RETRACTED: Antitumor activity of bortezomib in human cancer cells with acquired resistance to anti-epidermal growth factor receptor tyrosine kinase inhibitors

Identification of potential edible spices as EGFR and EGFR mutant T790M/L858R inhibitors by structure-based virtual screening and molecular dynamics

Epidermal growth factor receptor (EGFR) tyrosine kinases are overexpressed in several human cancers and could serve as a promising anti-cancer drug target. With this in view, the main aim of the present study was to identify spices having the potential to inhibit EGFR tyrosine kinase. The structure-based virtual screening of spice database consisting of 1439 compounds with EGFR tyrosine kinase (PDB ID: 3W32) was carried out using Glide. Top scored 18 hits (XP Glide Score ≥ -10.0 kcal/mol) was further docked with three EGFR tyrosine kinases and three EGFR T790M/L858R mutants using AutodockVina, followed by ADME filtration. The best three hits were further refined by Molecular Dynamics (MD) simulation and MM-GBSA-based binding energy calculation. The overall docking results of the selected hits with both EGFR and EGFR T790M/L858R were quite satisfactory and showed strong binding compared to the three coligands. Detailed MD analysis of CL_07, AC_11 and AS_49 also showed the stability of the protein-ligand complexes. Moreover, the hits were drug-like, and MM-GBSA binding free energy of CL_07 and AS_49 was established to be far better. AC_11 was found to be similar to the known inhibitor Gefitinib. Most of the potential hits are available in Allium cepa, CL_07 and AS_49 available in Curcuma longa and Allium sativum, respectively. Therefore, these three spices could be used as a potential therapeutic candidate against cancer caused by overexpression of EGFR after validation of the observations of this study in in-vitro experiments. Further extensive work is needed to improve the scaffolds CL_07, AC_11, AC_17, and AS_49 as potential anti-cancer drugs.Communicated by Ramaswamy H. Sarma.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

Enhanced Antitumor Effect of Trastuzumab and Duligotuzumab or Ipatasertib Combination in HER-2 Positive Gastric Cancer Cells

Simple Summary

The ToGA trial has demonstrated, in HER2-expressing patients, that unresectable and advanced gastric cancer, chemotherapy and trastuzumab in combination increase overall survival, even if it is still unclear why after one year the same patients are non-responsive to trastuzumab treatment. Here, we have demonstrated that in HER2-positive gastric cancer cell lines, the addition of duligotuzumab, targeting HER3 receptor, or ipatasertib, targeting AKT protein, enhances the antitumor effect of trastuzumab in vitro through a full inhibition of the membrane signals, on HER2 and HER3, and of downstream signaling, including AKT, and MAPK pathways. Hence, this study suggests a novel and biomarker-driven therapeutic strategy supporting further evaluation of the anti-tumor efficacy of these combinations in HER2 human gastric cancer patients.

Abstract

The anti-HER2 monoclonal antibody trastuzumab is a key drug for the treatment of HER2-positive gastric cancer (GC); however, its activity is often limited by the onset of resistance and mechanisms of resistance are still poorly understood. Several targeted agents showed synergistic activity by concomitant use with trastuzumab in vitro and are under clinical investigation. The aim of this study was to assess the antitumor activity of duligotuzumab, an anti HER3/EGFR antibody or ipatasertib, an AKT inhibitor, combined with trastuzumab in a panel of HER2-positive human gastric cancer cells (GCC), and the efficacy of such combinations in HER2-resistant cells. We have assessed the efficacy of duligotuzumab or ipatasertib and trastuzumab in combination, analyzing proliferation, migration and apoptosis and downstream intracellular signaling in vitro on human HER2-positive GCC (NCI-N87, OE33, OE19) and in negative HER2 GCC (MKN28). We observed a reduction of proliferation, migration and apoptotic rate in HER2-positive OE33, OE19 and N87 cell lines with the combination of duligotuzumab or ipatasertib plus trastuzumab. In particular, in OE33 and OE19 cell lines, the same combined treatment inhibited the activation of proteins downstream of HER2, HER3, AKT and MAPK pathways. Targeting both HER2 and HER3, or HER2 and AKT, results in an improved antitumor effect on HER2-positive GCC.

