PARENT SESSION
1:30 PM to 3:30 PM
Tuesday, April 23, 2002
Poster Session 16 Gene Therapy
Room: Nevada Exhibition Center

(P21-224) Endostatin delivered by gene therapy improves in vivo tumor response to radiation.

Shi, Wenyin^*,1, Teschendorf, Christian², Siemann, Dietmar^1,3, ¹ Department of Pharmacology, Gainesville, FL² Department of Molecular Genetics, Knappschaftskrankenhaus, Germany³ Radiation Oncology, Gainesville, FL

ABSTRACT-
In the present study, we evaluated the antitumor efficacy of combining the angiogenic inhibitor endostatin with ionizing radiation in a model of human colorectal cancer (HT29). Mouse endostatin cDNA was cloned into a recombinant adeno-associate virus (rAAV) vector under the control of a constutive CMV- actin promoter. To achieve extended expression of endostatin in vivo, a single injection of various doses of rAAV-Endo was administered into the hind limb muscle of nude mice. Dose dependent elevations in serum endostatin levels could be detected as early as four weeks after treatment and plateau values were achieved within 6 to 8 weeks. A dose of 1 x 10⁹ i.u. resulted in a serum endostatin level of ~500 ng/ml. When HT29 cells were injected intradermally into these mice and tested in an in vivo angiogenesis assay, they induced significantly fewer vessels than did an equal number of tumor cells injected into control animals. In addition, the elevated endostatin levels were sufficient to suppress the initiation and subsequent growth of HT29 xenografts. For example, the time for HT29 xenografts to reach a size of ~200 mm³ was 13 days in the control group and 31 days in the group injected with 1 x 10⁹ i.u. rAAV-Endo. To test whether modulation of endostatin levels could alter the response of established tumors to radiation therapy, groups of mice, either control or injected with rAAV-Endo, were subsequently (6 weeks later) injected with HT29 tumor cells. Once the tumors reached a size of ~200 mm³, they were randomly allocated to no treatment or local irradiation with 10 Gy. Tumors were measured three times a week and the time to grow to five times the starting size was recorded. The data showed that while endostatin or 10 Gy alone resulted in a tumor growth delay of 12-13 days, the combination of therapies led to a growth delay of 27 days. These finds indicate that the delivery of endostatin via rAAV vectors may provide an efficient means of enhancing the antitumor efficacy of radiation therapy.

KEYWORDS: gene therapy, endostatin, angiogenesis, adeno-associate virus