Abrogation of transforming growth factor-alpha/epidermal growth factor receptor autocrine signaling by an RXR-selective retinoid (LGD1069, Targretin) in head and neck cancer cell lines.

Clinical studies have demonstrated that retinoids, including retinol (Vitamin A) and its synthetic derivatives, can eradicate leukoplakia and suppress the formation of squamous cell carcinoma of the head and neck (SCCHN). Nonselective retinoids have been shown to abrogate transcriptional activation of transforming growth factor-alpha (TGF-alpha) and epidermal growth factor receptor (EGFR), which characterize SCCHN. LGD1069 (Targretin) is a potent RXR-selective retinoic acid agonist with a reduced toxicity profile compared with other nonselective retinoids. We examined the effect of LGD1069 (10 microm) on cellular proliferation and expression of putative intermediate biomarker genes including TGF-alpha, EGFR, and RAR-beta in seven SCCHN cell lines. A quantitative reverse transcription-PCR assay using a novel "primer dropping" method was used to determine expression levels of EGFR, TGF-alpha, and RAR-beta before and after treatment with LGD1069 (10 microM). SCCHN proliferation was reduced by a mean of 50% at 4 days in seven SCCHN cell lines after LGD1069 treatment (P < or = 0.05). EGFR expression levels were decreased by a mean of 58.4% (P = 0.007), TGF-alpha levels were decreased by a mean of 28.8% (P = 0.01), and RAR-beta levels were increased by a mean of 60% (P = 0.03). TGF-alpha stimulation of EGFR is associated with constitutive signal transducer and activator of transcription 3 (Stat3) activation in SCCHN. Abrogation of constitutive Stat3 activation was seen with LGD1069 treatment. These results suggest that an RXR-selective retinoic acid decreases SCCHN proliferation in part by interfering with TGF-alpha/EGFR autocrine signaling.

Targeting growth factor receptors: integration of novel therapeutics in the management of head and neck cancer.

Tyrosine kinase (type 1) growth factor receptors include the erbB family. These cell surface receptors were discovered in the context of cellular transformation and have subsequently been found to be overexpressed in many types of human cancer. Cumulative evidence suggests that upregulation of the most well-characterized receptor, erbB1, also known as the epidermal growth factor receptor, plays a significant role in the development and progression of head and neck squamous cell carcinoma. A variety of strategies have been developed that specifically target epidermal growth factor receptor, including monoclonal antibodies, ligand-linked immunotoxins, tyrosine kinase inhibitors, and antisense approaches. Epidermal growth factor receptor blockade in head and neck squamous cell carcinoma cell lines and preclinical animal models inhibits cell proliferation and tumor growth. Clinical trials are under way to test the safety and efficacy of many of these targeting strategies in head and neck squamous cell carcinoma patients. Encouraging preliminary results combining an epidermal growth factor receptor targeting approaches with chemotherapy or radiotherapy suggest that interference with this growth factor receptor may enhance antitumor efficacy of standard therapies. As erbB family member interactions and downstream signaling pathways are elucidated in head and neck squamous cell carcinoma, specific targeting strategies may become incorporated into standard treatment approaches.

TGF-alpha antisense gene therapy inhibits head and neck squamous cell carcinoma growth in vivo.

Unlike normal mucosal squamous epithelial cells, head and neck squamous cell carcinomas (HNSCCs) overexpress TGF-alpha mRNA and protein which is required to sustain the proliferation of HNSCC cells in vitro. To determine whether TGF-alpha expression contributes to tumor growth in vivo, cationic liposome-mediated gene transfer was used to deliver an antisense expression construct targeting the human TGF-alpha gene into human head and neck tumor cells, grown as subcutaneous xenografts in nude mice. The TGF-alpha antisense gene was immediately detected in the cytoplasm of the tumor cells, translocated to the nucleus by 12 h and remained localized to the nucleus for up to 3 days. Direct inoculation of the TGF-alpha antisense (but not the corresponding sense) construct into established HNSCC tumors resulted in inhibition of tumor growth. Sustained antitumor effects were observed for up to 1 year after the treatments were discontinued. Down-modulation of TGF-alpha was accompanied by increased apoptosis in vivo. These experiments indicate that interference with the TGF-alpha/EGFR autocrine signaling pathway may be an effective therapeutic strategy for cancers which overexpress this ligand/receptor pair.

