Safety and Efficacy of Radiosynoviorthesis: A Prospective Canadian Multicenter Study.

Radiosynoviorthesis is approved in several European countries and the United States to treat refractory synovitis in many inflammatory joint diseases, such as rheumatoid arthritis, spondyloarthropathies, and other arthritic joint diseases. No radiopharmaceuticals for radiosynoviorthesis are currently approved in Canada. The aim of this Health Canada-approved trial was to demonstrate the safety and efficacy of radiosynoviorthesis. Methods: Between July 2012 and November 2017, we conducted a multicenter, prospective, interventional Canadian trial. Patients (n = 360) with synovitis refractory to standard treatments after failing 2 intraarticular glucocorticoid injections were included. They were followed up at 3, 6, and 12 mo. Outcome measures included adverse events (AEs) and clinical signs of synovitis (pain, swelling, and joint effusion) measured with the Health Assessment Questionnaire Disability Index, the Disease Activity Score, and the Visual Analog Scale. Results: In total, 392 joints were treated, including those reinjected after 6 mo (n = 34). Of these, 83.4% (327/392) were injected with [90Y]Y-citrate for the knees and 9.9% (39/392) with [186Re]Re-sulfide for medium-sized joints. Of the joints treated, 82.7% (324/392) were knees. Fifty-five AEs, most of them of mild grade, occurred and resolved without sequelae and were not life-threatening. The incidence of radiosynoviorthesis-related AEs was 9.4% (34/360). The proportion of patients showing an improvement in synovitis symptoms after radiosynoviorthesis was significant at 3 mo and was maintained up to 12 mo (P < 0.001). Conclusion: This study confirmed the safety of radiosynoviorthesis in the treatment of patients with synovitis refractory to standard treatments. There is evidence of sustained clinical efficacy at 12 mo, suggesting that radiosynoviorthesis is an effective treatment for improving synovitis symptoms.

18F-4FMFES and 18F-FDG PET/CT in Estrogen Receptor-Positive Endometrial Carcinomas: Preliminary Report.

This article reports the preliminary results of a phase II clinical trial investigating the use of the estrogen receptor (ER)-targeting PET tracer 4-fluoro-11ß-methoxy-16α-18F-fluoroestradiol (18F-4FMFES) and 18F-FDG PET in endometrial cancers. In parallel, noninvasive interventions were attempted to slow progression of 18F-4FMFES metabolites in the intestines to reduce abdominal background uptake. Methods: In an ongoing study, 25 patients who received prior pathologic confirmation of an ER-positive endometrial cancer or endometrial intraepithelial neoplasia agreed to participate in the ongoing clinical trial. Patients were scheduled for 18F-FDG and 18F-4FMFES PET/CT imaging in random order and within 2 wk. Patients were administered either 4 mg of loperamide orally before 18F-4FMFES tracer injection or repeated intravenous injection of 20 mg of hyoscine N-butylbromide during 18F-4FMFES PET/CT. Regions of interest covering the whole abdomen and excluding the liver, bladder, and uterus were drawn for the 18F-4FMFES PET images, and an SUV threshold of more than 4 was applied. The volume of the resulting region was compared between the different interventions to estimate the extent of the intestinal background uptake. Results: Repeated injection of hyoscine N-butylbromide substantially reduced the intestinal background volume, whereas loperamide had a significant but moderate effect. 18F-4FMFES tumor SUVmax ranged from 3.0 to 14.4 (9.4 ± 3.2), whereas 18F-FDG SUVmax ranged from 0 to 22.0 (7.5 ± 5.1). Tumor-to-background ratio was significantly higher for 18F-4FMFES (16.4 ± 5.4) than for 18F-FDG (7.4 ± 4.6). Significant differences were observed between grade 1 and higher-grade tumors concerning 18F-4FMFES uptake and contrast, 18F-FDG uptake, and the 18F-FDG/18F-4FMFES uptake ratio. Conclusion: It is possible to improve 18F-4FMFES abdominal background using hyoscine N-butylbromide. Both 18F-FDG and 18F-4FMFES PET are suitable for detection of ER-positive endometrial cancers, although 18F-4FMFES yielded a better tumor contrast than did 18F-FDG.

Cross-Species Physiological Assessment of Brain Estrogen Receptor Expression Using 18F-FES and 18F-4FMFES PET Imaging.

