Variability in transport and biotransformation of cytarabine is associated with its toxicity in peripheral blood mononuclear cells

Association of Single-Nucleotide Polymorphisms in Capecitabine Bioactivation Pathway with Adjuvant Therapy Safety in Colorectal Cancer Patients

Capecitabine, an oral prodrug of 5-fluorouracil (5-FU), is part of the standard treatment of colorectal cancer (CRC). Severe adverse dose limiting reactions that impair treatment safety and lead to treatment suspension remain a relevant concern. Single-nucleotide polymorphisms (SNPs) in genes involved in the activation of capecitabine may alter the bioavailability of 5-FU and thereby affect therapy outcomes. The aim of this study was to evaluate the association of these SNPs with severe toxicity and treatment suspension in patients with CRC treated with capecitabine-based therapy. An ambispective cohort study was conducted, including 161 patients with CRC. SNPs were analyzed using real-time PCR with TaqMan® probes. Toxicity was assessed according to the National Cancer Institute Common Terminology Criteria for Adverse Events v.5.0. CES1 rs71647871-A was associated with a severe hand-foot syndrome (p = 0.030; OR = 11.92; 95% CI = 1.46-73.47; GG vs. A). CDA rs1048977-CC (p = 0.030; OR = 2.30; 95% CI 1.09-5.00; T vs. CC) and capecitabine monotherapy (p = 0.003; OR = 3.13; 95% CI 1.49-6.81) were associated with treatment suspension due to toxicity. SNPs CES1 rs71647871 and CDA rs1048977 may act as potential predictive biomarkers of safety in patients with CRC under capecitabine-based adjuvant therapy.

Pharmacogenetics of ABCB1, CDA, DCK, GSTT1, GSTM1 and outcomes in a cohort of pediatric acute myeloid leukemia patients from Colombia

BACKGROUND AND AIM

Different studies have shown pharmacogenetic variants related to drug toxicity in acute myeloid leukemia (AML) patients. Our aim was to identify the association between ABCB1, CDA, DCK, GSTT1, and GSTM1 variants with clinical outcomes and toxicity in pediatric patients with AML.

METHODS

Fifty-one confirmed de novo AML pediatric patients were included. A SNaPshot™ assay and conventional PCR were used to evaluate ABCB1, CDA, DCK, GSTT1, and GSTM1 variants. Clinical outcomes and toxicity associations were evaluated using odds ratios and Chi-square analysis.

RESULTS

Patients carrying ABCB1 (1236C > T, rs1128503) GG genotype in had a 6.8 OR (CI 95% 1.08-42.73, p = .044) for cardiotoxicity as compared to patients carrying either AA or GA genotypes 0.14 OR (CI 95% 0.023-0.92, p = .044). For ABCB1 (1236G > A rs1128503/2677C > A/T rs2032582/3435G > A rs1045642) AA/AA/AA combined genotypes had a strong association with death after HSTC OR 13.73 (CI 95% 1.94-97.17, p = .009). Combined genotypes GG/CC/GG with CDA (79A > C, rs2072671) CA genotype or CDA (-451G > A, rs532545) CT genotype, had a 4.11 OR (CI 95% 2.32-725, p = .007) and 3.8 OR (CI 95% 2.23-6.47, p = .027) with MRD >0.1% after first chemotherapy cycle, respectively.

CONCLUSION

Our results highlight the importance of pharmacogenetic analysis in pediatric AML, particularly in populations with a high degree of admixture, and might be useful as a future tool for patient stratification for treatment.

