Oncogenes, cancer and analytical cytology

Ploidy and Proliferation Evaluated by Flow Cytometry. An Overview of Techniques and Impact in Oncology

Flow cytometric methods for the assessment of nuclear and chromosomal DNA content and of cell proliferation (including methods based on pulse-chase of bromodeoxyuridine and on monoclonal antibodies against nuclear oncoproteins and proliferation-associated antigens) are illustrated by examples and analyzed critically. The impact of most of these techniques for the study of human solid tumors, with exception of nuclear DNA content evaluation, appears still limited. In particular, new studies of cell lines and clinical material from human tumors using new proliferation markers and multiparameter flow cytometry are necessary to solve a considerable number of methodologic and scientific problems.

Analysis of DNA aneuploidy and c-myc oncoprotein content of canine plasma cell tumors using flow cytometry

To derive a method for determining malignant potential of plasma cell tumors, a retrospective analysis of the DNA ploidy and relative p62c-myc oncoprotein content using bivariate flow cytometry was performed on 23 formalin-fixed, paraffin-embedded tissues from 23 dogs. The samples included one tissue each from 17 males and six females 2 to 16 years of age (mean = 7.5 years). Twelve breeds were represented, including three Cocker Spaniels, three Golden Retrievers, and five of mixed breed. Ten of the samples were histologically classified as malignant-plasma cell tumors, and ten specimens were classified as benign. Three samples of plasmacytic inflammation, from two Cocker Spaniels and one Shih Tsu, were included as controls. The ploidy and relative c-myc content data obtained were compared with the histologic grade. A significant difference in ploidy was found between benign and malignant tumors (P < or = 0.05). Five of nine malignant plasma cell tumors were aneuploid; the remainder were diploid (4/9) or tetraploid (1/9). Only one of the benign plasmacytomas was aneuploid (1/10), whereas six were diploid (6/10), and three were tetraploid (3/10). All of the controls were diploid (3/32). When relative amounts of p62c-myc from malignant and benign tumors were compared by flow cytometry, a greater significant difference was established (P < or = 0.01) than bu using aneuploidy alone. Relative values of p62c-myc content ranged from 219 to 553 units in 8/10 malignant plasma cell tumors and from 86 to 392 units in 3/10 benign plasmacytomas.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors linked to tumor recurrence of human hepatocellular carcinoma after hepatic resection

A total of 238 patients who received curative hepatic resections during the last 10 yr were observed to search for the risk factors linked to early tumor recurrence of human hepatocellular carcinoma after hepatectomy. The results revealed that tumor size, tumor appearance and DNA ploidy were the factors in predicting tumor recurrence after resection for hepatocellular carcinoma. Patients with a tumor size less than or equal to 5 cm or a tumor appearance of the solitary type had better disease-free survival than did those with a tumor size greater than 5 cm or a tumor appearance of multiple/daughter nodule types (p < 0.05). Although patients with pattern III (aneuploid with > or = 2 G0/G1 peaks) hepatoma had fewer statistically significant differences (p = 0.19) than did those with pattern I (diploid) or pattern II (aneuploid with single G0/G1 peak) tumors in predicting tumor recurrence, they did have poorer results in terms of the overall survival rate (p < 0.05). We conclude that patients with hepatocellular carcinoma having the aforementioned risk factors should be observed closely.

Fixation of mammalian cells for flow cytometric evaluation of DNA content and nuclear immunofluorescence

