The absence of human equilibrative nucleoside transporter 1 expression predicts nonresponse to gemcitabine-containing chemotherapy in non-small cell lung cancer

Addressing the Clinical Importance of Equilibrative Nucleoside Transporters in Drug Discovery and Development

The US Food and Drug Administration (FDA), European Medicines Agency (EMA), and Pharmaceuticals and Medical Devices Agency (PMDA) guidances on small-molecule drug-drug interactions (DDIs), with input from the International Transporter Consortium (ITC), recommend the evaluation of nine drug transporters. Although other clinically relevant drug uptake and efflux transporters have been discussed in ITC white papers, they have been excluded from further recommendation by the ITC and are not included in current regulatory guidances. These include the ubiquitously expressed equilibrative nucleoside transporters (ENT) 1 and ENT2, which have been recognized by the ITC for their potential role in clinically relevant nucleoside analog drug interactions for patients with cancer. Although there is comparatively limited clinical evidence supporting their role in DDI risk or other adverse drug reactions (ADRs) compared with the nine highlighted transporters, several in vitro and in vivo studies have identified ENT interactions with non-nucleoside/non-nucleotide drugs, in addition to nucleoside/nucleotide analogs. Some noteworthy examples of compounds that interact with ENTs include cannabidiol and selected protein kinase inhibitors, as well as the nucleoside analogs remdesivir, EIDD-1931, gemcitabine, and fialuridine. Consequently, DDIs involving the ENTs may be responsible for therapeutic inefficacy or off-target toxicity. Evidence suggests that ENT1 and ENT2 should be considered as transporters potentially involved in clinically relevant DDIs and ADRs, thereby warranting further investigation and regulatory consideration.

Pharmacogenomics of soft tissue sarcomas: New horizons to understand efficacy and toxicity

Clinical responses to anticancer therapies in advanced soft tissue sarcoma (STS) are unfortunately limited to a small subset of patients. Much of the inter-individual variability in treatment efficacy and risk of toxicities is as result of polymorphisms in genes encoding proteins involved in drug pharmacokinetics and pharmacodynamics. Therefore, the detection of pharmacogenomics (PGx) biomarkers that might predict drug response and toxicity can be useful to explain the genetic basis for the differences in treatment efficacy and toxicity among STS patients. PGx markers are frequently located in transporters, drug-metabolizing enzyme genes, drug targets, or HLA alleles. Along this line, genetic variability harbouring in the germline genome of the patients can influence systemic pharmacokinetics and pharmacodynamics of the treatments, acting as predictive biomarkers for drug-induced toxicity and treatment efficacy. By linking drug activity to the functional complexity of cancer genomes, also systematic pharmacogenomic profiling in cancer cell lines and primary STS samples represents area of active investigation that could eventually lead to enhanced efficacy and offer a powerful biomarker discovery platform to optimize current treatments and improve the knowledge about the individual's drug response in STS patients into the clinical practice.

"Open Sesame?": Biomarker Status of the Human Equilibrative Nucleoside Transporter-1 and Molecular Mechanisms Influencing its Expression and Activity in the Uptake and Cytotoxicity of Gemcitabine in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive tumor characterized by early invasiveness, rapid progression and resistance to treatment. For more than twenty years, gemcitabine has been the main therapy for PDAC both in the palliative and adjuvant setting. After the introduction of FOLFIRINOX as an upfront treatment for metastatic disease, gemcitabine is still commonly used in combination with nab-paclitaxel as an alternative first-line regimen, as well as a monotherapy in elderly patients unfit for combination chemotherapy. As a hydrophilic nucleoside analogue, gemcitabine requires nucleoside transporters to permeate the plasma membrane, and a major role in the uptake of this drug is played by human equilibrative nucleoside transporter 1 (hENT-1). Several studies have proposed hENT-1 as a biomarker for gemcitabine efficacy in PDAC. A recent comprehensive multimodal analysis of hENT-1 status evaluated its predictive role by both immunohistochemistry (with five different antibodies), and quantitative-PCR, supporting the use of the 10D7G2 antibody. High hENT-1 levels observed with this antibody were associated with prolonged disease-free status and overall-survival in patients receiving gemcitabine adjuvant chemotherapy. This commentary aims to critically discuss this analysis and lists molecular factors influencing hENT-1 expression. Improved knowledge on these factors should help the identification of subgroups of patients who may benefit from specific therapies and overcome the limitations of traditional biomarker studies.

Human equilibrative nucleoside transporter 1 (hENT1) expression as a predictive biomarker for gemcitabine chemotherapy in biliary tract cancer

Gemcitabine is a principal chemotherapeutic agent for biliary tract cancer (BTC). Expression of human equilibrative nucleoside transporter 1 (hENT1) is regarded as a potential predictive biomarker for a gemcitabine response in some cancers. This study was conducted to investigate the association between hENT1 expression and the effects of gemcitabine on BTC cell lines and on patients with advanced BTC receiving gemcitabine-based chemotherapy. A total of four BTC cell lines, HuCCT1, SNU-478, SNU-1079, and SNU-1196, were tested. mRNA and protein expression levels of hENT1 were measured by quantitative reverse-transcription polymerase chain reaction and western blotting, respectively. Cell viability after gemcitabine treatment was measured in a chemosensitivity assay. For clinical assessment, 40 patients with unresectable or recurrent BTC who were treated with gemcitabine (1000 mg/m²) and cisplatin (25 mg/m²) between June 2012 and May 2014 were enrolled. Among the four cell lines, SNU1196 showed the highest mRNA and protein levels of hENT1. Expression of hENT1 showed a linear correlation with the log value of the half-maximal inhibitory concentration of gemcitabine. During incubation with gemcitabine, pretreatment with hENT1-specific small interfering RNA (siRNA) resulted in higher cell viability than that in samples pretreated with control siRNA. In a clinical evaluation, the median progression-free survival was 24 and 11 weeks among patients with strong and weak intratumoral hENT1 immunohistochemical staining (P = 0.05), and the median overall survival was 52 and 26 weeks (P = 0.15), respectively. In conclusion, this study showed that increased hENT1 expression is associated with a stronger toxic effect of gemcitabine on BTC cell lines. The clinical outcomes in this study suggest that increased intratumoral hENT1 immunohistochemical staining is a possible biomarker predicting better therapeutic effects of gemcitabine on patients with advanced BTC. Further studies are needed to determine the precise role of hENT1 in BTC.

Correlation of 4'-[methyl-11C]-thiothymidine uptake with human equilibrative nucleoside transporter-1 and thymidine kinase-1 expressions in patients with newly diagnosed gliomas

OBJECTIVE

We examined expressions of human equilibrative nucleoside transporter-1 (hENT1) and thymidine kinase-1 (TK1), the key enzyme in 4'-[methyl-¹¹C]-thiothymidine (4DST) phosphorylation, to elucidate the mechanism of 4DST uptake in patients with newly diagnosed gliomas.

