LKB1 mutation in large cell carcinoma of the lung

Preclinical evidence using synthetic compounds and natural products indicates that AMPK represents a potential pharmacological target for the therapy of pulmonary diseases

Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) is a highly conserved eukaryotic enzyme discovered as a key regulator of cellular energy homeostasis, with anti-inflammation, antioxidative stress, anticancer, and antifibrosis beneficial effects. AMPK is dysregulated in human pulmonary diseases such as acute lung injury, nonsmall cell lung cancer, pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. This review provides an overview of the beneficial role of natural, synthetic, and Chinese traditional medicines AMPK modulators in pulmonary diseases, and highlights the role of the AMPK signaling pathway in the lung, emphasizing the importance of finding lead compounds and drugs that can target and modulate AMPK to treat the lung diseases.

Anticarcinogenic Effects of Gold Nanoparticles and Metformin Against MCF-7 and A549 Cells

Metformin is commonly prescribed to people with diabetes. Metformin has been shown in previous studies to be able to prevent the growth of cancer cells. This study aims to investigate the effects of metformin and gold nanoparticles in MCF7 breast cancer and A549 lung cell lines. The effects of metformin and gold nanoparticles on MCF7 breast cancer and A549 lung cells were determined on cells grown in 24 h cell culture. MCF-7 and A549 cells were incubated for 24 h with the treatment of escalating molar concentrations of ifosfamide. The MTT assay was used to determine the cytotoxicity of metformin toward MCF7 and A549 cell lines. The expression of Bax, BCL2, PI3K, Akt3, mTOR, Hsp60, Hsp70, and TNF-α was measured by RT-PCR. Metformin and gold nanoparticles inhibited the proliferation of MCF-7 and A549 cells in a dose and time-dependent manner with an IC50 value of 5 µM and 10 µg/mL. RT-PCR assays showed ifosfamide + metformin + gold nanoparticles significantly reduced the expression of BCL2, PI3K, Akt3, mTOR, Hsp60 and Hsp70 and increased the expression of TNF-α and Bax. The findings obtained in this study suggest that further studies should be conducted, and metformin and gold nanoparticles can be used in breast cancer and lung cancer treatments.

Identification of a novel mitochondria-localized LKB1 variant required for the regulation of the oxidative stress response

The tumor suppressor Liver Kinase B1 (LKB1) is a multifunctional serine/threonine protein kinase that regulates cell metabolism, polarity, and growth and is associated with Peutz-Jeghers Syndrome and cancer predisposition. The LKB1 gene comprises 10 exons and 9 introns. Three spliced LKB1 variants have been documented, and they reside mainly in the cytoplasm, although two possess a nuclear-localization sequence (NLS) and are able to shuttle into the nucleus. Here, we report the identification of a fourth and novel LKB1 isoform that is, interestingly, targeted to the mitochondria. We show that this mitochondria-localized LKB1 (mLKB1) is generated from alternative splicing in the 5' region of the transcript and translated from an alternative initiation codon encoded by a previously unknown exon 1b (131 bp) hidden within the long intron 1 of LKB1 gene. We found by replacing the N-terminal NLS of the canonical LKB1 isoform, the N-terminus of the alternatively spliced mLKB1 variant encodes a mitochondrial transit peptide that allows it to localize to the mitochondria. We further demonstrate that mLKB1 colocalizes histologically with mitochondria-resident ATP Synthase and NAD-dependent deacetylase sirtuin-3, mitochondrial (SIRT3) and that its expression is rapidly and transiently upregulated by oxidative stress. We conclude that this novel LKB1 isoform, mLKB1, plays a critical role in regulating mitochondrial metabolic activity and oxidative stress response.

PIM kinases inhibit AMPK activation and promote tumorigenicity by phosphorylating LKB1

BACKGROUND

The oncogenic PIM kinases and the tumor-suppressive LKB1 kinase have both been implicated in the regulation of cell growth and metabolism, albeit in opposite directions. Here we investigated whether these kinases interact with each other to influence AMPK activation and tumorigenic growth of prostate and breast cancer cells.

METHODS

We first determined how PIM and LKB1 kinases affect AMPK phosphorylation levels. We then used in vitro kinase assays to demonstrate that LKB1 is phosphorylated by PIM kinases, and site-directed mutagenesis to identify the PIM target sites in LKB1. The cellular functions of PIM and LKB1 kinases were evaluated using either pan-PIM inhibitors or CRISPR/Cas9 genomic editing, with which all three PIM family members and/or LKB1 were knocked out from PC3 prostate and MCF7 breast cancer cell lines. In addition to cell proliferation assays, we examined the effects of PIM and/or LKB1 loss on tumor growth using the chick embryo chorioallantoic membrane (CAM) xenograft model.

RESULTS

We provide both genetic and pharmacological evidence to demonstrate that inhibition of PIM expression or activity increases phosphorylation of AMPK at Thr172 in both PC3 and MCF7 cells, but not in their derivatives lacking LKB1. This is explained by our observation that all three PIM family kinases can phosphorylate LKB1 at Ser334. Wild-type LKB1, but not its phosphodeficient derivative, can restore PIM inhibitor-induced AMPK phosphorylation in LKB1 knock-out cells. In the CAM model, loss of LKB1 enhances tumorigenicity of PC3 xenografts, while cells lacking both LKB1 and PIMs exhibit slower proliferation rates and form smaller tumors.

CONCLUSION

PIM kinases are novel negative regulators of LKB1 that affect AMPK activity in an LKB1-dependent fashion. The impairment of cell proliferation and tumor growth in cells lacking both LKB1 and PIMs indicates that these kinases possess a shared signaling role in the context of cancer. These data also suggest that PIM inhibitors may be a rational therapeutic option for LKB1-deficient tumors. Video Abstract.

Metformin impairs cisplatin resistance effects in A549 lung cancer cells through mTOR signaling and other metabolic pathways

Lung cancer is the leading cause of cancer‑associated death worldwide and exhibits intrinsic and acquired therapeutic resistance to cisplatin (CIS). The present study investigated the role of mTOR signaling and other signaling pathways after metformin (MET) treatment in control and cisplatin‑resistant A549 cells, mapping pathways and possible targets involved in CIS sensitivity. MTT, flow cytometry, clonogenic assay, western blotting, proteomic analysis using the Stable Isotope Labeling by Amino acids in Cell culture (SILAC) approach and reverse transcription‑quantitative PCR were performed. The results revealed that CIS treatment induced mTOR signaling pathway overactivation, and the mTOR status was restored by MET. MET and the mTOR inhibitor rapamycin (RAPA) decreased the viability in control and resistant cells, and decreased the cell size increase induced by CIS. In control cells, MET and RAPA decreased colony formation after 72 h and decreased IC₅₀ values, potentiating the effects of CIS. Proteomics analysis revealed important pathways regulated by MET, including transcription, RNA processing and IL‑12‑mediated signaling. In CIS‑resistant cells, MET regulated the apoptotic process, oxidative stress and G₂/M transition. Annexin 4 (ANXA4) and superoxide dismutase 2 (SOD2), involved in apoptosis and oxidative stress, respectively, were chosen to validate the SILAC analysis and may represent potential therapeutic targets for lung cancer treatment. In conclusion, the chemosensitizing and antiproliferative effects of MET were associated with mTOR signaling and with potential novel targets, such as ANXA4 and SOD2, in human lung cancer cells.

