To explore how core backbone modifications influence prostate-specific membrane antigen (PSMA) targeting, we synthesized a series of novel peptidomimetics replacing the classic urea linkage of established radiotracers with a carbamate functionality. This panel systematically varied side chain length (aspartic vs. aminoadipic acid), stereocenter configuration (S/S vs. S/R diastereomers), and the radiometal chelator (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid [DOTA] vs. N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid [HBED-CC]). In vitro binding assays in LNCaP cells revealed that the carbamate backbone severely compromised PSMA affinity (Ki) for short-chain aspartic acid derivatives, whereas long-chain aminoadipic acid conjugates successfully retained low-nanomolar potencies. Across all variations, S/S configurations displayed superior affinities over S/R counterparts, demonstrating that natural stereochemistry is essential for optimal binding pocket interactions. Although both conjugates showed high in vitro potency, high-temperature radiolabeling of the DOTA derivative with gallium-68 caused thermal degradation via hydrolytic cleavage and intramolecular cyclization of the carbamate backbone. Conversely, the companion HBED-CC conjugate, 37(S/S), was successfully radiolabeled at ambient temperature without structural compromise to yield the intact radiotracer, 40(S/S). In vivo positron emission tomography (PET) imaging and biodistribution studies of 40(S/S) in LNCaP tumor-bearing mice demonstrated high tumor uptake (∼12%ID/g) at 1 h post-injection, rapid renal clearance, and excellent tumor-to-background ratios (tumor-to-muscle: ∼23; tumor-to-bone: ∼36). These findings demonstrate that carbamate backbones can successfully mimic urea linkages in PSMA ligands, provided they are paired with precise side chain lengths and mild radiolabeling conditions.

The gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled receptor that is overexpressed in many solid cancers and is a promising target for cancer imaging and therapy. However, high pancreas uptake is a major concern in the application of reported GRPR-targeting radiopharmaceuticals, particularly for targeted radioligand therapy. To lower pancreas uptake, we explored Ga-complexed TacsBOMB2, TacsBOMB3, TacsBOMB4, TacsBOMB5, and TacsBOMB6 derived from a potent GRPR antagonist sequence, [Leu13ψThz14]Bombesin(7–14), and compared their potential for cancer imaging with [68Ga]Ga-RM2. The Ki(GRPR) values of Ga-TacsBOMB2, Ga-TacsBOMB3, Ga-TacsBOMB4, Ga-TacsBOMB5, Ga-TacsBOMB6, and Ga-RM2 were 7.08 ± 0.65, 4.29 ± 0.46, 458 ± 38.6, 6.09 ± 0.95, 5.12 ± 0.57, and 1.51 ± 0.24 nM, respectively. [68Ga]Ga-TacsBOMB2, [68Ga]Ga-TacsBOMB3, [68Ga]Ga-TacsBOMB5, [68Ga]Ga-TacsBOMB6, and [68Ga]Ga-RM2 clearly show PC-3 tumor xenografts in positron emission tomography (PET) images, while [68Ga]Ga-TacsBOMB5 shows the highest tumor uptake (15.7 ± 2.17 %ID/g) among them. Most importantly, the pancreas uptake values of [68Ga]Ga-TacsBOMB2 (2.81 ± 0.78 %ID/g), [68Ga]Ga-TacsBOMB3 (7.26 ± 1.00 %ID/g), [68Ga]Ga-TacsBOMB5 (1.98 ± 0.10 %ID/g), and [68Ga]Ga-TacsBOMB6 (6.50 ± 0.36 %ID/g) were much lower than the value of [68Ga]Ga-RM2 (41.9 ± 10.1 %ID/g). Among the tested [Leu13ψThz14]Bombesin(7–14) derivatives, [68Ga]Ga-TacsBOMB5 has the highest tumor uptake and tumor-to-background contrast ratios, which is promising for clinical translation to detect GRPR-expressing tumors. Due to the low pancreas uptake of its derivatives, [Leu13ψThz14]Bombesin(7–14) represents a promising pharmacophore for the design of GRPR-targeting radiopharmaceuticals, especially for targeted radioligand therapy application.

