Synthetic lethal interaction of combined BCL-XL and MEK inhibition promotes tumor regressions in KRAS mutant cancer models

[Effect and significance of BH3-only protein in targeted therapy of non-small cell lung cancer]

肺癌死亡率居全球恶性肿瘤死亡之首，非小细胞肺癌是肺癌中最常见的类型。在传统的抗肺癌治疗中，促进细胞凋亡是非小细胞肺癌治疗的一个重要组成部分，但抗肿瘤药物存在毒副作用大和耐药性等问题。因此，寻找新的抗肿瘤药物作用靶点成为非小细胞肺癌治疗的重点之一。BH3-only蛋白在凋亡的启动及凋亡通路的沟通中发挥极其重要的作用。BIM是BH3-only蛋白家族中的核心成员。以BIM为靶点的治疗在非小细胞肺癌的治疗中具有不可取代的作用。本文简单介绍了BCL-2家族和其中的BH3-only促凋亡蛋白，并且阐述了BIM、BH3-only蛋白在非小细胞肺癌靶向治疗中的重要作用。

Preclinical efficacy of MEK inhibition in Nras-mutant AML

Oncogenic NRAS mutations are highly prevalent in acute myeloid leukemia (AML). Genetic analysis supports the hypothesis that NRAS mutations cooperate with antecedent molecular lesions in leukemogenesis, but have limited independent prognostic significance. Using short hairpin RNA-mediated knockdown in human cell lines and primary mouse leukemias, we show that AML cells with NRAS/Nras mutations are dependent on continued oncogene expression in vitro and in vivo. Using the Mx1-Cre transgene to inactivate a conditional mutant Nras allele, we analyzed hematopoiesis and hematopoietic stem and progenitor cells (HSPCs) under normal and stressed conditions and found that HSPCs lacking Nras expression are functionally equivalent to normal HSPCs in the adult mouse. Treating recipient mice transplanted with primary Nras(G12D) AMLs with 2 potent allosteric mitogen-activated protein kinase kinase (MEK) inhibitors (PD0325901 or trametinib/GlaxoSmithKline 1120212) significantly prolonged survival and reduced proliferation but did not induce apoptosis, promote differentiation, or drive clonal evolution. The phosphatidylinositol 3-kinase inhibitor GDC-0941 was ineffective as a single agent and did not augment the activity of PD0325901. All mice ultimately succumbed to progressive leukemia. Together, these data validate oncogenic N-Ras signaling as a therapeutic target in AML and support testing combination regimens that include MEK inhibitors.

BYL719, a selective inhibitor of phosphoinositide 3-Kinase α, enhances the effect of selumetinib (AZD6244, ARRY-142886) in KRAS-mutant non-small cell lung cancer

PURPOSE

KRAS is frequently mutated in non-small cell lung cancers (NSCLC), resulting in activation of the MEK/ERK pathway. Because there are currently no drugs that target oncogenic KRAS, MEK inhibitors have been tested clinically as a possible treatment option for patients with NSCLC. However, KRAS-mutant cancers exhibit resistance to MEK inhibitors. Therefore, a combinational strategy is necessary for effective therapy. To address this, we investigated the therapeutic effects of combining selumetinib, a MEK1/2 inhibitor, with BYL719, a PI3Kα inhibitor.

METHODS

We evaluated the effects of selumetinib and BYL719 in vitro and in vivo in NSCLC cell lines.

RESULTS

The combination of BYL719 and selumetinib resulted in synergistic cytotoxic activity compared with the single agents alone in KRAS-mutant NSCLC cells. At the molecular level, we found that AKT activation strongly influenced the sensitivity of KRAS-mutant NSCLC cells to selumetinib. Selumetinib upregulated phospho-AKT and phosphorylated BAD at ser136, which is responsible for intrinsic drug resistance in KRAS-mutant NSCLC cells. In contrast, inhibition of the PI3K/AKT pathway by BYL719 hindered selumetinib-induced BAD phosphorylation and increased the antitumor efficacy of selumetinib. Furthermore, selumetinib and BYL719 combination therapy showed synergy in the suppression of A549 xenograft tumor growth. On analysis of the pharmacodynamics, selumetinib and BYL719 together resulted in effective inhibition of both p-ERK and p-AKT expression in tumor tissue.

CONCLUSION

Taken together, these data suggest that combination treatment with selumetinib and BYL719 is a promising therapeutic approach to overcoming resistance to MEK inhibitors.

The cell of origin and subtype of K-Ras-induced lung tumors are modified by Notch and Sox2

K-Ras activation with a CC10(Scgb1a1)-CreER driver leads to lung adenocarcinoma in a subset of alveolar type II cells and hyperplasia in the bronchioalveolar duct region. Xu et al. find that Notch inhibition strongly inhibits adenocarcinoma formation but promotes squamous hyperplasia in the alveoli. In contrast, activation of Notch leads to widespread Sox2⁺, Sox9⁺, and CC10⁺ papillary adenocarcinomas throughout the bronchioles. Sox2 binds to NOTCH1 and NOTCH2 regulatory regions and reduces Notch1 and Notch2 transcripts. This study shows that the cell of origin of K-Ras-induced tumors depends on levels of Sox2 expression affecting Notch signaling.

