Immunohistochemical and genetic evaluation of deoxycytidine kinase in pancreatic cancer: relationship to molecular mechanisms of gemcitabine resistance and survival

Genomic profiling guides the choice of molecular targeted therapy of pancreatic cancer

Pancreatic cancer has the worst five-year survival rate of all malignancies due to its aggressive progression and resistance to therapy. Current therapies are limited to gemcitabine-based chemotherapeutics, surgery, and radiation. The current trend toward "personalized genomic medicine" has the potential to improve the treatment options for pancreatic cancer. Gene identification and genetic alterations like single nucleotide polymorphisms and mutations will allow physicians to predict the efficacy and toxicity of drugs, which could help diagnose pancreatic cancer, guide neoadjuvant or adjuvant treatment, and evaluate patients' prognosis. This article reviews the multifaceted roles of genomics and pharmacogenomics in pancreatic cancer.

Gemcitabine-based therapy for pancreatic cancer using the squalenoyl nucleoside monophosphate nanoassemblies

Gemcitabine is currently the most effective agent against advanced pancreatic cancer. However, the major therapeutic hurdles using gemcitabine include rapid inactivation by blood deaminases and fast development of cell chemoresistance, induced by down-regulation of deoxycytidine kinase or nucleoside transporters. To overcome the above drawbacks we designed recently a novel nanomedicine strategy based on squalenoyl prodrug of 5'-monophosphate gemcitabine (SQdFdC-MP). This amphiphilic conjugate self-organized in water into unilamellar vesicles with a mean diameter of 100 nm. In this study the antitumor efficacy of SQdFdC-MP nanoassemblies (NAs) on chemoresistant and chemosensitive pancreatic adenocarcinoma models have been investigated. Cell viability assays showed that SQdFdC-MP NAs displayed higher antiproliferative and cytotoxic effects, particularly in chemoresistant pancreatic tumor cells. In in vivo studies, SQdFdC-MP NAs decreased significantly the growth (∼70%) of human MiaPaCa2 xenografts, also preventing tumor cell invasion, whereas native dFdC did not display any anticancer activity when tumor growth inhibition was only 35% with SQdFdC NAs. These results correlated with a reduction of Ki-67 antigen and the induction of apoptosis mediated by caspase-3 activation in tumor cells. These findings demonstrated the feasibility of utilizing SQdFdC-MP NAs to make tumor cells more sensitive to gemcitabine and thus providing an efficient new therapeutic alternative for pancreatic adenocarcinoma.

Targeting the Warburg effect with a novel glucose transporter inhibitor to overcome gemcitabine resistance in pancreatic cancer cells

Gemcitabine resistance remains a significant clinical challenge. Here, we used a novel glucose transporter (Glut) inhibitor, CG-5, as a proof-of-concept compound to investigate the therapeutic utility of targeting the Warburg effect to overcome gemcitabine resistance in pancreatic cancer. The effects of gemcitabine and/or CG-5 on viability, survival, glucose uptake and DNA damage were evaluated in gemcitabine-sensitive and gemcitabine-resistant pancreatic cancer cell lines. Mechanistic studies were conducted to determine the molecular basis of gemcitabine resistance and the mechanism of CG-5-induced sensitization to gemcitabine. The effects of CG-5 on gemcitabine sensitivity were investigated in a xenograft tumor model of gemcitabine-resistant pancreatic cancer. In contrast to gemcitabine-sensitive pancreatic cancer cells, the resistant Panc-1 and Panc-1(GemR) cells responded to gemcitabine by increasing the expression of ribonucleotide reductase M2 catalytic subunit (RRM2) through E2F1-mediated transcriptional activation. Acting as a pan-Glut inhibitor, CG-5 abrogated this gemcitabine-induced upregulation of RRM2 through decreased E2F1 expression, thereby enhancing gemcitabine-induced DNA damage and inhibition of cell survival. This CG-5-induced inhibition of E2F1 expression was mediated by the induction of a previously unreported E2F1-targeted microRNA, miR-520f. The addition of oral CG-5 to gemcitabine therapy caused greater suppression of Panc-1(GemR) xenograft tumor growth in vivo than either drug alone. Glut inhibition may be an effective strategy to enhance gemcitabine activity for the treatment of pancreatic cancer.

Patient-derived xenograft models: an emerging platform for translational cancer research

Recently, there has been an increasing interest in the development and characterization of patient-derived tumor xenograft (PDX) models for cancer research. PDX models mostly retain the principal histologic and genetic characteristics of their donor tumor and remain stable across passages. These models have been shown to be predictive of clinical outcomes and are being used for preclinical drug evaluation, biomarker identification, biologic studies, and personalized medicine strategies. This article summarizes the current state of the art in this field, including methodologic issues, available collections, practical applications, challenges and shortcomings, and future directions, and introduces a European consortium of PDX models.

SIGNIFICANCE

PDX models are increasingly used in translational cancer research. These models are useful for drug screening, biomarker development, and the preclinical evaluation of personalized medicine strategies. This review provides a timely overview of the key characteristics of PDX models and a detailed discussion of future directions in the field.

Gemcitabine: metabolism and molecular mechanisms of action, sensitivity and chemoresistance in pancreatic cancer

Gemcitabine is the first-line treatment for pancreatic adenocarcinoma, but is increasingly used to treat breast, bladder, and non-small cell lung cancers. Despite such broad use, intrinsic and acquired chemoresistance is common. In general, the underlying mechanisms of chemoresistance are poorly understood. Here, current knowledge of gemcitabine metabolism, mechanisms of action, sensitivity and chemoresistance reported over the past two decades are reviewed; and we also offer new perspectives to improve gemcitabine efficacy with particular reference to the treatment of pancreatic cancer.

