In Vitro Assessment of a Peptide Nucleic Acid (PNA) - Peptide Conjugate Labeled With an Auger-Emitting Radionuclide for Prostate Cell Killing

Abstract

Abstract : The ultimate goal of the research is to develop new treatment reagents for metastatic prostate cancer. Unfortunately, treatment of metastatic prostate cancer is problematic as the cells can become resistant to the therapy being used. Therefore, this exploratory research was directed at developing new therapy reagents that will not be affected by changes within cells. The therapy reagents use a radioactive material, Auger electron emitting radionuclides, to help solve the problem. Auger emission is quite different from emission from other radioactive materials as they have short-range electron emissions that are very toxic to cells and are not affected by other biological factors. Importantly, the very short particle range can greatly decrease the toxicity outside of the cells that it is targeted to. The studies focused primarily on the synthesis of a peptide nucleic acid (PNA) that has an Auger-emitter (1-125) incorporated. By design the PNA Will bind with mRNA and DNA associated with insulin-like growth factor receptor that is upregulated on PC-3 prostate cancer cells. The first objective was to obtain a thymine analog, an iodouracil-amino acid for incorporating into a PNA. This was accomplished in 8 synthetic steps. However, the tri-n-butylstannyluracil-amino acid required to couple with the PNA could not be prepared in the same manner. Therefore, a second synthetic route was undertaken which proved to be successful. The iodouracilamino acid derivative and tri-n-butylstannyluracil amino acid derivative were coupled with a free amine on the PNA to form new PNA molecules (iodouracil conjugate was used as standard for radioiodinated derivative). The stannyl-PNA was readily radioiodinated to give the desired 125\iodo-PNA. To obtain selective targeting to PC-3 prostate cancer cells and cause internalization of the PNA, the peptide bombesin was coupled to the PNA. Because the PNA have very low solubility in water, a polyethyleneglycol (PEG) linker was used.