Cell type-specific conditional activation of oncogenic K-Ras is a powerful tool for investigating the cell of origin of adenocarcinomas in the mouse lung. Our previous studies showed that K-Ras activation with a CC10(Scgb1a1)-CreER driver leads to adenocarcinoma in a subset of alveolar type II cells and hyperplasia in the bronchioalveolar duct region. However, no tumors develop in the bronchioles, although recombination occurs throughout this region. To explore underlying mechanisms, we simultaneously modulated either Notch signaling or Sox2 levels in the CC10⁺ cells along with activation of K-Ras. Inhibition of Notch strongly inhibits adenocarcinoma formation but promotes squamous hyperplasia in the alveoli. In contrast, activation of Notch leads to widespread Sox2⁺, Sox9⁺, and CC10⁺ papillary adenocarcinomas throughout the bronchioles. Chromatin immunoprecipitation demonstrates Sox2 binding to NOTCH1 and NOTCH2 regulatory regions. In transgenic mouse models, overexpression of Sox2 leads to a significant reduction of Notch1 and Notch2 transcripts, while a 50% reduction in Sox2 leads to widespread papillary adenocarcinoma in the bronchioles. Taken together, our data demonstrate that the cell of origin of K-Ras-induced tumors in the lung depends on levels of Sox2 expression affecting Notch signaling. In addition, the subtype of tumors arising from type II cells is determined in part by Notch activation or suppression.

Drugging the undruggable RAS: Mission possible?

Despite more than three decades of intensive effort, no effective pharmacological inhibitors of the RAS oncoproteins have reached the clinic, prompting the widely held perception that RAS proteins are 'undruggable'. However, recent data from the laboratory and the clinic have renewed our hope for the development of RAS-inhibitory molecules. In this Review, we summarize the progress and the promise of five key approaches. Firstly, we focus on the prospects of using direct inhibitors of RAS. Secondly, we address the issue of whether blocking RAS membrane association is a viable approach. Thirdly, we assess the status of targeting RAS downstream effector signalling, which is arguably the most favourable current approach. Fourthly, we address whether the search for synthetic lethal interactors of mutant RAS still holds promise. Finally, RAS-mediated changes in cell metabolism have recently been described and we discuss whether these changes could be exploited for new therapeutic directions. We conclude with perspectives on how additional complexities, which are not yet fully understood, may affect each of these approaches.

Synthetic lethal vulnerabilities of cancer

The great majority of targeted anticancer drugs inhibit mutated oncogenes that display increased activity. Yet many tumors do not contain such actionable aberrations, such as those harboring loss-of-function mutations. The notion of targeting synthetic lethal vulnerabilities in cancer cells has provided an alternative approach to exploiting more of the genetic and epigenetic changes acquired during tumorigenesis. Here, we review synthetic lethality as a therapeutic concept that exploits the inherent differences between normal cells and cancer cells. Furthermore, we provide an overview of the screening approaches that can be used to identify synthetic lethal interactions in human cells and present several recently identified interactions that may be pharmacologically exploited. Finally, we indicate some of the challenges of translating synthetic lethal interactions into the clinic and how these may be overcome.

Feedback and redundancy in receptor tyrosine kinase signaling: relevance to cancer therapies

Mammalian cells have multiple regulatory mechanisms to deal with perturbations in cellular homeostasis, including feedback loops and crosstalk between the major signaling pathways. While these mechanisms are critically required to help cells survive under dynamic physiological circumstances, they also pose an impediment to the effective treatment of cancer. In this review, we describe what has been learned about interactions between receptor tyrosine kinase-dependent signaling pathways, and how this knowledge can be used to design rational and more effective combination therapies for cancer.

Moving from histological subtyping to molecular characterization: new treatment opportunities in advanced non-small-cell lung cancer

Over the last 10 years, the systemic treatment of advanced non-small-cell lung cancer has progressively moved away from the 'one-size-fits-all' approach to histological subtyping. Currently, there is a progressive implementation of targeted therapies based on specific molecular characteristics such as the EGF receptor sensitizing mutations and the anaplastic lymphoma kinase rearrangements. Despite the availability of effective agents against these abnormalities, acquired resistance is still a major issue. A new generation of tyrosine kinase inhibitors for EGF receptor and anaplastic lymphoma kinase targeting acquired resistance mechanisms have been recently investigated. Several promising tyrosine kinase inhibitors that hit other targets are also in clinical development, including: rat sarcoma gene/MEK, BRAF1, PIK3A, c-mesenchymal-epithelial transition, c-ros oncogene 1, rearranged during transfection, human EGFR 2, FGFR, VEGFR, PDGFR and discoidin death receptor 2. Furthermore, new advances in immunology have been achieved through the discovery of vaccines and immune checkpoint pathways such as the cytotoxic T-lymphocyte-associated antigen-4, programmed cell death protein 1 and its ligands.

Oncogenic KRAS signalling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is almost universally fatal. The annual number of deaths equals the number of newly diagnosed cases, despite maximal treatment. The overall 5-year survival rate of <5% has remained stubbornly unchanged over the last 30 years, despite tremendous efforts in preclinical and clinical science. There is unquestionably an urgent need to further improve our understanding of pancreatic cancer biology, treatment response and relapse, and to identify novel therapeutic targets. Rigorous research in the field has uncovered genetic aberrations that occur during PDAC development and progression. In most cases, PDAC is initiated by oncogenic mutant KRAS, which has been shown to drive pancreatic neoplasia. However, all attempts to target KRAS directly have failed in the clinic and KRAS is widely assumed to be undruggable. This has led to intense efforts to identify druggable critical downstream targets and nodes orchestrated by mutationally activated KRAS. This includes context-specific KRAS effector pathways, synthetic lethal interaction partners and KRAS-driven metabolic changes. Here, we review recent advances in oncogenic KRAS signalling and discuss how these might benefit PDAC treatment in the future.

Intrinsic and acquired resistance to MEK1/2 inhibitors in cancer

Recent clinical data with BRAF and MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase 1/2] inhibitors have demonstrated the remarkable potential of targeting the RAF-MEK1/2-ERK1/2 signalling cascade for the treatment of certain cancers. Despite these advances, however, only a subset of patients respond to these agents in the first instance, and, of those that do, acquired resistance invariably develops after several months. Studies in vitro have identified various mechanisms that can underpin intrinsic and acquired resistance to MEK1/2 inhibitors, and these frequently recapitulate those observed clinically. In the present article, we review these mechanisms and also discuss recent advances in our understanding of how MEK1/2 inhibitor activity is influenced by pathway feedback.

