Correlation of cytidine deaminase polymorphisms and activity with clinical outcome in gemcitabine-/platinum-treated advanced non-small-cell lung cancer patients

Pharmacological mechanisms underlying the interaction of the nucleoside analogue gemcitabine with the c-MET inhibitor tivantinib in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy with limited treatment options, highlighting the urgent need for innovative approaches. A promising target for new anticancer therapies across various tumor types is the receptor tyrosine kinase c-MET. Here, we examined the impact of the c-MET inhibitor tivantinib in combination with gemcitabine on both primary and immortalized PDAC cells, and we investigated the mechanism underlying this combined treatment's effects. Our findings demonstrate that tivantinib is synergistic with gemcitabine, which is not related to cytidine deaminase but to inhibition of the polymerization of tubulin. Moreover, these drugs affected the expression of microRNAs miR-21 and miR-34, which regulate key oncogenic pathways. These findings might have an impact on the selection of patients for future trials.

Genetic polymorphisms as potential pharmacogenetic biomarkers for platinum-based chemotherapy in non-small cell lung cancer

Platinum-based chemotherapy (PBC) is a widely used treatment for various solid tumors, including non-small cell lung cancer (NSCLC). However, its efficacy is often compromised by the emergence of drug resistance in patients. There is growing evidence that genetic variations may influence the susceptibility of NSCLC patients to develop resistance to PBC. Here, we provide a comprehensive overview of the mechanisms underlying platinum drug resistance and highlight the important role that genetic polymorphisms play in this process. This paper discussed the genetic variants that regulate DNA repair, cellular movement, drug transport, metabolic processing, and immune response, with a focus on their effects on response to PBC. The potential applications of these genetic polymorphisms as predictive indicators in clinical practice are explored, as are the challenges associated with their implementation.

Cytidine deaminase enzyme activity is a predictive biomarker in gemcitabine-treated cancer patients

BACKGROUND

Gemcitabine is a chemotherapeutic agent, widely used for the treatment of many types of cancer. Cytidine deaminase (CDA) enzyme plays an important role in the metabolism of gemcitabine. This study aimed to assess the power of serum CDA residual activity in predicting drug efficacy and toxicity in gemcitabine-treated cancer patients.

METHODS

This prospective observational study enrolled 63 patients with different types of malignancies who received gemcitabine chemotherapy between May 2019 and January 2022. Blood samples were obtained before the initiation of chemotherapy and serum CDA residual activity was determined using a modification of the Berthelot assay. The patients were followed up for at least 12 months up to 41 months. Overall survival was recorded and treatment-related toxicities were documented according to National Cancer Institute Common Terminology Criteria.

RESULTS

Kaplan-Meier analysis showed that patients with a lower than median CDA value (≤ 8.06 U/mg protein) had a significantly longer survival compared to patients with higher CDA values (> 8.06 U/mg, P ˂ 0.005). Among several potentially involved factors, a significant association between CDA activity and overall survival was observed in univariate analysis (HR = 4.219, 95% CI 1.40-12.74, P = 0.011). On the other hand, the rate of anemia was significantly higher in low-CDA patients compared to high-CDA individuals (P < 0.05).

CONCLUSION

These findings suggest that CDA activity could be a promising biomarker to predict survival and the occurrence of anemia in cancer patients treated with gemcitabine.

Influence of Single-Nucleotide Polymorphisms on Clinical Outcomes of Capecitabine-Based Chemotherapy in Colorectal Cancer Patients: A Systematic Review

The aim of this systematic review was to provide a comprehensive overview of the literature published in the last decade on the association of single-nucleotide polymorphisms in genes involved in the pharmacodynamic and pharmacokinetic pathways of capecitabine with treatment outcomes among colorectal cancer patients. A systematic search of the literature published in the last 10 years was carried out in two databases (Medline and Scopus) using keywords related to the objective. Quality assessment of the studies included was performed using an assessment tool derived from the Strengthening the Reporting of Genetic Association (STREGA) statement. Thirteen studies were included in this systematic review. Genes involved in bioactivation, metabolism, transport, mechanism of action of capecitabine, DNA repair, and folate cycle were associated with toxicity. Meanwhile, genes related to DNA repair were associated with therapy effectiveness. This systematic review reveals that several SNPs other than the four DPYD variants that are screened in clinical practice could have an impact on treatment outcomes. These findings suggest the identification of future predictive biomarkers of effectiveness and toxicity in colorectal cancer patients treated with capecitabine. However, the evidence is sparse and requires further validation.

