The ERBB network facilitates KRAS-driven lung tumorigenesis

TRIB3-EGFR interaction promotes lung cancer progression and defines a therapeutic target

High expression or aberrant activation of epidermal growth factor receptor (EGFR) is related to tumor progression and therapy resistance across cancer types, including non-small cell lung cancer (NSCLC). EGFR tyrosine kinase inhibitors (TKIs) are first-line therapy for NSCLC. However, patients eventually deteriorate after inevitable acquisition of EGFR TKI-resistant mutations, highlighting the need for therapeutics with alternative mechanisms of action. Here, we report that the elevated tribbles pseudokinase 3 (TRIB3) is positively associated with EGFR stability and NSCLC progression. TRIB3 interacts with EGFR and recruits PKCα to induce a Thr654 phosphorylation and WWP1-induced Lys689 ubiquitination in the EGFR juxtamembrane region, which enhances EGFR recycling, stability, downstream activity, and NSCLC stemness. Disturbing the TRIB3-EGFR interaction with a stapled peptide attenuates NSCLC progression by accelerating EGFR degradation and sensitizes NSCLC cells to chemotherapeutic agents. These findings indicate that targeting EGFR degradation is a previously unappreciated therapeutic option in EGFR-related NSCLC.

Targeting KRAS Mutant Non-Small-Cell Lung Cancer: Past, Present and Future

Lung cancer is the most frequent cancer with an aggressive clinical course and high mortality rates. Most cases are diagnosed at advanced stages when treatment options are limited and the efficacy of chemotherapy is poor. The disease has a complex and heterogeneous background with non-small-cell lung cancer (NSCLC) accounting for 85% of patients and lung adenocarcinoma being the most common histological subtype. Almost 30% of adenocarcinomas of the lung are driven by an activating Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation. The ability to inhibit the oncogenic KRAS has been the holy grail of cancer research and the search for inhibitors is immensely ongoing as KRAS-mutated tumors are among the most aggressive and refractory to treatment. Therapeutic strategies tailored for KRAS+ NSCLC rely on the blockage of KRAS functional output, cellular dependencies, metabolic features, KRAS membrane associations, direct targeting of KRAS and immunotherapy. In this review, we provide an update on the most recent advances in anti-KRAS therapy for lung tumors with mechanistic insights into biological diversity and potential clinical implications.

RAS-targeted therapies: is the undruggable drugged?

RAS (KRAS, NRAS and HRAS) is the most frequently mutated gene family in cancers, and, consequently, investigators have sought an effective RAS inhibitor for more than three decades. Even 10 years ago, RAS inhibitors were so elusive that RAS was termed 'undruggable'. Now, with the success of allele-specific covalent inhibitors against the most frequently mutated version of RAS in non-small-cell lung cancer, KRAS^G12C, we have the opportunity to evaluate the best therapeutic strategies to treat RAS-driven cancers. Mutation-specific biochemical properties, as well as the tissue of origin, are likely to affect the effectiveness of such treatments. Currently, direct inhibition of mutant RAS through allele-specific inhibitors provides the best therapeutic approach. Therapies that target RAS-activating pathways or RAS effector pathways could be combined with these direct RAS inhibitors, immune checkpoint inhibitors or T cell-targeting approaches to treat RAS-mutant tumours. Here we review recent advances in therapies that target mutant RAS proteins and discuss the future challenges of these therapies, including combination strategies.

Repression of the Type I Interferon Pathway Underlies MYC- and KRAS-Dependent Evasion of NK and B Cells in Pancreatic Ductal Adenocarcinoma

MYC is implicated in the development and progression of pancreatic cancer, yet the precise level of MYC deregulation required to contribute to tumor development has been difficult to define. We used modestly elevated expression of human MYC, driven from the Rosa26 locus, to investigate the pancreatic phenotypes arising in mice from an approximation of MYC trisomy. We show that this level of MYC alone suffices to drive pancreatic neuroendocrine tumors, and to accelerate progression of KRAS-initiated precursor lesions to metastatic pancreatic ductal adenocarcinoma (PDAC). Our phenotype exposed suppression of the type I interferon (IFN) pathway by the combined actions of MYC and KRAS, and we present evidence of repressive MYC-MIZ1 complexes binding directly to the promoters of the genes encodiing the type I IFN regulators IRF5, IRF7, STAT1, and STAT2. Derepression of IFN regulator genes allows pancreatic tumor infiltration by B and natural killer (NK) cells, resulting in increased survival. SIGNIFICANCE: We define herein a novel mechanism of evasion of NK cell-mediated immunity through the combined actions of endogenously expressed mutant KRAS and modestly deregulated expression of MYC, via suppression of the type I IFN pathway. Restoration of IFN signaling may improve outcomes for patients with PDAC.This article is highlighted in the In This Issue feature, p. 747.

