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The design and radiosynthesis of [18F]NT376, a high potency inhibitor of class-IIa histone deacetylases (HDAC) is reported. We utilized a three-step radiochemical approach that led to the radiosynthesis of [18F]NT376 in a good radiochemical yield, (17.0 ± 3%, decay corrected), high radiochemical purity (> 97%) and relatively high molar activity of 185.0 GBq/µmol (> 5.0 Ci/µmol). The repositioning of the 18F-radiolabel into a phenyl ring (18F-Fluoro-aryl) of the class-IIa HDAC inhibitor avoided the shortcomings of the direct radiolabeling of the 5-trifluoromethyl-1,2,4-oxadiazole moiety that was reported by us previously and was associated with low molar activity (0.74–1.51 GBq/µmol, 20–41 mCi/µmol). This radiochemical approach could find a wider application for radiolabeling similar molecules with good radiochemical yield and high molar activity. [ABSTRACT FROM AUTHOR]

Given our interest in the utility of liposomes for molecular imaging and theranostics, we investigated how coating the outer layer of the liposome affects internalization by breast cancer cell lines in vitro and in breast tumor tissues in vivo. Indeed, we discovered that a remarkably high liposomal uptake can be achieved by DBCO (dibenzocyclooctyne) soft coating. Our data demonstrates that decorating the terminal lipid with a DBCO moiety at a specific density induces increased tumor uptake in vivo (tumor uptake ~ 50%) compared to conventional undecorated liposome (tumor uptake ~ 20%). In this study, we report improved visualization of breast cancer cells in vivo using a 4T1 orthotopic breast cancer model and primary breast tumor xenograft models MDA-MB-231 and MDA-MB-436. L-PEG2000-DBCO coated liposomes demonstrate increased accumulation in breast cancer cells independent of tumor size, type, position, receptor expression, as well as the condition of the host mice. We expect these findings to have a major positive impact on the practical utility of liposomes in image-guided applications and precision medicine theranostics. [ABSTRACT FROM AUTHOR]

Introduction Earlier, we reported syntheses of ethyl- β- d-galactopyranosyl-(1,4′)-2′-deoxy-2′-[18F]fluoro- β- d-glucopyranoside (Et-[18F]FDL) and 1′-[18F]fluoroethyl- β- d-lactose ([18F]-FEL) for positron emission tomography (PET) of pancreatic carcinoma. Et-[18F]FDL requires a precursor, which involves 11 steps to synthesize and produces overall low yields. Synthesis of precursors for [18F]-FEL requires four steps, but those precursors produced low radiochemical yields. Here, we report new precursors and an improved synthesis of [18F]-FEL. Method Two precursors, 1′-(methanesulfonyl)ethyl-2′,3′,6′,2,3,4,6-hepta- O-acetyl- β- d-lactose 2a and 1′-( p-nitrophenyl-sulfonyl)ethyl-2′,3′,6′,2,3,4,6-hepta- O-acetyl- β- d-lactose 2b, were synthesized from lactose in four steps. Radiofluorination reactions were performed using K18F/kryptofix and the crude product [18F]-3 was purified by HPLC. Basic hydrolysis of [18F]-3 produced 1′-[18F]fluoroethyl- β- d-lactose [18F]-4, which was neutralized, diluted with saline, filtered on a 0.22-µm filter, and analyzed by radio-TLC. Results The average radiochemical yields of [18F]-4 (d. c.) from 2a and 2b were 21% ( n = 6) and 65% ( n = 6), respectively, with >99% radiochemical purity and specific activity of 55.5 GBq/µmol. Synthesis time was 90-95 min from the end of bombardment. Conclusion An improved synthesis of [18F]FEL has been achieved in high yields, with high purity and specific activity. Precursor 2b with this method should be applicable for high yield automated production in a commercial synthesis module for clinical application. [ABSTRACT FROM AUTHOR]

