KRAS Mutant Non-small Cell Lung Cancer Cell Lines Research Articles

Palbociclib resistance confers dependence on an FGFR-MAP kinase-mTOR-driven pathway in KRAS-mutant non-small cell lung cancer.

CDK4 is emerging as a target in KRAS-mutant non-small cell lung cancer (NSCLC). We demonstrate that KRAS-mutant NSCLC cell lines are initially sensitive to the CDK4/6 inhibitor palbociclib, but readily acquire resistance associated with increased expression of CDK6, D-type cyclins and cyclin E. Resistant cells also demonstrated increased ERK1/2 activity and sensitivity to MEK and ERK inhibitors. Moreover, MEK inhibition reduced the expression and activity of cell cycle proteins mediating palbociclib resistance. In resistant cells, ERK activated mTOR, driven in part by upstream FGFR1 signaling resulting from the extracellular secretion of FGF ligands. A genetically-engineered mouse model of KRAS-mutant NSCLC initially sensitive to palbociclib similarly developed acquired resistance with increased expression of cell cycle mediators, ERK1/2 and FGFR1. In this model, resistance was delayed with combined palbociclib and MEK inhibitor treatment. These findings implicate an FGFR1–MAP kinase–mTOR pathway resulting in increased expression of D-cyclins and CDK6 that confers palbociclib resistance and indicate that CDK4/6 inhibition acts to promote MAP kinase dependence.

Abstract 5918: A novel glutathione S-transferase P (GSTP) siRNA (NDT-05-1040) for the treatment of KRAS-driven non-small cell lung cancer

Abstract Lung cancer is the most common form of cancer worldwide and the leading cause of cancer-related deaths. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancers, and KRAS mutation occurs in 25-30% of NSCLC. However, to date, direct therapeutic targeting of KRAS has not been achieved. Our approach to developing a KRAS mutant NSCLC therapeutic agent was to identify a selective novel target involved in modulating signaling proteins in the RAS pathway without impacting healthy cells. Numerous studies have shown that glutathione S-transferase P (GSTP) is strongly upregulated in many cancer types, specifically lung, colon, and pancreas. Besides being a well-known Phase II detoxification enzyme, GSTP is also known to influence cell signaling through interaction with MAP kinases such as JNK and c-jun. We therefore hypothesized that GSTP knockdown (KD) could be an effective therapeutic approach to treat KRAS mutant tumors. To test this hypothesis, we designed a series of novel GSTP siRNAs and identified our lead candidate, a highly potent and selective GSTP siRNA (NDT-05-1040) to specifically target and downregulate GSTP protein. A panel of KRAS mutant NSCLC cell lines was utilized to determine the GSTP KD potency and antiproliferative activity of NDT-05-1040. Western blot analysis and co-immunoprecipitation (co-IP) were conducted to identify the proteins that were regulated by GSTP in the proliferation and apoptosis pathways. These studies demonstrated that NDT-05-1040 is a very potent and selective GSTP siRNA. Furthermore, transfection of NDT-05-1040 led to significant growth inhibition and induced apoptosis in NSCLC cells without affecting normal cell viability. Western blot analysis showed that NDT-05-1040 effectively decreased the phosphorylation of CRAF, ERK, MEK, in the MAP kinase pathway. Interestingly, with NDT-05-1040 treatment, the phosphorylation of Akt and mTOR in the PI3K pathway was also decreased. Moreover, the activity of p-JNK, PUMA, caspase-3/7, and p53 in the KRAS mutant cells was upregulated by NDT-05-1040. Co-IP experiments demonstrated that GSTP formed a complex with both p-CRAF and JNK. In summary, GSTP KD by NDT-05-1040 targeted the RAS/MEK/ERK, Akt, mTOR and apoptosis pathways. This selective multipronged attack on the growth and survival pathways of cancer cells makes it a compelling target and could potentially serve as a novel therapeutic agent for KRAS mutant NSCLC. Citation Format: Cima Cina, Jens Harborth, Zhihong O'Brien, Nish Beltran-Raygoza, Jung-kang Jin, Jessica Xu, Sang Jun Lee, Kwok Tsang, Jiping Yao, Roger Adami, Sonya Zabludoff, Wenbin Ying. A novel glutathione S-transferase P (GSTP) siRNA (NDT-05-1040) for the treatment of KRAS-driven non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5918.

Abstract SY19-02: Novel mechanisms of acquired resistance to selective CDK4/6 inhibition

Abstract CDK4/6 inhibition is now part of the standard armamentarium for patients with estrogen receptor (ER)-positive breast cancer, so that understanding mechanisms of resistance is a pressing issue. We have identified identified increased CDK6 expression as a key determinant of acquired resistance after exposure to palbociclib in ER-positive breast cancer cells. Increased CDK6 in resistant cells is dependent on TGF-β pathway suppression via miR-432-5p expression. Exosomal miR-432-5p expression mediated transfer of the resistance phenotype between neighboring cell populations, causing previously sensitive cells to acquire CDK4/6 inhibitor resistance. We confirmed these data in pretreatment and postprogression biopsies from a parotid cancer patient who had responded to ribociclib, demonstrating that this resistance mechanism is clinically relevant. Additionally, this CDK4/6 inhibitor resistance phenotype can be reversed in vitro and in vivo by a prolonged drug holiday, which restored drug sensitivity. CDK4 is also emerging as a target in KRAS-mutant non-small cell lung cancer (NSCLC). We have demonstrated that KRAS-mutant NSCLC cell lines are initially sensitive to palbociclib, but readily acquire resistance associated with increased expression of CDK6, D-cyclins, and cyclin E. Resistant cells also demonstrated increased ERK1/2 activity and sensitivity to MEK and ERK inhibitors. Moreover, MEK inhibition reduced the expression and activity of cell cycle proteins mediating palbociclib resistance. In resistant cells, ERK activated mTOR, driven in part by upstream FGFR1 signaling resulting from the extracellular secretion of FGF ligands. A genetically engineered mouse model of KRAS-mutant NSCLC initially sensitive to palbociclib similarly developed acquired resistance with increased expression of cell cycle mediators, ERK1/2 and FGFR1. In this model, resistance was delayed with combined palbociclib and MEK inhibitor treatment. These findings implicate an FGFR1-MAP kinase-mTOR pathway resulting in increased expression of D-cyclins and CDK6 that confers palbociclib resistance, and indicate that CDK4/6 inhibition acts to promote MAP kinase dependence. Citation Format: Geoffrey I. Shapiro. Novel mechanisms of acquired resistance to selective CDK4/6 inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr SY19-02.

