Michael Mingzhao Xing

Highly Prevalent Genetic Alterations in Receptor Tyrosine Kinases and Phosphatidylinositol 3-Kinase/Akt and Mitogen-Activated Protein Kinase Pathways in Anaplastic and Follicular Thyroid Cancers

CONTEXT Genetic alterations in receptor tyrosine kinases (RTKs) and phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK pathways have not been fully defined in anaplastic and follicular thyroid cancers [anaplastic thyroid cancer (ATC), follicular thyroid cancer (FTC)]. OBJECTIVE The objective of the study was to explore a wide-range genetic basis for the involvement of these pathways in ATC. DESIGN We examined mutations and copy number gains of a large panel of genes in these pathways and corresponding phosphorylation of ERK (p-ERK) and Akt. RESULTS We found frequent copy gains of RTK genes, including EGFR, PDGFRalpha and -beta, VEGFR1 and 2, KIT, and MET and in PIK3Ca, PIK3Cb, and PDK1 genes in the PI3K/Akt pathway. Mutations of Ras, PIK3Ca, PTEN, and BRAF genes and RET/PTC rearrangements were common, whereas mutations in PDK1, Akt1, Akt2, and RTK genes were uncommon in ATC. Overall, 46 of 48 ATC (95.8%) harbored at least one genetic alteration, and coexistence of two or more was seen in 37 of 48 ATC (77.1%). These genetic alterations were somewhat less common in FTC. Genetic alterations that could activate both the PI3K/Akt and MAPK pathways were found in 39 of 48 ATC (81.3%). RTK gene copy gains were preferentially associated with p-Akt, suggesting their dominant role in activating the PI3K/Akt pathway. The phosphorylation of Akt was far more common than p-ERK in FTC, and both were relatively common and often coexisted in ATC. CONCLUSIONS Genetic alterations in the RTKs and PI3K/Akt and MAPK pathways are extremely prevalent in ATC and FTC, providing a strong genetic basis for an extensive role of these signaling pathways and the development of therapies targeting these pathways for ATC and FTC, particularly the former.

Association of High Iodine Intake with the T1799A BRAF Mutation in Papillary Thyroid Cancer

CONTEXT Epidemiological studies have indicated that high iodine intake might be a risk factor for papillary thyroid cancer (PTC), which commonly harbors the oncogenic T1799A BRAF mutation. OBJECTIVE The objective of the study was to investigate the relationship between BRAF mutation in PTC and iodine intake in patients. SUBJECTS AND METHODS We analyzed and compared the prevalences of the T1799A BRAF mutation in classical PTC of 1032 patients from five regions in China that uniquely harbor different iodine contents in natural drinking water, ranging from normal (10-21 microg/liter) to high (104-287 microg/liter). The BRAF mutation was identified by direct DNA sequencing. RESULTS The prevalence of BRAF mutation was significantly higher in any of the regions with high iodine content than any of the regions with normal iodine content. Overall, BRAF mutation was found in 387 of 559 PTC with high iodine content (69%) vs. 252 of 473 PTC with normal iodine content (53%), with an odds ratio of 1.97 (95% confidence interval 1.53-2.55) for the association of BRAF mutation with high iodine content (P < 0.0001). In addition, clinicopathological correlation analysis, the largest one of its type ever, showed that BRAF mutation was significantly associated with extrathyroidal invasion, lymph node metastasis, and advanced tumor stages of PTC. CONCLUSIONS High iodine intake seems to be a significant risk factor for the occurrence of BRAF mutation in thyroid gland and may therefore be a risk factor for the development of PTC. This large study also confirmed the association of BRAF mutation with poorer clinicopathological outcomes of PTC.

ANAPLASTIC THYROID CANCERS HARBOR NOVEL ONCOGENIC MUTATIONS OF THE ALK GENE

Thyroid cancer is the most common endocrine cancer, and targeted approaches to treat it pose considerable interest. In this study, we report the discovery of ALK gene mutations in thyroid cancer that may rationalize clinical evaluation of anaplastic lymphoma kinase (ALK) inhibitors in this setting. In undifferentiated anaplastic thyroid cancer (ATC), we identified two novel point mutations, C3592T and G3602A, in exon 23 of the ALK gene, with a prevalence of 11.11%, but found no mutations in the matched normal tissues or in well-differentiated thyroid cancers. These two mutations, resulting in L1198F and G1201E amino acid changes, respectively, both reside within the ALK tyrosine kinase domain where they dramatically increased tyrosine kinase activities. Similarly, these mutations heightened the ability of ALK to activate the phosphatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein (MAP) kinase pathways in established mouse cells. Further investigations showed that these two ALK mutants strongly promoted cell focus formation, anchorage-independent growth, and cell invasion. Similar oncogenic properties were observed in the neuroblastoma-associated ALK mutants K1062M and F1174L but not in wild-type ALK. Overall, our results reveal two novel gain-of-function mutations of ALK in certain ATCs, and they suggest efforts to clinically evaluate the use of ALK kinase inhibitors to treat patients who harbor ATCs with these mutations.

