Flow cytometric screening for selective toxicity to multidrug-resistant cells.

Mixed cultures originally containing doxorubicin [(DOX) NCS-123127]-sensitive leukemia P388 (P388/S) cells and DOX-resistant leukemia P388 (P388/R) cells were treated with drugs for 1 hour or with radiation, grown until the cell numbers had increased 250 times (8 cell doublings), and incubated with 2 micrograms daunorubicin (NCS-82151)/ml for 1 hour. The fluorescence of intracellular anthracycline measured on a flow cytometer was used as a marker to distinguish P388/S and P388/R cells. The proportions of low-fluorescent P388/R cells and high-fluorescent P388/S cells were determined from fluorescence histograms. Selective toxicity for multidrug-resistant P388/R cells was indicated by the decreased proportion of these cells in the mixed cultures. In untreated cultures grown from suspensions containing equal proportions of P388/R and P388/S cells, the mean proportion of P388/R cells after 4 days' growth was 34.4%. DOX eliminated P388/S cells from mixed cultures. Nitrogen mustard [(HN2) NCS-762] and x-rays were selectively toxic to P388/R cells. The selectivity of HN2 and x-rays was observed in a narrow dose range by the absence of selective inhibition at low doses, the decreased proportion of P388/R cells at moderate doses, and the killing of all cells in mixed cultures at high doses. Combination treatment of mixed cultures with DOX plus x-rays, or HN2 plus x-rays, produced complete inhibition of growth. Mixed cultures recovered after treatment with DOX plus HN2 contained only P388/R cells. Results obtained by colony-formation assay showed the same patterns of relative sensitivity for P388/R and P388/S cells as the data obtained by flow cytometry (FCM) selectivity assay. FCM analysis of mixed cultures detected selective toxicity for P388/R cells after treatments, characterized by approximately 1 log higher cell killing of P388/R cells than of P388/S cells. It was concluded that FCM analysis of mixed cultures provided a sensitive and reliable assay for fast screening of drugs for selective toxicity to multidrug-resistant cells.

Flow cytometry analysis of DNA damage and the evaluation of cytotoxicity of alkylating agents.

Monoclonal antibody (MAb) F7-26 generated against nitrogen mustard (HN2)-treated DNA (O.S. Frankfurt, Exp. Cell Res., 170: 369-380, 1987) reacted with regions of local DNA denaturation (distortion) induced by DNA alkylation. The relationship between immunoreactivity of cellular DNA with MAb F7-26 and cytotoxic effects of HN2, L-phenylalanine mustard (L-PAM), and 1,3-bis(2-chloroethyl)-1-nitrosourea was studied in HeLa S3 cultures. Cells were treated with drugs for 1 h and assessed for cell survival by colony formation assay and for DNA immunoreactivity by flow cytometry. Cells were fixed in ethanol, exposed to MAb, and stained with fluorescein-labeled anti-mouse immunoglobulin. Immunofluorescence (IF) intensity was measured on a flow cytometer. For each drug the cell killing and the binding of MAb to DNA appeared in the same dose ranges. A strong correlation (r = 0.96) between cell survival (log10 surviving fraction) and IF was observed when data for HN2, L-PAM, and 1,3-bis(2-chloroethyl)-1-nitrosourea were combined. This correlation was apparent in the range of 1-5 log10 cell killing. Enhancement of L-PAM cytotoxicity by buthionine sulfoximine (BSO) or hyperthermia was accompanied by a proportional increase of DNA immunoreactivity with MAb F7-26. The enhancement factors calculated from survival curves (a ratio of the dose decreasing cell survival by 1 log10 for L-PAM alone to that for L-PAM combined with modulating factor) were 1.67, 1.58, and 3.07 for BSO, hyperthermia, and BSO plus hyperthermia, respectively. For the same treatment regimens the enhancement factors calculated from drug dose-IF curves were 1.73, 1.34, and 3.79. A strong correlation between log10 surviving fraction and IF intensity (r = 0.93) was observed when data for L-PAM alone or L-PAM combined with BSO and/or hyperthermia were considered together in the range of 1-6 log10 cell killing. The cytotoxicity of alkylating agents and nitrosoureas and the effectiveness of factors modulating chemotherapeutic effects can be predicted by flow cytometry analysis of DNA immunoreactivity with MAb F7-26.

