Gene therapy may be a possible treatment for cancer and specifically ovarian cancer. The presence of abnormal genes may be one of the reasons that cancer cells grow or become resistant to chemotherapy drugs. In other cases, normal genes that control abnormal growth may be lacking. Finally, it may be possible to insert into cancer cells genes that will make the cancer cell susceptible to certain drugs.

Gene therapy for cancer depends on finding ways to transport the therapeutic gene to the cell and "inject" the gene into the cell. Almost all gene therapy experiments for cancer treatment have used a virus as the means of gene delivery. The Principal Investigator of Project #3 and his colleagues have extensive experience with the Sindbis virus. They have developed a method to allow the Sindbis virus to target cancer cells. In preliminary testing, these targeted Sindbis viruses can efficiently infect ovarian cancer cell lines. In other tumor types tested in mouse cancer models, the targeted Sindbis viruses were able to target the cancer cells and had no toxicity in the animals.

The purpose of this application is to develop better vectors and reagents that will make gene therapy of ovarian cancer more successful.

The specific aims of the project are as follows: (1) Develop at least three Sindbis virus-based delivery systems (vectors) that will be able to target growing human ovarian tumors in mice. The Sindbis virus vectors will be studied to determine to what degree the vectors alone cause cancer cell death or apoptosis. (2) Perform studies that will determine the best method of drug delivery in the mouse. The PI will work closely with the Pharmacology section of the Laboratory core described in the core facility section. (3) Complete the preparation of cell lines that may be able to manufacture sufficient Sindbis virus vectors to allow for the clinical testing.

The proposed studies involve the construction by molecular biology techniques of three targetable Sindbis vectors capable of destroying human tumors growing in mice. The virus vectors will be more toxic as compared to the Sindbis alone in that they will carry genes capable of causing cell death or by reversing the malignant growth pattern. Three alternative mechanisms of achieving this goal will be tested. One virus vector will deliver or encode in a cancer cell the thymidine kinase gene. If this thymidine kinase gene is successfully transferred to a cancer cell and the cells with this gene are exposed to ganciclovir, the effect is to prevent DNA replication in dividing cells. A second gene causes cell death by interacting with death suppressor molecules (Bcl-2) in the target cells. A third vector allows expression of p53, which is capable of reversing the malignant growth pattern and causing cell death (apoptosis). The potency of these vectors and dosing schedules will be detennined in vivo. These studies will also include extensive pharmacokinetics analyses. Finally, a packaging cell will be produced using special insect cells (these insect-derived cells are resistant to Sindbis vector-induced apoptosis) to provide a continuous source of Sindbis vectors for further testing in mouse and potentially human studies.