(617g) Guanosine Prodrug Incorporated Polymeric Nanocarriers for Suicide Gene Therapy

The most prominent suicide gene therapy is the use of herpes simplex virus thymidine kinase (HSVtk) in conjunction with a variety of guanosine-based prodrugs (ganciclovir and acyclovir). Currently, introduction of the gene for a foreign enzyme and the prodrugs are administered in a two-step process. First, the foreign gene is delivered into the targeted cancer cells, expressed and released into the cytoplasm. Then the prodrug is administered and activated to its cytotoxic form by the gene-expressed exogenous enzyme. Many gene delivery systems have been proposed for suicide gene therapy most focusing on the use of viral vectors to deliver the prodrug activation gene. In this study, a one-step approach was harnessed to deliver gene and prodrug through polymeric nanocarriers.

Guanosine-based GCV and ACV were used as the initiators in ring-opening polymerization of ε-caprolactone to form hydrophobic GCV-PCL and ACV-PCL, which were then grafted to hydrophilic chitosan to form amphiphilic copolymers for the preparation of stable micellar nanoparticles. The synthesized amphiphilic copolymers were validated by ¹H NMR and FTIR. Self-assembly behavior of micellar nanoparticles was determined by TEM, particle size and charge and critical micelle concentration (CMC). Polymeric nanocarriers complexed with HSVtk plasmids were cultured with colorectal HT-29 cancer cells and toxicity measured. ¹H NMR analysis shows successful synthesis of guanosine-based prodrugs to PCL. FTIR spectra reveal characteristic absorption peaks associated with chitosan and PCL are simultaneously present in amphiphilic copolymers - GCV-PCL-Chitosan and ACV-PCL-Chitosan. CMC of ACV-PCL-Chitosan copolymer was measured to be 0.0056 mg/ml, while size measured by dynamic light scattering was detected to be 150-220 nm, with a zeta potential of +20.14 mV. Toxicity results demonstrate that GCV-PCL-Chitosan/HSVtk and ACV-PCL-Chitosan/HSVtk nanocarriers are a feasible approach to kill HT-29 cells. The anti-cancer efficacy was further enhanced by encapsulated SN38 within the hydrophobic core of guanosine prodrug incorporated polymeric micelles.