Mammalian tissue culture cells were fixed with 3 different alcoholic fixatives--acetone:methanol, EtOH, and MeOH. The quality of the resulting DNA histograms was evaluated by comparison of CV, G1/G2 ratio, G1 mode, cell aggregation, and debris formation; 81-90% MeOH (final concentration) was determined to be the optimal fixative by these criteria. A procedure was then examined using a prefix with paraformaldehyde followed by MeOH (PF/MeOH). This procedure produced cell preparations with reduced debris and aggregation, equivalent mode and ratio, but increased CV when compared with MeOH fixation. Both MeOH and PF/MeOH fixation procedures were then compared for their utility in dual staining for DNA and intracellular immunofluorescence for a nuclear protein, SV40 T antigen (Tag). Since alcohols are known to affect immunofluorescence staining of some antigens, fixation with paraformaldehyde followed by Triton X-100 permeabilization (PF/TX) was also included in this comparison to generalize the study by providing an alternative to MeOH permeabilization. The three procedures were evaluated for the quality of the sample by measuring the same descriptors of the DNA parameter as in the alcohol study. PF/TX consistently produced samples with decreased DNA CV and less debris and aggregation compared to MeOH methods. Two criteria were used to evaluate immunofluorescence--the amount of Tag measured and reproducibility. All MeOH methods were equivalently reproducible with CV's less than 3%. PF/TX was slightly less so with a CV of less than 6%. In contrast, different levels of Tag were measured for each procedure. For mouse 3T3 cells infected with a recombinant retroviral vector encoding T antigen, the level of T antigen measured after PF/MeOH was 21% greater than in MeOH fixed cells, and the level in PF/TX fixed cells was 37% less. The fraction of fluorescence specific to T antigen for these cells was 79-83% for all procedures. The lower levels measured after fixation by PF/TX were shown to be due to epitope masking. Why higher levels are measured with PF/MeOH procedures is unknown at present but may be due to antigen retention. Therefore, each of these fixation methods may be used with confidence in reliability but they are not equivalent with respect to the molecular architecture of the nucleus. It is postulated that PF/TX permeabilizes cells but cells retain native supramolecular structure, whereas MeOH based fixatives disrupt this structure and randomize availability of epitope to antibody. If so, the two procedures could be used as complementary procedures to study gene expression and function.

Prediction of relapse or survival after resection in human hepatomas by DNA flow cytometry

To investigate the change of DNA content and the effect of synthetic phase (S-phase) fraction on hepatocytes and hepatomas, DNA content and S-phase fraction were measured by flow cytometry in human livers and hepatoma tissues. The ploidy status of nontumor parts of resected hepatoma, fetal liver, and focal nodular hyperplasia were diploid, similar to that of the normal liver. Three patterns of DNA ploidy in human hepatoma cells were newly classified, namely, pattern I, diploid tumors; pattern II, aneuploid tumors with single G0/G1 peak; and pattern III, aneuploid tumors with more than one G0/G1 peaks. Among the 130 resectable hepatomas measured for DNA ploidy status, 84 (64.6%) were pattern I, 20 (15.4%) pattern II, and 26 (20%) pattern III. Multivariate analyses for those 130 patients who underwent hepatic resection showed that, in addition to tumor size, DNA ploidy was another prognostic factor in predicting overall survival and disease-free survival. Patients with small tumors (less than 5 cm) had a significantly higher overall survival rate than those with large tumor (greater than 5 cm). Patients with pattern III hepatomas had a significantly lower overall survival rate and a higher recurrent rate than did those with pattern I or pattern II tumors. The S-phase fraction was a significant predictor of overall survival rate in patients with pattern II, but not with pattern I, tumors. We conclude that DNA flow-cytometric measurements of ploidy and S-phase fraction are potential important prognostic predictors in patients with resectable hepatomas.

Immunofluorescent labeling of centromeres for flow cytometric analysis

A procedure to stain the centromeric region of chromosomes for dual beam flow cytometric analysis is described. Serum from a CREST (Scleroderma syndrome) patient presenting a high titer of anticentromeric antibodies was chosen on the basis of specificity of labeling of cells on slides. The high affinity of the antibodies to centromeres and low binding to chromosomal arms allowed the development of an indirect immunofluorescent labeling procedure using isolated and unfixed chromosomes stabilized by Mg++ ions. Discontinuous Ficoll gradients were used to separate chromosomes from unbound antibodies. With this procedure, chromosome clumping and degradation were minimal. The chromosomes were then stained with the DNA dyes Hoechst 33258 and chromomycin A3, before dual beam flow cytometric analysis. Flow karyotypes, with good chromosome peak resolution, were obtained for both human and hamster chromosomes subjected to the immunolabeling procedure. For quantification of FITC fluorescence due to bound antibody, chromosomes were counterstained with Hoechst only. The FITC intensity of antibody-labeled human and hamster chromosomes were 4-10 and 20 times greater than control chromosomes, respectively. These results suggest that the staining procedure may be suitable for immunolabeling of chromosomes with antibodies recognizing other nuclear proteins and their subsequent quantification by flow cytometry.