Flow cytometric analysis of DNA damage and repair in the cells resistant to alkylating agents.

DNA damage in the cells sensitive and resistant to alkylating agents was determined by flow cytometry analysis of cells stained with anti-DNA monoclonal antibody (MOAB) F7-26. MOAB F7-26 interacted with single-stranded regions in alkylated DNA, and the binding of antibody to the cells increased in proportion to the decrease in cell viability. Development of resistance to L-phenylalanine mustard (L-PAM) in A2780 cells was associated with decreased immunoreactivity of DNA with MOAB F7-26. Fluorescence was significantly lower in resistant cells than in sensitive cells, and the difference in the binding of MOAB between two cell types increased with the dose of L-PAM. The enhancement of L-PAM cytotoxicity to resistant cells by buthionine sulfoximine and hyperthermia was accompanied by a proportional increase of MOAB F7-26 binding to DNA. The same relative potential of sensitization regimens was established by cell survival and MOAB staining. The time course of DNA repair established by decrease of MOAB binding after L-PAM removal was similar in sensitive and resistant cells. Resistance of A2780 cells to L-PAM was associated with low initial level of DNA damage and with decreased cytotoxicity per unit of damage. We conclude that resistant cells could be distinguished from sensitive cells by staining with MOAB F7-26 and that the sensitization of resistant cells could be quantitatively predicted by flow cytometry analysis of MOAB binding.

Intercellular transfer of drug resistance.

The effect of L-phenylalanine mustard (L-PAM) on heterogeneous cell populations containing sensitive and resistant cells was evaluated by flow cytometric analysis of DNA damage. Cell cultures were treated with L-PAM for 1 h, fixed, and stained with anti-DNA monoclonal antibody which detects DNA damage induced by alkylating agents. DNA damage was significantly lower in sensitive A2780 cells cocultured with resistant A549 or A2780/PAM cells than in A2780 cells grown separately. Decrease of DNA damage in sensitive cells did not occur when sensitive and resistant cells were grown in common medium without direct contact. Transfer of drug resistance in cocultures was prevented by phorbol ester which is known to inhibit metabolic cooperation via cell junctions. Treatment of cocultures with buthionine sulfoximine increased DNA damage in resistant cells and prevented decrease of DNA damage in sensitive cells. Glutathione (GSH) content in A2780 cells cocultured with A549 cells was significantly higher than GSH content in A2780 cells grown separately. We conclude that decreased response of sensitive cells in cocultures was induced by contact transfer of GSH from GSH-rich resistant cells to sensitive cells. Intercellular transfer of drug resistance demonstrated by analysis of DNA damage was confirmed by colony formation assay. Treatment with L-PAM and Adriamycin killed all cells in A2780/MDR and A549 cultures. Coculture of these lines survived combination treatment because transfer of GSH to multidrug-resistant cells from GSH-rich A549 cells induced resistance to L-PAM and Adriamycin in a single cell. The presence of 2% A549 cells increased resistance of A2780/MDR cells to L-PAM. Phorbol ester eliminated resistance of coculture to combination treatment. Metabolic cooperation between cell subsets with different mechanisms of drug resistance induced resistance to treatment with drugs of different classes (multiclass drug resistance). Inhibition of cell cooperation may improve the response of tumors to combination chemotherapy.

Macromolecular and cell cycle effects of different classes of agents inducing the maturation of human myeloblastic leukemia (ML-1) cells.

