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Purpose:Prostate-specific membrane antigen (PSMA) targeting radioligands deliver radiation to PSMA-expressing cells. However, the relationship between PSMA levels and intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell, and the fraction of PSMA+ cells in a tumor.Experimental Design:RM1 cells expressing different levels of PSMA (PSMA−, PSMA+, PSMA++, PSMA+++; study 1) or a mix of PSMA+ and PSMA− RM1 (study 2, 4) or PC-3/PC-3-PIP (study 3) cells at various ratios were injected into mice. Mice received 177Lu- (studies 1–3) or 225Ac- (study 4) PSMA617. Tumor growth was monitored. Two days post-RLT, tumors were resected in a subset of mice. Radioligand uptake and DNA damage were quantified.Results:177Lu-PSMA617 efficacy increased with increasing PSMA levels (study 1) and fractions of PSMA positive cells (studies 2, 3) in both, the RM1 and PC-3-PIP models. In tumors resected 2 days post-RLT, PSMA expression correlated with 177Lu-PSMA617 uptake and the degree of DNA damage. Compared with 177Lu-PSMA617, 225Ac-PSMA617 improved overall antitumor effectiveness and tended to enhance the differences in therapeutic efficacy between experimental groups.Conclusions:In the current models, both the degree of PSMA expression and the fraction of PSMA+ cells correlate with 177Lu-/225Ac-PSMA617 tumor uptake and DNA damage, and thus, RLT efficacy. Low or heterogeneous PSMA expression represents a resistance mechanism to RLT.See related commentary by Ravi Kumar and Hofman, p. 2774

Absolute tumor volumes and bodyweights

Relative tumor volumes, 177Lu-/225Ac-PSMA617 uptake and 53BP1 IRS

Purpose: Fibroblast activation protein (FAP)-expressing cancer-associated fibroblasts confer treatment resistance, promote metastasis and immunosuppression. Because FAP is overexpressed in many cancers, radiolabeled molecules targeting FAP are studied for their use as pan-cancer theranostic agents. This study aims to establish the spectrum of FAP expression across various cancers by immunohistochemistry and to explore whether gallium-68 FAPi-46 (68Ga-FAPi-46) PET biodistribution faithfully reflects FAP expression from resected cancer and non-cancer specimens. Methods: We conducted a FAP expression screening by using immunohistochemistry on a pan-cancer human tissue microarray (TMA) (141 patients, 14 different types of cancer) and an interim analysis of a prospective exploratory imaging trial in cancer patients. Volunteer patients underwent one whole body 68Ga-FAPi-46 PET/CT scan and subsequently, surgical resection of their primary tumor and/or metastasis. 68Ga-FAPi-46 PET maximum standardized uptake value (SUVmax and SUVmean) was correlated with FAP immunohistochemistry score in cancer and non-cancer tissues for each patient. Results: FAP was expressed across all 14 cancers types on TMA with variable intensity and frequency, ranging from 25 to 100% (mean 76.6±25.3%). Strong FAP expression was observed in 50-100% of cancers of the bile duct, bladder, colon, esophagus, stomach, lung, oropharynx, ovary and pancreas. Fifteen patients with various cancer types (colorectal (n = 4), head and neck (n = 3), pancreas (n = 2), breast (n = 2), stomach (n = 1), esophagus (n = 2) and uterus (n = 1)) underwent surgery following their 68Ga-FAPi-46 PET/CT scan within a mean time interval of 16.1±14.4 days. 68Ga-FAPi-46 SUVs and immunohistochemistry scores were higher in cancer than in normal tissue: mean SUVmax 7.7 vs 1.6 (p

The University of California Los Angeles (UCLA) and University of California San Francisco (UCSF) codeveloped 68Ga-PSMA-11 by conducting a bicentric pivotal phase 3 clinical trial for PET imaging for prostate cancer. On December 1, 2020, 2 separate new drug applications (NDAs) submitted by each institution (NDA 212642 for UCLA and NDA 212643 for UCSF) were approved by the Food and Drug Administration as the first drug for PET imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer. This article briefly describes the background, clinical development, regulatory approach, and regulatory process for NDA filing and approval. In the second part of this article, key chemistry, manufacturing, and controls (CMC) information is provided to facilitate abbreviated new drug application (ANDA) submission.

Microfluidics offers numerous advantages for the synthesis of short-lived radiolabeled imaging tracers: performing 18F-radiosyntheses in microliter-scale droplets has exhibited high efficiency, speed, and molar activity as well as low reagent consumption. However, most reports have been at the preclinical scale. In this study we integrate a [18F]fluoride concentrator and a microdroplet synthesizer to explore the possibility of synthesizing patient doses and multi-patient batches of clinically-acceptable tracers. In the integrated system, [18F]fluoride (up to 41 GBq [1.1 Ci]) in [18O]H2O (1 mL) was first concentrated ∼80-fold and then efficiently transferred to the 8 μL reaction chip as a series of small (∼0.5 μL) droplets. Each droplet rapidly dried at the reaction site of the pre-heated chip, resulting in localized accumulation of large amounts of radioactivity in the form of dried [18F]TBAF complex. The PET tracer [18F]fallypride was synthesized from this concentrated activity in an overall synthesis time of ∼50 min (including radioisotope concentration and transfer, droplet radiosynthesis, purification, and formulation), in amounts up to 7.2 GBq [0.19 Ci], sufficient for multiple clinical PET scans. The resulting batches of [18F]fallypride passed all QC tests needed to ensure safety for clinical injection. This integrated technology enabled for the first time the impact of a wide range of activity levels on droplet radiosynthesis to be studied. Furthermore, this substantial increase in scale expands the applications of droplet radiosynthesis to the production of clinically-relevant amounts of radiopharmaceuticals, and potentially even centralized production of clinical tracers in radiopharmacies. The overall system could be applied to fundamental studies of droplet-based radiochemical reactions, or to the production of radiopharmaceuticals labeled with a variety of isotopes used for imaging and/or targeted radiotherapeutics.

Fibroblast activation protein (FAP)-expressing cancer-associated fibroblasts confer treatment resistance and promote metastasis and immunosuppression. Because FAP is overexpressed in many cancers, radiolabeled molecules targeting FAP are studied for their use as pancancer theranostic agents. This study aimed to establish the spectrum of FAP expression across various cancers by immunohistochemistry and to explore whether

The objective of this study was to determine prospectively the efficacy profile of 2 activity regimens of (177)Lu-PSMA therapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC): 6.0 vs. 7.4 GBq. Methods: RESIST-PC (NCT03042312) was a prospective multicenter phase 2 trial. Patients with progressive mCRPC after ≥ 1 novel androgen-axis drug, either chemotherapy naïve or postchemotherapy, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA expression by PSMA PET were eligible. Patients were randomized (1:1) into 2 activity groups (6.0 or 7.4 GBq) and received up to 4 cycles every 8 wk. The primary endpoint was the efficacy of (177)Lu-PSMA measured by the prostate-specific antigen (PSA) response rate (RR) after 2 cycles (≥50% decline from baseline). Secondary endpoints included the PSA RR (≥50% decline) at any time (best response), and overall survival (OS). Results: The study was closed at enrollment of 71/200 planned patients because of sponsorship transfer. We report here the efficacy of the University of California Los Angeles cohort results only (n = 43). The PSA RRs after 2 cycles and at any time were 11/40 (28%, 95% CI 15–44), 6/13 (46%, 95% CI 19–75), and 5/27 (19%, 95% CI 6–38), and 16/43 (37%, 95% CI 23–53), 7/14 (50%, 95% CI 23–77), and 9/29 (31%, 95% CI 15–51) in the whole cohort, the 6.0-GBq group, and the 7.4-GBq group, respectively (P = 0.12 and P = 0.31). The median OS was 14.0 mo (95% CI 10.1–17.9), 15.8 (95% CI 11.8–19.4), and 13.5 (95% CI 10.0–17.0) in the whole cohort, the 6.0-GBq group, and the 7.4 GBq group, respectively (P = 0.87). OS was longer in patients who experienced a PSA decline ≥ 50% at any time than in those who did not: median, 20.8 versus 10.8 mo (P = 0.005). Conclusion: In this prospective phase 2 trial of (177)Lu-PSMA for mCRPC, the median OS was 14 mo. Despite the heterogeneous study population and the premature study termination, the efficacy profile of (177)Lu-PSMA appeared to be favorable and comparable with both activity regimens (6.0 vs. 7.4 GBq). Results justify confirmation with real-world data matched-pair analysis and further clinical trials to refine and optimize the (177)Lu-PSMA therapy administration scheme to improve tumor radiation dose delivery and efficacy.