METHODS

A total of 19 patients with newly diagnosed gliomas were examined with 4DST PET. Tumor lesions were identified as areas of focally increased uptake, exceeding that of normal brain background. For semi-quantitative analysis, tumor-to-contralateral normal brain tissue (T/N) ratio was determined by dividing the maximal standardized uptake value (SUV) for tumor by that of the mean SUV for reference tissue. The expressions of hENT1, TK1 and Ki-67 in tumor specimens were examined by immunohistochemistry and compared with 4DST T/N ratio.

RESULTS

All but two gliomas showed focally increased 4DST uptake. All gliomas showed hENT1 staining, except one grade II glioma, which was also not visualized on 4DST PET. A significant correlation was observed between T/N ratio and hENT1 score (ρ = 0.90, p < 0.001). All gliomas showed TK1 staining, except two gliomas which were also not visualized on 4DST PET. There was a significant correlation between T/N ratio and TK1 score (ρ = 0.92, p < 0.001). There was a significant correlation between T/N ratio and Ki-67 index (ρ = 0.50, p < 0.03).

CONCLUSION

Results of this preliminary study indicate that expressions of hENT1 and TK1 appear to be important determinants of 4DST uptake in newly diagnosed gliomas.

Human equilibrative nucleoside transporter 1 gene expression is associated with gemcitabine efficacy in advanced leiomyosarcoma and angiosarcoma

Background:

The expression of human equilibrative nucleoside transporter 1 (hENT1), the major gemcitabine transporter into cells, has been thoroughly investigated as a predictive marker of response to gemcitabine in pancreatic cancer and biliary tract cancers. Since gemcitabine is widely used in the treatment of leiomyosarcoma and angiosarcoma, we investigated the correlation between hENT1 expression and gemcitabine efficacy in these sarcoma subtypes.

Methods:

We retrospectively identified 71 patients affected by advanced angiosarcoma (26) or leiomyosarcoma (45) treated within five Italian referral centres for sarcoma; among them, 49 patients (15 angiosarcoma, 34 leiomyosarcoma) were treated with gemcitabine. All tumour samples were analysed for hENT1 expression by real-time PCR. Median 2^–ΔCt value was used as the cutoff to dichotomise patients into ‘high’ expression and ‘low’ expression groups. Kaplan–Meier analysis was performed to estimate progression-free survival (PFS) and overall survival (OS).

Results:

We found a significant association between high hENT1 expression levels and favourable outcome in terms of PFS and OS compared to cases with low hENT1 expression in leiomyosarcoma treated with gemcitabine (PFS: 6.8 vs 3.2 months, P=0.004; OS: 14.9 vs 8.5 months, P=0.007). In addition, hENT1 overexpression correlated with a significant improvement in PFS (9.3 vs 4.5 months; P=0.02) and OS (20.6 vs 10.8 months; P=0.001) in angiosarcoma patients treated with gemcitabine.

Conclusions:

Our study suggests that higher hENT1 expression are associated to gemcitabine efficacy both in patients with advanced leiomyosarcoma and angiosarcoma.

Enhancing Drug Efficacy and Therapeutic Index through Cheminformatics-Based Selection of Small Molecule Binary Weapons That Improve Transporter-Mediated Targeting: A Cytotoxicity System Based on Gemcitabine

The transport of drug molecules is mainly determined by the distribution of influx and efflux transporters for which they are substrates. To enable tissue targeting, we sought to develop the idea that we might affect the transporter-mediated disposition of small-molecule drugs via the addition of a second small molecule that of itself had no inhibitory pharmacological effect but that influenced the expression of transporters for the primary drug. We refer to this as a “binary weapon” strategy. The experimental system tested the ability of a molecule that on its own had no cytotoxic effect to increase the toxicity of the nucleoside analog gemcitabine to Panc1 pancreatic cancer cells. An initial phenotypic screen of a 500-member polar drug (fragment) library yielded three “hits.” The structures of 20 of the other 2,000 members of this library suite had a Tanimoto similarity greater than 0.7 to those of the initial hits, and each was itself a hit (the cheminformatics thus providing for a massive enrichment). We chose the top six representatives for further study. They fell into three clusters whose members bore reasonable structural similarities to each other (two were in fact isomers), lending strength to the self-consistency of both our conceptual and experimental strategies. Existing literature had suggested that indole-3-carbinol might play a similar role to that of our fragments, but in our hands it was without effect; nor was it structurally similar to any of our hits. As there was no evidence that the fragments could affect toxicity directly, we looked for effects on transporter transcript levels. In our hands, only the ENT1-3 uptake and ABCC2,3,4,5, and 10 efflux transporters displayed measurable transcripts in Panc1 cultures, along with a ribonucleoside reductase RRM1 known to affect gemcitabine toxicity. Very strikingly, the addition of gemcitabine alone increased the expression of the transcript for ABCC2 (MRP2) by more than 12-fold, and that of RRM1 by more than fourfold, and each of the fragment “hits” served to reverse this. However, an inhibitor of ABCC2 was without significant effect, implying that RRM1 was possibly the more significant player. These effects were somewhat selective for Panc cells. It seems, therefore, that while the effects we measured were here mediated more by efflux than influx transporters, and potentially by other means, the binary weapon idea is hereby fully confirmed: it is indeed possible to find molecules that manipulate the expression of transporters that are involved in the bioactivity of a pharmaceutical drug. This opens up an entirely new area, that of chemical genomics-based drug targeting.

Predictors of chemotherapy efficacy in non-small-cell lung cancer: a challenging landscape

BACKGROUND

Conventional cytotoxic chemotherapy (CCC) is the backbone of non-small-cell lung cancer (NSCLC) treatment since decades and still represents a key element of the therapeutic armamentarium. Contrary to molecularly targeted therapies and immune therapies, for which predictive biomarkers of activity have been actively looked for and developed in parallel to the drug development process ('companion biomarkers'), no patient selection biomarker is currently available for CCC, precluding customizing treatment.

MATERIALS AND METHODS

We reviewed preclinical and clinical studies that assessed potential predictive biomarkers of CCC used in NSCLC (platinum, antimetabolites, topoisomerase inhibitors, and spindle poisons). Biomarker evaluation method, analytical validity, and robustness are described and challenged for each biomarker.

RESULTS

The best-validated predictive biomarkers for efficacy are currently ERCC1, RRM1, and TS for platinum agents, gemcitabine and pemetrexed, respectively. Other potential biomarkers include hENT1 for gemcitabine, class III β-tubulin for spindle poisons, TOP2A expression and CEP17 duplication (mostly studied for predicting anthracyclines efficacy) whose applicability concerning etoposide would deserve further evaluation. However, none of these biomarkers has till now been validated prospectively in an appropriately designed and powered randomised trial, and none of them is currently ready for implementation in routine clinical practice.

