Retroviral transduction of human dihydropyrimidine dehydrogenase cDNA confers resistance to 5-fluorouracil in murine hematopoietic progenitor cells and human CD34+-enriched peripheral blood progenitor cells

Exploring the potential of P-glycoprotein inhibitors in the targeted delivery of anti-cancer drugs: A comprehensive review

Due to the high prevalence of cancer, progress in the management of cancer is the need of the hour. Most cancer patients develop chemotherapeutic drug resistance, and many remain insidious due to overexpression of Multidrug Resistance Protein 1 (MDR1), also known as Permeability-glycoprotein (P-gp) or ABCB1 transporter (ATP-binding cassette subfamily B member 1). P-gp, a transmembrane protein that protects vital organs from outside chemicals, expels medications from malignant cells. The blood-brain barrier (BBB), gastrointestinal tract (GIT), kidneys, liver, pancreas, and cancer cells overexpress P-gp on their apical surfaces, making treatment inefficient and resistant. Compounds that compete with anticancer medicines for transportation or directly inhibit P-gp may overcome biological barriers. Developing nanotechnology-based formulations may help overcome P-gp-mediated efflux and improve bioavailability and cell chemotherapeutic agent accumulation. Nanocarriers transport pharmaceuticals via receptor-mediated endocytosis, unlike passive diffusion, which bypasses ABCB1. Anticancer drugs and P-gp inhibitors in nanocarriers may synergistically increase drug accumulation and chemotherapeutic agent toxicity. The projection of desirable binding and effect may be procured initially by molecular docking of the inhibitor with P-gp, enabling the reduction of preliminary trials in formulation development. Here, P-gp-mediated efflux and several possible outcomes to overcome the problems associated with currently prevalent cancer treatments are highlighted.

The BRCT Domain from the Homologue of the Oncogene PES1 in Leishmania major (LmjPES) Promotes Malignancy and Drug Resistance in Mammalian Cells

Around 15% of cancer cases are attributable to infectious agents. Epidemiological studies suggest that an association between leishmaniasis and cancer does exist. Recently, the homologue of PES1 in Leishmania major (LmjPES) was described to be involved in parasite infectivity. Mammalian PES1 protein has been implicated in cellular processes like cell cycle regulation. Its BRCT domain has been identified as a key factor in DNA damage-responsive checkpoints. This work aimed to elucidate the hypothetical oncogenic implication of BRCT domain from LmjPES in host cells. We generated a lentivirus carrying this BRCT domain sequence (lentiBRCT) and a lentivirus expressing the luciferase protein (lentiLuc), as control. Then, HEK293T and NIH/3T3 mammalian cells were infected with these lentiviruses. We observed that the expression of BRCT domain from LmjPES conferred to mammal cells in vitro a greater replication rate and higher survival. In in vivo experiments, we observed faster tumor growth in mice inoculated with lentiBRCT respect to lentiLuc HEK293T infected cells. Moreover, the lentiBRCT infected cells were less sensitive to the genotoxic drugs. Accordingly, gene expression profiling analysis revealed that BRCT domain from LmjPES protein altered the expression of proliferation- (DTX3L, CPA4, BHLHE41, BMP2, DHRS2, S100A1 and PARP9), survival- (BMP2 and CARD9) and chemoresistance-related genes (DPYD, Dok3, DTX3L, PARP9 and DHRS2). Altogether, our results reinforced the idea that in eukaryotes, horizontal gene transfer might be also achieved by parasitism like Leishmania infection driving therefore to some crucial biological changes such as proliferation and drug resistance.

5-Fluorouracil efficacy requires anti-tumor immunity triggered by cancer-cell-intrinsic STING

5-Fluorouracil (5-FU) is a widely used chemotherapeutic drug, but the mechanisms underlying 5-FU efficacy in immunocompetent hosts in vivo remain largely elusive. Through modeling 5-FU response of murine colon and melanoma tumors, we report that effective reduction of tumor burden by 5-FU is dependent on anti-tumor immunity triggered by the activation of cancer-cell-intrinsic STING. While the loss of STING does not induce 5-FU resistance in vitro, effective 5-FU responsiveness in vivo requires cancer-cell-intrinsic cGAS, STING, and subsequent type I interferon (IFN) production, as well as IFN-sensing by bone-marrow-derived cells. In the absence of cancer-cell-intrinsic STING, a much higher dose of 5-FU is needed to reduce tumor burden. 5-FU treatment leads to increased intratumoral T cells, and T-cell depletion significantly reduces the efficacy of 5-FU in vivo. In human colorectal specimens, higher STING expression is associated with better survival and responsiveness to chemotherapy. Our results support a model in which 5-FU triggers cancer-cell-initiated anti-tumor immunity to reduce tumor burden, and our findings could be harnessed to improve therapeutic effectiveness and toxicity for colon and other cancers.

Regulation of REG4 Expression and Prediction of 5-Fluorouracil Sensitivity by CDX2 in Ovarian Mucinous Carcinoma

BACKGROUND/AIM

The biological importance of the caudal-related homeobox transcription factor CDX2 in acquiring resistance to anticancer drugs has been studied in ovarian mucinous carcinoma. CDX2 promotes the expression of multidrug resistance 1 (MDR1) and confers resistance to paclitaxel. The regenerating islet-derived family member 4 (REG4) gene is a potential target gene of CDX2. In this study, we investigated the relationship between the expression of CDX2 and Reg IV and the regulation of Reg IV expression and examined novel chemotherapeutic regimens.

MATERIALS AND METHODS

The regulation of Reg IV expression by CDX2 and sensitivity of 5-fluorouracil (5-FU) were evaluated using ovarian mucinous cancer cell lines.

