Combination chemotherapy directed at the components of nucleoside diphosphate reductase

SLC29A1 single nucleotide polymorphisms as independent prognostic predictors for survival of patients with acute myeloid leukemia: an in vitro study

Background

The mechanism behind poor survival of acute myeloid leukemia (AML) patients with 1-barabinofuranosylcytosine (Ara-C) based treatment remains unclear. This study aimed to assess the pharmacogenomic effects of Ara-C metabolic pathway in patients with AML.

Methods

The genotypes of 19 single nucleotide polymorphisms (SNPs) of DCK, CDA and SLC29A1from 100 AML patients treated with Ara-C were examined. All the SNPs were screened with ligase detection reaction assay. The transcription analysis of genes was examined by quantitative real time polymerase chain reaction. The association between clinical outcome and gene variants was evaluated by Kaplan-Meier method.

Results

Genotypes of rs9394992 and rs324148 for SLC29A1 in remission patients were significantly different from those in relapsed ones. Post-induction overall survival (OS) significantly decreased in patients with the CC genotype of rs324148 compared with CT and TT genotypes (hazard ratio [HR] = 2.997 [95% confidence interval (CI): 1.71-5.27]). As compared with CT and TT genotype, patients with the CC genotype of rs9394992 had longer survival time (HR = 0.25 [95% CI: 0.075-0.81]; HR = 0.43 [95% CI: 0.24-0.78]) and longer disease-free survival (DFS) (HR = 0.52 [95% CI: 0.29-0.93]; HR = 0.15 [95% CI: 0.05-0.47]) as well As compared with CT and TT genotype, patients with the CC genotype of rs324148 had shorter DFS (HR = 3.18 [95% CI: 1.76-5.76]). Additionally, patients with adverse karyotypes had shorter DFS (HR = 0.17 [95% CI: 0.05-0.54]) and OS (HR = 0.18 [95% CI: 0.05-0.68]).

Conclusions

AML patients with low activity of SLC29A1 genotype have shorter DFS and OS in Ara-C based therapy. Genotypes of rs9394992 and rs324148 may be independent prognostic predictors for the survival of AML patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-014-0090-9) contains supplementary material, which is available to authorized users.

A phase I study of Triapine in combination with doxorubicin in patients with advanced solid tumors

PURPOSE

To assess the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), pharmacokinetics and antitumor activity of Triapine administered in combination with doxorubicin.

STUDY DESIGN

Patients were treated with doxorubicin intravenously (IV) on day 1 and Triapine IV on days 1-4 of a 21-day cycle. The starting dose (level 1) was doxorubicin 60 mg/m(2) and Triapine 25 mg/m(2). PK analysis was performed at various time-points before and after treatment.

RESULTS

Twenty patients received a total of 49 courses of treatment on study. At dose level 2 (doxorubicin 60 mg/m(2), Triapine 45 mg/m(2)), two patients experienced DLTs (febrile neutropenia, grade 4 thrombocytopenia). An additional three patients were enrolled at dose level 1 without initial toxicity. Enrollment then resumed at dose level 2a with a decreased dose of doxorubicin (45 mg/m(2)) with Triapine 45 mg/m(2). The two patients enrolled on this level had two DLTs (diarrhea, CVA). Enrollment was planned to resume at dose level 1; however, the sixth patient enrolled to this cohort developed grade 5 heart failure (ejection fraction 20%, pretreatment EF 62%) after the second course. Thus, doxorubicin and Triapine were reduced to 45 and 25 mg/m(2), respectively (level 1a), prior to resuming enrollment at dose level 1, the MTD. The main drug-related toxicity was myelosuppression. Non-hematologic toxicities included mild-to-moderate fatigue, grade 3 diarrhea and grade 4 CVA. There was one treatment-related death due to heart failure. While no objective responses were observed, subjective evidence of clinical activity was observed in patients with refractory melanoma and prostate cancer.

CONCLUSIONS

Pretreated patients with advanced malignancies can tolerate the combination of Triapine and doxorubicin at doses that achieve subjective clinical benefit with the main treatment-related toxicities being myelosuppression and fatigue. The MTD was determined to be doxorubicin 60 mg/m(2) on day 1 and Triapine 25 mg/m(2) on days 1-4 of a 21-day cycle.

Phase II study of Triapine in patients with metastatic renal cell carcinoma: a trial of the National Cancer Institute of Canada Clinical Trials Group (NCIC IND.161)

Triapine is a novel small molecule ribonucleotide reductase inhibitor that showed activity in renal cell carcinoma (RCC) cell lines. Evaluating new agents with novel mechanisms remains of interest for patients with incurable RCC. This was a single-arm, multicentre phase II trial where Triapine was given at a schedule of 96 mg/m2 2-h infusion daily x 4 repeated every 2 weeks in patients with recurrent RCC. A median of four cycles of Triapine was administered to 19 eligible patients. One response was seen (7%.) Median time to progression was 3.6 months. Common adverse events (AEs) were grade 1-2, with fatigue in 74%, nausea in 68% and vomiting in 58%. However grade 3/4 neutropenia was seen in 79% and acute reactions of hypoxia, hypotension, methemoglobinemia were seen. Dose reductions/delays due to AEs were common with only 47% of patients receiving > 90% of planned dose intensity. The study closed, at the end of stage 1 as it did not meet the minimal efficacy criteria to proceed. Further evaluation of Triapine at this dose and schedule in patients with advanced kidney cancer is not recommended.