CONCLUSION

The search for predictive biomarkers to CCC has been proven challenging. If a plethora of biomarkers have been evaluated either in the preclinical or in the clinical setting, none of them is ready for clinical implementation yet. Considering that most mechanisms of resistance or sensitivity to CCC are multifactorial, a combinatorial approach might be relevant and further efforts are required.

Influx transporter variants as predictors of cancer chemotherapy-induced toxicity: systematic review and meta-analysis

AIM

Chemotherapeutic agents have been shown to increase lung patient survival, however their use may be limited by their serious adverse effects. We aimed to assess int impact of pharmacogenetic variation of influx transporters on inter-individual patient variation in adverse drug reactions.

PATIENTS & METHODS

We conducted a meta-analysis and systemic review and identified 16 publications, totaling 1510 patients, to be eligible for review.

RESULTS

Meta-analysis showed east-Asian patients expressing SLCO1B1 521T>C or 1118G>A to have a two- to fourfold increased risk of irinotecan-induced neutropenia but not diarrhea. American patients, expressing SLC19A1 IVS2(4935) G>A, were further associated with pemetrexed/gemcitabine-induced grade 3+ leukopenia.

CONCLUSION

Future studies should look to robust validation of SLCO1B1 and SLC19A1 as prognostic markers in the management of lung cancer patients.

Chemotherapy Resistance in Lung Cancer

Despite a growing interest in development of non-cytotoxic targeted agents, systemic chemotherapy is still the mainstay of treatment for both non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). However, chemotherapy resistance limits our ability to effectively treat advanced lung cancer. Some lung tumors are intrinsically resistant to chemotherapy, and in virtually all cases, even the initial responders rapidly develop acquired resistance. While targeting histology could result in enhanced tumor sensitivity to a particular chemotherapeutic agent, better understanding of molecular determinants of chemotherapy sensitivity/resistance would be critically important. Development of predictive biomarkers to personalize chemotherapeutic agents and combining novel agents targeting specific resistance pathways with standard chemotherapy could be some promising strategies to overcome chemotherapy resistance in lung cancer. In this chapter, we will discuss some key mechanisms of resistance for commonly used chemotherapeutic agents in lung cancer.

Pharmacogenomics in the treatment of lung cancer: an update

Significant advances have been made in the analysis of the human genome in the first decades of the 21st century and understanding of tumor biology has matured greatly. The identification of tumor-associated mutations and the pathways involved has led to the development of targeted anticancer therapies. However, the challenge now in using chemotherapy to treat nonsmall-cell lung cancer is to identify more molecular markers predictive of drug sensitivity and determine the optimal drug sequences in order to tailor treatment to each patient. This approach could permit selection of patients who could benefit most from a specific type of chemotherapy by matching their tumor and individual genetic profile. Nevertheless, this potential has been limited so far by reliance on the single biomarker approach, though this is now on the way to being overcome through whole genome studies.

Preparation of intravenous injection nanoformulation of VESylated gemcitabine by co-assembly with TPGS and its anti-tumor activity in pancreatic tumor-bearing mice

Our recent publication showed that VES-dFdC nanocapsules in pure water could be obtained via the self-assembling of VES-dFdC prodrug synthesized by coupling gemcitabine (dFdC) with vitamin E succinate (VES). To prepare the intravenous injection nanoformulation, we present here a novel strategy to improve the stability and drug concentration of VES-dFdC nanoformulation in PBS or isotonic solution. Particularly, D-α-tocopheryl polyethylene glycol succinate (TPGS), usually used as drug solubilizer and coincidentally contains the same VES moiety as VES-dFdC prodrug and PEG chain, is selected to co-assemble with VES-dFdC prodrug. The zeta potentials of all the TPGS/VES-dFdC co-assemblies were close to 0 mV, and their particle size measured by dynamic light scattering (DLS) decreased from 113 to 36 nm with increasing TPGS/VES-dFdC molar ratios from 0.15 to 1.5. Stable colloidal suspensions were obtained without aggregates in PBS at 4 °C in one month or isotonic solution at 37 °C in one week, and the weight concentration of VES-dFdC prodrug increased from 7 to 17 mg/mL when the molar ratios of TPGS/VES-dFdC ranged from 0.5/1 to 1.5/1. The concentration of VES-dFdC prodrug was high enough to be used as intravenous injection nanoformulation in nude mice. Interestingly, along with the increase of TPGS/VES-dFdC molar ratios from 0.3/1 to 1.5/1, the morphology of TPGS/VES-dFdC co-assemblies changed from loose nanocapsule to compact micelle revealed by transmission electron microscope (TEM). Finally, the co-assembly of TPGS/VES-dFdC (TPGS/VES-dFdC: 1/1) was selected as intravenous injection nanoformulation to evaluate the antitumor activity. Compared with native dFdC, TPGS/VES-dFdC nanoformulation with 0.2mmol/kg of dosage showed similar low toxicity in vivo, but 4.7 times high of tumor inhibition rate in nude mice with pre-established BxPC-3 tumors.

Enhanced cellular uptake and intracellular drug controlled release of VESylated gemcitabine prodrug nanocapsules

Gemcitabine, 2',2'-difluoro-2'-deoxycytidine (dFdC), is the first-line antitumor agent in the treatment of pancreatic tumors. However, it possesses certain drawbacks, such as poor biological half-life resulted from rapid metabolism and the induction of resistance, leading to its restricted therapeutic potential. With the purpose of overcoming the above drawbacks, we developed a novel VESylated gemcitabine (VES-dFdC) prodrug by coupling the N4-amino group of the pyrimidine ring of dFdC to the carboxylic group of vitamin E succinate (VES). The resulting amphiphilic compound could protect the N4-amino group of the pyrimidine ring of dFdC from being degraded by cytidine deaminase. What is more, the prodrug was able to form nanocapsules in aqueous media (similar to the structure of cytomembrane), confirmed by transmission electron microscope (TEM). Their average particle size is about 107 nm with zeta potential of -33.4 mV measured by dynamic light scattering (DLS). VES-dFdC nanocapsules showed accelerated accumulative drug release profile in simulated lysosome environment (sodium acetate buffer pH 5+cathepsin B, an enzyme in lysosome), due to the easily hydrolyzed property of amide bond by cathepsin B, while rather stable in PBS (pH 7.4) or sodium acetate buffer (pH 5.0) without cathepsin B, indicating their enhanced intracellular drug controlled release manner. Besides, VES-dFdC prodrug nanocapsules showed enhanced cellular uptake ability, and the amount of cellular uptake of the nanocapsules by the pancreatic cancer cell line BxPC-3 is seventy times higher than that of native gemcitabine in the first 1.5 h. Compared with free gemcitabine, VES-dFdC nanocapsules showed essentially increased growth inhibition activity against BxPC-3 cells, indicating its great potential as prodrug for pancreatic tumor therapy with improved antitumor activity.

