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Release: Aug. 27, 2001

UI team begins study of vaccine to treat prostate cancer

IOWA CITY, Iowa -- A team of University of Iowa Health Care physicians and researchers has launched the nation's first clinical trial of an adenovirus–prostate-specific antigen (PSA) vaccine for treatment of prostate cancer that has failed other treatments.

The Phase I study is designed initially to test the optimal dosage at which the vaccine, a type of gene therapy, can safely be given to patients.

The clinical study is being co-led by David Lubaroff, Ph.D., UI professor of urology and microbiology, and Richard Williams, M.D., the Rubin H. Flocks Chair in Urology, and professor and head of the department. The vaccine was designed in Lubaroff's laboratory and also draws on UI research led by Timothy Ratliff, Ph.D., the Anderson-Hebbeln Professor of Urology.

The UI Health Care trial also will help determine how well the vaccine stimulates an immune response and if this response has a therapeutic effect on prostate cancer.

Eligible patients will specifically be selected by the investigators through a screening process and will include men whose prostates have been removed or have been treated by radiation. In addition, the eligible study participants are already receiving hormone treatment and have a tumor in the prostate or cancer that is known to have metastasized from the prostate (spread to other parts of the body such as the bone).

Some of the patients will previously have been treated at the Holden Comprehensive Cancer Center at the UI. Patients will be selected to receive different dosages of vaccine in one of two types of injectable forms, either a saline-based solution or a gel matrix.

"This is the first study in a series of four vaccines we're developing that may help us treat patients with hormone-resistant prostate cancer," Williams said. "Our hope is that this vaccine or one of the other three vaccines, or perhaps two or more of them in combination, will be effective in halting the progression of prostate cancer."

Lubaroff said that vaccine therapy for any cancer is a relatively new area of research. In addition to the UI study, investigations on other prostate cancer vaccines are under way at other institutions.

"The advantage of a vaccine is that it can use the patient's own immune system to treat the cancer rather than administering other drugs that may or may not be specific to the cancer," Lubaroff said. "In addition, the vaccine can help enhance the immune response over time."

Two patients already have received the treatment, which involves an injection and an overnight stay at the UI Clinical Research Center, Williams said.

"The immunization is similar to the one a person gets for diphtheria-pertussis-tetanus, in that it's injected just barely under the skin," Williams said.

To create the vaccine, the team used a virus that causes the common cold but which has been engineered to be non-infective in humans. The disabled virus, known as an adenovirus, can then be used as a vector, or carrier, of other genes that researchers insert into the virus.

"We inserted the gene for prostate-specific antigen into the disabled virus," Lubaroff explained. "Through an injection, the virus enters cells and helps produce PSA. The hope then is the body will respond to the presence of PSA with an immune response that fights the cancer."

Specifically, the PSA introduced via the vaccine should stimulate the immune system to produce anti-PSA antibodies and lymphocytes, which lead to the destruction of PSA-producing cells. This is expected to help shrink tumors.

"Because the patients in this trial will have measurable disease, we should be able to see if their lesions have decreased in size within a few weeks after the immunization treatment," Williams said. "We also can monitor the prostate-specific antigen, which is a measure of the volume of cancer in a patient. The PSA levels should decrease if the tumor actually responds to the therapy."

Because the patients in the study have a minimally functioning or no prostate, any PSA present will be known to be produced by tumor cells. Eighteen patients will be treated in the Phase I study. Williams said that if the initial investigation is successful, it will be expanded to include more patients.

The researchers will also try to determine whether a special gel, a collagen matrix known as Gelfoam, helps the vaccine maximize its potential.

In pre-clinical studies done in collaboration with Ratliff's laboratory and based on research by Robert Siemens, M.D., former UI research fellow in urology, Lubaroff's laboratory showed that the gel helps the virus reach its destination and induce a stronger anti-PSA response.

"Our laboratory findings indicate the Gelfoam augments the potential of the PSA-containing virus we inject," Lubaroff said. "This augmentation may be due to a slower, more sustained release of the virus in the body or by the activation of other biologically active cells."

Lubaroff, an immunologist, added, "This is an exciting and unique opportunity to see if we can use a person's own body to fight cancer through a vaccine."

Other UI investigators involved in the study include Jack Gerstbrein, a physician assistant in urology; Brian Link, M.D., assistant professor of internal medicine; and Michael O'Donnell, M.D., associate professor of urology. Additional UI individuals participating in the study include nurses in the Holden Comprehensive Cancer Center and the Clinical Research Center.

Prostate cancer is the second leading cause of death among men in the United States. African American males are at a higher risk for the disease than are other men.

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