Replication-deficient adenovirus vectors are efficient vehicles for delivering therapeutic genes into mammalian cells. However, the high doses required to produce effective gene transfer in vivo can also cause unwanted cellular toxicity. To improve replication-deficient adenovirus transgene expression while minimizing adverse reactions, we have tested polycationic compounds for their ability to enhance adenovirus adsorption. We demonstrate increased transgene expression after mixing adenovirus preparations with
polycations, cationic
lipids, and CaCl2 prior to transduction in vitro. An E1-deleted adenovirus vector was admixed with various
polycations, and
beta-galactosidase (beta-gal) activity was evaluated. The optimal polycation concentrations for augmenting adenovirus-mediated gene transfer were 5-10 microg/mL
polybrene, 400 microg/mL
protamine sulfate, 10 microg/mL N-(1-[2,3-dioleoyloxy]propyl)-N,N,N-trimethylammonium methylsulfate (
DOTAP), 2.5 microg/mL
Lipofectamine, and 62.5 mM CaCl2.
Polycations enhanced beta-gal expression in three of six established cell lines. Similar results were obtained using primary
tumor cell cultures, where beta-gal expression was increased 1.5- to 10.7-fold (mean = 3.6) by
polybrene, 1.8- to 7.5-fold (mean = 3.4) by
DOTAP, and 2.3- to 10.4-fold (mean = 4.8) by
protamine sulfate. Adenovirus transduction efficiency in two primary
leukemia isolates was improved by 3- and 4.5-fold. We were unable to demonstrate any benefit when adenovirus was admixed with
protamine sulfate prior to intratumoral injection in a xenogeneic severe combined immunodeficient mouse
melanoma tumor model. Further studies will determine whether
polycations can improve intratumoral gene transfer.