Targeting cancer-associated fibroblasts (CAFs) has become an attractive goal for diagnostic imaging and therapy because they can constitute as much as 90% of a tumor mass. The serine protease fibroblast activation protein (FAP) is overexpressed selectively in CAFs, drawing interest in FAP as a stromal target. The quinoline-based FAP inhibitor (FAPI) PET tracer 68Ga-FAPI-04 has been previously shown to yield high tumor-to-background ratios (TBRs) in patients with various cancers. Recent developments toward an improved compound for therapeutic application have identified FAPI-46 as a promising agent because of an increased tumor retention time in comparison with FAPI-04. Here, we present a PET biodistribution and radiation dosimetry study of 68Ga-FAPI-46 in cancer patients. Methods: Six patients with different cancers underwent serial 68Ga-FAPI-46 PET/CT scans at 3 time points after radiotracer injection: 10 min, 1 h, and 3 h. The source organs consisted of the kidneys, bladder, liver, heart, spleen, bone marrow, uterus, and remainder of body. OLINDA/EXM software, version 1.1, was used to fit and integrate the kinetic organ activity data to yield total-body and organ time-integrated activity coefficients and residence times and, finally, organ-absorbed doses. SUVs and TBR were generated from the contoured tumor and source-organ volumes. Spheric volumes in muscle and blood pool were also obtained for TBR (tumor SUVmax/organ SUVmean). Results: At all time points, average SUVmax was highest in the liver. Tumor and organ SUVmean decreased over time, whereas TBRs in all organs but the uterus increased. The organs with the highest effective doses were bladder wall (2.41E-03 mSv/MBq), followed by ovaries (1.15E-03 mSv/MBq) and red marrow (8.49E-04 mSv/MBq). The average effective total-body dose was 7.80E-03 mSv/MBq. Conclusion: 68Ga-FAPI-46 PET/CT has a favorable dosimetry profile, with an estimated whole-body dose of 5.3 mSv for an administration of 200 MBq (5.4 mCi) of 68Ga-FAPI-46 (1.56 ± 0.26 mSv from the PET tracer and 3.7 mSv from 1 low-dose CT scan). The biodistribution study showed high TBRs increasing over time, suggesting high diagnostic performance and favorable tracer kinetics for potential therapeutic applications.

IntroductionRadio thin layer chromatography (radio-TLC) is commonly used to analyze purity of radiopharmaceuticals or to determine the reaction conversion when optimizing radiosynthesis processes. In applications where there are few radioactive species, radio-TLC is preferred over radio-high-performance liquid chromatography due to its simplicity and relatively quick analysis time. However, with current radio-TLC methods, it remains cumbersome to analyze a large number of samples during reaction optimization. In a couple of studies, Cerenkov luminescence imaging (CLI) has been used for reading radio-TLC plates spotted with a variety of isotopes. We show that this approach can be extended to develop a high-throughput approach for radio-TLC analysis of many samples.MethodsThe high-throughput radio-TLC analysis was carried out by performing parallel development of multiple radioactive samples spotted on a single TLC plate, followed by simultaneous readout of the separated samples using Cerenkov imaging. Using custom-written MATLAB software, images were processed and regions of interest (ROIs) were drawn to enclose the radioactive regions/spots. For each sample, the proportion of integrated signal in each ROI was computed. Various crude samples of [18F]fallypride, [18F]FET and [177Lu]Lu-PSMA-617 were prepared for demonstration of this new method.ResultsBenefiting from a parallel developing process and high resolution of CLI-based readout, total analysis time for eight [18F]fallypride samples was 7.5min (2.5min for parallel developing, 5min for parallel readout), which was significantly shorter than the 48min needed using conventional approaches (24min for sequential developing, 24min for sequential readout on a radio-TLC scanner). The greater separation resolution of CLI enabled the discovery of a low-abundance side product from a crude [18F]FET sample that was not discernable using the radio-TLC scanner. Using the CLI-based readout method, we also observed that high labeling efficiency (99%) of [177Lu]Lu-PSMA-617 can be achieved in just 10min, rather than the typical 30min timeframe used.ConclusionsCerenkov imaging in combination with parallel developing of multiple samples on a single TLC plate proved to be a practical method for rapid, high-throughput radio-TLC analysis.

Prostate-specific membrane antigen (PSMA) ligand PET induces management changes in patients with prostate cancer. We aim to better characterize the impact of (68)Ga-PSMA-11 PET ((68)Ga-PSMA PET) on management of recurrent prostate cancer in a large prospective cohort. Methods: We report management changes after (68)Ga-PSMA PET, a secondary endpoint of a prospective multicenter trial in men with biochemical recurrence of prostate cancer. Pre-PET (Q1), post-PET (Q2), and posttreatment (Q3) questionnaires were sent to referring physicians recording site of recurrence and intended (Q1 to Q2 change) and implemented (Q3) therapeutic and diagnostic management. Results: Q1 and Q2 response was collected for 382 of 635 patients (60%, intended cohort), and Q1, Q2, and Q3 response was collected for 206 patients (32%, implemented cohort). An intended management change occurred in 260 of 382 (68%) patients. The intended change was considered major in 176 of 382 (46%) patients. Major changes occurred most often for patients with prostate-specific antigen of 0.5 to less than 2.0 ng/mL (81/147, 55%). By analysis of stage groups, management change was consistent with PET disease location, that is, a majority of major changes toward active surveillance (47%) for unknown disease site (103/382, 27%), toward local or focal therapy (56%) for locoregional disease (126/382, 33%), and toward systemic therapy (69% M1a; 43% M1b/c) for metastatic disease (153/382, 40%). According to Q3 responses, the intended management was implemented in 160 of 206 (78%) patients. In total, 150 intended diagnostic tests, mostly CT (n = 43, 29%) and bone scans or (18)F-NaF PET (n = 52, 35%), were prevented by (68)Ga-PSMA PET; 73 tests, mostly biopsies (n = 44, 60%) as requested by the study protocol, were triggered. Conclusion: According to referring physicians, sites of recurrence were clarified by (68)Ga-PSMA PET, and disease localization translated into management changes in more than half of patients with biochemical recurrence of prostate cancer.

Prostate-specific membrane antigen (PSMA) ligand PET induces management changes in patients with prostate cancer. We aim to better characterize the impact of 68Ga-PSMA-11 PET (68Ga-PSMA PET) on management of recurrent prostate cancer in a large prospective cohort. Methods: We report management changes after 68Ga-PSMA PET, a secondary endpoint of a prospective multicenter trial in men with biochemical recurrence of prostate cancer. Pre-PET (Q1), post-PET (Q2), and posttreatment (Q3) questionnaires were sent to referring physicians recording site of recurrence and intended (Q1 to Q2 change) and implemented (Q3) therapeutic and diagnostic management. Results: Q1 and Q2 response was collected for 382 of 635 patients (60%, intended cohort), and Q1, Q2, and Q3 response was collected for 206 patients (32%, implemented cohort). An intended management change occurred in 260 of 382 (68%) patients. The intended change was considered major in 176 of 382 (46%) patients. Major changes occurred most often for patients with prostate-specific antigen of 0.5 to less than 2.0 ng/mL (81/147, 55%). By analysis of stage groups, management change was consistent with PET disease location, that is, a majority of major changes toward active surveillance (47%) for unknown disease site (103/382, 27%), toward local or focal therapy (56%) for locoregional disease (126/382, 33%), and toward systemic therapy (69% M1a; 43% M1b/c) for metastatic disease (153/382, 40%). According to Q3 responses, the intended management was implemented in 160 of 206 (78%) patients. In total, 150 intended diagnostic tests, mostly CT (n = 43, 29%) and bone scans or 18F-NaF PET (n = 52, 35%), were prevented by 68Ga-PSMA PET; 73 tests, mostly biopsies (n = 44, 60%) as requested by the study protocol, were triggered. Conclusion: According to referring physicians, sites of recurrence were clarified by 68Ga-PSMA PET, and disease localization translated into management changes in more than half of patients with biochemical recurrence of prostate cancer.