A systems biology approach to personalizing therapeutic combinations

The identification of evidence-based, efficacious drug combinations for each cancer, among thousands of potential permutations, is a daunting task. In this perspective, we propose a systematic approach to defining such combinations by molecularly benchmarking a drug against a desired state of efficacy using model systems.

Ras/Raf/MEK/ERK Pathway Activation in Childhood Acute Lymphoblastic Leukemia and Its Therapeutic Targeting

Deregulation of the Ras/Raf/MEK/extracellular signal-regulated kinase pathway is a common event in childhood acute lymphoblastic leukemia and is caused by point mutation, gene deletion, and chromosomal translocation of a vast array of gene types, highlighting its importance in leukemia biology. Pathway activation can be therapeutically exploited and may guide new therapies needed for relapsed acute lymphoblastic leukemia and other high risk subgroups.

Applications of RNA interference high-throughput screening technology in cancer biology and virology

RNA interference (RNAi) is an ancient intra-cellular mechanism that regulates gene expression and cell function. Large-scale gene silencing using RNAi high-throughput screening (HTS) has opened an exciting frontier to systematically study gene function in mammalian cells. This approach enables researchers to identify gene function in a given biological context and will provide considerable novel insight. Here, we review RNAi HTS strategies and applications using case studies in cancer biology and virology.

Molecular pathways: the basis for rational combination using MEK inhibitors in KRAS-mutant cancers

Mutations in RAS oncogenes are frequently observed in human cancers, and the mutations result in activation of the RAS-RAF-MEK-ERK pathway, leading to cell proliferation and survival. The pathway is, therefore, a potent therapeutic target in the RAS-mutant cancers. MEK inhibitors can specifically block the pathway and are one of the key types of drugs for the treatment of the RAS-mutant cancers. As RAS proteins activate other downstream signaling proteins in addition to the RAS-RAF-MEK-ERK pathway, combination therapeutic approaches with MEK inhibitors are also being evaluated. Moreover, MEK inhibitors can arrest cancer cells in G1 phase and repress prosurvival Bcl2 family proteins such as MCL1 and BCL2/BCLXL, and increase expression of Bim, a proapoptotic BH3-only family protein. This mechanism may explain the efficacy of the combination of MEK inhibitors with cytotoxic agents or other targeted inhibitors. A better understanding of the pathway will help us with development of rational combinations for the treatment of the RAS-mutant cancers.

A RAS renaissance: emerging targeted therapies for KRAS-mutated non-small cell lung cancer

Of the numerous oncogenes implicated in human cancer, the most common and perhaps the most elusive to target pharmacologically is RAS. Since the discovery of RAS in the 1960s, numerous studies have elucidated the mechanism of activity, regulation, and intracellular trafficking of the RAS gene products, and of its regulatory pathways. These pathways yielded druggable targets, such as farnesyltransferase, during the 1980s to 1990s. Unfortunately, early clinical trials investigating farnesyltransferase inhibitors yielded disappointing results, and subsequent interest by pharmaceutical companies in targeting RAS waned. However, recent advances including the identification of novel regulatory enzymes (e.g., Rce1, Icmt, Pdeδ), siRNA-based synthetic lethality screens, and fragment-based small-molecule screens, have resulted in a "Ras renaissance," signified by new Ras and Ras pathway-targeted therapies that have led to new clinical trials of patients with Ras-driven cancers. This review gives an overview of KRas signaling pathways with an emphasis on novel targets and targeted therapies, using non-small cell lung cancer as a case example.

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.

Primary and acquired resistance to EGFR-targeted therapies in colorectal cancer: impact on future treatment strategies

Only approximately 10 % of genetically unselected patients with chemorefractory metastatic colorectal cancer experience tumor regression when treated with the anti-epidermal growth factor receptor (EGFR) antibodies cetuximab or panitumumab (“primary” or “de novo” resistance). Moreover, nearly all patients whose tumors initially respond inevitably become refractory (“secondary” or “acquired” resistance). An ever-increasing number of predictors of both primary and acquired resistance to anti-EGFR antibodies have been described, and it is now evident that most of the underlying mechanisms significantly overlap. By trying to extrapolate a unifying perspective out of many idiosyncratic details, here, we discuss the molecular underpinnings of therapeutic resistance, summarize research efforts aimed to improve patient selection, and present alternative therapeutic strategies that are now under development to increase response and combat relapse.

Oncogenic KRAS signalling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is almost universally fatal. The annual number of deaths equals the number of newly diagnosed cases, despite maximal treatment. The overall 5-year survival rate of <5% has remained stubbornly unchanged over the last 30 years, despite tremendous efforts in preclinical and clinical science. There is unquestionably an urgent need to further improve our understanding of pancreatic cancer biology, treatment response and relapse, and to identify novel therapeutic targets. Rigorous research in the field has uncovered genetic aberrations that occur during PDAC development and progression. In most cases, PDAC is initiated by oncogenic mutant KRAS, which has been shown to drive pancreatic neoplasia. However, all attempts to target KRAS directly have failed in the clinic and KRAS is widely assumed to be undruggable. This has led to intense efforts to identify druggable critical downstream targets and nodes orchestrated by mutationally activated KRAS. This includes context-specific KRAS effector pathways, synthetic lethal interaction partners and KRAS-driven metabolic changes. Here, we review recent advances in oncogenic KRAS signalling and discuss how these might benefit PDAC treatment in the future.