Antihypertensive agents that limit ventricular hypertrophy inhibit cardiac expression of insulin-like growth factor-I.

BACKGROUND: Left ventricular hypertrophy (LVH) is a generalized adaptation to altered myocardial load. Hypertension induces significant increases in ventricular IGF-I gene expression that occur coordinately with development of LVH. To test whether IGF-I promotes initiation of LVH, we examined ventricular IGF-I mRNA content in spontaneously hypertensive rats (SHRs) treated with antihypertensive drugs that limit or permit LVH. METHODS: Prehypertensive SHRs were left untreated or treated with enalapril, nifedipine, or hydralazine. Systolic blood pressure (SBP), hypertrophy index (ventricular weight/body weight), and ventricular IGF-I mRNA levels were examined 2, 4, and 6 weeks after beginning therapy in the experimental groups. RESULTS: Systolic blood pressure reached hypertensive levels after 2 weeks in untreated animals, and was controlled in the treated animals. The hypertrophy index in untreated animals was significantly elevated at 4 weeks. By 6 weeks, the hypertrophy indices of both the enalapril- and nifedipine-treated groups were significantly lower than that of the untreated group. In contrast, the hypertrophy index of the hydralazine-treated animals remained comparable to that of the untreated animals. By 4 weeks, IGF-I mRNA levels in the enalapril- and nifedipine-treated groups were significantly lower than those in the untreated and hydralazine-treated groups. CONCLUSIONS: We conclude that: (1) antihypertensive drugs that reduce LVH blunt ventricular IGF-I mRNA content; and (2) the hemodynamic effects of antihypertensives may be dissociated from their ability to promote or limit a hypertrophic response. The clear association of LVH with ventricular IGF-I mRNA content suggests that IGF-I is an important determinant of ventricular growth. Our data also suggest that angiotensin-converting enzyme inhibitors and calcium channel blockers may reduce LVH by inhibiting cardiac IGF-I gene expression.

An allelotype of papillary thyroid cancer.

Although papillary carcinoma accounts for approximately 70% of all thyroid cancers, preliminary studies of allelic loss have thus far not identified any areas of chromosomal deletion. We evaluated 30 papillary thyroid carcinomas for chromosomal loss/allelic imbalance by testing at least 2 microsatellite markers from every autosomal arm. Fifteen of the 30 tumors tested exhibited loss of heterozygosity/allelic imbalance (LOH/AI) at one or more loci. Chromosomal arms with frequent LOH/AI included 4q, 5p, 7p and 11p. An average of 1.1 chromosomal arms displayed LOH/AI in each individual tumor. Therefore, 4q, 5p, 7p and, to a lesser extent, 11p display significant LOH/AI in papillary thyroid cancer, which indicates the presence of putative tumor-suppressor gene loci at these chromosomal arms.

Induction of myocardial insulin-like growth factor-I gene expression in left ventricular hypertrophy.

