Tailoring tyrosine kinase inhibitors to fit the lung cancer genome

Tyrosine kinase inhibitors (TKIs) have been in use as cancer therapeutics for nearly a decade, and their utility in targeting specific malignancies with defined genetic lesions has proven to be remarkably effective. Recent efforts to characterize the spectrum of genetic lesions found in non-small cell lung carcinoma (NSCLC) have provided important insights into the molecular basis of this disease and have also revealed a wide array of tyrosine kinases that might be effectively targeted for rationally designed therapies. The findings of these studies, however, also provide a cautionary tale about the limitations of single-agent therapies, which fail to account for the genetic heterogeneity and pathway redundancy that characterize advanced NSCLC. Emergence of drug resistance mechanisms to specific TKIs, such as gefitinib and erlotinib, suggests that more sophisticated chemotherapeutic paradigms that target multiple pathways at the same time will be required to effectively treat this disease.     

EMT: A mechanism for escape from EGFR-targeted therapy in lung cancer

Epithelial mesenchymal transition (EMT) is a reversible developmental genetic programme of transdifferentiation of polarised epithelial cells to mesenchymal cells. In cancer, EMT is an important factor of tumour cell plasticity and has received increasing attention for its role in the resistance to conventional and targeted therapies. In this paper we provide an overview of EMT in human malignancies, and discuss contribution of EMT to the development of the resistance to Epidermal Growth Factor Receptor (EGFR)-targeted therapies in non-small cell lung cancer (NSCLC). Patients with the tumours bearing specific mutations in EGFR have a good clinical response to selective EGFR inhibitors, but the resistance inevitably develops. Several mechanisms responsible for the resistance include secondary mutations in the EGFR gene, genetic or non-mutational activation of alternative survival pathways, transdifferentiation of NSCLC to the small cell lung cancer histotype, or formation of resistant tumours with mesenchymal characteristics. Mechanistically, application of an EGFR inhibitor does not kill all cancer cells; some cells survive the exposure to a drug, and undergo genetic evolution towards resistance. Here, we present a theory that these quiescent or slow-proliferating drug-tolerant cell populations, or so-called “persisters”, are generated via EMT pathways. We review the EMT-activated mechanisms of cell survival in NSCLC, which include activation of ABC transporters and EMT-associated receptor tyrosine kinase AXL, immune evasion, and epigenetic reprogramming. We propose that therapeutic inhibition of these pathways would eliminate pools of persister cells and prevent or delay cancer recurrence when applied in combination with the agents targeting EGFR.     

Blockade of the ERK or PI3K-Akt signaling pathway enhances the cytotoxicity of histone deacetylase inhibitors in tumor cells resistant to gefitinib or imatinib

Deregulated activation of protein tyrosine kinases, such as the epidermal growth factor receptor (EGFR) and Abl, is associated with human cancers including non-small cell lung cancer (NSCLC) and chronic myeloid leukemia (CML). Although inhibitors of such activated kinases have proved to be of therapeutic benefit in individuals with NSCLC or CML, some patients manifest intrinsic or acquired resistance to these drugs. We now show that, whereas blockade of either the extracellular signal-regulated kinase (ERK) pathway or the phosphatidylinositol 3-kinase (PI3K)-Akt pathway alone induced only a low level of cell death, it markedly sensitized NSCLC or CML cells to the induction of apoptosis by histone deacetylase (HDAC) inhibitors. Such enhanced cell death induced by the respective drug combinations was apparent even in NSCLC or CML cells exhibiting resistance to EGFR or Abl tyrosine kinase inhibitors, respectively. Co-administration of a cytostatic signaling pathway inhibitor may contribute to the development of safer anticancer strategies by lowering the required dose of cytotoxic HDAC inhibitors for a variety of cancers.     

