Targeted disruption of the transition protein 2 gene affects sperm chromatin structure and reduces fertility in mice

During mammalian spermiogenesis, major restructuring of chromatin takes place. In the mouse, the histones are replaced by the transition proteins, TP1 and TP2, which are in turn replaced by the protamines, P1 and P2. To investigate the role of TP2, we generated mice with a targeted deletion of its gene, Tnp2. Spermatogenesis in Tnp2 null mice was almost normal, with testis weights and epididymal sperm counts being unaffected. The only abnormality in testicular histology was a slight increase of sperm retention in stage IX to XI tubules. Epididymal sperm from Tnp2-null mice showed an increase in abnormal tail, but not head, morphology. The mice were fertile but produced small litters. In step 12 to 16 spermatid nuclei from Tnp2-null mice, there was normal displacement of histones, a compensatory translationally regulated increase in TP1 levels, and elevated levels of precursor and partially processed forms of P2. Electron microscopy revealed abnormal focal condensations of chromatin in step 11 to 13 spermatids and progressive chromatin condensation in later spermatids, but condensation was still incomplete in epididymal sperm. Compared to that of the wild type, the sperm chromatin of these mutants was more accessible to intercalating dyes and more susceptible to acid denaturation, which is believed to indicate DNA strand breaks. We conclude that TP2 is not a critical factor for shaping of the sperm nucleus, histone displacement, initiation of chromatin condensation, binding of protamines to DNA, or fertility but that it is necessary for maintaining the normal processing of P2 and, consequently, the completion of chromatin condensation.

"Mitotic drive" of expanded CTG repeats in myotonic dystrophy type 1 (DM1)

In myotonic dystrophy type 1 (DM1), an expanded CTG repeat shows repeat size instability in somatic and germ line tissues with a strong bias toward further expansion. To investigate the mechanism of this expansion bias, 29 DM1 and six normal lymphoblastoid cell lines (LBCLs) were single-cell cloned from blood cells of 18 DM1 patients and six normal subjects. In all 29 cell lines, the expanded CTG repeat alleles gradually shifted toward further expansion by "step-wise" mutations. Of these 29 cell lines, eight yielded a rapidly proliferating mutant with a gain of large repeat size that became the major allele population, eventually replacing the progenitor allele population. By mixing cell lines with different repeat expansions, we found that cells with larger CTG repeat expansion had a growth advantage over those with smaller expansions in culture. This growth advantage was attributable to increased cell proliferation mediated by Erk1,2 activation, which is negatively regulated by p21(WAF1). This phenomenon, which we designated "mitotic drive" , is a novel mechanism which can explain the expansion bias of DM1 CTG repeat instability at the tissue level, on a basis independent of the DNA-based expansion models. The lifespans of the DM1 LBCLs were significantly shorter than normal cell lines. Thus, we propose a hypothesis that DM1 LBCLs drive themselves to extinction through a process related to increased proliferation.

The nuclear death domain protein p84N5 activates a G2/M cell cycle checkpoint prior to the onset of apoptosis

In contrast to extracellular signals, the mechanisms utilized to transduce nuclear apoptotic signals are not well understood. Characterizing these mechanisms is important for predicting how tumors will respond to genotoxic radiation or chemotherapy. The retinoblastoma (Rb) tumor suppressor protein can regulate apoptosis triggered by DNA damage through an unknown mechanism. The nuclear death domain-containing protein p84N5 can induce apoptosis that is inhibited by association with Rb. The pattern of caspase and NF-kappaB activation during p84N5-induced apoptosis is similar to p53-independent cellular responses to DNA damage. One hallmark of this response is the activation of a G(2)/M cell cycle checkpoint. In this report, we characterize the effects of p84N5 on the cell cycle. Expression of p84N5 induces changes in cell cycle distribution and kinetics that are consistent with the activation of a G(2)/M cell cycle checkpoint. Like the radiation-induced checkpoint, caffeine blocks p84N5-induced G(2)/M arrest but not subsequent apoptotic cell death. The p84N5-induced checkpoint is functional in ataxia telangiectasia-mutated kinase-deficient cells. We conclude that p84N5 induces an ataxia telangiectasia-mutated kinase (ATM)-independent, caffeine-sensitive G(2)/M cell cycle arrest prior to the onset of apoptosis. This conclusion is consistent with the hypotheses that p84N5 functions in an Rb-regulated cellular response that is similar to that triggered by DNA damage.

Simultaneous estimation of T(G2+M), T(S), and T(pot) using single sample dynamic tumor data from bivariate DNA-thymidine analogue cytometry

BACKGROUND

Estimating the duration of S phase (T(S) ) and the potential doubling time (T(pot) ) from a single time measurement of the movement of cells using bivariate cytometry is common. However, these estimates require an assumption of the duration of G2 + M (T(G2+M) ). Inspection of the measured dynamic quantities, relative movement [RM(t)], fractions of labeled divided and undivided cells (f(lu)(t) and f(ld)(t)) suggests that T(G2+M), T(S), and T(pot) can be determined simultaneously.

METHODS

An equation connecting the growth of the cell population, time, and the dynamic quantities was determined. The equation cannot be solved analytically, but accurate approximations can be used to find T(pot). From this result, the value of T(G2+M) can be determined from f(ld)(t), and T(S) can be determined from RM(t).

RESULTS

Kinetic parameters obtained from single time estimates using the new method compared to those obtained from the analysis of multiple time-point measurements of MCa-K and MCa-4 murine tumors are shown to be in close agreement. Moreover, estimates of T(G2+M) in MCa-4 tumors, treated with paclitaxel, provide extra information on the changes in T(G2+M). When applied to the rat R3327-G prostate tumor model following androgen ablation, a correlation analysis of the T(pot) values obtained by the new and previous single time-point methods demonstrates that the rank order from shortest to longest T(pot) values are largely preserved.

CONCLUSIONS

The new procedure makes direct estimation of T(G2+M) possible from single time-dynamic measurements. The results from previous studies on T(S) and T(pot) are largely unchanged, but extra information is now available.

Relationship of Ki-67 labeling index to DNA-ploidy, S-phase fraction, and outcome in prostate cancer treated with radiotherapy

BACKGROUND

Our purpose was to evaluate the relationship of Ki-67 labeling index (Ki67-LI) to deoxyribonucleic acid (DNA) ploidy, S phase fraction (SPF), other clinical prognostic factors, and clinical outcome for patients with prostate cancer treated by external beam radiotherapy.

METHODS

Tissue was retrieved from 42 patients who underwent transurethral resection of the prostate before treatment with external beam radiotherapy between 1987-1993. DNA histogram profiles were classified as diploid (diploid + near-diploid) and nondiploid (tetraploid + aneuploid). Immunohistochemical staining of Ki-67 by the MIB-1 monoclonal antibody was used to calculate Ki67-LI. Median patient follow-up was 62 months. Treatment failure was defined as two consecutive rises in serum prostate-specific antigen (PSA) or clinical evidence of disease recurrence.

RESULTS

The mean and median Ki67-LIs were 3.1 and 2.4, respectively (range, 0-12.4). Mean Ki67-LI values were significantly associated with higher stage, Gleason score, and pretreatment PSA. Nondiploid tumors had significantly higher Ki67-LIs, as did patients who failed radiotherapy over the follow-up period. SPF was not significantly correlated with Ki67-LI. As a categorical variable, the most significant relationships were seen when Ki67-LI was subdivided into thirds around the median (Ki67-LI </=1.5%, Ki67-LI >1.5-3.5%, and Ki67-LI >3.5%). This trichotomous variable correlated significantly with pretreatment PSA (P = 0.0008), tumor stage (P = 0.016), Gleason score (P = 0.024), and treatment failure (P = 0.0015), but not with DNA-ploidy (P = 0.15). In actuarial univariate analyses, Ki67-LI appeared to be a more significant predictor of patient outcome (P = 0.003) than DNA-ploidy (P = 0.035).

