Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2-5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151-363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

The global biogeography of tree leaf form and habit

Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit (evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17-34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.

Native diversity buffers against severity of non-native tree invasions

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5-7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Effects of productivity on biodiversity in forest ecosystems across the United States and China

In the global campaign against biodiversity loss in forest ecosystems, land managers need to know the status of forest biodiversity, but practical guidelines for conserving biodiversity in forest management are lacking. A major obstacle is the incomplete understanding of the relationship between site primary productivity and plant diversity, due to insufficient ecosystem-wide data, especially for taxonomically and structurally diverse forest ecosystems. We investigated the effects of site productivity (the site's inherent capacity to grow timber) on tree species richness across 19 types of forest ecosystems in North America and China through 3 ground-sourced forest inventory data sets (U.S. Forest Inventory and Analysis, Cooperative Alaska Forest Inventory, and Chinese Forest Management Planning Inventory). All forest types conformed to a consistent and highly significant (P < 0.001) hump-shaped unimodal relationship, of which the generalized coefficients of determination averaged 20.5% over all the forest types. That is, tree species richness first increased as productivity increased at a progressively slower rate, and, after reaching a maximum, richness started to decline. Our consistent findings suggest that forests of high productivity would sustain few species because they consist mostly of flat homogeneous areas lacking an environmental gradient along which a diversity of species with different habitats can coexist. The consistency of the productivity-biodiversity relationship among the 3 data sets we examined makes it possible to quantify the expected tree species richness that a forest stand is capable of sustaining, and a comparison between the actual species richness and the sustainable values can be useful in prioritizing conservation efforts.

A brief history of numbers and statistics with cytometric applications

A brief history of numbers and statistics traces the development of numbers from prehistory to completion of our current system of numeration with the introduction of the decimal fraction by Viete, Stevin, Burgi, and Galileo at the turn of the 16th century. This was followed by the development of what we now know as probability theory by Pascal, Fermat, and Huygens in the mid-17th century which arose in connection with questions in gambling with dice and can be regarded as the origin of statistics. The three main probability distributions on which statistics depend were introduced and/or formalized between the mid-17th and early 19th centuries: the binomial distribution by Pascal; the normal distribution by de Moivre, Gauss, and Laplace, and the Poisson distribution by Poisson. The formal discipline of statistics commenced with the works of Pearson, Yule, and Gosset at the turn of the 19th century when the first statistical tests were introduced. Elementary descriptions of the statistical tests most likely to be used in conjunction with cytometric data are given and it is shown how these can be applied to the analysis of difficult immunofluorescence distributions when there is overlap between the labeled and unlabeled cell populations.

Proof without prejudice revisited: immunofluorescence histogram analysis using cumulative frequency subtraction plus ratio analysis of means

BACKGROUND

Apart from the work of Lampariello and colleagues (Cytometry 15:294-301, 1994; Cytometry 32:241-254, 1998), very little analytical work has been carried out for analysis of immunofluorescence distributions containing an overlapping mixture of labeled and unlabeled cells. The methods developed tend to rely on fitting theoretical distributions to the relevant populations. However, the method described here attempts to produce an analytical solution.

METHODS

A new method for immunofluorescence histogram analysis is presented. It uses cumulative frequency distribution subtraction of the test sample from the control to predict the mean of a labeled cell component embedded within a histogram containing unlabeled cells. Ratio analysis of means (RAM) was then carried out to calculate the labeled fraction. The results were submitted to Kolmogorov-Smirnov analysis and Student's t-test for validation at a given level of probability.

RESULTS

The method was developed with a data set exhibiting a small "positive" shoulder, which was predicted to contain a labeled fraction comprising 8.0% of the total at the 99% confidence limit. It was then tested with data analyzed and published previously where the Johnson Su family of distributions was used in curve fitting.

CONCLUSIONS

There was good agreement between the known and predicted proportions of labeled cells. However, the method is dependent on the symmetry of the distributions. Some minor systematic errors were encountered due, in part, to skewed experimental distributions.

Characteristics of a novel deep red/infrared fluorescent cell-permeant DNA probe, DRAQ5, in intact human cells analyzed by flow cytometry, confocal and multiphoton microscopy

BACKGROUND

The multiparameter fluorometric analysis of intact and fixed cells often requires the use of a nuclear DNA discrimination signal with spectral separation from visible range fluorochromes. We have developed a novel deep red fluorescing bisalkylaminoanthraquinone, DRAQ5 (Ex(lambdamax) 646 nm; Em(lambdamax) 681 nm; Em(lambdarange) 665->800 nm), with high affinity for DNA and a high capacity to enter living cells. We describe here the spectral characteristics and applications of this synthetic compound, particularly in relation to cytometric analysis of the cell cycle.

METHODS

Cultured human tumor cells were examined for the ability to nuclear locate DRAQ5 using single and multiphoton laser scanning microscopy (LSM) and multiparameter flow cytometry.

RESULTS

Multiparameter flow cytometry shows that the dye can rapidly report the cellular DNA content of live and fixed cells at a resolution level adequate for cell cycle analysis and the cycle-specific expression of cellular proteins (e.g., cyclin B1). The preferential excitation of DRAQ5 by laser red lines (633/647 nm) was found to offer a means of fluorescence signal discrimination by selective excitation, with greatly reduced emission overlap with UV-excitable and visible range fluophors as compared with propidium iodide. LSM reveals nuclear architecture and clearly defines chromosomal elements in live cells. DRAQ5 was found to permit multiphoton imaging of nuclei using a 1,047-nm emitting mode-locked YLF laser. The unusual spectral properties of DRAQ5 also permit live cell DNA analysis using conventional 488 nm excitation and the single-photon imaging of nuclear fluorescence using laser excitation between 488 nm and low infrared (IR; 780 nm) wavelengths. Single and multiphoton microscopy studies revealed the ability of DRAQ5 to report three-dimensional nuclear structure and location in live cells expressing endoplasmic reticulum targeted-GFP, MitoTracker-stained mitochondria, or a vital cell probe for free zinc (Zinquin).