RESULTS

The correlation of CDX2 with Reg IV expression was demonstrated in ovarian mucinous carcinoma. Reg IV expression was enhanced by transfection of CDX2 and was suppressed by inhibition of CDX2 expression. OMC-3 cells with ectopically overexpressed CDX2 showed enhanced apoptosis and sensitivity to 5-FU.

CONCLUSION

CDX2 promotes resistance to paclitaxel and sensitivity to 5-FU. Novel 5-FU-based chemotherapy based on CDX2 may be used in ovarian mucinous carcinoma.

5-fluorouracil and other fluoropyrimidines in colorectal cancer: Past, present and future

5-Fluorouracil (5-FU) is an essential component of systemic chemotherapy for colorectal cancer (CRC) in the palliative and adjuvant settings. Over the past four decades, several modulation strategies including the implementation of 5-FU-based combination regimens and 5-FU pro-drugs have been developed and tested to increase the anti-tumor activity of 5-FU and to overcome the clinical resistance. Despite the encouraging progress in CRC therapy to date, the patients' response rates to therapy continue to remain low and the patients' benefit from 5-FU-based therapy is frequently compromised by the development of chemoresistance. Inter-individual differences in the treatment response in CRC patients may originate in the unique genetic and epigenetic make-up of each individual. The critical element in the current trend of personalized medicine is the proper comprehension of causes and mechanisms contributing to the low or lack of sensitivity of tumor tissue to 5-FU-based therapy. The identification and validation of predictive biomarkers for existing 5-FU-based and new targeted therapies for CRC treatment will likely improve patients' outcomes in the future. Herein we present a comprehensive review summarizing options of CRC treatment and the mechanisms of 5-FU action at the molecular level, including both anabolic and catabolic ways. The main part of this review comprises the currently known molecular mechanisms underlying the chemoresistance in CRC patients. We also focus on various 5-FU pro-drugs developed to increase the amount of circulating 5-FU and to limit toxicity. Finally, we propose future directions of personalized CRC therapy according to the latest published evidence.

Colon Cancer Cells Gene Expression Signature As Response to 5- Fluorouracil, Oxaliplatin, and Folinic Acid Treatment

5-FU cytotoxicity mechanism has been assigned both to the miss-incorporation of fluoronucleotides into RNA and DNA and to the inhibition of thymidylate synthase. 5-FU is one of the most widely used chemotherapeutic drugs, although it has severe side effects that may vary between patients. Pharmacogenetic studies related to 5-FU have been traditionally focused on the rate-limiting catabolic enzyme, dihydropyrimidine dehydrogenase that breaks 80–85% of 5-FU into its inactive metabolite. Choosing the right dosing scheme and chemotherapy strategy for each individual patient remains challenging for personalized chemotherapy management. In the general effort toward reduction of colorectal cancer mortality, in vitro screening studies play a very important role. To accelerate translation research, increasing interest has been focused on using in vivo-like models such as three-dimensional spheroids. The development of higher throughput assays to quantify phenotypic changes in spheroids is an active research area. Consequently, in this study we used the microarray technology to reveal the HT-29 colorectal adenocarcinoma cells gene expression signature as response to 5-FU/OXP/FA treatment in a state of the art 3D culture system. We report here an increased reactive oxygen species production under treatment, correlated with a decrease in cell viability and proliferation potential. With respect to the HT-29 cells gene expression under the treatment with 5-FU/OXP/FA, we found 15.247 genes that were significantly differentially expressed (p < 0.05) with a fold change higher that two-fold. Among these, 7136 genes were upregulated and 8111 genes were downregulated under experimental conditions as compared to untreated cells. The most relevant and statistic significant (p < 0.01) pathways in the experiment are associated with the genes that displayed significant differential expression and are related to intracellular signaling, oxidative stress, apoptosis, and cancer.

Cancer chemoresistance; biochemical and molecular aspects: a brief overview

The effectiveness of chemotherapy is one of the main challenges in cancer treatment and resistance to classic drugs and traditional treatment processes is an obstacle to this goal. Drug resistance that may be inherent or adventitious can cause poor treatment outcome and tumor relapse. In most cases, resistance to a drug can lead to resistance to many other drugs structure and function of which is not necessarily similar to the first drug. This phenomenon is the main mechanism behind failure of many of metastatic cancers. There are various molecular mechanisms involved in multidrug resistance, including change in the activity of membrane transporters (such as ABC transporters), increase of drug metabolism, change of the target enzyme (such as mutations that change thymidylate synthase and topoisomerases), promotion of DNA damage repair, and escape from drug induced apoptosis. Clinical and laboratory investigations on biomarkers involved in the response to chemotherapy have characterized the key factors behind the failure of treatments. Knowing the molecular factors involved in drug resistance may help us to develop new strategies for more promising chemotherapy and reduce the rate of relapse. In this brief review, molecular mechanisms and tumor microenvironment leading to decreased drug sensitivity, and strategies of reversing drug resistance are described.

Pharmacologic resistance in colorectal cancer: a review

Colorectal cancer (CRC) persists as one of the most prevalent and deadly tumor types in both men and women worldwide. This is in spite of widespread, effective measures of preventive screening, and also major advances in treatment options. Despite advances in cytotoxic and targeted therapy, resistance to chemotherapy remains one of the greatest challenges in long-term management of incurable metastatic disease and eventually contributes to death as tumors accumulate means of evading treatment. We performed a comprehensive literature search on the data available through PubMed, Medline, Scopus, and the ASCO Annual Symposium abstracts through June 2015 for the purpose of this review. We discuss the current state of knowledge of clinically relevant mechanisms of resistance to cytotoxic and targeted therapies now in use for the treatment of CRC.

