21-OH 6,19-epoxyprogesterone: a new dissociated glucocorticoid with antiinflammatory properties but without anti-apoptotic effects on chemotherapeutic treated mouse mammary tumor cells

ORQUEDA, ANDRÉS; VELEIRO, ADRIANA S.; BAL DE KIER JOFFE, ELISA; KORDON, EDITH C; BURTON, GERARDO; PECCI, ADALI

Boston Massachussets, USA,

Congreso; AACR Frontiers in Basic Cancer Research; 2009

AACR

Glucocorticoids (GCs) are widely used as coadyuvants in the treatment of solid tumors with chemotherapics such as paclitaxel (PXL) and doxorubicin (DOXO). However, clinical evidence supports the idea that GCs may induce resistance to these antitumor therapies. To improve cancer treatment quality , intense efforts are being made to design new dissociated steroids (steroid receptor glucocorticoid modulators (SRGMs). These compounds should mimic only the beneficial aspects of glucocorticoid therapy without inducing the undesired side effects in cancer patients. We have previously shown that dexamethasone (Dex), a well-known synthetic GC, inhibits PXL or DOXO induced apoptosis in breast tumor cells through a mechanism involving Bcl-XL and Bcl-2 induction. Here, our goal was to compare Dex effects with those triggered by 21-OH-6,19-epoxyprogesterone (21-OH-6,19-OP), which is a rigid steroid considered a passive GC antagonist. Molecular dynamic simulation studies predicted that 21OH-6,19OP is unable to induce GR/21-OH-6,19-OP complex homodimerization and/or binding to coactivators, making these complex incapable to directly activate gene transcription (Alvarez, et al J Med Chem. 2008. 13:1352). The effects of 21-OH-6,19-OP on apoptosis induced by DOXO or PXL in the epithelial mouse mammary tumor cell line LM3 was determined by analyzing Caspase-3 activity and gene and protein expression of antiapoptotic members of the Bcl family, i.e. Bcl-2 and Bcl-XL. The results show that, contrary to Dex, 21-OH-6,19-OP cannot reverse apoptosis induced by DOXO or PXL in LM3 cells. In fact, 21-OH-6,19-OP and Dex differentially regulate Bcl-2 and Bcl-XL expression. Dex´s reversion on chemotherapic induced apoptosis (Dex+DOXO o Dex+PXL) correlates with an increase in Bcl-XL levels, while 21-O-H-6, 19-OP does not affect neither cell death nor Bcl-XL levels. The relevanceof Bcl-XL involvement in DOXO resistance of cells treated with Dex was confirmed by knocking-down Bcl-XL with specific siRNA. Silencing Bcl-XL expression directly implicated loss of antiapoptotic GC effects. On the other hand, 21-OH-6,19-OP antiinflammatory action was also evaluated on the lung epithelial tumor cell line A549 by determining Interleukin-8 (IL-8) and Cyclooxygenase-2 (COX-2) expression in the presence of  the Tumor Necrosis Factor-alpha (TNF-a). Expression levels of IL-8 and COX-2, measured by qRT-PCR, indicate that 21-OH-6,19-OP may have antiinflammatory effects as it reverses these inflammation markers expression induced by TNF-a in lung epithelial cells. Together, these findings suggest that 21-OH-6,19-OP is a SRGM that keeps glucocorticoid antiinflammatory properties without antiapoptotic effects, thus becoming a novel candidate for treatment of solid tumors as breast cancer.