PURPOSE: A retrospective analysis was performed of preclinical and clinical data acquired during the evaluation of the estrogen receptor (ER) PET tracer 4-fluoro-11ß-methoxy-16α-[18F]-fluoroestradiol (4FMFES) and its comparison with 16α-[18F]-fluoroestradiol (FES) in mice, rats, and humans with a focus on the brain uptake. PROCEDURES: Breast cancer tumor-bearing female BALB/c mice from a previous study and female Sprague-Dawley rats (control and ovariectomized) were imaged by 4FMFES or FES-PET imaging. Immediately after, low-dose CT was performed in the same bed position. Semi-quantitative analysis was conducted to extract %ID/g data. Small cohorts of mice and rats were imaged with 4FMFES in an ultra-high-resolution small animal PET scanner prototype (LabPET II). Rat brains were dissected and imaged separately with both PET and autoradiography. In parallel, 31 breast cancer patients were enrolled in a clinical phase II study to compare 4FMFES with FES for oncological assessment. Since the head was included in the field of view, brain uptake of discernable foci was measured and reported as SUVMax. RESULTS: Regardless of the species studied, 4FMFES and FES uptake were relatively uniform in most regions of the brain, except for bilateral foci at the base of the skull, at the midsection of the brain. Anatomical localization of the PET signal using CT image fusion indicates that the signal origins from the pituitary in all studied species. 4FMFES yielded lower pituitary uptake than FES in patients, but an inverse trend was observed in rodents. 4FMFES pituitary contrast was higher than FES in all assessed groups. High-resolution small animal imaging of the brain of rats and mice revealed a supplemental signal anterior to the pituitary, which is likely to be the medial preoptic area. Dissection data further confirmed those findings and revealed additional signals corresponding to the arcuate and ventromedial nuclei, along with the medial and cortical amygdala. CONCLUSION: 4FMFES allowed visualization of ER expression in the pituitary in humans and two different rodent species with better contrast than FES. Improvement in clinical spatial resolution might allow visualization and analysis of other ER-rich brain areas in humans. Further work is now possible to link 4FMFES pituitary uptake to cognitive functions.

A preclinical PET dual-tracer imaging protocol for ER and HER2 phenotyping in breast cancer xenografts.

BACKGROUND: Nuclear medicine is on the constant search of precision radiopharmaceutical approaches to improve patient management. Although discordant expression of the estrogen receptor (ER) and the human epidermal growth factor receptor 2 (HER2) in breast cancer is a known dilemma for appropriate patient management, traditional tumor sampling is often difficult or impractical. While 2-deoxy-2[18F]fluoro-D-glucose (18F-FDG)-positron emission tomography (PET) is an option to detect subclinical metastases, it does not provide phenotype information. Radiolabeled antibodies are able to specifically target expressed cell surface receptors. However, their long circulating half-lives (days) require labeling with long-lived isotopes, such as 89Zr, in order to allow sufficient time for tracer clearance from the blood compartment and to accumulate adequately in target tumors and, thus, generate high-quality PET images. The aim of this study was to develop a dual-tracer PET imaging approach consisting of a fast-clearing small molecule and a slow-clearing antibody. This approach was evaluated in a model consisting of mice harboring separate breast cancer xenografts with either an ER+/HER2- or ER-/HER2+ phenotype, comparable to human metastatic disease with intertumor heterogeneity. Lastly, the aim of our study was to determine the feasibility of specifically identifying these two important phenotypes in an acceptable time window. METHODS: Female nude mice were subcutaneously implanted on opposite shoulders with the ER+/HER2- and ER-/HER2+ MCF-7 and JIMT-1 tumor cell lines, respectively. A second model was developed consisting of mice implanted orthotopically with either MCF-7 or JIMT-1 cells. Pharmacokinetic analysis, serial PET imaging, and biodistribution were first performed for [89Zr]Zr-DFO-trastuzumab (89Zr-T) up to 8 days post-injection (p.i.) in JIMT-1 bearing mice. Region-of-interest (ROI) and biodistribution-derived uptake (% injected-activity/gram of tissue [%IA/g]) values and tumor-to-background ratios were obtained. Results were compared in order to validate ROI and identify early time points that provided high contrast tumor images. For the dual-tracer approach, cohorts of tumor-bearing mice were then subjected to sequential tracer PET imaging. On day 1, mice were administered 4-fluoro-11ß-methoxy-16α-[18F]-fluoroestradiol (4FMFES) which targets ER and imaged 45 min p.i. This was immediately followed by the injection of 89Zr-T. Mice were then imaged on day 3 or day 7. ROI analysis was performed, and uptake was calculated in tumors and selected healthy organs for all radiotracers. Quality of tumor targeting for all tracers was evaluated by tumor contrast visualization, tumor and normal tissue uptake, and tumor-to-background ratios. RESULTS: 89Zr-T provided sufficiently high tumor and low background uptake values that furnished high contrast tumor images by 48 h p.i. For the dual-tracer approach, 4FMFES provided tumor uptake values that were significantly increased in MCF-7 tumors. When 89Zr-T-PET was combined with 18F-4FMFES-PET, the entire dual-tracer sequential-imaging procedure provided specific high-quality contrast images of ER+/HER2- MCF-7 and ER-/HER2+ JIMT-1 tumors for 4FMFES and 89Zr-T, respectively, as short as 72 h from start to finish. CONCLUSIONS: This protocol can provide high contrast images of tumors expressing ER or HER2 within 3 days from injection of 4FMFES to final scan of 89Zr-T and, hence, provides a basis for future dual-tracer combinations that include antibodies.

Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting.

Antibody-conjugates (ACs) modified with virus-derived peptides are a potentially powerful class of tumor cell delivery agents for molecular payloads used in cancer treatment and imaging due to increased cellular accumulation over current ACs. During early AC in vitro development, fluorescence techniques and radioimmunoassays are sufficient for determining intracellular localization, accumulation efficiency, and target cell specificity. Currently, there is no consensus on standardized methods for preparing cells for evaluating AC intracellular accumulation and localization. The initial testing of ACs modified with virus-derived peptides is critical especially if several candidates have been constructed. Determining intracellular accumulation by fluorescence can be affected by background signal from ACs at the cell surface and complicate the interpretation of accumulation. For radioimmunoassays, typically treated cells are fractionated and the radioactivity in different cell compartments measured. However, cell lysis varies from cell to cell and often nuclear and cytoplasmic compartments are not adequately isolated. This can produce misleading data on payload delivery properties. The intravenous injection of radiolabeled virus-derived peptide-modified ACs in tumor bearing mice followed by radionuclide imaging is a powerful method for determining tumor targeting and payload delivery properties at the in vivo phase of development. However, this is a relatively recent advancement and few groups have evaluated virus-derived peptide-modified ACs in this manner. We describe the processing of treated cells to more accurately evaluate virus-derived peptide-modified AC accumulation when using confocal microscopy and radioimmunoassays. Specifically, a method for trypsinizing cells to remove cell surface bound ACs. We also provide a method for improving cellular fractionation. Lastly, this protocol provides an in vivo method using positron emission tomography (PET) for evaluating initial tumor targeting properties in tumor-bearing mice. We use the radioisotope 64Cu (t1/2 = 12.7 h) as an example payload in this protocol.

NLS-Cholic Acid Conjugation to IL-5Rα-Specific Antibody Improves Cellular Accumulation and In Vivo Tumor-Targeting Properties in a Bladder Cancer Model.