A Genome-scale CRISPR Screen Identifies the ERBB and mTOR Signaling Networks as Key Determinants of Response to PI3K Inhibition in Pancreatic Cancer

KRAS mutation is a key driver of pancreatic cancer and PI3K pathway activity is an additional requirement for Kras-induced tumorigenesis. Clinical trials of PI3K pathway inhibitors in pancreatic cancer have shown limited responses. Understanding the molecular basis for this lack of efficacy may direct future treatment strategies with emerging PI3K inhibitors. We sought new therapeutic approaches that synergize with PI3K inhibitors through pooled CRISPR modifier genetic screening and a drug combination screen. ERBB family receptor tyrosine kinase signaling and mTOR signaling were key modifiers of sensitivity to alpelisib and pictilisib. Inhibition of the ERBB family or mTOR was synergistic with PI3K inhibition in spheroid, stromal cocultures. Near-complete loss of ribosomal S6 phosphorylation was associated with synergy. Genetic alterations in the ERBB-PI3K signaling axis were associated with decreased survival of patients with pancreatic cancer. Suppression of the PI3K/mTOR axis is potentiated by dual PI3K and ERBB family or mTOR inhibition. Surprisingly, despite the presence of oncogenic KRAS, thought to bestow independence from receptor tyrosine kinase signaling, inhibition of the ERBB family blocks downstream pathway activation and synergizes with PI3K inhibitors. Further exploration of these therapeutic combinations is warranted for the treatment of pancreatic cancer.

EGFR inhibition triggers an adaptive response by co-opting antiviral signaling pathways in lung cancer

EGFR inhibition is an effective treatment in the minority of non-small cell lung cancer (NSCLC) cases harboring EGFR-activating mutations, but not in EGFR wild type (EGFRwt) tumors. Here, we demonstrate that EGFR inhibition triggers an antiviral defense pathway in NSCLC. Inhibiting mutant EGFR triggers Type I IFN-I upregulation via a RIG-I-TBK1-IRF3 pathway. The ubiquitin ligase TRIM32 associates with TBK1 upon EGFR inhibition, and is required for K63-linked ubiquitination and TBK1 activation. Inhibiting EGFRwt upregulates interferons via an NF-κB-dependent pathway. Inhibition of IFN signaling enhances EGFR-TKI sensitivity in EGFR mutant NSCLC and renders EGFRwt/KRAS mutant NSCLC sensitive to EGFR inhibition in xenograft and immunocompetent mouse models. Furthermore, NSCLC tumors with decreased IFN-I expression are more responsive to EGFR TKI treatment. We propose that IFN-I signaling is a major determinant of EGFR-TKI sensitivity in NSCLC and that a combination of EGFR TKI plus IFN-neutralizing antibody could be useful in most NSCLC patients.

Influence of EGFR-activating mutations on sensitivity to tyrosine kinase inhibitors in a KRAS mutant non-small cell lung cancer cell line

In non-small cell lung cancer (NSCLC), oncogenic driver mutations including those in KRAS and EGFR are typically mutually exclusive. However, recent reports indicate that multiple driver mutations are found in a certain percentage of cancers, and that the therapeutic responses of such cases with co-mutations of driver genes are largely unclear. Here, using CRISPR-Cas9-mediated genome editing, we generated isogenic cell lines harboring one or two copies of an EGFR-activating mutation from the human NSCLC cell line A549, which is known to harbor a homozygous KRAS gene mutation. In comparison with parent cells with KRAS mutation alone, cells with concomitant EGFR mutation exhibited higher sensitivity to EGFR-tyrosine kinase inhibitors (TKIs) but not to conventional anti-cancer drugs. In particular, cells with two copies of EGFR mutation were markedly more sensitive to EGFR-TKIs compared with parent cells. Thus, the presence of concomitant EGFR mutation can affect the TKI response of KRAS-mutated cells, implying that EGFR-TKI may represent an effective treatment option against NSCLC with EGFR/KRAS co-mutation.