RING finger protein 38 induces the drug resistance of cisplatin in non-small-cell lung cancer

Cisplatin resistance of non-small-cell lung cancer (NSCLC) needs to be well elucidated. RING finger protein (RNF38) has been proposed as a biomarker of NSCLC poor prognosis. However, its role in drug resistance in NSCLC is poorly understood. RNF38 expression was detected in normal lung epithelial cell and four NSCLC cell lines. RNF38 was stably overexpressed in A549 and H460 cells or silenced in H1975 and cisplatin-resistant A549 cells (A549-CDDP resistant) using lentiviral vectors. RNF38 expression levels were determined using quantitative real-time polymerase chain reaction and western blotting analysis. Cell viability in response to different concentrations of cisplatin was evaluated by Cell Counting Kit-8 assay. RNF38 expression levels were markedly elevated in NSCLC cells and cells harboring high RNF38 were less sensitive to cisplatin. Overexpression of RNF38 reduced, while RNF38 silencing increased the drug sensitivity of cisplatin in NSCLC cells. Cisplatin-resistant cells expressed high RNF38 level. RNF38 silencing promoted cell apoptosis and enhanced the drug sensitivity of cisplatin in cisplatin-resistant NSCLC cells. These findings indicate that RNF38 might induce cisplatin resistance of NSCLC cells via promoting cell apoptosis and RNF38 could be a novel target for rectify cisplatin resistance in NSCLC cases.     

Angio-associated migratory cell protein interacts with epidermal growth factor receptor and enhances proliferation and drug resistance in human non-small cell lung cancer cells

Angio-associated migratory cell protein (AAMP) is expressed in some human cancer cells. Previous studies have shown AAMP high expression predicted poor prognosis. But its biological role in non-small cell lung cancer (NSCLC) cells is still unknown. In our present study, we attempted to explore the functions of AAMP in NSCLC cells. According to our findings, AAMP knockdown inhibited lung cancer cell proliferation and inhibited lung cancer cell tumorigenesis in the mouse xenograft model. Epidermal growth factor receptor (EGFR) is a primary receptor tyrosine kinase (RTK) that promotes proliferation and plays an important role in cancer pathology. We found AAMP interacted with EGFR and enhanced its dimerization and phosphorylation at tyrosine 1173 which activated ERK1/2 in NSCLC cells. In addition, we showed AAMP conferred the lung cancer cells resistance to chemotherapeutic agents such as icotinib and doxorubicin. Taken together, our data indicate that loss of AAMP from NSCLC inhibits tumor growth and elevates drug sensitivity, and these findings have clinical implications to treat NSCLC cancers.     

In silico identification of thiostrepton as an inhibitor of cancer stem cell growth and an enhancer for chemotherapy in non–small‐cell lung cancer

Cancer stem cells (CSCs) play an important role in cancer treatment resistance and disease progression. Identifying an effective anti‐CSC agent may lead to improved disease control. We used CSC‐associated gene signatures to identify drug candidates that may inhibit CSC growth by reversing the CSC gene signature. Thiostrepton, a natural cyclic oligopeptide antibiotic, was the top‐ranked candidate. In non–small‐cell lung cancer (NSCLC) cells, thiostrepton inhibited CSC growth in vitro and reduced protein expression of cancer stemness markers, including CD133, Nanog and Oct4A. In addition, metastasis‐associated Src tyrosine kinase signalling, cell migration and epithelial‐to‐mesenchymal transition (EMT) were all inhibited by thiostrepton. Mechanistically, thiostrepton treatment led to elevated levels of tumour suppressor miR‐98. Thiostrepton combined with gemcitabine synergistically suppressed NSCLC cell growth and induced apoptosis. The inhibition of NSCLC tumours and CSC growth by thiostrepton was also demonstrated in vivo. Our findings indicate that thiostrepton, an established drug identified in silico, is an inhibitor of CSC growth and a potential enhancer of chemotherapy in NSCLC.     

Dynamic BH3 profiling identifies active BH3 mimetic combinations in non-small cell lung cancer

Conventional chemotherapy is still of great utility in oncology and rationally constructing combinations with it remains a top priority. Drug-induced mitochondrial apoptotic priming, measured by dynamic BH3 profiling (DBP), has been shown in multiple cancers to identify drugs that promote apoptosis in vivo. We therefore hypothesized that we could use DBP to identify drugs that would render cancers more sensitive to conventional chemotherapy. We found that targeted agents that increased priming of non-small cell lung cancer (NSCLC) tumor cells resulted in increased sensitivity to chemotherapy in vitro. To assess whether targeted agents that increase priming might enhance the efficacy of cytotoxic agents in vivo as well, we carried out an efficacy study in a PC9 xenograft mouse model. The BH3 mimetic navitoclax, which antagonizes BCL-xL, BCL-w, and BCL-2, consistently primed NSCLC tumors in vitro and in vivo. The BH3 mimetic venetoclax, which electively antagonizes BCL-2, did not. Combining navitoclax with etoposide significantly reduced tumor burden compared to either single agent, while adding venetoclax to etoposide had no effect on tumor burden. Next, we assessed priming of primary patient NSCLC tumor cells on drugs from a clinically relevant oncology combination screen (CROCS). Results confirmed for the first time the utility of BCL-xL inhibition by navitoclax in priming primary NSCLC tumor cells and identified combinations that primed further. This is a demonstration of the principle that DBP can be used as a functional precision medicine tool to rationally construct combination drug regimens that include BH3 mimetics in solid tumors like NSCLC.Subject terms: Non-small-cell lung cancer, Apoptosis, Predictive markers     