Solute Carrier Family 29A1 Mediates In Vitro Resistance to Azacitidine in Acute Myeloid Leukemia Cell Lines

Azacitidine (AZA) is commonly used hypomethylating agent for higher risk myelodysplastic syndromes and acute myeloid leukemia (AML). Although some patients achieve remission, eventually most patients fail AZA therapy. Comprehensive analysis of intracellular uptake and retention (IUR) of carbon-labeled AZA (¹⁴C-AZA), gene expression, transporter pump activity with or without inhibitors, and cytotoxicity in naïve and resistant cell lines provided insight into the mechanism of AZA resistance. AML cell lines were exposed to increasing concentrations of AZA to create resistant clones. ¹⁴C-AZA IUR was significantly lower in MOLM-13- (1.65 ± 0.08 ng vs. 5.79 ± 0.18 ng; p < 0.0001) and SKM-1- (1.10 ± 0.08 vs. 5.08 ± 0.26 ng; p < 0.0001) resistant cells compared to respective parental cells. Importantly, ¹⁴C-AZA IUR progressively reduced with downregulation of SLC29A1 expression in MOLM-13- and SKM-1-resistant cells. Furthermore, nitrobenzyl mercaptopurine riboside, an SLC29A inhibitor, reduced ¹⁴C-AZA IUR in MOLM-13 (5.79 ± 0.18 vs. 2.07 ± 0.23, p < 0.0001) and SKM-1-naive cells (5.08 ± 2.59 vs. 1.39 ± 0.19, p = 0.0002) and reduced efficacy of AZA. As the expression of cellular efflux pumps such as ABCB1 and ABCG2 did not change in AZA-resistant cells, they are unlikely contribute to AZA resistance. Therefore, the current study provides a causal link between in vitro AZA resistance and downregulation of cellular influx transporter SLC29A1.

HYAL4-V1/Chondroitinase (Chase) Drives Gemcitabine Resistance and Predicts Chemotherapy Failure in Patients with Bladder Cancer

PURPOSE

Gemcitabine-based chemotherapy regimens are first-line for several advanced cancers. Because of better tolerability, gemcitabine + cisplatin is a preferred neoadjuvant, adjuvant, and/or palliative chemotherapy regimen for advanced bladder cancer. Nevertheless, predicting treatment failure and overcoming resistance remain unmet clinical needs. We discovered that splice variant (V1) of HYAL-4 is a first-in-class eukaryotic chondroitinase (Chase), and CD44 is its major substrate. V1 is upregulated in bladder cancer and drives a malignant phenotype. In this study, we investigated whether V1 drives chemotherapy resistance.

EXPERIMENTAL DESIGN

V1 expression was measured in muscle-invasive bladder cancer (MIBC) specimens by qRT-PCR and IHC. HYAL-4 wild-type (Wt) and V1 were stably expressed or silenced in normal urothelial and three bladder cancer cell lines. Transfectants were analyzed for chemoresistance and associated mechanism in preclinical models.

RESULTS

V1 levels in MIBC specimens of patients who developed metastasis, predicted response to gemcitabine + cisplatin adjuvant/salvage treatment and disease-specific mortality. V1-expressing bladder cells were resistant to gemcitabine but not to cisplatin. V1 expression neither affected gemcitabine influx nor the drug-efflux transporters. Instead, V1 increased gemcitabine metabolism and subsequent efflux of difluorodeoxyuridine, by upregulating cytidine deaminase (CDA) expression through increased CD44-JAK2/STAT3 signaling. CDA inhibitor tetrahydrouridine resensitized V1-expressing cells to gemcitabine. While gemcitabine (25-50 mg/kg) inhibited bladder cancer xenograft growth, V1-expressing tumors were resistant. Low-dose combination of gemcitabine and tetrahydrouridine abrogated the growth of V1 tumors with minimal toxicity.

CONCLUSIONS

V1/Chase drives gemcitabine resistance and potentially predicts gemcitabine + cisplatin failure. CDA inhibition resensitizes V1-expressing tumors to gemcitabine. Because several chemotherapy regimens include gemcitabine, our study could have broad significance.

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.

Clinical update on hypomethylating agents

Hypomethylating agents (HMAs), azacitidine and decitabine, are standards of care in higher-risk myelodysplastic syndromes and in acute myeloid leukemia patients ineligible for intensive therapy. Over the last 10 years, research efforts have sought to better understand their mechanism of action, both at the molecular and cellular level. These efforts have yet to robustly identify biomarkers for these agents. The clinical activity of HMAs in myeloid neoplasms has been firmly established now but still remains of limited magnitude. Besides optimized use at different stages of the disease, most of the expected clinical progress with HMAs will come from the development of second-generation compounds orally available and/or with improved pharmacokinetics, and from the search, so far mostly empirical, of HMA-based synergistic drug combinations.