Cholangiocarcinoma cell line TK may be useful for the pharmacokinetic study of the chemotherapeutic agent gemcitabine

Cholangiocarcinoma is a disease with a poor prognosis. A human cholangiocarcinoma cell line, TK, was previously established to enable further understanding of the disease. We conducted this investigation to determine whether or not the TK line is useful for pharmacokinetic study of the chemotherapeutic agent gemcitabine (GEM). Along with the BXPC3 human pancreatic adenocarcinoma cell line, the sensitivity to and effects on the TK cell line of GEM were compared. The influence of deoxycytidine kinase (dCK) transduction was also comparatively investigated. The effects of GEM in terms of drug sensitivity of the TK cell line, cell cycle and levels of transcripts of key enzymes were comparable to the BXPC3 cell line. Responses to the drug were similar in both cell lines. In contrast to pancreatic carcinoma, cell lines for research on cholangiocarcinoma have been limited. This study suggests the application of the TK cell line to the pharmacokinetic study of the chemosensitization of therapeutic drugs, such as GEM.

Facile method for determination of deoxycytidine kinase activity in biological milieus

A new analytical method for determining deoxycytidine kinase (dCK) activity in biological milieus using luminescence is reported here. This method, based on utilizing adenosine triphosphate (ATP) as the sole phosphate donor in the kinase reaction and monitoring ATP consumption via a luciferase-based chemiluminescence reaction, is capable of detecting dCK activity without the use of specific substrates or radioisotope techniques. Comparing with the reverse-phase high-performance liquid chromatography method, this new method is suggested to be efficient and sensitive. Further, application of the proposed method for profiling dCK activity in cultured cancer cells revealed that a cervix cell line exhibited the highest dCK activity to gemcitabine metabolism.

Do hENT1 and RRM1 predict the clinical benefit of gemcitabine in pancreatic cancer?

Gemcitabine is a nucleoside analog that is indicated in the treatment of pancreatic cancer. In order to provide a better use of this drug, the search for immunohistological markers is a hot topic in the field of pancreatic cancer. In particular, the use of nucleoside transporter hENT1 and the intracellular target of gemcitabine RRM1 are current subjects for discussion. We have analyzed the majority of studies of hENT1 and RRM1 on pancreatic cancer, and will discuss the further directions that might be followed in order to integrate these proteins in routine clinical practice. The data that is currently available would benefit from the completion of well-designed randomized trials in order to confirm the clinical value of hENT1 and RRM1 as biomarkers in pancreatic cancer patients.

An innovative hydrogel of gemcitabine-loaded lipid nanocapsules: when the drug is a key player of the nanomedicine structure

A new method to form a nanoparticle-structured hydrogel is reported; it is based on the drug being loaded into the nanoparticles to form a solid structure. A lipophilic form of gemcitabine (modified lauroyl), an anti-cancer drug, was encapsulated in lipid nanocapsules (LNCs), using a phase-inversion temperature process. A gel was formed spontaneously, depending on the LNC concentration. The drug loading, measured with total entrapment efficiency, and the rheological properties of the gel were assessed. Physical studies (surface tension measurements) showed that modified gemcitabine was localised at the oil-water interface of the LNC, and that the gemcitabine moieties of the prodrug were exposed to the water phase. This particular assembly promoted inter-LNC interactions via hydrogen bonds between gemcitabine moieties that led to an LNC gel structure in water, without a matrix, like a tridimensional pearl necklace. Dilution of the gel produced a gemcitabine-loaded LNC suspension in water, and these nanoparticles presented cytotoxic activity to various cancer cell lines to a greater degree than the native drug. Finally, the syringeability of the formulation was successfully tested and perspectives of its use as a nanomedicine (intratumoural or subcutaneous injection) can be foreseen.

dCK expression correlates with 5-fluorouracil efficacy and HuR cytoplasmic expression in pancreatic cancer: a dual-institutional follow-up with the RTOG 9704 trial

Deoxycytidine kinase (dCK) and human antigen R (HuR) have been associated with response to gemcitabine in small studies. The present study investigates the prognostic and predictive value of dCK and HuR expression levels for sensitivity to gemcitabine and 5-fluorouracil (5-FU) in a large phase III adjuvant trial with chemoradiation backbone in pancreatic ductal adenocarcinoma (PDA). The dCK and HuR expression levels were determined by immunohistochemistry on a tissue microarray of 165 resected PDAs from the Radiation Therapy Oncology Group (RTOG) 9704 trial. Association with overall survival (OS) and disease-free survival (DFS) status were analyzed using the log-rank test and the Cox proportional hazards model. Experiments with cultured PDA cells were performed to explore mechanisms linking dCK and HuR expression to drug sensitivity. dCK expression levels were associated with improved OS for all patients analyzed from RTOG 9704 (HR: 0.66, 95% CI [0.47-0.93], P = 0.015). In a subset analysis based on treatment arm, the effect was restricted to patients receiving 5-FU (HR: 0.53, 95% CI [0.33-0.85], P = 0.0078). Studies in cultured cells confirmed that dCK expression rendered cells more sensitive to 5-FU. HuR cytoplasmic expression was neither prognostic nor predictive of treatment response. Previous studies along with drug sensitivity and biochemical studies demonstrate that radiation interferes with HuR's regulatory effects on dCK, and could account for the negative findings herein based on the clinical study design (i.e., inclusion of radiation). Finally, we demonstrate that 5-FU can increase HuR function by enhancing HuR translocation from the nucleus to the cytoplasm, similar to the effect of gemcitabine in PDA cells. For the first time, in the pre-treatment tumor samples, dCK and HuR cytoplasmic expression were strongly correlated (chi-square P = 0.015). This dual-institutional follow up study, in a multi-institutional PDA randomized clinical trial, observed that dCK expression levels were prognostic and had predictive value for sensitivity to 5-FU.

A meta-analysis of gemcitabine biomarkers in patients with pancreaticobiliary cancers

OBJECTIVES

The objective of this study was to summarize all clinical studies evaluating the prognostic role of gemcitabine (GEM) metabolic genes in pancreaticobiliary (PB) cancer patients receiving GEM therapy in the neoadjuvant, adjuvant, or palliative settings.

METHODS

Meta-analyses were performed to calculate the pooled hazard ratios for each gene by each clinical outcome (overall survival [OS], disease-free survival [DFS], and progression-free survival) using a random-effects approach.