Synthesis and biological evaluation of a peptide-paclitaxel conjugate which targets the integrin αvβ₆

The integrin α(v)β(6) is an emergent biomarker for non-small cell lung cancer (NSCLC) as well as other carcinomas. We previously developed a tetrameric peptide, referred to as H2009.1, which binds α(v)β(6) and displays minimal affinity for other RGD-binding integrins. Here we report the use of this peptide to actively deliver paclitaxel to α(v)β(6)-positive cells. We synthesized a water soluble paclitaxel-H2009.1 peptide conjugate in which the 2'-position of paclitaxel is attached to the tetrameric peptide via an ester linkage. The conjugate maintains its specificity for α(v)β(6)-expressing NSCLC cells, resulting in selective cytotoxicity. Treatment of α(v)β(6)-positive cells with the conjugate results in cell cycle arrest followed by induction of apoptosis in the same manner as free paclitaxel. However, initiation of apoptosis and the resultant cell death is delayed compared to free drug. The conjugate demonstrates anti-tumor activity in a H2009 xenograft model of NSCLC with efficacy comparable to treatment with free paclitaxel.     

Impaired DNA double-strand breaks repair by kinesin family member 4A inhibition renders human H1299 non-small-cell lung cancer cells sensitive to cisplatin

Patients with non-small-cell lung cancer (NSCLC) are routinely treated with the platinum-based chemotherapeutics such as cisplatin. The drug exerts anticancer effects via multiple mechanisms, including DNA double-strand breaks (DSBs). Enhanced DNA DSB repair capacity would be associated with innate or acquired drug resistance. However, despite strong evidence for the role of the chromokinesin kinesin family member 4A (KIF4A) in DSB repair, the relationship between the chromokinesin and cisplatin sensitivity of human NSCLC cells remains unknown. Furthermore, little is known regarding the effect of targeting KIF4A on the function of DSB repair-related proteins in these cells. In the current study, we demonstrated that cisplatin treatment stimulated the expression of KIF4A protein in human NSCLC cells. Depletion of KIF4A by small interfering RNA significantly enhanced cisplatin-induced cell cycle arrest in S and G2/M phases and cytotoxicity in human NSCLC cells. Furthermore, we found that KIF4A inhibition suppressed the ability of cisplatin to induce BRCA2 and Rad51 focus formation and limits the further increase in poly(ADP-ribose) polymerase 1 activity induced by cisplatin treatment in human NSCLC cells. These studies thus identify the chromokinesin KIF4A as a novel modulator of cisplatin sensitivity that is significantly enhanced by the chromokinesin in human NSCLC cells via multiple mechanisms.     

Inhibition of Hedgehog signaling sensitizes NSCLC cells to standard therapies through modulation of EMT-regulating miRNAs

Background

Epidermal growth factor receptor- tyrosine kinase inhibitors (EGFR-TKIs) benefit Non-small cell lung cancer (NSCLC) patients, and an EGFR-TKIi erlotinib, is approved for patients with recurrent NSCLC. However, resistance to erlotinib is a major clinical problem. Earlier we have demonstrated the role of Hedgehog (Hh) signaling in Epithelial-to-Mesenchymal transition (EMT) of NSCLC cells, leading to increased proliferation and invasion. Here, we investigated the role of Hh signaling in erlotinib resistance of TGF-β1-induced NSCLC cells that are reminiscent of EMT cells.

Methods

Hh signaling was inhibited by specific siRNA and by GDC-0449, a small molecule antagonist of G protein coupled receptor smoothened in the Hh pathway. Not all NSCLC patients are likely to benefit from EGFR-TKIs and, therefore, cisplatin was used to further demonstrate a role of inhibition of Hh signaling in sensitization of resistant EMT cells. Specific pre- and anti-miRNA preparations were used to study the mechanistic involvement of miRNAs in drug resistance mechanism.

