Chromatid breakage: differential effect of inhibitors of DNA synthesis during G 2 phase

The cell cycle specificity of chromatid breakage induced by inhibitors of DNA synthesis depends on the mechanism of drug action. 5-Hydroxy-2-formylpyridine thiosemicarbazone, hydroxyurea, and guanazole, compounds that inhibit ribonucleotide reductase, do not cause chromatid breakage during G(2) phase. In contrast, two active antitumor agents, arabinosylcytosine and 5-azacytidine, which are either incorporated into polynucleotides or affect DNA polymerase, produce chromatid breakage during G(2) phase. All of these agents except guanazole also induce breakage in S phase.

Effective combination treatment of advanced acute lymphocytic leukemia with cytosine arabinoside (NSC-63878) and L-asparaginase (NSC-109229)

The combination of cytosine arabinoside and L-asparaginase induced remission in 15 of 22 children (68%) with previously treated acute lymphocytic leukemia (ALL). Eight of these patients were in remission after the second week of treatment and seven were in remission after the fourth week. The combination was well tolerated. These preliminary results suggest that these two agents have an additive therapeutic effect in inducing remissions in children with advanced ALL.

Chromatid breakage: cytosine arabinoside-induced lesions inhibited by ultraviolet irradiation

Exposure to ultraviolet light can reduce the frequency of chromatid breaks induced by cytosine arabinoside in the DNA synthetic and post-DNA synthetic phases of the cell cycle. This effect can be correlated temporally with a decrease in the uptake of tritiated thymidine after ultraviolet treatment, implying that the genesis of such breakage is intimately related to DNA synthesis and that such synthesis is not confined to the DNA synthetic phase.

Effect of 1-beta-D-arabinofuranosylcytosine on cell cycle passage time

1-beta-D-Arabinofuranosylcytosine (ara-C) affects the passage rate of cells from S to G2 phase to a greater extent than from G1 to S. This finding is consistent with the fact that the compound may have its major biological effect during the latter part of S and the early part of G2. The magnitude of these effects is related to the dose and duration of ara-C administration. Inhibition of DNA synthesis can occur without disturbances in transit time.

An approach to the emotional support of fatally ill children

When children with leukemia were en couraged to ask questions about their ill ness, they asked many. These questions were straightforward, demonstrating their interest in learning about their illness, and emphasiz ing their need to place events in perspective. Much of the staff's initial fear and appre hension regarding their ability to deal with problems centering around life and death were gradually resolved as they began to ap proach these problems with the information gathered from the children rather than with the preconceived prejudices obtained from other adults.