Leflunomide Suppresses the Growth of LKB1-Inactivated Tumors in the Immune-Competent Host and Attenuates Distant Cancer Metastasis

Liver kinase B1 (LKB1)-inactivated tumors are vulnerable to the disruption of pyrimidine metabolism, and leflunomide emerges as a therapeutic candidate because its active metabolite, A77-1726, inhibits dihydroorotate dehydrogenase, which is essential for de novo pyrimidine biosynthesis. However, it is unclear whether leflunomide inhibits LKB1-inactivated tumors in vivo, and whether its inhibitory effect on the immune system will promote tumor growth. Here, we carried out a comprehensive analysis of leflunomide treatment in various LKB1-inactivated murine xenografts, patient-derived xenografts, and genetically engineered mouse models. We also generated a mouse tumor-derived cancer cell line, WRJ388, that could metastasize to the lung within a month after subcutaneous implantation in all animals. This model was used to assess the ability of leflunomide to control distant metastasis. Leflunomide treatment shrank a HeLa xenograft and attenuated the growth of an H460 xenograft, a patient-derived xenograft, and lung adenocarcinoma in the immune-competent genetically engineered mouse models. Interestingly, leflunomide suppressed tumor growth through at least three different mechanisms. It caused apoptosis in HeLa cells, induced G₁ cell-cycle arrest in H460 cells, and promoted S-phase cell-cycle arrest in WRJ388 cells. Finally, leflunomide treatment prevented lung metastasis in 78% of the animals in our novel lung cancer metastasis model. In combination, these results demonstrated that leflunomide utilizes different pathways to suppress the growth of LKB1-inactivated tumors, and it also prevents cancer metastasis at distant sites. Therefore, leflunomide should be evaluated as a therapeutic agent for tumors with LKB1 inactivation.

microRNA-519d Induces Autophagy and Apoptosis of Human Hepatocellular Carcinoma Cells Through Activation of the AMPK Signaling Pathway via Rab10

Background and Aim

Hepatocellular carcinoma (HCC) is a type of cancer with high mortality rates. The overexpression of microRNA-519d (miR-519d) has been explored in different types of cancers, which could significantly help suppress cancer development. This study aimed to investigate the interaction of miR-519d with its target gene, Rab10, as well as its effects on cell proliferation and autophagy in HCC cells through modulation of the AMPK signaling pathway.

Methods

Microarray analysis was used to analyze the differentially expressed genes in HCC, and the target genes of the screened-out miRNA were predicted and verified. The expression of miR-519d and Rab10, AMPK signaling pathway-related proteins, apoptosis- and autophagy-related proteins was determined by RT-qPCR and Western blot analysis in HCC tissues and cell lines. Lastly, the effects of miR-519d and Rab10 in HCC cell proliferation, apoptosis, and mouse tumour xenograft in vivo were examined through gain- and loss-of-function experiments.

Results

MiR-519d was down-regulated and Rab10 was upregulated in HCC tissues and cell lines. Overexpression of miR-519d decreased the expression of Rab10, mTOR, and Bcl-2, but increased the expression of Bax, Beclin1, Atg5, and p53. Upregulated miR-519d and downregulated Rab10 expression suppressed cell proliferation and induced cell apoptosis and autophagy in HCC cells. Finally, upregulation of miR-519d inhibited tumour growth in vivo.

Conclusion

The result obtained in this study indicates that up-regulation of miR-519d inhibits proliferation and promotes apoptosis and autophagy of HCC cells through activation of the AMPK signaling pathway via downregulating Rab10, which provides a potential target for the treatment of HCC.

The natural compound gracillin exerts potent antitumor activity by targeting mitochondrial complex II

Mitochondria play a pivotal role in cancer bioenergetics and are considered a potential target for anticancer therapy. Considering the limited efficacy and toxicity of currently available mitochondria-targeting agents, it is necessary to develop effective mitochondria-targeting anticancer drugs. By screening a large chemical library consisting of natural products with diverse chemical entities, we identified gracillin, a steroidal saponin, as a mitochondria-targeting antitumor drug. Gracillin displayed broad-spectrum inhibitory effects on the viability of a large panel of human cancer cell lines, including those carrying acquired resistance to chemotherapy or EGFR-targeting drugs, by inducing apoptosis. We show that gracillin attenuates mitochondria-mediated cellular bioenergetics by suppressing ATP synthesis and by producing reactive oxygen species (ROS). Mechanistically, gracillin disrupts complex II (CII) function by abrogating succinate dehydrogenase (SDH) activity without affecting the succinate:ubiquinone reductase. The gracillin-induced cell death was potentiated by 3-nitropropionic acid (3-NPA) or thenoyltrifluoroacetone (TTFA), which inhibit CII by binding to the active site of SDHA or to the ubiquinone-binding site, respectively. Finally, we show that gracillin effectively suppressed the mutant-Kras-driven lung tumorigenesis and the growth of xenograft tumors derived from cell lines or patient tissues. Gracillin displayed no obvious pathophysiological features in mice. Collectively, gracillin has potential as a CII-targeting antitumor drug.

Effect of Cetuximab and EGFR Small Interfering RNA Combination Treatment in NSCLC Cell Lines with Wild Type EGFR and Use of KRAS as a Possible Biomarker for Treatment Responsiveness

Background

The epidermal growth factor receptor (EGFR) is a therapeutic target for patients with non-small cell lung cancer (NSCLC). Cetuximab is an anti-EGFR monoclonal antibody that inhibits EGFR signaling and proliferation of colorectal cancer and head and neck cancers. Since only few NSCLC patients benefit from cetuximab therapy, we evaluated a novel combination treatment using cetuximab and EGFR small interfering RNA (siRNA) to strongly suppress EGFR signaling and searched for a biomarker in NSCLC cell lines harboring wild-type EGFR.

Methods

Alterations in EGFR and its downstream genes in five NSCLC cell lines (A549, Lu99, 86-2, Sq19 and Ma10) were assessed through sequencing. The protein expression levels of these molecules were assessed through western blotting. The effect of combination treatment was determined through cell proliferation assay, caspase-3/7 assay, invasion assay, and migration assay.

Results

All cell lines were harboring wild-type EGFR, whereas KRAS, PTEN, TP53 and TP53 were mutated in A549 and Lu99; Lu99 and Sq19; Lu99, 86-2, Sq19 and Ma10; and A549, 86-2, and Sq19 cell lines, respectively. PTEN was not expressed in Sq19, and LKB1 was not expressed in both A549 and Sq19. TP53 was not expressed in both A549 and Lu99. The combination of cetuximab and EGFR siRNA significantly suppressed cell proliferation in 86-2, Sq19 and Ma10, which express wild-type KRAS. It induced apoptosis in A549, 86-2 and Ma10 cells, which express wild type PTEN. The combination treatment had no effect either on cell invasion nor migration in all cell lines.

Conclusion

EGFR targeted therapy using the combination of cetuximab and EGFR siRNA is effective in NSCLC cell lines harboring wild-type EGFR. Wild-type KRAS may act as a potential biomarker for response to combination treatment by the induction of apoptosis in cells with wild-type PTEN.