²²⁵Ac-PSMA-617 targeted-therapy has demonstrated efficacy in 75-85% of patients; however, responses are not durable. We aimed to establish translatable mouse models of disseminated prostate cancer (PCa) to evaluate effectiveness of ²²⁵Ac-PSMA-617 at various disease stages. Methods: C4-2, C4-2B, or 22Rv1 cells were injected into the left ventricle of male NSG mice. Disease progression was monitored using bioluminescence imaging (BLI). For treatment, mice were injected with 40 kBq ²²⁵Ac-PSMA-617 at one (early treatment cohort) or three weeks (late treatment cohort) post-inoculation. Treatment efficacy was monitored by BLI of whole-body tumor burden. Mice were sacrificed based on body conditioning score. Results: C4-2 cells yielded metastases in liver, lungs, spleen, stomach, bones, and brain - achieving a clinically relevant model of widespread metastatic disease. The disease burden in the early treatment cohort was stable over 27 weeks in 5/9 mice and progressive in 4/9 mice. These mice were sacrificed due to brain metastases. Median survival of the late treatment cohort was superior to controls (13 vs. 7 weeks; p

5549 Background: This was an open-label randomized prospective bi-centric single-arm phase II clinical trial of 177Lu-PSMA-617 molecular radiotherapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC) conducted at University of California Los Angeles (USA) and Excel Diagnostics & Nuclear Oncology Center (Houston, TX, USA) (NCT03042312). The study was investigator-initiated under an investigational new drug approval protocol (IND#133661) with authorization of charging for investigational drug (cost-recovery, Title 21 CFR 312.8). We report here the post-hoc analysis of overall survival (OS) in a single-study site cohort (UCLA). Methods: Patients with progressive mCRPC (biochemical, radiographic, or clinical) after ≥1 novel androgen axis drug (NAAD), either chemotherapy (CTX) naïve or post-CTX, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA-target expression by PET were eligible. Patients received up to 4 cycles of 177Lu-PSMA-617 every 8±1 weeks and were randomized into 2 treatment activities groups (6.0 or 7.4 GBq). Efficacy was defined as serum PSA decline of ≥50% from baseline and served as primary endpoint (hypothesis: ≥40% of responders after 2 cycles). Results: 43 patients were randomized to the 6.0 GBq (n= 14) and 7.4 GBq (n=29) treatment arms. 11/43 (26%) were CTX naïve while 10/43 (23%), 12/43 (28%), 5/43 (12%) and 5/43 (12%) had received 1, 2, 3 or 4 CTX regimens. Median baseline PSA was 29.2 ng/ml (mean 228.8, range 0.5-2082.6). 21/43 (49%) completed 4 cycles of 177Lu-PSMA-617 whereas 4/43 (9%), 13/43 (30%) and 5/43 (12%) underwent 1, 2 and 3 cycles. PSA decline of ≥50% was observed in 11/43 of patients (26%) after 2 cycles and in 16/43 (37%) at any time (best PSA response). 9/43 (21%) had a PSA decline of ≥90% and 23/43 (53%) had any PSA decline (>0%). After a median follow-up of 19.5 months the median OS was 14.8, 15.7 and 13.5 months in the whole cohort, the 6.0 GBq and 7.4 GBq treatment arms, respectively (p=0.68). Patients showing a PSA decline of ≥50% after 2 cycles and at any time had a longer OS: median 20.1 months vs. 13.6 (p=0.091) and 20.1 vs. 11.6 (p=0.002), respectively. Conclusions: In this post-hoc analysis of a single-site cohort of 43 patients included in a prospective phase II trial the median OS after 177Lu-PSMA-617 molecular radiotherapy in patients with progressive mCRPC was 14.8 months. There was no difference of efficacy between the 6.0 GBq and 7.4 GBq treatment arms. Clinical trial information: NCT03042312 .

Purpose: Prostate-specific membrane antigen (PSMA) targeting radioligands deliver radiation to PSMA-expressing cells. However, the relationship between PSMA levels and intralesion heterogeneity of PSMA expression, and cytotoxic radiation by radioligand therapy (RLT) is unknown. Here we investigate RLT efficacy as function of PSMA levels/cell, and the fraction of PSMA+ cells in a tumor. Experimental Design: RM1 cells expressing different levels of PSMA (PSMA−, PSMA+, PSMA++, PSMA+++; study 1) or a mix of PSMA+ and PSMA− RM1 (study 2, 4) or PC-3/PC-3-PIP (study 3) cells at various ratios were injected into mice. Mice received 177Lu- (studies 1–3) or 225Ac- (study 4) PSMA617. Tumor growth was monitored. Two days post-RLT, tumors were resected in a subset of mice. Radioligand uptake and DNA damage were quantified. Results: 177Lu-PSMA617 efficacy increased with increasing PSMA levels (study 1) and fractions of PSMA positive cells (studies 2, 3) in both, the RM1 and PC-3-PIP models. In tumors resected 2 days post-RLT, PSMA expression correlated with 177Lu-PSMA617 uptake and the degree of DNA damage. Compared with 177Lu-PSMA617, 225Ac-PSMA617 improved overall antitumor effectiveness and tended to enhance the differences in therapeutic efficacy between experimental groups. Conclusions: In the current models, both the degree of PSMA expression and the fraction of PSMA+ cells correlate with 177Lu-/225Ac-PSMA617 tumor uptake and DNA damage, and thus, RLT efficacy. Low or heterogeneous PSMA expression represents a resistance mechanism to RLT. See related commentary by Ravi Kumar and Hofman, p. 2774

To improve prostate-specific membrane antigen (PSMA)–targeted theranostic approaches, robust murine models of prostate cancer are needed. However, important characteristics of preclinical PSMA imaging—that is, the reproducibility of the imaging signal and the relationship between quantitative cell surface PSMA expression and lesion detectability with small-animal PET/CT—have not been defined yet. Methods: Murine prostate cancer RM1 sublines (ras myc transformed cells of C57BL/6 prostate origin) expressing varying levels of human PSMA were injected into the shoulder of C57BL/6 mice on day 0. 68Ga-PSMA11 PET/CT was performed on days 7 and 8 and interpreted by 2 masked readers to determine interday and interreader reproducibility. PSMA expression was quantified on days 7 and 8 by flow cytometry of fine-needle aspiration tumor biopsy samples. Cell surface PSMA expression was correlated with PET signal. The threshold for PET positivity was based on the clinical Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria. Results: The maximum and average percentages of injected 68Ga-PSMA11 activity per gram of tissue (%IA/g) correlated nearly perfectly as determined by 2 independent readers and on 2 separate days (intraclass correlation coefficient, 1.00/0.89 and 0.95/0.88, respectively). The number of PSMA molecules per cell increased from the RM1-yellow fluorescent protein subline (PSMA−; 2,000/cell) to the RM1-low subline (PSMA+; 17,000/cell), the RM1-medium subline (PSMA++; 22,000/cell), and the RM1-PGLS subline (PSMA-positive, green fluorescent protein–positive, and luciferase-positive; PSMA+++; 45,000/cell). Expression levels correlated with the visual positivity rate on 68Ga-PSMA11 PET and with the PSMA PET %IA/g. The PSMA threshold for PET positivity was approximately 20,000 per cell. Signal correlation was close at lower PSMA levels (RM1-low to RM1-medium; 10–23 %IA/g) but was lost at higher PSMA levels (RM1-medium to RM1-PGLS; 23–27 %IA/g). Conclusion: The in vivo relationship between 68Ga-PSMA11 PET/CT and PSMA expression level in a murine model of prostate cancer was robust for lower cell surface PSMA expression levels (≤22,000/cell). Thus, preclinical 68Ga-PSMA11 PET/CT can be used as an imaging biomarker to test PSMA-targeted interventions in murine models.

