Background/aims: This study investigates the application of protein based therapeutic suicide enzyme/prodrug approaches providing novel means for both safe and effective local therapeutic regimes in solid tumors.
Methods: Employing a novel cell permeable peptide, known as the translocation motif (TLM) of hepatitis B virus, E. coli cytosine deaminase (BCDase) suicide fusion proteins were generated.
Results: TLM fusion proteins formed hexamers (as do parental wtBCDase proteins) and retained the specific enzymatic activity of cytosine conversion to uracil also being comparable to parental wtBCDase proteins. However, only BCDase-TLM fusion proteins, but not TLM-BCDase fusion nor parental wtBCDase proteins were found to be taken up to the cytoplasm of target cells as demonstrated both by confocal laser scanning microscopy and cell fractionation. Uptake of BCDase-TLM worked both efficiently and rapidly and was found to be independent from the endosomal pathway. Since BCDase-TLM fusion proteins completely retained their suicide enzymatic activity in the course of translocation across the plasma membrane their usage as profound inducers of chemo-sensitivity to 5-FC strongly is suggested.
Conclusions: Future therapeutic local application of cell-permeable BCDase-TLM fusion proteins together with a systemic 5-FC prodrug application could result in profound antitumor activities without apparent side effects.