Liver kinase B1/adenosine monophosphate-activated protein kinase signaling axis induces p21/WAF1 expression in a p53-dependent manner

Liver kinase B1 (LKB1) encodes a serine/threonine kinase and functions as a tumor suppressor. LKB1 loss-of-function somatic mutations are frequently observed in sporadic types of cancer, particularly in lung cancer. Ectopic LKB1 induces growth arrest by upregulating p21/cyclin dependent kinase inhibitor 1A (WAF1) in LKB1 deficient cervical and melanoma cancer cell lines. However, the underlying molecular mechanism remains to be elucidated. The present study built upon previous observations by confirming that the ectopic expression level of LKB1 significantly reduced colony formation of LKB1-deficient lung cancer cells. Mechanistically, the present study demonstrated that LKB1 overexpression significantly induced p21/WAF1 expression in a kinase-dependent manner. Conversely, LKB1 stable knockdown resulted in a decrease in p21/WAF1 expression level in colon cancer cells. In addition, it was revealed that pharmacological activation of adenosine monophosphate protein kinase (AMPK) by 2-deoxyglucose significantly increased the p21/WAF1 expression level, suggesting that AMPK acts downstream of LKB1 to induce p21/WAF1 expression. Furthermore, the present study demonstrated that functional p53 was required for p21/WAF1 induction by LKB1. Phosphorylation of p53-Ser¹⁵ was increased by ectopic LKB1 or AMPK activation. Taken together, these results suggested that LKB1 acts via its substrate, AMPK, to upregulate p21/WAF1 expression in a p53-dependent manner. Therefore, the present study identified an important signaling axis, providing novel molecular insights into the tumor suppressor role of LKB1.

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 (kras^G12D/wt/p53^-/-/lkb1^wt/wt) and t2 (kras^G12D/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.

Post-translational regulation contributes to the loss of LKB1 expression through SIRT1 deacetylase in osteosarcomas

Background:

The most prevalent form of bone cancer is osteosarcoma (OS), which is associated with poor prognosis in case of metastases formation. Mice harbouring liver kinase B1 (LKB1^+/−) develop osteoblastoma-like tumours. Therefore, we asked whether loss of LKB1 gene has a role in the pathogenesis of human OS.

Methods:

Osteosarcomas (n=259) were screened for LKB1 and sirtuin 1 (SIRT1) protein expression using immunohistochemistry and western blot. Those cases were also screened for LKB1 genetic alterations by next-generation sequencing, Sanger sequencing, restriction fragment length polymorphism and fluorescence in situ hybridisation approaches. We studied LKB1 protein degradation through SIRT1 expression. MicroRNA expression investigations were also conducted to identify the microRNAs involved in the SIRT1/LKB1 pathway.

Results:

Forty-one per cent (106 out of 259) OS had lost LKB1 protein expression with no evident genetic anomalies. We obtained evidence that SIRT1 impairs LKB1 protein stability, and that SIRT1 depletion leads to accumulation of LKB1 in OS cell lines resulting in growth arrest. Further investigations revealed the role of miR-204 in the regulation of SIRT1 expression, which impairs LKB1 stability.

Conclusions:

We demonstrated the involvement of sequential regulation of miR-204/SIRT1/LKB1 in OS cases and showed a mechanism for the loss of expression of LKB1 tumour suppressor in this malignancy.

A clinical drug library screen identifies clobetasol propionate as an NRF2 inhibitor with potential therapeutic efficacy in KEAP1 mutant lung cancer

The Kelch-like ECH-associated protein 1 (KEAP1)-nuclear factor E2-related factor 2 (NRF2)pathway has a central role in cellular antioxidant defense. NRF2 activation due to KEAP1 or NRF2 mutations occurs frequently in many cancers, suggesting that NRF2 inhibition could be a promising therapeutic strategy. However, no potent NRF2 inhibitors are clinically available to date. To develop potent NRF2 inhibitors for therapeutic purpose, we screened ~4000 clinical compounds and determined clobetasol propionate (CP) as the most potent NRF2 inhibitor. Mechanistically, CP prevented nuclear accumulation and promoted β-TrCP-dependent degradation of NRF2 in a glucocorticoid receptor- and a glycogen synthase kinase 3 (GSK3)-dependent manner. As a result, CP induced oxidative stress and strongly suppressed the anchorage-independent growth of tumors with KEAP1 mutation, but not with the wild-type KEAP1. Further, CP alone or in combination with rapamycin strongly inhibited the in vitro and in vivo growth of tumors harboring mutations in KEAP1 or both KEAP1 and LKB1 that are frequently observed in lung cancer. Thus, CP could be a repurposed therapeutic agent for cancers with high NRF2 activity. We also proposed that the use CP and rapamycin in combination could be a potential therapeutic strategy for tumors harboring both KEAP1 and LKB1 mutations.

2-Deoxyglucose Suppresses ERK Phosphorylation in LKB1 and Ras Wild-Type Non-Small Cell Lung Cancer Cells

Tumor cells rely on aerobic glycolysis to generate ATP, namely the "Warburg" effect. 2-deoxyglucose (2-DG) is well characterized as a glycolytic inhibitor, but its effect on cellular signaling pathways has not been fully elucidated. Herein, we sought to investigate the effect of 2-DG on ERK function in lung cancer cells. We found that 2-DG inhibits ERK phosphorylation in a time and dose-dependent manner in lung cancer cells. This inhibition requires functional LKB1. LKB1 knockdown in LKB1 wildtype cells correlated with an increase in the basal level of p-ERK. Restoration of LKB1 in LKB1-null cells significantly inhibits ERK activation. Blocking AMPK function with AMPK inhibitor, AMPK siRNA or DN-AMPK diminishes the inhibitory effect of 2-DG on ERK, suggesting that 2-DG—induced ERK inhibition is mediated by LKB1/AMPK signaling. Moreover, IGF1-induced ERK phosphorylation is significantly decreased by 2-DG. Conversely, a subset of oncogenic mutants of K-Ras, the main upstream regulator of ERK, blocks 2-DG—induced LKB1/AMPK signaling. These findings reveal the potential cross-talk between LKB1/AMPK and ERK signaling and help to better understand the mechanism of action of 2-DG.

TIF-IA: An oncogenic target of pre-ribosomal RNA synthesis

Cancer cells devote the majority of their energy consumption to ribosome biogenesis, and pre-ribosomal RNA transcription accounts for 30-50% of all transcriptional activity. This aberrantly elevated biological activity is an attractive target for cancer therapeutic intervention if approaches can be developed to circumvent the development of side effects in normal cells. TIF-IA is a transcription factor that connects RNA polymerase I with the UBF/SL-1 complex to initiate the transcription of pre-ribosomal RNA. Its function is conserved in eukaryotes from yeast to mammals, and its activity is promoted by the phosphorylation of various oncogenic kinases in cancer cells. The depletion of TIF-IA induces cell death in lung cancer cells and mouse embryonic fibroblasts but not in several other normal tissue types evaluated in knock-out studies. Furthermore, the nuclear accumulation of TIF-IA under UTP down-regulated conditions requires the activity of LKB1 kinase, and LKB1-inactivated cancer cells are susceptible to cell death under such stress conditions. Therefore, TIF-IA may be a unique target to suppress ribosome biogenesis without significantly impacting the survival of normal tissues.

Targeting AMPK signaling in combating ovarian cancers: opportunities and challenges

The development and strategic application of effective anticancer therapies have turned out to be one of the most critical approaches of managing human cancers. Nevertheless, drug resistance is the major obstacle for clinical management of these diseases especially ovarian cancer. In the past years, substantial studies have been carried out with the aim of exploring alternative therapeutic approaches to enhance efficacy of current chemotherapeutic regimes and reduce the side effects caused in order to produce significant advantages in overall survival and to improve patients' quality of life. Targeting cancer cell metabolism by the application of AMP-activated protein kinase (AMPK)-activating agents is believed to be one of the most plausible attempts. AMPK activators such as 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside, A23187, metformin, and bitter melon extract not only prevent cancer progression and metastasis but can also be applied as a supplement to enhance the efficacy of cisplatin-based chemotherapy in human cancers such as ovarian cancer. However, because of the undesirable outcomes along with the frequent toxic side effects of most pharmaceutical AMPK activators that have been utilized in clinical trials, attentions of current studies have been aimed at the identification of replaceable reagents from nutraceuticals or traditional medicines. However, the underlying molecular mechanisms of many nutraceuticals in anticancer still remain obscure. Therefore, better understanding of the functional characterization and regulatory mechanism of natural AMPK activators would help pharmaceutical development in opening an area to intervene ovarian cancer and other human cancers.