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.

Ras oncogene expression and DNA content in plasma cell dyscrasias: a flow cytofluorimetric study

Using bivariate flow cytofluorometry, we have determined the nuclear DNA distribution and the expression of the p21 protein (coded by the Ha-ras oncogene) in the bone marrow (BM) cells of five solid tumour patients having histologically normal BM and in those of 57 patients with plasma cell dyscrasia (28 with monoclonal gammopathies of undertermined significance, MGUS, and 29 with multiple myeloma, MM). All normal and MGUS and 21/29 (72.4%) MM BM had diploid modal DNA content and 8/29 (27.6%) MM BM had both diploid and hyperdiploid cell populations. In normal and MGUS BM, the level of the p21 oncoprotein was low and uniform in all G0/G1, S and G2 cells (median fluorescence values in arbitrary units were 6.1 and 7.5, respectively). The level of p21 was increased both in different aliquots of G0/G1 cells and in the S and G2 cells in diploid MM (median value for G0/G1 cells was 20), and especially in MM with hyperdiploid clones (median value for hyperdiploid cells was 40.5, P less than 0.005 with respect to normal and MGUS BM and less than 0.005 with respect to diploid MM BM). The p21 expression was greater in patients with advanced (stage III) than in earlier MM (stages I + II) (P less than 0.005), and it was directly related to the BMPC infiltration (r = 0.7; P less than 0.005). Since p21 expression is greater in MM than in both normal and MGUS BM, Ha-ras could be involved in the malignant plasma cell transformation that distinguishes MM from MGUS.

Limitations in the measurement of c-myc oncoprotein and other nuclear antigens by flow cytometry

Recent developments in cell fixation, quantitative immunocytochemistry, and flow cytometry allow for the quantification of a variety of oncoproteins and other proliferation-associated antigens in both fresh and archival pathology material. These studies provide evidence that the standard tissue deparaffinization/dissociation technique significantly reduces the amount of c-myc oncoprotein remaining for analysis. To examine the factor(s) responsible for this observation, individual variables of the deparaffinization/dissociation technique including type of fixative, pepsin concentration, pepsinization times, pH, and exposure to organic solvents were examined in HeLa-S3 cells. The cells were stained with monoclonal antibodies either to the c-myc oncoprotein or to p105, a prolifera-tion-associated nuclear antigen. Protein-levels were measured on the basis of anti-c-myc or anti-p105 immunofluorescence by flow cytometry and were found not be affected significantly by type of fixative, exposure to organic solvents, acid pH solution, or mechanical disruption. Levels of c-myc oncoprotein were reduced by over 50%, however, when cells were exposed to 0.5% pepsin, whereas p105 was more resilient with only an approximately 7% reduction following the same treatment. Thus, careful examination of aspects of the deparaffinization/dissociation technique appears to be a necessary prerequisite for quantification of specific nuclear proteins from dissociated tissue specimens.

Flow cytometry using paraffin-embedded tissue: five years on

The use of paraffin-embedded tissue for flow cytometry is reviewed. A number of technical modifications of the original 1983 method have been described, aimed at improving the accuracy of DNA measurements by minimizing cell debris or reducing coefficients of variation, and at simplifying sample preparation. Over 100 clinical studies have now been reported, mainly assessing the effect of DNA index on prognosis, and those published up until mid-1988 are summarized in an appendix. More recently there have been developments in the use of monoclonal antibodies to measure oncogene products or proliferation markers in addition to DNA content. Detailed clinical evaluation and standardization of these more sophisticated methods is still some way ahead, but as was the case with DNA index, the use of archival material from patients whose outcome is already known should speed this process.

