Antitumor effects of a novel chromosome region maintenance 1 (CRM1) inhibitor on non-small cell lung cancer cells in vitro and in mouse tumor xenografts

Top 100 most-cited articles on apoptosis of non-small cell lung cancer over the past two decades: a bibliometrics analysis

Background

Recently there has been an increasing number of studies have explored apoptosis mechanisms in lung cancer (LC). However, no researchers have conducted a bibliometric analysis of the most cited articles in this field.

Objective

To examine the top 100 most influential and cited publications on apoptosis in non-small cell lung cancer (NSCLC) from 2004 to 2023, summarizing research trends and key focus areas.

Methods

This study utilized the Web of Science Core Database (WOSCC) to research NSCLC apoptosis from 2004 to 2023, using keyword selection and manual screening for article searches. Bibliometrix package of R software 4.3.1 was used to generate distribution statistics for the top ten institutions, journals and authors. Citespace6.2. R6 was used to create the visualization maps for keyword co-occurrence and clustering. VOSviewer1.6.19 was used to conduct cluster analysis of publishing countries (regions), with data exported to SCImago Graphica for geographic visualization and cooperation analysis. VOSviewer1.6.19 was used to produced co-citation maps of institutions, journals, authors, and references.

Results

From 2004 to 2023, 13316 articles were retrieved, and the top 100 most cited were chosen. These were authored by 934 individuals from 269 institutions across 18 countries and appeared in 45 journals. Citations ranged from 150 to 1,389, with a median of 209.5. The most influential articles appeared in 2005 and 2007 (n=13). The leading countries (regions), institutions, journals and authors were identified as the United States (n=60), Harvard University (n=64), CANCER RESEARCH (n=15), SUN M and YANG JS (n=6). The top five keywords were "expression", "activation", "apoptosis", "pathway" and "gefitinib". This study indicates that enhancing apoptosis through circular RNA regulation and targeting the Nrf2 signaling pathway could become a key research focus in recent years.

Conclusion

Apoptosis has been the subject of extensive research over many years, particularly in relation to its role in the pathogenesis, diagnosis, and treatment of NSCLC. This study aims to identify highly influential articles and forecast emerging research trends, thereby offering insights into novel therapeutic targets and strategies to overcome drug resistance. The findings are intended to serve as a valuable reference for scholars engaged in this field of study.

Targeting XPO1 for fighting relapsed/refractory diseases: The research progress of XPO1 inhibitors

XPO1 is an influential member of the nuclear transporter protein family. The proteins and RNA transported by XPO1 are related to the occurrence and development of many diseases, including refractory tumor diseases and various viral infectious diseases. XPO1 is upregulated in many malignant tumors and is associated with poor prognosis. This article reviews the anti-tumor and anti-viral mechanisms of XPO1, and summarizes the biomarkers that predict the response to XPO1 inhibitors and the research progress of XPO1 as a biomarker in different diseases. In addition, we also summarize the research status of XPO1 inhibitors, and discuss the structure-activity relationship of preclinical inhibitors targeting XPO1 and the research status of XPO1 inhibitor resistance mechanisms.

The nuclear export protein exportin-1 in solid malignant tumours: From biology to clinical trials

BACKGROUND

Exportin-1 (XPO1), a crucial protein regulating nuclear-cytoplasmic transport, is frequently overexpressed in various cancers, driving tumor progression and drug resistance. This makes XPO1 an attractive therapeutic target. Over the past few decades, the number of available nuclear export-selective inhibitors has been increasing. Only KPT-330 (selinexor) has been successfully used for treating haematological malignancies, and KPT-8602 (eltanexor) has been used for treating haematologic tumours in clinical trials. However, the use of nuclear export-selective inhibitors for the inhibition of XPO1 expression has yet to be thoroughly investigated in clinical studies and therapeutic outcomes for solid tumours.

METHODS

We collected numerous literatures to explain the efficacy of XPO1 Inhibitors in preclinical and clinical studies of a wide range of solid tumours.

RESULTS

In this review, we focus on the nuclear export function of XPO1 and results from clinical trials of its inhibitors in solid malignant tumours. We summarized the mechanism of action and therapeutic potential of XPO1 inhibitors, as well as adverse effects and response biomarkers.

CONCLUSION

XPO1 inhibition has emerged as a promising therapeutic strategy in the fight against cancer, offering a novel approach to targeting tumorigenic processes and overcoming drug resistance. SINE compounds have demonstrated efficacy in a wide range of solid tumours, and ongoing research is focused on optimizing their use, identifying response biomarkers, and developing effective combination therapies.