LKB1 gene inactivation does not sensitize non-small cell lung cancer cells to mTOR inhibitors in vitro

AIM

Previous study has shown that endometrial cancers with LKB1 inactivation are highly responsive to mTOR inhibitors. In this study we examined the effect of LKB1 gene status on mTOR inhibitor responses in non-small cell lung cancer (NSCLC) cells.

METHODS

Lung cancer cell lines Calu-1, H460, H1299, H1792, and A549 were treated with the mTOR inhibitors rapamycin or everolimus (RAD001). The mTOR activity was evaluated by measuring the phosphorylation of 4EBP1 and S6K, the two primary mTOR substrates. Cells proliferation was measured by MTS or sulforhodamine B assays.

RESULTS

The basal level of mTOR activity in LKB1 mutant A549 and H460 cells was significantly higher than that in LKB1 wild-type Calu-1 and H1792 cells. However, the LKB1 mutant A549 and H460 cells were not more sensitive to the mTOR inhibitors than the LKB1 wild-type Calu-1 and H1792 cells. Moreover, knockdown of LKB1 gene in H1299 cells did not increase the sensitivity to the mTOR inhibitors. Treatment with rapamycin or RAD001 significantly increased the phosphorylation of AKT in both LKB1 wild-type and LKB1 mutant NSCLC cells, which was attenuated by the PI3K inhibitor LY294002. Furthermore, RAD001 combined with LY294002 markedly enhanced the growth inhibition on LKB1 wild-type H1792 cells and LKB1 mutant A549 cells.

CONCLUSION

LKB1 gene inactivation in NSCLC cells does not increase the sensitivity to the mTOR inhibitors. The negative feedback activation of AKT by mTOR inhibition may contribute to the resistance of NSCLC cells to mTOR inhibitors.

Advances in the early detection of lung cancer using analysis of volatile organic compounds: from imaging to sensors

According to the World Health Organization (WHO), 1.37 million people died of lung cancer all around the world in 2008, occupying the first place in all cancer-related deaths. However, this number might be decreased if patients were detected earlier and treated appropriately. Unfortunately, traditional imaging techniques are not sufficiently satisfactory for early detection of lung cancer because of limitations. As one alternative, breath volatile organic compounds (VOCs) may reflect the biochemical status of the body and provide clues to some diseases including lung cancer at early stage. Early detection of lung cancer based on breath analysis is becoming more and more valued because it is non-invasive, sensitive, inexpensive and simple. In this review article, we analyze the limitations of traditional imaging techniques in the early detection of lung cancer, illustrate possible mechanisms of the production of VOCs in cancerous cells, present evidence that supports the detection of such disease using breath analysis, and summarize the advances in the study of E-noses based on gas sensitive sensors. In conclusion, the analysis of breath VOCs is a better choice for the early detection of lung cancer compared to imaging techniques. We recommend a more comprehensive technique that integrates the analysis of VOCs and non-VOCs in breath. In addition, VOCs in urine may also be a trend in research on the early detection of lung cancer.

Re-expression of LKB1 in LKB1-mutant EKVX cells leads to resistance to paclitaxel through the up-regulation of MDR1 expression

OBJECTIVES

The tumor suppressor LKB1 has recently been shown to be involved in the regulation of microtubule dynamics, thus cancer cells with inactivated LKB1 may have developed a means to overcome dysregulated microtubule functions, making them intrinsically resistant to microtubule targeting agents. Here, we generated isogenic LKB1-wild type and mutant non-small cell lung cancer (NSCLC) cell lines to evaluate the role of LKB1 in paclitaxel resistance.

MATERIALS AND METHODS

SRB, flow cytometry and immunoblotting were used to assess cell proliferation and apoptosis in NSCLC cell lines after paclitaxel treatment. Expression of LKB1 was restored in LKB1-null cells by retrovirus infection and was reduced in LKB1-wild type cells by shRNA knock down.

RESULTS AND CONCLUSION

The restoration of LKB1 in LKB1-null cells failed to promote paclitaxel-induced apoptosis in both p53-wild type and p53-mutant backgrounds, indicating that LKB1 was not required for paclitaxel-induced apoptosis. Interestingly, the re-establishment of LKB1 expression led to the up-regulation of class III beta-tubulin and MDR1 in EKVX cells. The up-regulation of MDR1 protein and transcripts in EKVX cells was specifically associated with the expression of wild-type LKB1 and mainly responsible for the increased cellular resistance to paclitaxel. However, the presence of LKB1 protein was not required to maintain this increased MDR1 expression even though there was no genetic amplification or promoter de-methylation of the ABCB1 locus in EKVX-LKB1-WT cells. These data suggest that LKB1 does not promote paclitaxel-induced apoptosis in most NSCLC cell lines. In contrast, in some NSCLC, the presence of LKB1 may facilitate increases in either MDR1 or class III beta-tubulin expression which can lead to paclitaxel resistance.

LKB1 Tumor Suppressor: Therapeutic Opportunities Knock when LKB1 Is Inactivated

LKB1 is commonly thought of as a tumor suppressor gene because its hereditary mutation is responsible for a cancer syndrome, and somatic inactivation of LKB1 is found in non-small cell lung cancer, melanoma, and cervical cancers. However, unlike other tumor suppressors whose main function is to either suppress cell proliferation or promote cell death, one of the functions of LKB1-regulated AMPK signaling is to suppress cell proliferation in order to promote cell survival under energetic stress conditions. This unique, pro-survival function of LKB1 has led to the discovery of reagents, such as phenformin, that specifically exploit the vulnerability of LKB1-null cells in their defect in sensing energetic stress. Such targeted agents represent a novel treatment strategy because they induce cell killing when LKB1 is absent. This review article summarizes various vulnerabilities of LKB1-mutant cells that have been reported in the literature and discusses the potential of using existing or developing novel reagents to target cancer cells with defective LKB1.

Energy restriction mimetic agents to target cancer cells: comparison between 2-deoxyglucose and thiazolidinediones

The use of energy restriction mimetic agents (ERMAs) to selectively target cancer cells addicted to glycolysis could be a promising therapeutic approach. Thiazolidinediones (TZDs) are synthetic agonists of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ that were developed to treat type II diabetes. These compounds also display anticancer effects which appear mainly to be independent of their PPARγ agonist activity but the molecular mechanisms involved in the anticancer action are not yet well understood. Results obtained on ciglitazone derivatives, mainly in prostate cancer cell models, suggest that these compounds could act as ERMAs. In the present paper, we introduce how compounds like 2-deoxyglucose target the Warburg effect and then we discuss the possibility that the PPARγ-independent effects of various TZD could result from their action as ERMAs.

[Molecular mechanism of erlotinib resistance in epidermal growth factor receptor mutant non-small cell lung cancer cell line H1650]

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression and mutations were existed in more than 40% of the lung cancer, and it's the one of molecular targets in clinical treatment. But the EGFR tyrosine kinase inhibitors (TKI)-resistance is becoming a challenging clinical problem as following the application of EGFR-TKIs, Gefitinib or Erlotinib. However, the mechanistic explanation for resistance in the some cases is still lacking. Here we researched the resistance mechanism of H1650 cells.