BACKGROUND: Left ventricular hypertrophy is a generalized adaptation to increased afterload, but the growth factors mediating this response have not been identified. To explore whether the hypertrophic response was associated with changes in local insulin-like growth factor-I (IGF-I) gene regulation, we examined the induction of the cardiac IGF-I gene in three models of systolic hypertension and resultant hypertrophy. METHODS AND RESULTS: The model systems were suprarenal aortic constriction, uninephrectomized spontaneously hypertensive rats (SHR), and uninephrectomized, deoxycorticosterone-treated, saline-fed rats (DOCA salt). Systolic blood pressure reached hypertensive levels at 3 to 4 weeks in all three systems. A differential increase in ventricular weight to body weight (hypertrophy) occurred at 3 weeks in the SHR and aortic constriction models and at 4 weeks in the DOCA salt model. Ventricular IGF-I mRNA was detected by solution hybridization/RNase protection assay. IGF-I mRNA levels increased in all three systems coincident with the onset of hypertension and the development of ventricular hypertrophy. Maximum induction was 10-fold over control at 5 weeks in the aortic constriction model, 8-fold at 3 weeks in the SHR, and 6-fold at 6 weeks in the DOCA salt model. IGF-I mRNA levels returned to control values by the end of the experimental period despite continued hypertension and hypertrophy in all three systems. In contrast, ventricular c-myc mRNA content increased twofold to threefold at 1 week and returned to control levels by 2 weeks. Ventricular IGF-I receptor mRNA levels were unchanged over the time course studied. The increased ventricular IGF-I mRNA content was reflected in an increased ventricular IGF-I protein content, as determined both by radioimmunoassay and immunofluorescence histochemistry. CONCLUSIONS: We conclude that (1) hypertension induces significant increases in cardiac IGF-I mRNA and protein that occur coordinately with its onset and early in the development of hypertrophy, (2) IGF-I mRNA levels normalize as the hypertrophic response is established, (3) in comparison to IGF-I, both c-myc and IGF-I receptor genes are differentially controlled in experimental hypertension. These findings suggest that IGF-I may participate in initiating ventricular hypertrophy in response to altered loading conditions. The consistency of these findings in models of high-, moderate-, and low-renin hypertension suggests that they occur independently of the systemic renin-angiotensin endocrine axis.

Discordant, organ-specific regulation of insulin-like growth factor-I messenger ribonucleic acid in insulin-deficient diabetes in rats.

Linear growth retardation is common in uncontrolled insulin-deficient diabetes, but individual organs such as kidney may hypertrophy. To explore whether this heterogeneity of response might be mediated by differential local insulin-like growth factor-I (IGF-I) gene regulation, we injected rats with ip saline, 65, 120, or 175 mg/kg streptozotocin (STZ). Diabetics were untreated or received daily insulin. Animals were killed 24, 48, or 72 h after documentation of diabetes, and liver, kidney, and lung messenger RNA (mRNA) content analyzed by solution hybridization/RNase protection assay. Untreated diabetics had 10- to 100-fold reductions in hepatic IGF-I mRNA apparent as early as 24 h, and the magnitude of these changes varied directly with the severity of diabetes. In contrast, kidney IGF-I mRNA content increased by 400-500% at 24 h in untreated diabetics given 175 mg/kg STZ, and by 100-200% at 48 h in those given 120 mg/kg STZ, with return to control levels by 72 h. Renal IGF-I mRNA levels actually decreased by 250-350% at 24 h in rats injected with 65 mg/kg STZ, returning to supranormal values by 72 h. These results suggest that severity and/or duration of the metabolic abnormality qualitatively and quantitatively affect this response in the kidney. Liver and kidney IGF-I mRNA levels approached normal with insulin therapy and were similar to controls in rats which received STZ but did not develop diabetes. Lung IGF-I mRNA levels were minimally altered in all experimental groups. At the time point and STZ dosage at which liver IGF-I mRNA changes were most dramatic, little change in liver alpha-tubulin mRNA was noted. At the time point and STZ dosages at which kidney IGF-I mRNA induction was most dramatic, renal IGF-I receptor mRNA was only minimally changed, and renal alpha-tubulin mRNA was modestly reduced. In summary: 1) hepatic IGF-I mRNAs are dramatically reduced, and renal IGF-I mRNAs are significantly increased soon after the onset of insulin-deficient diabetes in STZ-treated rats; 2) insulin therapy restores IGF-I mRNA levels toward normal; and 3) these changes in IGF-I mRNA content are specific and are not the result of hepatic or renal STZ toxicity. These data suggest that IGF-I gene expression is regulated in a discordant, organ-specific manner in diabetes, and that metabolic factors in addition to GH may differentially modulate the endocrine and paracrine effects of IGF-I on growth.