RESULTS

The search strategy identified 16 eligible studies, composed of 632 PB patients total, with moderate quality. Compared with low expression, pooled hazard ratios for OS of hENT1, dCK, RRM1, RRM2, and DPD were 0.37 (95% confidence interval [CI], 0.28-0.47), 0.40 (95% CI, 0.20-0.80), 2.21 (95% CI, 1.12-4.36), 2.13 (95% CI, 1.00-4.52), and 1.91 (95% CI, 1.16-3.17), respectively. A similar trend was observed for each of these biomarkers in DFS and progression-free survival prognostication. Subgroup analyses for hENT1 showed a comparable survival correlation in the adjuvant and palliative settings.

CONCLUSIONS

High expression of hENT1 in PB cancer patients receiving GEM-based adjuvant therapy is associated with improved OS and DFS and may be the best examined prognostic marker to date. Evidence for other biomarkers is limited by a small number of publications investigating these markers.

Human equilibrative nucleoside transporter 1 (hENT1): do we really have a new predictive biomarker of chemotherapy outcome in pancreatic cancer patients?

Although systemic chemotherapy significantly improves the overall survival of pancreatic cancer patients, the prognosis remains extremely poor. The development of a drug resistance, either de novo or induced resistance, significantly limits the effectiveness of chemotherapy. SLC29A1 gene encodes human equilibrative nucleoside transporter 1 (hENT1) protein that is mediating the transport of nucleotides, both purines and pyrimidines, into the tumor cells. The aim of this mini-review is to summarize the current information concerning the prognostic and predictive role of SLC29A1 transporter (hENT1) expression in pancreatic cancer. Increased expression of SLC29A1 in vitro has been described as a potential critical factor determining the sensitivity of pancreatic cancer cells to gemcitabine and 5-fluorouracil, the principal cytotoxic agents used in the treatment of pancreatic cancer. The reports on the relationship between SLC29A1 expression and prognosis of patients with pancreatic cancer are currently rather conflicting. However, majority of studies on patients with resected pancreatic cancer have suggested that high SLC29A1expression may be predictive of improved survival in patients treated with gemcitabine. SLC29A1 has not been shown to represent a predictive biomarker for patients treated by 5-fluorouracil. In conclusion, potential prognostic and predictive role of SLC29A1 has been demonstrated for selected subset of patients.

Post-transcriptional controls by ribonucleoprotein complexes in the acquisition of drug resistance

Acquisition of drug resistance leads to failure of anti-cancer treatments and therapies. Although several successive chemotherapies are available, along with efforts towards clinical applications of new anti-cancer drugs, it is generally realized that there is a long way to go to treat cancers. Resistance to anti-cancer drugs results from various factors, including genetic as well as epigenetic differences in tumors. Determining the molecular and cellular mechanisms responsible for the acquisition of drug resistance may be a helpful approach for the development of new therapeutic strategies to overcome treatment failure. Several studies have shown that the acquisition of drug resistance is tightly regulated by post-transcriptional regulators such as RNA binding proteins (RBPs) and microRNAs (miRNAs), which change the stability and translation of mRNAs encoding factors involved in cell survival, proliferation, epithelial-mesenchymal transition, and drug metabolism. Here, we review our current understanding of ribonucleoprotein complexes, including RBPs and miRNAs, which play critical roles in the acquisition of drug resistance and have potential clinical implications for cancer.

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.

RABL6A Promotes Oxaliplatin Resistance in Tumor Cells and Is a New Marker of Survival for Resected Pancreatic Ductal Adenocarcinoma Patients

Pancreatic ductal adenocarcinoma (PDAC) is characterized by early recurrence following pancreatectomy, rapid progression, and chemoresistance. Novel prognostic and predictive biomarkers are urgently needed to both stratify patients for clinical trials and select patients for adjuvant therapy regimens. This study sought to determine the biological significance of RABL6A (RAB, member RAS oncogene family-like protein 6 isoform A), a novel pancreatic protein, in PDAC. Analyses of RABL6A protein expression in PDAC specimens from 73 patients who underwent pancreatic resection showed that RABL6A levels are altered in 74% of tumors relative to adjacent benign ductal epithelium. Undetectable RABL6A expression, found in 7% (5/73) of patients, correlated with improved overall survival (range 41 to 118 months with 3/5 patients still living), while patients with RABL6A expression had a worse outcome (range 3.3 to 100 months, median survival 20.3 months) (P = 0.0134). In agreement with those findings, RABL6A expression was increased in pancreatic cancer cell lines compared to normal pancreatic epithelial cells, and its knockdown inhibited pancreatic cancer cell proliferation and induced apoptosis. Moreover, RABL6A depletion selectively sensitized cells to oxaliplatin-induced arrest and death. This work reveals that RABL6A promotes the proliferation, survival, and oxaliplatin resistance of PDAC cells, whereas its loss is associated with extended survival in patients with resected PDAC. Such data suggest RABL6A is a novel biomarker of PDAC and potential target for anticancer therapy.

Mitoxantrone targets human ubiquitin-specific peptidase 11 (USP11) and is a potent inhibitor of pancreatic cancer cell survival

Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related death in the United States, with a 95% five-year mortality rate. For over a decade, gemcitabine (GEM) has been the established first-line treatment for this disease despite suboptimal response rates. The development of PARP inhibitors that target the DNA damage repair (DDR) system in PDA cells has generated encouraging results. Ubiquitin-specific peptidase 11 (USP11), an enzyme that interacts with the DDR protein BRCA2, was recently discovered to play a key role in DNA double-strand break repair and may be a novel therapeutic target. A systematic high-throughput approach was used to biochemically screen 2,000 U.S. Food and Drug Administration (FDA)-approved compounds for inhibition of USP11 enzymatic activity. Six pharmacologically active small molecules that inhibit USP11 enzymatic activity were identified. An in vitro drug sensitivity assay demonstrated that one of these USP11 inhibitors, mitoxantrone, impacted PDA cell survival with an IC50 of less than 10 nM. Importantly, across six different PDA cell lines, two with defects in the Fanconi anemia/BRCA2 pathway (Hs766T and Capan-1), mitoxantrone is 40- to 20,000-fold more potent than GEM, with increased endogenous USP11 mRNA levels associated with increased sensitivity to mitoxantrone. Interestingly, USP11 silencing in PDA cells also enhanced sensitivity to GEM. These findings establish a preclinical model for the rapid discovery of FDA-approved compounds and identify USP11 as a target of mitoxantrone in PDA.

