a SUVmax equal to or greater than 4.8, or visually greater than the parotid gland, should be considered suspicious for recurrence. Otherwise, recurrence should be considered unlikely. Application of the IIC resulted in a sensitivity of 80%, specificity of 77-85%, PPV of 73-80%, and NPV of 83-85% across the readers. Conclusions: This is the first prospective multicenter trial to evaluate PET characteristics of suspected recurrent BM after RT, verified by histopathology. Qualitative and quantitative IIC show 18F-fluciclovine to be a high-performing diagnostic tool. These IIC will help evaluate the diagnostic performance of 18F-fluciclovine PET in future trials. Clinical trial information: NCT04410367 .