A pragmatic approach to the analysis of DNA histograms with a definable G1 peak

DNA damaging and cell cycle effects of the topoisomerase I poison camptothecin in irradiated human cells

This study addressed the potential radiosensitizing and DNA-damaging actions of the DNA topoisomerase I poison camptothecin (CPT) on SV40 transformed normal (MRC5CVI) and ataxia-telangiectasia (AT5BIVA) fibroblast cell lines. In both cell lines CPT induced a dose-dependent delay of cells in S phase, followed by a dose-dependent trapping in G2/M phase. Acute X-irradiation produced patterns of G2/M arrest and S-phase delay similar to those observed for CPT in the MRC5CVI cell line, but no S phase delay was observed in the AT5BIVA cell line consistent with the ataxiatelangiectasia phenotype of this cell line. X-irradiation of CPT-treated cells resulted in additive prolongation of S phase delay in MRC5CVI cultures and additive effects for cell killing in both cell lines. The potential for topoisomerase I-DNA cross-linking by CPT was not altered by 24h pretreatment with CPT, or by acute X-irradiation. Hypersensitivity of AT5BIVA to CPT was not attributable to elevated levels of complex trapping. These findings suggest that in a rapidly proliferating human tumour there is unlikely to be synergistic therapeutic gain when the two agents are used concurrently, and that previously reported radiosensitization by CPT is restricted to G0 phase cells.

The effect of sodium butyrate on the growth characteristics of human cervix tumour cells

Sodium butyrate has been shown to affect cell proliferation, and, at concentrations above approximately 0.5 mM, to cause cell death in some tumour cell lines. When combined with cytotoxic drugs increase in chemosensitivity has been observed. We are presently carrying out a study of the combined effects of sodium butyrate and cytotoxic drugs on cultured cervix tumour cells. To provide a baseline for this study we have carried out a systematic investigation of the effects of sodium butyrate alone on the growth characteristics of cervix tumour cells cultured as multicell spheroids. This has shown that concentrations of n-butyrate of 0.005 mM to 0.50 mM decrease cell proliferation without inducing cell death, the effect increasing with increasing concentration. Butyrate concentrations greater than 0.50 mM cause cell death after a period of 5 to 15 days exposure, dependent on concentration. Concentrations of 0.010 mM and above cause fragmentation of, and increased cell shedding from, multicell spheroids, suggesting an effect on the cell surface. Concentrations of butyrate greater than 0.10 mM cause a considerable increase in the synthesis of cytokeratin, as shown by reaction with cytokeratin antibody. Correlated with this is a marked increase in cell size, concentrations of butyrate of 2.0 or 3.0 mM leading to an approximate doubling of cell diameter, followed by cell disintegration. The effects of butyrate less than 0.25 mM are readily reversible. At concentrations greater than 0.25 mM the effects are reversible up to a limit of about 7 to 20 days depending on concentration, even when cytokeratin synthesis has been induced.

Collateral resistance to photon and neutron irradiation is associated with acquired cis-platinum resistance in human ovarian tumour cells

The melphalan resistant variant of the human ovarian OAW42 tumour cell line has previously been shown to be collaterally resistant to photon irradiation, but not to fast neutrons. In the present study, the "in vitro" photon and neutron radiosensitivity of human ovarian OAW42 tumour cells with acquired resistance to cis-platinum has been studied, to determine whether a similar pattern of cross-resistance exists between cis-platinum and these ionising radiations. Analysis of SF2 values suggests that resistance to cis-platinum conferred a 3-fold decrease in sensitivity to photons, primarily attributable to a 5-fold decrease in the magnitude of the initial slope (alpha). Depletion of GSH by BSO restored the magnitude of alpha to a value similar to that of the parental line. However, cis-platinum resistant OAW42/CP cells, in contrast to melphalan resistant cells, were 1.5-fold more resistant to "fast" neutrons (assessed at D0.1 survival level) than the parental OAW42 cell line. The mechanism for the collateral resistance between cis-platinum, and both photons and neutrons remains to be determined, but although GSH levels may be directly, or indirectly involved in the collateral resistance to photons, they would appear not to involved with the mechanisms responsible for collateral neutron resistance, in the cis-platinum resistant human ovarian cell lines used in this study.

