The Antiproliferative and Apoptotic Effects of a Novel Quinazoline Carrying Substituted-Sulfonamides: In Vitro and Molecular Docking Study

In order to investigate for a new effective and safe anticancer drug, we synthesized a novel series of quinazoline containing biologically active substituted-sulfonamide moiety at 3- position 4a-n. The structure of the newly prepared compounds was proved by microanalysis, IR, ¹H-NMR, ¹³C-NMR and mass spectral data. All the synthesized compounds were evaluated for their in vitro cytotoxic activity in numerous cancer cell lines including A549, HepG-2, LoVo and MCF-7 and normal HUVEC cell line. The two most active compounds 4d and 4f were then tested for their apoptosis induction using DNA content and Annexin V-FITC/PI staining. Moreover, apoptosis initiation was also confirmed using RT-PCR and Western blot. To further understand the binding preferences of quinazoline sulfonamides, docking simulations were used. Among the fourteen new synthesized compounds, we found that compounds 4d and 4f exerted the strongest cytotoxicity against MCF-7 cells with an IC₅₀ value of 2.5 and 5 μM, respectively. Flow cytometry data revealed the ability of compounds 4d and 4f to mediate apoptosis and arrest cell cycle growth at G1 phase. Furthermore, RT-PCR and Western blot results suggested that both 4d and 4f activates apoptotic cell death pathway in MCF-7 cells. Molecular docking assessments indicated that compounds 4d and 4f fit perfectly into Bcl2's active site. Based on the biological properties, we conclude that both compounds 4d and 4f could be used as a new type of anticancer agent, which provides a scientific basis for further research into the treatment of cancer.

Novel sulphonamide-bearing methoxyquinazolinone derivatives as anticancer and apoptosis inducers: synthesis, biological evaluation and in silico studies

We synthesised a new series of sulphonamide-bearing quinazolinone derivatives 5-18 and evaluated their in vitro cytotoxicity in various cancer cell lines (A549, HepG-2, LoVo and MCF-7) and in normal human cells (HUVEC). Compounds 6 and 10 exhibited the higher activity against all the cancer cell lines compared with 5-flourourcil as positive control. The ability of the most promising compounds 6 and 10 to induce cell cycle arrest and apoptosis in breast cancer (MCF-7) cells was evaluated by flow cytometry. Reverse transcriptase-polymerase chain reaction and western blotting were used to evaluate the expression of apoptosis-related markers. We found that the 2-tolylthioacetamide derivative 6 and the 3-ethyl phenyl thioacetamide derivative 10 exhibited cytotoxic activity comparable to that of 5-fluorouracil as reference drug in MCF-7 and LoVo colon cancer cells. Cell cycle analysis showed a concentration-dependent accumulation of cells in the sub-G1 phase upon treatment with both compounds. The Annexin V-fluorescein isothiocyanate/propidium iodide assay showed that the compounds 6 and 10 increased the early and late apoptosis cell death modes in a dose-dependent manner. These compounds downregulated the expression of B-cell lymphoma-2 (Bcl-2), while increasing that of p53, Bcl-2-like protein 4, and caspase-7, at the mRNA and protein levels. Molecular docking of compounds 6 and 10 with Bcl-2 predicted them to show moderate − high binding affinity (6: −7.5 kcal/mol, 10: −7.9 kcal/mol) and interactions with key central substrate cavity residues. Overall, compounds 6 and 10 were found to be promising anticancer and apoptosis-inducing agents.

Differential Gene Expression in Erlotinib-Treated Fibroblasts

BACKGROUND

Therapies targeting the epidermal growth factor receptor (EGFR) result in a painful rash, the most common and debilitating toxicity among patients with non-small cell lung cancer (NSCLC) who take EGFR tyrosine kinase inhibitor (TKI) therapy; however, predicting the development and the severity of the rash is difficult.

OBJECTIVE

The aim of this study was to examine how erlotinib-an EGFR TKI that NSCLC patients take to stop or slow tumor growth-altered the transcriptome of dermal fibroblasts.

METHODS

Dermal fibroblasts (ATCC PCS-201-012) were seeded in cell culture flasks, grown under standard conditions, and transferred to cell culture dishes. Cells were treated once daily for 3 days with erlotinib 100 nM (n = 5), erlotinib 1 μM (n = 5), vehicle 1 μM (dimethyl sulfoxide) (n = 5), or no treatment (n = 5). Total RNA was extracted using a standard TRIzol method and hybridized using Affymetrix GeneChip Human Genome U133 Plus 2.0 arrays. Raw intensities generated from the arrays were normalized using a Robust Multiarray Average method and analyzed using analysis of variance in Limma R software. Differentially expressed genes were analyzed using Ingenuity Pathway Analysis to identify canonical or noncanonical signaling pathways enriched in this dataset.

RESULTS

We selected genes for investigation based on their potential role in wound healing (AQP3), rash development (CCL2), fibroblast activation (PALLD), cancer and cancer progression (GDF-15, SLC7A11, MMP12, and DIRAS3), and cell cycle control (CDC6). We were able to validate four of these genes by both Western blot analysis and quantitative polymerase chain reaction (MMP12, CCL2, CDC6, and SLC7A11).

DISCUSSION

If found predictive of rash in future studies using patient samples, our findings may help to identify those at risk for severe rash so that (a) the dose of EGFR TKI therapy may be adjusted; (b) additional treatments for the rash can be developed; and/or (c) precise, patient-centered interventions can be developed so that patients with cancer can better self-manage their rash and adhere to EGFR TKI treatment.