IMPLICATIONS

This high-throughput approach provides a strong rationale to study mitoxantrone in an early-phase clinical setting for the treatment of PDA.

Clinicopathological significance of deoxycytidine kinase expression in esophageal squamous cell carcinoma

Deoxycytidine kinase (dCK) mediates the rate-limiting catabolic step in the activation of gemcitabine. Gemcitabine is a key drug for pancreatic and biliary tract cancer. However, gemcitabine is not widely used for esophageal squamous cell carcinoma (ESCC). In this study, we analyzed the expression of dCK in ESCC and evaluated the possibility of gemcitabine treatment for ESCC. In total, 76 ESCC patients who underwent esophagectomy between 1990 and 2008 were analyzed. dCK expression was analyzed immunohistochemically using tissue microarray and compared to the clinocopathological characteristics of the patients. Results identified 41 patients positive for dCK and 35 patients negative for dCK. A significant association was observed between dCK expression and gender (P=0.01), whereas the remaining factors were not associated with dCK expression. Prognosis of the patients with a high dCK expression was significantly worse than that of the patients with a low dCK expression (P=0.022). Furthermore, dCK expression was an independent prognostic factor regarding cause-specific prognosis (risk ratio, 2.2; P=0.031). In conclustion, the results of the present study suggested that dCK expression is a prognostic factor of the ESCC patients.

A retrospective study of chemotherapy with cisplatin plus gemcitabine after the failure of gemcitabine monotherapy for biliary tract cancer

OBJECTIVE

Before the ABC-02 trial, because there was no standard chemotherapy for patients with advanced biliary tract cancer, we treated them with gemcitabine alone. However, recently cisplatin plus gemcitabine became the standard first-line chemotherapy. We assessed the benefits of gemcitabine plus cisplatin chemotherapy after failed gemcitabine monotherapy.

METHODS

We retrospectively examined patients with advanced biliary tract cancer who were treated with gemcitabine plus cisplatin chemotherapy after failed gemcitabine monotherapy. They had adequate organ function, including renal function and Eastern Cooperative Oncology Group performance status 0-1. The treatment consisted of cisplatin (25 mg/m(2) of body surface area) plus gemcitabine (1000 mg/m(2)) on Days 1 and 8 for every 3 weeks.

RESULTS

Between December 2010 and January 2013, 20 patients were treated. The median age was 63 years. There were 15 males and 5 females. The ratio of intrahepatic bile duct, gall bladder and extrahepatic bile duct was 9:6:5. The ratio of locally advanced and metastatic disease was 2:18, and the ratio of PS0 and PS1 was 5:15. The objective response rate was 15.0%, and the tumour control rate was 60.0%. The median progression-free survival was 6.5 months (95% confidence interval, 2.1-6.9 months). The median overall survival was 13.7 months (95% confidence interval, 8.3-19.7 months). Grade 3-4 toxic events included neutropenia (30%), anaemia (20%) and thrombocytopenia (5%).

CONCLUSION

Cisplatin plus gemcitabine could be an optional therapy for unresectable or recurrent biliary tract cancer after failed gemcitabine monotherapy.

Hypoxia-induced deoxycytidine kinase expression contributes to apoptosis in chronic lung disease

Chronic obstructive pulmonary disease (COPD) is characterized by persistent inflammation and tissue remodeling and is a leading cause of death in the United States. Increased apoptosis of pulmonary epithelial cells is thought to play a role in COPD development and progression. Identification of signaling pathways resulting in increased apoptosis in COPD can be used in the development of novel therapeutic interventions. Deoxyadenosine (dAdo) is a DNA breakdown product that amplifies lymphocyte apoptosis by being phosphorylated to deoxyadenosine triphosphate (dATP). dAdo is maintained at low levels by adenosine deaminase (ADA). This study demonstrated that mice lacking ADA developed COPD manifestations in association with elevated dAdo and dATP levels and increased apoptosis in the lung. Deoxycitidine kinase (DCK), a major enzyme for dAdo phosphorylation, was up-regulated in mouse and human airway epithelial cells in association with air-space enlargement. Hypoxia was identified as a novel regulator of DCK, and inhibition of DCK resulted in diminished dAdo-mediated apoptosis in the lungs. Our results suggest that activating the dAdo-DCK-dATP pathway directly results in increased apoptosis in the lungs of mice with air-space enlargement and suggests a novel therapeutic target for the treatment of COPD.

Algorithmic modeling quantifies the complementary contribution of metabolic inhibitions to gemcitabine efficacy

Gemcitabine (2,2-difluorodeoxycytidine, dFdC) is a prodrug widely used for treating various carcinomas. Gemcitabine exerts its clinical effect by depleting the deoxyribonucleotide pools, and incorporating its triphosphate metabolite (dFdC-TP) into DNA, thereby inhibiting DNA synthesis. This process blocks the cell cycle in the early S phase, eventually resulting in apoptosis. The incorporation of gemcitabine into DNA takes place in competition with the natural nucleoside dCTP. The mechanisms of indirect competition between these cascades for common resources are given with the race for DNA incorporation; in clinical studies dedicated to singling out mechanisms of resistance, ribonucleotide reductase (RR) and deoxycytidine kinase (dCK) and human equilibrative nucleoside transporter1 (hENT1) have been associated to efficacy of gemcitabine with respect to their roles in the synthesis cascades of dFdC-TP and dCTP. However, the direct competition, which manifests itself in terms of inhibitions between these cascades, remains to be quantified. We propose an algorithmic model of gemcitabine mechanism of action, verified with respect to independent experimental data. We performed in silico experiments in different virtual conditions, otherwise difficult in vivo, to evaluate the contribution of the inhibitory mechanisms to gemcitabine efficacy. In agreement with the experimental data, our model indicates that the inhibitions due to the association of dCTP with dCK and the association of gemcitabine diphosphate metabolite (dFdC-DP) with RR play a key role in adjusting the efficacy. While the former tunes the catalysis of the rate-limiting first phosphorylation of dFdC, the latter is responsible for depletion of dCTP pools, thereby contributing to gemcitabine efficacy with a dependency on nucleoside transport efficiency. Our simulations predict the existence of a continuum of non-efficacy to high-efficacy regimes, where the levels of dFdC-TP and dCTP are coupled in a complementary manner, which can explain the resistance to this drug in some patients.