Abstract 2254: Dynamic network topologies analysis in proteomics data of NSCLC cell lines using a new pipeline based on machine learning tools

Abstract Background: Non-small cell lung cancer (NSCLC) is the most common subtype of lung cancer, characterizing ~80% of lung cancer diagnoses. Thus, the development of novel therapies for NSCLC is of primary importance in oncology. The aim of this study was to develop a novel cancer systems biology approach to understand the complex interactions in NSCLC and predict the response to target treatments. We combined proteomic experimental data with a machine learning tool to discover the diverse signaling networks of both KRAS mutant (MUT) and wild-type (WT) NSCLC cell lines (CL). Material and Methods: Eight NSCLC CL (5 KRAS MUT and 3 KRAS WT) were subjected to reverse phase protein microarray (RPPA) to explore the activation level of 183 proteins treated with selumetinib (SE) and its combination with everolimus (EV) or tamoxifen (TA). Measures were taken at 6 time points: 5 minutes (min), 1, 2 , 6 and 24 hours (h). RPPA was performed also on the baseline and on CL with only dimethyl sulfoxide. Recursive Feature Elimination with Support Vector Machine (RFE-SVM) was used to identify the subset of proteins/features that optimally separated samples in 2 groups. In order to build the interaction network from this subset and browse the main pathways involved, we used Reactome FI and the Pathway Enrichment tool, two Cytoscape plugins for network-based data analysis. Results: We applied RFE-SVM to discover the most divergent proteins between control and treated samples in the whole CL panel. For all the 3 drug combinations, the network in output contained not only the target of the corresponding drug, but also showed the activation of other parallel pathways. The analysis revealed also that all drugs were mainly effective in a short time, since the number of significant proteins was considerably higher at 5 min and 1 h. For instance, SE treatment activated NGFR, mTOR, PI3K-Akt and proteoglycans pathways in addition to the MAPK pathway. Network at 1 h contained 25 proteins linked by 76 interactions, while at 6 and 24 h the distinctive subsets of features included only 2 and 4 proteins. Then, we applied RFE-SVM to analyze KRAS MUT vs WT CLs. The algorithm showed that treated KRAS MUT CL had a more complex signaling network than the WT ones. Indeed, in SE WT samples MER and ERK were the main relevant proteins to distinguish from the control. In treated KRAS MUT samples, a complex network of 70 proteins and 278 interactions was active during the first hour. Conclusion: The proposed framework processes high-throughput data and identifies new possible molecular targets in cancer research. This approach is highly flexible for a multitude of data and purposes. We applied it to a RPPA dataset of NSCLC CL and it revealed that all drug combinations had fast dynamics and that KRAS MUT CL had a more complicated response due to a higher number of active pathways. Citation Format: Chiara Antonini, Lorenzo Tomassoni, Elisa Baldelli, Vienna Ludovini, Sara Baglivo, Mariaelena Pierobon, Emanuel F Petricoin, Lucio Crinò, Paolo Valigi, Fortunato Bianconi. Dynamic network topologies analysis in proteomics data of NSCLC cell lines using a new pipeline based on machine learning tools [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2254.

Abstract 4362: Identification of novel combinatorial synthetic lethal vulnerabilities in KRAS-driven lung cancer

Abstract Lung cancer is the number one cause of cancer-related deaths worldwide. The most prevalent type of lung cancer is Non-Small Cell Lung Cancer (NSCLC). A significant number of patients with NSCLC carry oncogenic KRAS mutations. However, the efforts to target KRAS directly have thus far proven unsuccessful and tumors harboring mutations in this gene remain the most difficult to treat, highlighting the need for alternative approaches. One promising strategy is to target KRAS-dependent cancers through synthetic lethality. However, KRAS activates multiple effector pathways, suggesting that targeting one gene may not be sufficient to fully inhibit KRAS oncogenesis. Therefore, we propose that targeting combinations of genes that together are synthetic lethal with KRAS may constitute a better therapeutic strategy. Furthermore, we hypothesize that a targeted approach focused on the protein-protein interaction network proximal to KRAS may be more effective than the current emphasis on genome-wide screens. To discover novel, combinatorial KRAS synthetic lethal genes, we used affinity purification/mass spectrometry (AP/MS), to systematically identify KRAS interacting proteins and construct a detailed map of protein-protein interactions centered on KRAS. Based on this network we designed a CRISPR/Cas9 library targeting pairwise combinations of KRAS-interacting genes. Using this library we simultaneously knocked-out pairs of 119 genes in two KRAS-driven non-small cell lung cancer (NSCLC) cell lines (A549 and H23). Knock-out of many gene pairs synergistically impaired growth of these cells, while the knock-out of each of the genes alone had no or little effect. We chose 20 most promising targets for further screening in vitro and in vivo in a panel of 9 KRAS-mutant and KRAS wild type Cas9-expressing NSCLC cell lines. We also selected six gene pairs that had the most synergistic effect on growth in A549 and H23 cells for individual validation in Cas9-expressing NSCLC cell lines and normal human bronchial epithelial cells (HBECs). We found that the simultaneous knock-out of one pair of genes, Rap1GDS1 and RhoA, significantly decreased growth of KRAS-dependent NSCLC cells, while having a limited effect on KRAS-independent cells or HBECs. Moreover the knock-out of either of these genes alone had no effect on growth in any of the cell lines, suggesting that only the combination of these two genes is synthetically lethal with KRAS. We are currently performing further validation in organoid cultures and in vivo. Additional validation and human relevance will be determined using patient-derived xenografts (PDX). Citation Format: Kaja Kostyrko, Marcus R. Kelly, Kyuho Han, Edwin E. Jeng, David W. Morgens, Michael C. Bassik, Peter K. Jackson, Alejandro Sweet-Cordero. Identification of novel combinatorial synthetic lethal vulnerabilities in KRAS-driven lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4362.