Induction of the mitochondria-mediated apoptosis in human esophageal cancer cells by DS2, a newly synthetic diterpenoid analog, is regulated by Bax and caused by generation of reactive oxygen species

Ent-kaurane diterpene compounds have attracted considerable attention in recent years due to its antitumor, antibacterial, and antiviral activities. However, the clinical development of natural kaurane diterpenes, for example, oridonin for cancer therapy has been hampered by its relatively moderate potency, limited bioavailability. Herein, we report a newly synthetic analog of natural ent-kaurane diterpene, DS2, which exhibits significantly improved activity of antiproliferation against various cancer cell lines relative to oridonin. DS2 treatment triggers the mitochondria-mediated apoptosis and cell cycle arrest in human esophageal cancer cell lines (EC9706, EC109). Interestingly, normal human esophageal epithelial cells (HEECs) and normal human liver cells (HL-7702) are both significantly more resistant to the growth inhibition by DS2 compared with esophageal cancer cells. The DS2-induced apoptosis in EC9706 cells correlated with the drop of mitochondrial membrane potential (MMP), release of cytochrome c into the cytosol and activation of caspase-9 and -3. The induction of proapoptotic proteins p21 and Bax were also observed in DS2-treated cells. The DS2-induced apoptosis was significantly attenuated by knockdown of Bax proteins. Meanwhile, the DS2 treatment caused generation of reactive oxygen species (ROS) in human esophageal cancer cells, but not in HEECs, which was attenuated by pretreatment with ROS scavenger N-acetylcysteine (NAC). More interestingly, the antioxidants pretreatment completely attenuated DS2 mediated loss of the MMP and apoptosis, as well as Bax expression and growth inhibition. In conclusion, the present study reveals that the mitochondria-mediated cell death by DS2 is associated with Bax regulation and ROS generation, and understanding the function and mechanism of DS2 will help us to design better anti-cancer drugs.

Drug resistance in cancer: molecular evolution and compensatory proliferation

Targeted therapies have revolutionized cancer treatment. Unfortunately, their success is limited due to the development of drug resistance within the tumor, which is an evolutionary process. Understanding how drug resistance evolves is a prerequisite to a better success of targeted therapies. Resistance is usually explained as a response to evolutionary pressure imposed by treatment. Thus, evolutionary understanding can and should be used in the design and treatment of cancer. In this article, drug-resistance to targeted therapies is reviewed from an evolutionary standpoint. The concept of apoptosis-induced compensatory proliferation (AICP) is developed. It is shown that AICP helps to explain some of the phenomena that are observed experimentally in cancers. Finally, potential drug targets are suggested in light of AICP.

Cladosporol A triggers apoptosis sensitivity by ROS-mediated autophagic flux in human breast cancer cells

Background

Endophytes have proven to be an invaluable resource of chemically diverse secondary metabolites that act as excellent lead compounds for anticancer drug discovery. Here we report the promising cytotoxic effects of Cladosporol A (HPLC purified >98%) isolated from endophytic fungus Cladosporium cladosporioides collected from Datura innoxia. Cladosporol A was subjected to in vitro cytotoxicity assay against NCI60 panel of human cancer cells using MTT assay. We further investigated the molecular mechanism(s) of Cladosporol A induced cell death in human breast (MCF-7) cancer cells. Mechanistically early events of cell death were studied using DAPI, Annexin V-FITC staining assay. Furthermore, immunofluorescence studies were carried to see the involvement of intrinsic pathway leading to mitochondrial dysfunction, cytochrome c release, Bax/Bcl-2 regulation and flowcytometrically measured membrane potential loss of mitochondria in human breast (MCF-7) cancer cells after Cladosporol A treatment. The interplay between apoptosis and autophagy was studied by microtubule dynamics, expression of pro-apoptotic protein p21 and autophagic markers monodansylcadaverine staining and LC3b expression.

Results

Among NCI60 human cancer cell line panel Cladosporol A showed least IC₅₀ value against human breast (MCF-7) cancer cells. The early events of apoptosis were characterized by phosphatidylserine exposure. It disrupts microtubule dynamics and also induces expression of pro-apoptotic protein p21. Moreover treatment of Cladosporol A significantly induced MMP loss, release of cytochrome c, Bcl-2 down regulation, Bax upregulation as well as increased monodansylcadaverine (MDC) staining and leads to LC3-I to LC3-II conversion.

Conclusion

Our experimental data suggests that Cladosporol A depolymerize microtubules, sensitize programmed cell death via ROS mediated autophagic flux leading to mitophagic cell death.

Graphical abstract

The proposed mechanism of Cladosporol A -triggered apoptotic as well as autophagic death of human breast cancer (MCF-7) cells. The figure shows that Cladosporol A induced apoptosis through ROS mediated mitochondrial pathway and increased p21 protein expression in MCF-7 cells in vitro.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0141-0) contains supplementary material, which is available to authorized users.

Urolithin C, a gut metabolite of ellagic acid, induces apoptosis in PC12 cells through a mitochondria-mediated pathway

Urolithin C includes apoptosis in PC12 cells through a mitochondria-mediated pathway.

A novel colchicine-based microtubule inhibitor exhibits potent antitumor activity by inducing mitochondrial mediated apoptosis in MIA PaCa-2 pancreatic cancer cells

Colchicine, an antimitotic alkaloid isolated from Colchicum autumnale, is a classical drug for treatment of gout and familial Mediterranean fever. It causes antiproliferative effects through the inhibition of microtubule formation, which leads to mitotic arrest and cell death by apoptosis. Here, we report that a novel colchicine analog, 4o (N-[(7S)-1,2,3-trimethoxy-9-oxo-10-[3-(trifluoromethyl)-4-chlorophenylamino]-5,6,7,9-tetrahydrobenzo[a]heptalen-7-yl]acetamide), which exhibited potent anticancer activities both in vitro and in vivo. In this study, 4o with excellent pharmacokinetic profile and no P-gp induction liability displayed strong inhibition of proliferation against various human cancer cell lines. However, pancreatic cancer cell line MIA PaCa-2 was found to be more sensitive towards 4o and showed strong inhibition in concentration and time-dependent manner. By increasing intracellular reactive oxygen species (ROS) levels, 4o induced endoplasmic reticular stress and mitochondrial dysfunction in MIA PaCa-2 cells. Blockage of ROS production reversed 4o-induced endoplasmic reticulum (ER) stress, calcium release, and cell death. More importantly, it revealed that increased ROS generation might be an effective strategy in treating human pancreatic cancer. Further 4o treatment induced mitotic arrest, altered the expression of cell cycle-associated proteins, and disrupted the microtubules in MIA PaCa-2 cells. 4o treatment caused loss of mitochondrial membrane potential, cytochrome c release, upregulation of Bax, downregulation of Bcl-2, and cleavage of caspase-3, thereby showing activation of mitochondrial mediated apoptosis. The in vivo anticancer activity of the compound was studied using sarcoma-180 (ascitic) and leukemia (P388 lymphocytic and L1210 lymphoid) models in mice and showed promising antitumor activity with the least toxicity unlike colchicine. Such studies have hitherto not been reported. Taken together, these findings highlighted that 4o, a potent derivative of colchicine, causes tumor regression with reduced toxicity and provides a novel anticancer candidate for the therapeutic use.