KEY POINTS

Exportin-1 (XPO1) plays a critical role in mediating nucleocytoplasmic transport and cell cycle. XPO1 dysfunction promotes tumourigenesis and drug resistance within solid tumours. The therapeutic potential and ongoing researches on XPO1 inhibitors in the treatment of solid tumours. Additional researches are essential to address safety concerns and identify biomarkers for predicting patient response to XPO1 inhibitors.

Epigenetic Alterations and Mechanisms That Drive Resistance to Targeted Cancer Therapies

Cancer is a complex disease and cancer cells typically harbor multiple genetic and epigenetic alterations. Large-scale sequencing of patient-derived cancer samples has identified several druggable driver oncogenes. Many of these oncogenes can be pharmacologically targeted to provide effective therapies for breast cancer, leukemia, lung cancer, melanoma, lymphoma, and other cancer types. Initial responses to these agents can be robust in many cancer types and some patients with cancer experience sustained tumor inhibition. However, resistance to these targeted therapeutics frequently emerges, either from intrinsic or acquired mechanisms, posing a major clinical hurdle for effective treatment. Several resistance mechanisms, both cell autonomous and cell nonautonomous, have been identified in different cancer types. Here we describe how alterations of the transcriptome, transcription factors, DNA, and chromatin regulatory proteins confer resistance to targeted therapeutic agents. We also elaborate on how these studies have identified underlying epigenetic factors that drive drug resistance and oncogenic pathways, with direct implications for the prevention and treatment of drug-resistant cancer.

Antitumor efficacy of XPO1 inhibitor Selinexor in KRAS-mutant lung adenocarcinoma patient-derived xenografts

Gain-of-function Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations occur in 25% of lung adenocarcinomas, and these tumors are challenging to treat. Some preclinical work, largely based on cell lines, suggested KRASmut lung cancers are especially dependent on the nuclear export protein exportin-1 (XPO1), while other work supports XPO1 being a broader cancer dependency. To investigate the sensitivity of KRASmut lung cancers to XPO1 inhibition in models that more closely match clinical tumors, we treated 10 independently established lung cancer patient-derived tumor xenografts (PDXs) with the clinical XPO1 inhibitor, Selinexor. Monotherapy with Selinexor reduced tumor growth in all KRASmut PDXs, which included 4 different codon mutations, and was more effective than the clinical MEK1/2 inhibitor, Trametinib. Selinexor was equally effective in KRASG12C and KRASG12D tumors, with TP53 mutations being a biomarker for a weaker drug response. By mining genome-wide dropout datasets, we identified XPO1 as a universal cancer cell dependency and confirmed this functionally in two KRASWT PDX models harboring kinase drivers. However, targeted kinase inhibitors were more effective than Selinexor in these models. Our findings support continued investigation of XPO1 inhibitors in KRASmut lung adenocarcinoma, regardless of the codon alteration.

Impact of XPO1 mutations on survival outcomes in metastatic non-small cell lung cancer (NSCLC)

BACKGROUND

Nuclear protein transport is essential in guiding the traffic of important proteins and RNAs between the nucleus and cytoplasm. Export of proteins from the nucleus is mostly regulated by Exportin 1 (XPO1). In cancer, XPO1 is almost universally hyperactive and can promote the export of important tumor suppressors to the cytoplasm. Currently, there are no studies evaluating XPO1 amplifications and mutations in NSCLC and the impact on outcomes.

METHODS

Tumor samples were analyzed using next-generation sequencing (NGS) (NextSeq, 592 Genes), immunohistochemistry (IHC), and whole transcriptome sequencing (WTS, NovaSeq) (Caris Life Sciences, Phoenix, AZ). Survival was extracted from insurance claims data and calculated from time of tissue collection to last contact using Kaplan-Meier estimate.

RESULTS

Among 18,218 NSCLC tumors sequenced, 26 harbored XPO1 mutations and 24 had amplifications. XPO1 mutant tumors were more likely to have high TMB (79% vs. 52%, p = 0.007) and less likely to have high PD-L1 (32% vs. 68%, p = 0.03). KRAS co-mutations were seen in 19% (n = 5) and EGFR co-mutations were rare (n = 2). Among the 17,449 NSCLC tumors with clinical data, there were 24 XPO1 mutant. Comparison of survival between XPO1 mutant and WT showed a negative association with a hazard ratio (HR) of 1.932 (95% CI: 1.144-3.264 p = 0.012). XPO1 amplification was not associated with survival.

