The response of 4 human ovarian carcinoma cell lines to retinoic acid was found to be related to the histological type and degree of differentiation of these tumor cells. The 2 serous cell lines NIHOVCAR3 and OVCCR1 were the most sensitive to the antiproliferative effect of RA. This inhibition was associated with morphological and biological changes that were indicative of differentiation. The undifferentiated IGROV1 cell line was not affected by RA. Since the effects of RA are thought to be mediated by nuclear retinoic acid receptors (RARs), the expression of RARs in human ovarian cancer cells was studied. RAR alpha was detected as mRNA species of 3.1 and 2.6 kb in all 4 cell lines. RAR beta was not detected in any of the cell lines, while RAR gamma (3 kb) was expressed in all of the ovarian cancer cells but at a very low level in the RA-resistant IGROV1 cells.

All-trans retinoic acid (ATRA) has been previously shown to inhibit the proliferation of some human ovarian carcinoma cell lines, and this inhibition was accompanied by cellular changes that were indicative of differentiation (Caliaro et al, 1994). In this work, a pretreatment of these adenocarcinoma cells with ATRA, for their respective doubling time, enhanced cisplatin (CDDP) cytotoxicity in the cell ines that were sensitive to its antiproliferative effect, but not in the ATRA-resistant ones. Results were assessed using median effect analysis in two ATRA-sensitive cell lines (OVCCR1 and NIHOVCAR3 cells) and in one ATRA-insensitive cell line (IGROV1 cells). Synergy between these two agents was observed only in cells sensitive to ATRA, regardless of their relative sensitivity to CDDP. Potential mechanisms for this synergy were investigated. ATRA did not increase the cellular platinum content, did not decrease the cellular glutathione and had no influence on the metallothionein IIA mRNA levels in NIHOVCAR3 cells. Moreover, the protein kinase C (PKC) activity was modulated by this differentiating agent in all cell lines tested, indicating that this activity was not directly involved in this potentiation. However, an ATRA inhibition of glutathione-S-transferase activity associated with an increase in the total DNA adducts formation could explain the potentiation of the CDDP cytotoxicity observed in NIHOVCAR3 cells. Finally, the ATRA modulation of the epidermal growth factor (EGF) receptor mRNA level could also be implicated in this synergy. Images Figure 7

Human ovarian carcinoma cells (2008 and its cisplatin-resistant sub-line 2008/C13*) were sensitized to cisplatin by treatment with human recombinant gamma interferon (IFN gamma). IFN gamma produced no significant change in the uptake of CDDP. Exposure of 2008 and 2008/C13* cells to IFN gamma resulted in a time-dependent decrease of cellular glutathione and total glutathione-S-transferase activity, principally the pi isoform. By contrast, the treatment of 2008 and 2008/C13* cell lines with IFN gamma induced rather than suppressed metallothionein IIA mRNA levels. IFN gamma changed neither the formation of total platinum-DNA adducts, nor DNA repair. A significant decrease in c-erbB-2 expression was observed both in sensitive and in resistant cell lines after treatment with IFN gamma, and this decrease was dose-dependent. Our results indicate that the mechanism of IFN gamma-induced sensitization in human ovarian-cancer cell lines is multifactorial.