Synergy of WEE1 and mTOR Inhibition in Mutant KRAS-Driven Lung Cancers.

Purpose:KRAS-activating mutations are the most common oncogenic driver in non-small cell lung cancer (NSCLC), but efforts to directly target mutant KRAS have proved a formidable challenge. Therefore, multitargeted therapy may offer a plausible strategy to effectively treat KRAS-driven NSCLCs. Here, we evaluate the efficacy and mechanistic rationale for combining mTOR and WEE1 inhibition as a potential therapy for lung cancers harboring KRAS mutations.Experimental Design: We investigated the synergistic effect of combining mTOR and WEE1 inhibitors on cell viability, apoptosis, and DNA damage repair response using a panel of human KRAS-mutant and wild type NSCLC cell lines and patient-derived xenograft cell lines. Murine autochthonous and human transplant models were used to test the therapeutic efficacy and pharmacodynamic effects of dual treatment.Results: We demonstrate that combined inhibition of mTOR and WEE1 induced potent synergistic cytotoxic effects selectively in KRAS-mutant NSCLC cell lines, delayed human tumor xenograft growth and caused tumor regression in a murine lung adenocarcinoma model. Mechanistically, we show that inhibition of mTOR potentiates WEE1 inhibition by abrogating compensatory activation of DNA repair, exacerbating DNA damage in KRAS-mutant NSCLC, and that this effect is due in part to reduction in cyclin D1.Conclusions: These findings demonstrate that compromised DNA repair underlies the observed potent synergy of WEE1 and mTOR inhibition and support clinical evaluation of this dual therapy for patients with KRAS-mutant lung cancers. Clin Cancer Res; 23(22); 6993-7005. ©2017 AACR.

Regulation of autophagy, NF-κB signaling, and cell viability by miR-124 in KRAS mutant mesenchymal-like NSCLC cells.

KRAS mutant non-small cell lung cancer (NSCLC) may be classified into epithelial or mesenchymal subtypes. Despite having the same "driver" mutation, mesenchymal NSCLCs are less responsive than are epithelial NSCLCs to inhibition of the RAS pathway. Identifying alternative networks that promote survival specifically in mesenchymal NSCLC may lead to more effective treatments for this subtype. Through their numerous targets in cellular signaling pathways, noncoding microRNAs (miRNAs) often function as tumor suppressors or oncogenes. In particular, some miRNAs regulate the epithelial-mesenchymal transition (EMT). We derived an EMT-related miRNA signature by profiling the abundance of miRNAs in a panel of epithelial (KE) or mesenchymal (KM) KRAS mutant NSCLC cell lines. This signature revealed a number of suppressed miRNAs in KM cell lines, including members of the miR-200 family, which can suppress tumor progression by inhibiting EMT. Reconstituting KM cells with one of these miRNAs, miR-124, disrupted autophagy and decreased cell survival by reducing the abundance of p62, which is both an adaptor for selective autophagy and a regulator of the transcription factor nuclear factor κB (NF-κB). Suppression of p62 by miR-124 correlated with reduced abundance of the autophagy activator beclin 1 (BECN1), the ubiquitin ligase TRAF6, and the NF-κB subunit RELA/p65. The abundance of miR-124 inversely correlated with the expression of BECN1 and TRAF6 in patient NSCLC samples. These findings reveal how the loss of miR-124 promotes cell survival networks in the aggressive mesenchymal subtype of KRAS mutant NSCLC, which might lead to improved subtype-selective therapeutic strategies for patients.

Phenformin enhances the therapeutic effect of selumetinib in KRAS-mutant non-small cell lung cancer irrespective of LKB1 status.

MEK inhibition is potentially valuable in targeting KRAS-mutant non-small cell lung cancer (NSCLC). Here, we analyzed whether concomitant LKB1 mutation alters sensitivity to the MEK inhibitor selumetinib, and whether the metabolism drug phenformin can enhance the therapeutic effect of selumetinib in isogenic cell lines with different LKB1 status. Isogenic pairs of KRAS-mutant NSCLC cell lines A549, H460 and H157, each with wild-type and null LKB1, as well as genetically engineered mouse-derived cell lines 634 (krasG12D/wt/p53-/-/lkb1wt/wt) and t2 (krasG12D/wt/p53-/-/lkb1-/-) were used in vitro to analyze the activities of selumetinib, phenformin and their combination. Synergy was measured and potential mechanisms investigated. The in vitro findings were then confirmed in vivo using xenograft models. The re-expression of wild type LKB1 increased phospho-ERK level, suggesting that restored dependency on MEK->ERK->MAPK signaling might have contributed to the enhanced sensitivity to selumetinib. In contrast, the loss of LKB1 sensitized cells to phenformin. At certain combination ratios, phenformin and selumetinib showed synergistic activity regardless of LKB1 status. Their combination reduced phospho-ERK and S6 levels and induced potent apoptosis, but was likely through different mechanisms in cells with different LKB1 status. Finally, in xenograft models bearing isogenic A549 cells, we confirmed that loss of LKB1 confers resistance to selumetinib, and phenformin significantly enhances the therapeutic effect of selumetinib. Irrespective of LKB1 status, phenformin may enhance the anti-tumor effect of selumetinib in KRAS-mutant NSCLC. The dual targeting of MEK and cancer metabolism may provide a useful strategy to treat this subset of lung cancer.