CONCLUSIONS

XPO1 pathogenic mutations were associated with a poor survival in NSCLC. Although XPO1 mutations are rare in NSCLC, further studies to assess its associations with treatment responses are warranted.

Inhibition of Kpnβ1 mediated nuclear import enhances cisplatin chemosensitivity in cervical cancer

Background

Inhibition of nuclear import via Karyopherin beta 1 (Kpnβ1) shows potential as an anti-cancer approach. This study investigated the use of nuclear import inhibitor, INI-43, in combination with cisplatin.

Methods

Cervical cancer cells were pre-treated with INI-43 before treatment with cisplatin, and MTT cell viability and apoptosis assays performed. Activity and localisation of p53 and NFκB was determined after co-treatment of cells.

Results

Pre-treatment of cervical cancer cells with INI-43 at sublethal concentrations enhanced cisplatin sensitivity, evident through decreased cell viability and enhanced apoptosis. Kpnβ1 knock-down cells similarly displayed increased sensitivity to cisplatin. Combination index determination using the Chou-Talalay method revealed that INI-43 and cisplatin engaged in synergistic interactions. p53 was found to be involved in the cell death response to combination treatment as its inhibition abolished the enhanced cell death observed. INI-43 pre-treatment resulted in moderately stabilized p53 and induced p53 reporter activity, which translated to increased p21 and decreased Mcl-1 upon cisplatin combination treatment. Furthermore, cisplatin treatment led to nuclear import of NFκB, which was diminished upon pre-treatment with INI-43. NFκB reporter activity and expression of NFκB transcriptional targets, cyclin D1, c-Myc and XIAP, showed decreased levels after combination treatment compared to single cisplatin treatment and this associated with enhanced DNA damage.

Conclusions

Taken together, this study shows that INI-43 pre-treatment significantly enhances cisplatin sensitivity in cervical cancer cells, mediated through stabilization of p53 and decreased nuclear import of NFκB. Hence this study suggests the possible synergistic use of nuclear import inhibition and cisplatin to treat cervical cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07819-3.

Targeted CRM1-inhibition perturbs leukemogenic NUP214 fusion proteins and exerts anti-cancer effects in leukemia cell lines with NUP214 rearrangements

Chromosomal translocations fusing the locus of nucleoporin NUP214 each with the proto-oncogenes SET and DEK are recurrent in, largely intractable, acute leukemias. The molecular basis underlying the pathogenesis of SET-NUP214 and DEK-NUP214 are still poorly understood, but both chimeras inhibit protein nuclear export mediated by the β-karyopherin CRM1. In this report, we show that SET-NUP214 and DEK-NUP214 both disturb the localization of proteins essential for nucleocytoplasmic transport, in particular for CRM1-mediated protein export. Endogenous and exogenous SET-NUP214 and DEK-NUP214 form nuclear bodies. These nuclear bodies disperse upon targeted inhibition of CRM1 and the two fusion proteins re-localize throughout the nucleoplasm. Moreover, SET-NUP214 and DEK-NUP214 nuclear bodies reestablish shortly after removal of CRM1 inhibitors. Likewise, cell viability, metabolism, and proliferation of leukemia cell lines harboring SET-NUP214 and DEK-NUP214 are compromised by CRM1 inhibition, which is even sustained after clearance from CRM1 antagonists. Our results indicate CRM1 as a possible therapeutic target in NUP214-related leukemia. This is especially important, since no specific or targeted treatment options for NUP214 driven leukemia are available yet.

Transcriptome Profiling of Acquired Gefitinib Resistant Lung Cancer Cells Reveals Dramatically Changed Transcription Programs and New Treatment Targets

Background: Targeted therapy for lung cancer with epidermal growth factor receptor (EGFR) mutations with tyrosine kinase inhibitors (TKIs) represents one of the major breakthroughs in lung cancer management. However, gradually developed resistance to these drugs prevents sustained clinical benefits and calls for resistant mechanism research and identification of new therapeutic targets. Acquired T790M mutation accounts for the majority of resistance cases, yet transcriptome changes in these cells are less characterized, and it is not known if new treatment targets exist by available drugs.

Methods: Transcriptome profiling was performed for lung cancer cell line PC9 and its resistant line PC9GR after long-term exposure to gefitinib through RNA sequencing. Differentially expressed genes and changed pathways were identified along with existing drugs targeting these upregulated genes. Using 144 lung cancer cell lines with both gene expression and drug response data from the cancer cell line encyclopedia (CCLE) and Cancer Therapeutics Response Portal (CTRP), we screened 549 drugs whose response was correlated with these upregulated genes in PC9GR cells, and top drugs were evaluated for their response in both PC9 and PC9GR cells.

