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Sunmi Park, Mark C Willingham, Jun Qi and Sheue-Yann Cheng

Compelling epidemiological evidence shows a strong positive correlation of obesity with thyroid cancer. In vivo studies have provided molecular evidence that high-fat-diet-induced obesity promotes thyroid cancer progression by aberrantly activating leptin-JAK2-STAT3 signaling in a mouse model of thyroid cancer (Thrb PV/PV Pten +/ mice). The Thrb PV/PV Pten +/ mouse expresses a dominantly negative thyroid hormone receptor β (denoted as PV) and a deletion of one single allele of the Pten gene. The Thrb PV/PV Pten +/ mouse spontaneously develops follicular thyroid cancer, which allows its use as a preclinical mouse model to test potential therapeutics. We recently showed that inhibition of STAT3 activity by a specific inhibitor markedly delays thyroid cancer progression in high-fat-diet-induced obese Thrb PV/PV Pten +/ mice (HFD-Thrb PV/PV Pten +/ mice). Further, metformin, a widely used antidiabetic drug, blocks invasion and metastasis, but not thyroid tumor growth in HFD-Thrb PV/PV Pten +/ mice. To improve efficacy in reducing thyroid tumor growth, we treated HFD-Thrb PV/PV Pten +/ with JQ1, a potent inhibitor of the activity of bromodomain and extraterminal domain (BET) and with metformin. We found that the combined treatment synergistically suppressed thyroid tumor growth by attenuating STAT3 and ERK signaling, resulting in decreased anti-apoptotic key regulators such as Mcl-1, Bcl-2 and survivin and increased pro-apoptotic regulators such as Bim, BAD and cleave caspase 3. Furthermore, combined treatment of JQ1 and metformin reduced cMyc protein levels to suppress vascular invasion, anaplasia and lung metastasis. These findings indicate that combined treatment is more effective than metformin alone and suggest a novel treatment modality for obesity-activated thyroid cancer.

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Benjamin Boyerinas, Sun-Mi Park, Annika Hau, Andrea E Murmann and Marcus E Peter

MicroRNAs (miRNAs or miRs) are small noncoding RNAs capable of regulating gene expression at the translational level. Current evidence suggests that a significant portion of the human genome is regulated by microRNAs, and many reports have demonstrated that microRNA expression is deregulated in human cancer. The let-7 family of microRNAs, first discovered in Caenorhabditis elegans, is functionally conserved from worms to humans. The human let-7 family contains 13 members located on nine different chromosomes, and many human cancers have deregulated let-7 expression. A growing body of evidence suggests that restoration of let-7 expression may be a useful therapeutic option in cancers, where its expression has been lost. In this review, we discuss the role of let-7 in normal development and differentiation, and provide an overview of the relationship between deregulated let-7 expression and tumorigenesis. The regulation of let-7 expression, cancer-relevant let-7 targets, and the relationship between let-7 and drug sensitivity are highlighted.

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Xuguang Zhu, Sunmi Park, Woo Kyung Lee and Sheue-yann Cheng

Anaplastic thyroid cancer (ATC) is an aggressive malignancy with limited treatment options. We explored novel treatment modalities by targeting epigenetic modifications using inhibitors of BET (e.g. BRD4) activity. We evaluated the efficacy in the treatment of ATC of a novel BET inhibitor, PLX51107 (PLX), currently in clinical trials for other solid tumors and hematologic malignancies, alone or combined with a MEK inhibitor, PD0325901(PD). To elucidate the effects of these inhibitors on growth of ATC, we treated ATC cells derived from patient tumors (THJ-11T and THJ-16T cells) and mouse xenograft tumors with inhibitors. We found PLX and PD inhibitors singly inhibited proliferation of both human ATC cells lines, but together exhibited stronger inhibition of proliferation. In mouse xenografts, the combination treatment almost totally blocked growth in xenograft tumors derived from both ATC cells. PD effectively attenuated MEK-ERK signaling, which was further enhanced by PLX in the combined treatment in cultured cells and tumors. Importantly, the combination of PLX and PD acted synergistically to suppress MYC transcription to increase p27 in decreasing tumor cell proliferation. PLX and PD cooperated to upregulate pro-apoptotic proteins to promote apoptosis. These two inhibitors converged to reduce the binding of BRD4 to the MYC promoter to suppress the MYC expression. These findings indicate that combined treatment of BET and MEK-ERK inhibitors was more effective to treat ATC than single targeted treatment. Synergistic suppression of MYC transcription via collaborative actions on chromatin modifications suggested that targeting epigenetic modifications could provide novel treatment opportunities for ATC.