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Senior Citizen Health & Medicine
Prostate Cancer Vaccine Successfully Prevents Cancer
in 90 Percent of Lab Mice
Might work for men with rising levels of PSA, says
USC researcher
 Feb.
1, 2008 – A universal worry for older men is the threat of prostate
cancer but there is very encouraging news from researchers at the
University of Southern California that are working on a vaccine to
prevent it. In a recent test it prevented the development of cancer in
90 percent of young mice genetically predestined to develop the disease.
In the February 1 issue of Cancer Research, they
suggest the same strategy might work for men with rising levels of PSA
(prostate specific antigen), a potential diagnostic indicator of
prostate cancer.
“By early vaccination, we have basically given
these mice life-long protection against a disease they were destined to
have,” said the study’s lead investigator, W. Martin Kast, Ph.D., a
professor of Molecular Microbiology & Immunology and Obstetrics &
Gynecology at the Norris Comprehensive Cancer Center.
“This has never been done before and, with further
research, could represent a paradigm shift in the management of human
prostate cancer.”
Now, men with rising PSA levels but no other signs
of cancer are advised “watchful waiting” – no treatment until signs of
the cancer appear, Kast says.
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 Age
is the most important risk factor for prostate cancer. More than
65% of cases are diagnosed in men over age 65 - average age at
the time of diagnosis is 70. –
NIH SeniorHealth |
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“But what if instead of a watchful wait, we
vaccinate? That could change the course of the disease.”
The study findings also represent a new way to
think about the use of therapeutic prostate cancer vaccines, Kast says.
Vaccines now in testing are designed to treat men whose cancers are
advanced and unresponsive to therapy, and results have offered limited
clinical benefit, he says. This novel approach targets the precancerous
state with the aim of preventing cancer from developing, he says.
The Kast team’s preventive vaccine is designed to
mount an immune response against prostate stem cell antigen (PSCA), the
protein target of some therapeutic vaccines under development. PSCA, a
membrane protein, is over-expressed in about one-third of early-stage
prostate cancers, but expression ramps up in all prostate tumors as they
grow and advance. PSCA is also expressed at low-levels in normal
prostate gland tissue as well as in the bladder, colon, kidney and
stomach.
The researchers created a prime-boost vaccination
scheme using two kinds of vaccines and tested it in 8-week-old mice that
were genetically altered to develop prostate cancer later in life. The
first vaccine simply delivered a fragment of DNA that coded for PSCA,
thus producing an influx of PSCA protein to alert the immune system. The
booster shot, given two weeks later, used a modified horse virus to
deliver the PSCA gene.
“Confronting the immune system in two different
ways forces it to mount a strong response,” Kast said.
In the experimental group, two of 20 mice developed
prostate cancer at the end of one year, and by contrast, all control
mice had died of the disease.
Researchers found that mice in the experimental
group had all developed very small tumors that did not progress.
“There were tiny nodules of prostate cancer in the
mice that were surrounded by an army of immune system cells,” Kast said.
“The vaccination turned the cancer into a chronic, manageable disease.”
The vaccination strategy also works with other
antigens, Kast says. The researchers recently tried another prostate
cancer membrane target and found that after 1.5 years, 65 percent of
experimental mice were still alive, and of those that died, the
suspected cause was old age.
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More About
Prostate Cancer |
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The prostate is the gland below a man's
bladder that produces fluid for semen. Prostate cancer is the
third most common cause of death from cancer in men of all ages.
It is rare in men younger than 40.
Levels of a substance called prostate
specific antigen (PSA) is often high in men with prostate
cancer. However, PSA can also be high with other
prostate conditions. Since the PSA test became common, most
prostate cancers are found before they cause symptoms. Symptoms
of prostate cancer may include
● Problems passing urine, such as
pain, difficulty starting or stopping the stream, or dribbling
● Low back pain
● Pain with ejaculation
Prostate cancer treatment often depends
on the stage of the cancer. How fast the cancer grows and how
different it is from surrounding tissue helps determine the
stage. Treatment may include surgery, radiation therapy,
chemotherapy or control of hormones that affect the cancer.
