Considerations in the design of possible cell cycle effective drugs

Enhancement of bone marrow radioprotection and reduction of WR-2721 toxicity by Ocimum sanctum

The radioprotective effect of the leaf extract of Ocimum sanctum (OE) in combination with WR-2721 (WR) was investigated on mouse bone marrow. Adult Swiss mice were injected intraperitoneally (i.p.) with OE (10 mg/kg on 5 consecutive days), or 100-400 mg/kg WR (single dose) or combination of the two or double-distilled water (DDW) and whole-body exposed to 4.5 Gy gamma-irradiation (RT). Metaphase plates were prepared from femur bone marrow on days 1, 2, 7 and 14 post-treatment and chromosomal aberrations were scored. The maximum number of aberrant cells was observed at 24 h after irradiation in all the groups. However, pretreatment with OE or WR individually resulted in a significant decrease in aberrant cells as well as different types of aberrations. The combination of the two further enhanced this effect; resulting in a 2-fold increase in the protection factor (PF = 6.68) compared to 400 mg/kg WR alone. The percent aberrant cells decreased linear-quadratically with WR dose when given individually, while in the OE + WR pretreatment animals the values showed a linear dose response. Combination of OE with WR doses above 200 mg/kg completely eliminated rings, polyploidy and pulverization of chromosomes. Percent aberrant cells decreased with time in all groups, though the values remained higher than normal even on day 14 in the RT alone as well as those treated with single agent + RT. WR doses above 200 mg/kg before RT resulted in significantly higher frequency of aberrant cells compared to RT and OE + RT groups on day 14, suggesting delayed WR toxicity; but combination of OE with WR brought down these values to normal level, indicating that OE combination, in addition to enhancing WR protection, may also act as a detoxifier. The protective effect of OE and WR is also reflected in the enhancement of bone marrow CFU survival. Both OE and WR possessed significant free radical scavenging activity in vitro. The combination of the two further enhanced this effect, suggesting that the enhanced free radical scavenging activity by combining the two protectors results in the higher bone marrow cell protection. The significant elevation in chromosome protection obtained by combining OE with WR, with reduction in the latter's toxicity at higher doses, suggests that the combination may have promise for radioprotection in humans.

Methods for the analysis of cellular kinetics in PHA-stimulated blood lymphocytes using BrdU incorporation. A comparative study

The cellular cycle (cc) span was measured by using differential sister-chromatid staining (DSCS) and applying the following methods: cellular cycle time (cct) according to the graphic method of Dutrillaux and Fosse (G-cct); the analytical equation (A-cct) proposed in the present paper, and the average generation time (AGT) suggested by Ivett and Tice. The mean values obtained by the three methods were 12.5, 12.7, and 19.5 h, respectively. A-cct is the more precise method, since the equation of the analytical procedure allows the utilization of numerical data, and when the graphical method is used, the values plotted in a graph may vary according to the employed scale. Cct is the choice over AGT because the first evaluates actively dividing cells and only considers those at M2 or M3. It will be useful to study cell proliferation kinetics in genetic pathological conditions and to investigate with accuracy the effect of cytostatic and cytotoxic drugs.

Cell cycle modifications of breast cancers during neoadjuvant chemotherapy: a flow cytometry study on fine needle aspirates

Breast cancer cells from 92 patients were obtained by repeated fine needle sampling and analysed by flow cytometry for cell cycle modifications during neoadjuvant chemotherapy. Modifications of the histograms were observed for 47 of the 71 informative cases (66%), the most frequent concerning S-phase (increase or decrease) and G2M accumulation. These modifications correlated well with the efficacy of cytotoxic chemotherapy (P < 0.0001). A significant relationship between clinical regression and pretreatment proliferative activity was also observed, with 31/35 (89%) responders in the high proliferation group (S-phase fraction > 5% or BrdU labelling index > 3.3%) compared to 20/36 (56%) in the low proliferation group (P < 0.002). For patients undergoing chemotherapy including doxorubicin, a high incidence of G2M accumulation was observed (33%), a modification which was rare (4.5%) for a regimen with no anthracycline, for which S-phase was the most frequently modified cell cycle compartment (64%). The measurement of the pretreatment tumour proliferative activity as well as the early kinetic modifications, as indicators of response, may prove interesting parameters for the future management of neoadjuvant chemotherapy.