Results

siRNA-mediated inhibition as well as pharmacological inhibition of Hh signaling abrogated resistance of NSCLC cells to erlotinib and cisplatin. It also resulted in re-sensitization of TGF-β1-induced A549 (A549M) cells as well the mesenchymal phenotypic H1299 cells to erlotinib and cisplatin treatment with concomitant up-regulation of cancer stem cell (CSC) markers (Sox2, Nanog and EpCAM) and down-regulation of miR-200 and let-7 family miRNAs. Ectopic up-regulation of miRNAs, especially miR-200b and let-7c, significantly diminished the erlotinib resistance of A549M cells. Inhibition of Hh signaling by GDC-0449 in EMT cells resulted in the attenuation of CSC markers and up-regulation of miR-200b and let-7c, leading to sensitization of EMT cells to drug treatment, thus, confirming a connection between Hh signaling, miRNAs and drug resistance.

Conclusions

We demonstrate that Hh pathway, through EMT-induction, leads to reduced sensitivity to EGFR-TKIs in NSCLCs. Therefore, targeting Hh pathway may lead to the reversal of EMT phenotype and improve the therapeutic efficacy of EGFR-TKIs in NSCLC patients.

     

Raloxifene-encapsulated hyaluronic acid-decorated chitosan nanoparticles selectively induce apoptosis in lung cancer cells

Non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC) are leading causes of cancer mortality and morbidity around the world. Despite the recent advances in their diagnosis and therapy, their prognosis remains poor owing to the development of drug resistance and metastasis. Raloxifene (RX), a drug first used in the treatment of osteoporosis, was recently approved for NSCLC and HCC prevention. Unfortunately, many of the therapies that use RX are likely to become ineffective due to drug resistance. Herein, we developed a novel delivery strategy by utilizing hyaluronic acid (HA) and chitosan (CS) complexation to increase the half-life and activity of RX. Consequently, we explored the pro-apoptotic and cytotoxic effects of RX-HA-CS nanoparticles (NPs) against NSCLC (A549) and HCC (HepG2 and Huh-7) cell lines. The highest entrapment efficiency (EE%) was noted in RX-HA-CS NPs (92%) compared to RX-HA NPs (87.5%) and RX-CS NPs (68%). In addition, RX-HA-CS NPs induced the highest cytotoxicity against A549 cells compared to other platforms. The significant suppression of A549 cell viability was achieved via glucose uptake reduction resulting in diminished bioenergetics of cancer cells and activation of apoptosis via nitric oxide level elevation. This study is the first to assess the efficacy of RX in its HA-CS nano-formulation against lung and liver cancer cells and demonstrated its selective cytotoxic and apoptotic potential against human lung A549 cancer cell line. These findings demonstrate a promising drug delivery system to help mitigate drug resistance in lung cancer.     

Cx31.1 acts as a tumour suppressor in non-small cell lung cancer (NSCLC) cell lines through inhibition of cell proliferation and metastasis

Reduced connexin expression and loss of gap junction function is a characteristic of many cancers, including lung cancer. However, there are little reports about the relation between Cx31.1 and lung cancer. This study was conducted to investigate the effect of Cx31.1 on non-small cell lung cancer (NSCLC). We found that the Cx31.1 was down-regulated in NSCLC cell lines, and the expression levels were reversely related with their metastatic potential. We ectopically expressed Cx31.1 in H1299 NSCLC cell line to examine the influence of Cx31.1 overexpression. The results showed that overexpression of Cx31.1 in H1299 cells reduced cell proliferation, induced a delay in the G(1) phase, inhibited anchorage-independent growth and suppressed cell migration and invasion. The cell cycle delay and cell migration and invasion suppressive effects of Cx31.1 were partially reversed by siRNA targeting mRNA of Cx31.1. Moreover, xenografts of Cx31.1 overexpressing H1299 cells showed reduced tumourigenicity. These results suggested that Cx31.1 has tumour-suppressive properties. Further investigation indicated that cyclin D3 may be responsible for Cx31.1-induced G(1) phase delay. Importantly, Cx31.1 increased the expression of epithelial markers, such as cytokeratin 18, and decreased expression of mesenchymal markers, such as vimentin, indicating a Cx31.1-mediated partial shift from a mesenchymal towards an epithelial phenotype. We concluded that Cx31.1 inhibit the malignant properties of NSCLC cell lines, the mechanisms under this may include regulation of EMT.     