The role of Reg IV in colorectal cancer, as a potential therapeutic target

Regenerating islet-derived family, member 4 (Reg IV), a member of the Reg gene family, has been reported to be overexpressed in gastrointestinal tract cancers. Reg IV overexpression in tumor cells has been associated with carcinogenesis, tissue regeneration, proliferation and resistance to apoptosis. Reg IV activates the epidermal growth factor receptor (EGFR) signaling pathway in colon cancer and increases expression of B-cell lymphoma-2 (Bcl-2) and B-cell lymphoma-extra large (Bcl-xl), which are associated with the inhibition of apoptosis, results in mitogenic signaling in colon cancer cells, increase cell proliferation, metastasis and decreased apoptosis. Reg IV treatment inhibits 5-fluorouracil induced apoptosis, at least two mechanisms are involved in inhibition of apoptosis by Reg IV, including Bcl-2 and dihydropyrimidine dehydrogenase (DPD). These studies may lead to novel therapeutic strategies for cancers expressing Reg IV. Recently, one proteoglycan was confirmed to disrupt this signaling pathway to perform antitumor effect. This review summaries current knowledge of the expression and roles of Reg IV in human colorectal cancer, describes the possible signaling pathway which Reg IV activates, and discusses the relevance of Reg IV as a potential therapeutic target for cancer treatment.

γ-Glutamyl hydrolase modulation significantly influences global and gene-specific DNA methylation and gene expression in human colon and breast cancer cells

γ-Glutamyl hydrolase (GGH) plays an important role in folate homeostasis by catalyzing hydrolysis of polyglutamylated folate into monoglutamates. Polyglutamylated folates are better substrates for several enzymes involved in the generation of S-adenosylmethionine, the primary methyl group donor, and hence, GGH modulation may affect DNA methylation. DNA methylation is an important epigenetic determinant in gene expression, in the maintenance of DNA integrity and stability, and in chromatin modifications, and aberrant or dysregulation of DNA methylation has been mechanistically linked to the development of human diseases including cancer. Using a recently developed in vitro model of GGH modulation in HCT116 colon and MDA-MB-435 breast cancer cells, we investigated whether GGH modulation would affect global and gene-specific DNA methylation and whether these alterations were associated with significant gene expression changes. In both cell lines, GGH overexpression decreased global DNA methylation and DNA methyltransferase (DNMT) activity, while GGH inhibition increased global DNA methylation and DNMT activity. Epigenomic and gene expression analyses revealed that GGH modulation influenced CpG promoter DNA methylation and gene expression involved in important biological pathways including cell cycle, cellular development, and cellular growth and proliferation. Some of the observed altered gene expression appeared to be regulated by changes in CpG promoter DNA methylation. Our data suggest that the GGH modulation-induced changes in total intracellular folate concentrations and content of long-chain folylpolyglutamates are associated with functionally significant DNA methylation alterations in several important biological pathways.

Data-driven assessment of the association of polymorphisms in 5-Fluorouracil metabolism genes with outcome in adjuvant treatment of colorectal cancer

A major challenge in the assessment of medicines, treatment options, etc., is to establish a framework for the comparison of risks and benefits of many different types and magnitudes, a framework that at the same time allows a clear distinction between the roles played by the statistical analyses of data and by judgements based on personal experience and expertise. The purpose of this study was to demonstrate how clinical data can be weighted, scored and presented by the use of an eight-step data-driven benefit-risk assessment method, where two genetic profiles are compared. Our aim was to present a comprehensive approach that is simple to apply, allows direct comparison of different types of risks and benefits, quantifies the clinical relevance of data and is tailored for the comparison of different options. We analysed a cohort of 302 patients with colorectal cancer treated with 5-Fluorouracil (5-FU). Endpoints were cure rate, survival rate, time-to-death (TTD), time-to-relapse (TTR) and main adverse drug reactions. Multifactor dimensionality reduction (MDR) was used to identify genetic interaction profiles associated with outcome. We have been able to demonstrate that a specific MDR-derived combination (the MDR-1 group) of dihydropyrimidine dehydrogenase and thymidylate synthase polymorphisms is associated with increased and clinically significant difference for cure and survival rates, TTD and probably also for TTR, which are seen as the most important endpoints. An inferior profile was observed for severe myocardial ischaemia. A probably inferior profile was seen for severe arthralgia/myalgia and severe infections. A clear superior profile was seen for severe mucositis/stomatitis. The proposed approach offers comprehensive, data-driven assessment that can facilitate decision processes, for example, in a clinical setting. It employs descriptive statistical methods to highlight the clinically relevant differences between options.

The association of polymorphisms in 5-fluorouracil metabolism genes with outcome in adjuvant treatment of colorectal cancer

AIM

The purpose of this study was to investigate whether specific combinations of polymorphisms in 5-fluorouracil (5-FU) metabolism-related genes were associated with outcome in 5-FU-based adjuvant treatment of colorectal cancer.

METHODS

We analyzed two cohorts of 302 and 290 patients, respectively, one cohort for exploratory analyses and another cohort for validating the exploratory analyses. A total of ten polymorphisms in genes involved in 5-FU pharmacodynamics and pharmacokinetics were studied. End points were disease-free survival (DFS) and overall survival. Multifactor dimensionality reduction was used to identify genetic interaction profiles associated with outcome.

RESULTS

Low-expression alleles in thymidylate synthase (TYMS) were associated with decreased DFS and overall survival (DFS:hazard ratio [HR] exploration 2.65 [1.40-4.65]; p = 0.004, HR validation 1.69 [1.03-2.66]; p = 0.03). A specific multifactor dimensionality reduction derived combination of dihydropyrimidine dehydrogenase and TYMS polymorphisms was associated with increased DFS (HR exploration 0.69 [0.49-0.98]; p = 0.04, HR validation 0.66 [0.45-0.95]; p = 0.03). Specific combinations of functional polymorphisms in DPYD and TYMS were demonstrated to be associated with DFS and overall survival in patients receiving adjuvant 5-FU-based treatment. Specifically high TYMS expression alleles seem to be associated with decreased DFS.

