Re-programming pullulan for targeting and controlled release of doxorubicin to the hepatocellular carcinoma cells
A novel bioconjugate for hepatocellular carcinoma (HCC) targeting was obtained by pullulan re-programming, which involves the backbone oxidation and conjugation of targeting peptide and doxorubicin (Doxo) through a releasable linker. Preliminary in vivo studies showed that the oxidation of 40 glucopyranose units (GPU) out of 100 remarkably reduced the pullulan unspecific liver tropism. This oxidized polymer was functionalized with PreS1 to selectively target the HCC and with rhodamine (Rhod) as label to perform in vitro cell up-take investigations. PreS1 and Rhod were conjugated to the aldehydes present along the oxidized pullulan backbone through a 3.4 and 2 kDa PEG spacer, respectively, and by reductive amination. The resulting PreS1-Pull-Rhod contained a mean of 8 PreS1 per oxidized pullulan chain. Cell culture studies were performed by using HepG2/SERPINB3 cells that overexpress the serpine B3 receptor and control HepG2/EMPTY cells that do not overexpress the receptor. A comparative study by cytofluorimetry and confocal microscopy performed using PreS1-Pull-Rhod and Pull-Rhod (control polymer) showed that PreS1 conveys to the conjugate high cell selectivity. Afterwards, the oxidized pullulan was exploited to generate a targeted drug delivery system by conjugation of Doxo to the polymer backbone through a hydrazone pH-sensitive bond and NH2-PEG3.4 kDa-PreS1. The PreS1-Pull-Doxo conjugate showed a two-fold increase of anticancer activity with respect to the control Pull-Doxo towards HepG2/SERPINB3 cells.