Comparative evaluation of fresh, fixed, and cryopreserved solid tumor cells for reliable flow cytometry of DNA and tumor associated antigen

Five different protocols for the short-term preservation of cells used for multiparameter flow cytometric assay of tumour associated antigens (TAA) and DNA were assessed in cell suspensions prepared by mechanical disaggregation of 15 gynecological tumors. The protocols at 4 degrees C were 1) storage in buffer, 2) storage in 50% methanol, and 3) storage in buffer after formalin fixation. Tissues were also cryopreserved as cell suspensions and tissue blocks. When the TAA expression and DNA histograms of the preserved cells were compared with those in fresh cell suspensions, cryopreservation was found to be the best method: TAA expression was well preserved and there was a good correlation between TAA expression and the quality of the DNA histograms, respectively, in fresh and cryopreserved cells (RS: 0.82-0.91, P less than 0.001 for all TAAs). The cell suspensions preserved at 4 degrees C all showed a significant increase in background fluorescence (P less than 0.05) and a reduction in the TAA specific fluorescence (P less than 0.011). Methanol fixation was better than buffered formalin for the proteins studied, though both gave significantly worse results than cryopreservation. The quality of these cell suspensions and the correlation with TAA measurements in fresh cell suspensions deteriorated progressively with time, particularly if they were stored more than a week.

Multiparameter flow-cytometric quantitation of epidermal growth factor receptor and c-erbB-2 oncoprotein in normal and neoplastic tissues of the female genital tract

A novel multiparameter flow-cytometric method was used to quantify the expression of epidermal growth factor receptor (EGFR) and c-erbB-2 oncoprotein on 85 cryopreserved normal tissues (30 ovary, 29 endometrium, 16 cervix) and 67 carcinomas (31 ovarian, 18 cervical, 15 endometrial, 3 vulvar). Overexpression of the EGFR and c-erbB-2 oncoproteins was found in respectively 3/31 (9%) and 10/31 (32%) ovarian carcinomas, 13/18 (72%) and 7/18 (38%) cervical carcinomas, and 2/15 (13%) and 2/15 (13%) endometrial carcinomas. Oncoprotein expression was significantly higher in the malignant tumors (for all tumor sites) than in the corresponding normal tissues (P less than 0.034 for all combinations). Aneuploid tumors expressed levels of EGFR and c-erbB-2 oncoprotein significantly higher than those of DNA diploid tumors (P = 0.042 and P = 0.048, respectively). Oncoprotein could be detected in nearly all normal tissues: expression was higher in premenopausal than in postmenopausal patients (EGFR, P = 0.07; c-erbB-2, P less than 0.001). The present study supports the idea that EGFR and c-erbB-2 may play an important role in the autocrine, paracrine, and/or endocrine growth control and differentiation of normal tissues. Alteration in the expression of these oncoproteins is probably involved in malignant transformation and tumorigenesis.

Reduced nuclear binding of a DNA minor groove ligand (Hoechst 33342) and its impact on cytotoxicity in drug resistant murine cell lines

The reduced cellular uptake, and subsequent reduced nuclear availability, of cytotoxic agents is a factor in the resistance of mammalian cells to anti-cancer drugs that act by interaction with DNA. The whole cell uptake, nuclear binding and cytotoxicity of a DNA-specific ligand, Hoechst dye number 33342 (Ho342), has been studied in cytotoxic drug resistant variants of a murine tumour cell line. Cell lines showing various degrees of cross-resistance to adriamycin as a part of the phenotype of classical multi-drug resistance (MDR) demonstrated a reduction in intranuclear Ho342 content, up to a maximum of 35% of the level found in the parent as assessed by flow cytometry, despite similar levels of whole cell uptake determined using radiolabelled ligand. Ability to limit nuclear accessibility of Ho342 correlated closely with cellular resistance to Ho342 and to adriamycin. All drug resistant cell lines showed a significant increase in nuclear accessibility to Ho342 after verapamil treatment, including a methotrexate resistant cell line. The methotrexate resistant variant, not demonstrating MDR, showed reduced nuclear binding of Ho342 but increased cell kill associated with a propensity to develop a population of cells showing extra DNA replication in response to Ho342 exposure. Differences between cell lines in the relationship between Ho342-induced cell cycle perturbation and cell kill supported the conclusion that modulation of several pathways of response to cytotoxic agents had occurred in the development of drug resistance.