Interaction of gallium nitrate with other inhibitors of ribonucleotide reductase: effects on the proliferation of human leukemic cells

Ribonucleotide reductase, a key enzyme in deoxyribonucleotide synthesis, is an important target for cancer chemotherapy. Drugs that inhibit its individual components may act synergistically to block DNA synthesis. Prior work has established that gallium inhibits the R2 subunit of ribonucleotide reductase. We show that gallium acts synergistically with the ribonucleotide reductase inhibitors gemcitabine and hydroxyurea to inhibit the proliferation of CCRF-CEM cells. In contrast, combinations of gallium with the ribonucleotide reductase inhibitors amidox, didox, or trimidox produced antagonistic effects on cell growth. Spectroscopy analysis revealed that as a result of their metal-binding properties, amidox, didox and trimidox formed complexes with gallium, thus negating potential synergistic actions. Our results have important implications in the design of clinical trials using these ribonucleotide reductase inhibitors in combination.

The enzyme ribonucleotide reductase: target for antitumor and anti-HIV therapy

Ribonucleotide reductase is the rate-limiting enzyme of DNA synthesis, and it has been shown to be linked with malignant transformation and tumor cell proliferation. It was therefore considered as an excellent target for cancer chemotherapy. This article reviews the in vitro and in vivo effects of hydroxyurea the first inhibitor of the enzyme, which is currently used in general clinical practice. In addition, we summarize the results obtained with other inhibitors of the enzyme; for instance, polyhydroxy-substituted benzohydroxamic acid derivatives, a promising group of inhibitors of ribonucleotide reductase that was synthesized by Bart van'T Riet and investigated by our group. In vitro as well as animal data and pharmacokinetic results are reviewed and possible implications for an improvement in the management of various patient groups are outlined.

Biochemical and antitumor activity of trimidox, a new inhibitor of ribonucleotide reductase

Trimidox (3,4,5-trihydroxybenzamidoxime), a newly synthesized analog of didox (N,3,4-trihydroxybenzamide) reduced the activity of ribonucleotide reductase (EC 1.17.4.1) in extracts of L1210 cells by 50% (50% growth-inhibitory concentration, IC50) at 5 microM, whereas hydroxyurea, the only ribonucleotide reductase inhibitor in clinical use, exhibited an IC50 of 500 microM. Ribonucleotide reductase activity was also measured in situ by incubating L1210 cells for 24 h with trimidox at 7.5 microM, a concentration that inhibits cell proliferation by 50% (IC50) or at 100 microM for 2 h; these concentrations resulted in a decrease in enzyme activity to 22% and 50% of the control value, respectively. Trimidox and hydroxyurea were cytotoxic to L1210 cells with IC50 values of 7.5 and 50 microM, respectively. Versus ribonucleotide reductase, trimidox and hydroxyurea yielded IC50 values of 12 and 87 microM, respectively. A dose-dependent increase in life span was observed in mice bearing intraperitoneally transplanted L1210 tumors. Trimidox treatment (200 mg/kg; q1dx9) significantly increased the life span of mice bearing L1210 leukemia (by 82% in male mice and 112% in female mice). The anti-tumor activity appeared more pronounced in female mice than in male mice. Viewed in concert, these findings suggest that trimidox is a new and potent inhibitor of ribonucleotide reductase and that it is a promising candidate for the chemotherapy of cancer in humans.

Inhibitory effect of new imidazole derivatives on the proliferation and nucleic acid synthesis of leukemic cells

New derivatives of imidazothiazole and imidazobenzothiazole were tested in vitro for their potential antiproliferative activity. Four imidazobenzothiazole derivatives exhibited a cytotoxic activity against two leukemic cell lines, compound I being the most effective. Cell cycle kinetics studies showed that this drug delays the progression of cells from G1 to S and G2 M phases. An inhibitory effect on DNA and RNA synthesis was also observed. The antiproliferative effect of this compound, analogue of immunosuppressive agents, suggested that it could be of interest for a therapeutic use and for the synthesis of new derivatives.

Studies on the mechanisms of inhibition of L1210 cell growth by 3,4-dihydroxybenzohydroxamic acid and 3,4-dihydroxybenzamidoxime

Didox and Amidox inhibit L1210 cell growth in culture. At least one of the mechanisms in the mode(s) of action of the compounds is directed at the ribonucleotide reductase site. Partially purified preparations of ribonucleotide reductase activity are inhibited by Amidox and Didox. The formation of deoxycytidine nucleotides from [14C]cytidine in intact L1210 cells is also blocked. Didox and Amidox cause the decrease in the intracellular pools of the four dNTPs. Hydroxyurea-resistant L1210 cells are not cross-resistant to either Didox or Amidox. These data suggest that Didox and Amidox are not inhibiting ribonucleotide reductase through a mechanism similar to hydroxyurea.