Results: In addition to the acquired T790M mutation, the resistant PC9GR cells had very different transcription programs from the sensitive PC9 cells. Multiple pathways were changed with the top ones including TNFA signaling, androgen/estrogen response, P53 pathway, MTORC1 signaling, hypoxia, and epithelial mesenchymal transition. Thirty-two upregulated genes had available drugs that can potentially be effective in treating the resistant cells. From the response profiles of CCLE, we found 17 drugs whose responses were associated with at least four of these upregulated genes. Among the four drugs evaluated (dasatinib, KPT-185, trametinib, and pluripotin), all except trametinib demonstrated strong inhibitory effects on the resistant PC9GR cells, among which KPT185 was the most potent. KPT-185 suppressed growth, caused apoptosis, and inhibited migration of the PC9GR cells at similar (or better) rates as the sensitive PC9 cells in a dose-dependent manner.

Conclusions: Acquired TKI-resistant lung cancer cells (PC9GR) have dramatically changed transcription and pathway regulation, which expose new treatment targets. Existing drugs may be repurposed to treat those patients with developed resistance to TKIs.

XPO1-dependent nuclear export as a target for cancer therapy

Cellular homeostasis requires the proper nuclear-cytoplasmic partitioning of large molecules, which is often deregulated in cancer. XPO1 is an export receptor responsible for the nuclear-cytoplasmic transport of hundreds of proteins and multiple RNA species. XPO1 is frequently overexpressed and/or mutated in human cancers and functions as an oncogenic driver. Suppression of XPO1-mediated nuclear export, therefore, presents a unique therapeutic strategy. In this review, we summarize the physiological functions of XPO1 as well as the development of various XPO1 inhibitors and provide an update on the recent clinical trials of the SINE compounds. We also discuss potential future research directions on the molecular function of XPO1 and the clinical application of XPO1 inhibitors.

The past, present, and future of CRM1/XPO1 inhibitors

Therapies targeted at inhibiting nucleo-cytoplasmic transport have found broad applications in the field of oncology. Chromosome region maintenance 1 (CRM1), better known as exportin 1 (XPO1), is the protein transporter responsible for the nucleo-cytoplasmic shuttling of most of the tumor suppressor proteins (TSP) and growth regulatory factors. XPO1 is also upregulated in many malignancies and associated with a poor prognosis. Its inhibition has been a target of therapy, and hence, the selective inhibitors of nuclear transport (SINE) compounds were developed as a novel class of anti-cancer agents. The most well-known SINE agent is selinexor (KPT-330) and has been widely tested in phase I and II clinical trials in both solid tumors and hematologic malignancies. This review discusses how dysregulation of XPO1 promotes tumorigenesis, the historical considerations in the development of SINE compounds, and their role in current clinical therapies.

CRM1, a novel independent prognostic factor overexpressed in invasive breast carcinoma of poor prognosis

Breast cancer (BC) is the most commonly diagnosed cancer in females globally and is more aggressive at later stages. Chromosome region maintenance 1 (CRM1) is involved in the nuclear export of proteins and RNAs and has been associated with a number of malignancies. However, the clinicopathological significance of its expression in BC remains to be elucidated therefore this was investigated in the present study. CRM1 expression in 280 breast cancer tissues and 60 normal tissues was retrospectively analyzed using immunohistochemistry (IHC) and western blotting. IHC investigation demonstrated that CRM1 expression was significantly increased in BC compared with the normal breast epithelium (P<0.0001). Overexpression of CRM1 was markedly associated with poor prognostic characteristics, including larger tumor size (P=0.024), positive lymph node metastasis (P=0.032), invasive histological type (P=0.004) and distant metastasis (P=0.026). Significant associations were also observed between increased CRM1 expression and the progesterone receptor (P=0.028) and Ki67 (P=0.019). Kaplan-Meier survival analysis demonstrated that patients with high CRM1 expression exhibited a reduced disease-free survival and overall survival compared with those with low CRM1 expression (P=0.013). In the multivariate analysis, CRM1 expression (P=0.011), tumor size (P=0.001) and lymph node metastasis (P<0.001) were independent prognostic markers of BC. In conclusion, CRM1 serves an important role in BC and may serve as a predictive and prognostic factor for a poor outcome in patients with BC.