Flow cytometry: clinical applications in haematology

The time interval between the development of a new technique or methodology and its acceptance, if successful, as a recognized clinical application can be many years. The application of flow cytometry to reticulocyte counting, for example, has taken 8 years from the appearance of the first publication, and in 1990 it is still in its infancy as a clinical method. It is therefore a challenging task to anticipate which of the methodologies currently under development will achieve acceptance. It would be impossible to deal with all the candidates in the space available, and so a review is provided to those methods that may have potential applications in clinical haematology, together with some of the more practical details of methods that have recently been demonstrated to be viable in the clinical laboratory. The first category consists of leukocyte enumeration and studies on bone marrow, neutrophils, platelets and cellular DNA content, whilst the second covers reticulocyte counting and total red cell volume measurement. The contribution of flow cytometry to the field of immunophenotyping haematological disorders is probably unique in already being clinically acceptable. Finally, the question of quality control is addressed, as this is an essential prerequisite to the adoption of any new method in the clinical laboratory.

Protooncogene amplification and tumor ploidy in human ovarian neoplasms

DNA from 24 ovarian tumors, including 16 carcinomas, was examined for amplification of the proto-oncogenes c-myc, int-2, and rc-erbB-2. All cases of carcinoma were also examined by flow cytometry for DNA ploidy and cell cycle analysis, and eight cases of carcinoma were examined for estrogen and progesterone receptors. Protooncogene amplification was not detected in the DNA of benign ovarian neoplasms, or of ovarian carcinomas with low malignant potential. Amplification of c-myc was detected in six of 12 cases of invasive carcinoma, int-2 amplification was present in one case, and c-erbB-2 amplification was not detected in any case. Among the seven cases evidencing protooncogene amplification, three cases showed aneuploidy in tumor DNA, while four showed diploidy. Two cases which showed aneuploidy in tumor DNA did not demonstrate any degree of protooncogene amplification. Protooncogene amplification was frequently associated with morphologic nuclear anaplasia and high mitotic count. Six of the seven cases demonstrating c-myc or int-2 were of the serous type or showed some degree of serous differentiation, while none of the four cases of purely mucinous carcinoma had evidence of amplification. While the total number of cases in the study was limited, it would appear from the trend demonstrated by the data that protooncogene amplification (particularly c-myc) may be involved in the pathogenesis of aggressive common epithelial tumors of the ovary.

Serous papillary adenocarcinoma of the endometrium. Analysis of proto-oncogene amplification, flow cytometry, estrogen and progesterone receptors, and immunohistochemistry

Primary and metastatic tumor tissues of serous papillary adenocarcinoma of the endometrium were examined for the following: (1) amplification of int-2, c-erbB-2 and c-myc proto-oncogenes by Southern blot hybridization; (2) DNA ploidy by flow cytometric study; (3) and expression of specific proteins, such as estrogen and progesterone receptors, keratin, vimentin, and carcinoembryonic antigen (CEA) using immunohistochemical and biochemical techniques. Amplification of c-myc was observed in the specimens from the endometrium (ten-fold) and from omental metastasis (five-fold). Both int-2 and c-erbB-2 amplification were not observed. The tumor showed aneuploidy, with the specimens from the endometrium and omental metastasis exhibiting multiple populations of aneuploid tumor cells. Estrogen and progesterone receptors could not be detected biochemically; however, immunohistochemically, estrogen receptors were observed in tumor cells forming papillary structures but not in the tumor cells of the solid, more poorly differentiated areas. A similar distribution was observed for both low and high molecular weight keratin. The findings of c-myc amplification and aneuploidy in the serous papillary adenocarcinoma of the endometrium are consistent with its aggressive behavior observed clinically and emphasize the importance of distinguishing this lesion from other types of endometrial carcinoma.

