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The article presents a study which examines the evidence for water mediated electron transfer (ET) through bis-amino acid donor-bridge-acceptor oligomers (DBA). It states that water molecules influence electron transport in biomolecules and play a significant role in biologically vital processes in living cells. It explains the importance of water in determining the activation energy for ET reactions.

Purpose: This study was motivated by the need for better positron emission tomography (PET)-compatible tools to image bacterial infection. Our previous efforts have targeted bacteria-specific metabolism via assimilation of carbon-11 labeled d-amino acids into the bacterial cell wall. Since the chemical determinants of this incorporation are not fully understood, we sought a high-throughput method to label d-amino acid derived structures with fluorine-18. Our strategy employed a chemical biology approach, whereby an azide (-N 3 ) bearing d-amino acid is incorporated into peptidoglycan muropeptides, with subsequent "click" cycloaddition with an 18 F-labeled strained cyclooctyne partner. Procedures: A water-soluble, 18 F-labeled and dibenzocyclooctyne (DBCO)-derived radiotracer ([ 18 F]FB-sulfo-DBCO) was synthesized. This tracer was incubated with pathogenic bacteria treated with azide-bearing d-amino acids, and incorporated 18 F was determined via gamma counting. In vitro uptake in bacteria previously treated with azide-modified d-amino acids was compared to that in cultures treated with amino acid controls. The biodistribution of [ 18 F]FB-sulfo-DBCO was studied in a cohort of healthy mice with implications for future in vivo imaging. Results: The new strain-promoted azide-alkyne cycloaddition (SPAAC) radiotracer [ 18 F]FB-sulfo-DBCO was synthesized with high radiochemical yield and purity via N -succinimidyl 4-[ 18 F]fluorobenzoate ([ 18 F]SFB). Accumulation of [ 18 F]FB-sulfo-DBCO was significantly higher in several bacteria treated with azide-modified d-amino acids than in controls; for example, we observed 7 times greater [ 18 F]FB-sulfo-DBCO ligation in Staphylococcus aureus cultures incubated with 3-azido-d-alanine versus those incubated with d-alanine. Conclusions: The SPAAC radiotracer [ 18 F]FB-sulfo-DBCO was validated in vitro via metabolic labeling of azide-bearing peptidoglycan muropeptides. d-Amino acid-derived PET radiotracers may be more efficiently screened via [ 18 F]FB-sulfo-DBCO modification.

For the past several decades, chimeric antigen receptor T-cell therapies have shown promise in the treatment of cancers. These treatments would greatly benefit from companion imaging biomarkers to follow the trafficking of T cells in vivo. Methods: Using synthetic biology, we engineered T cells with a chimeric receptor synthetic intramembrane proteolysis receptor (SNIPR) that induces overexpression of an exogenous reporter gene cassette on recognition of specific tumor markers. We then applied a SNIPR-based PET reporter system to 2 cancer-relevant antigens, human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor variant III (EGFRvIII), commonly expressed in breast and glial tumors, respectively. Results: Antigen-specific reporter induction of the SNIPR PET T cells was confirmed in vitro using green fluorescent protein fluorescence, luciferase luminescence, and the HSV-TK PET reporter with 9-(4- 18 F-fluoro-3-[hydroxymethyl]butyl)guanine ([ 18 F]FHBG). T cells associated with their target antigens were successfully imaged using PET in dual-xenograft HER2+/HER2- and EGFRvIII+/EGFRvIII- animal models, with more than 10-fold higher [ 18 F]FHBG signals seen in antigen-expressing tumors versus the corresponding controls. Conclusion: The main innovation found in this work was PET detection of T cells via specific antigen-induced signals, in contrast to reporter systems relying on constitutive gene expression., (© 2023 by the Society of Nuclear Medicine and Molecular Imaging.)