Determinants of the interindividual variability in serum cytidine deaminase activity of patients with solid tumours

AIMS

Cytidine deaminase (CDA) activity in cancer patients' serum has been proposed as a predictive biomarker for efficacy and toxicity of nucleoside analogues. However, discrepant results about its predictive value have been reported due to the high interindividual variability in CDA activity. This study aimed at identifying determinants of this interindividual variability.

METHODS

From December 2014 to November 2015, 183 patients were prospectively included. Serum CDA activity, biological and clinical characteristics as well as five common single nucleotide polymorphisms (SNPs) in the CDA gene (c.-451C > T, c.-92A > G, c.-33_-31delC, c.79A > C, c.435 T > C) were analysed. Associations between clinical characteristics, pharmacogenetic variants and CDA activity were univariately tested. P < 0.1-candidate variables were analysed through a multivariate analysis. The association between CDA activity and toxicity was assessed for the 56 gemcitabine-treated patients. Intraindividual variability in CDA activity was explored in six pancreatic cancer patients treated with gemcitabine.

RESULTS

Median CDA activity was 3.97 U mg^-1 (range 1.53-15.49 U mg^-1 ). A univariate analysis showed that CDA activity was statistically associated with Eastern Cooperative Oncology Group performance status, mild or severe malnutrition, inflammatory syndrome, leucocyte count, neutrophil count, albumin, C-reactive protein and -c.-33_-31delC single nucleotide polymorphism. A multivariate analysis identified that only neutrophil count (P < 0.0001) and severe malnutrition (P = 0.0278) were independently associated with CDA activity. Low CDA activity (<2 U mg^-1 ) was not statistically associated with severe gemcitabine-related toxicities (P = 0.16). A decrease in CDA activity was observed during the longitudinal follow-up of six pancreatic cancer patients treated with gemcitabine (P = 0.03).

CONCLUSIONS

These results suggest that neutrophil count and malnutrition should be considered for the interpretation of pretherapeutic CDA activity.

CDA as a predictive marker for life-threatening toxicities in patients with AML treated with cytarabine

Cytarabine (Ara-C) is the backbone of acute myeloid leukemia (AML) chemotherapy. Little is known about possible risk factors predictive for the frequent (ie, up to 16%) life-threatening or lethal toxicities caused by Ara-C. Ara-C is detoxified in the liver by a single enzyme, cytidine deaminase (CDA), coded by a gene known to be highly polymorphic. In this proof-of-concept study, we particularly investigated the role of the CDA poor metabolizer (PM) phenotype in Ara-C toxicities. CDA phenotyping (measurement of CDA residual activity in serum) and genotyping (search for the CDA*2 allelic variant) were performed in 58 adult patients with AML treated with the standard 7+3 (Ara-C + anthracyclines) protocol. Statistically significantly lower CDA activity was observed in patients experiencing severe/lethal toxicities as compared with patients who did not (1.5 ± 0.7 U/mg vs 3.95 ± 3.1 U/mg; Student t test P < .001). Subsequent receiver operating characteristic analysis identified a threshold in CDA activity (ie, 2 U/mg) associated with PM syndrome and increased risk of developing severe toxicities. Five percent of patients experienced lethal toxicities, all displaying CDA PM status (1.3 ± 0.5 U/mg). In terms of efficacy, a trend toward higher response rates and longer progression-free survival and overall survival were observed in patients with low CDA activity. Taken together, the results of this study strongly suggest that CDA is a predictive marker of life-threatening toxicities in patients with AML receiving induction therapy with standard Ara-C.

Cytidine deaminase enzymatic activity is a prognostic biomarker in gemcitabine/platinum-treated advanced non-small-cell lung cancer: a prospective validation study

Background

Cytidine deaminase (CDA) plays a crucial role in the degradation of gemcitabine. In our previous retrospective study, CDA enzymatic activity was the strongest prognostic biomarker of the activity and efficacy of platinum/gemcitabine combinations. The aim of this prospective study was to validate the prognostic role of CDA activity in the first-line treatment of advanced non-small-cell lung cancer.

Methods

A total of 124 untreated patients received standard doses of platinum/gemcitabine. CDA activity was baseline measured in plasma samples by spectrophotometric assay.

Results

Using the median CDA level as cut-off, in the patients with high versus low CDA activity the response rate was 25.0% (95% CI, 14.7–37.8) and 54.1% (95% CI, 40.8–66.9), P = 0.0013; the 6-month progression rate was 34.5% (95% CI, 22.6–46.6) and 54.1% (95% CI, 40.9–65.6), HR = 2.01 (95% CI, 1.32–3.06), P < 0.001; the 1-year survival rate was 23.3% (95% CI, 13.6–34.6) and 57.3% (95% CI, 43.9–68.6), HR = 2.20 (95% CI, 1.46–3.34), P = 0.0002, respectively. CDA activity resulted to be an independent prognostic factor for progression and survival at multivariate analysis.

