Prevention of lung cancer progression by bexarotene in mouse models

Department of Surgery and the Siteman Cancer Center, Washington University School of Medicine, St Louis, MO 63110, USA.
Oncogene (Impact Factor: 8.46). 04/2006; 25(9):1320-9. DOI: 10.1038/sj.onc.1209180
Source: PubMed


Bexarotene (Targretin), is a synthetic high-affinity RXR receptor agonist with limited affinity for RAR receptors. Bexarotene has shown efficacy in a phase I/II trial of non-small-cell lung cancers. However, the chemopreventive efficacy of bexarotene has not been determined in mouse lung cancer models. In this study, we have investigated the ability of bexarotene to inhibit lung tumor progression in the mutant A/J mouse models with genetic alterations in p53 or K-ras, two of the most commonly altered genes in human lung tumorigenesis. Mice were administered vinyl carbamate (VC), a carcinogen, by a single intraperitoneal injection (i.p.) at 6 weeks of age. Bexarotene was given by gavage starting at 16 weeks after VC and was continued for 12 weeks. Although all mice developed lung tumors, only 7% of lung tumors were adenocarcinomas in wild-type mice, whereas 22 and 26% of lung tumors were adenocarcinomas in p53 transgenic or K-ras heterozygous deficient mice. Bexarotene inhibited both tumor multiplicity and tumor volume in mice of all three genotypes. Furthermore, bexarotene reduced the progression of adenoma to adenocarcinoma by approximately 50% in both p53(wt/wt)K-ras(ko/wt) and p53(wt/wt)K-ras(wt/wt) mice. Thus, bexarotene appears to be an effective preventive agent against lung tumor growth and progression.