CONCLUSION

The fluorescence excitation and emission characteristics of DRAQ5 in living and fixed cells permit the incorporation of the measurement of cellular DNA content into a variety of multiparameter cytometric analyses.

Mammalian S-phase checkpoint integrity is dependent on transformation status and purine deoxyribonucleosides

In eukaryotic cells arrested in S-phase, checkpoint controls normally restrain mitosis until after replication. We have identified an array of previously unsuspected factors that modulate this restraint, using transformed hamster cells in which cycle controls are known to be altered in S-phase arrest. Arrested cells accumulate cyclin B, the regulatory partner of the mitotic p34(cdc2) kinase, which is normally not abundant until late G(2) phase; treatment of arrested cells with caffeine produces rapid S-phase condensation. We show here that such S-phase checkpoint slippage, as visualised through caffeine-dependent S-phase condensation, correlates with rodent origin and transformed status, is opposed by reverse transformation, and is favoured by c-src and opposed by wnt1 overexpression. Slippage is also dependent on a prolonged replicative arrest, and is favoured by arrest with hydroxyurea, which inhibits ribonucleotide reductase. This last is a key enzyme in deoxyribonucleotide synthesis, recently identified as a determinant of malignancy. Addition of deoxyribonucleosides shows that rapid S-phase condensation is suppressed by a novel checkpoint mechanism: purine (but not pyrimidine) deoxyribonucleosides, like reverse transformation, suppress cyclin B/p34(cdc2) activation by caffeine, but not cyclin B accumulation. Thus, ribonucleotide reductase has an unexpectedly complex role in mammalian cell cycle regulation: not only is it regulated in response to cycle progression, but its products can also reciprocally influence cell cycle control kinase activation.

The early fluidic and optical physics of cytometry

All forms of cytometry, depend on the basic laws of physics, including those of fluidics, optics, and electronics, most of which were established centuries ago. Flow cytometry depends critically on the fluidics presenting each individual cell with precision to the sensing volume. This is intersected by a high-intensity light source, and light scattering and fluorescence from suitably stained constituents in each cell are captured by the light-collecting optics and measured. The works and observations of Bernoulli and Euler in the 18th century, Reynolds in the 19th century, and Crosland-Taylor in the 20th century in the field of fluid dynamics laid the foundations for hydrodynamic focussing, which is the primary prerequisite for presenting individual cells to the sensing volume. In addition, electrostatic cell sorters must have the ability to generate stable droplet formation in the jet-stream issuing from the flow chamber nozzle. The origins here can be traced to work carried out in the early to mid-19th century by Savart, Magnus, and Thomson. Flow, image, and confocal cytometry are all dependent on the laws of optics, including those of reflection and refraction as well as numerous other optical principles. The observations and works of Socrates, Ptolemy, Snel, and Descartes between about BC 370 and 1637 were of seminal importance in developing the laws of reflection and refraction. In the mid-17th century Hooke illustrated the power of magnifying glasses and microscopy in his Micrographia and Newton was responsible for explaining colours in the spectrum. Huygens, toward the end of the 17th century, put forward the concept of point source light propagation contributing to a wave front. Finally, Thomas Young, early in the 19th century, established the wave form of light from interference patterns. Most people will be familiar with some of these discoveries and the investigators who carried out the work; some people will be familiar with all of these. However, very few people are likely to have had the opportunity and privilege to access the very early works and the original data and manuscripts, or translations thereof, which laid the foundations of physics that enabled our discipline to be established. It is always important for any discipline to remember its roots and to appreciate the seed from which those roots grew, for it is much easier to learn and fully understand when we have a knowledge of the source and the logical progressions that lead from one discovery to the next. This knowledge lends perspective to our current endeavours as the past, after all, created the present, which in turn contributes to the future. In this article, which was presented as an invited lecture at the 9th Canadian Consensus meeting on AIDS, I have attempted to trace the origins of the early work on the physics of fluidics and optics, which laid the foundations.

Multivariate analyses of DNA index, p62c-myc, and clinicopathological status of patients with ovarian cancer

AIM

To determine if either DNA index or p62c-myc is an independent prognostic variable in ovarian cancer.

METHODS

Multivariate and univariate analyses of the relation between DNA index, p62c-myc, FIGO stage, histological type, tumour grade, completeness of surgery, and patient survival in ovarian cancer were examined.

RESULTS

Multivariate analysis showed significant association of survival only with stage and grade. There was no relation between survival and DNA index.

CONCLUSIONS

DNA index is not an independent prognostic variable in ovarian cancer.

Flow cytometric analysis and confocal imaging of anticancer alkylaminoanthraquinones and their N-oxides in intact human cells using 647-nm krypton laser excitation

Flow cytometry and laser-scanning confocal fluorescence microscopy have been used in the study of the pharmacodynamics, in single intact cells, of two novel alkylaminoanthraquinones (AQ4 and AQ6), structurally based upon the mid-red excitable but very weakly fluorescent anticancer agent mitoxantrone, together with their respective N-oxide derivatives (AQ4NO and AQ6NO). The drug design rationale was that N-oxide modifications generates prodrug forms suitable for selective bioreductive-activation in hypoxic tumor cells. DNA-binding ranked in the order of mitoxantrone > AQ6 > AQ4 > AQ6NO >> AQ4NO. Using both cytometric methods a similar ranking was found for whole cell and nuclear location in human transformed fibroblasts. However, AQ6 showed enhanced nuclear uptake compared with mitoxantrone, in keeping with its greater capacity to inhibit DNA synthesis. Partial charge neutralisation by N-oxide derivatization resulted in loss of DNA synthesis inhibition but retention of the ability to accumulate in the cytosol, an important property for prodrug development. We conclude that both flow cytometry and confocal imaging revealed biologically significant differences between analogues for subcellular distribution and retention properties. The study demonstrates the potential for these complementary 647-nm krypton laser line-based fluorometric methods to provide relevant structure-activity information in anthraquinone drug-design programmes.