Carfilzomib inhibits the growth of lung adenocarcinoma via upregulation of Gadd45a expression

Proteasome inhibitors have shown remarkable success in the treatment of hematologic neoplasm. There has been a lot of attention to applying these drugs for solid tumor treatment. Recent preclinical study has signified the effectiveness on cell proliferation inhibition in lung adenocarcinoma treated by carfilzomib (CFZ), a second generation proteasome inhibitor. However, no insight has been gained regarding the mechanism. In this study, we have systematically investigated the CFZ functions in cell proliferation and growth, cell cycle arrest, and apoptosis in lung adenocarcinoma cells. Flow cytometry experiments showed that CFZ significantly induced G2/M cell cycle arrest and apoptosis in lung adenocarcinoma. MTS and colony formation assays revealed that CFZ substantially inhibited survival of lung adenocarcinoma cells. All results were consistently correlated to the upregulation expression of Gadd45a, which is an important gene in modulating cell cycle arrest and apoptosis in response to physiologic and environmental stresses. Here, upregulation of Gadd45a expression was observed after CFZ treatment. Knocking down Gadd45a expression suppressed G2/M arrest and apoptosis in CFZ-treated cells, and reduced cytotoxicity of this drug. The protein expression analysis has further identified that the AKT/FOXO3a pathway is involved in Gadd45a upregulation after CFZ treatment. These findings unveil a novel mechanism of proteasome inhibitor in anti-solid tumor activity, and shed light on novel preferable therapeutic strategy for lung adenocarcinoma. We believe that Gadd45a expression can be a highly promising candidate predictor in evaluating the efficacy of proteasome inhibitors in solid tumor therapy.

Antitumor efficacy of Kisspeptin in human malignant mesothelioma cells

Purpose

Kisspeptin signaling, via its receptors GPR54, could be an essential players in the inhibition of mesothelioma progression, invasion and metastasis formation. The loss of KiSS1 by tumor cells has been associated with a metastatic phenotype but the mechanistic insights of this process are still unknown.

Experimental design

The blockade of the metastatic process at early stage is a hot topic in cancer research. We studied the role of KiSS1 on proliferation, invasiveness, migration abilities of mesothelioma cell lines focusing on the effect on epithelial-to-mesenchymal transition (EMT).

Results

Treatment with the KiSS1 peptide or with a synthesis peptide with longer half-life, the FTM080, significantly inhibited cell proliferation, migration and invasion of mesothelioma cell lines; the same treatment reduced the activity of MMP-2 and MMP-9 determining consequently a marked reduction in the invasiveness of primary tumors and metastases. Thespecificexpression of EMT markers, as E-caderin, Vimentin, Slug and Snail, suggested the inhibition of EMT after treatment with KiSS1 as well as the preservation of epithelial components.

Conclusion

Our results support anti-proliferative effect of KiSS1 in cancer cells and suggest that targeting the KiSS1/GPR54 system may represent a novel therapeutic approach for mesothelioma.

Efficacy of continuous EGFR-inhibition and role of Hedgehog in EGFR acquired resistance in human lung cancer cells with activating mutation of EGFR

Purpose

The aim of this work was to investigate the efficacy of sequential treatment with first-, second- and third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors and the mechanisms of acquired resistance occurring during the sequential use of these inhibitors.

Experimental design

We developed an in vivo model of acquired resistance to EGFR-inhibitors by treating nude mice xenografted with HCC827, a human non-small-cell lung cancer (NSCLC) cell line harboring EGFR activating mutation, with a sequence of first-generation EGFR tyrosine kinase inhibitors (EGFR-TKIs) (erlotinib and gefitinib), of second-generation EGFR-TKI (afatinib) plus/minus the anti-EGFR monoclonal antibody cetuximab, and of third-generation EGFR-TKI (osimertinib).

