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FOR IMMEDIATE RELEASE
Therapeutic Prostate Cancer Vaccine
Shows Promise in Early Clinical Study
-- Dana-Farber Cancer Institute, National
Cancer Institute and
Therion Biologics Report in Clinical Cancer
Research Results
of a Phase I Study of Therion's PROSTVAC vaccine
--
Boston, MA and Cambridge, MA, May 11, 2000 -
Dana-Farber Cancer Institute (DFCI), the National
Cancer Institute (NCI) and Therion Biologics today
reported in Clinical Cancer Research promising
early clinical results for PROSTVAC, Therion's lead
therapeutic vaccine for prostate cancer. In a Phase
I study, 33 men with advanced cancer of the
prostate were treated with three consecutive
monthly doses of PROSTVAC. Data from the trial
indicated that vaccination with PROSTVAC was
well-tolerated in all patients. In addition,
stabilization of PSA levels was observed for at
least 6 months in 14 of 33 patients, and 9 patients
remained stable for 11 to 25 months. Therion's
PROSTVAC vaccine is comprised of a recombinant
vaccinia virus, commonly known for its use in the
smallpox vaccine, engineered to express human
prostate specific antigen (PSA). The vaccine was
designed and developed as part of a Collaborative
Research and Development Agreement (CRADA) between
The Laboratory of Tumor Immunology and Biology (Dr.
Jeffrey Schlom, Chief) of the NCI and Therion.
"Although prostate cancer is currently the second
leading cause of death in American men, there
remains a lack of effective treatments for
recurrent disease," said Joseph Paul Eder, Jr.,
M.D., of the Dana-Farber Cancer Institute and
principal investigator for the study. "Patients
with recurrent prostate cancer and rising PSA
levels are currently treated by hormonal therapies
associated with significant side effects or by a
'watch-and-wait' protocol. By incorporating the PSA
antigen, which is expressed only by prostate cells,
PROSTVAC is designed to stimulate the body's immune
response against tumor cells. For patients with
recurrent prostate cancer, PROSTVAC may offer a
safe, alternative method to stabilize disease
progression."
Study Design
Patients enrolled in the Phase I study were
previously diagnosed with rising PSA levels after
undergoing radical prostatectomy, radiation therapy
or both for treatment of prostate cancer. Patients
were divided into 3 cohorts and received 3
escalating dose levels of PROSTVAC. Ten of 21
patients who received the highest dose level of
PROSTVAC also received granulocyte-macrophage
colony-stimulating factor (GM-CSF) as an
immunostimulatory adjuvant. Cells from 7 of these
patients were assayed for development of a
PSA-specific cellular immune response.
Trial Results
Results of the study showed that no
vaccine-related toxicity was observed in any
patient beyond a low-grade reaction at the site of
inoculation. In the 10 patients treated with
GM-CSF, only one patient developed fever and rapid
heartbeat after the first dose of GM-CSF, but
tolerated subsequent GM-CSF doses. PSA levels
remained stable for at least 6 months in 14 of 33
men treated with PROSTVAC, with or without the
addition of GM-CSF. In addition, 9 patients
remained stable for 11 to 25 months. Of the 7
patients evaluated for PSA-specific immune
responses, 5 demonstrated at least a two-fold
increase of precursor T-cells specific for PSA
after vaccination.
The stabilization of PSA levels in these patients
correlated with the absence of any other
indications of disease progression. However, the
eventual rise in PSA levels over time suggests that
boosting at periodic intervals may be required for
sustained stabilization. Subsequent protocols may
benefit by utilizing a diversified "prime-boost"
protocol, which refers to an immune-conditioning
regimen in which a PSA-expressing pox virus vector
is first used to prime the immune system and a
different, immunologically unrelated pox virus
vector incorporating the same PSA antigen is
subsequently administered to boost the immune
response.
"This preliminary trial showed no significant
disease progression for at least six months in over
40% of study subjects, demonstrating for the first
time in human cancer patients that a recombinant
vector expressing PSA may be useful for developing
a cell-mediated immunotherapy approach to treat
prostate cancer," said Dennis L. Panicali, Ph.D.,
President and Chief Executive Officer of Therion.
"Because we observed that the patients' immune
responses were generated primarily through the
initial dose of PROSTVAC, we believe a prime-boost
protocol may help increase the activity of our
vaccine. Based on data from this trial and other
studies, we are currently evaluating a prime-boost
approach for PROSTVAC in two Phase II trials in
collaboration with Dana-Farber and the Eastern
Cooperative Oncology Group."
Dana-Farber Cancer Institute is among the leading
cancer research and treatment centers in the United
States, and is the only center in New England to be
both a federally-designated Comprehensive Cancer
Center and Center for AIDS Research. Visit
www.dana-farber.net for more information.
Therion Biologics Corporation is engaged in the
development of therapeutic vaccines for cancer and
preventive vaccines for AIDS. Currently, Therion
has nine products in Phase I and Phase II clinical
development for the treatment of major cancers,
including prostate, colorectal and breast cancer
and melanoma. The Company also has a major
corporate alliance with Aventis Pasteur for the
development of therapeutic vaccines for colorectal
and lung cancers and melanoma. Therion is
headquartered in Cambridge, Massachusetts.
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Contacts:
Dennis L. Panicali, Ph.D.
President and CEO
Therion Biologics Corporation
(617) 876-7779
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Heidi Sprang or
Sharon Karlsberg
Feinstein Kean Healthcare Inc
(617) 577-8110
http://www.fkhealth.com
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