Abstract 317: Combination of a novel ERK1/2 inhibitor (LY3214996) with CDK4 and CDK6 inhibitor (abemaciclib) enhances antitumor efficacy in KRAS mutant non-small cell lung cancer (NSCLC)

Abstract ERK1/2, a key downstream effector of RAS mutations, is involved in the signaling network which drives cell proliferation, survival, metastasis and cancer resistance to drug treatment (including MEK and BRAF inhibitors). Lung cancer is a leading cause of cancer death worldwide. KRAS mutation present in up to 30% of NSCLC patients is associated with a poor prognosis and represents an unmet medical need. In KRAS mutant NSCLC, enhanced ERK activation cooperates with dysregulation of the cell cycle checkpoint (e.g., cyclin D, CDK4 and CDK6 complex), and contributes to tumor progression; thus, the simultaneous inhibition of ERK and the CDK4/6 pathway is hypothesized to augment tumor growth inhibition. LY3214996, a novel and highly selective small molecule inhibitor of ERK1 and ERK2, is currently in phase I clinical trial and has been shown to inhibit cell proliferation in RAS or BRAF mutant tumor cells in vitro and xenograft tumor growth in vivo. Abemaciclib, a CDK4 and CDK6-selective inhibitor is currently in phase III studies for ER positive breast cancer and KRAS mutant NSCLC. In this study we explore the potential efficacy of combined inhibition of ERK1/2 and CDK4 and CDK6 in KRAS mutant NSCLC. The combination of LY3214996 and abemaciclib synergistically inhibited cell proliferation in 85% of KRAS mutant cells in an unbiased NSCLC panel. Combination treatment with LY3214996 and abemaciclib significantly decreased levels of phospho- p90RSK, phospho-Rb, phospho-S6 and Ki67; and synergistically inhibited cell proliferation and survival in KRAS mutant NSCLC cell lines including NCI-H2122 (G-12C), A549 (G-12S) and NCI-H441 (G-12V). Subsequent in vivo studies showed that the combination treatment with LY3214996 and abemaciclib was well tolerated and led to more robust tumor growth inhibition or regression in all KRAS mutant NSCLC xenograft models (H2122, A549 and H441) compared with either single agent treatment (p≤0.002). Furthermore, in xenograft tumors the combination of LY3214996 and abemaciclib resulted in more significant reduction of phospho-p90RSK, phospho-Rb, phospho-S6 and Ki67 in H2122 tumors compared with either single agent. Overall, the combined inhibition of ERK1/2 and CDK4 and CDK6 was tolerated and enhanced antitumor efficacy in several KRAS mutant NSCLC preclinical models. These data support the feasibility of combining ERK inhibitor LY3214996 with CDK4 and CDK6 inhibitor abemaciclib as a promising strategy for the treatment of KRAS mutant NSCLC patients, and provides the rationale for the combination study in the on-going phase I LY3214996 clinic trial (NCT02857270). Citation Format: Wenjuan Wu, Shripad V. Bhagwat, Constance King, Susan Pratt, Xueqian Gong, Julie Stewart, Bonita Jones, Robert Flack, Richard Beckman, Beverly Falcon, Jason Manro, William T. McMillen, Ramon V. Tiu, Sheng-Bin Peng, Christoph Reinhard, Sajan Joseph, Sean Buchanan. Combination of a novel ERK1/2 inhibitor (LY3214996) with CDK4 and CDK6 inhibitor (abemaciclib) enhances antitumor efficacy in KRAS mutant non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 317. doi:10.1158/1538-7445.AM2017-317

KRAS-mutation status dependent effect of zoledronic acid in human non-small cell cancer preclinical models.

BackgroundIn non-small cell lung cancer (NSCLC) KRAS-mutant status is a negative prognostic and predictive factor. Nitrogen-containing bisphosphonates inhibit prenylation of small G-proteins (e.g. Ras, Rac, Rho) and thus may affect proliferation and migration. In our preclinical work, we investigated the effect of an aminobisphosphonate compound (zoledronic acid) on mutant and wild type KRAS-expressing human NSCLC cell lines.ResultsWe confirmed that zoledronic acid was unable to inhibit the prenylation of mutant K-Ras unlike in the case of wild type K-Ras. In case of in vitro proliferation, the KRAS-mutant human NSCLC cell lines showed resistance to zoledronic acid wild-type KRAS-cells proved to be sensitive. Combinatory application of zoledronic acid enhanced the cytostatic effect of cisplatin. Zoledronic acid did not induce significant apoptosis. In xenograft model, zoledronic acid significantly reduced the weight of wild type KRAS-EGFR-expressing xenograft tumor by decreasing the proliferative capacity. Futhermore, zoledronic acid induced VEGF expression and improved in vivo tumor vascularization.Materials and methodsMembrane association of K-Ras was examined by Western-blot. In vitro cell viability, apoptotic cell death and migration were measured in NSCLC lines with different molecular background. The in vivo effect of zoledronic acid was investigated in a SCID mouse subcutaneous xenograft model.ConclusionsThe in vitro and in vivo inhibitory effect of zoledronic acid was based on the blockade of cell cycle in wild type KRAS-expressing human NSCLC cells. The zoledronic acid induced vascularization supported in vivo cytostatic effect. Our preclinical investigation suggests that patients with wild type KRAS-expressing NSCLC could potentially benefit from aminobisphosphonate therapy.

Abstract 3099: KRAS and clinical context: Differential dynamic signaling output of KRAS mutant lung, colorectal and pancreatic cancer cell lines when exposed to targeted anticancer drugs

