Increased accuracy and speed of absorption cytometric DNA measurements by automatic corrections for nuclear darkness

Chromosomal variations within aneuploid cancer lines

Aneuploid cancers exhibit a wide spectrum of clinical aggressiveness, possibly because of varying chromosome compositions. To test this, karyotypes from the diploid CCD-34Lu fibroblast and the aneuploid A549 and SUIT-2 cancer lines underwent fluorescence in situ hybridization (FISH) and DAPI counterstaining. The number of DAPI-stained and FISH-identified chromosomes, 1-22, X,Y, as well as structural abnormalities, were counted and compared using the chi(2), Mann-Whitney rank sum test and the Levene's equality of variance. Virtually all of the evaluable diploid CCD-34Lu karyotypes had 46 chromosomes with two normal-appearing homologues. The aneuploid chromosome numbers per karyotype were highly variable, averaging 62 and 72 for the A549 and SUIT-2 lines, respectively. However, the A549 chromosome numbers were more narrowly distributed than the SUIT-2 karyotype chromosome numbers. Furthermore, 25% of the A549 chromosomes had structural abnormalities compared to only 7% of the SUIT-2 chromosomes. The chromosomal compositions of the aneuploid A549 and SUIT-2 cancer lines are widely divergent, suggesting that diverse genetic alterations, rather than chance, may govern the chromosome makeups of aneuploid cancers.

Evidence for altered cell-cycle traverse of the non-modal cells of the heteroploid MCa-11 line

Classic stem cell theory states that the growth of heteroploid cell populations is due to the proliferation of 'main stemline' cells with modal DNA content and chromosome number. Cells with non-modal DNA content and chromosome number are thought to be blocked and/or destroyed at mitosis. To test this, we studied two chromosomally stable cell populations (mouse bone marrow and WCHE-5 cells) and one heteroploid, chromosomally diverse cell line (MCa-11). The heteroploid MCa-11 cells showed significant [3H]dT labelling for cells with DNA contents below the modal G0/G1 peak and above the modal G2 peaks (P < 0.001). This was consistent with the presence of cells with the non-modal DNA content that were engaged in replicative DNA synthesis. A percentage labelled mitosis analysis showed that MCa-11 cells with non-modal DNA content and chromosome number were able to complete mitosis, although with prolonged pre-karyokinetic time. These results suggest that many non-modal cells present in heteroploid cell populations are capable of continued proliferation.

A comparison of flow cytometric and absorption cytometric DNA values as prognostic indicators for pancreatic carcinoma

BACKGROUND

The DNA content of 30 adenocarcinomas of the head of the pancreas was measured by flow and absorption cytometric analysis.

METHODS

Each of the patients in this study had curative pancreatoduodenectomy. The absorption cytometric measurements were done in a research laboratory, and the flow cytometric measurements were performed in a commercial laboratory. The DNA measurements were done on nuclei disaggregated from pancreatic cancer tissue blocks without the examiner knowing whether the patient had survived.

RESULTS

Twenty-one of the 30 cancers were found to be aneuploid by absorption cytometric analysis, whereas only 1 of the 30 cancers was aneuploid by flow cytometric analysis. This difference was statistically significant (P < 0.001).

CONCLUSIONS

Univariate and multivariate analyses showed that the absorption cytometric DNA measurements were stronger prognostic determinants for patient survival than were the flow cytometric DNA measurements, indicating that some caution may be warranted in the interpretation of commercially obtained DNA distributions of pancreatic carcinomas.

Non-random distribution of abnormal mitoses in heteroploid cell lines

We have performed absorption-cytometric DNA measurements of the DNA contents of the G0/G1, G2, metaphase, and telophase cells of the heteroploid MCa-11 and HL-60 lines, as well as the WCHE-5 line which has a narrowly restricted number of chromosomes. We found that morphologically unbalanced mitoses occurred much more frequently in telophase-cell pairs of the heteroploid MCa-11 and HL-60 lines than in those of the chromosomally stable WCHE-5 line. Furthermore, the morphologically unbalanced mitoses represented unequal segregation of DNA into each of the daughter telophase nuclei. Such mitotic segregation errors (MSE) occurred almost exclusively in telophase cells with DNA contents which were above, or below, the DNA content of the modal telophase population. The net effect of these non-random, unblanced divisions of heteroploid cells with non-modal DNA contents is to produce one daughter cell with a DNA content that tends to return to the modal DNA content peak.

Pancreatic cancer cell DNA content correlates with long-term survival after pancreatoduodenectomy

The DNA content of 47 adenocarcinomas arising in the head of the pancreas from patients who had undergone successful pancreatoduodenectomy was measured. The DNA measurements of each tumor were made without knowledge of the clinical course by absorption cytometry performed on Feulgen-stained nuclei that had been disaggregated from pancreatic cancer tissue blocks. Forty-seven evaluable DNA distributions were obtained from specimens taken between 1975 and 1988. Of the 47 tumors, 19 (40%) were diploid and 28 (60%) were aneuploid cancers. The 19 patients with diploid cancers had a median survival time of 25 months. Median survival of the 28 patients with aneuploid cancers was 10.5 months. This difference was statistically significant (p = 0.003). A multivariate life table regression analysis demonstrated that the ploidy and proliferative index as determined by absorption cytometry were independent prognostic factors, as strong as or stronger than the number of positive nodes and tumor size. Thus cellular DNA content appears to be one of the most important predictors of survival in patients with adenocarcinoma of the head of the pancreas who have successfully undergone a pancreaticoduodenectomy.