CONCLUSIONS

The Ki67-LI correlated with known prognostic factors such as pretreatment PSA, tumor stage, and Gleason score, and was also weakly related to DNA-ploidy. In comparison to DNA-ploidy, Ki67 LI seems to be a better correlate of treatment outcome.

Enhancement of radiosensitivity of wild-type p53 human glioma cells by adenovirus-mediated delivery of the p53 gene

OBJECT

The authors sought to determine whether combining p53 gene transfer with radiation therapy would enhance the therapeutic killing of p53 wild-type glioma cells. It has been shown in several reports that adenovirus-mediated delivery of the p53 gene into p53 mutant gliomas results in dramatic apoptosis, but has little effect on gliomas containing wild-type p53 alleles. Therefore, p53 gene therapy alone may not be a clinically effective treatment for gliomas because most gliomas are composed of both p53 mutant and wild-type cell populations. One potential approach to overcome this problem is to exploit the role p53 plays as an important determinant in the cellular response to ionizing radiation.

METHODS

In vitro experiments were performed using the glioma cell line U87MG, which contains wild-type p53. Comparisons were made to the glioma cell line U251MG, which contains a mutant p53 allele. Monolayer cultures were infected with an adenovirus containing wild-type p53 (Ad5CMV-p53), a control vector (dl312), or Dulbecco's modified Eagle's medium (DMEM). Two days later, cultures were irradiated and colony-forming efficiency was determined. Transfection with p53 had only a minor effect on the plating efficiency of nonirradiated U87MG cells, reducing the plating efficiency from 0.23 +/- 0.01 in DMEM to 0.22 +/- 0.04 after addition of Ad5CMV-p53. However, p53 transfection significantly enhanced the radiosensitivity of these cells. The dose enhancement factor at a surviving fraction of 0.10 was 1.5, and the surviving fraction at 2 Gy was reduced from 0.61 in untransfected controls to 0.38 in p53-transfected cells. Transfection of the viral vector control (dl312) had no effect on U87MG radiosensitivity. In comparison, transfection of Ad5CMV-p53 into the p53 mutant cell line U251 MG resulted in a significant decrease in the surviving fraction of these cells compared with controls, and no radiosensitization was detected. To determine whether Ad5CMV-p53-mediated radiosensitization of U87MG cells involved an increase in the propensity of these cells to undergo apoptosis, flow cytometric analysis of terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridinetriphosphate nick-end labeling-stained cells was performed. Whereas the amount of radiation-induced apoptosis in uninfected and dl312-infected control cells was relatively small (2.1 +/- 0.05% and 3.7 +/- 0.5%, respectively), the combination of Ad5CMV-p53 infection and radiation treatment significantly increased the apoptotic frequency (18.6 +/- 1.4%). To determine whether infection with Ad5CMV-p53 resulted in increased expression of functional exogenous p53 protein, Western blot analysis of p53 was performed on U87MG cells that were exposed to 9 Gy of radiation 2 days after exposure to Ad5CMV-p53, dl312, or DMEM. Infection with Ad5CMV-p53 alone increased p53 levels compared with DMEM- or dl312-treated cells. Irradiation of AdSCMV-p53-infected cells resulted in a further increase in p53 that reached a maximum at 2 hours postirradiation. To determine whether exogenous p53 provided by Ad5CMV-p53 had transactivating activity, U87MG cells were treated as described earlier and p21 messenger RNA levels were determined. Infection of U87MG cells with Ad5CMV-p53 only resulted in an increase in p21 compared with DMEM- and dl312-treated cells. Irradiation of AdSCMV-p53-infected cells resulted in an additional time-dependent increase in p21 expression.

CONCLUSIONS

These data indicate that adenovirus-mediated delivery of p53 may enhance the radioresponse of brain tumor cells containing wild-type p53 and that this radiosensitization may involve converting from a clonogenic to the more sensitive apoptotic form of cell death. Although the mechanism underlying this enhanced apoptotic susceptibility is unknown, the AdSCMV-p53-infected cells have a higher level of p53 protein, which increases further after irradiation, and this exogenous p53 is transcriptionally active. (ABSTRACT TRUNCATE

Resistance of differentiating spermatogonia to radiation-induced apoptosis and loss in p53-deficient mice

The effect of the p53 gene on the survival of mouse testicular cells was evaluated by analysis of degenerating and terminal transferase-mediated end labeling (TUNEL)-positive cells and the subsequent production of further differentiated progeny. In p53 null mice, in contrast to wild-type mice, radiation induced negligible levels of degenerating or TUNEL-positive differentiating spermatogonia within 24 h. This was correlated with higher production of differentiated progeny of the differentiating spermatogonia in p53 null mice. Contrary to the differentiating spermatogonia, the stem spermatogonia of p53 null mice produced fewer differentiated progeny after irradiation than did the stem cells of wild-type mice. We conclude that, because the degeneration and TUNEL positivity of the differentiating spermatogonia in mice of different genotypes were correlated with each other and were dependent on p53, this process is indeed apoptosis. In the differentiating spermatogonia, p53-dependent apoptosis accounted for the bulk of the loss of their progeny after irradiation. Furthermore, whereas the differentiating spermatogonia died by apoptosis that was dependent on p53, the stem spermatogonia, which are more radioresistant, did not.

Can we detect or predict the presence of occult nodal metastases in patients with squamous carcinoma of the oral tongue?

BACKGROUND

When to do a neck dissection as part of the surgical treatment for a patient with squamous carcinoma of the oral tongue is controversial, particularly when the primary can be resected without entering the neck. If the patient who is at high risk for having occult nodal disease in the neck can be identified, node dissection with the glossectomy could be justified. To better identify patients for this procedure, we correlated various tumor and patient factors along with preoperative diagnostic studies with the presence or absence of pathologically positive nodes in a group of patients who underwent node dissection.

METHODS

Ninety-one previously untreated patients with biopsy-proved squamous carcinoma of the oral tongue were prospectively studied. All patients had a glossectomy and neck dissection as their initial treatment. The pathology findings (ie, lymph nodes with squamous cancer) were correlated with many preoperative and intraoperative factors, and a statistical analysis was made.

RESULTS

The use of computed tomography and ultrasound was not better than the clinical examination in determining the presence or absence of nodal metastases. The best predictors were depth of muscle invasion, double DNA aneuploidy, and histologic differentiation of the tumor.

CONCLUSIONS

All patients with stage T2-T4 squamous cancers of the oral tongue should have an elective dissection of the neck. Patients with T1N0 cancer who have a double DNA-aneuploid tumor, depth of muscle invasion > 4 mm, or have a poorly differentiated cancer should definitely undergo elective neck dissection. Ultrasound and computed tomography are of little value in predicting which patients have positive nodes.

Supraadditive apoptotic response of R3327-G rat prostate tumors to androgen ablation and radiation

PURPOSE

Androgen ablation is often combined with radiation in the treatment of patients with prostate cancer, yet, the optimal sequencing and the mechanisms governing the interaction are not understood. The objectives were to determine if cell killing via apoptosis is enhanced when the combined treatment is administered and to define the relationship of changes in this form of cell killing to tumor volume growth delay.

MATERIALS AND METHODS

Dunning R3327-G rat prostate tumors, grown in the flanks of Copenhagen rats, were used at a volume of approximately 1 cc. Androgen ablation was initiated by castration, and androgen restoration was achieved with 0.5 cm silastic tube implants containing testosterone. 60Co was used for irradiation. The terminal deoxynucleotidyl transferase (TUNEL) histochemical assay was used to quantify apoptosis.