Context: Fibroblast activation protein (FAP)-expressing cancer associated fibroblasts (CAFs), a major component of tumor stroma, confer treatment resistance, promote local progression, metastasis and immunosuppression. Because FAP is selectively expressed in the tumor stroma of many cancers, radiolabeled small molecule ligands targeting FAP are being explored for their use as pan-cancer theranostic agents. As a required step for further translation and approval by regulatory agencies FAPi PET imaging must be show to be a reliable biomarker of FAP expression in cancer and non-cancer tissues. The aim of the study is to define the incidence and degree of FAP expression by immunohistochemistry (IHC) across various cancers using Tissue Microarrays (TMAs) and to explore whether gallium-68 FAPi-46 PET image biodistribution faithfully reflects tumor FAP expression from resected tumor and non-tumor specimens. Methods: This was a prospective, exploratory, open-label, single-center imaging trial in cancer patients conducted in 2020. Patients scheduled to undergo surgical resection of the primary tumor and/or metastases were eligible. Patients underwent one whole body 68Ga-FAPI-46 PET/CT scan and subsequently underwent surgical resection of the primary tumor and/or metastasis. The primary endpoint measure was the Correlation of 68Ga-FAPI-46 PET maximum standardized uptake value (SUVmax) with FAP IHC score in cancer and non-cancer tissue. Results: The incidence of FAP expression in TMAs from 14 cancers ranged from 25 to 100% (mean 76.6± 25.3). 15 patients with the following cancer types were included: colorectal (n=4), head and neck (n=3), pancreas (n=2), breast (n=2), stomach (n=1), esophagus (n=2) and uterus (n=1). All 15 patients subsequently underwent surgery after the scan with a mean time interval of16.1 ± 14.4 days (range 1 - 50 days). Tumor resection was not attempted in 2 patients because unresectable. FAPI SUVmax and IHC score were higher in cancer tissue than in normal tissue: mean FAPI SUVmax 7.4±4.6 (range 1.5-15.9) vs 1.6±1.2 (range 0.4-5.1), (p Citation Format: Christine E. Mona, Matthias Benz, Firat Hikmat, Tristan G. Grogan, Katharina Lueckerath, Aria A. Razmaria, Rana Riahi, Roger Slavik, Mark D. Grigis, Giuseppe Carlucci, Kimberly A. Kelly, Johannes Czernin, David W. Dawson, Jeremie Calais. Validation of FAPi PET biodistribution by immunohistochemistry in patients with solid cancers: a prospective exploratory study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB038.

Background: Despite decades of experience with bone marrow transplantation, there has not been prior whole body visualization of the engraftment of hematopoietic stem cell (HSC) in bone marrow in humans. The herpes simplex virus type 1 sr39 thymidine kinase (sr39tk) gene is a positron emission tomography (PET) reporter/suicide gene that can be used to genetically label cells and track them in vivo based on the ability to retain the PET tracer [18F]FHBG, which is a penciclovir analogue. Methods: Three patients with metastatic sarcoma were treated with gene-modified autologous CD34+ peripheral blood stem cells (PBSCs) transduced with a lentiviral vector encoding both a transgenic T-cell receptor against the tumor antigen NY-ESO-1 and the sr39tk reporter/suicide gene after a reduced intensity conditioning regimen of busulfan and fludarabine. These gene-modified stem cells were co-administered with gene-modified autologous T-cells also encoding the NY-ESO-1 T-cell receptor. The primary endpoint was safety and feasibility, while an exploratory endpoint was standardized uptake value of [18F]FHBG PET between post-transplant day +25 and day +120 scans to study the biodistribution of the gene-modified PBSCs and progeny T cells. Results: Two patients (NYSCT-01 and NYSCT-03) demonstrated robust engraftment the gene-modified PBSCs in bone marrow niches by day +25-30, as demonstrated by whole body [18F]FHBG PET. PET signal was evident throughout the body in the bone marrow in the scalp, jaw, vertebrae, ribs, pelvis, femur and other bones with significant areas of bone marrow. The third patient (NYSCT-05), whose product had much lower transduction efficiency, did not display any engraftment signal at day +28. Patient NYSCT-01 demonstrated loss of [18F]FHBG signal at day +120, with no detectable T-cell progeny in peripheral circulation. Patient NYSCT-03 developed a post-transplant de novo multidrug-resistant cytomegalovirus (CMV) viremia at day +58 which ultimately required treatment with systemic ganciclovir, and passed away prior to her day +120 PET scan. Patient NYSCT-05 developed a post-transplant CMV reactivation viremia on day +45, which responded to oral valganciclovir treatment. Conclusions: PET imaging allowed visualization of the successful engraftment of sr39tk reporter gene-labeled HSCs in bone marrow niches. Further studies are needed to determine mechanisms of loss of engraftment due to immunogenicity of the sr39tk gene, or insufficient transduction efficiency. Citation Format: Theodore S. Nowicki, Beata Berent-Maoz, Cristina Puig-Saus, Paula Kaplan-Lefko, Ignacio Baselga Carretero, Ameya Champhekar, Giuseppe Carlucci, Mignonette Macabali, Ivan Perez Garcilazo, Agustin Vega-Crespo, Jonathan Rodriguez, Bartosz Chmielowski, Arun Singh, Martin Allen-Auerbach, Shaojun Zhu, Roger Slavik, Begonya Comin-Anduix, John Williams, Antoni Ribas. Whole body imaging of genetically labeled hematopoietic stem cells in human subjects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 436.

New radiolabeled probes for positron-emission tomography (PET) are providing an ever-increasing ability to answer diverse research and clinical questions and to facilitate the discovery, development, and clinical use of drugs in patient care. Despite the high equipment and facility costs to produce PET probes, many radiopharmacies and radiochemistry laboratories use a dedicated radiosynthesizer to produce each probe, even if the equipment is idle much of the time, to avoid the challenges of reconfiguring the system fluidics to switch from one probe to another. To meet growing demand, more cost-efficient approaches are being developed, such as radiosynthesizers based on disposable "cassettes," that do not require reconfiguration to switch among probes. However, most cassette-based systems make sacrifices in synthesis complexity or tolerated reaction conditions, and some do not support custom programming, thereby limiting their generality. In contrast, the design of the ELIXYS FLEX/CHEM cassette-based synthesizer supports higher temperatures and pressures than other systems while also facilitating flexible synthesis development. In this paper, the syntheses of 24 known PET probes are adapted to this system to explore the possibility of using a single radiosynthesizer and hot cell for production of a diverse array of compounds with wide-ranging synthesis requirements, alongside synthesis development efforts. Most probes were produced with yields and synthesis times comparable to literature reports, and because hardware modification was unnecessary, it was convenient to frequently switch among probes based on demand. Although our facility supplies probes for preclinical imaging, the same workflow would be applicable in a clinical setting.

Introduction Endarterectomized human atherosclerotic plaques are a valuable basis for gene expression studies to disclose novel imaging biomarkers and therapeutic targets, such as the cannabinoid receptor type 2 (CB2). In this work, CB2 is expressed on activated immune cells, which are abundant in inflamed plaques. We evaluated the CB2-specific radiotracer [ 11 C]RS-016 for imaging vascular inflammation in human and mouse atherosclerotic lesions. Methods The differential gene expression of microscopically classified human carotid plaques was evaluated using quantitative polymerase chain reaction. In addition, CB2 expression levels in human plaques were investigated by in vitro autoradiography. As an appropriate animal model we used apolipoprotein E knockout mice (ApoE KO) with shear stress-induced atherosclerosis to evaluate CB2 levels in vivo. Positron emission tomography (PET) was performed with both the CB2 radioligand [ 11 C]RS-016 and the metabolic radiotracer [ 18 F]fluorodeoxyglucose ([ 18 F]FDG) at various time points. Retrospectively, carotids were dissected for histopathology and gene expression analysis. Results We identified 28 human genes differentially expressed in atherosclerotic plaques compared to normal arteries of which 12 were upregulated preferentially in vulnerable plaques. The latter group included members of matrix metalloproteinase family and the T-lymphocyte activation antigens CD80 and CD86. CB2 was upregulated by 2-fold in human atherosclerotic plaques correlating with CD68 expression levels. Specific in vitro binding of [ 11 C]RS-016 was predominantly observed to plaques. In vivo PET imaging of ApoE KO mice revealed accumulation of [ 11 C]RS-016 and [ 18 F]FDG in atherosclerotic plaques. Development of advanced plaques with elevated CB2 and CD68 levels were found in vitro in ApoE KO mice resembling human vulnerable plaques. Conclusion We identified human genes associated with plaque vulnerability, which potentially could serve as novel imaging or therapeutic targets. The CB2-specific radiotracer [ 11 C]RS-016 detected human plaques by in vitro autoradiography and accumulated in vivo in plaques of ApoE KO mice, however not exclusively in vulnerable plaques.