Nucleoside transporter proteins as biomarkers of drug responsiveness and drug targets

Nucleoside and nucleobase analogs are currently used in the treatment of solid tumors, lymphoproliferative diseases, viral infections such as hepatitis and AIDS, and some inflammatory diseases such as Crohn. Two gene families are implicated in the uptake of nucleosides and nucleoside analogs into cells, SCL28 and SLC29. The former encodes hCNT1, hCNT2, and hCNT3 proteins. They translocate nucleosides in a Na⁺ coupled manner with high affinity and some substrate selectivity, being hCNT1 and hCNT2 pyrimidine- and purine-preferring, respectively, and hCNT3 a broad selectivity transporter. SLC29 genes encode four members, being hENT1 and hENT2 the only two which are unequivocally implicated in the translocation of nucleosides and nucleobases (the latter mostly via hENT2) at the cell plasma membrane. Some nucleoside-derived drugs can also interact with and be translocated by members of the SLC22 gene family, particularly hOCT and hOAT proteins. Inter-individual differences in transporter function and perhaps, more importantly, altered expression associated with the disease itself might modulate the transporter profile of target cells, thereby determining drug bioavailability and action. Drug transporter pharmacology has been periodically reviewed. Thus, with this contribution we aim at providing a state-of-the-art overview of the clinical evidence generated so far supporting the concept that these membrane proteins can indeed be biomarkers suitable for diagnosis and/or prognosis. Last but not least, some of these transporter proteins can also be envisaged as drug targets, as long as they can show “transceptor” functions, in some cases related to their role as modulators of extracellular adenosine levels, thereby providing a functional link between P1 receptors and transporters.

Clinical potential of elacytarabine in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) has been treated for over four decades with standard induction chemotherapy including seven days of cytosine arabinoside (cytarabine, ara-C) infusion. Cytarabine, while effective in killing leukemic cells, is subject to development of several resistance mechanisms rendering the drug ineffective in many patients. Elacytarabine, a lipophilic 5'-elaidic acid ester or nucleoside analogue of cytosine arabinoside, was created with the intent of overcoming resistance mechanisms including reduced expression of the human equilibrative nucleoside transporter 1 (hENT1) required for cytarabine entry into cells, as well as increased activity of cytidine deaminase (CDA) which breaks down the active metabolite of cytarabine, ara-CTP. Elacytarabine enters cells independently of transporters, has a longer half life compared with cytarabine and is not subject to deactivation by CDA. Preclinical data were encouraging although subsequent clinical studies have failed to show superiority of elacytarabine compared with standard of care as monotherapy in patients with AML. Clinical trials utilizing elacytarabine in combination with anthracyclines are ongoing. Use of hENT1 expression as a predictive marker for cytarabine or elacytarabine response has been studied with no conclusive validation to date. Despite promising early results, the jury is still out in regards to this novel agent as an effective alternative to standard cytarabine therapy in acute leukemias, especially in combination with additional agents such as anthracyclines.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.

Effect of hENT1 polymorphism G-706C on clinical outcomes of gemcitabine-containing chemotherapy for Chinese non-small-cell lung cancer patients

AIM

To identify the single-nucleotide polymorphism (SNP) of hENT1 G-706C that is associated with response to gemcitabine-containing chemotherapy, and to determine the prognosis in patients with non-small-cell lung cancer (NSCLC).

METHODS

Patients with stage III (A+B) or IV NSCLC were recruited for this study (n=225). Each subject received gemcitabine-containing chemotherapy. The association between human equilibrative nucleoside transporter 1 (hENT1) polymorphism G-706C (rs61758845) and therapeutic effect was evaluated. The SNP hENT1 G-706C was genotyped by polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) assays.

RESULTS

The polymorphic genotype and the allele frequency of hENT1 G-706C was significantly different between chemotherapy responders and non-responders; to be specific, the response rate of patients carrying an hENT1-706 GG allele was higher than that of patients with a GC or CC genotype. Logistic regression analysis showed that having the GC or CC genotypes was associated with a higher risk of being a non-responder compared with having the GG genotype (OR=2.34, 95% CI: 1.14-4.80; P=0.02). The overall survival in patients with the GG genotype was significantly longer than in those with GC or CC genotype (19.0 versus 15.1 months, P<0.001). The hazard ratio for the (GC+CC) genotype was 1.89 (95% CI: 1.23-2.90) compared with GG carriers (P=0.004).

CONCLUSIONS

The hENT1 genetic polymorphism of hENT1 G-706C was associated with response to the gemcitabine-containing chemotherapy and prognosis of NSCLC. Moreover, assaying this SNP in blood cells may represent a valuable biomarker for individualized treatment for NSCLC patients.

hENT1 expression is predictive of gemcitabine outcome in pancreatic cancer: A systematic review

High human equilibrative nucleoside transporter 1 (hENT1)-expression has shown a survival benefit in pancreatic cancer patients treated with gemcitabine in several studies. The aim of this systematic review was to summarize the results and try to assess the predictive value of hENT1 for determining gemcitabine outcome in pancreatic cancer. Relevant articles were obtained from PubMed, Embase and Cochrane databases. Studies evaluating hENT1-expression in pancreatic tumor cells from patients treated with gemcitabine were selected. Outcome measures were overall survival, disease-free survival (DFS), toxicity and response rate. The database searches identified 10 studies that met the eligibility criteria, and a total of 855 patients were included. Nine of 10 studies showed a statistically significant longer overall survival in univariate analyses in patients with high hENT1-expression compared to those with low expression. In the 7 studies that reported DFS as an outcome measure, 6 had statistically longer DFS in the high hENT1 groups. Both toxicity and response rate were reported in only 2 articles and it was therefore hard to draw any major conclusions. This review provides evidence that hENT1 is a predictive marker for pancreatic cancer patients treated with gemcitabine. Some limitations of the review have to be taken into consideration, the majority of the included studies had a retrospective design, and there was no standardized scoring protocol for hENT1-expression.

Preparation, optimization and in vitro characterization of stearoyl-gemcitabine polymeric micelles: a comparison with its self-assembled nanoparticles

Although gemcitabine (Gem) constitutes first-line therapy for pancreatic cancer, its clinical outcome suffers from rapid metabolism and acquired drug resistance. To overcome its limitations, several lipophilic prodrugs including 4-(N)-stearoyl Gem (GemC18) have been studied for their efficacy over Gem. Herein, we aimed to prepare and characterize the GemC18-loaded poly(ethylene glycol)-poly(d,l-lactide) (PEG-PLA) polymeric micelles (PMs) as well as its self-assembled nanoparticles (NPs). A D-optimal design was also utilized to investigate the effects of formulation variables, namely initial drug/polymer ratio, total solid content, and the type of organic solvent on properties of GemC18-loaded PMs. The optimized formulation showed a particle size of about 120 nm, encapsulation efficiency >90%, and a sustained release behavior of the drug. Alternatively, the prodrug NPs were harvested in larger size (∼300 nm) and more negative zeta potential, but less chemical stability compared to the optimized PMs. In Panc-1 and AsPC-1 cell lines, both GemC18-loaded PMs and NPs were significantly more cytotoxic than GemC18 solution. Chiefly, they could effectively reduce the viability of Gem high-resistant AsPC-1 cells in culture, whereas the molar equivalent doses of Gem did not show any acceptable cytotoxicity. Thus, these results suggest a promising direction for alternative Gem delivery systems for future therapeutic applications.

