Spontaneous Glioblastoma in Dogs: Preclinical Model for High Capacity Adenoviral Vector-Mediated Experimental Gene Therapy

MARIANELA CANDOLFI; JAMES F CURTIN; W S NICHOLS; MARIANA PUNTEL; GWENDALYN D KING; WEIDONG XIONG; KURT M KROEGER; CHUNYAN LIU; PEDRO R LOWENSTEIN; MARIA G CASTRO

Seattle, WA, EEUU

Congreso; American Society of Gene Therapy 10 Annual Meeting; 2007

We evaluated the dog spontaneous GBM as a large animal model for translational gene therapy strategies. We determined the neuropathology of these tumors and the extent to which it resembles human GBM. We also determined the feasibility of infecting dog normal brain tissue by injecting adenoviral vectors (Ads) expressing reporter and therapeutic transgenes in the cortex of healthy Beagle dogs. Since human patients usually exhibit preexisting immunity against Ads, we determined the anti-Ad immune status of outbreed dogs. We found that dog GBMs exhibit characteristic features of the human GBM, including necrosis, pseudopalizading, neovascularization, endothelial proliferation and invasion into non-neoplastic brain. In the brain of healthy Beagle dogs we administered Ad expressing the B-Galactosidase, or the therapeutic transgenes: TK, which kills glioma cells in the presence of ganciclovir (GCV), and the immunostimulatory Flt3L, which attracts antigen presenting cells to the brain and the tumor mass. Transgene expression was detected in neurons and astrocytes 7 days post-injection without adverse clinical or neuropathological side effects. We assessed the presence of neutralizing antibodies in serum from 17 outbred dogs recruited for our study. We found that 60% exhibited neutralizing antibodies against Ads. These data suggest that GBM-bearing dogs would also mimic the immune status of human patients in clinical trials. Our results suggest that high capacity-Ads are excellent candidates for treating dog GBM, since their expression is not inhibited by anti-Ad immune responses. Thus, we assessed the ability of HC-Ad vectors expressing TK and Flt3L to infect dog GBM cells in culture. HC-Ads were effective at transducing dog GBM cells. HC-Ad-TK elicited strong cytotoxic effects when combined with GCV. Our data indicate that dogs bearing spontaneous GBM constitute an attractive animal model for testing novel therapeutic approaches in a spontaneous tumor in the context of a larger brain.