Receptor-mediated internalization followed by trafficking and degradation of antibody-conjugates (ACs) via the endosomal-lysosomal pathway is the major mechanism for delivering molecular payloads inside target tumor cells. Although a mainstay for delivering payloads with clinically approved ACs in cancer treatment and imaging, tumor cells are often able to decrease intracellular payload concentrations and thereby reduce the effectiveness of the desired application. Thus, increasing payload intracellular accumulation has become a focus of attention for designing next-generation ACs. We developed a composite compound (ChAcNLS) that enables ACs to escape endosome entrapment and route to the nucleus resulting in the increased intracellular accumulation as an interleukin-5 receptor α-subunit (IL-5Rα)-targeted agent for muscle invasive bladder cancer (MIBC). We constructed 64Cu-A14-ChAcNLS, 64Cu-A14-NLS, and 64Cu-A14 and evaluated their performance by employing mechanistic studies for endosome escape coupled to nuclear routing and determining whether this delivery system results in improved 64Cu cellular accumulation. ACs consisting of ∼20 ChAcNLS or NLS moieties per 64Cu-A14 were prepared in good yield, high monomer content, and maintaining high affinity for IL-5Rα. Confocal microscopy analysis demonstrated ChAcNLS mediated efficient endosome escape and nuclear localization. 64Cu-A14-ChAcNLS increased 64Cu cellular accumulation in HT-1376 and HT-B9 cells relative to 64Cu-A14 and 64Cu-A14-NLS. In addition, we tested 64Cu-A14-ChAcNLS in vivo to evaluate its tissue distribution properties and, ultimately, tumor uptake and targeting. A model of human IL-5Rα MIBC was developed by implanting NOD/SCID mice with subcutaneous HT-1376 or HT-B9MIBC tumors, which grow containing high and low IL-5Rα-positive tumor cell densities, respectively. ACs were intravenously injected, and daily blood sampling, biodistribution at 48 and 96 h, and positron emission tomography (PET) at 24 and 48 h were performed. Region of interest (ROI) analysis was also performed on reconstructed PET images. Pharmacokinetic analysis and biodistribution studies showed that 64Cu-A14-ChAcNLS had faster clearance rates from the blood and healthy organs relative to 64Cu-A14. However, 64Cu-A14-ChAcNLS maintained comparable tumor accumulation relative to 64Cu-A14. This resulted in 64Cu-A14-ChAcNLS having superior tumor/normal tissue ratios at both 48 and 96 h biodistribution time points. Visualization of AC distribution by PET and ROI analysis confirmed that 64Cu-A14-ChAcNLS had improved targeting of MIBC tumor relative to 64Cu-A14. In addition, 64Cu-A14 modified with only NLS had poor tumor targeting. This was a result of poor tumor uptake due to extremely rapid clearance. Thus, the overall findings in this model of human IL-5Rα-positive MIBC describe an endosome escape-nuclear localization cholic-acid-linked peptide that substantially enhances AC cellular accumulation and tumor targeting.

Evaluation of a novel GRPR antagonist for prostate cancer PET imaging: [64Cu]-DOTHA2-PEG-RM26.

INTRODUCTION: Gastrin releasing peptide receptors (GRPRs) are significantly over-expressed on a large proportion of prostate cancers making them prime candidates for receptor-mediated nuclear imaging by PET. Recently, we synthesized a novel bifunctional chelator (BFC) bearing hydroxamic acid arms (DOTHA2). Here we investigated the potential of a novel DOTHA2-conjugated, 64Cu-radiolabeled GRPR peptide antagonist, [D-Phe6-Sta13-Leu14-NH2]bombesin(6-14) (DOTHA2-PEG-RM26) to visualize prostate tumors by PET imaging. METHODS: DOTHA2-PEG-RM26 was conveniently and efficiently assembled on solid support. The compound was radiolabeled with 64Cu and its affinity, stability, cellular uptake on PC3 prostate cancer cells were evaluated. The in vitro and in vivo behavior of [64Cu]DOTHA2-PEG-RM26 was examined by PET imaging using human PC3 prostate cancer xenografts and its behavior was compared to that of the analogous [64Cu]NOTA-PEG-RM26. RESULTS: The inhibition constant of natCu-DOTHA2-PEG-RM26 was in the low nanomolar range (0.68±0.19 nM). The [64Cu]DOTHA2-PEG-RM26 conjugate was prepared with a labeling yield >95% and molar activity of 56±3 GBq/µmol after a 5-min room temperature labeling. [64Cu]-DOTHA2-PEG-RM26 demonstrated rapid blood and renal clearance as well as a high tumor uptake. Small animal PET images confirmed high and specific uptake in PC3 tumor. Both [64Cu]-DOTHA2-PEG-RM26 and [64Cu]-NOTA-PEG-RM26 displayed similar tumor and normal tissue uptakes at early time point post injection. CONCLUSIONS: [64Cu]-DOTHA2-PEG-RM26 allows visualization of prostate tumors by PET imaging. DOTHA2 enables fast 64Cu chelation under mild condition, and as such could be used advantageously for the development of other 64Cu-labeled peptide-derived PET tracers.

Improved Estrogen Receptor Assessment by PET Using the Novel Radiotracer 18F-4FMFES in Estrogen Receptor-Positive Breast Cancer Patients: An Ongoing Phase II Clinical Trial.