Cytophotometry in tumor pathology. A critical review of methods and applications, and some results of DNA analysis

In tumor pathology the quantitation of cellular substances can be of diagnostic value. Microscope cytophotometry and digital image analysis and, on the other hand, flow cytometry are supplementary methods for measuring, each with a typical spectrum of application. The methods are predominantly used for DNA analysis: Static and image cytophotometry are applicable to cytologic and histologic slides preferably for identifying stem lines in tumors of heterogenous morphology and in merely circumscribed lesions (e.g., precancerous lesions). On the other hand, sampling errors due to preselection, and the often low number of cells actually measured, may preclude the possibility of exact cell cycle analysis. This is, in fact, an important additional option of flow cytometry resulting from the high resolution of DNA histograms, which is explained by the large number of cells that can be measured in a short period. Sampling errors in flow cytometry may result from the preparation of single cell suspensions which in certain tumor entities may suppress a varying amount of particularly fragile cells or nuclei. The prognostic significance of DNA ploidy, stem line heterogeneity and S-phase fraction is clearly described in quite a number of tumor entities. Independent of its prognostic value, the cytometric identification of stem lines might be particularly useful in the follow-up of tumor patients, where it may indicate the effectivity of systemic therapy. The development of therapeutic concepts is aptly supported by flow cytometric cell cycle analysis which helps to assess the in vitro effect of combined cytostatics on the proliferative process. Moreover, multiparameter analysis of biopsy samples may provide greater accuracy in characterising individual tumor stem lines and may furthermore help to develop improved protocols for the therapy of solid tumors.

Statistical evaluation of cell kinetic data from DNA flow cytometry (FCM) by the EM algorithm

Flow cytometric DNA measurements yield the amount of DNA for each of a large number of cells. A DNA histogram normally consists of a mixture of one or more constellations of G0/G1-, S-, G2/M-phase cells, together with internal standards, debris, background noise, and one or more populations of clumped cells. We have modelled typical DNA histograms as a mixed distribution with Gaussian densities for the G0/G1 and G2/M phases, an S-phase density, assumed to be uniform between the G0/G1 and G2/M peaks, observed with a Gaussian error, and with Gaussian densities for standards of chicken and trout red blood cells. The debris is modelled as a truncated exponential distribution, and we also have included a uniform background noise distribution over the whole observation interval. We have explored a new approach for maximum-likelihood analyses of complex DNA histograms by the application of the EM algorithm. This algorithm was used for four observed DNA histograms of varying complexity. Our results show that the algorithm works very well, and it converges to reasonable values for all parameters. In simulations from the estimated models, we have investigated bias, variance, and correlations of the estimates.

Flow cytometry chamber with 4 pi light collection suitable for epifluorescence microscopes

A compact, solid, spherico-ellipsoidal chamber (SEC), which has approaching 4 pi ("all around") light collection, has been developed for flow cytometry. This was mounted onto the stage of a standard fluorescence photomicroscope, and the camera was replaced by a photomultiplier. Both components can be added or removed in minutes. The increased light collection efficiency of the SEC (about 85%) compared with about 4% from standard chambers enabled a fluorescence microscope with a 50 W mercury vapour lamp to "double" as a flow cytometer. The system was tested with microbeads and cells stained for DNA with ethidium bromide, and results were comparable to those obtained with our laser-based instrument.

Oestrogen potentiates topoisomerase-II-mediated cytotoxicity in an activated subpopulation of human breast cancer cells: implications for cytotoxic drug resistance in solid tumours

