Irreversible pyrimidine based EGFR inhibitors, including WZ4002, selectively inhibit both EGFR activating and EGFR inhibitor resistant T790M mutations more potently than wild type EGFR. While this class of mutant selective EGFR inhibitors is effective clinically in lung cancer patients harboring EGFR T790M, prior preclinical studies demonstrate that acquired resistance can occur through genomic alterations that activate ERK1/2 signaling. Here we find that ERK1/2 reactivation occurs rapidly following WZ4002 treatment. Concomitant inhibition of ERK1/2 by the MEK inhibitor trametinib prevents ERK1/2 reactivation, enhances WZ4002 induced apoptosis and inhibits the emergence of resistance in WZ4002 sensitive models known to acquire resistance via both T790M dependent and independent mechanisms. Resistance to WZ4002 in combination with trametinib eventually emerges due to AKT/mTOR reactivation. These data suggest that initial co-targeting of EGFR and MEK could significantly impede the development of acquired resistance in mutant EGFR lung cancer.

The discovery of oncogenic driver mutations and the subsequent developments in targeted therapies have led to improved outcomes for subsets of lung cancer patients. The identification of additional oncogenic and drug-sensitive alterations may similarly lead to new therapeutic approaches for lung cancer. We identify and characterize novel FGFR2 extracellular domain insertion mutations and demonstrate that they are both oncogenic and sensitive to inhibition by FGFR kinase inhibitors. We demonstrate that the mechanism of FGFR2 activation and subsequent transformation is mediated by ligand-independent dimerization and activation of FGFR2 kinase activity. Both FGFR2-mutant forms are predominantly located in the endoplasmic reticulum and Golgi but nevertheless can activate downstream signaling pathways through their interactions with fibroblast growth factor receptor substrate 2 (FRS2). Our findings provide a rationale for therapeutically targeting this unique subset of FGFR2-mutant cancers as well as insight into their oncogenic mechanisms. Cancer Res; 75(15); 3139-46. Ó2015 AACR.

MEKK1 is a mitogen-activated protein kinase kinase kinase (MAP3K) that activates the MAPK JNK and is required for microtubule inhibitor-induced apoptosis in B cells. Here, we find that apoptosis induced by actin disruption via cytochalasin D and by the protein phosphatase 1/2A inhibitor okadaic acid also requires MEKK1 activation. To elucidate the functional requirements for activation of the MEKK1-dependent apoptotic pathway, we created mutations within MEKK1. MEKK1-deficient cells were complemented with MEKK1 containing mutations in either the ubiquitin interacting motif (UIM), plant homeodomain (PHD), caspase cleavage site or the kinase domain at near endogenous levels of expression and tested for their sensitivity to each drug. We found that both the kinase activity and the PHD domain of MEKK1 are required for JNK activation and efficient induction of apoptosis by drugs causing cytoskeletal disruption. Furthermore, we discovered that modification of MEKK1 and its localization depends on the integrity of the PHD.

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Background: EGFR kinase inhibitors, including erlotinib, are effective treatments for patients with EGFR mutant lung cancer. However, resistance inevitably develops, most commonly (60%) mediated by an EGFR secondary mutation EGFR T790M. Mutant selective EGFR inhibitors (WZ4002, AZD9291, CO-1686) are effective in preclinical models and clinically (AZD9291 & CO-1686) in EGFR T790M patients (response rates (RR) > 50%) but are less effective in patients with non-T790M mediated drug resistance (AZD9291 RR ∼10%). Combination of afatinib and cetuximab is effective in both T790M (32% RR) and non-T790M (25% RR) mediated resistance but is associated with significant toxicity. We evaluated whether cetuximab could add to the efficacy of a mutant selective EGFR inhibitor and whether the combination was also effective in a model of non-T790M mediated resistance. Methods: Mice harboring xenografts from PC9GR (EGFR Del 19/T790M), H1975 (EGFR L858R/T790M), HCC827GR (EGFR Del 19/MET amplification) cells or genetically engineered mouse models (GEMMS) expressing EGFR L858R/T790M were treated with vehicle, WZ4002 alone, cetuximab alone or the combination. We compared the efficacy of the treatments and evaluated for tumor cures (defined as tumor disappearance and lack of regrowth following 6 weeks of drug withdrawal). In addition, we evaluated the impact of the treatments on EGFR signaling and apoptosis. Results: In the EGFR T790M xenograft models (PC9GR and H1975), the combination of WZ4002 and cetuximab was more effective than either single agent. Only the combination led to tumor cures (5/15 in PC9GR and 3/18 in H1975) while none were observed with the single agents. In the HCC827GR xenografts, the combination of WZ4002/cetuximab was more effective than the single agents but did not lead to any cures. Evaluation of the tumors from treated mice revealed that the efficacy of the combination correlates with effective degradation of EGFR and MET (in HCC827GR). In the L858R/T790M GEMMs, the combination led to significantly greater tumor shrinkage compared to single agents. Evaluation of treated tumors revealed enhanced apoptosis in the combination treated mice. Conclusions: The addition of cetuximab enhances the efficacy of the mutant selective EGFR inhibitor WZ4002 in vivo by increasing the single agent efficacy in both EGFR T790M and non-T790M models. Clinical trials of mutant selective EGFR inhibitors and cetuximab are warranted. Citation Format: Erin M. Tricker, Chunxiao Xu, Kwok-Kin Wong, Pasi A. Janne. Efficacy of cetuximab and mutant selective EGFR inhibitor WZ4002 in EGFR T790M and non-T790M models of erlotinib resistant non-small cell lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2595. doi:10.1158/1538-7445.AM2015-2595