Influence of Bioluminescence Imaging Dynamics by D-Luciferin Uptake and Efflux Mechanisms

Bioluminescence imaging (BLI) detects light generated by luciferase-mediated oxidation of substrate and is used widely for evaluating transgene expression in cell-based assays and in vivo in relevant preclinical models. The most commonly used luciferase for in vivo applications is firefly luciferase (fLuc), for which D-luciferin serves as the substrate. We demonstrated previously that the expression of the ABCG2 efflux transporter can significantly reduce BLI signal output and that HhAntag-691 can inhibit the efflux of D-luciferin, thereby enhancing BLI signal. Here we show that an HhAntag-691-sensitive uptake mechanism facilitates the intracellular concentration of D-luciferin and that the BLI dynamics of different cell lines are coregulated by this uptake mechanism in conjunction with ABCG2-mediated efflux. After administration of D-luciferin, the HhAntag-691-sensitive uptake mechanism generates a rapid increase in BLI signal that decreases over time, whereas ABCG2-mediated efflux stably reduces signal output. We implicate SLC22A4 (OCTN1), a member of the organic cation/zwitterion uptake transporter family, as one potential mediator of the HhAntag-691-sensitive D-luciferin uptake. These findings provide insight into mechanisms that contribute to the cellular uptake kinetics and in vivo biodistribution of D-luciferin

Synthesis of [125I]IodoDPA-713, a New Probe for Imaging Inflammation

[(125)I]IodoDPA-713 [(125)I]1, which targets the translocator protein (TSPO, 18 KDa), was synthesized in seven steps from methyl-4-methoxybenzoate as a tool for quantification of inflammation in preclinical models. Preliminary in vitro autoradiography and in vivo small animal imaging were performed using [(125)I]1 in a neurotoxicant-treated rat and in a murine model of lung inflammation, respectively. The radiochemical yield of [(125)I]1 was 44 ± 6% with a specific radioactivity of 51.8 GBq/μmol (1,400 mCi/μmol) and > 99% radiochemical purity. Preliminary studies showed that [(125)I]1 demonstrated increased specific binding to TSPO in a neurotoxicant-treated rat and increased radiopharmaceutical uptake in the lungs of an experimental inflammation model of lung inflammation. Compound [(125)I]1 is a new, convenient probe for preclinical studies of TSPO activity

Influence of Bioluminescence Imaging Dynamics by D-Luciferin Uptake and Efflux Mechanisms

Bioluminescence imaging (BLI) detects light generated by luciferase-mediated oxidation of substrate and is used widely for evaluating transgene expression in cell-based assays and in vivo in relevant preclinical models. The most commonly used luciferase for in vivo applications is firefly luciferase (fLuc), for which D-luciferin serves as the substrate. We demonstrated previously that the expression of the ABCG2 efflux transporter can significantly reduce BLI signal output and that HhAntag-691 can inhibit the efflux of D-luciferin, thereby enhancing BLI signal. Here we show that an HhAntag-691-sensitive uptake mechanism facilitates the intracellular concentration of D-luciferin and that the BLI dynamics of different cell lines are coregulated by this uptake mechanism in conjunction with ABCG2-mediated efflux. After administration of D-luciferin, the HhAntag-691-sensitive uptake mechanism generates a rapid increase in BLI signal that decreases over time, whereas ABCG2-mediated efflux stably reduces signal output. We implicate SLC22A4 (OCTN1), a member of the organic cation/zwitterion uptake transporter family, as one potential mediator of the HhAntag-691-sensitive D-luciferin uptake. These findings provide insight into mechanisms that contribute to the cellular uptake kinetics and in vivo biodistribution of D-luciferin

Enhancement of Radiotherapy with Human Mesenchymal Stem Cells Containing Gold Nanoparticles

Radiotherapy is a common approach for the treatment of a wide variety of cancer types. Available data indicate that nanoparticles can enhance the effect of radiotherapy. We report the use of human mesenchymal stem cells to selectively deliver gold nanoparticles (GNPs) to MDA-MB-231 breast tumor xenografts in mice for the purpose of enhancing the effect of radiation therapy. Targeted delivery of GNPs to the tumor site, followed by irradiation of the tumor, enabled control of tumor growth. The results indicate that tumor-selective GNP delivery by human mesenchymal stem cells may represent a viable way to enhance the effectiveness of radiotherapy

