PROJEKTI
   

Project
Acronym:  
Name: Development of novel C-5 fluoroalkyl N-acyclic pyrimidine nucleoside analogs as PET tracer for in situ monitoring of gene and cell-based therapies using HSV1-TK as a reporter gene 
Project status: From: 2009-11-01 To: 2013-07-01 (Completed)
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Type (Programme): Ostali 
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Project cost: -
Project funding: -
Project coordinator
Organisation Name: ETH-Zurich  
Organisation adress: Wolfgang-Pauli-Strasse 10 
Organisation country: Švicarska 
Contact person name: Simon M. Ametamey 
Contact person email:  
Croatian partner
Organisation name: Fakultet kemijskog inženjerstva i tehnologije 
Organisation address: Marulićev trg 19 
Contact person name: Silvana Raić-Malić
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Contact person e-mail: Email 
Partners
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Short description of project
Positron emission tomography (PET), a radionuclide-based imaging modality, allows to noninvasively, repetitively and quantitatively image biological processes with highest available sensitivity. The most studied system for the visualization of gene expression in animals and humans is Herpes virus type 1 thymidine kinase (HSV1-TK), the enzyme product of the reporter gene HSV1-tk. As molecular probes, several pyrimidine and purine analogs labeled with either iodine-124 or fluorine-18 as HSV1-TK substrates have been synthesized and evaluated as potential imaging agents for HSV1-TK expression in vivo. However, most of the PET reporter probes including 18F-9-[4-fluoro-3-(hydroxymethyl)butyl]guanine (18F-FHBG), the most widely used reporter probe, are plagued with several shortcomings such as unfavorable pharmacokinetics, cytotoxicity and the so-called bystander effect i.e. the killing of non-transduced tumor cells by activated drug carried from the nearby HSV1-tk transduced cells. Both the pyrimidine and purine class of substrates are phosphorylated by HSV1-TK to their corresponding monophosphates and are metabolically trapped in transfected cells. A striking difference is that while all pyrimidine nucleoside analogues show low, if any, bystander killing effect, purine derivatives such as ganciclovir are endowed with bystander killer effect. Recently, in the effort of further exploring the pyrimidine scaffold as putative starting point for development of novel PET tracers we have identified a new series of C-6 alkylated pyrimidines as HSV1-TK substrates. In a preliminary study, we synthesized a C-6 pyrimidine derivative, 6-(2,3-dihydroxypropyl)-5-(18F-fluoromethyl)pyrimidine-2,4-dione (18F-fluoromethyl-HHT), and evaluated its potential both in vitro and in vivo using murine B16F1 melanoma cell line which was transduced with viral thymidine kinase (TK). The results showed that 18F-fluoromethyl-HHT is far superior compared to 18F-FHBG. 18F-Fluoromethyl-HHT was efficiently phosphorylated and the HSV1-TK expressing tumors in a mouse could clearly be visualized using PET imaging. However, 18F-fluoromethyl-HHT lacks in vivo stability. The principal aim of this project is to explore further the substitution of the pyrimidine scaffold by developing novel C-5 fluoroalkyl N-acyclic pyrimidine nucleoside analogs as PET reporter probes with improved pharmacodynamic and pharmacokinetic profile for imaging HSV1-TK expression in vivo. The best nontoxic candidate which would be specifically and efficiently phosphorylated by HSV1-TK will be labeled with 18F radionuclide. Thus, appropriate precursor will be prepared and its 18F radiolabeling will be accomplished using standard nucleophilic substitution reaction on appropriate leaving groups. For the in vivo PET studies, we plan to demonstrate the monitoring efficiency of the PET reporter probe using the best PET reporter probe and mice bearing locally transplanted HSV1-TK transduced tumor cells. The results of these studies will contribute to improve noninvasive gene therapy monitoring with PET since this new generation of PET reporter probes will have greater sensitivity and specificity.  
Short description of the task performed by Croatian partner
 


   

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