Primary resistance to chemotherapeutic agents is a major problem in the management of advanced cancer. By using oestrogen to modulate the topoisomerase II content of T-47D human breast cancer cells, we show here that cell subpopulations resistant to the topoisomerase-II-interactive drug VPI6 (etoposide) can be identified and quantified using single-cell analytical techniques. Immunohistochemical studies reveal topoisomerase II to be present in approximately 10% of control cells compared with 30% of oestrogen-stimulated cells, and this difference is reflected in the proportions of cells exhibiting VPI6-induced cell-cycle delay. This moderate increase in overall cell sensitivity is accompanied by massive enhancement of clonogenic cell kill, suggesting that oestrogen enhances VPI6 cytotoxicity by recruiting a clonogenic cell subpopulation characterized by increased topoisomerase II content. Flow cytometry confirms that the increase in topoisomerase II is localized to an activated G1-phase cell subset. We conclude that (i) single-cell analysis of cellular topoisomerase II content is predictive of VPI6 chemosensitivity; (ii) the existence of resistant tumour-cell subpopulations does not necessarily indicate the presence of phenotypically divergent subclones; and (iii) rational strategies for eliminating tumour resistance may be based on biological manipulation of specific cytotoxic drug targets.

Variance within homogeneous phytoplankton populations, I: Theoretical framework for interpreting histograms

A framework is presented for interpreting frequency distributions of volume or fluorescence as measured by a flow cytometer on homogeneous phytoplankton populations. The framework, based on both laboratory experience and theoretical concepts, is illustrated with the use of a simulation model. Asynchronous, synchronous, and phased populations were simulated, with constant and variable growth patterns over the cell cycle. Though simulations produced a wide variety of histogram shapes, including multimodal distributions, the primary difference between asynchronous and synchronous/phased distributions lies in their temporal variation. Histograms that are constant in time indicate asynchronous populations; when populations are not asynchronous, their histogram shapes vary with a periodicity on the same time scale as the cell cycle. A probability density function for the case of asynchronous populations with a constant growth rate is derived. When fitted to simulated histograms this two-parameter density function yields estimates of the two parameters: mean and variance of cell volume (or mass) at age 0.

Flow cytometric analysis of Hoechst 33342 uptake as an indicator of multi-drug resistance in human lung cancer

Cytotoxic drug resistance developing after chemotherapy is thought to be the main cause of treatment failure in several human tumours, including small cell lung cancer (SCLC). Cell lines showing drug resistance following prolonged exposure to a single agent frequently acquire resistance to several functionally unrelated drugs, the phenomenon of multi-drug resistance (MDR). Classical MDR is thought to arise from changes effecting a reduction in intracellular availability of cytotoxic drugs. We describe a flow cytometry (FCM) technique to monitor the MDR phenotype in drug resistant variants of SCLC and non-SCLC cell lines. The technique is based on a multiparametric analysis of the nuclear binding of a model chemotherapeutic agent, the fluorescent dye Hoechst 33342 (Ho342), which is capable of supra-vital staining of DNA in intact, viable cells. A laboratory derived drug resistant SCLC cell line, H69/LX4, showed a significant (30%) reduction in nuclear binding compared to the parental line H69/P. Exposure to verapamil (VPL) rapidly increased (within 2 min) nuclear binding of Ho342, and the new equilibrium of nuclear staining, attained within 20 min, remained lower than the level achieved in the parental cell line, suggesting some ability of H69/LX4 to limit the effect of the drug efflux blocker. A drug resistant large cell carcinoma line showed only a small reduction (10%) in nuclear binding when compared to the parent line, and this difference was not altered by VPL. A drug resistant adenocarcinoma line showed less than 10% difference in nuclear binding compared with the parental line and neither line was significantly affected by VPL treatment. Our findings suggest that different mechanisms of resistance may occur in lung tumours of different tissue types. This technique may be extended to the rapid and direct examination of biopsy specimens of human solid tumours for evidence of multi-drug resistance.

Model system evaluating fluorescein-labeled microbeads as internal standards to calibrate fluorescence intensity on flow cytometers

Fluorescence intensity calibration was evaluated in a model system for flow cytometers using commercially available fluorescein-labeled microbeads as internal standards and stabilized fluoresceinated thymus cell nuclei (Fluorotrol) as surrogates for stained mononuclear cells. Spectrophotometrically determined calibration values for the microbeads were used to generate a standard curve that converted green fluorescence histogram channels into molecular equivalents of soluble fluorescein (MESF). In 19 analyses repeated during a single run, the coefficients of variation (CVs) for the derived MESF values on both dimly and brightly stained Fluorotrol populations were less than 2%. In 26 separate determinations over 14 weeks, the CVs of the derived MESF values were less than 3%. The MESF values of the dim and bright Fluorotrol populations derived from the microbead standard curves were both about 50% lower than those determined by direct spectrophotometric analysis of Fluorotrol. The analytical imprecision of fluorescence intensity measurements in this idealized model system has a CV less than 3%, and the analytical inaccuracy shows that calibration in MESF units remains uncertain over about a two-fold range.

