Perturbation of cell cycle of human leukaemic myeloblasts in vivo by cytosine arabinoside

Cell kinetics after high dose cytosine arabinoside in patients with acute myelocytic leukemia

In this study 10 patients with acute myelocytic leukemia (AML) each received a rapid intravenous injection of high dose cytosine arabinoside (HD Ara-C; 1 g/m2). Bone marrow aspirates were obtained before and after Ara-C administration to determine the percentage of cells in S-phase measured by flow cytometry. In 5 out of 10 cases synchronization of the leukemic cells in S-phase of the cell cycle was observed. However, the time of maximum synchronization turned out to be difficult to predict. Therefore, the strong correlation between percentage of cells in S-phase at diagnosis and the time of maximal accumulation of S-phase cells after Ara-C administration, as observed by others in childhood AML, could not be confirmed for adult AML patients. Although synchronization of AML cells after in vivo Ara-C administration could be demonstrated in at least half of the patients, the practical consequences are such that clinical application was hampered.

Cell kinetic effect of low dose arabinosyl cytosine

Low dose arabinosyl cytosine (ARA-C) is effective for treatment of acute non-lymphocytic leukaemia (ANLL). The mechanism of action is not clearly understood and it was suggested that low doses of the drug could induce leukaemic cells to differentiate. We investigated the effect of low dose ARA-C (20 mg/m2/d, divided into two doses s.c. at 12 h intervals, x 20 d) on the cell cycle distribution of leukaemic cells in four cases of ANLL. By comparison, four other cases of ANLL were studied during treatment with standard dose ARA-C (200 mg/m2/d as a continuous i.v. infusion x 7 d). Both treatments induced an accumulation of leukaemic cells in post G1 phases, at a variable extent and rate. During treatment by low dose ARA-C, the mitotic index (MI) fell slowly to zero in two patients who achieved a complete remission (CR), while it fell but recovered during treatment in the patients who did not achieve a CR. The MI fell rapidly to zero in the four cases treated by standard dose, who achieved a CR. These data are consistent with the known cytotoxic activity of ARA-C, via inhibition and slowing of DNA synthesis leading to defective cell proliferation and to cell death.

Cultured human tumour cells may be arrested in all stages of the cycle during stationary phase: demonstration of quiescent cells in G1, S and G2 phase

Six human colon carcinoma cell lines were induced to enter stationary phase of growth by nutrient deprivation and cell crowding. Growth kinetics parameters (cell number, flow cytometric analysis of DNA distribution, and labelling and mitotic indices) were measured sequentially for all lines during the various stages of in vitro growth. Our results demonstrated that a substantial fraction of cells (9-18%) were located in G2 phase when they changed from an exponential to a stationary mode of growth. Moreover, a large number of cells in stationary phase of growth had an S-phase DNA content, as determined by flow cytometry, but failed to incorporate radioactive DNA precursors (up to 15-fold difference). To substantiate these findings, cells in stationary phase of growth were induced to enter exponential growth by re-seeding in fresh medium at a lower density. Subsequently observed changes in DNA-compartment distribution, and in labelling and mitotic indices were those expected from cells that had been arrested at different stages of the cycle during their previous stationary phase. Thus, the non-proliferating quiescent state (Q), traditionally located 'somewhere' in G1 phase, appears to be composed also of cells that can be arrested at other stages of the cycle (Qs and QG2). Although the proportion of such cells is rather small, their contribution to the growth kinetics behaviour of human in vivo tumours will become apparent following 'recruiting' or 'synchronizing' clinical manoeuvres and will prevent the formation of a clear-cut wave of synchronized cells.

