A quantitative method for evaluating bivariate flow cytometric data obtained using monoclonal antibodies to bromodeoxyuridine

Multiparameter Cell Cycle Analysis

Cell cycle cytometry and analysis are essential tools for studying cells of model organisms and natural populations (e.g., bone marrow). Methods have not changed much for many years. The simplest and most common protocol is DNA content analysis, which is extensively published and reviewed. The next most common protocol, 5-bromo-2-deoxyuridine S phase labeling detected by specific antibodies, is also well published and reviewed. More recently, S phase labeling using 5'-ethynyl-2'-deoxyuridine incorporation and a chemical reaction to label substituted DNA has been established as a basic, reliable protocol. Multiple antibody labeling to detect epitopes on cell cycle regulated proteins, which is what this chapter is about, is the most complex of these cytometric cell cycle assays, requiring knowledge of the chemistry of fixation, the biochemistry of antibody-antigen reactions, and spectral compensation. However, because this knowledge is relatively well presented methodologically in many papers and reviews, this chapter will present a minimal Methods section for one mammalian cell type and an extended Notes section, focusing on aspects that are problematic or not well described in the literature. Most of the presented work involves how to segment the data to produce a complete, progressive, and compartmentalized cell cycle analysis from early G1 to late mitosis (telophase). A more recent development, using fluorescent proteins fused with proteins or peptides that are degraded by ubiquitination during specific periods of the cell cycle, termed "Fucci" (fluorescent, ubiquitination-based cell cycle indicators) provide an analysis similar in concept to multiple antibody labeling, except in this case cells can be analyzed while living and transgenic organisms can be created to perform cell cycle analysis ex or in vivo (Sakaue-Sawano et al., Cell 132:487-498, 2007). This technology will not be discussed.

A new biomarker for mitotic cells

Many epitopes are phosphorylated during mitosis. These epitopes are useful biomarkers for mitotic cells. The most commonly used are MPM-2 and serine 10 of histone H3. Here we investigated the use of an antibody generated against a phospho peptide matching residues 774-788 of the human retinoblastoma protein 1 (Rb) to detect mitotic cells. Human cell lines were stained with DNA dyes and antibodies reactive with epitopes defined by antibody MPM-2, phospho-S10-histone-H3, and the phospho-serine peptide, TRPPTLSPIPHIPRC (phospho-S780-Rb). Immunoreactivity and DNA content were measured by flow and image cytometry. Correlation and pattern recognition analyses were performed on list mode data. Western blots and immunoprecipitation were used to investigate the number of peptides reactive with phospho-S780-Rb and the relationship between reactivity with this antibody and MPM-2. Costaining for bromodeoxyuridine (BrdU) was used to determine acid resistance of the phospho-S780-Rb epitope. Cell cycle related phospho-S780-Rb immunofluorescence correlated strongly with that of MPM-2. Laser scanning cytometry showed that phospho-S780-Rb immunofluorescence is expressed at high levels on all stages of mitotic cells. Western blotting and immunoprecipitation showed that the epitope is expressed on several peptides including Rb protein. Costaining of BrdU showed that the epitope is stable to acid. Kinetic experiments showed utility in complex cell cycle analysis aimed at measuring cell cycle transition state timing. The phospho-S780-Rb epitope is a robust marker of mitosis that allows cytometric detection of mitotic cells beginning with chromatin condensation and ending after cytokinesis. Costaining of cells with DNA dyes allows discrimination and counting of mitotic cells and post-cytokinetic ("newborn") cells. To facilitate use without confusion about specificity, we suggest the trivial name, pS780 for this mitotic epitope.

Flow cytometry after bromodeoxyuridine labeling to measure S and G2+M phase durations plus doubling times in vitro and in vivo

This protocol describes methods for calculating the proliferative parameters of cell populations. The basis of the technique is to label cells, either in vitro or in vivo, with halogenated thymidine analogs, such as bromodeoxyuridine (BrdU). Bivariate DNA-BrdU flow cytometry is used to analyze the BrdU-labeled and unlabeled cells. The enumeration of specific cohorts of cells that either have or have not divided in the interval between labeling and cell/tissue sampling permits the calculation of the potential doubling time (T(pot)) of the population, plus the durations of DNA synthesis (T(S)) and the G2+M phase (T(G2+M)) of the cell cycle. The method provides information that is not otherwise available, namely inhibition of DNA synthesis and the separate evaluation of cell-cycle effects in BrdU-labeled and unlabeled subpopulations. Ethanol-fixed samples take 1 d to prepare and stain, and reliable parameter estimates might be obtained from measurements made at a single time point after labeling.