In this study, we developed angiotensin-converting enzyme 2 (ACE2)-specific, peptide-derived 68 Ga-labeled radiotracers, motivated by the hypotheses that ACE2 is an important determinant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) susceptibility and that modulation of ACE2 in coronavirus disease 2019 (COVID-19) drives severe organ injury. Methods: A series of NOTA-conjugated peptides derived from the known ACE2 inhibitor DX600 were synthesized, with variable linker identity. Since DX600 bears 2 cystine residues, both linear and cyclic peptides were studied. An ACE2 inhibition assay was used to identify lead compounds, which were labeled with 68 Ga to generate peptide radiotracers ( 68 Ga-NOTA-PEP). The aminocaproate-derived radiotracer 68 Ga-NOTA-PEP4 was subsequently studied in a humanized ACE2 (hACE2) transgenic model. Results: Cyclic DX-600-derived peptides had markedly lower half-maximal inhibitory concentrations than their linear counterparts. The 3 cyclic peptides with triglycine, aminocaproate, and polyethylene glycol linkers had calculated half-maximal inhibitory concentrations similar to or lower than the parent DX600 molecule. Peptides were readily labeled with 68 Ga, and the biodistribution of 68 Ga-NOTA-PEP4 was determined in an hACE2 transgenic murine cohort. Pharmacologic concentrations of coadministered NOTA-PEP (blocking) showed a significant reduction of 68 Ga-NOTA-PEP4 signals in the heart, liver, lungs, and small intestine. Ex vivo hACE2 activity in these organs was confirmed as a correlate to in vivo results. Conclusion: NOTA-conjugated cyclic peptides derived from the known ACE2 inhibitor DX600 retain their activity when N-conjugated for 68 Ga chelation. In vivo studies in a transgenic hACE2 murine model using the lead tracer, 68 Ga-NOTA-PEP4, showed specific binding in the heart, liver, lungs and intestine-organs known to be affected in SARS-CoV-2 infection. These results suggest that 68 Ga-NOTA-PEP4 could be used to detect organ-specific suppression of ACE2 in SARS-CoV-2-infected murine models and COVID-19 patients., (© 2021 by the Society of Nuclear Medicine and Molecular Imaging.)

Found in biomolecules, pharmaceuticals, and agrochemicals, amide-containing molecules are ubiquitous in nature, and their derivatization represents a significant methodological goal in fluorine chemistry. Trifluoromethyl amides have emerged as important functional groups frequently found in pharmaceutical compounds. To date, there is no strategy for synthesizing N -trifluoromethyl amides from abundant organic carboxylic acid derivatives, which are ideal starting materials in amide synthesis. Here, we report the synthesis of N -trifluoromethyl amides from carboxylic acid halides and esters under mild conditions via isothiocyanates in the presence of silver fluoride at room temperature. Through this strategy, isothiocyanates are desulfurized with AgF, and then the formed derivative is acylated to afford N -trifluoromethyl amides, including previously inaccessible structures. This method shows broad scope, provides a platform for rapidly generating N -trifluoromethyl amides by virtue of the diversity and availability of both reaction partners, and should find application in the modification of advanced intermediates., Competing Interests: DECLARATION OF INTERESTS The authors declare no competing interests.

Noninvasive methods to study glucocorticoid receptor (GR) signaling are urgently needed to elaborate the complexity of GR signaling in normal physiology and human disorders, as well as to identify selective GR modulators to treat diseases. Here, we report evidence supporting translational studies with (±)- 11 C-5-(4-fluorobenzyl)-10-methoxy-2,2,4-trimethyl-2,5-dihydro-1H-chromeno[3,4-f]-quinoline ((±)- 11 C-YJH08), a radioligand for PET that engages the ligand binding domain on GR. Methods: (±)- 11 C-YJH08 was synthesized by reacting the phenol precursor with 11 C-methyl iodide. The biodistribution was studied in vivo. Specific binding was tested in vivo with adrenalectomy and ligand competition. A library of analogs was synthesized and studied in vitro and in vivo to understand the (±)- 11 C-YJH08 structure-activity relationship. Rodent dosimetry studies were performed to estimate the human-equivalent doses of (±)- 11 C-YJH08. Results: (±)- 11 C-YJH08 was synthesized by reaction of the phenolic precursor with 11 C-methyl iodide, giving a radiochemical yield of 51.7% ± 4.7% (decay-corrected to starting 11 C-methyl iodide). Specific binding was observed in many tissues, including the brain. An analysis of the (±)-YJH08 structure-activity relationship showed that ( R )- and ( S )-enantiomers are equally avid for GR by occupying discrete binding modes. A focused chemical screen revealed that the aryl fluoride motif on YJH08 is essential for high-affinity GR binding in vitro, high tissue uptake in vivo, and efficient passage across the blood-brain barrier. Lastly, we performed dosimetry studies on rodents, from which we estimated the human-equivalent doses of (±)- 11 C-YJH08 to be commensurate with the widely used 11 C and 18 F tracers. Conclusion: These studies reveal the molecular determinants of a high-affinity and high-selectivity ligand-receptor interaction and support the use of (±)- 11 C-YJH08 PET to make the first measurements of GR expression in human subjects., (© 2021 by the Society of Nuclear Medicine and Molecular Imaging.)

