Increased expression of peripheral benzodiazepine receptor (PBR) in dimethylbenz[a]anthracene-induced mammary tumors in rats

Mapping of Translocator Protein (18 kDa) in Peripheral Sterile Inflammatory Disease and Cancer through PET Imaging

Positron emission tomography (PET) imaging of the translocator 18 kDa protein (TSPO) with radioligands has become an effective means of research in peripheral inflammatory conditions that occur in many diseases and cancers. The peripheral sterile inflammatory diseases (PSIDs) are associated with a diverse group of disorders that comprises numerous enduring insults including the cardiovascular, respiratory, gastrointestinal, or musculoskeletal system. TSPO has recently been introduced as a potential biomarker for peripheral sterile inflammatory diseases (PSIDs). The major critical issue related to PSIDs is its timely characterization and localization of inflammatory foci for proper therapy of patients. As an alternative to metabolic imaging, protein imaging expressed on immune cells after activation is of great importance. The five transmembrane domain translocator protein-18 kDa (TSPO) is upregulated on the mitochondrial cell surface of macrophages during inflammation, serving as a potential ligand for PET tracers. Additionally, the overexpressed TSPO protein has been positively correlated with various tumor malignancies. In view of the association of escalated TSPO expression in both disease conditions, it is an immensely important biomarker for PET imaging in oncology and PSIDs. In this review, we summarize the most outstanding advances on TSPO-targeted PSIDs and cancer in the development of TSPO ligands as a potential diagnostic tool, specifically discussing the last five years.

Differential Expressions of p53, p53R2, hRRM2 and PBR in Chronic Lymphocytic Leukemia: A Correlation with Intracellular Cholesterol

Regulation of intracellular cholesterol homeostasis exists under balance between intracellular biosynthesis and uptake from extracellular origin by cell surface transport proteins. Expected role of cholesterol on either tumor suppressor gene and/or DNA synthesis has been aimed in the present study to explore intracellular cholesterol homeostasis in CLL subjects. Higher expressions of p53R2 (p53 dependent subunit of ribonucleotide reductase) and p53 were found in lymphocytes of chronic human lymphocytic leukemia as comparison to their normal counterparts. Inverse relation was found with p53 independent R2 subunit (in human hRRM2) of ribonucleotide reductase, which was found to be decreased from its control group. More expression of peripheral type benzodiazepine receptor, a cholesterol transporter, was noticed in isolated nuclear fraction with simultaneous increase of cholesterol concentration in cytoplasmic and nuclear compartments. A parallel increase of cholesterol in cell nucleus with increased p53R2 expression shows priority of the involvement of cholesterol in the process of cell replication.

[18F]DPA-714, [18F]PBR111 and [18F]FEDAA1106-selective radioligands for imaging TSPO 18 kDa with PET: automated radiosynthesis on a TRACERLAb FX-FN synthesizer and quality controls

Imaging of TSPO 18 kDa with PET is more and more considered as a relevant biomarker of inflammation in numerous diseases. Development of new radiotracers for TSPO 18 kDa has seen acceleration in the last years and the challenge today is to make available large amounts of such a radiotracer in compliance with GMP standards for application in humans. We present in this technical note automated productions of [(18)F]DPA-714, [(18)F]PBR111 and [(18)F]FEDAA1106, three promising radiotracers for TSPO 18 kDa imaging, using a TRACERlab FX-FN synthesizer. This note also includes the quality control data of the validation batches for the manufacturing qualification of clinical production of [(18)F]DPA-714.

TSPO 18 kDa (PBR) Targeted Photosensitizers for Cancer Imaging (PET) and PDT

Translocator protein (TSPO) 18 kDa overexpression has been observed in a large variety of human cancers, especially breast cancers. PK 11195, an isoquinoline analogue, is one of the ligands of highest TSPO binding affinity. Due to the long biological half life of our photosensitizers, there is a need to label them with a long lived radioisotope, for example I-124. Our objectives are to find translocator protein targeted photosensitizers for both tumor imaging (PET) and photodynamic therapy (PDT). I-PK 11195 is conjugated with the tumor avid photosensitizer HPPH. We find that those two tumor avid components complement each other and make the conjugate molecule even more tumor avid; compared to the photosensitizer itself, the conjugate is found to show improved PDT efficacy. It is concluded that I-PK 11195 can be a good vehicle to deliver radionuclide and photosensitizer to TSPO overexpressed tumor regions. Such conjugates could be useful for both tumor imaging (PET) and PDT.