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.

Elacytarabine (CP-4055) in the treatment of acute myeloid leukemia

Elacytarabine (formerly CP-4055) is a lipid-conjugated derivative of the nucleoside analog cytarabine. Elacytarabine was rationally designed to circumvent cytarabine resistance related to decreased cellular uptake, due to the ability of the lipophilic drug moiety to enter the cell without the requirement of specialized nuclear transport proteins, including the hENT1. In preclinical and clinical studies, elacytarabine has demonstrated both safety and efficacy in acute myeloid leukemia (AML), with noteworthy activity among the cytarabine-refractory AML population. Elacytarabine was granted orphan drug designation status from the European Commission in 2007 and from the US FDA in 2008, with a fast-track approval designation from the FDA in 2010. Results of a recent randomized Phase III clinical trial, however, failed to show superiority of elacytarabine over the investigator's choice of therapy for relapsed or refractory AML.

Pancreatic cancer: why is it so hard to treat?

No common malignancy is as rapidly and inevitably fatal as pancreatic ductal adenocarcinoma (PDA). This grim fact has driven substantial research efforts into this disease in recent decades. Unfortunately, the investment has yet to result in a meaningful increase in 5-year survival. This has prompted many pancreatic cancer researchers and advocates to redouble their efforts, but also requires one to step back and ask why the previous efforts were lacking and to consider why pancreatic cancer is so difficult to treat. The difficulties are legion. PDA is characterized by an insidious clinical syndrome, but is rarely diagnosed at a time when surgical resection is feasible. We lack markers of early detection and screening programs remain unproven even in high risk populations. The location of the tumor in the retroperitoneum, the advanced age of patients, and the systemic effects of disease limit the options for local therapy. Chemotherapy may provide a small benefit, but most efforts to improve on the current regimens consistently and stubbornly fail in advanced clinical trials. The molecular and cellular features of ductal pancreatic tumors are aggressive and underlay multiple levels of therapeutic resistance. Non-cell-autonomous features including stromal proliferation, reduced vascular density and immune suppression also contribute to therapeutic resistance. Growing awareness of these the fundamental features of PDA has begun to guide ongoing research efforts. Clinical trials are now specifically targeting these tumor properties and actively focusing on the therapeutic implications of tumor stroma. As reviewed here, reflecting on the fundamental question of why pancreatic cancer is so difficult to treat is a necessary and informative exercise that will aid our efforts to improve patient outcomes. These efforts will lead to improvements in clinical trial design, expand our focus to include the molecular and histologic implications of novel treatment paradigms, and ultimately change the lives of our patients.

Human equilibrative nucleoside transporter 1 level does not predict prognosis in pancreatic cancer patients treated with neoadjuvant chemoradiation including gemcitabine

BACKGROUND

Gemcitabine is a key drug for the treatment of pancreatic cancer. Human equilibrative nucleoside transporter 1 (hENT1) is a major transporter responsible for gemcitabine uptake into cells. This study was conducted to elucidate the association between expression level of hENT1 and outcome for pancreatic cancer patients treated with neoadjuvant therapy including gemcitabine.

METHODS

Sixty-three patients who underwent neoadjuvant chemoradiation followed by curative surgery for pancreatic ductal adenocarcinomas were included. Immunohistochemistry was performed using resected specimens and the staining intensity of hENT1 was scored as having no staining, low staining, or high staining; the former two were defined as negative expression of hENT1. The association between expression level of hENT1 and overall survival was evaluated by Cox proportional regression model.

RESULTS

Expression level of hENT1 was evaluated as positive in 22 (35%) patients, and as negative in 41 (65%) patients. Univariate analysis showed that regional lymph node metastasis, vascular permeation, and perineural invasion are prognostic factors; however, expression level of hENT1 did not reach statistical significance. Multivariate analysis showed only vascular permeation as a prognostic factor.

CONCLUSIONS

Expression level of hENT1 was not associated with prognosis for pancreatic cancer patients who were treated with neoadjuvant chemoradiation including gemcitabine.

Finding novel pharmaceuticals in the systems biology era using multiple effective drug targets, phenotypic screening and knowledge of transporters: where drug discovery went wrong and how to fix it

Despite the sequencing of the human genome, the rate of innovative and successful drug discovery in the pharmaceutical industry has continued to decrease. Leaving aside regulatory matters, the fundamental and interlinked intellectual issues proposed to be largely responsible for this are: (a) the move from 'function-first' to 'target-first' methods of screening and drug discovery; (b) the belief that successful drugs should and do interact solely with single, individual targets, despite natural evolution's selection for biochemical networks that are robust to individual parameter changes; (c) an over-reliance on the rule-of-5 to constrain biophysical and chemical properties of drug libraries; (d) the general abandoning of natural products that do not obey the rule-of-5; (e) an incorrect belief that drugs diffuse passively into (and presumably out of) cells across the bilayers portions of membranes, according to their lipophilicity; (f) a widespread failure to recognize the overwhelmingly important role of proteinaceous transporters, as well as their expression profiles, in determining drug distribution in and between different tissues and individual patients; and (g) the general failure to use engineering principles to model biology in parallel with performing 'wet' experiments, such that 'what if?' experiments can be performed in silico to assess the likely success of any strategy. These facts/ideas are illustrated with a reasonably extensive literature review. Success in turning round drug discovery consequently requires: (a) decent systems biology models of human biochemical networks; (b) the use of these (iteratively with experiments) to model how drugs need to interact with multiple targets to have substantive effects on the phenotype; (c) the adoption of polypharmacology and/or cocktails of drugs as a desirable goal in itself; (d) the incorporation of drug transporters into systems biology models, en route to full and multiscale systems biology models that incorporate drug absorption, distribution, metabolism and excretion; (e) a return to 'function-first' or phenotypic screening; and (f) novel methods for inferring modes of action by measuring the properties on system variables at all levels of the 'omes. Such a strategy offers the opportunity of achieving a state where we can hope to predict biological processes and the effect of pharmaceutical agents upon them. Consequently, this should both lower attrition rates and raise the rates of discovery of effective drugs substantially.

Pharmacogenetics of conventional chemotherapy in non-small-cell lung cancer: a changing landscape?