Diverse BRAF Gene Fusions Confer Resistance to EGFR-Targeted Therapy via Differential Modulation of BRAF Activity

Fusion genes can be oncogenic drivers in a variety of cancer types and represent potential targets for targeted therapy. The BRAF gene is frequently involved in oncogenic gene fusions, with fusion frequencies of 0.2%-3% throughout different cancers. However, BRAF fusions rarely occur in the same gene configuration, potentially challenging personalized therapy design. In particular, the impact of the wide variety of fusion partners on the oncogenic role of BRAF during tumor growth and drug response is unknown. Here, we used patient-derived colorectal cancer organoids to functionally characterize and cross-compare BRAF fusions containing various partner genes (AGAP3, DLG1, and TRIM24) with respect to cellular behavior, downstream signaling activation, and response to targeted therapies. We demonstrate that 5' fusion partners mainly promote canonical oncogenic BRAF activity by replacing the auto-inhibitory N-terminal region. In addition, the 5' partner of BRAF fusions influences their subcellular localization and intracellular signaling capacity, revealing distinct subsets of affected signaling pathways and altered gene expression. Presence of the different BRAF fusions resulted in varying sensitivities to combinatorial inhibition of MEK and the EGF receptor family. However, all BRAF fusions conveyed resistance to targeted monotherapy against the EGF receptor family, suggesting that BRAF fusions should be screened alongside other MAPK pathway alterations to identify patients with metastatic colorectal cancer to exclude from anti-EGFR-targeted treatment. IMPLICATIONS: Although intracellular signaling and sensitivity to targeted therapies of BRAF fusion genes are influenced by their 5' fusion partner, we show that all investigated BRAF fusions confer resistance to clinically relevant EGFR inhibition.

Targeting the Tumor Microenvironment: An Unexplored Strategy for Mutant KRAS Tumors

Current evidence strongly suggests that cancer cells depend on the microenvironment in order to thrive. In fact, signals from the surrounding tumor microenvironment are crucial for cancer cells´ aggressiveness, altering their expression profile and favoring their metastatic potential. As such, targeting the tumor microenvironment to impair cancer progression became an attractive therapeutic option. Interestingly, it has been shown that oncogenic KRAS signaling promotes a pro-tumorigenic microenvironment, and the associated crosstalk alters the expression profile of cancer cells. These findings award KRAS a key role in controlling the interactions between cancer cells and the microenvironment, granting cancer a poor prognosis. Given the lack of effective approaches to target KRAS itself or its downstream effectors in the clinic, exploring such interactions may open new perspectives on possible therapeutic strategies to hinder mutant KRAS tumors. This review highlights those communications and their implications for the development of effective therapies or to provide insights regarding response to existing regimens.

KRAS: A Promising Therapeutic Target for Cancer Treatment

Kirsten rat sarcoma 2 viral oncogene homolog (KRAS) is the most commonly mutated oncogene in human cancer. The developments of many cancers depend on sustained expression and signaling of KRAS, which makes KRAS a high-priority therapeutic target. Scientists have not successfully developed drugs that target KRAS, although efforts have been made last three decades. In this review, we highlight the emerging experimental strategies of impairing KRAS membrane localization and the direct targeting of KRAS. We also conclude the combinatorial therapies and RNA interference technology for the treatment of KRAS mutant cancers. Moreover, the virtual screening approach to discover novel KRAS inhibitors and synthetic lethality interactors of KRAS are discussed in detail.

Identification of Resistance Pathways Specific to Malignancy Using Organoid Models of Pancreatic Cancer

PURPOSE

KRAS is mutated in the majority of pancreatic ductal adenocarcinoma. MAPK and PI3K-AKT are primary KRAS effector pathways, but combined MAPK and PI3K inhibition has not been demonstrated to be clinically effective to date. We explore the resistance mechanisms uniquely employed by malignant cells.

EXPERIMENTAL DESIGN

We evaluated the expression and activation of receptor tyrosine kinases in response to combined MEK and AKT inhibition in KPC mice and pancreatic ductal organoids. In addition, we sought to determine the therapeutic efficacy of targeting resistance pathways induced by MEK and AKT inhibition in order to identify malignant-specific vulnerabilities.