Evolution of oligoleukemia

Chronic lithium administration to 22 patients with oligoleukemia did not alleviate cytopenia or stimulate bone marrow proliferative activity. The authors identified, however, pretreatment characteristics discriminating two evolutionary endpoints of oligoleukemia (marrow failure, 10 patients; overt acute leukemia, 12 patients): higher marrow leukemic infiltrate, normal myeloid precursor proportion, platelet count, and female sex all favored eventual transition to overt leukemia which, in comparison with marrow failure, was associated with a significantly longer survival duration from symptoms. For patients developing overt leukemia, survival from diagnosis was inversely correlated with the degree of marrow leukemic infiltrate. The lack of lithium responsiveness in oligoleukemia is consistent with the concept of differentiated leukemia with abnormalities either at the level of a lithium-responsive adherent cell elaborating colony stimulating activity (CSA) or at the level of CSA-responsive CFUs.

Cell kinetic studies after high dose Ara-C and adriamycin treatment in a slowly growing rat leukemia model (BNML) for human acute myelocytic leukemia

The effect of high-dose cytosine arabinoside (Ara-C; 1-beta-D-arabinofuranosyl cytosine) injections (200 mg/kg i.v.) on cell cycle perturbation was investigated in a slowly growing rat leukemia (BNML) which is a realistic model for human acute myelocytic leukemia. Flow cytometric analysis showed an initial decrease of cells in S phase from 26 to 13% and a subsequent accumulation of up to 50% at 10-14 h after injection. The low number of S phase cells during the first 8 h might be due to a combination of cell kill in S phase and a block at the G1/S boundary. The results make it very likely that the origin of the accumulated S phase cells is the resting compartment and that these recruited cells enter the proliferation phase as a synchronized cell population. By repeating the Ara-C injection at the time of accumulation of cells in S phase, a similar synchronized wave of recruited cells to that after the first Ara-C injection was observed. Flow cytometric analysis after Adriamycin (7.7 mg/kg i.v.) treatment, which has been shown to be cytotoxic for BNML cells, showed no changes in cell cycle distribution. It was concluded that Adriamycin might have the same toxicity for cells in all of the different cell cycle phases. The application of these data with respect to effective tumor load reduction is discussed in a second report.

Sequential vincristine, arabinosylcytosine and adriamycin in acute leukemia: cytologic and cytokinetic studies

Cytokinetic and cytocidal effects exerted on peripheral blood blasts by sequential administration of vincristine (VCR) 2 mg on day 1, arabinosylcytosine (Ara-c) 50-60 mg/m2/12 hr from day 2-4), and Adriamycin (ADM, Farmitalia, Milan, Italy, 40-60 mg/m2 on day 5) have been examined in 22 courses of treatment performed on 12 patients with nonlymphoblastic and in 4 with lymphoblastic acute leukemia. In 4 patients, the bone marrow blasts wee examined before and also after VCR-Ara-c administration. In vitro tritiated thymidine autoradiography and propidium iodide-DNA flow cytometry were employed for kinetic studies. Blasts disappeared from blood with a median half time of 35 hr. After VCR-Ara-c administration, a significant increase in labeling index (LI) and in the aliquot of cells with DNA content between the diploid (2n) and the tetraploid (4n) values was observed in 80% of the courses in peripheral blood blasts and in all courses in bone marrow blasts. The median grain count over the labeled nuclei was decreased, and the 4n cell percentage and the bone marrow blast mitotic index did not increase. These findings suggest that the increase in the S phase fraction of blast population is due to cell synchronization. Increase in the S phase appears to heighten the cytocidal effect of ADM. The aliquot of the blasts cleared from blood after ADM were in fact related directly to the degree of labeling index increase observed during the previous administration of VCR and Ara-c.

L.H. Gray Medal lecture: cell kinetics and radiation oncology

Development of the study of human tumor cell kinetics during the past decades has deepened our understanding of the natural history of human cancers. Mathematical models based on the data which have been accumulated may help to evaluate, for the various types of human tumors, the time during their growth that the dissemination process occurred and to calculate the size distribution of the subclinical metastases at the time of treatment of the primary tumor. The perturbations caused by radiotherapy and chemotherapy are complex and include reassortment of surviving cells and repopulation. Currently it appears difficult in clinical practice to take advantage of cell reassortment while the differences in the rate and in the duration of repopulation between normal and neoplastic tissues are exploited in most therapeutic regimens. A better knowledge of cell and tissue kinetics following treatment may help to optimize the treatment scheduling in particular during combined administration of radiotherapy and chemotherapy. The study of the kinetics of proliferation in normal tissue has shown the existence of several types of inhibitory and stimulatory humoral factors. These, when purified, can be used to manipulate the proliferation of critical normal tissues in order to protect them during the administration of cell cycle specific drug or to accelerate their regeneration after treatment.

