Synchronization of the mitotic cycle in acute leukaemia

Treatment of childhood acute myelogenous leukemia with an intensive regimen (AML-87) that individualizes etoposide and cytarabine dosages: short- and long-term effects

The purpose of this study was to assess the feasibility and efficacy of a treatment regimen for pediatric acute myelogenous leukemia (AML) that uses four rotating drug pairs and adjusts dosages of etoposide and cytarabine to target specific plasma concentrations. Thirty-one girls and 27 boys (median age, 9.7 years) with de novo AML were treated on the protocol. Six cycles of chemotherapy were planned. Cycles 1 to 4 comprised the drug combinations cytarabine plus etoposide, cytarabine plus daunomycin, etoposide plus amsacrine, and etoposide plus azacitidine, respectively. For cycles 5 and 6, the first two combinations were repeated. Dosages were adjusted to achieve plasma concentrations of 1.0 microM +/- 0.1 microM cytarabine and 30 microM +/- 0.3 microM etoposide. Forty-four patients (76%) entered complete remission. Of those, 24 have had relapses; 23 remain alive in first or subsequent remission. The 5-year event-free survival (EFS) estimate was 31.0% +/- 5.9%; the 5-year survival estimate was 41.4% +/- 6.3%. Six patients (10%) died of the toxic effects of therapy. Severe neutropenia occurred in all cycles. Long-term complications of therapy included hepatitis C, cardiac insufficiency, and hearing loss. Adjustment of cytarabine and etoposide dosage was feasible for achieving targeted plasma drug concentrations; however, the potential clinical efficacy of this approach was offset by substantial acute and long-term toxicity.

Cytokinetic study on the effects of N4-behenoyl-1-beta-D-arabinofuranosylcytosine on murine leukemic cells L 1210: a comparison with the effects of 1-beta-D-arabinofuranosylcytosine

The effects of N4-behenoyl-1-beta-D-arabinofuranosylcytosine (BH-AC) on the cell cycle of murine leukemic cells (L 1210 cells) were compared with those of 1-beta-D-arabinofuranosylcytosine (ara-C), known to be effective for acute leukemia. In a cytokinetic study, a combination of Feulgen microcytofluorometry and tritiated thymidine autoradiography (3H-TdR ARG) was used to measure DNA content and to determine DNA synthesis simultaneously in a single cell. Administration of 200 mg/kg of BH-AC significantly prolonged the survival time of mice bearing L 1210. In addition, the cells in the G1 + S1 phases increased with time, accounting for 94.4 per cent of all cells measured at 48 h after the administration, compared to 73.7 per cent before administration. On the other hand, following the administration of 86 mg/kg of ara-C (equivalent to 200 mg/kg of BH-AC), the percentage of cells in the S1 + S2 phases increased maximally to 75.9 per cent at 18 h. Cytokinetic studies further showed that BH-AC administration blocks DNA synthesis of the cells in the S-phase for a longer period than does ara-C. These results suggest that the prolonged inhibition by BH-AC on DNA synthesis allows cells to accumulate in the S-phase to a greater degree.

[Effect of trenimon on single phases of the cell cycle of Yoshida ascites tumor cells (author's transl)]

Yoshida ascites tumor cells were synchronized in suspension cultures with thymidine in excess or with fluordeoxyuridine. Cells were washed after incubation with thymidine or treated with thymidine after incubation with fluordeoxyuridine. 2 h after terminating the S phase blockade 74--80% of the cells are S phase cells, 6 h later 70--80% of the cells had accumulated in the G 2 phase. Cultures enriched with cells of the S phase or the G 2 phase were treated with Trenimon. Increase of cell numbers within the following 48 h was inhibited in both cases in the same order of magnitude. In addition cells in various phases of growth were separated by density gradient zentrifugation and treated with Trenimon. Again cell numbers after 48 h were identical.

[Experiments and theoretical cell kinetic calculations on the problem of in vivo synchronization with vincristine in L 1210 ascites tumor cells and crypt cells of the mouse (author's transl)]

Experiments are described on synchronizing L 1210 ascites tumor cells and jejunal crypt cells of the mouse with vincristine. In both cases the percentage of mitoses increases to a peak value 4 hrs after application of vincristine and decreases during the following 8 hrs ("releasing time") to the level of the normal mitotic index. Following this first mitotic peak no futher peak of neither the mitotic nor the labeling index was observed during 48 hrs in L 1210 ascites tumor cells and during 38 hrs in crypt epithelia. Thus, in both cell types it was not possible to obtain a synchronizing effect by applying vincristine. Based on cell kinetic considerations it was examined whether peaks of the mitotic as well as the labeling index can be expected at all under the given circumstances. The results show that the theoretical course of the mitotic index coincides with the measured values. This means that no peak of the mitotic index can be expected from the theoretical point of view. In calculating the time course of the labeling index the theoretical curve proved to depend to a high degree on the variations of the cycle time which are not known in detail, especially not after application of vincristine. However, the theoretical conditions show that also in the case of the labeling index no peak can be expected. This agrees with the experimental results. The general significance of a long "releasing time" of 8 hrs or more for the lack of a synchronizing effect is discussed.

Synchronization and recruitment in acute leukemia

The in vivo effects of several chemotherapeutic agents on the mitotic cycle of leukemic blasts in the bone marrow were evaluated by serial measurements of cells in mitosis and in deoxyribonucleic acid (DNA) synthesis as indicated by ability to incorporate tritiated thymidine or tritiated deoxyuridine. 28 studies were done in 23 children and 1 adult. The changes in the marrow after a single injection of L-asparaginase, hydrocortisone, cyclophosphamide, cytosine arabinoside, methotrexate, and an exchange transfusion (62% of the total blood volume) were evaluated. L-asparaginase and hydrocortisone were found to arrest the entry of cells into the S period. Cyclophosphamide appeared to inhibit DNA synthesis, arrest cells in mitosis, and inhibit the entry of cells into the S period. Cytosine arabinoside, and methotrexate inhibited DNA synthesis. During the period of time the cells were inhibited in the S phase by these two drugs, cells continued to enter the S period. Thus partial synchronization was achieved after these two drugs. An exchange transfusion had no consistent effect on the mitotic cycle, but partial synchronization in the S period was seen in one patient. To take advantage of the ability of cystosine arabinoside, to synchronize leukemic cells in the S phase, a second cycle-dependent drug was given at the time the leukemic blasts were synchronized. The second cycle-dependent drugs evaluated were vincristine, methotrexate, and cytosine arabinoside given by intravenous drip over a 12 hr period. Recruitment was found after cytosine arabinoside alone, and after prior synchronization with cytosine arabinoside and then the administration of either of these drugs. The results of these studies indicate that a greater therapeutic advantage can be achieved by a second cycle-dependent drug after synchronization than after the second drug alone.