Abstract: Direct fluorination at the 2′-arabino-position of a pyrimidine nucleoside has been a long-standing challenge, yet we recently reported such a stereospecific fluorination for the first time in the synthesis of [18F]FMAU, albeit in low yields. Herein we report the results of an investigation on stereospecific fluorination on a variety of precursors for synthesis of [18F]FMAU. Several precursors were synthesized in multiple steps and fluorination was performed at the 2′-arabino-position using K[18F]/kryptofix 2.2.2. All precursors produced [18F]FMAU in low yields. [Copyright &y& Elsevier]

Abstract: Introduction: The cannabinoid receptor type 2 (CB2) is an important target for development of drugs and imaging agents for diseases, such as neuroinflammation, neurodegeneration and cancer. Recently, we reported synthesis and results of in vitro receptor binding of a focused library of fluorinated 2-oxoquinoline derivatives as CB2 receptor ligands. Some of the compounds demonstrated to be good CB2-specific ligands with Ki values in the nanomolar to subnanomolar concentrations; therefore, we pursued the development of their 18F-labeled analogues that should be useful for positron emission tomography (PET) imaging of CB2 receptor expression. Here, we report the radiosynthesis of two 18F-labeled 2-oxoquinoline derivatives and the preliminary in vitro and ex vivo evaluation of one compound as a CB2-specific radioligand. Methods: 4-[18F]fluorobenzyl amine [18F]-3 was prepared by radiofluorination of 4-cyano-N,N,N-trimethylanilinium triflate salt followed by reduction with LiAlH4 and then coupled with acid chlorides 11 and 12 to afford [18F]-13 and [18F]-14. In vitro CB2 receptor binding assay was performed using U87 cells transduced with CB2 and CB1 receptor. Ex vivo autoradiography was performed with [18F]-14 on spleen and on CB2- and CB1-expressing and wild-type U87 subcutaneous tumors grown in mice. Results: The radiochemical yields of [18F]-13 and [18F]-14 were 10%–15.0% with an average of 12% (n=10); radiochemical purity was >99% with specific activity 1200 mCi/μmol. The dissociation constant Kd for [18F]-14 was 3.4 nM. Ex vivo autoradiography showed accumulation of [18F]-14 in the CB2-expressing tumor. Conclusion: Two new [18F]-labeled CB2 ligands have been synthesized. Compound [18F]-14 appears to be a potential PET imaging agent for the assessment of CB2 receptor expression; however, poor solubility restrain its use in vivo. [Copyright &y& Elsevier]

The synthesis, biochemical evaluation and radiosynthesis of a cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor and radioligand was performed. NT431, a newly synthesized 4-fluorobenzyl-abemaciclib, exhibited high potency to CDK4/6 and against four cancer cell lines with IC 50 similar to that of the parent abemaciclib. We performed a two-step one-pot radiosynthesis to produce [ 18 F]NT431 with good radiochemical yield (9.6 ± 3%, n = 3, decay uncorrected), high radiochemical purity (>95%), and high molar activity (>370 GBq/µmol (>10.0 Ci/µmol). In vitro autoradiography confirmed the specific binding of [ 18 F]NT431 to CDK4/6 in brain tissues. Dynamic PET imaging supports that both [ 18 F]NT431 and the parent abemaciclib crossed the BBB albeit with modest brain uptake. Therefore, we conclude that it is unlikely that NT431 or abemaciclib (FDA approved drug) can accumulate in the brain in sufficient concentrations to be potentially effective against breast cancer brain metastases or brain cancers. However, despite the modest BBB penetration, [ 18 F]NT431 represents an important step towards the development and evaluation of a new generation of CDK4/6 inhibitors with superior BBB penetration for the treatment and visualization of CDK4/6 positive tumors in the CNS. Also, [ 18 F]NT431 may have potential application in peripheral tumors such as breast cancer and other CDK4/6 positive tumors.