Results

HCC827-derived xenografts and with acquired resistance to EGFR-inhibitors were sensitive to the sequential use of first-, second- and third-generation EGFR-TKIs. Continuous EGFR inhibition of first-generation resistant tumors by sequential treatment with afatinib plus/minus cetuximab, followed by osimertinib, represented an effective therapeutic strategy in this model. Whereas T790M resistance mutation was not detected, a major mechanism of acquired resistance was the activation of components of the Hedgehog (Hh) pathway. This phenomenon was accompanied by epithelial-to-mesenchymal transition. Cell lines established in vitro from gefitinib-, or afatinib- or osimertinib-resistant tumors showed metastatic properties and maintained EGFR-TKIs resistance in vitro, that was reverted by the combined blockade of Hh, with the selective SMO inhibitor sonidegib, and EGFR.

Conclusions

EGFR-mutant NSCLC can benefit from continuous treatment with EGFR-inhibitors, indepenently from mechanisms of resistance. In a complex and heterogenous scenario, Hh showed an important role in mediating resistance to EGFR-inhibitors through the induction of mesenchymal properties.

Synergistic effects of combining proteasome inhibitors with chemotherapeutic drugs in lung cancer cells

Background

The prognosis for patients with disseminated lung cancer is poor and current treatments have limited survival benefit as resistance often occurs, and is often associated with significant toxicity. A possible strategy to improve treatment and evade chemoresistance may be to find new combinations of drugs. The aim of this study was to analyze the potential of combining proteasome inhibitors (PIs) with chemotherapeutic drugs used in the routine treatment for lung cancer patients.

Results

The median-effect method was applied to the Fluorometric Microculture Cytotoxicity Assay (FMCA) to evaluate effects of combining two different PIs (bortezomib and b-AP15) with clinically used chemotherapeutic drugs representing different mechanisms of action (cisplatin, gefitinib, gemcitabine and vinorelbine) in two lung cancer cell lines (one sensitive and one resistant). Proteasome inhibition in combination with cisplatin, gemcitabine or vinorelbine had synergistic effects in at least one of the tested cell lines. Furthermore, the effect of gefitinib appeared strongly potentiated by the PI in the least resistant lung cancer cell line, although the level of synergy could not be determined with the median-effect method.

Conclusions

Combining PIs with cisplatin, gefitinib, gemcitabine or vinorelbine show potential as new combination chemotherapy for the treatment of lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s13104-017-2842-z) contains supplementary material, which is available to authorized users.

Phosphatidylinositol 3-kinase (PI3Kα)/AKT axis blockade with taselisib or ipatasertib enhances the efficacy of anti-microtubule drugs in human breast cancer cells

Purpose

The Phosphatidylinositol 3-kinase (PI3Ks) pathway is commonly altereted in breast cancer patients, but its role is still unclear. Taselisib, a mutant PI3Kα selective inhibitor, and ipatasertib, an AKT inhibitor, are currently under investigation in clinical trials in combination with paclitaxel or hormonal therapies in breast cancer. The aim of this study was to evaluate if PI3K or AKT inhibition can prevent resistance to chemotherapy and potentiate its efficacy.

Experimental design

The efficacy of combined treatment of ipatasertib and taselisib plus vinorelbine or paclitaxel or eribulin was evaluated in vitro on human breast cancer cells (with different expression profile of hormonal receptors, HER2, and of PI3Ka mutation) on cell survival by using MTT (3,(4,5-dimethylthiazol-2)2,5 difeniltetrazolium bromide) and colony forming assays on cell apoptosis by flow-cytometry analysis. We also investigated the effect of combined treatment on downstream intracellular signaling, by western blot analysis, and on metastatic properties, by migration assays. Finally, we analyzed changes in cell cytoskeleton by immunofluorescence.

Results

A significant synergism of ipatasertib or taselisib plus anti-microtubule chemotherapy in terms of anti-proliferative, pro-apoptotic and anti-metastatic effect was observed. The combined treatment completely inhibited the activation of proteins downstream of PI3K and MAPK pathways and affected the expression of survivin. Combined treatments completely disorganized the cytoskeleton in human breast cancer cells, with contemporary delocalization of survivin from cytoplasm to nucleus, thus suggesting a potential mechanism for this combination.

Conclusions

Targeting PI3K may enhance the efficacy of anti-microtubule drugs in human breast cancer cells.

