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High-resolution in vivo imaging of gene expression is not possible in opaque animals by existing techniques. Here we present a new approach for obtaining such images by magnetic resonance imaging (MRI) using an MRI contrast agent that can indicate reporter gene expression in living animals. We have prepared MRI contrast agents in which the access of water to the first coordination sphere of a chelated paramagnetic ion is blocked with a substrate that can be removed by enzymatic cleavage. Following cleavage, the paramagnetic ion can interact directly with water protons to increase the MR signal. Here, we report an agent where galactopyranose is the blocking group. This group renders the MRI contrast agent sensitive to expression of the commonly used marker gene, beta-galactosidase. To cellular resolution, regions of higher intensity in the MR image correlate with regions expressing marker enzyme. These results offer the promise of in vivo mapping of gene expression in transgenic animals and validate a general approach for constructing a family of MRI contrast agents that respond to biological activity.

Redox-active self-assembled monolayers (SAMs) provide an excellent platform for investigating electron transfer kinetics. Using a well-defined bridge, a redox center can be positioned at a fixed distance from the electrode and electron transfer kinetics probed using a variety of electrochemical techniques. Cyclic voltammetry, AC voltammetry, electrochemical impedance spectroscopy, and chronoamperometry are most commonly used to determine the rate of electron transfer of redoxactivated SAMs. A variety of redox species have been attached to SAMs, and include transition metal complexes (e.g., ferrocene, ruthenium pentaammine, osmium bisbipyridine, metal clusters) and organic molecules (e.g., galvinol, C 60 ). SAMs offer an ideal environment to study the outer-sphere interactions of redox species. The composition and integrity of the monolayer and the electrode material influence the electron transfer kinetics and can be investigated using electrochemical methods. Theoretical models have been developed for investigating SAM structure. This review discusses methods and monolayer compositions for electrochemical measurements of redox-active SAMs.

Glioblastoma multiforme (GBM) is a neurologically debilitating disease that culminates in death 14 to 16 months after diagnosis. An incomplete understanding of how cataloged genetic aberrations promote therapy resistance, combined with ineffective drug delivery to the central nervous system, has rendered GBM incurable. Functional genomics efforts have implicated several oncogenes in GBM pathogenesis but have rarely led to the implementation of targeted therapies. This is partly because many “undruggable” oncogenes cannot be targeted by small molecules or antibodies. We preclinically evaluate an RNA interference (RNAi)–based nanomedicine platform, based on spherical nucleic acid (SNA) nanoparticle conjugates, to neutralize oncogene expression in GBM. SNAs consist of gold nanoparticles covalently functionalized with densely packed, highly oriented small interfering RNA duplexes. In the absence of auxiliary transfection strategies or chemical modifications, SNAs efficiently entered primary and transformed glial cells in vitro. In vivo, the SNAs penetrated the blood-brain barrier and blood-tumor barrier to disseminate throughout xenogeneic glioma explants. SNAs targeting the oncoprotein Bcl2Like12 (Bcl2L12)—an effector caspase and p53 inhibitor overexpressed in GBM relative to normal brain and low-grade astrocytomas—were effective in knocking down endogenous Bcl2L12 mRNA and protein levels, and sensitized glioma cells toward therapy-induced apoptosis by enhancing effector caspase and p53 activity. Further, systemically delivered SNAs reduced Bcl2L12 expression in intracerebral GBM, increased intratumoral apoptosis, and reduced tumor burden and progression in xenografted mice, without adverse side effects. Thus, silencing antiapoptotic signaling using SNAs represents a new approach for systemic RNAi therapy for GBM and possibly other lethal malignancies.

A noninvasive means to map biological structure is offered by magnetic resonance imaging (MRI). A new class of MRI contrast agents is described where the relaxivity of the complex is modified by the activity of a specific enzyme (β‐galactosidase, [Eq. (a)]). This type of agent offers the promise of direct three‐dimensional visualization of gene expression in the form of an acquired MR image.

A Gd(III)-nanodiamond conjugate [Gd(III)-ND] was prepared and characterized, enabling detection of nanodiamonds by MR imaging. The Gd(III)-ND particles significantly reduced the T1 of water protons with a per-Gd(III) relaxivity of 58.82 ± 1.18 mM−1s−1 at 1.5 Tesla (60 MHz). This represents a tenfold increase compared to the monomer Gd(III) complex (r1 = 5.42 ± 0.20 mM−1s−1) and is among the highest per-Gd(III) relaxivities reported.

ConspectusMagnetic resonance imaging (MRI) has become increasingly popular in molecular imaging and clinical radiology because it is non-invasive and capable of producing three-dimensional representations of opaque organisms with high spatial and temporal resolution. While approximately 35% of all clinical MR scans utilize contrast media, a primary limitation of MR imaging is the low sensitivity to detect contrast agents requiring high concentrations of agent for enhanced signal intensity (0.1-0.6 mM). 1 A number of strategies have been employed to amplify the observed in vivo signal of MR contrast agents. Approaches include attachment of Gd(III) chelates to polymers, proteins and particles, encapsulation into micelles and caged structures, and targeting to receptors. While each of these approaches has yielded significant increases in the relaxivity of MR contrast agents (and therefore sensitivity), all of these classes of complexes possess intrinsic background signal and function solely as anatomical reporters due to their constitutive activity.In order to reduce the background signal and simultaneously create probes that are modulated by biochemical events, caged complexes were designed to coordinatively saturate the paramagnetic ion. Coupled with amplification strategies, these agents represent a means to selectively modulate the observed MR signal and function as in vivo biochemical reporters. For example, to create an in vivo MR assay of enzymatic activities and secondary messengers, agents have been designed and synthesized with removable protection groups that largely prevent access of water to a paramagnetic center. By limiting the access of bulk water (q-modulation) the unprocessed agent is designed to be an ineffective contrast agent, and hence serves as a reliable marker for regions of enzyme activity or secondary messengers.In this Account we describe our results toward designing new classes of MR agents that are i. responsive to in vivo physiological or biochemical events ii. cell-permeable to increase local concentration, and iii. attached to large molecules or are synthesized with multiply labeled conjugates for signal amplification. Magnetic Resonance ImagingImaging with nuclear magnetic resonance (NMR) spectroscopy was first introduced by the pioneering work of Lauterbur in 1973. 2 MRI exploits the differences in the relaxation rates of nuclear spins due to an applied magnetic field. MR detects the electromagnetic radiation emitted from the transition of higher energy nuclei to a lower energy level. While nuclei with a spin quantum number of I = ½ such as 1 H, 13 C, 19 F and 31 P are used, the majority of current MR technology is based on 1 H nuclei. The NMR signal is relatively low compared to other tmeade@northwestern.edu. spectroscopic methods, however due to the large number of protons in a typical sample, detection is possible. Current MR images are acquired using magnetic field strengths from 1.5 to 7 Tesla in clinical applications, and as high as 19T for high-resolution molecular imaging....

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