Systemic therapies for pancreatic cancer--the role of pharmacogenetics

Effective systemic treatment of pancreatic cancer remains a major challenge, with progress hampered by drug resistance and treatment related toxicities. Currently available cytotoxic agents as monotherapy or in combination have provided only a modest survival benefit for patients with advanced disease. Disappointing phase III results with gemcitabine-based combinations in patients with advanced pancreatic cancer might be related to poor efficacy of systemic therapies in unselected patients. Future research strategies should prioritize identification of predictive markers through pharmacogenetic investigations. The individualization of patient treatment through pharmacogenetics may help to improve outcome by maximizing efficacy whilst lowering toxicity. This review provides an update on the pharmacogenetics of pancreatic cancer treatment and its influence on treatment benefits and toxicity.

Systemic therapies for pancreatic cancer--the role of pharmacogenetics

Effective systemic treatment of pancreatic cancer remains a major challenge, with progress hampered by drug resistance and treatment related toxicities. Currently available cytotoxic agents as monotherapy or in combination have provided only a modest survival benefit for patients with advanced disease. Disappointing phase III results with gemcitabine-based combinations in patients with advanced pancreatic cancer might be related to poor efficacy of systemic therapies in unselected patients. Future research strategies should prioritize identification of predictive markers through pharmacogenetic investigations. The individualization of patient treatment through pharmacogenetics may help to improve outcome by maximizing efficacy whilst lowering toxicity. This review provides an update on the pharmacogenetics of pancreatic cancer treatment and its influence on treatment benefits and toxicity.

Gemcitabine versus Modified Gemcitabine: a review of several promising chemical modifications

Gemcitabine, an anticancer agent which acts against a wide range of solid tumors, is known to be rapidly deaminated in blood to the inactive metabolite 2',2'-difluorodeoxyuridine and to be rapidly excreted by the urine. Moreover, many cancers develop resistance against this drug, such as loss of transporters and kinases responsible for the first phosphorylation step. To increase its therapeutic levels, gemcitabine is administered at high doses (1000 mg/m(2)) causing side effects (neutropenia, nausea, and so forth). To improve its metabolic stability and cytotoxic activity and to limit the phenomena of resistance many alternatives have emerged, such as the synthesis of prodrugs. Modifying an anticancer agent is not new; paclitaxel or ara-C has been subjected to such changes. This review summarizes the various chemical modifications that can be found in the 4-(N)- and 5'-positions of gemcitabine. They can provide (i) a protection against deamination, (ii) a better storage and (iii) a prolonged release in the cell, (iv) a possible use in the case of deoxycytidine kinase deficiency, and (v) transporter deficiency. These new gemcitabine-based sysems have the potential to improve the clinical outcome of a chemotherapy strategy.

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.

Overcoming nucleoside analog chemoresistance of pancreatic cancer: a therapeutic challenge

Clinical refractoriness to nucleoside analogs (e.g., gemcitabine, capecitabine) is a major scientific problem and is one of the main reasons underlying the extremely poor prognostic state of pancreatic cancer. The drugs' effects are suboptimal partly due to cellular mechanisms limiting their transport, activation, and overall efficacy. Nonetheless, novel therapeutic approaches are presently under study to circumvent nucleoside analog resistance in pancreatic cancer. With these new approaches come additional challenges to be addressed. This review describes the determinants of chemoresistance in the gemcitabine cytotoxicity pathways, provides an overview of investigational approaches for overcoming chemoresistance, and discusses new challenges presented. Understanding the future directions of the field may assist in the successful development of novel treatment strategies for enhancing chemotherapeutic efficacy in pancreatic cancer.

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.

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.

Identification of NME5 as a contributor to innate resistance to gemcitabine in pancreatic cancer cells

The limited therapeutic effect of gemcitabine on pancreatic cancer is largely attributed to pre-existing or acquired resistance of the tumor cells. This study was aimed at screening for candidate resistance-related gene(s) and elucidating the underlying mechanisms. NME5 was found to be highly expressed in an innate gemcitabine-resistant human pancreatic cancer sample and the cell line PAXC002 derived from the sample. Downregulation of NME5 significantly reversed gemcitabine resistance in PAXC002 cells, whereas NME5 overexpression induced gemcitabine resistance in the pancreatic cancer cell line BxPC-3. NME5 attenuated the induction of apoptosis and cell cycle arrest induced by gemcitabine, probably accounting for the blunted sensitivity to gemcitabine. Furthermore, NME5 was demonstrated to play its role in a nuclear factor kappaB (NF-κB)-dependent manner. NME5 was capable of directly binding NF-κB, and possibly regulated its expression level in PAXC002 cells. Our results also suggest that NF-κB is a key executor of NME5 in regulating apoptosis and cell cycle. All of these data suggest that NME5 is a promising target for relieving innate gemcitabine resistance in pancreatic cancer cells.