Systematic Review of Pharmacogenetics of ABC and SLC Transporter Genes in Acute Myeloid Leukemia

Antineoplastic uptake by blast cells in acute myeloid leukemia (AML) could be influenced by influx and efflux transporters, especially solute carriers (SLCs) and ATP-binding cassette family (ABC) pumps. Genetic variability in SLC and ABC could produce interindividual differences in clinical outcomes. A systematic review was performed to evaluate the influence of SLC and ABC polymorphisms and their combinations on efficacy and safety in AML cohorts. Anthracycline intake was especially influenced by SLCO1B1 polymorphisms, associated with lower hepatic uptake, showing higher survival rates and toxicity in AML studies. The variant alleles of ABCB1 were related to anthracycline intracellular accumulation, increasing complete remission, survival and toxicity. Similar findings have been suggested with ABCC1 and ABCG2 polymorphisms. Polymorphisms of SLC29A1, responsible for cytarabine uptake, demonstrated significant associations with survival and response in Asian populations. Promising results were observed with SLC and ABC combinations regarding anthracycline toxicities. Knowledge of the role of transporter pharmacogenetics could explain the differences observed in drug disposition in the blast. Further studies including novel targeted therapies should be performed to determine the influence of genetic variability to individualize chemotherapy schemes.

The Transporter-Mediated Cellular Uptake and Efflux of Pharmaceutical Drugs and Biotechnology Products: How and Why Phospholipid Bilayer Transport Is Negligible in Real Biomembranes

Over the years, my colleagues and I have come to realise that the likelihood of pharmaceutical drugs being able to diffuse through whatever unhindered phospholipid bilayer may exist in intact biological membranes in vivo is vanishingly low. This is because (i) most real biomembranes are mostly protein, not lipid, (ii) unlike purely lipid bilayers that can form transient aqueous channels, the high concentrations of proteins serve to stop such activity, (iii) natural evolution long ago selected against transport methods that just let any undesirable products enter a cell, (iv) transporters have now been identified for all kinds of molecules (even water) that were once thought not to require them, (v) many experiments show a massive variation in the uptake of drugs between different cells, tissues, and organisms, that cannot be explained if lipid bilayer transport is significant or if efflux were the only differentiator, and (vi) many experiments that manipulate the expression level of individual transporters as an independent variable demonstrate their role in drug and nutrient uptake (including in cytotoxicity or adverse drug reactions). This makes such transporters valuable both as a means of targeting drugs (not least anti-infectives) to selected cells or tissues and also as drug targets. The same considerations apply to the exploitation of substrate uptake and product efflux transporters in biotechnology. We are also beginning to recognise that transporters are more promiscuous, and antiporter activity is much more widespread, than had been realised, and that such processes are adaptive (i.e., were selected by natural evolution). The purpose of the present review is to summarise the above, and to rehearse and update readers on recent developments. These developments lead us to retain and indeed to strengthen our contention that for transmembrane pharmaceutical drug transport "phospholipid bilayer transport is negligible".

Response and Toxicity to Cytarabine Therapy in Leukemia and Lymphoma: From Dose Puzzle to Pharmacogenomic Biomarkers

Simple Summary

In this review, the authors propose a crosswise examination of cytarabine-related issues ranging from the spectrum of clinical activity and severe toxicities, through updated cellular pharmacology and drug formulations, to the genetic variants associated with drug-induced phenotypes. Cytarabine (cytosine arabinoside; Ara-C) in multiagent chemotherapy regimens is often used for leukemia or lymphoma treatments, as well as neoplastic meningitis. Chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. The individual variability in clinical response to Leukemia & Lymphoma treatments among patients appears to be associated with intracellular accumulation of Ara-CTP due to genetic variants related to metabolic enzymes. The review provides exhaustive information on the effects of Ara-C-based therapies, the adverse drug reaction will also be provided including bone pain, ocular toxicity (corneal pain, keratoconjunctivitis, and blurred vision), maculopapular rash, and occasional chest pain. Evidence for predicting the response to cytarabine-based treatments will be highlighted, pointing at their significant impact on the routine management of blood cancers.

