Molecular mechanisms underlying the synergistic interaction of erlotinib, an epidermal growth factor receptor tyrosine kinase inhibitor, with the multitargeted antifolate pemetrexed in non-small-cell lung cancer cells

Thymidylate synthase as a determinant of pemetrexed sensitivity in non-small cell lung cancer

Background:

Although a high level of thymidylate synthase (TS) expression in malignant tumours has been suggested to be related to a reduced sensitivity to the antifolate drug pemetrexed, no direct evidence for such an association has been demonstrated in non-small cell lung cancer (NSCLC). We have now investigated the effect of TS overexpression on pemetrexed sensitivity in NSCLC cells.

Methods:

We established NSCLC cell lines that stably overexpress TS and examined the effects of such overexpression on the cytotoxicity of pemetrexed both in vitro and in xenograft models. We further examined the relation between TS expression in tumour specimens from NSCLC patients and the tumour response to pemetrexed by immunohistochemical analysis.

Results:

The sensitivity of NSCLC cells overexpressing TS to the antiproliferative effect of pemetrexed was markedly reduced compared with that of control cells. The inhibition of DNA synthesis and induction of apoptosis by pemetrexed were also greatly attenuated by forced expression of TS. Furthermore, tumours formed by TS-overexpressing NSCLC cells in nude mice were resistant to the growth-inhibitory effect of pemetrexed observed with control tumours. Finally, the level of TS expression in tumours of non-responding patients was significantly higher than that in those of responders, suggestive of an inverse correlation between TS expression and tumour response to pemetrexed.

Conclusion:

A high level of TS expression confers a reduced sensitivity to pemetrexed. TS expression is thus a potential predictive marker for response to pemetrexed-based chemotherapy in NSCLC patients.

Molecular mechanism of the schedule-dependent synergistic interaction in EGFR-mutant non-small cell lung cancer cell lines treated with paclitaxel and gefitinib

Background

Chemotherapy combined concurrently with TKIs produced a negative interaction and failed to improve survival when compared with chemotherapy or TKIs alone in the treatment of non-small cell lung cancer (NSCLC). The present study investigated the sequence-dependent interaction between paclitaxel and gefitinib and clarified the underlying mechanism.

Methods

The effects on cell proliferation, EGFR signaling pathway, and TGFα expression were evaluated in a panel of human NSCLC cell lines harboring EGFR mutations with three different combination sequences: sequential treatment with paclitaxel followed by gefitinib (T→G), sequential treatment with gefitinib followed by paclitaxel (G→T), or concomitant treatment (T + G).

Results

The sequence-dependent anti-proliferative effects differed between EGFR-TKI-sensitive and -resistant cell lines carrying EGFR mutations. A synergistic anti-proliferative activity was obtained with paclitaxel treatment followed by gefitinib in all cell lines, with mean CI values of 0.63 in Hcc827, 0.54 in PC-9, 0.81 in PC-9/GR, and 0.77 in H1650 cells for the T→G sequence. The mean CI values for the G→T sequence were 1.29 in Hcc827, 1.16 in PC-9, 1.52 in PC-9/GR, and 1.5 in H1650 cells. The mean CI values for T+G concomitant treatment were 0.88 in Hcc827, 0.91 in PC-9, 1.05 in PC-9/GR, and 1.18 in H1650 cells. Paclitaxel produced a dose-dependent increase in EGFR phosphorylation. Paclitaxel significantly increased EGFR phosphorylation compared with that in untreated controls (mean differences: +50% in Hcc827, + 56% in PC-9, + 39% in PC-9/GR, and + 69% in H1650 cells; p < 0.05). The T→G sequence produced significantly greater inhibition of EGFR phosphorylation compared with the opposite sequence (mean differences: -58% in Hcc827, -38% in PC-9, -35% in PC-9/GR, and -30% in H1650 cells; p < 0.05). Addition of a neutralizing anti-TGFα antibody abolished paclitaxel-induced activation of the EGFR pathway in PC-9 and H1650 cells. Sequence-dependent TGFα expression and release are responsible for the sequence-dependent EGFR pathway modulation.

Conclusion

The data suggest that the sequence of paclitaxel followed by gefitinib is an appropriate treatment combination for NSCLC cell lines harboring EGFR mutations. Our results provide molecular evidence to support clinical treatment strategies for patients with lung cancer.

