In vivo induction of resistance to gemcitabine results in increased expression of ribonucleotide reductase subunit M1 as the major determinant

Prognostic and predictive markers for personalized adjuvant therapy for non-small-cell lung cancer patients

Adjuvant chemotherapy following surgical resection in non-small-cell lung cancer patients with large tumors (>4 cm) or tumors with lymph node metastases has emerged as a standard of care. The benefits of adjuvant chemotherapy are modest, with a 5-year survival improvement of only 5–10%. In addition, survival rates of 25% or greater with surgery alone suggest that some patients do not need adjuvant therapy. Therefore, there is a need to develop prognostic and predictive markers to identify patients in need of adjuvant therapy and the patients likely to benefit from such therapy. Many factors have been evaluated for this purpose and some of these factors, such as visceral pleural invasion, can influence the decision to use adjuvant chemotherapy. However, most of the available data are retrospective, which limits the utility of these markers in current practice. Ongoing trials are evaluating many promising markers and may guide adjuvant therapy in the future.

Crizotinib inhibits metabolic inactivation of gemcitabine in c-Met-driven pancreatic carcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains a major unsolved health problem. Most drugs that pass preclinical tests fail in these patients, emphasizing the need of improved preclinical models to test novel anticancer strategies. Here, we developed four orthotopic mouse models using primary human PDAC cells genetically engineered to express firefly- and Gaussia luciferase, simplifying the ability to monitor tumor growth and metastasis longitudinally in individual animals with MRI and high-frequency ultrasound. In these models, we conducted detailed histopathologic and immunohistochemical analyses on paraffin-embedded pancreatic tissues and metastatic lesions in liver, lungs, and lymph nodes. Genetic characteristics were compared with the originator tumor and primary tumor cells using array-based comparative genomic hybridization, using frozen specimens obtained by laser microdissection. Notably, the orthotopic human xenografts in these models recapitulated the phenotype of human PDACs, including hypovascular and hypoxic areas. Pursuing genomic and immunohistochemical evidence revealed an increased copy number and overexpression of c-Met in one of the models; we examined the preclinical efficacy of c-Met inhibitors in vitro and in vivo. In particular, we found that crizotinib decreased tumor dimension, prolonged survival, and increased blood and tissue concentrations of gemcitabine, synergizing with a cytidine deaminase-mediated mechanism of action. Together, these more readily imaged orthotopic PDAC models displayed genetic, histopathologic, and metastatic features similar to their human tumors of origin. Moreover, their use pointed to c-Met as a candidate therapeutic target in PDAC and highlighted crizotinib and gemcitabine as a synergistic combination of drugs warranting clinical evaluation for PDAC treatment.

Re-challenge chemotherapy with gemcitabine plus carboplatin in patients with non-small cell lung cancer

Despite recent improvements to current therapies and the emergence of novel agents to manage advanced non-small cell lung cancer (NSCLC), the patients' overall survival remains poor. Re-challenging with first-line chemotherapy upon relapse is common in the management of small cell lung cancer but is not well reported for advanced NSCLC. NSCLC relapse has been attributed to acquired drug resistance, but the repopulation of sensitive clones may also play a role, in which case re-challenge may be appropriate. Here, we report the results of re-challenge with gemcitabine plus carboplatin in 22 patients from a single institution who had previously received gemcitabine plus platinum in the first-line setting and had either partial response or a progression-free interval of longer than 6 months. In this retrospective study, the charts of patients who underwent second-line chemotherapy for NSCLC in our cancer center between January 2005 and April 2010 were reviewed. All the patients who received a combination of gemcitabine and carboplatin for re-challenge were included in the study. These patients were offered second-line treatment on confirmation of clear radiological disease progression. The overall response rate was 15% and disease control rate was 75%. The median survival time was 10.4 months, with 46% of patients alive at 1 year. These results suggest that re-challenge chemotherapy should be considered in selected patients with radiological partial response or a progression-free survival of longer than 6 months to the initial therapy.

Gemcitabine eliminates double minute chromosomes from human ovarian cancer cells

Double minute chromosomes are cytogenetic manifestations of gene amplification frequently seen in cancer cells. Genes amplified on double minute chromosomes include oncogenes and multi-drug resistant genes. These genes encode proteins which contribute to cancer formation, cancer progression, and development of resistance to drugs used in cancer treatment. Elimination of double minute chromosomes, and therefore genes amplified on them, is an effective way to decrease the malignancy of cancer cells. We investigated the effectiveness of a cancer drug, gemcitabine, on the loss of double minute chromosomes from the ovarian cancer cell line UACC-1598. Gemcitabine is able to decrease the number of double minute chromosomes in cells at a 7500X lower concentration than the commonly used cancer drug hydroxyurea. Amplified genes present on the double minute chromosomes are decreased at the DNA level upon gemcitabine treatment. Gemcitabine, even at a low nanomolar concentration, is able to cause DNA damage. The selective incorporation of double minutes chromatin and γ-H2AX signals into micronuclei provides a strong link between DNA damage and the loss of double minute chromosomes from gemcitabine treated cells. Cells treated with gemcitabine also showed decreased cell growth, colony formation, and invasion. Together, our results suggest that gemcitabine is effective in decreasing double minute chromosomes and this affects the biology of ovarian cancer cells.

Kinesin spindle protein (KSP) inhibitors in combination with chemotherapeutic agents for cancer therapy

A diverse group of proteins, the activities of which are precisely orchestrated during mitosis, have emerged as targets for cancer therapeutics; these include the Aurora kinases (AKs), Polo-like kinases (PLKs), and the kinesin spindle protein (KSP). KSP is essential for the proper separation of spindle poles during mitosis. Agents that target KSP selectively act on cells undergoing cell division, which means that KSP inhibitors are mitosis-specific drugs, and have demonstrated remarkable activities in vitro. However, a significant obstacle to the success of KSP inhibitors is that these compounds, with tremendous efficacy in vitro, have demonstrated little or even no antitumor activity in vivo. Accumulated data suggest that a combination of KSP inhibitors with various cytostatic drugs will result in a more powerful tumor-killing effect than monotherapy. Combination therapies might predominate and represent the next frontier in the discovery research of KSP inhibitors as potential anticancer drugs. Few published studies have reviewed combination therapy using KSP inhibitors. Herein we provide a comprehensive review of the literature on KSP inhibitor monotherapy and therapeutic combinations. The current state and problems are also discussed.

Pancreatic cancer - cost for overtreatment with gemcitabine

Gemcitabine has been the standard chemotherapeutic agent in pancreatic cancer. However, two-thirds of pancreatic tumors display low expression of human equilibrative nucleoside transporter 1 (hENT1), which mediates cellular entry of the drug, and do not respond to gemcitabine therapy. The objective was to determine the costs of gemcitabine overtreatment and the cost-effectiveness of hENT1 testing using a Swedish pancreatic cancer cohort.

MATERIAL AND METHODS

The study population included 87 patients that were diagnosed with pancreatic cancer during 2008-2010 at Skåne University Hospital, Lund. A detailed review of treatments, side effects and resource utilization was performed. The proportion of hENT1-low was estimated at two-thirds based on previous evaluations of tumor samples from the Radiation Therapy Oncology Group (RTOG) trial 9704, the German AIO Pancreatic Cancer Group (AIO-PK) trial 0104, the Low hENT1 and Adenocarcinoma of the Pancreas (LEAP) trial and the authors' own institution. The cost of the hENT1 test was estimated at €50-200.

RESULTS

Sixty patients received gemcitabine and the other 27 best supportive care. Drug administration and hospitalization were the main expenditures. Grade 3 and 4 toxicities occurred in 42%, the most common being neutropenia (18%). The hospital costs related to gemcitabine overtreatment amounted to €5358 per pancreatic cancer patient, corresponding to as much as one-third of the total treatment cost. The health economical costs amounted to €9449 per patient when including indirect costs. Using hENT1 testing to select patients for gemcitabine therapy would save €8.6 million in Sweden each year.

CONCLUSION

Total costs related to gemcitabine overtreatment were high. Individualizing gemcitabine treatment is cost-saving and would reduce unnecessary treatment-related toxicity.