Discovery of selective small-molecule HDAC6 inhibitor for overcoming proteasome inhibitor resistance in multiple myeloma

Multiple myeloma (MM) has proven clinically susceptible to modulation of pathways of protein homeostasis. Blockade of proteasomal degradation of polyubiquitinated misfolded proteins by the proteasome inhibitor bortezomib (BTZ) achieves responses and prolongs survival in MM, but long-term treatment with BTZ leads to drug-resistant relapse in most patients. In a proof-of-concept study, we previously demonstrated that blocking aggresomal breakdown of polyubiquitinated misfolded proteins with the histone deacetylase 6 (HDAC6) inhibitor tubacin enhances BTZ-induced cytotoxicity in MM cells in vitro. However, these foundational studies were limited by the pharmacologic liabilities of tubacin as a chemical probe with only in vitro utility. Emerging from a focused library synthesis, a potent, selective, and bioavailable HDAC6 inhibitor, WT161, was created to study the mechanism of action of HDAC6 inhibition in MM alone and in combination with BTZ. WT161 in combination with BTZ triggers significant accumulation of polyubiquitinated proteins and cell stress, followed by caspase activation and apoptosis. More importantly, this combination treatment was effective in BTZ-resistant cells and in the presence of bone marrow stromal cells, which have been shown to mediate MM cell drug resistance. The activity of WT161 was confirmed in our human MM cell xenograft mouse model and established the framework for clinical trials of the combination treatment to improve patient outcomes in MM.

Drug resistance analysis of gefitinib-targeted therapy in non-small cell lung cancer

The aim of the study was to examine the drug resistance analysis of gefitinib-targeted therapy in non-small cell lung cancer (NSCLC). In total, 156 NSCLC patients without surgical treatment were selected, including 117 cases of adenocarcinoma (75%), to receive single gefitinib 0.25 g/day or combined with platinum chemotherapy. Computed tomography was used to evaluate tumor growth for the response and non-response groups. The chemotherapy regimen was changed or combined with radiotherapy in the non-response group. Tumor progression or metastasis in the response group was considered as the generation of drug resistance. The chemotherapy regimen was altered in the response group. Eleven cases had tumor response in the non-response group after the chemotherapy regimen was adjusted (20%), 33 cases had complete response (CR) (32.7%), 44 cases had partial response (PR) (43.6%), and 24 cases had stable disease (SD) (23.8%) in the response group. The drug resistance rates of CR, PR, and SD showed no significant difference (P>0.05). However, the drug-resistant time of CR was significantly delayed and the difference was statistically significant (P<0.05). The response rates of CR, PR, and SD patients regaining the response rate showed no statistical significance after the chemotherapy regimen was adjusted, and the difference was not statistically significant (P>0.05). In conclusion, gefitinib-targeted therapy in NSCLC showed certain drug resistance, which may not be related to the response.

Src inhibitors act through different mechanisms in Non-Small Cell Lung Cancer models depending on EGFR and RAS mutational status

Resistance to the EGFR tyrosine kinase inhibitors (TKIs) gefitinib and erlotinib, often related to Ras or secondary EGFR mutations, is a relevant clinical issue in Non-Small Cell Lung Cancer (NSCLC). Although Src TK has been involved in such resistance, clinical development of its inhibitors has been so far limited.

To better define the molecular targets of the Src TKIs saracatinib, dasatinib and bosutinib, we used a variety of in vitro/in vivo studies.

Kinase assays supported by docking analysis demonstrated that all the compounds directly inhibit EGFR TK variants. However, in live cells only saracatinib efficiently reduced EGFR activation, while dasatinib was the most effective agent in inhibiting Src TK. Consistently, a pronounced anti-proliferative effect was achieved with saracatinib, in EGFR mutant cells, or with dasatinib, in wt EGFR/Ras mutant cells, poorly dependent on EGFR and erlotinib-resistant. We then identified the most effective drug combinations to overcome resistance to EGFR inhibitors, both in vitro and in nude mice: in T790M EGFR erlotinib-resistant cells, saracatinib with the anti-EGFR mAb cetuximab; in Ras mutant erlotinib-resistant models, dasatinib with the MEK inhibitor selumetinib.

Src inhibitors may act with different mechanisms in NSCLCs, depending on EGFR/Ras mutational profile, and may be integrated with EGFR or MEK inhibitors for different cohorts of NSCLCs.