After encouraging preclinical and human dosimetry results for the novel estrogen receptor (ER) PET radiotracer 4-fluoro-11ß-methoxy-16α-18F-fluoroestradiol (18F-4FMFES), a phase II clinical trial was initiated to compare the PET imaging diagnostic potential of 18F-4FMFES with that of 16α-18F-fluoroestradiol (18F-FES) in ER-positive (ER+) breast cancer patients. Methods: Patients diagnosed with ER+ breast cancer (n = 31) were recruited for this study, including 6 who underwent mastectomy or axillary node dissection. For each patient, 18F-FES and 18F-4FMFES PET/CT scans were done sequentially (within a week) and in random order. One hour after injection of either radiotracer, a head-to-thigh static scan with a 2-min acquisition per bed position was obtained. Blood samples were taken at different times after injection to assess each tracer metabolism by reverse-phase thin-layer chromatography. The SUVmean of nonspecific tissues and the SUVmax of the tumor were evaluated for each detected lesion, and tumor-to-nonspecific organ ratios were calculated. Results: Blood metabolite analysis 60 min after injection of the tracer showed a 2.5-fold increase in metabolic stability of 18F-4FMFES over 18F-FES. Although for most foci 18F-4FMFES PET had an SUVmax similar to that of 18F-FES PET, tumor contrast improved substantially in all cases. Lower uptake was consistently observed in nonspecific tissues for 18F-4FMFES, notably a 4-fold decrease in blood-pool activity as compared with 18F-FES. Consequently, image quality was considerably improved using 18F-4FMFES, with lower overall background activity. As a result, 18F-4FMFES successfully identified 9 more lesions than 18F-FES. Conclusion: This phase II study with ER+ breast cancer patients showed that 18F-4FMFES PET achieves a lower nonspecific signal and better tumor contrast than 18F-FES PET, resulting in improved diagnostic confidence and lower false-negative diagnoses.

Targeting IL-5Rα with antibody-conjugates reveals a strategy for imaging and therapy for invasive bladder cancer.

Despite the high interest and concern due to an increasing incidence and death rate, patients who develop muscle invasive bladder cancer (MIBC) have few options available. However, the past decade has produced many candidate bladder tumor-specific markers but further development of these markers is still needed for creating effective targeted medications to solve this urgent need. Interleukin-5 receptor α-subunit (IL-5Rα) has recently been reported to be involved in MIBC progression. Thus, we aimed to validate IL-5Rα as a target for antibody-conjugates to better manage patients with MIBC. Patients were recruited and their tumors were processed for IL-5Rα immunohistochemical analysis. NOD/SCID mice were also heterotopically implanted with the human MIBC HT-1376 and HT-B9 cell lines and established xenografts immunohistochemically evaluated for IL-5Rα and compared against patient tumors. Using the mAb A14, an antibody-drug conjugate (ADC) and a radiolabeled immunoconjugate (RIC) were developed by conjugating to vinblastine and to the positron emitter copper-64 (64Cu), respectively. As a proof-of-concept for ADC and RIC efficacy, in vitro cytotoxicity and in vivo positron emission tomography (PET) imaging in tumor-bearing mice were performed, respectively. In addition, as rapid internalization and accumulation are important components for effective antibody-conjugates, we evaluated these aspects in response to IL-5 and 64Cu-A14 treatments. Our findings suggest that although IL-5Rα protein expression is preferentially increased in MIBC, it is rapid IL-5Rα-mediated internalization allowing vinblastine-A14 to have cytotoxic activity and 64Cu-A14 to detect MIBC tumors in vivo. This is the first report to elucidate the potential of IL-5Rα as an attractive MIBC target for antibody-conjugate applications.

The loss of P2X7 receptor expression leads to increase intestinal glucose transit and hepatic steatosis.

In intestinal epithelial cells (IEC), it was reported that the activation of the P2X7 receptor leads to the internalization of the glucose transporter GLUT2, which is accompanied by a reduction of IEC capacity to transport glucose. In this study, we used P2rx7 -/- mice to decipher P2X7 functions in intestinal glucose transport and to evaluate the impacts on metabolism. Immunohistochemistry analyses revealed the presence of GLUT2 at the apical domain of P2rx7 -/- jejunum enterocytes. Positron emission tomography and biodistribution studies demonstrated that glucose was more efficiently delivered to the circulation of knockout animals. These findings correlated with increase blood glucose, insulin, triglycerides and cholesterol levels. In fact, P2rx7 -/- mice had increased serum triglyceride and cholesterol levels and displayed glucose intolerance and resistance to insulin. Finally, P2rx7 -/- mice developed a hepatic steatosis characterized by a reduction of Acaca, Acacb, Fasn and Acox1 mRNA expression, as well as for ACC and FAS protein expression. Our study suggests that P2X7 could play a central role in metabolic diseases.