The aim of this study was to investigate the effect of replacing Glu in the Lys-urea-Glu PSMA-targeting pharmacophore of [68Ga]Ga-HTK03041 with a close analog on the uptake of kidneys, salivary glands and PSMA-expressing tumor xenografts. Methods: HTK03161, HTK03149 and HTK03189A/B were obtained by replacing Glu in HTK03041 with Asp, Aad (L-2-aminoadipic acid) and Api (2-aminopimelic acid), respectively. PSMA binding affinities were measured by competition binding assays. PET imaging and biodistribution studies of 68Ga-labeled ligands were performed in LNCaP tumor-bearing mice. The best candidate HTK03149 was selected and radiolabeled with 177Lu, and SPECT imaging and biodistribution studies were performed in LNCaP tumor-bearing mice. Radiation dosimetry calculation was conducted using the OLINDA software. Radioligand therapy study was performed in LNCaP tumor-bearing mice treated with [177Lu]Lu-HTK03149 (9.3-148 MBq), [177Lu]Lu-PSMA-617 (37 MBq) or natLu-HTK03149 (500 pmol). Results: PSMA binding affinities (Ki) of Ga-HTK03161, Ga-HTK03149, Ga-HTK03189A and Lu-HTK03149 were 3.88±0.66, 6.99±0.80, 550±35.7 and 1.57±0.42 nM, respectively. PET imaging showed that all 68Ga-labeled HTK03161, HTK03149 and HTK03189A/B were excreted mainly via the renal pathway and had minimal uptake in all organs/tissues including kidneys and salivary glands. Tumor xenografts were clearly visualized in PET images of [68Ga]Ga-HTK03161 and [68Ga]Ga-HTK03149 but were barely visualized using [68Ga]Ga-HTK03189A/B. Tumor uptake values for [68Ga]Ga-HTK03161, [68Ga]Ga-HTK03149, [68Ga]Ga-HTK0189A and [68Ga]Ga-HTK03189B were 12.7±1.91, 19.1±6.37, 2.10±0.28 and 0.67±0.15 %IA/g, respectively at 1h post-injection, and their average kidney and salivary gland uptake values were 2.13-4.41 and 0.20-0.23 %IA/g, respectively. Longitudinal SPECT imaging studies showed that [177Lu]Lu-HTK03149 was excreted mainly through the renal pathway with high uptake in LNCaP tumors and minimal uptake in all normal organs/tissues. The tumor uptake of [177Lu]Lu-HTK03149 peaked at 4h post-injection (20.9±2.99 %IA/g) and the uptake was sustained over time. Compared to [177Lu]Lu-PSMA-617, [177Lu]Lu-HTK03149 had 145% increase in tumor absorbed dose but 70% less in kidney absorbed dose, leading to an 7.1-fold increase in tumor-to-kidney absorbed dose ratio. Radioligand therapy studies showed that only half of the [177Lu]Lu-PSMA-617 injected dosage was needed for [177Lu]Lu-HTK03149 to achieve the same median survival. Conclusion: Replacing Glu in the PSMA-targeting Lys-urea-Glu pharmacophore of [68Ga]Ga-HTK03041 with Asp and Aad generates [68Ga]Ga-HTK03161 and [68Ga]Ga-HTK03149, respectively, and the new derivatives retain high uptake in LNCaP tumors and have minimal uptake in normal organs/tissues including kidneys and salivary glands. [177Lu]Lu-HTK03149 also retain high uptake in LNCaP tumors and has minimal uptake in normal organs/tissues, and is, therefore, promising for clinical translation to treat prostate cancer.

C-X-C chemokine receptor 4 (CXCR4) is highly expressed in cancers, contributing to proliferation, metastasis, and a poor prognosis. The noninvasive imaging of CXCR4 can enable the detection and characterization of aggressive cancers with poor outcomes. Currently, no 18F-labeled CXCR4 positron emission tomography (PET) radiotracer has demonstrated imaging contrast comparable to [68Ga]Ga-Pentixafor, a CXCR4-targeting radioligand. We, therefore, aimed to develop a high-contrast CXCR4-targeting radiotracer by incorporating a hydrophilic linker and trifluoroborate radioprosthesis to LY2510924, a known CXCR4 antagonist. A carboxy-ammoniomethyl-trifluoroborate (PepBF3) moiety was conjugated to the LY2510924-derived peptide possessing a triglutamate linker via amide bond formation to obtain BL08, whereas an alkyne ammoniomethyl-trifluoroborate (AMBF3) moiety was conjugated using the copper-catalyzed [3+2] cycloaddition click reaction to obtain BL09. BL08 and BL09 were radiolabeled with [18F]fluoride ion using 18F-19F isotope exchange. Pentixafor was radiolabeled with [68Ga]GaCl3. Side-by-side PET imaging and biodistribution studies were performed on immunocompromised mice bearing Daudi Burkitt lymphoma xenografts. The biodistribution of [18F]BL08 and [18F]BL09 showed tumor uptake at 2 h postinjection (p.i.) (5.67 ± 1.25%ID/g and 5.83 ± 0.92%ID/g, respectively), which were concordant with the results of PET imaging. [18F]BL08 had low background activity, providing tumor-to-blood, -muscle, and -liver ratios of 72 ± 20, 339 ± 81, and 14 ± 3 (2 h p.i.), respectively. [18F]BL09 behaved similarly, with ratios of 64 ± 20, 239 ± 72, and 17 ± 3 (2 h p.i.), respectively. This resulted in high-contrast visualization of tumors on PET imaging for both radiotracers. [18F]BL08 exhibited lower kidney uptake (2.2 ± 0.5%ID/g) compared to [18F]BL09 (7.6 ± 1.0%ID/g) at 2 h p.i. [18F]BL08 and [18F]BL09 demonstrated higher tumor-to-blood, -muscle, and -liver ratios compared to [68Ga]Ga-Pentixafor (18.9 ± 2.7, 95.4 ± 36.7, and 5.9 ± 0.7 at 2 h p.i., respectively). In conclusion, [18F]BL08 and [18F]BL09 enable high-contrast visualization of CXCR4 expression in Daudi xenografts. Based on high tumor-to-organ ratios, [18F]BL08 may prove a valuable new tool for CXCR4-targeted PET imaging with potential for translation. The use of a PepBF3 moiety is a new approach for the orthogonal conjugation of organotrifluoroborates for 18F-labeling of peptides.

