To date, essentially all mutational combinations involving L858R studied thus far were found to exist in-cis, suggesting potentialcismutation-to-mutation cooperation in EGFR signaling and possibly tumorigenesis (Tamet al., 2006). proliferation, and differentially alter sensitivity of EGFR phosphorylation inhibition by ERBB family inhibitors in an inhibitor-specific fashion. Mutations of the conserved ion pair E884-R958 may result in conformational changes that alter kinase substrate recognition. The analogous E1271K-MET mutation conferred differential sensitivity towards preclinical MET inhibitors SU11274 (unchanged), and PHA665752 (more sensitive). Systematic bioinformatics analysis of the mutation catalog in the human kinome (COSMIC) revealed the presence of cancer-associated mutations involving the conserved E884 homologous residue, and adjacent residues at the ion pair, in known proto-oncogenes (KIT, RET, MET, FAK) and tumor suppressor gene (LKB1). Targeted therapy using small molecule inhibitors should take into account potential cooperative effects of multiple kinase mutations, and their specific effects on downstream signaling and inhibitor sensitivity. Improved efficacy of targeted kinase inhibitors may be achieved by targeting the dominant activating mutations present. Keywords:EGFR, MET, mutation, tyrosine kinase inhibitor, sensitivity, resistance, structure, kinome == Introduction == Targeted therapy using epidermal growth factor receptor (EGFR) kinase inhibitors represents a major therapeutic advance in Lactose lung cancer treatment. Somatic mutations of the EGFR gene, most commonly L858R (exon 21) and short in-frame deletions in exon 19, have recently been identified as catalytic domain Lactose name mutation hotspots (Shigematsuet al., 2006). These mutations confer enhanced sensitivity towards the anilinoquinazoline kinase inhibitors gefitinib and erlotinib (Lynchet al., 2004;Paezet al., 2004). A mutation conferring resistance to these two kinase inhibitors, T790M (exon 20), has also been found in the EGFR kinase domain name and can take into account about half of the cases of acquired resistance (Kobayashiet al., 2005). There are a number of other kinase domain name mutations of EGFR that Lactose occur at lower frequencies, most often in combination with L858R (Tamet al., 2006). However, how these mutations might interact when present together in-cisis unknown. We recently identified a novel EGFR kinase domain name somatic mutation, E884K (Glu884Lys, exon 22) in a patient with stage IV non-small-cell lung cancer Lactose (NSCLC), in combination with the L858R mutation (L858R+E884K) (Choonget al., 2006). The patient initially received carboplatin/paclitaxel and erlotinib and then developed brain metastasis on maintenance erlotinib. In spite of further treatment with whole brain radiation, temozolomide, and irinotecan, the patient’s disease progressed to symptomatic leptomeningeal carcinomatosis, which responded to gefitinib, a year after being off an EGFR kinase inhibitor. The L858R+E884K double mutation was found both in her pretreatment diagnostic thoracic lymph node biopsy specimen as well as the tumor cells (extracted by laser microdissection) within the cerebrospinal fluid during the course of leptomeningeal metastases (Choonget al., 2006). The E884K mutation represents the first mutation reported to show an apparent differential response to the two EGFR kinase inhibitors erlotinib and gefitinib, while L858R was known to be sensitizing to both. These findings led to our hypothesis that EGFR kinase mutations can work in concert to differentially alter inhibitor sensitivity and downstream signaling. Further biochemical analysis in our current study indicates that this double mutant EGFR (L858R+E884K) responds differently to gefitinib and erlotinib. We now show that E884K works in concert with L858R, and in a dominant fashion, to mediate differential sensitivity to kinase inhibitors via altered phosphorylation of AKT and STAT3 and were correlated with differential cellular cytotoxicity and induction of the apoptotic marker cleaved-PARP(Asp214) by EGFR Rabbit polyclonal to PCMTD1 Lactose inhibitors. Using a combination of bioinformatics and structural analyses, we further characterized.