Abstract

Cytarabine is a pyrimidine nucleoside analog, commonly used in multiagent chemotherapy regimens for the treatment of leukemia and lymphoma, as well as for neoplastic meningitis. Ara-C-based chemotherapy regimens can induce a suboptimal clinical outcome in a fraction of patients. Several studies suggest that the individual variability in clinical response to Leukemia & Lymphoma treatments among patients, underlying either Ara-C mechanism resistance or toxicity, appears to be associated with the intracellular accumulation and retention of Ara-CTP due to genetic variants related to metabolic enzymes. Herein, we reported (a) the latest Pharmacogenomics biomarkers associated with the response to cytarabine and (b) the new drug formulations with optimized pharmacokinetics. The purpose of this review is to provide readers with detailed and comprehensive information on the effects of Ara-C-based therapies, from biological to clinical practice, maintaining high the interest of both researcher and clinical hematologist. This review could help clinicians in predicting the response to cytarabine-based treatments.

Associations of cytosine deaminase gene polymorphisms with effectiveness of gemcitabine/cisplatin chemotherapy in patients of Xinjiang Uyghur and Han nationality with non-small cell lung cancer

BACKGROUND

Cytidine deaminase (CDA) polymorphisms may affect the response to gemcitabine/cisplatin chemotherapy in patients with non-small cell lung cancer (NSCLC). This study is designed to investigate the associations of CDA-79A>C and 208G>A polymorphisms and gemcitabine/cisplatin chemotherapy effectiveness in Xinjiang Uyghur and Han patients.

METHODS

This prospective cohort study enrolled consecutive patients with stage IIIb/IV NSCLC administered gemcitabine/cisplatin chemotherapy at the First Affiliated Hospital, Medical College of Shihezi University and the First People's Hospital, Kashgar Region. CDA-A79C and CDA-G208A polymorphisms were detected by direct sequencing. Progression-free survival was analyzed by the Kaplan-Meier method. Associations of A79C and G208A polymorphisms with treatment effectiveness and progression-free survival were analyzed using logistic regression and multivariate Cox regression analyses. Subgroup analyses based on ethnicity were performed.

RESULTS

The study enrolled 120 patients. A79C and G208A polymorphisms followed the Hardy-Weinberg equilibrium. The frequencies of the AA, AC, and CC genotypes and the A and C alleles of A79C were 52.2%, 29.9%, 17.9%, 67.2%, and 32.8%, respectively, in Han patients and 75.4%, 18.9%, 5.7%, 84.9%, and 5.1%, respectively, in Uyghur patients. Uyghur patients had lower frequencies of A79C-AC/CC genotypes, A79C-C allele, G208A-GA genotype, and G208A-A allele (P<0.05). Compared with A79C-AA, the odds of ineffective chemotherapy were increased for A79C-AC (odds ratio [OR] 2.818; 95% confidence interval [95% CI] 1.031, 7.705; P=0.043) and A79C-CC (OR 9.864; 95% CI 1.232, 78.966; P=0.031). G208A polymorphisms did not influence chemotherapy effectiveness. Chemotherapy was more effective in Han patients than in Uyghur patients for A79C-AC and G208A-GG. Progression-free survival was longer for A79C-AA versus A79C-AC/CC (10 vs. 7 months, P=0.004) and G208A-GA/AA vs. G208A-AA (12 vs. 8 months, P=0.010). Polymorphisms of A79C (hazard ratio [HR] 1.617; 95% CI 1.009, 2.592; P=0.046) and G208A (HR 2.193; 95% CI 1.055, 4.557; P=0.035) were associated with progression-free survival.

CONCLUSION

For Uyghur and Han ethnic groups, A79C and G208A polymorphisms can be used as a promising biomarker for the chemotherapy efficacy and prognosis of NSCLC.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.

