Tissue temperature is a fundamental physiological parameter that can provide insight into pathological processes. The purpose of this study was to develop and characterize a novel paramagnetic chemical exchange saturation transfer (CEST) agent suitable for in vivo temperature mapping at 9.4T. The CEST properties of the europium (Eu 3؉ ) complex of the DOTAMGlycine (Gly)-Phenylalanine (Phe) ligand were studied in vitro at 9.4T as a function of temperature, pH, and agent concentration. The transfer of magnetization (CEST effect) from the bound water to bulk water pools was ϳ75% greater for Eu 3؉ -DOTAMGly-Phe compared to Eu 3؉ -DOTAM-Gly at physiologic temperature (38°C) and pH (7.0 pH units) when using power level sufficiently low for in vivo imaging. Unlike Eu 3؉ -DOTAM-Gly, whose CEST effect decreased with increasing temperature in the physiologic range, the CEST effect of Eu 3؉ -DOTAM-Gly-Phe was optimal at body temperature. A strong linear dependence of the chemical shift of the bound water pool on temperature was observed (0.3 ppm/°C), which was insensitive to pH and agent concentration. Temperature maps with SDs < 1°C were acquired at 9.4T in phantoms containing: 1) phantom A, an aqueous solution of 10 mM Eu 3؉ -DOTAM-Gly-Phe; 2) phantom B, 5% bovine serum albumin ( Tissue temperature and pH are important physiological parameters that are closely related to tissue metabolism. Therefore, noninvasive techniques to measure these parameters have many medical applications (1-5), including for cancer and stroke. For example, tumor temperature can be related to the pathological processes within the tumor (1), while knowledge of tumor pH may aid in diagnosis and in choosing appropriate chemotherapeutic agents. Such agents are weak acids or bases, therefore, their accumulation within cells and, hence, their efficacy depends on the transmembrane pH gradient (4,5). In vivo tissue temperature measurements are often made with invasive probes (i.e., thermocouples), which provide high sensitivity and temporal resolution in localized regions but cannot monitor a whole organ simultaneously. More recently, noninvasive methods for temperature measurement using magnetic resonance imaging (MRI) have been developed (2). These methods are based mainly on the temperaturedependence of the NMR T 1 relaxation time, chemical shift, or diffusion coefficient of water protons (2). Among these MR methods, relating the chemical shift of water protons to temperature is the most widely used. However, the low temperature sensitivity (ϳ0.01 ppm/°C) of this technique limits its application to situations with large temperature variations.More recently, the feasibility of MR thermometry based on the strong temperature dependence of the chemical shifts of paramagnetic lanthanide (Ln) complexes has been explored (3). More specifically, the process of chemical exchange saturation transfer (CEST), in conjunction with paramagnetic lanthanide complexes (i.e., PARACEST), can be used to create high-resolution temperature maps with greater sensitivity tha...

Anti-miRs are oligonucleotide inhibitors complementary to miRNAs that have been used extensively as tools to gain understanding of specific miRNA functions and as potential therapeutics. We showed previously that peptide nucleic acid (PNA) anti-miRs containing a few attached Lys residues were potent miRNA inhibitors. Using miR-122 as an example, we report here the PNA sequence and attached amino acid requirements for efficient miRNA targeting and show that anti-miR activity is enhanced substantially by the presence of a terminal-free thiol group, such as a Cys residue, primarily due to better cellular uptake. We show that anti-miR activity of a Cys-containing PNA is achieved by cell uptake through both clathrin-dependent and independent routes. With the aid of two PNA analogues having intrinsic fluorescence, thiazole orange (TO)-PNA and [bis-o-(aminoethoxy)phenyl]pyrrolocytosine (BoPhpC)-PNA, we explored the subcellular localization of PNA anti-miRs and our data suggest that anti-miR targeting of miR-122 may take place in or associated with endosomal compartments. Our findings are valuable for further design of PNAs and other oligonucleotides as potent anti-miR agents.