Cell proliferation kinetics of six xenografted human cervix carcinomas: comparison of autoradiography and bromodeoxyuridine labelling methods

Cell kinetic and histologic parameters of six xenografted tumours with volume doubling times ranging from 6 to 43 d were investigated in order to obtain kinetic information on a panel of tumours to be used in radiobiological studies. The six tumours covered a range of histologies and their DNA indices varied from 2.7 to 1.4. The length of the cell cycle (Tc), potential doubling time (Tpot) and labelling index (LI) were determined by continuous labelling with [3H]TdR and autoradiography in three tumours, Tc varied from 30 to 40 h. Determinations of the length of the S phase (Ts) were found to be less reliable by this method. Data on Ts and LI were also determined in all six tumours using bromodeoxyuridine (Brd) labelling and the single sample method: values of Tpot were slightly longer than those obtained via the autoradiographic method. In addition, multiple samples were taken after BrdU labelling. Tc was determined by fitting the data obtained from mid-S, mid-G2 and mid-G1 windows to curves described by a damped oscillator. Data obtained via the mid-S window were found to be most reliable. Generally, cell cycle times obtained by the BrdU method were longer than those observed with the autoradiographic method. Differences between the two methods could be explained by inaccuracies in the determination of Ts, LI and Tc and differences in the experimental approach. We consider the BrdU labelling method to be a suitable alternative for the time-consuming autoradiography, if data on Ts or Tpot are sufficient. Due to difficulties in the reproducibility of the immunofluorescence staining and asynchronization of cells approximately 10 h after labelling, the method of windows analysis was affected by similar problems to those observed in interpretation of percentage labelled mitosis (PLM) curves. However, the method may serve as an alternative to determine cell cycle times in vitro and, if improved technically, in vivo. Careful comparison of the data obtained from mid-S, mid-G1 and mid-G2 windows may increase the reliability of the determination of cell kinetic parameters.

Kinetics of chromosomal aberrations and first mitosis division in human lymphocytes exposed to mitomycin C

In order to understand the relationship between the chromosomal damage detectable at the first mitosis after mutagen treatment and the induced mitotic delay we studied the time pattern of both mitotic indices and chromosomal aberration frequencies in human lymphocytes treated in G1 with mitomycin C (2.5 microM) and cultured in vitro in the presence of 5-bromo-2'-deoxyuridine. Mitotic delay was observed in treated cells cultured for 81 h. At this point an increase in the frequency of chromosomal aberrations is evident and a higher proportion of abnormal cells enters mitosis, the long delay being due to the extensiveness of DNA damage. The importance of cell cycle progression for the detection of the maximal amount of induced chromosomal damage is discussed.

The kinetics of terminal deoxynucleotidyl transferase-positive cells in the mixed colony assay

Human bone marrow was treated with cytolytic monoclonal antibodies BA-1, BA-2 and BA-3 and examined for terminal deoxynucleotidyl transferase-positive (TdT+) cells during culture in the mixed colony assay. The kinetics of TdT+ cells was compared with untreated bone marrow controls over a 14-day culture period. In control cultures a progressive decline in the number of TdT+ cells occurred during the first three days and by day 4 no TdT+ cells were observed. In antibody-treated cell cultures in which all or the majority of TdT+ cells were removed, no TdT+ cells were detectable after 24 h. Both control and antibody-treated cultures showed comparable colony formation from myeloid, erythroid and multipotential progenitor cells by day 14. The results therefore suggest that the mixed colony assay does not support the growth of TdT+ cells or the production of TdT+ cells from TdT- precursors.

Use of flow cytometry in the measurement of cell mitotic cycle

Variations in many cellular characteristics during the cell cycle can be analyzed simply and directly by flow cytometry. Using multiparameter analysis of DNA content, RNA content, cell size and 5-bromodeoxyuridine (BrdUrd) incorporation, it is now possible to define cells' positions in the cell cycle with a precision previously unimaginable. It is also possible, by using the sorting function of the flow cytometer, to separate populations in different phases of the cell cycle for biological and biochemical studies. This review describes the technical aspects of flow cytometric instrumentation, DNA staining procedures, and the cytometric applications of both in cell cycle analysis including some of the more innovative, new approaches with antibody against BrdUrd.

Cell cycle phase sensitivity to cis-dichloro-bis (isopropylamine) trans-dihydroxy platinum (IV) (CHIP)

Cis-dichloro-bis (isopropylamine) trans-dihydroxy platinum (IV) (CHIP) is a second generation platinum coordination complex now in Phase II clinical trials. In vitro studies with Chinese Hamster Ovary cell cultures show that CHIP is a phase-sensitive drug, being most cytotoxic to cells in early G1 phase and least toxic to late S and G2 phase cells. The dose-modifying factor between the drug sensitivity of cells treated in G1 and in late S phase is 1.6. These findings and their clinical significance are discussed with respect to the phase sensitivity of other cytotoxic agents.