EFFECT OF PROGESTERONE AND RU486 ON CISPLATINUM RESISTANCE IN OVARIAN CANCER CELLS

Abstract

Epithelial ovarian cancer (EOC), the third most common cancer in women, has the highest mortality rate of any gynecological cancer. The primary chemotherapeutic treatment for EOC is one of the platinum drugs, such as carboplatinum or cisplatinum. Platinum drug treatment in combination with taxol is often more effective than platinum alone. However, development of resistance to the platinum drugs is common and leads to relapse of EOC. Therefore, it is important to find alternative treatments that can enhance the effectiveness of the platinum drugs and reverse resistance to platinum. Progesterone is a physiologically relevant hormone in the ovary and reported to increase apoptosis in epithelial cells, so we examined the effect of progesterone on the platinum sensitive and resistant cell lines OV2008 and C13, respectively. As with other steroids, progesterone regulates many cells via nuclear receptors and recent studies have indicated that steroid hormones may interact with the PI3- kinase pathway as well. Therefore, we also used RU486, a progesterone receptor antagonist and wortmannin, a PI3-kinase inhibitor. Treatment of OV2008 with 10, 20, 30, 50, or 100 μM cisplatinum (CisPt) caused a dosedependent decrease in cell viability (89 −24%). In contrast, even 100 μM CisPt only caused a decrease in viability to 83% in the C13 cells, confirming that this cell line is resistant to CisPt. In the next set of experiments, cells were treated with 8.0 μM progesterone, 8.0 μM RU486, or 1.0 μM wortmannin in the absence or presence of 30 μM CisPt. Experiments were repeated 3 to 14 times. Treatment of either OV2008 or C13 cells with progesterone or wortmannin had no effect on cell viability (90 −97 %), nor did progesterone or wortmannin alter the effect of 30 μM CisPt on cell viability in either cell line (65 −69 % or 88 −97 % for OV2008 or C13, respectively). Although RU486 alone significantly decreased cell viability in OV2008 to 78.3 ± 5.5 % and C13 to 80.4 ± 4.2 %, RU486 did not alter the effect of CisPt on either cell line. Interestingly, combining progesterone + RU486 further decreased the viability of OV2008 cells to 64.2 ± 8.2 %, but didn't enhance the CisPt effect (58.7 ± 5.6 %). Conversely, progesterone + RU486 without CisPt was no more effective at lowering viability in C13 cells than RU486 alone. However, treatment of C13 cells with CisPt and progesterone + RU486 significantly decreased cell viability to 59.2 ± 7.4 %, thus reversing the resistance to CisPt in these C13 cells. The effect of combining wortmannin + progesterone + RU486 wasn't significantly different from that of progesterone + RU486 without or with CisPt treatment. Thus, the progesterone + RU486 combination appears to significantly inhibit cell viability in OV2008 and to reverse the CisPt resistance in the C13 cells. It is not yet clear by what mechanism this agonist and its antagonist work together to produce these effects, but it doesn't appear to involve the PI3-kinase pathway. (Supported by an OBR Research Challenge Grant) (poster)