1alpha,25-Dihydroxyvitamin D and fish oil synergistically inhibit G1/S-phase transition in prostate cancer cells

Laboratory and epidemiological studies have indicated that 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] and dietary omega3-polyunsaturated fatty acids (PUFAs) are capable of inhibiting prostate cancer at the initiation and progression stages. The objective of this study is to investigate the influence of 1alpha,25(OH)(2)D(3) and PUFAs in the form of fish oil applied alone or in combination on cell cycle kinetics in the exponentially growing androgen-dependent and -independent prostate cancer cells. Our data indicate that the high passage androgen-independent cell line, LNCaP-c115 had a much greater inhibitory response at the level of the G(1)/S-phase transition in response to fish oil treatment than androgen-dependent low passage LNCaP-c38 cells. When LNCaP-c38 and LNCaP-c115 cells were treated with fish oil (50mug/ml), 1alpha,25(OH)(2)D(3) (10(-8)M) or fish oil (50mug/ml)+1alpha,25(OH)(2)D(3) (10(-8)M), a synergistic growth inhibitory effect was observed with 1alpha,25(OH)(2)D(3)+fish oil group in LNCaP-c115 cell line at the levels of the G(1)/S-phase transition and cell division. This interaction appears to be specific for androgen-independent prostate cancer cell lines. Based on these results, we hypothesize that dietary components, such as omega3PUFAs and Vitamin D, have the potential to delay the progression of prostate cancer cells to an aggressive and un-treatable state.

Fish oil slows S phase progression and may cause upstream shift of DHFR replication origin ori-beta in CHO cells

Fish oils (FOs) have been noted to reduce growth and proliferation of certain tumor cells, effects usually attributed to the content of polyunsaturated fatty acids of the n-3 family, which are thought to modulate cellular signaling pathways. We investigated the influence of FO on cell cycle kinetics of cultured Chinese hamster ovary cells. Exponentially growing cells were labeled with 5-bromo-2'-deoxyuridine (BrdU) and analyzed by flow cytometry after 5-day treatment with exogenous fat. Bivariate BrdU-DNA analysis indicated slower progression through S phase and thus longer S phase duration time in FO- but not corn oil-treated or control cells. We hypothesize that FO treatment might interfere with spatial/temporal organization of replication origins. Therefore, we mapped the well-characterized replication origin ori-beta downstream of the dihydrofolate reductase gene with the nascent strand length assay. Three DNA marker segments with known positions relative to this origin were amplified by PCR. By quantitatively assessing DNA length of the fragments in all fractions containing these markers, the location of ori-beta was established. In control or corn oil-treated cells, the location of ori-beta was consistent with previous studies. However, in FO-treated cells, DNA replication appears to start from a new site located farther upstream from ori-beta, suggesting a different replication initiation pattern. This study suggests novel mechanism(s) by which fats affect cell proliferation and DNA replication in mammalian cells.

DNA global hypomethylation in EBV-transformed interphase nuclei

In tumors, DNA is often globally hypomethylated compared to DNA extracted from normal tissues. This observation is usually made after extraction and exhaustive digestion of DNA followed by analysis of nucleosides by chromatography or digestion with restriction enzymes, gel analysis, and hybridization. This approach provides an average value which does not give information on the various cell subpopulations included in heterogeneous samples. Therefore an immunochemical technique was set up with the aim of demonstrating, in a population of mixed cells, the possibility of detecting the presence of individual nuclei containing hypomethylated DNA, on a cell-by-cell basis. Monoclonal antibodies to 5-methylcytidine were used to label cells grown in vitro. Under appropriate fixation and permeabilization conditions, interphase nuclei were labeled. Quantitative differences in the labeling were detected between Epstein-Barr virus-transformed cells and normal peripheral blood monocytes by flow cytometry analysis. Similar differences were observed by fluorescence microscopy. Both results were confirmed by Southern transfer and hybridization of DNA fragments generated by restriction enzyme digestion. This observation, which is in accordance with the occurrence of global DNA hypomethylation in tumors as established by chromatography, opens the field for the analysis of fresh tumor samples by flow cytometry and microscopy.

Repopulation characteristics and cell kinetic parameters resulting from multi-fraction irradiation of xenograft tumors in SCID mice

PURPOSE

Cell kinetics and repopulation rates during multifraction irradiation have previously been measured in SiHa human cervical carcinoma cells grown as spheroids. The current study applied similar techniques to SiHa tumor xenografts with the ultimate goal of assessing the clinical prognostic value of in situ cell kinetics.

METHODS AND MATERIALS

SiHa (human squamous cell cervical tumor) cells were inoculated subcutaneously in the flank or back of SCID mice. When tumors reached a size of 200-300 mg, they received 25 Gy in 10 fractions over 5 days. Tumor regrowth and cell kinetics parameters were followed during treatment, and for 10 days after completion by measuring tumor volume and analyzing cellular BrdUrd and IdUrd incorporation with flow cytometry.

RESULTS

Tumor volume was of limited use in assessing response to irradiation. The fraction of proliferating cells increased early during irradiation as did the labeling index; potential doubling time (Tpot) decreased during treatment and returned to the pre-irradiation value after treatment. Cell cycle time remained relatively constant throughout the experiments.

CONCLUSION

These results confirm the feasibility of evaluating cell cycle kinetics and repopulation parameters in a murine tumor model undergoing a fractionated course of irradiation. Repopulation of clonogenic tumor cells occurred more rapidly than predicted by pretreatment measurements, primarily due to an increased growth fraction and consequent decrease in Tpot.