Leptomycin B reduces primary and acquired resistance of gefitinib in lung cancer cells

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) gefitinib has demonstrated dramatic clinical efficacy in non-small cell lung cancer (NSCLC) patients. However, its therapeutic efficacy is ultimately limited by the development of acquired drug resistance. The aim of this study was to explore the potential utility of chromosome region maintenance 1 (CRM1) inhibitor leptomycin B (LMB) in combination with gefitinib to overcome primary and acquired gefitinib resistance in NSCLC cells. The combinative effects of gefitinib and LMB were evaluated by MTT and its underlining mechanism was assessed by flow cytometry and Western blot. LMB displayed a synergistic effect on gefitinib-induced cytotoxicity in A549 (IC50: 25.0±2.1μM of gefitinib+LMB vs. 32.0±2.5μM of gefitinib alone, p<0.05). Gefitinib+LMB caused a significantly different cell cycle distribution and signaling pathways involved in EGFR/survivin/p21 compared with gefitinib. A549 cells then were treated with progressively increased concentrations of gefitinib (A549GR) or in combination with LMB (A549GLR) over 10months to generate gefitinib resistance. IC50 of gefitinib in A549GLR (37.0±2.8μM) was significantly lower than that in A549GR (53.0±3.0μM, p<0.05), which indicates that LMB could reverse gefitinib-induced resistance in A549. Further mechanism investigation revealed that the expression patterns of EGFR pathway and epithelial-mesenchymal transition (EMT) markers in A549, A549GR, and A549GLR were significantly different. In conclusion, LMB at a very low concentration (0.5nM) combined with gefitinib showed synergistic therapeutic effects and ameliorated the development of gefitinib-induced resistance in lung cancer cells.

Therapeutic Targeting of Nuclear Export Inhibition in Lung Cancer

Intracellular compartmentalization and trafficking of molecules plays a critical role in complex and essential cellular processes. In lung cancer and other malignancies, aberrant nucleocytoplasmic transport of tumor suppressor proteins and cell cycle regulators results in tumorigenesis and inactivation of apoptosis. Pharmacologic agents targeting this process, termed selective inhibitors of nuclear export (SINE), have demonstrated antitumor efficacy in preclinical models and human clinical trials. Exportin-1 (XPO1), which serves as the sole exporter of several tumor suppressor proteins and cell cycle regulators, including retinoblastoma, adenomatous polyposis coli, p53, p73, p21, p27, forkhead box O, signal transducer and activator of transcription 3, inhibitor of κB, topoisomerase II, and protease activated receptor 4-is the principal focus of development of SINE. The most extensively studied of the SINE to date, the exportin-1 inhibitor selinexor (KPT-330 [Karyopharm Therapeutics, Inc., Newton Centre, MA]), has demonstrated single-agent anticancer activity and synergistic effects in combination regimens against multiple cancer types, with principal toxicities of low-grade cytopenias and gastrointestinal effects. SINE may have particular relevance in KRAS-driven tumors, for which this treatment strategy demonstrates significant synthetic lethality. A multicenter phase 1/2 clinical trial of selinexor in previously treated advanced KRAS-mutant NSCLC is under way.

Expression of chromosomal regional maintenance protein-1 may be associated with subcellular survivin expression in human gastric and colorectal carcinoma

Survivin, a member of the inhibitor of apoptosis protein family, is a potential prognostic marker and molecular target for anticancer therapies. Chromosomal regional maintenance protein-1 (CRM-1) mediates the nuclear export of proteins such as survivin. The aims of the present study were to compare the expression and subcellular localization of CRM-1 in human gastric and colorectal carcinomas and to assess the association between CRM-1 and survivin expression in these tumor types. The nuclear and cytoplasmic CRM-1 expression rates in gastric carcinoma were 61% (42/69) and 29% (20/69), respectively, while the nuclear and cytoplasmic CRM-1 expression rates in colorectal carcinoma were 55% (43/78) and 37% (29/78), respectively. Nuclear and cytoplasmic CRM-1 expression was found to be significantly correlated with nuclear and cytoplasmic survivin expression in colorectal carcinoma, but not gastric carcinoma. These results indicate that CRM-1 expression patterns differ between gastric and colorectal carcinomas and thus, we hypothesize that CRM-1-mediated nuclear export of survivin may be deregulated in gastric carcinoma. Therefore, CRM-1 may exhibit different functions in gastric and colorectal carcinoma.

