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PURPOSE: Vascular endothelial growth factor (VEGF) is a major mitogen for endothelial cells and enhances vascular permeability. Enhanced VEGF secretion is found in human cancers and correlates with increased tumor neovascularization. ZD6474 is a p.o. bioavailable, VEGF flk-1/KDR receptor (VEGFR-2) tyrosine kinase inhibitor with antitumor activity in many human cancer xenografts and is currently in Phase I clinical development. EXPERIMENTAL DESIGN: We tested the effects of ZD6474 on EGFR phosphorylation in cell expressing functional epidermal growth factor receptor (EGFR) and the antiproliferative and the proapoptotic activity of ZD6474 alone or in combination taxanes in human cancer cell lines with functional EGFR but lacking VEGFR-2. The antitumor activity of this drug was also tested in nude mice bearing established GEO colon cancer xenografts. RESULTS: ZD6474 causes a dose-dependent inhibition of EGFR phosphorylation in mouse NIH-EGFR fibroblasts and human MCF-10A ras breast cancer cells, two cell lines that overexpress the human EGFR. ZD6474 treatment resulted in a dose-dependent inhibition of soft agar growth in seven human cell lines (breast, colon, gastric, and ovarian) with functional EGFR but lacking VEGFR-2. A dose-dependent supra-additive effect in growth inhibition and in apoptosis in vitro was observed by the combined treatment with ZD6474 and paclitaxel or docetaxel. ZD6474 treatment of nude mice bearing palpable GEO colon cancer xenografts (which are sensitive to inhibition of EGFR signaling) induced dose-dependent tumor growth inhibition. Immunohistochemical analysis revealed a significant dose-dependent reduction of neoangiogenesis. The antitumor activity of ZD6474 in GEO tumor xenografts was also found to be enhanced when combined with paclitaxel. Tumor regression was observed in all mice after treatment with ZD6474 plus paclitaxel, and it was accompanied by a significant potentiation in inhibition of angiogenesis. Six of 20 mice had no histological evidence of tumors after treatment with ZD6474 plus paclitaxel. CONCLUSIONS: This study suggests that in addition to inhibiting endothelial cell proliferation by blocking VEGF-induced signaling, ZD6474 may also be able to inhibit cancer cell growth by blocking EGFR autocrine signaling. These results provide also a rationale for the clinical evaluation of ZD6474 combined with taxanes in cancer patients.

RET/papillary thyroid carcinoma (PTC) oncogenes, generated by recombination of the tyrosine kinase-encoding domain of RET with different heterologous genes, are prevalent in papillary carcinomas of the thyroid. Point mutations of RET cause multiple endocrine neoplasia type 2 (MEN2) familial cancer syndrome and are found in sporadic medullary thyroid carcinomas. Here, we show that ZD6474, a low molecular weight tyrosine kinase inhibitor, blocks the enzymatic activity of RET-derived oncoproteins at a one-half maximal inhibitory concentration of 100 nM. ZD6474 blocked in vivo phosphorylation and signaling of the RET/PTC3 and RET/MEN2B oncoproteins and of an epidermal growth factor (EGF)-activated EGF-receptor/RET chimeric receptor. RET/PTC3-transformed cells-treated ZD6474 lost proliferative autonomy and showed morphological reversion. ZD6474 prevented the growth of two human PTC cell lines that carry spontaneous RET/PTC1 rearrangements. Finally, it blocked anchorage-independent growth of RET/PTC3-transformed NIH3T3 fibroblasts and the formation of tumors after injection of NIH-RET/PTC3 cells into nude mice. Thus, targeting RET oncogenes with ZD6474 might offer a potential treatment strategy for carcinomas sustaining oncogenic activation of RET.

Oncogenic activation of the RET receptor tyrosine kinase is common in different human cancers. We found that the pyrazolo-pyrimidine PP1 inhibited RET-derived oncoproteins with a half maximal inhibitor concentration of 80 nM. Furthermore, RET/PTC3-transformed cells treated with 5 microM of PP1 lost proliferative autonomy and showed morphological reversion. PP1 prevented the growth of two human papillary thyroid carcinoma cell lines that carry spontaneous RET/PTC1 rearrangements and blocked anchorage-independent growth and tumorigenicity in nude mice of NIH3T3 fibroblasts expressing the RET/PTC3 oncogene. These findings suggest targeting RET oncogenes with PP1 or related compounds as a novel treatment strategy for RET-associated neoplasms.