The effect of nitrous oxide on the cell cycle in human bone marrow

The effect of 24 h exposure to nitrous oxide on the cell division cycle in human bone marrow has been studied in vivo using the technique of DNA flow microfluorimetry. All patients who received nitrous oxide showed a significant increase in the proportion of early S-phase cells with a decrease in late S, G2 and mitotic cells. These changes resemble those seen following the use of S-phase-specific cytotoxic drugs. Control patients showed no such effect. Parallel studies have suggested that interference with the function of vitamin B12 underlies this response. Nitrous oxide may provide a convenient method for studying the cell kinetic aspects of acute B12 deficiency and the possibility of using it to increase the therapeutic index of antitumour drugs is discussed.

The proliferative activity of leukaemic myeloblasts following the intravenous infusion of cytarabine

Serial bone marrow aspirates were obtained from 16 adults with acute myeloid leukaemia (AML) before and after a single infusion of cytarabine (5.0 mg/kg i.v. over 30 min). Changes in the proliferative activity of the leukaemic myeloblasts were monitored by determination of the labelling index (LI) and the mitotic index (MI). There was a significant fall in both LI and MI within a few hours of the administration of cytarabine (P = 0.005). In 14 of the 16 cases the LI subsequently rose to observed maxima 0.3% to 14.1% (mean 5.0%) above the preinfusion LI, 11 to 77 hours (mean 40.8 h) after the infusion (P less than 0.05). The MI returned to the mean pretreatment level within the period of observation in 11 of the 16 cases. In general, the changes in MI followed those in LI; the results are consistent with cytarabine-induced arrest or death of leukaemic blast cells in S phase. Because of the variability in timing of kinetic changes in leukaemic myeloblasts following cytarabine, it is not possible to institute remission induction therapy consistently at the time of maximum synchronization with any fixed chemotherapeutic schedule. Furthermore, the degree of synchronization attained is, in general, small, limiting the prospect of exploiting synchronization with cytarabine as a means of improving the remission rate for AML.

Arabinosyl cytosine in chronic myeloid leukaemia: evidence for high cytokinetic sensitivity of myeloblasts

The effect of a single and of repeated i.v. push dose(s) of Arabinosyl Cytosine (ARA-C) has been investigated in 9 chronic myeloid leukaemia (CML) patients in non-blastic phase. This was done by determining separately the relative compartment size, the mitotic index (IM), and the in vitro 3H-TdR labelling index (IL) of marrow and blood myeloblasts (MB) and promyelocytes plus myelocytes (PMC + MC), before and at intervals after the drug. After a single dose of ARA-C, the IL of marrow MB declines rapidly, and recovers thereafter, often with an overshoot at 15 h. After 2 to 4 doses of ARA-C, the IL of marrow and blood MB rises by a factor of 2 to 3, and is maintained at a plateau during further treatment. The behaviour of the IL of blood MB is not always the same as that of marrow MB. The IM of marrow MB does not rise proportionally to the IL, and sometimes is even found to be decreased. It is suggested that these kinetic perturbations reflect an accumulation of MB in S-phase where many but not all of them are trapped and sooner or later die off. With a few exceptions, ARA-C induces only milder kinetic perturbations in marrow and blood PMC+MC. The overall results of this study are in agreement with the generally accepted mechanism of action of ARA-C (S-phase specific effector agent), and with studies that indicate that the effect of ARA-C depends on the growth pattern and on the degree of maturation of the target cells. It is suggested that a proper evaluation of ARA-C on a cell population should take into account the existence of different cell pools, provided with different proliferative activity and potential, and with variable degrees of maturation.