Novel piperazine core compound induces death in human liver cancer cells: possible pharmacological properties

The current study evaluates the cytotoxic mechanism of a novel piperazine derivate designated as PCC against human liver cancer cells. In this context, human liver cancer cell lines, SNU-475 and 243, human monocyte/macrophage cell line, CRL-9855, and human B lymphocyte cell line, CCL-156, were used to determine the IC₅₀ of PCC using the standard MTT assay. PCC displayed a strong suppressive effect on SNU-475 and SNU-423 cells with an IC₅₀ value of 6.98 ± 0.11 μg/ml and 7.76 ± 0.45 μg/ml respectively, after 24 h of treatment. Significant dipping in the mitochondrial membrane potential and elevation in the released of cytochrome c from the mitochondria indicated the induction of the intrinsic apoptosis pathway by PCC. Activation of this pathway was further evidenced by significant activation of caspase 3/7 and 9. PCC was also shown to activate the extrinsic pathways of apoptosis via activation of caspase-8 which is linked to the suppression of NF-ƙB translocation to the nucleus. Cell cycle arrest in the G1 phase was confirmed by flow cytometry and up-regulation of glutathione reductase expression was quantified by qPCR. This study suggests that PCC is a simultaneous inducer of intrinsic and extrinsic pathways of apoptosis in liver cancer cell lines.

Zoledronic acid increases the antitumor effect of gefitinib treatment for non-small cell lung cancer with EGFR mutations

Non-small cell lung cancer (NSCLC) patients with epithelial growth factor receptor (EGFR) mutations and bone metastases are often concurrently administered tyrosine kinase inhibitors (TKIs) and bisphosphonates. Yet, the effects and mechanisms of these agents are unclear. In the present study, we aimed to ascertain whether zoledronic acid (ZA) increases the antitumor effects of gefitinib treatment on NSCLC with EGFR mutations and the related mechanisms of action. The effects of ZA and gefitinib on NSCLC tumor cells with EGFR mutations (HCC827, HCC827 GR and H1975) in regards to proliferation, apoptosis, cell cycle and signaling pathways were detected. ZA increased the antitumor effects of gefitinib on NSCLC with EGFR activating mutations and TKI resistance in vitro. Gefitinib caused cell cycle arrest in the G0/G1 phase, ZA induced S phase accumulation and the effect of the combined treatment was neutralization. Combined treatment obviously inhibited STAT3 and/or p‑STAT3 protein expression compared with treatment with each single drug in vitro and in vivo, and it also significantly inhibited TKI resistance NSCLC tumor growth in vivo. In conclusion, ZA increased the antitumor effects of gefitinib on NSCLC with EGFR activating mutations and TKI resistance by regulating the cell cycle, inducing caspase-3 expression and inhibiting STAT3 expression.

Mechanism of action of novel piperazine containing a toxicant against human liver cancer cells

The purpose of this study was to assess the cytotoxic potential of a novel piperazine derivative (PCC) against human liver cancer cells. SNU-475 and 423 human liver cancer cell lines were used to determine the IC50 of PCC using the standard MTT assay. PCC displayed a strong suppressive effect on liver cancer cells with an IC50 value of 6.98 ± 0.11 µM and 7.76 ± 0.45 µM against SNU-475 and SNU-423 respectively after 24 h of treatment. Significant dipping in the mitochondrial membrane potential and elevation in the released of cytochrome c from the mitochondria indicated the induction of the intrinsic apoptosis pathway by PCC. Activation of this pathway was further evidenced by significant activation of caspase 3/7 and 9. PCC was also shown to activate the extrinsic pathways of apoptosis via activation of caspase-8 which is linked to the suppression of NF-κB translocation to the nucleus. Cell cycle arrest in the G1 phase was confirmed by flow cytometry and up-regulation of glutathione reductase expression was quantified by qPCR. Results of this study suggest that PCC is a potent anti-cancer agent inducing both intrinsic and extrinsic pathways of apoptosis in liver cancer cell lines.

LKB1 deficiency enhances sensitivity to energetic stress induced by erlotinib treatment in non-small-cell lung cancer (NSCLC) cells

The tumor suppressor serine/threonine kinase 11 (STK11 or LKB1) is mutated in 20-30% of patients with non-small-cell lung cancer (NSCLC). Loss of LKB1-adenosine monophosphate-activated protein kinase (AMPK) signaling confers sensitivity to metabolic inhibition or stress-induced mitochondrial insults. We tested the hypothesis that loss of LKB1 sensitizes NSCLC cells to energetic stress induced by treatment with erlotinib. LKB1-deficient cells exhibited enhanced sensitivity to erlotinib in vitro and in vivo that was associated with alterations in energy metabolism and mitochondrial dysfunction. Loss of LKB1 expression altered the cellular response to erlotinib treatment, resulting in impaired ATP homeostasis and an increase in reactive oxygen species. Furthermore, erlotinib selectively blocked mammalian target of rapamycin signaling, inhibited cell growth and activated apoptosis in LKB1-deficient cells. Erlotinib treatment also induced AMPK activation despite loss of LKB1 expression, which was partially reduced by the application of a calcium/calmodulin-dependent protein kinase kinase 2 inhibitor (STO-609) or calcium chelator (BAPTA-AM). These findings may have significant implications for the design of novel NSCLC treatments that target dysregulated metabolic and signaling pathways in LKB1-deficient tumors.

Direct Activation of Bax Protein for Cancer Therapy

Bax, a central cell death regulator, is an indispensable gateway to mitochondrial dysfunction and a major proapoptotic member of the B-cell lymphoma 2 (Bcl-2) family proteins that control apoptosis in normal and cancer cells. Dysfunction of apoptosis renders the cancer cell resistant to treatment as well as promotes tumorigenesis. Bax activation induces mitochondrial membrane permeabilization, thereby leading to the release of apoptotic factor cytochrome c and consequently cancer cell death. A number of drugs in clinical use are known to indirectly activate Bax. Intriguingly, recent efforts demonstrate that Bax can serve as a promising direct target for small-molecule drug discovery. Several direct Bax activators have been identified to hold promise for cancer therapy with the advantages of specificity and the potential of overcoming chemo- and radioresistance. Further investigation of this new class of drug candidates will be needed to advance them into the clinic as a novel means to treat cancer.