Reproducibility of measurements of potential doubling time of tumour cells in the multicentre National Cancer Institute protocol T92-0045

We compared the flow cytometric measurement and analysis of the potential doubling time (Tpot) between three centres involved in the National Cancer Institute (NCI) protocol T92-0045. The primary purpose was to understand and minimize the variation within the measurement. A total of 102 specimens were selected at random from patients entered into the trial. Samples were prepared, stained, run and analysed in each centre and a single set of data analysed by all three centres. Analysis of the disc data set revealed that the measurement of labelling index (LI) was robust and reproducible. The estimation of duration of S-phase (T(S)) was subject to errors of profile interpretation, particularly DNA ploidy status, and analysis. The LI dominated the variation in Tpot such that the level of final agreement, after removal of outliers and ploidy agreement, reached correlation coefficients of 0.9. The sample data showed poor agreement within each of the components of the measurement. There was some improvement when ploidy was in agreement, but correlation coefficients failed to exceed values of 0.5 for Tpot. The data suggest that observer-associated analysis of T(S) and tissue processing and tumour heterogeneity were the major causes of variability in the Tpot measurement. The first two aspects can be standardized and minimized, but heterogeneity will remain a problem with biopsy techniques.

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma

PURPOSE

Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts.

METHODS AND MATERIALS

In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry.

RESULTS

In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc.

CONCLUSION

Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Cell kinetics and repopulation mechanisms during multifraction irradiation of spheroids

BACKGROUND AND PURPOSE

The objective of the present study was to evaluate the predictive potential of cell kinetic parameters and repopulation rates determined by flow cytometry during multifraction irradiation of spheroids, a system in which the fate of all cells can be determined with high precision. Ultimately, similar analytical techniques should provide a reproducible and prognostically significant clinical predictive assay.

MATERIALS AND METHODS

Multicellular spheroids of Chinese hamster V79 lung cells were irradiated with 2.5 Gy of 250 kVp X-rays twice daily to a total dose of 25 Gy. Repopulation parameters and cell kinetic parameters were followed throughout the irradiation period and for 5 days after completion of exposure.

RESULTS

(1) Regrowth (RG) took place early during multifraction irradiation. (2) Potential doubling time (Tpot) decreased steadily from the early part of treatment, remaining of short duration until the spheroids almost attained the pre-treatment number of clonogenic cells. (3) Accelerated repopulation was mainly due to a decreased cell loss factor (phi) and increased growth fraction (GF), although a modest decrease in cell cycle time (tc) was suggested. (4) Phi decreased during exponential RG. (5) Other parameters such as observed doubling time (td) and labelling index (LI) paralleled these findings.

CONCLUSIONS

Clonogen repopulation that began early in the irradiation scheme and accelerated rapidly is not consistent with the prevailing view that accelerated repopulation begins several weeks into clinical protocols. Also, pre-treatment Tpot did not adequately estimate the repopulation speed in the spheroids. Equivalent studies in animal tumour systems, and then in the clinic, are consequently indicated and of some urgency.

S-phase fraction, 5-bromo-2'-deoxy-uridine labelling index, duration of S-phase, potential doubling time, and DNA index in benign and malignant brain tumors

Seventy-one histologically malignant brain tumors, 52 histologically benign brain tumors, and 14 cerebral metastases were characterized according to DNA content and proliferative capacity. DNA ploidy, DNA index (DI), S-phase fraction (SPF), 5-bromo-2'-deoxy-uridine (BrdUrd) labelling index (LI), duration of S-phase (Ts), and potential doubling time (Tpot) were assessed by flow cytometry (FCM). In histologically benign tumors, a high percentage of DNA diploid tumors and a low proliferative capacity in DNA diploid tumors were found. Histologically malignant tumors and cerebral metastases were both found to be characterized by a low percentage of DNA diploid tumors and a high proliferative capacity in DNA diploid tumors. The proliferative capacity of DNA aneuploid benign tumors and that of DNA aneuploid malignant tumors, however, appeared not to differ significantly. The number of DNA aneuploid tumors was small. Duration of S-phase was short (range 3.9-4.7 hr) and appeared not to differ between the three groups. From this, the observed differences in Tpot values should be accredited mainly to differences in LI. High-grade as well as low-grade gliomas both appeared to be characterized by malignant (FCM) features, i.e., 1) a high percentage DNA aneuploidy, 2) a high mean DI (for DI > 1), and 3) a high proliferative capacity.

Tumor repopulation during radiotheraphy: quantitation in two xenografted human tumors

PURPOSE

"Accelerated repopulation" has generated considerable recent interest. Our purpose in this study was to determine whether flow cytometry measurements like those used for classical Tpot determinations could be used to quantify the rate of repopulation, and the time of its initiation in irradiated human tumor xenografts.

METHODS AND MATERIALS

Two human tumor cell lines (SiHa, a squamous cell cervix carcinoma, and WiDr, an adenocarcinoma of the colon) were grown as subcutaneous xenografts in SCID mice. Tpot was measured in a conventional manner using flow cytometry, for control tumors and for tumors exposed to five fractions of 4 Gy twice daily over a 2-day interval. For the irradiated tumors, Tpot measurements were conducted 48 h following the final exposure.

RESULTS

Active proliferation even after irradiation was observed in both the radiosensitive SiHa and more radioresistant WiDr tumors, and the estimated repopulation rate was at least as fast as would have been predicted by the pre-treatment Tpot estimates.