Etoposide-induced cell cycle delay and arrest-dependent modulation of DNA topoisomerase II in small-cell lung cancer cells

As an approach to the rational design of combination chemotherapy involving the anti-cancer DNA topoisomerase II poison etoposide (VP-16), we have studied the dynamic changes occurring in small-cell lung cancer (SCLC) cell populations during protracted VP-16 exposure. Cytometric methods were used to analyse changes in target enzyme availability and cell cycle progression in a SCLC cell line, mutant for the tumour-suppressor gene p53 and defective in the ability to arrest at the G1/S phase boundary. At concentrations up to 0.25 microM VP-16, cells became arrested in G2 by 24 h exposure, whereas at concentrations 0.25-2 microM G2 arrest was preceded by a dose-dependent early S-phase delay, confirmed by bromodeoxyuridine incorporation. Recovery potential was determined by stathmokinetic analysis and was studied further in aphidicolin-synchronised cultures released from G1/S and subsequently exposed to VP-16 in early S-phase. Cells not experiencing a VP-16-induced S-phase delay entered G2 delay dependent upon the continued presence of VP-16. These cells could progress to mitosis during a 6-24 h period after drug removal. Cells experiencing an early S-phase delay remained in long-term G2 arrest with greatly reducing ability to enter mitosis up to 24 h after removal of VP-16. Irreversible G2 arrest was delimited by the induction of significant levels of DNA cleavage or fragmentation, not associated with overt apoptosis, in the majority of cells. Western blotting of whole-cell preparations showed increases in topoisomerase II levels (up to 4-fold) attributable to cell cycle redistribution, while nuclei from cells recovering from S-phase delay showed enhanced immunoreactivity with an anti-topoisomerase II alpha antibody. The results imply that traverse of G1/S and early S-phase in the presence of a specific topoisomerase II poison gives rise to progressive low-level trapping of topoisomerase II alpha, enhanced topoisomerase II alpha availability and the subsequent irreversible arrest in G2 of cells showing limited DNA fragmentation. We suggest that protracted, low-dose chemotherapeutic regimens incorporating VP-16 are preferentially active towards cells attempting G1/S transition and have the potential for increasing the subsequent action of other topoisomerase II-targeted agents through target enzyme modulation. Combination modalities which prevent such dynamic changes occurring would act to reduce the effectiveness of the VP-16 component.

Expression of c-erbB-2, c-myc, and c-ras oncoproteins, insulin-like growth factor receptor I, and epidermal growth factor receptor in ovarian carcinoma

AIMS

To assess whether the overexpression of five dominant oncogene encoded proteins is crucial to the pathogenesis of ovarian carcinoma and whether this provides any useful prognostic information.

METHODS

The expression of the insulin-like growth factor 1 receptor (ILGFR 1), epidermal growth factor receptor (EGFR), and the c-erbB-2, c-ras, and c-myc products was studied by multiparameter flow cytometry in 80 patients with epithelial ovarian cancer for whom long term follow up was available.

RESULTS

Overexpression of ILGFR 1, EGFR, c-erbB-2, c-ras and c-myc was found in, respectively, nine of 80 (11%), 10 of 80 (12%), 19 of 80 (24%), 16 of 80 (20%) and 28 of 80 (35%) ovarian carcinomas. The levels of expression of ILGFR 1, EGFR, c-erbB-2 and c-ras were significantly higher in the tumours of patients with recurrent or persistent disease after chemotherapy than in the tumours of patients at initial presentation (p < 0.02). Multivariate analysis showed that residual tumour (p < 0.001), FIGO stage (p = 0.002), EGFR overexpression (p = 0.030) and previous chemotherapy (p = 0.034) were independent variables for predicting survival.

CONCLUSIONS

Overexpression of these oncoproteins only occurs in a small proportion of ovarian carcinomas but may have an important role in the progression of the disease.

Heparin decreases the rate of proliferation of rat vascular smooth muscle cells by releasing transforming growth factor beta-like activity from serum

OBJECTIVES

Various heparins have been reported to inhibit the proliferation of vascular smooth muscle cells (VSMCs). The effects of eight chemically distinct heparins on the cell cycle and differentiation of primary and passaged cultures of rat aortic VSMCs have been characterised and the mechanism of heparin action investigated.

METHODS

VSMCs from adult rat aorta were prepared by enzyme dispersion and stimulated to enter the cell cycle with 10% serum in the presence or absence of heparin. Progressions through S phase and M phase were measured by [3H]-thymidine incorporation and cell counting respectively. Flow cytometry was used to confirm the effects of heparin on VSMC cell cycle progression. The effect of heparin on VSMC differentiation was investigated by analysing smooth muscle specific myosin heavy chain content of the cells after heparin treatment.

RESULTS

Eight heparins at concentrations between 5 micrograms.ml-1 and 100 micrograms.ml-1 partially inhibited VSMC proliferation (27% to 76% 96 hours after addition of heparin), but did not affect the entry of the cells into S phase. Flow cytometry confirmed that VSMC populations in the presence of heparin contained significantly (p < 0.005) more cells in the G2/M phase of the cell cycle than control populations. Heparin also blocked the dedifferentiation of primary cultures of VSMCs stimulated by serum. These effects of heparin were completely reversed by the presence of a neutralising antiserum to transforming growth factor beta (TGF beta) and heparin attached to agarose beads was as effective as free heparin as a growth inhibitor of VSMCs.

CONCLUSIONS

Heparins of varying molecular weight and anticoagulant properties all partially inhibited VSMC proliferation predominantly by extending the G2/M phase of the cell cycle. Heparin also inhibited dedifferentiation of primary cultures of VSMCs. Heparin (< 100 micrograms.ml-1) acted extracellularly to release TGF beta from serum, which accounted for the effects of heparin on proliferation and differentiation.