Inhibiting Tankyrases sensitizes KRAS-mutant cancer cells to MEK inhibitors via FGFR2 feedback signaling

Tankyrases (TNKS) play roles in Wnt signaling, telomere homeostasis, and mitosis, offering attractive targets for anticancer treatment. Using unbiased combination screening in a large panel of cancer cell lines, we have identified a strong synergy between TNKS and MEK inhibitors (MEKi) in KRAS-mutant cancer cells. Our study uncovers a novel function of TNKS in the relief of a feedback loop induced by MEK inhibition on FGFR2 signaling pathway. Moreover, dual inhibition of TNKS and MEK leads to more robust apoptosis and antitumor activity both in vitro and in vivo than effects observed by previously reported MEKi combinations. Altogether, our results show how a novel combination of TNKS and MEK inhibitors can be highly effective in targeting KRAS-mutant cancers by suppressing a newly discovered resistance mechanism.

From mice to men: GEMMs as trial patients for new NSCLC therapies

Given the large socio-economic burden of cancer, there is an urgent need for in vivo animal cancer models that can provide a rationale for personalised therapeutic regimens that are translatable to the clinic. Recent developments in establishing mouse models that closely resemble human lung cancers involve the application of genetically engineered mouse models (GEMMs) for use in drug efficacy studies or to guide patient therapy. Here, we review recent applications of GEMMs in non-small cell lung cancer research for drug development and their potential in aiding biomarker discovery and understanding of biological mechanisms behind clinical outcomes and drug interactions.

Molecular pathways and therapeutic targets in lung cancer

Lung cancer is still the leading cause of cancer death worldwide. Both histologically and molecularly lung cancer is heterogeneous. This review summarizes the current knowledge of the pathways involved in the various types of lung cancer with an emphasis on the clinical implications of the increasing number of actionable molecular targets. It describes the major pathways and molecular alterations implicated in the development and progression of non-small cell lung cancer (adenocarcinoma and squamous cancer), and of small cell carcinoma, emphasizing the molecular alterations comprising the specific blueprints in each group. The approved and investigational targeted therapies as well as the immune therapies, and clinical trials exploring the variety of targeted approaches to treatment of lung cancer are the main focus of this review.

Intrinsic resistance to MEK inhibition in KRAS mutant lung and colon cancer through transcriptional induction of ERBB3

There are no effective therapies for the ~30% of human malignancies with mutant RAS oncogenes. Using a kinome-centered synthetic lethality screen, we find that suppression of the ERBB3 receptor tyrosine kinase sensitizes KRAS mutant lung and colon cancer cells to MEK inhibitors. We show that MEK inhibition results in MYC-dependent transcriptional upregulation of ERBB3, which is responsible for intrinsic drug resistance. Drugs targeting both EGFR and ERBB2, each capable of forming heterodimers with ERBB3, can reverse unresponsiveness to MEK inhibition by decreasing inhibitory phosphorylation of the proapoptotic proteins BAD and BIM. Moreover, ERBB3 protein level is a biomarker of response to combinatorial treatment. These data suggest a combination strategy for treating KRAS mutant colon and lung cancers and a way to identify the tumors that are most likely to benefit from such combinatorial treatment.

Not just gRASping at flaws: finding vulnerabilities to develop novel therapies for treating KRAS mutant cancers

Mutations in Kirsten rat-sarcoma (KRAS) are well appreciated to be major drivers of human cancers through dysregulation of multiple growth and survival pathways. Similar to many other non-kinase oncogenes and tumor suppressors, efforts to directly target KRAS pharmaceutically have not yet materialized. As a result, there is broad interest in an alternative approach to develop therapies that induce synthetic lethality in cancers with mutant KRAS, therefore exposing the particular vulnerabilities of these cancers. Fueling these efforts is our increased understanding into the biology driving KRAS mutant cancers, in particular the important pathways that mutant KRAS governs to promote survival. In this mini-review, we summarize the latest approaches to treat KRAS mutant cancers and the rationale behind them.

Synthetic lethal screening reveals FGFR as one of the combinatorial targets to overcome resistance to Met-targeted therapy

Met is a receptor tyrosine kinase that promotes cancer progression. In addition, Met has been implicated in resistance of tumors to various targeted therapies such as epidermal growth factor receptor inhibitors in lung cancers, and has been prioritized as a key molecular target for cancer therapy. However, the underlying mechanism of resistance to Met-targeting drugs is poorly understood. Here, we describe screening of 1310 genes to search for key regulators related to drug resistance to an anti-Met therapeutic antibody (SAIT301) by using a small interfering RNA-based synthetic lethal screening method. We found that knockdown of 69 genes in Met-amplified MKN45 cells sensitized the antitumor activity of SAIT301. Pathway analysis of these 69 genes implicated fibroblast growth factor receptor (FGFR) as a key regulator for antiproliferative effects of Met-targeting drugs. Inhibition of FGFR3 increased target cell apoptosis through the suppression of Bcl-xL expression, followed by reduced cancer cell growth in the presence of Met-targeting drugs. Treatment of cells with the FGFR inhibitors substantially restored the efficacy of SAIT301 in SAIT301-resistant cells and enhanced the efficacy in SAIT301-sensitive cells. In addition to FGFR3, integrin β3 is another potential target for combination treatment with SAIT301. Suppression of integrin β3 decreased AKT phosphorylation in SAIT301-resistant cells and restored SAIT301 responsiveness in HCC1954 cells, which are resistant to SAIT301. Gene expression analysis using CCLE database shows that cancer cells with high levels of FGFR and integrin β3 are resistant to crizotinib treatment, suggesting that FGFR and integrin β3 could be used as predictive markers for Met-targeted therapy and provide a potential therapeutic option to overcome acquired and innate resistance for the Met-targeting drugs.

PI3K/mTOR dual inhibitor NVP-BEZ235 decreases Mcl-1 expression and sensitizes ovarian carcinoma cells to Bcl-xL-targeting strategies, provided that Bim expression is induced

We previously showed that Bcl-xL and Mcl-1 cooperatively protect platinum-resistant ovarian cancer cells from apoptosis. Here we assessed the anticancer potential of combining ABT-737-induced inhibition of Bcl-xL with Mcl-1 inhibition via PI3K/Akt/mTOR pathway disruption using NVP-BEZ235. NVP-BEZ235 inhibited cell proliferation without inducing apoptosis. It strongly repressed Mcl-1 expression and induced Puma expression in both cell lines tested while differentially modulating Bim between the two. Interestingly, NVP-BEZ235 efficiently sensitized ovarian carcinoma cells to ABT-737, provided that Bim expression was induced. Moreover, inhibiting the ERK1/2 pathway restored Bim expression and sensitized low Bim-expressing cancer cells to the BEZ235/ABT-737 treatment.