CONCLUSIONS

Our data clearly indicate tumor cell proliferation after only a few fractions of radiation exposure in these human tumor xenografts. Additionally, the data suggest that pretreatment Tpot values may underestimate the actual regrowth rate.

Effects of interferon and PKC modulators on human glioma protein kinase C, cell proliferation, and cell cycle

The in-vitro effects of human interferon alpha-2b (HuIFN alpha-2b), protein kinase C (PKC) agonist [TPA (12-0-tetra-decanoyl-phorbol-13-acetate)] and PKC inhibitor (calphostin C) on human glioma (U-373 MG) PKC activity, cell proliferation and cell cycle were compared. HuIFN alpha-2b and TPA increased PKC activity, elevated the number of cells in DNA synthesis (S) phase and decreased cell proliferation by similar magnitudes. Calphostin C inhibited PKC activity, increased the number of cells in S phase and produced strong cytotoxic effects (IC50 150 nM). Higher concentrations of calphostin C with or without serum induced an additional block in gap2 and mitosis. We conclude that HuIFN alpha-2b's mode of action may be directly or indirectly affecting PKC. The response produced by HuIFN alpha-2b is similar to TPA (potent PKC activation and S phase arrest).

Spontaneous metastasis, proliferation characteristics and radiation sensitivity of fractionated irradiation recurrent and unirradiated human xenografts

PURPOSE

Do tumor cells which survive high dose fractionated irradiation exhibit modified metastasis activity, proliferation kinetics, and/or radiation sensitivity? To address this question experimentally, we have studied three recurrent human tumor xenograft systems.

METHODS AND MATERIALS

Three models were derived from a soft tissue sarcoma (HSTS26T), a colon adenocarcinoma (HCT15), and a glioblastoma (HGL21) which had recurred after 90 Gy, 109 Gy, or 77.4 Gy administered in 30 equal doses, respectively. Their production of spontaneous metastasis and cell proliferation characteristics were studied in early generation xenografts in SCID mice, and were compared to those in their previously unirradiated counterparts. As a control, we have also studied each tumor as a post-surgical recurrence. Specimens from the irradiated recurrent and their unirradiated primary tumors were cultured in vitro and their radiation sensitivity determined by clonogenic assay.

RESULTS

The three irradiated recurrent tumor systems retained the individual histological features of their unirradiated primary xenografts. A lower metastatic incidence was observed in two of the three irradiated recurrent tumor lines in comparison with their unirradiated control tumors and their surgical recurrent counterparts. No significant differences were found between the irradiated recurrent tumors and their unirradiated counterparts with respect to: volume doubling time, growth time, potential doubling time, mitotic index, PCNA index, and SF2 values.

CONCLUSIONS

High dose irradiation given in 30 fractions did not increase the metastatic activity in the three human tumor xenograft systems. Furthermore, the fractionated irradiation did not significantly change their proliferation characteristics and cellular radiation sensitivity.

Accelerated repopulation during fractionated irradiation of a murine ovarian carcinoma: downregulation of apoptosis as a possible mechanism

PURPOSE

To test whether accelerated tumor clonogen repopulation occurs during continuous fractionated radiotherapy of a slow-growing mouse ovarian tumor, and if so whether the accelerated rate of repopulation is predicted by the pretreatment potential doubling time, and whether changes in apoptotic response are a possible mechanism for this change.

METHODS AND MATERIALS

The rate of clonogen production during fractionated radiotherapy was followed using the tumor-control assay, with an independent determination of the sensitivity to repeated dose fractions in vivo in the absence of repopulation. The pretreatment potential doubling time was measured by bromodeoxyuridine (BrdUrd) labeling and fluorescence measurements. The apoptotic and mitotic indices at various times during treatment were scored histologically.

RESULTS

The slow-growing (pretreatment volume doubling time 6 days) ovarian tumor OCA responds to daily irradiation with 6 Gy under hypoxia by negligible tumor clonogen production in the first few days, followed by a change at about 9 days to accelerated repopulation, after which the effective clonogen doubling time Tclon was about 2 days, near the pretreatment Tpot of 1.7 days. Alternative interpretations of the data, such as a change in radiosensitivity vs. a change in the repopulation rate or acceleration at 3 days as opposed to 9 days, were shown to be unlikely. This change was accompanied by a reduced apoptotic response (measured morphometrically).

CONCLUSIONS

When sensitivity to fractionated doses has been corrected for in vivo, this slow-growing mouse tumor exhibits a change to accelerated clonogen production during a continuous radiotherapy regimen that is accompanied or preceded by a reduced histologic apoptotic response. Tclon during accelerated repopulation was slightly longer than the pretreatment Tpot.

