Positron Emission Tomography Imaging of Cell Trafficking: A Method of Cell Radiolabeling

Stem cell and chimeric antigen receptor (CAR) T-cell therapies are emerging as promising therapeutics for organ regeneration and as immunotherapy for various cancers. Despite significant progress having been made in these areas, there is still more to be learned to better understand the pharmacokinetics and pharmacodynamics of the administered therapeutic cells in the living system. For noninvasive, in vivo tracking of cells with positron emission tomography (PET), a novel [89Zr]Zr-p-isothiocyanatobenzyl-desferrioxamine ([89Zr]Zr-DBN)-mediated cell radiolabeling method has been developed utilizing 89Zr (t1/2 78.4 h). The present protocol describes a [89Zr]Zr-DBN-mediated, ready-to-use, radiolabeling synthon for direct radiolabeling of variety of cells, including mesenchymal stem cells, lineage-guided cardiopoietic stem cells, liver regenerating hepatocytes, white blood cells, melanoma cells, and dendritic cells. The developed methodology enables noninvasive PET imaging of cell trafficking for up to 7 days post-administration without affecting the nature or the function of the radiolabeled cells. Additionally, this protocol describes a stepwise method for the radiosynthesis of [89Zr]Zr-DBN, biocompatible formulation of [89Zr]Zr-DBN, preparation of cells for radiolabeling, and finally the radiolabeling of cells with [89Zr]Zr-DBN, including all the intricate details needed for the successful radiolabeling of cells.

Design, Synthesis, and Preliminary Evaluation of [68Ga]Ga-NOTA-Insulin as a PET Probe in an Alzheimer's Disease Mouse Model

Aberrant insulin signaling has been considered one of the risk factors for the development of Alzheimer's disease (AD) and has drawn considerable attention from the research community to further study its role in AD pathophysiology. Herein, we describe the development of an insulin-based novel positron emission tomography (PET) probe, [⁶⁸Ga]Ga-NOTA-insulin, to noninvasively study the role of insulin in AD. The developed PET probe [⁶⁸Ga]Ga-NOTA-insulin showed a significantly higher uptake (0.396 ± 0.055 SUV) in the AD mouse brain compared to the normal (0.140 ± 0.027 SUV) mouse brain at 5 min post injection and also showed a similar trend at 10, 15, and 20 min post injection. In addition, [⁶⁸Ga]Ga-NOTA-insulin was found to have a differential uptake in various brain regions at 30 min post injection. Among the brain regions, the cortex, thalamus, brain stem, and cerebellum showed a significantly higher standard uptake value (SUV) of [⁶⁸Ga]Ga-NOTA-insulin in AD mice as compared to normal mice. The inhibition of the insulin receptor (IR) with an insulin receptor antagonist peptide (S961) in normal mice showed a similar brain uptake profile of [⁶⁸Ga]Ga-NOTA-insulin as it was observed in the AD case, suggesting nonfunctional IR in AD and the presence of an alternative insulin uptake route in the absence of a functional IR. The Gjedde-Patlak graphical analysis was also performed to predict the input rate of [⁶⁸Ga]Ga-NOTA-insulin into the brain using MicroPET imaging data and supported the in vivo results. The [⁶⁸Ga]Ga-NOTA-insulin PET probe was successfully synthesized and evaluated in a mouse model of AD in comparison with [¹⁸F]AV1451 and [¹¹C]PIB to noninvasively study the role of insulin in AD pathophysiology.

A new solid target design for the production of 89Zr and radiosynthesis of high molar activity [89Zr]Zr-DBN

Due to the advent of various biologics like antibodies, proteins, cells, viruses, and extracellular vesicles as biomarkers for disease diagnosis, progression, and as therapeutics, there exists a need to have a simple and ready to use radiolabeling synthon to enable noninvasive imaging trafficking studies. Previously, we reported [⁸⁹Zr]zirconium-p-isothiocyanatobenzyl-desferrioxamine ([⁸⁹Zr]Zr-DBN) as a synthon for the radiolabeling of biologics to allow PET imaging of cell trafficking. In this study, we focused on improving the molar activity (A_m) of [⁸⁹Zr]Zr-DBN, by enhancing ⁸⁹Zr production on a low-energy cyclotron and developing a new reverse phase HPLC method to purify [⁸⁹Zr]Zr-DBN. To enhance ⁸⁹Zr production, a new solid target was designed, and production yield was optimized by varying, thickness of yttrium foil, beam current, irradiation duration and proton beam energy. After optimization, 4.78±0.33 GBq (129.3±8.9 mCi) of ⁸⁹Zr was produced at 40 µA for 180 min (3 h) proton irradiation decay corrected to the end of bombardment with a saturation yield of 4.56±0.31 MBq/µA. Additionally, after reverse phase HPLC purification the molar activity of [⁸⁹Zr]Zr-DBN was found to be in 165-316 GBq/µmol range. The high molar activity of [⁸⁹Zr]Zr-DBN also allowed radiolabeling of low concentration of proteins in relatively higher yield. The stability of [⁸⁹Zr]Zr-DBN was measured over time with and without the presence of ascorbic acid. The newly designed solid target assembly and HPLC method of [⁸⁹Zr]Zr-DBN purification can be adopted in the routine production of ⁸⁹Zr and [⁸⁹Zr]Zr-DBN, respectively.

Cyclotron Production of PET Radiometals in Liquid Targets: Aspects and Prospects

The present review describes the methodological aspects and prospects of the production of Positron Emission Tomography (PET) radiometals in a liquid target using low-medium energy medical cyclotrons. The main objective of this review is to delineate and discuss the critical factors involved in the liquid target production of radiometals, including type of salt solution, solution composition, beam energy, beam current, the effect of irradiation duration (length of irradiation) and challenges posed by in-target chemistry in relation with irradiation parameters. We also summarize the optimal parameters for the production of various radiometals in liquid targets. Additionally, we discuss the future prospects of PET radiometals production in the liquid targets for academic research and clinical applications. Significant emphasis has been given to the production of ⁶⁸Ga using liquid targets due to the growing demand for ⁶⁸Ga labeled PSMA vectors, [⁶⁸Ga]- Ga-DOTATATE, [⁶⁸Ga]Ga-DOTANOC and some upcoming ⁶⁸Ga labeled radiopharmaceuticals. Other PET radiometals included in the discussion are ⁸⁶Y, ⁶³Zn and ⁸⁹Zr.

Development of a Clinically Relevant Reporter for Chimeric Antigen Receptor T-cell Expansion, Trafficking, and Toxicity

Although chimeric antigen receptor T (CART)-cell therapy has been successful in treating certain hematologic malignancies, wider adoption of CART-cell therapy is limited because of minimal activity in solid tumors and development of life-threatening toxicities, including cytokine release syndrome (CRS). There is a lack of a robust, clinically relevant imaging platform to monitor in vivo expansion and trafficking to tumor sites. To address this, we utilized the sodium iodide symporter (NIS) as a platform to image and track CART cells. We engineered CD19-directed and B-cell maturation antigen (BCMA)-directed CART cells to express NIS (NIS⁺CART19 and NIS⁺BCMA-CART, respectively) and tested the sensitivity of ¹⁸F-TFB-PET to detect trafficking and expansion in systemic and localized tumor models and in a CART-cell toxicity model. NIS⁺CART19 and NIS⁺BCMA-CART cells were generated through dual transduction with two vectors and demonstrated exclusive ¹²⁵I uptake in vitro. ¹⁸F-TFB-PET detected NIS⁺CART cells in vivo to a sensitivity level of 40,000 cells. ¹⁸F-TFB-PET confirmed NIS⁺BCMA-CART-cell trafficking to the tumor sites in localized and systemic tumor models. In a xenograft model for CART-cell toxicity, ¹⁸F-TFB-PET revealed significant systemic uptake, correlating with CART-cell in vivo expansion, cytokine production, and development of CRS-associated clinical symptoms. NIS provides a sensitive, clinically applicable platform for CART-cell imaging with PET scan. ¹⁸F-TFB-PET detected CART-cell trafficking to tumor sites and in vivo expansion, correlating with the development of clinical and laboratory markers of CRS. These studies demonstrate a noninvasive, clinically relevant method to assess CART-cell functions in vivo.

Evaluation of Zn, Cu, and Se Levels in the North American Autism Spectrum Disorder Population

Metal ion dyshomeostasis and disparate levels of biometals like zinc (Zn), copper (Cu), and selenium (Se) have been implicated as a potential causative factor for Autism Spectrum Disorder (ASD). In this study, we have enrolled 129 children (aged 2–4 years) in North America, of which 64 children had a diagnosis of ASD and 65 were controls. Hair, nail, and blood samples were collected and quantitatively analyzed for Zn, Cu and Se using inductively coupled plasma mass spectrometry (ICP-MS). Of the analyzed biometals, serum Se (116.83 ± 14.84 ng/mL) was found to be significantly lower in male ASD cases compared to male healthy controls (128.21 ± 9.11 ng/mL; p < 0.005). A similar trend was found for nail Se levels in ASD (1.01 ± 0.15 mcg/g) versus that of controls (1.11 ± 0.17 mcg/g) with a p-value of 0.0132 using a stratified Wilcoxon rank sum testing. The level of Se in ASD cohort was co-analyzed for psychometric correlation and found a negative correlation between total ADOS score and serum Se levels. However, we did not observe any significant difference in Zn, Cu, and Zn/Cu ratio in ASD cases versus controls in this cohort of North American children. Further studies are recommended to better understand the biology of the relationship between Se and ASD status.