Conclusions

This study validated prospectively the prognostic role of the CDA activity and should prompt larger and adequately designed randomised prospective studies to establish the predictive impact of this test in improving the outcome of selected patients.

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.

Intracellular pharmacokinetics of gemcitabine, its deaminated metabolite 2',2'-difluorodeoxyuridine and their nucleotides

AIMS

Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdC) is a prodrug that has to be phosphorylated within the tumour cell to become active. Intracellularly formed gemcitabine diphosphate (dFdCDP) and triphosphate (dFdCTP) are considered responsible for the antineoplastic effects of gemcitabine. However, a major part of gemcitabine is converted into 2',2'-difluoro-2'-deoxyuridine (dFdU) by deamination. In the cell, dFdU can also be phosphorylated to its monophosphate (dFdUMP), diphosphate (dFdUDP) and triphosphate (dFdUTP). In vitro data suggest that these dFdU nucleotides might also contribute to the antitumour effects, although little is known about their intracellular pharmacokinetics (PK). Therefore, the objective of the present study was to gain insight into the intracellular PK of all dFdC and dFdU nucleotides formed during gemcitabine treatment.

METHODS

Peripheral blood mononuclear cell (PBMC) samples were collected from 38 patients receiving gemcitabine, at multiple time points after infusion. Gemcitabine, dFdU and their nucleotides were quantified in PBMCs. In addition, gemcitabine and dFdU plasma concentrations were monitored. The individual PK parameters in plasma and in PBMCs were determined.

RESULTS

Both in plasma and in PBMCs, dFdU was present in higher concentrations than gemcitabine [mean intracellular area under the concentration-time curve from time zero to 24 h (AUC_0-24 h ) 1650 vs. 95 μM*h]. However, the dFdUMP, dFdUDP and dFdUTP concentrations in PBMCs were much lower than the dFdCDP and dFdCTP concentrations. The mean AUC_0-24 h for dFdUTP was 312 μM*h vs. 2640 μM*h for dFdCTP.

CONCLUSIONS

The study provides the first complete picture of all nucleotides that are formed intracellularly during gemcitabine treatment. Low intracellular dFdU nucleotide concentrations were found, which calls into question the relevance of these nucleotides for the cytotoxic effects of gemcitabine.

Population Pharmacokinetics of Gemcitabine and dFdU in Pancreatic Cancer Patients Using an Optimal Design, Sparse Sampling Approach

BACKGROUND

Gemcitabine remains a pillar in pancreatic cancer treatment. However, toxicities are frequently observed. Dose adjustment based on therapeutic drug monitoring might help decrease the occurrence of toxicities. In this context, this work aims at describing the pharmacokinetics (PK) of gemcitabine and its metabolite dFdU in pancreatic cancer patients and at identifying the main sources of their PK variability using a population PK approach, despite a sparse sampled-population and heterogeneous administration and sampling protocols.

METHODS

Data from 38 patients were included in the analysis. The 3 optimal sampling times were determined using KineticPro and the population PK analysis was performed on Monolix. Available patient characteristics, including cytidine deaminase (CDA) status, were tested as covariates. Correlation between PK parameters and occurrence of severe hematological toxicities was also investigated.

RESULTS

A two-compartment model best fitted the gemcitabine and dFdU PK data (volume of distribution and clearance for gemcitabine: V1 = 45 L and CL1 = 4.03 L/min; for dFdU: V2 = 36 L and CL2 = 0.226 L/min). Renal function was found to influence gemcitabine clearance, and body surface area to impact the volume of distribution of dFdU. However, neither CDA status nor the occurrence of toxicities was correlated to PK parameters.

CONCLUSIONS

Despite sparse sampling and heterogeneous administration and sampling protocols, population and individual PK parameters of gemcitabine and dFdU were successfully estimated using Monolix population PK software. The estimated parameters were consistent with previously published results. Surprisingly, CDA activity did not influence gemcitabine PK, which was explained by the absence of CDA-deficient patients enrolled in the study. This work suggests that even sparse data are valuable to estimate population and individual PK parameters in patients, which will be usable to individualize the dose for an optimized benefit to risk ratio.