Heterogeneous cell kinetics in tumors analyzed with a simulation model for bromodeoxyuridine single and multiple labeling

Bromodeoxyuridine (BrdUrd) labeling of DNA and flow cytometry measurement of bivariate BrdUrd-DNA content distributions yield proportions of cells in the cycle phases. After application of BrdUrd, with time, these proportions change according to the cell kinetic parameters of the investigated cell line or tumor. In a previous study of S-phase transit time using the relative movement method, we obtained better fits with S-duration distributions rather than constant values (Baisch and Otto: Cell Prolif 26:439-448, 1993). Now, we have developed a simulation model using asymmetric phase duration distributions in all phases of the cell cycle to fit the experimental data after single or multiple BrdUrd labeling. The model includes transit of cells from proliferating to quiescent compartments in all phases. The results yield the phase duration distributions, mean and median percentages of quiescent cells in all phases, growth fraction, and potential doubling time. The model was used to fit data of five renal cell carcinomas xenotransplanted into nude mice that were obtained after single and multiple labeling up to 93 hours. The estimated phase duration distributions varied from narrow to extremely asymmetric. In particular, TG2M duration and asymmetry were nearly as large as those of G1 phase in some tumors. The contribution of inter- and intratumoral heterogeneity cannot be separated by the simulation model, but evidence of intratumoral heterogeneity is provided by DNA content distributions at extended time spans after BrdUrd labeling.

Cellular kinetics in rectal cancer

Measurements of dynamic tumour cell kinetic parameters, particularly the potential doubling time (Tpot) may have potential as predictive assays for treatment outcome after radiotherapy. This paper details the distributions of Tpot and other kinetic and DNA content parameters measured in rectal cancers. Biopsies were taken from 119 patients approximately 6 h after infusion of 200 mg m-2 bromodeoxyuridine (BrdUrd). The samples were analysed by bivariate DNA/BrdUrd flow cytometry. The primary purpose of the study was to measure the kinetic parameters of labelling index (LI), duration of S-phase (TS) and Tpot. Secondarily, tumour DNA ploidy (DNA index) and S-phase fractions (SPFs) were also estimated from the univariate DNA histograms. The 101 evaluable patients were classified according to clinical stage as T2 (n = 12), T3 (n = 53), T4 (n = 28) or recurrent tumours (n = 8). Of the evaluable tumours, 73 were DNA aneuploid. The median LI, TS, and Tpot of the aneuploid tumours were 21%, 20 h and 3.3 days respectively. The calculated LI, TS, and Tpot of diploid tumours were subject to uncertainties because of the contribution of normal cells. The LI and SPF of all tumours were, however, significantly (P < 0.001) correlated, having a correlation coefficient of only 0.76. The wide distributions of values for LI (quartiles 13.5%, 26.9%) and Tpot (quartiles 2.4, 5.6 days) that were found are necessary baseline information if these parameters are to be useful in individual treatment selection or as predictors of treatment outcome.

Proliferation measurements with flow cytometry Tpot in cancer of the uterine cervix: correlation between two laboratories and preliminary clinical results

PURPOSE

To assess the prognostic value of the pretreatment potential doubling time (Tpot) in carcinoma of the uterine cervix, relative to other established clinical factors.

METHODS AND MATERIALS

Fifty-two patients with cervical cancer were studied prospectively from March 1991 to October 1993. Pretreatment evaluation included examination under anesthesia and tumor biopsy 6 h following the intravenous administration of bromodeoxyuridine (200 mg). Tpot was determined by deriving the labeling index (LI) and S-phase synthesis time (Ts) using flow cytometry. Six patients were not evaluable and excluded. The remaining 46 patients (average age 55 years) were treated uniformly with radical radiation therapy. There were 39 squamous carcinomas and 7 adenocarcinomas. Fédération Internationale de Gynécologie et d'Obstétrique (FIGO) stages were: Ib and IIa, 12 patients; IIb, 18 patients; III and IV, 16 patients. The median external beam dose was 50 Gy (range, 45-52.8 Gy) delivered in 25 fractions. The median intracavitary dose was 40 Gy (range. 25.5-40 Gy) delivered with a single line source to a point 2 cm lateral of the midline, with a mean dose rate of 0.71 Gy/h. The median overall treatment time was 45 days (range, 34-73 days). As of July 31, 1994, 12 patients had died of disease, and the average follow-up for alive patients was 1.4 years (range, 0.5-3.3 years).

RESULTS

There were 27 tumors with diploid deoxyribonucleic acid (DNA) content and 19 tumors were aneuploid. The median and mean Tpot for the 46 patients were 5.5 and 6.6 days, respectively [range, 2.0-25.6 days; coefficient of variation (CV), 74%]. For 25 patients where Tpot measurements were performed at two separate laboratories, there was a fair correlation (r = 0.74), but systematic differences were detected suggesting that the lack of agreement was not simply due to intratumoral variation. To date, 30 patients remained disease free, while 8 patients had pelvic failure and 9 patients developed distant metastases as the first failure site (1 patient developed both at the same time). In univariate analysis, the only significant prognostic factor for disease-free survival was tumor size (p = 0.004). A short Tpot (or high LI) and long overall treatment time (OTT) were weakly associated with poorer disease-free survival, although not statistically significant (1/Tpot, p = 0.14; LI, p = 0.23; OTT, p = 0.04). Age, FIGO stage, hemoglobin level, S-phase fraction, DNA ploidy, and Ts were not associated with disease-free survival. Multiple regression analysis was not performed because of the relatively small number of patients and short follow-up.