High kidney uptake is a common feature of peptide-based radiopharmaceuticals, leading to reduced detection sensitivity for lesions adjacent to kidneys and lower maximum tolerated therapeutic dose. In this study, we evaluated if the Met-Val-Lys (MVK) linker could be used to lower kidney uptake of 68Ga-labeled DOTA-conjugated peptides and peptidomimetics. A model compound, [68Ga]Ga-DOTA-AmBz-MVK(Ac)-OH (AmBz: aminomethylbenzoyl), and its derivative, [68Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH, coupled with the PSMA (prostate-specific membrane antigen)-targeting motif of the previously reported HTK01166 were synthesized and evaluated to determine if they could be recognized and cleaved by the renal brush border enzymes. Additionally, positron emission tomography (PET) imaging, ex vivo biodistribution and in vivo stability studies were conducted in mice to evaluate their pharmacokinetics. [68Ga]Ga-DOTA-AmBz-MVK(Ac)-OH was effectively cleaved specifically by neutral endopeptidase (NEP) of renal brush border enzymes at the Met-Val amide bond, and the radio-metabolite [68Ga]Ga-DOTA-AmBz-Met-OH was rapidly excreted via the renal pathway with minimal kidney retention. [68Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH retained its PSMA-targeting capability and was also cleaved by NEP, although less effectively when compared to [68Ga]Ga-DOTA-AmBz-MVK(Ac)-OH. The kidney uptake of [68Ga]Ga-DOTA-AmBz-MVK(HTK01166)-OH was 30% less compared to that of [68Ga]Ga-HTK01166. Our data demonstrated that derivatives of [68Ga]Ga-DOTA-AmBz-MVK-OH can be cleaved specifically by NEP, and therefore, MVK can be a promising cleavable linker for use to reduce kidney uptake of radiolabeled DOTA-conjugated peptides and peptidomimetics.

We report a single-molecule radiotracer that can be labeled independently with F-18-fluoride or radiometals (Cu-64, Lu-177) in a single step. A prostate-specific membrane antigen (PSMA)-targeting ligand, armed with both an organotrifluoroborate and a metal-chelator (DOTA), was designed to optionally afford F-18-, Cu-64- or Lu-177-labeled products that were injected into mice bearing prostate cancer (LNCaP) xenografts. PET/CT images and ex vivo biodistribution data show high, specific tumor uptake irrespective of which radionuclide is used, thereby demonstrating a new approach to combining, in a single molecule, F-18-labeling capabilities for PET imaging with radiometalation for potential imaging and therapeutic applications.