RESULTS

Tumors from intact and castrate unirradiated control rats had average apoptotic indices (percent of apoptotic cells) of 0.4 and 1.0%, respectively. The apoptotic index varied only slightly over time (3 h to 28 days) after castration (range 0.75-1.43%). Irradiation of intact rats to 7 Gy resulted in a peak apoptotic response at 6 h of 2.3%. A supraadditive apoptotic response was seen when castration was initiated 3 days prior to 7 Gy radiation, with peak levels of about 10.1%. When the radiation was administered at increasing times beyond 3 days after castration, the apoptotic response gradually diminished and was back to levels seen in intact rats by 28 days after castration. Tumor volume growth delay studies were consistent with, but not conclusive proof of, a supraadditive effect when the combination was used.

DISCUSSION

A supraadditive apoptotic response was seen when androgen ablation and radiation were used to treat androgen sensitive R3327-G rat prostate tumors. This supraadditive effect was dependent on the timing of the two treatments. Further studies are required to more fully define the optimal timing and administration of androgen ablation and radiation.

S phase determination in intact colonic crypts by histone H3 messenger RNA in situ hybridization and confocal microscopy

Proliferating cells have a restricted three-dimensional spatial distribution within the crypt, which is the proliferative unit of the colon. Accurate quantitative and spatial analyses of S phase cells in the colon have therefore been limited by histological techniques. To overcome these limitations, S phase cells in microdissected intact colonic crypts of control, modified-starved, and refed rats were labeled by histone H3 in situ hybridization and analyzed by confocal microscopy. High-resolution digital images of the crypt cell nuclei stained with cyanine nucleic acid and of the labeled S phase cells were produced from confocal microscopic optical crypt sections. The S phase labeling index (LI) per whole crypt significantly (P < 0.001) discriminated the proliferative differences between control, modified-starved, and refed rats and correlated (r = 0.92) with the LI determined from histological crypt sections of the same rats. The variance component of the LI attributable to differences between whole crypts, 0.44 (95% confidence interval, 0.38-0.51), was considerably smaller than that attributable to differences between histological crypt sections, 6.07 (95% confidence interval, 5.18-6.96). Confocal microscopy and histone H3 in situ hybridization of intact three-dimensional crypts enables precise in vitro quantitation and spatial analysis of the total and S phase crypt cells.

Enhanced radioresponse of paclitaxel-sensitive and -resistant tumours in vivo

Paclitaxel is a potent chemotherapeutic drug and also has the potential to act as a radioenhancing agent. The latter is based on its ability to arrest cells in the radiosensitive G2M phases of the cell cycle; the weight of supporting evidence is derived mainly from in vitro studies. Our previous in vivo experiments identified enhanced tumour radioresponse predominantly attributable to tumour reoxygenation occurring as a result of paclitaxel-induced apoptosis. The current study investigated whether paclitaxel enhanced the radioresponse of tumours which are insensitive to apoptosis induction, but exhibited mitotic arrest, and compared the degree and kinetics of the response to that in tumours which develop apoptosis. The mouse mammary carcinoma MCa-29 (apoptosis sensitive) and the squamous cell carcinoma SCC-VII (apoptosis resistant) were used. In addition, the study investigated whether paclitaxel affected normal skin radioresponse to determine if a therapeutic gain could be achieved. Paclitaxel enhanced the radioresponse of both types of tumours. In the SCC-VII tumour, radiopotentiation occurred within 12 h of paclitaxel administration coincident with mitotic arrest, where enhancement factors (EFs) ranged from 1.15 to 1.37. In MCa-29 tumour, the effect was greater, EFs ranging from 1.59 to 1.91 and occurred between 24 and 72 h after paclitaxel when apoptosis was the predominant microscopic feature of treated tumours and when tumour oxygenation was found to be increased. The acute skin radioresponse and late leg contracture response were essentially unaffected by prior treatment with paclitaxel. Therefore, by two distinct mechanisms, paclitaxel was able to enhance the radioresponse of paclitaxel-sensitive and -resistant tumours, but not the normal tissue radioresponse, thus providing true therapeutic gain.

Quiescence in R3327-G rat prostate tumors after androgen ablation

Androgen ablation is frequently used in conjunction with radiotherapy in the treatment of high-risk prostate cancer. Androgen ablation-induced cell kinetic changes could result in sub-additive (increased quiescence) or supra-additive (reduction in repopulation) interactions with radiotherapy. The cell kinetic changes were studied in R3327-G Dunning rat prostate tumors grown in vivo using double thymidine analogue labeling and flow cytometry, the terminal deoxynucleotidyl transferase-mediated nick end labeling assay for apoptosis, and measurements of tumor cell numbers. Tumors grown in intact and castrate male rats were continuously labeled for various periods of time with chlorodeoxyuridine and pulse-labeled with iododeoxyuridine 8 h before tumor removal. Androgen ablation resulted in a maximal reduction in labeling index (10 to 1.6%) and an increase in potential doubling time (Tpot; 6-42 days) within 3 days, which was related to a reduction in growth fraction (65% to <10%). In contrast, the length of S-phase was minimally altered (19 to 23 h). The response to androgen ablation involved little apoptosis and no necrosis, and Tpot was approximately the same as the tumor volume doubling time. Hence, the increase in Tpot was mainly the result of a shift to quiescence, and this shift occurred with minimal cell loss. Because quiescence is usually associated with radioresistance, these cell kinetic changes suggest that a sub-additive interaction may occur for some prostate cancers when androgen ablation and irradiation are given together.

The significance of DNA-ploidy and S-phase fraction in node-positive (stage D1) prostate cancer treated with androgen ablation

BACKGROUND

The prognostic significance of primary tumor DNA-ploidy and S-phase fraction (SPF) was evaluated in patients treated with androgen ablation for regionally localized node-positive prostate cancer.

METHODS

All patients were diagnosed with lymph node involvement by pelvic lymphadenectomy between 1984 and 1992 and were treated only with androgen ablation. Median follow-up was 45 months. Adequate material for DNA/nuclear protein flow cytometric analysis was available in 33 patients.

RESULTS

The tumors were classified as diploid in 11, near-diploid in 4, tetraploid in 10, and aneuploid in 8 cases. Grouping the patients by nonaneuploidy (diploid and near-diploid and tetraploid) and aneuploidy revealed actuarial 4-year disease progression rates of 14 and 48% (log-rank, P = 0.04), and overall survival rates of 100 and 61% (P = 0.008); however, biochemical progression (rising prostate-specific antigen profile) rates were similar at around 70%. In contrast, SPF was not significantly related to any of the endpoints tested. Several other potential prognostic factors were examined and none correlated significantly with disease progression or survival.

CONCLUSIONS

The biochemical progression rates for patients with nonaneuploid and aneuploid tumors were comparable and high, while the disease progression rates were higher and survival rates lower for those with aneuploid tumors. These data indicate that the lead time from biochemical to disease progression and death was shorter with aneuploidy. That these relationships were observed in such a small patient population attest to the strength of DNA-ploidy as a prognostic factor in this cohort.