CONCLUSIONS

Tpot values determined with current techniques by different laboratories cannot be used interchangeably for the purpose of therapy decisions. Vigorous quality assurance and standardization of the laboratory procedures and analysis methods are important to reduce interlaboratory variation. In this uniformly treated group of patients with cancer of the uterine cervix, traditional clinical prognostic factors remain the most important. Preliminary data suggest that the flow cytometry-determined Tpot and labeling index predict for disease-free survival, although a larger number of patients with longer follow-up is required to assess the true prognostic significance of these assays and to determine if their effect is independent of other clinical factors.

The effect of combining recombinant human tumor necrosis factor-alpha with local radiation on tumor control probability of a human glioblastoma multiforme xenograft in nude mice

PURPOSE

To evaluate the antitumor activity of recombinant human tumor necrosis factor-alpha (rHuTNF-alpha) on a human glioblastoma multiforme (U87) xenograft in nude mice, and to study the effect of combining rHuTNF-alpha with local radiation on the tumor control probability of this tumor model.

METHODS AND MATERIALS

U87 xenograft was transplanted SC into the right hindleg of NCr/Sed nude mice (7-8 weeks old, male). When tumors reached a volume of about 110 mm3, mice were randomly assigned to treatment: rHuTNF-alpha alone compared with normal saline control; or local radiation plus rHuTNF-alpha vs. local radiation plus normal saline. Parameters of growth delay, volume doubling time, percentage of necrosis, and cell loss factor were used to assess the antitumor effects of rHuTNF-alpha on this tumor. The TCD50 (tumor control dose 50%) was used as an endpoint to determine the effect of combining rHuTNF-alpha with local radiation.

RESULTS

Tumor growth in mice treated with a dose of 150 micrograms/kg body weight rHuTNF-alpha, IP injection daily for 7 consecutive days, was delayed about 8 days compared to that in controls. Tumors in the treatment group had a significantly longer volume doubling time, and were smaller in volume and more necrotic than matched tumors in control group. rHuTNF-alpha also induced a 2.3 times increase of cell loss factor. The administration of the above-mentioned dose of rHuTNF-alpha starting 24 h after single doses of localized irradiation under hypoxic condition, resulted in a significant reduction in TCD50 from the control value of 60.9 Gy to 50.5 Gy (p < 0.01).

CONCLUSION

rHuTNF-alpha exhibits an antitumor effect against U87 xenograft in nude mice, as evidenced by an increased delay in tumor growth as well as cell loss factor. Also, there was an augmentation of tumor curability when given in combination with radiotherapy, resulting in a significantly lower TCD50 value in the treatment vs. the control groups.

Can measurements of potential doubling time (Tpot) be compared between laboratories? A quality control study

The purpose of this study was to investigate the reproducibility of potential doubling time measurements of human tumors in different laboratories and to distinguish which steps in the measurement procedure were subject to the greatest variation. This was achieved by comparing measurements on the same source material in two different laboratories in which three aspects of the technique were separately studied, namely, preparation and staining of the nuclear suspensions, running the samples on the flow cytometer (FCM), and analyzing the two-parameter FCM data. This involved exchange between the two centers of fixed tumor material, stained nuclear suspensions, and FCM data on floppy disks. The analysis step was found to be the least variable step. For DNA synthesis time, Ts, and the labeling index, LI, the coefficients of determination (R2) ranged from 92% to 95.4%. A small systematic bias was observed, with one center measuring approximately 15% higher values for both LI and Ts. Different criteria for window placements were found to be a contributing factor. Variations in the FCM step were approximately equal to those for analysis, with no systematic deviations. Variations for the preparation and staining step were the largest (R2 = 60.5% and 38.1% for LI and Ts, respectively). However, this step was the only one subject to intratumoral variability, which was the largest contributing factor to the variations observed. In addition, however, LI was on average 41% higher in one center compared to the other, resulting in a systematic bias. Differences in the level of green fluorescence of the labeled cells implicated antibody differences as a possible cause. The variations found here for the three procedural aspects were significantly smaller than variations observed between tumors, a requirement for a predictive assay. Suggestions for implementation of quality control procedures include objective (computer-assisted) data analysis on two-parameter histograms and optimization of antibody combinations.

Insulin-like growth factor-1 is not mitogenic for the Walker-256 carcinosarcoma

This study was designed to determine whether intravenous infusion of recombinant human insulin-like growth factor 1 (IGF-1) stimulates tumor growth. In order to determine the potential interaction between nutrition and IGF-1 administration the study was conducted in fasting rats and during continuous feeding by total parenteral nutrition. Tumor cell cycle kinetics including labeling index, DNA synthesis time, cell cycle time in Go/G1, and G2/M in the total cell cycle, and potential doubling time were determined by flow cytometry after in vivo pulse labeling the rats bearing the Walker-256 Carcinosarcoma with 5'-bromo-2'-deoxyuridine (BrdUrd). The results show that IGF-1 treatment has no significant effects on the proliferative characteristics of the tumor model regardless of the feeding status of the animal. This study provides preliminary cell-cycle kinetics data on the short-term effect of IGF-1 on tumor growth. Failure to show a significant effect of IGF-1 on the proliferative characteristics of the tumor suggests that IGF-1 may be given to cancer patients in amounts sufficient to promote weight gain without deleterious stimulation of tumor proliferation.