RESULTS

Combined MEK and AKT inhibition modestly extended the survival of KPC mice and increased Egfr and ErbB2 phosphorylation levels. Tumor organoids, but not their normal counterparts, exhibited elevated phosphorylation of ERBB2 and ERBB3 after MEK and AKT blockade. A pan-ERBB inhibitor synergized with MEK and AKT blockade in human PDA organoids, whereas this was not observed for the EGFR inhibitor erlotinib. Combined MEK and ERBB inhibitor treatment of human organoid orthotopic xenografts was sufficient to cause tumor regression in short-term intervention studies.

CONCLUSIONS

Analyses of normal and tumor pancreatic organoids revealed the importance of ERBB activation during MEK and AKT blockade primarily in the malignant cultures. The lack of ERBB hyperactivation in normal organoids suggests a larger therapeutic index. In our models, pan-ERBB inhibition was synergistic with dual inhibition of MEK and AKT, and the combination of a pan-ERBB inhibitor with MEK antagonists showed the highest activity both in vitro and in vivo.

Not the comfy chair! Cancer drugs that act against multiple active sites

Introduction: Discoveries of novel signal transduction pathways in the 1990s stimulated drug companies to develop small molecule tyrosine kinase and serine / threonine kinase inhibitors which were based on catalytic site inhibition. All kinases bind ATP and catalyze phosphate transfer and, therefore, inhibitors that block ATP binding and its metabolism would be predicted to have a known on-target specificity but were also likely to have many unknown or unrecognized targets due to similarities in all ATP binding pockets. This on-target off-target biology of kinase inhibitors, which exhibit a "signal" in the clinic, means that therapeutically valuable agents are acting through unknown biological processes to mediate their anti-tumor effects.Areas covered: This perspective discusses drug therapies whose actions cannot be explained by their actions on the original targeted kinase; it concludes with a methodology to screen for changes in cell signaling via in-cell western immunoblotting.Expert opinion: Most malignancies do not depend on survival signaling from one specific mutated proto-oncogene, especially for previously treated malignancies where multiple clonal variants of the primary tumor have evolved. Hence, the concept of a highly "personalized medicine" approach fails because it is unlikely that a specific therapy will kill all clonal variants of the tumor.

Inhibiting Pathways Predicted From a Steroid Hormone Gene Signature Yields Synergistic Antitumor Effects in NSCLC

INTRODUCTION

Mounting evidence supports a role for estrogen signaling in NSCLC progression. We previously reported a seven-gene signature that predicts prognosis in estrogen receptor β positive (ERβ+) NSCLC. The signature defines a network comprised of ER and human EGFR-2/3 (HER2/HER3) signaling.

METHODS

We tested the efficacy of combining the pan-HER inhibitor, dacomitinib, with the estrogen antagonist, fulvestrant, in ERβ+ NSCLC models with differing genotypes. We assessed the potency of this combination on xenograft growth and survival of host mice, and the ability to reverse the gene signature associated with poor outcome.

RESULTS

Synergy was observed between dacomitinib and fulvestrant in three human ERβ+ NSCLC models: 201T (wild-type EGFR), A549 (KRAS mutant), and HCC827 (EGFR 19 deletion) with combination indices of 0.1-0.6. The combination, but not single agents, completely reversed the gene signature associated with poor prognosis in a mechanism that is largely mediated by activator protein 1 downregulation. In vivo, the combination also induced tumor regression and reversed the gene signature. In HCC827 xenografts treated with the combination, survival of mice was prolonged after therapy discontinuation, tumors that recurred were less aggressive, and two mechanisms of HER inhibitor resistance involving c-Met activation and PTEN loss were blocked.

CONCLUSIONS

The combination of an ER blocker and a pan-HER inhibitor provides synergistic efficacy in different models of ERβ+ NSCLC. Our data support the use of this combination clinically, considering its ability to induce potent antitumor effects and produce a gene signature that predicts better clinical outcomes.

Afatinib restrains K-RAS-driven lung tumorigenesis

On the basis of clinical trials using first-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), it became a doctrine that V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (K-RAS) mutations drive resistance to EGFR inhibition in non-small cell lung cancer (NSCLC). Conversely, we provide evidence that EGFR signaling is engaged in K-RAS-driven lung tumorigenesis in humans and in mice. Specifically, genetic mouse models revealed that deletion of Egfr quenches mutant K-RAS activity and transiently reduces tumor growth. However, EGFR inhibition initiates a rapid resistance mechanism involving non-EGFR ERBB family members. This tumor escape mechanism clarifies the disappointing outcome of first-generation TKIs and suggests high therapeutic potential of pan-ERBB inhibitors. On the basis of various experimental models including genetically engineered mouse models, patient-derived and cell line-derived xenografts, and in vitro experiments, we demonstrate that the U.S. Food and Drug Administration-approved pan-ERBB inhibitor afatinib effectively impairs K-RAS-driven lung tumorigenesis. Our data support reconsidering the use of pan-ERBB inhibition in clinical trials to treat K-RAS-mutated NSCLC.