Effect of ribonucleotide reductase inhibitors on the growth of human colon carcinoma HT-29 cells in culture

The effects of ribonucleotide reductase inhibitors on the growth of the human colon carcinoma cell line HT-29 were examined. Inhibitors were chosen for these studies that were specifically directed at each of the subunits of ribonucleotide reductase. The concentrations of drugs required to inhibit the growth of HT-29 cells by 50% (IC50) for hydroxyurea, 2,3-dihydro-lH-pyrazole-[2,3a]imidazole (IMPY), and 4-methyl-5-amino-l-formyl-isoquinoline thiosemicarbazone (MAIQ) were 206, 996, and 3.2 microM, respectively. Although the IC50 for deoxyadenosine alone was greater than 2,000 microM, in the presence of 5 microM erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), which protects deoxyadenosine from deamination by adenosine deaminase, it was reduced to 112 microM. The IC50 for deoxyguanosine was 1,060 microM. The addition of 8-aminoguanosine to protect deoxyguanosine from phosphorolysis by purine nucleoside phosphorylase did not increase the toxicity of deoxyguanosine in HT-29 cells. The combination of MAIQ or IMPY and deoxyadenosine/EHNA gave strong synergistic inhibition of HT-29 cell growth. The results of these studies indicate that ribonucleotide reductase inhibitors effectively block the growth of human colon carcinoma HT-29 cells and that combinations of inhibitors directed at the individual subunits of reductase result in synergistic inhibition of HT-29 cell growth in culture.

Molecular and cellular characterization of drug resistant hamster cell lines with alterations in ribonucleotide reductase

Ribonucleotide reductase consists of 2 protein components frequently called M1 and M2. Hydroxyurea specifically inhibits DNA synthesis by interacting with the M2 protein and destroying a unique tyrosyl-free radical. We have carried out a molecular and cellular characterization of 2 Chinese hamster ovary cell lines exhibiting either low (HN(R)-AT) or relatively high (H(R)-R2T) resistance to the cytotoxic effects of hydroxyurea. Both drug-resistant lines have an increased level of ribonucleotide reductase activity. EPR measurements for tyrosyl-free radical content and studies with M1-specific antibodies indicated that the elevation in enzyme activity was entirely due to an increase in the M2 component. Studies with M1 cDNA showed that both drug-resistant cell lines contained a wild-type level of M1 mRNA and a wild-type M1 gene copy number. Studies with M2 cDNA indicated that the 2 drug-resistant lines possessed elevated levels of M2 message that could explain the observed increase in M2 component. The elevation of M2 mRNA in the most resistant line, H(R)-R2T, was due to an increase in M2 gene copy number. The low resistant cell line, HN(R)-AT, exhibited a wild-type M2 gene copy number, indicating that the increase in M2 gene message occurred through a process other than gene amplification. Enzyme kinetic studies with partially purified preparations from both drug resistant lines showed reduced sensitivity to hydroxyurea and to the negative allosteric effector, dATP. In addition to hydroxyurea, H(R)-R2T cells were also resistant to several other drugs whose site of action is the M2 component. Furthermore, H(R)-R2T cells were not cross-resistant to colchicine or puromycin, suggesting that hydroxyurea-resistant cells do not share the multi-drug resistance phenotype, which is frequently associated with cross-resistance to these drugs.

Properties of N-hydroxy-N'-aminoguanidine derivatives as inhibitors of mammalian ribonucleotide reductase

In previous studies, N-hydroxy-N'-aminoguanidine (HAG) derivatives were demonstrated to suppress growth and clonogenicity of tumor cells which correlated with the inhibition of ribonucleotide reductase and DNA synthesis. The present work has focused on the properties of five HAG derivatives as inhibitors of the ribonucleotide reductase from Ehrlich ascites tumor cells. HAG derivatives acted as non-competitive inhibitors of ribonucleotide reductase with respect to the substrates CDP and ADP. The apparent Ki values for the various HAG derivatives as inhibitors of CDP reductase ranged from 3.4 to 543 microM. However, the apparent Ki values for these inhibitors with respect to ADP reductase were 2- to 10-fold lower than the respective values for CDP reductase. After a preincubation of HAG derivatives and ribonucleotide reductase in the absence of substrates, an increased inhibition was observed. The activity of the inhibited enzyme could be restored by passage over a Sephadex G-25 column and subsequent incubation with dithioerythritol. The addition of either the non-heme iron subunit or the effector-binding subunit to the intact enzyme in the assay mixture resulted in a diminished inhibition of ADP reduction. Inhibition by HAG derivatives of ribonucleotide reductase activity in the test tube was not enhanced by iron chelators. However, a combination of HAG compounds and iron chelators synergistically inhibited the growth of L1210 cells.