Protection from procarbazine-induced testicular damage by hormonal pretreatment does not involve arrest of spermatogonial proliferation

Hormone treatments that suppress sperm production enhance the recovery of spermatogenesis after gonadal exposure to various cytotoxic agents. It has generally been assumed that the mechanism of protection involved an arrest of spermatogonial kinetics. To test this hypothesis critically, we examined spermatogonial kinetics and numbers in rats in which the completion of spermatogenesis was suppressed with a 6-week testosterone plus 17beta-estradiol treatment that protected the testis from procarbazine-induced damage. Histological examination showed that the numbers of A-aligned, intermediate, and B spermatogonia and preleptotene spermatocytes and their mitoses were unaffected by testosterone plus 17beta-estradiol treatment. Flow cytometric analysis of bromodeoxyuridine-labeled cells showed that the percentage of diploid cells undergoing DNA synthesis, the progression of B spermatogonia and preleptotene spermatocytes through S-phase, the division of intermediate and B spermatogonia, the entry of intermediate spermatogonia into their next S-phase as type B cells, and the progression of cells through meiotic prophase were either unchanged or very slightly increased. Thus, changes in spermatogonial numbers or suppression of their proliferation cannot account for protection of spermatogenesis from exposure to cytotoxic agents.

Cell kinetic analysis of intact rat colonic crypts by confocal microscopy and immunofluorescence

BACKGROUND & AIMS

Precise quantitative and spatial analysis of cell cycle-related biomarkers in colonic crypts is often vital for studies of colon carcinogenesis and cancer prevention. To overcome the limitations of histology, confocal laser microscopy of microdissected whole crypts was used to quantitate S phase and mitotic cells.

METHODS

Microdissected distal colonic crypts were studied in a modified rat starvation refeeding model. S phase cells were labeled in vivo with 5-bromodeoxyuridine. Mitotic cells were labeled with MPM2 (antibody to mitosis-specific epitope) and also assessed for chromatin morphology with propidium iodide. Sequential optical crypt sections, produced by confocal microscopy, were digitally imaged. S phase labeling indices per whole crypt were also compared with those derived by conventional immunohistochemistry.

RESULTS

S phase and mitotic cells were clearly discriminated without background staining. The labeled S phase cell number and fraction per whole crypt were significantly decreased with starvation and increased with refeeding. Variability in the labeling index between whole crypts analyzed by confocal microscopy was significantly smaller than between histological crypt sections. Consequently, the intervention contributed to 92.2% of the total variability of the labeling index in whole crypts but only to 59% of the variability in histological sections.

CONCLUSIONS

Major limitations of histology are overcome by crypt microdissection and confocal microscopic analysis. The total crypt cell population as well as labeled M phase and S phase cells can be imaged, localized, and quantitated with improved precision.

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.

Apoptosis and downstaging after preoperative radiotherapy for muscle-invasive bladder cancer

PURPOSE

To determine the relationship between pretreatment apoptosis levels and clinical-to-pathologic downstaging resulting from preoperative radiotherapy.

METHODS AND MATERIALS

Between 1960-1983, 338 patients were dispositioned to receive preoperative radiotherapy 4-6 weeks prior to radical cystectomy for muscle-invasive transitional cell carcinoma of the bladder. Of these, adequate hematoxylin and eosin stained tissue sections for morphologic analysis of apoptosis were available in 158 patients. These patients were treated to a median dose of 50 Gy at 2 Gy per fraction. Median follow-up was 90 months. The apoptotic index (AI) was calculated from the ratio of the number of apoptotic cells divided by the total counted and multiplied by 100. A minimum of 500 cells were counted from each patient.

RESULTS

The average AI for the whole group (n = 158) was 2.0 +/- 1.3 (+/- SD), with a median of 1.8. The association of AI to clinical stage was significant with AI averages of 1.8 for Stage T2 (n = 56), 1.9 for T3a (n = 51), and 2.4 for T3b (p = 0.038, Kendall Correlation). The relationship of AI to radiotherapy response also was significant with an average of 2.2 for those who were downstaged (n = 103), 1.9 for those in whom the stage remained unchanged (n = 20), and 1.7 for those who were upstaged (n = 35, p = 0.054, Kendall Correlation). The other significant correlations with AI were for the factors, grade, mitotic index, number of tumors, and gender. The AI was then categorized into three groups ( < or = 1, > 1, and < or = 3, and > 3) to examine the prognostic significance of this parameter. The distributions of patients by clinical stage, grade, mitotic index, number of tumors, radiotherapy response, and hemoglobin level were significantly associated with AI using this grouping. When the analysis of the distribution of patients by radiation response and AI was segregated by stage, a significant correlation was observed only for those with Stage T3b disease (p = 0.006); 93% of T3b patients with an AI > 3 were downstaged, while in 7% the stage remained unchanged and none were upstaged. The relationship of AI to 5-year actuarial patient outcome was investigated using several end points and although no significant correlations were observed, a trend was seen for improved survival when AI was > 3 (71% vs. 41%, p = 0.09) for Stage T3b patients.

CONCLUSION

The AI correlated most strongly with radiotherapy response for patients with clinical stage T3b disease, the one subgroup of patients wherein preoperative radiotherapy is likely to be of the most benefit. Further investigation of pretreatment apoptosis levels as a marker of anticancer response is needed, especially for patients treated with chemotherapy and radiotherapy with the goal of bladder preservation.

Histone H3 messenger RNA in situ hybridization correlates with in vivo bromodeoxyuridine labeling of S-phase cells in rat colonic epithelium

Measurements of cell cycle phase fractions, particularly S-phase, are useful for studies of cell biology and carcinogenesis. Up-regulation of histone gene expression is tightly coupled to the G1-S-phase transition of the cell cycle, and mRNA levels rise 30-100-fold during S-phase. Labeling of histone H3 mRNA using in situ hybridization (ISH) was assessed as a measure of S-phase cells and compared with that found using in vivo 5-bromodeoxyuridine (BrdUrd) labeling in formalin-fixed rat colonic crypts under baseline, modified 72-h starvation, and 24-h refeeding conditions. The labeling index scored in single-labeled sections by histone H3 ISH tightly correlated with that found by in vivo BrdUrd labeling (r = 0.99, p < 0.0001) and clearly discriminated between the control, starved, and refed states (P < 0.001). In 180 crypt sections double labeled using histone H3 ISH and BrdUrd, 92% of 1572 labeled cells exhibited both nuclear BrdUrd and cytoplasmic histone H3 label. It is concluded that histone H3 ISH is an accurate measure of the S-phase fraction and provides an alternative to in vivo BrdUrd labeling in rat colon. This finding warrants validation in human studies.

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.

Cell cycle analysis of synchronized Chinese hamster cells using bromodeoxyuridine labeling and flow cytometry

Chinese hamster ovary cells were synchronized into purified populations of viable G1-, S-, G2-, and M-phase cells by a combination of methods, including growth arrest, aphidicolin block, cell cycle progression, mitotic shake-off, and centrifugal elutriation. The DNA content and bromodeoxyuridine (BrdUrd) labeling index were measured in each purified fraction by dual-parameter flow cytometry. The cell cycle distributions determined from the DNA measurements alone (single parameter) were compared with those calculated from both DNA and BrdUrd data (dual parameter). The results show that highly purified cells can be obtained using these methods, but the assessed purity depends on the method of cell cycle analysis. Using the single versus dual parameter measurement to determine cell cycle distributions gave similar results for most phases of the cell cycle, except for cells near the transition from G1- to S-phase and S- to G2-phase. There the BrdUrd labeling index determined by flow cytometry was more sensitive for detecting small amounts of DNA synthesis. As an alternative to flow cytometry, a simple method of measuring BrdUrd labeling index on cell smears was used and gave the same result as flow cytometry. Measuring both DNA content and DNA synthesis improves characterization of synchronized cell populations, especially at the transitions in and out of S-phase, when cells are undergoing dramatic shifts in biochemical activity.