(18)F-clofarabine, a nucleotide purine analog, is a substrate for deoxycytidine kinase (dCK), a key enzyme in the deoxyribonucleoside salvage pathway. (18)F-clofarabine might be used to measure dCK expression and thus serve as a predictive biomarker for tumor responses to dCK-dependent prodrugs or small-molecule dCK inhibitors, respectively. As a prerequisite for clinical translation, we determined the human whole-body and organ dosimetry of (18)F-clofarabine. Methods: Five healthy volunteers were injected intravenously with 232.4 ± 1.5 MBq of (18)F-clofarabine. Immediately after tracer injection, a dynamic scan of the entire chest was acquired for 30 min. This was followed by 3 static whole-body scans at 45, 90, and 135 min after tracer injection. Regions of interest were drawn around multiple organs on the CT scan and copied to the PET scans. Organ activity was determined and absorbed dose was estimated with OLINDA/EXM software. Results: The urinary bladder (critical organ), liver, kidney, and spleen exhibited the highest uptake. For an activity of 250 MBq, the absorbed doses in the bladder, liver, kidney, and spleen were 58.5, 6.6, 6.3, and 4.3 mGy, respectively. The average effective dose coefficient was 5.1 mSv. Conclusion: Our results hint that (18)F-clofarabine can be used safely in humans to measure tissue dCK expression. Future studies will determine whether (18)F-clofarabine may serve as a predictive biomarker for responses to dCK-dependent prodrugs or small-molecule dCK inhibitors.

Targeting cancer-associated fibroblasts (CAFs) has become an attractive goal for diagnostic imaging and therapy because they can constitute as much as 90% of a tumor mass. The serine protease fibroblast activation protein (FAP) is overexpressed selectively in CAFs, drawing interest in FAP as a stromal target. The quinoline-based FAP inhibitor (FAPI) PET tracer (68)Ga-FAPI-04 has been previously shown to yield high tumor-to-background ratios (TBRs) in patients with various cancers. Recent developments toward an improved compound for therapeutic application have identified FAPI-46 as a promising agent because of an increased tumor retention time in comparison with FAPI-04. Here, we present a PET biodistribution and radiation dosimetry study of (68)Ga-FAPI-46 in cancer patients. Methods: Six patients with different cancers underwent serial (68)Ga-FAPI-46 PET/CT scans at 3 time points after radiotracer injection: 10 min, 1 h, and 3 h. The source organs consisted of the kidneys, bladder, liver, heart, spleen, bone marrow, uterus, and remainder of body. OLINDA/EXM software, version 1.1, was used to fit and integrate the kinetic organ activity data to yield total-body and organ time-integrated activity coefficients and residence times and, finally, organ-absorbed doses. SUVs and TBR were generated from the contoured tumor and source-organ volumes. Spheric volumes in muscle and blood pool were also obtained for TBR (tumor SUV(max)/organ SUV(mean)). Results: At all time points, average SUV(max) was highest in the liver. Tumor and organ SUV(mean) decreased over time, whereas TBRs in all organs but the uterus increased. The organs with the highest effective doses were bladder wall (2.41E−03 mSv/MBq), followed by ovaries (1.15E−03 mSv/MBq) and red marrow (8.49E−04 mSv/MBq). The average effective total-body dose was 7.80E−03 mSv/MBq. Conclusion: (68)Ga-FAPI-46 PET/CT has a favorable dosimetry profile, with an estimated whole-body dose of 5.3 mSv for an administration of 200 MBq (5.4 mCi) of (68)Ga-FAPI-46 (1.56 ± 0.26 mSv from the PET tracer and 3.7 mSv from 1 low-dose CT scan). The biodistribution study showed high TBRs increasing over time, suggesting high diagnostic performance and favorable tracer kinetics for potential therapeutic applications.

In light of the United States Food and Drug Administration (FDA) requirement of 21 CFR 212 current Good Manufacturing Practice (cGMP) for FDA-approved position emission tomography (PET) drugs, the University of California Los Angeles (UCLA) Biomedical Cyclotron (BMC) transformed from a pre-cGMP era academic cyclotron and radiochemistry facility to a current cGMP-compliant PET drug manufacturer. In this article, we share the financial and regulatory compliance aspects of the "transformation" required to develop a sustainable quality system to support the production of two PET drugs under Abbreviated New Drug Applications (ANDAs).

Biosynthesis of the pyrimidine nucleotide uridine monophosphate (UMP) is essential for cell proliferation and is achieved by the activity of convergent de novo and salvage metabolic pathways. Here we report the development and application of a cell-based metabolic modifier screening platform that leverages the redundancy in pyrimidine metabolism for the discovery of selective UMP biosynthesis modulators. In evaluating a library of protein kinase inhibitors, we identified multiple compounds that possess nucleotide metabolism-modifying activity. The JNK inhibitor JNK-IN-8 was found to potently inhibit nucleoside transport and engage ENT1. The PDK1 inhibitor OSU-03012 (also known as AR-12) and the RAF inhibitor TAK-632 were shown to inhibit the therapeutically-relevant enzyme dihydroorotate dehydrogenase (DHODH) and their affinities were unambiguously confirmed through in vitro assays and co-crystallization with human DHODH.

INTRODUCTION AND OBJECTIVES:This is a prospective single-center, single-arm, head-to-head phase 3 comparative study of paired 18F-fluciclovine (FACBC) and 68Ga-PSMA-11 (PSMA) PET/CT scans for local...

Background: National Comprehensive Cancer Network guidelines consider 18F-fluciclovine PET-CT for prostate cancer biochemical recurrence localisation after radical prostatectomy, whereas European Association of Urology guidelines recommend prostate-specific membrane antigen (PSMA) PET-CT. To the best of our knowledge, no prospective head-to-head comparison between these tests has been done so far. The aim of this study was to compare prospectively paired 18F-fluciclovine and PSMA PET-CT scans for localising biochemical recurrence of prostate cancer after radical prostatectomy in patients with low prostate-specific antigen (PSA) concentrations (

The trend to inform personalized molecular radiotherapy with molecular imaging diagnostics, a concept referred to as theranostics, has transformed the field of nuclear medicine in recent years. The development of theranostic pairs comprising somatostatin receptor (SSTR)-targeting nuclear imaging probes and therapeutic agents for the treatment of patients with neuroendocrine tumors (NETs) has been a driving force behind this development. With the Neuroendocrine Tumor Therapy (NETTER-1) phase 3 trial reporting encouraging results in the treatment of well-differentiated, metastatic midgut NETs, peptide radioligand therapy (RLT) with the 177Lu-labeled somatostatin analog (SSA) [177Lu]Lu-DOTA-TATE is now anticipated to become the standard of care. On the diagnostics side, the field is currently dominated by 68Ga-labeled SSAs for the molecular imaging of NETs with positron emission tomography-computed tomography (PET/CT). PET/CT imaging with SSAs such as [68Ga]Ga-DOTA-TATE, [68Ga]Ga-DOTA-TOC, and [68Ga]Ga-DOTA-NOC allows for NET staging with high accuracy and is used to qualify patients for RLT. Driven by the demand for PET/CT imaging of NETs, a commercial kit for the production of [68Ga]Ga-DOTA-TATE (NETSPOT) was approved by the U.S. Food and Drug Administration (FDA). The synthesis of 68Ga-labeled SSAs from a 68Ge/68Ga-generator is straightforward and allows for a decentralized production, but there are economic and logistic difficulties associated with these approaches that warrant the search for a viable, generator-independent alternative. The clinical introduction of an 18F-labeled SSTR-imaging probe can help mitigate the shortcomings of the generator-based synthesis approach, but despite extensive research efforts, none of the proposed 18F-labeled SSAs has been translated past prospective first-in-humans studies so far. Here, we review the current state of probe-development from a translational viewpoint and make a case for a clinically viable, 18F-labeled alternative to the current standard [68Ga]Ga-DOTA-TATE.

A cell-based metabolic modifier screening platform for the discovery of modulators of convergent pyrimidine nucleotide biosynthetic pathways was designed and implemented. In screening a library of protein kinase inhibitors, multiple compounds were shown to possess previously uncharacterized nucleotide metabolism-modifying activity. The JNK inhibitor JNK-IN-8 was found to be a potent inhibitor of nucleoside transport, a property which was confirmed using nucleoside-analog Positron Emission Tomography (PET) imaging in mice. The PDK1 inhibitor OSU-03012 (also known as AR-12) and the RAF inhibitor TAK-632 were shown to inhibit the therapeutically relevant enzyme dihydroorotate dehydrogenase (DHODH) and their affinities were unambiguously confirmed through in vitro assays and co-crystallization with human DHODH.