Analysis of drug interactions

Most of the current therapies against cancer, and also those against immune diseases or viral infections, consist of empirically designed combination strategies, combining a variety of therapeutic agents. Drug combinations are widely used because multiple drugs affect multiple targets and cell subpopulations. The primary aim is a mutual enhancement of the therapeutic effects, while other benefits may include decreased side effects and the delay or prevention of drug resistance. The large majority of combination regimens are being developed empirically and there are few experimental studies designed to explore thoroughly different drug combinations, using appropriate methods of analysis. However, the study of patterns of possible metabolic and biological interactions in preclinical models, as well as scheduling, should improve the development of most drug combinations. The definition of synergism is that the combination is more effective than each agent separately, e.g., one of the agents augments the actions of the second drug. The definition of antagonism is that the combination is less effective than the single agents, e.g. one of the agents counteracts the actions of the other. A combination can be studied by combining the two agents in various different ways, such as simultaneous or sequential combination schedules. It is essential to test the potency of a combination, before evaluation in the clinic, to prevent antagonistic actions. However, one should realize that an antagonistic action may be desired when toxicity is concerned, i.e. one drug decreases the side effects of another drug. Several attempts have been made to quantitatively measure the dose-effect relationship of each drug alone and its combinations and to determine whether a given combination would gain a synergistic effect. One of the most widely used ways to evaluate whether a combination is effective is the median-drug effect analysis method. Using this method, a combination index (CI) is calculated from drug cytotoxicity or growth inhibition curves. To calculate a CI, the computer software Calcusyn can be used, taking the entire shape of the growth inhibition curve into account for calculating whether a combination is synergistic, additive, or antagonistic. Here, we describe how combinations can be designed in vitro and how to analyze them using Calcusyn or Compusyn. Moreover, pitfalls, limitations, and advantages of using these combinations and Calcusyn/Compusyn are described.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

Cellular and molecular mechanisms for the synergistic cytotoxicity elicited by oxaliplatin and pemetrexed in colon cancer cell lines

PURPOSE

Oxaliplatin effect in the treatment of colorectal cancer is improved upon combination with thymidylate synthase (TS) inhibitors. Pemetrexed is polyglutamated by the folylpolyglutamate synthase (FPGS) and blocks folate metabolism and DNA synthesis by inhibiting TS, dihydrofolate reductase (DHFR) and glycinamide ribonucleotide formyltransferase (GARFT). The present study evaluates the pharmacological interaction between oxaliplatin and pemetrexed in colorectal cancer cells.

METHODS

Human HT29, WiDr, SW620 and LS174T cells were treated with oxaliplatin and pemetrexed. Drug interaction was studied using the combination index method, while cell cycle was investigated with flow cytometry. The effects of drugs on Akt phosphorylation and apoptosis were studied with ELISA and fluorescence microscopy, respectively. RT-PCR analysis was performed to assess whether drugs modulated the expression of pemetrexed targets and of genes involved in DNA repair (ERCC1 and ERCC2). Finally, platinum-DNA adduct levels were detected by ultra-sensitive multi-collector inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

A dose-dependent inhibition of cell growth was observed after drug exposure, while a synergistic interaction was detected preferentially with sequential combinations. Oxaliplatin enhanced cellular population in the S-phase. Drug combinations increased apoptotic indices with respect to single agents, and both drugs inhibited Akt phosphorylation. RT-PCR analysis showed a correlation between the FPGS/(TS x DHFR x GARFT) ratio and pemetrexed sensitivity, as well as a downregulation of ERCC1, ERCC2, TS, DHFR and GARFT after drug exposure. In addition, pretreatment with pemetrexed resulted in an increase of oxaliplatin-DNA adducts.

CONCLUSION

These data demonstrate that oxaliplatin and pemetrexed synergistically interact against colon cancer cells, through modulation of cell cycle, inhibition of Akt phosphorylation, induction of apoptosis and modulation of gene expression.

Validation of a novel statistical model for assessing the synergy of combined-agent cancer chemoprevention