Specific staining of iododeoxyuridine and bromodeoxyuridine in tumors double labelled in vivo: a cell kinetic analysis

The simultaneous and specific staining of iododeoxyuridine (IdUrd) and chlorodeoxyuridine (CldUrd) allows for more accurate estimates of potential doubling time (Tpot). Because CldUrd is not approved for human use, the procedure was adapted for the staining of IdUrd and bromodeoxy-uridine (BrdUrd). The fluorescein isothiocyanate-conjugated B44 antibody (B44-FITC) stained both IdUrd and BrdUrd in tumor nuclei labelled singly with one or the other pyrimidine analogue. However, when MCaK tumors in exponential growth in vivo were pulse labelled with both IdUrd and BrdUrd, the staining of BrdUrd was not seen, and the labelling pattern reflected specificity to IdUrd. These observations were confirmed using tumors pulse labelled with IdUrd and/or BrdUrd at 6 h and/or 0.3 h prior to tumor removal in all possible combinations. Simultaneous specific staining of BrdUrd by Br3 and of IdUrd by B44-FITC was documented by quantification of labelling indices (LIs) from double-labelled tumors. The specificity of B44-FITC for IdUrd in double-labelled tumors was due to a greater affinity of this antibody for IdUrd than for BrdUrd. This technique allowed for two independent estimates of LI and Tpot when tumors were double labelled for 3.0 and 5.5 h. Both IdUrd and BrdUrd are approved for clinical use, and this double-labelling technique should prove to be valuable for measuring the cell kinetics of solid tumors in vivo.

Relationship of tumor DNA-ploidy to serum prostate-specific antigen doubling time after radiotherapy for prostate cancer

OBJECTIVES

DNA-ploidy is a strong prognostic factor for prostate cancer patients treated with definitive external beam radiotherapy. Using DNA/nuclear protein flow cytometry, three prognostic groups based on DNA-ploidy were identified: from good to poor, these are diploid, near-diploid, and nondiploid tumors. Since recent evidence indicates that the rate at which prostate-specific antigen (PSA) increases in the presence of biochemical failure is predictive of the time to clinical relapse, we examined the relationship between DNA-ploidy and PSA doubling time (PSA-DT).

METHODS

Formalin-fixed paraffin-embedded tissues from 76 patients treated at M.D. Anderson Cancer Center with definitive radiotherapy alone were analyzed for ploidy using DNA/nuclear protein flow cytometry. Of these, 24 of the 27 patients with a rising PSA profile had three or more post-treatment PSA values from which the PSA-DTs were calculated. PSA-DTs were estimated using nonlinear regression techniques.

RESULTS

The average PSA-DT for the 24 patients in this cohort was 11.3 +/- 10.5 months (+/- SD) with a median of 8.4 months. Diploidy (n = 3) was associated with a PSA-DT of 27.0 +/- 22.8 months, near-diploidy (n = 7) with a PSA-DT of 12.2 +/- 5.7 months, and non-diploidy (n = 14) with a PSA-DT of 7.5 +/- 5.7 months (p = 0.004, Spearman rank test). Stage, grade, and pretreatment PSA, as well as the endpoints of local control, freedom from metastases, and freedom from any relapse, did not correlate significantly with PSA-DT values. However, when patients were subdivided by PSA-DT into those with values 10 months or less (n = 14) and those more than 10 months (n = 10), there was a correlation with 3-year actuarial freedom from relapse: 28% and 74%, respectively (p < 0.01, log-rank). This subdivision of PSA-DT also correlated with DNA-ploidy (p = 0.03, chi-square) and stage (p = 0.04).

CONCLUSIONS

The results show that there is a significant correlation of DNA-ploidy with PSA-DT. Diploidy was associated with the longest PSA-DTs, near-diploidy with intermediate PSA-DTs, and nondiploidy with short PSA-DTs. Patients with short PSA-DTs also had significantly higher actuarial rates of disease relapse at 3 years. These data confirm that PSA-DT is a strong predictor of tumor behavior and that patients who have nondiploid tumors probably require more aggressive, combined modality, treatment.

Relationships between DNA damage and the survival of murine bone marrow cells irradiated in situ

The relationships between DNA damage and the survival of murine bone marrow cells irradiated in situ were examined. Cell survival was assayed by the ability of bone marrow cells from irradiated mice to form colonies in vitro (CFU-C). DNA double-strand breaks (DSBs) were measured by neutral (nondenaturing) filter elution and pulsed-field gel electrophoresis (PFGE). Double-strand breaks were measured in the proliferating bone marrow cells, identified by injecting the mice with [3H]dThd at various times before gamma irradiation, as a model of the behavior of the radiosensitive target cells. To assess how the DNA lesions measured using these techniques correlated with cell killing, the effect of the radioprotective agent WR-2721 on the induction of DSBs in proliferating bone marrow cells was compared with its effect on CFU-C survival. WR-2721 protected against the killing of both granulocyte-macrophage and erythroid burst-forming CFU-C by a factor of about 2. In contrast, little (1.2-fold) protection was observed in the PFGE assay at radiation doses between 5 and 20 Gy. Similarly, at the lowest dose studied (5 Gy) there was little protection against DSBs as measured by neutral elution; only after doses of between 10 and 30 Gy was significant protection observed. Thus the previously reported predictive relationship between DSBs and cell survival in vitro does not appear to extend directly to murine bone marrow cells irradiated in vivo.

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.

Near-diploidy: a new prognostic factor for clinically localized prostate cancer treated with external beam radiation therapy

BACKGROUND

DNA ploidy is a significant prognostic factor in patients with prostate cancer. Using DNA/nuclear protein flow cytometry, a subpopulation of tumors with near-diploid DNA is identifiable. The prognostic significance of near-diploidy was examined.

METHODS

Paraffin-embedded formalin fixed prostate tumor tissue from patients treated at M. D. Anderson Cancer Center with external beam radiation therapy was processed for DNA/nuclear protein flow cytometry. All patients had pretreatment and follow-up serum prostate specific antigen (PSA) levels. Seventy-six specimens were suitable for flow cytometric analysis. Tumors were classified as either diploid (n = 30), near-diploid (n = 24), or nondiploid (n = 22, tetraploid and aneuploid). Median follow-up time was 36 months.

RESULTS

Diploid tumors were associated with a significantly better actuarial outcome at 4 years, compared with near-diploid tumors, using either biochemical relapse (rising PSA) or a composite end point of a rising PSA or clinical relapse (16% versus 52% relapse, P < 0.05, log-rank). Moreover, patients who had nondiploid tumors had the worst prognosis (77% relapse, composite end point). No significant difference was observed between diploid and near-diploid neoplasms regarding actuarial local control, freedom from metastasis, freedom from clinical relapse, or overall survival time. A Cox proportional hazards model, using the composite end point of a rising PSA or relapse, was performed with ploidy categorized as diploid, near-diploid, and nondiploid; pretreatment PSA, DNA ploidy, and tumor grade were found to be independent prognostic factors. When ploidy was categorized as diploid or near-diploid (nondiploid tumors excluded), pretreatment serum PSA and DNA ploidy were independent predictors of outcome. Ploidy remained an independent prognostic factor even when nondiploid tumors were excluded.

CONCLUSIONS

These data show that patients who have near-diploid tumors have an intermediate prognosis between the more favorable diploid tumors and the less favorable nondiploid tumors.

The prognostic significance of DNA ploidy in clinically localized prostate cancer treated with radiation therapy

PURPOSE

To determine the prognostic significance of deoxyribonucleic acid (DNA) ploidy in comparison to pretreatment prostate specific antigen (PSA) and other prognostic factors for patients with adenocarcinoma of the prostate treated with external beam radiotherapy.

METHODS AND MATERIALS

Paraffin-embedded prostatic adenocarcinoma material was obtained from patients treated from 1987-1991. Sufficient histologic material for flow cytometric DNA content analysis was obtained from 86 patients and adequate histograms were obtained from 76 of these. The DNA histogram profiles were classified as diploid, tetraploid, or aneuploid. Median patient follow-up was 36 months.