New Horizons in KRAS-Mutant Lung Cancer: Dawn After Darkness

In non-small cell lung cancer (NSCLC), the most frequent oncogenic mutation in western countries is KRAS, for which, however, there remains no clinically approved targeted therapies. Recent progress on high biological heterogeneity including diverse KRAS point mutations, varying dependence on mutant KRAS, wide spectrum of other co-occurring genetic alterations, as well as distinct cellular status across the epithelial-to-mesenchymal transition (EMT), has not only deepened our understanding about the pathobiology of KRAS-mutant NSCLC but also brought about unprecedented new hopes for precision treatment of patients. In this review, we provide an update on the most recent advances in KRAS-mutant lung cancer, with a focus on mechanistic insights into tumor heterogeneity, the potential clinic implications and new therapies on horizons tailored for KRAS-mutant lung cancer.

Whole Transcriptome Analysis Identifies TNS4 as a Key Effector of Cetuximab and a Regulator of the Oncogenic Activity of KRAS Mutant Colorectal Cancer Cell Lines

The targeting of activated epidermal growth factor receptor (EGFR) with therapeutic anti-EGFR monoclonal antibodies (mAbs) such as cetuximab and panitumumab has been used as an effective strategy in the treatment of colorectal cancer (CRC). However, its clinical efficacy occurs only in a limited number of patients. Here, we performed whole-transcriptome analysis in xenograft mouse tumors induced by KRAS^G12D mutation-bearing LS174T CRC cells following treatment with either cetuximab or PBS. Through integrated analyses of differential gene expression with TCGA and CCLE public database, we identified TNS4, overexpressed in CRC patients and KRAS mutation-harboring CRC cell lines, significantly downregulated by cetuximab. While ablation of TNS4 expression via shRNA results in significant growth inhibition of LS174T, DLD1, WiDr, and DiFi CRC cell lines, conversely, its ectopic expression increases the oncogenic growth of these cells. Furthermore, TNS4 expression is transcriptionally regulated by MAP kinase signaling pathway. Consistent with this finding, selumetinib, a MEK1/2 inhibitor, suppressed oncogenic activity of CRC cells, and this effect is more profound in combination with cetuximab. Altogether, we propose that TNS4 plays a crucial role in CRC tumorigenesis, and that suppression of TNS4 would be an effective therapeutic strategy in treating a subset of cetuximab-refractory CRC patients including KRAS activating mutations.

Neratinib inhibits Hippo/YAP signaling, reduces mutant K-RAS expression, and kills pancreatic and blood cancer cells

Prior studies demonstrated that the irreversible ERBB1/2/4 inhibitor neratinib caused plasma membrane-associated mutant K-RAS to localize in intracellular vesicles, concomitant with its degradation. Herein, we discovered that neratinib interacted with the chemically distinct irreversible ERBB1/2/4 inhibitor afatinib to reduce expression of ERBB1, ERBB2, K-RAS and N-RAS; this was associated with greater-than-additive cell killing of pancreatic tumor cells. Knock down of Beclin1, ATG16L1, Rubicon or cathepsin B significantly lowered the ability of neratinib to reduce ERBB1 and K-RAS expression, and to cause tumor cell death. Knock down of ATM-AMPK suppressed vesicle formation and knock down of cathepsin B-AIF significantly reduced neratinib lethality. PKG phosphorylates K-RAS and HMG CoA reductase inhibitors reduce K-RAS farnesylation both of which remove K-RAS from the plasma membrane, abolishing its activity. Neratinib interacted with the PKG activator sildenafil and the HMG CoA reductase inhibitor atorvastatin to further reduce K-RAS expression, and to further enhance cell killing. Neratinib is also a Ste20 kinase family inhibitor and in carcinoma cells, and hematopoietic cancer cells lacking ERBB1/2/4, it reduced K-RAS expression and the phosphorylation of MST1/3/4/Ezrin by ~ 30%. Neratinib increased LATS1 phosphorylation as well as that of YAP and TAZ also by ~ 30%, caused the majority of YAP to translocate into the cytosol and reduced YAP/TAZ protein levels. Neratinib lethality was enhanced by knock down of YAP. Neratinib, in a Rubicon-dependent fashion, reduced PAK1 phosphorylation and that of its substrate Merlin. Our data demonstrate that neratinib coordinately suppresses both mutant K-RAS and YAP function to kill pancreatic tumor cells.

