GENE THERAPY

Gene Therapy Offers New Hope for Leukemia Treatment Gene therapy, one of the most exciting of these new approaches, is being studied at the Arlin Cancer Institute by Dr. Eric Feldman, director of the Leukemia Service and Clinical Research, in conjunction with Dr. Tauseef Ahmed, chief of Oncology and Hematology, and Nader G. Abraham, Ph.D., director of the Gene Therapy Program at New York Medical College.

An avalanche of news articles on anti-angiogenesis and molecular genetic technology put the spotlight on the array of sophisticated new biotechnologic approaches to cancer treatment being developed at pioneering cancer centers across the U.S.

Gene therapy, one of the most exciting of these new approaches, is being studied at the Arlin Cancer Institute by Dr. Eric Feldman, director of the Leukemia Service and Clinical Research, in conjunction with Dr. Tauseef Ahmed, Medical Director of the Arlin Cancer Institute and chief of Oncology and Hematology, and Nader G. Abraham, Ph.D., director of the Gene Therapy Program at New York Medical College.

Early in 1999, Dr. Feldman, building on basic research by Dr. Abraham, will begin the first clinical trial of its kind to determine if a specific type of gene transfer therapy can be used to successfully treat patients with chronic myelogenic leukemia (CML). Following is an interview with Drs. Feldman and Ahmed regarding this latest project in the effort to define new cancer treatment options.

Q. What role does the gene play in the human body? Each gene in the human cell contains a stretch of DNA about half a meter long that carries within it the directions for making a specific protein. When a gene is mutated, its protein product may not be made at all or may work poorly. This flaw, in turn, may cause the cell to function improperly, causing disease. Since the early 1970s, scientists have been looking into ways to correct abnormal genes and thereby eliminate disease. In some cases, scientists have attempted to replace a defective gene on a chromosome as in the case of adenosine deaminase deficiency (ADA), a rare genetic disorder that severely impairs immunity. However, most research has focused on the insertion of a gene into a selected cell type to instill some new property. For example, scientists have tried to stimulate cancer cells to make substances that kill the cells directly or cause the immune system to attack the cancer.

Q. Can you give some examples of how gene therapy might be used to treat cancer? To combat the fact that cancer cells often are able to evade detection by the body's immune system, scientists have tried to insert genes that make cytokines, such as the dendritic cell activator GMCSF, which make the body recognize the tumor cells as different. Investigators also are looking at ways to insert normal p53 genes, or tumor suppressor genes, into cancers growing in the body. In most human cancers, the p53 gene, which secretes a protein that halts irregular cell division, has mutated so that it no longer serves as a check on uncontrolled cell growth. When a normal copy of this gene is introduced into cancer cells in the laboratory, those cells return to a more regular growth pattern or self-destruct.

Q. How are genes inserted? To succeed with any type of gene therapy, it is necessary to have a safe and effective means of transferring the gene into specific cells. These are known as vectors. Vectors act as gene delivery vehicles or shuttles to carry genetic material into a cell and alter it. Vectors currently under study include retroviruses, adenoviruses, adeno- associated viruses, liposomes and naked DNA. Viruses have received the most attention because they are designed specifically to enter cells and express their genes there. Retroviruses permanently insert copies of their genes into the chromosomes of the cells they invade. To convert a wild virus into a safe vector, scientists replace viral genes with ones specifying therapeutic proteins while leaving the viral elements needed for gene expression. In our project, we are using a retrovirus that does not cause human disease.

Q. Can you describe your gene therapy project? Gene transfer therapy is a promising new way to treat patients with chronic myelogenic leukemia (CML). There are currently two ways of treating CML: either with allogenic bone marrow transplant or with systemic injections of interferon. Both approaches have limitations: A donor cannot always be found for bone marrow transplant; and interferon injections have many side effects and are only effective in 20 to 40% of patients. Our hypothesis is by putting the interferon gene into cells in the bone marrow, we can stimulate the production of interferon where it is most needed to fight the cancer, and at the same time reduce the systemic effects typically associated with interferon. We plan to use this approach to treat patients with CML and other cancers in the near future.