METHODS

Using real-time RT-PCR to analyze the EGFR mRNA expression level in EGFR wild-type non-small cell lung cancer (NSCLC) cells; MTT analysis detected the cytotoxicity for NSCLC cells to Erlotinib; Western blot analysis examined the mutant situations and the downstream signaling protein phosphorylation level in EGFR-mutant NSCLC cells with the treatment of Erlotinib or/and PI3K inhibitor, LY294002.

RESULTS

In the EGFR wild-type NSCLC cells, the expression level of EGFR mRNA varied dramatically and all the cells showed resistant to Erlotinib; In the EGFR-mutant cells, HCC827 and H1650 (the same activating-mutation type), HCC827 cells were Erlotinib-sensitive as well as H1650 demonstrated primary relative resistance. Western blot analysis showed the loss of PTEN and the p-AKT level was not inhibited with the treatment of Erlotinib or/and LY294002 in H1650 cells, while HCC827 cells were no PTEN loss and definitively decrease of p-AKT level.

CONCLUSIONS

EGFR wild-type NSCLC cells were resistant to Erlotinib no matter of how EGFR mRNA expression level. EGFR-activating mutations correlated with responses to Erlotinib. The PTEN loss and activation of AKT signaling pathway contributed to Erlotinib resistance in EGFR-mutant NSCLC cell line H1650.

Molecular mechanisms of LKB1 induced cell cycle arrest

LKB1 is a serine/threonine protein kinase mutated in patients with Peutz-Jeghers syndrome. Biallelic inactivation of LKB1 is present in up to 30% of cases of non-small cell lung cancer (NSCLC). As a tumor suppressor, LKB1 functions in arresting the cell cycle and inhibiting cell growth. LKB1 leads to induction of p21/WAF1 expression in a p53-dependent mechanism, which is mediated by cytoplasmic LKB1 initiating negative regulation of cell growth or nuclear LKB1 directly involved in transcriptional regulation of p21/WAF1. Alternatively, p53 and p21/WAF1-independent mechanism of regulating cell cycle by LKB1 is also reported.

Dysregulation of mTOR activity through LKB1 inactivation

Mammalian target of rapamycin (mTOR) is aberrantly activated in many cancer types, and two rapamycin derivatives are currently approved by the Food and Drug Administration (FDA) of the United States for treating renal cell carcinoma. Mechanistically, mTOR is hyperactivated in human cancers either due to the genetic activation of its upstream activating signaling pathways or the genetic inactivation of its negative regulators. The tumor suppressor liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11), is involved in cell polarity, cell detachment and adhesion, tumor metastasis, and energetic stress response. A key role of LKB1 is to negatively regulate the activity of mTOR complex 1 (mTORC1). This review summarizes the molecular basis of this negative interaction and recent research progress in this area.

Negative regulation of mTOR activity by LKB1-AMPK signaling in non-small cell lung cancer cells

AIM

To investigate the role of LKB1 in regulation of mTOR signaling in non-small cell lung cancer (NSCLC) cells.

METHODS

LKB1 protein expression and phosphorylation of AMPK, 4E-BP1 and S6K in the cells were assessed using Western blotting in various NSCLC cell lines (A549, H460, H1792, Calu-1 and H1299). Energy stress was mimicked by treating the cells with 2-deoxyglucose (2-DG). Compound C was used to inhibit AMPK activity. Cell growth was measured using the MTS assay.

RESULTS

LKB1 protein was expressed in LKB1 wild-type Calu-1, H1299 and H1792 cells, but it was undetected in LKB1 mutant A549 and H460 cells. Treatment of the LKB1 wild-type cells with 2-DG (5, 10 and 25 mmol/L) augmented the phosphorylation of AMPK in dose- and time-dependent manners. In the LKB1 wild-type cells, 2-DG dramatically suppressed the phosphorylation of two mTOR targets, 4E-BP1 and S6K, whereas the LKB1 mutant A549 and H460 cells were highly resistant to 2-DG-induced inhibition on mTOR activity. In addition, stable knockdown of LKB1 in H1299 cells impaired 2-DG-induced inhibition on mTOR activity. Pretreatment of H1299 and H1792 cells with the AMPK inhibitor compound C (10 μmol/L) blocked 2-DG-induced inhibition on mTOR activity. 2-DG inhibited the growth of H1299 cells more effectively than that of H460 cells; stable knockdown of LKB1 in H1299 cells attenuated the growth inhibition caused by 2-DG.

CONCLUSION

In non-small cell lung cancer cells, LKB1/AMPK signaling negatively regulates mTOR activity and contributes to cell growth inhibition in response to energy stress.

Molecular dissection of AKT activation in lung cancer cell lines

AKT is a critical signaling node downstream of phosphoinositide 3-kinase (PI3K), which is often activated in cancer. We analyzed the state of activation of AKT in 80 human non-small cell lung carcinoma cell lines under serum starvation conditions. We identified 13 lines, which showed persistent AKT activation in the absence of serum. In 12 of 13 lines, AKT activation could be attributed to loss of PTEN, activating mutation in EGF receptor (EGFR) or PIK3CA, or amplification of ERBB2. HCC2429 was the only cell line that had no alterations in those genes, but had high phospho-AKT(Ser473) levels under serum starvation conditions. However, the activation of AKT in HCC2429 was PI3K- and mTOR complex 2 (mTORC2)-dependent based upon use of specific inhibitors. Kinome tyrosine phosphorylation profiling showed that both Notch and SRC were highly activated in this cell line. Despite the activation of Notch, AKT activation and cell survival were not affected by Notch inhibitors DAPT or compound E. In contrast, SRC inhibitors PP2 and dasatinib both significantly decreased pAKT(Ser473) levels and reduced cell survival by inducing apoptosis. Furthermore, a combination of SRC and mTOR inhibition synergistically blocked activation of AKT and induced apoptosis. Overexpression of SRC has been identified previously in human lung cancers, and these results suggest that a combination of SRC and mTOR inhibitors may have unique therapeutic benefit for a subset of lung cancers with these molecular features.

Metformin impairs the growth of liver kinase B1-intact cervical cancer cells

OBJECTIVE

Metformin is one of the most widely used drugs for the treatment of type 2 diabetes. Recent investigations demonstrated that application of metformin reduces cancer risk. The present study aimed to determine the role of liver kinase B1 (LKB1) in the response of cervical cancer cells to metformin.

METHODS

LKB1 expression and the integrity of LKB1-AMPK signaling were determined with immunoblot in 6 cervical cancer cell lines. Cellular sensitivity to metformin was analyzed with MTT assay.

RESULTS

Metformin inhibited growth of cervical cancer cells, C33A, Me180, and CaSki, but was less effective against HeLa, HT-3, and MS751 cells. Analyzing the expression status and the integrity of LKB1-AMPK-mTOR signaling, we found that cervical cancer cells sensitive to metformin were LKB1 intact and exerted an integral AMPK-mTOR signaling response after the treatment. Ectopic expression of LKB1 with stable transduction system or inducible expression construct in endogenous LKB1 deficient cells improved the activation of AMPK, promoted the inhibition of mTOR, and prompted the sensitivity of cells to metformin. In contrast, knock-down of LKB1 compromised cellular response to metformin. Our further investigation demonstrated that metformin could induce both apoptosis and autophagy in cervical cancer cells when LKB1 is expressed.

CONCLUSIONS

Metformin is a potential drug for the treatment of cervical cancers, in particular to those with intact LKB1 expression. Administration of cell metabolism agonists may enhance LKB1 tumor suppression, inhibit cell growth, and reduce tumor cell viability via the activation of LKB1-AMPK signaling.