DOTA is commonly used for radiometal chelation in molecular imaging. Yet in the absence of a radiometal, DOTA is hypothesized to promote renal clearance of F-18-labeled peptide tracers. In light of an increasing interest in the use of F18 for PET, here the effect of DOTA is evaluated for the first time with an F-18-labeled tracer and is found to significantly improve the quality of images acquired through positron emission tomography (PET). We chose to image the peptide LLP2A that recognizes the transmembrane protein very-late antigen 4 (VLA-4) that is overexpressed by many cancers. Since it is known that [F-18]RBF3-PEG(2)-LLP2A derivatives gave low tumor uptake values and significant GI tract accumulation, this ligand thus represents an ideal means of testing the additive effects of a DOTA group on clearance while permitting a facile, userfriendly, one-step F-18-labeling. A newly designed RBF3-LLP2A bioconjugate with an appended DOTA moiety increased nearly 3-fold and reduced GI accumulation by more than 10-fold. The DOTA-AMBF(3)-PEG(2)-LLP2A was radiolabeled by isotope exchange and was purified by semiprep HPLC and C18 cartridge elution. Male C57BL/6J mice bearing B16-F10 melanoma tumors that overexpress the VLA-4 target were used to evaluate [F-18]DOTA-AMBF(3)-PEG(2)-LLP2A using a combination of static and dynamic PET scans, biodistribution studies, and blocking controls at 1 h post injection (p.i.). The precursor peptide was synthesized and F-18-labeled to provide formulations with mean (+/- SD) radiochemical purities of 95.9 +/- 1.8%, in radiochemical yields of 4.8 +/- 2.9% having molar activities of 131.7 +/- 50.3 GBq/mu mol. In vivo static PET images of [F-18]DOTA-AMBF(3)-PEG(2)-LLP2A provided clear tumor visualization, and biodistribution studies showed that tumor uptake was 9.46 +/- 2.19% injected dose per gram of tissue (%ID/g) with high tumor/muscle and tumor/blood contrast ratios of similar to 8 and similar to 10, respectively. Blocking confirmed the specificity of [F-18]DOTA-AMBF(3)-PEG(2)-LLP2A to VLA-4 in the tumor and the bone marrow. Dynamic PET showed clearance of [F-18]DOTA-AMBF(3)-PEG(2)-LLP2A mainly via the renal pathway, wherein accumulation in the intestines was reduced 10-fold compared to our previously investigated LLP2A's, while spleen uptake was at levels similar to previously reported LLP2A-chelator radiotracers. [F-18]DOTA-AMBF(3)-PEG(2)-LLP2A represents a promising VLA-4 radiotracer and provides key evidence as to how a DOTA appendage can significantly reduce GI uptake in favor of urinary excretion. Implications for the development of dual-isotope theranostics that exploit the use fluorine-18 for imaging and DOTA to chelate therapeutic metal cations for therapy are discussed.

1008 Introduction: DOTA is a mainstay radioprosthetic group for use in radiometallation. However, in the absence of a radiometal, its role in favoring renal clearance represents an underutilized approach for 18F-labeled tracers. To show the benefits of using a DOTA moiety to favor renal clearance, we used the peptide LLP2A that recognizes the transmembrane protein very-late antigen 4 (VLA-4) that is overexpressed by many cancers. Previously, we showed that [18F]RBF3-PEG2-LLP2A derivatives gave low tumor uptake values and significant GI tract accumulation. Here, we designed a new RBF3-LLP2A bioconjugate with an appended DOTA moiety, which increased tumor uptake and reduced GI accumulation. Methods: A modified LLP2A-PEG2-NH2 conjugate equipped with an 18F-trifluoroborate radioprosthetic, AMBF3, and a DOTA moiety was synthesized. The DOTA-AMBF3-PEG2-LLP2A was radiolabeled by isotope exchange and was purified by semi-prep HPLC and C18 cartridge elution. Male C57BL/6J mice bearing B16-F10 melanoma tumors that overexpress the VLA-4 target were used to evaluate DOTA-[18F]AMBF3-PEG2-LLP2A using a combination of static and dynamic PET scans, biodistribution studies and blocking controls at 1h post injection (p.i.). Results: Precursor peptide was synthesized and 18F-labeled to provide formulations with mean (±SD) radiochemical purities of 95.9 ± 1.8 %, in radiochemical yields of 4.8 ± 2.9 % having molar activities of 131.7 ± 50.3 GBq/μmol. In vivo static PET images of [18F]DOTA-AMBF3-PEG2-LLP2A provided clear tumor visualization, and biodistribution studies showed that tumor uptake was 9.46 ± 2.19 percent injected dose per gram of tissue (%ID/g) with high tumor:muscle and tumor:blood contrast ratios of ~8 and ~10, respectively. Blocking confirmed the specificity of [18F]DOTA-AMBF3-PEG2-LLP2A to VLA-4 in the tumor and the bone marrow. Dynamic PET showed clearance of [18F]DOTA-AMBF3-PEG2-LLP2A mainly via the renal pathway, wherein accumulation in the intestines was reduced ~10-fold compared to our previously investigated LLP2A’s, while spleen uptake was at levels similar to previously reported LLP2A-chelator radiotracers. Conclusions: [18F]DOTA-AMBF3-PEG2-LLP2A represents a promising VLA-4 radiotracer and demonstrates how a DOTA appendage can favor urinary excretion.