Discrepancies among the metaphase, telophase, and the G0/G1 and G2 DNA peaks of heteroploid cell lines

Heteroploid cell populations often show narrow peaks of G0/G1 and G2/M DNA content and broadly distributed chromosome numbers. This was originally explained by the selective metaphase arrest of the cells that have non-modal chromosome numbers. To test whether this explanation applies, we have measured the chromosome number distributions, as well as the G0/G1, G2, metaphase (M), and telophase (T) DNA distributions, of the cell lines WCHE-5, MCa-11, and HL-60. The WCHE-5 cells had narrowly distributed chromosome numbers and G0/G1 G2, M, and T DNA peaks. The MCa-11 and HL-60 cells also had narrowly distributed G0/G1 and G2 DNA peaks, but broadly distributed chromosome numbers and M and T DNA peaks. The widths of the MCa-11 and HL-60 M- and T-cell DNA peaks were similar to those of their chromosome number peaks, suggesting that all cells were completing mitosis, regardless of chromosome number or DNA content. Thus, selective metaphase arrest does not seem to be the cause of the narrow G0/G1 and G2 DNA peaks of heteroploid cell populations.

Comparison of absorption measurements of DNA stain content by utilizing video and scanning image cytometers

After staining with the Feulgen reaction, the DNA stain contents of 155 mouse bone marrow cells and 22 adjacent chicken erythrocytes were measured by absorption image cytometry by utilizing two different systems--a scanning cytometer and a video cytometer. In the scanning cytometer (M85 microdensitometer, Vickers Instruments, Malden, MA), a spot of light was scanned across the cell. In the video cytometer (TAS Plus, E. Leitz, Rockleigh, NJ), the microscope field, which may contain several nuclei, was imaged onto a Plumbicon video camera. With each system, cells were scanned, digitized into their elementary pixels, and analyzed to determine their integrated absorbance. Comparison of the DNA stain contents of the same G0/G1 bone marrow cells and chicken erythrocytes, as measured by video and scanning cytometry, showed that both techniques gave comparable results; scanning cytometry is more precise. The coefficients of variation of the measurements for the G0/G1 bone marrow cells and for the chicken erythrocytes were 5.9% and 7.0%, respectively, when measured by video cytometry at the absorption peak (584 nm), compared to 4.1% and 3.5%, respectively, for the same cells when measured by scanning cytometry off the absorption peak (615 nm). The video-based measurements were relatively lower than the scanning measurements for darkly stained cells; this suggests that glare and other optical errors which increase with stain darkness caused greater systematic errors in the video cytometer than they did in the scanning cytometer.

Combined flow and absorption DNA measurements of [3H]TdR-labelled tumour cells. I. Studies of MCa-11 cells grown as tumours in vivo and as exponential cultures in vitro

Flow cytometry of cellular DNA content provides rapid estimates of DNA distributions, i.e. the proportions of cells in the different phases of the cell cycle. Measurements of DNA alone, however, yield no kinetic information and can make it difficult to resolve the cell cycle distributions of normal and transformed cells present in tumour biopsy specimens. The use of absorption cytophotometry of the Feulgen DNA content and [3H]TdR labelling of the same nuclei provides objective criteria to distinguish the ranges of DNA content for G0/G1, S, and G2/M cells. We now report on a study in which we combined flow and absorption cytometry to resolve the cell cycle distributions of host and tumour cells present in biopsy specimens of MCa-11 mouse mammary tumours labelled in vivo for 0.5 hr with [3H]TdR. A similar analysis of exponential monolayer cultures, labelled for 5 min with [3H]TdR under pulse-chase conditions, revealed a highly synchronous traversal of almost all cells through the different phases of the cell cycle. Combination of the flow and absorption methods also allowed us to detect G2 tumour cells in vivo and a minor tumour stem-line in vitro, to show that these two techniques are complementary and yield new information when they are combined.

Cytophotometric determination of unscheduled DNA synthesis

We describe a cytophotometric assay for unscheduled DNA synthesis (UDS) in asynchronously growing cells. Monolayer cultures of human HEp-2 and mouse MCa-11 cells were incubated with the carcinogen methyl-methane sulfonate (MMS), as well as with hydroxyurea and (3H)thymidine. Slides were prepared, and the DNA contents and areas of nuclei were measured by absorption cytophotometry. The labeling of the nuclei, determined on the basis of their DNA content to be in G0/G1, was selectively measured after the preparation of autoradiographs. The labeling of the G0/G1 cells increased with increasing doses of MMS. We also found that the increased nuclear labeling after MMS treatment was not due to induction of replicative DNA synthesis or selective destruction of G0/G1 cells. The results of this assay compared favorably with a standard biochemical method for measuring unscheduled DNA synthesis by benzoylated naphthoylated DEAE cellulose chromatography.

Random signal variation as a cause of systematic microdensitometric error

A high noise/signal ratio in microdensitometry, owing, for example, to the use of a very small measuring spot or light at an extreme of the spectrum, decreases the precision (increases the variability) of results. This can be compensated for by making more measurements, but under some circumstances random signal variations can also cause systematic errors that are not so easily corrected. The present article explains how such errors can arise when measuring either very pale or very dense objects and suggests methods to detect and avoid them. The principles described are applicable to many types of microdensitometer, not only the Vickers flying-spot instruments used in this investigation.