Abstract Background Clinical trials have shown that cancers originating from different tissues driven by the same oncogene respond differently to targeted anticancer drugs. We aimed to understand different signaling patterns in KRAS mutant cells derived from non-small cell lung cancer (NSCLC), colorectal cancer (CRC) and pancreatic cancer. Materials and methods We optimized a 50 phosphoprotein antibody-based assay on the Luminex 200 platform. We then exposed a panel of 15 KRAS mutant cell lines (5 cell lines each originating in the lung, pancreas and colon) to a DMSO control (n = 3) and clinically significant concentrations (Cmax achieved in humans adjusted for protein binding in culture medium) of a PI3K (GDC-0941), AKT (AZD5363), m-TOR (everolimus), BRAF (vemurafenib), EGFR (gefitinib), MEK (trametinib) and an HSP90 inhibitor (luminespib) for 1 hr. We quantified the change in phosphorylation of proteins for each drug compared to control. Logistic regression analysis was used to analyse differences between KRAS-driven cell lines originating from different anatomical sites. Results There were changes in phosphorylation related to the pharmacodynamic effects of the drug independent of cell line of origin; however, there were interesting differences between KRAS mutant cells originating from different anatomical sites. In NSCLC cell lines, p-EGFR levels changed significantly less when exposed to PI3K, AKT and m-TOR inhibitors (p = 0.047, 0.022 and 0.047, respectively) when compared to cells originating from CRC and pancreatic cancer. CRC cell lines, when compared to NSCLC and pancreatic cancer cell lines, showed significantly less changes in phosphorylation of key cell cycle regulators such as CHK1 when exposed to PI3K, AKT and m-TOR inhibitors, (p = 0.001, 0.047 and 0.047, respectively) and RB when exposed to an AKT and m-TOR inhibitor (p = 0.047 and 0.047, respectively). Interestingly, pancreatic cell lines showed significantly more changes in p-m-TOR compared to CRC and NSCLC cell lines following exposure to PI3K and AKT inhibitors (p = 0.0095 and 0.022, respectively). Of note, drugs not directly targeting the PI3K pathway differentially regulated different nodes in the PI3K pathway, for example, BRAF inhibitors significantly differentially changed levels of phosphorylation at different nodes in the PI3K pathway such as AKT in NSCLC cell lines, p = 0.047, p70S6K in CRC cell lines, p = 0.0472 and PRAS40 in the pancreatic cancer cell lines, p = 0.022. Conclusion These results suggest that there are significant differences in signaling patterns caused by PI3K pathway inhibitors in KRAS mutant NSCLC, CRC and pancreatic cancer cell lines. Our findings shed light on the putative use of PI3K pathway inhibitors in KRAS mutant cancers. They also question the universal application of solely using genetic mutations to stratify patients in ‘basket’ clinical studies. Citation Format: Adam Stewart, Elizabeth Coker, Anna Minchom, Parames Thavasu, Alexandros Georgiou, Anguraj Sadanandam, Timothy A. Yap, Johann S. de Bono, Bissan Al-Lazikani, Udai Banerji. KRAS and clinical context: Differential dynamic signaling output of KRAS mutant lung, colorectal and pancreatic cancer cell lines when exposed to targeted anticancer drugs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3099.

PKCδ regulates integrin αVβ3 expression and transformed growth of K-ras dependent lung cancer cells.

We have previously shown that Protein Kinase C delta (PKCδ) functions as a tumor promoter in non-small cell lung cancer (NSCLC), specifically in the context of K-ras addiction. Here we define a novel PKCδ -> integrin αVβ3->Extracellular signal-Regulated Kinase (ERK) pathway that regulates the transformed growth of K-ras dependent NSCLC cells. To explore how PKCδ regulates tumorigenesis, we performed mRNA expression analysis in four KRAS mutant NSCLC cell lines that stably express scrambled shRNA or a PKCδ targeted shRNA. Analysis of PKCδ-dependent mRNA expression identified 3183 regulated genes, 210 of which were specifically regulated in K-ras dependent cells. Genes that regulate extracellular matrix and focal adhesion pathways were most highly represented in this later group. In particular, expression of the integrin pair, αVβ3, was specifically reduced in K-ras dependent cells with depletion of PKCδ, and correlated with reduced ERK activation and reduced transformed growth as assayed by clonogenic survival. Re-expression of PKCδ restored ITGAV and ITGB3 mRNA expression, ERK activation and transformed growth, and this could be blocked by pretreatment with a αVβ3 function-blocking antibody, demonstrating a requirement for integrin αVβ3 downstream of PKCδ. Similarly, expression of integrin αV restored ERK activation and transformed growth in PKCδ depleted cells, and this could also be inhibited by pretreatment with PD98059. Our studies demonstrate an essential role for αVβ3 and ERK signalingdownstream of PKCδ in regulating the survival of K-ras dependent NSCLC cells, and identify PKCδ as a novel therapeutic target for the subset of NSCLC patients with K-ras dependent tumors.

Abstract LB-C02: A KRAS dependency microRNA signature reveals a p62/Sqstm1-centered autophagy network regulated by mir-124

Abstract Background Non-small cell lung cancer (NSCLC) is derived from broncho-alveolar epithelial cells. NSCLCs frequently harbor mutations in the KRAS oncogene, yet only a subset of NSCLC cell lines depend on KRAS for sustained survival signaling. Cells that are more epithelial are highly KRAS dependent, whereas mesenchymal-like cells are KRAS independent for cell survival signaling. KRAS mutations are commonly associated with resistance to anti-cancer therapeutics. An important drug resistance mechanism is altered cellular plasticity, via a process known as epithelial-to-mesenchymal transition (EMT). Here, we aimed to identify and elucidate a KRAS dependent microRNA (miRNA) signaling network in epithelial cancer cells that modulates malignant growth and proliferation as well as cellular plasticity in NSCLC. Methods Differential miRNA expression in 6 KRAS mutant NSCLC cell lines (3 KRAS independent versus 3 KRAS dependent) was determined using Taqman low-density qPCR arrays (TLDA). To explore the functional relevance of differentially regulated miRNAs, gain-of-function studies by reconstitution experiments were performed using miRNA mimics in a panel of six KRAS independent cell lines. The molecular targets of mir-124-2 were computationally identified by TargetScan or miRWalk and experimentally verified using 3'UTR luciferase-based assays. Functional rescue of cell viability defects was determined by forced expression of GFP-p62/Sqstm1 in KRAS independent lung cancer cell lines. Results We identified a distinct differential miRNA expression profile in KRAS dependent versus KRAS independent NSCLC cells. This KRAS dependency miRNA signature included members of the mir-200 family, mir-34c and mir-205. Mir-200 and mir-205 reconstitution in KRAS independent cells modulated epithelial plasticity by down regulating Zeb1 protein expression and, thereby, increasing E-cadherin levels. Ectopic introduction of a subset of miRNAs in KRAS independent cells caused a consistent and pronounced loss of cell viability in all cell lines tested, including mir124, mir-625 and mir-518-3p. Ectopic expression of mir124 in KRAS independent cells caused cell viability defects by inducing apoptosis and autophagy. Using bioinformatics databases, we isolated p62/Sqstm1 and REL-A as key predicted targets of mir124-2. Mir-124-2 reconstitution in KRAS independent NSCLC cell lines caused decreased p62/Sqstm1 and REL-A protein expression levels. The effect of mir-124 on p62/Sqstm1 expression was verified using a p62-3'UTR-Luciferase construct. Overexpression of GFP-p62 in KRAS independent cells rescued the cell viability defects by mir124-2. Conclusion MiR-124 expression is down regulated in KRAS independent NSCLC cells. Reintroduction of mir124-2 induces cell viability defects in part, by targeting p62/Sqstm1 and REL-A. We conclude that, mir-124 down regulates p62/Sqstm1 expression to activate autophagic flux. This leads to down regulation of the NFκB pathway and subsequent reduction in expression of pro-survival genes such as IL-6 and IL-1β. Taken together, mir124-2 acts as a tumor suppressor in KRAS mutant NSCLC cells and provides a mechanistic link between activation of autophagy and control of proinflammatory signaling in NSCLC cell survival. Overexpression of mir124-2 might be of potential therapeutic value for the treatment of KRAS mutant NSCLC. Citation Format: ANITA K. MEHTA, Kevin Hua, William Whipple, Minh-Thuy Nguyen, Stephanie Bartley, Margaret McGuiness, Jeff Settleman, Joanne Weidhaas, Anurag Singh. A KRAS dependency microRNA signature reveals a p62/Sqstm1-centered autophagy network regulated by mir-124. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-C02.