In vitro prediction of the efficacy of molecularly targeted cancer therapy by Raman spectral imaging

Mutational acquired resistance is a major challenge in cancer therapy. Somatic tumours harbouring some oncogenic mutations are characterised by a high mortality rate. Surprisingly, preclinical evaluation methods do not show clearly resistance of mutated cancers to some drugs. Here, we implemented Raman spectral imaging to investigate the oncogenic mutation resistance to epidermal growth factor receptor targeting therapy. Colon cancer cells with and without oncogenic mutations such as KRAS and BRAF mutations were treated with erlotinib, an inhibitor of epidermal growth factor receptor, in order to detect the impact of these mutations on Raman spectra of the cells. Clinical studies suggested that oncogenic KRAS and BRAF mutations inhibit the response to erlotinib therapy in patients, but this effect is not observed in vitro. The Raman results indicate that erlotinib induces large spectral changes in SW-48 cells that harbour wild-type KRAS and BRAF. These spectral changes can be used as a marker of response to therapy. HT-29 cells (BRAF mutated) and SW-480 cells (KRAS mutated) display a smaller and no significant response, respectively. However, the erlotinib effect on these cells is not observed when phosphorylation of extracellular-signal-regulated kinase and AKT is monitored by Western blot, where this phosphorylation is the conventional in vitro test. Lipid droplets show a large response to erlotinib only in the case of cells harbouring wild-type KRAS and BRAF, as indicated by Raman difference spectra. This study shows the great potential of Raman spectral imaging as an in vitro tool for detecting mutational drug resistance.

Housing temperature-induced stress drives therapeutic resistance in murine tumour models through β2-adrenergic receptor activation

Cancer research relies heavily on murine models for evaluating the anti-tumour efficacy of therapies. Here we show that the sensitivity of several pancreatic tumour models to cytotoxic therapies is significantly increased when mice are housed at a thermoneutral ambient temperature of 30 °C compared with the standard temperature of 22 °C. Further, we find that baseline levels of norepinephrine as well as the levels of several anti-apoptotic molecules are elevated in tumours from mice housed at 22 °C. The sensitivity of tumours to cytotoxic therapies is also enhanced by administering a β-adrenergic receptor antagonist to mice housed at 22 °C. These data demonstrate that standard housing causes a degree of cold stress sufficient to impact the signalling pathways related to tumour-cell survival and affect the outcome of pre-clinical experiments. Furthermore, these data highlight the significant role of host physiological factors in regulating the sensitivity of tumours to therapy.

Evodiamine induces G2/M arrest and apoptosis via mitochondrial and endoplasmic reticulum pathways in H446 and H1688 human small-cell lung cancer cells

The goal of this study was to evaluate the ability of EVO to decrease cell viability and promote cell cycle arrest and apoptosis in small cell lung cancer (SCLC) cells. Lung cancer has the highest incidence and mortality rates among all cancers. Chemotherapy is the primary treatment for SCLC; however, the drugs that are currently used for SCLC are less effective than those used for non-small cell lung cancer (NSCLC). Therefore, it is necessary to develop new drugs to treat SCLC. In this study, the effects of evodiamine (EVO) on cell growth, cell cycle arrest and apoptosis were investigated in the human SCLC cell lines NCI-H446 and NCI-H1688. The results represent the first report that EVO can significantly inhibit the viability of both H446 and H1688 cells in dose- and time-dependent manners. EVO induced cell cycle arrest at G2/M phase, induced apoptosis by up-regulating the expression of caspase-12 and cytochrome C protein, and induced the expression of Bax mRNA and by down-regulating of the expression of Bcl-2 mRNA in both H446 and H1688 cells. However, there was no effect on the protein expression of caspase-8. Taken together, the inhibitory effects of EVO on the growth of H446 and H1688 cells might be attributable to G2/M arrest and subsequent apoptosis, through mitochondria-dependent and endoplasmic reticulum stress-induced pathways (intrinsic caspase-dependent pathways) but not through the death receptor-induced pathway (extrinsic caspase-dependent pathway). Our findings suggest that EVO is a promising novel and potent antitumor drug candidate for SCLC. Furthermore, the cell cycle, the mitochondria and the ER stress pathways are rational targets for the future development of an EVO delivery system to treat SCLC.

PE‑induced apoptosis in SMMC‑7721 cells: involvement of Erk and Stat signalling pathways

Emerging evidence indicates that the redistribution of phosphatidylethanolamine (PE) across the bilayer of the plasma membrane is an important molecular marker for apoptosis. However, the effect of PE on apoptosis and the underlying mechanism of PE remain unclear. In the current study, MTT and flow cytometric assays were used to examine the effects of PE on apoptosis in SMMC‑7721 cells. The level of mitochondrial membrane potential (ΔΨm) and the expression of Bax, Bcl‑2, caspase‑3, phospho‑Erk and phospho‑Stat1/2 in SMMC‑7721 cells that were exposed to PE were also investigated. The results showed that PE inhibited proliferation, caused G0/G1 phase cell cycle arrest and induced apoptosis in SMMC‑7721 cells in a dose‑dependent manner. Rhodamine 123 staining showed that the treatment of SMMC‑7721 cells with different concentrations of PE for 24 h significantly decreased the level of ΔΨm and exerted dose‑dependent effects. Using immunofluorescence and western blotting, we found that the expression of Bax was upregulated, whereas that of Bcl‑2 was downregulated in PE‑induced apoptotic cells. In addition, these events were accompanied by an increase in caspase‑3 expression in a dose‑dependent manner following PE treatment. PE‑induced apoptosis was accompanied by a decrease in Erk phospho-rylation and by the activation of Stat1/2 phosphorylation in SMMC‑7721 cells. In conclusion, the results suggested that PE‑induced apoptosis is involved in upregulating the Bax/Bcl‑2 protein ratio and decreasing the ΔΨm. Moreover, the results showed that the Erk and Stat1/2 signalling pathways may be involved in the process of PE‑induced apoptosis.

The autophagy inhibitor chloroquine overcomes the innate resistance of wild-type EGFR non-small-cell lung cancer cells to erlotinib

INTRODUCTION

The epidermal growth factor receptor (EGFR) inhibitor erlotinib is much less effective in non-small-cell lung cancer (NSCLC) tumors with wild-type EGFR, than in tumors with activating EGFR mutations. Autophagy is a tightly regulated lysosomal self-digestion process, which may alternatively promote cell survival or type II cell death. This study assessed the role of autophagy in erlotinib-mediated cytotoxicity.

METHODS

We used wild-type EGFR erlotinib-sensitive and erlotinib-resistant NSCLC cell lines to determine whether inhibiting autophagy by a therapeutic agent potentiated the antitumor activity of erlotinib in vitro and in vivo.