Diminished WNT -> β-catenin -> c-MYC signaling is a barrier for malignant progression of BRAFV600E-induced lung tumors

Oncogene-induced senescence (OIS) is proposed as a cellular defense mechanism that restrains malignant progression of oncogene-expressing, initiated tumor cells. Consistent with this, expression of BRAF(V600E) in the mouse lung epithelium elicits benign tumors that fail to progress to cancer due to an apparent senescence-like proliferative arrest. Here we demonstrate that nuclear β-catenin → c-MYC signaling is essential for early stage proliferation of BRAF(V600E)-induced lung tumors and is inactivated in the subsequent senescence-like state. Furthermore, either β-catenin silencing or pharmacological blockade of Porcupine, an acyl-transferase essential for WNT ligand secretion and activity, significantly inhibited BRAF(V600E)-initiated lung tumorigenesis. Conversely, sustained activity of β-catenin or c-MYC significantly enhanced BRAF(V600E)-induced lung tumorigenesis and rescued the anti-tumor effects of Porcupine blockade. These data indicate that early stage BRAF(V600E)-induced lung tumors are WNT-dependent and suggest that inactivation of WNT → β-catenin → c-MYC signaling is a trigger for the senescence-like proliferative arrest that constrains the expansion and malignant progression of BRAF(V600E)-initiated lung tumors. Moreover, these data further suggest that the trigger for OIS in initiated BRAF(V600E)-expressing lung tumor cells is not simply a surfeit of signals from oncogenic BRAF but an insufficiency of WNT → β-catenin → c-MYC signaling. These data have implications for understanding how genetic abnormalities cooperate to initiate and promote lung carcinogenesis.

Combination PI3K/MEK inhibition promotes tumor apoptosis and regression in PIK3CA wild-type, KRAS mutant colorectal cancer

PI3K inhibition in combination with other agents has not been studied in the context of PIK3CA wild-type, KRAS mutant cancer. In a screen of phospho-kinases, PI3K inhibition of KRAS mutant colorectal cancer cells activated the MAPK pathway. Combination PI3K/MEK inhibition with NVP-BKM120 and PD-0325901 induced tumor regression in a mouse model of PIK3CA wild-type, KRAS mutant colorectal cancer, which was mediated by inhibition of mTORC1, inhibition of MCL-1, and activation of BIM. These findings implicate mitochondrial-dependent apoptotic mechanisms as determinants for the efficacy of PI3K/MEK inhibition in the treatment of PIK3CA wild-type, KRAS mutant cancer.

A personalized treatment for lung cancer: molecular pathways, targeted therapies, and genomic characterization

Lung cancer is a heterogeneous, complex, and challenging disease to treat. With the arrival of genotyping and genomic profiling, our simple binary division of lung cancer into non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) is no longer acceptable. In the past decade and with the advent of personalized medicine, multiple advances have been made in understanding the underlying biology and molecular mechanisms of lung cancer. Lung cancer is no longer considered a single disease entity and is now being subdivided into molecular subtypes with dedicated targeted and chemotherapeutic strategies. The concept of using information from a patient's tumor to make therapeutic and treatment decisions has revolutionized the landscape for cancer care and research in general.Management of non-small-cell lung cancer, in particular, has seen several of these advances, with the understanding of activating mutations in EGFR, fusion genes involving ALK, rearrangements in ROS-1, and ongoing research in targeted therapies for K-RAS and MET. The next era of personalized treatment for lung cancer will involve a comprehensive genomic characterization of adenocarcinoma, squamous-cell carcinoma, and small-cell carcinoma into various subtypes. Future directions will involve incorporation of molecular characteristics and next generation sequencing into screening strategies to improve early detection, while also having applications for joint treatment decision making in the clinics with patients and practitioners. Personalization of therapy will involve close collaboration between the laboratory and the clinic. Given the heterogeneity and complexity of lung cancer treatment with respect to histology, tumor stage, and genomic characterization, mind mapping has been developed as one of many tools which can assist physicians in this era of personalized medicine. We attempt to utilize the above tool throughout this chapter, while reviewing lung cancer epidemiology, lung cancer treatment, and the genomic characterization of lung cancer.

Targeting BCL2-Proteins for the Treatment of Solid Tumours

Due to their central role in the regulation of apoptosis, the antiapoptotic BCL2-proteins are highly promising targets for the development of novel anticancer treatments. To this end, several strategies have been developed to inhibit BCL2, BCL-XL, BCL-w, and MCL1. While early clinical trials in haematological malignancies demonstrated exciting single-agent activity of BCL2-inhibitors, the response in solid tumours was limited, indicating that, in solid tumours, different strategies have to be developed in order to successfully treat patients with BCL2-inhibitors. In this review, the function of the different antiapoptotic BCL2-proteins and their role in solid tumours will be discussed. In addition, a comprehensive analysis of current small molecules targeting these antiapoptotic BCL2-proteins (e.g., ABT-737, ABT-263, ABT-199, TW-37, sabutoclax, obatoclax, and MIM1) will be provided including a discussion of the results of any clinical trials. This analysis will summarise the potential of BCL2-inhibitors for the treatment of solid tumours and will unravel novel approaches to utilise these inhibitors in clinical applications.

mTOR inhibition specifically sensitizes colorectal cancers with KRAS or BRAF mutations to BCL-2/BCL-XL inhibition by suppressing MCL-1

