© 1997 by Oxford University Press
Journal Of The National Cancer Institute, Vol 89, 446-452, Copyright © 1997 by Oxford University Press
PE Lovat, H Irving, M Annicchiarico-Petruzzelli, F Bernassola, AJ Malcolm, AD Pearson, G Melino and CP Redfern
BACKGROUND: The overall survival rate for patients with neuroblastoma has
improved over the past two decades, but long-term survival for the subgroup
of patients with high-risk disease remains low. In recent years, there has
been interest in the potential clinical use of drugs able to induce
differentiation of neuroblastoma cells. Since 9-cis- retinoic acid induces
better and more sustained differentiation of neuroblastoma in vitro than
other retinoic acid isomers, this may be a more appropriate retinoid for
use in neuroblastoma therapy. PURPOSE: The purpose of this work was to
compare the long-term effects of all- trans- and 9-cis-retinoic acid on
neuroblastoma differentiation using an N-type (neuroblastic) cell line, SH
SY 5Y, as an in vitro model. In addition, we wanted to find out whether
9-cis-retinoic acid would induce programmed cell death (apoptosis) in these
N-type neuroblastoma cells and to determine whether the effects of either
9-cis- or all- trans-retinoic acid are dependent on their continued
presence in the culture medium. METHODS: SH SY 5Y cells were incubated in
either the continued presence of all-trans- or 9-cis-retinoic acid or for 5
days with retinoic acid followed by culture in the absence of retinoid for
up to 13 days. Morphologic changes were observed using phase-contrast and
scanning electron microscopy. Apoptosis was determined by flow cytometry of
propidium iodide-stained cells and by using terminal deoxynucleotidyl
transferase to end-label DNA fragments in situ in apoptotic cells. RESULTS:
Culture of SH SY 5Y cells with all-trans- or 9-cis retinoic acid for 5 days
induced morphologic differentiation and inhibited cell growth. These
effects were maintained in the continuous presence of each retinoic acid
isomer but were more profound in cells treated with 9-cis-retinoic acid.
The differentiation of cells treated with all-trans-retinoic acid was
reversible once retinoic acid was removed from the medium. Conversely,
apoptosis was induced in cells treated with 9-cis-retinoic acid for 5 days
and cultured for 9 days (4 days after washout) but not in cells cultured in
the continuous presence of 9-cis-retinoic acid. This effect was specific to
9-cis- retinoic acid. CONCLUSIONS: Previous studies have demonstrated
differential responses to all-trans-retinoic acid in N- and S-type
(substrate-adherent or Schwann-like) neuroblastoma cells: Apoptosis is
induced in S-type cells, whereas differentiation occurs in N-type cells.
The present results show that, unlike all-trans-retinoic acid, 9-
cis-retinoic acid induces both differentiation and apoptosis in N-type SH
SY 5Y neuroblastoma cells. However, apoptosis was dependent on removal of
9-cis-retinoic acid from the culture medium. IMPLICATIONS: Since both
differentiation and apoptosis are involved in tumor regression,
9-cis-retinoic acid may be a more appropriate retinoid for clinical trials
in neuroblastoma. The dependence of apoptosis on treatment and subsequent
removal of 9-cis-retinoic acid implies that drug scheduling may be an
important parameter affecting therapeutic efficacy.
ARTICLES
Apoptosis of N-type neuroblastoma cells after differentiation with 9- cis-retinoic acid and subsequent washout
Department of Medicine, University of Newcastle Upon Tyne, U.K.
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