AXL is a tyrosine kinase receptor activated by GAS6 and regulates cancer cell proliferation migration and angiogenesis. We studied AXL as new therapeutic target in colorectal cancer (CRC). Expression and activation of AXL and GAS6 were evaluated in a panel of human CRC cell lines. AXL gene silencing or pharmacologic inhibition with foretinib suppressed proliferation, migration and survival in CRC cells. In an orthotopic colon model of human HCT116 CRC cells overexpressing AXL, foretinib treatment caused significant inhibition of tumour growth and peritoneal metastatic spreading. AXL and GAS6 overexpression by immunohistochemistry (IHC) were found in 76,7% and 73.5%, respectively, of 223 human CRC specimens, correlating with less differentiated histological grading. GAS6 overexpression was associated with nodes involvement and tumour stage. AXL gene was found amplified by Fluorescence in situ hybridization (FISH) in 8/146 cases (5,4%) of CRC samples. Taken together, AXL inhibition could represent a novel therapeutic approach in CRC.

Inappropriate activation of the RET receptor tyrosine kinase causes development of papillary and medullary thyroid cancer. We have previously shown that pyrazolopyrimidine is a potent inhibitor of the RET kinase. Here, we show that 4-amino-5-(4-chloro-phenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) (PP2), another pyrazolopyrimidine, blocks the enzymatic activity of the isolated RET kinase and RET/PTC1 oncoprotein at IC(50) in the nanomolar range. PP2 blocked in vivo phosphorylation and signaling of the RET/PTC1 oncoprotein. PP2 prevented serum-independent growth of RET/PTC1-transformed NIH3T3 fibroblasts and of TPC1 and FB2, two human papillary thyroid carcinoma cell lines that carry spontaneous RET/PTC1 rearrangements. Finally, PP2 blocked invasion of type I collagen matrix by TPC1 cells. Thus, pyrazolopirimidines hold promise for the treatment of human cancers sustaining oncogenic activation of RET.

Purpose: In colorectal cancer, the activation of the intracellular RAS–RAF and PIK3CA–AKT pathways has been implicated in the resistance to anti-EGFR mAbs. We have investigated the role of regorafenib, an oral multikinase inhibitor, in combination with cetuximab, an anti-EGFR mAb, to overcome anti-EGFR resistance. Experimental Design: We have tested, in vitro and in vivo, the effects of regorafenib in a panel of human colorectal cancer cell lines with a KRAS mutation (SW480, SW620, HCT116, LOVO, and HCT15) or with a BRAF mutation (HT29), as models of intrinsic resistance to cetuximab treatment, and in two human colorectal cancer cell lines (GEO and SW48) that are cetuximab-sensitive, as well as in their derived cells with acquired resistance to cetuximab (GEO-CR and SW48-CR). Results: Treatment with regorafenib determined a dose-dependent growth inhibition in all colorectal cancer cell lines. The combined treatment with cetuximab and regorafenib induced synergistic antiproliferative and apoptotic effects in cetuximab-resistant cell lines by blocking MAPK and AKT pathways. Nude mice were injected s.c. with HCT116, HCT15, GEO-CR, and SW48-CR cells. The combined treatment caused significant tumor growth inhibition. Synergistic antitumor activity of regorafenib plus cetuximab was also observed in an orthotopic colorectal cancer model of HCT116 cells. In particular, the combined treatment induced a significant tumor growth inhibition in the primary tumor site (cecum) and completely prevented metastasis formation. Conclusions: The combined treatment with cetuximab and regorafenib could be a strategy to overcome resistance to anti-EGFR therapies in metastatic colorectal cancer patients. Clin Cancer Res; 21(13); 2975–83. ©2015 AACR.