Adjuvant pharmacotherapy in the management of elderly patients with pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fourth or fifth leading cause of death from cancer in Western industrialized countries. Surgical resection is the only chance of cure, but only 15-20 % of cases are potentially resectable at presentation, and despite complete resection, the overall prognosis remains relatively poor. Adjuvant therapy has modestly improved cure rates. The majority of patients with pancreatic cancer are over the age of 65 years. But this age group is underrepresented within clinical trials, and it is unknown whether older patients achieve similar results to younger ones in terms of survival and treatment tolerance. In addition, there are no clinical trials dedicated to the elderly. Retrospective studies coming from the non-resectable setting provide some understanding on outcomes in older patients with PDAC. To date, we can reasonably argue that selected elderly patients with PDAC can benefit from curative surgery and postoperative chemotherapy as do their younger counterparts, without a significant increase in morbidity and mortality. Gemcitabine should be preferred to 5-fluorouracil on the basis of a better risk-benefit balance.

Inhibition of checkpoint kinase 2 (CHK2) enhances sensitivity of pancreatic adenocarcinoma cells to gemcitabine

Checkpoint kinase 2 (CHK2) plays pivotal function as an effector of cell cycle checkpoint arrest following DNA damage. Recently, we found that co-treatment of NSC109555 (a potent and selective CHK2 inhibitor) potentiated the cytotoxic effect of gemcitabine (GEM) in pancreatic cancer MIA PaCa-2 cells. Here, we further examined whether NSC109555 could enhance the antitumour effect of GEM in pancreatic adenocarcinoma cell lines. In this study, the combination treatment of NSC109555 plus GEM demonstrated strong synergistic antitumour effect in four pancreatic cancer cells (MIA PaCa-2, CFPAC-1, Panc-1 and BxPC-3). In addition, the GEM/NSC109555 combination significantly increased the level of intracellular reactive oxygen species (ROS), accompanied by induction of apoptotic cell death. Inhibition of ROS generation by N-acetyl cysteine (NAC) significantly reversed the effect of GEM/NSC109555 in apoptosis and cytotoxicity. Furthermore, genetic knockdown of CHK2 by siRNA enhanced GEM-induced apoptotic cell death. These findings suggest that inhibition of CHK2 would be a beneficial therapeutic approach for pancreatic cancer therapy in clinical treatment.

A kinome screen identifies checkpoint kinase 1 (CHK1) as a sensitizer for RRM1-dependent gemcitabine efficacy

Gemcitabine is among the most efficacious and widely used antimetabolite agents. Its molecular targets are ribonucleotide reductase M1 (RRM1) and elongating DNA. Acquired and de novo resistance as a result of RRM1 overexpression are major obstacles to therapeutic efficacy. We deployed a synthetic lethality screen to investigate if knockdown of 87 selected protein kinases by siRNA could overcome RRM1-dependent gemcitabine resistance in high and low RRM1-expressing model systems. The models included genetically RRM1-modified lung and breast cancer cell lines, cell lines with gemcitabine-induced RRM1 overexpression, and a series of naturally gemcitabine-resistant cell lines. Lead molecular targets were validated by determination of differential gemcitabine activity using cell lines with and without target knock down, and by assessing synergistic activity between gemcitabine and an inhibitor of the lead target. CHK1 was identified has the kinase with the most significant and robust interaction, and it was validated using AZD7762, a small-molecule ATP-competitive inhibitor of CHK1 activation. Synergism between CHK1 inhibition and RRM1-dependent gemcitabine efficacy was observed in cells with high RRM1 levels, while antagonism was observed in cells with low RRM1 levels. In addition, four cell lines with natural gemcitabine resistance demonstrated improved gemcitabine efficacy after CHK1 inhibition. In tumor specimens from 187 patients with non-small-cell lung cancer, total CHK1 and RRM1 in situ protein levels were significantly (p = 0.003) and inversely correlated. We conclude that inhibition of CHK1 may have its greatest clinical utility in malignancies where gemcitabine resistance is a result of elevated RRM1 levels. We also conclude that CHK1 inhibition in tumors with low RRM1 levels may be detrimental to gemcitabine efficacy.

H-gemcitabine: a new gemcitabine prodrug for treating cancer

In this report, we present a new strategy for targeting chemotherapeutics to tumors, based on targeting extracellular DNA. A gemcitabine prodrug was synthesized, termed H-gemcitabine, which is composed of Hoechst conjugated to gemcitabine. H-gemcitabine has low toxicity because it is membrane-impermeable; however, it still has high tumor efficacy because of its ability to target gemcitabine to E-DNA in tumors. We demonstrate here that H-gemcitabine has a wider therapeutic window than free gemcitabine.

The effect of the acid-sensitivity of 4-(N)-stearoyl gemcitabine-loaded micelles on drug resistance caused by RRM1 overexpression

Chemoresistance is a major issue for most gemcitabine-related chemotherapies. The overexpression of ribonucleotide reductase subunit M1 (RRM1) plays a key role in gemcitabine resistance. In this study, we synthesized a new highly acid-sensitive amphiphilic micelle material by conjugating hydrophilic polyethylene glycol with a hydrophobic stearic acid derivative (C18) using a hydrazone bond, which was named as PHC-2. A lipophilic prodrug of gemcitabine, 4-(N)-stearoyl gemcitabine (GemC18), was loaded into micelles prepared with PHC-2, a previously synthesized less acid-sensitive PHC-1, and their acid-insensitive counterpart, PAC. GemC18 loaded in acid-sensitive micelles can overcome gemcitabine resistance, and GemC18 in the highly acid-sensitive PHC-2 micelles was more cytotoxic than in the less acid-sensitive PHC-1 micelles. Mechanistic studies revealed that upon cellular uptake and lysosomal delivery, GemC18 in the acid-sensitive micelles was released and hydrolyzed more efficiently. Furthermore, GemC18 loaded in the highly acid-sensitive PHC-2 micelles inhibited the expression of RRM1 and increased the level of gemcitabine triphosphate (dFdCTP) in gemcitabine resistant tumor cells. The strategy of delivering lipophilized nucleoside analogs using highly acid-sensitive micelles may represent a new platform technology to increase the antitumor activity of nucleoside analogs and to overcome tumor cell resistance to them.

In vitro and in vivo studies of pharmacokinetics and antitumor efficacy of D07001-F4, an oral gemcitabine formulation

PURPOSE

The chemotherapy agent gemcitabine is currently administered intravenously because the drug has poor oral bioavailability. In order to assess the pharmacokinetics and antitumor activity of D07001-F4, a new self-microemulsifying oral drug delivery system preparation of gemcitabine, this study was performed to compare the effect of D07001-F4 with administered gemcitabine in vitro and in vivo.

METHODS

D07001-F4 pharmacokinetics was examined by evaluation of in vitro deamination of D07001-F4 and gemcitabine hydrochloride by recombinant human cytidine deaminase (rhCDA) and in vivo evaluation of D07001-F4 pharmacokinetics in mice. Antitumor activity was evaluated by comparing the effect of D07001-F4 and gemcitabine hydrochloride in inhibiting growth in nine cancer cell lines and by examining the effect of D07001-F4 and gemcitabine in two xenograft tumor models in mice.

RESULTS

In vitro deamination of D07001-F4 by rhCDA was 3.3-fold slower than deamination of gemcitabine hydrochloride. Growth inhibition by D07001-F4 of 7 of the 8 cancer cell lines was increased compared with that seen with gemcitabine hydrochloride, and D07001-F4 inhibited the growth of pancreatic and colon cancer xenografts. In vivo pharmacokinetics showed the oral bioavailability of D07001-F4 to be 34%.

CONCLUSIONS

D07001-F4 was effective against several cancer types, was metabolized more slowly than gemcitabine hydrochloride, and exhibited enhanced oral bioavailability.

Levels of gemcitabine transport and metabolism proteins predict survival times of patients treated with gemcitabine for pancreatic adenocarcinoma

BACKGROUND & AIMS

Patients who undergo surgery for pancreatic ductal adenocarcinoma (PDAC) frequently receive adjuvant gemcitabine chemotherapy. Key determinants of gemcitabine cytotoxicity include the activities of the human equilibrative nucleoside transporter 1 (hENT1), deoxycytidine kinase (dCK), and ribonucleotide reductase subunit 1 (RRM1). We investigated whether tumor levels of these proteins were associated with efficacy of gemcitabine therapy following surgery.