Q. What is interferon? How does it work to destroy cancer cells and why do you expect to see fewer side effects with gene transfer therapy than with systemic injections of interferon? Interferon is a naturally-occurring protein produced by many cells in the body. We have known for some time that it has both anti-viral and anti?tumor properties. Interferon works to destroy leukemic cells by increasing the adhesion molecule present in the cells. In other words, interferon makes the leukemic cells sticky like normal cells. This causes the leukemic cells not to divide as much, which makes normal blood production possible. When interferon is given by injection, millions of units of interferon must be given to achieve a therapeutic effect because the interferon goes throughout the body before it reaches the site where it is most needed. By causing the stem cells to produce interferon, we will get local production of interferon where it is needed, and so much less interferon will be necessary.

Q. How did you arrive at the interferon/retroviral construct? We arrived at this construct through collaboration with a group of scientists at the University of Tokyo. Dr. Asano, a professor at the University, successfully cloned the interferon gene. Using his methods as a starting point, Dr. Abraham then linked the interferon with the LXSN retrovirus, a non?replicative virus capable of getting into the cell without running amok and making the patient sick.

Q. What effect does the transfer of this viral/gene product have on cells? If our hypothesis is correct, the viral/gene product will cause cells to produce interferon in the bone marrow, which would destroy any remaining cancer cells. This particular retrovirus is a very safe one and we hope there will be no negative effects on the cells as a result of the transfer. The risks that exist, however, are that the retrovirus would insert itself into an essential gene or that the interferon itself would prove toxic to the patient. We know the effects of giving interferon systemically, however, and believe there will be fewer toxic side effects when the interferon is produced locally in the bone marrow.

Q. Please describe CD 34+ cells? CD 34+, cells are the closest we can come to the stem cells that produce all of our red and white blood cells. When this cell is given to a patient, it homes back to his or her bone marrow and starts producing normal bone marrow cells.

Q. What is the Philadelphia chromosome? The Philadelphia Chromosome is a genetic abnormality associated with CML. A group of scientists in Philadelphia discovered that when a piece of the ninth chromosome breaks off and joins with chromosome 22, and a piece of chromosome 22 breaks off and joins with chromosome nine, it creates a setting in which bone marrow cells are transformed. Normal bone marrow cells become leukemic.

Q. Can you achieve blood production without Philadelphia chromosomes in patients with CML? There are two populations of cells in the bone marrow of a patient with CML. There are normal cells that have the normal chromosome pattern and leukemic cells that have the Philadelphia chromosome. If you suppress the leukemic cells with chemotherapy you can see normal cells that produce normal blood. We will select just the normal cells. A CD 34+ selection column and various methodologies are used to isolate the normal cells by picking up certain identifiers on the cell surface.

Q. How do you plan to use this technology to treat people with CML? We plan to open a clinical trial early next year involving 15 to 20 patients. The study will be limited to patients with CML who have no possible donor for a bone marrow transplant and thus need to be rescued by their own stem cells. Initially, we are also going to focus on patients who have not responded to or can't tolerate systemic injections of interferon. Patients will be given high dose chemotherapy to reduce the amount of cancer in the blood and to allow us to harvest healthy stem cells. The retrovirus will then be used to transfer the interferon gene into the healthy stem cells through a process called transfection. Patients will receive a second dose of chemotherapy and will be rescued with interferon?transfected cells We hope these cells will start producing interferon in the bone marrow, which will destroy the remaining cancer with fewer toxic side effects than systemic injections of interferon.

Q. What is on the horizon? If this trial is successful, we can move on to a multi?center trial involving many more patients from participating institutions across the country to compare the efficacy of systemic interferon injections with the gene transfer approach. The interferon gene may be used in other settings as well. If our project is successful, it will allow us to develop other gene projects to attack other diseases including heart disease and hypertension. Once you have the technology, it can be applied to many other uses.

Address: Department of Radiation Medicine, Zalmen A. Arlin Cancer Institute, Westchester Medical Center, 95 Grasslands Road, Valhalla, NY 10595, Phone: 914-493-8561, Email: info@cancerdocs-radiation.com