Clusterin antisense complexed with chitosan for controlled intratumoral delivery

The purpose of this work was to characterize an injectable, intratumoral, controlled release delivery system for clusterin antisense oligonucleotide (clusterin ASO) based on clusterin ASO complexed with chitosan microparticles (CC complexes) and blended with a biodegradable polymeric paste (CC in paste). The effect of clusterin ASO/chitosan ratio on the physicochemical properties of CC complexes and the influence of chitosan and polymeric paste on the in vitro release and stability of clusterin ASO were investigated. Chitosan had an intrinsic pKa of 6.2. Chitosan particles incubated at different pHs swelled to approximately 600% of their dry weight and had a mean diameter of approximately 200 μm. As the amount of chitosan in CC complexes was increased or as the pH was decreased, zeta potentials became increasingly less negatively charged and the amount of clusterin ASO complexed with chitosan increased. Clusterin ASO released into PBS or plasma in vitro from polymeric paste and CC in paste in a similar manner with a burst phase of release followed by a slow sustained release. The ratio of clusterin ASO to chitosan and incorporation into polymeric paste influenced the rate and extent of clusterin ASO release. Inclusion of clusterin ASO with or without chitosan in polymeric paste inhibited the in vitro degradation of clusterin ASO in plasma. Treatment of PC-3 cells in vitro with clusterin ASO alone or clusterin ASO released from the various formulations resulted in 52–62% inhibition of the expression of clusterin protein. Degradation studies showed that approximately 40% of the full-length clusterin ASO remained from both clusterin ASO alone and CC complex samples when incubated in 50% plasma in vitro for 4 days. In conclusion, the amount of clusterin ASO loaded into microparticulate chitosan was dependent on the amount of chitosan present and the pH of the environment and clusterin ASO released from the various formulations in a controlled manner and in a bioactive form.