Class presentation: January 17, 2005.
Paper presented: Lynch et al., New England Journal of Medicine. 350(21):2129-2139, 2004.
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I. NSCLC, EGFR and Gefitinib
For both men and women, lung carcinoma is the leading cause of cancer death in the United States and worldwide (1). From a histological viewpoint, 80% of lung cancers are non-small-cell lung cancers (NSCLC), and adenocarcinomas are a subgroup of these (2). On May 5, 2003, gefitinib (Iressa (TM)) was approved by the US FDA as a monotherapy for patients with NSCLC after failure of both platinum-based and docetaxel chemotherapies, based on the results of two Phase 2 trials, IDEAL-1 and IDEAL-2 (3, 4). Although the response to gefitinib was unpredictable and manifest in only a small percentage of patients with NSCLC (~10%), the rapid and profound response seen in this subgroup led to its FDA approval (5).
Gefitinib targets the ATP cleft of the epidermal growth factor receptor (EGFR), which is overexpressed in 40-80% of non-small-cell lung cancers (6). While elevated EGFR expression is common in lung cancers, neither EGFR expression levels nor phosphorylation state correlate with the response to gefitinib (2). Further, clinical trials have shown higher response rates to gefitinib in Japanese vs. European-derived populations (7). In the United States positive clinical responses to gefitinib have been observed most often in females, nonsmokers, and in patients with adenocarcinoma (8, 9).
In independent studies, Paez et al, publishing in the June 4, 2004 edition of Science (10), and Lynch et al, reporting in the May 20, 2004 edition of The New England Journal of Medicine (5), isolated mutations in the same domains of the EGFR from lung tumor samples of patients that reponded well to gefitinib. All of the mutations were either within the ATP binding cleft of the EGFR or positioned such that their deletion would alter the conformation of the binding domain (10, 5). I will discuss the findings of the Lynch group (5) in greater detail, an hypothesis for the increased sensitivity to gefitinib in patients with specific mutations in the EGFR (5) and the results of a Phase III survival study comparing gefitinib plus Best Supportive Care to placebo plus Best Supportive Care for patients with advanced NSCLC who had received one or two prior chemotherapy regiments and were refractory or intolerant to their most recent regiment (11).
II. Activating Mutations in EGFR and Responsiveness of NSCLC to Gefitinib; study by Lynch et al.
Of 275 patients that were treated with gefitinib since 2000 at the Massachusetts General Hospital in Boston, Massachusetts, 25 patients had a significant clinical response to the drug (5). In practice this was a partial response as defined by the response evaluation criteria in solid tumors (12). Tumor specimens procured at the time of diagnosis were available for 9 of these patients (5). Characteristics of these patients are summarized in Table 1. Among these 9 patients, the median survival after beginning drug treatment exceeded 18 months. As was previously reported, Lynch et al. found that most of the patients that responded well to gefitinib were women, had never smoked and had been diagnosed with adenocarcinoma (8,9 and Table 1). The dramatic response to gefitinib by Patient 6 was representative of the group. After 6 weeks of 250mg of gefitinib per day, he showed marked regression of the mass in his right lung (Figure 1A and 1B).
Lynch and colleagues hypothesized that the patients who responded well to gefitinib had acquired somatic mutations in the EGFR. Because rearrangements in the extracellular domain of the EGFR are common in gliomas (13), they first examined this domain for rearrangements. When none were found they sequenced the entire EGFR gene for mutations. Heterozygous mutations of the EGFR were found in eight of the nine patients. These were all clustered within the catalytic kinase domain of the EGFR (Table 2 and Figure 2).
Since the frequency of EGFR mutation in NSCLC had not been investigated, Lynch et al., sequenced the EGFR in tumors from 25 additional patients with NSCLC that had not participated in the gefitinib study. Of these, two patients with adenocarcinoma carried heterozygous mutations in the kinase domain identical to those found in patients that had responded well to gefitinib (Table 2). With increasing evidence of mutations clustering within the catalytic kinase domain, the group sequenced exons 19 and 21 of the EGFR in 95 primary tumors and 108 cancer-derived cell lines of various tumor types (Supplementary Appendix). They found no additional mutations and hypothesized that this was an indication that only cancers in which EGFR plays a critical role in tumorigenesis would carry EGFR mutations.
