Jinyuan Zhou

Using the amide proton signals of intracellular proteins and peptides to detect pH effects in MRI

In the past decade, it has become possible to use the nuclear (proton, 1H) signal of the hydrogen atoms in water for noninvasive assessment of functional and physiological parameters with magnetic resonance imaging (MRI). Here we show that it is possible to produce pH-sensitive MRI contrast by exploiting the exchange between the hydrogen atoms of water and the amide hydrogen atoms of endogenous mobile cellular proteins and peptides. Although amide proton concentrations are in the millimolar range, we achieved a detection sensitivity of several percent on the water signal (molar concentration). The pH dependence of the signal was calibrated in situ, using phosphorus spectroscopy to determine pH, and proton exchange spectroscopy to measure the amide proton transfer rate. To show the potential of amide proton transfer (APT) contrast for detecting acute stroke, pH effects were noninvasively imaged in ischemic rat brain. This observation opens the possibility of using intrinsic pH contrast, as well as protein- and/or peptide-content contrast, as diagnostic tools in clinical imaging.

Amide proton transfer (APT) contrast for imaging of brain tumors

In this work we demonstrate that specific MR image contrast can be produced in the water signal that reflects endogenous cellular protein and peptide content in intracranial rat 9L gliosarcomas. Although the concentration of these mobile proteins and peptides is only in the millimolar range, a detection sensitivity of several percent on the water signal (molar concentration) was achieved. This was accomplished with detection sensitivity enhancement by selective radiofrequency (RF) labeling of the amide protons, and by utilizing the effective transfer of this label to water via hydrogen exchange. Brain tumors were also assessed by conventional T1‐weighted, T2‐weighted, and diffusion‐weighted imaging. Whereas these commonly‐used approaches yielded heterogeneous images, the new amide proton transfer (APT) technique showed a single well‐defined region of hyperintensity that was assigned to brain tumor tissue. Magn Reson Med 50:1120–1126, 2003.

Differentiation between glioma and radiation necrosis using molecular magnetic resonance imaging of endogenous proteins and peptides

It remains difficult to distinguish tumor recurrence from radiation necrosis after brain tumor therapy. Here we show that these lesions can be distinguished using the amide proton transfer (APT) magnetic resonance imaging (MRI) signals of endogenous cellular proteins and peptides as an imaging biomarker. When comparing two models of orthotopic glioma (SF188/V+ glioma and 9L gliosarcoma) with a model of radiation necrosis in rats, we could clearly differentiate viable glioma (hyperintense) from radiation necrosis (hypointense to isointense) by APT MRI. When we irradiated rats with U87MG gliomas, the APT signals in the irradiated tumors had decreased substantially by 3 d and 6 d after radiation. The amide protons that can be detected by APT provide a unique and noninvasive MRI biomarker for distinguishing viable malignancy from radiation necrosis and predicting tumor response to therapy.

Quantitative description of proton exchange processes between water and endogenous and exogenous agents for WEX, CEST, and APT experiments.

The proton exchange processes between water and solutes containing exchangeable protons have recently become of interest for monitoring pH effects, detecting cellular mobile proteins and peptides, and enhancing the detection sensitivity of various low‐concentration endogenous and exogenous species. In this work, the analytic expressions for water exchange (WEX) filter spectroscopy, chemical exchange‐dependent saturation transfer (CEST), and amide proton transfer (APT) experiments are derived by the use of Bloch equations with exchange terms. The effects of the initial states for the system, the difference between a steady state and a saturation state, and the relative contributions of the forward and backward exchange processes are discussed. The theory, in combination with numerical calculations, provides a useful tool for designing experimental schemes and assessing magnetization transfer (MT) processes between water protons and solvent‐exchangeable protons. As an example, the case of endogenous amide proton exchange in the rat brain at 4.7 T is analyzed in detail. Magn Reson Med 51:945–952, 2004.

Amide proton transfer MR imaging of prostate cancer: A preliminary study

To evaluate the capability of amide proton transfer (APT) MR imaging for detection of prostate cancer that typically shows a higher tumor cell proliferation rate and cellular density leading to an MRI‐detectable overall elevated mobile protein level in higher grade tumors.

Suppression of human glioma xenografts with second-generation IL13R-specific chimeric antigen receptor-modified T cells.

Purpose: Glioblastoma multiforme (GBM) remains highly incurable, with frequent recurrences after standard therapies of maximal surgical resection, radiation, and chemotherapy. To address the need for new treatments, we have undertaken a chimeric antigen receptor (CAR) “designer T cell” (dTc) immunotherapeutic strategy by exploiting interleukin (IL)13 receptor α-2 (IL13Rα2) as a GBM-selective target. Experimental Design: We tested a second-generation IL13 “zetakine” CAR composed of a mutated IL13 extracellular domain linked to intracellular signaling elements of the CD28 costimulatory molecule and CD3ζ. The aim of the mutation (IL13.E13K.R109K) was to enhance selectivity of the CAR for recognition and killing of IL13Rα2+ GBMs while sparing normal cells bearing the composite IL13Rα1/IL4Rα receptor. Results: Our aim was partially realized with improved recognition of tumor and reduced but persisting activity against normal tissue IL13Rα1+ cells by the IL13.E13K.R109K CAR. We show that these IL13 dTcs were efficient in killing IL13Rα2+ glioma cell targets with abundant secretion of cytokines IL2 and IFNγ, and they displayed enhanced tumor-induced expansion versus control unmodified T cells in vitro. In an in vivo test with a human glioma xenograft model, single intracranial injections of IL13 dTc into tumor sites resulted in marked increases in animal survivals. Conclusions: These data raise the possibility of immune targeting of diffusely invasive GBM cells either via dTc infusion into resection cavities to prevent GBM recurrence or via direct stereotactic injection of dTcs to suppress inoperable or recurrent tumors. Systemic administration of these IL13 dTc could be complicated by reaction against normal tissues expressing IL13Ra1. Clin Cancer Res; 18(21); 5949–60. ©2012 AACR.