Lung cancer is the leading cause of cancer death, developing over prolonged periods through genetic and epigenetic changes induced and exacerbated by tobacco exposure. Many epigenetic changes, including DNA methylation and histone methylation and acetylation, are reversible. The use of agents that can modulate these aberrations are a potentially effective approach to cancer chemoprevention. Combined epigenetic-targeting agents have gained interest for their potential to increase efficacy and lower toxicity. The present study applied recently developed statistical methods to validate the combined effects of the demethylating agent 5-aza-2-deoxycytidine (5-AZA-CdR, or AZA, or decitabine) and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA or vorinostat). This validation compared AZA alone with SAHA alone and with their combinations (at later or earlier time points and in varying doses) for inhibiting the growth of cell lines of an in vitro lung carcinogenesis system. This system comprises isogenic premalignant and malignant cells that are immortalized (earlier premalignant), transformed (later premalignant), and tumorigenic human bronchial epithelial cells [immortalized BEAS-2B and its derivatives 1799 (immortalized), 1198 (transformed), and 1170-I (tumorigenic)]. AZA alone and SAHA alone produced a limited (<50%) inhibition of cell growth, whereas combined AZA and SAHA inhibited cell growth more than either agent alone, reaching 90% inhibition under some conditions. Results of drug interaction analyses in the E(max) model and semiparametric model supported the conclusion that drug combinations exert synergistic effects (i.e., beyond additivity in the Loewe model). The present results show the applicability of our novel statistical methodology for quantitatively assessing drug synergy across a wide range of doses of agents with complex dose-response profiles, a methodology with great potential for advancing the development of chemopreventive combinations.

Identification of thymidylate synthase as a potential therapeutic target for lung cancer

Background:

Thymidylate synthase (TS), a key enzyme in the de novo synthesis of thymidine, is an important chemotherapeutic target for malignant tumours including lung cancer. Although inhibition of TS has an antiproliferative effect in cancer cells, the precise mechanism of this effect has remained unclear.

Methods:

We examined the effects of TS inhibition with an RNA interference-based approach. The effect of TS depletion on the growth of lung cancer cells was examined using colorimetric assay and flow cytometry.

Results:

Measurement of the enzymatic activity of TS in 30 human lung cancer cell lines revealed that such activity differs among tumour histotypes. Almost complete elimination of TS activity by RNA interference resulted in inhibition of cell proliferation in all tested cell lines, suggestive of a pivotal role for TS in cell proliferation independent of the original level of enzyme activity. The antiproliferative effect of TS depletion was accompanied by arrest of cells in S phase of the cell cycle and the induction of caspase-dependent apoptosis as well as by changes in the expression levels of cyclin E and c-Myc. Moreover, TS depletion induced downregulation of the antiapoptotic protein X-linked inhibitor of apoptosis (XIAP), and it seemed to activate the mitochondrial pathway of apoptosis.

Conclusion:

Our data provide insight into the biological relevance of TS as well as a basis for clinical development of TS-targeted therapy for lung cancer.

Drug interactions among the epidermal growth factor receptor inhibitors, other biologics and cytotoxic agents

The epidermal growth factor receptor (EGFR) signalling pathway is a key element in the growth of several epithelial malignancies. Small molecules tyrosine kinase inhibitors (TKIs) and anti-EGFR monoclonal antibodies (mAbs) prevent the phosphorylation of the receptor, leading to cell cycle arrest at G(1) phase, apoptosis, inhibition of angiogenesis and metastasis. To increase the antitumoral effects of EGFR inhibitors (EGFRIs), a number of combinatory regimens have been evaluated and planned with standard cytotoxic drugs and/or inhibitors of EGFR complementary pathways such as mTOR, VEGF and Ras/Raf/ERK. Compared to EGFRI monotherapy, the combination approach is a promising strategy to improve tumor response and survival. However, pharmacokinetic (absorption, distribution, metabolism and excretion) and pharmacodynamic drug interactions can occur, affecting the outcome. Pharmacokinetics of TKIs can be affected by drugs used in combination: conversely, pharmacokinetic interactions have not been reported for EGFR mAbs. Potential pharmacokinetic interactions occur between EGFRIs and other factors such as food and hydrocarbons in tobacco smoke were also considered. EGFRIs are characterized by a number of pharmacodynamic interactions that must be taken into consideration to avoid adverse events, to increase antitumoral activity, and define potential new strategies for developing efficient combination regimens. In this context, treatment schedule and drug sequence appear to be particularly relevant for combination regimens with EGFRIs. Improved molecular characterisation of the EGFR pathway and its complementary pathways in tumor cells is required to better define predictive pharmacokinetic and pharmacodynamic biomarkers for optimum treatment outcome.

In vitro sequence-dependent synergism between paclitaxel and gefitinib in human lung cancer cell lines

PURPOSE

In clinical trials, the epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) administered concomitantly with first-line cytotoxicity chemotherapy failed to confer a survival benefit to patients with non-small-cell lung cancer (NSCLC). The aim of this study was to test whether paclitaxel followed by gefitinib is superior to other treatment schedules of NSCLC cell lines and to clarify the underlying mechanisms.

