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.

Proliferation kinetics of recruited cells in a mouse mammary carcinoma

Solid tumors contain populations of proliferating (P) and quiescent (Q) cells. Shifting between these populations occurs continuously and cells are recruited from quiescence to proliferate (Q-->P) as a result of exogenously applied or endogenous cell depleting stimuli. Direct measurements of the proliferation kinetics of these Q-->P cells in solid tumors are difficult to make because of the much larger percentage of P-cells. In order to specifically analyze the kinetics of the Q-->P cells, double thymidine analogue labeling was used. This was accomplished by first labeling in vivo all of the P-cells in MCaK tumors using continuous exposure to chlorodeoxyuridine (CldUrd) administered by a minipump over 21 h. About 75% of the aneuploid cells are P-cells based on CldUrd labeling. At different times after the pumps were removed, the tumors were pulse-labeled with iododeoxyuridine (IdUrd) and harvested 6 h later. A 3-color flow cytometry assay was used to simultaneously and independently analyze CldUrd and IdUrd incorporation, as well as DNA content. The Q-->P cells were identified as having only been labeled with IdUrd. The length of their S-phase was calculated from the movement of the Q-->P cells during the 6 h after IdUrd labeling. The results showed the length of S-phase for the recruited cells to be slightly, but significantly, longer than the length of S-phase for the total cells (11 h versus 9 h, respectively). Thus, the recruited cells appear to have slightly slower kinetics than the proliferating cells in the absence of a perturbing stimulus such as radiotherapy or chemotherapy.

Modulation of target enzyme associated with the action of antifolates

The cytotoxicity and molecular effects of antifolate thymidylate synthase inhibitor, ICI-D1694, against human ileocecal carcinoma, were evaluated. The drug concentration for 50% inhibition of cell growth by ICI-D1694 is 73 nM and 3 nM following 2 hr and 72 hr exposure, respectively. The drug induces high level of DNA single strand breaks in a time dependent manner, but subsequent to maximum inhibition of thymidylate synthase. Drug effects can be reversed by thymidine and leucovorin at > 1 microM concentrations. Leucovorin action is primarily at the cell membrane level, competing with the transport and activation of ICI-D1694. Thymidine, however, exerts its competitive effect primarily at the level of thymidylate synthase.

Calculating potential doubling time using monoclonal antibodies specific for two halogenated thymidine analogues

PURPOSE

A new flow cytometric technique that allows for two-incorporated thymidine analogues to be measured simultaneously and independently has been used to improve the accuracy of in vivo cell kinetic estimates, i.e., the length of S-phase (TS) and potential doubling time (Tpot).

METHODS AND MATERIALS

The analogues chlorodeoxyuridine and iododeoxyuridine were injected at different times into mice bearing the mouse mammary tumor MCaK. At different times after labeling, the tumors were harvested and prepared for three color flow cytometric analysis of DNA, chlorodeoxyuridine, and iododeoxyuridine. Control experiments showed that similar estimates of Tpot were obtained from each label when administered singly, or as staggered pulses. Comparisons were made between TS and Tpot calculated from a single label (single point), from the averaged result of the two labels from the same tumor (two point-ave), and from the simultaneous nonlinear fitting of the measured parameters from the two labels, from the same tumor (two point-fit). These estimates of TS and Tpot were then compared to reference values obtained by fitting the pooled measured parameters from all the tumors, that were labeled for different periods of time.

RESULTS

While all of the methods resulted in similar mean estimates of TS and Tpot that were close to the reference values, the fewest assumptions, and the least variability in the results, were obtained using the two point-fit data.

CONCLUSION

The estimation of Tpot using two thymidine analogues is more accurate than that obtained from a single label.

Effect of caloric restriction on aflatoxin B1-induced DNA synthesis, AFB1-DNA binding and cell proliferation in Fischer 344 rats

Young adult male Fischer rats maintained on a reduced calorie diet (60% of ad libitum food consumption) for 6 weeks showed a decrease in the binding of aflatoxin B1 (AFB1) to hepatic or renal nuclear DNA and a reduction of AFB1-induced hepatocellular damage. Repeated dosing of rats with AFB1 resulted in the inhibition of hepatic and renal DNA synthesis measured by [3H]thymidine incorporation. However, the rate of DNA synthesis was greater in ad libitum (AL) rats than in calorically restricted (CR) animals. Three days after AFB1 dosing, the rate of DNA synthesis had recovered to the control level. Cell cycle analyses measured by a flow cytometric method on kidney cells of both AL and CR rats showed that there were no significant changes in cell populations in the S phase between these two groups of rats. AFB1 inhibited the cell proliferation on an average of 33%. The restoration of the cell proliferation in kidney cells was found on the third day after AFB1 dosing. The rate of the regenerative cell proliferation was found to be slightly greater in AL rats than in CR animals. The AFB1-induced regenerative DNA synthesis in both liver and kidney was retarded by CR.