Abstract 1770: A role of nicotinamide phosphoribosyltransferase in growth of KRAS mutant non-small cell lung cancer

Abstract Background: KRAS mutations are frequently found in non-small cell lung cancer (NSCLC). The KRAS mutations could be predictive of resistance to targeted therapy like epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) or a prognostic factor in NSCLC. No successful targeted therapy currently exists to treat patients with KRAS mutant NSCLC, and novel therapeutic strategies are needed to prolong survival in patients with KRAS mutant NSCLC. Nicotinamide phosphoribosyltransferase (nampt) is a rate-limiting enzyme in NAD+ salvage, and we previously reported that nampt is a potent therapeutic target in NSCLC. Based on the analysis result of GEO database, we found that expression of nampt is associated with RAS-MAPK signaling pathway in NSCLC, and we therefore, conducted an in vitro study to evaluate a role of nampt in growth of KRAS mutant NSCLC. Methods: We used a panel of KRAS mutant NSCLC cell lines (A427, A549, H157, H23, H1792, H2009, H358, H441, Calu6, Calu1). The cells were treated with a nampt inhibitor, FK866, and acid phosphatase (APH) assay (Thermo SCIENTIFIC) was used to evaluate cell viability of the KRAS mutant cells. Changes in expression of MAPK signaling pathway and BCL2 family proteins (antibodies from Cell Signaling and Santa Cruz) were evaluated by western blot. Apoptosis of the cells treated with FK866 was detected using an Annexin V FITC apoptosis detection kit (BD Biosciences). FACS analysis was performed using a BD FACSAria II cytometer (BD Bioscience). Autophagic proteolysis was studied by Cyto-ID autophagy detection kit (Cosmo Bio), and the expression of the fluorescent signal was visualized by a FV1000 confocal microscope (OLYMPUS JAPAN). Results: We found that the sensitivity to FK866 was different among the KRAS mutant cell lines, and for instance, A427 cells were sensitive while H157 cells were resistant. FK866 suppressed growth of KRAS mutant NSCLC and decreased expression of p-ERK expression in the cell line sensitive to FK866. We will report alteration of apoptosis and autophagy in the KRAS mutant NSCLC treated with FK866. Conclusion: Nampt could be a potent therapeutic target in KRAS mutant NSCLC. Citation Format: Shunsuke Okumura, Takaaki Sasaki, Yoshinobu Ohsaki. A role of nicotinamide phosphoribosyltransferase in growth of KRAS mutant 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 1770. doi:10.1158/1538-7445.AM2015-1770

Abstract 762: Ganetespib resistance in KRAS mutant NSCLC is mediated through bypassing the G2/M checkpoint and reactivating the PI3K/MTOR pathway

Abstract One third of all malignancies and approximately 25% of non-small cell lung cancer (NSCLC) patients have KRAS mutations, which in turn activate several growth regulatory signaling pathways including RAF/MEK/ERK and PI3K/AKT/MTOR. Unfortunately, there are no current therapies targeting this critical oncogene. Heat shock protein 90 (HSP90) is a molecular chaperone required for the stability of hundreds of ‘client’ proteins, many of which are effectors of KRAS. Unfortunately, limited efficacy was observed in early clinical studies of single agent HSP90 inhibitors (HSP90i) in KRAS mutant NSCLC. Here, we examined the mechanism(s) of acquired resistance to ganetespib in KRAS mutant NSCLC to develop rationale combinations with ganetespib. Ganetespib, a Phase 3 HSP90i, was potently cytotoxic in a panel of KRAS mutant NSCLC cell lines and promoted decreased expression and activity of both RAF/MEK/ERK and PI3K/AKT/MTOR pathway members. Contrary to prior reports with other HSP90i, we found that ganetespib dependent growth inhibition was independent of its ability to stabilize p53 or induce apoptosis. We derived three KRAS mutant NSCLC ganetespib resistant (GR) cell lines to identify the resistance mechanism(s) and reveal targetable pathways to overcome this resistance. First, we demonstrated that A549-GR cells are cross-resistant to a first generation HSP90i, 17-AAG, suggesting that altered metabolism of ganetespib is unlikely to explain this resistance. Moreover, the ganetespib induced G2/M checkpoint arrest observed in A549 parental cells was significantly diminished in A549-GR cells. These results suggest that bypass of this checkpoint may be an important part of the resistance mechanism. Furthermore, we demonstrated that A549-GR cells were cross-resistant to docetaxel, an antimicrotubule agent. In addition, expression and activity of the PI3K/AKT/mTOR pathway members were significantly increased suggesting that reactivation of PI3K/AKT/mTOR pathway may be responsible for the observed resistance. To test this hypothesis, we treated parental and GR cells with a dual PI3K/mTOR inhibitor, BEZ235. Remarkably, A549-GR cells were more sensitive to BEZ235 compared to the parental ones suggesting that the acquired ganetespib resistance lead to increased dependence on the PI3K/mTOR pathway. Interestingly, a key activator of the PI3K/mTOR pathway, p90 ribosomal S6 kinase (RSK) was strikingly increased in the GR cells. Furthermore, A549-GR cells showed increased sensitivity to two highly specific RSK inhibitors, BI-D1870 and SL0101. These data suggests that the combination of inhibitors for HSP90 and PI3K/mTOR may prevent ganetespib resistance and/or help overcome the resistance after single agent treatment, providing the preclinical rationale for our planned Phase I/II trial of the combination of ganetespib and a dual PI3K/MTOR inhibitor in KRAS mutant NSCLC. Citation Format: Suman Chatterjee, Timothy F. Burns. Ganetespib resistance in KRAS mutant NSCLC is mediated through bypassing the G2/M checkpoint and reactivating the PI3K/MTOR pathway. [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 762. doi:10.1158/1538-7445.AM2015-762