Pharmacogenetics might be used to select patients who may benefit from specific chemotherapy that best matches the individual and tumor genetic profile, thus allowing maximum activity and minimal toxicity. Even if most studies in non-small-cell lung cancer yielded contradictory results, several potential biomarkers for sensitivity/resistance to platinum compounds, gemcitabine, taxanes and pemetrexed have been proposed. However, these markers need to be validated within larger prospective randomized trials of customized chemotherapy in homogeneous populations. Other critical points include the optimization/standardization of technical procedures, and further studies to unravel the extremely complex regulation of gene function. From this perspective, the evaluation of key factors influencing genotype-phenotype relationships, such as miRNAs, and functional studies to clarify pharmacokinetic/pharmacodynamic interactions, are fundamental for the pharmacogenetic optimization of cancer chemotherapy. Finally, limitation of the traditional pharmacogenetic approach relying only on candidate genes suspected of affecting drug response is now being overcome by the use of novel genome-wide studies.

Human equilibrative nucleoside transporter 1 expression is a strong independent prognostic factor in UICC T3-T4 pancreatic cancer patients treated with preoperative gemcitabine-based chemoradiotherapy

BACKGROUND/PURPOSE

We aimed to determine the relationship between the intratumoral expression of human equilibrative nucleoside transporter (hENT1), the main gemcitabine transporter into cells, and the outcome of gemcitabine-based chemoradiotherapy (Gem-CRT) in patients with International Union Against Cancer (UICC) T3-T4 pancreatic adenocarcinoma.

METHODS

The expressions of hENT1, thymidylate synthase (TS), and dihydropyrimidine dehydrogenase were immunohistochemically analyzed using the resected specimens from 55 patients (T3, 38 and T4, 17) who had received curative-intent resection after Gem-CRT.

RESULTS

The status of hENT1 expression (positive in 39 and negative in 16) was significantly associated with "clinical efficacy" (defined as more than 50% reduction of the serum carbohydrate antigen [CA] 19-9 level with stable disease [SD] or partial response [PR] according to the Response Evaluation Criteria in Solid Tumors [RECIST]) for Gem-CRT. The 1- and 3-year overall survival (OS) rates were significantly higher in the positive hENT1 expression group (82.9, 39.5%) than in the negative expression group (42.9, 14.3%) (p = 0.0037). According to combination analysis of hENT1 and TS expressions, the 1- and 3-year OS rates were significantly higher in the positive-low combination (89.1, 51.0%) group than in the negative-high group (66.7, 0%) (p = 0.023). Multivariate analysis revealed that positive hENT1 expression and R0 resection were significant prognostic factors for OS.

CONCLUSIONS

The hENT1 expression in pancreatic adenocarcinoma strongly influences the outcome of preoperative Gem-CRT treatment. This biomarker could become a useful predictor of therapeutic effect for gemcitabine-based therapy in pancreatic cancer patients.

[Efficacy and toxicity of pemetrexed or gemcitabine combined with cisplatin in the treatment of patients with advanced non-small cell lung cancer]

BACKGROUND AND OBJECTIVE

Due to the various inter-individual differences in the biological characteristics of tumor cells, as well as issues on the efficacy, adverse reactions, and defects of existing drugs, we compared the clinical efficacy and toxicity of pemetrexed and gemcitabine combined with cisplatin for the treatment of previously untreated advanced non-small cell lung cancer (NSCLC).

METHODS

251 patients were randomly divided into pemetrexed combined with cisplatin group (PP group) with 127 cases and gemcitabine combined with cisplatin group (GP group) with 124 cases. PP group received pemetrexed 500 mg/m² iv infusion d1 and cisplatin 75 mg/m² iv infusion d1, whereas GP group received gemcitabine 1,000 mg/m² iv infusion d1,8 and cisplatin 75 mg/m² iv infusion d1. The treatment cycle was once every three weeks. In addition, folic acid, vitamin B12, and dexamethasone were administered in both groups.

RESULTS

The total clinical effective rates in PP group and GP group were 25.20% and 17.74%, respectively. The total efficiencies of non-squamous cell carcinoma were 27.62% and 16.00%. The tumor progression duration in these two groups was 6.5 and 5.6 months, respectively. The median survival time in the two groups was 16.9 and 17.0 months, respectively, with 59.62% and 65.87% survival rates of 1 year and 27.28% and 27.93% survival rates of 2 years, respectively. The total efficacy of non-squamous cell carcinoma in the PP group was significantly higher than that in GP group. The results were statistically significant. However, there were no significant differences in total response rates, tumor progression duration, and median survival rates of 1 and 2 years. The rate of adverse reactions, including white blood cell reduction, lower platelet count, lower hemoglobin, and hair loss in the PP group was significantly lower than that in the GP group. The results were statistically significant.

CONCLUSION

The clinical efficacy of pemetrexed and gemcitabine combined with cisplatin for the treatment of previously untreated advanced NSCLC was roughly the same, but the adverse reactions decreased significantly in the PP group compared with those in the GP group. Therefore, pemetrexed combined with cisplatin can be used as a safe and effective drug for clinical first-line treatment for previously untreated NSCLC.

Human equilibrative nucleoside transporter 1 expression predicts survival of advanced cholangiocarcinoma patients treated with gemcitabine-based adjuvant chemotherapy after surgical resection

OBJECTIVE

The aim of this study was to evaluate whether intratumoral human equilibrative nucleoside transporter 1 (hENT1) expression can predict the survival of advanced cholangiocarcinoma patients treated with adjuvant gemcitabine-based chemotherapy (AGC) after surgical resection.

BACKGROUND

There have been no reports concerning a useful predictive biomarker in patients with cholangiocarcinoma treated with adjuvant gemcitabine chemotherapy.

METHODS

Intratumoral hENT1 expression was investigated immunohistochemically in 105 patients with resected advanced cholangiocarcinoma. Relationships between intratumoral hENT1 expression and clinicopathological factors were evaluated by univariate and multivariate analyses. This study was a retrospective analysis on retrospectively collected tissue and data.

RESULTS

Fifty-one patients received AGC, and 54 did not. High and low intratumoral hENT1 expression was found in 74 (70%) and 31 patients (30%), respectively. There were no significant differences in clinicopathological factors between patients with high hENT1 expression and those with low hENT1 expression. Survival patients with high hENT1 expression were significantly better than those with low hENT1 expression among patients who received AGC (P = 0.008), but not among patients who did not (P = 0.894). Moreover, a significant difference in survival between patients who received AGC and those who did not was observed among patients with high hENT1 expression (P = 0.002), but not among patients with low hENT1 expression (P = 0.525). Intratumoral hENT1 expression was only an independent predictive factor for patients treated with AGC by multivariate analysis (P = 0.027).

CONCLUSIONS

Intratumoral hENT1 expression may be a potent predictive marker for advanced cholangiocarcinoma patients treated with AGC.