Clinical determinants of response to irinotecan-based therapy derived from cell line models

PURPOSE

In an attempt to identify genes that are involved in resistance to SN38, the active metabolite of irinotecan (also known as CPT-11), we carried out DNA microarray profiling of matched HCT116 human colon cancer parental cell lines and SN38-resistant cell lines following treatment with SN38 over time.

EXPERIMENTAL DESIGN

Data analysis identified a list of genes that were acutely altered in the parental cells following SN38 treatment as well as constitutively altered in the SN38-resistant cells.

RESULTS

Independent validation of 20% of these genes by quantitative reverse transcription-PCR revealed a strong correlation with the microarray results: Pearson's correlation was 0.781 (r(2) = 0.61, P < 0.000001) for those genes that were acutely altered in the parental setting following SN38 treatment and 0.795 (r(2) = 0.63, P < 0.000002) for those genes that were constitutively altered in the SN38-resistant cells. We then assessed the ability of our in vitro-derived gene list to predict clinical response to 5-fluorouracil/irinotecan using pretreatment metastatic biopsies from responding and nonresponding colorectal cancer patients using both unsupervised and supervised approaches. When principal components analysis was used with our in vitro classifier gene list, a good separation between responding and nonresponding patients was obtained, with only one nonresponding and two responding patients separating with the incorrect groups. Supervised class prediction using support vector machines algorithm identified a 16-gene classifier with 75% overall accuracy, 81.8% sensitivity, and 66.6% specificity.

CONCLUSIONS

These results suggest that in vitro-derived gene lists can be used to predict clinical response to chemotherapy in colorectal cancer.

Reg IV is a serum biomarker for gastric cancer patients and predicts response to 5-fluorouracil-based chemotherapy

Regenerating gene family, member 4 (Reg IV), a secreted protein, is overexpressed in several cancers, including gastric cancer (GC). In the present study, we measured Reg IV levels in sera from patients with GC by enzyme-linked immunosorbent assay. We also examined the effect of forced Reg IV expression on the apoptotic susceptibility to 5-fluorouracil (5-FU). Forced expression of Reg IV inhibited 5-FU-induced apoptosis. Induction of Bcl-2 and dihydropyrimidine dehydrogenase was involved in inhibition of apoptosis. Among 36 GC patients treated with a combination chemotherapy of low-dose 5-FU and cisplatin, all 14 Reg IV-positive patients showed no change or disease progression. The serum Reg IV concentration was similar between healthy individuals (mean+/-s.e., 0.52+/-0.05 ng/ml) and patients with chronic-active gastritis (0.36+/-0.09 ng/ml). However, the serum Reg IV concentration in presurgical GC patients was significantly elevated (1.96+/-0.17 ng/ml), even at stage I. The diagnostic sensitivity of serum Reg IV (36.1%) was superior to that of serum carcinoembryonic antigen (11.5%) or carbohydrate antigen 19-9 (13.1%). These results indicate that expression of Reg IV is a marker for prediction of resistance to 5-FU-based chemotherapy in patients with GC. Serum Reg IV represents a novel biomarker for GC.

Drug resistance, predictive markers and pharmacogenomics in colorectal cancer

Resistance to chemotherapy limits the effectiveness of current cancer therapies, including those used to treat colorectal cancer, which is the second most common cause of cancer death in Europe and the United States. 5-Fluorouracil-based chemotherapy regimens are the standard treatment for colorectal cancer in both the adjuvant and advanced disease settings. Drug resistance is thought to cause treatment failure in over 90% of patients with metastatic cancer, while drug resistant micrometastic tumour cells may also reduce the impact of adjuvant chemotherapy treatment. The identification of panels of biomarkers that not only identify those patients most likely to benefit from chemotherapy treatment, but also which chemotherapies to use, would be a major advance. In this review, we describe molecular mechanisms of drug resistance that may be relevant to colorectal cancer. We also describe the results of predictive biomarker studies in this disease. Finally, we discuss how pharmacogenomics and other high through-put technologies may impact on the clinical management of colorectal cancer in the future.

Coexpression of the Uracil Phosphoribosyltransferase Gene with a Chimeric Human Nerve Growth Factor Receptor/Cytosine Deaminase Fusion Gene, Using a Single Retroviral Vector, Augments Cytotoxicity of Transduced Human T Cells Exposed to 5-Fluorocytosine

Donor T lymphocytes genetically engineered to express a "suicide gene" to facilitate negative selection represent a promising strategy for the management of graft-versus-host disease occurring after allogeneic hematopoietic cell transplantation (HCT). For this purpose, the herpes simplex virus thymidine kinase (HSV-tk) gene, although well studied, has limitations. Cytosine deaminase (CD), an alternative gene for negative selection, converts 5-fluorocytosine (5-FC) to the toxic metabolite 5-fluorouracil (5-FU). Sensitivity of cells to 5-FU can be further increased by expression of uracil phosphoribosyltransferase (UPRT), which catalyzes the conversion of 5-FU to 5-fluorouridine monophosphate. By using a chimeric gene (NG/CD) expressing the truncated human nerve growth factor receptor (NGFR) for positive selection fused to the Saccharomyces cerevisiae CD gene, we investigated strategies to achieve optimal T cell eradication by CD and UPRT expression, utilizing a single retroviral vector. Three vector strategies were compared on the basis of NGFR expression by flow cytometry, western analysis, and enzymatic activity. A construct (NG/CDiU) expressing UPRT and NG/CD, using a bicistronic message, provided the greatest UPRT activity and killing, reducing the lethal dose of 5-FC sufficient to eradicate 90% of cells from 38.7 microg/ml (300 microM) (NG/CD expression alone) to 0.13 microg/ml (1 microM). This approach provides an effective alternative to the HSV-tk system for eradication of donor T lymphocytes after allogeneic HCT.