5'-nucleotidase cN-II emerges as a new predictive biomarker of response to gemcitabine/platinum combination chemotherapy in non-small cell lung cancer

A number of pharmacogenetic studies have been carried out in non-small-cell lung cancer (NSCLC) to identify and characterize genes involved in chemotherapy activity. However, the results obtained so far are controversial and no reliable biomarker is currently used to predict clinical benefit from platinum-based chemotherapy, which represents the cornerstone of treatment of advanced NSCLC. This study investigated the expression levels of ERCC1 and of six genes (RRM1, RRM2, hENT1, dCK, cN-II and CDA) involved in gemcitabine metabolism in locally/advanced NSCLC patients treated with gemcitabine/platinum combination. Gene expression was assessed by quantitative-PCR in laser-microdissected specimens and correlated with tumor response. Frequency distribution of responses above and below the median expression level of biomarkers was compared using a two-sided Fisher’s test. 5′-nucleotidase (cN-II) was the only gene differently expressed (p = 0.016) in the responders (complete/partial-response) compared to non-responders (stable/progressive disease). In the multivariate analysis, overexpression of this catabolic enzyme of gemcitabine remained a significant negative predictive factor. Patients with low cN-II had a modest trend toward increased survival, while both survival and progression-free survival were significantly longer in a more homogenous validation cohort of 40 advanced NSCLC (8.0 vs. 5.1 months, p = 0.026). Moreover, in vitro studies showed that silencing or pharmacological inhibition of cN-II increased the cytotoxicity of gemcitabine. This is the first study demonstrating the role of cN-II as a predictor of response to gemcitabine/platinum combinations in NSCLC. Its validation in prospective studies may improve clinical outcome of selected patients.

Single-nucleotide polymorphisms in the genes of CES2, CDA and enzymatic activity of CDA for prediction of the efficacy of capecitabine-containing chemotherapy in patients with metastatic breast cancer

We examined whether genetic polymorphisms (SNPs) in the capecitabine activation pathway and CDA enzymatic activity were associated with prognosis, benefit from capecitabine-containing treatment or capecitabine-related toxicities. The study population comprised 188 metastatic breast cancer patients of the ATX trial (EudraCT 2006-006058-83) randomized for first-line paclitaxel and bevacizumab with (ATX) or without capecitabine (AT). Cumulative capecitabine dose until grade ≥2 hand-foot syndrome or until first dose reduction were toxicity endpoints. We genotyped CDA c.-451C>T (rs532545), CDA c.-33delC (rs3215400) and CES2 c.-806C>G (rs11075646). CDA activity in baseline serum was measured with a spectrophotometric assay and values were analyzed using a median cut-off or as continuous variable. CDA c.-33delC was prognostic for overall survival (OS) independent of hormone receptor status. For the predictive analysis, progression-free survival benefit from ATX over AT was observed in patients with a CDA c.-33del/del or del/insC genotype, a CDA c.-451CC or CT genotype, and a CES2 c.-806CC genotype compared with their counterparts. There was a higher response rate for ATX over AT in patients with a CDA c.-451CT or TT genotype. Patients with high CDA enzymatic activity had more benefit from capecitabine, while this was marginally observed in the CDA low group. Toxicity endpoints were not associated with any candidate markers. In conclusion, CDA c.-33delC was associated with OS. Since particular SNPs in CDA and CES2 were associated with benefit from the addition of capecitabine to AT, their predictive value should be explored in a higher number of patients.

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.

Impact of Polymorphic Variations of Gemcitabine Metabolism, DNA Damage Repair, and Drug-Resistance Genes on the Effect of High-Dose Chemotherapy for Relapsed or Refractory Lymphoid Malignancies

The goal of this study was to determine whether single nucleotide polymorphisms (SNPs) in genes involved in gemcitabine metabolism, DNA damage repair, multidrug resistance, and alkylator detoxification influence the clinical outcome of patients with refractory/relapsed lymphoid malignancies receiving high-dose gemcitabine/busulfan/melphalan (Gem/Bu/Mel) with autologous stem cell support. We evaluated 21 germline SNPs of the gemcitabine metabolism genes CDA, deoxycytidine kinase, and hCNT3; DNA damage repair genes RECQL, X-ray repair complementing 1, RAD54L, ATM, ATR, MLH1, MSH2, MSH3, TREX1, EXO1, and TP73; and multidrug-resistance genes MRP2 and MRP5; as well as glutathione-S-transferase GSTP1 in 153 patients with relapsed or refractory lymphoma or myeloma receiving Gem/Bu/Mel. We studied the association of genotypes with overall survival (OS), progression-free survival (PFS), and nonhematological grade 3 or 4 toxicity. CDA C111T and TREX1 Ex14-460C>T genotypes had a significant effect on OS (P = .007 and P = .005, respectively), and CDA C111T, ATR C340T, and EXO1 P757L genotypes were significant predictors for severe toxicity (P = .037, P = .024, and P = .025, respectively) in multivariable models that adjusted for clinical variables. The multi-SNP risk score analysis identified the combined genotypes of TREX1 Ex14-460 TT and hCNT3 Ex5 +25A>G AA as significant predictors for OS and the combination of MRP2 Ex10 + 40GG/GA and MLH1 IVS12-169 TT as significant predictor for PFS. Polymorphic variants of certain genes involved in gemcitabine metabolism and DNA damage repair pathways may be potential biomarkers for clinical outcome in patients with refractory/relapsed lymphoid tumors receiving Gem/Bu/Mel.