Cancer Treatment in the Genomic Era

The complexity of human cancer underlies its devastating clinical consequences. Drugs designed to target the genetic alterations that drive cancer have improved the outcome for many patients, but not the majority of them. Here, we review the genomic landscape of cancer, how genomic data can provide much more than a sum of its parts, and the approaches developed to identify and validate genomic alterations with potential therapeutic value. We highlight notable successes and pitfalls in predicting the value of potential therapeutic targets and discuss the use of multi-omic data to better understand cancer dependencies and drug sensitivity. We discuss how integrated approaches to collecting, curating, and sharing these large data sets might improve the identification and prioritization of cancer vulnerabilities as well as patient stratification within clinical trials. Finally, we outline how future approaches might improve the efficiency and speed of translating genomic data into clinically effective therapies and how the use of unbiased genome-wide information can identify novel predictive biomarkers that can be either simple or complex.

KRASG12C inhibition produces a driver-limited state revealing collateral dependencies

Inhibitors targeting KRAS^G12C, a mutant form of the guanosine triphosphatase (GTPase) KRAS, are a promising new class of oncogene-specific therapeutics for the treatment of tumors driven by the mutant protein. These inhibitors react with the mutant cysteine residue by binding covalently to the switch-II pocket (S-IIP) that is present only in the inactive guanosine diphosphate (GDP)-bound form of KRAS^G12C, sparing the wild-type protein. We used a genome-scale CRISPR interference (CRISPRi) functional genomics platform to systematically identify genetic interactions with a KRAS^G12C inhibitor in cellular models of KRAS^G12C mutant lung and pancreatic cancer. Our data revealed genes that were selectively essential in this oncogenic driver-limited cell state, meaning that their loss enhanced cellular susceptibility to direct KRAS^G12C inhibition. We termed such genes "collateral dependencies" (CDs) and identified two classes of combination therapies targeting these CDs that increased KRAS^G12C target engagement or blocked residual survival pathways in cells and in vivo. From our findings, we propose a framework for assessing genetic dependencies induced by oncogene inhibition.

Identification of a Clinically Relevant Signature for Early Progression in KRAS-Driven Lung Adenocarcinoma

Inducible genetically defined mouse models of cancer uniquely facilitate the investigation of early events in cancer progression, however, there are valid concerns about the ability of such models to faithfully recapitulate human disease. We developed an inducible mouse model of progressive lung adenocarcinoma (LuAd) that combines sporadic activation of oncogenic KRasG12D with modest overexpression of c-MYC (KM model). Histological examination revealed a highly reproducible spontaneous transition from low-grade adenocarcinoma to locally invasive adenocarcinoma within 6 weeks of oncogene activation. Laser-capture microdissection coupled with RNA-SEQ (ribonucleic acid sequencing) was employed to determine transcriptional changes associated with tumour progression. Upregulated genes were triaged for relevance to human LuAd using datasets from Oncomine and cBioportal. Selected genes were validated by RNAi screening in human lung cancer cell lines and examined for association with lung cancer patient overall survival using KMplot.com. Depletion of progression-associated genes resulted in pronounced viability and/or cell migration defects in human lung cancer cells. Progression-associated genes moreover exhibited strong associations with overall survival, specifically in human lung adenocarcinoma, but not in squamous cell carcinoma. The KM mouse model faithfully recapitulates key molecular events in human adenocarcinoma of the lung and is a useful tool for mechanistic interrogation of KRAS-driven LuAd progression.

