Inhibition of the T790M Gatekeeper Mutant of the Epidermal Growth Factor Receptor by EXEL-7647

Abstract

Purpose: Agents inhibiting the epidermal growth factor receptor (EGFR) have shown clinical benefit in a subset of non^small cell lung cancer patients expressing amplified or mutationally activated EGFR. However, responsive patients can relapse as a result of selection for EGFR gene mutations that confer resistance to ATP competitive EGFR inhibitors, such as erlotinib and gefitinib.We describe here the activity of EXEL-7647 (XL647), a novel spectrum-selective kinase inhibitor with potent activity against the EGF and vascular endothelial growth factor receptor tyrosine kinase families, against both wild-type (WT) and mutant EGFR in vitro and in vivo. Experimental Design: The activity of EGFR inhibitors against WTand mutant EGFRs and their effect on downstream signal transduction was examined in cellular assays and in vivo using A431 and MDA-MB-231 (WT EGFR) and H1975 (L858R andT790M mutant EGFR) xenograft tumors.Results: EXEL-7647 shows potent and long-lived inhibition of the WT EGFR in vivo. In addition, EXEL-7647 inhibits cellular proliferation and EGFR pathway activation in the erlotinib-resistant H1975 cell line that harbors a double mutation (L858R and T790M) in the EGFR gene. In vivo efficacy studies show that EXEL-7647 substantially inhibited the growth of H1975 xenograft tumors and reduced both tumor EGFR signaling and tumor vessel density. Additionally, EXEL-7647, in contrast to erlotinib, substantially inhibited the growth and vascularization of MDA-MB-231 xenografts, a model which is more reliant on signaling through vascular endothelial growth factor receptors. Conclusions: These studies provide a preclinical basis for clinical trials of XL647 in solid tumors and in patients bearing tumors that are resistant to existing EGFR-targeted therapies.

EXEL-7647 Inhibits Mutant Forms of ErbB2 Associated with Lapatinib Resistance and Neoplastic Transformation

“…ErbB2 T798I and EGFR T790M mutations have comparable levels of resistance to lapatinib and provide evidence that ErbB2 T798I may have clinical relevance for lapatinib resistance. EXEL-7647 was shown previously to inhibit the EGFR T790M variant (23): in the present study, we also show that ErbB2 T798I is susceptible to inhibition by EXEL-7647.…”

“…Similarly, defined resistance-associated mutation profiles are emerging in gastrointestinal stromal tumors following clinical treatment with imatinib and sunitinib (9,21,22). Several small-molecule EGFR-targeted drugs are emerging that inhibit the EGFR T790M mutation associated with resistance to erlotinib and gefitinib in non -small cell lung cancer, including EXEL-7647 (23), , and the irreversible inhibitor HKI-272 (25).…”

Inhibition of N-Linked Glycosylation Disrupts Receptor Tyrosine Kinase Signaling in Tumor Cells

“…This has confirmed the concept that inhibition of multiple RTKs may be of therapeutic benefit (28)(29)(30). In an effort to test this concept, we have undertaken a new strategy to disrupt the posttranslational machinery (i.e., N-linked glycosylation) to decrease the protein level and activity of a broad range of cell surface receptors.…”

Characterization of the Activity of the PI3K/mTOR Inhibitor XL765 (SAR245409) in Tumor Models with Diverse Genetic Alterations Affecting the PI3K Pathway

“…Kinase activity for PI3K isoforms was measured as the percentage of ATP consumed following the kinase reaction using luciferase-luciferin-coupled chemiluminescence as previously described (25), with ATP concentrations approximately equal to the K m for each respective kinase. Kinase reactions were initiated by combining test compounds, ATP and kinase in a 20 mL volume.…”

“…Tumors were collected at the indicated time points and tumor lysates were prepared as previously described (25). Pooled lysates were analyzed by Western immunoblotting.…”