STE20-related kinase adaptor protein α (STRADα) regulates cell polarity and invasion through PAK1 signaling in LKB1-null cells

LKB1 is a Ser/Thr kinase, and its activity is regulated by the pseudokinase, STE20-related adaptor α (STRADα). The STRADα-LKB1 pathway plays critical roles in epithelial cell polarity, neuronal polarity, and cancer metastasis. Though much attention is given to the STRADα-LKB1 pathway, the function of STRADα itself, including a role outside of the LKB1 pathway, has not been well-studied. Data in Caenorhabditis elegans suggest that STRADα has an LKB1-independent role in regulating cell polarity, and therefore we tested the hypothesis that STRADα regulates cancer cell polarity and motility when wild-type LKB1 is absent. These results show that STRADα protein is reduced in LKB1-null cell lines (mutation or homozygous deletion) and this partial degradation occurs through the Hsp90-dependent proteasome pathway. The remaining STRADα participates in cell polarity and invasion, such that STRADα depletion results in misaligned lamellipodia, improper Golgi positioning, and reduced invasion. To probe the molecular basis of this defect, we show that STRADα associates in a complex with PAK1, and STRADα loss disrupts PAK1 activity via Thr(423) PAK1 phosphorylation. When STRADα is depleted, PAK1-induced invasion could not occur, suggesting that STRADα is necessary for PAK1 to drive motility. Furthermore, STRADα overexpression caused increased activity of the PAK1-activating protein, rac1, and a constitutively active rac1 mutant (Q61L) rescued pPAK(Thr423) and STRADα invasion defects. Taken together, these results show that a STRADα-rac1-PAK1 pathway regulates cell polarity and invasion in LKB1-null cells. It also suggests that while the function of LKB1 and STRADα undoubtedly overlap, they may also have mutually exclusive roles.

Genetic and epigenetic changes in lung carcinoma and their clinical implications

Lung cancer is the leading cause of cancer deaths worldwide. Recent advance in targeted therapy for lung cancer patients with epidermal growth factor receptor (EGFR) mutations has demonstrated a promising development toward personalized therapy for lung cancer patients. The development of lung cancer is a complex process, involving a series of genetic and epigenetic changes. Tobacco smoke is the predominant etiologic risk factor for lung cancer. However, some lung cancers, especially adenocarcinomas, arise in patients who have never smoked, suggesting the importance of host genetic/epigenetic susceptibility in the occurrence and development of lung cancer. Understanding of these genetic and epigenetic changes will further aid in the biomarker-driven personalized therapy for lung cancer patients. In this review, we summarize the genetic and epigenetic alterations observed in lung cancers, including chromosomal loss of heterozygosity, tumor-suppressor gene mutation, gene methylation, histone modification, and microRNA expression changes. Clinical and preclinical studies have implied specific genetic/epigenetic changes for clinical application in lung cancer patients. However, more efforts are required in validation of the identified molecular markers in lung cancer patients for early detections, assessment for treatment response, and survival predictions.

Frequent homozygous deletion of the LKB1/STK11 gene in non-small cell lung cancer

LKB1/STK11 is a tumor suppressor and a negative regulator of mammalian target of rapamycin signaling. It is inactivated in 30% of lung cancer cell lines but only 5-15% of primary lung adenocarcinomas. There is evidence that homozygous deletion (HD) of chromosome 19p at the LKB locus contributes to the inactivation of the gene in primary human lung cancers. Here, we used several complementary genetic approaches to assess the LKB1 locus in primary non-small cell lung cancers (NSCLCs). We first analyzed 124 NSCLC cases for allelic imbalance using eight microsatellite markers on chromosome 19p, which revealed an overall rate of 65% (80 of 124) loss of heterozygosity (LOH). We next used chromogenic in situ hybridization (CISH) to directly examine the chromosomal status of the LKB1 locus. In all, 65 of 124 LOH tested samples were available for CISH and 58 of those (89%) showed either loss of one copy of chromosome 19p (LOH, 40 of 65 cases, 62%) or both copies (HD 18 of 65 cases, 28%). The occurrence of HD was significantly more frequent in Caucasian (35%) than in African-American patients (6%) (P=0.04). A total of 62 of 124 samples with LOH at one or both markers immediately flanking the LKB1 gene were further analyzed by directly sequencing the complete coding region, which identified 7 of 62 (11%) tumors with somatic mutations in the gene. Jointly, our data identified total inactivation of the LKB1 gene by either HD or LOH with somatic mutation in 39% of tested samples, whereas loss of chromosome 19p region by HD or LOH at the LKB1 region occured in 90% of NSCLC.

Cancer-associated loss-of-function mutations implicate DAPK3 as a tumor-suppressing kinase

Cancer kinome sequencing studies have identified several protein kinases predicted to possess driver (i.e., causal) mutations. Using bioinformatic applications, we have pinpointed DAPK3 (ZIPK) as a novel cancer-associated kinase with functional mutations. Evaluation of nonsynonymous point mutations, discovered in DAPK3 in various tumors (T112M, D161N, and P216S), reveals that all three mutations decrease or abolish kinase activity. Furthermore, phenotypic assays indicate that the three mutations observed in cancer abrogate the function of the kinase to regulate both the cell cycle and cell survival. Coexpression of wild-type (WT) and cancer mutant kinases shows that the cancer mutants dominantly inhibit the function of the WT kinase. Reconstitution of a non-small cell lung cancer cell line that harbors an endogenous mutation in DAPK3 (P216S) with WT DAPK3 resulted in decreased cellular aggregation and increased sensitivity to chemotherapy. Our results suggest that DAPK3 is a tumor suppressor in which loss-of-function mutations promote increased cell survival, proliferation, cellular aggregation, and increased resistance to chemotherapy.

Liver kinase B1 (LKB1) in the pathogenesis of epithelial cancers

LKB1 acts as a master kinase, with its major protein targets being the family of AMPKs. Through activation of multiple signaling pathways, LKB1's main physiologic functions involve regulating cellular growth, metabolism, and polarity. Germline mutations in LKB1 result in Peutz-Jeghers Syndrome, a rare cancer susceptibility syndrome. In addition, multiple LKB1 mutations have been identified in sporadic cancers, especially those of the lung. Recent studies from a variety of murine models have helped characterize LKB1's role in the pathogenesis of epithelial cancers. In some tumor types, LKB1 might function chiefly to suppress cell growth or invasion, while in other cases, it may serve to prevent metastasis. Moreover, molecular signatures of individual tumors likely influence LKB1's operational role, as multiple studies have shown that LKB1 can synergize with other tumor suppressors and/or oncogenes to accelerate tumorigenesis. To date, LKB1 has been considered mainly a tumor suppressor; however, some studies have suggested its potential oncogenic role, mainly through the suppression of apoptosis. In short, LKB1 is a tissue and context-specific kinase. This review aims to summarize our current understanding of its role in the pathogenesis of epithelial cancers.

Homozygous deletion of the STK11/LKB1 locus and the generation of novel fusion transcripts in cervical cancer cells

The STK11/LKB1 gene encodes a ubiquitously expressed serine/threonine kinase that is mutated in multiple sporadic cancers including non-small cell lung carcinomas, pancreatic cancers, and melanomas. LKB1 plays a role in multiple cellular functions including cell growth, cell cycle progression, metabolism, cell polarity, and migration. To date, only a limited number of studies have assessed the status of LKB1 in cervical cancers. Herein, we investigate DNA methylation, DNA mutation, and transcription at the LKB1 locus in cervical cancer cell lines. We identified homozygous deletions of 25-85kb in the HeLa and SiHa cell lines. Deletion breakpoint analysis in HeLa cells revealed that the deletion resulted from an Alu-recombination-mediated deletion (ARMD) and generated a novel LKB1 fusion transcript driven by an uncharacterized CpG island promoter located approximately 11kb upstream of LKB1. Although the homozygous deletion in SiHa cells removes the entire LKB1 gene and portions of the neighboring genes SBNO2 and c19orf26, this deletion also generates a fusion transcript driven by the c19orf26 promoter and composed of both c19orf26 and SBNO2 sequences. Further analyses of public gene expression and mutation databases suggest that LKB1 and its neighboring genes are frequently dysregulated in primary cervical cancers. Thus, homozygous deletions affecting LKB1 in cervical cancers may generate multiple fusion transcripts involving LKB1, SBNO2, and c19orf26.