Purpose: Detection of bacteria-specific metabolism via positron emission tomography (PET) is an emerging strategy to image human pathogens, with dramatic implications for clinical practice. In silico and in vitro screening tools have recently been applied to this problem, with several monosaccharides including l-arabinose showing rapid accumulation in Escherichia coli and other organisms. Our goal for this study was to evaluate several synthetically viable arabinofuranose-derived 18 F analogs for their incorporation into pathogenic bacteria., Procedures: We synthesized four radiolabeled arabinofuranose-derived sugars: 2-deoxy-2-[ 18 F]fluoro-arabinofuranoses (d-2- 18 F-AF and l-2- 18 F-AF) and 5-deoxy-5-[ 18 F]fluoro-arabinofuranoses (d-5- 18 F-AF and l-5- 18 F-AF). The arabinofuranoses were synthesized from 18 F - via triflated, peracetylated precursors analogous to the most common radiosynthesis of 2-deoxy-2-[ 18 F]fluoro-d-glucose ([ 18 F]FDG). These radiotracers were screened for their uptake into E. coli and Staphylococcus aureus. Subsequently, the sensitivity of d-2- 18 F-AF and l-2- 18 F-AF to key human pathogens was investigated in vitro., Results: All 18 F radiotracer targets were synthesized in high radiochemical purity. In the screening study, d-2- 18 F-AF and l-2- 18 F-AF showed greater accumulation in E. coli than in S. aureus. When evaluated in a panel of pathologic microorganisms, both d-2- 18 F-AF and l-2- 18 F-AF demonstrated sensitivity to most gram-positive and gram-negative bacteria., Conclusions: Arabinofuranose-derived 18 F PET radiotracers can be synthesized with high radiochemical purity. Our study showed absence of bacterial accumulation for 5-substitued analogs, a finding that may have mechanistic implications for related tracers. Both d-2- 18 F-AF and l-2- 18 F-AF showed sensitivity to most gram-negative and gram-positive organisms. Future in vivo studies will evaluate the diagnostic accuracy of these radiotracers in animal models of infection., (© 2020 John Wiley & Sons, Ltd.)

Incorporation of d-amino acids into peptidoglycan is a unique metabolic feature of bacteria. Since d-amino acids are not metabolic substrates in most mammalian tissues, this difference can be exploited to detect living bacteria in vivo . Given the prevalence of d-alanine in peptidoglycan muropeptides, as well as its role in several antibiotic mechanisms, we targeted this amino acid for positron emission tomography (PET) radiotracer development. d-[3- 11 C]Alanine and the dipeptide d-[3- 11 C]alanyl-d-alanine were synthesized via asymmetric alkylation of glycine-derived Schiff-base precursors with [ 11 C]methyl iodide in the presence of a cinchonidinium phase-transfer catalyst. In cell experiments, both tracers showed accumulation by a wide variety of both Gram-positive and Gram-negative pathogens including Staphylococcus aureus and Pseudomonas aeruginosa . In a mouse model of acute bacterial myositis, d-[3- 11 C]alanine was accumulated by living microorganisms but was not taken up in areas of sterile inflammation. When compared to existing clinical nuclear imaging tools, specifically 2-deoxy-2-[ 18 F]fluoro-d-glucose and a gallium citrate radiotracer, d-alanine showed more bacteria-specific uptake. Decreased d-[3- 11 C]alanine uptake was also observed in antibiotic-sensitive microbes after antimicrobial therapy, when compared to that in resistant organisms. Finally, prominent uptake of d-[3- 11 C]alanine uptake was seen in rodent models of discitis-osteomyelitis and P. aeruginosa pneumonia. These data provide strong justification for clinical translation of d-[3- 11 C]alanine to address a number of important human infections., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The glucocorticoid receptor (GR) is an emerging drug target for several common and deadly solid tumors like breast and prostate cancer, and clinical trials studying the antitumor effects of GR antagonists are beginning. Since GR expression can be variable in tumor cells, and virtually all normal mammalian tissues express some GR, we hypothesized that an imaging tool capable of detecting GR positive tumors and/or measuring GR occupancy by drug in tumor and normal tissues could improve the precision application of anti-GR therapies in the clinic. To this end, we developed a fluorine-18 labeled corticosteroid termed GR02 that potently binds the endogenous ligand binding pocket on full length GR. Binding of 18 F-GR02 was suppressed in many normal tissues by co-treatment with mifepristone, a GR antagonist in human use, and was elevated in many normal tissues among mice lacking circulating corticosteroids due to adrenalectomy. 18 F-GR02 also accumulated in GR positive subcutaneous and subrenal capsule prostate cancer models, and uptake in tumors was competed by mifepristone. Combined with a straightforward and high yielding radiosynthesis, these data establish the foundation for near-term clinical translation of 18 F-GR02., Competing Interests: CONFLICTS OF INTEREST M.J.E. is a shareholder and former SAB member of ORIC Pharmaceuticals, Inc. M.J.E. received research support from GE Healthcare.