Enhanced sensitivity to camptothecin in ataxia-telangiectasia cells and its relationship with the expression of DNA topoisomerase I

The antitumour drug camptothecin (CPT) can trap covalently bound topoisomerase I-DNA intermediates as complexes which conceal single-strand scissions. In an attempt to evaluate the cytotoxic potential of these lesions in human cells we have measured: (1) cell cycle delay and cell killing by CPT in primary and transformed fibroblasts, and in lymphoblastoid lines derived from normal, X-ray sensitive ataxia-telangiectasia (A-T) and xeroderma pigmentosum (XP) donors; (2) the properties of sublines obtained by high-dose selection in CPT: (3) levels of drug-induced DNA strand scission in intact cells; (4) the cellular availability of extractable topoisomerase I. The drug induced a marked cell cycle block in G2 phase, the magnitude of the block being closely related to cell kill. XP group A cells showed normal sensitivity to CPT, whereas A-T derived cells were consistently hypersensitive (3-5 fold) in a manner which could not be related to a primary deficiency in topoisomerase I activity, abnormal capacity for complex formation or anomalies in the intracellular generation of DNA strand breaks. A CPT-resistant A-T subline had reduced topoisomerase I activity but retained the characteristic of hypersensitivity to X-radiation. The subline lost resistance upon in vitro passage with evidence that resistance was initially an unstable feature of a subpopulation of cells. The findings have implications for the role of topoisomerase I in the in vitro phenotype of A-T cells, and the contribution made by topoisomerase I-dependent damage to the cytotoxic action of CPT.

Comparison of automated and manual techniques for analysis of DNA frequency distributions in bladder washings

Quantitative methods for interpretation of flow cytometry DNA histograms are required for the widespread clinical use of this technology. The usefulness of a histogram analysis technique in this setting requires that it be operator independent, easy to implement in a clinical laboratory, and provide high sensitivity to the desired information. Additionally, the technique must be tolerant of the relatively low signal-to-noise ratios often found in DNA distributions obtained from clinical samples. Among the factors that have been used to assess the malignant potential of tumors are the presence of an aneuploid population, the proportion of hyperdiploid cells, the width of the G1 peak, the DNA index, and the fraction of cells in S. A computer-based method has been developed for extraction of the above-mentioned features from DNA histograms. The program detects peaks in the histogram and uses straight-line fits to the cumulative frequency distribution to define cell population bounds. A test set of 44 histograms compiled from bladder irrigation specimens obtained from patients with a present or past history of transitional cell carcinoma (TCC) was analyzed by five collaborating laboratories forming a Network sponsored by the National Cancer Institute (NCI). This test set was used to evaluate the performance of the computer-based method by comparing results with those of four expert observers. In this preliminary analysis, perfect agreement was found in the detection of aneuploid cell populations by all observers and the computer-based method. Correlation of percent hyperdiploid cell fraction was also excellent.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of intracellular esterases by antitumour chloroethylnitrosoureas. Measurement by flow cytometry and correlation with molecular carbamoylation activity