Antiproliferative effect of peripheral benzodiazepine receptor antagonist PK11195 in rat mammary tumor cells

This study aims to establish the antiproliferative effects of PK11195, a peripheral benzodiazepine receptor antagonist (PBR) in rat mammary tumor cells. Breast tumors were induced by administration of a carcinogen, dimethylbenz[a]anthracene to 50-day-old female rats maintained on a standard AIN-76A diet with casein as the protein source. The tumors were developed approximately after 120 days. The tumors were of grade I (20%), grade II (60%), and grade III (20%). The tumors were isolated and cultured in DMEM/F12 media with supplements. We characterized the properties of the isolated cells and study the effect of PK11195 on those cells. We were successful in growing breast tumor cells up to 30 passages for cellular characterization. These cells had high reactivity with Ki-67 and PCNA antibodies suggesting high proliferation rate. These cells were highly invasive as evident by matrigel invading ability. Furthermore, these cells acquired a positive response for CD-31 and VEGF antibodies suggesting angiogenic potential, and also possessed migrating ability/motility as evident by the wound healing properties. These cells expressed elevated levels of PBR, a cancer promoting gene. The proliferation, invasion and migration appear to decrease when treated with PK11195, a PBR antagonist. Furthermore, PK11195 treatment caused an increase in apoptosis as evident by increase in the levels of annexin V. However, the inhibition of cell proliferation by PK11195 was counteracted by Ro5-4864, a PBR agonist. Thus, PBR antagonist may be a potential therapeutic agent for the control of aggressiveness of breast cancer.

Translocator protein (18 kDa) mediates the pro-growth effects of diazepam on Ehrlich tumor cells in vivo

The Translocator Protein (TSPO), previously known as the peripheral-type benzodiazepine receptor, is a ubiquitous drug- and cholesterol-binding protein that is up regulated in several types of cancer cells. TSPO drug ligands (e.g., diazepam) induce or inhibit tumor cell proliferation, depending on the dose and tissue origin. We have previously shown that TSPO is expressed in Ehrlich tumor cells and that diazepam increases proliferation of these cells in vitro. Here, we investigated the in vivo effects of diazepam on Ehrlich tumor growth and the role of TSPO in mediating this process. Oral administration of diazepam to mice (3.0mg/kg/day for 7 days) produced plasma and ascitic fluid drug concentrations of 83.83 and 54.12 nM, respectively. Diazepam increased Ehrlich tumor growth, likely due to its ability to increase tumor cell proliferation and Reactive Oxygen Species production. Radioligand binding assays and nucleotide sequencing revealed that Ehrlich tumor cell TSPO had the same pharmacological and biochemical properties as TSPO described in other tumor cells. The estimated K(d) for PK 11195 in Ehrlich tumor cells was 0.44 nM and 8.70 nM (low and high binding site, respectively). Structurally diverse TSPO drug ligands with exclusive affinity for TSPO (i.e., 4-chlordiazepam, Ro5-4864, and isoquinoline-carboxamide PK 11195) also increased Ehrlich tumor growth. However, clonazepam, a GABA(A)-specific ligand with no affinity for TSPO, failed to do so. Taken together, these data suggest that diazepam induces in vivo Ehrlich tumor growth in a TSPO-dependent manner.

Control of peripheral benzodiazepine receptor-mediated breast cancer in rats by soy protein

Soy protein is known to have breast tumor suppressing activity. The expression of peripheral benzodiazepine receptors (PBRs), currently renamed as translocator protein (TSPO) and their associated functions, such as nuclear cholesterol uptake and content also have been shown to be increased in breast cancer. Here we investigated whether the breast tumor suppressing effects of soy protein is mediated by down-regulation of PBR expression and function. Breast tumors were induced by gavage administration of a single dose (80 mg/kg) of dimethylbenz[a]anthracene (DMBA) into 50-d old female Sprague Dawley rats, maintained on a standard AIN-76A diet containing either casein or soy protein. Approximately 120 d following DMBA administration, the animals were sacrificed. All tumors were detected by palpation and at autopsy biopsy specimens were taken for histological grading. The ligand binding capacity, expression, and protein levels of PBRs, their nuclear localization and function, such as nuclear cholesterol uptake and content, were significantly increased in the tumors. However, replacement of casein by soy protein in the diet caused a significant decrease in all of these parameters. These data suggest that soy protein inhibits breast tumor development by decreasing the expression of the tumor-promoting gene, which encodes PBRs.