Colorectal cancers harboring KRAS or BRAF mutations are refractory to current targeted therapies. Using data from a high-throughput drug screen, we have developed a novel therapeutic strategy that targets the apoptotic machinery using the BCL-2 family inhibitor ABT-263 (navitoclax) in combination with a TORC1/2 inhibitor, AZD8055. This combination leads to efficient apoptosis specifically in KRAS- and BRAF-mutant but not wild-type (WT) colorectal cancer cells. This specific susceptibility results from TORC1/2 inhibition leading to suppression of MCL-1 expression in mutant, but not WT, colorectal cancers, leading to abrogation of BIM/MCL-1 complexes. This combination strategy leads to tumor regressions in both KRAS-mutant colorectal cancer xenograft and genetically engineered mouse models of colorectal cancer, but not in the corresponding KRAS-WT colorectal cancer models. These data suggest that the combination of BCL-2/BCL-XL inhibitors with TORC1/2 inhibitors constitutes a promising targeted therapy strategy to treat these recalcitrant cancers.

Targeted therapies in development for non-small cell lung cancer

The iterative discovery in various malignancies during the past decades that a number of aberrant tumorigenic processes and signal transduction pathways are mediated by "druggable" protein kinases has led to a revolutionary change in drug development. In non-small cell lung cancer (NSCLC), the ErbB family of receptors (e.g., EGFR [epidermal growth factor receptor], HER2 [human epidermal growth factor receptor 2]), RAS (rat sarcoma gene), BRAF (v-raf murine sarcoma viral oncogene homolog B1), MAPK (mitogen-activated protein kinase) c-MET (c-mesenchymal-epithelial transition), FGFR (fibroblast growth factor receptor), DDR2 (discoidin domain receptor 2), PIK3CA (phosphatidylinositol-4,5-bisphosphate3-kinase, catalytic subunit alpha)), PTEN (phosphatase and tensin homolog), AKT (protein kinase B), ALK (anaplastic lym phoma kinase), RET (rearranged during transfection), ROS1 (reactive oxygen species 1) and EPH (erythropoietin-producing hepatoma) are key targets of various agents currently in clinical development. These oncogenic targets exert their selective growth advantage through various intercommunicating pathways, such as through RAS/RAF/MEK, phosphoinositide 3-kinase/AKT/mammalian target of rapamycin and SRC-signal transduction and transcription signaling. The recent clinical studies, EGFR tyrosine kinase inhibitors and crizotinib were considered as strongly effective targeted therapies in metastatic NSCLC. Currently, five molecular targeted agents were approved for treatment of advanced NSCLC: Gefitinib, erlotinib and afatinib for positive EGFR mutation, crizotinib for positive echinoderm microtubule-associated protein-like 4 (EML4)-ALK translocation and bevacizumab. Moreover, oncogenic mutant proteins are subject to regulation by protein trafficking pathways, specifically through the heat shock protein 90 system. Drug combinations affecting various nodes in these signaling and intracellular processes are predicted and demonstrated to be synergistic and advantageous in overcoming treatment resistance compared with monotherapy approaches. Understanding the role of the tumor microenvironment in the development and maintenance of the malignant phenotype provided additional therapeutic approaches as well. More recently, improved knowledge on tumor immunology has set the stage for promising immunotherapies in NSCLC. This review will focus on the rationale for the development of targeted therapies in NSCLC and the various strategies employed in preventing or overcoming the inevitable occurrence of treatment resistance.

BET bromodomain inhibition triggers apoptosis of NF1-associated malignant peripheral nerve sheath tumors through Bim induction

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive sarcomas that develop sporadically or in neurofibromatosis type 1 (NF1) patients. There is no effective treatment for MPNSTs and they are typically fatal. To gain insights into MPNST pathogenesis, we utilized an MPNST mouse model that allowed us to study the evolution of these tumors at the transcriptome level. Strikingly, in MPNSTs we found upregulation of a chromatin regulator, Brd4, and show that BRD4 inhibition profoundly suppresses both growth and tumorigenesis. Our findings reveal roles for BET bromodomains in MPNST development and report a mechanism by which bromodomain inhibition induces apoptosis through induction of proapoptotic Bim, which may represent a paradigm shift in therapy for MPNST patients. Moreover, these findings indicate epigenetic mechanisms underlying the balance of anti- and proapoptotic molecules and that bromodomain inhibition can shift this balance in favor of cancer cell apoptosis.

Epithelial-to-mesenchymal transition rewires the molecular path to PI3K-dependent proliferation

Tumors showing evidence of epithelial-to-mesenchymal transition (EMT) have been associated with metastasis, drug resistance, and poor prognosis. Heterogeneity along the EMT spectrum is observed between and within tumors. To develop effective therapeutics, a mechanistic understanding of how EMT affects the molecular requirements for proliferation is needed. We found that although cells use phosphoinositide 3-kinase (PI3K) for proliferation in both the epithelial and mesenchymal states, EMT rewires the mechanism of PI3K pathway activation. In epithelial cells, autocrine ERBB3 activation maintains PI3K signaling, whereas after EMT, downregulation of ERBB3 disrupts autocrine signaling to PI3K. Loss of ERBB3 leads to reduced serum-independent proliferation after EMT that can be rescued through reactivation of PI3K by enhanced signaling from p110α, ERBB3 reexpression, or growth factor stimulation. In vivo, we demonstrate that PIK3CA expression is upregulated in mesenchymal tumors with low levels of ERBB3. This study defines how ERBB3 downregulation after EMT affects PI3K-dependent proliferation.

SIGNIFICANCE

This study describes a mechanism through which EMT transition alters the proliferative potential of cells by modulating ERBB3 expression. Furthermore, it demonstrates the potential for multiple molecular routes to drive proliferation in different cell states, illustrating how changes in EMT status can rewire signaling upstream of cell proliferation.