RESULTS

Erlotinib at a clinically relevant concentration (2 μM) induced autophagy in NSCLC cells with wild-type EGFR, and the degree of induction was greater in cells that were resistant than sensitive, suggesting that autophagy is cytoprotective. This was confirmed by knockdown of the autophagy-related gene Atg-5, and by using the autophagy inhibitor chloroquine (CQ), both of which increased the cytotoxicity of erlotinib. The synergistic activity of CQ was not because of the potentiation of erlotinib's effects on autophagy, cell-cycle arrest, and inhibition of both EGFR or downstream signaling of EGFR. Rather, CQ markedly activated apoptosis in the cells. The ability of CQ to potentiate the antitumor activity of erlotinib was also seen in mice bearing NSCLC tumor xenografts.

CONCLUSIONS

The ability to adapt to anti-EGFR therapy by triggering autophagy may be a key determinant for resistance to erlotinib in wild-type EGFR NSCLC. Inhibition of autophagy by CQ represents a novel strategy to broaden the spectrum of erlotinib efficacy in wild-type EGFR NSCLC tumors.

Erlotinib : a guide to its use in first-line treatment of non-small-cell lung cancer with epidermal growth factor-activating mutations

In the EU, the approved use of erlotinib (Tarceva(®)), an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, has recently been expanded to include first-line treatment of locally advanced or metastatic non-small-cell lung cancer (NSCLC) in patients with EGFR-activating mutations. In randomized, open-label, phase III clinical trials, oral erlotinib reduced the risk of progression, improved response rates, and was well tolerated relative to standard platinum-based doublet chemotherapy in Caucasian and Asian populations with advanced NSCLC with EGFR-activating mutations.

Inhibition of CIP2A determines erlotinib-induced apoptosis in hepatocellular carcinoma

Erlotinib is a small-molecular inhibitor of epidermal growth factor receptor (EGFR). Here, we identify that cancerous inhibitor of protein phosphatase 2A (CIP2A) is a major determinant mediating erlotinib-induced apoptosis in hepatocellular carcinoma (HCC). Erlotinib showed differential effects on apoptosis in 4 human HCC cell lines. Erlotinib induced significant apoptosis in Hep3B and PLC5 cell lines; however, Huh-7 and HA59T cell lines showed resistance to erlotinib-induced apoptosis at all tested doses. Down-regulation of CIP2A, a cellular inhibitor of protein phosphatase 2A (PP2A), mediated the apoptotic effect of erlotinib in HCC. Erlotinib inhibited CIP2A in a dose- and time-dependent manner in all sensitive HCC cells whereas no alterations in CIP2A were found in resistant cells. Overexpression of CIP2A upregulated phospho-Akt and protected Hep3B cells from erlotinib-induced apoptosis. In addition, silencing CIP2A by siRNA restored the effects of erlotinib in Huh-7 cells. Moreover, adding okadaic acid, a PP2A inhibitor, abolished the effects of erlotinib on apoptosis in Hep3B cells; and forskolin, a PP2A agonist enhanced the effect of erlotinib in resistant HA59T cells. Combining Akt inhibitor MK-2206 with erlotinib restored the sensitivity of HA59T cells to erlotinib. Furthermore, in vivo xenograft data showed that erlotinib inhibited the growth of PLC5 tumor but had no effect on Huh-7 tumor. Erlotinib downregulated CIP2A and upregulated PP2A activity in PLC5 tumors, but not in Huh-7 tumors. In conclusion, inhibition of CIP2A determines the effects of erlotinib on apoptosis in HCC. CIP2A may be useful as a therapeutic biomarker for predicting clinical response to erlotinib in HCC treatment.

Role of erlotinib in the treatment of non-small cell lung cancer: clinical outcomes in wild-type epidermal growth factor receptor patients

Erlotinib is an orally administered small molecule inhibitor of epidermal growth factor receptor (EGFR) tyrosine kinase. Erlotinib at the standard oral daily dose of 150 mg is approved for the treatment of unselected chemorefractory advanced non-small cell lung cancer patients as well as maintenance therapy after first-line chemotherapy. The European Medicines Agency has recently also approved erlotinib as the first-line therapy in patients with EGFR mutations. Although recent studies have identified higher response rates and improved survival with erlotinib in a subset of patients with EGFR mutations, the survival benefit from single agent erlotinib in chemorefractory patients and in the maintenance setting is well observed in EGFR wild-type patients. The role of single agent erlotinib in the first-line setting in special subsets of EGFR wild-type patients (elderly, poor performance status, non-smokers) needs to be further determined. The combination of erlotinib with other targeted therapies has shown promising results and warrants further studies in EGFR wild-type patients.

Correlation between epidermal growth factor receptor-specific nanobody uptake and tumor burden: a tool for noninvasive monitoring of tumor response to therapy

PURPOSE

Nanobodies represent an interesting class of probes for the generic development of molecular imaging agents. We studied the relationship between tumor uptake of the epidermal growth factor receptor (EGFR)-specific nanobody (99m)Tc-7C12 and tumor burden and evaluated the possibility of using this probe to monitor tumor response to erlotinib.

PROCEDURES

The specificity and affinity of (99m)Tc-7C12 was determined on A431 cells. Cells expressing firefly luciferase were used to evaluate tumor burden using bioluminescence imaging. We evaluated the effect of erlotinib on tumor burden and (99m)Tc-7C12 uptake in vitro as well as in vivo. In vivo bioluminescence imaging was performed followed by pinhole single-photon emission computed tomography/micro-computed tomography.

RESULTS

(99m)Tc-7C12 binds specifically to the receptor with high affinity (3.67 ± 0.59 nM). Erlotinib reduced tumor uptake and cell viability in a concentration-dependent manner. Tumor uptake of (99m)Tc-7C12 showed good correlation with tumor burden. Erlotinib treatment resulted in a progressive reduction of tumor burden and tumor uptake of (99m)Tc-7C12.

CONCLUSION

(99m)Tc-7C12 binds to EGFR with high affinity and specificity. Tumor uptake is correlated with tumor burden. Quantification of (99m)Tc-7C12 uptake is promising for monitoring therapy response of EGFR-expressing tumors.