The development of new positron-emission tomography (PET) tracers is enabling researchers and clinicians to image an increasingly wide array of biological targets and processes. However, the increasing number of different tracers creates challenges for their production at radiopharmacies. While historically it has been practical to dedicate a custom-configured radiosynthesizer and hot cell for the repeated production of each individual tracer, it is becoming necessary to change this workflow. Recent commercial radiosynthesizers based on disposable cassettes/kits for each tracer simplify the production of multiple tracers with one set of equipment by eliminating the need for custom tracer-specific modifications. Furthermore, some of these radiosynthesizers enable the operator to develop and optimize their own synthesis protocols in addition to purchasing commercially-available kits. In this protocol, we describe the general procedure for how the manual synthesis of a new PET tracer can be automated on one of these radiosynthesizers and validated for the production of clinical-grade tracers. As an example, we use the ELIXYS radiosynthesizer, a flexible cassette-based radiochemistry tool that can support both PET tracer development efforts, as well as routine clinical probe manufacturing on the same system, to produce [18F]Clofarabine ([18F]CFA), a PET tracer to measure in vivo deoxycytidine kinase (dCK) enzyme activity. Translating a manual synthesis involves breaking down the synthetic protocol into basic radiochemistry processes that are then translated into intuitive chemistry "unit operations" supported by the synthesizer software. These operations can then rapidly be converted into an automated synthesis program by assembling them using the drag-and-drop interface. After basic testing, the synthesis and purification procedure may require optimization to achieve the desired yield and purity. Once the desired performance is achieved, a validation of the synthesis is carried out to determine its suitability for the production of the radiotracer for clinical use.

Prostate-specific membrane antigen (PSMA)–targeted radioligand therapy (RLT) is effective against prostate cancer (PCa), but all patients relapse eventually. Poor understanding of the underlying resistance mechanisms represents a key barrier to development of more effective RLT. We investigate the proteome and phosphoproteome in a mouse model of PCa to identify signaling adaptations triggered by PSMA RLT. Methods: Therapeutic efficacy of PSMA RLT was assessed by tumor volume measurements, time to progression, and survival in C4-2 or C4-2 TP53(−/−) tumor-bearing nonobese diabetic scid γ-mice. Two days after RLT, the proteome and phosphoproteome were analyzed by mass spectrometry. Results: PSMA RLT significantly improved disease control in a dose-dependent manner. Proteome and phosphoproteome datasets revealed activation of genotoxic stress response pathways, including deregulation of DNA damage/replication stress response, TP53, androgen receptor, phosphatidylinositol-3-kinase/AKT, and MYC signaling. C4-2 TP53(−/−) tumors were less sensitive to PSMA RLT than were parental counterparts, supporting a role for TP53 in mediating RLT responsiveness. Conclusion: We identified signaling alterations that may mediate resistance to PSMA RLT in a PCa mouse model. Our data enable the development of rational synergistic RLT-combination therapies to improve outcomes for PCa patients.

The cannabinoid receptor type 2 (CB2) is part of the endocannabinoid system and has gained growing attention in recent years because of its important role in neuroinflammatory/neurodegenerative diseases. Recently, we reported on a carbon-11 labeled 4-oxo-quinoline derivative, designated RS-016, as a promising radiotracer for imaging CB2 using PET. In this study, three novel fluorinated analogs of RS-016 were designed, synthesized, and pharmacologically evaluated. The results of our efforts led to the identification of N-(1-adamantyl)-1-(2-(2-fluoroethoxy)ethyl)-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxamide (RS-126) as the most potent candidate for evaluation as a CB2 PET ligand. [(18) F]RS-126 was obtained in ≥ 99% radiochemical purity with an average specific radioactivity of 98 GBq/μmol at the end of the radiosynthesis. [(18) F]RS-126 showed a logD7.4 value of 1.99 and is stable in vitro in rat and human plasma over 120 min, whereas 55% intact parent compound was found in vivo in rat blood plasma at 10 min post injection. In vitro autoradiographic studies with CB2-positive rat spleen tissue revealed high and blockable binding which was confirmed in in vivo displacement experiments with rats by dynamic PET imaging. Ex vivo biodistribution studies confirmed accumulation of [(18) F]RS-126 in rat spleen with a specificity of 79% under blocking conditions. The moderate elevated CB2 levels in LPS-treated mice brain did not permit the detection of CB2 by [(18) F]RS-126 using PET imaging. In summary, [(18) F]RS-126 demonstrated high specificity toward CB2 receptor in vitro and in vivo and is a promising radioligand for imaging CB2 receptor expression. Cannabinoid receptor type 2 (CB2) is an interesting target for PET imaging. Specific binding of [(18) F]RS-126 in CB2-positive spleen tissue (white arrow head) was confirmed in in vivo displacement experiments with rats. Time activity curve of [(18) F]RS-126 in the spleen after the addition of GW405833 (CB2 specific ligand, green) demonstrates faster radiotracer elimination (blue) compared to the tracer only (red).

Radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-targeting ligands is effective in ~50% of patients with advanced prostate cancer (PC). Causes for RLT failure are not well understood. The prevalent PSMA heterogeneity in PC might contribute to RLT failure. Here we investigate the relationship between RLT efficacy and PSMA levels per cell, and PSMA heterogeneity. PC cells expressing different levels of PSMA (RM1-PSMA low, medium, high, or RM1-YFP that do not express PSMA), or a mix of PSMA− and PSMA+ cells (RM1-YFP/ RM1-PSMA-high; PC3/ PC3-PIP) at various ratios were subcutaneously injected into NSG mice. Mice were treated with 177Lu- or 225Ac-PSMA617 (RLT) and tumor growth was monitored. In a subset of mice, radioligand uptake (γ-counting), DNA damage and PSMA expression (anti-53BP1 and -PSMA immunohistochemistry, respectively) were quantified in tumors resected 2 days after RLT. Increasing PSMA levels and fractions of PSMA+ cells improved RLT efficacy in both, the RM1 and PC3 model. PSMA expression correlated with radioligand uptake into the tumor and the degree of DNA damage and. Treatment with 225Ac-PSMA617 (vs. 177Lu-PSMA617) improved RLT outcomes and tended to enhance the differences in therapeutic efficacy between experimental groups. Taken together, we demonstrate in mouse models of PC that optimal anti-tumor efficacy of RLT hinges on homogenously high target expression. Although PSMA-RLT is effective even in tumors with low PSMA levels or with a small number of PSMA+ cells, low or heterogeneous PSMA expression might result in undertreatment and selection of treatment resistant clones. Systematic assessment of intra- and inter-lesion PSMA heterogeneity is currently not feasible clinically; however, this issue might be addressed by individual patient dosimetry to optimize safely delivered maximal tumor doses. Clinical studies designed to determine intra- and inter-lesion PSMA heterogeneity and to optimize PSMA-RLT for each patient are highly warranted. Citation Format: Katharina Lueckerath, Kyle Current, Catherine Meyer, Clara Magyar, Christine E. Mona, Joel Almajano, Roger Slavik, Andreea D. Stuparu, Chloe Cheng, David Dawson, Caius Radu, Johannes Czernin. Heterogeneous tumor PSMA expression represents a resistance mechanism to PSMA-targeted radioligand therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5345.

292 Background: Prostate-specific membrane antigen ligand positron emission tomography (PSMA PET) induced management changes in up to every second patient in smaller clinical trials. We aim to determine the impact of 68Ga-PSMA-11 PET/CT on management of biochemically recurrent prostate cancer in a large prospective cohort. Methods: We report management changes following PSMA PET, a secondary endpoint of a prospective multicenter trial in men with prostate cancer biochemical recurrence (NCT02940262 and NCT03353740). Pre-PET, Post-PET and Post-Treatment Questionnaires were sent to referring physicians recording working clinical summaries, intended and implemented therapeutic and diagnostic management. Results: Intended management change occurred in 260/382 (68%) patients. Intended change was considered major in 176/382 (46%) patients. Management pathway aligned with PET findings, i.e. change towards local/focal therapy for locoregional disease (54/126 patients, 44%) and towards systemic therapy or combination approaches for metastatic disease (106/153 patients, 69%). Intended management was implemented in 160/206 (78%) patients. Perceived site of disease was unknown in 259/382 (68%) patients before and 111/382 (29%) patients after PSMA PET. A total of 150 intended diagnostic tests, mostly CT (n=43, 29%) and bone Scans/NaF-PET (n=52, 35%), were prevented by PSMA PET. A total of 73 tests, mostly biopsies (n=44, 60%) requested by the study protocol, were triggered. Conclusions: Disease localization by PSMA PET translated into management changes in more than half of patients with biochemical recurrence of prostate cancer. More than twice as many diagnostic tests were prevented than triggered following PET. Clinical trial information: NCT02940262 and NCT03353740.