Ex Vivo Cell Therapy by Ectopic Hepatocyte Transplantation Treats the Porcine Tyrosinemia Model of Acute Liver Failure

The effectiveness of cell-based therapies to treat liver failure is often limited by the diseased liver environment. Here, we provide preclinical proof of concept for hepatocyte transplantation into lymph nodes as a cure for liver failure in a large-animal model with hereditary tyrosinemia type 1 (HT1), a metabolic liver disease caused by deficiency of fumarylacetoacetate hydrolase (FAH) enzyme. Autologous porcine hepatocytes were transduced ex vivo with a lentiviral vector carrying the pig Fah gene and transplanted into mesenteric lymph nodes. Hepatocytes showed early (6 h) and durable (8 months) engraftment in lymph nodes, with reproduction of vascular and hepatic microarchitecture. Subsequently, hepatocytes migrated to and repopulated the native diseased liver. The corrected cells generated sufficient liver mass to clinically ameliorate the acute liver failure and HT1 disease as early as 97 days post-transplantation. Integration site analysis defined the corrected hepatocytes in the liver as a subpopulation of hepatocytes from lymph nodes, indicating that the lymph nodes served as a source for healthy hepatocytes to repopulate a diseased liver. Therefore, ectopic transplantation of healthy hepatocytes cures this pig model of liver failure and presents a promising approach for the development of cures for liver disease in patients.

Dual-Isotope SPECT Imaging with NIS Reporter Gene and Duramycin to Visualize Tumor Susceptibility to Oncolytic Virus Infection

Noninvasive dual-imaging methods that provide an early readout on tumor permissiveness to virus infection and tumor cell death could be valuable in optimizing development of oncolytic virotherapies. Here, we have used the sodium iodide symporter (NIS) and 125I radiotracer to detect infection and replicative spread of an oncolytic vesicular stomatitis virus (VSV) in VSV-susceptible (MPC-11 tumor) versus VSV-resistant (CT26 tumor) tumors in BALB/c mice. In conjunction, tumor cell death was imaged simultaneously using technetium (99mTc)-duramycin that binds phosphatidylethanolamine in apoptotic and necrotic cells. Dual-isotope single-photon emission computed tomography/computed tomography (SPECT/CT) imaging showed areas of virus infection (NIS and 125I), which overlapped well with areas of tumor cell death (99mTc-duramycin imaging) in susceptible tumors. Multiple infectious foci arose early in MPC-11 tumors, which rapidly expanded throughout the tumor parenchyma over time. There was a dose-dependent increase in numbers of infectious centers and 99mTc-duramycin-positive areas with viral dose. In contrast, NIS or duramycin signals were minimal in VSV-resistant CT26 tumors. Combinatorial use of NIS and 99mTc-duramycin SPECT imaging for simultaneous monitoring of oncolytic virotherapy (OV) spread and the presence or absence of treatment-associated cell death could be useful to guide development of combination treatment strategies to enhance therapeutic outcome.

Radiation induced oxidation of [18F]fluorothia fatty acids under cGMP manufacturing conditions

OBJECTIVE

The objectives of the present work were to optimize and validate the synthesis and stability of 14(R,S)-[¹⁸F]fluoro-6-thia-heptadecanoic acid ([¹⁸F]FTHA) and 16-[¹⁸F]fluoro-4-thia-palmitic acid ([¹⁸F]FTP) under cGMP conditions for clinical applications.

METHODS

Benzyl-14-(R,S)-tosyloxy-6-thiaheptadecanoate and methyl 16-bromo-4-thia-palmitate were used as precursors for the synthesis of [¹⁸F]FTHA and [¹⁸F]FTP, respectively. For comparison, a fatty acid analog lacking a thia-substitution, 16-[¹⁸F]fluoro-palmitic acid ([¹⁸F]FP), was synthesized from the precursor methyl 16-bromo-palmitate. A standard nucleophilic reaction using cryptand (Kryptofix/K222, 8.1 mg), potassium carbonate (K₂CO₃, 4.0 mg) and ¹⁸F-fluoride were employed for the ¹⁸F-labeling and potassium hydroxide (0.8 M) was used for the post-labeling ester hydrolysis. The final products were purified via reverse phase semi-preparative HPLC and concentrated via trap and release on a C-18 plus solid phase extraction cartridge. The radiochemical purities of the [¹⁸F]fluorothia fatty acids and [¹⁸F]FP were examined over a period of 4 h post-synthesis using an analytical HPLC. All the syntheses were optimized in an automated TRACERlab FX-N Pro synthesizer. Liquid chromatography mass spectrometry (LCMS) and high resolution mass spectrometry (HRMS) was employed to study the identity and nature of side products formed during radiosynthesis and as a consequence of post-synthesis radiation induced oxidation.

RESULTS

Radiosyntheses of [¹⁸F]FTHA, [¹⁸F]FTP and [¹⁸F]FP were achieved in moderate (8-20% uncorrected) yields. However, it was observed that the HPLC-purified [¹⁸F]fluorothia fatty acids, [¹⁸F]FTHA and [¹⁸F]FTP at higher radioactivity concentrations (>1.11 GBq/mL, 30 mCi/mL) underwent formation of ¹⁸F-labeled side products over time but [¹⁸F]FP (lacking a sulfur heteroatom) remained stable up to 4 h post-synthesis. Various radiation protectors like ethanol and ascorbic acid were examined to minimize the formation of side products formed during [¹⁸F]FTHA and [¹⁸F]FTP synthesis but showed only limited to no effect. Analysis of the side products by LCMS showed formation of sulfoxides of both [¹⁸F]FTHA and [¹⁸F]FTP. The identity of the sulfoxide side product was further confirmed by synthesizing a non-radioactive reference standard of the sulfoxide analog of FTP and matching retention times on HPLC and molecular ion peaks on LC/HRMS. Radiation-induced oxidation of the sulfur heteroatom was mitigated by dilution of product with isotonic saline to reduce the radioactivity concentration to <0.518 GBq/mL (14 mCi/mL).

CONCLUSIONS

Successful automated synthesis of [¹⁸F]fluorothia fatty acids were carried out in cGMP facility for their routine production and clinical applications. Instability of [¹⁸F]fluorothia fatty acids were observed at radioactivity concentrations exceeding 1.11 GBq/mL (30 mCi/mL) but mitigated through dilution of the product to <0.518 GBq/mL (14 mCi/mL). The identities of the side products formed were established as the sulfoxides of the respective thia fatty acids caused by radiation-induced oxidation of the sulfur heteroatom.

Cyclotron production of 68Ga in a liquid target: Effects of solution composition and irradiation parameters

OBJECTIVES

To optimize ⁶⁸Ga production using a liquid cyclotron target, investigations were performed to compare production yields using different concentrations of [⁶⁸Zn]Zn(NO₃)₂, nitric acid, and irradiation parameters.

METHODS

Different concentrations of [⁶⁸Zn]Zn(NO₃)₂ (0.6 M, 1.2 M and 1.42 M) in varying normality of nitric acid (0.8-1.5 N) were prepared and irradiated with protons (incident energy ~14 MeV) using a BMLT-2 liquid target at different beam currents (30-50 μA) and irradiation times (30-60 min). The ⁶⁸Ga production and saturation yields were calculated and compared. [⁶⁸Ga]GaCl₃ was isolated using in-house developed hydroxamate resin and optimized for routine application. Recycling of [⁶⁸Zn]Zn(NO₃)₂ from the recovered target solution was also investigated.

RESULTS

On increasing concentration of [⁶⁸Zn]Zn(NO₃)₂ from 0.6 M to 1.2 M in 0.8 N nitric acid, decay corrected yield of ⁶⁸Ga at EOB was found to be 1.64 GBq (44.4 mCi) and 3.37 GBq (91.0 mCi), respectively at 30 μA beam current, indicating production yield was proportional to zinc nitrate concentration for a 30 min irradiation. However, when beam current was increased to 40 μA while maintaining nitric acid concentration at 0.8 N, the proportional relationship of ⁶⁸Zn-concentration with ⁶⁸Ga production yield was lost [0.6 M, 2.29 GBq (61.9 mCi); 1.2 M, 3.6 GBq (97.3 mCi)] for a 30 min irradiation. In fact, the effect was more profound for 60 min irradiations [0.6 M, 2.96 GBq (80.0 mCi); 1.2 M, 4.25 GBq (115 mCi)]. Increasing nitric acid concentration to 1.25-1.5 N improved ⁶⁸Ga production yield for 40 μA, 60-min irradiations (1.2 M; 5.17 GBq (140 mCi)). MP-AES analysis showed metal impurities as <0.20 μg Ga (n = 3), <0.93 μg Zn (n = 3) and < 2.7 μg Fe (n = 3). Based on above finding, 1.42 M [⁶⁸Zn]Zn(NO₃)₂ in 1.2 N-HNO₃ solutions were also studied to achieve highest production yields of 9.85 ± 2.09 GBq (266 ± 57 mCi) for 60 min irradiation at 40 μA beam current. After recycling,> 99% pure recycled [⁶⁸Zn]zinc nitrate was obtained in 82.6 ± 13.6% yield.

CONCLUSIONS

⁶⁸Ga production yields were dependent on all four variables: concentrations of [⁶⁸Zn]Zn(NO₃)₂ and nitric acid, beam current and duration of irradiation. Of note, increasing beam current and irradiation time may require increased concentrations of nitric acid to achieve expected increments in ⁶⁸Ga production yield.

