title: RNA expression of genes involved in cytarabine metabolism and transport predicts cytarabine response in acute myeloid leukemia.
abstract: BACKGROUND
  Variation in terms of outcome and toxic side effects of treatment exists among acute myeloid leukemia (AML) patients on chemotherapy with cytarabine (Ara-C) and daunorubicin (Dnr). Candidate Ara-C metabolizing gene expression in primary AML cells is proposed to account for this variation.
  
  
  METHODS
  Ex vivo Ara-C sensitivity was determined in primary AML samples using MTT assay. mRNA expression of candidate Ara-C metabolizing genes were evaluated by RQPCR analysis. Global gene expression profiling was carried out for identifying differentially expressed genes between exvivo Ara-C sensitive and resistant samples.
  
  
  RESULTS
  Wide interindividual variations in ex vivo Ara-C cytotoxicity were observed among samples from patients with AML and were stratified into sensitive, intermediately sensitive and resistant, based on IC50 values obtained by MTT assay. RNA expression of deoxycytidine kinase (DCK), human equilibrative nucleoside transporter-1 (ENT1) and ribonucleotide reductase M1 (RRM1) were significantly higher and cytidine deaminase (CDA) was significantly lower in ex vivo Ara-C sensitive samples. Higher DCK and RRM1 expression in AML patient's blast correlated with better DFS. Ara-C resistance index (RI), a mathematically derived quotient was proposed based on candidate gene expression pattern. Ara-C ex vivo sensitive samples were found to have significantly lower RI compared with resistant as well as samples from patients presenting with relapse. Patients with low RI supposedly highly sensitive to Ara-C were found to have higher incidence of induction death (p = 0.002; RR: 4.35 [95% CI: 1.69-11.22]). Global gene expression profiling undertaken to find out additional contributors of Ara-C resistance identified many apoptosis as well as metabolic pathway genes to be differentially expressed between Ara-C resistant and sensitive samples.
  
  
  CONCLUSIONS
  This study highlights the importance of evaluating expression of candidate Ara-C metabolizing genes in predicting ex vivo drug response as well as treatment outcome. RI could be a predictor of ex vivo Ara-C response irrespective of cytogenetic and molecular risk groups and a potential biomarker for AML treatment outcome and toxicity. Original submitted 22 December 2014; Revision submitted 9 April 2015.
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Ajay
authors.initials: A
authors.lastname: Abraham
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Savitha
authors.initials: S
authors.lastname: Varatharajan
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Sreeja
authors.initials: S
authors.lastname: Karathedath
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Chepsy
authors.initials: C
authors.lastname: Philip
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Kavitha M
authors.initials: KM
authors.lastname: Lakshmi
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Ashok Kumar
authors.initials: AK
authors.lastname: Jayavelu
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Ezhilpavai
authors.initials: E
authors.lastname: Mohanan
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Nancy Beryl
authors.initials: NB
authors.lastname: Janet
authors.affiliation: Cytogenetics Unit, Christian Medical College, Vellore, India.
authors.forename: Vivi M
authors.initials: VM
authors.lastname: Srivastava
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Ramachandran V
authors.initials: RV
authors.lastname: Shaji
authors.affiliation: Department of Preventive Medicine, Northwestern University, Chicago, IL, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Aby
authors.initials: A
authors.lastname: Abraham
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Auro
authors.initials: A
authors.lastname: Viswabandya
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Biju
authors.initials: B
authors.lastname: George
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Mammen
authors.initials: M
authors.lastname: Chandy
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Alok
authors.initials: A
authors.lastname: Srivastava
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Vikram
authors.initials: V
authors.lastname: Mathews
authors.affiliation: Department of Haematology, Christian Medical College, Vellore, India.
authors.forename: Poonkuzhali
authors.initials: P
authors.lastname: Balasubramanian
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000009:adverse effects; D017209:Apoptosis / Q000187:drug effects; D003561:Cytarabine / Q000008:administration & dosage* / Q000009:adverse effects / Q000378:metabolism; D003564:Cytidine Deaminase / Q000096:biosynthesis* / Q000235:genetics; D003630:Daunorubicin / Q000008:administration & dosage; D003842:Deoxycytidine Kinase / Q000096:biosynthesis* / Q000235:genetics; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D033721:Equilibrative Nucleoside Transporter 1 / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D015973:Gene Expression Regulation, Leukemic; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D012262:Ribonucleoside Diphosphate Reductase; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000964:Antimetabolites, Antineoplastic; D033721:Equilibrative Nucleoside Transporter 1; C438649:SLC29A1 protein, human; D025521:Tumor Suppressor Proteins; D003561:Cytarabine; C475286:RRM1 protein, human; D012262:Ribonucleoside Diphosphate Reductase; D003842:Deoxycytidine Kinase; D003564:Cytidine Deaminase; D003630:Daunorubicin
keywords: acute myeloid leukemia; cytarabine; drug resistance