RESULTS

There were 54 patients with diploid tumors, and 22 with nondiploid tumors (11 tetraploid and 11 aneuploid). Since the disease outcome for tetraploid and aneuploid tumors was the same, these were pooled (nondiploid tumors). The distribution of diploidy and nondiploidy correlated with pretreatment PSA (p < 0.0005) and grade (p = 0.055), but not with stage, pretreatment prostatic acid phosphatase, transurethral resection, pretreatment serum testosterone, or age. In actuarial univariate analyses, DNA ploidy was a significant predictor of outcome for local failure, distant metastases, any clinical relapse, rising PSA, and rising PSA and/or relapse. Ploidy was not a significant predictor of overall survival, although there were only six deaths. Diploidy predicted for improved outcome, for example, 34.6% incidence of a rising PSA and/or relapse at 4 years compared to 76.9% with nondiploidy (p < 0.0001). An actuarial univariate analysis of other potential prognostic factors using the composite endpoint of rising PSA and/or relapse also revealed pretreatment PSA, grade, pretreatment prostatic acid phosphatase, stage, and serum testosterone to be significant predictors of outcome. In Cox proportional hazards analysis, pretreatment PSA, DNA ploidy, and grade were the only independent prognostic factors for disease outcome using the composite endpoint.

CONCLUSION

DNA ploidy is an independent predictor of outcome in patients with Stages T1-T3 prostate cancer treated with definitive external beam radiotherapy.

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.

Hormonal protection from procarbazine-induced testicular damage is selective for survival and recovery of stem spermatogonia

Procarbazine produces long-term sterility in the male by killing stem spermatogonia. The degree and selectivity of protection of stem spermatogonia in rats from procarbazine by pretreatment with steroid hormones were investigated. Male LBNF1 rats were treated for 6 weeks with Silastic implants containing testosterone plus 17 beta-estradiol. The hormone-treated rats and sham-treated controls were given a single injection of graded doses of procarbazine and the hormone implants were removed the next day. Spermatogonial stem cell survival and function, assessed by the repopulation indices and sperm head counts 10 weeks later, showed that stem spermatogonia were protected by testosterone plus 17 beta-estradiol treatment from the toxic effects of procarbazine with a dose-modifying protection factor of about 2.5. In contrast, there was no hormonal protection from the procarbazine-induced killing of differentiating spermatogonia, preleptotene spermatocytes, and spermatocytes in meiotic prophase or from the delay in maturation of round spermatids, assessed 9 days after procarbazine injection by histological or flow cytometric methods. In addition, there was no hormonal protection from the procarbazine-induced decline in body weights and lymphocyte counts, indicating that the gastrointestinal, neurological, and hematological systems were not protected. The specificity of protection indicates that the hormonal protection of the stem spermatogonia is not the result of a systemic or overall testicular decrease in drug delivery, decrease in bioactivation, nor increase in drug detoxification, except possibly within the stem cells themselves. We conclude that the degree of hormonal protection and its specificity would be appropriate for clinical application provided that the mechanism of protection is elucidated and appears applicable to humans.

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.

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.

Influence of intracellular thiol and polyamine levels on radioprotection by aminothiols

We examined the effect of manipulating the levels of two endogenous radioprotectors, glutathione (GSH) and polyamines, on the ability of exogenous aminothiols to protect Chinese hamster ovary cells from the lethal effects of gamma-radiation. Treatment with 0.5 mmol dm-3 buthionine sulfoximine (BSO) for 24 h depleted GSH levels to < 1% of control and significantly sensitized the cells to irradiation in air. Undepleted control cells were protected by WR-1065 (4 mmol dm-3; 30-min preirradiation treatment at 37 degrees C) by 2.09-fold (range 1.98-2.21) at the 10% survival level, whereas BSO-treated cells were protected by a factor of 1.98 (range 1.95-2.14) at this survival level. Thus, GSH depletion had no significant effect on the radioprotective capacity of WR-1065. Treating cells with 1 mmol dm-3 alpha-difluoromethyl ornithine (DFMO) for 48 h depleted the polyamines putrescine and spermidine to very low levels, while spermine was not significantly depleted. DFMO also sensitized cells to aerobic irradiation. WR-1065 protected DFMO-treated cells by 2.29-fold (range 2.08-2.53), whereas undepleted control cells were protected by 2.09-fold (range 1.98-2.21) at the 10% survival level. Thus, WR-1065 appeared to offset the radiosensitizing effect of the DFMO treatment. Cysteamine, on the other hand, protected control and DFMO-treated cells to the same extent. We also examined the effect of combinations of exogenous thiols on radiosensitivity. Cells were treated with WR-1065 (4 mmol dm-3) for 30 min and then with increasing concentrations of dithiothreitol for 5 min prior to irradiation. The protective effects of these two thiols were simply additive.

Recognition and reduction of artifacts from autolysis in paraffin-embedded tissue using DNA/nuclear protein flow cytometry

Artifacts from autolysis can be a problem in retrospective flow-cytometric analyses of DNA content in paraffin-embedded tissues. Autolyzed tissue from rat liver, human liver, and rat spleen were stained for DNA and nuclear protein to determine if this technique would be useful in identifying partially degraded cells. After the tissue was deparaffinized and rehydrated, the nuclei were isolated using 0.5% pepsin. Propidium iodide (PI) and fluorescein isothiocyanate (FITC) were used to stain DNA and nuclear protein. When unfixed rat liver tissue was allowed to undergo autolysis at 4 degrees C for 24-48 h before fixation, there was a progressive broadening of the G1 and G2M DNA peaks and a slight increase in the average DNA contents of these peaks. Nuclei that stained more intensely with PI also stained more intensely with FITC. Similar results were obtained using human liver and rat spleen. Sometimes the increased PI staining resulted in a false aneuploid peak. The distinctive skewing of the DNA/nuclear protein histograms from autolysis was reduced by increasing the incubation of the tissue in 0.5% pepsin from 0.5 h to 1.5 h during the nuclei-isolation step. The DNA/nuclear protein method provides a means for identifying artifacts from autolysis, whereas the extended pepsin treatment provides a means for reducing these artifacts.

Flow cytometric analysis of two incorporated halogenated thymidine analogues and DNA in a mouse mammary tumor grown in vivo

A technique was developed for the staining of nuclei for DNA using propidium iodide, and incorporated chlorodeoxyuridine (CldUrd) and iododeoxyuridine (IdUrd) using two monoclonal antibodies that showed negligible cross-reactivity. The mouse mammary solid tumor MCaK was labeled in vivo by intraperitoneal injection of the nucleosides. Tumor cell nuclei were stained after isolation from ethanol-fixed solid tumor tissue and acid denaturation. The Br3 antibody, which specifically recognizes CldUrd, was applied first, followed by indirect staining with goat anti-mouse phycoerythrin. The direct fluorescein isothiocyanate conjugate of the B44 antibody, which specifically recognizes IdUrd, was then applied. In the direct conjugate form this antibody reacted only minimally with CldUrd. The nuclei were then stained with propidium iodide. With this dye combination the coefficients of variations of the DNA histograms were consistently in the 2-4% range. Two other dye combinations were compared. The propidium iodide/phycoerythrin/fluorescein isothiocyanate dye combination was the simplest because of the compatibility with single laser flow cytometry.