Carfilzomib demonstrates broad anti-tumor activity in pre-clinical non-small cell and small cell lung cancer models

BACKGROUND

Carfilzomib (CFZ) is a proteasome inhibitor that selectively and irreversibly binds to its target and has been approved in the US for treatment of relapsed and refractory multiple myeloma. Phase 1B studies of CFZ reported signals of clinical activity in solid tumors, including small cell lung cancer (SCLC). The aim of this study was to investigate the activity of CFZ in lung cancer models.

METHODS

A diverse panel of human lung cancer cell lines and a SHP77 small cell lung cancer xenograft model were used to investigate the anti-tumor activity of CFZ.

RESULTS

CFZ treatment inhibited both the constitutive proteasome and the immunoproteasome in lung cancer cell lines. CFZ had marked anti-proliferative activity in A549, H1993, H520, H460, and H1299 non-small cell lung cancer (NSCLC) cell lines, with IC50 values after 96 hour exposure from <1.0 nM to 36 nM. CFZ had more variable effects in the SHP77 and DMS114 SCLC cell lines, with IC50 values at 96 hours from <1 nM to 203 nM. Western blot analysis of CFZ-treated H1993 and SHP77 cells showed cleavage of poly ADP ribose polymerase (PARP) and caspase-3, indicative of apoptosis, and induction of microtubule-associated protein-1 light chain-3B (LC3B), indicative of autophagy. In SHP77 flank xenograft tumors, CFZ monotherapy inhibited tumor growth and prolonged survival, while no additive or synergistic anti-tumor efficacy was observed for CFZ + cisplatin (CDDP).

CONCLUSIONS

CFZ demonstrated anti-proliferative activity in lung cancer cell lines in vitro and resulted in a significant survival advantage in mice with SHP77 SCLC xenografts, supporting further pre-clinical and clinical investigations of CFZ in NSCLC and SCLC.

Efficient apoptosis and necrosis induction by proteasome inhibitor: bortezomib in the DLD-1 human colon cancer cell line

The inhibition of the 26S proteasome evokes endoplasmic reticulum stress, which has been shown to be implicated in the antitumoral effects of proteasome inhibitors. The cellular and molecular effects of the proteasome inhibitor—bortezomib—on human colon cancer cells are as yet poorly characterized. Bortezomib selectively induces apoptosis in some cancer cells. However, the nature of its selectivity remains unknown. Previously, we demonstrated that, in contrast to normal fibroblasts, bortezomib treatment evoked strong effect on apoptosis of breast cancer cells incubated in hypoxic and normoxic conditions. The study presented here provides novel information on the cellular effects of bortezomib in DLD-1 colon cancer cells line. We observe twofold higher percentage of apoptotic cells incubated for 48 h with 25 and 50 nmol/l of bortezomib in hypoxic conditions and four-, fivefold increase in normoxic conditions in comparison to control cells, incubated without bortezomib. It is of interest that bortezomib evokes strong effect on necrosis of DLD-1 colon cancer cell line. We observe the sixfold increase in necrosis of DLD-1 cells incubated with 25 or 50 nmol/l of bortezomib for 48 h in hypoxia and fourfold increase in normoxic conditions in comparison to adequate controls. We suggest that bortezomib may be candidates for further evaluation as chemotherapeutic agents for human colon cancer.

Hypoxia enhances the senescence effect of bortezomib--the proteasome inhibitor--on human skin fibroblasts

The 26S proteasome inhibitor, bortezomib, selectively induces apoptosis in some cancer cells. However, the nature of its selectivity remains unknown. The study presented here provides novel information on cellular effects of bortezomib in normal fibroblasts. We have found that in normoxic conditions the percent of apoptotic cells did not change significantly, independently on incubation time and examined concentration of bortezomib (25 nmol/L or 50 nmol/L). In hypoxic conditions we did not observe any effect of bortezomib on apoptosis of fibroblasts incubated for 24 h and 48 h in comparison to control. Only in the case of fibroblasts incubated for 12 hours in hypoxia significant increase in apoptosis, dependent on concentration of bortezomib, was observed. Our study has shown that bortezomib causes a time-dependent increase in senescence of normal fibroblasts, especially of these incubated in hypoxic conditions. Moreover, we demonstrated that oxygen regulated protein 150 (ORP150) expression was induced in fibroblasts in hypoxia conditions only, suggesting that this protein may play an important role in the cytoprotective response to environmental stress.