Cell proliferation and protein synthesis in human leukaemic myeloblasts after cytosine arabinoside therapy

The effect of a single intravenous bolus injection of cytosine arabinoside (ARA-C) on the cytokinetics and 3H-leucine uptake of leukaemic myeloblasts in bone marrow and blood was studied at intervals up to 96 h after ARA-C in five patients with previously untreated acute myelogenous leukaemia. An early decrease in mitotic index and in 3H-thymidine labelling was observed in four of five patients and pretreatment values were reached again within the observation period. Changes suggesting synchronization were not observed. ARA-C induced a marked decrease in protein synthesis in the leukaemic myeloblasts as estimated from either a decrease in the 3H-leucine labelling index or the mean grain count of 3H-leucine labelled cells. It is suggested that ARA-C is incorporated also by cell which are not in S-phase and has a prolonged biochemical effect on the leukaemic cells.

Manipulation of the mitotic cycle in the treatment of acute myelogenous leukaemia

A priming dose of cytosine arabinoside (Ara C) was given to 16 children and five adults with acute myelogenous leukaemia (AML) to synchronize leukaemia cells in the DNA synthesis (S) phase of the mitotic cycle. An infusion of this drug, which was continued for 12 h, was started at the time of partial synchronization and was repeated every 6-12 h until the bone marrow was very hypocellular. Complete remission was achieved in 12 of 16 children and in all adults. Two of the four children went into complete remission with the addition of two doses of daunorubicin or adriamycin. These results suggest that partial synchronization of cells in the S phase results in a therapeutic advanatage in the use of Ara C for induction of a remission of AML and that manipulation of the mitotic cycle, as monitored by kinetic studies, may be helpful in planning optimal schedules for drug administration.

Bone-marrow-profileration patterns in acute myeloblastic leukaemia determined by pulse cytophotometry

The proliferation patterns of normal and leukaemic bone-marrow were studied by measuring the D.N.A. content of large numbers of cells by pulse cytophotometry (P.C.P.). In nineteen normal bone-marrow samples an average of 66-3% of the bone-marrow cells were in the G1 phase (2n D.N.A.), 26-1% in the S phase (2n smaller than D.N.A. smaller than 4n), and 7-5% in G2+M phase (4n D.N.A.). The percentages of S-phase cells determined by autoradiography and P.C.P. correlated well, both in normal and in leukaemic bone-marrow. In 25 patients with untreated acute myeloblastic leukaemia (A.M.L.) lower percentages of cells were found in S and G2+M phases, indicating a smaller proliferating pool compared with normal bone-marrow. The likelihood of a complete remission being attained in A.M.L. with the first treatment course was correlated with the percentage of S-phase cells present before treatment. At remission in A.M.L. the proliferation pattern was restored to normal.

Prediction of the response to chemotherapy in acute leukemia

The prognostic value of the in vitro incorporation of labeled thymidine was evaluated in 53 cases of acute leukemia, by means of autoradiography and liquid scintillation (LS) count. A higher rate of incorporation before therapy with higher labeling index and LS- specific activity was observed in patients who later responded to chemotherapy with a complete remission. The in vitro depression of labeled thymidine incorporation after incubation with the two drugs selected for the induction therapy was more marked in those who responded to therapy than in the nonresponders. The in vitro incorporation of 3H-thymidine was also evaluated after 48 hours of chemotherapy ("vivo-vitro" test). A decrease of the incorporation was observed frequently in the responders. On the other hand, in the group of nonresponders, there was generally an increase of the incorporation measured by the liquid scintillation count, often contrasting with a decrease of the labeling index, and corresponding to a higher rate of intracellular incorporation. The prognostic value of these findings appears to be significant, as it allows the response to chemotherapy to be predicted, as well as allowing the selection of the various cytotoxic drugs.