BODIPY-17α-ethynylestradiol conjugates: Synthesis, fluorescence properties and receptor binding affinities.

In vivo imaging of estrogen receptor (ER) densities in human breast cancer is a potential tool to stage disease, guide treatment protocols and follow-up on treatment outcome. Both positron emission tomography (PET) and fluorescence imaging have received ample attention to detect ligand-ER interaction. In this study we prepared BODIPY-estradiol conjugates using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as fluorescent probe and estradiol derivatives as ligand and established their relative binding affinity (RBA) for the ERα. The synthesis of the conjugates involves attachment of a BODIPY moiety to the C17α-position of estradiol using Sonogashira or click reactions of iodo-BODIPY or aza-BODIPY with various 17α-ethynylestradiol (EE2) derivatives. The highest RBA for the ERα was observed with the EE2-BODIPY conjugate (7) featuring a linear eight carbon spacer chain. Cell uptake studies and in vivo imaging experiments in an ER-positive mouse tumor model are in progress.

Impact of dianionic and dicationic linkers on tumor uptake and biodistribution of [64 Cu]Cu/NOTA peptide-based gastrin-releasing peptide receptors antagonists.

In this study, we investigated for the first time the influence of 2-aminoethyl-piperazine-1-carboxylic acid (APCA) and amino-hexanedioic-1-acid (AHDA) on tumor uptake and elimination kinetics of [64 Cu]-radiolabeled gastrin releasing peptide receptors (GRPR) antagonists. Three GRPR antagonists containing the RM26 sequence were synthesized and conjugated with NOTA via different linkers (LK): polyethylene glycol (PEG-neutral), APCA (dicationic) or AHDA (dianionic). The NOTA-LK-RM26 peptides were radiolabeled with 64 Cu to assess their pharmacokinetic and positron emission tomography (PET) imaging properties using PC3 tumor-bearing athymic nude mice. The inhibition constants (Ki ) of the 3 nat Cu/NOTA-LK-RM26 peptides bearing PEG, dicationic and dianionic linkers were 0.98 ± 0.48 nM, 0.95 ± 0.21 nM, and 17.97 ± 2.79 nM, respectively. The [64 Cu] NOTA-LK-RM26 conjugates were prepared with labeling yields superior to 95% and specific activities of 67 to 77 TBq/mmol. The 3 radiopeptides were stable in vivo and showed GRPR-specific uptake in pancreas with a very fast washout of this tissue observed for [64 Cu]-NOTA-AHDA-RM26 peptide. Results from imaging studies displayed specific PC3 tumor uptake for both [64 Cu]-NOTA-APCA- and AHDA-RM26, similar kidney elimination and fast liver washout. Considering their adequate imaging characteristics, [64 Cu]-NOTA-LK-RM26 bearing APCA- and AHDA-linkers are promising candidates for GRPR-targeted PET imaging prostate cancer.

Development of bifunctional chelates bearing hydroxamate arms for highly efficient (64)Cu radiolabeling.

Convenient approaches for the synthesis of DOTHA2 and NOTHA2, two cyclic bifunctional chelates (BFCs) bearing hydroxamate arms, have been developed. These novel BFCs coordinate (64)Cu with fast kinetics at room temperature in a wide range of concentrations and pH. The corresponding radiochemical complexes showed high stability, low residual activity in various tissues, and fast clearance in normal mice. The ability to conjugate DOTHA2 to both a small peptide and a large protein is also reported.

Assessment of the novel estrogen receptor PET tracer 4-fluoro-11ß-methoxy-16α-[(18)F]fluoroestradiol (4FMFES) by PET imaging in a breast cancer murine model.