Can flow cytoenzymology be applied to measure membrane-bound enzyme kinetics? Assessment by analysis of gamma-glutamyl transpeptidase activity

We describe an improved technique which allows the analysis of enzyme reaction kinetics for gamma-glutamyl transpeptidase (gamma-GT) by flow cytometry. This is technically difficult because of the location of the enzyme on the external surface of the cell membrane leading to the rapid escape of the product. The reaction is determined by monitoring the conversion of gamma-glutamyl aminomethylcoumarin to aminomethylcoumarin. Reaction kinetics are described for BL8 hepatocyte and JB1 hepatoma cells lines, together with inhibition kinetics for the active site-directed glutamine analogue L-(alpha-S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid. We show that it is possible to follow the reaction dynamics in a heterogeneous mixture of BL8 and JB1 cells allowing discrimination of the two cell types based on gamma-GT activity. Improvements for further optimizing the assay of this important enzyme are suggested.

Multiparameter flow cytometric analysis of a novel cytotoxin (factor 2) induced tumor cell membrane permeability

An improved twin-probe multiparameter flow cytometric technique was applied to examine a novel cytotoxin, Factor (F2), induced tumor cell permeability. Ability to retain preloaded intracellular bis-carboxyethyl carboxyfluorescein (BCECF, green fluorescence) and to exclude extracellular propidium (red fluorescence) was measured simultaneously with forward and right-angle scatter. In addition to the two expected cell populations which were stained green negative, red positive ("membrane-damaged" and "non-viable", Region 2), and green positive, red negative ("membrane intact" and "viable", Region 3), a third population was seen which fluoresced neither green nor red and displayed intermediate light scatter characteristics (Region 1). K562 cells progressed from Region 3 to Region 1, and then from Region 1 to Region 2 after treatment with F2. These results suggest that sequential changes in membrane structure lead to increased permeability, first with respect to intracellular BCECF and then in turn to extracellular propidium. Flow cytometric changes caused by F2 were detectable 10 min after treatment with 2.5 U/ml of F2, and 5 min after 10 or 40 U/ml of F2. Flow cytometric analysis showed that F2-induced tumor cell lysis and growth inhibition were accompanied by rapid alternations in tumor cell membrane permeability. Flow cytometric analysis also distinguished F2 cytotoxicity from phorbol myristate acetate (PMA) associated cytotoxicity to K562 cells and determined that F2 produced spontaneously or induced by PMA and/or ciprofloxacin had a similar ability to induce tumor cell membrane permeability change.

Flow cytometric measurement of cell components other than DNA: virtues, limitations, and applications in gynecologic oncology

Flow cytometry is a high-precision technique for rapid analysis and sorting of cells and particles. In theory, it can be used to measure any cell constituent, provided that a fluorescent tracer is available that reacts specifically and stoichiometrically with that constituent. The technique provides statistical accuracy, reproducibility, and sensitivity and allows simultaneous measurement of several constituents on a cell-to-cell basis. The main drawback of flow cytometry is the lack of visual control and structural information in solid tissues. Careful sample preparation, quality control of all staining and instrumentation procedures, and the use of immunohistologic or cytologic controls are essential for high-quality flow cytometric analysis. The technique has been used successfully for simultaneous measurement of DNA and tumor-associated antigens, oncogene products, proliferation markers, and markers for multidrug resistance in cultured cell lines and in cell suspensions prepared from solid tumors and cervical smears. Flow cytometry has the potential to play an important role in the study of carcinogenesis. With an appropriate panel of monoclonal antibodies, the technique can be used for screening, "biochemical" diagnosis of neoplasia, and rapid drug, hormone, and radiotherapy sensitivity tests.

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.

Flow cytometric and immunohistochemical analysis of p62c-myc oncoprotein in the bronchial epithelium of lung cancer patients

The expression of p62c-myc in bronchial resection lines (BRLs) from lung cancer and control patients, has been examined by immunohistochemistry and parallel flow cytometry using antibodies directed against the p62c-myc oncoprotein. Both methods indicated a marked increase in nuclear p62c-myc levels in BRLs from tumour cases as compared to control BRLs. Immunohistochemistry also revealed greater cytoplasmic positivity in BRLs from cancer patients than from control cases. Flow cytometric quantitation of nuclear p62c-myc confirmed the immunohistochemical findings demonstrating that the median level of nuclear p62-myc fluorescence in BRLs from tumour cases was 1919 fluorescence units (FU) (range:216-7367 FU) and 144 FU (range:0-1365 FU) for non-tumour control BRLs. No consistent difference in p62c-myc fluorescence was observed between BRLs from smokers and non smokers. Both methods indicated that in lung tumour cases, nuclear p62c-myc was increased in histologically normal and abnormal BRLs, suggesting that hyperexpression of this protein is an early event preceding detectable morphological change. These results suggest that increased p62c-myc levels may be an early event in the pathogenesis of lung cancer.

c-myc protein product is a marker of DNA synthesis but not of malignancy in human gastrointestinal tissues and tumours

c-myc is a conserved cellular gene. The gene product is a nuclear-bound 62,000 molecular weight phosphoprotein (p62c-myc). Although p62c-myc levels have been measured in colorectal cancers, little is known about the expression of the protein in upper gastrointestinal tumours and tissues. Studies were performed on tumour and mucosal specimens from 87 patients with colorectal cancer, from two with polyposis coli, from six with squamous oesophageal carcinomas and from 18 with gastric carcinomas. The mean p62c-myc content was measured in units of fluorescence in the G1 diploid and G2 diploid peaks of the cell cycle by multiparameter flow cytometry using the 6E10 antibody. The nuclear p62c-myc content increased with DNA synthesis in tumours and mucosa. G2 levels of p62c-myc were higher in glandular mucosa than in adenocarcinomas. No differences in peak nuclear c-myc expression were found in relation to histological grade or to anatomical site of colorectal tumours. There was a broadly inverse relationship between G2 p62c-myc levels in tumours and mucosa and their in vivo 5-bromo-2'-deoxyuridine labelling indices. Nuclear p62c-myc levels are cell cycle related but the protein has not been shown to be a marker of increased tissue proliferation or of gastrointestinal malignancy. The reduction of the nuclear p62c-myc content of many adenocarcinoma cells compared with glandular mucosa cells suggests that reduced synthesis or nuclear retention of the normal protein may be a factor in the development of gastrointestinal adenocarcinomas, although the mechanism by which this may occur is not clear.