Influence of cytarabine metabolic pathway polymorphisms in acute myeloid leukemia induction treatment

Cytarabine is considered the most effective chemotherapeutic option in acute myeloid leukemia (AML). The impact of 10 polymorphisms in cytarabine metabolic pathway genes were evaluated in 225 adult de novo AML patients. Variant alleles of DCK rs2306744 and CDA rs602950 showed higher complete remission (p = .024, p = .045), with lower survival rates for variant alleles of CDA rs2072671 (p = .015, p = .045, p = .032), rs3215400 (p = .033) and wild-type genotype of rs602950 (p = .039, .014). Induction death (p = .033) and lower survival rates (p = .021, p = .047) were correlated to RRM1 rs9937 variant allele. In addition, variant alleles of CDA rs532545 and rs602950 were related to skin toxicity (p = .031, p = .049) and mucositis to DCK rs2306744 minor allele (p = .046). Other toxicities associated to variant alleles were hepatotoxicity to NT5C2 rs11598702 (p = .032), lung toxicity (p = .031) and thrombocytopenia to DCK rs4694362 (p = .046). This study supports the interest of cytarabine pathway polymorphisms regarding efficacy and toxicity of AML therapy in a coherent integrated manner.

Pharmacokinetics and pharmacogenetics of Gemcitabine as a mainstay in adult and pediatric oncology: an EORTC-PAMM perspective

Gemcitabine is an antimetabolite ranking among the most prescribed anticancer drugs worldwide. This nucleoside analog exerts its antiproliferative action after tumoral conversion into active triphosphorylated nucleotides interfering with DNA synthesis and targeting ribonucleotide reductase. Gemcitabine is a mainstay for treating pancreatic and lung cancers, alone or in combination with several cytotoxic drugs (nab-paclitaxel, cisplatin and oxaliplatin), and is an option in a variety of other solid or hematological cancers. Several determinants of response have been identified with gemcitabine, i.e., membrane transporters, activating and inactivating enzymes at the tumor level, or Hedgehog signaling pathway. More recent studies have investigated how germinal genetic polymorphisms affecting cytidine deaminase, the enzyme responsible for the liver disposition of gemcitabine, could act as well as a marker for clinical outcome (i.e., toxicity, efficacy) at the bedside. Besides, constant efforts have been made to develop alternative chemical derivatives or encapsulated forms of gemcitabine, as an attempt to improve its metabolism and pharmacokinetics profile. Overall, gemcitabine is a drug paradigmatic for constant searches of the scientific community to improve its administration through the development of personalized medicine in oncology.

The influence of cytidine deaminase -33delC polymorphism on treatment outcome with high-dose cytarabine in Chinese patients with relapsed acute myeloid leukaemia

WHAT IS KNOWN AND OBJECTIVE

Identification of biomarkers that could predict high-dose cytarabine (Ara-C) efficacy and toxicity is a key issue in individualized therapy. The aim of our study was to evaluate the influence of cytidine deaminase (CDA) single nucleotide polymorphisms (SNPs) -451G>A (rs532545), 435C>T (rs1048977) and -33delC (rs3215400) on treatment outcome in patients with relapsed acute myeloid leukaemia (AML) after high-dose Ara-C chemotherapy.

METHODS

In total, 173 patients with relapsed AML, treated with high-dose Ara-C chemotherapy, were genotyped for three polymorphisms in CDA gene using the allele-specific matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assays. Binary logistic regression was used to evaluate the influence of selected polymorphisms on tumour response and occurrence of treatment-related toxicity.

RESULTS AND DISCUSSION

The CC genotype at -33delC, a promoter polymorphism, increased the odds of overall response rate (odds ratio [OR] = 5·125; 95% confidence intervals (CI) = 2·446-10·74; P = 0·0008) and grade ≥3 infection toxicity incidence rate (OR = 3·572; 95% CI = 1·68-7·594; P = 0·003). In multivariable analysis, this polymorphism was a potential independent prognostic marker for the risk of overall response (P = 0·011), but not grade ≥3 infection toxicity incidence rate (P = 0·49). Two other polymorphisms, -451G>A and 435C>T, did not influence treatment outcome, including overall response rate, infection toxicity and nausea/vomiting, in patients with relapsed AML (P > 0·05).

WHAT IS NEW AND CONCLUSION

The findings suggest that CDA -33delC variant might be a potential marker for predicting treatment outcome in Chinese patients with relapsed AML given high-dose cytarabine chemotherapy.