Noninvasive biomarkers that detect the activity of important oncogenic drivers could significantly improve cancer diagnosis and management of treatment. The goal of this study was to determine whether 68 Ga-citrate (which avidly binds to circulating transferrin) can detect MYC-positive prostate cancer tumors, as the transferrin receptor is a direct MYC target gene. PET imaging paired with 68 Ga-citrate and molecular analysis of preclinical models, human cell-free DNA (cfDNA), and clinical biopsies were conducted to determine whether 68 Ga-citrate can detect MYC-positive prostate cancer. Importantly, 68 Ga-citrate detected human prostate cancer models in a MYC-dependent fashion. In patients with castration-resistant prostate cancer, analysis of cfDNA revealed that all patients with 68 Ga-citrate avid tumors had a gain of at least one MYC copy number. Moreover, biopsy of two PET avid metastases showed molecular or histologic features characteristic of MYC hyperactivity. These data demonstrate that 68 Ga-citrate targets prostate cancer tumors with MYC hyperactivity. A larger prospective study is ongoing to demonstrate the specificity of 68 Ga-citrate for tumors with hyperactive MYC. Implications: Noninvasive measurement of MYC activity with quantitative imaging modalities could substantially increase our understanding of the role of MYC signaling in clinical settings for which invasive techniques are challenging to implement or do not characterize the biology of all tumors in a patient. Moreover, measuring MYC activity noninvasively opens the opportunity to study changes in MYC signaling in patients under targeted therapeutic conditions thought to indirectly inhibit MYC. Mol Cancer Res; 15(9); 1221-9. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Purpose: mTOR regulates many normal physiological processes and when hyperactive can drive numerous cancers and human diseases. However, it is very challenging to detect and quantify mTOR signaling noninvasively in clinically relevant animal models of disease or man. We hypothesized that a nuclear imaging tool measuring intracellular mTOR activity could address this unmet need. Experimental Design: Although the biochemical activity of mTOR is not directly amenable to nuclear imaging probe development, we show that the transferrin receptor can be used to indirectly measure intracellular changes in mTOR activity. Results: After verifying that the uptake of radiolabeled transferrin (the soluble ligand of the transferrin receptor) is stimulated by active mTORC1 in vitro , we showed that 89 Zr-labeled transferrin (Tf) can measure mTORC1 signaling dynamics in normal and cancerous mouse tissues with PET. Finally, we show that 89 Zr-Tf can detect the upregulation of mTORC1 by tumor cells to escape the antitumor effects of a standard-of-care antiandrogen, which is to our knowledge the first example of applying PET to interrogate the biology of treatment resistant cancer. Conclusions: In summary, we have developed the first quantitative assay to provide a comprehensive measurement of mTOR signaling dynamics in vivo , in specific normal tissues, and during tumor development in genetically engineered animal models using a nuclear imaging tool that is readily translatable to man. Clin Cancer Res; 23(12); 3045-52. ©2016 AACR ., (©2016 American Association for Cancer Research.)