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.

Multi-parameter flow cytometric quantitation of the expression of the tumor-associated antigen SM3 in normal and neoplastic ovarian tissues. A comparison with HMFG1 and HMFG2

SM3 is a monoclonal antibody that reacts with a peptide epitope in the core protein of polymorphic epithelial mucin. Multi-parameter flow cytometry was used to characterize the expression of SM3 and compare it with two related tumor-associated antigens, HMFG1 and HMFG2, in cell suspensions of 44 malignant ovarian tumors, 15 benign ovarian tumors, and 16 normal ovaries. Tumor-associated antigen expression was significantly higher in malignant ovarian neoplasms than in benign neoplasms (P less than 0.001 for all three antigens). SM3 was expressed more specifically in malignant than benign tumors but had a lower affinity than HMFG1 and HMFG2. Multi-parameter flow cytometric evaluation of a panel of monoclonal antibodies can be used to help in choosing the best antibody for immunohistochemistry, imaging, and eventually treatment of ovarian tumors.

Multiparametric flow cytometry of the modulation of tumor cell membrane permeability by developmental antitumor ether lipid SRI 62-834 in EMT6 mouse mammary tumor and HL-60 human promyelocytic leukemia cells

(+-)-2-[Hydroxy[tetrahydro-2-(octadecyloxy)methylfuran-2- yl]methoxyl]phosphinyloxy-N,N,N-trimethylethaniminium hydroxide, inner salt (SRI 62-834) is a tetrahydrofuran analogue of platelet activating factor (PAF) that is currently entering clinical trial. Like other ether lipids it is of interest as a membrane-active antitumor agent. Here, we have used two-color multiparameter flow cytometry to study simultaneously its effects on cell membrane permeability, intracellular pH, and cell size/structure of EMT6 mouse mammary tumor cells and HL-60 human promyelocytic leukemia cells in vitro. Concentrations as low as 1 microM up to 100 microM SRI 62-834 caused a rapid, dose-dependent increase in membrane permeability, initially towards outward efflux of the preloaded fluorescein probe bis(carboxyethyl)carboxyfluorescein (green fluorescence) and then towards influx of extracellular propidium (red fluorescence). At the same time, median cell size from light scatter was reduced with an increased coefficient of variation, and the proportion of cell debris was elevated. In vitro antitumor activity was seen over the same concentration range, as measured by tetrazolium dye reduction and cell growth curves. Neither low concentrations of PAF (50 nM) nor the potent PAF antagonist 3-[4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f][1,2,4]tria- zolo[4,3a][1,4]diazepin-2-yl]-1-(4-morpholinyl)-1-propanone (0.5-100 microM) had any influence on the membrane effects of SRI 62-834, and at higher concentrations (1-200 microM) PAF mimicked the behavior of SRI 62-834. In addition, the PAF antagonist did not modulate the cytotoxicity of SRI 62-834 or PAF. HL-60 cells were more sensitive to SRI 62-834 than were EMT6 cells in terms of both cytotoxicity and membrane permeability. However, PAF was more potent than SRI 62-834 in causing membrane permeabilization with both cell lines, whereas PAF was less active than SRI 62-834 in cytotoxicity assays. The results support a membrane-damaging role in the cytotoxicity of SRI 62-834 but suggest that additional factors are also involved. Membrane permeabilization may be related to its reported effects on protein kinase C-dependent intracellular calcium signaling but apparently does not involve a conventional PAF receptor in HL-60 or EMT6 cells.

Detection of multidrug resistance and quantification of responses of human tumour cells to cytotoxic agents using flow cytometric spectral shift analysis of Hoechst 33,342-DNA fluorescence

We describe the application of a flow cytometric technique for assessing the radiation or drug sensitivity characteristics of human tumour cells. The technique makes use of the phenomenon that a red shift occurs in the fluorescence emission spectrum of a DNA-specific dye (Hoechst 33,342) as an increasing number of dye molecules bind to nuclear DNA. Intact, viable cells undergo a time-dependent spectral shift that can be distinguished from the rapid shift observed in cells with damaged membranes by the use of multiparametric flow cytometry. The responses of various human cell lines were compared, namely, those of normal and ataxia-telangiectasia (A-T) lymphoblastoid lines, a small-cell lung carcinoma line and its (in vitro) derived multidrug-resistant variants. A close correlation was found between dye toxicity and the degree of DNA binding of Hoechst 33,342 independent of cellular DNA content, with lymphoblastoid and multidrug-resistant small-cell lung cancer cells showing enhanced and restricted dye-binding rates, respectively. VP16- and radiation-induced cell kill was found to result in a quantifiable increase in the fraction of cells undergoing a rapid spectral shift and was capable of detecting the increased radiation sensitivity of A-T-derived cells. Spectral shift analysis provides a rapid method for assessing the responses of tumour cells to cytotoxic agents and for determining the general ability of cells to protect cellular DNA from a model DNA-binding agent (Hoechst 33,342) that participates in the multidrug resistance phenotype.

Tumour growth dynamics

Tumour growth has been shown to approximate to the exponential in human cancers and, in general, the doubling times range from weeks to months. In contrast, the replicative processes at the cellular level, the cell cycle is completed within a time interval of a few tenths of hours in the majority of cell types. This discrepancy is due to cell loss within the tumour and a growth fraction of less than unity. In normal tissues a steady state renewal system operates, which contains the enormous proliferative potential and tumour growth is a manifestation of a breakdown of normal regulatory feedback mechanisms. Techniques are now available which can quantitate the rate constant for cell production in human tumours and these measurements are being used to design specific treatment for special tumours.

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.