After the identification of the high-affinity glutamate-ureido scaffold, the design of several potent 18F- and 68Ga-labeled tracers has allowed spectacular progress in imaging recurrent prostate cancer by targeting the prostate-specific membrane antigen (PSMA). We evaluated a series of PSMA-targeting probes that are 18F-labeled in a single step for PET imaging of prostate cancer. Methods: We prepared 8 trifluoroborate constructs for prostate cancer imaging, to study the influence of the linker and the trifluoroborate prosthetic on pharmacokinetics and image quality. After 1-step labeling by 19F-18F isotopic exchange, the radiotracers were injected in mice bearing LNCaP xenografts, with or without blocking controls, to assess specific uptake. PET/CT images and biodistribution data were acquired at 1 h after injection and compared with 18F-DCFPyL on the same mouse strain and tumor model. Results: All tracers exhibited nanomolar affinities, were labeled in good radiochemical yields at high molar activities, and exhibited high tumor uptake in LNCaP xenografts with clearance from nontarget organs. Most derivatives with a naphthylalanine linker showed significant gastrointestinal excretion. A radiotracer incorporating this linker with a dual trifluoroborate-glutamate labeling moiety showed high tumor uptake, low background activity, and no liver or gastrointestinal track accumulation. Conclusion: PSMA-targeting probes with trifluoroborate prosthetic groups represent promising candidates for prostate cancer imaging because of facile labeling while affording high tumor uptake values and contrast ratios that are similar to those obtained with 18F-DCFPyL.

Introduction: The transmembrane alpha(4)beta(1) integrin receptor, or very-late antigen 4 (VLA-4), is associated with tumor metastasis and angiogenesis, the development of chemotherapeutic drug resistance, and is overexpressed in multiple myelomas, osteosarcomas, lymphomas, leukemias, and melanomas. The peptidomimetic, LLP2A, is a high-affinity ligand with specificity for the extracellular portion of VLA-4 and several conjugates have been evaluated in vivo by NIR-fluorescence, (111)ln-SPECT and Ga-68- and Cu-64-PET imaging, but to date, not with F-18-PET. Methods: Using two highly stable organotrifluoroborate prosthetic groups: ammoniumdimethyl-trifluoroborate (AMBF(3)) and a new N-pyridinyl-para-trifluoroborate (N-Pyr-p-BF3), both capable of facile aqueous F-18-labeling by isotope exchange (IEX), we present the first PET imaging evaluations of two [F-18]R-BF3--PEG(2)-LLP2A tracers using VLA-4 overexpressing B16-F10 murine melanoma tumor mouse models. Results: Here, we demonstrate successful one-step F-18-labeling of both conjugates with wet NCA [F-18]F- in radiochemical yields of up to 11.6% within 75 min at molar activities of 40-100 GBq/mu mol. Average tumor uptake values based on ex vivo biodistribution values were 4.4%ID/g (11) and 2.8%ID/g (12) using F-18-labeled LLP2A-conjugates with the two prosthetic groups: N-Pyr-p-BF3 (5) and alkyl-N,N-dimethylammonio-BF3 (AMBF(3)) (7), respectively, and was found to be target-specific as evidenced by in vivo blocking controls. Dynamic PET scanning and biodistribution studies revealed slow clearance of the [F-18]R-BF3--PEG(2)-LLP2A tracers from the tumors, and also substantial uptake in the intestines, gall bladder, liver and bladder. Observed bone uptake was blockable, consistent with known VLA-4 expression in hematopoietic stem cells found in bone marrow. Conclusions: These studies show that these [F-18]R-BF3--PEG(2)-LLP2A conjugates (11 and 12) are promising VIA-4 targeting radiotracers, yet, further optimization will be required to reduce uptake in the gastro-intestinal tract. (C) 2018 Elsevier Inc. All rights reserved.

