Activation of the RAS/RAF/ERK signaling pathway contributes to resistance to sunitinib in thyroid carcinoma cell lines.

CONTEXT: Sunitinib is currently being evaluated in advanced human thyroid carcinomas, based on the rationale that the vascular endothelial growth factor and platelet-derived growth factor receptors and the RET/PTC rearrangement are valuable targets for the treatment of this malignancy. However, criteria for selecting thyroid tumors that may benefit from sunitinib are lacking. DESIGN: The effect of activating somatic mutations in the KRAS and BRAF genes on the responsiveness to sunitinib was evaluated in a panel of thyroid cancer cell lines harboring wild-type KRAS and BRAF genes, the RET/PTC1 rearrangement, the G12R KRAS, or the V600E BRAF mutation. RESULTS: Sunitinib was found to selectively inhibit cell proliferation, induce cell accumulation in the G0-G1 phase, and inhibit the phosphorylation of ERK1/2 in both KRAS/BRAF wild-type thyroid cancer cells and in tumor cells harboring the RET/PTC rearrangement, whereas it was completely ineffective in KRAS- or BRAF-mutated thyroid carcinoma cells. This differential antitumor activity of sunitinib did not correlate with the expression profile of the vascular endothelial growth factor receptors 1, 2, and 3, platelet-derived growth factor receptor-α and cKIT genes. Of note, the constitutive activation of RAS/RAF/ERK signaling in KRAS/BRAF wild-type cells by transfection of the R12 HRAS or V600E BRAF mutants or stimulation with epithelial growth factor resulted in the loss of responsiveness to sunitinib, whereas pharmacological inhibition of MAPK kinase activity resulted in the resensitization of KRAS- or BRAF-mutated cells to the multikinase inhibitor. CONCLUSIONS: The constitutive activation of the RAS/RAF/ERK pathway may favor resistance to sunitinib in thyroid carcinoma cells.

Targeting epidermal growth factor receptor 1 signaling in human thyroid-stimulating hormone-independent thyroid carcinoma FRO cells results in a more chemosensitive and less angiogenic phenotype.

BACKGROUND: Poorly differentiated and anaplastic thyroid cancers are aggressive malignancies unresponsive to standard treatments. The mechanisms responsible for the progression of thyroid tumors toward a thyroid-stimulating hormone (TSH)-independent phenotype are still under discussion, and a better understanding of them may provide novel molecular targets for the treatment of this disease. We evaluated the hypothesis that epithelial growth factor (EGF) signaling may play a role in favoring the loss of TSH dependency in human differentiated thyroid tumor cells. METHODS: The sensitivity to EGF stimulation was evaluated in follicular thyroid carcinoma WRO cells that retain some features of thyroid cell differentiation and in undifferentiated TSH-independent thyroid carcinoma FRO cells. RESULTS: It was observed that, while both cell lines are characterized by a similar EGF-dependent activation of the RAS/MAPK signaling pathway, only FRO cells exhibited a significant induction of phosphoAKT, cell proliferation, and migration as well as the up-regulation of vascular endothelial growth factor-A expression in response to EGF. On the other hand, the inhibition of epidermal growth factor receptor 1 signaling by its tyrosine kinase inhibitor, erlotinib, caused a selective down-regulation of FRO cell proliferation and induced a phenotype more sensitive to the proapoptotic activity of anthracyclins and taxoids. By contrast, the protracted stimulation of TSH-dependent WRO cells with EGF induced the loss of TSH dependency and the rearrangement of F-actin cytoskeleton. CONCLUSIONS: These results suggest that the acquired sensitivity to EGF in these thyroid tumor cells may be responsible for the loss of differentiation in the transition toward a TSH-independent, invasive, and chemoresistant phenotype.

TRAP1, a novel mitochondrial chaperone responsible for multi-drug resistance and protection from apoptotis in human colorectal carcinoma cells.

TRAP1 is a component of a pro-survival mitochondrial pathway up-regulated in tumor cells. The evaluation of TRAP1 expression in 26 human colorectal carcinomas showed up-regulation in 17/26 tumors. Accordingly, TRAP1 levels were increased in HT-29 colorectal carcinoma cells resistant to 5-fluorouracil, oxaliplatin and irinotecan. Thus, we investigated the role of TRAP1 in multi-drug resistance in human colorectal cancer. Interestingly, TRAP1 overexpression leads to 5-fluorouracil-, oxaliplatin- and irinotecan-resistant phenotypes in different neoplastic cells. Conversely, the inhibition of TRAP1 activity by TRAP1 ATPase antagonist, shepherdin, increased the sensitivity to oxaliplatin and irinotecan in colorectal carcinoma cells resistant to the single agents. These results suggest that the increased expression of TRAP1 could be part of a pro-survival pathway responsible for multi-drug resistance.

Reverse transcriptase inhibitors induce cell differentiation and enhance the immunogenic phenotype in human renal clear-cell carcinoma.

Reverse transcriptase (RT) inhibitors are emerging as a novel class of anticancer differentiating agents, active in several human tumor cell models, such as melanoma and prostate, thyroid and colon carcinoma. Indeed, much evidence suggests that they may act by inhibiting endogenous RT, a gene highly expressed in undifferentiated and transformed cells. We therefore evaluated whether endogenous RT may represent a new molecular target in the treatment of human renal clear-cell carcinoma, a neoplasm with very low sensitivity to standard pharmacological therapies. Efavirenz and nevirapine, 2 non-nucleosidic RT inhibitors commonly used in HIV patients, either induced a reversible downregulation of cell proliferation or enhanced cell differentiation in primary cultures of human renal carcinoma cells characterized by high levels of endogenous RT activity. Both agents upregulated the expression of the vitamin D receptor and calbindin 28k genes, which are constitutively expressed in renal tubular cells, and induced vitamin D signaling by enhancing the ability of tumor cells to upregulate the vitamin D-dependent gene, CYP24. Furthermore, efavirenz- and nevirapine-differentiated tumor cells exhibited an immunogenic phenotype with an increased expression of HLA-I and CD40 antigens and an enhanced ability to elicit a specific T-cell response in mixed lymphocyte/tumor-cell cultures. Indeed, renal carcinoma cells exposed to efavirenz induced a CD8(+)CCR7-CD45RA(-) effector memory T-cell phenotype, whereas untreated RCC cells induced a CD8(+)CCR7(+)CD45RA(-) central memory T-cell phenotype. These data suggest that RT inhibitors may be a novel tool in the treatment of human renal clear-cell carcinoma, potentially able to enhance the immunogenic potential of tumor cell.