MiR‐34b‐3p represses cell proliferation,cell cycle progression and cell apoptosis in non‐small‐cell lung cancer (NSCLC) by targeting CDK4

Lung cancer is the most common incident cancer, with a high mortality worldwide, and non‐small‐cell lung cancer (NSCLC) accounts for approximately 85% of cases. Numerous studies have shown that the aberrant expression of microRNAs (miRNAs) is associated with the development and progression of cancers. However, the clinical significance and biological roles of most miRNAs in NSCLC remain elusive. In this study, we identified a novel miRNA, miR‐34b‐3p, that suppressed NSCLC cell growth and investigated the underlying mechanism. miR‐34b‐3p was down‐regulated in both NSCLC tumour tissues and lung cancer cell lines (H1299 and A549). The overexpression of miR‐34b‐3p suppressed lung cancer cell (H1299 and A549) growth, including proliferation inhibition, cell cycle arrest and increased apoptosis. Furthermore, luciferase reporter assays confirmed that miR‐34b‐3p could bind to the cyclin‐dependent kinase 4 (CDK4) mRNA 3′‐untranslated region (3′‐UTR) to suppress the expression of CDK4 in NSCLC cells. H1299 and A549 cell proliferation inhibition is mediated by cell cycle arrest and apoptosis with CDK4 interference. Moreover, CDK4 overexpression effectively reversed miR‐34‐3p‐repressed NSCLC cell growth. In conclusion, our findings reveal that miR‐34b‐3p might function as a tumour suppressor in NSCLC by targeting CDK4 and that miR‐34b‐3p may, therefore, serve as a biomarker for the diagnosis and treatment of NSCLC.     

Endogenous thrombopoietin promotes non‐small‐cell lung carcinoma cell proliferation and migration by regulating EGFR signalling

Thrombopoietin (TPO) is a haematopoietic cytokine mainly produced by the liver and kidneys, which stimulates the production and maturation of megakaryocytes. In the past decade, numerous studies have investigated the effects of TPO outside the haematopoietic system; however, the role of TPO in the progression of solid cancer, particularly lung cancer, has not been well studied. Exogenous TPO does not affect non‐small‐cell lung cancer (NSCLC) cells as these cells show no or extremely low TPO receptor expression; therefore, in this study, we focused on endogenous TPO produced by NSCLC cells. Immunohistochemical analysis of 150 paired NSCLC and adjacent normal tissues indicated that TPO was highly expressed in NSCLC tissues and correlated with clinicopathological parameters including differentiation, P‐TNM stage, lymph node metastasis and tumour size. Suppressing endogenous TPO by small interfering RNA inhibited the proliferation and migration of NSCLC cells. Moreover, TPO interacted with the EGFR protein and delayed ligand‐induced EGFR degradation, thus enhancing EGFR signalling. Notably, overexpressing TPO in EGF‐stimulated NSCLC cells facilitated cell proliferation and migration, whereas no obvious changes were observed without EGF stimulation. Our results suggest that endogenous TPO promotes tumorigenicity of NSCLC via regulating EGFR signalling and thus could be a therapeutic target for treating NSCLC.     

Peroxiredoxin-I is an autoimmunogenic tumor antigen in non-small cell lung cancer

In eukaryotic cells, peroxiredoxins are both antioxidants and regulators of H(2)O(2)-mediated signaling. We previously found that peroxiredoxin-I (Prx-I) was overexpressed in non-small cell lung cancer (NSCLC) tissue. Since overexpressed protein can induce a humoral immune response, we examined whether serum from NSCLC patients exhibited immunoreactivity against Prx-I using Western blotting. We found that 25 (47%) of 53 NSCLC patients tested had autoantibodies against Prx-I in their sera, whereas such activity was detected in 4 (8%) sera from 50 healthy subjects. Prx-I itself was detected in the sera from 18 (34%) of 53 NSCLC patients but in only 1 (2%) serum from 50 controls. Moreover, 17% of NSCLC sera were positive to both Prx-I antibody and antigen but none in control sera. The data indicate both Prx-I autoantibody and circulating antigen are potential biomarkers for use in serological diagnosis of NSCLC. Interestingly enough, we found that Prx-I was secreted by lung adenocarcinoma cells (A549) but not by non-cancer lung cells (BEAS 2B) or breast cancer cells (MCF7). This cell culture study suggests the possibility of Prx-I secretion from NSCLC tumor tissues.