The peptidomimetic, LLP2A, is a specific, high-affinity ligand for α4β1 integrin receptors. Previously, several PEGylated LLP2A conjugates were evaluated in vivo as imaging agents for the detection of lymphoma, leukemia, multiple myeloma and melanoma tumours via NIR-fluorescence, 111In-SPECT, and 64Cu- and 68Ga-PET imaging. Despite these successes, to date there is no report of an 18F-labeled LLP2A conjugate. Notably, fluorine-18 is a preferred radionuclide for PET imaging, yet its short half-life and general inactivity under aqueous conditions present challenges for peptide labeling. A simple method for labeling complex biomolecules can be achieved with arylboronic acids that readily capture aqueous [18F]-fluoride ion resulting in an 18F-labeled aryltrifluoroborate ([18F]-ArBF3-) radioprosthetic group. Herein, we present the first radiosynthesis of an 18F-labeled LLP2A conjugate by both one-step 18F-labeling and one-pot two-step 18F-labeling post-'click' conjugation of the 18F-alkynyl-ArBF3- prosthetic. Competition with a fluorescent conjugate of LLP2A demonstrated specific binding of the non-radioactive isotopolog ArBF3--PEG2-LLP2A to α4β1 integrin-expressing MOLT-4 leukemia cells, as evidenced and confirmed by fluorescence microscopy. This work provides a key first step in the development of an expanding library of [18F]-R-BF3--LLP2A radiotracers for PET imaging.

To impart effective cellular damage via photodynamic therapy (PDT), it is vital to deliver the appropriate light dose and photosensitizer concentration, and to monitor the PDT dose delivered at the site of interest. In vivo monitoring of photosensitizers has in large part relied on their fluorescence emission. Palladium-containing photosensitizers have shown promising clinical results by demonstrating near full conversion of light to PDT activity at the cost of having undetectable fluorescence. We demonstrate that, through the coupling of plasmonic nanoparticles with palladium-photosensitizers, surface-enhanced Raman scattering (SERS) provides both reporting and monitoring capability to otherwise quiescent molecules. Nano-enabled SERS reporting of photosensitizers allows for the decoupling of the therapeutic and imaging mechanisms so that both phenomena can be optimized independently. Most importantly, the design enables the use of the same laser wavelength to stimulate both the PDT and imaging features, opening the potential for real-time dosimetry of photosensitizer concentration and PDT dose delivery by SERS monitoring.

Most animals store energy as long-chain triacylglycerols (lcTAGs). Trace amounts of acetylated triacylglycerols (acTAGs) have been reported in animals, but are not accumulated, likely because they have lower energy density than lcTAGs. Here we report that acTAGs comprise 36% of the neutral lipid pool of overwintering prepupae of the goldenrod gall fly, Eurosta solidaginis, while only 17% of the neutral lipid pool is made up of typical lcTAGs. These high concentrations of acTAGs, present only during winter, appear to be synthesized by E. solidaginis and are not found in other freeze-tolerant insects, nor in the plant host. The mixture of acTAGs found in E. solidaginis has a significantly lower melting point than equivalent lcTAGs, and thus remains liquid at temperatures at which E. solidaginis is frozen in the field, and depresses the melting point of aqueous solutions in a manner unusual for neutral lipids. We note that accumulation of acTAGs coincides with preparation for overwintering and the seasonal acquisition of freeze tolerance. This is the first observation of accumulation of acTAGs by an animal, and the first evidence of dynamic interconversion between acTAGs and lcTAGs during development and in response to stress.

Here we show the facile synthesis of 13(2)-17(3)-bacteriochlorophyllone a (12), with a distinct seven-membered exocyclic F-ring formed by 13(2)-17(3)-cyclization of bacteriopheophorbide a (16). This is the latest reported bacteriochlorin with such an exocyclic F-ring since 1975 (13(2)-17(3)-cyclobacteriopheophorbide a-enol, 11), and is an analog of previously described natural exo-cyclic F-ring-containing porphyrins (1-4) and chlorins (5-10). The structure of 12 was confirmed using a combination of 1D H-1 NMR, 2D COSY H-1 NMR, Jmod C-13 NMR and HRMS analysis. The biological activity of 12 was explored, and we found that this compound does not possess strong antioxidant activity like its natural product counterparts, but is a capable photosensitizer for photodynamic therapy.

