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Cancer Therapy: Clinical |
Authors' Affiliations: Departments of 1 Medicine, 2 Pathology, and 3 Radiation and Cellular Oncology, University of Chicago, Chicago, Illinois; 4 Cancer Center and 5 Department of Pathology, Massachusetts General Hospital, Charlestown, Massachusetts; and 6 Massachusetts Eye and Ear Infirmary, Boston, Massachusetts
Requests for reprints: Daniel A. Haber, Massachusetts General Hospital Cancer Center, CNY7, 149 13th Street, Charlestown, MA 02129. Phone: 617-724-7805; Fax: 617-724-6919; E-mail: haber{at}helix.mgh.harvard.edu.
| Abstract |
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Experimental Design: We sequenced the kinase domain of EGFR and exon 20 of ERBB2 in tumor specimens from eight responsive patients. In addition, mutational analysis was done on tumor specimens from nine gefitinib nonresponders and 65 unselected cases of SCCHN.
Results: None of eight TKI-responsive specimens had mutations within the kinase domain of EGFR. EGFR amplification was also not associated with drug responsiveness. However, a single responsive case had a somatic missense mutation within exon 20 of ERBB2.
Conclusion: Our data indicate that unlike NSCLC, EGFR kinase mutations are rare in unselected cases of SCCHN within the United States and are not linked to gefitinib or erlotinib responses in SCCHN. Alternative mechanisms, including ERBB2 mutations, may underlie responsiveness in this tumor type.
40,000 individuals in the United States (1). Despite current therapeutic modalities, as many as half these will recur, or develop metastases, and eventually succumb to their disease, highlighting the need for alternative forms of therapeutic intervention. Because epidermal growth factor receptor (EGFR: ERBB1 and HER1) is almost universally expressed in SCCHN and high levels of expression have been correlated with a poor clinical prognosis (26), clinical trials were undertaken to assess the efficacy of kinase inhibitors that target this growth factor, including gefitinib and erlotinib (7), reporting significant responses in up to 11% of patients refractory to other therapies (8). Although the response rate of SCCHN to gefitinib and erlotinib is comparable with that seen in nonsmall cell lung cancer (NSCLC), the demographic and histologic variables associated with responsive cases differ remarkably. In lung cancer, drug responses are characteristically seen in adenocarcinomas arising in nonsmokers, with an increased frequency among women and Asians (9, 10). In contrast, responsive cases of SCCHN were indistinguishable from nonresponsive cases in terms of their histology or associated history of tobacco exposure (8).
In NSCLC, clinical responses to gefitinib or erlotinib have recently been ascribed to the presence of activating mutations within the kinase domain of EGFR (1116). Experimentally, cells expressing these mutant receptors seem dependent upon altered survival signals transduced by these receptors, which themselves also display increased sensitivity to inhibition by gefitinib (17). Thus, at least in a subset of NSCLC, somatic mutations in EGFR seem to drive tumorigenesis and provide a biologically relevant target for therapeutic intervention. Clinically, these mutations are associated with dramatic responses to EGFR tyrosine kinase inhibitors (TKI) and may define a biological subset of NSCLC patients. To determine if this molecular mechanism extends to SCCHN, we sequenced the kinase domain of EGFR (exons 18-24) in tumors from gefitinib or erlotinib responsive cases as well as untreated cases from the United States.
| Materials and Methods |
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Exons 18 to 24 of EGFR and exon 20 of ERBB2 were amplified using nested PCR consisting of an initial primary PCR followed by a secondary PCR. Primer pairs (sense and antisense) used in the initial amplification of EGFR were as follows: exon 18, CAAGTGCCGTGTCCTGGCACCCAAGC and CCAAACACTCAGTGAAACAAAGAG; exon 19, GCAATATCAGCCTTAGGTGCGGCTC and CATAGAAAGTGAACATTTAGGATGTG; exon 20, CCATGAGTACGTATTTTGAAACTC and CATATCCCCATGGCAAACTCTTGC; exon 21, CTAACGTTCGCCAGCCATAAGTCC and GCTGCGAGCTCACCCAGAATGTCTGG; exon 22, GAGCAGCCCTGAACTCCGTCAGACTG and CTCAGTACAATAGATAGACAGCAATG; exon 23, CAGGACTACAGAAATGTAGGTTTC and GTGCCTGCCTTAAGTAATGTGATGAC; exon 24, GACTGGAAGTGTCGCATCACCAATG and GGTTTAATAATGCGATCTGGGACAC. The primer pair (CTGTGGGCCATGGCT GTGGTTTG and GGAATGGGAAGCACCCATGTAGACC) was used in an initial amplification of exon 20 of ERBB2. Primary reactions contained 2 µL genomic DNA as a template in a 25-µL reaction consisting of 1x buffer, 50 µmol/L deoxynucleotide triphosphate, 200 nmol/L sense primer, 200 nmol/L antisense primer, and 0.8 unit Expand Taq (Roche Diagnostics, Mannheim, Germany).