Addition of fresh medium induces cell cycle and conformation changes in p53, a tumour suppressor protein

Using analytical flow cytometry we have monitored changes in the conformation of p53 through the cell cycle under different conditions of cell growth. Conformational variants of murine p53 are characterized by reactivity with monoclonal antibodies PAb246, PAb248 and PAb421. In proliferating cells, p53 conformation was independent of the cell cycle. Addition of fresh medium, however, resulted in loss of p53 reactivity with PAb246 (p53-246(0]. Mutant p53, which lacks suppressor function, is also p53-246(0). Thus in SV3T3 cells p53-246(0) may reflect a change in p53 tertiary structure that is induced by growth stimulation and is compatible with the normal cell growth response. We argue that p53-246(0) and p53-246+ may exert positive and negative constraints in cell growth control. By stabilising p53-246(0) activating mutants of p53 would favour cell proliferation with dominant effect.

Mitoxantrone-DNA binding and the induction of topoisomerase II associated DNA damage in multi-drug resistant small cell lung cancer cells

The cytotoxicity anti-tumour intercalating agents such as the anthraquinone mitoxantrone is thought to relate to DNA binding and the trapping of DNA topoisomerase II complexes on cellular DNA. We have studied the uptake, nuclear location, DNA binding mode and DNA damaging capacity of mitoxantrone in a small cell lung carcinoma cell line (NCI-H69) compared with an in vitro-derived variant subline (NCI-H69/LX4) that exhibits "classical" multi-drug resistance (MDR). Variant cells maintained under doxorubicin selection showed reduced RNA levels that returned to control values within 7 days of growth under non-selective conditions. Variant cells released from selection stress showed resistance to DNA cleavage by doxorubicin, mitoxantrone, 4'-epidoxorubicin, 4'-deoxy-doxorubicin but reduced resistance to aclacinomycin A and a 9-alkyl substituted anthracycline in broad agreement with the cross-resistance patterns for cytotoxicity. Mitoxantrone treated NCI-H69 cells were found to accumulate DNA-protein crosslinks during a 4 hr post-treatment incubation period whereas variant cells maintained depressed levels of crosslinking. There was no apparent abnormality in the availability or drug sensitivity of topoisomerase II assayed in crude nuclear extracts of NCI-H69/LX4 cells. Whole cell uptake of radiolabelled mitoxantrone was depressed (50%) in NCI-H69/LX4 compared with NCI-H69, whereas assessment of nuclear-bound drug in individual cells by a fluorescence quenching technique showed at least a 10-fold greater level of target protection. The quenching results provide evidence of a high affinity, saturable mode of drug binding, favoured at low drug concentrations, that correlated with DNA cleavage capacity. We propose that the cytotoxic action of mitoxantrone is dependent upon a restricted and persistent form of binding to DNA that favours the long-term or progressive trapping of topoisomerase II complexes.

Tissue preparation for simultaneous flow cytometric quantitation of tumour associated antigens and DNA in solid tumours

A multiparameter flow cytometric assay for the simultaneous study of tumour associated antigens (TAA) and DNA in fresh solid tumours was devised. Cell suspensions were prepared by disaggregating unfixed solid tumour samples mechanically over a stainless steel mesh. Indirect immunofluorescence was used to identify the TAA, and DNA was stained with propidium iodide. Cell morphology was well preserved, cell clumping was negligible, and high quality indirect immunofluorescence quality indirect immunofluorescence and DNA staining were obtained. The technique is simple, rapid, and reproducible. Multiparameter assays can be developed to study prognostic indicators such as membrane oncoproteins, receptors, and multidrug resistance in solid tumours. With a suitable panel of antibodies the technique might become an aid in the differential diagnosis and biochemical diagnosis of some solid tumours.

Caffeine overcomes a restriction point associated with DNA replication, but does not accelerate mitosis

Mitotic chromosome condensation is normally dependent on the previous completion of replication. Caffeine spectacularly deranges cell cycle controls after DNA polymerase inhibition or DNA damage; it induces the condensation, in cells that have not completed replication, of fragmented nuclear structures, analogous to the S-phase prematurely condensed chromosomes seen when replicating cells are fused with mitotic cells. Caffeine has been reported to induce S-phase condensation in cells where replication is arrested, by accelerating cell cycle progression as well as by uncoupling it from replication; for, in BHK or CHO hamster cells arrested in early S-phase and given caffeine, condensed chromosomes appear well before the normal time at which mitosis occurs in cells released from arrest. However, we have found that this apparent acceleration depends on the technique of synchrony and cell line employed. In other cells, and in synchronized hamster cells where the cycle has not been subjected to prolonged continual arrest, condensation in replication-arrested cells given caffeine occurs at the same time as normal mitosis in parallel populations where replication is allowed to proceed. This caffeine-induced condensation is therefore "premature" with respect to the chromatin structure of the S-phase nucleus, but not with respect to the timing of the normal cycle. Caffeine in replication-arrested cells thus overcomes the restriction on the formation of mitotic condensing factors that is normally imposed during DNA replication, but does not accelerate the timing of condensation unless cycle controls have previously been disturbed by synchronization procedures.

An improved method for the detection of cell surface antigens in samples of low viability using flow cytometry

A high non-specific background fluorescence signal was observed when cell surface antigen analysis was carried out using flow cytometry on a cell sample which contained a high proportion of dead and dying cells. To overcome this problem it was necessary to analyse the cells in three stages. First the intact cells were identified by their forward (FWD) and 90 degree scatter profile. These cells were gated-on, then analysed on the basis of their FWD scatter and propidium iodide (PI) signal, allowing the dead PI positive cells to be gated out. The PI negative cells were then displayed using their 90 degree scatter and fluorescence signals following staining with the irrelevant antibody control. This revealed a population of dead cells, which despite being PI negative, were non-specifically binding antibody molecules. Such multiparameter analysis permitted the successful analysis of cell surface antigens in preparations of low viability by gating out the high background fluorescence associated with dead PI positive and negative cells.