Three-dimensional amide proton transfer MR imaging of gliomas: Initial experience and comparison with gadolinium enhancement.

To investigate the feasibility of a three‐dimensional amide‐proton‐transfer (APT) imaging sequence with gradient‐ and spin‐echo readouts at 3 Tesla in patients with high‐ or low‐grade gliomas.

Fast 3D Chemical Exchange Saturation Transfer (CEST) Imaging of the Human Brain

Chemical exchange saturation transfer magnetic resonance imaging can detect low‐concentration compounds with exchangeable protons through saturation transfer to water. This technique is generally slow, as it requires acquisition of saturation images at multiple frequencies. In addition, multislice imaging is complicated by saturation effects differing from slice to slice because of relaxation losses. In this study, a fast three‐dimensional chemical exchange saturation transfer imaging sequence is presented that allows whole‐brain coverage for a frequency‐dependent saturation spectrum (z‐spectrum, 26 frequencies) in less than 10 min. The approach employs a three‐dimensional gradient‐ and spin‐echo readout using a prototype 32‐channel phased‐array coil, combined with two‐dimensional sensitivity encoding accelerations. Results from a homogenous protein‐containing phantom at 3T show that the sequence produced a uniform contrast across all slices. To show translational feasibility, scans were also performed on five healthy human subjects. Results for chemical exchange saturation transfer images at 3.5 ppm downfield of the water resonance, so‐called amide proton transfer images, show that lipid signals are sufficiently suppressed and artifacts caused by B0 inhomogeneity can be removed in postprocessing. The scan time and image quality of these in vivo results show that three‐dimensional chemical exchange saturation trasfer MRI using gradient‐ and spin‐echo acquisition is feasible for whole‐brain chemical exchange saturation transfer studies at 3T in a clinical time frame. Magn Reson Med, 2010.

Size-induced enhancement of chemical exchange saturation transfer (CEST) contrast in liposomes.

Liposome-based chemical exchange saturation transfer (lipoCEST) agents have shown great sensitivity and potential for molecular magnetic resonance imaging (MRI). Here we demonstrate that the size of liposomes can be exploited to enhance the lipoCEST contrast. A concise analytical model is developed to describe the contrast dependence on size for an ensemble of liposomes. The model attributes the increased lipoCEST contrast in smaller liposomes to their larger surface-to-volume ratio, causing an increased membrane water exchange rate. Experimentally measured rates correlate with size, in agreement with the model. The water permeability of liposomal membrane is found to be 1.11 +/- 0.14 microm/s for the specific lipid composition at 22 degrees C. Availability of the model allows rational design of the size of liposomes and quantification of their properties. These new theoretical and experimental tools are expected to benefit applications of liposomes to sensing the cellular environment, targeting and imaging biological processes, and optimizing drug delivery properties.

Chemical exchange saturation transfer MR imaging of articular cartilage glycosaminoglycans at 3 T: Accuracy of B0 Field Inhomogeneity corrections with gradient echo method

Glycosaminoglycan Chemical Exchange Saturation Transfer (gagCEST) is an important molecular MRI methodology developed to assess changes in cartilage GAG concentrations. The correction for B0 field inhomogeneity is technically crucial in gagCEST imaging. This study evaluates the accuracy of the B0 estimation determined by the dual gradient echo method and the effect on gagCEST measurements. The results were compared with those from the commonly used z-spectrum method. Eleven knee patients and three healthy volunteers were scanned. Dual gradient echo B0 maps with different ∆TE values (1, 2, 4, 8, and 10 ms) were acquired. The asymmetry of the magnetization transfer ratio at 1 ppm offset referred to the bulk water frequency, MTRasym(1 ppm), was used to quantify cartilage GAG levels. The B0 shifts for all knee patients using the z-spectrum and dual gradient echo methods are strongly correlated for all ∆TE values used (r = 0.997 to 0.786, corresponding to ∆TE = 10 to 1 ms). The corrected MTRasym(1 ppm) values using the z-spectrum method (1.34% ± 0.74%) highly agree only with those using the dual gradient echo methods with ∆TE = 10 ms (1.72% ± 0.80%; r = 0.924) and 8 ms (1.50% ± 0.82%; r = 0.712). The dual gradient echo method with longer ∆TE values (more than 8 ms) has an excellent correlation with the z-spectrum method for gagCEST imaging at 3T.