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

A method is presented for analyzing data from bivariate analysis of cell populations exposed to bromodeoxyuridine and subsequently examined both for the presence of BrdUrd and for the cellular DNA content. It is shown that certain features may be defined in the bivariate data which are constant independent both of cell type and, within limits, experimental variability. These landmark features include the ratio of red, DNA, fluorescence of G2 + M cells to G1 cells, the ratio of green fluorescence corresponding to the non-specific binding of unlabeled G2 + M cells to unlabeled G1 cells, and the distribution of green fluorescence in unlabeled cells. The landmarks make it possible to standardize rules for establishing the separation line between-labeled and unlabeled cells as required in these experiments to obtain estimates of cytokinetic parameters. Values obtained for the DNA synthesis time and the potential doubling time which result from different decision rules for distinguishing labeled from unlabeled are compared in two murine tumor lines. The potential doubling time, but not the DNA synthesis time is shown to depend sensitively on the separation line. Suggestions are presented for analyzing clinical data with this procedure.

Measuring cell proliferation by relative movement. I. Introduction and in vitro studies

This paper presents two new ways of analysing data which may be obtained from pulse labelling a population of cells with bromodeoxyuridine and analysing that population as a function of time with bivariate flow cytometry. The progression of cells is measured by the change in position in the cell cycle, as shown by a change in the mean DNA content of the labelled and unlabelled cells. The particular measures of the mean DNA content used are extensions of the relative movement of the labelled undivided cells, RMlu(t), which was introduced by Begg and co-workers to measure the DNA synthesis time, TS. In general, the relative movement is defined as the mean DNA fluorescence of a population of cells less the DNA fluorescence of the cells in G1 and divided by the difference in DNA fluorescence of the cells in G2 + M and G1. In this paper we examine the relative movements of all the labelled cells and all of the unlabelled cells, denoted RML(t) and RMU(t) respectively. It is found that RML(t) and RMU(t) exhibit clear cyclic behaviour and distinguishable characteristics which depend directly on the transit times (T) of the cell cycle phases, i.e. TG1, TS and TG2 + M. Furthermore, the peak heights of the RMU(t) curve are shown to depend strongly on the growth fraction of the population under consideration. A theoretical treatment of the curves so obtained is presented, and is shown to yield values in close agreement with those from other methods for measuring these transit times and a lower limit to values for the growth fraction of Chinese hamster ovary cells grown in vitro.

Molecular genetic evidence for a differentiation-proliferation coupling during DMSO-induced myeloid maturation of HL-60 cells: role of the transcription elongation block in the c-myc gene

Proliferation-differentiation coupling was studied during dimethyl sulfoxide (DMSO)-induced myeloid maturation of HL-60 cells using transcription of the myeloperoxidase (MPO) and c-myc genes as indicators of differentiation and proliferation, respectively. Concomitant cell cycle kinetic analysis correlated the proliferation and transcription patterns. Transcription, cell cycle phases and rate of DNA synthesis were examined for up to 5 days of induction and, at 1-day intervals, analyzed during a 24-h reculture without the inducer. DMSO suppressed transcription of the c-myc and MPO genes with a t1/2 of 16 min and 7 h, respectively. The ability to recover transcription following reculture diminished with the progression of the induction and ultimately was lost; concomitantly, the cells irreversibly lost the capacity to divide. This indicated that the differentiation and proliferation processes are inseparable and that terminal differentiation accompanies irreversible proliferation arrest in HL-60 cells. We also studied the kinetics of the block to transcription elongation at the exon 1-intron 1 boundary of the c-myc gene. This block produces a 0.38 kb truncated transcript that is constitutively expressed in somatic cells (Re et al., Oncogene 5, 1247, 1990). During induction the level of the 0.38 kb RNA increased, while that of the complete c-myc mRNA decreased, indicating that this truncated RNA is generated instead of message through a monotonously initiated transcriptional process. Transcription initiation and synthesis of the 0.3 kb RNA persisted in terminally differentiated cells, suggesting a role for this RNA in non-proliferating cells.

Evaluation of flow cytometric methods for determining population potential doubling times using cultured cells

Various methods have been proposed for determining the potential doubling times (Tpot) of mammalian cell populations by using flow cytometric techniques after labeling the cells with bromodeoxyuridine (BrdUrd). We show here that, in a well-defined in vitro system where multiple time measurements are possible, all the methods give similar results that are close to the true population doubling time. Of ultimate interest, however, is the accuracy of determination of Tpot from a single time point. In this paper we compare the accuracy and precision of the methods in making such determinations at different times after labeling. The relative movement (RM) of BrdUrd-labeled cells that have not divided at the time of assay allows for computation of the length of S phase (Ts). The precision of estimation of Ts was enhanced when a quantity, v (a function of the fraction of BrdUrd-labeled divided and the fraction of BrdUrd-labeled undivided cells), was used to estimate the initial intercept of RM. Furthermore, calculation of Tpot from the formula, Tpot = ln(2) Ts/v, gave values closest to the observed population doubling time. It is suggested that the use of RM with v be the analytical method of choice for the calculation of Tpot from single time-point observations, preferably made at times between the length of the G2 and M phases (TG2M) and Ts.

Measuring potential doubling times of murine tumors using flow cytometry

Flow cytometric analysis of bromodeoxyuridine (BrdUrd) labeled cells has led to the description of various methods for determining population potential doubling times (Tpot) from samples obtained at a single time point. There have been several reports of results from human tumor samples using these various methods of analysis, but little documentation of the validity of these approaches in experimental tumor models. Recently, we reported results using in vitro cell cultures and determined the most reliable method for these. In this paper we report the results of this methodology when applied to two in vivo murine tumor models (MCaK and FSA). The analytic approach tested is summarized as follows: The relative movement (RMlu(t], a measure of the mean DNA fluorescence of BrdUrd-labeled cells that have not undergone division at the time of sampling, and a quantity v, a function of the fractions of BrdUrd-labeled divided and undivided cells, were measured for a series of time points following labeling. From each value of RMlu(t) an estimate of the length of S-phase (TS) was computed and from each v and TS a value for Tpot was found. These results were compared to the values of TS and Tpot obtained by fitting all the values simultaneously. Tumor MCaK values of TS and Tpot of 9.6 and 28.0 h were obtained from fitting all of the data. Tumor FSA gave values of 16.8 and 42.3 h for TS and Tpot, respectively. The results of this analysis show that single time point measurements can give reliable estimates of TS and Tpot.

New methods for calculating kinetic properties of cells in vitro using pulse labelling with bromodeoxyuridine

The transit times of Chinese hamster ovary cells through the phases of their cell cycle were measured using dual parameter flow cytometry to measure DNA content and the presence of monoclonal antibodies to bromodeoxyuridine. Up to four separate populations can be accurately measured: unlabelled cells in G2 + M; labelled cells that have not yet divided; labelled cells that have already divided; and the unlabelled cells that were originally in G1 plus the cells that were originally in G2 + M and have since divided. The fractions of cells in these populations can be easily followed in time and the usual kinetic properties can be estimated from these fractions, or combinations thereof, including the times through G1, S, G2 + M and the cycle time. We present equations for analysing this type of data and comment on which equations are most appropriate for measuring specific kinetic properties of the cells.

The accuracy of fine needle aspiration biopsy for flow cytometric determination of tumor DNA content

The use of fine needle aspiration (FNA) to obtain a diagnosis of malignancy is established in the practice of oncology, but there is little information on its accuracy in sampling tumor DNA content. We therefore compared flow cytometric DNA data obtained from FNA-derived samples with that obtained after digestion of the same murine tumor from which the aspirates had been taken. Fifteen female C3Hf/Kam mice were implanted with MCA-29 tumor cells from the same source tumor. MCA-29 is a multiploid mammary adenocarcinoma with two aneuploid populations (DNA Index of A = 1.67, B = 1.89). The tumors were grown to a mean size of 8.6 mm. After sacrifice, three FNAs were performed on each tumor, following which the whole tumor (WT) was excised and homogenized. All FNA and WT samples were digested with 0.04% pepsin and the nuclei stained with propidium iodide in preparation for flow cytometry. DNA histograms of the aspirates were compared with the corresponding WT histograms. Any single FNA detected population A in all (100%) cases and detected the less prominent population B in 94.3% of instances. Any single FNA was able to detect the same populations that were present in the whole tumor in 95.4% of cases, while the set of three aspirates matched the corresponding WT in 100% of cases. We conclude that FNA DNA histograms are accurate for the assessment of ploidy, but that in order to ensure detection of all tumor populations present, multiple aspirates are needed.

