Exploring Translocator Protein (TSPO) Medicinal Chemistry: An Approach for Targeting Radionuclides and Boron Atoms to Mitochondria

Translocator protein 18 kDa [TSPO or peripheral-type benzodiazepine receptor (PBR)] was identified in the search of binding sites for benzodiazepine anxiolytic drugs in peripheral regions. In these areas, binding sites for TSPO ligands were recognized in steroid-producing tissues. TSPO plays an important role in many cellular functions, and its coding sequence is highly conserved across species. TSPO is located predominantly on the membrane of mitochondria and is overexpressed in several solid cancers. TSPO basal expression in the CNS is low, but it becomes high in neurodegenerative conditions. Thus, TSPO constitutes not only as an outstanding drug target but also as a valuable marker for the diagnosis of a number of diseases. The aim of the present article is to show the lesson we have learned from our activity in TSPO medicinal chemistry and in approaching the targeted delivery to mitochondria by means of TSPO ligands

Radiosynthesis and preliminary biological evaluation of [18F]VC701, a radioligand for translocator protein. G. Di Grigoli, C. Monterisi, S. Belloli, V. Masiello, L. S. Politi, S. Valenti, M. Paolino, M. Anzini, M. Matarrese, A. Cappelli, R.M. Moresco

Positron emission tomography (PET) can be used to monitor in vivo translocator protein (TSPO) expression by using specific radioligands. Recently, several [11C]PK11195 analogues have been synthesized to improve binding stability and brain availability. [18F]VC701 was synthesized and validated in CD healthy rats by biodistribution and inhibition analysis. Imaging studies were also conducted on animals injected unilaterally in the striatum with quinolinic acid (QA) to evaluate the TSPO ligand uptake in a neuroinflammation/neurodegenerative model. [18F]VC701 was synthesized with a good chemical and radiochemical purity and specific activity higher than 37 GBq/mmol. Kinetic studies performed on healthy animals showed the highest tracer biodistribution in TSPO-rich organs, and preadministration of cold PK11195 caused an overall radioactivity reduction. Metabolism studies showed the absence of radio metabolites in the rat brain of QA lesioned rats, and biodistribution analysis revealed a progressive increase in radioactivity ratios (lesioned to nonlesioned striatum) during time, reaching an approximate value of 5 4 hours after tracer injection. These results encourage further evaluation of this TSPO radioligand in other models of central and peripheral diseases

Type I consensus interferon (CIFN) gene transfer into human melanoma cells up-regulates p53 and enhances cisplatin-induced apoptosis: implications for new therapeutic strategies with IFN-alpha

In this study, we describe the effects produced by the retroviral transduction of human type I consensus IFN (CIFN) coding sequence into the 8863 and 1B6 human melanoma cell lines, derived from a metastatic and a primary human melanoma, respectively. Melanoma cell lines producing approximately 10(3) IU/ml of IFN were obtained. Interestingly, cisplatin treatment of IFN-producing 8863 and 1B6 melanoma cells resulted in a three- to four-fold increase in the percentage of apoptotic cells with respect to similarly treated parental or control-transduced cell cultures. A similar effect, although less intense, was caused by cultivation of parental melanoma cells in the presence of exogenous CIFN. The increased susceptibility of the IFN-producing melanoma cell lines to cisplatin-induced apoptosis was associated with an IFN-dependent accumulation of p53, which also correlated with a decrease in Bcl-2 expression. Addition of exogenous CIFN to parental melanoma cells resulted in similar although weaker modulations of p53 and Bcl-2 expression. Cisplatin administration to nude mice bearing 3-day-old IFN-producing 8863 tumors resulted in complete tumor regression, while only a partial tumor inhibition was observed upon cisplatin treatment of mice bearing parental or control-transduced 8863 tumors. Starting the cisplatin treatment 7 days after tumor cell injection still resulted in a stronger inhibition of tumor growth in the mice bearing IFN-producing 8863 tumors as compared with parental tumor-bearing mice. A comparable therapeutic effect was obtained after repeated peritumoral administration of 10(3) IU of exogenous CIFN and cisplatin treatment. Interestingly, a spontaneous tumor regression was observed in nude mice injected with IFN-producing 1B6 cells, in contrast to the progressive tumor growth occurring in mice receiving a similar inoculum of the parental or control-transduced 1B6 melanoma cells. Repeated peritumoral administration of 10(3) IU of exogenous CIFN to mice bearing parental 1B6 tumors caused only a transient inhibition of tumor growth. These results indicate that type I IFN gene transfer is an effective approach for suppressing the tumorigenic phenotype of human melanoma cells and for increasing the efficacy of anticancer drugs. These observations together with our previous findings showing the importance of IFN-alpha-T cell interactions in the generation of an antitumor response in mouse models, underline the interest of using type I IFN in gene therapy strategies for the treatment of human melanoma