PURPOSE: The aim of this study was to compare the in vivo stability, uptake, and positron emission tomography (PET) imaging performance of a novel estrogen receptor PET tracer, 4-fluoro-11ß-methoxy-16α-[(18)F]fluoroestradiol (4FMFES), with 16α-[(18)F]fluoroestradiol (FES). PROCEDURES: MC7-L1 and MC4-L2 (ER+) cell lines and their ERα-knockdown variants (ERαKD) were implanted subcutaneously in Balb/c mice. After 21 days, mice were imaged using either FES or 4FMFES. One hour post-injection, static images were acquired for 30 min and the tumor %ID/g uptake values were derived. Biodistribution data were also obtained 1 h following the injection of either FES or 4FMFES. Blood samples were taken at different times and analyzed on thin-layer chromatography to quantify the presence of radiometabolites for each radiotracer. To assess specific targeting to the estrogen receptors, mice bearing only ER+ tumors were treated with the competitive ER inhibitor fulvestrant 48 h prior to imaging with 4FMFES. RESULTS: Metabolic stability was found to be similar for both tracers in mice. Both FES and 4FMFES differentiated ER+ tumors from ERαKD tumors in biodistribution and PET imaging studies. 4FMFES achieved a significantly higher %ID/g uptake in ER+ tumors and MC4-L2 ERαKD tumors than FES in the PET imaging studies. Also, tumor-to-background ratio was higher in ER+ tumors using 4FMFES compared to FES. Dissection data showed a significantly higher %ID/g in all tested cell lines and ER-rich tissues using 4FMFES versus FES. Fulvestrant-treated mice had either low or undetectable tumor uptake. CONCLUSION: In a tumor-bearing mouse model, 4FMFES achieves better specific tumor uptake and better contrast than FES, making it a promising candidate for ER imaging.

Quantitative hormone therapy follow-up in an ER+/ERαKD mouse tumor model using FDG and [11C]-methionine PET imaging.

BACKGROUND: The estrogen receptor α (ERα) is known to play an important role in the modulation of tumor response to hormone therapy. In this work, the effect of different hormone therapies on tumors having different ERα expression levels was followed up in vivo in a mouse model by PET imaging using 2-deoxy-2-[18F]fluoro-d-glucose (FDG) and [11C]-methionine ([11C]-MET). A new model of MC7-L1 ERα-knockdown (ERαKD) tumor cell lines was designed as a negative estrogen receptor control to follow up the effects of changes in ERα expression on the early metabolic tumor response to different hormone therapies. METHODS: MC7-L1 (ER+) and MC7-L1 ERα-knockdown cell lines were implanted subcutaneously in Balb/c mice and allowed to grow up to 4 mm in diameter. Animals were separated into 4 groups (n = 4 or 5) and treated with a pure antiestrogen (fulvestrant), an aromatase inhibitor (letrozole), a selective estrogen receptor modulator (tamoxifen), or not treated (control). Tumor metabolic activity was assessed by PET imaging with FDG and [11C]-MET at days 0 (before treatment), 7, and 14 after the treatment. Tumor uptake of each radiotracer in %ID/g was measured for each tumor at each time point and compared to tumor growth. Quantitative PCR (qPCR) was performed to verify the expression of breast cancer-related genes (ERα, ErbB2, progesterone receptor (PR), and BRCA1) in each tumor cell lines. RESULTS: While both ER+ and ERαKD tumors had similar uptake of both radiotracers without treatment, higher uptake values were generally seen in ERαKD tumors after 7 and 14 days of treatment, indicating that ERαKD tumors behave in a similar fashion as hormone-unresponsive tumors. Furthermore, the ERα-specific downregulation induced a slight PR expression decrease and overexpression of BRCA1 and ErbB2. CONCLUSION: The results indicate that the proposed ER+/ERαKD tumor-bearing mouse model is suitable to test pure antiestrogen and aromatase inhibitor therapies in vivo in a preclinical setting and could help to elucidate the impact of ERα levels on tumor response to hormone therapy.

[18F]-fluoroestradiol quantitative PET imaging to differentiate ER+ and ERα-knockdown breast tumors in mice.