Suppressing activity of tributyrin on hepatocarcinogenesis is associated with inhibiting the p53-CRM1 interaction and changing the cellular compartmentalization of p53 protein

Hepatocellular carcinoma (HCC), an aggressive and the fastest growing life-threatening cancer worldwide, is often diagnosed at intermediate or advanced stages of the disease, which substantially limits therapeutic approaches for its successful treatment. This indicates that the prevention of hepatocarcinogenesis is probably the most promising approach to reduce both the HCC incidence and cancer-related mortality. In previous studies, we demonstrated a potent chemopreventive effect of tributyrin, a butyric acid prodrug, on experimental hepatocarcinogenesis. The cancer-inhibitory effect of tributyrin was linked to the suppression of sustained cell proliferation and induction of apoptotic cell death driven by an activation of the p53 apoptotic signaling pathway. The goal of the present study was to investigate the underlying molecular mechanisms linked to tributyrin-mediated p53 activation. Using in vivo and in vitro models of liver cancer, we demonstrate that an increase in the level of p53 protein in nuclei, a decrease in the level of cytoplasmic p53, and, consequently, an increase in the ratio of nuclear/cytoplasmic p53 in rat preneoplastic livers and in rat and human HCC cell lines caused by tributyrin or sodium butyrate treatments was associated with a marked increase in the level of nuclear chromosome region maintenance 1 (CRM1) protein. Mechanistically, the increase in the level of nuclear p53 protein was associated with a substantially reduced binding interaction between CRM1 and p53. The results demonstrate that the cancer-inhibitory activity of sodium butyrate and its derivatives on liver carcinogenesis may be attributed to retention of p53 and CRM1 proteins in the nucleus, an event that may trigger activation of p53-mediated apoptotic cell death in neoplastic cells.

Epigenetic priming of non-small cell lung cancer cell lines to the antiproliferative and differentiating effects of all-trans retinoic acid

PURPOSE

The retinoic acid signaling pathway, crucial for differentiation, is silenced by epigenetic mechanisms in many cancers. Epigenetically active, chromatin-modifying agents offer a novel treatment approach, by reactivating aberrantly silenced genes in tumor cells and by sensitizing them to subsequent treatments. We hypothesized that the treatment of non-small cell lung cancer (NSCLC) cells with a histone deacetylase (HDAC) inhibitor may prime them to the antiproliferative and differentiating activity of all-trans retinoic acid.

METHODS

The NSCLC cell lines A549, NCI-H460 and HCC827 were treated with ATRA (2 µM) and the pan-HDAC inhibitor panobinostat (LBH589; 10-35 nM).

RESULTS

While treatment with ATRA alone showed only very modest effects, panobinostat reduced cellular proliferation by at least 50 %. Notably, the combination of panobinostat and ATRA had additive and synergistic effects, respectively, on growth inhibition and differentiation, with almost no cytotoxicity. Effects were strongest in A549, followed by the EGFR-mutant HCC827, and least pronounced in NCI-H460. Global histone H3 acetylation was strongly induced by panobinostat; interestingly, ATRA alone had also an effect on histone acetylation, which was synergistically enhanced when the HDAC inhibitor was added. The combination of the two drugs additively decreased expression of phospho-ERK and phospho-AKT, whereas p53 and p21(CIP1/WAF1) proteins were both induced.

CONCLUSION

Panobinostat sensitized, to varying degrees, all three cell lines to the antiproliferative and differentiating effects of ATRA, with synergistic histone H3 acetylation. Combination therapy with an epigenetic drug and ATRA may offer an alternative to aggressive chemotherapy even in primary ATRA-insensitive tumors, such as adenocarcinomas of the lung.

Deciphering mechanisms of drug sensitivity and resistance to Selective Inhibitor of Nuclear Export (SINE) compounds

BACKGROUND

Exportin 1 (XPO1) is a well-characterized nuclear export protein whose expression is up-regulated in many types of cancers and functions to transport key tumor suppressor proteins (TSPs) from the nucleus. Karyopharm Therapeutics has developed a series of small-molecule Selective Inhibitor of Nuclear Export (SINE) compounds, which have been shown to block XPO1 function both in vitro and in vivo. The drug candidate, selinexor (KPT-330), is currently in Phase-II/IIb clinical trials for treatment of both hematologic and solid tumors. The present study sought to decipher the mechanisms that render cells either sensitive or resistant to treatment with SINE compounds, represented by KPT-185, an early analogue of KPT-330.

METHODS

Using the human fibrosarcoma HT1080 cell line, resistance to SINE was acquired over a period of 10 months of constant incubation with increasing concentration of KPT-185. Cell viability was assayed by MTT. Immunofluorescence was used to compare nuclear export of TSPs. Fluorescence activated cell sorting (FACS), quantitative polymerase chain reaction (qPCR), and immunoblots were used to measure effects on cell cycle, gene expression, and cell death. RNA from naïve and drug treated parental and resistant cells was analyzed by Affymetrix microarrays.