Have we made progress in pharmacogenomics? The implementation of molecular markers in colon cancer

For the last 40 years, 5-fluorouracil (5-FU) has remained the treatment of choice in both the adjuvant and advanced treatment of colorectal cancer (CRC). However, 5-FU monotherapy produces response rates of only 10–20% in the advanced setting. 5-FU has been combined with newer agents, such as oxaliplatin and irinotecan, and this has significantly increased response rates to 40–50% in the advanced setting. More recently, novel biological agents, such as the monoclonal antibodies targeting either the epidermal growth factor receptor or vascular endothelial growth factor, have shown to provide additional clinical benefit for patients with metastatic CRC. A number of predictive markers have been identified for CRC to date. However, their usefulness as individual markers of response has led to somewhat inconclusive results. Therefore, there is a need to identify panels of predictive markers of response to therapy for advanced CRC, in order to improve these disappointing response rates. The advent of high-throughput methodologies, such as microarrays, enables tumor samples to be profiled on a global scale. This technology has been utilized to develop predictive markers for a wide range of tumor types to date, and hopefully this technology can be translated into the CRC setting with the hope of predicting the response of each individual tumor to chemotherapy.

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Protection of cytidine deaminase gene gainst toxicity of high-dose chemotherapy in mice

AIM: To observe the tolerance to high-dose cytarabine (Ara-C) in mice after the cytidine deaminase (CD) gene is transfected into mouse bone marrow cells, and to explore the feasibility of chemotherapy combined with the tolerance of myelosuppression.

METHODS: Human cytidine deaminase gene was transfected into mouse bone marrow cells by retroviral vector. Then the colony-forming unit granulocyte-macrophage (CFU-GM) was observed in the cells of marrow donor and acceptor mice treated with Ara-C. DNA was extracted from the cells and the drug-resistant genes were detected by polymerase chain reaction (PCR). The blood cell count, weight and survival rate of the mice treated with Ara-C were analyzed.

RESULTS: Drug-resistant colonies appeared both in the bone marrow cells of donor and acceptor mice treated with Ara-C, and the CFU-GMs were 52% and 54% respectively, which were significantly higher than those of the controls (χ²= 124.62, 126.26; both P<0.01). The survival rate was significantly higher in CD-transfected mice as compared with that in the controls (χ² = 7.42, P<0.01), and the blood cell count and body weight decreased less and recovered sooner. CD gene was expressed in the bone marrow cells of transfected mice.

CONCLUSION: Drug-resistant gene can not only integrate and express in mouse bone marrow cells, but also promote the tolerance to high-dose Ara-C.

Role of Genomic Markers in Colorectal Cancer Treatment

For the last four decades, fluorouracil (FU) has been the main treatment of choice in colorectal cancer (CRC) in both the advanced and adjuvant settings. In the advanced setting, FU monotherapy produces response rates of only 10% to 20%. Furthermore, in resected stage III CRC, FU monotherapy has increased overall survival by only 20%. The combination of FU with newer therapies such as oxaliplatin and irinotecan has significantly improved response rates to 40% to 50%. Despite these improvements, more than half of advanced CRC patients derive no benefit from treatment; this is due to either acquired or inherent drug resistance. This review aims to highlight the current prognostic and predictive markers that have been identified for CRC to date. The limited use of these predictive markers underscores the importance of and need for multiple marker testing in order to improve response rates and decrease toxicity. This review will also focus on high throughput methods to identify panels of predictive markers for CRC, which ultimately aim to tailor treatment according to an individual patient and tumor profile.

Genome-wide expression analysis of therapy-resistant tumors reveals SPARC as a novel target for cancer therapy

Overcoming resistance to chemotherapy and radiation therapy has been a difficult but important goal in the effort to cure cancer. We used gene-expression microarrays to identify differentially expressed genes involved in colorectal cancer resistance to chemotherapy and identified secreted protein, acidic and rich in cysteine (osteonectin) (SPARC) as a putative resistance-reversal gene by demonstrating low SPARC expression in refractory human MIP101 colon cancer cells. We were able to achieve restoration of their radiosensitivity and sensitivity to 5-fluorouracil and irinotecan by reexpression of SPARC in tumor xenografts. Moreover, treatment of mice with SPARC conferred increased sensitivity to chemotherapy and led to significant regression of xenografted tumors. The results show that modulation of SPARC expression affects colorectal cancer sensitivity to radiation and chemotherapy. SPARC-based gene or protein therapy may ameliorate the emergence of resistant clones and eradicate existing refractory clones and offers a novel approach to treating cancer.

Protection of hematopoietic stem cells from pemetrexed toxicity by retroviral gene transfer with a mutant dihydrofolate reductase-mutant thymidylate synthase fusion gene

