Quantitative structure-activity analyses of nitrobenzene toxicity to Tetrahymena pyriformis

Toxicity data for the 50% growth inhibitory concentration against Tetrahymena pyriformis (log (IGC50-1)) for 42 alkyl- and halogen-substituted nitro- and dinitrobenzenes were obtained experimentally. Log (IGC50-1) along with the hydrophobicity, the logarithm of the 1-octanol/water partition coefficient (log Kow), and the molecular orbital properties, the lowest unoccupied molecular orbital energy (Elumo) and maximum acceptor superdelocalizability (Amax), were used to develop quantitative structure-activity relationships (QSARs). All the nitroaromatic compounds tested had toxicity in excess of baseline, nonpolar narcosis. The nitrobenzenes were thought to elicit their toxic response through multiple (and mixed) mechanisms. No high-quality relationship was observed between toxicity and hydrophobicity, or Elumo, individually. However, a strong relationship ¿log (IGC50-1) = 16.4(Amax) - 4.64; n = 42, r2 = 0.847, s = 0.279, F = 229¿ was obtained. In an effort to improve predictability, two-parameter QSAR, or response surface, analyses were performed. These analyses resulted in the following QSARs: ¿log (IGC50-1) = 0.206(log Kow) - 16.0(Amax) - 5.04; n = 42, r2 = 0.897, s = 0.229, F = 180¿ and ¿log (IGC50-1) = 0.467(log Kow) - 1.60(Elumo) - 2.55; n = 42, r2 = 0.881, s = 0.246, F = 154¿.

Population growth kinetics of Tetrahymena pyriformis exposed to selected nonpolar narcotics

This study describes effects of selected nonpolar narcotics of varying hydrophobicity (quantified by the 1-octanol-water partition coefficient, log Kow) and molecular structure on the population growth kinetics of the freshwater ciliate Tetrahymena pyriformis. The response of Tetrahymena exposed to different nonpolar narcotics varied from a change in generation time to a change in lag phase with similar generation time compared to control. Two narcotics with high (>3.00), intermediate (>0.00 and <3.00), and low log Kow (<0. 00) values were tested. Growth of Tetrahymena inhibited up to 85% by the high log Kow toxicants (2-decanone and butylbenzene) grew with similar rates as the control, but exhibited increased lag time, suggesting that the protozoan became acclimated to toxicant stress. Results from growth of Tetrahymena in the low log Kow toxicants (ethanol and acetone) indicate an increased generation time with increasing concentration. Cells inhibited by the intermediate log Kow chemicals, 1-pentanol and anisole, exhibited a response that was a combination of the previously mentioned two contrary responses. Cells inhibited <35% with 1-pentanol and <50% with anisole grew with similar generation times as control flasks, whereas in cells inhibited >35% or >50%, respectively, the doubling times were longer than control growth.

Growth kinetics of preexposed and naive populations of Tetrahymena pyriformis to 2-decanone and acetone

The growth kinetics of preexposed and naive Tetrahymena pyriformis grown in the presence of one hydrophilic and one hydrophobic nonpolar narcotic (acetone and 2-decanone, respectively) have been evaluated. The response of naive Tetrahymena exposed to nonpolar narcotics varied from a change in generation time upon exposure to hydrophilic chemical to a change in lag phase with similar generation time compared to control upon exposure to hydrophobic compounds. Tetrahymena grown in the presence of low concentrations of 2-decanone and then transferred to higher concentrations acclimated to the presence of the toxicant. Acclimation was demonstrated by reduced lag phases compared to naive cells. Results of population growth studies of Tetrahymena grown in the presence of low concentrations of acetone and then transferred to higher concentrations of acetone exhibit the same pattern, an increased generation time with increasing concentration with no lag time, as naive populations. Additionally, the observed generation times in acetone were cumulative relative to the transfer concentration as well as the acclimation concentration. The most feasible explanation for this phenomenon is the interaction of the toxicants with the plasma membrane.

GM-CSF and asparaginase potentiate ara-C cytotoxicity in HL-60 cells

In preparation for a clinical trial using GM-CSF on days 4-10 of sequential high-dose cytarabine (ara-C) and asparaginase (ASNase) on days 1-3 and 8-10, potential interactions between the protein synthesis inhibitor ASNase and GM-CSF were evaluated. Granulocyte-macrophage colony-stimulating factor (GM-CSF) can stimulate acute myeloid leukemia (AML) cells to proliferate in vitro and in vivo. Log phase HL-60 cells were exposed to ara-C (10 microM x 3 h) and/or ASNase (10 U/ml during the last 2 h of ara-C). Ara-C and/or ASNase was removed and cells were incubated with or without GM-CSF (10 ng/ml). After 24, 48 and 72 h of GM-CSF there was no significant difference in the S phase fraction of cells exposed to ASNase prior to GM-CSF. Soft agar cloning efficiency was determined after retreatment with ara-C +/- ASNase 24 h into the GM-CSF incubation. GM-CSF enhanced cytotoxicity for all combinations, although this effect was of borderline significance (P = 0.0621); addition of ASNase to the treatment regimen significantly (P = 0.0229) enhanced cytotoxicity without any evidence of a negative interaction with GM-CSF. In addition, ara-C metabolism was assessed during simultaneous exposure to ara-C (10 microM x 3 h) +/- ASNase (10 U/ml the last 2 h) +/- GM-CSF (10 ng/ml beginning 24 h prior to ara-C). Ara-C incorporated into DNA (P = 0.0302) and ara-CTP formation (P = 0.0084 and P = 0.0003 at 2 and 3 h timepoints, respectively) were both increased significantly by GM-CSF, with modest non-significant increases with ASNase exposures. Neither ASNase nor GM-CSF inhibited the effects of the other in this in vitro model. Therefore, when appropriately scheduled, both GM-CSF and ASNase may potentiate ara-C cytotoxicity.

