We have previously demonstrated that important regulatory elements responsible for regulated expression of the human GLUT4 promoter are located between -1154 and -412 relative to transcription initiation (Olson, A. L., and Pessin, J. E. (1995) J. Biol. Chem. 270, 23491-23495). Through further analysis of this promoter regulatory region, we have identified a perfectly conserved myocyte enhancer factor 2 (MEF2)-binding domain (-CTAAAAATAG-) that is necessary, but not sufficient, to support tissue-specific expression of a chloramphenicol acetyltransferase reporter gene in transgenic mice. Biochemical analysis of this DNA element demonstrated the formation of a specific DNA-protein complex using nuclear extracts isolated from heart, hindquarter skeletal muscle, and adipose tissue but not from liver. DNA binding studies indicated that this element functionally interacted with the MEF2A and/or MEF2C MADS family of DNA binding transcription factors. MEF2 DNA binding activity was substantially reduced in nuclear extracts isolated from both heart and skeletal muscle of diabetic mice, which correlated with decreased transcription rate of the GLUT4 gene. MEF2 binding activity completely recovered to control levels following insulin treatment. Together these data demonstrated that MEF2 binding activity is necessary for regulation of the GLUT4 gene promoter in muscle and adipose tissue.

Regulation of growth, differentiation, and apoptosis by synthetic retinoids can occur through mechanisms that are dependent and independent of their ability to bind and activate nuclear retinoic acid receptors. The objective of this study was to determine if increasing flexibility of the heteroarotinoid structure would affect the specificity of the synthetic retinoids for the receptors and for their regulation of cancerous and nonmalignant cells. Methods were developed to produce the first examples of heteroarotinoids 15a − 15h, which contain urea and/or thiourea linking groups between two aryl rings. Substituents at the para position of the single phenyl ring were either an ester, a nitro group, or a sulfonamide group. Ovarian cancer cell lines Caov-3, OVCAR-3, SK-OV-3, UCI-101, and 222 were utilized, and the inhibitory prowess of the heteroarotinoids was referenced to that of 4-HPR (25). Similar to 4-HPR (25), the heteroarotinoids inhibited growth of all cell lines at micromolar concentrations. Although the heteroarotinoids did not activate retinoic acid receptors, the agents induced potent growth inhibition against the cancer cells with weak activity against normal and benign cells. The growth inhibition was associated with cell loss and induction of reactive oxygen species.

The anti-cancer activities and toxicities of retinoic acid (RA) and synthetic retinoids are mediated through nuclear RA receptors (RARs) and retinoid X receptors (RXRs) that act as transcription factors. Heteroarotinoids (Hets), which contain a heteroatom in the cyclic ring of an arotinoid structure, exhibit similar anti-cancer activities, but reduced toxicity in vivo, in comparison to parent retinoids and RA. A new class of Flexible Hets (Flex-Hets), which contain 3-atom urea or thiourea linkers, regulate growth and differentiation similar to RA, but do not activate RARs or RXRs. In addition, Flex-Hets induce potent apoptosis in ovarian cancer and in head and neck cancer cell lines through the intrinsic mitochondrial pathway. In this study, 4 cervical cancer cell lines were growth inhibited by micromolar concentrations of Flex-Hets to greater extents than RAR/RXR active retinoids. The most potent Flex-Het (SHetA2) inhibited each cell line of the National Cancer Institute's human tumor cell line panel at micromolar concentrations. Oral administration of Flex-Hets (SHetA2 and SHetA4) inhibited growth of OVCAR-3 ovarian cancer xenografts to similar extents as administration of a RAR/RXR-panagonist (SHet50) and Fenretinide (4-HPR) in vivo. None of these compounds induced evidence of skin, bone or liver toxicity, or increased levels of serum alanine aminotransferase (ALT) in the treated mice. Topical application of Flex-Hets did not induce skin irritation in vivo, whereas a RAR/RXR-panagonist (NHet17) and a RARgamma-selective agonist (SHet65) induced similar irritancy as RA. In conclusion, Flex-Hets exhibit improved therapeutic ratios for multiple cancer types over RAR and/or RXR agonists.

OBM portends a poor prognosis, however, long-term survival is possible. Patients appear to benefit from therapy, especially selected groups of OBM patients with single brain metastasis treated with radiation therapy and surgery.

At clinically achievable concentrations, all retinoids tested decrease the growth fraction, induce differentiation and apoptosis. Induction of MUC1 expression is implicated in the mechanisms of action.