To investigate the functional properties of the identified mutations, Lynch and colleagues created mutant constructs of the EGFR identical to the L747-P753insS deletion and the L858R missense mutation. They transiently transfected these and wt EGFR into Cos-7 cells. Neither wt nor the mutant EGFR was autophosphorylated in the absence of serum or growth factors (Figures 3A and 3B). However, when EGF was added the mutant receptors displayed two to three times the level of activation as the wt receptor and remained activated up to twelve times longer than the wt (Figure 3A).
Since gefitinib targets the ATP binding cleft of EGFR and seven of the eight mutations were found to reside near the cleft, the group set out to examine if these mutant proteins had an altered sensitivity to gefitinib. Wt and mutant EGFR-transfected Cos-7 cells were treated with increasing doses of gefitinib. Activation of both mutant receptors was inhibited by 50% with doses 10-fold lower than that required for the wt receptor , indicating an increased sensitivity of the mutant receptors to gefitinib (Figures 3C and 3D).
Lynch et al., identified mutations in the EGFR of a small subgroup of NSCLC that correlate with a dramatic response to gefitinib (5). They suggest that due to the heterozygous nature of these mutations, they likely exert a dominant effect on the gene. In addition, the mutations cluster near the catalytic kinase domain where both ATP and compounds such as gefitinib bind (Figure 4). They propose that these mutations alter the position of critical residues in and near the binding cleft, thereby stablizing their interactions with ATP or gefitinib, explaining the increased EGFR activation after ligand binding and increased sensitivity of the mutants to gefitinib (5).
III. Clinical Implications for Patients with Activating EGFR Mutations
The correlation between response to gefitinib and specific activating mutations in the EGFR elucidated by the Paez (10) and Lynch (5) groups in a subgroup of NSCLC patients suggests that these mutations may serve as predictors for the reponsiveness to gefitinib, and may be useful in identifying patients likely to benefit from gefitinib therapy.
IV. Phase III Survival Study in NSCLC Patients: Gefitinib vs. Placebo
The FDA approved the use of gefitinib in May of 2003, under the accelerated approval program for the treatment of patients with NSCLC who had failed two or more courses of chemotherapy (3). Gefitinib was approved because two clinical trials showed that it precipitated tumor shrinkage in about 10% of patients, and this was thought likely to increase a patient's overall survival (11). One of the requirements for gefitinib's approval under the FDA's accelerated approval program is that the sponsor, (AstraZeneca, in this case), must study the drug further to verify the expected benefit (11). In accordance with this requirement, AstraZeneca enrolled 1692 NSCLC patients in the Iressa Survival in Lung Cancer (ISEL) study to determine if gefitinib would prolong survival as compared to a placebo (14). On December 17, 2004, results from the primary endpoint in the study showed that although there was a significant improvement in tumor shrinkage, this did not correspond to prolonged survival in patients using gefitinib (14). AstraZeneca has suspended the promotion of gefitinib for NSCLC while these trial data are further analyzed (15).
V. References
1. Jemel, A., Tiwari, R.C., Murray, T., Ghafoor,
A., Samuels, A., Ward, E., Feurer, E., Thun, M., 2004. Cancer Statistics,
2004. CA Cancer J. Clin. 54(1): 8-29.
2. Minna, J., Gazdar, A.F., Sprang, S.R., Hertz, J., 2004. A bull's eye for targeted lung cancer therapy. Science, 304: 1458-1461.
3. Cohen, M.H., Williams, G.A., Sridhara, R., Chen, G., Pazdur, R., 2003.
FDA drug approval summary: Gefitinib (ZD 1839) (Iressa) Tablets. Oncologist, 8: 303-306.