Functional Characterization of the T1799-1801del and A1799-1816ins BRAF Mutations in Papillary Thyroid Cancer

No abstract available at this time.

Genetic alterations in the phosphoinositide 3-kinase/Akt signaling pathway confer sensitivity of thyroid cancer cells to therapeutic targeting of Akt and mammalian target of rapamycin

We investigated the genotype-dependent therapeutic potential of targeting the phosphoinositide 3-kinase (PI3K)/Akt pathway for thyroid cancer. Proliferation of TPC1, Hth7, FTC133, OCUT1, K1, and BCPAP cells that harbored PI3K/Akt-activating genetic alterations was potently inhibited by the Akt inhibitor perifosine, whereas SW1736, Hth74, WRO, KAT18, and TAD2 cells that harbored no genetic alterations had no or only modest responses. Inhibition of Akt phosphorylation by perifosine was seen in these cells. Genetic-dependent apoptosis was induced by perifosine in cells selectively tested. Similarly, potent inhibition of cell proliferation by the mammalian target of rapamycin (mTOR) inhibitor temsirolimus occurred in virtually all the cells harboring genetic alterations, whereas modest inhibition was seen in some of the cells not harboring genetic alterations. Temsirolimus inhibited the phosphorylation of p70S6K, a substrate of mTOR. Knockdown of Akt1/2 or mTOR by shRNA approach inhibited the proliferation and colony formation of FTC133 and OCUT1 cells that harbored genetic alterations in the PI3K/Akt pathway but had no effect on SW1736 and KAT18 cells that did not. Transfection with PIK3CA mutants greatly sensitized SW1736 cells to perifosine and temsirolimus. Growth of xenograft tumors derived from FTC133 cells but not SW1736 cells in nude mice was dramatically inhibited by perifosine. Thus, this work for the first time shows that genetic alterations in the PI3K/Akt pathway confer thyroid cancer cells addiction to this pathway and their sensitivity to inhibition by targeting Akt and mTOR. This genotype-based targeting of the PI3K/Akt pathway using Akt and mTOR inhibitors may offer an effective therapeutic strategy for thyroid cancer and warrants further studies.

Hypermethylation of the DNA mismatch repair gene hMLH1 and its association with lymph node metastasis and T1799A BRAF mutation in patients with papillary thyroid cancer.

It remains to be investigated whether the aberrant methylation of DNA repair genes plays a pathogenic role in BRAF mutation‐promoted tumorigenesis of papillary thyroid cancer (PTC).

IQGAP1 Plays an Important Role in the Invasiveness of Thyroid Cancer

Purpose: This study was designed to explore the role of IQGAP1 in the invasiveness of thyroid cancer and its potential as a novel prognostic marker and therapeutic target in this cancer. Experimental Design: We examined IQGAP1 copy gain and its relationship with clinicopathologic outcomes of thyroid cancer and investigated its role in cell invasion and molecules involved in the process. Results: We found IQGAP1 copy number (CN) gain ≥3 in 1 of 30 (3%), 24 of 74 (32%), 44 of 107 (41%), 8 of 16 (50%), and 27 of 41 (66%) of benign thyroid tumor, follicular variant papillary thyroid cancer (FVPTC), follicular thyroid cancer (FTC), tall cell papillary thyroid cancer (PTC), and anaplastic thyroid cancer, respectively, in the increasing order of invasiveness of these tumors. A similar tumor distribution trend of CN ≥4 was also seen. IQGAP1 copy gain was positively correlated with IQGAP1 protein expression. It was significantly associated with extrathyroidal and vascular invasion of FVPTC and FTC and, remarkably, a 50%–60% rate of multifocality and recurrence of BRAF mutation–positive PTC (P = 0.01 and 0.02, respectively). The siRNA knockdown of IQGAP1 dramatically inhibited thyroid cancer cell invasion and colony formation. Coimmunoprecipitation assay showed direct interaction of IQGAP1 with E-cadherin, a known invasion-suppressing molecule, which was upregulated when IQGAP1 was knocked down. This provided a mechanism for the invasive role of IQGAP1 in thyroid cancer. In contrast, IQGAP3 lacked all these functions. Conclusions: IQGAP1, through genetic copy gain, plays an important role in the invasiveness of thyroid cancer and may represent a novel prognostic marker and therapeutic target for this cancer. Clin Cancer Res; 16(24); 6009–18. ©2010 AACR.

The T1790A BRAF mutation (L597Q) in childhood acute lymphoblastic leukemia is a functional oncogene

The T1790A BRAF mutation (L597Q) in childhood acute lymphoblastic leukemia is a functional oncogene