Ribozymes as a Tool to Inhibit Artery Smooth Muscle Cell Proliferation Following Percutaneous Transluminal Angioplasty.

 
G. Grassi¹, A. Kuhn¹, J.J. Schnorr¹, H. Koehn¹, M. Grassi³, G. Bauriedel², P. Di Nardo⁴, R. Kandolf1.
¹Department of Molecular Pathology, University of Tuebingen, Germany, ²Department of Cardiology, University of Bonn, Germany; ³Department of Chemical Engineering, University of Trieste, Italy; ⁴Department of Molecular Cardiology, University of Tor Vergata, Roma, Italy.
 

Dietary fats play a relevant role in the development of atherosclerosis which very often results in the partial occlusion of the vessel lumen. In this case a possible therapeutical approach is represented by percutaneous transluminal angioplasty (PTA). However, in about 30 to 50 % of the cases PTA is followed by artery re-occlusion mostly due to vascular smooth muscle cell proliferation (VSMC). Therefore, we based our therapeutical approach on the inhibition VSMC growth by hammerhead ribozymes. These are short RNA molecules capable of specifically cleave a phosphodiester bond within a RNA molecule. As ribozyme targets we have chosen the mRNAs of E2F1 and cyclin E genes which play a key role in the transition from G1 to S phase of the cell cycle. Ribozyme accessible cleavage sites were mapped on the two full length mRNAs by the RNase H digestion technique. Based on these results, ribozymes directed against the two targets were generated with 8 nucleotides per binding arm and tested in vitro under single turnover conditions. Cleavage reactions were performed under physiological conditions of temperature and pH. The most active ribozymes had kreact/Km ratios between 50 and 80x10⁴ M^-1min^-1 which are among the best values so far described for ribozymes targeted against long mRNAs. In addition we investigated the effect on ribozyme cleavage efficiency of the variation of the binding arm lengths. As a result of these experiments we found that the optimal binding arm length was in the range of 8-12 nucleotides. The in vivo effectiveness of the most active ribozymes will be tested in human smooth muscle cells grown either in the presence or in the absence of the specific active ribozyme. The possible ribozyme antisense effect will be tested using inactive ribozymes bearing a mutation in the active core which abolishes the catalytic activity but not the possibility to bind to the target. Cell cycle progression will be evaluated by facs analysis. In conclusion our data represent the first example of in vitro highly active ribozymes targeted against cyclin E and E2F1 mRNAs. In addition, preliminary in vivo studies indicate that our ribozymes are active also in vivo.

 
  
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