METHODS

Human lung cancer cell lines with wild-type and mutant-type EGFR genes were used as in vitro models to define the differential effects of various schedules of paclitaxel with gefitinib treatment on cell growth, signaling pathway, and cell cycle distribution.

RESULTS

Sequence-dependent antiproliferative effects differed between EGFR-TKI-resistant and EGFR-TKI-sensitive lung cancer cell lines. Exposure to paclitaxel resulted in an increased pEGFR level. This increase in phosphorylation was inhibited by subsequent exposure to gefitinib, whereas during the reverse sequence, the inhibition effect was reduced. After paclitaxel exposure, a higher level of pEGFR was observed in mitotic than in interphase cells. The sequence of paclitaxel followed by gefitinib resulted in greater anti-VEGF activity than did the reverse sequence. We confirmed that gefitinib arrested cells in G1, and paclitaxel arrested them in S phase. The sequence of paclitaxel followed by gefitinib arrested cells in G1, whereas the reverse sequence arrested cells in S and G2 phases.

CONCLUSIONS

These findings suggest that the sequence of paclitaxel followed by gefitinib may be superior to other sequences in treating NSCLC cell lines. Our results also provide molecular evidence to support clinical treatment strategies for patients with lung cancer.

Maintenance therapy for metastatic non-small-cell lung cancer - the role of pemetrexed

Over the last several years, we have greatly enhanced our understanding of tumor biology and have now integrated novel and molecular-targeted therapies into front-line treatment for locally advanced and metastatic non-small-cell lung cancer (NSCLC). Despite all the recent advances, the improvement in survival outcomes for these patients has been measured in weeks compared to historical controls. Clinical researchers continue to search for the silver bullet that will allow oncologists to treat lung cancer as a chronic illness and prolong life well beyond the statistical barrier of 1 year for these patients. In that vein, maintenance therapy is emerging as a new treatment option in the metastatic setting. However, there is much controversy over the validity and cost-effectiveness of this modality. Recently, a phase III trial of pemetrexed maintenance versus best supportive care in the setting of metastatic NSCLC following non-progression after 4 cycles of platinum-based doublet therapy showed significant survival outcomes of the treatment group. This article will review the current available treatment options in metastatic NSCLC, including maintenance regimens, with particular attention paid to the recent pemetrexed study.

Inhibition of aldose reductase prevents growth factor-induced G1-S phase transition through the AKT/phosphoinositide 3-kinase/E2F-1 pathway in human colon cancer cells

Colon cancer is the leading cause of cancer death in both men and women worldwide. The deregulated cell cycle control or decreased apoptosis of normal epithelial cells leading to uncontrolled proliferation is one of the major features of tumor progression. We have previously shown that aldose reductase (AR), a NADPH-dependent aldo-keto reductase, has been shown to be involved in growth factor-induced proliferation of colon cancer cells. Herein, we report that inhibition of AR prevents epidermal growth factor (EGF)- and basic fibroblast growth factor (bFGF)-induced HT29 cell proliferation by accumulating cells at G(1) phase of cell cycle. Similar results were observed in SW480 and HCT-116 colon cancer cells. Treatment of HT29 cells with AR inhibitor, sorbinil or zopolrestat, prevented the EGF- and bFGF-induced DNA binding activity of E2F-1 and phosphorylation of retinoblastoma protein. Inhibition of AR also prevented EGF- and bFGF-induced phosphorylation of cyclin-dependent kinase (cdk)-2 and expression of G(1)-S transition regulatory proteins such as cyclin D1, cdk4, proliferating cell nuclear antigen, cyclin E, and c-myc. More importantly, inhibition of AR prevented the EGF- and bFGF-induced activation of phosphoinositide 3-kinase/AKT and reactive oxygen species generation in colon cancer cells. Further, inhibition of AR also prevented the tumor growth of human colon cancer cells in nude mouse xenografts. Collectively, these results show that AR mediates EGF- and bFGF-induced colon cancer cell proliferation by activating or expressing G(1)-S phase proteins such as E2F-1, cdks, and cyclins through the reactive oxygen species/phosphoinositide 3-kinase/AKT pathway, indicating the use of AR inhibitors in the prevention of colon carcinogenesis. Mol Cancer Ther; 9(4); 813-24. (c)2010 AACR.