NanomedicineVol. 9, No. 3 Research HighlightsFree AccessHighlights from the latest articles in nanomedicineShuai Shao & Jonathan F LovellShuai ShaoDepartment of Biomedical Engineering & Department of Chemical & Biological Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA & Jonathan F LovellDepartment of Biomedical Engineering & Department of Chemical & Biological Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USAPublished Online:20 Apr 2014https://doi.org/10.2217/nnm.13.215AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInRedditEmail Evaluation of: Wu Y, Kwak K, Agarwal K et al. Detection of extracellular RNAs in cancer and viral infection via tethered cationic lipoplex nanoparticles containing molecular beacons. Anal. Chem. 23, 11265–11274 (2013).Earlier detection of cancer is crucial for improving patient outcomes. Treatments are more successful and less painful if the disease can be caught in the early stage. miRNAs are now known to play numerous crucial roles in cancer pathogenesis. Some miRNAs are also attractive cancer biomarkers since they circulate in the blood, entrapped in cell-derived extracellular nanovesicles known as exosomes. The current standard method for detecting nucleic acids from serum makes use of quantitative reverse-transcriptase PCR. This process, while well-established, requires skilled operators and is relatively laborious, expensive and time-consuming, precluding widespread point-of-care diagnostics. Thus, simpler and more sensitive detection schemes for exosomal miRNA are desirable.Wu and colleagues at Ohio State University (USA) have come up with a novel detection scheme for miRNAs in circulating exosomes. They entrapped molecular beacons specific to miR-21 (an miRNA implicated in lung cancer) into cationic lipid nanoparticles. Molecular beacons are nucleic acid probes that maintain a hairpin conformation that attenuates their fluorescence until they hybridize specifically to their target sequence, in which case they open and increase their fluorescence. The negatively charged exosomes carrying miR-21 fused with the cationic lipid nanoparticles. Subsequently, the molecular beacons mixed with the internal contents of the exosomes and if the exosomes contained miR-21, the molecular beacons would light up within the fused compartment. This process was visualized on surfaces using total internal reflection microscopy. Since not all exosomes originate from cancer-related cells and contain miR-21, the beauty of the technique relies on the direct visualization of single exosome fusion events. The molecular beacon approach performed exquisitely for cancer detection based on analysis of human serum samples from either lung cancer patients or healthy volunteers. This experimental approach was orders of magnitude more sensitive than conventional quantitative reverse-transcriptase PCR. This highly promising approach, which also validated detection of viral RNAs, warrants further experimentation with larger sample sizes.Evaluation of: Wu C, Han D, Chen T et al. Building a multifunctional aptamer-based DNA nanoassembly for targeted cancer therapy. J. Am. Chem. Soc. 135(49), 18644–18650 (2013).1D-, 2D- and 3D-programmed nucleic acid structures have garnered much attention for their striking shapes and intricate patterns, offering infinite creative design possibilities. These structures have also attracted interest in the field of cancer therapy, since shape and size are parameters known to be highly influential for the delivery of drugs into tumors and cancer cells. Because of difficulties in precisely modifying 3D nucleic acid nanostructures with functional ligands, most approaches have made use of passive targeting based on the enhanced permeability and retention effect of tumors, but this is not suitable for all types of cancers, such as leukemia.Wu et al. developed a multifunctional and programmable aptamer-based DNA nanoassembly for drug delivery. Using a modular bottom-up construction scheme, functional DNA domains and connector DNA domains were self-assembled to form a building unit. Then, the nanoparticles were cemented in place with the photocross-linking of hundreds of these units in order to create a multifunctional nanoassembly. The size of the DNA nanoassembly could be controlled by changing the concentration of the building units prior to photopolymerization and also displayed good biostability without intrinsic cytotoxicity. The anticancer drug doxorubicin, which naturally intercalates into double-stranded DNA, could readily be loaded into the nanoparticle. The nanoassembly could be targeted and internalized by cancer cells with the decoration of targeting aptamer nucleic acids that recognized surface markers on the target cells. This work demonstrates the potential of nucleic acid-based photopolymerizable nanoassemblies as a drug delivery platform. Demonstration of in vivo efficacy will be required for this nascent technology to further show its potential.Evaluation of: Imran ul-haq M, Hamilton JL, Lai BF et al. Design of long circulating non-toxic dendritic polymers for the removal of iron in vivo. ACS Nano 7(12), 10704–10716 (2013).Most small water-soluble molecules exhibit rapid systemic clearance in vivo via renal filtration. A prolonged circulation time of small molecules via conjugation or incorporation into higher molecular weight complexes has been extensively demonstrated. However, depending on the intended purpose, the conjugated complex may not retain its original function and could even exhibit toxicity. Due to their higher molecular weight and organic nature, conjugation to biocompatible polymers is an attractive option. Recent work from Imran ul-haq et al. has demonstrated such an approach with the eventual goal of treating side-effects of patients requiring chronic red blood cell transfusions. This process often leads to a transfusional iron overload, which damages patient organs if the metal remains in the circulation for too long.A nontoxic dendritic polymer was designed using hyperbranched polyglycerol as a backbone. Desferoxamine, a clinically used iron chelator, was used either conjugated to the polyglycerol or in free form. The polyglycerol–desferoxamine avoided rapid blood clearance based on its larger size and exhibited an astounding 484-fold increase in circulating half-life compared with standard desferoxamine. The polyglycerol–desferoxamine nanoparticle could bind iron effectively, exhibited excellent blood compatibility and demonstrated efficacy in preclinical animal experiments. Beyond its significance for transfusion patients, this work demonstrates the dramatic size-mediated effects that can occur in vivo when small molecules are conjugated to larger nanoscaffolds.Evaluation of: Zhao Y, van Rooy I, Hak S et al. Near-infrared fluorescence energy transfer imaging of nanoparticle accumulation and dissociation kinetics in tumor-bearing mice. ACS Nano 7(11), 10362–10370 (2013).Self-assembled nanoparticles often exhibit good biocompatibility, but exactly what happens to their self-assembly status after they are injected into the body is difficult to elucidate. Better understanding of the behavior of nanoparticles could lead to more rationally-designed drug nanocarriers. Recently, Zhao et al. have developed a quantum dot (QD) lipid nanoparticle system that enables improved understanding of nanoparticle behavior in vivo. Because of their brightness and optical stability, quantum dots are useful agents for tracking other nanoparticles in biological systems. Self-assembled lipidic nanoparticles with entrapped quantum dots and PEGylation were developed. These exhibited good biocompatibility and could serve as nanocarriers for various therapeutic agents.Self-assembly was probed in vivo using Förster resonance energy transfer (FRET), which is an optical technique that indicates when molecules are within a few nanometers of each other. FRET imaging techniques were developed to observe nanoparticle accumulation and dissociation kinetics in tumor-bearing mice. QDs were used as FRET donors and were coated by a PEGylated lipid monolayer, which incorporated other small molecule dyes that served as FRET acceptors. Varying the amount of dye in the lipid monolayer could control the degree to which the QD fluorescence was quenched. Imaging revealed the self-assembled lipidic nanoparticles dissociated after the hybrid nanoparticles were injected intravenously. By spectrally resolved imaging of the QD, dye and FRET channel, spatial and temporal analysis of nanoparticle accumulation and dissociation kinetics was possible. Different biodistributions of the QDs and lipid-incorporated dyes were observed. This research provides modular in vivo tools to better understand self-assembled nanoparticle behavior in real-time and demonstrates the utility of FRET imaging.Financial & competing interests disclosureThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript.FiguresReferencesRelatedDetails Vol. 9, No. 3 Follow us on social media for the latest updates Metrics History Published online 20 April 2014 Published in print March 2014 Information© Future Medicine LtdPDF download