[Saponins in the fruit pedicels of Panax notoginseng (Burk.) F.H. Chen (continue)]

Six saponins were isolated from the fruit pedicels of Panax notoginseng. Five of them were identified as gypenoside-XVII, -XV, ginsenoside-Rb1, and notoginsenoside-Fc, -Fa on the basis of chemical methods, spectroscopic analysis and comparison with authentic standards. Quantitative determination of the major saponins in fruit pedicels from the plant was made by thin layer chromatography-densitometry.

[Saponins in fruits pedicels of Panax notoginseng (Burk.). F.H. Chen]

Six saponins were isolated from the fruit pedicels of Panax notoginseng for the first time. They were identified as ginsenoside-Rc, -Rb3, -Re, notoginsenoside-Fe, -R1 and gypenoside IX by chemical and spectroscopic analysis.

Overexpression of the c-erbB-2/neu–encoded p185 protein in primary lung cancer

The c-erbB-2/neu gene encodes a transmembrane protein of 185 kDa (p185) with tyrosine kinase activity and extensive sequence homology to epidermal growth factor receptor. Amplification and overexpression of the c-erbB-2/neu gene has been shown in certain human tumors and is postulated to be important in human carcinogenesis. High levels of expression of the c-erbB-2/neu gene have been reported in non-small-cell lung cancer (NSCLC) cell lines and primary tumors from the United States. Since geographical and cultural factors may contribute to the development of certain types of cancer, we examined p185 examined p185 expression in 120 tumors from Chinese patients with lung cancers of different cell types and used immunohistochemical staining to determine the extent and general significance of p185 expression in human primary lung cancer. Our results demonstrate that 58.8% of the NSCLCs expressed p185 and that expression of p185 was observed only in NSCLC and not in small-cell lung cancers. Thirty-three of 41 adenocarcinomas and 24 of 55 squamous cell carcinomas among the NSCLCs examined were found to express p185 at levels different from those of normal lung. For the squamous cell carcinomas, p185 expression was correlated with lymph node metastasis (P less than 0.01), but for the adenocarcinomas, it was not (P greater than 0.05). In addition, expression of p185 in NSCLC was significantly more frequent in patients in advanced clinical stages. Our findings indicate that p185 expression is a frequent event and a general phenomenon in NSCLC and is correlated with poor clinical prognostic indicators, suggesting that expression of p185 may be of potential prognostic importance in NSCLC.

Cytogenetic studies on a human rectal carcinoma cell line (HR-8348)

Cytogenetic properties of a human rectal carcinoma cell line (HR-8348) established in China are described. The early (29th passage) and late (93rd passage) passage cells were used for chromosome analysis. HR-8348 was found to have an essentially triploid karyotype. This distribution of chromosome numbers was rather dispersed in early passage, whereas it was concentrated in the 65-70 range in late passage. G-banded karyotype analysis also showed that the numerical distribution of chromosomes was dispersed in early passage and was associated with more abnormal chromosomes. In late passage, the numerical distribution became more stable and the number of abnormal chromosomes was reduced. In 60 metaphases analyzed, 10 marker chromosomes were found. The frequencies of M1, M2 and M3 were 100% in both early and late passage cells. The morphological characteristics of these marker chromosomes and their possible origin and role in the pathogenesis of colorectal carcinoma are discussed.

Cytogenetic studies on peripheral lymphocytes of members from two multiple familial polyposis coli families

Cytogenetic studies were carried out on peripheral lymphocytes of 30 members from two typical familial polyposis coli (FPC) families. It was found that, under low folic acid culture conditions, the chromosome aberration rate of FPC family members (10%) was much higher than that of the control group (2.3%). No significant difference in SCE was found between the two groups. We suggest that the chromosome aberration rate under certain conditions may be used as a parameter for the early detection of FPC in certain FPC families. The analysis of fragile sites sensitive to low folic acid in FPC family members revealed that besides the significant increase of 3p14, which is frequently seen in tumor patients, other unique sites (1p22, 1p32 and 6q21) were also present in most of the FPC patients. Fragile sites 1p22, 1p32 and 6q21 are located near certain well known oncogene loci; thus, they may have something to do with the pathogenesis of FPC. The actual relationship between these fragile sites and FPC remains to be elucidated.