Noninvasive evaluation of fat-carbohydrate metabolic switching in heart and contracting skeletal muscle

The ability of heart and skeletal muscle (SM) to switch between fat and carbohydrate oxidation is of high interest in the study of metabolic diseases and exercise physiology. Positron emission tomography (PET) imaging with the glucose analog 2-[¹⁸F]fluoro-2-deoxy-glucose (¹⁸F-FDG) provides a noninvasive means to quantitate glucose metabolic rates. However, evaluation of fatty acid oxidation (FAO) rates by PET has been limited by the lack of a suitable FAO probe. We have developed a metabolically trapped oleate analog, ( Z)-18-[¹⁸F]fluoro-4-thia-octadec-9-enoate (¹⁸F-FTO), and investigated the feasibility of using ¹⁸F-FTO and ¹⁸F-FDG to measure FAO and glucose uptake, respectively, in heart and SM of rats in vivo. To enhance the metabolic rates in SM, the vastus lateralis (VL) muscle was electrically stimulated in fasted rats for 30 min before and 30 min following radiotracer injection. The responses of radiotracer uptake patterns to pharmacological inhibition of FAO were assessed by pretreatment of the rats with the carnitine palmitoyl-transferase-1 (CPT-1) inhibitor sodium 2-[5-(4-chlorophenyl)-pentyl]oxirane-2-carboxylate (POCA). Small-animal PET images and biodistribution data with ¹⁸F-FTO and ¹⁸F-FDG demonstrated profound metabolic switching for energy provision in the myocardium from exogenous fatty acids to glucose in control and CPT-1-inhibited rats, respectively. Uptake of both radiotracers was low in unstimulated SM. In stimulated VL muscle, ¹⁸F-FTO and ¹⁸F-FDG uptakes were increased 4.4- and 28-fold, respectively, and CPT-1 inhibition only affected ¹⁸F-FTO uptake (66% decrease). ¹⁸F-FTO is a FAO-dependent PET probe that may allow assessment of energy substrate metabolic switching in conjunction with ¹⁸F-FDG and other metabolic probes.

Cloning, function, and localization of human, canine, and Drosophila ZIP10 (SLC39A10), a Zn2+ transporter

Zinc (Zn²⁺) is the second most abundant trace element, but is considered a micronutrient, as it is a cofactor for many enzymes and transcription factors. Whereas Zn²⁺ deficiency can cause cognitive immune or metabolic dysfunction and infertility, excess Zn²⁺ is nephrotoxic. As for other ions and solutes, Zn²⁺ is moved into and out of cells by specific membrane transporters: ZnT, Zip, and NRAMP/DMT proteins. ZIP10 is reported to be localized at the apical membrane of renal proximal tubules in rats, where it is believed to play a role in Zn²⁺ import. Renal regulation of Zn²⁺ is of particular interest in light of growing evidence that Zn²⁺ may play a role in kidney stone formation. The objective of this study was to show that ZIP10 homologs transport Zn²⁺, as well as ZIP10, kidney localization across species. We cloned ZIP10 from dog, human, and Drosophila ( CG10006), tested clones for Zn²⁺ uptake in Xenopus oocytes and localized the protein in renal structures. CG10006, rather than foi (fear-of-intimacy, CG6817) is the primary ZIP10 homolog found in Drosophila Malpighian tubules. The ZIP10 antibody recognizes recombinant dog, human, and Drosophila ZIP10 proteins. Immunohistochemistry reveals that ZIP10 in higher mammals is found not only in the proximal tubule, but also in the collecting duct system. These ZIP10 proteins show Zn²⁺ transport. Together, these studies reveal ZIP10 kidney localization, a role in renal Zn²⁺ transport, and indicates that CG10006 is a Drosophila homolog of ZIP10.

[18F]Tetrafluoroborate ([18F]TFB) and its analogs for PET imaging of the sodium/iodide symporter

Sodium/iodide symporter (NIS)-mediated iodide uptake in thyroid follicular cells is the basis of clinical utilization of radioiodines. The cloning of the NIS gene enabled applications of NIS as a reporter gene in both preclinical and translational research. Non-invasive NIS imaging with radioactive iodides and iodide analogs has gained much interest in recent years for evaluation of thyroid cancer and NIS reporter expression. Although radioiodines and [^99mTc]pertechnetate ([^99mTc]TcO₄^-) have been utilized in positron emission tomography (PET) and single photon emission computed tomography (SPECT), they may suffer from limitations of availability, undesirable decay properties or imaging sensitivity (SPECT versus PET). Recently, [¹⁸F]tetrafluoroborate ([¹⁸F]TFB or [¹⁸F]BF₄^-) and other fluorine-18 labeled iodide analogs have emerged as a promising iodide analog for PET imaging. These fluorine-18 labeled probes have practical radiosyntheses and biochemical properties that allow them to closely mimic iodide transport by NIS in thyroid, as well as in other NIS-expressing tissues. Unlike radioiodides, they do not undergo organification in thyroid cells, which results in an advantage of relatively lower uptake in normal thyroid tissue. Initial clinical trials of [¹⁸F]TFB have been completed in healthy human subjects and thyroid cancer patients. The excellent imaging properties of [¹⁸F]TFB for evaluation of NIS-expressing tissues indicate its bright future in PET NIS imaging. This review focuses on the recent evolution of [¹⁸F]TFB and other iodide analogs and their potential value in research and clinical practice.

Reassessment of the Transport Mechanism of the Human Zinc Transporter SLC39A2

The human zinc transporter SLC39A2, also known as ZIP2, was shown to mediate zinc transport that could be inhibited at pH <7.0 and stimulated by HCO₃^-, suggesting a Zn²⁺/HCO₃^- cotransport mechanism [Gaither, L. A., and Eide, D. J. (2000) J. Biol. Chem. 275, 5560-5564]. In contrast, recent experiments in our laboratory indicated that the functional activity of ZIP2 increases at acidic pH [Franz, M. C., et al. (2014) J. Biomol. Screening 19, 909-916]. The study presented here was therefore designed to reexamine the findings about the pH dependence and to extend the functional characterization of ZIP2. Our current results show that ZIP2-mediated transport is modulated by extracellular pH but independent of the H⁺ driving force. Also, in our experiments, ZIP2-mediated transport is not modulated by extracellular HCO₃^-. Moreover, a high extracellular [K⁺], which induces depolarization, inhibited ZIP2-mediated transport, indicating that the transport mechanism is voltage-dependent. We also show that ZIP2 mediates the uptake of Cd²⁺ ( K_m ∼ 1.57 μM) in a pH-dependent manner ( K_H⁺ ∼ 66 nM). Cd²⁺ transport is inhibited by extracellular [Zn²⁺] (IC₅₀ ∼ 0.32 μM), [Cu²⁺] (IC₅₀ ∼ 1.81 μM), and to a lesser extent [Co²⁺], but not by [Mn²⁺] or [Ba²⁺]. Fe²⁺ is not transported by ZIP2. Accordingly, the substrate selectivity of ZIP2 decreases in the following order: Zn²⁺ > Cd²⁺ ≥ Cu²⁺ > Co²⁺. Altogether, we propose that ZIP2 is a facilitated divalent metal ion transporter that can be modulated by extracellular pH and membrane potential. Given that ZIP2 expression has been reported in acidic environments [Desouki, M. M., et al. (2007) Mol. Cancer 6, 37; Inoue, Y., et al. (2014) J. Biol. Chem. 289, 21451-21462; Tao, Y. T., et al. (2013) Mol. Biol. Rep. 40, 4979-4984], we suggest that the herein described H⁺-mediated regulatory mechanism might be important for determining the velocity and direction of the transport process.

Curative ex vivo liver-directed gene therapy in a pig model of hereditary tyrosinemia type 1

We tested the hypothesis that ex vivo hepatocyte gene therapy can correct the metabolic disorder in fumarylacetoacetate hydrolase-deficient (Fah(-/-)) pigs, a large animal model of hereditary tyrosinemia type 1 (HT1). Recipient Fah(-/-) pigs underwent partial liver resection and hepatocyte isolation by collagenase digestion. Hepatocytes were transduced with one or both of the lentiviral vectors expressing the therapeutic Fah and the reporter sodium-iodide symporter (Nis) genes under control of the thyroxine-binding globulin promoter. Pigs received autologous transplants of hepatocytes by portal vein infusion. After transplantation, the protective drug 2-(2-nitro-4-trifluoromethylbenzyol)-1,3 cyclohexanedione (NTBC) was withheld from recipient pigs to provide a selective advantage for expansion of corrected FAH(+) cells. Proliferation of transplanted cells, assessed by both immunohistochemistry and noninvasive positron emission tomography imaging of NIS-labeled cells, demonstrated near-complete liver repopulation by gene-corrected cells. Tyrosine and succinylacetone levels improved to within normal range, demonstrating complete correction of tyrosine metabolism. In addition, repopulation of the Fah(-/-) liver with transplanted cells inhibited the onset of severe fibrosis, a characteristic of nontransplanted Fah(-/-) pigs. This study demonstrates correction of disease in a pig model of metabolic liver disease by ex vivo gene therapy. To date, ex vivo gene therapy has only been successful in small animal models. We conclude that further exploration of ex vivo hepatocyte genetic correction is warranted for clinical use.

