gw-501516 and Breast-Neoplasms

A growing body of experimental evidence strongly suggests that cannabidiolic acid (CBDA), a major component of the fiber-type cannabis plant, exerts a variety of biological activities. We have reported that CBDA can abrogate cyclooxygenase-2 (COX-2) expression and its enzymatic activity. It is established that aberrant expression of COX-2 correlates with the degree of malignancy in breast cancer. Although the reduction of COX-2 expression by CBDA offers an attractive medicinal application, the molecular mechanisms underlying these effects have not fully been established. It has been reported that COX-2 expression is positively controlled by peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in some cancerous cells, although there is "no" modulatory element for PPARβ/δ on the COX-2 promoter. No previous studies have examined whether an interaction between PPARβ/δ-mediated signaling and COX-2 expression exists in MDA-MB-231 cells. We confirmed, for the first time, that COX-2 expression is positively modulated by PPARβ/δ-mediated signaling in MDA-MB-231 cells. CBDA inhibits PPARβ/δ-mediated transcriptional activation stimulated by the PPARβ/δ-specific agonist, GW501516. Furthermore, the disappearance of cellular actin stress fibers, a hallmark of PPARβ/δ and COX-2 pathway activation, as evoked by the GW501516, was effectively reversed by CBDA. Activator protein-1 (AP-1)-driven transcriptional activity directly involved in the regulation of COX-2 was abrogated by the PPARβ/δ-specific inverse agonists (GSK0660/ST-247). Thus, it is implicated that there is positive interaction between PPARβ/δ and AP-1 in regulation of COX-2. These data support the concept that CBDA is a functional down-regulator of COX-2 through the abrogation of PPARβ/δ-related signaling, at least in part, in MDA-MB-231 cells.

Topics: Breast Neoplasms; Cannabinoids; Cyclooxygenase 2; Female; Gene Expression; Humans; PPAR delta; Signal Transduction; Sulfones; Thiazoles; Thiophenes; Transcription Factor AP-1; Tumor Cells, Cultured

Peroxisome proliferator-activated receptor (PPAR) δ is a promising therapeutic target in metabolic and inflammatory disorders. However, its role in oncogenesis is controversial, and its therapeutic potential remains to be determined. In our study, we show that ligand-activated PPARδ forms a complex with the proto-oncogene product c-Myc. The interaction of PPARδ with c-Myc affected the transcriptional activity of c-Myc and the expression of its target genes. The PPARδ-dependent regulation of c-Myc activity was associated with decreased tumorigenicity in breast cancer cells. Administration of the PPARδ ligand GW501516 inhibited tumor growth in xenograft model mice bearing MDA-MB-231 cells stably expressing wild-type PPARδ, but not those expressing dominant-negative PPARδ, by interfering with c-Myc function through protein-protein interaction. Our results indicating that PPARδ forms an antitumorigenic complex with c-Myc in the presence of ligand suggest a potential role of PPARδ in breast cancer development.

Topics: A549 Cells; Animals; Breast Neoplasms; Carcinogenesis; Cell Line; Cell Line, Tumor; Cell Transformation, Neoplastic; Gene Expression Regulation, Neoplastic; HEK293 Cells; HeLa Cells; Humans; Ligands; MCF-7 Cells; PC12 Cells; PPAR delta; Proto-Oncogene Mas; Proto-Oncogene Proteins c-myc; Rats; RNA, Small Interfering; Thiazoles

The nuclear receptor peroxisome proliferator-activated receptor delta [PPARdelta/beta (NR1C2)] has been implicated in colorectal carcinogenesis by various molecular genetic observations. These observations have recently been supported by studies of activation of PPARdelta by pharmacological agents. Here we present the first report of the stimulation of breast and prostate cancer cell growth using PPARdelta selective agonists. Activation of PPARdelta with compound F stimulated proliferation in breast (T47D, MCF7) and prostate (LNCaP, PNT1A) cell lines, which are responsive to sex hormones. Conversely, we have found that several steroid-independent cell lines, including colon lines, were unresponsive to compound F. These findings were confirmed with an additional high-affinity PPARdelta agonist, GW501516. Conditional expression of PPARdelta in MCF7 Tet-On cells resulted in a doxycycline-enhanced response to GW501516, thus providing direct genetic evidence for the role of PPARdelta in the proliferative response to this drug. Activation of PPARdelta in T47D cells resulted in increased expression of the proliferation marker Cdk2 and also vascular endothelial growth factor alpha (VEGFalpha) and its receptor, FLT-1, thus, suggesting that PPARdelta may initiate an autocrine loop for cellular proliferation and possibly angiogenesis. Consistent with this hypothesis, we demonstrated a pro-proliferative effect of GW501516 on human umbilical vein endothelial cell cultures and found that GW501516 also regulated the expression of VEGFalpha and FLT-1 in these cells. Our observations provide the first evidence that activation of PPARdelta can result in increased growth in breast and prostate cancer cell lines and primary endothelial cells and supports the possibility that PPARdelta antagonists may be of therapeutic value in the treatment of breast and prostate cancer.

Topics: Breast Neoplasms; Cell Division; Cell Line, Tumor; Colonic Neoplasms; Female; Gene Expression; Genes, cdc; Genes, Reporter; Humans; Ligands; Luciferases; Male; Neoplasms, Hormone-Dependent; Prostatic Neoplasms; Receptors, Cytoplasmic and Nuclear; Receptors, Estrogen; Response Elements; RNA, Messenger; Signal Transduction; Thiazoles; Transcription Factors; Transcriptional Activation