Preclinical Comparative Study of ⁶⁸Ga-Labeled DOTA, NOTA, and HBED-CC Chelated Radiotracers for Targeting PSMA

⁶⁸Ga-labeled, low-molecular-weight imaging agents that target the prostate-specific membrane antigen (PSMA) are increasingly used clinically to detect prostate and other cancers with positron emission tomography (PET). The goal of this study was to compare the pharmacokinetics of three PSMA-targeted radiotracers: ^<b>68</b><b>Ga-1</b>, using DOTA-monoamide as the chelating agent; ^<b>68</b><b>Ga-2</b>, containing the macrocyclic chelating agent <i>p</i>-SCN-Bn-NOTA; and ⁶⁸Ga-DKFZ-PSMA-11, currently in clinical trials, which uses the acyclic chelating agent, HBED-CC. The PSMA-targeting scaffold for all three agents utilized a similar Glu-urea-Lys-linker construct. Each radiotracer enabled visualization of PSMA+ PC3 PIP tumor, kidney, and urinary bladder as early as 15 min post-injection using small animal PET/computed tomography (PET/CT). ^<b>68</b><b>Ga-2</b> demonstrated the fastest rate of clearance from all tissues in this series and displayed higher uptake in PSMA+ PC3 PIP tumor compared to ^<b>68</b><b>Ga-1</b> at 1 h post-injection. There was no significant difference in PSMA+ PC3 PIP tumor uptake for the three agents at 2 and 3 h post-injection. ⁶⁸Ga-DKFZ-PSMA-11 demonstrated the highest uptake and retention in normal tissues, including kidney, blood, spleen, and salivary glands and PSMA-negative PC3 flu tumors up to 3 h post-injection. In this preclinical evaluation ^<b>68</b><b>Ga-2</b> had the most advantageous characteristics for PSMA-targeted PET imaging

¹¹¹In- and IRDye800CW-Labeled PLA–PEG Nanoparticle for Imaging Prostate-Specific Membrane Antigen-Expressing Tissues

Targeted delivery of drug-encapsulated nanoparticles is a promising new approach to safe and effective therapeutics for cancer. Here we investigate the pharmacokinetics and biodistribution of a prostate-specific membrane antigen (PSMA)-targeted nanoparticle based on a poly­(lactic acid)–polyethylene glycol copolymer by utilizing single photon emission computed tomography (SPECT) and fluorescence imaging of a low-molecular-weight, PSMA-targeting moiety attached to the surface and oriented toward the outside environment. Tissue biodistribution of the radioactive, PSMA-targeted nanoparticles in mice containing PSMA­(+) PC3 PIP and PSMA(−) PC3 flu (control) tumors demonstrated similar accumulation compared to the untargeted particles within all tissues except for the tumor and liver by 96 h postinjection. For PSMA­(+) PC3 PIP tumor, the targeted nanoparticle demonstrated retention of 6.58% injected dose (ID)/g at 48 h and remained nearly at that level out to 96 h, whereas the untargeted nanoparticle showed a 48 h retention of 8.17% ID/g followed by a significant clearance to 2.37% ID/g at 96 h (<i>P</i> < 0.02). On the other hand, for control tumor, both targeted and untargeted particles displayed similar 48 h retentions and rates of clearance over 96 h. <i>Ex vivo</i> microscopic analysis with near-infrared versions of the nanoparticles indicated retention within PSMA­(+) tumor epithelial cells as well as tumor-associated macrophages for targeted particles and primarily macrophage-associated uptake for the untargeted particles. Retention in control tumor was primarily associated with tumor vasculature and macrophages. The data demonstrate the utility of radioimaging to assess nanoparticle biodistribution and suggest that active targeting has a modest positive effect on tumor localization of PSMA-targeted PLA–PEG nanoparticles that have been derivatized for imaging