Evaluation of cell-penetrating peptide/adenovirus particles for transduction of CAR-negative cells.

Adenovirus (Ad) is a promising gene therapy vector, and is used currently in more than 23% of clinical gene therapy trials. The viral vector, however, has drawbacks such as immunogenicity, promiscuous tropism, and the inability to infect certain types of cells. The focus of this work was to develop an improved vector through electrostatic formation of a complex between negatively charged Ad and positively charged cell-penetrating peptides (CPPs), including Tat, Penetratin, polyarginine, and Pep1. The resulting complexes were demonstrated to be capable of transducing cells that lack the coxsackie-adenovirus receptor (CAR), and are otherwise difficult to infect with native Ad. The transduction efficiency of the complexes was optimized by varying the multiplicity of infection, complex formation time, and ratio of CPPs to Ad, which improved the transduction efficiency of CPP/Ad on CAR-negative cells more than 100-fold compared with unmodified Ad. The size of the CPP/Ad complex was initially less than 300 nm, but stability studies performed in the presence of serum indicate that the complex aggregates with serum after an extended period of time. The results of the current study indicate that electrostatic modification of Ad with CPPs provides a relevant platform for developing effective Ad-based gene therapy vectors.

Protein impurities from cell culture dramatically impact transduction efficiency of polymer/virus hybrid vectors.

Polyethylenimine (PEI) was used recently with murine leukemia virus-like particles (MLV-VLPs) to produce a hybrid vector that possesses advantages over the native virus; the transduction efficiency of this vector, however, was less than the transduction efficiency of the native virus. The cause of the reduced efficiency was hypothesized to be related to the involvement of proteins in PEI/MLV-VLP complex formation and overall complex size. To test the hypothesis and potentially improve the efficiency of the hybrid vector, ultracentrifugation and size exclusion chromatography were used to purify MLV-VLP and to study the effect of proteins in cell culture medium on complex formation. Based on dynamic light scattering and electron microscopy, complexes formed from the purified MLV-VLPs were smaller, but surprisingly, less efficient than complexes formed from unpurified MLV-VLPs. The addition of protein to purified MLV-VLPs showed that the initial efficiency could be restored and that the purification strategy was not inactivating the MLV-VLPs. Further, by optimizing the amount of protein added to the purified MLV-VLPs, the level of transduction by PEI/MLV-VLP improved 1.6-fold. Particle characterization showed a correlation between the size of the PEI/MLV-VLP complex and the transduction efficiency, which is likely a result of greater sedimentation and cell contact during in vitro studies.