METHODS

Sequential samples of resected PDACs were retrospectively collected from 434 patients at 5 centers; 142 patients did not receive adjuvant treatment (33%), 243 received adjuvant gemcitabine-based regimens (56%), and 49 received nongemcitabine regimens (11%). We measured protein levels of hENT1, dCK, and RRM1 by semiquantitative immunohistochemistry with tissue microarrays and investigated their relationship with patients' overall survival time.

RESULTS

The median overall survival time of patients was 32.0 months. Among patients who did not receive adjuvant treatment, levels of hENT1, RRM1, and dCK were not associated with survival time. Among patients who received gemcitabine, high levels of hENT1 and dCK were significantly associated with longer survival time (hazard ratios of 0.34 [P < .0001] and 0.57 [P = .012], respectively). Interaction tests for gemcitabine administration and hENT1 and dCK status were statistically significant (P = .0007 and P = .016, respectively). On multivariate analysis of this population, hENT1 and dCK retained independent predictive values, and those patients with high levels of each protein had the longest survival times following adjuvant therapy with gemcitabine.

CONCLUSIONS

High levels of hENT1 and dCK in PDAC predict longer survival times in patients treated with adjuvant gemcitabine.

Silencing of ribonucleotide reductase subunit M1 potentiates the antitumor activity of gemcitabine in resistant cancer cells

Gemcitabine is a deoxycytidine analog used for the treatment of a wide range of solid tumors. Its efficacy is however often reduced due to the development of resistance. Ribonucleotide reductase M1 subunit (RRM1) is a key determinant of gemcitabine resistance, and tumor cells that overexpress RRM1 are resistant to the cytotoxicity of gemcitabine. In the present study, we showed that RRM1-specific small interfering RNA (siRNA), when complexed with polyethylenimine, effectively downregulated the expression of RRM1 protein in mouse tumor cells that overexpress RRM1, both in vitro and in vivo. More importantly, systemic administration of the RRM1-specific siRNA significantly inhibited the growth of RRM1-overexpressing tumors in mice and sensitized the tumors to gemcitabine treatment. These findings suggest that silencing RRM1 expression using siRNA could potentially be an effective strategy to overcome gemcitabine resistance.

Personalized therapy for non-small cell lung cancer: which drug for which patient?

The elucidation of the molecular alterations in non-small cell lung cancer (NSCLC) and the development of molecularly targeted agents have permanently shifted NSCLC therapy to a personalized approach. In the metastatic setting, the addition of the anti-vascular endothelial growth factor monoclonal antibody, bevacizumab, to chemotherapy improves overall survival. The oral epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, gefitinib and erlotinib, prolong progression-free survival in patients selected for the presence of an EGFR activating mutation. The monoclonal antibody to EGFR, cetuximab, improves survival in patients with metastatic NSCLC, and the inhibitor of the echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion protein, crizotinib, has resulted in an unprecedented overall survival advantage in patients harboring the EML4-ALK translocation. In the adjuvant setting, gefitinib has not been shown to improve patient survival outcomes; however, there are several ongoing clinical trials in the adjuvant setting evaluating the role of erlotinib, bevacizumab, and the MAGE-A3 and MUC1 vaccines. The realm of personalized lung cancer therapy also includes the study of chemotherapy selected on the basis of the pharmacogenetic profile of a patient's tumor. Several ongoing clinical trials in both the metastatic and adjuvant settings are studying the excision repair cross-complementing group 1 (ERCC1) protein, the ribonucleotide reductase subunit 1 (RRM1) protein, thymidylate synthase, and BRCA1 as predictors of chemotherapy response. This review will outline the current state of the art of personalized NSCLC therapy.

Expression of RRM1 and its association with resistancy to gemcitabine-based chemotherapy in advanced nasopharyngeal carcinoma

Gemcitabine has high activity against nasopharyngeal carcinoma (NPC). The level of ribonucleotide reductase subunit M1 (RRM1) expression is closely related to the efficacy of gemcitabine on non-small cell lung cancer and pancreatic cancer. However, the expression of RRM1 and its association with sensitivity to gemcitabine-based chemotherapy in advanced NPC is not known. In this study, we retrospectively collected 48 formalin-fixed, paraffin-embedded NPC tissues to evaluate the expression of RRM1 using immunohistochemistry. All patients were diagnosed and treated with gemcitabine-based chemotherapy at Sun Yat-sen University Cancer Center. RRM1 expression was positive in 17(35%) patients. RRM1 expression was not associated with sex, age, performance status, WHO histological type, number of distant metastases, previous treatment, or cycles of gemcitabine-based chemotherapy(P> 0.05). The progression-free survival of the RRM1-positive group was shorter than that of the RRM1-negative group (5 months vs. 7 months, P = 0.036), and the response rate of the RRM1-positive group was somewhat lower than that of the RRM1-negative group (51.6% vs. 35.3%, P = 0.278). There was no significant difference in median survival between the RRM1-positive and RRM1-negative groups (22 months vs. 19 months, P = 0.540). Our results show that RRM1-negative expression is related with longer progression-free survival in advanced NPC patients treated with gemcitabine-based regimens.

An evaluation of small-molecule p53 activators as chemoprotectants ameliorating adverse effects of anticancer drugs in normal cells

Pharmacological activation of wild-type p53 has been found to protect normal cells in culture from cytotoxicity and nuclear aberrations caused by conventional cancer therapeutics. Hence, small-molecule p53 activators could have clinical benefits as chemoprotectants for cancer patients bearing p53-mutant tumors. We have evaluated 16 p53-based cyclotherapy regimes combining p53 activators tenovin-6, leptomycin B, nutlin-3 and low dose actinomycin D, with clinically utilized chemotherapeutic agents (S- and M-phase poisons), vinblastine, vinorelbine, cytosine arabinoside and gemcitabine. All the p53 activators induce reversible cell-cycle arrest in primary human fibroblasts and protect them from both S- and M-phase poisons. Furthermore, studies with p53-mutant cancer cell lines show that nutlin-3 and low dose actinomycin D do not affect the sensitivity of these cells to any of the chemotherapeutics tested. Thus, these two small molecules could be suitable choices for cyclotherapy regimes involving S- or M-phase poisons. In contrast, pre-incubation of p53-mutant cells with tenovin-6 or leptomycin B reduces the efficacy of vinca alkaloids, suggesting that these p53 activators could be effective as chemoprotectants if combined with S- but not M-phase poisons. Discrepancies were observed between the levels of protection detected immediately after treatment and following recovery in fresh medium. This highlights the need to assess both short- and long-term effects when evaluating compounds as potential chemoprotectants for cancer therapy.

Stratification of nucleoside analog chemotherapy using 1-(2'-deoxy-2'-18F-fluoro-β-D-arabinofuranosyl)cytosine and 1-(2'-deoxy-2'-18F-fluoro-β-L-arabinofuranosyl)-5-methylcytosine PET

The ability to measure tumor determinants of response to nucleoside analog (NA) chemotherapy agents such as gemcitabine and related compounds could significantly affect the management of several types of cancer. Previously we showed that the accumulation in tumors of the new PET tracer 1-(2'-deoxy-2'-(18)F-fluoro-β-d-arabinofuranosyl)cytosine ((18)F-FAC) is predictive of responses to gemcitabine. (18)F-FAC retention in cells requires deoxycytidine kinase (dCK), a rate-limiting enzyme in the deoxyribonucleoside salvage metabolism and in gemcitabine conversion from an inactive prodrug to a cytotoxic compound. The objectives of the current study were to determine whether (18)F-FAC tumor uptake is also influenced by cytidine deaminase (CDA), a determinant of resistance to gemcitabine; to develop a new PET assay using (18)F-FAC and the related probe 1-(2'-deoxy-2'-(18)F-fluoro-β-l-arabinofuranosyl)-5-methylcytosine (l-(18)F-FMAC) to profile tumor lesions for both dCK and CDA enzymatic activities; and to determine whether this PET assay can identify the most effective NA chemotherapy against tumors with differential expression of dCK and CDA.