Synthesis and evaluation of 18F-hexafluorophosphate as a novel PET probe for imaging of sodium/iodide symporter in a murine C6-glioma tumor model

Noninvasive imaging of iodide uptake via the sodium/iodide symporter (NIS) has received great interest for evaluation of thyroid cancer and reporter imaging of NIS-expressing viral therapies. In this study, we investigate ¹⁸F-labeled hexafluorophosphate (HFP or PF₆^-) as a high-affinity iodide analog for NIS imaging. ¹⁸F-HFP was synthesized by radiofluorination of phosphorus pentafluoride·N-methylpyrrolidine complex and evaluated in human NIS (hNIS)-expressing C6 glioma cells and a C6 glioma xenograft mouse model. ¹⁸F-HFP was obtained in radiochemical yield of 10 ± 5%, radiochemical purity of >96% and specific radioactivity of 604 ± 18 MBq/µmol. Specific uptake of ¹⁸F-HFP and high affinity of ¹⁹F-HFP were observed in hNIS+ C6-glioma cells. PET imaging showed robust uptake of ¹⁸F-HFP in NIS-expressing tissues (thyroid, stomach, and hNIS+ C6 glioma xenografts), and the uptake of ¹⁸F-HFP was blocked by NaClO₄ pretreatment. Specific accumulation in hNIS-expressing xenograft (hNIS+) was observed relative to isogenic control tumor (hNIS-). Clearance of ¹⁸F-HFP was predominantly through renal excretion. The biodistribution showed consistent results with PET imaging. Minimal bone uptake was observed over 2 h period post-injection, indicating excellent in vivo stability of ¹⁸F-HFP. Although improvement in specific radioactivity is desirable, the results indicate that ¹⁸F-HFP is a promising candidate radiotracer for further evaluation for NIS imaging.

Safety, pharmacokinetics, metabolism and radiation dosimetry of 18F-tetrafluoroborate (18F-TFB) in healthy human subjects

BACKGROUND

18F-Tetrafluoroborate (18F-TFB) is a promising iodide analog for PET imaging of thyroid cancer and sodium/iodide symporter (NIS) reporter activity in viral therapy applications. The aim of this study was to evaluate the safety, pharmacokinetics, biodistribution, and radiation dosimetry of high-specific activity 18F-TFB in healthy human subjects.

METHODS

18F-TFB was synthesized with specific activity of 3.2 ± 1.3 GBq/μmol (at the end of synthesis). Dynamic and whole-body static PET/CT scans over 4 h were performed after intravenous administration of 18F-TFB (333-407 MBq) in four female and four male healthy volunteers (35 ± 11 years old). Samples of venous blood and urine were collected over the imaging period and analyzed by ion-chromatography HPLC to determine tracer stability. Vital signs and clinical laboratory safety assays were measured to evaluate safety.

RESULTS

18F-TFB administration was well tolerated with no significant findings on vital signs and no clinically meaningful changes in clinical laboratory assays. Left-ventricular blood pool time-activity curves showed a multi-phasic blood clearance of 18F-radioactivity with the two rapid clearance phases over the first 20 min, followed by a slower clearance phase. HPLC analysis showed insignificant 18F-labeled metabolites in the blood and urine over the length of the study (4 h). High uptakes were seen in the thyroid, stomach, salivary glands, and bladder. Urinary clearance of 18F-TFB was prominent. Metabolic stability was evidenced by low accumulation of 18F-radioactivity in the bone. Effective doses were 0.036 mSv/MBq in males and 0.064 mSv/MBq in females (p = 0.08, not significant).

CONCLUSIONS

This initial study in healthy human subjects showed 18F-TFB was safe and distributed in the human body similar to other iodide analogs. These data support further translational studies with 18F-TFB as NIS gene reporter and imaging biomarker for thyroid cancer and other disease processes that import iodide.

First PET Imaging Studies With 63Zn-Zinc Citrate in Healthy Human Participants and Patients With Alzheimer Disease

Abnormalities in zinc homeostasis are indicated in many human diseases, including Alzheimer disease (AD). ⁶³Zn-zinc citrate was developed as a positron emission tomography (PET) imaging probe of zinc transport and used in a first-in-human study in 6 healthy elderly individuals and 6 patients with clinically confirmed AD. Dynamic PET imaging of the brain was performed for 30 minutes following intravenous administration of ⁶³Zn-zinc citrate (∼330 MBq). Subsequently, body PET images were acquired. Urine and venous blood were analyzed to give information on urinary excretion and pharmacokinetics. Regional cerebral ⁶³Zn clearances were compared with ¹¹C-Pittsburgh Compound B (¹¹C-PiB) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) imaging data. ⁶³Zn-zinc citrate was well tolerated in human participants with no adverse events monitored. Tissues of highest uptake were liver, pancreas, and kidney, with moderate uptake being seen in intestines, prostate (in males), thyroid, spleen, stomach, pituitary, and salivary glands. Moderate brain uptake was observed, and regional dependencies were observed in ⁶³Zn clearance kinetics in relationship with regions of high amyloid-β plaque burden (¹¹C-PiB) and ¹⁸F-FDG hypometabolism. In conclusion, zinc transport was successfully imaged in human participants using the PET probe ⁶³Zn-zinc citrate. Primary sites of uptake in the digestive system accent the role of zinc in gastrointestinal function. Preliminary information on zinc kinetics in patients with AD evidenced regional differences in clearance rates in correspondence with regional amyloid-β pathology, warranting further imaging studies of zinc homeostasis in patients with AD.

Synthesis of 18F-Tetrafluoroborate via Radiofluorination of Boron Trifluoride and Evaluation in a Murine C6-Glioma Tumor Model

The sodium/iodide symporter (NIS) is under investigation as a reporter for noninvasive imaging of gene expression. Although (18)F-tetrafluoroborate ((18)F-TFB, (18)F-BF4 (-)) has shown promise as a PET imaging probe for NIS, the current synthesis method using isotopic exchange gives suboptimal radiochemical yield and specific activity. The aim of this study was to synthesize (18)F-TFB via direct radiofluorination on boron trifluoride (BF3) to enhance both labeling yield and specific activity and evaluation of specific activity influence on tumor uptake.

METHODS

An automated synthesis of (18)F-TFB was developed whereby cyclotron-produced (18)F-fluoride was trapped on a quaternary methyl ammonium anion exchange cartridge, then allowed to react with BF3 freshly preformulated in petroleum ether/tetrahydrofuran (50:1). The resultant (18)F-TFB product was retained on the quaternary methyl ammonium anion exchange cartridge. After the cartridge was rinsed with tetrahydrofuran and water, (18)F-TFB was eluted from the cartridge with isotonic saline, passing through 3 neutral alumina cartridges and a sterilizing filter. Preclinical imaging studies with (18)F-TFB were performed in athymic mice bearing NIS-expressing C6-glioma subcutaneous xenografted tumors to determine the influence of specific activity on tumor uptake.

RESULTS

Under optimized conditions, (18)F-TFB was synthesized in a radiochemical yield of 20.0% ± 0.7% (n = 3, uncorrected for decay) and greater than 98% radiochemical purity in a synthesis time of 10 min. Specific activities of 8.84 ± 0.56 GBq/μmol (n = 3) were achieved from starting (18)F-fluoride radioactivities of 40-44 GBq. An avid uptake of (18)F-TFB was observed in human NIS (hNIS)-expressing C6-glioma xenografts as well as expected NIS-mediated uptake in the thyroid and stomach. There was a positive correlation between the uptake of (18)F-TFB in hNIS-expressing tumor and specific activity.

CONCLUSION

A rapid, practical, and high-specific-activity synthesis of the NIS reporter probe (18)F-TFB was achieved via direct radiofluorination on BF3 using an automated synthesis system. The synthesis of high-specific-activity (18)F-TFB should enable future clinical studies with hNIS gene reporter viral constructs.

Assessment of myocardial metabolic flexibility and work efficiency in human type 2 diabetes using 16-[18F]fluoro-4-thiapalmitate, a novel PET fatty acid tracer

Altered myocardial fuel selection likely underlies cardiac disease risk in diabetes, affecting oxygen demand and myocardial metabolic flexibility. We investigated myocardial fuel selection and metabolic flexibility in human type 2 diabetes mellitus (T2DM), using positron emission tomography to measure rates of myocardial fatty acid oxidation {16-[(18)F]fluoro-4-thia-palmitate (FTP)} and myocardial perfusion and total oxidation ([(11)C]acetate). Participants underwent paired studies under fasting conditions, comparing 3-h insulin + glucose euglycemic clamp conditions (120 mU·m(-2)·min(-1)) to 3-h saline infusion. Lean controls (n = 10) were compared with glycemically controlled volunteers with T2DM (n = 8). Insulin augmented heart rate, blood pressure, and stroke index in both groups (all P < 0.01) and significantly increased myocardial oxygen consumption (P = 0.04) and perfusion (P = 0.01) in both groups. Insulin suppressed available nonesterified fatty acids (P < 0.0001), but fatty acid concentrations were higher in T2DM under both conditions (P < 0.001). Insulin-induced suppression of fatty acid oxidation was seen in both groups (P < 0.0001). However, fatty acid oxidation rates were higher under both conditions in T2DM (P = 0.003). Myocardial work efficiency was lower in T2DM (P = 0.006) and decreased in both groups with the insulin-induced increase in work and shift in fuel utilization (P = 0.01). Augmented fatty acid oxidation is present under baseline and insulin-treated conditions in T2DM, with impaired insulin-induced shifts away from fatty acid oxidation. This is accompanied by reduced work efficiency, possibly due to greater oxygen consumption with fatty acid metabolism. These observations suggest that improved fatty acid suppression, or reductions in myocardial fatty acid uptake and retention, could be therapeutic targets to improve myocardial ischemia tolerance in T2DM.