Neoplasms of endometrial stroma: histopathologic and flow cytometric analysis with clinical correlation

Ten neoplasms of endometrial stroma (one stromal nodule, four endolymphatic stromal myoses, and five stromal sarcomas) were compared using clinical data as well as histopathologic and flow cytometric parameters. None of the patients with stromal nodules or endolymphatic stromal myosis had extrauterine disease at presentation or tumors displaying a mitotic rate greater than 10/10 hpf (high-power fields), nuclear pleomorphism, atypical mitotic figures, DNA aneuploidy, or a high proliferative index (greater than 10% S phase cells). The stromal nodules were circumscribed and behaved in a benign fashion. The patients with endolymphatic stromal myosis had infiltrative tumors that behaved as low-grade cancers with good responses to therapy. Four of the five patients with stromal sarcoma had extrauterine disease at presentation as well as tumors characterized by a mitotic rate much greater than 10 mitoses/10 hpf, nuclear pleomorphism, atypical mitotic figures, DNA aneuploidy, and a high proliferative index. These four patients had aggressive disease with poor response to therapy. The fifth of the stromal sarcomas had a high mitotic rate, but lacked the other features linked with aggressive behavior; this patient has responded well to treatment. The mitotic count may not be the most useful criterion for predicting biologic behavior in endometrial stromal tumors since it does not always reflect an increased rate of cell turnover as demonstrated by the percentage of cells in the S phase. DNA analysis by flow cytometry yields a more accurate picture of tumor behavior.

Flow cytometric discrimination of mitotic nuclei by right-angle light scatter

Flow cytometry has been used to demonstrate alterations in protein, RNA, and DNA content of cells as they traverse the cell cycle. Employing fluorescein isothiocyanate (FITC) to stain protein and propidium iodide (PI) to stain nucleic acids, multiple regions within the G1 and G2 phases of the cell cycle, in addition to the M phase, can be distinguished. In this study, cytograms of the 90 degree light scatter signal vs. PI fluorescence were remarkably similar to those of FITC fluorescence vs. PI fluorescence, suggesting a relationship between 90 degree light scatter and protein content. M-phase nuclei can be distinguished from G2-phase nuclei on cytograms of 90 degree light scatter vs. PI fluorescence. However, the percentage of mitotic nuclei obtained by this technique is less than that found by light microscopic analysis. Flow cytometric parameters of nuclei prepared by nonionic detergent (NP40) lysis in Dulbecco's PBS, Vindelov's buffer, or Pollack's hypotonic EDTA/Tris buffer were compared. The best resolution of mitotic nuclei was obtained in Pollack's buffer. However, the stainability of the M-phase nuclei is reduced, and the nuclei are located in the late S/G2 region of the single-parameter histogram.

Analysis of simian virus 40 infection of CV-1 cells by quantitative two-color fluorescence with flow cytometry

Quantitative two-color fluorescent analysis of Simian virus (SV40) infection of permissive CV-1 cells was investigated. Analysis included by quantitation of cellular DNA, the early viral tumor (T) antigen with a monoclonal antibody, and late viral (V) antigens with a polyclonal antibody. T antigen was detected in all phases of the cell cycle at 6 and 12 h, after SV40 infection of growth arrested cells. At later time intervals, the percentage of T-antigen-positive cells increased with the induction of the cells into successive rounds of DNA synthesis and an increase in tetraploid-polyploid cells. The amount of T antigen per cell increased as the cells entered the successive stages of the cell cycle (G0/G1----G2 + M----tetraploid S and G2 + M). The V antigen from adsorbed virus was detected immediately after infection. Synthesis of V antigen began in late S and G2 + M phases of the cell cycle. This quantitative analysis allows a definitive determination of antigen per cell in a population correlated with the cell cycle and may be useful in correlating viral and cellular events with transformation.