Purpose: Although cetuximab, an anti-EGF receptor (EGFR) monoclonal antibody, is an effective treatment for patients with KRAS wild-type metastatic colorectal cancer (mCRC), its clinical use is limited by onset of resistance. Experimental Design: We characterized two colorectal cancer models to study the mechanisms of acquired resistance to cetuximab. Results: Following chronic treatment of nude mice bearing cetuximab-sensitive human GEO colon xenografts, cetuximab-resistant GEO (GEO-CR) cells were obtained. In GEO-CR cells, proliferation and survival signals were constitutively active despite EGFR inhibition by cetuximab treatment. Whole gene expression profiling identified a series of genes involved in the hepatocyte growth factor (HGF)-MET–dependent pathways, which were upregulated in GEO-CR cells. Furthermore, activated, phosphorylated MET was detected in GEO-CR cells. A second colorectal cancer cell line with acquired resistance to cetuximab was obtained (SW48-CR). Inhibition of MET expression by siRNA restored cetuximab sensitivity in GEO-CR and SW48-CR cells, whereas exogenous activation of MET by HGF stimulation in cetuximab-sensitive GEO and SW48 cells induced resistance to cetuximab. Treatment of GEO-CR and SW48-CR cells with PHA665752, a selective MET inhibitor, inhibited cell growth, proliferation, and survival signals and impaired cancer cell migration. Overexpression of TGF-α, a specific EGFR ligand, was involved in the acquisition of cetuximab resistance in GEO-CR and SW48-CR cells. In fact, TGF-α overexpression induced the EGFR–MET interaction, with subsequent MET phosphorylation and activation of MET downstream effectors in GEO-CR and SW48-CR cells. Conclusions: These results suggest that overexpression of TGF-α through induction of EGFR–MET interaction contributes to cetuximab resistance in colorectal cancer cells. The combined inhibition of EGFR and MET receptor could represent a strategy for preventing and/or overcoming cetuximab resistance in patients with colorectal cancer. Clin Cancer Res; 19(24); 6751–65. ©2013 AACR.

Purpose: EGF receptor (EGFR) tyrosine kinase inhibitors (TKI) have been found to be effective against lung cancer, but clinical resistance to these agents has developed as their usage has increased. Metformin is a widely used antidiabetic drug and also displays significant growth-inhibitory and proapoptotic effects in several cancer models, alone or in combination with chemotherapeutic drugs. Experimental Design: The effects of gefitinib, a selective EGFR-TKI, and metformin on a panel of non–small cell lung cancer (NSCLC) cell lines were assessed by using MTT, bromide assay, flow cytometry, anchorage-independent growth, coimmunoprecipitation, and Western blot analysis. Results: The combination of metformin with gefitinib induced a strong antiproliferative and proapoptotic effect in NSCLC cell lines that harbored wild-type LKB1 gene. Treatment with metformin as single agent, however, induced an activation and phosphorylation of mitogen-activated protein kinase (MAPK) through an increased C-RAF/B-RAF heterodimerization. The inhibition of EGFR phosphorylation and of downstream signaling by adding gefitinib to metformin treatment abrogated this phenomenon and induced a strong apoptotic effect in vitro and in vivo. Conclusions: Metformin and gefitinib are synergistic in LKB1 wild-type NSCLC cells. However, further studies are required to investigate better the effect of metformin action on the RAS/RAF/MAPK pathway and the best context in which to use metformin in combination with molecular targeted agents. Clin Cancer Res; 19(13); 3508–19. ©2013 AACR.

Oncogenic conversion of the RET tyrosine kinase is a frequent feature of medullary thyroid carcinoma (MTC). ZD6474 (vandetanib) is an ATP-competitive inhibitor of RET, epidermal growth factor receptor (EGFR), and vascular endothelial growth factor receptors kinases. In this study, we have studied ZD6474 mechanism of action in TT and MZ-CRC-1 human MTC cell lines, carrying cysteine 634 to tryptophan (C634W) and methionine 918 to threonine (M918T) RET mutation respectively. ZD6474 blunted MTC cell proliferation and RET, Shc and p44/p42 mitogen-activated protein kinase (MAPK) phosphorylation. Single receptor knockdown by RNA interference showed that MTC cells depended on RET for proliferation. Adoptive expression of the ZD6474-resistant V804M RET mutant rescued proliferation of TT cells under ZD6474 treatment, showing that RET is a key ZD6474 target in these MTC cells. Upon RET inhibition, adoptive stimulation of EGFR partially rescued TT cell proliferation, MAPK signaling, and expression of cell-cycle-related genes. This suggests that simultaneous inhibition of RET and EGFR by ZD6474 may overcome the risk of MTC cells to escape from RET blockade through compensatory over-activation of EGFR.