Abstract A31: Activity-based protein profiling reveals adaptive response to pharmacological MEK inhibition in KRAS mutant non-small cell lung cancer

Abstract KRAS mutations account for development of approximately 30% of lung adenocarcinomas. While RAF-MEK-ERK signaling cascade is a key regulator of RAS-mediated proliferation and survival, the clinical efficacy of MEK inhibitors is still underwhelming in RAS-driven cancers. We treated KRAS mutant non-small cell lung cancer (NSCLC) cell lines with two MEK inhibitors (AZD6244 and MEK162) currently in clinical development. In all cell lines tested (N=11), we failed to observe significant effects on cell viability or induction of apoptosis. Because increasing evidence indicates that cancer cells undergo adaptive proteomic rewiring in response to kinase inhibitors, we performed activity-based protein profiling (ABPP) after treating 11 KRAS mutant NSCLC cell lines with MEK inhibitors in order to identify global enzymatic changes potentially involved in these adaptive processes. Our ABPP approach employs desthiobiotin-ATP probe, which enables selective labeling of active sites in ATP-binding proteins including kinases, chaperones and metabolic enzymes. Labeled proteins were subsequently purified and analyzed by mass spectrometry-based proteomics technique. Our ABPP results revealed that MEK inhibitors increased levels of multiple receptor tyrosine kinases (RTK) including EGFR and MET. MEK inhibitors induced MET phosphorylation and EGF-mediated AKT phosphorylation was markedly enhanced in the presence of MEK inhibitors, indicating increased RTK activity in adaptive response to MEK inhibition. We also found that MEK inhibition led to increased multiple heat shock proteins including HSP90 and HSP70, suggesting the possibility of chaperone-mediated adaptive resistance. Finally, MEK inhibitors globally increased enzymes involved in glucose utilization pathways implicating metabolic alterations in adaptive response to MEK inhibition. Collectively, our systematic activity-based proteomic profiling approach provides novel insights into adaptive resistance mechanisms to MEK inhibitors, suggesting rational combination treatment strategies for KRAS mutant NSCLC. Updated works will be presented. Citation Format: Jae-Young Kim, Bin Fang, Eric A. Welsh, Fumi Kinose, Jiannong Li, Steven A. Eschrich, John M. Koomen, Eric B. Haura. H. Activity-based protein profiling reveals adaptive response to pharmacological MEK inhibition in KRAS mutant non-small cell lung cancer. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A31. doi: 10.1158/1557-3125.RASONC14-A31

Abstract 3405: E12 and E47 are essential for TWIST1 dependent suppression of oncogene-induced senescence in NSCLC

Abstract Lung cancer is the leading cause of cancer death in the United States and in the world. Non-small cell lung cancer (NSCLC) is not a single disease entity, but a collection of distinct oncogene driven neoplasms. The most common driver oncogene in NSCLC is mutant-KRAS, which is present in 20-25% of all NSCLC and for which no effective therapies exist. In addition, acquired resistance to the current therapy for the two most frequently observed targetable driver oncogenes in NSCLC, mutant-EGFR and the ALK translocations, is inevitable. Clearly there is a need for novel therapeutic strategies to target these oncogene driven lung cancers. The basic helix-loop-helix (bHLH) transcription factor TWIST1 plays several critical roles in promoting tumorigenesis through inhibition of apoptosis, promotion of metastasis through induction of epithelial-mesenchymal transition (EMT) and inhibition of oncogene-induced senescence (OIS). We recently demonstrated that TWIST1 is essential for tumor maintenance in human NSCLC containing mutant KRAS, mutant EGFR, or amplified cMET. Moreover we have shown that Twist1 cooperates with Kras to induce adenocarcinoma of the lung in mouse models and that inhibition of Twist1 in both a murine model and in human cell lines causes OIS or in some cases apoptosis. We have previously demonstrated that reactivation of OIS after inhibition of TWIST1 occurs independently of the RB/p16, p53/p21 or p27 pathways. In the current study, we examined the role of the TWIST1 binding partners E12 and E47, which are encoded by the E2A locus, in mediating TWIST1 dependent suppression of OIS. E2A encoded proteins have previously been demonstrated to act as tumor suppressors through inhibition of cell proliferation. However, E12 and E47 are overexpressed in several tumor types and this expression can lead to chemoresistance. Furthermore, previous studies have demonstrated that the E12-TWIST1 heterodimerization stabilizes both proteins and in some cases, enhances TWIST1 activity. In our study we have shown that in human KRAS mutant NSCLC cell lines the silencing of the E2A gene products phenocopies the silencing of TWIST1 by inducing either OIS or apoptosis. Furthermore, we have observed significant downregulation of TWIST1 after silencing the E2A gene products. Conversely, overexpression of either E12 or E47 leads to increased TWIST1 protein levels. Interestingly, TWIST1 overexpression leads to E12/E47 stabilization suggesting that heterodimer formation results in a reciprocal stabilization of the binding partner. Finally, we have shown that harmine, a harmala alkaloid that leads to degradation of TWIST1, inhibits NSCLC cell line growth and decreases both E12/E47 levels as well. These data suggest that E12/E47 are essential for TWIST mediated suppression of OIS and that targeting of the TWIST1-E12/E47 axis may be an effective therapeutic strategy against oncogene driven NSCLC. Citation Format: Lucia Mazzacurati, Sarah NH Chatley, Zachary Yochum, Charles M. Rudin, Phuoc T. Tran, Timothy F. Burns. E12 and E47 are essential for TWIST1 dependent suppression of oncogene-induced senescence in NSCLC. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3405. doi:10.1158/1538-7445.AM2014-3405

