Elucidation of molecular events mediating induction of apoptosis by synthetic retinoids using a CD437-resistant ovarian carcinoma cell line

Retinoids have great promise in the area of cancer therapy and chemoprevention. Although some tumor cells are sensitive to the growth inhibitory effect of all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-((1-Admantyl)-4-hydroxyphenyl)-2-naphthalenecarboxylic acid (CD437) is a conformationally restricted synthetic retinoid that induces growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. To better understand the mechanism by which CD437 induces apoptosis in ovarian tumor cell lines, we prepared a cell line, CA-CD437R, from the ATRA-sensitive ovarian cell line, CA-OV-3, which was resistant to CD437. We found that the CD437-resistant cell line was also resistant to the induction of apoptosis by tumor necrosis factor-alpha but not resistant to the induction of apoptosis by another synthetic retinoid, fenretinide N-(4-hydroxyphenyl)retinamide. We also show that this cell line remains ATRA-sensitive and exhibits no deficiencies in RAR function. Analysis of this CD437-resistant cell line suggests that the pathway for induction of apoptosis by CD437 is similar to the pathway utilized by tumor necrosis factor-alpha and different from the pathway induced by the synthetic retinoid, fenretinide N-(4-hydroxyphenyl)retinamide. The CA-CD437R cell line is a valuable tool, permitting us to further elucidate the molecular events that mediate apoptosis induced by CD437 and other synthetic retinoids. Results of experiments utilizing this cell line suggest that the alteration responsible for resistance of CA-CD437R cells to CD437 induced event maps after the activation of p38 and TR3 expression, prior to mitochondrial depolarization, subsequent release of cytochrome c and activation of caspase-9 and caspase-3.