Deamination of glutamine is a prerequisite for optimal asparagine deamination by asparaginases in vivo (CCG-1961).

BACKGROUND: Glutamine (Gln) deamination by asparaginase (ASNase) appears to contribute in the decrease of serum asparagine (Asn) levels and enhance leukemic cell apoptosis. The pharmacodynamic (PD) rationale is based on the role of Gln as the main amino group donor for Asn synthesis from aspartate by the enzyme asparagine synthetase (AS). MATERIALS AND METHODS: Relationships between ASNase enzymatic activity and Asn or Gln levels were examined in 274 pairs of pre- and post-ASNase serum specimens from 200 high-risk acute lymphoblastic leukemia (ALL) patients from the Children's Cancer Group (CCG-1961). Data were analyzed according to a novel PD model based on previous best-fit projections (NONMEM) from the CCG-1962 standard-risk ALL study. RESULTS: The PD results from high-risk and standard-risk ALL patients were superimposable. The percentages of Asn and Gln deamination were predicted by ASNase activity in patients' sera. Pharmacodynamic analyses strongly suggested that > 90% deamination of Gln must occur before optimal Asn deamination takes place in vivo. Asparaginase activity > or = 0.4 IU/ml yielded mean Gln and Asn % deamination values of 90%. Lower ASNase concentrations yielded lower Gln or Asn % deamination. This ASNase concentration coincides with the in vitro determined IC50 value on CEM/0 human T-lymphoblastic leukemia cells. CONCLUSION: Asparaginase activity of > or = 0.4 IU/ml provided optimal Asn and Gln deamination in high-risk ALL patients. Deamination of Gln correlates with enhanced serum Asn deamination in vivo. Therefore, deamination of Gln may enhance the antileukemic effect of ASNase.

Changes of amino acid serum levels in pediatric patients with higher-risk acute lymphoblastic leukemia (CCG-1961).

BACKGROUND: Deamination of asparagine (Asn) and glutamine (Gln) by asparaginases (ASNase) is associated with good prognosis in acute lymphoblastic leukemia (ALL). Chemotherapy drugs used for ALL may accelerate catabolism of other amino acids (AA). MATERIALS AND METHODS: We studied ASNase activity and changes of Asn, Gln, serine (Ser), threonine (Thr), histidine (His), proline (Pro) and arginine (Arg) levels and sought relationships in sera from 73 pediatric ALL patients, who received ASNase-containing chemotherapy. RESULTS: Asparaginase activity averaged 0.4+/-0.34 IU/ml (mean+/-SDEV) in all specimens. All AA decreased after treatment, ranging from 18.6%-82.6% of control. Asparaginase activity of 0.7 IU/ml provided 90% Asn and Gl deamination. The data were dichotomized in subsets of low ASNase (range 0.02-0.39 IU/ml, mean=0.17+/-0.09 IU/ml) and high ASNase (range 0.4-1.69 IU/ml and mean=0.72+/-0.32 IU/ml). Asparagine and Gln % deamination values were correlated with ASNase activity (p=0.0002 and p=0.0001). Similarly, decreases of Arg and Ser levels were also correlated, p =0.0009 and p=0.032, respectively. In the high ASNase subset, a 39% decrease of Arg and 26% of Ser was obtained. Low ASNase activity was correlated with lower Asn and Gln % deamination and with moderate decrease of Ser (14.6%) and Arg (19.6%). Threonine, Pro and His also decreased, but no correlations were obtained with ASNase activity. CONCLUSION: Asparagine, Gln and five other AA declined during ASNase treatment. Asparagine and Gln % deamination values are highly correlated with serum ASNase activity. Asparaginase may indirectly cause moderate depletion of serum Arg and Ser levels, providing an enhancement in leukemia blasts apoptosis. Toxicity from the ASNase and other drugs could enhance the decrease of AA serum levels. Further studies are needed to verify these findings and their potential clinical importance in the treatment of ALL patients.

Characterization and drug resistance patterns of Ewing's sarcoma family tumor cell lines.

Despite intensive treatment with chemotherapy, radiotherapy and surgery, over 70% of patients with metastatic Ewing's Sarcoma Family of Tumors (EFT) will die of their disease. We hypothesize that properly characterized laboratory models reflecting the drug resistance of clinical tumors will facilitate the application of new therapeutic agents to EFT. To determine resistance patterns, we studied newly established EFT cell lines derived from different points in therapy: two established at diagnosis (CHLA-9, CHLA-32), two after chemotherapy and progressive disease (CHLA-10, CHLA-25), and two at relapse after myeloablative therapy and autologous bone marrow transplantation (post-ABMT) (CHLA-258, COG-E-352). The new lines were compared to widely studied EFT lines TC-71, TC-32, SK-N-MC, and A-673. These lines were extensively characterized with regard to identity (short tandem repeat (STR) analysis), p53, p16/14 status, and EWS/ETS breakpoint and target gene expression profile. The DIMSCAN cytotoxicity assay was used to assess in vitro drug sensitivity to standard chemotherapy agents. No association was found between drug resistance and the expression of EWS/ETS regulated genes in the EFT cell lines. No consistent association was observed between drug sensitivity and p53 functionality or between drug sensitivity and p16/14 functionality across the cell lines. Exposure to chemotherapy prior to cell line initiation correlated with drug resistance of EFT cell lines in 5/8 tested agents at clinically achievable concentrations (CAC) or the lower tested concentration (LTC): (cyclophosphamide (as 4-HC) and doxorubicin at CAC, etoposide, irinotecan (as SN-38) and melphalan at LTC; P<0.1 for one agent, and P<0.05 for four agents. This panel of well-characterized drug-sensitive and drug-resistant cell lines will facilitate in vitro preclinical testing of new agents for EFT.

Flow cytometry analysis of single-strand DNA damage in neuroblastoma cell lines using the F7-26 monoclonal antibody.

The F7-26 monoclonal antibody (Mab) has been reported to be specific for single-strand DNA damage (ssDNA) and to also identify cells in apoptosis. We carriedout studies to determine if F7-26 binding measured by flow cytometry was able to specifically identify exogenous ssDNA as opposed to DNA damage from apoptosis. Neuroblastoma cells were treated with melphalan (L-PAM), fenretinide, 4-hydroperoxycyclophosphamide (4-HC)+/-pan-caspase inhibitor BOC-d-fmk, topotecan or with 10Gy gamma radiation+/-hydrogen peroxide (H2O2) and fixed immediately postradiation. Cytotoxicity was measured by DIMSCAN digital imaging fluorescence assay. The degree of ssDNA damage was analyzed by flow cytometry using Mab F7-26, with DNA visualized by propidium iodide counterstaining. Flow cytometry was used to measure apoptosis detected by terminal deoxynucleotidyltransferase (TUNEL) assay and reactive oxygen species (ROS) by carboxy-dichlorofluorescein diacetate. Irradiated and immediately fixed neuroblastoma cells showed increased ssDNA, but not apoptosis by TUNEL (TUNEL-negative). 4-HC or L-PAM+/-BOC-d-fmk increased ssDNA (F7-26-positive), but BOC-d-fmk prevented TUNEL staining. Fenretinide increased apoptosis by TUNEL but not ssDNA damage detected with F7-26. Enhanced ssDNA in neuroblastoma cells treated with radiation+H2O2 was associated with increased ROS. Topotecan increased both ssDNA and cytotoxicity in 4-HC-treated cells. These data demonstrate that Mab F7-26 recognized ssDNA due to exogenous DNA damage, rather than apoptosis. This assay should be useful to characterize the mechanism of action of antineoplastic drugs.