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    • "While the present study found no qualitative differences as regards to the activation of the Raf/MEK/ERK (MAPK) and PI3-K/Akt effector pathways (as evident by phospho-Erk1/2 and -Akt staining) between tumours from K-ras +/− and K-ras tmΔ4A/− mice it remains to be determined whether the K-ras 4A and 4B oncoproteins differ in their ability to activate these pathways when expressed at endogenous levels or, indeed, whether they differentially affect other pathways given that K-ras 4B G12C can activate the p38-MAPK and Ral/GDS pathways, in addition to Raf/MEK/ERK(MAPK), in mouse lung [18], and K-ras G12D activates MKK4 (mitogenactivated protein kinase kinase 4) in mouse lung tumours, which is a downstream mediator of Rac1 whose activation contributes to ras-induced cellular transformation [see 41]. Loss of the wild-type K-ras allele in human and mouse lung tumours is linked with tumour progression as evident by adenocarcinoma development [21] [22] [23]. In contrast, the present study found adenoma was the predominant (N96%) lung tumour type in K-ras +/− and K-ras tmΔ4A/− mice at 5 months after MNU treatment, when Zhang et al. [21] also culled their MNU-treated K-ras +/− mice. "
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    ABSTRACT: To examine the roles of endogenous K-ras 4A and K-ras 4B splice variants in tumorigenesis, murine lung carcinogenesis was induced by N-methyl-N-nitrosourea (MNU), which causes a K-ras mutation (G12D) that jointly affects both isoforms. Compared with age-matched K-ras(tmDelta4A/-) mice (where tumours can express mutationally activated K-ras 4B only), tumour number and size were significantly higher in K-ras(+/-) mice (where tumours can also express mutationally activated K-ras 4A), and significantly lower in K-ras(tmDelta4A/tmDelta4A) mice (where tumours can express both wild-type and activated K-ras 4B). MNU induced significantly more, and larger, tumours in wild-type than K-ras(tmDelta4A/tmDelta4A) mice which differ in that only tumours in wild-type mice can express wild-type and activated K-ras 4A. Lung tumours in all genotypes were predominantly papillary adenomas, and tumours from K-ras(+/-) and K-ras(tmDelta4A/-) mice exhibited phospho-Erk1/2 and phospho-Akt staining. Hence (1) mutationally activated K-ras 4B is sufficient to activate the Raf/MEK/ERK(MAPK) and PI3-K/Akt pathways, and initiate lung tumorigenesis, (2) when expressed with activated K-ras 4B, mutationally activated K-ras 4A further promotes lung tumour formation and growth (both in the presence and absence of its wild-type isoform) but does not affect either tumour pathology or progression, and (3) wild-type K-ras 4B, either directly or indirectly, reduces tumour number and size.
    Experimental Cell Research 04/2008; 314(5):1105-14. DOI:10.1016/j.yexcr.2007.11.004 · 3.25 Impact Factor
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    ABSTRACT: The human retinoid X receptor alpha (hRXRalpha) is a member of the nuclear receptor super-family of ligand-activated transcription factors. The Doyle laboratory has previously engineered a variety of functional hRXRalpha variants that activate gene expression in response to synthetic ligands (LG335 and γ-oxo-1-pyrenebutyric acid), compounds that are poor activators of wild-type hRXRalpha. The variants generally no longer respond to the wild-type ligand 9-cis retinoic acid. To enable targeting of these engineered receptors to arbitrary DNA sequences, we developed a program, ESPSearch, for identifying short or specific sequences in DNA or protein. ESPSearch enables identification of combinations of known zinc finger motifs to target arbitrary genes, as well having several other applications. The ability to target any DNA sequence means that the engineered receptors can be directed to control any gene. The ligand binding, self-association, coactivator interactions, and unfolding properties of the ligand binding domain of wild-type hRXRalpha were characterized. Our expression and purification protocol improves upon existing methods, providing high purity protein in a single step with more than twice prior yields. A general fluorescence-based method for measuring ligand affinity with hRXRalpha was developed, and used to determine binding constants for the small molecules. The presence of a peptide containing the binding motif from coactivator proteins (LxxLL) differentially increased the affinity of the receptor for the ligands. Assays to determine the self-association give a Kd for the dimer-tetramer equilibrium of 35 µM. hRXRalpha was found to denature irreversibly when heated, but shifts in apparent Tm due to ligands correlates strongly with the ligand binding affinities. Our results clarify disparities in existing reports and provide a benchmark for comparison. Reliable analysis of our data led to the development of a computer program for rigorous, automated data fitting. Nine functional variants of hRXRalpha were characterized to probe correlations between biophysical properties and the observed functional activity of the receptors, which differ significantly from wild-type. Although the correlation between ligand binding affinity and melting temperature was strong for all variants, there was essentially no correlation between ligand binding and activation of the variants. The mutations, which are all contained within the binding pocket, have significant long-range effects on the protein, causing changes in ligand-LxxLL interactions and oligomerization of the variants. Experimental and computational analysis of selected mutations suggests that they are highly coupled, complicating protein design. However, the large variation in properties amongst the variants also suggests that hRXRalpha can be mutated extensively while still retaining function. The long-range impact of binding pocket mutations will need to be taken into account in future engineering projects, as hRXRalpha is a flexible, dynamic protein. Ph.D. Committee Chair: Doyle, Donald; Committee Member: Bommarius, Andreas; Committee Member: Harvey, Stephen; Committee Member: Hud, Nicholas; Committee Member: Kubanek, Julia
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    ABSTRACT: A rexinoid, targretin, and two retinoids, 9-cis retinoic acid (9cRA) and 4-hydroxyphenylretinamide (4HPR), were examined for their effects on gene expression in rat mammary gland, liver, and lung tissues. The chemopreventive effects of these agents have largely been attributed to their ability to interact with retinoic acid receptors (RAR) and/or retinoid X receptors (RXR). Targretin interacts with the RXR receptors. 9cRA interacts with both the RAR and RXR receptors, whereas 4HPR has a moderate affinity primarily for RAR gamma. Based on previous studies on mammary chemoprevention, targretin (150 mg/kg diet), 9cRA (100 mg/kg diet), and 4HPR (782 mg/kg diet), were administered to rats continually in their diet for 7 days. Tissue- and agent-specific expression differences were determined by comparing tissues from treated rats with those from rats given a control diet. There were significantly more changes associated with targretin than 9cRA or 4HPR. Only a limited number of expression changes were found with 4HPR treatment. For each organ, targretin- and 9cRA-treated tissues clustered closely together, whereas 4HPR-treated tissues clustered with the tissues from the control diet group. In contrast to 9cRA treatment, targretin treatment altered genes that involved fatty acid metabolism and modulation of various cytochromes P450 in the liver, clearly demonstrating the very disparate nature of these two retinoids. These expression signatures could provide useful pharmacodynamic biomarkers for retinoid treatment and chemoprevention.
    Molecular Cancer Therapeutics 05/2006; 5(4):1060-72. DOI:10.1158/1535-7163.MCT-05-0322 · 5.68 Impact Factor
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