Bortezomib-induced sensitization of malignant human glioma cells to vorinostat-induced apoptosis depends on reactive oxygen species production, mitochondrial dysfunction, Noxa upregulation, Mcl-1 cleavage, and DNA damage

Glioblastomas are invasive tumors with poor prognosis despite current therapies. Histone deacetylase inhibitors (HDACIs) represent a class of agents that can modulate gene expression to reduce tumor growth, and we and others have noted some antiglioma activity from HDACIs, such as vorinostat, although insufficient to warrant use as monotherapy. We have recently demonstrated that proteasome inhibitors, such as bortezomib, dramatically sensitized highly resistant glioma cells to apoptosis induction, suggesting that proteasomal inhibition may be a promising combination strategy for glioma therapeutics. In this study, we examined whether bortezomib could enhance response to HDAC inhibition in glioma cells. Although primary cells from glioblastoma multiforme (GBM) patients and established glioma cell lines did not show significant induction of apoptosis with vorinostat treatment alone, the combination of vorinostat plus bortezomib significantly enhanced apoptosis. The enhanced efficacy was due to proapoptotic mitochondrial injury and increased generation of reactive oxygen species. Our results also revealed that combination of bortezomib with vorinostat enhanced apoptosis by increasing Mcl-1 cleavage, Noxa upregulation, Bak and Bax activation, and cytochrome c release. Further downregulation of Mcl-1 using shRNA enhanced cell killing by the bortezomib/vorinostat combination. Vorinostat induced a rapid and sustained phosphorylation of histone H2AX in primary GBM and T98G cells, and this effect was significantly enhanced by co-administration of bortezomib. Vorinostat/bortezomib combination also induced Rad51 downregulation, which plays an important role in the synergistic enhancement of DNA damage and apoptosis. The significantly enhanced antitumor activity that results from the combination of bortezomib and HDACIs offers promise as a novel treatment for glioma patients.

Cell cycle arrest and apoptosis induced by methyl 3,5-dicaffeoyl quinate in human colon cancer cells: Involvement of the PI3K/Akt and MAP kinase pathways

Methyl 3,5-dicaffeoyl quinate (MDQ) is a flavonoid glucoside found in several plants that scavenges 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals and peroxynitrite, and inhibits the formation of cholesteryl ester hydroperoxide during the copper ion-induced oxidation of blood plasma in rats. In this study, MDQ inhibited proliferation and induced apoptosis in HT-29 cells in a dose-dependent manner as detected by 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), trypan blue exclusion, and flow cytometric assays. Western blot analysis showed that apoptosis was dependent on caspase-3 activity. PARP cleavage and the cytosolic release of cytochrome c from mitochondria increased significantly. In addition, these events were accompanied by a collapse in the mitochondrial membrane potential and a decreased Bcl-2/Bax ratio. Furthermore, the MDQ-induced G(0)/G(1) arrest was correlated with an increase in p27 and a decrease in cyclin D1 and p53. MDQ also inhibited the phosphorylation of PI3K/Akt and ERK; significantly reduced NF-κB; and in general displayed a significant anti-proliferative effect via a cell cycle arrest and apoptotic induction in HT-29 cells. These results suggest that MDQ has therapeutic potential against human colon carcinoma.

Liposomal delivery of MicroRNA-7-expressing plasmid overcomes epidermal growth factor receptor tyrosine kinase inhibitor-resistance in lung cancer cells

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) have been strikingly effective in lung cancers harboring activating EGFR mutations. Unfortunately, the cancer cells eventually acquire resistance to EGFR-TKI. Approximately 50% of the acquired resistance involves a secondary T790M mutation. To overcome the resistance, we focused on EGFR suppression using microRNA-7 (miR-7), targeting multiple sites in the 3'-untranslated region of EGFR mRNA. Two EGFR-TKI-sensitive cell lines (PC-9 and H3255) and two EGFR-TKI-resistant cell lines harboring T790M (RPC-9 and H1975) were used. We constructed miR-7-2 containing miR-7-expressing plasmid. After transfection of the miR-7-expressing plasmid, using cationic liposomes, a quantitative PCR and dual luciferase assay were conducted to examine the efficacy. The antiproliferative effect was evaluated using a cell count assay and xenograft model. Protein expression was examined by Western blotting. The miR-7 expression level of the transfectants was approximately 30-fold higher, and the luciferase activity was ablated by 92%. miR-7 significantly inhibited cell growth not only in PC-9 and H3255 but also in RPC-9 and H1975. Expression of insulin receptor substrate-1 (IRS-1), RAF-1, and EGFR was suppressed in the four cell lines. Injection of the miR-7-expressing plasmid revealed marked tumor regression in a mouse xenograft model using RPC-9 and H1975. EGFR, RAF-1, and IRS-1 were suppressed in the residual tumors. These findings indicate promising therapeutic applications of miR-7-expressing plasmids against EGFR oncogene-addicted lung cancers including T790M resistance by liposomal delivery.

Cell death signaling and anticancer therapy

For a long time, it was commonly believed that efficient anticancer regimens would either trigger the apoptotic demise of tumor cells or induce a permanent arrest in the G₁ phase of the cell cycle, i.e., senescence. The recent discovery that necrosis can occur in a regulated fashion and the increasingly more precise characterization of the underlying molecular mechanisms have raised great interest, as non-apoptotic pathways might be instrumental to circumvent the resistance of cancer cells to conventional, pro-apoptotic therapeutic regimens. Moreover, it has been shown that some anticancer regimens engage lethal signaling cascades that can ignite multiple oncosuppressive mechanisms, including apoptosis, necrosis, and senescence. Among these signaling pathways is mitotic catastrophe, whose role as a bona fide cell death mechanism has recently been reconsidered. Thus, anticancer regimens get ever more sophisticated, and often distinct strategies are combined to maximize efficacy and minimize side effects. In this review, we will discuss the importance of apoptosis, necrosis, and mitotic catastrophe in the response of tumor cells to the most common clinically employed and experimental anticancer agents.

Synergistic anticancer effects of combined γ-tocotrienol with statin or receptor tyrosine kinase inhibitor treatment

Systemic chemotherapy is the only current method of treatment that provides some chance for long-term survival in patients with advanced or metastatic cancer. γ-Tocotrienol is a natural form of vitamin E found in high concentrations in palm oil and displays potent anticancer effects, but limited absorption and transport of by the body has made it difficult to obtain and sustain therapeutic levels in the blood and target tissues. Statins are inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase and are an example of a promising cancer chemotherapeutic agent whose clinical usefulness has been limited due to high-dose toxicity. Similarly, erlotinib and gefitinib are anticancer agents that inhibit the activation of individual HER/ErbB receptor subtypes, but have shown limited clinical success because of heterodimerization between different EGF receptor family members that can rescue cancer cells from agents directed against a single receptor subtype. Recent studies have investigated the anticancer effectiveness of low-dose treatment of various statins or EGF receptor inhibitors alone and in combination with γ-tocotrienol on highly malignant +SA mouse mammary epithelial cells in vitro. Combined treatment with subeffective doses of γ-tocotrienol with these other chemotherapeutic agents resulted in a synergistic inhibition of +SA cell growth and viability. These findings strongly suggest that combined treatment of γ-tocotrienol with other anticancer agents may not only provide an enhanced therapeutic response but also provide a means to avoid the toxicity, low bioavailability, or limited therapeutic action associated with high-dose monotherapy.

