Robert P. Wersto

Flow cytometric DNA analysis of human solid tumors: A review of the interpretation of DNA histograms☆

A survey of over 225 recent studies examining the relationship between the flow cytometric DNA analysis of solid tumors and clinical prognosis indicates that criteria used to classify DNA histograms are variable and often inconsistent with the recommendations proposed by the Convention on Nomenclature for DNA Cytometry. Numerous reports not only lack unambiguous descriptions of the histogram features used to differentiate diploid from aneuploid DNA distributions, but also inadequately describe the technical aspects of data acquisition, standardization, and inclusion or exclusion of subpopulations by gating. In many cases, the coefficient of variation of the diploid and aneuploid G0/1 peaks, which would allow an assessment of histogram quality, is not reported. Because of the differences in DNA histogram interpretation, extrapolation of the results among laboratories may be difficult and is probably not reliable. This review summarizes the criteria that have been used to classify the DNA histograms and illustrates the effects of these different classifiers on DNA ploidy analysis and clinical conclusions.

Predictive value of DNA measurements in bladder washings. Comparison of flow cytometry, image cytophotometry, and cytology in patients with a past history of urothelial tumors

Comparative DNA ploidy measurements were carried out by flow cytometry and by image analysis on cells in 71 bladder washing specimens from 50 patients with past histories of bladder tumors. Among the specimens classified as diploid or questionable by flow cytometry, 14 showed the presence of aneuploid DNA values documented by image analysis. In 18 of the 50 patients, recurrent tumors were observed during a relatively brief period of follow‐up. In 15 of them the DNA pattern was aneuploid and in three it was questionable. In nine of the 15 patients, both methods of DNA analysis disclosed aneuploidy, but in six patients aneuploidy was detected by image analysis only. A combination of DNA aneuploidy, whether observed by flow cytometry, image analysis, or both, and of positive or suspicious urine cytology is highly predictive of recurrence of high grade bladder tumors. Image analysis of DNA content in bladder washings adds information of clinical value above and beyond that obtained by flow cytometry.

Cell cycle-dependent reactivity with the monoclonal antibody Ki-67 during myeloid cell differentiation☆

The specificity and sensitivity of the monoclonal antibody Ki-67 in identifying proliferating cell compartments was tested with the human promyelocytic leukemia cell line HL-60 using multi-parameter flow cytometry. While correlated measurements of DNA content and Ki-67 immunofluorescence indicated that the antigen was present in all phases of the cell cycle, reactivity with the antibody was highest in proliferating S and G2+M cells. The analysis of the BrdU content of cells sorted on the basis of reactivity with Ki-67 showed a correlation between Ki-67 reactivity and BrdU uptake. In HL-60 cells induced to differentiate with dimethyl sulfoxide (DMSO), the loss of reactivity with Ki-67 paralleled the exit of cells from the cell cycle. This was not observed in DMSO-resistant HL-60 cells. These results validate the usefulness of the Ki-67 antibody for determining the proliferative stage of mammalian cells in culture.

Flow cytometry and feulgen cytophotometry in evaluation of effusions

Fifty‐eight effusions (42 pleural and 16 ascitic fluids) from patients with and without cancer were analyzed by conventional cytology and the results compared with DNA patterns generated by flow cytometry of 104 nuclei and several modes of Feulgen cytophotometry. In 31 patients (24 without evidence of cancer and seven with history of cancer and cytologically negative fluids), the fluids were diploid by flow cytometry. One fluid with atypical cells from a lymphoma suspect was also diploid. Flow cytometry of 26 cytologically cancerous fluids disclosed aneuploid DNA patterns in 16 and diploid patterns in ten. Feulgen cytophotometry of 11 of these fluids (three aneuploid, eight diploid) was performed on nuclear preparations identical to those used in flow cytometry and on restained smears used for visual analysis. The analysis was performed in two modes: as a study of 500 sequential nuclei in an automated system, mimicking flow cytometry, and visually selected large, presumably malignant nuclei. In nine of the 11 cases, the DNA content of visually selected cancer cells was aneuploid, even though this DNA pattern was not evident in the analysis of 500 sequential cells. In two cases, both diploid by flow cytometry, the Feulgen analysis confirmed the presence of cancer cells in the diploid range. In samples of 104 nuclei representing a mixed population of cells occurring in effusions, the presence of aneuploid cancer cells may not be disclosed by conventional flow cytometry. A larger sample of cells, a detailed analysis of DNA histograms, and perhaps sorting of select cells in the hypertetraploid range, may prove essential before flow cytometry can be accepted as a diagnostic tool in the laboratory in the assessment of effusions.

Interinstitutional variability in DNA flow cytometric analysis of tumors: The national Cancer Institute's Flow Cytometry Network experience

Flow cytometric DNA analysis of human urinary bladder specimens may be clinically useful for prognosis in transitional cell (urothelial) carcinoma and for detecting recurrence after treatment. However, many important methodological differences exist among institutions which have described this technique, and it has not previously been shown that data from different institutions are comparable. The National Cancer Institute has created a Flow Cytometry Network to address the need for technology assessment of flow cytometry. This report describes the independent flow cytometric analysis and interpretation of “unknown” paraffin‐embedded bladder tumor specimens by the five Network institutions. Although important differences in method existed among the institutions, substantial agreement was achieved in actual data generated and their interpretation. This suggests that a consensus regarding acceptable laboratory performance of this technique could be reached, which should faciliate its more widespread clinical implementation.