Cell line modeling for systems medicine in cancers (review)

Unexpected drug efficacy or resistance is poorly understood in cancers because of the lack of systematic analyses of drug response profiles in cancer tissues of various genotypic backgrounds. The recent development of high-throughput technologies has allowed massive screening of chemicals and drugs against panels of heterogeneous cancer cell lines. In parallel, multi-level omics datasets, including genome-wide genetic alterations, gene expression and protein regulation, have been generated from diverse sets of cancer cell lines, thus providing a surrogate system, known as cancer cell line modeling, that can represent cancer diversity. Taken together, recent efforts with cancer cell line modeling have enabled a systematic understanding of the causal factors of varied drug responses in cancers. These large-scale association studies could potentially predict and optimize target windows for drug treatment in cancer patients. The present review provides an overview of the major types of cell line-based large datasets and their applications in cancer studies. Moreover, this review discusses recent integrated approaches that use multi-level datasets to discover synergistic drug combination or repositioning for cancer treatment.

Role of apoptosis in colon cancer biology, therapy, and prevention

Deregulation of apoptosis is a hallmark of human cancer and contributes to therapeutic resistance. Recent advances in cancer genomics reveal a myriad of alterations in key pathways that directly or indirectly increase tumor cell survival. This review will outline the pathways of apoptosis in mammalian cells, and highlight the common alterations of apoptosis regulators found in colon cancer, the role of apoptosis and underlying mechanisms in colon cancer treatment and prevention, including recent advances on investigational agents, such as kinase inhibitors, proteasome inhibitors, HSP90 inhibitors, BH3 mimetics, TRAIL, and IAP antagonists. Topics will also include novel concepts, as well as opportunities and challenges for drug discovery and combination therapy by exploring cancer-specific genetic defects, and therefore selective induction of apoptosis in cancer cells. Although the emphasis is on colon cancer, the main theme and many of the aspects are applicable to other solid tumors.

The end of KRAS, and other, cancers? A new way forward

Mutant KRAS, as well as other mutant driver genes and epidriver genes, is a dominant determinant of resistance to cancer therapeutics. The recent introduction of targeting therapies based on drugs that inhibit the kinase catalytic function of nodal points along the Ras/extracellular-signal-regulated kinase (ERK) and the phosphatidylinositol-3-kinase (PI3K)/Akt cascades is meeting with limited success. Against this background, recent evidence shows that the β-galactoside-binding protein (βGBP) molecule, a physiological PI3K inhibitor, is a potent inducer of apoptosis in KRAS-mutant cancer cells (along with other aggressive cancer cells of different genetic makeup) and that it is therapeutically effective in vivo. Absence of p53 or phosphatase and tensin homolog (PTEN) tumor suppressor function or added activating PI3K mutations does not affect βGBP function. In contrast to the concept of one drug against one target, βGBP operates through alternative physiological routes.

An interactive resource to identify cancer genetic and lineage dependencies targeted by small molecules

The high rate of clinical response to protein-kinase-targeting drugs matched to cancer patients with specific genomic alterations has prompted efforts to use cancer cell line (CCL) profiling to identify additional biomarkers of small-molecule sensitivities. We have quantitatively measured the sensitivity of 242 genomically characterized CCLs to an Informer Set of 354 small molecules that target many nodes in cell circuitry, uncovering protein dependencies that: (1) associate with specific cancer-genomic alterations and (2) can be targeted by small molecules. We have created the Cancer Therapeutics Response Portal (http://www.broadinstitute.org/ctrp) to enable users to correlate genetic features to sensitivity in individual lineages and control for confounding factors of CCL profiling. We report a candidate dependency, associating activating mutations in the oncogene β-catenin with sensitivity to the Bcl-2 family antagonist, navitoclax. The resource can be used to develop novel therapeutic hypotheses and to accelerate discovery of drugs matched to patients by their cancer genotype and lineage.

Synthetic lethal genetic screens in Ras mutant cancers

Mutations in the Ras family of small GTPases are among the most frequent oncogenic events in human cancer. Difficulties in targeting Ras itself and the limited efficacy in targeting its effector kinases have spurred the search for Ras synthetic lethal genes that could shed new light on the biology of Ras-driven cancer and lead to new therapeutic strategies. Advances in mammalian RNAi technology have enabled high-throughput functional screens for Ras synthetic lethal interactions. In this chapter, we summarize the strategies and findings from these screens and discuss future improvement for Ras synthetic lethality studies.

High-resolution network biology: connecting sequence with function

Proteins are not monolithic entities; rather, they can contain multiple domains that mediate distinct interactions, and their functionality can be regulated through post-translational modifications at multiple distinct sites. Traditionally, network biology has ignored such properties of proteins and has instead examined either the physical interactions of whole proteins or the consequences of removing entire genes. In this Review, we discuss experimental and computational methods to increase the resolution of protein-protein, genetic and drug-gene interaction studies to the domain and residue levels. Such work will be crucial for using interaction networks to connect sequence and structural information, and to understand the biological consequences of disease-associated mutations, which will hopefully lead to more effective therapeutic strategies.

Advances towards the design and development of personalized non-small-cell lung cancer drug therapy

INTRODUCTION

Non-small-cell lung cancer (NSCLC) subtypes are driven by specific genetic aberrations. For reasons such as this, there is a call for treatment personalization. The ability to instigate NSCLC fragmentation poses new methodological problems, and new 'driver' molecular aberrations are being discovered at an unprecedented pace.

AREAS COVERED

This article describes the clinical development of epidermal growth factor-tyrosine kinase inhibitors (EGFR-TKIs) and crizotinib for EGFR-mutant and anaplastic lymphoma kinase (ALK)-rearranged NSCLC. Further, the authors briefly describe the emerging molecular targets in NSCLC, in terms of both rationale for therapeutic targeting and strategies, for clinical development.

