Liver-targeting of primaquine-(poly-γ-glutamic acid) and its degradation in rat hepatocytes

We have synthesized poly-γ-glutamic acid (PGA) modified with a synthetic trivalent glyco-ligand (TriGalNAc) for the hepatocyte asialoglycoprotein receptor (ASGP-R). We investigated in vivo distribution of unmodified PGA and TriGalNAc-modified PGA (TriGalNAc-PGA) in mice after intravenous injection. Most of unmodified PGA administered was transported to the bladder over 20-80 min, suggesting a rapid excretion of unmodified PGA into urine. In contrast, TriGalNAc-PGA was found exclusively in the liver over the same period of time. We further synthesized TriGalNAc-PGA-primaquine conjugate (TriGalNAc-PGA-PQ), and investigated binding, uptake, and catabolism of the conjugate by rat hepatocytes. Our studies indicated that approximately 250 ng per million cells of the conjugate bound to one million rat hepatocytes at 0 C, and approximately 2 μg per million cells of the conjugate was taken up over 7 h incubation at 37 C. Furthermore, our results suggested that TriGalNAc-PGA-PQ was almost completely degraded over 24 h, and small degradation products were secreted into cell culture medium. The results described in this report suggest that the TriGalNAc ligand can serve as an excellent targeting device for delivery of PGA-conjugates to the liver hepatocytes, and rat hepatocytes possess sufficient capacity to digest PGA even modified with other substituents.