With the knowledge that the dominant photodynamic therapy (PDT) mechanism of 1a (WST09) switched from type 2 to type 1 for 1b (WST11) upon taurine-driven E-ring opening, we hypothesized that taurine-driven E-ring opening of bacteriochlorophyll derivatives and net-charge variations would modulate reactive oxygen species (ROS) photogeneration. Eight bacteriochlorophyll a derivatives were synthesized with varying charges that either contained the E ring (2a-5a) or were synthesized by taurine-driven E-ring opening (2b-5b). Time-dependent density functional theory (TDDFT) modeling showed that all derivatives would be type 2 PDT-active, and ROS-activated fluorescent probes were used to investigate the photogeneration of a combination of type 1 and type 2 PDT ROS in organic- and aqueous-based solutions. These investigations validated our predictive modeling calculations and showed that taurine-driven E-ring opening and increasing negative charge generally enhanced ROS photogeneration in aqueous solutions. We propose that these structure-activity relationships may provide simple strategies for designing bacteriochlorins that efficiently generate ROS upon photoirradiation.

Photoacoustic imaging provides high-resolution images at depths beyond the optical diffusion limit. To broaden its utility, there is need for molecular sensors capable of detecting environmental stimuli through alterations in photoacoustic signal. Photosynthetic organisms have evolved ingenious strategies to optimize light absorption through nanoscale ordered dye aggregation. Here, we use this concept to synthesize a stimuli-responsive nanoswitch with a large optical absorbance and sensing capabilities. Ordered dye aggregation between light-harvesting porphyrins was achieved through intercalation within thermoresponsive nanovesicles. This causes an absorbance red-shift of 74 nm and a 2.7-fold increase in absorptivity of the Qy-band, with concomitant changes in its photoacoustic spectrum. This spectral feature can be reversibly switched by exceeding a temperature threshold. Using this thermochromic property, we noninvasively determined a localized temperature change in vivo, relevant for monitoring thermal therapies of solid tumors. Similar strategies may be applied alongside photoacoustic imaging, to detect other stimuli such as pH and enzymatic activity.