> Overviews
●
Detailed Guide: Prostate Cancer(American Cancer Society) -
Also available in
Spanish
●
Prostate Cancer (National Cancer Institute)
●
Prostate Cancer (PDQ): Treatment (National
Cancer Institute) - Also available in
Spanish
●
Prostate Cancer: What You Need to Know(American Academy of
Family Physicians) - Also available in
Spanish
●
Report to the Nation on Prostate Cancer: A Guide for Men and
Their Families(Prostate Cancer Foundation) - Large PDF file
More Information and Links at MedlinePLUS |
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Crucially, investigators further found that treated
mice did not develop autoimmune disease, a side effect that could
develop if the vaccine had also targeted PSCA expression in normal
cells. “Theoretically, the vaccine could produce a response in any
tissue that expresses the antigen, but the fact that PSCA is expressed
in such low levels in normal tissue may prevent that complication,” he
said.
Still, studies in humans are needed to ensure
autoimmunity does not develop, Kast says.
“We feel this is a very promising approach,” he
said. “With just two shots, the vaccine will prime immune cells to be on
the lookout for any cell that over-expresses PSCA.”
Editor’s Notes:
The study was funded by a pre-doctoral training
grant from the National Institutes of Health and a grant from the
Margaret E. Early Medical Research Trust. Co-authors include researchers
from the University of Southern California as well as from AlphaVax,
inc., of Research Triangle Park, North Carolina.
The mission of the American Association for Cancer
Research is to prevent and cure cancer. Founded in 1907, AACR is the
world's oldest and largest professional organization dedicated to
advancing cancer research. The membership includes nearly 27,000 basic,
translational, and clinical researchers; health care professionals; and
cancer survivors and advocates in the United States and more than 70
other countries. AACR marshals the full spectrum of expertise from the
cancer community to accelerate progress in the prevention, diagnosis and
treatment of cancer through high-quality scientific and educational
programs.
American Association for Cancer Research
Links to more SeniorJournal.com reports on
Prostate Cancer:
New Male Sling Helps Prostate Cancer Survivors with
Urinary Incontinence
Losing urine control is frustrating for the
more than 2 million men -
Aug. 29, 2007
Cancer Cells Zapped by Electrical Impulses with Invention by Engineers
Clinical trials come next for test on prostate cancer victims
July 6, 2007
Researchers Say They
Have Found a Better Test for Prostate Cancer?
April 26, 2007
Proteins from Inflammation are 'Smoking Gun' in Spread of Prostate
Cancer
March 19, 2007
Obesity and
Prostate Cancer a Deadly Combination, Study Finds
March 15, 2007
Seniors May Increase Risk of Heart Disease from Prostate Cancer
Treatment
Feb. 26, 2007
Prostate Cancer
Patients Have High Survival Rates with Seed Implants
January 31, 2007
Radiation Therapy
Combo Cures Prostate Cancer Long-Term
January 4, 2007
Lack
of Sons Puts Men at Higher Risk for Prostate Cancer Says New Study
January 3, 2007
Elderly Men
Survive Prostate Cancer 'Significantly' Longer if Treated
December 22, 2006
Octogenarians Not Too Old for Cancer Surgery, Say Mayo Clinic
Researchers
November 27, 2006
Prostate
Cancer Studies Find Benefit to Radiation, No Harm in Testosterone
Replacement in Older Men
November 14, 2006
Prostate
Cancer Cells Killed by Protein Made by the Cancer
November 10, 2006
Researchers
Urge New Approach to Prostate Cancer Screening with Early PSA Base
November 1, 2006
Prostate Cancer Appears Cured in 89 Percent of Men Treated with IMRT
September 27, 2006
PSA of
Prostate Cancer Victims Can Predict How Long They Will Survive
August 25, 2006
Large Study Finds Some Prostate Cancer Patients
Possibly Overtreated
August 15, 2006
Plant-Based Diet with Stress Reduction Slows
Progression of Prostate Cancer
August 15, 2006 - Also in this news report you will find links
to more associations between prostate cancer and nutrition and
supplements.
Prostate Cancer Cells Killed by RNA-Based Drug
August 10, 2006
Men Found with Prostate Cancer Rush to Judgment on
Treatment
June 26, 2006
Potential of Prostate Cancer Spread Detected Early
by New Test
June 21, 2006
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