In the United States, bladder cancer is the second most common cancer of the urogenital tract with over 68,000 new cases and 14,000 deaths in 2008 1
. While the majority of lesions are superficial at diagnosis, the risks of recurrence and progression are high and close long-term monitoring is required, which makes bladder cancer one of the costliest diseases 2
. Despite therapy nearly half of all patients with superficial disease experience relapse or progression within 5 years. Patients who present with advanced disease have, even with multimodal therapy, only 20-40% survival at 5 years. Thus, more effective treatment strategies, aimed at reducing the recurrence and progression of superficial bladder cancer as well as improving therapeutic outcome in patients with advanced disease, are needed.
Gene therapy has garnered significant attention as a therapeutic approach for bladder cancer disease 3
. Viral vectors that have been explored for bladder cancer gene therapy include herpes virus, retrovirus, adeno-associated virus (AAV), and adenovirus. Adenoviral delivery of therapeutic transgenes is particularly attractive since these vectors infect a wide range of cells with high efficiency but remain episomal thus minimizing the risk of insertional mutations. Despite the widespread use of adenoviral vectors for transgene expression, in vivo use of adenovirus faces significant hurdles. Neutralization of type 5 adenovirus by pre-existing or induced antibodies results in a significant decrease of target cell infection 4, 5
. In addition, following intravenous delivery adenovirus is inactivated by interactions with cells of the innate immune system as well as platelets and erythrocytes 6, 7
; these ‘non-specific’ interactions limit the efficacy of the delivered viral vectors and lead to toxicity 8
. Since adenovirus can be delivered to malignant lesions in the bladder by intravesical instillation, complications associated with systemic delivery may be reduced but cannot be completely avoided. Additionally, challenges such as effective transduction of target cells remain. Adenovirus enters cells via a cell surface protein known as coxsackie and adenovirus receptor (CAR) that physiologically functions as an adhesion protein 9
. In bladder cancer, decreased CAR expression has been associated with increased tumor invasiveness and poor prognosis 10
. Thus the development of strategies to overcome obstacles associated with immune clearance and viral transduction of CAR negative cells are needed.
Cationic lipids and polymers have been employed to enhance adenovirus-mediated gene delivery 11-18
. Cationic lipids and macromolecules can overcome the repulsion between the negatively charged adenoviral surfaces and anionic glycosaminoglycan coated epithelial cells, leading to enhanced adenoviral infection in cells that downregulate CAR19
. For example, cationic polymers including poly-L-lysine11
and poly(ethylene imine) (pEI)16
have been previously used for enhancing adenoviral infection but the toxicity of these polymers is a significant limitation to their subsequent use. Thus, while enhancing adenoviral infectivity with cationic polymers remains a promising approach, new polymers that demonstrate high infectivity and low toxicities are needed in order to realize the promise of this strategy. We have recently generated and screened a library of cationic polymers for binding anionic plasmid DNA for cancer cell transfection 20
. A number of candidate polymers demonstrated higher transfection efficacies and lower cytotoxicites compared to the commonly used polymer, pEI. In the current study, we investigated the ability of a candidate polymer from this library to enhance adenoviral transduction in CAR-negative bladder cancer cells. We observed that the candidate polymer, ethyleneglycol diglycidyl ether (EGDE)-3,3′-diamino-N-methyl dipropylamine (3,3′) or EGDE-3,3′, demonstrated higher efficacies for enhancing adenoviral transgene expression than pEI. In addition, complexing EGDE-3,3′ with an adenovirus expressing TRAIL enhanced bladder cancer cell death. Our results underscore the opportunities presented by novel biocompatible polymers for enhancing adenoviral infection and apoptosis of bladder cancer cells.