Preclinical rationale for synergistic interaction of pemetrexed and cytotoxic nucleoside analogues

Cytotoxic nucleoside analogues are widely used in cancer chemotherapy. We used the cytosine arabinoside (Ara-C)-resistant erythroleukaemia cell line K562 and the Ara-C-sensitive myeloid leukaemia cell line HL60 to examine the differential expression of molecular markers. We found increased expression levels of deoxycytidine kinase (dCK) and human equilibrative nucleoside transporter 1 (hENT1) and decreased levels of multidrug resistance protein 5 (ABCC5) and ribonucleoside reductase subunit M1 (RRM1) expression in Ara-C-sensitive HL60 cells. We previously established the pemetrexed (MTA)-resistant small cell lung cancer cell lines PC6/MTA-0.4 and PC6/MTA-1.6 and found that MTA-resistant cells are more sensitive to gemcitabine (GEM) and Ara-C compared with parental PC-6 cells. We examined the molecular markers for GEM and Ara-C sensitivity in MTA-resistant cells and found increased gene expression of dCK and hENT1. Furthermore, treatment with MTA resulted in increased expression of dCK and hENT1 and decreased expression of ABCC5 and RRM1, concomitant with the alteration of the resistance to Ara-C in Ara-C-resistant K562 cells. These results provide evidence that the chemotherapeutic activity of the combination of MTA and cytotoxic nucleoside analogues is synergistic with regard to the alteration of metabolic molecules.

Enhanced anticancer activity of gemcitabine coupling with conjugated linoleic acid against human breast cancer in vitro and in vivo

Gemcitabine (GEM) is a nucleoside analog agent against a wide variety of tumors. To overcome its limitation of rapid metabolism in vivo that results in short circulation time and poor antitumor efficacy, a novel prodrug (CLA-GEM conjugate) has been developed through the covalent coupling of conjugated linoleic acid (CLA) to N(4)-amino group of GEM. The chemical structure of CLA-GEM conjugate was identified by NMR, FTIR and other methods. From in vitro tests, it was demonstrated that the linkage with CLA increased the plasma stability of GEM as well as the antitumor activity against human breast tumor cells (MCF-7). Importantly, it also altered the transport pattern of GEM across cell membrane (MCF-7 and MDA-MB-231), evidenced by the little effect of nucleoside transporter inhibitors (NBMPR and dipyridamole) on the IC(50) values of CLA-GEM, instead of the great effect on that of unmodified GEM. In vivo pharmacokinetic study showed that the CLA-GEM conjugate had a longer plasma half-life and a higher bioavailability compared to that of unmodified GEM. Significant stronger antitumor activity was observed in the nude mice xenografted MCF-7 breast tumor after treated with CLA-GEM than that of unmodified GEM, while no significant body weight loss was found in all treatments. In conclusion, the novel CLA-GEM conjugate prepared in this study would be a promising prodrug of gemcitabine for future clinical use.

Elacytarabine has single-agent activity in patients with advanced acute myeloid leukaemia

Elacytarabine is a novel cytotoxic nucleoside analogue, independent of nucleoside transporters (e.g. human Equilibrative Nucleoside Transporter 1 [hENT1]) for cell uptake, and mechanisms of action similar to those of cytarabine. This Phase II study assessed the efficacy and safety of elacytarabine in patients with advanced stage acute myeloid leukaemia (AML). Patients received 2000 mg/m(2) per d continuously i.v. during days 1-5 every 3 weeks. Patients were matched by six risk factors with historical controls; remission rate (assessed after 1 or 2 cycles) and 6-month survival were compared. Sixty-one patients, median age 58 years, were enrolled; 52% had five or six risk factors. The remission rate was 18% (95% confidence interval: 9-30%) vs. 4% in controls (P < 0·0001), 6-month survival rate was 43%, median overall survival was 5·3 months (vs. 1·5 months); 10 patients (16%) were referred for stem cell transplantation after treatment. Side effects were predictable and manageable. The most common grade 3/4 non-haematological adverse events were febrile neutropenia, hypokalemia, fatigue, hyponatraemia, dyspnoea and pyrexia. Thirty-day all-cause mortality, after start of treatment, was 13% vs. 25% in controls. Elacytarabine has monotherapy activity in patients with advanced AML. This study provides proof-of-concept that lipid esterification of nucleoside analogues is clinically relevant.

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.

[Advances of drug resistance marker of gemcitabine for non-small cell lung cancer]

随着药物基因组学、药物遗传学的发展，基因指导下个体化治疗成为提高非小细胞肺癌（non-small cell lung cancer, NSCLC）化疗疗效的有效途径之一。确定药物的相关预测性分子标志物从而指导临床治疗、提高疗效被广泛关注。吉西他滨是目前NSCLC常用化疗药物之一，本文主要阐述了近年来吉西他滨药物耐药相关基因在NSCLC个体化治疗方面的研究进展。

Xenobiotic metabolism and disposition in human lung: transcript profiling in non-tumoral and tumoral tissues

The lung is directly exposed to a wide variety of inhaled toxicants and carcinogens. In order to improve our knowledge of the cellular processing of these compounds in the respiratory tract, we investigated the mRNA expression level of 380 genes encoding xenobiotic-metabolizing enzymes (XME), transporters, nuclear receptors and transcription factors, in pulmonary parenchyma (PP), bronchial mucosa (BM) and tumoral lung tissues from 12 patients with non-small cell lung cancer (NSCLC). Using a high throughput quantitative real-time RT-PCR method, we found that ADH1B, CYP4B1, CES1 and GSTP1 are the major XME genes expressed both in BM and PP. Our results also documented the predominant role played by the xenosensor AhR in human lung. The gene expression profiles were different for BM and PP, with a tendency toward increased mRNA levels of phase I and phase II XME genes in BM, suggesting major differences in the initial stages of xenobiotic metabolism. Some of the significantly overexpressed genes in BM (i.e. CYP2F1, CYP2A13, CYP2W1, NQO1…) encode proteins involved in the bioactivation of procarcinogens, pointing out distinct susceptibility to xenobiotics and their toxic effects between these two tissue types. Additionally, interindividual differences in transcript levels observed for some genes may be of genetic origin and may contribute to the variability in response to environmental exposure and, consequently, in the risk of developing lung diseases. A global decrease in gene expression was observed in tumoral specimens. Some of the proteins are involved in the metabolism or transport of anti-cancer drugs and their influence in the response of tumors to chemotherapy should be considered. In conclusion, the present study provides an overview of the cellular response to toxicants and drugs in healthy and cancerous human lung tissues, and thus improves our understanding of the mechanisms of chemical carcinogenesis as well as cellular resistance to chemotherapy.