4. Gordon, J.A., 2003. FDA approves Iressa for the treatment of advanced lung cancer. The Doctor's Lounge.net, Monday May 19, 2003.
5. Lynch, T.J., Bell, D.W., Sordella, R., Gurubhagavatula, S., Okimoto,
R., Brannigan, B.W., Harris, P.L., Haserlat, S.M., Supko, J.G., Haluska,
F.G., Louis, D.N., Christiani, D.C., Settleman, J., Haber, D.A., 2004. Activating
mutations in the epidermal growth factor receptor underlying responsiveness
of non-small-cell lung cancer to gefitinib. N. Engl. J. Med., 350(21): 2129-2139.
6. Arteaga, C.L., 2003. ErbB-targeted therapeutic approaches in human cancer. Exp Cell Res, 284: 122-30.
7. Fukuoka, M., Yano, S., Giaccone, G., Tamura, T., Nakagawa, K., Douillard,
J., Nishiwaki, Y., Vansteenkiste, J., Kudoh, S., Rischin, D., Eek, R., Horai,
T., Noda, K., Takata, I., Smit, E., Averbuch, S., Macleod, A., Feyereislova,
A., Dong, R., Baselga, J., 2003. Multi-institutional randomized phase II
trial of gefitinib for previously treated patients with advanced non-small-cell
lung cancer. J. Clin. Oncol., 21: 2237-2246.
8. Kris, M.G., Natale, R.B., Herbst, R.S., Lynch, T.J., Prager, D., Belani,
C.P., Schiller, J.H., Kelly, K., Spiridonidis, H., Sandler, A., Albain,
K.S., Cella, D., Wolf, M.K., Averbuch, S.D., Ochs, J.J., Kay, A.C., 2003.
Efficacy of gefitinib, an inhibitor of the epidermal growth factor receptor
tyrosine kinase, in symptomatic patients with non-small cell lung cancer
: a randomized trial. JAMA, 290(16):2149-2158.
9. J”nne, P.A., Gurubhagavatula, S., Yeap, B.Y., Lucca, J., Ostler, P.,
Skarin, A.T., Fidias, P., Lynch,T.J., Johnson, B.E., 2004. Outcomes of patients
with advanced non-small cell lung cancer treated with gefitinib (ZD1839,
'Iressa') on an expanded access study. Lung Cancer, 44(2): 221-230.
10. Paez, J.G., J”nne, P.A., Lee, J.C., Tracy, S., Greulich, H., Gabriel,
S., Herman, P., Kaye, F.J., Kindeman, N., Boggon, T.J., Naoki, K., Sasaki,
H., Fujii, Y., Eck, M.J., Sellers, W.R., Johnson, B.E., Meyerson, M., 2004.
EGFR mutations in lung cancer: correlation with clinical response to gefitinib
therapy. Science, 304, 1497-1500.
11. FDA, 2004. FDA statement on Iressa. FDA.gov, December 17, 2004.
12. Therasse, P., Arbuck, S.G., Eisenhauer, E.A., Wanders, J., Kaplan,
R.S., Rubinstein, L., Verweij, J., Van Glabbeke, M., van Oosterom, A.T.,
Christian, M.C., Gwyther, S.G., 2000. New guidelines to evaluate the response
to treatment in solid tumors. J Natl Cancer Inst, 92: 205-216.
13. Frederick, L., Wang, X-Y., Eley, G., James, C.D., 2000. Diversity
and frequency of epidermal growth factor receptor mutations in human glioblastomas.
Cancer Res, 60: 1383-1387.
14. AstraZeneca, 2004. Gefitinib (Iressa) lung cancer trial shows no overall
survival advantage in a highly refractory population. Astrazeneca.com, December 17, 2004.
15. AstraZeneca, 2004. Doctor letter regarding Iressa (gefitinib) ISEL data. Astrazeneca.com., December 17, 2004.
Presented by Paula Knittle (Kuzontkoski de Fernandez) (Paula.M.Knittle @ dartmouth.edu)