INTRODUCTION: The purpose of this study was to develop a noninvasive model in tumor-bearing mice to investigate the use of 16α-[(18)F]fluoro-17ß-estradiol (FES) positron emission tomography (PET) imaging as a tool to discriminate between tumors having different estrogen receptor (ER) α status. METHODS: MC7-L1 and MC4-L2 murine mammary adenocarcinoma cell lines (ER+) received a small hairpin RNA targeting the ERα gene by lentiviral infection. In vitro assessment of ERα levels of the new cell lines (MC7-L1 and MC4-L2 ERα-knockdown; ERαKD), compared to the parental cell lines, was performed by immunoblotting (-75% ERα protein) and binding assays (-50% estrogen binding). These cell lines were implanted subcutaneously in Balb/c mice and allowed to grow up to a volume of at least 20 mm(3). FES and [(18)F]fluorodeoxyglucose (FDG) PET images were acquired to measure FES and FDG uptake in the various tumors. RESULTS: FES uptake as assessed by PET imaging was 1.06±0.21 percent injected dose per gram of tissue (%ID/g) for MC7-L1 tumors and 0.47±0.08 %ID/g for MC7-L1 ERαKD tumors. MC4-L2 tumors had a FES uptake of 1.03±0.30 %ID/g, whereas its ERαKD equivalent was 0.51±0.19 %ID/g. Each ERαKD tumor had a significantly lower %ID/g value, by ~50%, than its ER+ counterpart. Biodistribution studies confirmed these findings and gave %ID/g values that were not significantly different from PET imaging data. FDG PET showed no significant uptake difference between the ER+ and ERαKD tumors, indicating that the metabolic phenotype of the ERαKD cell lines was not altered. CONCLUSION: FES PET imaging was able to reliably differentiate between tumors having differences in their ERα expression in vivo, in a mouse model. Quantitative data obtained by FES PET were in concordance with biodistribution studies and in vitro assays. It is concluded that FES PET imaging can likely be used to monitor subtle ER status changes during the course of hormone therapy.

Complementary roles of yeast Rad4p and Rad34p in nucleotide excision repair of active and inactive rRNA gene chromatin.

Nucleotide excision repair (NER) removes a plethora of DNA lesions. It is performed by a large multisubunit protein complex that finds and repairs damaged DNA in different chromatin contexts and nuclear domains. The nucleolus is the most transcriptionally active domain, and in yeast, transcription-coupled NER occurs in RNA polymerase I-transcribed genes (rDNA). Here we have analyzed the roles of two members of the xeroderma pigmentosum group C family of proteins, Rad4p and Rad34p, during NER in the active and inactive rDNA. We report that Rad4p is essential for repair in the intergenic spacer, the inactive rDNA coding region, and for strand-specific repair at the transcription initiation site, whereas Rad34p is not. Rad34p is necessary for transcription-coupled NER that starts about 40 nucleotides downstream of the transcription initiation site of the active rDNA, whereas Rad4p is not. Thus, although Rad4p and Rad34p share sequence homology, their roles in NER in the rDNA locus are almost entirely distinct and complementary. These results provide evidences that transcription-coupled NER and global genome NER participate in the removal of UV-induced DNA lesions from the transcribed strand of active rDNA. Furthermore, nonnucleosome rDNA is repaired faster than nucleosome rDNA, indicating that an open chromatin structure facilitates NER in vivo.

Repair-independent chromatin assembly onto active ribosomal genes in yeast after UV irradiation.

Chromatin rearrangements occur during repair of cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). Thereafter, the original structure must be restored to retain normal genomic functions. How NER proceeds through nonnucleosomal chromatin and how open chromatin is reestablished after repair are unknown. We analyzed NER in ribosomal genes (rDNA), which are present in multiple copies but only a fraction are actively transcribed and nonnucleosomal. We show that removal of CPDs is fast in the active rDNA and that chromatin reorganization occurs during NER. Furthermore, chromatin assembles on nonnucleosomal rDNA during the early events of NER but in the absence of DNA repair. The resumption of transcription after removal of CPDs correlates with the reappearance of nonnucleosomal chromatin. To date, only the passage of replication machinery was thought to package ribosomal genes in nucleosomes. In this report, we show that early events after formation of UV photoproducts in DNA also promote chromatin assembly.

Psoralen photocrosslinking, a tool to study the chromatin structure of RNA polymerase I--transcribed ribosomal genes.

The chromatin structure of RNA polymerase I--transcribed ribosomal DNA (rDNA) is well characterized. In most organisms, i.e., lower eukaryotes, plants, and animals, only a fraction of ribosomal genes are transcriptionally active. At the chromatin level inactive rDNA is assembled into arrays of nucleosomes, whereas transcriptionally active rDNA does not contain canonical nucleosomes. To separate inactive (nucleosomal) and active (non-nucleosomal) rDNA, the technique of psoralen photocrosslinking has been used successfully both in vitro and in vivo. In Saccharomyces cerevisiae, the structure of rDNA chromatin has been particularly well studied during transcription and during DNA replication. Thus, the yeast rDNA locus has become a good model system to study the interplay of all nuclear DNA processes and chromatin. In this review we focused on the studies of chromatin in ribosomal genes and how these results have helped to address the fundamental question: What is the structure of chromatin in the coding regions of genes?