Role of Genetic Polymorphisms of Deoxycytidine Kinase and Cytidine Deaminase to Predict Risk of Death in Children with Acute Myeloid Leukemia

Cytarabine is one of the most effective antineoplastic agents among those used for the treatment of acute myeloid leukemia. However, some patients develop resistance and/or severe side effects to the drug, which may interfere with the efficacy of the treatment. The polymorphisms of some Ara-C metabolizing enzymes seem to affect outcome and toxicity in AML patients receiving cytarabine. We conducted this study in a cohort of Mexican pediatric patients with AML to investigate whether the polymorphisms of the deoxycytidine kinase and cytidine deaminase enzymes are implicated in clinical response and toxicity. Bone marrow and/or peripheral blood samples obtained at diagnosis from 27 previously untreated pediatric patients with de novo AML were processed for genotyping and in vitro chemosensitivity assay, and we analyzed the impact of genotypes and in vitro sensitivity on disease outcome and toxicity. In the multivariate Cox regression analysis, we found that age at diagnosis, wild-type genotype of the CDA A79C polymorphism, and wild-type genotype of the dCK C360G polymorphism were the most significant prognostic factors for predicting the risk of death.

Role of cytidine deaminase in toxicity and efficacy of nucleosidic analogs

INTRODUCTION

Nucleosidic analogs such as pyrimidine and purine derivatives are mainstay in the field of treating cancers, both in adults and in children. All these drugs act as antimetabolite compounds, that is, they interfere with the ability of cancer cells to synthesize the nucleosides or the nucleotides necessary for proliferation and progression. As with most cytotoxics, maintaining patients in their therapeutic window is challenging, and predicting changes in drug exposure is critical to ensure an optimal efficacy/toxicity balance.

AREAS COVERED

Among the antimetabolites, a small but widely prescribed number of drugs (i.e., gemcitabine, capecitabine, cytarabine, azacytidine) share a same metabolic pattern driven by a liver enzyme, cytidine deaminase (CDA), coded by a gene displaying several genetic and epigenetic polymorphisms. Consequently, CDA activity is erratic, ranging from deficient to ultra-rapid deaminator patients, with subsequent impact on drug pharmacokinetics and pharmacodynamics eventually. This review provides an update on the variety of clinical studies and case-reports investigating on CDA status as a marker for clinical outcome in cancer patients treated with nucleosidic analogs.

EXPERT OPINION

Whereas sorting patients on the basis of their CDA genotype remains tricky because of unclear genotype-to-phenotype relationships, developing functional strategies (i.e., phenotype-based status determination) could help to use CDA status as a biomarker for developing adaptive dosing strategies with nucleosidic analogs.

Uptake carriers and oncology drug safety

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics in multiple tissues. Many of these transporters are highly expressed in the gastrointestinal tract, liver, and kidney and are considered to be of particular importance in governing drug absorption, elimination, and cellular sensitivity of specific organs to a wide variety of oncology drugs. Although the majority of studies on the interaction of oncology drugs with SLC have been restricted to the use of exploratory in vitro model systems, emerging evidence suggests that several SLCs, including OCT2 and OATP1B1, contribute to clinically important phenotypes associated with those agents. Recent literature has indicated that modulation of SLC activity may result in drug-drug interactions, and genetic polymorphisms in SLC genes have been described that can affect the handling of substrates. Alteration of SLC function by either of these mechanisms has been demonstrated to contribute to interindividual variability in the pharmacokinetics and toxicity associated with several oncology drugs. In this report, we provide an update on this rapidly emerging field.