Check samples for laboratory self-assessment in DNA flow cytometry. The national cancer institute's flow cytometry network experience

The National Cancer Institutes Flow Cytometry Network (NCI‐FCN) is attempting to facilitate the transfer of flow cytometry (FCM) of exfoliated bladder cells from the research laboratory to the clinical laboratory. Demonstrating interinstitutional consistency in FCM analysis of replicate specimens simulating clinical barbotage specimens, fixed to allow easy transporation and storage at room temperature was one specific objective. Simulated barbotage specimens were prepared by mixing cultured aneuploid bladder carcinoma cells with normal or mitogen‐stimulated peripheral blood mononuclear cells in different ratios. The samples were fixed in 10% formalin for 30 minutes, stored in buffer, and enucleated with pepsin, pH 1.5, before staining with propidium iodide for FCM DNA analysis. Preservation in ethanol or other common DNA cytochemcal reagents was found to be unsatisfactory. In contrast, the formalin‐fixed samples showed excellent preservation of quantitative DNA fluorescence and coefficient of variation of histogram peaks for over 2 weeks. Exchange of eight fixed specimens among five network laboratories that analyzed them as “unknowns” showed good overall agreement on histogram data and interpretation, although some noteworthy interlaboratory differences were found. This technique could be used for self‐assessment surveys of clinical laboratory performance in DNA FCM of bladder barbotage specimens.

Ethanol fixation of bladder irrigation specimens for flow cytometric analysis. A multiinstitutional study from the bladder cancer flow cytometry network

Ethanol preservation of voided and catheterized urine has long been the standard for urinary cytologic study. In this report ethanol preservation of bladder irrigation specimens was evaluated for flow cytometric analysis in a multiinstitutional study requiring specimen transport. Specimens from ten patients obtained at one center were preserved for varying periods of time in 50% ethanol, then distributed by express mail to four other participating centers, up to 3000 miles distant. On receipt, from 1 to 3 weeks after collection, the samples were processed and examined by flow cytometric study using propidium iodide as the fluorochrome. Forty‐six of the 50 (92%) analyzed specimens gave satisfactory histograms. In 41 of the 46 adequate samples (89%), an aneuploid peak in the alcohol preserved (propidium iodide stained) specimen correlated well with the fresh (acridine orange stained) specimen. However, there was variable loss of DNA stainability with a broadening of the coefficient of variation in some alcohol‐preserved specimens and an increase in cellular debris so that measurements of DNA index and percent hyperdiploid cells were considered unreliable. The authors conclude that ethanol preservation of bladder irrigation specimens for short periods of time may be a feasible alternative when flow cytometric analysis cannot be carried out on fresh specimens, but that this is not optimal fixation for specimens that must be transported and further studies of other fixatives are recommended.

Lysophosphatidylcholine cell depolarization: Increased membrane permeability for use in the determination of cell membrane potentials

Current techniques for the determination of cellular membrane potentials based on the uptake of a radiolabeled lipophilic cation, [3H]triphenylmethylphosphonium, and the cyanine dye, DiOC5(3), were analyzed in terms of the proportions of these probes which are accumulated due to potential-dependent and potential-independent forces. Measurements were made of probe uptake in two model systems: rabbit type II pneumocytes and human promyelocytic HL60 cells. For both cell types, the membrane potential-independent component of triphenylmethylphosphonium uptake was found to be a function of several variables, including the length of exposure of the cells to the transport facilitator tetraphenylboron, the concentration of tetraphenylboron, and the integrity of the cell membrane. To accurately determine the magnitude of the potential-independent component of probe uptake by type II and HL60 cells, the cell-permeabilizing agent lysophosphatidylcholine was used. The ability of lysophosphatidylcholine to depolarize cell membranes and accurately predict membrane potential-independent accumulation was found to be equal to or superior to several other techniques commonly used to achieve membrane depolarization (e.g. gramicidin, valinomycin plus high external potassium). Lysophosphatidylcholine cell treatment was found to be a simple, rapid, and accurate technique to increase cell membrane permeability and allow equilibration of intra- and extracellular ions. The method is shown to be useful for determining membrane potential-independent accumulation of both radiolabeled and fluorescent probes of membrane potential.

Influence of human papillomavirus on DNA ploidy determination in genital condylomas

It has been reported that deoxyribonuclease (DNAse) treatment does not destroy viral DNA, but it does digest native nuclear DNA. To determine what effect, if any, papillomavirus infection has on DNA ploidy values of genitourinary condylomas, DNA was measured with and without DNAse exposure in seven urethral condylomas, shown by prior in situ hybridization to contain abundant human papillomavirus types 6 and 11. Normal human skin was used as a negative control. Consecutive paraffin‐embedded tissue sections were stained according to Feulgen before and after DNAse treatment. The DNA was measured by image analysis. In control tissue, DNAse obliterated DNA, and the Feulgen reaction was negative. In six of seven condylomas the DNA content was reduced, but a measureable Feulgen reaction was still present in isolated cells. In the seventh case there were no significant changes in the histograms. This observation strongly suggests that the presence of human papillomavirus has a significant effect on measurements of DNA ploidy in genital condylomas and, by implication, possibly also in other tissues containing the virus. Possible mechanisms are discussed.