Quantitative proteomic approach to understand metabolic adaptation in non-small cell lung cancer.

KRAS mutations in non-small cell lung cancer (NSCLC) are a predictor of resistance to EGFR-targeted therapies. Because approaches to target RAS signaling have been unsuccessful, targeting lung cancer metabolism might help to develop a new strategy that could overcome drug resistance in such cancer. In this study, we applied a large screening quantitative proteomic analysis to evidence key enzymes involved in metabolic adaptations in lung cancer. We carried out the proteomic analysis of two KRAS-mutated NSCLC cell lines (A549 and NCI-H460) and a non tumoral bronchial cell line (BEAS-2B) using an iTRAQ (isobaric tags for relative and absolute quantitation) approach combined with two-dimensional fractionation (OFFGEL/RP nanoLC) and MALDI-TOF/TOF mass spectrometry analysis. Protein targets identified by our iTRAQ approach were validated by Western blotting analysis. Among 1038 proteins identified and 834 proteins quantified, 49 and 82 proteins were respectively found differently expressed in A549 and NCI-H460 cells compared to the BEAS-2B non tumoral cell line. Regarding the metabolic pathways, enzymes involved in glycolysis (GAPDH/PKM2/LDH-A/LDH-B) and pentose phosphate pathway (PPP) (G6PD/TKT/6PGD) were up-regulated. The up-regulation of enzyme expression in PPP is correlated to their enzyme activity and will be further investigated to confirm those enzymes as promising metabolic targets for the development of new therapeutic treatments or biomarker assay for NSCLC.

GATA2 is Epigenetically Repressed in Human and Mouse Lung Tumors and Is Not Requisite for Survival of KRAS Mutant Lung Cancer

GATA2 was recently described as a critical survival factor and therapeutic target for KRAS mutant non-small-cell lung cancer (NSCLC). However, whether this role is affected by epigenetic repression of GATA2 in lung cancer is unclear. GATA2 expression and promoter CpG island methylation were evaluated using human and mouse NSCLC cell lines and tumor-normal pairs. In vitro assays were used to study GATA2 repression on cell survival and during tobacco carcinogen-induced transformation. GATA2 expression in KRAS wild-type (n = 15) and mutant (n = 10) NSCLC cell lines and primary lung tumors (n = 24) was significantly lower, 1.3- to 33.6-fold (p = 2.2 × 10(9)), compared with corresponding normal lung. GATA2 promoter was unmethylated in normal lung (0 of 10) but frequently methylated in lung tumors (96%, 159 of 165) and NSCLC cell lines (97%, 30 of 31). This highly prevalent aberrant methylation was independently validated using The Cancer Genome Atlas data for 369 NSCLC tumor-normal pairs. In vitro studies using an established carcinogen-induced premalignancy model revealed that GATA2 expression was initially repressed by chromatin remodeling followed by cytosine methylation during transformation. Similarly, expression of GATA2 in NNK-induced mouse lung tumors (n = 6) and cell lines (n = 5) was fivefold and 100-fold lower, respectively, than normal mouse lung. Finally, siRNA-mediated knockdown of GATA2 in KRAS mutant (human [n = 4] and murine [n = 5]) and wild-type (human [n = 4]) NSCLC cell lines showed that further reduction of expression (up to 95%) does not induce cell death. GATA2 is epigenetically repressed in human and mouse lung tumors and its further inhibition is not a valid therapeutic strategy for KRAS mutant lung cancer.

Failure to induce apoptosis via BCL-2 family proteins underlies lack of efficacy of combined MEK and PI3K inhibitors for KRAS-mutant lung cancers.

Although several groups have demonstrated that concomitant use of MEK and phosphoinositide 3-kinase (PI3K) inhibitors (MEKi/PI3Ki) can induce dramatic tumor regressions in mouse models of KRAS-mutant non-small cell lung cancer (NSCLC), ongoing clinical trials investigating this strategy have been underwhelming to date. While efficacy may be hampered by a narrow therapeutic index, the contribution of biologic heterogeneity in the response of KRAS-mutant NSCLCs to MEKi/PI3Ki has been largely unexplored. In this study, we find that most human KRAS-mutant NSCLC cell lines fail to undergo marked apoptosis in response to MEKi/PI3Ki, which is key for tumor responsiveness in vivo. This heterogeneity of apoptotic response occurs despite relatively uniform induction of growth arrest. Using a targeted short hairpin RNA screen of BCL-2 family members, we identify BIM, PUMA, and BCL-XL as key regulators of the apoptotic response induced by MEKi/PI3Ki, with decreased expression of BIM and PUMA relative to BCL-XL in cell lines with intrinsic resistance. In addition, by modeling adaptive resistance to MEKi/PI3Ki both in vitro and in vivo, we find that, upon the development of resistance, tumors have a diminished apoptotic response due to downregulation of BIM and PUMA. These results suggest that the inability to induce apoptosis may limit the effectiveness of MEKi/PI3Ki for KRAS-mutant NSCLCs by contributing to intrinsic and adaptive resistance to this therapy.