BackgroundProstate-specific membrane antigen (PSMA)-directed radioligand therapy (RLT) is a promising yet not curative approach in castration-resistant (CR) prostate cancer (PC). Rational combination therapies may improve treatment efficacy. Here, we explored the effect of androgen receptor blockade (ARB) on PSMA expression visualized by PET and its potential additive effect when combined with 177Lu-PSMA RLT in a mouse model of prostate cancer.MethodsMice bearing human CRPC (C4-2 cells) xenografts were treated with 10mg/kg enzalutamide (ENZ), with 50mg/kg bicalutamide (BIC), or vehicle (control) for 21days. PSMA expression was evaluated by 68Ga-PSMA11 PET/CT and quantified by flow cytometry of tumor fine needle aspirations before treatment and on days 23, 29, 34, and 39 post-therapy induction. For the RLT combination approach, mice bearing C4-2 tumors were treated with 10mg/kg ENZ or vehicle for 21days before receiving either 15MBq (84GBq/μmol) 177Lu-PSMA617 or vehicle. DNA damage was assessed as phospho-γH2A.X foci in tumor biopsies. Reduction of tumor volume on CT and survival were used as study endpoints.ResultsTumor growth was delayed by ARB while 68Ga-PSMA11 uptake increased up to 2.3-fold over time when compared to controls. ABR-induced upregulation of PSMA expression was confirmed by flow cytometry. Phospho-γH2A.X levels increased 1.8- and 3.4-fold at 48h in response to single treatment ENZ or RLT and ENZ+RLT, respectively. Despite significantly greater DNA damage and persistent increase of PSMA expression at the time of RLT, no additional tumor growth retardation was observed in the ENZ+RLT group (vs. RLT only, p = 0.372 at day 81). Median survival did not improve significantly when ENZ was combined with RLT.ConclusionARB-mediated increases in PSMA expression in PC xenografts were evident by 68Ga-PSMA11 PET imaging and flow cytometry. 177Lu-PSMA617 effectively decreased C4-2 tumor size. However, while pre-treatment with ARB increased DNA damage significantly, it did not result in synergistic effects when combined with RLT.

Background Peptides labeled with positron-emitting isotopes are emerging as a versatile class of compounds for the development of highly specific, targeted imaging agents for diagnostic imaging via positron-emission tomography (PET) and for precision medicine via theranostic applications. Despite the success of peptides labeled with gallium-68 (for imaging) or lutetium-177 (for therapy) in the clinical management of patients with neuroendocrine tumors or prostate cancer, there are significant advantages of using fluorine-18 for imaging. Recent developments have greatly simplified such labeling: in particular, labeling of organotrifluoroborates via isotopic exchange can readily be performed in a single-step under aqueous conditions and without the need for HPLC purification. Though an automated synthesis has not yet been explored, microfluidic approaches have emerged for 18F-labeling with high speed, minimal reagents, and high molar activity compared to conventional approaches. As a proof-of-concept, we performed microfluidic labeling of an octreotate analog ([18F]AMBF3-TATE), a promising 18F-labeled analog that could compete with [68Ga]Ga-DOTATATE with the advantage of providing a greater number of patient doses per batch produced. Methods Both [18F]AMBF3-TATE and [68Ga]Ga-DOTATATE were labeled, the former by microscale methods adapted from manual labeling, and were imaged in mice bearing human SSTR2-overexpressing, rat SSTR2 wildtype, and SSTR2-negative xenografts. Furthermore, a dosimetry analysis was performed for [18F]AMBF3-TATE. Results The micro-synthesis exhibited highly-repeatable performance with radiochemical conversion of 50 ± 6% (n = 15), overall decay-corrected radiochemical yield of 16 ± 1% (n = 5) in ~40 min, radiochemical purity >99%, and high molar activity. Preclinical imaging with [18F]AMBF3-TATE in SSTR2 tumor models correlated well with [68Ga]Ga-DOTATATE. The favorable biodistribution, with the highest tracer accumulation in the bladder followed distantly by gastrointestinal tissues, resulted in 1.26 × 10−2 mSv/MBq maximal estimated effective dose in human, a value lower than that reported for current clinical 18F- and 68Ga-labeled compounds. Conclusions The combination of novel chemical approaches to 18F-labeling and microdroplet radiochemistry have the potential to serve as a platform for greatly simplified development and production of 18F-labeled peptide tracers. Favorable preclinical imaging and dosimetry of [18F]AMBF3-TATE, combined with a convenient synthesis, validate this assertion and suggest strong potential for clinical translation.

BACKGROUND: Peptides labeled with positron-emitting isotopes are emerging as a versatile class of compounds for the development of highly specific, targeted imaging agents for diagnostic imaging via positron-emission tomography (PET) and for precision medicine via theranostic applications. Despite the success of peptides labeled with gallium-68 (for imaging) or lutetium-177 (for therapy) in the clinical management of patients with neuroendocrine tumors or prostate cancer, there are significant advantages of using fluorine-18 for imaging. Recent developments have greatly simplified such labeling: in particular, labeling of organotrifluoroborates via isotopic exchange can readily be performed in a single-step under aqueous conditions and without the need for HPLC purification. Though an automated synthesis has not yet been explored, microfluidic approaches have emerged for (18)F-labeling with high speed, minimal reagents, and high molar activity compared to conventional approaches. As a proof-of-concept, we performed microfluidic labeling of an octreotate analog ([(18)F]AMBF(3)-TATE), a promising (18)F-labeled analog that could compete with [(68)Ga]Ga-DOTATATE with the advantage of providing a greater number of patient doses per batch produced. METHODS: Both [(18)F]AMBF(3)-TATE and [(68)Ga]Ga-DOTATATE were labeled, the former by microscale methods adapted from manual labeling, and were imaged in mice bearing human SSTR2-overexpressing, rat SSTR2 wildtype, and SSTR2-negative xenografts. Furthermore, a dosimetry analysis was performed for [(18)F]AMBF(3)-TATE. RESULTS: The micro-synthesis exhibited highly-repeatable performance with radiochemical conversion of 50±6% (n=15), overall decay-corrected radiochemical yield of 16±1% (n=5) in ~40 min, radiochemical purity >99%, and high molar activity. Preclinical imaging with [(18)F]AMBF(3)-TATE in SSTR2 tumor models correlated well with [(68)Ga]Ga-DOTATATE. The favorable biodistribution, with highest tracer accumulation in the bladder followed distantly by gastrointestinal tissues, resulted in 1.26×10(−2) mSv/MBq maximal estimated effective dose in human, a value lower than that reported for current clinical (18)F- and (68)Ga-labeled compounds. CONCLUSIONS: The combination of novel chemical approaches to (18)F-labeling and microdroplet radiochemistry have the potential to serve as a platform for greatly simplified development and production of (18)F-labeled peptide tracers. Favorable preclinical imaging and dosimetry of [(18)F]AMBF(3)-TATE, combined with a convenient synthesis, validate this assertion and suggest strong potential for clinical translation.

In this prospective survey of referring physicians, we investigated whether and how 68Ga-labeled prostate-specific membrane antigen 11 (68Ga-PSMA-11) PET/CT affects the implemented management of prostate cancer patients with biochemical recurrence (BCR). Methods: We conducted a prospective survey of physicians (NCT02940262) who referred 161 patients with prostate cancer BCR (median prostate-specific antigen value, 1.7 ng/mL; range, 0.05-202 ng/mL). Referring physicians completed one questionnaire before the scan to indicate the treatment plan without 68Ga-PSMA-11 PET/CT information (Q1; n = 101), one immediately after the scan to denote intended management changes (Q2; n = 101), and one 3-6 mo later to document the final implemented management (Q3; n = 56). The implemented management was also obtained via electronic chart review or patient contact (n = 45). Results: A complete documented management strategy (Q1 + Q2 + implemented management) was available for 101 of 161 patients (63%). Seventy-six of these (75%) had a positive 68Ga-PSMA-11 PET/CT result. The implemented management differed from the prescan intended management (Q1) in 54 of 101 patients (53%). The postscan intended management (Q2) differed from the prescan intended management (Q1) in 62 of 101 patients (61%); however, these intended changes were not implemented in 29 of 62 patients (47%). Pelvic nodal and extrapelvic metastatic disease on 68Ga-PSMA-11 PET/CT (PSMA T0N1M0 and PSMA T0N1M1 patterns) was significantly associated with implemented management changes (P = 0.001 and 0.05). Conclusion: Information from 68Ga-PSMA-11 PET/CT brings about management changes in more than 50% of prostate cancer patients with BCR (54/101; 53%). However, intended management changes early after 68Ga-PSMA-11 PET/CT frequently differ from implemented management changes.

