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Curriculum vitae
Laboratory of Molecular Biology |
Biography:
Dr. Pastan is Chief of the Laboratory of Molecular Biology, Division of
Basic Sciences. He obtained his M.D. from Tufts University, received his
medical training at Yale University and research training at NIH with Earl
Stadtman. He established the Laboratory of Molecular Biology in 1970.
He is a member of The National Academy of Arts and Sciences and a Fellow
of the AAAS and The American Society of Microbiology.
Research:
Currently 1.2 million Americans develop cancer each year and about 500,000
die from the disease, because most cancers cannot be cured once they have
metastasized. To develop a new treatment for metastatic cancer, we have
used genetic engineering to modify a powerful bacterial toxin, Pseudomonas
exotoxin A (PE), so that instead of killing normal cells it selectively
kills cancer cells. PE is a three domain protein composed of 613 amino
acids. Anti-cancer agents are produced by deleting its binding domain (aa
1-252) and replacing it with the Fv fragment of an antibody or with a growth
factor that binds to antigens present on cancer cells. These agents are
termed recombinant immunotoxins (RITs). We have made RITs that target Ley
present on colon, breast, lung and other epithelial cancers (B3(Fv)-PE38),
that target the EGF receptor overexpressed on glioblastomas (TGF-alpha-PE38),
that target mutant EGF receptors present on glioblastomas [MR-1(Fv)-PE38KDEL],
and that target the IL2 receptor present on many T and B cell leukemias
and lymphomas LMB-2 or anti-Tac(Fv)-PE38 and that target CD22 on B cell
malignancies and that target BL22 or RFB4(dsFv)-PE38 ovarian cancers and
mesotheliomas (SS1P). These agents are produced in E. coli because large
amounts can be readily purified from this source. When administered to
mice with the appropriate human cancer xenograft, all these RITs produce
complete tumor regressions. Most of these agents are now in clinical trials
in humans and several have produced complete and partial remissions in
humans with cancer.
An
ideal immunotoxin should be very active so that only small amounts need
to be given to cause tumor regressions, small in size so that it can penetrate
into cancers, stable so it remains functional during the 5-10 hours required
to reach the interior of a cancer, and nonimmunogenic so it can be given
repeatedly. Our current research is to design and produce recombinant immunotoxins
with these properties. Size has been decreased and antitumor activity has
been increased by identifying and deleting unnecessary sequences in the
toxin. Initially, recombinant immunotoxins contained amino acids 253-613
of PE (domains II and III). We determined that amino acids 364-395 can
be deleted without loss of activity. Increased stability has been obtained
by designing disulfide linked Fv fragments which are connected by cysteines
engineered into the framework region of the Fvs. These dsFv immunotoxins
are up to 100-fold more stable than conventional single-chain immunotoxins
and have higher antitumor activity. To reduce immunogenecity, we are carrying
out site specific PEGylation by inserting cysteine residues at various
positions in the RIT.
Since
differentation antigens often continue to be expressed in cancers, they
are excellent targets for the immunotherapy of cancer. Therefore,
we have initiated a research project to identify new prostate and breast
cancer-specific antigens. To do this we have developed a computer-based
method that searches the EST database and identifies novel genes. Several
new genes have been discovered by this approach that appear to have an
important role in the prostate and other candidates are now being characterized
that are found in prostate and breast cancers.
Collaborators
on this research include Robert Kreitman, M.D., David FitzGerald, Ph.D.,
Byungkook Lee, Ph.D., Laboratory of Molecular Biology, DBS, NCI; Darell
Bigner, M.D., Duke University Medical Center; Thomas Waldmann, M.D., Metabolism
Branch, DBS, NCI; Jorge Carrasquillo, M.D., Nuclear Medicine, Clinical
Center; and Shigetada Nakanishi, M.D., Institute for Immunology, Kyoto
University.
Recent
Publications:
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Contact Information:
Laboratory
of Molecular Biology,
NCI,
NIH
Building
37, Room 4E16
37
CONVENT DR MSC 4255
BETHESDA
MD 20892-4255
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