The R -enantiomer of the nonsteroidal antiinflammatory drug etodolac binds retinoid X receptor and induces tumor-selective apoptosis

Abstract

Prostate cancer is often slowly progressive, and it can be difficult to treat with conventional cytotoxic drugs. Nonsteroidal antiinflammatory drugs inhibit the development of prostate cancer, but the mechanism of chemoprevention is unknown. Here, we show that the R-enantiomer of the nonsteroidal antiinflammatory drug etodolac inhibited tumor development and metastasis in the transgenic mouse adenocarcinoma of the prostate (TRAMP) model, by selective induction of apoptosis in the tumor cells. This proapoptotic effect was associated with loss of the retinoid X receptor (RXR␣) protein in the adenocarcinoma cells, but not in normal prostatic epithelium. R-etodolac specifically bound recombinant RXR␣, inhibited RXR␣ transcriptional activity, and induced its degradation by a ubiquitin and proteasome-dependent pathway. The apoptotic effect of R-etodolac could be controlled by manipulating cellular RXR␣ levels. These results document that pharmacologic antagonism of RXR␣ transactivation is achievable and can have profound inhibitory effects in cancer development.cancer ͉ prostate ͉ R-etodolac ͉ ubiquitin ͉ chemoprevention S everal epidemiological studies have shown that the use of nonsteroidal antiinflammatory drugs (NSAIDs) is associated with a reduced incidence of clinically detectable prostate cancer (1-3). The side effects of cyclooxygenase (COX) inhibitors preclude the use of these agents in many elderly men (4). Thus, there is a major need to determine whether there are chemopreventative, and antimetastatic effects of NSAIDs that can be separated from COX inhibition. Controversy has permeated this field, because many of the COX-independent actions of NSAIDs are measurable only at concentrations that are not safely achievable in vivo, and because the members of this structurally diverse group of drugs are metabolized extensively and can exert different mechanisms of action (5, 6).Various NSAIDs have been demonstrated to induce apoptosis in malignant cells (7-9). Etodolac is a commercially available NSAID containing a racemic mixture, in which the S-enantiomer has COX inhibitory activity, whereas the R-enantiomer does not (10). Unlike all other chiral NSAIDs, the two enantiomers of etodolac are not metabolically interconvertible. Moreover, the R-enantiomer is metabolized much more slowly than the S-enantiomer, and it accumulates to 10-fold higher concentrations than the S-enantiomer in plasma (11). In a recent study, sufficient plasma levels of R-etodolac were achieved after oral gavage in a xenograft prostate cancer model to diminish the growth of the transplanted tumor (12).The in vivo effect of R-etodolac was associated with enhancement of peroxisome proliferator-activated receptor ␥ (PPAR␥) transactivation (12). PPAR␥, as well as other nuclear hormone receptors, forms heterodimers with the retinoid X receptor ␣ (RXR␣) (13,14), which has been implicated in the pathogenesis of prostate cancer (15). The effect of RXR␣ may be due to its induction of apoptosis through its interaction with other proteins (16)(17)(18)...

Repression of β-catenin function in malignant cells by nonsteroidal antiinflammatory drugs

“…However, antagonism of ␤-catenin by R-etodolac could not be attributed to PPAR-␥ or RXR-␣ activation. This NSAID-like agent has been shown to inhibit the ability of a high-affinity RXR-␣ ligand to activate transcription (39). As shown here, it also blocked the troglitazoneinduced association of PPAR-␥ with its binding protein (Fig.…”

“…The binding could be related to the chemopreventive actions of the drugs, because high-affinity synthetic ligands of PPAR-␥, such as troglitazone, can prevent the development of colon, prostate, and breast cancer in some animal models (36)(37)(38). Recently, the NSAID-like molecule R-etodolac was also reported to bind the PPAR-␥ coactivator retinoid X receptor ␣ (RXR-␣) (39). However, it is not clear how the functions of ␤-catenin, RXR-␣, and PPAR-␥ are connected.…”

R-Etodolac decreases β-catenin levels along with survival and proliferation of hepatoma cells

“…Thus, it is attractive to consider alternate agents that lack the adverse consequences of COX-2 inhibition. R-Etodolac has been shown to have antitumor effects in several cancer cell lines and lacks COX-inhibitory activity [21][22][23]. Our results demonstrate that R-Etodolac inhibits survival and proliferation of HCC cells lines in a dosedependent manner and may be potentially useful in HCC treatment or chemoprophylaxis.…”

“…Therapeutic use of the R-Etodolac, therefore, offers the potential advantage of minimizing COX-dependent side effects. Antineoplastic effects of R-Etodolac have been recently shown in chronic lymphocytic leukemia (CLL), multiple myeloma, and prostate cancer [21][22][23]. Here, we demonstrate the anti-β-catenin properties of Celecoxib at high doses and of R-Etodolac at physiological doses on hepatoma cell lines, which was associated with their diminished survival and proliferation.…”

Novel etodolac analog SDX-308 (CEP-18082) induces cytotoxicity in multiple myeloma cells associated with inhibition of β-catenin/TCF pathway

“…4,5 2,5-Dimethyl-celecoxib, a COX-2 inhibitor celecoxib derivative lacking COX-2 activity, also has cytotoxic activity against prostate cancer 46 and MM. 47 Moreover, R-etodolac, an enantiomer of the NSAID etodolac lacking COX inhibitory activity, has cytotoxic activity against CLL, 6 prostate cancer 48,49 and MM. 3,50 In this study, we demonstrated that the novel etodolac derivative SDX-308 inhibits b-catenin/TCF pathway and induces MM cytotoxicity, without significant COX inhibition.…”