Multiparametric analysis of cell membrane permeability by two colour flow cytometry with complementary fluorescent probes

We describe an improved twin-probe multiparameter flow cytometric technique to examine cell membrane permeability. Ability to retain preloaded intracellular bis-carboxyethyl carboxy fluorescein (BCECF, green fluorescence) and to exclude extracellular propidium (red fluorescence) is measured, simultaneously with forward and right-angle scatter. This has significant advantages over an earlier method using fluorescein together with ethidium. In addition to the two expected cell populations which were stained green positive, red negative (by convention membrane "intact" and "viable," Region 1) and green negative, red positive ("membrane-damaged" and "non-viable," Region 3), a third population was seen which fluoresced neither green nor red and displayed intermediate light scatter characteristics (Region 2). This was true for each of 9 cell types in vitro. For EMT6 mouse mammary tumour cells held under sub-optimal conditions or treated with membrane-active drugs, progression from Region 1 to Region 2 was observed, followed by further progression from Region 2 to Region 3. Cells eventually accumulated in Region 3. These results suggest that sequential changes in membrane structure lead to increased permeability, first with respect to intracellular BCECF and in turn to extracellular propidium.

Effects of 3-aminobenzamide on cellular ribosomal RNA content and cell cycle progression in inhibitor resistant and sensitive L1210 cells

The poly(ADP-ribosyl)ation inhibitor 3 aminobenzamide (3AB) is used extensively to probe the involvement of post-translational modifications of proteins in the control of DNA repair and cell cycle progression. However, 3AB appears to lack specificity for the synthetase, and the use of excessive concentrations of the inhibitor may adversely affect the potential responsiveness of cells to DNA-damaging agents. Here we address the concentration dependency of the cellular impact of 3AB alone by using flow cytometry to analyze the cell cycle phase-dependent, anti-proliferative effects of 3AB on mouse L1210 cells together with fluctuations in RNA (predominantly ribosomal) levels. We report that 3AB, at cytostatic concentrations, does not block cells in G2 committed to mitosis but imposes an immediate G1 and S phase arrest. Eventually cells arrested in G1 and S phase can reenter cycle but become irreversibly blocked in G2 and are incapable either of progression to mitosis or of the reinitiation of DNA synthesis when cytokinesis is blocked by colcemid exposure. 3AB exposure rapidly reduced RNA levels in all phases of the cell cycle with recovery from depletion apparent only at nontoxic concentrations (5 mM). The responses of a 3AB-resistant subline, capable of sustained culture growth in a normally cytostatic concentration of inhibitor (25 mM), suggest a close association between the sensitivity to RNA depletion and cell cycle arrest.

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.

The MTT assay underestimates the growth inhibitory effects of interferons

The growth inhibitory effects of interferons, IFN-alpha and IFN-gamma on human lung cancer cell lines were studied using both a tetrazolium (MTT) colorimetric assay and direct cell counting. Significant discrepancies between the two assays were observed, the MTT assay consistently underestimating the growth inhibitory effects of the IFNs. There was no direct chemical effect of the IFNs on the tetrazolium reduction process. IFN treated cells showed increased cell size compared with control cells, although there was little or no change in cell cycle distribution. Mitochondrial activity was 30-50% greater in IFN-gamma treated cells (COR-L23) than the controls. Reduced formazan production per cell was observed in medium which had supported cell growth for several days. Differential 'medium conditioning' led to a difference in formazan production per cell between IFN and control cells and this was the major basis of the observed discrepancy. This discrepancy was not due to the differences in the glucose concentrations between these media. However, differences in pH between the media proved to be the major contributory factor of the discrepancy.

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.

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.

Regulation of cell cycle duration by c-myc levels

Early passage murine fibroblasts infected with retroviral vectors carrying human c-myc 'minigenes' express high levels of c-myc and have a dramatically shortened G1-phase of the cell cycle. Cells infected with viruses where c-myc is expressed from the viral LTR (MSN-4 virus) express more c-myc protein than cells infected with viruses where c-myc is expressed from the SV40 early promoter (NSM-7 virus). Populations of cells were infected with high titre viruses, selected for drug-resistance, pulse labelled with bromodeoxyuridine (BrdUrd) and chased in BrdUrd free media. This allows accurate, simultaneous, measurement of the rate of exit of unlabelled cells from G1 and progression of BrdUrd-labelled cells through S-phase. The length of the G1-phase in cell populations infected with the MSN-4 virus is 4.65 h, a reduction of nearly 30% compared to the G1-phase length of 6.50 h seen in cells infected with the VSN-2 control virus. Cells infected with NSM-7 virus show an intermediate phenotype and have a G1-phase of 5.25 h. The lengths of the S-phase (4.50 to 4.75 h) and G2 + M phases (2.75 h) were not significantly altered by exogenous c-myc expression. When chases are performed in growth-factor free media, the G1-phase of infected and non-infected cells is extended by approximately 2 h. Cells infected with the c-myc viruses continue to cycle more rapidly than uninfected cells. Growth factor-deprived cells, restimulated with serum, show similar alterations of the cell cycle kinetics. MSN-4 and NSM-7 infected cells, expressing high levels of c-myc, enter S-phase 2 to 4 h earlier, but less synchronously, than control cells, and sustain subsequent rounds of DNA synthesis, while control cells do not. However, cells carrying activated c-myc genes have nearly-normal morphologies and are not tumourgenic in syngenic mice. These results demonstrate that c-myc levels are rate limiting for events in G1, and the length of G1 varies proportionally with the level of exogenous c-myc expression.

The expression of c-myc related to the proliferation and transformation of rat liver-derived epithelial cells

The expression of c-myc protein was studied in primary cultures of rat hepatocytes and rat liver-derived epithelial cell lines. The levels of the protein were determined by flow cytometry using a monoclonal antibody to the c-myc protein. Freshly isolated hepatocytes from normal adult male Fischer F344 rats had low but detectable levels of the protein which were similar in the different ploidies. Higher levels were detected in immortalised but untransformed rat liver cell lines, and increased expression was observed during passage through the cell cycle. Following in vitro transformation of one of the immortalised epithelial cell lines by ras genes, similar levels of c-myc expression to those present in the untransformed cells was maintained. Transformation by activated aflatoxin B1 (AFB1) resulted in lower levels of expression. The cell cycle related level of expression was also seen in the transformed cells. Similar results to those observed in the in vitro ras transfected liver-derived cell lines were obtained from in vivo AFB1-induced rat hepatoma cell lines. These results demonstrate that continuously dividing rat liver-derived cell lines have higher levels of expression of c-myc protein than non-dividing, freshly isolated hepatocytes, and that there is no further elevation in the levels observed when these cell lines are transformed. In some cases decreased levels can result from malignant transformation.