Kinetics of cell labeling and thymidine replacement after continuous infusion of halogenated pyrimidines in vivo

PURPOSE

Iododeoxyuridine (IdUrd) is a halogenated pyrimidine which has been recognized as a clinical radiosensitizer. It is generally agreed that the extent of radiosensitization correlates with the degree of thymidine substitution in DNA. Controversy exists regarding the optimal administration schedule to achieve maximum radiosensitization. To obtain more information relating to this problem, we present experiments on an in vivo human tumor xenograft continuously exposed to a fixed serum concentration of halogenated pyrimidines so as to study the kinetics of cell labeling and thymidine replacement.

METHODS AND MATERIALS

Human colon tumor (HCT-116) cells were injected subcutaneously into nude mice. After 10 days, most animals (> 90%) developed measurable tumor nodules with a volume doubling time of 5 +/- 1 days. Once the tumors reached a cross-sectional area of 0.25-0.30 cm2, miniosmotic pumps were implanted to deliver a dose of 100 mg/kg/day of IdUrd by continuous infusion. After an IdUrd exposure time of 1-7 days, blood and tumor tissue were collected.

RESULTS

The steady state serum IdUrd concentration was 0.95 +/- 0.1 microM, which is a clinically relevant concentration for a prolonged continuous intravenous infusion. The tumor cell potential doubling time (Tpot) was 25 +/- 2 h. The percent IdUrd thymidine replacement and the fraction of cells labeled, followed exponential saturation kinetics with a halflife of 33 +/- 9 and 27 +/- 2 h, respectively. After 5 days of exposure (congruent to 5 x Tpot), the thymidine replacement in tumor cells was 2.0 +/- 0.2% and the fraction of tumor cells labeled was 94 +/- 1%. Immunohistochemical staining of IdUrd labeled tumor tissues showed an exposure dependent gradient of cellular labeling that was initially highest in regions close to blood vessels. After 4 days of exposure at 100 mg/kg/day, there was an increase in the fraction of cells in G(0) + G1 and a decrease in the S phase population, suggesting a block between G1 and S phase.

CONCLUSION

We conclude that the in vivo kinetics of IdUrd thymidine replacement and fraction of cells labeled after continuous exposure followed exponential saturation kinetics with a halflife of approximately the potential doubling time of the tumor cell population. Simple modeling suggests that some form of prolonged, or briefly interrupted, continuous infusion should be considered for clinical administration because such schedules would leave fewer cells unsensitized than shorter infusions would. Even 10% of unlabeled clonogenic cells could explain the lack of dramatic clinical successes with IdUrd or BrdUrd sensitization.

Simultaneous cytokinetic measurement of aneuploid tumors and associated diploid cells following continuous labelling with chlorodeoxyuridine

Cells from a murine tumor, MCa-K, were continuously labelled with the thymidine analogue chlorodeoxyuridine (CldUrd) and analyzed by bivariate flow cytometry in order to measure the growth fraction (GF) and potential doubling time (Tpot) of both the DNA-aneuploid tumor cells and the associated DNA-diploid cells. MCa-K has a DNA index of 1.7, rendering two, partially overlapping, populations observable with labelled and unlabelled cells in each population. The data from these tumors may be divided into three regions of differing DNA content, with one region containing a pure DNA-diploid population, a second region with both cell types, and a third region including only DNA-aneuploid cells. Equations are presented to characterize the fractions of labelled cells in each region as a function of labelling time and cell type, thereby permitting estimation of the proliferative properties of the populations. These equations include the possibility that DNA-aneuploid cells cease cycling both in G1 and in S phase to account for the observed numbers of unlabelled cells with S phase contents. The estimated value of Tpot of the DNA-diploid cells is 126.0 h with a GF of 42%, while that of the DNA-aneuploid cells is 36.9 h with a GF of 69%. It is also estimated that between 2% and 6% of all DNA-aneuploid cells starting DNA synthesis cease cycling, leading to 25% of the cells having an S-phase DNA content being noncycling.

Double labelling to obtain S phase subpopulations: application to determine cell kinetics of diploid cells in an aneuploid tumour

We studied the cell kinetics of the murine mammary carcinoma MCa-K using iododeoxyuridine (IdUrd) and chlorodeoxyuridine (CldUrd) given at different times as independently detectable labels of S phase cells. The presence of IdUrd and CldUrd, and the amount of DNA were measured by three-colour flow cytometry making it possible to define three subpopulations within S phase and to measure the progression through the cell cycle during the time following labelling. In DNA histograms of these subpopulations, the diploid and aneuploid cells (which had a DNA index of 1.7) are essentially completely separated. From appropriate combinations of cells labelled with IdUrd only, CldUrd only, or both, it was possible to construct separate DNA distributions for the labelled diploid and aneuploid cells at the times of administration of each label. The kinetics of the diploid and aneuploid cells could be calculated for individual tumours from these two time points without having to make corrections for the presence of the second population. The diploid and aneuploid populations had indistinguishable S and G2 + M phase durations, T(S) and T(G2 + M), of about 9 and 2 h; however, the potential doubling time values for the aneuploid and diploid populations were 30.2 and 101.2 h respectively.