Genomics and pharmacogenomics of pancreatic adenocarcinoma

The last decade has brought significant advances in the development of molecularly targeted therapies for treatment of a variety of human malignancies. In contrast to other solid tumors, however, the impact of novel therapeutic strategies on clinical outcomes in patients with pancreas adenocarcinoma (PAC) has been limited to date. Gemcitabine was established as a standard of care for treatment of advanced PAC in 1997 based on an observed improvement in clinical benefit as adjudicated principally by pain scores and analgesic consumption, and demonstration of an overall survival (OS) benefit in a randomized comparison with 5-fluorouracil (5-FU). Since then, multiple agents targeting oncogenic signaling pathways and mediators of angiogenesis have failed to improve outcomes in phase III clinical trials when compared with gemcitabine monotherapy. An exception to this is the anti-epidermal growth factor receptor therapy erlotinib, which yielded a survival benefit in patients with advanced disease in combination with gemcitabine compared with gemcitabine alone, although this was a marginal incremental improvement for which the clinical significant has been heavily debated. More recently, the most significant therapeutic advance in PAC has come from the combination of several cytotoxic agents; infusional 5-FU, irinotecan and oxaliplatin. This combination chemotherapy regimen, known as FOLFIRINOX, improved survival in patients with an excellent functional status and stage IV disease by 4.3 months compared with gemcitabine alone. This improvement in survival did come at the cost expectedly of a significant increase in toxicities, including gastrointestinal and hematologic particularly. Other gemcitabine-based combination chemotherapy regimens including gemcitabine and platinum analogs and gemcitabine and capecitabine have consistently shown an increased response rate but no OS benefit in individual trials; albeit pooled and meta-analyses have indicated a survival benefit in good performance status patient for both these cytotoxic combinations. Accordingly, the 5-year survival for patients with PAC remains <5%, with an annual disease-specific mortality which approaches the incidence. The challenge remains therefore, to develop more effective systemic therapies against this challenging malignancy. Recent progress toward understanding the genetic events in the development of PAC, in combination with advances in the field of pharmacogenomics offer hope that we may build on achievements to-date to develop more effective therapeutic strategies for PAC in years to come.

Molecular predictors of gemcitabine response in pancreatic cancer

Gemcitabine is one of the most used anti-neoplastic drugs with documented activity in almost all major localizations of cancer. In pancreatic cancer treatment, gemcitabine occupies a prominent place as a first line chemotherapy, partly because of the paucity of other efficacious chemotherapy options. In fact, only a minority of pancreatic cancer patients display a response or even stability of disease with the drug. There are currently no clinically applicable means of predicting which patient will derive a clinical benefit from gemcitabine although several proposed markers have been studied. These markers are proteins involved in drug up-take, activation and catabolism or proteins that define the ability of the cell to undergo apoptosis in response to the drug. Several of these markers are reviewed in this paper. We also briefly discuss the possible role of stem cells in drug resistance to gemcitabine.

Challenges of drug resistance in the management of pancreatic cancer

The current treatment of choice for metastatic pancreatic cancer involves single-agent gemcitabine or a combination of gemcitabine with capecitabine or erlotinib (a tyrosine kinase inhibitor). Only 25&#x2013;30% of patients respond to this treatment and patients who do respond initially ultimately exhibit disease progression. Median survival for pancreatic cancer patients has reached a plateau due to inherent and acquired resistance to these agents. Key molecular factors implicated in this resistance include: deficiencies in drug uptake, alteration of drug targets, activation of DNA repair pathways, resistance to apoptosis and the contribution of the tumor microenvironment. Moreover, for newer agents including tyrosine kinase inhibitors, overexpression of signaling proteins, mutations in kinase domains, activation of alternative pathways, mutations of genes downstream of the target and/or amplification of the target represent key challenges for treatment efficacy. Here we will review the contribution of known mechanisms and markers of resistance to key pancreatic cancer drug treatments.

Deoxycytidine kinase is overexpressed in poor outcome breast cancer and determines responsiveness to nucleoside analogs

Only a minority of breast cancer patients responds to chemotherapy and we lack predictive biomarkers that help to select a patient-tailored therapy that takes into consideration the molecular heterogeneity of the cancer type. Responsiveness to the clinically important nucleoside analogs gemcitabine and decitabine may be critically determined by Deoxycytidine kinase (DCK) expression as this enzyme is required to convert the inactive prodrugs into their pharmacologically active forms. Here, we examined whether DCK is differentially expressed in breast cancer and evaluated whether DCK expression levels control responsiveness to these nucleoside analogs in vitro by experimentally modulating DCK expression levels. We examined DCK expression in gene expression data sets of breast tumors including the series of 295 consecutive patients that have been classified into low or high risk for recurrence using the MammaPrint 70 gene profile. We found that DCK is expressed at higher levels in patients having poor clinical outcome as judged by the MammaPrint assay. As such, patients that have a poor prognosis may thus be susceptible to treatment with nucleoside analogs. In support of this, we found a causal relationship between DCK levels and sensitivity to these nucleoside analogs in breast cancer cell lines. The data indicate that breast cancers that are at high risk of recurrence express higher levels of DCK, which we find to be strongly correlated to a favorable response to nucleoside analogs. The data suggest that DCK expression in breast cancer could be exploited to select patients that are likely to respond to treatment with nucleoside analogs.

Genexol inhibits primary tumour growth and metastases in gemcitabine-resistant pancreatic ductal adenocarcinoma

INTRODUCTION

Gemcitabine, the current standard of care for pancreatic ductal adenocarcinoma (PDA), has a less than 10% partial response rate. Genexol-PM, a modified form of paclitaxel, has been shown to have antitumour effects in clinical trials of metastatic breast and small-lung-cell carcinoma. The aim of the present study was to determine if Genexol would be a beneficial treatment for gemcitabine-resistant PDA.

MATERIALS AND METHODS

We measured the in vitro IC50s of gemcitabine and genexol in cell lines sensitive and resistant to gemcitabine. In vivo, animals with orthotopic pancreatic tumours, resistant to gemcitabine, were treated with phosphate-buffered saline (PBS), gemcitabine, Genexol or gemcitabine+Genexol. Tumour progression was monitored using red fluorescent protein imaging.

RESULTS

We showed equivalent IC50s for gemcitabine-sensitive and gemcitabine-resistant cell lines when treated with genexol. In vivo treatment with genexol resulted in a greater per cent reduction in tumour size, less metastatic spread and longer survival compared with treatment with gemcitabine.

DISCUSSION

Genexol proved to be an effective treatment for gemcitabine-resistant PDA. These data combined with the successful clinical use of genexol in Phase II trials of other malignancies suggests it maybe an effective treatment for pancreatic cancer, specifically for those patients resistant to gemcitabine.

Treatment of pancreatic cancer: what can we really predict today?