Yin and yang of cytidine deaminase roles in clinical response to azacitidine in the elderly: a pharmacogenetics tale

Azacitidine is a mainstay for treating hematological disorders. Azacitidine is metabolized by cytidine deaminase, coded by a highly polymorphic gene. Here, we present two elderly patients with opposite clinical outcomes after azacitidine treatment. First, an acute myeloid leukemia patient showed life-threatening toxicities, but outstanding complete remission, after a single round of azacitidine. Further investigations showed that this patient was cytidine deaminase 79A>C (rs2072671) homozygous with a marked deficient phenotype. Next, a chronic myelomonocytic leukemia patient displayed complete lack of response despite several cycles of azacitidine. This patient had a rapid-deaminator phenotype linked to the -31delC deletion (rs3215400). These polymorphisms lead to opposite clinical outcomes in patients with myelodysplastic syndromes treated with azacitidine, thus suggesting that determining cytidine deaminase status could help to forecast clinical outcome.

Cytidine Deaminase as a Molecular Predictor of Gemcitabine Response in Patients with Biliary Tract Cancer

OBJECTIVE

Gemcitabine-based chemotherapy is regarded as the standard treatment for biliary tract cancer (BTC). Potential biomarkers for gemcitabine response include the activities of cytidine deaminase (CDA), human equilibrative nucleoside transporter 1 (hENT1), deoxycytidine kinase (DCK), and ribonucleotide reductase M1 (RRM1). Here, we investigated whether single nucleotide polymorphisms (SNPs) in their encoding genes were associated with the efficacy of gemcitabine chemotherapy in treating BTC.

METHODS

We retrospectively evaluated 11 SNPs in the CDA, hENT1, DCK, human concentrative nucleoside transporter 3 (hCNT3), and RRM1 genes in 80 patients with unresectable, metastatic, or recurrent BTC who were treated with gemcitabine plus cisplatin.

RESULTS

After the results were adjusted for clinical predictors, the variant allele of rs1048977 in the CDA gene was associated with tumor response in a dominant model (OR, 0.23; 95% CI, 0.06-0.93; p = 0.039). No significant association was detected between the 11 SNPs and grade 3/4 toxicity.

CONCLUSIONS

Our findings suggest that the polymorphism of CDA may be a potential predictive marker for the efficacy of gemcitabine-based chemotherapy in patients with BTC.

Selection of the best blood compartment to measure cytidine deaminase activity to stratify for optimal gemcitabine or cytarabine treatment

Cytidine deaminase (CDA) plays a crucial role in the degradation of cytidine analogs, such as gemcitabine and cytarabine. Several studies showed that a low CDA activity is associated with more toxicity but a higher efficacy, while a high activity will lead to a lower efficacy but less toxicity. A stratified dosing strategy based on the relative CDA activity would increase efficiency. In order to predict these events, a reliable measurement of CDA with a validated method is crucial. We aimed to determine which phenotype assay would be most suitable; a spectrophotometric assay using cytidine as a substrate, or an HPLC assay using gemcitabine as a substrate. In serum and whole blood of 26 volunteers, both assays showed an excellent correlation (R>0.999), but not in plasma nor in red blood cells. Moreover, there was no difference between males and females. In conclusion, the spectrophotometric assay seems the most simple and cost-effective test. It should be performed in serum, while it should be normalized on protein content as measured by the Bicinchoninic Acid.

Cytidine deaminase polymorphism predicts toxicity of gemcitabine-based chemotherapy

BACKGROUND

The aim of this study was to ascertain whether single nucleotide polymorphisms of cytidine deaminase (CDA), a key enzyme in the metabolism pathway of gemcitabine, could predict clinical outcomes of cancer patients with gemcitabine-based chemotherapy.

METHODS

We searched MEDLINE and EMBASE up to January 2013 to identify eligible studies. A rigorous quality assessment of eligible studies was conducted according to the Newcastle-Ottawa Quality Assessment Scale. For each included study, the overall survival (OS), overall response rate (ORR) and toxicities were extracted and pooled using random-effects model.

