Blood, Vol. 92 No. 3 (August 1), 1998:
pp. 822-833
Intermittent, Repetitive Corticosteroid-Induced Upregulation of
Platelet Levels After Adenovirus-Mediated Transfer to the Liver of a
Chimeric Glucocorticoid-Responsive Promoter Controlling the
Thrombopoietin cDNA
Ko Narumi,
Motoyoshi Suzuki,
Wenru Song,
Malcolm A.S. Moore, and
Ronald G. Crystal
From the Division of Pulmonary and Critical Care Medicine, The New
York Hospital-Cornell Medical Center, New York; and James Ewing
Laboratory of Developmental Hematopoiesis, Memorial Sloan-Kettering
Cancer Center, New York, NY.
For many in vivo gene therapy clinical applications, it is desirable
to control the expression of the transferred transgene using
pharmacologic agents. To evaluate the feasibility of accomplishing this
using corticosteroids, pharmacologic agents widely used in clinical
medicine, we constructed replication deficient adenoviral (Ad) vectors
containing an expression cassette with a chimeric promoter comprised of
five glucocorticoid response elements (GRE) and the chloramphenicol
acetyltransferase reporter gene (AdGRE.CAT) or the murine
thrombopoietin cDNA (AdGRE.mTPO). In vitro studies showed the vectors
functioned as expected, with marked glucocorticoid-induced upregulation
of the CAT or mTPO transgenes. To evaluate the inducibility of the GRE
promoter in vivo, the AdGRE.CAT vector was administered intravenously
to C57B1/6 mice, and CAT activity was quantified in liver before and
after intraperitoneal administration of dexamethasone. The GRE promoter
activity was dependent on the dexamethasone dose, with a 100-fold
increase in CAT expression with 50 µg dexamethasone, similar to the
levels observed in vivo with the Rous sarcoma virus long terminal
repeat constitutive promoter. After dexamethasone administration,
maximum CAT activity was observed at day 2, with a slow decline to
baseline levels by 2 weeks. Based on these observations, we
hypothesized that a single administration of an Ad vector-mediated transfer of the chimeric GRE inducible promoter driving the mTPO cDNA
would enable repetitive administration of corticosteroids to
repetitively upregulate platelet levels for 1 to 2 weeks. The data show
that this occurs, with dexamethasone administration every 3 weeks
associated with 1-week elevations (at each 3-week interval) of serum
mTPO levels, megakaryocyte numbers in bone marrow, and platelet levels
fourfold to sixfold over baseline. Thus, with the appropriate promoter,
it is possible to use a commonly used pharmacologic agent to upregulate
the expression of a newly transferred gene on demand.
© 1998 by The American Society of Hematology.