Caspase-8 as a therapeutic target in cancer

Caspase-8 is an apical caspase which initiates programmed cell death following death receptor ligation. This central role in apoptosis has prompted significant clinical interest in regulating caspase-8 expression and proteolytic activity. However, caspase-8 has also been found to play a number of non-apoptotic roles in cells, such as promoting activation NF-κB signaling, regulating autophagy and altering endosomal trafficking, and enhancing cellular adhesion and migration. Therefore, depending upon the specific cellular context, caspase-8 may either potentiate or suppress tumor malignancy. Accordingly, a marked heterogeneity exists in the expression patterns of caspase-8 among different tumor types. Therapeutics have been developed which can increase caspase-8 expression, yet it remains unclear whether this approach will be beneficial in all cases. Care is warranted, and the role of caspase-8 should be addressed on a case by case basis.

Oleanolic acid and ursolic acid induce apoptosis in four human liver cancer cell lines

Apoptotic effects of oleanolic acid (OA) and ursolic acid (UA) on human liver cancer HepG2, Hep3B, Huh7 and HA22T cell lines were examined. OA or UA at 2, 4, 8 micromol/L were used and their effects on cell viability, DNA fragmentation, mitochondrial membrane potential (MMP), activity of Na(+)-K(+)-ATPase, caspase-3 and caspase-8, cell adhesion, level of intercellular adhesion molecule (ICAM)-1 and vascular endothelial growth factor (VEGF) in these cell lines were determined. OA or UA treatments concentration-dependently decreased cell viability and increased DNA fragmentation in HepG2 and Hep3B cell lines (P<0.05). However, these two compounds reduced viability and increased DNA fragmentation in Huh7 cell only at 4 and 8 micromol/L (P<0.05). OA or UA treatments concentration-dependently lowered MMP in HepG2, Hep3B and HA22T cell lines (P<0.05). These two compounds also concentration-dependently diminished Na(+)-K(+)-ATPase activity and VEGF level in four test cell lines (P<0.05). Besides Huh7 cell, OA or UA treatments concentration-dependently elevated caspase-3 and caspase-8 activities in other three cell lines (P<0.05). Besides HA22T cell, these two compounds concentration-dependently inhibited cell adhesion and decreased ICAM-1 level in other three cell lines (P<0.05). These findings support that OA and UA are potent anti-cancer agents to cause apoptosis in these liver cancer cell lines.

Enhanced antiproliferative and apoptotic response to combined treatment of gamma-tocotrienol with erlotinib or gefitinib in mammary tumor cells

Background

Aberrant ErbB receptor signaling is associated with various types of malignancies. γ-Tocotrienol is a member of the vitamin E family of compounds that displays potent anticancer activity that is associated with suppression in ErbB receptor phosphorylation and mitogenic signaling. Erlotinib and gefitinib are tyrosine kinase inhibitors that block ErbB1 receptor activation, whereas trastuzumab is a monoclonal antibody that has been designed to specifically inhibit ErbB2 receptor activation. However, the clinical effectiveness of these agents have been disappointing because of cooperation between different ErbB family members that can rescue cancer cells from agents directed against a single ErbB receptor subtype. It was hypothesized that targeting multiple ErbB receptor subtypes with combined treatment of γ-tocotrienol and ErbB receptor inhibitors would provide greater anticancer effects than monotherapy targeting only a single ErbB receptor subtype.

Methods

Highly malignant mouse +SA mammary epithelial cells were maintained in culture on serum-free defined media containing 10 ng/ml EGF as a mitogen. Cell viability wase determined by MTT assay, whereas Western blot and immunofluorescent staining was used to determine treatment effects on ErbB receptor subtype level and activation. Treatment-induced apoptosis was determined using annexin V staining and Western blot analysis of cleaved caspase-3 and PARP levels.

Results

Treatment with 3.5 μM γ-tocotrienol, 0.5 μM erlotinib or 1.0 μM gefitinib alone, significantly inhibited +SA tumor cell growth. Combined treatment with subeffective doses of erlotinib (0.25 μM) or gefitinib (0.5 μM) with subeffective doses of γ-tocotrienol (0.5-3.0 μM) significantly inhibited the growth and induced apoptosis in a dose-responsive manner. Trastuzumab treatment alone or in combination had no effect on +SA cell growth and viability. Combined treatment of γ-tocotrienol with erlotinib or gefitinib also cause a large decrease in ErbB3, ErbB4, and to a lesser extent ErbB2 receptor levels, and EGF-dependent ErbB2-4 tyrosine phosphorylation (activation), but had no effect on ErbB1 receptor levels or activation.

Conclusion

Combination treatment of γ-tocotrienol with specific ErbB receptor inhibitors is more effective in reducing mammary tumor cell growth and viability than high dose monotherapy, suggesting that targeting multiple ErbB receptors with combination therapy may significantly improve the therapeutic response in breast cancer patients.

Apoptotic effects of protocatechuic acid in human breast, lung, liver, cervix, and prostate cancer cells: potential mechanisms of action

Apoptotic effects of protocatechuic acid (PCA) at 1, 2, 4, 8 micromol/L on human breast cancer MCF7 cell, lung cancer A549 cell, HepG2 cell, cervix HeLa cell, and prostate cancer LNCaP cell were examined. Results showed that PCA concentration-dependently decreased cell viability, increased lactate dehydrogenase leakage, enhanced DNA fragmentation, reduced mitochondrial membrane potential, and lowered Na(+)-K(+)-ATPase activity for these cancer cells (P < 0.05). PCA also concentration-dependently elevated caspase-3 activity in five cancer cells (P < 0.05), but this agent at 2-8 micromol/L significantly increased caspase-8 activity (P < 0.05). PCA concentration-dependently decreased intercellular adhesion molecule level in test cancer cells (P < 0.05) but significantly inhibited cell adhesion at 2-8 micromol/L (P < 0.05). PCA also concentration-dependently lowered the levels of interleukin (IL)-6 and IL-8 in five cancer cells (P < 0.05), but this agent at 2-8 micromol/L significantly suppressed vascular endothelial growth factor production (P < 0.05). These findings suggest that PCA is a potent anticancer agent to cause apoptosis or retard invasion and metastasis in these five cancer cells.