AhR controls redox homeostasis and shapes the tumor microenvironment in BRCA1-associated breast cancer

Cancer cells have higher reactive oxygen species (ROS) than normal cells, due to genetic and metabolic alterations. An emerging scenario is that cancer cells increase ROS to activate protumorigenic signaling while activating antioxidant pathways to maintain redox homeostasis. Here we show that, in basal-like and BRCA1-related breast cancer (BC), ROS levels correlate with the expression and activity of the transcription factor aryl hydrocarbon receptor (AhR). Mechanistically, ROS triggers AhR nuclear accumulation and activation to promote the transcription of both antioxidant enzymes and the epidermal growth factor receptor (EGFR) ligand, amphiregulin (AREG). In a mouse model of BRCA1-related BC, cancer-associated AhR and AREG control tumor growth and production of chemokines to attract monocytes and activate proangiogenic function of macrophages in the tumor microenvironment. Interestingly, the expression of these chemokines as well as infiltration of monocyte-lineage cells (monocyte and macrophages) positively correlated with ROS levels in basal-like BC. These data support the existence of a coordinated link between cancer-intrinsic ROS regulation and the features of tumor microenvironment. Therapeutically, chemical inhibition of AhR activity sensitizes human BC models to Erlotinib, a selective EGFR tyrosine kinase inhibitor, suggesting a promising combinatorial anticancer effect of AhR and EGFR pathway inhibition. Thus, AhR represents an attractive target to inhibit redox homeostasis and modulate the tumor promoting microenvironment of basal-like and BRCA1-associated BC.

Neratinib and entinostat combine to rapidly reduce the expression of K-RAS, N-RAS, Gαq and Gα11 and kill uveal melanoma cells

There is no efficacious standard of care therapy for uveal melanoma. Unlike cutaneous disease, uveal melanoma does not exhibit RAS mutations but instead contains mutations with ~90% penetrance in either Gα_q or Gα₁₁. Previously we demonstrated that neratinib caused ERBB1/2/4 and RAS internalization into autolysosomes which resulted in their proteolytic degradation. In PDX isolates of uveal melanoma, neratinib caused the internalization and degradation of Gα_q and Gα₁₁ in parallel with ERBB1 breakdown. These effects were enhanced by the HDAC inhibitor entinostat. Similar data were obtained using GFP/RFP tagged forms of K-RAS V12. Down regulation of Gα_q and Gα₁₁ expression and RAS-GFP/RFP fluorescence required Beclin1 and ATG5. The [neratinib + entinostat] combination engaged multiple pathways to mediate killing. One was from ROS-dependent activation of ATM via AMPK-ULK1-ATG13-Beclin1/ATG5. Another pathway was from CD95 via caspase 8-RIP1/RIP3. A third was from reduced expression of HSP70, HSP90, HDAC6 and phosphorylation of eIF2α. Downstream of the mitochondrion both caspase 9 and AIF played roles in tumor cell execution. Knock down of ATM/AMPK/ULK-1 prevented ATG13 phosphorylation and degradation of RAS and Gα proteins. Over-expression of activated mTOR prevented ATG13 phosphorylation and suppressed killing. Knock down of eIF2α maintained BCL-XL and MCL-1 expression. Within 6h, [neratinib + entinostat] reduced the expression of the immunology biomarkers PD-L1, ODC, IDO-1 and enhanced MHCA levels. Our data demonstrate that [neratinib + entinostat] down-regulates oncogenic RAS and the two key oncogenic drivers present in most uveal melanoma patients and causes a multifactorial form of killing via mitochondrial dysfunction and toxic autophagy. Abbreviations: ERK: extracellular regulated kinase; PI3K: phosphatidyl inositol 3 kinase; ca: constitutively active; dn: dominant negative; ER: endoplasmic reticulum; AIF: apoptosis inducing factor; AMPK: AMP-dependent protein kinase; mTOR: mammalian target of rapamycin; JAK: Janus Kinase; STAT: Signal Transducers and Activators of Transcription; MAPK: mitogen activated protein kinase; PTEN: phosphatase and tensin homologue on chromosome ten; ROS: reactive oxygen species; CMV: empty vector plasmid or virus; si: small interfering; SCR: scrambled; IP: immunoprecipitation; VEH: vehicle; HDAC: histone deacetylase.

Breaking bad family ties: Pan-ERBB blockers inhibit KRAS driven lung tumorigenesis

Oncogenic K-RAS mutations were believed to lock the molecular switch in the ON state, independent of upstream activation. However, we demonstrate in preclinical models that activity of mutated K-RAS depends on upstream signaling events involving EGF receptor family members. This finding reveals a potential therapeutic vulnerability using pan-ERBB inhibitors to fight K-RAS mutated lung tumors.