Novel mutant-selective EGFR kinase inhibitors against EGFR T790M

Abstract

The clinical efficacy of epidermal growth factor receptor (EGFR) kinase inhibitors in EGFR-mutant non-small-cell lung cancer (NSCLC) is limited by the development of drug-resistance mutations, including the gatekeeper T790M mutation. Strategies targeting EGFR T790M with irreversible inhibitors have had limited success and are associated with toxicity due to concurrent inhibition of wild-type EGFR. All current EGFR inhibitors possess a structurally related quinazoline-based core scaffold and were identified as ATP-competitive inhibitors of wild-type EGFR. Here we identify a covalent pyrimidine EGFR inhibitor by screening an irreversible kinase inhibitor library specifically against EGFR T790M. These agents are 30- to 100-fold more potent against EGFR T790M, and up to 100-fold less potent against wild-type EGFR, than quinazoline-based EGFR inhibitors in vitro. They are also effective in murine models of lung cancer driven by EGFR T790M. Co-crystallization studies reveal a structural basis for the increased potency and mutant selectivity of these agents. These mutant-selective irreversible EGFR kinase inhibitors may be clinically more effective and better tolerated than quinazoline-based inhibitors. Our findings demonstrate that functional pharmacological screens against clinically important mutant kinases represent a powerful strategy to identify new classes of mutant-selective kinase inhibitors.

Figure 1. WZ4002, WZ3146 and WZ8040 are novel EGFR inhibitors, suppress the growth of EGFR T790M containing cell lines and inhibit EGFR phosphorylation

A. Chemical structures of the WZ compounds. B. IC₅₀ values (nM) for NSCLC cell lines (top) and Ba/F3 (bottom) cells, with genotypes corresponding to the NSCLC cell lines, treated with indicated drugs. Growth was assessed using the MTS survival assay. C. Comparison of WZ3146, WZ4002 and CL-387,785 on EGFR signaling in PC9 GR cells. The cells were treated with the indicated concentrations of each drug for 16 hours. Cell extracts were immunoblotted to detect the indicated proteins. D. Comparison of EGFR inhibitors on EGFR phosphorylation in 3T3 cells expressing del E746_A750/T90M. The cells were treated with indicated concentrations of each drug for 16 hours and stimulated with EGF (10 ng/ml) 15 minutes prior to lysis. Cell extracts were immunoblotted to detect the indicated proteins.

Figure 2. WZ4002 is less potent than quinazoline EGFR inhibitors against wild type EGFR in vitro and in vivo

A. EGFR vIII Ba/F3 cells treated with WZ or quinazoline EGFR inhibitors. The mean (n=6) and standard deviation is plotted for each drug and concentration. B. Comparison of EGFR inhibitors on EGFR phosphorylation in 3T3 cells expressing wild type EGFR. The cells were treated with indicated concentrations of each drug for 16 hours and stimulated with EGF (10 ng/ml) 15 minutes prior to lysis. Cell extracts were immunoblotted to detect the indicated proteins. C. Immunohistochemical analysis of skin from erlotinib or WZ4002 treated mice using EGFR and pY1173 EGFR. Only erlotinib treatment results in significant inhibition of EGFR phosphorylation. Scale bar, 50 μm. D. Quantification of frequency of phospho-EGFR staining from vehicle (n=3), erlotinib (n=3) and WZ4002 (n=2) treated mice. The mean and standard deviations are plotted for drug treatment.

Figure 3. Crystal Structure of WZ4002 bound to EGFR T790M

A. Chemical structures of WZ8040 and WZ4002 are shown schematically in a manner resembling the conformation adopted in complex with the kinase. B. Crystal structure of WZ4002 in complex with EGFR T790M mutant (PDB ID 3IKA). WZ4002 binds the active conformation of the kinase, with the both the regulatory C-helix and “DFG” segment of the activation loop in their inward, active positions. The EGFR kinase is shown in a ribbon representation (blue) with the bound inhibitor in yellow. Sidechain and mainchain atoms are shown for selected residues that contact the compound. Expected hydrogen bonds to the backbone amide and carbonyl atoms of Met 793 are indicated by dashed lines. Note also the covalent bond with Cys797. The structure was refined to a crystallographic R value of 21.3% (R_free=25.4%) with data extending to 2.9Å resolution (see methods for further crystallographic details).

Figure 4. WZ4002 inhibits EGFR phosphorylation and induces significant tumor regression in murine models of EGFR T790M

A. Two doses separated by 16 hours of WZ4002 (2.5 mg/kg or 25 mg/kg) or vehicle were administered to EGFR delE746_A750/T790M or L858R/T790M mice with MRI confirmed tumors. The mice were sacrificed, the lungs isolated and grossly dissected and subjected to cell lysis. Cell extracts were immunoblotted to detect the indicated proteins. B. Immunohistochemical analyses of tumors from EGFR delE746_A750/T790M mice from A. using indicated antibodies. Scale bar, 50 μm. C. Quantification of TUNEL and Ki67 positive cells from tumor nodules (n=4) from vehicle and WZ4002 treated mice. The mean and standard deviation are plotted. D. MRI images of vehicle or WZ4002 treated mice at baseline (0w) and following 2 weeks (2w) of treatment. E. Quantification of the relative tumor volume from MRI images from vehicle treated mice (E746_A750/T790M (n=3); L858R/T790M (n = 4)), and WZ4002 treated L858R/T790M (n=3) and E746_A750/T790M (n=3) mice. The mean and standard deviation are plotted. F. Tumors from vehicle and WZ4002 treated mice stained with hematoxylin and eosin. Low power view (inset) demonstrates near complete resolution of tumors in the WZ4002 treated mice. Scale bar, 100 μm.