Liarozole inhibits
cytochrome P-450-dependent
enzymes that play a key role in
all-trans-retinoic acid (ATRA) catabolism. In MCF-7 cells,
liarozole potentiates the antiproliferative effects of ATRA. The present study demonstrates this synergistic effect on cell differentiation of MCF-7 cell cultures as measured by immunocytochemistry for cytokeratins 8, 18, and 19, actin,
E-cadherin,
desmoglein and
desmoplakins I & II. ATRA concentration-dependently (10(-8) M-10(-6) M) induced changes in actin stress fibers and
cytokeratin intermediate filaments. These changes were accompanied by a more obvious interaction of these filaments with junctional complexes. Surface area and volume of the MCF-7 cells increased markedly after ATRA exposure, with extensive filopodia formation.
Liarozole (10(-6) M) alone had no effect on cell morphology,
cytokeratin or actin organization, or on cellular junctions. In combination with ATRA (10(-9) M and 10(-8) M),
liarozole potentiated the ATRA-induced effects. The MCF-7 cell cultures used showed morphological heterogeneity, consisting of at least two cellular subpopulations. This was reflected in the staining for
E-cadherin,
desmoglein and
desmoplakins I & II. ATRA increased
E-cadherin staining at cell-cell contact sites, but had no influence on the staining patterns of
desmoglein and
desmoplakins I & II. Similar to what has been observed for the cytoskeletal differentiation parameters,
liarozole alone had no influence on
E-cadherin,
desmoglein or
desmoplakins I & II expression, but in combination with ATRA again intensified the effects on
E-cadherin distribution. These effects on MCF-7 cells agree with previously obtained observations concerning the inhibition of ATRA catabolism by
liarozole. Furthermore, our data support the hypothesis that the antiproliferative properties of the
drug are accompanied by induction of differentiation.