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

Abstract

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.

The Translocator Protein

“…Effects on cell proliferation may be due to a small proportion of the protein being expressed within the cell nucleus. However, the effects of TSPO ligands on apoptosis and cell proliferation vary depending on ligand concentration, with antiproliferative and proapoptotic actions at micromolar concentrations but proproliferative effects through stimulation of mitosis and antiapoptotic effects at nanomolar concentrations (11,13).…”

“…Scatchard analysis of 3 H-PK11195 binding to Ehrlich tumor cells revealed 2 independent binding sites (13). Ehrlich tumor cells are a murine ascitic cell line, possessing high concentrations of polymeric TSPO.…”

The Translocator Protein as a Potential Molecular Target for Improved Treatment Efficacy in Photodynamic Therapy

“…In addition, a correlation between the progression of prostate, breast and colorectal cancer and the overexpression of TSPO has been shown [22,23,24,25,26]. There may, however, be other contributing factors such as the tissue of origin that may be instrumental in determining the role of the TSPO in cell proliferation [27]. Researchers were able to demonstrate that deregulation of TSPO expression or function contributes to cellular changes such as apoptosis during tumor progression [28].…”

Midazolam inhibits the hypoxia-induced up-regulation of erythropoietin in the central nervous system

“…3C). On the other hand, clonazepam, which is a GABA A receptor-specific ligand with no affinity for TSPO (Sakai et al, 2010), suppressed EPO induction in a concentration-dependent manner (Fig. 3D).…”