Managing pancreatic cancer remains a big challenge due to its worse course and prognosis. However, therapeutic options and multimodal strategies are increasing nowadays, including new agents, new regimens and chemoradiation. Recently, the FOLFIRTNOX regimen has been reported to be more active than gemcitabine in selected metastatic patients. In this setting, it will be of utmost interest to guide our therapeutic choice not only on clinical and pathological findings, but also on specific biomarkers that will predict tumor behavior and patient outcome (prognostic markers), and benefit from specific agents or regimens (predictive markers). In the near future, we will have to build both our therapeutic interventions and our clinical research based on an accurate patients' clinical selection and on biomolecular markers. In this review, we aimed to highlight and discuss some of the recent results reported on biomarkers in pancreatic cancer that may predict, i.e., preferential metastatic diffusion after surgery, like CXCR4, or predict gemcitabine efficacy in an adjuvant setting as well as in advanced disease, like hENT1. An important effort for translational research in pancreatic cancer research is thus required to validate such markers, while some important questions concerning tissue availability and processing, methodology of analysis, and design of future prospective trials, need to be addressed.

Integrating pharmacogenetics into gemcitabine dosing--time for a change?

Increasing the efficacy of anticancer agents and avoiding toxic effects is a critical issue in clinical oncology. Identifying biomarkers that predict clinical outcome would ensure improved patient care. Gemcitabine is widely used to treat various solid tumors as a single agent or in combination with other drugs. The therapeutic index of gemcitabine is narrow, and abnormal pharmacokinetics leading to changes in plasma exposure is a major cause of adverse effects. A number of biomarkers have been proposed to predict efficacy of gemcitabine, focusing on molecular determinants of response identified at the tumor level. Genetic and functional deregulations that affect the disposition of a drug could be the reason for life-threatening adverse effects or treatment failure. In particular, deregulation of cytidine deaminase, the enzyme responsible for detoxification of most nucleotide analogs, should be examined. Identifying and validating biomarkers for pharmacogenetic testing before administration of gemcitabine is a step towards personalized medicine.

Gene expression levels as predictive markers of outcome in pancreatic cancer after gemcitabine-based adjuvant chemotherapy

BACKGROUND AND AIMS

The standard palliative chemotherapy for pancreatic ductal adenocarcinoma (PDAC) is gemcitabine-based chemotherapy; however, PDAC still presents a major therapeutic challenge. The aims of this study were to investigate the expression pattern of genes involved in gemcitabine sensitivity in resected PDAC tissues and to determine correlations of gene expression with treatment outcome.

MATERIALS AND METHODS

We obtained formalin-fixed paraffin-embedded (FFPE) tissue samples from 70 patients with PDAC. Of the 70 patients, 40 received gemcitabine-based adjuvant chemotherapy (AC). We measured hENT1, dCK, CDA, RRM1, and RRM2 messenger RNA (mRNA) levels by quantitative real-time reverse transcription-polymerase chain reaction and determined the combined score (GEM score), based on the expression levels of hENT1, dCK, RRM1, and RRM2, to investigate the association with survival time. By determining the expression levels of these genes in endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) cytologic specimens, we investigated the feasibility of individualized chemotherapy.

RESULTS

High dCK (P = .0067), low RRM2 (P = .003), and high GEM score (P = .0003) groups had a significantly longer disease-free survival in the gemcitabine-treated group. A low GEM score (<2) was an independent predictive marker for poor outcome to gemcitabine-based AC as shown by multivariate analysis (P = .0081). Altered expression levels of these genes were distinguishable in microdissected neoplastic cells from EUS-FNA cytologic specimens.

CONCLUSIONS

Quantitative analyses of hENT1, dCK, RRM1, and RRM2 mRNA levels using FFPE tissue samples and microdissected neoplastic cells from EUS-FNA cytologic specimens may be useful in predicting the gemcitabine sensitivity of patients with PDAC.

Gemcitabine metabolic and transporter gene polymorphisms are associated with drug toxicity and efficacy in patients with locally advanced pancreatic cancer

BACKGROUND

It has not been well established whether genetic variations can be biomarkers for clinical outcome of gemcitabine therapy. The purpose of this study was to identify single nucleotide polymorphisms (SNPs) of gemcitabine metabolic and transporter genes that are associated with toxicity and efficacy of gemcitabine-based therapy in patients with locally advanced pancreatic cancer.

METHODS

The authors evaluated 17 SNPs of the CDA,dCK, DCTD, RRM1, hCNT1-3, and hENT1 genes in 149 patients with locally advanced pancreatic cancer who underwent gemcitabine-based chemoradiotherapy. The association of genotypes with neutropenia, tumor response to therapy, overall survival, and progression-free survival (PFS) was analyzed by logistic regression, log-rank test, Kaplan-Meier plot, and Cox proportional hazards regression.

RESULTS

The CDA A-76C, dCK C-1205T, RRM1 A33G, and hENT1 C913T genotypes were significantly associated with grade 3 to 4 neutropenia (P = .020, .015, .003, and .017, respectively).The CDA A-76C and hENT1 A-201G genotypes were significantly associated with tumor response to therapy (P = .017 and P = .019). A combined genotype effect of CDA A-76C, RRM1 A33G, RRM1 C-27A, and hENT1 A-201G on PFS was observed. Patients carrying 0 to 1 (n = 64), 2 (n = 50), or 3 to 4 (n = 17) at-risk genotypes had median PFS times of 8.3, 6.0, and 4.2 months, respectively (P = .002).

CONCLUSIONS

The results indicated that some polymorphic variations of drug metabolic and transporter genes may be potential biomarkers for clinical outcome of gemcitabine-based therapy in patients with locally advanced pancreatic cancer.

A 4-gene signature predicts survival of patients with resected adenocarcinoma of the esophagus, junction, and gastric cardia

BACKGROUND & AIMS

The incidence of esophageal and junctional adenocarcinoma has increased 6-fold in the past 30 years and 5-year survival remains approximately 20%. Current staging is limited in its ability to predict survival which has ramifications for treatment choices. The aim of this study was to generate and validate a molecular prognostic signature for esophageal adenocarcinoma.

METHODS

Gene expression profiling was performed and the resulting 42,000 gene signatures correlated with clinical and pathologic features for 75 snap-frozen esophageal and junctional resection specimens. External validation of selected targets was performed on 371 independent cases using immunohistochemistry to maximize clinical applicability.

