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 retinal (Vitam in A) and its synthetic derivatives, can eradicate leukoplakia and suppress the formation of squamous cell carcinoma of the head and neck (SCCHN). Non selective 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 compar ed with other nonselective retinoids. We examined the effect of LGD1069 (10 mum) on cellular proliferation and expression of putative intermediate bio marker genes including TGF-alpha, EGFR, and RAR-beta in seven SCCHN cell li nes. A quantitative reverse transcription-PCR assay using a novel "primer d ropping" method was used to determine expression levels of EGFR, TGF-alpha, and RAR-beta before and after treatment with LGD1069 (10 mum). SCCHN proli feration was reduced by a mean of 50% at 4 days in seven SCCHN cell lines a fter LGD1069 treatment (P less than or equal to 0.05). EGFR expression leve ls were decreased by a mean of 58.4% (P = 0.007), TGF-alpha levels were dec reased 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) ac tivation in SCCHN. Abrogation of constitutive Stat3 activation was seen wit h LGD1069 treatment. These results suggest that an RXR-selective retinoic a cid decreases SCCHN proliferation in part by interfering with TGF-alpha /EG FR autocrine Signaling.