Extended release of adenovirus from polymer microspheres: potential use in gene therapy for brain tumors

Current protocols for the treatment of intracerebral glioma are inadequate, with limited reduction in morbidity or mortality. As such, gene therapy paradigms have been developed. Initial progress in rodent models using in situ introduction of retroviral vector producer cells to transfer a cytotoxic gene product led to phase I clinical trials with limited success, due in part to immune responses to murine producer cells along with low level gene transfer. We and others have initiated studies to determine the effectiveness of adenoviral vectors to deliver cytotoxic and/or immuno-stimulatory gene products directly to tumor. Adenoviral vectors can be purified to high titers, are relatively stable upon formulation and storage, and can infect both dividing and non-dividing tumor cells. Also, they can be introduced in situ without helper virus or producer cells. However, gene transfer to glioma tissue with recombinant adenoviruses is not efficient, with multiplicities of infection greater than 50 infectious units/cell required for efficacy. At these doses the virus induces a potent immune response that further reduces gene transfer following re-administration. The inflammatory response to low doses of recombinant adenoviral vectors is less robust and does not preclude re-administration. Thus, strategies to increase efficiency coupled to low dose administration are desirable. To accomplish low dose administration we have developed a method to formulate recombinant adenoviral vectors in biodegradable microspheres. Poly (lactic-glycolic) acid (PLGA) microspheres containing recombinant adenovirus were prepared using a double emulsion technique, and viable virus released for greater than 10 days.