RESULTS

A total of 119 genes were associated significantly with survival and 270 genes with the number of involved lymph nodes. Filtering of these lists resulted in a shortlist of 10 genes taken forward to validation. Four genes proved to be prognostic at the protein level (deoxycytidine kinase [DCK], 3'-phosphoadenosine 5'-phosphosulfate synthase 2 [PAPSS2], sirtuin 2 [SIRT2], and tripartite motif-containing 44 [TRIM44]) and were combined to create a molecular prognostic signature. This 4-gene signature was highly predictive of survival in the independent external validation cohort (0/4 genes dysregulated 5-year survival, 58%; 95% confidence interval [CI], 36%-80%; 1-2/4 genes dysregulated 5-year survival, 26%; 95% CI, 20%-32%; and 3-4/4 genes dysregulated 5-year survival, 14%; 95% CI, 4%-24% (P = .001). Furthermore, this 4-gene signature was independently prognostic in a multivariable model together with the existing clinical TNM staging system (P = .013).

CONCLUSIONS

This study has generated a clinically applicable prognostic gene signature that independently predicts survival in an external validation cohort and may inform management decisions.

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.

The complexity of pancreatic ductal cancers and multidimensional strategies for therapeutic targeting

The directions of differentiation and the molecular features of ductal pancreatic cancer have by now been explored in reasonable detail. Already, diagnoses and therapeutic strategies benefit from observations distinguishing the major variant types of pancreatic cancer and the differing stages of disease at presentation. Additionally, individual patients differ within each variant type. In certain high-risk groups, this permits focused screening efforts. The tumorigenic influences that characterize individual patients are increasingly considered appropriate in defining clinical treatment plans. As a result, multiple variables affect success when individualizing screening or therapy. These competing variables often limit the potential for success: some variables dominate and should receive greater consideration than others. Simplistic expectations, often falsely optimistic, for individualized care may fail to 'pan out' in the real world. The development of individualized care will be efficient only when the full complexity of the disease is embraced.

Cancer epigenetics

Epigenetics refers to stable alterations in gene expression with no underlying modifications in the genetic sequence and is best exemplified by differentiation, in which multiple cell types diverge physiologically despite a common genetic code. Interest in this area of science has grown over the past decades, especially since it was found to play a major role in physiologic phenomena such as embryogenesis, imprinting, and X chromosome inactivation, and in disease states such as cancer. The latter had been previously thought of as a disease with an exclusive genetic etiology. However, recent data have demonstrated that the complexity of human carcinogenesis cannot be accounted for by genetic alterations alone, but also involves epigenetic changes in processes such as DNA methylation, histone modifications, and microRNA expression. In turn, these molecular alterations lead to permanent changes in the expression of genes that regulate the neoplastic phenotype, such as cellular growth and invasiveness. Targeting epigenetic modifiers has been referred to as epigenetic therapy. The success of this approach in hematopoietic malignancies validates the importance of epigenetic alterations in cancer, not only at the therapeutic level but also with regard to prevention, diagnosis, risk stratification, and prognosis.

Gene expression levels as predictive markers of outcome in pancreatic cancer after gemcitabine-based adjuvant chemotherapy

BACKGROUND AND AIMS

The standard palliative chemotherapy for pancreatic ductal adenocarcinoma (PDAC) is gemcitabine-based chemotherapy; however, PDAC still presents a major therapeutic challenge. The aims of this study were to investigate the expression pattern of genes involved in gemcitabine sensitivity in resected PDAC tissues and to determine correlations of gene expression with treatment outcome.

MATERIALS AND METHODS

We obtained formalin-fixed paraffin-embedded (FFPE) tissue samples from 70 patients with PDAC. Of the 70 patients, 40 received gemcitabine-based adjuvant chemotherapy (AC). We measured hENT1, dCK, CDA, RRM1, and RRM2 messenger RNA (mRNA) levels by quantitative real-time reverse transcription-polymerase chain reaction and determined the combined score (GEM score), based on the expression levels of hENT1, dCK, RRM1, and RRM2, to investigate the association with survival time. By determining the expression levels of these genes in endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) cytologic specimens, we investigated the feasibility of individualized chemotherapy.

RESULTS

High dCK (P = .0067), low RRM2 (P = .003), and high GEM score (P = .0003) groups had a significantly longer disease-free survival in the gemcitabine-treated group. A low GEM score (<2) was an independent predictive marker for poor outcome to gemcitabine-based AC as shown by multivariate analysis (P = .0081). Altered expression levels of these genes were distinguishable in microdissected neoplastic cells from EUS-FNA cytologic specimens.

CONCLUSIONS

Quantitative analyses of hENT1, dCK, RRM1, and RRM2 mRNA levels using FFPE tissue samples and microdissected neoplastic cells from EUS-FNA cytologic specimens may be useful in predicting the gemcitabine sensitivity of patients with PDAC.

Impact of biomarkers on non-small cell lung cancer treatment

Chemotherapy represents the mainstay of non-small cell lung cancer (NSCLC) treatment, but response is usually observed in only one out of three patients. Massive efforts have been carried out to identify biomarkers that might help clinicians to choose appropriate drugs, by identifying potentially sensitive subjects and spare toxicities in patients who are unlikely to benefit from treatment. Low excision repair cross-complementation group 1 (ERCC1) and ribonucleotide reductase M1 (RRM1) levels have been associated with increased sensitivity to cisplatin and gemcitabine, respectively, while reduced class III beta-tubulin expression has been associated with taxane activity. Initial prospective studies showed the feasibility of a customized approach based on biomarker assessment, and phase III trials will hopefully provide further validation of this approach. The impact of biomarkers for patient selection has now been well established for tyrosine kinase inhibitors (TKIs) of the epidermal growth factor receptor (EGFR), with EGFR mutations emerging as the most reliable predictor for improved outcome. Relevant clinical issues are represented by the identification of patients who can be reasonably excluded from treatment and by the development of therapeutic approaches able to overcome acquired resistance to anti-EGFR strategies.