Glycogen Synthase Kinase-3 (GSK-3)-Targeted Therapy and Imaging

Glycogen synthase kinase-3 (GSK-3) is associated with various key biological processes, including glucose regulation, apoptosis, protein synthesis, cell signaling, cellular transport, gene transcription, proliferation, and intracellular communication. Accordingly, GSK-3 has been implicated in a wide variety of diseases and specifically targeted for both therapeutic and imaging applications by a large number of academic laboratories and pharmaceutical companies. Here, we review the structure, function, expression levels, and ligand-binding properties of GSK-3 and its connection to various diseases. A selected list of highly potent GSK-3 inhibitors, with IC₅₀ <20 nM for adenosine triphosphate (ATP)-competitive inhibitors and IC₅₀ <5 μM for non-ATP-competitive inhibitors, were analyzed for structure activity relationships. Furthermore, ubiquitous expression of GSK-3 and its possible impact on therapy and imaging are also highlighted. Finally, a rational perspective and possible route to selective and effective GSK-3 inhibitors is discussed.

Tracking and Therapeutic Value of Human Adipose Tissue-derived Mesenchymal Stem Cell Transplantation in Reducing Venous Neointimal Hyperplasia Associated with Arteriovenous Fistula

PURPOSE

To determine if adventitial transplantation of human adipose tissue-derived mesenchymal stem cells (MSCs) to the outflow vein of B6.Cg-Foxn1(nu)/J mice with arteriovenous fistula (AVF) at the time of creation would reduce monocyte chemoattractant protein-1 (Mcp-1) gene expression and venous neointimal hyperplasia. The second aim was to track transplanted zirconium 89 ((89)Zr)-labeled MSCs serially with positron emission tomography (PET) for 21 days.

MATERIALS AND METHODS

All animal experiments were performed according to protocols approved by the institutional animal care and use committee. Fifty B6.Cg-Foxn1(nu)/J mice were used to accomplish the study aims. Green fluorescent protein was used to stably label 2.5 × 10(5) MSCs, which were injected into the adventitia of the outflow vein at the time of AVF creation in the MSC group. Eleven mice died after AVF placement. Animals were sacrificed on day 7 after AVF placement for real-time polymerase chain reaction (n = 6 for MSC and control groups) and histomorphometric (n = 6 for MSC and control groups) analyses and on day 21 for histomorphometric analysis only (n = 6 for MSC and control groups). In a separate group of experiments (n = 3), animals with transplanted (89)Zr-labeled MSCs were serially imaged with PET for 3 weeks. Multiple comparisons were performed with two-way analysis of variance, followed by the Student t test with post hoc Bonferroni correction.

RESULTS

In vessels with transplanted MSCs compared with control vessels, there was a significant decrease in Mcp-1 gene expression (day 7: mean reduction, 62%; P = .029), with a significant increase in the mean lumen vessel area (day 7: mean increase, 176% [P = .013]; day 21: mean increase, 415% [P = .011]). Moreover, this was accompanied by a significant decrease in Ki-67 index (proliferation on day 7: mean reduction, 81% [P = .0003]; proliferation on day 21: mean reduction, 60%, [P = .016]). Prolonged retention of MSCs at the adventitia was evidenced by serial PET images of (89)Zr-labeled cells.

CONCLUSION

Adventitial transplantation of MSCs decreases Mcp-1 gene expression, accompanied by a reduction in venous neointimal hyperplasia.

Production and Transport of Gaseous 18F-Synthons: 18F-Acyl Fluorides

Fluorine-18 (¹⁸F, T _1/2=109.7 min) is a positron-emitting isotope that has found extensive application as a radiolabel for positron emission tomography (PET). Although gaseous ¹¹C-CO₂ and ¹¹C-CH₄ are practically transported from cyclotron to radiochemistry processes, ¹⁸F-fluoride is routinely transported in aqueous solution because it is commonly produced by proton irradiation of ¹⁸O-enriched water. In most cases, subsequent dry-down steps are necessary to prepare reactive ¹⁸F-fluoride for radiofluorination. In this work, a simple module was designed to generate gaseous ¹⁸F-acyl fluorides from aqueous ¹⁸F-fluoride solution by solid phase ¹⁸F-radiofluorination of acyl anhydride. The gaseous ¹⁸F-acyl fluorides were purified through a column containing Porapak Q/Na₂SO₄, resulting in high yields (>86%), purities (>99%) and specific activities (>1200 GBq/μmol). Prototypic ¹⁸F-acetyl fluoride (¹⁸F-AcF) was readily transported through 15 m of 0.8 mm ID polypropylene tubing with low (0.64 ± 0.12 %) adsorption to the tubing. Following dissolution of ¹⁸F-AcF in solvent containing base, highly reactive ¹⁸F-flouride was generated immediately and used directly for ¹⁸F-labeling reactions. These data indicate that ¹⁸F-acyl fluorides represent a new paradigm for preparation and transport of anhydrous, reactive ¹⁸F-fluoride for radiofluorinations.

Novel (89)Zr cell labeling approach for PET-based cell trafficking studies

Background

With the recent growth of interest in cell-based therapies and radiolabeled cell products, there is a need to develop more robust cell labeling and imaging methods for in vivo tracking of living cells. This study describes evaluation of a novel cell labeling approach with the positron emission tomography (PET) isotope ⁸⁹Zr (T_1/2 = 78.4 h). ⁸⁹Zr may allow PET imaging measurements for several weeks and take advantage of the high sensitivity of PET imaging.

Methods

A novel cell labeling agent, ⁸⁹Zr-desferrioxamine-NCS (⁸⁹Zr-DBN), was synthesized. Mouse-derived melanoma cells (mMCs), dendritic cells (mDCs), and human mesenchymal stem cells (hMSCs) were covalently labeled with ⁸⁹Zr-DBN via the reaction between the NCS group on ⁸⁹Zr-DBN and primary amine groups present on cell surface membrane protein. The stability of the label on the cell was tested by cell efflux studies for 7 days. The effect of labeling on cellular viability was tested by proliferation, trypan blue, and cytotoxicity/apoptosis assays. The stability of label was also studied in in vivo mouse models by serial PET scans and ex vivo biodistribution following intravenous and intramyocardial injection of ⁸⁹Zr-labeled hMSCs. For comparison, imaging experiments were performed after intravenous injections of ⁸⁹Zr hydrogen phosphate (⁸⁹Zr(HPO₄)₂).

Results

The labeling agent, ⁸⁹Zr-DBN, was prepared in 55% ± 5% decay-corrected radiochemical yield measured by silica gel iTLC. The cell labeling efficiency was 30% to 50% after 30 min labeling depending on cell type. Radioactivity concentrations of labeled cells of up to 0.5 MBq/10⁶ cells were achieved without a negative effect on cellular viability. Cell efflux studies showed high stability of the radiolabel out to 7 days. Myocardially delivered ⁸⁹Zr-labeled hMSCs showed retention in the myocardium, as well as redistribution to the lung, liver, and bone. Intravenously administered ⁸⁹Zr-labeled hMSCs also distributed primarily to the lung, liver, and bone, whereas intravenous ⁸⁹Zr(HPO₄)₂ distributed to the liver and bone with no activity in the lung. Thus, the in vivo stability of the radiolabel on the hMSCs was evidenced.

Conclusions

We have developed a robust, general, and biostable ⁸⁹Zr-DBN-based cell labeling strategy with promise for wide applications of PET-based non-invasive in vivo cell trafficking.

Synthesis and preliminary evaluation of N-(16-18F-fluorohexadecanoyl)ethanolamine (18F-FHEA) as a PET probe of N-acylethanolamine metabolism in mouse brain

N-Acylethanolamines are lipid signaling molecules found throughout the plant and animal kingdoms. The best-known mammalian compound of this class is anandamide, N-arachidonoylethanolamine, one of the endogenous ligands of cannabinoid CB1 and CB2 receptors. Signaling by N-acylethanolamines is terminated by release of the ethanolamine moiety by hydrolyzing enzymes such as fatty acid amide hydrolase (FAAH) and N-acylethanolamine-hydrolyzing amidase (NAAA). Herein, we report the design and synthesis of N-(16-(18)F-fluorohexadecanoyl)ethanolamine ((18)F-FHEA) as a positron emission tomography (PET) probe for imaging the activity of N-acylethanolamine hydrolyzing enzymes in the brain. Following intravenous administration of (18)F-FHEA in Swiss Webster mice, (18)F-FHEA was extracted from blood by the brain and underwent hydrolysis at the amide bond and incorporation of the resultant (18)F-fluorofatty acid into complex lipid pools. Pretreatment of mice with the FAAH inhibitor URB-597 (1 mg/kg IP) resulted in significantly slower (18)F-FHEA incorporation into lipid pools, but overall (18)F concentrations in brain regions were not altered. Likewise, pretreatment with a NAAA inhibitor, (S)-N-(2-oxo-3-oxytanyl)biphenyl-4-carboxamide (30 mg/kg IV), did not significantly affect the uptake of (18)F-FHEA in the brain. Although evidence was found that (18)F-FHEA behaves as a substrate of FAAH in the brain, the lack of sensitivity of brain uptake kinetics to FAAH inhibition discourages its use as a metabolically trapped PET probe of N-acylethanolamine hydrolyzing enzyme activity.