A role of DNA topoisomerases in the active dissociation of DNA minor groove-ligand complexes. A flow cytometric study of inhibitor effects

The biological effects of a number of DNA ligands which interact with the minor groove of B-form DNA (e.g. netropsin, distamycin and Hoechst 33258) are thought to arise from the direct disturbance of the processes of DNA replication and transcription. Although ligand binding appears to be an important factor in cytotoxicity, the pathways by which drug molecules can be actively dissociated from nuclear DNA are unknown. Recent evidence suggests that minor groove ligands can distort the manner in which DNA associates with nucleosomal core particles and we have hypothesized that in an intact cell such imposed torsional stress could be subject to the action of cellular topoisomerases. We have used flow cytometry to study the effects of various inhibitors (including topoisomerase-interactive drugs) on the responses of a mutant cell line (HoeR415) to Hoechst 33342, given that the mutant shows resistance to the cytotoxicity of this DNA-specific dye due to an enhanced capacity to dissociate nuclear DNA-dye complexes. Ligand-DNA dissociation in the mutant was found to be energy-dependent but not specifically, affected by the drug-efflux blocker verapamil or by inhibitors of DNA synthesis. The topoisomerase II inhibitors novobiocin, VP16, nalidixic acid and the topoisomerase I-interactive drug camptothecin inhibited ligand-DNA dissociation to various extents with novobiocin being the most effective (100% inhibition at 1 mM). Both novobiocin and camptothecin were without effect on the nuclear loss of a DNA intercalator, adriamycin. We conclude that efficient topoisomerase activity is required for the active dissociation of DNA minor groove-ligand complexes.

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.

Nuclear structure and the control of DNA replication in the Xenopus embryo

We have developed a cell-free system from frog eggs that efficiently initiates and completes a single round of semi-conservative replication. 70-100% of sperm chromatin and up to 40% of plasmid DNA molecules are completely replicated in vitro. Before DNA is replicated it is assembled into nuclei surrounded by a double unit membrane studded with nuclear pores. Flow cytometry shows that initiation events are co-ordinated within individual nuclei, although different nuclei can start to replicate at different times in the same extract. This demonstrates the importance of nuclear structure in the control of DNA replication in this system. Only a single round of semi-conservative replication occurs in the cell-free system. This mirrors the way that only one round of DNA replication occurs in each cell cycle in vivo. When replicated nuclei are transferred to fresh extract they are unable to undergo another round of replication. However, if the nuclear envelope is permeabilised before nuclei are transferred to fresh extract, the DNA becomes capable of undergoing a further round of semi-conservative replication. These results suggest a simple model for the control of DNA replication within the cell cycle, whereby an essential initiation factor can only gain access to DNA when the nuclear envelope breaks down during mitosis.

Inhibition of cellular esterases by the antitumour imidazotetrazines mitozolomide and temozolomide: demonstration by flow cytometry and conventional spectrofluorimetry

Using flow cytometry and conventional spectrofluorimetry we have previously shown that chloroethylnitrosoureas (CNUs) can exhibit marked inhibition of cellular enzymes catalysing hydrolysis of fluorescein diacetate (FDA). More potent inhibition was seen for the carbamoylating CNUs, whereas alkylating agents were largely inactive. We now report results obtained with the developmental imidazotetrazines mitozolomide and temozolomide in comparison with BCNU, the novel alkylating agents clomesome and cyclodisone, and the active mitozolomide metabonate MCTIC. Inhibition of EMT6 mouse mammary-tumour esterases was seen for mitozolomide and temozolomide, and activity against purified porcine carboxylesterase was demonstrated. Flow cytometric analysis showed that inhibition occurred across the entire EMT6 cell population, with no evidence of a subpopulation resistant to enzyme inhibition. Inhibitory potency for the imidazotetrazines was much weaker than for BCNU. With EMT6 cells, I50 values from flow cytometry were 9.7 x 10(-3) M and 1.5 x 10(-3) M for mitozolomide and temozolomide compared with 3.7 x 10(-4) M for BCNU. These were higher than the ID50 values for in vitro antitumour activity (MTT assay), 8.5 x 10(-6) M in the case of mitozolomide and 1.2 x 10(-5) M for BCNU, but similar to that of 5.6 x 10(-4) M for the less toxic temozolomide. MCTIC and cyclodisone showed very low activity, but significant inhibition was seen for clomesome. The results are consistent with the view that the imidazotetrazines do not exhibit major carbamoylating ability, although significant effects are seen at cytotoxic concentrations of temozolomide. In addition, the potential for the generation of carbamoylating species at the enzyme active site cannot be ruled out.

Data compression: 8-dimensional flow cytometric data processing with 28K addressable computer memory

A method of data analysis for flow cytometry is presented which enables up to eight-dimensional data to be handled by a microcomputer with 28K addressable plus a further 32K non-addressable memory. The multi-parameter coordinates are coded into single numbers using a minimal modification of the array vector mapping equation. These code numbers, each of which corresponds to a given set of coordinates, and then ranked in ascending order according to magnitude and the frequency of each code number is found. Following this step the code is then decoded by integer arithmetic into its original coordinates which are then packed, together with the frequency, into two, three or four 16-bit words depending on the dimensionality of the data set. A five-dimensional data set is used as the illustration. Three regions were set on one two-dimensional data space and the five mono-dimensional histograms, plus a different bivariate distribution, were extracted in a single pass through the processed data file. In addition to considerable space saving the technique has two further attributes, namely, increased speed with which the user can appreciate multiparameter data and the ability to analyse such data sets with a microcomputer.