Efficient induction of apoptosis by proteasome inhibitor: bortezomib in the human breast cancer cell line MDA-MB-231

The cellular and molecular effects of the proteasome inhibitor—bortezomib—on breast cancer cells are as yet poorly characterised. Bortezomib selectively induces apoptosis in some cancer cells. However, the nature of its selectivity remains unknown. Previously, we demonstrated that: there was no effect of bortezomib action on apoptosis and a time-dependent increase in senescence of human skin fibroblasts. The study presented here provides novel information on cellular effects of bortezomib in breast cancer cells line MDA-MB-231. Our findings demonstrated that in contrast to normal fibroblasts, bortezomib treatment evoked a strong effect on apoptosis in breast cancer cells incubated in hypoxic and normoxic conditions. We observed a time-dependent increase up to 70 % in apoptosis of MDA-MB-231 cells in hypoxic and normoxic conditions. There was no effect of bortezomib action on senescence of these cells. We suggest that bortezomib may be candidates for further evaluation as chemotherapeutic agents for human breast cancer.

Mechanisms of proteasome inhibitor-induced cytotoxicity in malignant glioma

The 26S proteasome constitutes an essential degradation apparatus involved in the consistent recycling of misfolded and damaged proteins inside cells. The aberrant activation of the proteasome has been widely observed in various types of cancers and implicated in the development and progression of carcinogenesis. In the era of targeted therapies, the clinical use of proteasome inhibitors necessitates a better understanding of the molecular mechanisms of cell death responsible for their cytotoxic action, which are reviewed here in the context of sensitization of malignant gliomas, a tumor type particularly refractory to conventional treatments.

Knockdown of the Bcl-2 gene increases sensitivity to EGFR tyrosine kinase inhibitors in the H1975 lung cancer cell line harboring T790M mutation

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are being widely used as targeted therapy in non-small cell lung cancer (NSCLC), but most cases acquire drug-resistance in 9 months. However, the mechanisms of resistance are still not fully understood. Since it has been demonstrated that EGFR-TKI-mediated repression of downstream signaling cascades and apoptosis induction is a key mechanism through which EGFR-TKIs exert their cytotoxic effects, we reasoned that activation of downstream signaling pathways and changes in the expression of apoptosis-related proteins contribute to the acquired resistance to EGFR-TKIs. We analyzed the protein levels of p-Akt, Bcl-2, Bax between gefitinib-sensitive and gefitinib-resistant lung cancer cell lines and evaluated whether targeting the anti-apoptotic protein Bcl-2 induces cell apoptosis and further sensitizes resistant H1975 cells to gefitinib. The data showed that p-Akt was activated and accompanied by substantial Bcl-2 in the H1975 lung cancer cell line, whereas no evidence was observed in HCC827 cells. Using small interfering RNA (siRNA) to silence Bcl-2 in H1975 cells led to significant downregulation of Bcl-2 protein expression, decreased cell viability in vitro and induced intrinsic apoptosis confirmed by flow cytometry and PARP cleavage. In Bcl-2 siRNA-transfected cells, adding gefitinib further reduced the number of viable cells, induced apoptosis to a greater extent compared to either treatment alone. These preclinical data suggested that downregulation of Bcl-2 by RNAi in the gefitinib-resistant H1975 lung cancer cell line with T790M mutation enhanced the effects of gefitinib and may offer a novel therapeutic strategy for the treatment of NSCLC.