METHODS

Isogenic murine leukemic cell lines with defined dCK and CDA activities were generated by retroviral transduction. A cell viability assay was used to determine the sensitivity of the isogenic cell lines to the dCK-dependent NA prodrugs gemcitabine and clofarabine. In vitro enzymatic and cell-based tracer uptake assays and in vivo PET with (18)F-FAC and l-(18)F-FMAC were used to predict tumor responses to gemcitabine and clofarabine.

RESULTS

dCK and CDA activities measured by kinase and tracer uptake assays correlated with the sensitivity of isogenic cell lines to gemcitabine and clofarabine. Coexpression of CDA decreased the sensitivity of dCK-positive cells to gemcitabine treatment in vitro by 15-fold but did not affect responses to clofarabine. Coexpression of CDA decreased (18)F-FAC but not l-(18)F-FMAC, phosphorylation, and uptake by dCK-positive cells. (18)F-FAC and l-(18)F-FMAC PET estimates of the enzymatic activities of dCK and CDA in tumor implants in mice were predictive of responses to gemcitabine and clofarabine treatment in vivo.

CONCLUSION

These findings support the utility of PET-based phenotyping of tumor nucleoside metabolism for guiding the selection of NA prodrugs.

Synthesis and in vitro evaluation of novel lipophilic monophosphorylated gemcitabine derivatives and their nanoparticles

Gemcitabine hydrochloride (HCl) is approved for the treatment of a wide spectrum of solid tumors. However, the rapid development of resistance often makes gemcitabine less efficacious. In the present study, we synthesized several novel lipophilic monophosphorylated gemcitabine derivatives, incorporated them into solid lipid nanoparticles, and then evaluated their ability to overcome major known gemcitabine resistance mechanisms by evaluating their in vitro cytotoxicities in cancer cells that are deficient in deoxycytidine kinase (dCK), deficient in human equilibrative nucleoside transporter (hENT1), over-expressing ribonucleotide reductase M1 subunit (RRM1), or over-expressing RRM2. In dCK deficient cells, the monophosphorylated gemcitabine derivatives and their nanoparticles were up to 86-fold more cytotoxic than gemcitabine HCl. The majority of the gemcitabine derivatives and their nanoparticles were more cytotoxic than gemcitabine HCl in cells that over-expressing RRM1 or RRM2, and the gemcitabine derivatives in nanoparticles were also resistant to deamination by deoxycytidine deaminase. The gemcitabine derivatives (in nanoparticles) hold a great potential in overcoming gemcitabine resistance.

Attenuation of phosphorylation by deoxycytidine kinase is key to acquired gemcitabine resistance in a pancreatic cancer cell line: targeted proteomic and metabolomic analyses in PK9 cells

PURPOSE

Multiple proteins are involved in activation and inactivation of 2',2'-difluorodeoxycytidine (gemcitabine, dFdC). We aimed to clarify the mechanism of dFdC resistance in a pancreatic cancer cell line by applying a combination of targeted proteomic and metabolomic analyses.

METHODS

Twenty-five enzyme and transporter proteins and 6 metabolites were quantified in sensitive and resistant pancreatic cancer cell lines, PK9 and RPK9, respectively.

RESULTS

The protein concentration of deoxycytidine kinase (dCK) in RPK9 cells was less than 0.02-fold (2 %) compared with that in PK9 cells, whereas the differences (fold) were within a factor of 3 for other proteins. Targeted metabolomic analysis revealed that phosphorylated forms of dFdC were reduced to less than 0.2 % in RPK9 cells. The extracellular concentration of 2',2'-difluorodeoxyuridine (dFdU), an inactive metabolite of dFdC, reached the same level as the initial dFdC concentration in RPK9 cells. However, tetrahydrouridine treatment did not increase phosphorylated forms of dFdC and did not reverse dFdC resistance in RPK9 cells, though this treatment inhibits production of dFdU.

CONCLUSIONS

Combining targeted proteomics and metabolomics suggests that acquisition of resistance in RPK9 cells is due to attenuation of dFdC phosphorylation via suppression of dCK.

DNA methylation-independent reversion of gemcitabine resistance by hydralazine in cervical cancer cells

Background

Down regulation of genes coding for nucleoside transporters and drug metabolism responsible for uptake and metabolic activation of the nucleoside gemcitabine is related with acquired tumor resistance against this agent. Hydralazine has been shown to reverse doxorubicin resistance in a model of breast cancer. Here we wanted to investigate whether epigenetic mechanisms are responsible for acquiring resistance to gemcitabine and if hydralazine could restore gemcitabine sensitivity in cervical cancer cells.

Methodology/Principal Findings

The cervical cancer cell line CaLo cell line was cultured in the presence of increasing concentrations of gemcitabine. Down-regulation of hENT1 & dCK genes was observed in the resistant cells (CaLoGR) which was not associated with promoter methylation. Treatment with hydralazine reversed gemcitabine resistance and led to hENT1 and dCK gene reactivation in a DNA promoter methylation-independent manner. No changes in HDAC total activity nor in H3 and H4 acetylation at these promoters were observed. ChIP analysis showed H3K9m2 at hENT1 and dCK gene promoters which correlated with hyper-expression of G9A histone methyltransferase at RNA and protein level in the resistant cells. Hydralazine inhibited G9A methyltransferase activity in vitro and depletion of the G9A gene by iRNA restored gemcitabine sensitivity.

Conclusions/Significance

Our results demonstrate that acquired gemcitabine resistance is associated with DNA promoter methylation-independent hENT1 and dCK gene down-regulation and hyper-expression of G9A methyltransferase. Hydralazine reverts gemcitabine resistance in cervical cancer cells via inhibition of G9A histone methyltransferase.

The potential of exploiting DNA-repair defects for optimizing lung cancer treatment

The tumor genome is commonly aberrant as a consequence of mutagenic insult and incomplete DNA repair. DNA repair as a therapeutic target has recently received considerable attention owing to the promise of drugs that target tumor-specific DNA-repair enzymes and potentiate conventional cytotoxic therapy through mechanism-based approaches, such as synthetic lethality. Treatment for non-small-cell lung cancer (NSCLC) consists mainly of platinum-based chemotherapy regimens and improvements are urgently needed. Optimizing treatment according to tumor status for DNA-repair biomarkers, such as ERCC1, BRCA1 or RRM1, could predict response to platinum, taxanes and gemcitabine-based therapies, respectively, and might improve substantially the response of individual patients' tumors. Finally, recent data on germline variation in DNA-repair genes may also be informative. Here, we discuss how a molecular and functional DNA-repair classification of NSCLC may aid clinical decision making and improve patient outcome.

An RNA aptamer that specifically binds pancreatic adenocarcinoma up-regulated factor inhibits migration and growth of pancreatic cancer cells

Previously, we reported that a novel secretory protein, pancreatic adenocarcinoma up-regulated factor (PAUF), which is highly expressed in pancreatic cancer and mediates the growth and metastasis of pancreatic cancer cells. In this study, we generated and characterized a 2'-fluoropyrimidine modified RNA aptamer (P12FR2) directed against human PAUF. P12FR2 binds specifically to human PAUF with an estimated apparent K(D) of 77nM. P12FR2 aptamer inhibits PAUF-induced migration of PANC-1, human pancreatic cancer cells, in a wound healing assay. Moreover, intraperitoneal injection of P12FR2 decreased tumor growth by about 60% in an in vivo xenograft model with CFPAC-1 pancreatic cancer cells, without causing a loss of weight in the treated mice. Taken together, we propose here that PAUF-specific RNA aptamer, P12FR2, has the potential to be effective in the therapy of human pancreatic cancer.

RRM1 expression and clinical outcome of gemcitabine-containing chemotherapy for advanced non-small-cell lung cancer: a meta-analysis

BACKGROUND

The predictive value of RRM1 to therapeutic efficacy of gemicitabine-containing chemotherapy in patients with advanced non-small-cell lung cancer (NSCLC) remains disputable. This meta-analysis is performed to systematically evaluate whether RRM1 expression is associated with the clinical outcome of gemcitabine-containing regimen in advanced NSCLC.