To improve prostate-specific membrane antigen (PSMA)–targeted theranostic approaches, robust murine models of prostate cancer are needed. However, important characteristics of preclinical PSMA imaging—that is, the reproducibility of the imaging signal and the relationship between quantitative cell surface PSMA expression and lesion detectability with small-animal PET/CT—have not been defined yet. Methods: Murine prostate cancer RM1 sublines (ras myc transformed cells of C57BL/6 prostate origin) expressing varying levels of human PSMA were injected into the shoulder of C57BL/6 mice on day 0. (68)Ga-PSMA11 PET/CT was performed on days 7 and 8 and interpreted by 2 masked readers to determine interday and interreader reproducibility. PSMA expression was quantified on days 7 and 8 by flow cytometry of fine-needle aspiration tumor biopsy samples. Cell surface PSMA expression was correlated with PET signal. The threshold for PET positivity was based on the clinical Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria. Results: The maximum and average percentages of injected (68)Ga-PSMA11 activity per gram of tissue (%IA/g) correlated nearly perfectly as determined by 2 independent readers and on 2 separate days (intraclass correlation coefficient, 1.00/0.89 and 0.95/0.88, respectively). The number of PSMA molecules per cell increased from the RM1-yellow fluorescent protein subline (PSMA(−); 2,000/cell) to the RM1-low subline (PSMA(+); 17,000/cell), the RM1-medium subline (PSMA(++); 22,000/cell), and the RM1-PGLS subline (PSMA-positive, green fluorescent protein–positive, and luciferase-positive; PSMA(+++); 45,000/cell). Expression levels correlated with the visual positivity rate on (68)Ga-PSMA11 PET and with the PSMA PET %IA/g. The PSMA threshold for PET positivity was approximately 20,000 per cell. Signal correlation was close at lower PSMA levels (RM1-low to RM1-medium; 10–23 %IA/g) but was lost at higher PSMA levels (RM1-medium to RM1-PGLS; 23–27 %IA/g). Conclusion: The in vivo relationship between (68)Ga-PSMA11 PET/CT and PSMA expression level in a murine model of prostate cancer was robust for lower cell surface PSMA expression levels (≤22,000/cell). Thus, preclinical (68)Ga-PSMA11 PET/CT can be used as an imaging biomarker to test PSMA-targeted interventions in murine models.

As part of our efforts to develop CB2 PET imaging agents, we investigated 2,5,6-substituted pyridines as a novel class of potential CB2 PET ligands. A total of 21 novel compounds were designed, synthesized, and evaluated for their potency and binding properties toward human and rodent CB1 and CB2. The most promising ligand 6a was radiolabeled with carbon-11 to yield 16 ([(11)C]RSR-056). Specific binding of 16 to CB2-positive spleen tissue of rats and mice was demonstrated by in vitro autogadiography and verified in vivo in PET and biodistribution experiments. Furthermore, 16 was evaluated in a lipopolysaccharid (LPS) induced murine model of neuroinflammation. Brain radioactivity was strikingly higher in the LPS-treated mice than the control mice. Compound 16 is a promising radiotracer for imaging CB2 in rodents. It might serve as a tool for the investigation of CB2 receptor expression levels in healthy tissues and different neuroinflammatory disorders in humans.

Our goal is to develop a highly specific and selective PET brain tracer for imaging CB2 expression in patients with neuroinflammatory diseases. Based on our previous findings on a carbon-11 labeled 4-oxo-quinoline structure, designated KD2, further structural optimizations were performed, which led to the discovery of N-(1-adamantyl)-1-(2-ethoxyethyl)-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxamide (RS-016). Compared to KD2, RS-016 exhibits a higher binding affinity towards CB2 (Ki = 0.7 nM) with a selectivity over CB1 of >10,000 and lower lipophilicity (logD7.4 = 2.78). [11C]RS-016 was obtained in ≥99% radiochemical purity and up to 850 GBq/μmol specific radioactivity at the end of synthesis. In vitro autoradiography on rodent spleen tissue showed high specific binding to CB2. [11C]RS-016 was stable in vitro in rodent and human plasma over 40 min, whereas 47% intact compound was found in vivo in rat blood plasma 20 min post injection (p.i.). High specific binding to CB2 was observed in murine spleen tissues and postmortem ALS patient spinal cord tissues in vitro autoradiography, ex vivo biodistribution data confirmed the high and specific uptake of [11C]RS-016 in spleen region in rats. In vivo specificity of [11C]RS-016 could also be shown in brain by PET imaging using a murine neuroinflammation model, which has higher CB2 receptor expression level in the brain induced by lipopolysaccharide (LPS) application.

Clinical (177)Lu-PSMA-617 radioligand therapy (RLT) is applied in advanced-stage prostate cancer. However, to the best of our knowledge murine models to study the biologic effects of various activity levels have not been established. The aim of this study was to optimize specific and total activity for (177)Lu-PSMA-617 RLT in a syngeneic model of murine prostate cancer. Methods: Murine-reconstituted, oncogene-driven prostate cancer cells (0.1 × 10(6)) (RM1), transduced to express human prostate-specific membrane antigen (PSMA), were injected into the left flank of C57Bl6 immunocompetent mice. RLT was performed by administering a single tail vein injection of (177)Lu-PSMA-617 at different formulations for specific (60 MBq at high, 62 MBq/nmol; intermediate, 31 MBq/nmol; or low 15 MBq/nmol specific activity) or total activity (30, 60, or 120 MBq). Organ distribution was determined by ex vivo γ-counter measurement. DNA double-strand breaks were measured using anti–gamma-H2A.X (phospho S139) immunohistochemistry. Efficacy was assessed by serial CT tumor volumetry and (18)F-FDG PET metabolic volume. Toxicity was evaluated 4 wk after the start of RLT. Results: Mean tumor-to-kidney ratios ± SEM were 19 ± 5, 10 ± 5, and 2 ± 0 for high, intermediate, and low (each n = 3) specific activity, respectively. Four of 6 (67%) mice treated with intermediate or high specific activity and none of 6 (0%) mice treated with low specific activity or formulation demonstrated significant DNA double-strand breaks (≥5% γ-H2A.X–positive cells). High when compared with intermediate or low specific activity resulted in a lower mean ± SEM tumor load by histopathology (vital tissue, 4 ± 2 vs. 8 ± 3 mm(2); n = 3 vs. 6), day-4 (18)F-FDG PET (metabolic volume, 87 ± 23 vs. 118 ± 14 mm(3); n = 6 vs. 12), and day-7 CT (volume, 323 ± 122 vs. 590 ± 46 mm(3); n = 3 vs. 6; P = 0.039). (177)Lu-PSMA-617 (120 MBq) with high specific activity induced superior tumor growth inhibition (P = 0.021, n = 5/group) without subacute hematologic toxicity (n = 3/group). Conclusion: (177)Lu-PSMA-617 (120 MBq) and high specific activity resulted in the highest efficacy in a syngeneic model of murine prostate cancer. The model will be useful for studying the effects of PSMA-directed RLT combined with potentially synergistic pharmacologic approaches.

In this prospective referring-physician–based survey, we investigated the definite clinical impact of 68Ga-DOTATATE PET/CT on managing patients with neuroendocrine tumors (NETs). Methods: We prospectively studied 130 patients with 68Ga-DOTATATE PET/CT referred for initial or subsequent management decisions (NCT02174679). Referring physicians completed one questionnaire before the scan (Q1) to indicate the treatment plan without PET/CT information, one immediately after review of the imaging report to denote intended management changes (Q2), and one 6 mo later (Q3) to verify whether intended changes were in fact implemented. To further validate the Q3 responses, a systematic electronic chart review was conducted. Results: All 3 questionnaires were completed by referring physicians for 96 of 130 patients (74%). 68Ga-DOTATATE PET/CT resulted in intended management changes (Q2) in 48 of 96 patients (50%). These changes were finally implemented (Q3) in 36 of 48 patients (75%). Q3 responses were confirmed in all patients with an available electronic chart (36/96; 38%). Conclusion: This prospective study confirmed a significant impact of 68Ga-DOTATATE PET/CT on the intended management of patients with NETs (50% of changes) and notably demonstrated a high implementation rate (75%) of these intended management changes.