Preparation and preliminary evaluation of 63Zn-zinc citrate as a novel PET imaging biomarker for zinc

Abnormalities of zinc homeostasis are indicated in many human diseases. A noninvasive imaging method for monitoring zinc in the body would be useful to understand zinc dynamics in health and disease. To provide a PET imaging agent for zinc, we have investigated production of (63)Zn (half-life, 38.5 min) via the (63)Cu(p,n)(63)Zn reaction using isotopically enriched solutions of (63)Cu-copper nitrate. A solution target was used for rapid isolation of the (63)Zn radioisotope from the parent (63)Cu ions. Initial biologic evaluation was performed by biodistribution and PET imaging in normal mice.

METHODS

To produce (63)Zn, solutions of (63)Cu-copper nitrate in dilute nitric acid were irradiated by 14-MeV protons in a low-energy cyclotron. An automated module was used to purify (63)Zn from (63)Cu in the target solution. The (63)Cu-(63)Zn mixture was trapped on a cation-exchange resin and rinsed with water, and the (63)Zn was eluted using 0.05 N HCl in 90% acetone. The resulting solution was neutralized with NaHCO3, and the (63)Zn was then trapped on a carboxymethyl cartridge, washed with water, and eluted with isotonic 4% sodium citrate. Standard quality control tests were performed on the product according to current good manufacturing practice, including radionuclidic identity and purity, and measurement of nonradioactive Zn(+2), Cu(+2), Fe(+3), and Ni(+2) by ion-chromatography high-performance liquid chromatography. Biodistribution and PET imaging studies were performed in B6.SJL mice after intravenous administration of (63)Zn-zinc citrate. (63)Cu target material was recycled by eluting the initial resin with 4N HNO3.

RESULTS

Yields of 1.07 ± 0.22 GBq (uncorrected at 30-36 min after end of bombardment) of (63)Zn-zinc citrate were obtained with a 1.23 M (63)Cu-copper nitrate solution. Radionuclidic purity was greater than 99.9%, with copper content lower than 3 μg/batch. Specific activities were 41.2 ± 18.1 MBq/μg (uncorrected) for the (63)Zn product. PET and biodistribution studies in mice at 60 min showed expected high uptake in the pancreas (standard uptake value, 8.8 ± 3.2), liver (6.0 ± 1.9), upper intestine (4.7 ± 2.1), and kidney (4.2 ± 1.3).

CONCLUSION

A practical and current good manufacturing practice-compliant preparation of radionuclidically pure (63)Zn-zinc citrate has been developed that will enable PET imaging studies in animal and human studies. (63)Zn-zinc citrate showed the expected biodistribution in mice.

Cyclotron production of (68)Ga via the (68)Zn(p,n)(68)Ga reaction in aqueous solution

The objective of the present work is to extend the applicability of the solution target approach to the production of (68)Ga using a low energy cyclotron. Since the developed method does not require solid target infrastructure, it offers a convenient alternative to (68)Ge/(68)Ga generators for the routine production of (68)Ga. A new solution target with enhanced heat exchange capacity was designed and utilized with dual foils of Al (0.20 mm) and Havar (0.038 mm) separated by helium cooling to degrade the proton energy to ~14 MeV. The water-cooled solution target insert was made of Ta and its solution holding capacity (1.6 mL) was reduced to enhance heat transfer. An isotopically enriched (99.23%) 1.7 M solution of (68)Zn nitrate in 0.2 N nitric acid was utilized in a closed target system. After a 30 min irradiation at 20 μA, the target solution was unloaded to a receiving vessel and the target was rinsed with 1.6 mL water, which was combined with the target solution. An automated module was used to pass the solution through a cation-exchange column (AG-50W-X8, 200-400 mesh, hydrogen form) which efficiently trapped zinc and gallium isotopes. (68)Zn was subsequently eluted with 30 mL of 0.5 N HBr formulated in 80% acetone without any measurable loss of (68)Ga. (68)Ga was eluted with 7 mL of 3 N HCl solution with 92-96% elution efficiency. The radionuclidic purity was determined using an HPGe detector. Additionally, ICP-MS was employed to analyze for non-radioactive metal contaminants. The product yield was 192.5 ± 11.0 MBq/μ·h decay-corrected to EOB with a total processing time of 60-80 min. The radionuclidic purity of (68)Ga was found to be >99.9%, with the predominant contaminant being 67Ga. The ICP-MS analysis showed small quantities of Ga, Fe, Cu, Ni and Zn in the final product, with (68)Ga specific activity of 5.20-6.27 GBq/μg. Depending upon the user requirements, (68)Ga production yield can be further enhanced by increasing the (68)Zn concentration in the target solution and extending the irradiation time. In summary, a simple and efficient method of (68)Ga production was developed using low energy cyclotron and a solution target. The developed methodology offers a cost-effective alternative to the (68)Ge/(68)Ga generators for the production of (68)Ga.

Structure dependence of long-chain [18F]fluorothia fatty acids as myocardial fatty acid oxidation probes

In vivo imaging of regional fatty acid oxidation (FAO) rates would have considerable potential for evaluation of mammalian diseases. We have synthesized and evaluated 18F-labeled thia fatty acid analogues as metabolically trapped FAO probes to understand the effect of chain length, degree of unsaturation, and placement of the thia substituent on myocardial uptake and retention. 18-[18F]Fluoro-4-thia-(9Z)-octadec-9-enoic acid (3) showed excellent heart/background radioactivity concentration ratios along with highest retention in heart and liver. Pretreatment of rats with the CPT-1 inhibitor, POCA, caused >80% reduction in myocardial uptake of 16-[18F]fluoro-4-thiahexadecanoic acid (2) and 3, indicating high specificity for FAO. In contrast, 18-[18F]fluoro-4-thiaoctadecanoic acid (4) showed dramatically reduced myocardial uptake and blunted response to POCA. 18-[18F]Fluoro-6-thiaoctadecanoic acid (5) showed moderate myocardial uptake and no sensitivity of myocardial uptake to POCA. The results demonstrate relationships between structures of 18F-labeled thia fatty acid and uptake and their utility as FAO probes in various tissues.

Choline phosphorylation and regulation of transcription of choline kinase α in hypoxia

Choline kinase catalyzes the phosphorylation of choline, the first step of phospholipid synthesis. Increased phosphorylation of choline is a hallmark characteristic of the malignant phenotype in a variety of neoplasms. However, in hypoxic cancer cells, choline phosphorylation is decreased. To understand the mechanism behind this altered metabolic state, we examined the expression and regulation of the major choline kinase isoform, choline kinase α (ChKα), in hypoxic PC-3 human prostate cancer cells. Hypoxia decreased choline phosphorylation, choline kinase activity, and ChKα mRNA and protein levels. Promoter analysis studies revealed a region upstream of the ChKα gene bearing a conserved DNA consensus binding motif, hypoxia response element-7 (HRE7), at position -222 relative to +1 translation start site, for binding the hypoxia dependent master regulator transcription factor, hypoxia-inducible factor 1α (HIF-1α). Electrophoretic mobility shift competition/supershift assay and chromatin immunoprecipitation assay confirmed binding of HIF-1α to HRE7. A putative promoter of ChKα was isolated from PC-3 genomic DNA and cloned into a luciferase-based reporter vector system. In PC-3 cells, hypoxia decreased the expression of luciferase under the control of the ChKα promoter. Mutation of HRE7 abrogated this hypoxia effect, further demonstrating the involvement of HRE7 in hypoxia-sensitive regulation of ChKα. The results strongly suggest that transcriptional control of choline phosphorylation is largely mediated via HIF-1α binding to the newly identified HRE7.

Microwave-assisted radiosynthesis of [18F]fluorinated fatty acid analogs

Microwave reactors remain largely underutilized in the field of positron emission tomography (PET) chemistry. This is particularly unfortunate since microwave synthesis elegantly addresses two of the most critical issues of PET radiochemistry with short-lived radionuclides: reaction rate and side-product formation. In this study, we investigate the efficiency of synthesis of terminally [(18)F]fluorinated fatty acid analogs using a commercial microwave reactor in comparison with conventional heating (CH).

METHODS

The labeling precursors were methyl esters of terminally substituted alkyl bromides and iodides. Duration and temperatures of the [(18)F]fluorination reaction were varied. Chemical and radiochemical purities, and radiochemical yields were investigated for conventional (CH) and microwave-assisted (MW) radiosyntheses.

RESULTS

The results demonstrate that microwave heating enhanced [(18)F]fluoride incorporation to >95% (up to 55% improvement), while reducing reaction times to 2 min (∼ 10-fold reduction) or temperatures to 55-60 °C (20 °C reduction). Overall decay-corrected radiochemical yields of purified [(18)F]fluoro fatty acids were higher (MW = 49.0 ± 4.5%, CH = 23.6 ± 3.5%, P < .05) with microwave heating and side-products were notably fewer.

CONCLUSION

For routine synthesis of [(18)F]fluoro fatty acid analogs, microwave heating is faster, milder, cleaner, less variable and higher yielding than CH and therefore the preferred reaction method.