The occurrence of intestinal polyps in people at high risk for developing colorectal cancer provides an opportunity to test the efficacy of chemoprevention agents. In this situation of treating otherwise healthy people, the potential for toxicity must be minimal. The small molecule flexible heteroarotinoid (Flex-Het), called SHetA2, has chemoprevention activity in organotypic cultures in vitro and lack of toxicity at doses capable of inhibiting xenograft tumor growth in vivo. The objective of this study was to evaluate SHetA2 chemoprevention activity and toxicity in the APCMin/+ murine model. Oral administration of SHetA2 at 30 and 60 mg/kg five days per week for 12 weeks significantly reduced development of intestinal polyps by 40 to 60% depending on the dose and sex of the treatment group. Immunohistochemical and Western blot analysis of polyps demonstrated reduced levels of cyclin D1 and proliferating cell nuclear antigen (PCNA) in both SHetA2 treatment groups. Western blot analysis also demonstrated SHetA2 induction of E-cadherin, Bax and caspase 3 cleavage along with reduction in Bcl-2, cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF), consistent with SHetA2 regulation of apoptosis, inflammation and angiogenesis. Neither dose caused weight loss nor gross toxicity in APCMin/+ or wild type littermates. Magnetic resonance imaging (MRI) of cardiac function showed no evidence of SHetA2 toxicity. SHetA2 did not alter left ventricular wall thickness. In summary, SHetA2 exerts chemoprevention activity without overt or cardiac toxicity in the APCMin/+ model. SHetA2 modulation of biomarkers in colon polyps identifies potential pharmacodynamic endpoints for SHetA2 clinical trials.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by cyst formation initiated by dedifferentiation and proliferation of renal tubular epithelial cells. Renal tubular epithelial cells (RTC, derived from normal kidney tissue) in primary cultures exhibit both homogeneous expression of gamma-glutamyl transferase and low molecular weight cytokeratin, two different markers for proximal and distal renal epithelial cells, respectively. RTC in cultures also abnormally express the dedifferentiation markers vimentin and PAX-2, which are proteins normally expressed in epithelial cells lining cysts in ADPKD kidneys but not tubular cells in normal kidneys. In contrast, different cultures of cystic epithelial cells (CEC, derived from the cysts walls of polycystic kidneys) display variable expression of cytokeratin, gamma-glutamyl transferase, and PAX-2, but a constant level of vimentin. Importantly, RTC and CEC exhibit the capacity to convert to their respective original structures by forming tubules and cysts, respectively, when cultured in a three-dimensional gel matrix, whereas HK-2, LLC-PK1, and MDCK renal epithelial cell lines form cell aggregates or cysts. Our study demonstrates that the marker expression of the various epithelial cell types is not highly stable in primary cultures. Their modulation is different in cells originating from normal and ADPKD kidneys and in cells cultured in monolayer and three-dimensions. These results indicate the plasticity of epithelial cells that display a mixed epithelial/dedifferentiated/mesenchymal phenotype during their expansion in culture. However, RTC and CEC morphogenic epithelial properties in three-dimensional cultures are similar to those in vivo. Thus, this model is useful for studying the mechanisms leading to tubulogenesis and cystogenesis.

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by formation of cysts from tubular epithelial cells. Previous studies indicate that secretion of prostaglandin E2 (PGE2) into cyst fluid and production of cAMP underlie cyst expansion. However, the mechanism by which PGE2 directly stimulates cAMP formation and modulates cystogenesis is still unclear, because the particular E-prostanoid (EP) receptor mediating the PGE2 effect has not been characterized. Our goal is to define the PGE2 receptor subtype involved in ADPKD. We used a three-dimensional cell-culture system of human epithelial cells from normal and ADPKD kidneys in primary cultures to demonstrate that PGE2 induces cyst formation. Biochemical evidence gathered by using real-time RT-PCR mRNA analysis and immunodetection indicate the presence of EP2 receptor in cystic epithelial cells in ADPKD kidney. Pharmacological evidence obtained by using PGE2-selective analogs further demonstrates that EP2 mediates cAMP formation and cystogenesis. Functional evidence for a role of EP2 receptor in mediating cAMP signaling was also provided by inhibiting EP2 receptor expression with transfection of small interfering RNA in cystic epithelial cells. Our results indicate that PGE2 produced in cyst fluid binds to adjacent EP2 receptors located on the apical side of cysts and stimulates EP2 receptor expression. PGE2 binding to EP2 receptor leads to cAMP signaling and cystogenesis by a mechanism that involves protection of cystic epithelial cells from apoptosis. The role of EP2 receptor in mediating the PGE2 effect on stimulating cyst formation may have direct pharmacological implications for the treatment of polycystic kidney disease.