An evaluation of CA125, CA1 and peanut lectin immunoreactivity in epithelial ovarian neoplasms: correlation with histopathological features, prognostic variables and patient outcome

The ability to produce monoclonal antibodies to tumour associated antigens, together with advances in immunocytochemistry, provide the potential for establishing a new functional classification of human tumours. This approach was used to investigate whether the expression of CA125, CA1 and the Thomsen-Friedenreich antigens reflected the biological behaviour of ovarian tumours and, if so, had a potential role in the clinico-pathological assessment of ovarian neoplasms. Expression of these antigens was assessed in benign, borderline and malignant ovarian epithelial tumours and attempts were made to determine if there was any correlation between immunoreactivity and tumour grade, histological subtype, FIGO Stage, tumour ploidy or patient outcome. There was no evidence that expression of these antigens had clinical significance, although it is possible that reactivity with antibody OC125 might identify patients in whom CA125 antigen levels in the sera could be used as a marker to monitor disease progress.

Abnormal distribution of c-myc oncogene product in familial adenomatous polyposis

Monoclonal antibodies raised by synthetic peptide immunisation were used to determine the distribution of the protein product of the c-myc gene by immunocytochemical staining of archival wax embedded material from patients with familial adenomatous polyposis. Polyps from 18 cases of familial adenomatous polyposis, 10 of whom had developed malignant change, and 30 normal control colonic biopsy specimens were examined. A consistent staining pattern was observed in normal mucosa; nuclear staining in the basal proliferative zone; mixed nuclear and cytoplasmic staining in the maturation zone; and cytoplasmic localisation in the surface mature zone. In contrast, the polyps and carcinomata showed a mixed pattern of cytoplasmic and nuclear localisation in the basal proliferative zone with nuclear persistence throughout the crypts to the surface mature zone. This abnormal distribution of the c-myc oncogene product may have a role in the evolution of polyps and their subsequent malignant transformation into familial adenomatous polyposis.

Oncogene expression in ovarian cancer: a pilot study of c-myc oncoprotein in serous papillary ovarian cancer

The nuclear-associated protein product of the c-myc gene, p62c-myc, was assayed simultaneously with total DNA using flow cytometry in nuclei extracted from archival biopsies of serous papillary carcinoma of the ovary. The oncoprotein was probed with a synthetic peptide-induced mouse monoclonal antibody which was subsequently labeled with a fluorescent rabbit anti-mouse immunoglobulin and DNA was assayed using the nucleic acid fluorochrome propidium iodide. Serous papillary ovarian carcinoma expressed significantly higher p62c-myc levels compared with normal ovary (P less than 0.00003 Mann-Whitney U test). Biopsies classified as "borderline" low-potential malignancy exhibited levels between normal ovary and carcinoma. The difference between normal and "borderline" was significant at P less than 0.003, but no difference between "borderline" and frankly invasive biopsies was observed, P = 0.149. There was no difference among the histological grades of carcinomas. All normal ovaries had diploid DNA content as did 5/6 cases of "borderline" malignancy. The majority of cases of carcinoma, 28/36, were aneuploid. There was a statistically significant difference in the distribution of aneuploidy, P less than 0.005, between invasive carcinomas and those classified as "borderline" low-potential malignancy.

Flow cytometric quantitation of the c-myc oncoprotein in archival neoplastic biopsies of the colon

The c-myc oncogene encoded protein product, p62c-myc, was assayed simultaneously with DNA in populations of individual nuclei extracted from archival biopsies of colonic neoplasia. Both the protein and DNA were assayed fluorimetrically using flow cytometry with a synthetic peptide induced monoclonal antibody (MYC 1-6E10) for the protein and propidium iodide for DNA. The nuclear p62c-myc levels increased progressively from normal mucosa through polyps to carcinomas. However, there was a trend for the more poorly differentiated carcinomas to exhibit lower levels than moderately and well-differentiated tumours, p = 0.085. These results agree with those published previously with the same antibody using Western blotting for protein extracted from fresh frozen tissue and immunocytochemical assessment. Furthermore, flow cytometry is able to effect discriminations between subsets in heterogeneous populations using DNA as a second parameter which Western blot bulk studies cannot.