RESULTS

In total, data from 13 studies were included. CDA 208A>G and CDA 435C>T were not included in quantified synthesis due to limited data. CDA 79A>C polymorphism was not significantly associated with OS; however, patients carrying the variant CDA 79C allele were likely to have a poor survival, hazard ratio (HR)=1.03, 95% CI 0.957-1.27 (AC+CC vs. AA). CDA 79A>C polymorphism did not correlated with ORR, odds ratio (OR)=0.719, 95% CI 0.363-1.425 (AC+CC vs. AA). However, patients with the variant CDA 79C allele would experience more grade ≥ 3 leucopenia (OR=2.933, 95% CI 1.357-6.605) and tended to have more severe neutropenia (OR=1.313, 95% CI 0.157-10.981).

CONCLUSIONS

These results suggest that CDA 79A>C polymorphisms is a potential biomarker for toxicity of gemcitabine-based chemotherapy and a CDA testing before gemcitabine administration is preferred.

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.

Gemcitabine diphosphate choline is a major metabolite linked to the Kennedy pathway in pancreatic cancer models in vivo

BACKGROUND

The modest benefits of gemcitabine (dFdC) therapy in patients with pancreatic ductal adenocarcinoma (PDAC) are well documented, with drug delivery and metabolic lability cited as important contributing factors. We have used a mouse model of PDAC: KRAS(G12D); p53(R172H); pdx-Cre (KPC) that recapitulates the human disease to study dFdC intra-tumoural metabolism.

METHODS

LC-MS/MS and NMR were used to measure drug and physiological analytes. Cytotoxicity was assessed by the Sulphorhodamine B assay.

RESULTS

In KPC tumour tissue, we identified a new, Kennedy pathway-linked dFdC metabolite (gemcitabine diphosphate choline (GdPC)) present at equimolar amounts to its precursor, the accepted active metabolite gemcitabine triphosphate (dFdCTP). Utilising additional subcutaneous PDAC tumour models, we demonstrated an inverse correlation between GdPC/dFdCTP ratios and cytidine triphosphate (CTP). In tumour homogenates in vitro, CTP inhibited GdPC formation from dFdCTP, indicating competition between CTP and dFdCTP for CTP:phosphocholine cytidylyltransferase (CCT). As the structure of GdPC precludes entry into cells, potential cytotoxicity was assessed by stimulating CCT activity using linoleate in KPC cells in vitro, leading to increased GdPC concentration and synergistic growth inhibition after dFdC addition.

CONCLUSIONS

GdPC is an important element of the intra-tumoural dFdC metabolic pathway in vivo.

Rapid deaminator status is associated with poor clinical outcome in pancreatic cancer patients treated with a gemcitabine-based regimen

BACKGROUND

Gemcitabine is a mainstay in the treatment of biliary and pancreatic cancers, with limited efficacy in most settings. The gemcitabine elimination pattern is primarily driven by deamination in the liver by CDA. CDA is affected by genetic polymorphisms, leading to marked variations in activity and, subsequently, to erratic drug plasma exposures in patients administered with standard dosage. CDA deficiency has been a rising concern with gemcitabine since several studies have proven that poor metabolizer patients experience life-threatening toxicities upon drug intake. In theory, ultrarapid metabolizer (UM) patients should be conversely at risk of treatment failure, although thus far few studies have addressed this issue in digestive oncology.

PATIENTS & METHODS

A pilot study was conducted on 40 pancreatic cancer patients, all treated with gemcitabine-based therapy. CDA status was primarily established on a phenotypic basis determined by measurement of residual CDA enzymatic activity in serum. Additionally, a search for c208G>A and c79A>C polymorphisms was carried out.

RESULTS

No patients carrying c208G>A polymorphisms were found, and only heterozygous c79A>C patients were observed. Eight out of the 40 patients (i.e., 20%) were identified as UM, with CDA activities over 6 U/mg. CDA activity was significantly different between progressive disease patients and patients with controlled disease (8.4 vs 3 U/mg; p < 0.001). Conversely, fewer gemcitabine-related severe toxicities were observed in UM patients.

CONCLUSION

This pilot study strongly suggests that UM patients are nearly five-times more likely to have progressive disease than patients with normal or low CDA activities, and that beside molecular events at the tumor level, upstream deregulations affecting drug disposition should be taken into account.

The Impact of CDA A79C Gene Polymorphisms on the Response and Hematologic Toxicity in Gemcitabine-Treated Patients: A Meta-Analysis

Purpose

To investigate the impact of the cytidine deaminase (CDA) A79C polymorphism on both the response to gemcitabine in non-small cell lung cancer (NSCLC) patients and the risk of hematologic toxicities in patients bearing any kind of cancer taking gemcitabine.

Methods

The PubMed and Embase databases were searched from the first available article to January 2013. Eligible studies included clinical trials that contained the keywords “gemcitabine” or “cytidine deaminase” and information about response rate of NSCLC patients or hematologic toxicities in patients with any kind of cancer. Relative risk (RR) of different genotypes and 95% confidence intervals (CI) were calculated.