METHODS

An electronic search was conducted using the databases Pubmed, Medline, EMBASE, Cochrane library and CNKI, from inception to May, 2011. A systemic review of the studies on the association between RRM1 expression in advanced NSCLC and clinical outcome of gemcitabine-containing regimen was performed. Pooled odds ratios (OR) for the response rate, weighted median survival and time to progression were calculated using the software Revman 5.0.

RESULTS

The search strategy identified 18 eligible studies (n=1243). Response rate to gemcitabine-containing regimen was significantly higher in patients with low/negative RRM1 (OR=0.31, 95% CI 0.21-0.45, P<0.00001). NSCLC patients with low/negative RRM1 who were treated with gemicitabine-containing regimen survived 3.94 months longer (95% CI 2.15-5.73, P<0.0001) and had longer time to progression for 2.64 months (95% CI 0.39-4.89, P=0.02) than those with high/positive RRM1.

CONCLUSIONS

Low/negative RRM1 expression in advanced NSCLC was associated with higher response rate to gemcitabine-containing regimen and better prognosis. Large phase III randomized trials are required to identify whether RRM1 detection is clinically valuable for predicting the prognosis and sensitivity to gemcitabine-containing regimen in advanced NSCLC.

The C-terminal region of Bfl-1 sensitizes non-small cell lung cancer to gemcitabine-induced apoptosis by suppressing NF-κB activity and down-regulating Bfl-1

Gemcitabine is used to treat several cancers including lung cancer. However, tumor cells often escape gemcitabine-induced cell death via various mechanisms, which include modulating bcl-2 family members and NF-κB activation. We previously reported that the C-terminal region of Bfl-1 fused with GFP (BC) is sufficient to induce apoptosis in 293T cells. In the present study, we investigated the anti-tumor effect of combined BC gene therapy and gemcitabine chemotherapy in vitro and in vivo using non-small cell lung cancer cell lines and a xenograft model. Cell lines were resistant to low dose gemcitabine (4-40 ng/ml), which induced NF-κB activation and concomitant up-regulation of Bfl-1 (an NF-κB-regulated anti-apoptotic protein). BC induced the apoptosis of A549 and H157 cells with caspase-3 activation. Furthermore, co-treatment with BC and low dose gemcitabine synergistically and efficiently induced mitochondria-mediated apoptosis in these cells. When administered alone or with low dose gemcitabine, BC suppressed NF-κB activity, inhibited the nuclear translocation of p65/relA, and down-regulated Bfl-1 expression. Furthermore, direct suppression of Bfl-1 by RNA interference sensitized cells to gemcitabine-induced cell death, suggesting that Bfl-1 importantly regulates lung cancer cell sensitivity to gemcitabine. BC and gemcitabine co-treatment also showed a strong anti-tumor effect in a nude mouse/A549 xenograft model. These results suggest that lung cancer cells become resistant to gemcitabine via NF-κB activation and the subsequent overexpression of Bfl-1, and that BC, which has both pro-apoptotic and NF-κB inhibitory effects, could be harnessed as a gene therapy to complement gemcitabine chemotherapy in non-small cell lung cancer.

Stearoyl gemcitabine nanoparticles overcome resistance related to the over-expression of ribonucleotide reductase subunit M1

Gemcitabine is a deoxycytidine analog used in the treatment of various solid tumors. However, tumors often develop resistances over time, which becomes a major issue for most gemcitabine-related chemotherapies. In the present study, a previously reported stearoyl gemcitabine nanoparticle formulation (GemC18-NPs) was evaluated for its ability to overcome gemcitabine resistance. In the wild type CCRF-CEM human leukemia cells, the IC(50) value of GemC18-NPs was 9.5-fold greater than that of gemcitabine hydrochloride (HCl). However, in the CCRF-CEM-AraC-8C cells that are deficient in the human equilibrative nucleoside transporter-1, the IC(50) of GemC18-NPs was only 3.4-fold greater than that in the parent CCRF-CEM cells, whereas the IC(50) of gemcitabine HCl was 471-fold greater than that in the parent CCRF-CEM cells. The GemC18-NPs were also more cytotoxic than gemcitabine HCl in the deoxycytidine kinase deficient (CCRF-CEM/dCK(-/-)) tumor cells. Similar to gemcitabine HCl, GemC18-NPs induced apoptosis through caspase activation. Another gemcitabine-resistant tumor cell line, TC-1-GR, was developed in our laboratory. In the TC-1-GR cells, the IC(50) of GemC18-NPs was only 5% of that of gemcitabine HCl. Importantly, GemC18-NPs effectively controlled the growth of gemcitabine resistant TC-1-GR tumors in mice, whereas the molar equivalent dose of gemcitabine HCl did not show any activity against the growth of the TC-1-GR tumors. Proteomics analysis revealed that the TC-1-GR cells over-expressed ribonucleotide reductase M1, which was likely the cause of the acquired gemcitabine resistance in the TC-1-GR cells. To our best knowledge, this represents the first report demonstrating that a nanoparticle formulation of gemcitabine overcomes gemcitabine resistance related to ribonucleotide reductase M1 over-expression.

Time-dependent cytotoxic drugs selectively cooperate with IL-18 for cancer chemo-immunotherapy

Background

Time-dependent chemotherapeutic agents can selectively target tumor cells in susceptible phases of the cell cycle however a fraction of tumor cells in non-vulnerable cell cycle phases remain drug-resistant. Immunotherapy represents a promising approach to overcome the limitation of phase-specific drugs and improve their clinical efficacy. Here, we investigated the potential use of anticancer chemotherapeutic drugs in combination with IL-18, a cytokine with strong immunostimulatory properties.

Methods

Four chemotherapeutic drugs commonly used in ovarian cancer were first tested for the ability to increase the immunogenicity and killing of the murine ovarian cancer cell line ID8 in vitro. Chemotherapeutric agents with measured time-dependent immune-enhancing effects were then tested for antitumor effectiveness in vivo in combination with IL-18 immunotherapy using the ID8-Vegf ovarian cancer model.

Results

Paclitaxel or topotecan exposure alone mediated incomplete, time-dependent killing against the murine ovarian cancer cell line ID8 in vitro, whereas carboplatin or gemcitabine mediated comprehensive, dose-dependent killing. In the plateau phase of the time-dependent killing by topotecan or paclitaxel, drug-resistant ID8 cells were more immunogenic with elevated expression of MHC-I and Fas, and increased sensitivity to CTL and Fas agonistic antibody in vitro. Moreover, the antitumor effectiveness of time-dependent agents in vivo was significantly improved with the addition of IL-18 through a T cell-dependent mechanism, while the effectiveness of drugs without significant phase specificity were not.

Conclusions

Tumor immunotherapy with IL-18 can significantly augment the killing fraction of phase-specific chemotherapeutic drugs and provide survival benefit. The safety profile of IL-18 and its positive interactions with select anticancer chemotherapeutic agents strongly supports the clinical investigation of this combinatorial approach.

Synergistic antitumor activity of gemcitabine and ABT-737 in vitro and in vivo through disrupting the interaction of USP9X and Mcl-1

The Bcl-2 antagonist ABT-737 targets Bcl-2/Bcl-xL, but not Mcl-1, which may confer resistance to this agent in various cancers with high levels of Mcl-1. Here, we showed that the combination of gemcitabine and ABT-737 exhibited synergistic cytotoxicity and induced significant apoptosis in multiple cancer types, including lung, renal, bladder, and prostate cancers. The enhanced apoptosis induced by gemcitabine plus ABT-737 was accompanied by the greater extent of mitochondrial depolarization, caspases-3 activation, and PARP cleavage in 95-D and 5637 cell lines. Importantly, in ABT-737-resistant cancer cells, the interaction between USP9X and Mcl-1, which was increased by ABT-737 treatment, could be disrupted by gemcitabine, thus resulting in enhanced ubiquitination and the subsequent degradation of Mcl-1 and ultimately in the synergism of these two drugs. Moreover, the increased anticancer efficacy of gemcitabine combined with ABT-737 was further validated in a human lung cancer 95-D xenograft model in nude mice. Taken together, our data first showed the synergistic anticancer capabilities achieved by combining gemcitabine and ABT-737 and, second, opened new opportunities to use antiapoptotic Bcl-2 family members, which drive tumor cell resistance in current anticancer therapies, therapeutically.