Synthesis and preliminary evaluation of 18-(18)F-fluoro-4-thia-oleate as a PET probe of fatty acid oxidation

Fatty acid oxidation (FAO) is a major energy-providing process with important implications in cardiovascular, oncologic, neurologic, and metabolic diseases. A novel 4-thia oleate analog, 18-(18)F-fluoro-4-thia-oleate ((18)F-FTO), was evaluated in relationship to the previously developed palmitate analog 16-(18)F-fluoro-4-thia-palmitate ((18)F-FTP) as an FAO probe.

METHODS

(18)F-FTO was synthesized from a corresponding bromoester. Biodistribution and metabolite analysis studies were performed in rats. Preliminary small-animal PET studies were performed with (18)F-FTO and (18)F-FTP in rats.

RESULTS

A practical synthesis of (18)F-FTO was developed, providing a radiotracer of high radiochemical purity (>99%). In fasted rats, myocardial uptake of (18)F-FTO (0.70 +/- 0.30% dose kg [body mass]/g [tissue mass]) was similar to that of (18)F-FTP at 30 min after injection. At 2 h, myocardial uptake of (18)F-FTO was maintained, whereas (18)F-FTP uptake in the heart was 82% reduced. Similar to (18)F-FTP, (18)F-FTO uptake by the heart was approximately 80% reduced at 30 min by pretreatment of rats with the CPT-I inhibitor etomoxir. Folch-type extraction analyses showed 70-90% protein-bound fractions in the heart, liver, and skeletal muscle, consistent with efficient trafficking of (18)F-FTO to the mitochondrion with subsequent metabolism to protein-bound species. Preliminary small-animal PET studies showed rapid blood clearance and avid extraction of (18)F-FTO and of (18)F-FTP into the heart and liver. Images of (18)F-FTO accumulation in the rat myocardium were clearly superior to those of (18)F-FTP.

CONCLUSION

(18)F-FTO is shown to be a promising metabolically trapped FAO probe that warrants further evaluation.

Abstract LB-377: Regulation of expression of choline kinase by a conserved HIF1 binding hypoxia-responsive element

Hypoxic microenvironment and overexpression of choline kinase alpha (ChKa) have been associated with tumor malignancy, but the regulation of ChKa expression in hypoxic conditions is poorly understood. In this study, the effects of chronic hypoxia on choline metabolism and ChKa expression were examined in prostate cancer cell line, PC-3. Chronic hypoxia (1% O2, 24h) decreased proliferation rate and intracellular levels of phosphocholine, while intracellular levels of free choline were increased. Choline tracer uptake and washout studies confirmed the decreased rate of choline phosphorylation in hypoxic cells. Overexpression of HIF1a or DMOG exposure in normoxic PC-3 cells decreased both choline uptake and choline kinase activity. RT-PCR analysis showed decreased transcription of ChKa gene in hypoxic PC-3 correlating with decreased enzymatic activity of choline kinase in hypoxic cell extracts. Alignment of nucleotide sequence of the putative promoter region of ChKa from rat, mouse, chimpanzee and human revealed a highly conserved hypoxia responsive element upstream to transcription start site of ChKa. Electrophoretic mobility shift competition/supershift assay and chromatin immunoprecipitation-quantitative PCR assay confirmed binding of native HIF-1α protein to the conserved HRE. To understand the transcription control of ChKa under hypoxia, a putative promoter of ChKa was isolated from PC-3 genomic DNA and cloned into a luciferase (Luc) based reporter vector system. In PC-3, hypoxia decreased the expression of Luc under the control of the ChKa promoter. Mutation of the conserved HRE and subsequent Luc reporter assays demonstrated that this HRE is involved in hypoxia/HIF1α mediated regulation of ChKa. The results suggest that the decreased choline phosphorylation in PC-3 cells in response to hypoxia is mediated in part by the newly-identified conserved HIF1α binding HRE.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-377.

Use of pressure-hold test for sterilizing filter membrane integrity in radiopharmaceutical manufacturing

The bubble point test is the de facto standard for postproduction filter membrane integrity test in the radiopharmaceutical community. However, the bubble point test depends on a subjective visual assessment of bubbling rate that can be obscured by significant diffusive gas flows below the manufacturer's prescribed bubble point. To provide a more objective means to assess filter membrane integrity, this study evaluates the pressure-hold test as an alternative to the bubble point test. In our application of the pressure-hold test, the nonsterile side of the sterilizing filter is pressurized to 85% of the predetermined bubble point with nitrogen, the filter system is closed off from the pressurizing gas and the pressure is monitored over a prescribed time interval. The drop in pressure, which has a known relationship with diffusive gas flow, is used as a quantitative measure of membrane integrity. Characterization of the gas flow vs. pressure relationship of each filter/solution combination provides an objective and quantitative means for defining a critical value of pressure drop over which the membrane is indicated to be nonintegral. The method is applied to sterilizing filter integrity testing associated with the commonly produced radiopharmaceuticals, [(18)F]FDG and [(11)C]PIB. The method is shown to be robust, practical and amenable to automation in radiopharmaceutical manufacturing environments (e.g., hot cells).

Synthesis and evaluation of near-infrared (NIR) dye-herceptin conjugates as photoacoustic computed tomography (PCT) probes for HER2 expression in breast cancer

We are evaluating PCT imaging in conjunction with NIR dye labeled Herceptin antibody for noninvasive assessment of HER2 expression in tumors. Herceptin was labeled with Alexa Fluor-750 amine reactive dye for characterization of photoacoustic and fluorescence signals. Measurements were performed in solution and after incubation in cultured cell lines that were positive or negative in expression of HER2. The dye to antibody ratio was controlled to achieve a broad range of degree of labeling (DOL = 2 to 15). Photoacoustic signal intensity of Herceptin-dye conjugates in solution increased with increases over the entire DOL range studied. In contrast, fluorescence exhibited significant quenching for higher DOL. In vitro PCT imaging of the labeled HER2 (+) and HER2 (-) cells revealed the targeting specificity of the NIR dye labeled Herceptin. In HER2 (+) cells lines, photoacoustic signal intensity gradually increased with increasing DOL and with increasing number of cells. These results demonstrate that PCT-based measurement of HER2 receptor binding using NIR dye labeled Herceptin is feasible. The absence of a quenching effect with increased DOL advantages this method over traditional methods based on fluorescence measurement.

Cancer imaging with fluorine-18-labeled choline derivatives

The choline transporter and choline kinase enzyme frequently are overexpressed in malignancy. Therefore, positron-emitter-labeled compounds derived from choline have the potential to serve as oncologic probes for positron emission tomography. The fluorine-18 ((18)F)-labeled choline derivative fluorocholine (FCH) in particular has demonstrated potential utility for imaging of a variety of neoplasms, including those of the breast, prostate, liver, and brain. The pharmacokinetics of FCH and other choline tracers allow for whole-body imaging within minutes of injection while still achieving high tumor-to-background contrast in most organs, including the brain. These features, along with the possibility of imaging malignancies that have proved elusive with the use of (18)F-fluorodeoxyglucose positron emission tomography support further clinical investigations of (18)F-labeled choline tracers.

Synthesis and biodistribution of new radiolabeled high-affinity choline transporter inhibitors [11C]hemicholinium-3 and [18F]hemicholinium-3

The high-affinity choline transporter (CHT1) system is an attractive target for the development of positron emission tomography (PET) biomarkers to probe brain, cardiac, and cancer diseases. An efficient and convenient synthesis of new radiolabeled CHT1 inhibitors [(11)C]hemicholinium-3 and [(18)F]hemicholinium-3 by solid-phase extraction (SPE) technique using a cation-exchange CM Sep-Pak cartridge has been well developed. The preliminary evaluation of both tracers through biodistribution studies in 9L-glioma rats has been performed, and the uptakes in the heart and tumor were observed, while very low brain uptake was seen.

Evaluation of [11C]hemicholinium-15 and [18F]hemicholinium-15 as new potential PET tracers for the high-affinity choline uptake system in the heart

[(11)C]Hemicholinium-15 ([(11)C]HC-15) and [(18)F]hemicholinium-15 ([(18)F]HC-15) have been synthesized as new potential PET tracers for the heart high-affinity choline uptake (HACU) system. [(11)C]HC-15 was prepared by N-[(11)C]methylation of the appropriate precursor, 4-methyl-2-phenyl-morpholin-2-ol, using [(11)C]CH(3)OTf in 55-70% radiochemical yield decay corrected to end of bombardment (EOB) and 2-3Ci/mumol specific activity at end of synthesis (EOS). [(18)F]HC-15 was prepared by N-[(18)F]fluoromethylation of the precursor using [(18)F]FCH(2)OTf in 20-30% radiochemical yield decay corrected to EOB and >1.0Ci/mumol specific activity at EOS. The biodistribution of both compounds was determined in rats at 20min post-intravenous injection, and the results show the heart region uptakes 1.32+/-0.75%ID/g in R-ventricle for [(11)C]HC-15 and 1.28+/-0.81%ID/g in L-ventricle for [(18)F]HC-15, respectively. The dynamic PET imaging studies of [(11)C]HC-15 in rats were acquired 60min post-intravenous injection of the tracer using the IndyPET-II scanner. For the blocking experiments, the rats were intravenously pretreated with 3.0mg/kg of unlabeled HC-15 prior to [(11)C]HC-15 injection. [(11)C]HC-15 rat heart PET studies show rapid heart uptake to give clear heart images. The rat heart PET blocking studies found no significant blocking effect. The dynamic PET studies in normal and ablated dogs were performed using Siemens PET scanner with [(13)N]NH(3), [(11)C]HC-15, and [(18)F]HC-15. PET studies in dogs of both [(11)C]HC-15 and [(18)F]HC-15 also show significant heart uptake and give images of the heart. However, there is no significant change in [(11)C]HC-15 L-ventricle uptake following radiofrequency ablation in the dog. These results suggest that the localization of HC-15 tracers in the heart is mediated by non-specific processes, and the visualization of HC-15 tracers on the heart is related to non-specific binding of HACU.