Role of epidermal growth factor receptor degradation in cisplatin-induced cytotoxicity in head and neck cancer

Cisplatin and its analogues are the most commonly used agents in the treatment of head and neck squamous cell carcinoma. In this study, we investigated a possible role of epidermal growth factor (EGF) receptor (EGFR) phosphorylation and degradation in cisplatin-induced cytotoxicity. Cisplatin treatment led to an increase in initial EGFR phosphorylation at Y1045, the binding site of ubiquitin ligase, Casitas B-lineage lymphoma (c-Cbl), followed by ubiquitination in the relatively cisplatin-sensitive cell lines. However, cisplatin-resistant cell lines underwent minimal EGFR phosphorylation at the Y1045 site and minimal ubiquitination. We found that EGFR degradation in response to cisplatin was highly correlated with cytotoxicity in seven head and neck cancer cell lines. Pretreatment with EGF enhanced cisplatin-induced EGFR degradation and cytotoxicity, whereas erlotinib pretreatment blocked EGFR phosphorylation, degradation, and cisplatin-induced cytotoxicity. Expression of a mutant Y1045F EGFR, which is relatively resistant to c-Cbl-mediated degradation, in Chinese hamster ovary cells and the UMSCC11B human head and neck cancer cell line protected EGFR from cisplatin-induced degradation and enhanced cell survival compared with wild-type (WT) EGFR. Transfection of WT c-Cbl enhanced EGFR degradation and cisplatin-induced cytotoxicity compared with control vector. These results show that cisplatin-induced EGFR phosphorylation and subsequent ubiquitination and degradation is an important determinant of cisplatin sensitivity. Our findings suggest that treatment with an EGFR inhibitor before cisplatin would be antagonistic, as EGFR inhibition would protect EGFR from cisplatin-mediated phosphorylation and subsequent ubiquitination and degradation, which may explain the negative results of several recent clinical trials. Furthermore, they suggest that EGFR degradation is worth exploring as an early biomarker of response and as a target to improve outcome.

Molecular mechanism underlying the synergistic interaction between trifluorothymidine and the epidermal growth factor receptor inhibitor erlotinib in human colorectal cancer cell lines

The pyrimidine trifluorothymidine (TFT) inhibits thymidylate synthase (TS) and can be incorporated into the DNA. TFT, as part of TAS-102, is clinically evaluated in phase II studies as an oral chemotherapeutic agent. Erlotinib is a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR) that is often deregulated in colorectal cancer. This study investigated molecular mechanisms underlying the cytotoxic actions of the combination of an EGFR-tyrosine kinase inhibitor with TFT in colorectal cancer cells Caco2, WiDR, Lovo92, and Colo320. Drug interactions were examined by the sulforhodamine B assay and subsequent combination index (CI) analyses, cell cycle effects by FACS analysis of propidium iodide stained cells, Akt, MAPK and EGFR phosphorylation and expression levels by Western blotting and TS activity by the TS in situ assay. All combination schedules were synergistic in wt-EGFR expressing (but with mutated downstream pathways) WiDR and Lovo92 (CI 0.4-0.8) and very synergistic in Caco2 cells (with wt-EGFR and functional downstream pathways; CI 0.1-0.3), but in EGFR-lacking Colo320 cells, no additional activity was found (CI 1.0-1.2). Synergism was mostly related to the induction of cell cycle arrest and an erlotinib-mediated inhibition of the pro-survival signaling through Akt and MAPK that was activated (phosphorylated) by TFT. Erlotinib inhibited TS activity in EGFR-expressing cell lines, probably due to cell cycle arrest in the G(1) phase. TS activity was slightly lower in the combinations, probably due to cell cycle interference. Taken together, the combination of erlotinib with TFT seems to present a potential strategy in the field of molecular therapeutics.

Significance of thymidylate synthase for resistance to pemetrexed in lung cancer

Pemetrexed (MTA) is a multitargeted antifolate with promising clinical activity in lung cancer. We exposed the small cell lung cancer cell line PC6 to stepwise-increasing pemetrexed concentrations of 0.4, 1.6, and 4.0 microm, and established three pemetrexed-resistant lung cancer cell lines: PC6/MTA-0.4, PC6/MTA-1.6, and PC6/MTA-4.0 cells. To investigate the mechanisms of acquired resistance to pemetrexed, we measured the expression levels of the thymidylate synthase (TS), reduced folate carrier (RFC), and folylpoly-gamma-glutamate synthetase (FPGS) genes. TS gene expression was significantly increased in PC6/MTA-1.6 and PC6/MTA-4.0 cells relative to parental cells in a pemetrexed dose-dependent manner. In contrast, the levels of RFC gene expression in PC6/MTA-0.4 cells and FPGS in PC6/MTA-1.6 cells were significantly decreased, whereas the levels of both genes were restored in PC6/MTA-4.0 cells. Knockdown of TS expression using siRNA enhanced pemetrexed cytotoxicity in PC6/MTA-4.0 cells. The expression level of the TS gene was significantly correlated with the concentration of pemetrexed for 50% cell survival (IC(50)) in 11 non-small cell lung cancer cell lines. These results suggest that the alteration of molecular pharmacological factors in relation with pemetrexed resistance is dose-dependent, and that up-regulation of the expression of the TS gene may have an important role in the acquired resistance to pemetrexed. In addition, TS may be a predictive marker for pemetrexed sensitivity in lung cancer.