Synergistic effects of nelfinavir and bortezomib on proteotoxic death of NSCLC and multiple myeloma cells

Exploiting protein homeostasis is a new therapeutic approach in cancer. Nelfinavir (NFV) is an HIV protease inhibitor that induces endoplasmic reticulum (ER) stress in cancer cells. Under conditions of ER stress, misfolded proteins are transported from the ER back to the cytosol for subsequent degradation by the ubiquitin–proteasome system. Bortezomib (BZ) is a proteasome inhibitor and interferes with degradation of misfolded proteins. Here, we show that NFV and BZ enhance proteotoxicity in non-small cell lung cancer (NSCLC) and multiple myeloma (MM) cells. The combination synergistically inhibited cell proliferation and induced cell death. Activating transcription factor (ATF)3 and CCAAT-enhancer binding protein homologous protein (CHOP), markers of ER stress, were rapidly increased, and their siRNA-mediated knockdown inhibited cell death. Knockdown of double-stranded RNA activated protein kinase-like ER kinase, a signal transducer in ER stress, significantly decreased apoptosis. Pretreatment with the protein synthesis inhibitor, cycloheximide, decreased levels of ubiquitinated proteins, ATF3, CHOP, and the overall total cell death, suggesting that inhibition of protein synthesis increases cell survival by relieving proteotoxic stress. The NFV/BZ combination inhibited the growth of NSCLC xenografts, which correlated with the induction of markers of ER stress and apoptosis. Collectively, these data show that NFV and BZ enhance proteotoxicity in NSCLC and MM cells, and suggest that this combination could tip the precarious balance of protein homeostasis in cancer cells for therapeutic gain.

Sequential application of anticancer drugs enhances cell death by rewiring apoptotic signaling networks

Crosstalk and complexity within signaling pathways and their perturbation by oncogenes limit component-by-component approaches to understanding human disease. Network analysis of how normal and oncogenic signaling can be rewired by drugs may provide opportunities to target tumors with high specificity and efficacy. Using targeted inhibition of oncogenic signaling pathways, combined with DNA-damaging chemotherapy, we report that time-staggered EGFR inhibition, but not simultaneous coadministration, dramatically sensitizes a subset of triple-negative breast cancer cells to genotoxic drugs. Systems-level analysis-using high-density time-dependent measurements of signaling networks, gene expression profiles, and cell phenotypic responses in combination with mathematical modeling-revealed an approach for altering the intrinsic state of the cell through dynamic rewiring of oncogenic signaling pathways. This process converts these cells to a less tumorigenic state that is more susceptible to DNA damage-induced cell death by reactivation of an extrinsic apoptotic pathway whose function is suppressed in the oncogene-addicted state.

The 26S proteasome complex: an attractive target for cancer therapy

The 26S proteasome complex engages in an ATP-dependent proteolytic degradation of a variety of oncoproteins, transcription factors, cell cycle specific cyclins, cyclin-dependent kinase inhibitors, ornithine decarboxylase, and other key regulatory cellular proteins. Thus, the proteasome regulates either directly or indirectly many important cellular processes. Altered regulation of these cellular events is linked to the development of cancer. Therefore, the proteasome has become an attractive target for the treatment of numerous cancers. Several proteasome inhibitors that target the proteolytic active sites of the 26S proteasome complex have been developed and tested for anti-tumor activities. These proteasome inhibitors have displayed impressive anti-tumor functions by inducing apoptosis in different tumor types. Further, the proteasome inhibitors have been shown to induce cell cycle arrest, and inhibit angiogenesis, cell-cell adhesion, cell migration, immune and inflammatory responses, and DNA repair response. A number of proteasome inhibitors are now in clinical trials to treat multiple myeloma and solid tumors. Many other proteasome inhibitors with different efficiencies are being developed and tested for anti-tumor activities. Several proteasome inhibitors currently in clinical trials have shown significantly improved anti-tumor activities when combined with other drugs such as histone deacetylase (HDAC) inhibitors, Akt (protein kinase B) inhibitors, DNA damaging agents, Hsp90 (heat shock protein 90) inhibitors, and lenalidomide. The proteasome inhibitor bortezomib is now in the clinic to treat multiple myeloma and mantle cell lymphoma. Here, we discuss the 26S proteasome complex in carcinogenesis and different proteasome inhibitors with their potential therapeutic applications in treatment of numerous cancers.