Intratumoral heterogeneity of S phase transition in solid tumours determined by bromodeoxyuridine labelling and flow cytometry

Cell kinetics of human renal cell carcinomas xenotransplanted into nu/nu mice were analysed using the bromodeoxyuridine (BrdUrd) labelling method. Tumours were removed 0.5-14 h after injection of the BrdUrd solution. The tumour cells were stained with fluorescein isothiocyanate conjugated anti-BrdUrd antibodies and propidium iodide (DNA content). From the flow cytometry data the relative movement was calculated. Relative movement data of variable intervals after BrdUrd labelling were subjected to a fit procedure using log-normal distributions for S phase transition (T(s)). The log-normal distributions were modified by inflation factors in order to get extremely asymmetric distributions. The best fits to the experimental data were obtained using wide asymmetric T(s) distributions, indicating that progression through S phase in solid human tumours is considerably heterogeneous. This implies that the potential doubling time (T(pot)) is longer than calculated from a single measured relative movement value obtained a few hours after BrdUrd labelling.

Flow cytometric BrdUrd-pulse-chase study of heat-induced cell-cycle progression delays

The flow cytometric, bromodeoxyuridine (BrdUrd)-pulse-chase method was extended by analysing five kinetic parameters to study perturbed cell progression through the cell cycle. The method was used to analyse the cell-cycle perturbations induced by heat shock. Exponentially growing, asynchronous Chinese hamster ovary (CHO) cells were pulse labelled with BrdUrd and simultaneously heated at 43 degrees C for 5, 10 or 15 min. The cells were then incubated in a BrdUrd-free medium and, at various times thereafter, were prepared for flow cytometry. Five compartments (BrdUrd-labelled divided and undivided, and unlabelled G1, G1S, and G2) were defined in the resulting dual-parameter histograms. The fraction of cells and the mean DNA content, when appropriate, were calculated for each compartment. The rates of cell-cycle progression were assessed as time-dependent changes in the fraction of cells in a given compartment and/or the relative DNA content of cells within a given compartment. Linear regression analysis of the data revealed two distinct modes of alteration in cell progression: 1 a delay in cell transit (either out of or into a given compartment), and 2 a decrease in the rate of cell transit. Hyperthermia produced a delay in the exit of cells from the G1 compartment of approximately 16 min per minute of heat at 43 degrees C with no threshold. In contrast, the delay in the exit of cells from all other compartments showed a threshold of from 3 to 5 min at 43 degrees C. Above this threshold the delay in exit of cells from the BrdUrd-labelled, undivided compartment was approximately 25 min per minute of heat at 43 degrees C. The more complex dose-response function of this latter compartment may reflect the fact that it includes two cell-cycle phases, S and G2 + M. The decrease in the rate of transit out of G2 for cells heated in G2 was significantly larger than that for any other compartment, consistent with previous studies, which showed a G2 accumulation following hyperthermia. These results indicate that heat exposure induces very complex alterations in cell-cycle progression and that this flow cytometric method offers a straightforward approach for observing such alterations.

Determining Tpot in heterogeneous systems: a new approach illustrated with multicell spheroids

Like many tumors, multicell spheroids from Chinese hamster V79-171b fibroblasts display karyotypic heterogeneity as they enlarge. This creates significant problems for analysis of univariate DNA content histograms of cells from spheroids, and even for bivariate bromodeoxyuridine (BrdUrd)/DNA flow histograms. While attempting to routinely measure spheroid cell kinetics with the latter approach, a simple alternative that overcomes many of the inherent problems emerged. The exit rate of BrdUrd-labelled cells from the S-phase compartment(s), determined using standard DNA analysis software, is used to define the duration of S-phase and ultimately the potential doubling time of the clonogenic cell population. This approach appears to offer several advantages over the conventional "relative movement" technique for heterogeneous samples, particularly since the subjective distinction between labelled/divided tetraploid G1 cells vs. labelled/undivided diploid G2 is no longer required. Further, the technique avoids some potential artifacts that might be expected for heterogeneous tumors where cell subpopulations proliferate with quite different cell kinetics.

On the measurement of cytokinetics by continuous labeling with bromodeoxyuridine with applications to chick wing buds

The cytokinetic properties, specifically the phase-transit times, TG1, TS, and TG2+M, of chick wing bud cells were estimated using data obtained from continuous labeling of stage 20 embryos with bromodeoxyuridine (BrdUrd). The presence of BrdUrd was detected with monoclonal antibodies, and the amount of DNA in the cells was determined with propidium iodide. The fraction of cells in each cell cycle phase, the fraction of labeled cells, and the relative movement, a measure of the mean DNA content, of all labeled cells were evaluated using bivariate flow cytometry at successive times following introduction of the label. Equations are presented to describe the fraction of unlabeled cells in G2 + M, which gives a direct estimate of TG2+M; the fraction of all labeled cells, which can then be used to estimate TG1; and, finally, the relative movement, which provides an estimate of TS. Thus, the data measured in these experiments together provide estimates of the progression through the cell cycle of limb mesoderm cells.