Antitumour chloroethylnitrosoureas (Cnus) decompose in physiological conditions yielding alkylating species and organic isocyanates. While antitumour activity is mainly attributed to the alkylation of DNA, carbamoylation of intracellular proteins by isocyanates may also have pharmacological and toxicological relevance. We previously reported a novel dynamic flow cytoenzymological assay for esterase inhibition in intact murine cells by BCNU and related isocyanates, and proposed that this might form the basis of an assay for intracellular carbamoylation. We have now examined a wide range of Cnus, isocyanates, and alkylating agents for their ability to inhibit cellular esterases. BCNU, CCNU, their derived isocyanates, and the 4-OH metabolites of CCNU exhibited potent inhibitory activity (I50 values 5.5 x 10(-5)-7.3 x 10(-4) M). Chlorozotocin and GANU were relatively inactive (I50 much greater than 10(-2) M). ACNU, TCNU and the 2-OH metabolites of CCNU exhibited intermediate activity (I50 values 1.1 x 10(-3)-2.3 x 10(-2) M). Compounds not able to form isocyanates were essentially inactive. Poor membrane permeability was also implicated in the weak activity of chlorozotocin and GANU. There was overall a good correlation between esterase inhibition and chemical carbamoylating activity, but some particular differences were identified. We concluded that flow cytoenzymological assay appears to have the potential to provide useful measurement of intracellular protein carbamoylation by existing Cnus and novel derivatives, and also offers the advantage of cell subpopulation identification for in vivo evaluation of these agents.

Subpopulation analysis of drug-induced cell-cycle delay in human tumor cells using 90 degrees light scatter

A mitotic cell subset has been identified with nuclear light scatter. Colcemid-treated T-47D human breast cancer cells were permeabilised, stained with ethidium bromide, and analysed by flow cytometry. Cells with G2M DNA content exhibited a unimodal distribution for DNA fluorescence and forward scatter, but two peaks were discernible with 90 degrees light scatter. A discrete low-scattering cell cluster could be distinguished from the G2 cell subset on two-dimensional contour plots of 90 degrees light scatter vs. DNA fluorescence; this cluster was reproduced by mitotic shake-off experiments and varied quantitatively with mitotic indices determined either by microscopy or by stathmokinetic cell-cycle analysis of DNA fluorescence. Cell sorting confirmed that the low-scattering cell cluster comprised predominantly metaphase and anaphase cells. Identification of mitotic cells with this one-step technique enables rapid analysis of drug-induced cell-cycle delay in cell populations with different rates of cell-cycle traverse. Hence, vincristine-induced cytostasis is shown to arise in part because of premitotic G2 arrest, whereas etoposide is shown to affect cycling cells with equal sensitivity in quiescent and activated cell populations. The use of light scatter to discriminate mitotic cells in this way facilitates analysis of drug-induced cell-cycle delay and supplements the information obtainable by conventional cell-cycle analysis.

Characterisation of VP-16-induced DNA cleavage in oestrogen-stimulated human breast cancer cells

Cycling cells are recognised to be more susceptible than quiescent cells to the cytotoxic action of many commonly used cancer chemotherapeutic agents. We have found that oestrogen stimulation of T-47D human breast cancer cells is accompanied by a two-fold increase in VP-16-induced DNA cleavage as measured by alkaline DNA unwinding, and that this increase in DNA cleavage is accompanied by a corresponding enhancement of drug-induced cytostasis. The enhancement of VP-16-induced DNA cleavage seen with oestrogen exposure is antagonised both by antioestrogen treatment and by cycloheximide, an inhibitor of protein synthesis, but not by the DNA synthesis inhibitor aphidicolin. Increased c-myc protein synthesis is detectable within an hour of oestrogen exposure, while increased VP-16-induced DNA cleavage is detectable within 4h and increased DNA synthesis within 16h. Only small changes in cell-cycle distribution occur with oestrogen stimulation. In the absence of VP-16, oestrogen does not reduce DNA double-strandedness, nor does it induce changes in chromatin structure as measured by alterations in DNA superhelicity or chromatin accessibility. These findings suggest that oestrogen enhances VP-16-induced DNA damage in asynchronously growing G1-phase cells and that this enhancement may be dependent at some point upon de novo protein synthesis. Oestrogen pre-treatment of T-47D human breast cancer cells improves the therapeutic index of VP-16 without the need for cell synchronisation or highly precise drug scheduling.

Improved program for the analysis of DNA histograms

We describe a computer program which will rapidly analyze a set of DNA histograms without further operator intervention after the initial input. The algorithm used was modified from that of Watson et al. (Cytometry 8:1-8, 1987). The program, coded in Pascal, has been implemented on two different systems. It has been tested by using simulated data and experimental data from cells labelled with bromodeoxyuridine. The program has been in use in this and other laboratories for over two years and has proved to be robust and fast and to give a reasonable approximation to the experimental data. It is particularly useful when dealing with badly perturbed DNA histograms.