Antitumor activity of sorafenib in human cancer cell lines with acquired resistance to EGFR and VEGFR tyrosine kinase inhibitors

Treatment of non small cell lung cancer (NSCLC) and colorectal cancer (CRC) have substantially changed in the last years with the introduction of epidermal growth factor receptor (EGFR) inhibitors in the clinical practice. The understanding of mechanisms which regulate cells sensitivity to these drugs is necessary for their optimal use.An in vitro model of acquired resistance to two tyrosine kinase inhibitors (TKI) targeting the EGFR, erlotinib and gefitinib, and to a TKI targeting EGFR and VEGFR, vandetanib, was developed by continuously treating the human NSCLC cell line CALU-3 and the human CRC cell line HCT116 with escalating doses of each drug. MTT, western blot analysis, migration, invasion and anchorage-independent colony forming assays were conducted in vitro and experiments with established xenografts in athymic nude mice were performed in vivo in sensitive, wild type (WT) and TKI-resistant CALU-3 and HCT116 cell lines.As compared to WT CALU-3 and HCT116 human cancer cells, TKI-resistant cell lines showed a significant increase in the levels of activated, phosphorylated AKT, MAPK, and of survivin. Considering the role of RAS and RAF as downstream signals of both the EGFR and VEGFR pathways, we treated resistant cells with sorafenib, an inhibitor of C-RAF, B-RAF, c-KIT, FLT-3, RET, VEGFR-2, VEGFR-3, and PDGFR-β. Sorafenib reduced the activation of MEK and MAPK and caused an inhibition of cell proliferation, invasion, migration, anchorage-independent growth in vitro and of tumor growth in vivo of all TKI-resistant CALU-3 and HCT116 cell lines.These data suggest that resistance to EGFR inhibitors is predominantly driven by the RAS/RAF/MAPK pathway and can be overcame by treatment with sorafenib.

Antitumour efficacy of MEK inhibitors in human lung cancer cells and their derivatives with acquired resistance to different tyrosine kinase inhibitors

Background:

To study the molecular mechanisms regulating cancer cell resistance to four different tyrosine kinase inhibitors (TKIs): erlotinib, gefitinib, vandetanib and sorafenib.

Methods:

An in vitro model of acquired resistance to these TKIs was developed by continuously treating the human lung adenocarcinoma cell line CALU-3 with escalating doses of each drug. Transcriptional profiling was performed with Agilent whole genome microarrays. Western blot analysis, enzyme-linked immunosorbent (ELISA), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell proliferation, migration, invasion and anchorage-independent colony growth assays were conducted in vitro and experiments with established xenografts in athymic nude mice were performed in vivo in parental (P) and TKI-resistant (R) CALU-3 cell lines.

Results:

As compared with P-CALU-3 cells, in TKI-R CALU-3 cell lines a significant increase in the expression of activated, phosphorylated MET, IGF-1R, AKT, MEK, MAPK and of survivin was observed. Downregulation of E-cadherin and amphiregulin mRNAs and upregulation of vimentin, VE-cadherin, HIF-1α and vascular endothelial growth factor receptor-1 mRNAs were observed in all four TKI-R CALU-3 cell lines. All four TKI-R CALU-3 cells showed increased invasion, migration and anchorage-independent growth. Together, these data suggest epithelial to mesenchymal transition (EMT) in TKI-R CALU-3 cells. Treatment with several agents that target AKT, MET or IGF-1R did not affect TKI-R CALU-3 cell proliferation. In contrast, treatment with MSC19363669B and selumetinib, two selective MEK inhibitors, caused inhibition of cell proliferation, invasion, migration, anchorage-independent growth in vitro and of tumour growth in vivo of all four TKI-R CALU-3 cell lines.

Conclusion:

These data suggest that resistance to four different TKIs is characterised by EMT, which is MEK-inhibitor sensitive in human CALU-3 lung adenocarcinoma.

Proteasome inhibitors in cancer therapy

The ubiquitin proteasome pathway plays a critical role in regulating many processes in the cell which are important for tumour cell growth and survival. Inhibition of proteasome function has emerged as a powerful strategy for anti-cancer therapy. Clinical validation of the proteasome as a therapeutic target was achieved with bortezomib and has prompted the development of a second generation of proteasome inhibitors with improved pharmacological properties. This review summarises the main mechanisms of action of proteasome inhibitors in cancer, the development of proteasome inhibitors as therapeutic agents and the properties and progress of next generation proteasome inhibitors in the clinic.