Transmembrane diffusion of gemcitabine by a nanoparticulate squalenoyl prodrug: an original drug delivery pathway

We have designed an amphiphilic prodrug of gemcitabine (dFdC) by its covalent coupling to a derivative of squalene, a natural lipid. The resulting bioconjugate self-assembled spontaneously in water as nanoparticles that displayed a promising in vivo anticancer activity. The aim of the present study was to provide further insight into the in vitro subcellular localization and on the metabolization pathway of the prodrug. Cells treated with radiolabelled squalenoyl gemcitabine (SQdFdC) were studied by differential detergent permeation, and microautography coupled to fluorescent immunolabeling and confocal microscopy. This revealed that the bioconjugate accumulated within cellular membranes, especially in those of the endoplasmic reticulum. Radio-chromatography analysis proved that SQdFdC delivered dFdC directly in the cell cytoplasm. Mass spectrometry studies confirmed that gemcitabine was then either converted into its biologically active triphosphate metabolite or exported from the cells through membrane transporters. To our knowledge, this is the first description of such an intracellular drug delivery pathway. In vitro cytotoxicity assays revealed that SQdFdC was more active than dFdC on a transporter-deficient human resistant leukemia model, which was explained by the subcellular distribution of the drugs and their metabolites. The squalenoylation drug delivery strategy might, therefore, dramatically improve the efficacy of gemcitabine on transporter-deficient resistant cancer in the clinical context.

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.

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

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

Gemcitabine intercellular diffusion mediated by gap junctions: new implications for cancer therapy

Background

Solid tumors are often poorly vascularized, with cells that can be 100 μm away from blood vessels. These distant cells get less oxygen and nutrients and are exposed to lower doses of chemotherapeutic agents. As gap junctions allow the passage of small molecules between cells, we tested the possibility that the chemotherapeutic agent gemcitabine can diffuse through gap junctions in solid tumors.

Results

We first showed with a dye transfer assay that the glioblastoma and the osteosarcoma cells used in this study have functional gap junctions. These cells were genetically engineered to express the herpes simplex virus thymidine kinase (TK), and induced a "bystander effect" as demonstrated by the killing of TK-negative cells in presence of the nucleoside analogue ganciclovir (GCV). The ability of gemcitabine to induce a similar bystander effect was then tested by mixing cells treated with 3 μM gemcitabine for 24 hours with untreated cells at different ratios. In all cell lines tested, bystander cells were killed with ratios containing as low as 5% treated cells, and this toxic effect was reduced in presence of α-glycyrrhetinic acid (AGA), a specific gap junction inhibitor. We also showed that a 2- or a 24-hour gemcitabine treatment was more efficient to inhibit the growth of spheroids with functional gap junctions as compared to the same treatment made in presence of AGA. Finally, after a 24-hour gemcitabine treatment, the cell viability in spheroids was reduced by 92% as opposed to 51% in presence of AGA.

Conclusion

These results indicate that gemcitabine-mediated toxicity can diffuse through gap junctions, and they suggest that gemcitabine treatment could be more efficient for treating solid tumors that display gap junctions. The presence of these cellular channels could be used to predict the responsiveness to this nucleoside analogue therapy.

Drug transporter pharmacogenetics in nucleoside-based therapies

This article focuses on the different types of transporter proteins that have been implicated in the influx and efflux of nucleoside-derived drugs currently used in the treatment of cancer, viral infections (i.e., AIDS) and other conditions, including autoimmune and inflammatory diseases. Genetic variations in nucleoside-derived drug transporter proteins encoded by the gene families SLC15, SLC22, SLC28, SLC29, ABCB, ABCC and ABCG will be specifically considered. Variants known to affect biological function are summarized, with a particular emphasis on those for which clinical correlations have already been established. Given that relatively little is known regarding the genetic variability of the players involved in determining nucleoside-derived drug bioavailability, it is anticipated that major challenges will be faced in this area of research.

Human nucleoside transporters: biomarkers for response to nucleoside drugs

This review describes recent advances in developing human nucleoside transporters (hNTs) as biomarkers to predict response to nucleoside analog drugs with clinical activity. Understanding processes that contribute to drug response or lack thereof will provide strategies to potentiate efficacy or avoid toxicities of nucleoside analog drugs. hNT abundance, evaluated by immunohistochemical methods, has shown promise as a predictive marker to assess clinical drug response that could be used to identify patients who would most likely benefit from nucleoside analog drug treatment.

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.

Comparative proteomic profiling identified sorcin being associated with gemcitabine resistance in non-small cell lung cancer

Although gemcitabine-based chemotherapy is one of the more effective chemotherapy regimens against NSCLC, there are still many patients who do not benefit from this therapy. The mechanism of initial or acquired resistance to gemcitabine chemotherapy remains unknown. In this study, we investigated the protein profiling in gemcitabine-resistant and gemcitabine-sensitive NSCLC cell lines by a proteomic technology in order to identify novel gemcitabine resistance associated biomarkers for NSCLC patients. The proteomic profiling of NSCLC cell line H460 and its gemcitabine-resistant subline H460/GEM were compared by an isotope-coded affinity tag technology and tandem mass spectrometry. We further validated the expression of sorcin, a gemcitabine-resistance-related protein identified by proteomics, in 62 NSCLC specimens by immunohistochemistry. Fourteen gemcitabine resistance-related proteins were identified including nine up-regulated proteins and five down-regulated proteins. Immunohistochemical results demonstrated that sorcin staining was seen in 66.1% of NSCLC tumors, and sorcin overexpression was associated with gemcitabine resistance and a poor prognosis in NSCLC patients. In conclusion, sorcin might play an important role in the resistance to gemcitabine, and it could also be a novel candidate biomarker for predicting the response of NSCLC patients to gemcitabine treatment.

Pharmacogenetics and pharmacoepigenetics of gemcitabine

Gemcitabine (2',2'-difluoro 2'deoxycytidine, dFdC) is an analog of cytosine with distinctive pharmacological properties and a wide antitumor-activity spectrum. The pharmacological characteristics of gemcitabine are unique because two main classes of genes are essential for its antitumor effects: membrane transporter protein-coding genes, whose products are responsible for drug intracellular uptake, as well as enzyme-coding genes, which catalyze its activation and inactivation. The study of the pharmacogenetics and pharmacoepigenetics of these two gene classes is greatly required to optimize the drug's therapeutic use in cancer. This review aims to provide an update of genetic and epigenetic bases that may account for interindividual variation in therapeutic outcome exhibited by gemcitabine.

Towards to hENT1-nucleoside transporter selective imaging agents. Synthesis and in vitro evaluation of the radiolabeled SAENTA analogues

Three new potential hENT(1) inhibitors suitable for labeling with PET/SPECT radioisotopes were prepared from an advanced intermediate 4. They were tested for their capability to inhibit binding of SAENTA-fluorescein to HL60 leukemia cells in flow cytometry assay and SAENTA-I (5) was determined to be the most active compound. (131)I-5 showed high hENT(1)-specific binding (up to 54% ID) to 6 from 7 tested tumor cell lines and was chosen for further in vivo study.