Biomarkers of DNA repair and related pathways: significance in non-small cell lung cancer

PURPOSE OF REVIEW

To review selected biomarkers of DNA repair and related pathways as they relate to the management of patients with non-small cell lung cancer (NSCLC), emphasizing the role of individualized, chemotherapy for advanced disease, and discussing potential applications in early disease.

RECENT FINDINGS

The activity of molecular-targeted agents in NSCLC patients whose tumor possesses relevant biomarkers [such as epidermal growth factor receptor (EGFR) activating mutations and ALK translocations] has made personalized therapy possible. In addition, preclinical and clinical studies have shown that histopathological and biomolecular factors can correlate with clinical outcome in patients with NSCLC treated with chemotherapy. As a result, tumor histology is now routinely considered in selecting chemotherapy for NSCLC patients, such as pemetrexed for nonsquamous histology. Molecular tumor and host factors, including genes involved in DNA-repair and synthesis, are potentially even more relevant as predictive biomarkers of tumor response to chemotherapy. However, individual molecular markers and gene signatures need further validation and standardization, before routine use in the clinic can be recommended.

SUMMARY

In the era of molecular-targeted agents, individualized therapy based on molecular biomarkers has become a reality in the treatment of patients with advanced NSCLC. Further studies are needed to optimize current treatment algorithms with regard to biomarkers for chemotherapy benefit, to refine molecular markers, and to translate these findings to early stage NSCLC.

Squalenoyl gemcitabine nanomedicine overcomes the low efficacy of gemcitabine therapy in pancreatic cancer

Development of chemoresistance and rapid inactivation of gemcitabine (Gem), the standard therapy for advanced pancreatic cancer, are responsible of the major therapeutic failures. To overcome the above drawbacks we designed a novel nanomedicine strategy for Gem nanoparticle (NP) formulation based on squalene conjugation. The purpose was to investigate the antitumor efficacy of gemcitabine-squalene (SQ-Gem) NPs on chemoresistant and chemosensitive pancreatic adenocarcinoma models. Cell viability and apoptosis assays showed that SQ-Gem NPs displayed higher antiproliferative and cytotoxic effects, particularly in chemoresistant Panc1 tumor cells. In in vivo studies, compared to native Gem, SQ-Gem NPs decreased significantly the tumor growth, prevented tumor cell invasion, and prolonged the survival time of mice bearing orthotopic pancreatic tumors. These results correlate with a greater reduction of Ki-67 and induction of apoptosis. These findings demonstrate the feasibility of utilizing SQ-Gem NPs to make tumor cells more sensitive to Gem and thus provide an efficient new therapeutic alternative for pancreatic adenocarcinoma.

FROM THE CLINICAL EDITOR

Pancreatic malignancies represent some of the most notoriously treatment resistant cancer varieties. This paper discusses a novel and promising nanotechnology-based treatment approach, currently at the basic science stage.

Disrupted plasma membrane localization of equilibrative nucleoside transporter 2 in the chemoresistance of human pancreatic cells to gemcitabine (dFdCyd)

Although the nucleoside pyrimidine analogue gemcitabine is the most effective single agent in the palliation of advanced pancreatic cancer, cellular resistance to gemcitabine treatment is a major problem in the clinical scene. To clarify the molecular mechanisms responsible for chemoresistance to gemcitabine, mRNA expression of the key enzymes including cytidine deaminase (CDA), deoxycytidine kinase (dCK), 5'-nucleotidase (NT5), equilibrative nucleoside transporter 1 and 2 (ENT1 and ENT2), dCMP deaminase (dCMPK), ribonucleotide reductase M1 and M2 (RRM1 and RRM2), thymidylate synthase (TS) and CTP synthase (CTPS) was examined. The interacellular uptake of gemcitabine was greatly impaired in the chemoresistant cell lines due to dysfunction of ENT1 and ENT2. Protein expression of ENT1 and ENT2 and their protein coding sequences were not altered. Immunohistochemical and western blot analyses revealed that localization of ENT2 on the plasma membrane was disrupted. These data suggest that the disrupted localization of ENT2 is one of causes of the impaired uptake of gemcitabine, resulting in a gain of chemoresistance to gemcitabine.

Association of RRM1 -37A>C polymorphism with clinical outcome in colorectal cancer patients treated with gemcitabine-based chemotherapy

BACKGROUND

To investigate whether single nucleotide polymorphisms (SNPs) in gemcitabine (GMB) metabolism genes were associated with clinical outcome in pre-treated metastatic colorectal cancer (mCRC) patients.

PATIENTS AND METHODS

SNPs of hCNT1, hENT1, CDA, dCTD and RRM1 genes were evaluated in 95 mCRC patients and detected using TaqMan genotyping assays. Association of genotypes with overall response rate (ORR), time to progression (TTP) and overall survival (OS) was tested by univariate and multivariate analysis. RRM1 -37A>C polymorphism was correlated with GMB IC50 value and with the RRM1 gene expression level in CRC cell lines.

RESULTS

The ORR was 38.9%. The median TTP and OS were 4 and 14.3 months, respectively. By multivariate analysis, patients carrying the RRM1 -37CC genotype or the CDA A-76 C-containing allele had a significantly higher likelihood of achieving a tumour response. RRM1 -37A>C polymorphism remained associated with clinical efficacy (TTP). In vitro experiments, in CRC cell lines, showed that the RRM1 A-37C genotype was associated with the levels of RRM1 expression and with GMB IC50 values. Finally, the down-regulation of RRM1 with a specific siRNA strongly influenced GMB sensitivity.

CONCLUSION

RRM1 -37A>C polymorphism may represent a useful biomarker to select mCRC patients most likely to benefit from GMB-based salvage therapy.

Ribonucleotide reductase subunit M1 expression in resectable, muscle-invasive urothelial cancer correlates with survival in younger patients

OBJECTIVE

To assess whether high ribonucleotide reductase subunit M1 (RRM1) expression in patients with resected, muscle-invasive (T2-4NxM0) urothelial carcinoma (UC) correlated with longer overall survival (OS). RRM1 is the primary cellular target of gemcitabine and previous studies in resected early-stage lung cancer have shown a survival benefit for patients with high expression.

PATIENTS AND METHODS

In all, 84 radical cystectomy specimens with muscle-invasive UC were identified from existing tissue microarrays. The patients' medical records were retrospectively reviewed to confirm pathology and stage. Specimens were analysed for RRM1 expression using automated quantitative analysis. The median value of RRM1 was established a priori as the threshold for high and low expression.

RESULTS

The median age of the patients was 69 years. Stages were nearly equally distributed: 30%, 38%, and 32% for stage II, III, and IV, respectively. Most were high grade (99%) with no nodal involvement (69%). The median (range) OS was 2.0 (0-13.1) years. Tumoral RRM1 levels did not correlate with OS for the entire cohort, but when adjusted for age, high tumoral RRM1 expression in younger patients (aged <70 years) correlated with increased survival. Younger patients with high RRM1 expression had a median OS of 10.6 years compared with 1.6 years in older patients (P= 0.001). There was no difference in OS among low RRM1 expressors: 2.3 vs 1.6 years in younger and older patients, respectively (P= 0.22).

CONCLUSIONS

Our results suggest that high RRM1 expression may be prognostic for improved survival in patients with muscle-invasive UC aged <70 years.