Purpose: Cancer cell survival, invasion, and metastasis depend on cancer cell proliferation and on tumor-induced angiogenesis. We evaluated the efficacy of the combination of sorafenib and erlotinib or cetuximab. Experimental Design: Sorafenib, erlotinib, and cetuximab, alone or in combination, were tested in vitro in a panel of non–small cell lung cancer (NSCLC) and colorectal cancer cell lines and in vivo in H1299 tumor xenografts. Results: Epidermal growth factor receptor (EGFR) ligand mRNAs were expressed in all NSCLC and colorectal cancer cell lines with variable levels ranging from 0.4- to 8.1-fold as compared with GEO colorectal cancer cells. Lung cancer cells had the highest levels of vascular endothelial growth factors (VEGF) A, B, and C, and of VEGF receptors as compared with colorectal cancer cells. Combined treatments of sorafenib with erlotinib or cetuximab produced combination index values between 0.02 and 0.5, suggesting a significant synergistic activity to inhibit soft agar colony formation in all cancer cell lines, which was accompanied by a marked blockade in mitogen-activated protein kinase and AKT signals. The in vitro migration of H1299 cells, which expressed high levels of both VEGF ligands and receptors, was inhibited by treatment with sorafenib, and this effect was significantly increased by the combination with anti-EGFR drugs. In nude mice bearing established human H1299 xenografts, treatment with the combination of sorafenib and erlotinib or cetuximab caused a significant tumor growth delay resulting in 70 to 90 days increase in mice median overall survival as compared with single-agent sorafenib treatment. Conclusions: Combination treatment with sorafenib and erlotinib or cetuximab has synergistic antitumor effects in human colorectal and lung cancer cells. Clin Cancer Res; 16(20); 4990–5001. ©2010 AACR.

Human thyroid papillary carcinomas are characterized by rearrangements of the RET protooncogene with a number of heterologous genes, which generate the RET/papillary thyroid carcinoma (PTC) oncogenes. One of the most frequent variants of these recombination events is the fusion of the intracellular kinase-encoding domain of RET to the first 101 amino acids of a gene named H4(D10S170). We have characterized the H4(D10S170) gene product, showing that it is a ubiquitously expressed 55 KDa nuclear and cytosolic protein that is phosphorylated following serum stimulation. This phosphorylation was found to depend on mitogen-activated protein kinase (MAPK) Erk1/2 activity and to be associated to the relocation of H4(D10S170) from the nucleus to the cytosol. Overexpression of the H4(D10S170) gene was able to induce apoptosis of thyroid follicular epithelial cells; conversely a carboxy-terminal truncated H4(D10S170) mutant H4(1-101), corresponding to the portion included in the RET/PTC1 oncoprotein, behaved as dominant negative on the proapoptotic function and nuclear localization of H4(D10S170). Furthermore, conditional expression of the H4(D10S170)-dominant negative truncated mutant protected cells from stress-induced apoptosis. The substitution of serine 244 with alanine abrogated the apoptotic function of H4(D10S170). These data suggest that loss of the H4(D10S170) gene function might have a role in thyroid carcinogenesis by impairing apoptosis.

We show that treatment of a panel of thyroid carcinoma cell lines naturally harboring the RET/PTC1 oncogene, with the RET kinase inhibitors PP1 and ZD6474, results in reversible G1 arrest. This is accompanied by interruption of Shc and mitogen-activated protein kinase (MAPK) phosphorylation, reduced levels of G1 cyclins, and increased levels of the cyclin-dependent kinase inhibitor p27Kip1 because of a reduced protein turnover. MAP/extracellular signal-regulated kinase 1/2 inhibition by U0126 caused G1 cyclins down-regulation and p27Kip1 up-regulation as well. Forced expression of RET/PTC in normal thyroid follicular cells caused a MAPK- and proteasome-dependent down-regulation of p27Kip1. Reduction of p27Kip1 protein levels by antisense oligonucleotides abrogated the G1 arrest induced by RET/PTC blockade. Therefore, in thyroid cancer, RET/PTC-mediated MAPK activation contributes to p27Kip1 deregulation. This pathway is implicated in cell cycle progression and in response to small molecule kinase inhibitors.

We have previously demonstrated that HMGI proteins are required for the transformation of rat thyroid cells by v-mos and v-ras-Ki oncogenes. To determine whether HMGI proteins are also required for in vivo thyroid carcinogenesis, mice carrying a disrupted HMGI-C gene (pygmy mice) were either treated with radioactive iodine or crossed with transgenic mice carrying the E7 papilloma virus oncogene under the transcriptional control of thyroglobulin gene promoter. The pygmy mice developed thyroid carcinomas with the same frequency as occurred in wild-type mice without significant macroscopic and microscopic differences. Therefore, these results indicate that HMGI-C gene expression is not required in in vivo thyroid cell malignant transformation.