Despite advances in surgery,
chemotherapy and
radiotherapy, the outcomes of patients with GBM have not significantly improved.
Tumor recurrence in the
resection margins occurs in more than 80% of cases indicating aggressive treatment modalities, such as gene therapy are warranted. We have examined photochemical internalization (PCI) as a method for the non-viral transfection of the
cytosine deaminase (CD) suicide gene into
glioma cells. The CD gene encodes an
enzyme that can convert the nontoxic
antifungal agent,
5-fluorocytosine, into the chemotherapeutic
drug,
5-fluorouracil. Multicell
tumor spheroids derived from established rat and human
glioma cell lines were used as in vitro
tumor models. Plasmids containing either the CD gene alone or together with the
uracil phosphoribosyl
transferase (UPRT) gene combined with the gene carrier
protamine sulfate were employed in all experiments.PCI was performed with the
photosensitizer AlPcS2a and 670 nm
laser irradiance.
Protamine sulfate/CD
DNA polyplexes proved nontoxic but inefficient transfection agents due to endosomal entrapment. In contrast, PCI mediated CD gene transfection resulted in a significant inhibition of spheroid growth in the presence of, but not in the absence of, 5-FC. Repetitive PCI induced transfection was more efficient at low CD plasmid concentration than single treatment. The results clearly indicate that AlPcS2a-mediated PCI can be used to enhance transfection of a
tumor suicide gene such as CD, in
malignant glioma cells and cells transfected with both the CD and UPRT genes had a pronounced bystander effect.