Results

A total of 7 articles (623 patients from 6 studies) were included. The results showed that patients with wild type CDA (AA and AC) had a significantly lower rate of severe anemia than the homozygote mutant type CC (RR=0.308; 95%CI, 0.113-0.021, p=0.021). However, the rate of severe neutropenia, thrombocytopenia, and the response rate were identical between different CDA genotypes.

Conclusion

The A79C CDA polymorphism did not show a significant impact on the response rate to gemcitabine in NSCLC patients, while the wild type CDA genotype was indeed correlated to a lower rate of incidence of severe anemia in patients taking gemcitabine.

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

Pathway-based pharmacogenomics of gemcitabine pharmacokinetics in patients with solid tumors

AIM

The aim of this study was to evaluate the association of gemcitabine pathway SNPs with detailed pharmacokinetic measures obtained from solid tumor patients receiving gemcitabine-based therapy.

MATERIALS & METHODS

SNPs within nine gemcitabine pathway genes, namely CDA, CMPK, DCK, DCTD, NT5C2, NT5C3, SLC28A1, SLC28A3 and SLC29A1 were analyzed for association with gemcitabine pharmacokinetics.

RESULTS

Significant association of gemcitabine clearance with SNPs in NT5C2 was identified. Clearance of 2´,2´-difluorodeoxyuridine, a gemcitabine metabolite was significantly predicted by CDA, SLC29A1 and NT5C2 SNPs. This study reports an association of formation clearance of 2´,2´-difluoro-2´-deoxycytidine triphosphate, an active form of gemcitabine with SNPs within uptake transporters SLC28A1, SLC28A3 and SLC29A1.

CONCLUSION

Genetic variation in gemcitabine pathway genes is associated with its pharmacokinetics and hence could influence gemcitabine response. Our study identified pharmacogenetic markers that could be further tested in larger patient cohorts and could open up opportunities to individualize therapy in solid tumor patients.

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.

Lung cancer in women

Recent biological advances in tumor research provide clear evidence that lung cancer in females is different from that in males. These differences appear to have a direct impact on the clinical presentation, histology, and outcomes of lung cancer. Women are more likely to present with lung adenocarcinoma, tend to receive a diagnosis at an earlier age, and are more likely to be diagnosed with localized disease. Women may also be more predisposed to molecular aberrations resulting from the carcinogenic effects of tobacco, but do not appear to be more susceptible than men to developing lung cancer. The gender differences found in female lung cancer make it mandatory that gender stratification is used in clinical trials in order to improve the survival rates of patients with lung cancer.

Pharmacogenetics of chemotherapy efficacy in breast cancer

Large differences are observed in chemotherapy response between breast cancer patients, with a substantial part of this variability being explained by genetic factors. Polymorphisms in genes encoding drug-metabolizing enzymes, drug transporters and drug targets influence the pharmacokinetics and pharmacodynamics of these anticancer drugs, leading to differences in therapeutic efficacy. Pharmacogenetic investigations of breast cancer therapeutics focused on these candidate loci have been performed. This article summarizes the status of research to identify polymorphisms in genes that influence response to the chemotherapeutic agents used in breast cancer treatment and suggests future directions for this line of research. Understanding the genetic factors that predispose patients to poor treatment outcomes will help guide individualized therapeutic strategies to obtain maximal benefit.

Tetrahydrouridine inhibits cell proliferation through cell cycle regulation regardless of cytidine deaminase expression levels

Tetrahydrouridine (THU) is a well characterized and potent inhibitor of cytidine deaminase (CDA). Highly expressed CDA catalyzes and inactivates cytidine analogues, ultimately contributing to increased gemcitabine resistance. Therefore, a combination therapy of THU and gemcitabine is considered to be a potential and promising treatment for tumors with highly expressed CDA. In this study, we found that THU has an alternative mechanism for inhibiting cell growth which is independent of CDA expression. Three different carcinoma cell lines (MIAPaCa-2, H441, and H1299) exhibited decreased cell proliferation after sole administration of THU, while being unaffected by knocking down CDA. To investigate the mechanism of THU-induced cell growth inhibition, cell cycle analysis using flow cytometry was performed. This analysis revealed that THU caused an increased rate of G1-phase occurrence while S-phase occurrence was diminished. Similarly, Ki-67 staining further supported that THU reduces cell proliferation. We also found that THU regulates cell cycle progression at the G1/S checkpoint by suppressing E2F1. As a result, a combination regimen of THU and gemcitabine might be a more effective therapy than previously believed for pancreatic carcinoma since THU works as a CDA inhibitor, as well as an inhibitor of cell growth in some types of pancreatic carcinoma cells.