Effects of beta-all-trans retinoic acid on growth, proliferation, and cell death in a multicellular tumor spheroid model for squamous carcinomas

The growth of multicellular tumor spheroids, MTSs, from squamous carcinoma line MDA 886Ln was inhibited by beta-all-trans retinoic acid (RA). Inhibition occurred within 3 to 5 days of treatment, and MTS size then remained static for up to 2 weeks. Although their growth stopped, 10-day-treated MTSs incorporated [3H]thymidine into trichloroacetic acid-precipitable material, and the [3H]thymidine labeling index, determined by autoradiography, was equivalent between control and RA-treated MTSs. Bivariate flow cytometric analysis of bromodeoxyuridine-labeled MTSs showed equivalent S phase progression of labeled cells over an 8-hour chase. MTS growth stasis was not related to RA-induced cell cycle effects. Monitoring of MTSs for cell sloughing showed no significant cell shedding that could account for stasis. Quantitation of cell number and DNA content per MTS showed an RA-induced decrease. This was confirmed by histological analysis, which demonstrated the temporal appearance of acellular areas. MTS growth statis is thus related to an RA-induced cell loss in this MTS model for squamous carcinomas.

Comparative effect of the thiols dithiothreitol, cysteamine and WR-151326 on survival and on the induction of DNA damage in cultured Chinese hamster ovary cells exposed to gamma-radiation

We compared the ability of three thiols--dithiothreitol (DTT), cysteamine and WR-151326--to protect aerated Chinese hamster ovary cells from the lethal and DNA-damaging effects of gamma-radiation. These results were compared with earlier measurements for WR-1065 and WR-255591. The time-course and the concentration dependence of protection against cell killing was determined after 10 Gy of gamma-rays. The aminothiols cysteamine and WR-151326 protected at much lower extracellular concentrations than the simple thiol DTT; however, there was no clear difference between the behaviour of cysteamine, WR-151326, WR-1065 and WR-255591 in this respect. Protection by DTT and cysteamine was complete within 1 min, whereas for WR-151326, WR-1065 and WR-255591 about 30 min was required before protection began to reach a plateau. Based on these data, complete radiation survival curves were generated for each thiol and protection factors calculated. Effects on the induction of DNA single-strand breaks (ssb) and double-strand breaks (dsb) by gamma-rays were measured using alkaline (pH 12.1) and neutral (pH 7.0 and 9.6) elution, respectively. All three thiols protected against ssb induction, although to a significantly lower extent than against cell killing measured under identical conditions. Each thiol also protected against dsb induction. After high radiation doses the protection factors for dsb induction were also less than the protection factors for cell survival; however, when dsb were assayed using the low-dose replicate plating neutral elution method, the relative effect of each thiol on cell survival and on dsb induction appeared to be equivalent. The hierarchy of protection against both ssb and dsb induction (based on the extracellular thiol concentration required to produce a given degree of protection) was similar to that for cell survival, i.e., WR-151326 congruent to cysteamine less than DTT.

Improved method for computing potential doubling time from flow cytometric data

Relative movement methods use the timed progression of the mean fluorescence of cells which have been labeled with monoclonal antibodies against bromodeoxyuridine and displayed with bivariate flow cytometry according to DNA and label content to compute duration of DNA synthesis, TS. The relative movement is the difference of the mean DNA fluorescence of the labeled undivided cells from the G1 channel relative to the difference between the G1 and G2M channels. In this communication, we show how to extend this method to compute the potential doubling time, Tpot, the time required for a population of cells to double, given quiescent cells but no cell loss. A quantity v is introduced that is a function of the fraction of labeled divided cells and the fraction of labeled undivided cells. We show that v is independent of time and is equal to ln(2)Ts/Tpot so that Tpot (equal to ln(2)Ts/v) can be directly found from the information available in computing the relative movement. The method is applied to Chinese hamster ovary cells to demonstrate its utility.

The influence of bone marrow depletion on intestinal radiation damage

These experiments were designed to test the hypothesis that bone marrow damage contributes to lethality when the endpoint used is LD50 for gastrointestinal damage. Specific pathogen-free mice were irradiated to the total body, total abdomen, or to the total body followed by rescue with syngeneic bone marrow cells. The relationship between animal survival and jejunal crypt survival was also examined under these three experimental conditions. The LD50/10 after total abdominal irradiation (15.6 Gy) was higher than that for total body irradiation (11.4 Gy). Rescue with syngeneic bone marrow cells after total body irradiation also increased the LD50 10 days to 14.6 Gy. The proportion of animals surviving after total body irradiation depended on the number of bone marrow cells injected as a rescue inoculum. Hence gastrointestinal death after total body irradiation is influenced by bone marrow depletion. Crypt survival, however, was similar following all three experimental procedures. These data, therefore, demonstrate a dissociation between a clonogenic and lethality assay of intestinal damage. Furthermore, a comparison of crypt survival at the LD50 under the different conditions showed that a factor of 10 times more crypts were needed to rescue a mouse from gut lethality when the total body was irradiated than when only the total abdomen was treated. Hence, the concept of the intestinal "tissue rescuing unit" as a precise and constant number of crypts is inappropriate and will vary with the experimental conditions.

Time course of loss of residual radiation damage in murine skin assessed by retreatment

The amount of radiation damage remaining in mouse foot skin has been assessed by retreatment from 10 days to 6 months after a range of first doses. The acute skin reaction was used as the endpoint. Mice hind feet were first irradiated with a range of single doses (15-37.5 Gy) covering zero to near full effect. Feet were retreated with a full range of single doses together with groups of non-previously treated age-matched control mice. No age-related changes in radiation sensitivity were observed. Dose-response curves were constructed for all retreatment times for each priming dose, and isoeffect doses were calculated for both peak and average skin reactions. If 2-6 months were allowed to elapse before retreatment, the skin could be reirradiated as if it were previously untreated. However, if only 1 month was allowed to pass before retreatment, damage was 'remembered' after all first doses. The amount of damage 'remembered' in terms of dose was 11 Gy after a first dose of 37.5 Gy, and was less after the lower first doses.

Tissue repair and repopulation in the tumor bed effect

These experiments were designed to study the kinetics and magnitude of cell repair and repopulation in tissues whose damage results in the tumor bed effect. The right hind thighs of mice were irradiated with single doses or two equal gamma-ray fractions. Interfraction intervals ranging from 30 min to 24 h (to measure the kinetics of repair from sublethal damage) and 6 and 12 weeks (to determine the extent of repopulation) were used. One day after the second radiation dose 5 X 10(5) FSA tumor cells were inoculated into the center of the irradiated field. Radiation dose-response curves were obtained by calculating the time required for tumors to reach 12 mm diameter. No recovery occurred within 6 h of the radiation delivery as measured by this assay. Some recovery, 3.2-4.6 Gy above a single radiation dose, occurred when the interval between two fractions was 24 h. With increasing interfraction intervals of 6 and 12 weeks further dose sparing occurred in the amount of 5.0-6.9 and 7.5-8.3 Gy, respectively. The data suggest that repopulation is the major contributor to the radiation dose-sparing recovery of stromal tissue and that some proliferative response may occur as early as 1 day after the first irradiation.