ERCC1 and RRM1 in the international adjuvant lung trial by automated quantitative in situ analysis

The excision repair cross completing group 1 gene product (ERCC1) and the regulatory subunit of ribonucleotide reductase (RRM1) have been reported as being prognostic of outcome and predictive of therapeutic efficacy in patients with non-small cell lung cancer. Routinely processed surgical specimens from 784 patients from the International Adjuvant Lung Trial were arrayed as tissue microarrays. In situ protein levels were scored with an automated, quantitative analysis system, dichotomized into high and low marker categories, and analyzed for associations with patients' characteristics, survival, and benefit from adjuvant chemotherapy. Scores for both markers were significantly associated with contributing center (P < 0.001) and skewed, with the bulk of scores being low. High scores were more frequent in women for ERCC1 and RRM1 and in older patients and those with adenocarcinoma for RRM1. Low ERCC1 scores indicated significant benefit from adjuvant chemotherapy [hazard ratio (HR) = 0.73 for chemotherapy versus control, P = 0.02]. Although all other survival associations were not statistically significant, low RRM1 scores trended to indicate benefit from adjuvant chemotherapy (HR = 0.84, P = 0.25), and ERCC1 scores were marginally prognostic of survival (HR = 0.77 for high versus low scores, P = 0.10). We conclude that contributing center and specimen quality substantially affect the levels of both markers. Future trials should incorporate the collection and processing of tumor specimens prospectively on standardized protocols to better reveal the impact of biomarkers on clinically relevant outcomes.

The ribonucleotide reductase large subunit (RRM1) as a predictive factor in patients with cancer

The large subunit of human ribonucleotide reductase, RRM1, is involved in the regulation of cell proliferation, cell migration, tumour and metastasis development, and the synthesis of deoxyribonucleotides for DNA synthesis. It is also a cellular target for the chemotherapeutic agent, gemcitabine. RRM1 has been studied in a large number of patients with different types of cancer, such as non-small-cell lung cancer, pancreatic cancer, breast cancer, and biliary tract cancer, to establish its prognostic or predictive value when patients were treated with gemcitabine, and mRNA expression and genetic variants as determined by genotyping have in some cases been associated with clinical outcome of patients with cancer. Here, we review preclinical and clinical studies of RRM1 assessment and discuss the further steps in the development of this clinically pertinent biomarker.

HuR's role in gemcitabine efficacy: an exception or opportunity?

Over the next few years, research teams will focus on, and millions of dollars will be spent on, sorting through cancer genomes. Undoubtedly, 'druggable' targets and events will be discovered that will improve our understanding and, hopefully, treatment of cancer. Highlighting an alternative to this 'genome-centric' approach, this review will further explore an underappreciated mechanism of gene expression regulation, posttranscription mRNA:protein interactions. A key molecule involved in this mode of gene regulation is HuR and we have shown that HuR levels and HuR cellular distribution can predict how pancreatic cancer patients responded to the standard of care chemotherapy (i.e., gemcitabine). HuR regulates post-transcriptional processes through: (1) association with specific mRNA cargos with ARE-rich sequences and (2) stress-induced increased cytoplasmic protein levels. Over multiple laboratories and diverse tumor types, it has been shown that HuR supports tumor survival through its regulation of tumor-promoting transcripts such as VEGF. In this article, we will highlight a recent discovery that this potent post-transcriptional gene regulatory mechanism has an impact on a common chemotherapeutic, gemcitabine. Specifically, we have identified the mechanism by which HuR can regulate a key gemcitabine metabolic enzyme, deoxycytidine kinase. We will use this example to explore and hypothesize the functional roles that HuR may have on anticancer drug therapies. We will survey novel high throughput global gene expression analysis tools to discover novel HuR targets. Future multidisciplinary approaches focused on HuR biology will provide critical events and 'druggable' targets in cancer that large-scale genomic sequencing efforts will miss.

Parameters for individualizing systemic therapy in non-small cell lung cancer

Rational drug design based on molecular targets is starting to revolutionize cancer care. To maximize its potential for patients, a concomitant leveraging of molecular knowledge for selection of patients to future and current therapeutic options is paramount. The terms "individualized", "personalized", or "precision therapy" are currently used to describe these efforts. Here, we summarize current knowledge for selection of systemic targeted and cytotoxic therapy for patients with non-small-cell lung cancer. Based on this knowledge, we present a potential decision algorithm to best select patients for currently available therapies, which include the treatment options single-agent erlotinib or gefitinib, the ALK inhibitor crizotinib, double agent gemcitabine and platinum, double agent platinum and pemetrexed, and as a default option a taxane combined with a non-platinum drug, for instance a vinca alkaloid. The addition of bevacizumab to double-agent chemotherapy is also discussed. Currently available data on predictive biomarkers are largely based on subgroup or companion biomarker analyses of patient cohorts or clinical trials. Current and emerging markers must be incorporated prospectively into the design of clinical trials that test novel and established agents to better understand their clinical utility and to refine selection parameters and marker interactions. Future development will lead to increasing complexity in clinical decision making with substantial anticipated benefits to patients including increased therapeutic efficacy, reduced toxicity, and better quality of life.

Optimization and evaluation of electroporation delivery of siRNA in the human leukemic CEM cell line

In order to study nucleoside analog activation in the CEM cell line, a transfection protocol had to be optimized in order to silence an enzyme involved in nucleoside analog activation. Hematopoetic cell lines can be difficult to transfect with traditional lipid-based transfection, so the electroporation technique was used. Field strength, pulse length, temperature, electroporation media, siRNA concentration, among other conditions were tested in order to obtain approximately 70-80% mRNA and enzyme activity downregulation of the cytosolic enzyme deoxycytidine kinase (dCK), necessary for nucleoside analog activation. Downregulation was assessed at mRNA and enzyme activity levels. After optimizing the protocol, a microarray analysis was performed in order to investigate whether the downregulation was specific. Additionally two genes were differentially expressed besides the downregulation of dCK. These were however of unknown function. The leakage of intracellular nucleotides was also addressed in the electroporated cells since it can affect the DNA repair mechansism and the efficiency of nucleoside analogs. Three of these pools were increased compared to untreated, unelectroporated cells. The siRNA transfected cells with reduced dCK expression and activity showed reduced sensitivity to several nucleoside analogs as expected. The multidrug resistance to other drugs, as seen in nucleoside analog-induced resistant cells, was not seen with this model.

Modulation of the ribonucleotide reductase-antimetabolite drug interaction in cancer cell lines

RRM1 is a determinant of gemcitabine efficacy in cancer patients. However, the precision of predicting tumor response based on RRM1 levels is not optimal. We used gene-specific overexpression and RNA interference to assess RRM1's impact on different classes of cytotoxic agents, on drug-drug interactions, and the modulating impact of other molecular and cellular parameters. RRM1 was the dominant determinant of gemcitabine efficacy in various cancer cell lines. RRM1 also impacted the efficacy of other antimetabolite agents. It did not disrupt the interaction of two cytotoxic agents when combined. Cell lines with truncation, deletion, and null status of p53 were resistant to gemcitabine without apparent relationship to RRM1 levels. Pemetrexed and carboplatin sensitivity did not appear to be related to p53 mutation status. The impact of p53 mutations in patients treated with gemcitabine should be studied in prospective clinical trials to develop a model with improved precision of predicting drug efficacy.

Induction of resistance to the lipophilic cytarabine prodrug elacytarabine (CP-4055) in CEM leukemic cells

The deoxynucleoside analogs cytarabine (Ara-C) and gemcitabine (dFdC) are widely used in the treatment of cancer. Due to their hydrophilic nature they need the equilibrative (hENT) and concentrative (hCNT) nucleoside transporters to enter the cell. To bypass drug resistance due to decreased uptake, lipophilic 5'elaidic acid esters were synthesized, elacytarabine (CP-4055, from ara-C) and CP-4126 (from gemcitabine), which are currently in clinical development for solid and hematological tumors. We investigated whether resistance can be induced in vitro, and treated the CEM leukemic cell line with weekly increasing elacytarabine concentrations, up to 0.28 microM (10 times IC(50)). The IC(50) of the resistant CEM/CP-4055 was 35 microM, about 1,000 times that of the wildtype CEM, and comparable to that of CEM/dCK- (deoxycytidine kinase deficient) (22 microM). CEM/CP-4055 was also cross-resistant to Ara-C, gemcitabine and CP-4126 (28 and 33 microM, respectively). A low level of mRNA dCK was observed, and similar to CEM/dCK-, CEM/CP-4055 did not accumulate Ara-CTP after exposure to Ara-C or elacytarabine, which is consistent with a deficiency in dCK. In conclusion, elacytarabine induced resistance similar to Ara-C. This resistance was caused by downregulation of dCK.