Green tea extract inhibits nucleoside transport and potentiates the antitumor effect of antimetabolites

The present study provides evidence that green tea extract (GTE), consisting of polyphenol components, is a highly active nucleoside transport inhibitor. GTE markedly inhibited radiolabeled thymidine and uridine transport in mouse leukemia L1210 cells, with IC50 values of 3.2 and 8.0 mumol/L, respectively. GTE blocked the rescue effect of exogenous nucleosides and enhanced the cytotoxicity of AraC and MTX to L1210 cells and human hepatoma BEL-7402 cells. GTE markedly potentiated the inhibitory effect of AraC on leukemia L1210 and P388 in mice. These results indicate that GTE is potentially useful when combined with antimetabolites in cancer chemotherapy.

Some observations on the localization of mitomycin C-induced aberrations in human lymphocytes

Actively cycling human lymphocytes were treated with mitomycin C for 1 h (1.4 micrograms/ml) and then grown in medium containing 10 micrograms/ml bromodeoxyuridine. Serial 5-h colcemid accumulation samples were taken up to 35 h and the air-dried methaphase spreads stained for replication banding. A complete cell-cycle subphasing analysis was made, and classified cells scored for all categories of chromatid-type aberrations and their location. In spite of the high dose which produced massive delay and cycle perturbation, there was no evidence for selective lethality of early-S cells, in fact such cells were in excess. Extreme localization of aberrations to late-replicating (mostly centromeric) regions was found at all subphases and in pre-S cells. This rules out 'localization by default' as an explanation for the observed preferential occurrence of 'break points' in these regions. The frequency of incomplete intrachanges, low in late S, rises dramatically in early S to become maximal in pre-S cells.

Comparison between protracted and conventional dose rates of irradiation on the growth of the Bp8 mouse ascites sarcoma

Four days after inoculation, in vivo growing Bp8 mouse ascites sarcoma was irradiated with 1.75, 2.5 and 5 Gy at a dose rate of 0.0185 Gy/min. The results were compared with those obtained previously at a dose rate of 1.33 Gy/min. Using flow-cytometry and the mitotic index, the total number of tumour cells and the proportion of cells in the various parts of the cell cycle were determined up to 10 days after irradiation. In addition, from sequential analyses of the total number of cells in the various compartments of the cell cycle, the flow of cells through cell cycle was calculated. The total number of tumour cells at the plateau phase of growth, the mitotic index and flow calculations indicated that protracted irradiation was more effective than short-time irradiation following 2.5 Gy; no differences were found following 1.75 Gy, and a lesser effect following 5 Gy. While the cells during protracted irradiation were effectively blocked in G2 and in split-dose experiments a good repair capacity has been demonstrated, redistribution of cells in the cell cycle can apparently not explain the results. Induction of repair, dependent both on dose rate and on total dose, may explain the higher efficiency of protracted irradiation.

Repair in irradiated ascites tumour cells growing in vivo. An investigation of split doses related to cell cycle

Split dose irradiation with 2 X 2.5 Gy at intervals of 3 to 48 h was compared with the effect of a single irradiation with a 5 Gy dose in Bp8 mouse ascites sarcoma growing in vivo. The total number of cells and, using rapid-flow cytofluorometry, the proportions of cells in the various parts of the cell cycle were determined up to 10 days after irradiation. In addition, from sequential analyses of the total number of cells in the various compartments of the cell cycle, the flow of cells through the cell cycle was calculated. As judged by the growth in the total number of cells, a rapid repair of at least 20 per cent per h up to 3 h is followed by a slow repair of about one per cent per h during the following 45 h. The proportion of cells in the cell cycle following the conditioning dose did not differ enough to expect a significant influence on the mean radiation sensitivity of the cell population. At split time intervals of 12 to 48 h, after a transient early increase of the flow of cells through the cell cycle, the flow of cells was markedly reduced in all parts of the cell cycle with a maximum 24 to 48 h after the second dose of irradiation. This increase in the cell cycle time was not found following single dose irradiation and may influence the repair of potentially lethal cell damage.