Molecular analysis-based treatment strategies for the management of non-small cell lung cancer

Even with the introduction of targeted agents and the establishment of multiple lines of therapy, the median survival for patients with advanced non-small cell lung cancer (NSCLC) does not considerably extend beyond 1 year. Emerging research suggests that clinical characteristics alone are insufficient for selecting patients for therapies that may confer significant survival benefit. The discovery of predictive and prognostic molecular markers such as gene mutations in EGFR and KRAS as well as high tumor expression levels of DNA repair pathway components ribonucleotide reductase subunit 1 and excision repair cross-complementing group 1 has sparked an interest in the development of individualized therapy as a strategy for increasing survival in patients with NSCLC. Techniques to analyze molecular biomarkers, such as immunohistochemistry, fluorescence in situ hybridization, polymerase chain reaction, and, more recently, gene microarray techniques, are being investigated for their potential to accurately predict an individual patient's response to therapy. Many prospective trials are still needed to clarify and confirm the utility of molecular biomarkers for guiding treatment selection, and continued participation in clinical trials is critical for the development of tools to provide customized treatment plans for patients with NSCLC.

Pharmacogenomics of gemcitabine in non-small-cell lung cancer and other solid tumors

The validation of predictive biomarkers to tailor chemotherapy is a key issue in the development of effective treatment modalities against cancer. Examples of how genetics might affect drug response are offered by gemcitabine. A substantial number of potential biomarkers for sensitivity or resistance to gemcitabine have been proposed, including ribonucleotide reductase and cytidine deaminase polymorphisms, human equilibrative transporter-1 and ribonucleotide reductase gene-expression and AKT phosphorylation status. These markers displayed a significant relationship with disease response to the drug; however, their robustness needs to be evaluated within prospective studies. Moreover, recent trials of customized chemotherapy based on genetic markers have been carried out in non-small-cell lung cancer and promising pharmacogenetic determinants are gaining momentum, including BRCA1 and ERCC1. Hopefully, biomarkers to select patients most likely to respond to gemcitabine will be validated in the near future.

Molecular pathways involved in the synergistic interaction of the PKC beta inhibitor enzastaurin with the antifolate pemetrexed in non-small cell lung cancer cells

Conventional regimens have limited impact against non-small cell lung cancer (NSCLC). Current research is focusing on multiple pathways as potential targets, and this study investigated molecular mechanisms underlying the combination of the PKC beta inhibitor enzastaurin with the multitargeted antifolate pemetrexed in the NSCLC cells SW1573 and A549. Pharmacologic interaction was studied using the combination-index method, while cell cycle, apoptosis induction, VEGF secretion and ERK1/2 and Akt phosphorylation were studied by flow cytometry and ELISAs. Reverse transcription-PCR, western blot and activity assays were performed to assess whether enzastaurin influenced thymidylate synthase (TS) and the expression of multiple targets involved in cancer signaling and cell cycle distribution. Enzastaurin-pemetrexed combination was highly synergistic and significantly increased apoptosis. Enzastaurin reduced both phosphoCdc25C, resulting in G2/M checkpoint abrogation and apoptosis induction in pemetrexed-damaged cells, and GSK3 beta and Akt phosphorylation, which was additionally reduced by drug combination (-58% in A549). Enzastaurin also significantly reduced pemetrexed-induced upregulation of TS expression, possibly through E2F-1 reduction, whereas the combination decreased TS in situ activity (>50% in both cell lines) and VEGF secretion. The effects of enzastaurin on signaling pathways involved in cell cycle control, apoptosis and angiogenesis, as well as on the expression of genes involved in pemetrexed activity provide a strong experimental basis to their evaluation as pharmacodynamic markers in clinical trials of enzastaurin-pemetrexed combination in NSCLC patients.