Nested primers pairs used in secondary amplification of EGFR were exon 18, GCACCCAAGCCCATGCCGTGGCTGC and GAAACAAAGAGTAAAGTAGATGATGG; exon 19 CCTTAGGTGCGGCTCCACAGC and CATTTAGGATGTGGAGATGAGC; exon 20, GAAACTCAAGATCGCATTCATGC and GCAAACTCTTGCTATCCCAGGAG; exon 21, CAGCCATAAGTCCTCGACGTGG and CATCCTCCCC TGCATGTGTTAAAC; exon 22, GACGGGTCCTGGGGTGATCTGGCTC and CTCAGTACAATAGATAGACAGCAATG; exon 23, GTAGGTTTCTAAACATCAAGAAAC and GTGATGACATTTCTCCAGGGATGC; exon 24, CATCACCAATGCCTTCTTTAAGC and GCTGGAGGGTTTAATAATGCGATC. Exon 20 of ERBB2 was amplified using nested primers CTGTGGGCCATGGCTGTGGTTTG and GGAAGCACCCATGTAGACCTTCTGG. Nested reactions contained 2 µL primary PCR product as a template in a 25-µL reaction consisting of 1x buffer, 50 µmol/L deoxynucleotide triphosphate, 200 nmol/L sense primer, 200 nmol/L antisense primer, and 0.8 unit Expand Taq (Roche Diagnostics). Cycling conditions for both primary and secondary PCR reactions were 95°C for 15 minutes followed by 40 cycles consisting of 95°C for 30 seconds, 58°C for 30 seconds, 72°C for 45seconds followed by 72°C for 5 minutes. PCR amplicons were purified using exonuclease I (U.S. Biochemical, Cleveland, OH) and shrimp alkaline phosphatase (U.S. Biochemical) and diluted in water before bidirectional capillary sequencing, which was done using BigDye Terminator v1.1 chemistry (Applied Biosystems, Foster City, CA) in combination with an ABI3100 instrument according to the manufacturer's instructions. Electropherograms were aligned and reviewed using Sequence Navigator software.
Determination of EGFR copy number. EGFR copy number was determined by Taqman real-time quantitative PCR with Taqman Universal PCR mastermix and an ABI Prism 7900HT sequence detection system (Applied Biosystems). The primers (5'-3') and fluorogenic probe used for EGFR were CAATTGCCAGTTAACGTCTTCCTT (sense primer), TTTCTCACCTTCTGGGATCCA (antisense primer), and TCTCTCTGTCATAGGGAC (probe). For the control gene, PCDH7, these were GCTGCAATCTCCTCCCTGAA (sense primer), TGCCTTTTCTCACCTGCATTC (antisense primer), and CCACTGCTCCGACATG (probe).
| Results |
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| Discussion |
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7% of unselected cases of SCCHN from Korea (23). The fact that we did not observe such mutations among 65 cases of unselected SCCHN from the United States, 17 cases of patients treated with EGFR-TKI, nor among seven SCCHN cell lines reported previously (11), suggests that the frequency of EGFR mutations in SCCHN cancer may differ among ethnic groups. Such a difference in the prevalence of EGFR mutations between East Asian and European populations is now well established for NSCLC (12, 1416, 2426), and its extension to SCCHN is of considerable interest in searching for genetic and environmental risk factors. It will be important to determine whether EGFR mutations in Eastern Asian SCCHN patients are associated with response to EGFR-TKIs. Our findings further suggest that ERBB2 mutations may be linked to EGFR-TKI sensitivity in at least some of these responsive cases. Although ERBB2 mutations within this region of the gene have been described in NSCLC their functional relevance to gefitinib or erlotinib responsiveness, or dual inhibitors of EGFR/ERBB2, such as lapatinib or HKI-272, has not yet been evaluated. This observation has clinical significance, as EGFR mutational testing enters the clinical arena as a predictor of therapeutic response to TKI in lung cancer. Alternative mechanisms must be sought to explain the majority of responses in SCCHN.
The absence of EGFR mutations in TKI-responsive SCCHN studied here is perhaps not surprising, given the unique subset of lung cancers defined by such mutations (i.e., adenocarcinomas arising in never smokers), with apparent modulation by both sex and ethnic factors (1116, 2426). In our study, no such distinct phenotype was evident in responsive cases of SCCHN. In this context, it is interesting to note that a dose-response effect for gefitinib may exist in SCCHN cancers (response rates of 1% in a study using 250-mg daily dosing, versus 11% in a second study using a 500-mg dose; refs. 8, 27). Thus, in contrast to the exquisite sensitivity of tumors with mutant EGFR to gefitinib and the absence of different responses at these two doses (9, 10), inhibition of EGFR-dependent signaling even in responsive cases of SCCHN may require higher drug levels.
In conclusion, we note that most SCCHN cases responsive to gefitinib or erlotinib do not seem to have mutations in EGFR or ERBB2, as does a small subset of responsive NSCLC. Further studies are required to determine whether a unifying molecular mechanism may underlie TKI responsiveness in such cases and potentially in other tumor types where occasional gefitinib and erlotinib responses have been reported.
| Acknowledgments |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 4/29/05; revised 6/20/05; accepted 8/23/05.
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and EGFR in head and neck cancer. J Cell Biochem 1993;17F:18891.[CrossRef]
and EGFR protein in head and neck squamous cell carcinoma and patient survival. J Natl Cancer Inst 1998;90:82432.This article has been cited by other articles:
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