We utilized positron emission tomography (PET) imaging in vivo to map the spatiotemporal biodistribution/expression of class-IIa histone deacetylases (class-IIa HDACs) in the central nervous system (CNS). Herein we report an improved radiosynthesis of [ 18 F]NT160 using 4-hydroxy-TEMPO which led to a significant improvement in radiochemical yield and molar activity. PET imaging with [ 18 F]NT160, a highly potent class-IIa HDAC inhibitor, led to high-quality and high-contrast images of the brain. [ 18 F]NT160 displayed excellent pharmacokinetic and imaging characteristics: brain uptake is high in gray matter regions, tissue kinetics are appropriate for a 18 F-tracer, and specific binding for class-IIa HDACs is demonstrated by self-blockade. Higher uptake with [ 18 F]NT160 was observed in the hippocampus, thalamus, and cortex while the uptake in the cerebellum was relatively low. Overall, our current studies with [ 18 F]NT160 will likely facilitate the development and clinical translation of PET tracers for imaging of class-IIa HDACs biodistribution/expression in cancer and the CNS.

Deep-seated bacterial infections caused by pathogens such as Staphylococcus aureus are difficult to diagnose and treat and are thus a major threat to human health. In previous work we demonstrated that positron emission tomography (PET) imaging with 2-[ 18 F]F- p -aminobenzoic acid (2-[ 18 F]F-PABA) could noninvasively identify, localize, and monitor S. aureus infection with excellent sensitivity and specificity in a rodent soft tissue infection model. However, 2-[ 18 F]F-PABA is rapidly N-acetylated and eliminated, and in an attempt to improve radiotracer accumulation in bacteria we adopted a prodrug strategy in which the acid was protected by an ester and the amine was replaced with a nitro group. Metabolite analysis indicated that the nitro group of ethyl 2-[ 18 F]fluoro-4-nitrobenzoate (2-[ 18 F]F-ENB) is converted to the corresponding amine by bacteria-specific nitroreductases while the ester is hydrolyzed in vivo into the acid. PET/CT imaging of 2-[ 18 F]F-ENB and the corresponding acid 2-[ 18 F]F-NB in a rat soft tissue infection model demonstrated colocalization of the radiotracer with the bioluminescent signal arising from S. aureus Xen29, and demonstrated that the tracer could differentiate S. aureus infection from sterile inflammation. Significantly, the accumulation of both 2-[ 18 F]F-ENB and 2-[ 18 F]F-NB at the site of infection was 17-fold higher than at the site of sterile inflammation compared to 8-fold difference observed for 2-[ 18 F]F-PABA, supporting the proposal that the active radiotracer in vivo is 2-[ 18 F]F-NB. Collectively, these data suggest that 2-[ 18 F]F-ENB and 2-[ 18 F]F-NB have the potential for translation to humans as a rapid, noninvasive diagnostic tool to identify and localize S. aureus infections.

Sirtuin 1 (SIRT1) is a class III histone deacetylase that plays significant roles in the regulation of lifespan, metabolism, memory, and circadian rhythms and in the mechanisms of many diseases. However, methods of monitoring the pharmacodynamics of SIRT1-targeted drugs are limited to blood sampling because of the invasive nature of biopsies. For the noninvasive monitoring of the spatial and temporal dynamics of SIRT1 expression-activity in vivo by PET-CT-MRI, we developed a novel substrate-type radiotracer, [ 18 F]-2-fluorobenzoylaminohexanoicanilide (2-[ 18 F]BzAHA). PET-CT-MRI studies in rats demonstrated increased accumulation of 2-[ 18 F]BzAHA-derived radioactivity in the hypothalamus, hippocampus, nucleus accumbens, and locus coeruleus, consistent with autoradiographic and immunofluorescent (IMF) analyses of brain-tissue sections. Pretreatment with the SIRT1 specific inhibitor, EX-527 (5 mg/kg, ip), resulted in about a 20% reduction of 2-[ 18 F]BzAHA-derived-radioactivity accumulation in these structures. In vivo imaging of SIRT1 expression-activity should facilitate studies that improve the understanding of SIRT1-mediated regulation in the brain and aid in the development and clinical translation of SIRT1-targeted therapies.

A unique one-pot, high-yield desulfurative-fluorination-bromination reaction which leads to the synthesis of 2,5-dibromo-3-(1,1-difluoroalkyl)thiophenes is reported. A single dithiolane reactant can be used to produce both 2,5-dibromo-3-(1,1-difluoroalkyl)thiophene and 3-(1,1-difluoroalkyl)thiophene with longer alkyl chains.