Conjugation of poly-L-lysine to bacterial cytosine deaminase improves the efficacy of enzyme/prodrug cancer therapy

We previously observed that bacterial cytosine deaminase (bCD) conjugated with multimodal imaging reporter labeled poly-L-lysine (PLL) demonstrated high therapeutic efficacy in an enzyme/prodrug cancer therapeutic strategy. To understand the role of polyeationic PLL in the cellular uptake of bCD-PLL conjugate, two control molecules, bCD-BF, without the PLL moiety, and bCD-AcPLL, with all positive charges in PLL neutralized, were prepared. bCD-PLL demonstrated about 50 times higher cellular uptake than that of control molecules in human breast MDA-MB-231 cancer cells. Internalized bCD-PLL demonstrated high enzymatic stability in cell cultures as indicated by significant cytotoxicity after addition of prodrug, whereas no obvious cytotoxicity was detected by control molecules. These data indicate that conjugated PLL not only provides a multivalent modification platform to facilitate the delivery of a high payload of imaging reporters or targeting moieties without compromising enzymatic activity but also enhances therapeutic efficacy by accelerating the intracellular uptake of prodrug-activating enzyme.