Wortmannin potentiates roscovitine-induced growth inhibition in human solid tumor cells by repressing PI3K/Akt pathway

Roscovitine has been reported to have anti-tumor effects in some cancer cell lines. The phosphatidylinositol-3-kinase (PI3K) signaling, which activates protein kinase B (PKB)/Akt, is known to mediate cell survival. The current study examined the role of wortmannin, a PI3K inhibitor, as a chemosensitizer for roscovitine and its proposed mechanism of action. The results showed that wortmannin significantly chemosensitized three human tumor cell lines (A549, HCT116 and HeLa cells). In A549 cells, wortmannin increased roscovitine-induced apoptosis in a dose-dependent manner, which was correlated with the inhibition of phosphorylated PKB/Akt level. Wortmannin enhanced the effects of roscovitine by causing pronounced reduction of mitochondrial transmembrane potential (MMP) and increases of cytochrome c release and active caspase-3, as well as enhanced activation of Bax and Bad, including Bax oligomerization and mitochondrial translocation of Bax and Bad. Taken together, these results provide evidence for the potential application of roscovitine/wormannin combination in clinical treatment for solid tumors.

Genistein enhances the effect of epidermal growth factor receptor tyrosine kinase inhibitors and inhibits nuclear factor kappa B in nonsmall cell lung cancer cell lines

BACKGROUND

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have shown modest clinical benefit in patients with relapsed nonsmall cell lung cancer (NSCLC). Down-regulation of Akt appears to correlate with the antitumor activity of EGFR-TKIs. Akt activates nuclear factor kappa B (NF-kappaB), which transcribes genes important for cell survival, invasion, and metastasis. The authors hypothesized that genistein, through the inhibition of NF-kappaB, could enhance the activity of EGFR-TKIs in NSCLCs.

METHODS

Three NSCLC cell lines with various EGFR mutation status and sensitivities to EGFR-TKIs were selected: H3255 (L858R), H1650 (del E746-A750), and H1781 (wild-type EGFR). Cells were treated with erlotinib, gefitinib, genistein, or the combination of each of the EGFR-TKIs with genistein. Cell survival and apoptosis were assessed, and expression levels of EGFR, pAkt, cyclooxygenase-2 (COX-2), E-cadherin, prostaglandin E(2) (PGE(2)), and NF-kappaB were measured.

RESULTS

Both EGFR-TKIs demonstrated growth inhibition and apoptosis in each of the cell lines, but H1650 and H1781 were much less sensitive. Genistein demonstrated some antitumor activity in all cell lines, but enhanced growth inhibition and apoptosis when combined with the EGFR-TKIs in each of the cell lines. Both combinations down-regulated NF-kappaB significantly more than either agent alone in H3255. In addition, the combinations reduced the expression of EGFR, pAkt, COX-2, and PGE(2,) consistent with inactivation of NF-kappaB.

CONCLUSIONS

The authors concluded that genistein enhances the antitumor effects of EGFR-TKIs in 3 separate NSCLC cell lines. This enhanced activity is in part because of greater reduction in the DNA-binding activity of NF-kappaB when EGFR-TKIs were combined with genistein.

Mechanisms of tumor resistance to EGFR-targeted therapies

BACKGROUND

Much effort has been devoted to development of cancer therapies targeting EGFR, based on its role in regulating cell growth. Small-molecule and antibody EGFR inhibitors have clinical roles based on their efficacy in a subset of cancers, generally as components of combination therapies. Many cancers are either initially resistant to EGFR inhibitors or become resistant during treatment, limiting the efficacy of these reagents.

OBJECTIVE/METHODS

To review cellular resistance mechanisms to EGFR-targeted therapies.

RESULTS/CONCLUSIONS

The best validated of these mechanisms include activation of classic ATP-binding casette (ABC) multidrug transporters; activation or mutation of EGFR; and overexpression or activation of signaling proteins operating in relation to EGFR. We discuss current efforts and potential strategies to override these sources of resistance. We describe emerging systems-biology-based concepts of alternative resistance to EGFR-targeted therapies, and discuss their implications for use of EGFR-targeted and other targeted therapies.

Activation of ER stress and inhibition of EGFR N-glycosylation by tunicamycin enhances susceptibility of human non-small cell lung cancer cells to erlotinib

PURPOSE

The epidermal growth factor receptor (EGFR), an N-glycosylated transmembrane protein, is the target of erlotinib, an orally bioavailable agent approved for treatment of patients with non-small cell lung cancer (NSCLC). In this study, we examined whether inhibition of EGFR N-glycosylation and stimulation of endoplasmic reticulum (ER) stress by tunicamycin enhances erlotinib-induced growth inhibition in NSCLC cell lines.

METHODS

We examined the effects of tunicamycin and erlotinib on cytotoxicity of erlotinib-sensitive and resistant NSCLC cell lines, as well its effects on apoptotic pathways and on EGFR activation and subcellular localization.

RESULTS

A minimally cytotoxic concentration of tunicamycin (1 microM) resulted in approximatey 2.6-2.9 fold and approximatey 6.8-13.5 fold increase in erlotinib-induced antiproliferative effects in sensitive (H322 and H358) and resistant cell lines (A549 and H1650), respectively. We found that tunicamycin generated an aglycosylated form of 130 kDa EGFR. Tunicamycin additionally affected EGFR activation and subcellular localization. Interestingly, the combination of tunicamycin and erlotinib caused more inhibitory effect on EGFR phosphorylation than that of erlotinib alone. Moreover, the combination induced apoptosis in H1650 cells through induction of CHOP expression, activation of caspase-12 and caspase-3, cleavage of PARP and bak, and down-regulation of anti-apoptotic proteins bcl-xL and survivin.

CONCLUSIONS

Overall, our data demonstrate that tunicamycin significantly enhances the susceptibility of lung cancer cells to erlotinib, particularly sensitizing resistant cell lines to erlotinib, and that such sensitization may be associated with activation of the ER stress pathway and with inhibition of EGFR N-glycosylation.