Mixed Adenocarcinomas of the Lung: Place in New Proposals in Classification, Mandatory for Target Therapy

Context.—Lung cancer is one of the most frequent and lethal malignant neoplasms, but knowledge regarding the molecular basis of its pathogenesis is far from complete due to the striking diversity of different forms. The current lung cancer classification (World Health Organization 2004) can efficiently distinguish clinically relevant major subtypes (small cell and non–small cell carcinomas), but its results are partly inadequate when facing prognostic and therapeutic decisions for non–small cell carcinomas, especially for the group of tumors classified as adenocarcinoma. Lung adenocarcinoma comprises a heterogeneous group of tumors characterized by diverse morphologic features and molecular pathogenesis. The category of mixed adenocarcinomas includes most adenocarcinomas (approximately 80%) and, according to World Health Organization criteria, is defined by the occurrence of a mixed array of different patterns (acinar, papillary, bronchioloalveolar, solid with mucin). The histologic recognition of mixed adenocarcinoma is subjective and cannot consistently discriminate between responders and nonresponders to new targeted therapies (eg, tyrosine kinase inhibitors). Diagnostic problems are mainly related to the poor reproducibility of histologic criteria, especially when applied in small biopsies and cytology, and to the difficulty in assigning each form to a precisely defined entity, as needed by updated therapeutic approaches. In this evolving scenario, pathologists face new challenging diagnostic roles that include not only the precise morphologic definition of carcinoma subtypes but also their molecular characterization.

Objective.—To use a comprehensive critical analysis reconciling the overwhelming variety of biologic, morphologic, molecular, and clinical data to define new classification schemes for lung adenocarcinoma.

Data Sources.—Scientific literature and personal data were used.

Conclusions.—A new classification approach should redefine lung adenocarcinoma heterogeneity reconciling classic morphology, immunophenotypic and molecular features of neoplastic cells, and also relevant information provided by stem cell biology. This approach, which has been already successfully applied in World Health Organization classification of other tumors, could improve the recognition of new reproducible profiles for adenocarcinomas, more closely and reproducibly related to clinical features and response to specific therapies, limiting the use of “wastebasket” categories such as mixed adenocarcinoma.

The molecular mechanisms that underlie the tumor suppressor function of LKB1

Germline mutations of the LKB1 tumor suppressor gene result in Peutz-Jeghers syndrome (PJS) characterized by intestinal hamartomas and increased incidence of epithelial cancers. Inactivating mutations in LKB1 have also been found in certain sporadic human cancers and with particularly high frequency in lung cancer. LKB1 has now been demonstrated to play a crucial role in pulmonary tumorigenesis, controlling initiation, differentiation, and metastasis. Recent evidences showed that LKB1 is a multitasking kinase, with great potential in orchestrating cell activity. Thus far, LKB1 has been found to play a role in cell polarity, energy metabolism, apoptosis, cell cycle arrest, and cell proliferation, all of which may require the tumor suppressor function of this kinase and/or its catalytic activity. This review focuses on remarkable recent findings concerning the molecular mechanism by which the LKB1 protein kinase operates as a tumor suppressor and discusses the rational treatment strategies to individuals suffering from PJS and other common disorders related to LKB1 signaling.

BRG1 and LKB1: tales of two tumor suppressor genes on chromosome 19p and lung cancer

Losses of heterozygosity (LOH) of the short arm of chromosome 19 are frequent in lung cancer, suggesting that one or more tumor suppressor genes are present in this region. The LKB1 gene, also called STK11, is somatically inactivated through point mutations and large deletions in lung tumors, demonstrating that LKB1 is a target of the LOH of this chromosomal arm. Data from several independent groups have provided information about the profiles of lung tumors with LKB1 inactivation and it is generally agreed that this alteration strongly predominates in non-small cell lung cancer, in particular adenocarcinomas, in smokers. The LKB1 protein has serine-threonine kinase activity and is involved in the regulation of the cell energetic checkpoint through the phosphorylation and activation of adenosine monophosphate-dependent kinase (AMPK). LKB1 is also involved in other processes such as cell polarization, probably through substrates other than AMPK. Interestingly, another gene on chromosome 19p, BRG1, encoding a component of the SWI/SNF chromatin-remodeling complex, has emerged as a tumor suppressor gene that is altered in lung tumors. Similar to LKB1, BRG1 is somatically inactivated by point mutations or large deletions in lung tumors featuring LOH of chromosome 19p. These observations suggest an important role for BRG1 in lung cancer and highlight the need to further our understanding of the function of Brahma/SWI2-related gene 1 (BRG1) in cancer. Finally, simultaneous mutations at LKB1 and BRG1 are common in lung cancer cells, which exemplifies how a single event, LOH of chromosome 19p in this instance, targets two different tumor suppressors.

Akt-dependent and -independent mechanisms of mTOR regulation in cancer

The protein kinase mTOR (mammalian target of rapamycin) is a critical regulator of cellular metabolism, growth, and proliferation. These processes contribute to tumor formation, and many cancers are characterized by aberrant activation of mTOR. Although activating mutations in mTOR itself have not been identified, deregulation of upstream components that regulate mTOR are prevalent in cancer. The prototypic mechanism of mTOR regulation in cells is through activation of the PI3K/Akt pathway, but mTOR receives input from multiple signaling pathways. This review will discuss Akt-dependent and -independent mechanisms of mTOR regulation in response to mitogenic signals, as well as its regulation in response to energy and nutrient-sensing pathways. Preclinical and clinical studies have demonstrated that tumors bearing genetic alterations that activate mTOR are sensitive to pharmacologic inhibition of mTOR. Elucidation of novel pathways that regulate mTOR may help identify predictive factors for sensitivity to mTOR inhibitors, and could provide new therapeutic targets for inhibiting the mTOR pathway in cancer. This review will also highlight pharmacologic approaches that inhibit mTOR via activation of the AMP-activated protein kinase (AMPK), an important inhibitor of the mTOR pathway and an emerging target in cancer.

Sox7 Is an independent checkpoint for beta-catenin function in prostate and colon epithelial cells

The presence of somatic beta-catenin mutations in some prostate cancers implies that aberrant WNT signaling is involved in the cancer development. Although beta-catenin stability is regulated by a multicomponent destruction complex, mutational alterations of beta-catenin or other components of the destruction complexes are rare in prostate tumors. Therefore, beta-catenin may be regulated by another protein in the prostate. In fact, recent linkage and somatic deletion analyses in prostate cancers reveal a 1.4-Mb candidate tumor suppressor locus on 8p23.1, which includes the Sox7 gene. Here we show that Sox7 protein expression was indeed down-regulated in 47% (15 of 32) of prostate adenocarcinomas. In addition, Sox7 mRNA was down-regulated in 60% of snap-frozen tumors. This down-regulation was found to be due to tumor-specific promoter hypermethylation, which was present in 48% (10 of 21) of primary prostate tumors and 44% (11 of 25) of prostate cancer cell lines/xenografts. We discovered that Sox7 protein physically interacts with beta-catenin and suppresses beta-catenin-mediated transcription by depleting active beta-catenin. Furthermore, in HCT116 colorectal cancer cell lines with Sox7 inactivation, ectopic Sox7 expression suppressed cell proliferation and inhibited transcription that was activated by an endogenous mutant beta-catenin. Although nearly all colorectal cancers contain mutations in beta-catenin or adenomatous polyposis coli/axin, epigenetic silencing of Sox7 was still observed. These data suggest that Sox7 is a tumor suppressor that functions as an independent checkpoint for beta-catenin transcriptional activity. Inactivation of Sox7 could promote the development of a majority of colorectal tumors and approximately half of prostate tumors.