Growth kinetics of Bp8 mouse ascites sarcoma after single dose whole body irradiation. I. Analysis of the relative and total numbers of cells in various parts of the cell cycle

The effects of irradiation on the growth of the Bp8 mouse ascites sarcoma were analysed following doses of 1.75, 2.5, 5.0 and 8.0 Gy. From the total number of cells and the percentage of cells in G1, S-phase, G2 + M as measured by flow cytofluorometric DNA analysis and the mitotic index the total number of cells in the various parts of the cell cycle was estimated. After an initial delay in the increase in the cell numbers during the period of rapid growth the total number of cells shows a dose dependent decrease at the plateau stage of the ascites growth. This dose relationship is characterized by a shoulder type of curve with a D0 of about 6.5 Gy and Dq of about 2 Gy. This decrease in the total number of cells is caused by a decreasing number of G1, S-phase and mitotic cells while G2 cells generally remain at unchanged levels. This behaviour of the G2 cells reflects the preference of long-lasting blocking events in G2 of the cell cycle but may also indicate specific regulating processes linked to this type of cell. The ratio between the number of mitotic and G2 cells also decreases in a dose dependent way and is a sensitive indicator for irradiation effects even below the lowest dose (1.75 Gy) used in the present experiments.

Proliferation kinetics and specific behaviour of G2 cells of the Bp8 mouse ascites sarcoma in vivo

Growth characteristics of the Bp8 ascites sarcoma were investigated by means of evaluation of total cell number, the cellular DNA content, the mitotic index and the percentage of dead cells. Following intraperitoneal inoculation of 18 x 10(6) cells into NMRI mice a plateau level of about 1400 x 10(6) cells was reached after 7 days followed by a daily decline of 5 per cent up to day 14, the terminal stage of life. Based on the increase of the cell number and the distribution of cells in the cell cycle the flow rate through and the duration of the various parts of the cell cycle were calculated. Generally, the durations of all phases of the cell cycle including mitosis increased with age, most markedly after day 8 when the durations tended to become infinite. At the plateau phase the total number of G1, S-phase and mitotic cells decreased significantly while G2 cells remained at a constant level. This finding may be of interest in view of the concept of ascites tumour cells behaving as a regulated cell system.

Behaviour of the Bp8 mouse ascites sarcoma after partial body irradiation

Mice bearing the Bp8 mouse ascites sarcoma were 4 days after inoculation irradiated with 2.5, 5 and 8 Gy. By shielding the head and the upper part of the thorax the mice survival, compared with whole body irradiation, was markedly prolonged and the behaviour of the ascites tumour could be evaluated up to 30 days after inoculation. While about 10 days after irradiation the total number of tumour cells started to decrease and amounted to only 4 per cent 20 days later, the ascites volume increased up to 30 ml. Using flow-cytometric cellular DNA analysis, the proportions of cells in the various parts of the cell cycle were determined. After an initial G2 blockage, a partial blockage with an increase proportion of G2 cells was found up to 20 days after inoculation. While the total number of G1, S-phase and mitotic cells started to decrease on day 10, the total number of G2 cells was independent of the dose and was constant up to day 18. This behaviour may indicate specific regulating processes linked to G2 cells.

Growth kinetics of Bp8 mouse ascites sarcoma after single doses of whole body irradiation. II. Analysis of the progression of cells through the cell cycle

Bp8 ascites sarcoma cells growing in vivo were whole body irradiated with doses of 1.75 to 8 Gy. The inflow and outflow rates of cells in the various compartments of the cell cycle were estimated on the basis of sequential analysis of the total number of cells and from the proportion of cells in G1, S-phase, G2 and M. The flow through the compartments was calculated from these data and from the sizes of the cell pools. The durations of the mitotic delay, the G1-depletion and the early G2 blockage were linearly related to the dose. After release of the mitotic division delay the accumulation rate of cells in M and G1 decreased linearly with the dose; for G2, plateau values for the accumulation rate were found after 2.5 Gy. The outflow rates from G2 and M after release of the G2 blockage showed a shoulder type of dose-response with a D0 of 2.5 Gy and a n value of 1.5. In addition to an increase in the duration of G2, generally responsible for the increase in the total cell cycle time at about 24 hours after irradiation and an increase in the duration of the S-phase up to 12 hours after irradiation, an early increase in the duration of G1 and M was observed.

Radiation therapy of nasopharyngeal carcinoma

Carcinoma of the nasopharynx is one of the most frequent malignant tumors in the southern parts of China. A total of 3 263 cases treated with irradiation in the course of the thirty years since the Liberation have been analysed retrospectively. The 5-year survival rate has risen from 27.7 per cent for cases treated during 1955 to 1960 to 54 per cent for those treated in 1973. The technique of irradiation is described, emphasizing the importance of suitable techniques for the treatment of the cervical lymph nodes. The value of elective irradiation of cervical regions not involved clinically is elucidated. Finally, the causes of failure of treatment are discussed.