CDA gene polymorphisms and enzyme activity: genotype–phenotype relationship in an Italian–Caucasian population

Aim: To assess the distribution of CDA activity from whole blood of 142 healthy subjects, determining its main predictors among genetic (six CDA SNPs) and physiological factors (age and gender). Moreover, we performed a kinetic study of the two CDA protein variants (Q27 and K27) determined by the rs2072671 SNP. Materials & methods: CDA activity was assessed by HPLC. Selected CDA SNPs were genotyped by PCR-based methods. Recombinant CDA protein variants (Q27 and K27) were expressed in an Escherichia coli strain SØ5201 and kinetic assays were performed. Results: The mean value of CDA activity was 0.051 ± 0.024 mU/mg and followed a normal distribution in the study population. Carriers of the CDA*2B (-451T/-92G/-31Del/79C/435C) haplotype displayed higher CDA activity compared with the others. CDA -451G>A, -92A>G and 79A>C (K27Q) SNPs displayed significant associations with CDA activity. The best predictive model of CDA activity included the variables gender and CDA 79A>C (K27Q). Cytidine is the preferential substrate for the variant Q27. Conclusion: We suggest the analysis of both CDA activity and CDA 79A>C (K27Q) SNP in future prospective trials with cytidine analogs, alone or in combination, in order to identify the best marker to secure the administration of these anticancer therapies.

Original submitted 22 October 2012; Revision submitted 11 March 2013

Pharmacogenomics of gemcitabine metabolism: functional analysis of genetic variants in cytidine deaminase and deoxycytidine kinase

Gemcitabine (dFdC, 2',2'-difluorodeoxycytidine) is metabolized by cytidine deaminase (CDA) and deoxycytidine kinase (DCK), but the contribution of genetic variation in these enzymes to the variability in systemic exposure and response observed in cancer patients is unclear. Wild-type enzymes and variants of CDA (Lys27Gln and Ala70Thr) and DCK (Ile24Val, Ala119Gly, and Pro122Ser) were expressed in and purified from Escherichia coli, and enzyme kinetic parameters were estimated for cytarabine (Ara-C), dFdC, and its metabolite 2',2'-difluorodeoxyuridine (dFdU) as substrates. All three CDA proteins showed similar K(m) and V(max) for Ara-C and dFdC deamination, except for CDA70Thr, which had a 2.5-fold lower K(m) and 6-fold lower V(max) for Ara-C deamination. All four DCK proteins yielded comparable metabolic activity for Ara-C and dFdC monophosphorylation, except for DCK24Val, which demonstrated an approximately 2-fold increase (P < 0.05) in the intrinsic clearance of dFdC monophosphorylation due to a 40% decrease in K(m) (P < 0.05). DCK did not significantly contribute to dFdU monophosphorylation. In conclusion, the Lys27Gln substitution does not significantly modulate CDA activity toward dFdC, and therefore would not contribute to interindividual variability in response to gemcitabine. The higher in vitro catalytic efficiency of DCK24Val toward dFdC monophosphorylation may be relevant to dFdC clinical response. The substrate-dependent alterations in activities of CDA70Thr and DCK24Val in vitro were observed for the first time, and demonstrate that the in vivo consequences of these genetic variations should not be extrapolated from one substrate of these enzymes to another.

The role of transporters in the toxicity of nucleoside and nucleotide analogs

INTRODUCTION

Two families of nucleoside analogs have been developed to treat viral infections and cancer, but these compounds can cause tissue- and cell-specific toxicity related to their uptake and subcellular activity, which are dictated by host enzymes and transporters. Cellular uptake of these compounds requires nucleoside transporters that share functional similarities but differ in substrate specificity. Tissue-specific cellular expression of these transporters enables nucleoside analogs to produce their tissue-specific toxic effects, a limiting factor in the treatment of retroviruses and cancer.

AREAS COVERED

This review discusses the families of nucleoside transporters and how they mediate cellular uptake of nucleoside analogs. Specific focus is placed on examples of known cases of transporter-mediated cellular toxicity and classification of the toxicities resulting. Efflux transporters are also explored as a contributor to analog toxicity and cell-specific effects.

EXPERT OPINION

Efforts to modulate transporter uptake/clearance remain long-term goals of oncologists and virologists. Accordingly, subcellular approaches that either increase or decrease intracellular nucleoside analog concentrations are eagerly sought and include transporter inhibitors and targeting transporter expression. However, additional understanding of nucleoside transporter kinetics, tissue expression and genetic polymorphisms is required to design better molecules and better therapies.

