Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Troxacitabine (Troxatyl; BCH-4556; (-)-2'-deoxy-3'-oxacytidine), a deoxycytidine analogue with an unusual dioxolane structure and nonnatural L-configuration, has potent antitumor activity in animal models and is in clinical trials against human malignancies. The current work was undertaken to identify potential biochemical mechanisms of resistance to troxacitabine and to determine whether there are differences in resistance mechanisms between troxacitabine, gemcitabine, and cytarabine in human leukemic and solid tumor cell lines. The CCRF-CEM leukemia cell line was highly sensitive to the antiproliferative effects of troxacitabine, gemcitabine, and cytarabine with inhibition of proliferation by 50% observed at 160, 20, and 10 nM, respectively, whereas a deoxycytidine kinase (dCK)-deficient variant (CEM/dCK(-)) was resistant to all three drugs. In contrast, a nucleoside transport-deficient variant (CEM/ARAC8C) exhibited high levels of resistance to cytarabine (1150-fold) and gemcitabine (432-fold) but only minimal resistance to troxacitabine (7-fold). Analysis of troxacitabine transportability by the five molecularly characterized human nucleoside transporters [human equilibrative nucleoside transporters 1 and 2, human concentrative nucleoside transporter (hCNT) 1, hCNT2, and hCNT3] revealed that short- and long-term uptake of 10-30 microM [(3)H]troxacitabine was low and unaffected by the presence of either nucleoside transport inhibitors or high concentrations of nonradioactive troxacitabine. These results, which suggested that the major route of cellular uptake of troxacitabine was passive diffusion, demonstrated that deficiencies in nucleoside transport were unlikely to impart resistance to troxacitabine. A troxacitabine-resistant prostate cancer subline (DU145(R); 6300-fold) that exhibited reduced uptake of troxacitabine was cross-resistant to both gemcitabine (350-fold) and cytarabine (300-fold). dCK activity toward deoxycytidine in DU145(R) cell lysates was <20% of that in DU145 cell lysates, and no activity was detected toward troxacitabine. Sequence analysis of cDNAs encoding dCK revealed a mutation of a highly conserved amino acid (Trp(92)-->Leu) in DU145(R) dCK, providing a possible explanation for the reduced phosphorylation of troxacitabine in DU145(R) lysates. Reduced deamination of deoxycytidine was also observed in DU145(R) relative to DU145 cells, and this may have contributed to the overall resistance phenotype. These results, which demonstrated a different resistance profile for troxacitabine, gemcitabine, and cytarabine, suggest that troxacitabine may have an advantage over gemcitabine and cytarabine in human malignancies that lack or have low nucleoside transport activities.
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PMID:Mechanisms of uptake and resistance to troxacitabine, a novel deoxycytidine nucleoside analogue, in human leukemic and solid tumor cell lines. 1158 58

Unique among currently approved or in-development nucleoside analogs, troxacitabine (Troxatyl) is an L-nucleoside with significant cytotoxic activity. Its stereochemistry and cellular transport characteristics render it insensitive to some tumor cell mechanisms of resistance to D-nucleosides, such as cytarabine and fludarabine. Troxacitabine's dose-limiting toxicities were mucositis and hand-foot syndrome in patients with refractory leukemia. Three complete and one partial remissions were observed in 30 patients with refractory acute myeloid leukemia on a Phase I study. Significant activity in blastic phase of chronic myeloid leukemia was seen on a Phase II study. Combinations of troxacitabine with ara-C, topotecan and idarubicin are active in patients with refractory acute myeloid leukemia (AML). Phase II studies in patients with refractory lymphoproliferative diseases are ongoing. Troxacitabine merits further study in patients with hematological malignancies.
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PMID:Troxacitabine-based therapy of refractory leukemia. 1211 49

