TLN-4601 peripheral benzodiazepine receptor (PBR/TSPO) binding properties do not mediate apoptosis but confer tumor-specific accumulation.

TLN-4601 is a farnesylated dibenzodiazepinone isolated from Micromonospora sp. with an antiproliferative effect on several human cancer cell lines. Although the mechanism of action of TLN-4601 is unknown, our earlier work indicated that TLN-4601 binds the PBR (peripheral benzodiazepine receptor; more recently known as the translocator protein or TSPO), an 18 kDa protein associated with the mitochondrial permeability transition (mPT) pore. While the exact function of the PBR remains a matter of debate, it has been implicated in heme and steroid synthesis, cellular growth and differentiation, oxygen consumption and apoptosis. Using the Jurkat immortalized T-lymphocyte cell line, documented to have negligible PBR expression, and Jurkat cells stably transfected with a human PBR cDNA, the present study demonstrates that TLN-4601 induces apoptosis independently of PBR expression. As PBRs are overexpressed in brain tumors compared to normal brain, we examined if TLN-4601 would preferentially accumulate in tumors using an intra-cerebral tumor model. Our results demonstrate the ability of TLN-4601 to effectively bind the PBR in vivo as determined by competitive binding assay and receptor occupancy. Analysis of TLN-4601 tissue and plasma indicated that TLN-4601 preferentially accumulates in the tumor. Indeed, drug levels were 200-fold higher in the tumor compared to the normal brain. TLN-4601 accumulation in the tumor (176 µg/g) was also significant compared to liver (24.8 µg/g; 7-fold) and plasma (16.2 µg/mL; 11-fold). Taken together our data indicate that while PBR binding does not mediate cell growth inhibition and apoptosis, PBR binding may allow for the specific accumulation of TLN-4601 in PBR positive tumors.

Automatic segmentation of gadolinium-enhanced multiple sclerosis lesions.

Automatic detection and quantitation of contrast-enhanced lesions on MRI is expected to be useful in characterizing the disease state in multiple sclerosis (MS). The enhancing structures such as cerebral vasculature and regions with no blood-brain barrier complicate automated analysis of lesion enhancement. A pulse sequence that incorporates both stationary and marching saturation bands and gradient dephasing is described for suppressing the enhancements within the cerebral vasculature. A postprocessing technique based on automatic image segmentation is implemented for eliminating enhancing structures such as choroid plexus. All MS lesions larger than 5 mm3 have been successfully identified. The automated analysis produced no false-positives or false-negative lesions above this volume in 13 patients with MS who were evaluated using the acquisition and evaluation techniques described.

Volumetric analysis of white matter, gray matter, and CSF using fractional volume analysis.

Quantitative cerebral tissue volumes may be useful for an objective assessment of pathological changes in brain. Accurate determination of tissue volumes is complicated, however, by the partial volume averaging (PVA) effect. We have, therefore, developed a new pulse sequence that minimizes the PVA through the use of inversion-recovery (IR) and double inversion-recovery (DIR) techniques. This pulse sequence simultaneously acquires four different sets of images to provide the necessary information for volumetric analysis and reduces potential spatial misregistration of images due to patient motion. The image sets acquired from the proposed pulse sequence are 1) gray matter visible, 2) white matter visible, 3) FLAIR, and 4) fast spin-echo proton-density weighted images. An algorithm has been implemented to correct for differential T1-weighting and for tissue quantitation.

Implementation and evaluation of a new pulse sequence for rapid acquisition of double inversion recovery images for simultaneous suppression of white matter and CSF.

We describe a fast double inversion recovery (DIR) imaging sequence that effectively attenuates signal from both white matter and cerebrospinal fluid (CSF). The pulse sequence uses a novel inversion/excitation scheme and fast spin-echo readout to maximize scan efficiency. The white matter/CSF suppressed images can be acquired from the entire brain in approximately 6 minutes. Evaluation of the fast DIR sequence on patients with multiple sclerosis (MS) demonstrates high lesion conspicuity.

A dual approach for minimizing false lesion classifications on magnetic resonance images.

Segmentation methods based on dual-echo MR images are generally prone to significant false lesion classifications. We have minimized these false classifications by (1) improving the lesion-to-tissue contrast on MR images by developing a fast spin-echo sequence that incorporates both cerebrospinal fluid signal attenuation and magnetization transfer contrast and (2) including information from MR flow images. Studies on patients with multiple sclerosis indicate that this dual approach to tissue segmentation reduces the volume of false lesion classifications by an average of 87%.

Automatic removal of extrameningeal tissues from MR images of human brain.

An automatic technique for removal of extrameningeal tissues from MR images of human brain is described. The algorithm is based on the segmentation of images acquired with a fast dual-echo pulse sequence, which incorporates both fluid attenuation and magnetization transfer contrast for superior brain/extrameningeal tissue contrast compared to conventional MR sequences. Evaluation of this technique using MR images of six volunteers indicates rapid and consistent removal of extrameningeal tissues.

Three-dimensional MR image registration of the human brain.

An automatic three-dimensional technique for registration of MR images of human brain is described. The algorithm was tested, using MR images of human brain, and was found to estimate angular offsets to within 0.5 degrees and translational offsets to within about 1 pixel. The quality of final registration was evaluated by histogram analysis. The algorithm was found to be computationally efficient and robust.

Relative concentrations of proton MR visible neurochemicals in gray and white matter in human brain.

The relative distributions of N-acetylaspartate (NAA) + N-acetylaspartylglutamate (NAAG), creatine + phosphocreatine (Cr/PCr), and choline (Cho) in the gray and white matter of human brain were determined by utilizing proton magnetic resonance spectroscopic imaging (SI). The SI data was processed using an automated spectroscopic image processing algorithm, and image segmentation was performed using a supervised technique. Linear regression analysis indicated that the NAA + NAAG (2.01 ppm) and Cr/PCr (3.02 ppm) peaks are greater in gray matter compared with white matter. The large intersubject variation observed in the Cho (3.20 ppm) resonance prevented the assessment of its regional distribution with confidence.