RESULTS

Treatment of HT1080 cells with gradually increasing concentrations of SINE resulted in >100 fold decrease in sensitivity to SINE cytotoxicity. Resistant cells displayed prolonged cell cycle, reduced nuclear accumulation of TSPs, and similar changes in protein expression compared to parental cells, however the magnitude of the protein expression changes were more significant in parental cells. Microarray analyses comparing parental to resistant cells indicate that a number of key signaling pathways were altered in resistant cells including expression changes in genes involved in adhesion, apoptosis, and inflammation. While the patterns of changes in transcription following drug treatment are similar in parental and resistant cells, the extent of response was more robust in the parental cells.

CONCLUSIONS

These results suggest that SINE resistance is conferred by alterations in signaling pathways downstream of XPO1 inhibition. Modulation of these pathways could potentially overcome the resistance to nuclear export inhibitors.

Structural Basis of Targeting the Exportin CRM1 in Cancer

Recent studies have demonstrated the interference of nucleocytoplasmic trafficking with the establishment and maintenance of various cancers. Nucleocytoplasmic transport is highly regulated and coordinated, involving different nuclear transport factors or receptors, importins and exportins, that mediate cargo transport from the cytoplasm into the nucleus or the other way round, respectively. The exportin CRM1 (Chromosome region maintenance 1) exports a plethora of different protein cargoes and ribonucleoprotein complexes. Structural and biochemical analyses have enabled the deduction of individual steps of the CRM1 transport cycle. In addition, CRM1 turned out to be a valid target for anticancer drugs as it exports numerous proto-oncoproteins and tumor suppressors. Clearly, detailed understanding of the flexibility, regulatory features and cooperative binding properties of CRM1 for Ran and cargo is a prerequisite for the design of highly effective drugs. The first compound found to inhibit CRM1-dependent nuclear export was the natural drug Leptomycin B (LMB), which blocks export by competitively interacting with a highly conserved cleft on CRM1 required for nuclear export signal recognition. Clinical studies revealed serious side effects of LMB, leading to a search for alternative natural and synthetic drugs and hence a multitude of novel therapeutics. The present review examines recent progress in understanding the binding mode of natural and synthetic compounds and their inhibitory effects.

Ribosomal Biogenesis and Translational Flux Inhibition by the Selective Inhibitor of Nuclear Export (SINE) XPO1 Antagonist KPT-185

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma characterized by the aberrant expression of several growth-regulating, oncogenic effectors. Exportin 1 (XPO1) mediates the nucleocytoplasmic transport of numerous molecules including oncogenic growth-regulating factors, RNAs, and ribosomal subunits. In MCL cells, the small molecule KPT-185 blocks XPO1 function and exerts anti-proliferative effects. In this study, we investigated the molecular mechanisms of this putative anti-tumor effect on MCL cells using cell growth/viability assays, immunoblotting, gene expression analysis, and absolute quantification proteomics. KPT-185 exhibited a p53-independent anti-lymphoma effect on MCL cells, by suppression of oncogenic mediators (e.g., XPO1, cyclin D1, c-Myc, PIM1, and Bcl-2 family members), repression of ribosomal biogenesis, and downregulation of translation/chaperone proteins (e.g., PIM2, EEF1A1, EEF2, and HSP70) that are part of the translational/transcriptional network regulated by heat shock factor 1. These results elucidate a novel mechanism in which ribosomal biogenesis appears to be a key component through which XPO1 contributes to tumor cell survival. Thus, we propose that the blockade of XPO1 could be a promising, novel strategy for the treatment of MCL and other malignancies overexpressing XPO1.