Myelosuppression is one of the major side effects of most anticancer drugs. To confer myeloprotection, our laboratory generated drug-resistant mutants of select target human enzymes for gene transfer to the bone marrow. Mutants of two of these enzymes, dihydrofolate reductase (DHFR F/S) and thymidylate synthase (TS G52S), were previously shown to confer resistance to methotrexate and 5-FU, respectively, and recently a fusion cDNA of both mutant enzymes (DHFR F/S-TS G52S) was shown to confer dual resistance to both antimetabolites. In this study, we examined the sensitivity of the DHFR F/S-TS G52S fusion protein to the multitargeted antifolate, pemetrexed (LY231514, Alimta), which targets both DHFR and TS and is currently in phase III trials for the treatment of solid tumors and in combination with cisplatin has been shown to be an advance in the treatment of mesothelioma. The K(i) for the DHFR F/S portion of the purified fusion protein to pemetrexed was increased by greater than 9000-fold when compared to wtDHFR (8000 versus 0.86 nM), while the K(i) for the TS G52S portion of the fusion protein to pemetrexed was similar to that of wtTS (2.8 versus 3.1 nM). When the fusion gene was retrovirally transduced into NIH 3T3 fibroblasts, the IC(50) to pemetrexed was three- to four-fold higher than cells transduced with DHFR F/S or TS G52S alone (163 versus 53 and 45 nM, respectively). Similarly, expression of the DHFR F/S-TS G52S fusion gene in retrovirally transduced mouse marrow cells resulted in an increased survival of CFU-GM colonies when compared to cells transduced with either of the mutants alone. Co-expression of mutant DHFR and TS enzymes has additive effects in conferring resistance to pemetrexed-induced toxicity. This construct may be useful for conferring myeloprotection to patients receiving this drug.

Molecular mechanisms of drug resistance

Resistance to chemotherapy limits the effectiveness of anti-cancer drug treatment. Tumours may be intrinsically drug-resistant or develop resistance to chemotherapy during treatment. Acquired resistance is a particular problem, as tumours not only become resistant to the drugs originally used to treat them, but may also become cross-resistant to other drugs with different mechanisms of action. Resistance to chemotherapy is believed to cause treatment failure in over 90% of patients with metastatic cancer, and resistant micrometastic tumour cells may also reduce the effectiveness of chemotherapy in the adjuvant setting. Clearly, if drug resistance could be overcome, the impact on survival would be highly significant. This review focuses on molecular mechanisms of drug resistance that operate to reduce drug sensitivity in cancer cells. Drug resistance can occur at many levels, including increased drug efflux, drug inactivation, alterations in drug target, processing of drug-induced damage, and evasion of apoptosis. Advances in DNA microarray and proteomic technology, and the ongoing development of new targeted therapies have opened up new opportunities to combat drug resistance. We are now able to characterize the signalling pathways involved in regulating tumour cell response to chemotherapy more completely than ever before. This will facilitate the future development of rational combined chemotherapy regimens, in which the newer targeted therapies are used in combination with cytotoxic drugs to enhance chemotherapy activity. The ability to predict response to chemotherapy and to modulate this response with targeted therapies will permit selection of the best treatment for individual patients.

Protection against toxicity of high dose chemotherapy in mice transfected with double-mutant dihydrofolate reductase-cytidine deaminase gene

AIM: To explore the feasibility of transferring dihydrofolate reductase- (DHFR) gene and cytidine deaminase (CD) fusion gene into mouse bone marrow (BM) cells to induce resistance to high dose methotrexate (MTX) and cytosine arabinoside (Ara-C), and to improve the tolerance of myelosuppression following combination chemotherapy.

METHODS: Human double-mutant DHFR-CD fusion gene was transferred into mouse BM cells by retroviral vector Granulocyte-macrophage colony-forming unit (CFU-GM) assay was performed for retrovirally infected and drug treated mouse BM cells. DNA was extracted from mouse BM, and the expression of drug resistant genes was examined by PCR.

RESULTS: Drug resistant colonies were formed by donor mouse BM cells co-cultured with the retrovirus producing cells, as well as the BM cells from recipient mice transplanted with the fusion gene transfected BM cells (CFU-GM of donor mice was 14%, χ² = 42.55, P<0.01; CFU-GM of recipient mice was 20%, χ² = 44.26, P<0.01). The drug resistance to both MTX and Ara-C was also increased in the recipient mice. The survival rate of gene transferred mice was significantly higher compared with the control mice χ² = 7.42, P<0.01. Expression of the DHFR-CD fusion gene in the transfected mice was confirmed by PCR.

CONCLUSION: Double drug resistant genes can be integrated and expressed in mouse bone marrow cells; furthermore, they can increase the drug resistance to MTX and Ara-C.

Characterization of p53 wild-type and null isogenic colorectal cancer cell lines resistant to 5-fluorouracil, oxaliplatin, and irinotecan

To elucidate mechanisms of resistance to chemotherapies currently used in the first-line treatment of advanced colorectal cancer, we have developed a panel of HCT116 p53 wild-type (p53(+/+)) and null (p53(-/-)) isogenic colorectal cancer cell lines resistant to the antimetabolite 5-fluorouracil (5-FU), topoisomerase I inhibitor irinotecan (CPT-11), and DNA-damaging agent oxaliplatin. These cell lines were generated by repeated exposure to stepwise increasing concentrations of each drug over a period of several months. We have demonstrated a significant decrease in sensitivity to 5-FU, CPT-11, and oxaliplatin in each respective resistant cell line relative to the parental line as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis, with increases in IC(50 (72 h)) concentrations ranging from 3- to 65-fold. Using flow cytometry, we have also demonstrated compromised apoptosis and cell cycle arrest in 5-FU-, oxaliplatin-, and CPT-11-resistant cell lines compared with the parental lines after exposure to each drug. In addition, we found that resistance to 5-FU and oxaliplatin was higher in parental p53(-/-) cells compared with parental p53(+/+) cells, with an approximately 5-fold increase in IC(50 (72 h)) for each drug. In contrast, the IC(50 (72 h)) doses for CPT-11 were identical in the p53 wild-type and null cell lines. Furthermore, apoptosis after treatment with 5-FU and oxaliplatin, but not CPT-11, was significantly reduced in parental p53(-/-) cells compared with parental p53(+/+) cells. These data suggest that p53 may be an important determinant of sensitivity to 5-FU and oxaliplatin but not CPT-11. Using semiquantitative reverse transcription-PCR, we have demonstrated down-regulation of thymidine phosphorylase mRNA in both p53(+/+) and p53(-/-) 5-FU-resistant cells, suggesting that decreased production of 5-FU active metabolites may be an important resistance mechanism in these lines. In oxaliplatin-resistant cells, we noted increased mRNA levels of the nucleotide excision repair gene ERCC1 and ATP-binding cassette transporter breast cancer resistance protein. In CPT-11-resistant cells, we found reduced mRNA levels of carboxylesterase, the enzyme responsible for converting CPT-11 to its active metabolite SN-38, and topoisomerase I, the SN-38 target enzyme. In addition, we noted overexpression of breast cancer resistance protein in the CPT-11-resistant lines. These cell lines are ideal tools with which to identify novel determinants of drug resistance in both the presence and absence of wild-type p53.