The activity of the lipophilic nucleoside derivatives elacytarabine and CP-4126 in a panel of tumor cell lines resistant to nucleoside analogues

The clinical activity of pyrimidine analogues (araC and gemcitabine) is impaired by different mechanisms of resistance and several efforts to overcome this problem have been undertaken. Elacytarabine (CP-4055, araC-5'elaidic acid ester) and CP-4126 (gemcitabine-5'elaidic acid ester) are lipophilic fatty acid derivatives of the nucleoside analogues araC and gemcitabine, respectively, that are currently investigated in clinical trials in solid tumors and hematological malignancies. Here, we present results on the activity of elacytarabine and CP-4126 in a panel of tumor cell lines that are resistant to araC and gemcitabine and we discuss the potential use of these agents in the treatment of patients with drug resistance phenotypes. We conclude that elacytarabine and CP-4126 are active in cells with deficient nucleoside membrane transport and altered mismatch repair. These results should be taking into consideration for future clinical development of elacyatrabine and CP-4126.

Genetic factors influencing cytarabine therapy

The mainstay of acute myeloid leukemia chemotherapy is the nucleoside analog cytarabine (ara-C). Numerous studies suggest that the intracellular concentrations of the ara-C active metabolite, ara-CTP, vary widely among patients and, in turn, are associated with variability in clinical response to acute myeloid leukemia treatment. Thus, genetic variation in key genes in the ara-C metabolic pathway--specifically, deoxycytidine kinase (a rate-limiting activating enzyme), 5 nucleotidase, cytidine deaminase and deoxycytidylate deaminase (all three are inactivating enzymes), human equilibrative nucleoside transporter (ara-C uptake transporter) and ribonucleotide reductase (RRM1 and RRM2--enzymes regulating intracellular deoxycytidine triphosphate pools)--form the molecular basis of the interpatient variability observed in intracellular ara-CTP concentrations and response to ara-C. Understanding genetic variants in the key candidate genes involved in the metabolic activation of ara-C, as well as the pharmacodynamic targets of ara-C, will provide an opportunity to identify patients at an increased risk of adverse reactions or decreased likelihood of response, based upon their genetic profile, which in future could help in dose optimization to reduce drug toxicity without compromising efficacy. The pharmacogenetic studies on ara-C would also be equally applicable to other nucleoside analogs, such as gemcitabine, decitabine, clofarabine and so on, which are metabolized by the same pathway.

Trifluorothymidine resistance is associated with decreased thymidine kinase and equilibrative nucleoside transporter expression or increased secretory phospholipase A2

Trifluorothymidine (TFT) is part of the novel oral formulation TAS-102, which is currently evaluated in phase II studies. Drug resistance is an important limitation of cancer therapy. The aim of the present study was to induce resistance to TFT in H630 colon cancer cells using two different schedules and to analyze the resistance mechanism. Cells were exposed either continuously or intermittently to TFT, resulting in H630-cTFT and H630-4TFT, respectively. Cells were analyzed for cross-resistance, cell cycle, protein expression, and activity of thymidine phosphorylase (TP), thymidine kinase (TK), thymidylate synthase (TS), equilibrative nucleoside transporter (hENT), gene expression (microarray), and genomic alterations. Both cell lines were cross-resistant to 2'-deoxy-5-fluorouridine (>170-fold). Exposure to IC(75)-TFT increased the S/G(2)-M phase of H630 cells, whereas in the resistant variants, no change was observed. The two main target enzymes TS and TP remained unchanged in both TFT-resistant variants. In H630-4TFT cells, TK protein expression and activity were decreased, resulting in less activated TFT and was most likely the mechanism of TFT resistance. In H630-cTFT cells, hENT mRNA expression was decreased 2- to 3-fold, resulting in a 5- to 10-fold decreased TFT-nucleotide accumulation. Surprisingly, microarray-mRNA analysis revealed a strong increase of secretory phospholipase-A2 (sPLA2; 47-fold), which was also found by reverse transcription-PCR (RT-PCR; 211-fold). sPLA2 inhibition reversed TFT resistance partially. H630-cTFT had many chromosomal aberrations, but the exact role of sPLA2 in TFT resistance remains unclear. Altogether, resistance induction to TFT can lead to different mechanisms of resistance, including decreased TK protein expression and enzyme activity, decreased hENT expression, as well as (phospho)lipid metabolism. Mol Cancer Ther; 9(4); 1047-57. (c)2010 AACR.

Gemcitabine chemoresistance in pancreatic cancer: molecular mechanisms and potential solutions

Ductal pancreatic adenocarcinoma is associated with a very poor prognosis and most patients are given palliative care. Chemotherapy in the form of gemcitabine has been found to reduce disease-related pain, and the otherwise frequently occurring weight changes, to increase Karnofsky performance status and quality of life and has also resulted in a modest improvement in survival time. The intracellular uptake of gemcitabine is dependent on nucleoside transporters, predominantly human equilibrative nucleoside transporter-1 (hENT-1), which is over-expressed in human pancreatic adenocarcinoma cells. Cellular resistance to gemcitabine can be intrinsic or acquired during gemcitabine treatment. One of the mechanisms is a decrease in hENT-1 expression. Modifications of gemcitabine not rendering it dependent on the nucleoside transporter may be a successful future mode of chemotherapy treatment, and determination of the nucleoside receptor status at the time of diagnosis could potentially also contribute to a more targeted therapy in the future.

In situ protein expression of RRM1, ERCC1, and BRCA1 in metastatic breast cancer patients treated with gemcitabine-based chemotherapy

Ribonucleotide reductase 1 (RRM1) is a determinant of gemcitabine efficacy in non-small-cell lung cancer and pancreatic cancer. We investigated the protein levels of RRM1 and two other DNA repair enzymes, ERCC1 and BRCA1, in 55 metastatic breast cancer (MBC) patients undergoing gemcitabine-based chemotherapy. With automated in situ protein quantification (AQUA v1.6), the average scores for RRM1, ERCC1, and BRCA1 ranged from 245.6-2774.1, 74.0-410.3, and 54.4-1833.1, respectively. They were significantly associated with each other (Spearman's rho > or = .36; p < or = .007). Given their pattern of distribution, RRM1 and BRCA1 are potentially suitable markers for clinical decision making in MBC.

Antiproliferative activity, mechanism of action and oral antitumor activity of CP-4126, a fatty acid derivative of gemcitabine, in in vitro and in vivo tumor models

Gemcitabine is a deoxycytidine (dCyd) analog with activity in leukemia and solid tumors, which requires phosphorylation by deoxycytidine kinase (dCK). Decreased membrane transport is a mechanism of resistance to gemcitabine. In order to facilitate gemcitabine uptake and prolong retention in the cell, a lipophilic pro-drug was synthesized (CP-4126), with an elaidic fatty acid esterified at the 5'position. CP-4126 was tested in cell lines resistant to cytarabine, another dCyd analog or gemcitabine. Activity of gemcitabine and the derivative was comparable in the parent cell lines, while in dCK deficient cells all compounds were inactive. However, inhibition of nucleoside transport increased the IC(50) for gemcitabine up to 200-fold, but not for CP-4126, underlining the independence of a nucleoside transporter. For in vivo evaluation, nude mice bearing a human xenograft were treated intraperitoneally every third day for five doses at the maximal tolerated dose. In melanoma, sarcoma, lung, prostate, pancreatic and breast cancer xenografts, gemcitabine and CP-4126 were equally and highly effective; in four other xenografts moderately but equally active. In contrast to gemcitabine, CP-4126 could be administered orally, with a schedule and dose dependent toxicity and antitumor activity. In a colon cancer xenograft, antitumor activity of orally administered CP-4126 was equal to the intraperitoneally administered drug. In conclusion, CP-4126 is membrane transporter independent. Intraperitoneally administered CP-4126 was as effective as gemcitabine in several xenografts and CP-4126 is tolerated when orally administered. CP-4126 seems to be a promising new anticancer drug.