EXPERT OPINION

Target identification and validation in NSCLC still requires considerable effort, as not all of the molecular alterations are clear 'drivers' nor can they be efficiently targeted with available drugs. However, 50% of the NSCLC cases are without clear-defined molecular aberrations. Clinical trial methodology will need to develop novel paradigms for targeted drug development, aiming at the validation of an ideal 'biology-to-trial' approach. Despite significant challenges, a truly 'personalized' approach to NSCLC therapy appears to be within our reach.

ANTXR1, a stem cell-enriched functional biomarker, connects collagen signaling to cancer stem-like cells and metastasis in breast cancer

Cancer stem-like cells are thought to contribute to tumor recurrence. The anthrax toxin receptor 1 (ANTXR1) has been identified as a functional biomarker of normal stem cells and breast cancer stem-like cells. Primary stem cell-enriched basal cells (CD49f(+)/EpCAM(-)/Lin(-)) expressed higher levels of ANTXR1 compared with mature luminal cells. CD49f(+)/EpCAM(-), CD44(+)/EpCAM(-), CD44(+)/CD24(-), or ALDEFLUOR-positive subpopulations of breast cancer cells were enriched for ANTXR1 expression. CD44(+)/CD24(-)/ANTXR1(+) cells displayed enhanced self-renewal as measured by mammosphere assay compared with CD44(+)/CD24(-)/ANTXR1(-) cells. Activation of ANTXR1 by its natural ligand C5A, a fragment of collagen VI α3, increased stem cell self-renewal in mammosphere assays and Wnt signaling including the expression of the Wnt receptor-lipoprotein receptor-related protein 6 (LRP6), phosphorylation of GSK3α/β, and elevated expression of Wnt target genes. RNAi-mediated silencing of ANTXR1 enhanced the expression of luminal-enriched genes but diminished Wnt signaling including reduced LRP6 and ZEB1 expression, self-renewal, invasion, tumorigenicity, and metastasis. ANTXR1 silencing also reduced the expression of HSPA1A, which is overexpressed in metastatic breast cancer stem cells. Analysis of public databases revealed ANTXR1 amplification in medullary breast carcinoma and overexpression in estrogen receptor-negative breast cancers with the worst outcome. Furthermore, ANTXR1 is among the 10% most overexpressed genes in breast cancer and is coexpressed with collagen VI. Thus, ANTXR1:C5A interactions bridge a network of collagen cleavage and remodeling in the tumor microenvironment, linking it to a stemness signaling network that drives metastatic progression.

Metastatic SW620 colon cancer cells are primed for death when detached and can be sensitized to anoikis by the BH3-mimetic ABT-737

Anoikis, a Bax-dependent apoptosis triggered by detachment from the extracellular matrix, is often inhibited in metastatic cancer cells. Using a couple of isogenic human colon cancer cell lines derived either from the primary tumor (SW480) or from a lymph node metastasis (SW620), we found that only SW480 cells were sensitive to anoikis. Bim upregulation but not Mcl-1 degradation was determined to be a critical factor of anoikis initiation in SW480 cells. ERK-mediated phosphorylation targets Bim for ubiquitination and proteasomal degradation. A MEK inhibitor (PD0325901) was able to increase Bim expression in SW620 cells and to sensitize these cells to anoikis. Thus, in both cell lines anoikis is under the control of proteins of the Bcl-2 family. Most interestingly, the BH3-mimetic ABT-737 was found not only to increase the level of apoptosis in suspended SW480 cells but also to sensitize SW620 cells to anoikis. Accordingly, both cell lines cultured in suspension were found to be primed for death, as determined by the detection of Bcl-2:Bim and Bcl-xL:Bim complexes. In contrast, adherent SW480 and SW620 cells were resistant to ABT-737. This indicates that, whether or not they undergo anoikis, colon cancer cells that have detached from the extracellular matrix might go through a transient state, where they are sensitive to BH3 mimetics. This would confer to compounds such as Navitoclax or ABT-199 a therapeutic window where they could have anti-metastatic potential.

Strategies for improving outcomes in NSCLC: a look to the future

Advances in the management of non-small cell lung cancer (NSCLC) over the past 30 years have led to small increases in 5-year survival rates across Europe, though further improvements may require new treatment strategies. In order to improve efficiency and reduce the cost of development, future trials for new targeted agents in NSCLC should aim to recruit patients on the basis of tumour biology rather than clinical characteristics. However, identification of predictive biomarkers is required to maximise the benefits of new approaches and expedite the drug development process. Nevertheless, the NSCLC landscape is changing rapidly, and recent improvements in our understanding of the molecular biology of the disease will help in the identification of novel targeted agents as well as assisting in the development of personalised strategies for the numerous small subsets of defined NSCLC. Progress in imaging and treatment delivery is also likely to improve outcomes for patients with the disease. This article outlines recent progress in the treatment of NSCLC, identifies current challenges and describes proposals for improving the future management of the disease. It is hoped that implementation of some of these strategies will go some way to improving the outlook for patients with NSCLC.

Genetics and biomarkers in personalisation of lung cancer treatment

Non-small-cell lung cancer is often diagnosed at the metastatic stage, with median survival of just 1 year. The identification of driver mutations in the epidermal growth factor receptor (EGFR) as the primary oncogenic event in a subset of lung adenocarcinomas led to a model of targeted treatment and genetic profiling of the disease. EGFR tyrosine kinase inhibitors confer remission in 60% of patients, but responses are short-lived. The pre-existing EGFR Thr790Met mutation could be a subclonal driver responsible for these transient responses. Overexpression of AXL and reduced MED12 function are hallmarks of resistance to tyrosine kinase inhibitors in EGFR-mutant non-small-cell lung cancer. Crosstalk between signalling pathways is another mechanism of resistance; therefore, identification of the molecular components involved could lead to the development of combination therapies cotargeting these molecules instead of EGFR tyrosine kinase inhibitor monotherapy. Additionally, novel biomarkers could be identified through deep sequencing analysis of serial rebiopsies before and during treatment.