Improved methodology for intracellular enzyme reaction and inhibition kinetics by flow cytometry

Flow cytoenzymology is the determination of enzyme activities or concentrations in single intact cells. Using the flow cytometer built and designed in our laboratory and recent modifications to hardware and software, we have developed an improved dynamic flow cytoenzymological procedure for the assay of cellular enzyme kinetics. The reaction mixture is sampled continuously, and the computer clock incorporates time as a parameter for kinetic determinations. Conditions for cellular esterase analysis were optimized and the rates of hydrolysis of two fluorogenic substrates, fluorescein diacetate (FDA) and 4-methylumbelliferone acetate (MUA), by esterases in EMT6 mouse mammary tumor cells were studied. Reaction kinetics were characterized, and Km values of 19 and 72 microM were obtained for the hydrolysis of FDA and MUA respectively. The kinetics of the cellular efflux of fluorescein were investigated, and a half-life of 7.5 min obtained. Enzyme inhibition kinetics were investigated using the competitive substrates p-nitrophenyl acetate and phenyl acetate, and the carbamoylating agents physostigmine and n-butyl isocyanate. The latter was particularly potent with an I50 of 4.8 X 10(-5) M for FDA hydrolysis compared with 6.5 X 10(-3) M for physostigmine. The I50 of 8.8 X 10(-5) M for n-butyl isocyanate inhibition of MUA hydrolysis was similar to that obtained with FDA as substrate. By monitoring FDA and MUA reactions separately and simultaneously, we showed them to act as competitive substrates. A comparison of flow cytoenzymological and conventional spectrofluorimetric analysis was also made, and differences identified in some cases.

Influence of systematic errors on the evaluation of the S phase portions from DNA distributions of solid tumors as shown for 328 breast carcinomas

The portion of cells in S phase has proved to be a valuable prognostic indicator of early relapse and life expectancy, particularly in breast carcinoma. Comparisons of published data on samples of primary breast carcinoma biopsies showed that the values obtained by analyses of flow cytometric DNA distributions were generally higher than those of determinations based on the tritiated thymidine (3H-ThdR) labeling index (LI). Flow cytometric DNA analyses of 328 biopsy samples of primary breast carcinomas revealed that these differences could be explained by varying contributions of debris background. Since this influence is inversely proportional to the cell counts in each channel, it may cause considerable errors, particularly in the S phase channels, which normally contain the lowest counts of the DNA distributions. Two different mathematical rationales were tested in order to separate DNA distributions from the debris superimposition. No appreciable differences were found with respect to the essential results. After appropriate subtraction of the background levels, the previously reported discrepancies between cytometrically determined S phase portions and 3H-ThdR LI values disappeared, and good agreement was achieved for the comparable tumor samples of the present study. In conclusion, debris background subtractions should generally precede the DNA histogram analyses, particularly of solid tumors, in order to obtain reliable S phase values.

Effects of hyperthermia, irradiation, and cytotoxic drugs on fluorescein isothiocyanate staining intensity for flow cytofluorometry

Measurement of fluorescein isothiocyanate (FITC) staining intensity of cultured lymphoblastoid cells following hyperthermia showed large increases without concomitant increases in nuclear protein. Similar measurements of cells following incubation with cytotoxic drugs showed fluorescent intensity increases that exceeded the increases in nuclear protein that were due to the cell cycle blocking action of the drug. The reverse, however, was true for cells following irradiation. In contrast, FITC staining intensity and nuclear protein measurements of cells proceeding through the cell cycle after removal of the cycle blocking agent showed nearly parallel changes, although there were reproducible minor differences, especially following blocking with hydroxyurea. These results suggest that FITC staining intensity is a function not only of nuclear protein content but also of stain access to the reaction sites of the protein constituents of the chromatin. Thus, it is possible that FITC staining may be used as a probe of changes in chromatin structure following experimental manipulation of cells in vitro or treatment of tumors in vivo.