Epigallocatechin-3-gallate enhances the therapeutic effects of leptomycin B on human lung cancer a549 cells

Our previous studies have shown Leptomycin B (LMB) is a promising antilung cancer drug. Epigallocatechin-3-gallate (EGCG) has antitumor properties but a debatable clinical application. The objective of this study is to evaluate the combination therapeutic effect of LMB and EGCG and its molecular mechanisms in human lung cancer A549 cells. Increased cytotoxicity was observed in LMB+EGCG-treated cells compared to LMB-treated cells. Elevated ROS was maximized 2 h after treatment, and LMB+EGCG-treated cells had higher ROS levels compared to LMB. N-Acetyl-L-cysteine (NAC) studies confirmed the oxidative role of LMB and/or EGCG treatment. In comparison to the control, CYP3A4, SOD, GPX1, and p21 mRNA expression levels were increased 7.1-, 2.0-, 4.6-, and 13.1-fold in LMB-treated cells, respectively, while survivin was decreased 42.6-fold. Additionally, these increases of CYP3A4, SOD, and GPX1 were significantly reduced, while p21 was significantly increased in LMB+EGCG-treated cells compared to LMB-treated cells. The qRT-PCR results for p21 and survivin were further confirmed by Western blot. Our study first shows that LMB produces ROS and is possibly metabolized by CYP3A4, GPX1, and SOD in A549 cells, and combination treatment of LMB and EGCG augments LMB-induced cytotoxicity through enhanced ROS production and the modulation of drug metabolism and p21/survivin pathways.

Recent Advances on Small-Molecule Survivin Inhibitors

Survivin, a member of the inhibitor of apoptosisproteins family, is highly expressed in most human neoplasms, but its expression is very low or undetectable in terminally differentiated normal tissues. Survivin has been shown to inhibit cancer cell apoptosis and promote cell proliferation. The overexpression of survivin closely correlates with tumor progression and drug resistance. Because of its key role in tumor formation and maintenance, survivin is considered as an ideal target for anticancer treatment. However, the development of small-molecule survivin inhibitors has been challenging due to the requirement to disrupt the protein-protein interactions. Currently only a limited number of survivin inhibitors have been developed in recent years, and most of these inhibitors reduce survivin levels by interacting with other biomolecules instead of directly interacting with survivin protein. Despite these challenges, developing potent and selective small-molecule survivin inhibitors will be important in both basic science to better understand survivin biology and in translational research to develop potentially more effective, broad-spectrum anticancer agents. In this review, the functions of survivin and its role in cancer are summarized. Recent developments, challenges, and future direction of small-molecule survivin inhibitors are also discussed in detail.

Nucleo-cytoplasmic transport as a therapeutic target of cancer

Shuttling of specific proteins out of the nucleus is essential for the regulation of the cell cycle and proliferation of both normal and malignant tissues. Dysregulation of this fundamental process may affect many other important cellular processes such as tumor growth, inflammatory response, cell cycle, and apoptosis. It is known that XPO1 (Exportin-1/Chromosome Region Maintenance 1/CRM1) is the main mediator of nuclear export in many cell types. Nuclear proteins exported to the cytoplasm by XPO1 include the drug targets topoisomerase IIα (topo IIα) and BCR-ABL and tumor suppressor proteins such as Rb, APC, p53, p21, and p27. XPO1 can mediate cell proliferation through several pathways: (i) the sub-cellular localization of NES-containing oncogenes and tumor suppressor proteins, (ii) the control of the mitotic apparatus and chromosome segregation, and (iii) the maintenance of nuclear and chromosomal structures. The XPO1 protein is elevated in ovarian carcinoma, glioma, osteosarcoma, pancreatic and cervical cancer. There is a growing body of research indicating that XPO1 may have an important role as a prognostic marker in solid tumors. Because of this, nuclear export inhibition through XPO1 is a potential target for therapeutic intervention in many cancers. The best understood XPO1 inhibitors are the small molecule nuclear export inhibitors (NEIs; Leptomycin B and derivatives, ratjadones, PKF050-638, valtrate, ACA, CBS9106, selinexor/KPT-330, and verdinexor/KPT-335). Selinexor and verdinexor are orally bioavailable, highly potent, small molecules that are classified as Selective Inhibitors of Nuclear Export (SINE). KPT-330 is the only NEI currently in Phase I/II human clinical trials in hematological and solid cancers. Of all the potential targets in nuclear cytoplasmic transport, the nuclear export receptor XPO1 remains the best understood and most advanced therapeutic target for the treatment of cancer.

Selective inhibitors of nuclear export (SINE)--a novel class of anti-cancer agents

Dysregulation of the nucleo-cytoplasmic transport of proteins plays an important role in carcinogenesis. The nuclear export of proteins depends on the activity of transport proteins, exportins. Exportins belong to the karyopherin β superfamily. Exportin-1 (XPO1), also known as chromosomal region maintenance 1 (CRM1), mediates transport of around 220 proteins. In this review, we summarized the development of a new class of antitumor drugs, collectively known as selective inhibitors of nuclear export (SINE). KPT-330 (selinexor) as an oral agent is showing activities in early clinical trials in both solid tumors and hematological malignancies.