Effect of hypoxia on the uptake of [methyl-3H]choline, [1-14C] acetate and [18F]FDG in cultured prostate cancer cells

INTRODUCTION

Choline, acetate and glucose ([2-(18)F]fluoro-2-deoxyglucose, [(18)F]FDG) analogs are under investigation as positron emission tomography (PET) tracers for the imaging of prostate cancer; however, their response to tumor hypoxia has not been clarified.

METHODS

The uptake of [methyl-(3)H]choline, [1-(14)C]acetate and [(18)F]FDG was monitored in androgen-independent PC-3 cells and androgen-sensitive LNCaP cells under aerobic or anoxic conditions. The effect of androgen depletion was also examined.

RESULTS

PC-3 cells exhibited aerobic choline and acetate uptake five to six times higher than FDG uptake, whereas LNCaP cells showed choline uptake 2.2-fold higher than acetate uptake and 10-fold higher than FDG uptake. After 4 h of anoxia, PC-3 cells showed an 85% increase in FDG uptake, a 15% decrease in choline uptake and a 36% increase in acetate uptake, whereas LNCaP cells showed a 212% increase in FDG uptake, a 28% decrease in choline uptake and no change in acetate uptake. Androgen depletion resulted in a marked decrease in the uptake of all tracers in LNCaP cells but no changes in PC-3 cells.

CONCLUSION

In aerobic conditions, both PC-3 and LNCaP cells exhibited an order of uptake preference as follows: choline>acetate>FDG. In hypoxic cells, the order is reversed, reflecting diverse biochemical responses to hypoxia. These findings may help to explain PET imaging findings of the diverse responses of these tracers in different stages and locations of prostate cancer. Androgen depletion markedly suppressed the uptake of all three tracers in LNCaP cells, which suggests the potential for underestimation of the disease state when PET imaging is performed subsequent to antiandrogen therapy.

Choline transporter as a novel target for molecular imaging of cancer

Abnormalities of choline processing in cancer cells have been used as a basis for imaging of cancer with positron emission tomography and magnetic resonance spectroscopy. In this study, the transport mechanism for choline was investigated in cultured PC-3 prostate cancer cells. Furthermore, tritiated hemicholinium 3 (HC-3), a well-known inhibitor of choline transport, was studied as a prototypic molecular imaging probe in PC-3 cells and 9L glioma-bearing rats. [(3)H]Choline uptake by PC-3 cells was found to have both facilitative and nonfacilitative components. Facilitative transport was characterized by partial sodium dependence and intermediate affinity (K(M) = 9.7 +/- 0.8 microM). HC-3 inhibited choline with a K(I) of 10.5+/- 2.2 microM. Ouabain (1 mM) caused a 94% reduction in choline uptake. At physiologic choline concentration, phosphocholine was the rapid and predominant metabolic fate. The binding of [(3)H]HC-3 to PC-3 cells was rapid and specific (competitively blocked with unlabeled HC-3). Biodistribution of [(3)H]HC-3 in 9L glioma-bearing rats showed the ranking of uptake to be kidney > lung > tumor > liver > skeletal muscle congruent with blood > brain. In comparison with [(14)C]choline, [(3)H]HC-3 showed over twofold higher tumor uptake and favorable uptake ratios of tumor to blood, tumor to muscle, tumor to lung, and tumor to liver. The data demonstrate the quantitative importance of an intermediate-affinity, partially sodium-dependent choline transport system on choline processing in PC-3 cancer cells. The biodistribution properties of [(3)H]HC-3 in tumor-bearing rats encourage the development of molecular imaging probes based on choline transporter binding ligands.

Validation of 18F-fluoro-4-thia-palmitate as a PET probe for myocardial fatty acid oxidation: effects of hypoxia and composition of exogenous fatty acids

Fatty acid oxidation (FAO) is the predominant energy-producing pathway in the healthy heart. Abnormalities in FAO are associated with many ischemic and nonischemic disease states. The aim of the present study was to further validate 16-[(18)F]-fluoro-4-thia-palmitate ((18)F-FTP) as a metabolically trapped FAO probe in the isolated perfused rat heart model by examining both the effects of hypoxia and the effects of changes in exogenous fatty acid availability.

METHODS

Hearts were excised from Sprague-Dawley rats and perfused in the Langendorff mode with Krebs-Henseleit solution under the following conditions: palmitate at 0.4 mmol/L with 95% oxygen, palmitate at 0.4 mmol/L with 35% oxygen, palmitate at 0.2 mmol/L plus oleate at 0.2 mmol/L with 95% oxygen, and palmitate at 0.2 mmol/L plus oleate at 0.2 mmol/L with 35% oxygen. Hearts were paced at 270 beats per minute, and the rate of left ventricular pressure change (LV dP/dt) was monitored. (18)F-FTP in the perfusion medium was administered for 20 min, and this step was followed by a 20-min washout period without tracer in the perfusion medium. (18)F kinetics in the whole heart were monitored externally, and the time-activity curves were analyzed to determine the fractional trapping rate for (18)F-FTP (FTR(FTP)). A "lumped constant" (LC) was defined as the ratio of FTR(FTP) to the fractional rate of oxidation of fatty acid in the perfusion medium.

RESULTS

The kinetic data for (18)F-FTP demonstrated metabolic trapping of (18)F radioactivity that was insensitive to changes in the mixture of fatty acids in the perfusion medium but that was sensitive to the inhibition of mitochondrial FAO by hypoxia. LV dP/dt was reduced 47%-67% in hypoxic hearts relative to hearts with normal oxygenation (controls). FAO rates for palmitate and oleate were similar in group 3 (palmitate alone) and group 4 (palmitate and oleate). FAO was decreased 70%-76% with hypoxia, whereas FTR(FTP) was reduced 86%-88%, demonstrating hypersensitivity of a change in (18)F-FTP retention to FAO inhibition by oxygen deprivation. The (18)F-FTP LC was approximately 2 in myocardium with normal oxygenation and fell to 1.0-1.2 in hypoxic myocardium.

CONCLUSION

The results confirm (18)F-FTP to be a metabolically trapped palmitate analog that is capable of indicating rates of myocardial oxidation of exogenous long-chain fatty acids. The heterogeneous nature of fatty acids in plasma does not alter the quantitative analysis of (18)F-FTP kinetics. However, the decreased LC value in hypoxic myocardium suggests the need to develop an understanding of the relationship of (18)F-FTP processing to natural fatty acids at key limiting transport and metabolism processes, analogous to previous studies examining the LC values for radiolabeled deoxyglucose tracers used to estimate the glucose metabolic rate.

Therapeutic angiogenesis in chronically ischemic porcine myocardium: comparative effects of bFGF and VEGF

BACKGROUND

Both vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) have been used in preclinical studies to induce new blood vessel growth in ischemic cardiac muscle with promising results. However, clinical trials have been much less convincing and further work is needed. This study expands on prior work by comparing the long-term proangiogenic effects of direct intramyocardial (IM) injection of bFGF, as well as IM and intravenous (IV) VEGF in a porcine model of chronic hibernating myocardium.

METHODS

Mini-swine with proximal 90% left circumflex (LCx) coronary stenosis subtending chronically ischemic, viable (hibernating) myocardium by positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were randomized to IM bFGF (n = 5), IM VEGF(165) (n = 5), IV VEGF(165) (n = 5), IM vehicle (n = 5), or sham redo-thoracotomy (n = 4). The bFGF protein was administered in a total dose of 1.35 microg divided into 30 IM injections. IM VEGF(165) protein was administered in a total dose of 15 microg/kg divided into 30 injections; IV VEGF(165) was given at a dose of 50 ng. kg(-1). min(-1) for 200 minutes at three 72-hour intervals (30 microg/kg total dose). After 3 and 6 months the PET and DSE studies were repeated, and the animals were sacrificed for tissue vascular density and angiogenic protein analysis.

RESULTS

Myocardial blood flow (MBF) by PET was significantly improved 3 months posttreatment in the IM bFGF and IM VEGF(165) groups, differences that were sustained at 6 months. There was no significant increase in MBF 3-months posttreatment in the IV VEGF(165) group; however, at 6 months MBF was significantly improved. No change in MBF was seen in the IM vehicle or sham groups. Regional wall motion at rest and peak stress in the LCx region demonstrated small but statistically significant improvements by 6 months in the IM bFGF and IV VEGF(165) groups only; no improvement was seen in the IM VEGF(165), IM vehicle, or sham groups. Quantitative vascular density was significantly increased in the LCx regions of all treatment groups (IM bFGF, IM VEGF(165), IV VEGF(165)) 6-months postoperatively. No significant increase in LCx region myocardial bFGF or VEGF protein levels was seen in the treated animals at 6 months.

CONCLUSIONS

The IM bFGF, IM VEGF(165), and IV VEGF(165) all improve regional perfusion and vascular density 6-months posttherapy in the animal model utilized. Functional improvements were less consistent. Both bFGF and VEGF(165) may be useful therapies for improving regional perfusion in chronically ischemic myocardium, although combination therapy with additional growth factors or cellular therapies may be necessary if concomitant improvements in function are to be seen.