LKB1 is necessary for Akt-mediated phosphorylation of proapoptotic proteins

LKB1 plays the role of tumor suppressor, opposite to Akt, by negatively regulating mammalian target of rapamycin through the activation of AMP-activated protein kinase and TSC signaling. We have discovered a novel, potentially oncogenic role for LKB1 as a supporter of Akt-mediated phosphorylation of proapoptotic proteins. We found that Akt activation led to increased phosphorylation of FoxO3a at Thr(32) in LKB1 wild-type cells but not in LKB1-null cells. Depletion of LKB1 in the cells with wild-type LKB1 resulted in attenuation of that phosphorylation of FoxO3a by activated Akt, whereas the restoration of LKB1 function in LKB1-null cells reestablished Akt-mediated FoxO3a phosphorylation. On expanding our analysis to other Akt targets, using isogenic LKB1 knockdown cell line pairs and a phospho-specific antibody microarray, we observed that there was a requirement for LKB1 in the phosphorylation of other Akt downstream targets, including Ask1 (Ser(83)), Bad (Ser(136)), FoxO1 (Ser(319)), FoxO4 (Ser(197)), and glycogen synthase kinase 3beta (GSK3beta; Ser(9)). Because the phosphorylation of these sites by Akt suppresses apoptosis, the requirement of LKB1 suggests that LKB1 may have an antiapoptotic role in tumor cells with constitutively active Akt. Indeed, we found that the suppression of LKB1 expression led to apoptosis in three cell lines in which Akt is constitutively active but not in two cell lines without Akt activation. This observation may explain the lack of LKB1 somatic mutations in brain, breast, and colon cancers, where Akt is frequently activated due to mutations in phosphatidylinositol 3-kinase, PTEN, or Akt itself.

Analysis of volatile organic compounds in the exhaled breath for the diagnosis of lung cancer

Volatile organic compounds are able to be detected in the exhaled breath by a variety of sensing techniques. These volatiles may be produced by cellular metabolic processes, or inhaled/absorbed from exogenous sources. Lung cancer cells may produce and process these compounds different than normal cells. The differences may be detectable in the breath. The following manuscript will review the evidence supporting the premise that a unique chemical signature can be detected in the breath of patients with lung cancer, discuss the results of studies using mass spectrometry and nonspecific chemical sensing techniques to detect the unique lung cancer signature, and speculate on the advancements that must occur to develop a breath test accurate enough to be clinically useful.

2-Deoxyglucose induces Akt phosphorylation via a mechanism independent of LKB1/AMP-activated protein kinase signaling activation or glycolysis inhibition

The compound 2-deoxyglucose (2-DG) enhances chemotherapy/radiotherapy in cell lines and animal models, prompting two phase I clinical trials with this cancer therapeutic. Although its mechanism of action has not been fully elucidated, it is hypothesized that the molecular basis of 2-DG activity is related to glycolysis inhibition. Here, we report that 2-DG induced Akt phosphorylation at Thr(308) and Ser(473) as early as 15 min post-treatment. These phosphorylation events required phosphatidylinositol-3-kinase activity but were not related to LKB1/AMP-activated protein kinase signaling, the inhibition of glycolysis or epidermal growth factor receptor signaling. The 2-DG-mediated Akt phosphorylation also led to the phosphorylation of Akt downstream targets, such as Foxo3a, GSK3beta, and Chk1. Because the functional consequence of Akt activation includes chemotherapy/radiotherapy resistance, our data suggested that the combination of phosphatidylinositol-3-kinase/Akt inhibitory agents in 2-DG-based chemotherapy/radiotherapy may result in enhanced therapeutic efficacy.

Phosphatidylinositol ether lipid analogues induce AMP-activated protein kinase-dependent death in LKB1-mutant non small cell lung cancer cells

Loss of function of the tumor suppressor LKB1 occurs in 30% to 50% of lung adenocarcinomas. Because LKB1 activates AMP-activated protein kinase (AMPK), which can negatively regulate mTOR, AMPK activation might be desirable for cancer therapy. However, no known compounds activate AMPK independently of LKB1 in vivo, and the usefulness of activating AMPK in LKB1-mutant cancers is unknown. Here, we show that lipid-based Akt inhibitors, phosphatidylinositol ether lipid analogues (PIA), activate AMPK independently of LKB1. PIAs activated AMPK in LKB1-mutant non-small cell lung cancer (NSCLC) cell lines with similar concentration dependence as that required to inhibit Akt. However, AMPK activation was independent of Akt inhibition. AMPK activation was a major mechanism of mTOR inhibition. To assess whether another kinase capable of activating AMPK, CaMKK beta, contributed to PIA-induced AMPK activation, we used an inhibitor of CaMKK, STO-609. STO-609 inhibited PIA-induced AMPK activation in LKB1-mutant NSCLC cells, and delayed AMPK activation in wild-type LKB1 NSCLC cells. In addition, AMPK activation was not observed in NSCLC cells with mutant CaMKK beta, suggesting that CaMKK beta contributes to PIA-induced AMPK activation in cells. AMPK activation promoted PIA-induced cytotoxicity because PIAs were less cytotoxic in AMPKalpha-/- murine embryonic fibroblasts or LKB1-mutant NSCLC cells transfected with mutant AMPK. This mechanism was also relevant in vivo. Treatment of LKB1-mutant NSCLC xenografts with PIA decreased tumor volume by approximately 50% and activated AMPK. These studies show that PIAs recapitulate the activity of two tumor suppressors (PTEN and LKB1) that converge on mTOR. Moreover, they suggest that PIAs might have utility in the treatment of LKB1-mutant lung adenocarcinomas.

Prevalence and specificity of LKB1 genetic alterations in lung cancers

Germline LKB1 mutations cause Peutz-Jeghers syndrome, a hereditary disorder that predisposes to gastrointestinal hamartomatous polyposis and several types of malignant tumors. Somatic LKB1 alterations are rare in sporadic cancers, however, a few reports showed the presence of somatic alterations in a considerable fraction of lung cancers. To determine the prevalence and the specificity of LKB1 alterations in lung cancers, we examined a large number of lung cancer cell lines and lung adenocarcinoma (AdC) specimens for the alterations. LKB1 genetic alterations were frequently detected in the cell lines (21/70, 30%), especially in non-small cell lung cancers (NSCLCs) (20/51, 39%), and were significantly more frequent in cell lines with KRAS mutations. Point mutations were detected only in AdCs and large cell carcinomas, whereas homozygous deletions were detected in all histological types of lung cancer. Among lung AdC specimens, LKB1 mutations were found in seven (8%) of 91 male smokers but in none of 64 females and/or nonsmokers, and were significantly more frequent in poorly differentiated tumors. The difference in the frequency of LKB1 alterations between cell lines and tumor specimens was likely to be owing to masking of deletions by the contamination of noncancerous cells in the tumor specimens. These results indicate that somatic LKB1 genetic alterations preferentially occur in a subset of poorly differentiated lung AdCs that appear to correlate with smoking males.