Troxacitabine is a novel L-enantiomer nucleoside analog with unique properties in terms of its structure, pharmacokinetics, intracellular transport, and susceptibility to mechanisms of resistance. Troxacitabine has significant activity in patients with refractory myeloid leukemias, both as a single agent and when combined with standard anti-leukemia agents. In a cohort of 170 patients with refractory myeloid leukemia treated with troxacitabine-based regimens on Phase 1 or 2 studies, 10 (6%) had biopsy-proven extramedullary disease, either with or without bone marrow involvement. Six of these patients who received single-agent troxacitabine, 4 received a combination of troxacitabine and cytarabine. Complete response and disappearance of all extramedullary lesions were observed in 6 (60%) of these 10 patients. Two of the 6 responding patients relapsed within 3 months, 2 patients had remissions of 8 and 9 months duration, respectively, 1 patient is in on-going remission at 3, and 1 patient is lost to follow-up. Troxacitabine-based therapy had significant antileukemic activity in extramedullary myeloid leukemias and warrants further investigation in this clinical situation.
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PMID:Troxacitabine activity in extramedullary myeloid leukemia. 1224 82

Troxacitabine [BCH 4556; SPD 758; Troxatyl] is a DNA synthesis inhibitor. This profile has been selected from R&D Insight, a pharmaceutical intelligence database produced by Adis International Ltd. It is a member of a novel class of nucleoside analogues discovered by BioChem Pharma and is the first example of a synthetic L-nucleoside analogue to have shown anticancer activity in animal models. On 11 May 2001, BioChem Pharma was acquired by, and integrated into, Shire Pharmaceuticals Group. In February 2002 Shire announced that it intended to pursue development of troxacitabine as a treatment for solid tumours. In addition, Shire indicated that it would pursue the drug's development for acute myeloid leukaemia. In March 1999, phase II trials were initiated to investigate the efficacy and tolerability of troxacitabine in a variety of solid tumours including pancreas, prostate, colorectal, renal and non-small cell lung cancers and melanoma. The trials were conducted throughout North America and were closed to patient accrual in 2000. Two phase I combination chemotherapy trials in solid tumours (one with cisplatin and another with paclitaxel) have been initiated. One of these trials is in patients with pancreatic cancer. A phase III trial in patients with pancreatic cancer is expected to begin during the second or third quarter of 2003. In addition, further clinical development was initiated in May 2000, in the form of a combination chemotherapy trial in patients with acute leukaemia. A phase II trial in patients with acute myeloid leukaemia (AML) and chronic myeloid leukaemia-blast phase (CML-BP) has reported that troxacitabine demonstrated significant activity in these cancers. However, Shire indicated that no further development for CML-BP will be conducted. The company indicated that it would focus future development in the haematological malignancy area on AML and has initiated an exploratory phase III trial of troxacitabine in previously untreated patients with poor prognosis AML. The study will compare troxacitabine in combination with either cytarabine or idarubicin, with a control drug regimen. The aim is to identify the most promising treatment regimens in a relatively small number of patients before commencing the larger pivotal trial. A pivotal phase III trial is expected to begin in the first half of 2003. In September 2002, Shire Pharmaceuticals forecast Troxatyl to reach peak sales of $US100-200 million, for the indications of pancreatic cancer and myeloid leukaemia.
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PMID:Troxacitabine: BCH 4556, SPD 758, Troxatyl. 1284 94

Troxacitabine is a cytotoxic deoxycytidine analogue with an unnatural L-configuration, which is activated by deoxycytidine kinase (dCK). The configuration is responsible for differences in the uptake and metabolism of troxacitabine compared to other deoxynucleoside analogues. To determine whether troxacitabine has an advantage over other nucleoside analogues several cell lines resistant to cladribine and gemcitabine were exposed to troxacitabine, while blast cells from pediatric leukemia patients were tested for cross-resistance with other deoxynucleoside analogues. The gemcitabine resistant AG6000 (IC50: >3000 nM), and the cladribine resistant CEM (IC50: 150 nM) and HL-60 (IC50: >3000 nM) cell lines, all with no or decreased dCK expression, were less sensitive to troxacitabine than their wild type counterparts (IC50; A2780: 410, CEM: 71 and HL-60: 158 nM). dCK protein expression in CEM was higher than in HL-60, which, in turn, was higher than in A2780. Catalytically inactive p53 seems to increase the sensitivity to troxacitabine. The patient samples showed a large range of sensitivity to troxacitabine, similar to other deoxynucleoside analogues. Cross-resistance with all other deoxynucleoside analogues was observed.
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PMID:Cellular resistance against troxacitabine in human cell lines and pediatric patient acute myeloid leukemia blast cells. 1706 50