Leukapheresis induced changes in cell cycle distribution and nucleoside transporters in patients with untreated acute myeloid leukemia

Bone marrow leukemia cells from eight adults with untreated acute myeloid leukemia (AML) were evaluated before and after three daily leukaphereses to determine if mechanical cytoreduction can modulate the cell cycle distribution. The percentage of cells in S-phase and the proliferative fraction (PF = %S + %G2M) were determined by flow cytometry after dual labeling with bromodeoxyuridine and propidium iodide. Prior to pheresis the median %S and PF were 5.4 and 15.4%, respectively. The median change in %S was +2.5% (range -5.5 to +18.8) with increases greater than or equal to 3.7% in 4/8 patients. The median change in PF was +6.1% (range -13.8 to +25.3) with an increase of greater than or equal to 3.6% in 6/8 patients. The median absolute changes of 2.5 and 6.1% represent increases of 47% for %S and 40% for PF compared to the day 1 (pre-pheresis) median values. As the number of nucleoside transporters in the cell membrane [nitrobenzylmercaptopurine riboside (NBMPR) binding sites] has been related to the percentage of cells in S-phase and to cytosine arabinoside (ara-C) cellular pharmacology, these were also measured before and after leukapheresis. Changes in the number of NBMPR binding sites varied widely with a median increase of 365 sites per cell (range -26,061 to +10,396). The change in NBMPR sites was significantly and positively correlated with changes in %S (r = 0.829, p = 0.042). These data suggest that mechanical cytoreduction by leukapheresis can increase the fraction of leukemia cells in S-phase and the PF in some patients with AML. The increase in %S is accompanied by an increase in NBMPR binding sites per cell. These changes in leukemia cell characteristics would be expected to result in an increase in efficacy of ara-C or other S-phase specific agents.

S-phase fraction is not correlated with nucleoside transport in acute myeloid leukemia cells

The expression of nucleoside carrier [nitrobenzylmercaptopurine riboside (NBMPR) binding] sites has been related to proliferative fraction in cell lines and in patient myeloid and lymphoid blasts. This correlation was examined in patients with untreated acute myeloid leukemia (AML). Bone marrow blasts were incubated with 8 microM bromodeoxyuridine (BrdUrd) and dual-labeled with propidium iodide and anti-BrdUrd monoclonal antibody. Flow cytometry was used to determine the percentage of cells with detectable BrdUrd incorporation into DNA (%S) and the proliferative fraction (PF = %S+%G2M) in 63 patients; NBMPR binding sites were quantitated in samples from 29 patients. The median %S was 6.1% (range 0.6-25.9%) and the median PF was 13.0% (range 2.4-36.1%), with a median of 7243 NBMPR binding sites per cell (range 1716-27247). In contrast to a previous report which included bone marrow and peripheral blood blasts, %S in marrow blasts did not correlate with NBMPR binding sites per cell (r = 0.005, p = 0.979). Similarly, PF did not correlate with NBMPR sites per cell (r = 0.190, p = 0.325). This lack of correlation between leukemia cell proliferation and NBMPR binding sites per cell suggests that DNA synthesis in AML blasts depends primarily on de novo nucleoside synthesis rather than the usage of salvage pathways.

Correlation of the proliferative index of residual leukemia with outcome in patients treated with sequential high dose ara-C and asparaginase

Therapy of acute myelogenous leukemia (AML) with sequential high-dose ara-C and asparaginase (HiDAC----ASNase) on a day 1 and 8 schedule was designed to exploit potential recruitment of residual leukemia cells following initial cytoreduction from day 1 treatment. DNA flow cytometry was used to evaluate the proliferative index (%S + G2M) of bone marrow leukemia cells from pretreatment and day 8 marrow samples. The proliferative index on day 1, day 8, and incremental change (day 8 minus day 1) were analyzed for their correlation with bone marrow aplasia on day 15 and with the attainment of subsequent complete remission. Pretreatment (day 1) and the change in proliferative index did not correlate (p greater than 0.10) with day 15 marrow aplasia or with clinical outcome. However, the magnitude of the day 8 proliferative index did relate to the attainment of bone marrow aplasia on day 15 (p = 0.05) and the attainment of complete remission (p = 0.002). Recruitment of residual leukemia cells into the proliferative phases of the cell cycle may contribute to the unique efficacy of the day 1 and 8 schedule of HIDAC----ASNase. Additionally, the cytokinetics of residual leukemia after initial chemotherapy may be predictive of outcome and could be useful as a marker for the design of optimal therapeutic regimens.

Bromodeoxyuridine incorporation into DNA of human leukemia cells is not concentration dependent

Leukemia blasts isolated from bone marrow aspirates of 44 adults with acute leukemia were incubated for 1 h with 0.008-32 microM bromodeoxyuridine (Brd-Urd). After dual labeling with monoclonal anti-BrdUrd antibodies and propidium iodide, the cells were analyzed by flow cytometry. Percent labeled cells and intensity of labeling were similar over concentrations of BrdUrd ranging from 0.8-32 microM--a 40-fold range. Therefore, despite potential interpatient variability in nucleoside pharmacokinetics, commonly used doses of BrdUrd which are intended to achieve steady-state plasma concentrations in the 8.0 microM range can be expected to provide a reliable estimate of the S-phase fraction.