Identification of novel genes associated with the response to 5-FU treatment in gastric cancer cell lines using a cDNA microarray

The 5-Fluorouracil (5-FU) is an anticancer drug that is widely used in the treatment of cancer. To identify novel genes associated with 5-FU in gastric cancer, the time-dependent expression profiling of genes in response to 5-FU was examined in 5-FU sensitive and/or resistant gastric cancer cell lines using a 'KUGI 14 K cDNA chip' containing 14,081 unigenes obtained from human gastric cancer cell lines and tissues. By this analysis, we obtained 13 genes which are directly associated with sensitivity or resistance to 5-FU. Of these genes, 11 were found to be commonly up-regulated only in the 5-FU sensitive cell lines, and 2 were oppositely regulated in both of 5-FU sensitive and resistant cell lines. These genes were determined to be involved in cell surface, apoptosis, cell cycle and signal transduction. Of these genes, the expression levels of ZFP100, 4F2hc, FLJ11021, CSTF3, PPP1R14A, DDB2, C6orf139, CDKN1A, HOXC11 and FLJ38860 were confirmed by semi-quantitative RT-PCR. In addition, seven genes containing RRMI, UP1 and K-EST0037597 were found to be commonly up-regulated in both cell lines. In addition, the expression of genes such as TP, OPRT, TS and DPD, which have been previously known to be involved in 5-FU metabolism, were examined in both of 5-FU sensitive and resistant cell lines. These results provide not only predictive biomarkers for 5-FU sensitivity or resistance to human gastric cancer, but also a new molecular basis for understanding the mechanism of cellular cytoxicity to 5-FU.

Dihydropyrimidine dehydrogenase and the efficacy and toxicity of 5-fluorouracil

The identification of genetic factors associated with either responsiveness or resistance to 5-fluorouracil (5-FU) chemotherapy, as well as genetic factors predisposing patients to the development of severe 5-FU-associated toxicity, is increasingly being recognised as an important field of study. Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU). Although the role of tumoral levels as a prognostic factor for clinical responsiviness has not been firmly established, there is ample evidence that a deficiency of DPD is associated with severe toxicity after the administration of 5-FU. Patients with a partial DPD deficiency have an increased risk of developing grade IV neutropenia. In addition, the onset of toxicity occurred twice as fast compared with patients with a normal DPD activity. To date, 39 different mutations and polymorphisms have been identified in DPYD. The IVS14+1G>A mutation proved to be the most common one and was detected in 24-28% of all patients suffering from severe 5-FU toxicity. Thus, a deficiency of DPD appears to be an important pharmacogenetic syndrome.

Single Ascending Dose Tolerability, Pharmacokinetic–Pharmacodynamic Study of Dihydropyrimidine Dehydrogenase Inhibitor Ro 09-4889

PURPOSE

Ro 09-4889 was designed to enhance the anticancer efficacy of capecitabine (Xeloda) by generating a dihydropyrimidine dehydrogenase inhibitor (DPDi) 5-vinyluracil (5-VU) preferentially in tumor tissues. This study assessed the tolerance to Ro 09-4889 treatment, and related pharmacokinetic and pharmacodynamic data such as inhibition of DPD activity in peripheral blood mononuclear cells (PBMCs) and plasma uracil levels.

EXPERIMENTAL DESIGN

This was a single-center, double-blind, placebo-controlled, single-dose escalation study in 64 healthy male volunteers at 1-, 5-, 20-, 50-, 75-, 100-, and 200-mg oral dose of Ro 09-4889. Also, food effect was assessed separately in a group dosed with 20 mg of the compound.

RESULTS

No serious adverse effects or significant laboratory and electrocardiogram abnormalities were observed during the study. Ro 09-4889 has a short elimination half-life (t(1/2)) of 0.5 h, followed by metabolites 5'-deoxy-5-vinyluridine (5'-DVUR), 5'-deoxy-5-vinylcytidine (5'-DVCR), and 5-VU with t(1/2) of 1.3, 1.2, and 2 h, respectively. The major metabolite excreted in urine was 5-DVCR (45% of dose). The inhibition of PBMC DPD activity and the increase in plasma uracil were related to Ro 09-4889 dose. DPD inhibition versus dose and uracil AUC (area under the curve) versus dose were modeled using the E(max) model with a baseline effect. The model-predicted ED(50) value was 100 mg.

CONCLUSION

Single oral doses of Ro 09-4889 ranging from 1 to 200 mg were well tolerated. On the basis of these findings, a 10-to-30-mg dose range of Ro 09-4889 combined with capecitabine could be appropriate for further evaluation in cancer patients.