CDA deficiency as a possible culprit for life-threatening toxicities after cytarabine plus 6-mercaptopurine therapy: pharmacogenetic investigations

We describe here the case of a 7-year old girl with lymphoma who developed life-threatening toxicities upon cytarabine plus mercaptopurine. Surprisingly, initial investigations on canonical thiopurine methyltransferase genetic polymorphism proved to be negative. We focused next on deregulations affecting the CDA gene implicated in the liver disposition of cytarabine. This patient was homozygous for both the 79A>C and the -31delC polymorphisms on the CDA gene and promoter, two genotypes with reported opposite effects on CDA phenotype. To determine the CDA status of this patient, additional functional testing was performed and eventually demonstrated that this patient was a poor metabolizer. This case demonstrates that besides affecting thiopurine methyltransferase, dysregulations with CDA should be screened to anticipate toxicities with the cytarabine plus mercaptopurine combination.

Epigenetic cancer therapy: rationales, targets and drugs

The fundamental role of altered epigenetic modification patterns in tumorigenesis establishes epigenetic regulatory enzymes as important targets for cancer therapy. Over the past few years, several drugs with an epigenetic activity have received approval for the treatment of cancer patients, which has led to a detailed characterization of their modes of action. The results showed that both established drug classes, the histone deacetylase (HDAC) inhibitors and the DNA methyltransferase inhibitors, show substantial limitations in their epigenetic specificity. HDAC inhibitors are highly specific drugs, but the enzymes have a broad substrate specificity and deacetylate numerous proteins that are not associated with epigenetic regulation. Similarly, the induction of global DNA demethylation by non-specific inhibition of DNA methyltransferases shows pleiotropic effects on epigenetic regulation with no apparent tumor-specificity. Second-generation azanucleoside drugs have integrated the knowledge about the cellular uptake and metabolization pathways, but do not show any increased specificity for cancer epigenotypes. As such, the traditional rationale of epigenetic cancer therapy appears to be in need of refinement, as we move from the global inhibition of epigenetic modifications toward the identification and targeting of tumor-specific epigenetic programs. Recent studies have identified epigenetic mechanisms that promote self-renewal and developmental plasticity in cancer cells. Druggable somatic mutations in the corresponding epigenetic regulators are beginning to be identified and should facilitate the development of epigenetic therapy approaches with improved tumor specificity.

Rapid allele-specific PCR method for CDA 79A>C (K27Q) genotyping: a useful pharmacogenetic tool and world-wide polymorphism distribution

BACKGROUND

The CDA 79A>C (K27Q, rs2072671) functional SNP has recently shown a crucial role in the pharmacogenetics of cytidine-based anticancer drugs widely administered to different subsets of patients. Current gold standard in screening for the CDA rs2072671 is the sequence-based genotyping method. Here we developed a novel, rapid Allele-Specific PCR method for CDA rs2072671 genotyping.

METHODS

DNA was extracted from 324 healthy individuals from two different populations (Italian and Han Chinese). CDA rs2072671 genotyping was performed by Allele-Specific PCR. Sequencing was performed to validate the test results. Results obtained from population screening were compared to that already available in HapMap and in the literature.

RESULTS

Samples analyzed were successfully genotyped and the results were confirmed by sequencing. Genotype distribution does not differ significantly from that previously reported for each relative ethnic group. Also, the world-wide distribution of the CDA rs2072671 SNP is reported. A striking difference is present among the main ethnicities (p=1.715×10(-77)), with CDA*27Q allele showing the lowest frequency in African group (9.7%) and the highest in Caucasians (35.9%).

CONCLUSION

This Allele-Specific PCR method is a useful tool in pharmacogenetics research and a valid and reliable alternative for CDA rs2072671 screening where sequencing or Real-Time PCR is not available.