Restoration of Retinoid Sensitivity by MDR1 Ribozymes in Retinoic
Acid-Resistant Myeloid Leukemic Cells
Hiromichi Matsushita,
Masahiro Kizaki,
Hiroyuki Kobayashi,
Hironori Ueno,
Akihiro Muto,
Nobuyuki Takayama,
Norihiro Awaya,
Kentaro Kinjo,
Yutaka Hattori, and
Yasuo Ikeda
From the Division of Hematology, Keio University School of Medicine,
Tokyo; and the Department of Laboratory Medicine, National Defense
Medical College, Saitama, Japan.
Complete remission is achieved in a high proportion of patients with
acute promyelocytic leukemia (APL) after all-trans retinoic acid (RA) treatment, but most patients relapse and develop RA-resistant APL. We have previously reported that both RA-resistant HL-60 (HL-60R)
and APL cells express P-glycoprotein and MDR1 transcripts; and these
cells differentiate to mature granulocytes after culture with RA and
P-glycoprotein antagonist. Ribozymes have been shown to be able to
intercept a target RNA by catalytic activity. To address the role of
MDR1 in overcoming RA-resistance in APL cells, we investigated the
biologic effects of ribozymes against the MDR1 transcript in HL-60R
cells. These ribozymes efficiently cleaved MDR1 mRNA at a specific site
in vitro. The 196 MDR1 ribozyme was cloned into an expression vector,
and stably transfected (HL-60R/196Rz) cells were obtained. Expression
of MDR1 transcripts was decreased in HL-60R/196Rz cells compared with
parental HL-60R and empty vector-transfected (HL-60R/neo) cells.
Interestingly, RA inhibited cellular proliferation and induced
differentiation of HL-60R/196Rz cells in a dose-dependent manner,
suggesting reversal of drug resistance in HL-60R cells by the MDR1
ribozyme. These data are direct evidence that P-glycoprotein/MDR1 is
responsible in part for acquired resistance to RA in myeloid leukemic
cells. The MDR1 ribozyme may be a useful tool for investigating the
biology of retinoid resistance and may have therapeutic potential for
patients with RA-resistant APL.
Blood, Vol. 91 No. 7 (April 1), 1998:
pp. 2452-2458
© 1998 by The American Society of Hematology.