Human nerve growth factor receptor and cytosine deaminase fusion genes

Cytosine deaminase (CD) converts 5-fluorocytosine (5-FC) to the toxic metabolite 5-fluorouracil (5-FU), and has been investigated extensively as a potential tool for selective cellular eradication. In this paper, genetic constructs were designed to express the CD enzyme fused to the transmembrane and extracellular domains of the human nerve growth factor receptor (NGFR), thus allowing for positive identification of transduced cells by flow cytometry and positive selection by magnetic bead technology. Constructs were designed to encode a [Gly(4)Ser](2) flexible linker between the nucleic acid coding sequences for the NGFR and CD genes. Retroviral vectors constructed with wild-type CD and NG/CD fusion genes were used to transduce 3T3 fibroblasts and the human T cell line CEM. The function of CD fusion genes was comparable to that of wild-type genes as determined in cytotoxicity assays. By flow cytometry, the NGFR antigen was detectable after expression of the fusion gene derived from either Escherichia coli (NG/CDe) or Saccharomyces cerevisiae (NG/CDs), but the greatest antigen density was observed in cells transduced with the NG/CDs vector. Similarly, superior 5-FC sensitivity was observed with NG/CDs fusion gene in both murine fibroblasts and human T cells. In addition, CEM cells expressing NG/CDs were more efficiently eliminated in vivo. Engineering of cells utilizing the chimeric NG/CD genes provides a new modality in gene therapy allowing positive and negative selection using a single protein-coding sequence.

5-fluorouracil: mechanisms of action and clinical strategies

5-fluorouracil (5-FU) is widely used in the treatment of cancer. Over the past 20 years, increased understanding of the mechanism of action of 5-FU has led to the development of strategies that increase its anticancer activity. Despite these advances, drug resistance remains a significant limitation to the clinical use of 5-FU. Emerging technologies, such as DNA microarray profiling, have the potential to identify novel genes that are involved in mediating resistance to 5-FU. Such target genes might prove to be therapeutically valuable as new targets for chemotherapy, or as predictive biomarkers of response to 5-FU-based chemotherapy.

Transfer of drug resistance genes in hematopoietic progenitors for chemoprotection: is it still an option?

For numerous malignancies a relationship between the intensity of antineoplastic chemotherapy and tumor response has been demonstrated. Myelotoxicity is the main cause of chemotherapy-associated morbidity and of treatment delays. The concept of myeloprotective cytostatic drug resistance gene transfer to normal hematopoietic stem cells (HSC) therefore sparks great enthusiasm. While initial studies using murine retroviral vectors on murine HSC showed that the concept works, a number of clinical studies in the last decade were not informative because of limitations in transduction efficiency and transgene expression.Furthermore, possible side effects such as unforeseen transgene activity and vector integration-based leukemogenesis have been reported. Among others, these developments raised some scepticism against the feasibility of myeloprotective gene transfer. Recently, considerable improvements have been achieved in vector design, HSC manipulation, selection protocols and risk assessment methods which are discussed in detail here. Based on these experimental studies successful clinical trials can now be anticipated.

Novel aspects of resistance to drugs targeted to dihydrofolate reductase and thymidylate synthase

Drug resistance is often a limiting factor in successful chemotherapy. Our laboratory has been interested in studying mechanisms of resistance to drugs that are targeted to the thymidylate biosynthesis pathway especially those that target thymidylate synthase (TS) and dihydrofolate reductase (DHFR). We have used leukemia as a model system to study resistance to methotrexate (MTX) and colorectal cancer as the model system to study 5-fluorouracil (5-FU) resistance. In leukemias, we and others have shown that transport, efflux, polyglutamylation and hydrolase activities are major determinants of MTX resistance. We have further reported that some leukemic cells have an increase in DHFR gene copy number possibly contributing to the resistant phenotype. Recently, we have begun to study in detail the molecular mechanisms that govern translational regulation of DHFR in response to MTX as an additional resistance mechanism. Studies thus far involving colorectal tumors obtained from patients have focused predominantly on the predictive value of levels of TS expression and p53 mutations in determining response to 5-FU. Although the predictive value of these two measures appears to be significant, given the variety of resistance to 5-FU observed in cell lines, it is not likely that these are the only measures predictive of response or responsible for acquired resistance to this drug. The enzyme uridine-cytidine monophosphate kinase (UMPK) is an essential and rate-limiting enzyme in 5-FU activation while dihydropyrimidine dehydrogenase (DPD) is a catabolic enzyme that inactivates 5-FU. Alterations in UMPK and DPD may therefore explain failure of 5-FU response in the absence of alterations in TS or p53. Transcription factors that regulate TS may also influence drug sensitivity. We have found that mRNA levels of the E2F family of transcription factors correlates with TS message levels and are higher in lung metastases than in liver metastases of colorectal cancers. Moreover, gene copy number of the E2F-1 gene appears to be increased in a significant number of samples obtained from metastases of colorectal cancer. We have also generated mutants of both DHFR and TS that confer resistance to MTX as well as 5-FU by random as well as site-directed mutagenesis. These mutants used alone or as fusion cDNAs of the mutants have proven to be useful in transplant studies where transfer of these mutant cDNAs to bone marrow cells have been shown to confer drug resistance to recipients. The fusion cDNAs of DHFR such as the DHFR-herpes simplex virus type 1 thymidine kinase (HSVTK) are also useful for regulation of gene expression in vivo using MTX as the small molecule regulator that can be monitored by positron emission tomography (PET) scanning or by optical imaging using a fusion construct such as DHFR-EGFP.

Gene therapy for colorectal cancer

Gene therapy has been developed as a potential novel treatment modality for colorectal cancer. The preclinical data have been promising and several clinical trials are under way for colorectal cancer. Data from many phase 1 trials have proven the safety of the reagents, but have not yet demonstrated significant therapeutic benefit. In order to refine this approach, continuing efforts should be made to improve the antitumour potency, efficiency of gene delivery, and accuracy of gene targeting. It is likely that gene therapy will be integrated into pre-existing therapies including surgery, chemotherapy and radiotherapy to establish its niche in tomorrow's medicine.