The effect of various classes of differentiation-inducing agents on macromolecular synthesis was studied in a human myeloblastic leukemia cell line (ML-1). Antineoplastic drugs such as 1-beta-D-arabinofuranosylcytosine, daunorubicin, and actinomycin D caused early inhibition of DNA synthesis, which generally preceded the accrual of differentiation markers. In contrast, retinoic acid and conditioned medium from mitogen-stimulated leukocytes caused a delayed decline in DNA synthesis, which accompanied the appearance of maturing morphology. With 12-O-tetradecanoylphorbol-13-acetate, the decline in DNA synthesis was temporally linked to the onset of maturation, and this agent evidenced some properties of both the antineoplastic agents and the more physiological inducers, retinoic acid and conditioned medium. Antineoplastic agents and conditioned medium, when applied simultaneously, induced differentiation in an additive or synergistic manner, simulating the effects of 12-O-tetradecanoylphorbol-13-acetate. RNA and protein synthesis continued during maturation induced with all these agents, although a partial reduction in RNA synthesis was observed at later time points (greater than or equal to 24 hr). Agents incapable of inducing differentiation, such as cordycepin and cycloheximide, were characterized by a lack of sustained inhibition of DNA synthesis and/or by early (3 hr) inhibition of RNA or protein synthesis. The decline in DNA synthesis caused by the inducing agents was accompanied by decreased cell cycle progression, cells accumulating largely in G1 phase. With daunorubicin and actinomycin D, block of the G1-S transition was evident at 24 hr, whereas with conditioned medium and retinoic acid, accumulation in G1 occurred in a progressive fashion, greater than 77% of cells residing in this phase on Day 6. Maximal inducing doses of 12-O-tetradecanoylphorbol-13-acetate (greater than 80% differentiation) caused an accumulation of cells in G1, as well as an accumulation of cells with a G2-M-phase DNA content (approximately 40%). These observations indicate that early inhibition of DNA synthesis, with sparing of RNA and protein synthesis, is characteristic of the differentiation-inducing antineoplastic drugs examined. These agents may induce differentiation by inhibition of the proliferation path, whereas conditioned medium and retinoic acid may act by the stimulation of differentiation paths. Differentiation can be enhanced by the simultaneous application of agents targeting both of these paths.

Characterization of L1210 cell growth inhibition by the bacterial iron chelators parabactin and compound II.

Microbial siderophores represent a class of iron chelators characterized by their high affinity (i.e., formation constants, greater than 10(40) M) for ferric iron. Previously, we demonstrated that the bacterial siderophores, N-[3-(2,3-dihydroxybenzamido)propyl]-N-[4-(2, 3-dihydroxybenzamino)butryl]-2-(2-hydroxyphenyl) trans-5-methyloxazoline-4-carboxamide (Parabactin) and N1,N8-bis(2,3-dihydroxybenzoyl)spermidine (Compound II), inhibit the growth of L1210 cells and the replication of DNA (but not RNA) viruses at low micromolar concentrations (Biochem. Biophys. Res. Commun., 121: 848-854, 1984). The basis for this antiproliferative effect on L1210 cells has now been investigated further. Onset of growth inhibition induced by 5 microM Parabactin occurs much earlier than with an equimolar concentration of Compound II but, once established by either chelator, inhibition appears to be irreversible. Growth inhibition was fully preventable with exogenous FeCl3 when given at the same time as the chelators. Flow cytometric analysis revealed a G1-S cycle block following treatment for 4 h with either 5 microM Parabactin or 30 microM Compound II. The block was readily reversed with exogenous FeCl3, allowing cells to progress to mid-S phase by 3 h and to G1 again by 9 h. Thereafter, cells accumulated at a second block located at S phase. The treatment conditions required for the initial cell cycle block (at 4 h) were adapted for subsequent studies. Clonogenicity of L1210 cells in soft agar following a 4-h exposure was reduced to 22% of control by 5 microM Parabactin and to 16% by 30 microM Compound II. Neither growth inhibition in suspension culture nor decreased clonogenicity in soft agar could be reversed with exogenous iron, following treatment with the chelators. Both chelators caused an early and significant decrease in [14C]thymidine incorporation over the 4-h period (50% inhibitory concentration at 4 h, 0.4 microM for Parabactin and 6.0 microM for Compound II). [3H]Uridine incorporation was inhibited later than [14C]thymidine and to a much lesser extent, while [3H]leucine incorporation was not significantly affected. Treatment of cells with 5 microM Parabactin or Compound II for 4 h decreased deoxy-adenosine triphosphate pools by 38 and 70%, respectively, and increased deoxythymidine triphosphate pools by 67 and 36%, respectively, suggesting interference with ribonucleotide reductase. Indeed, extracts of cells treated for 4 h with either 5 microM Parabactin or 30 microM Compound II exhibit a 97 to 98% decrease in cytidine-5'-diphosphate reductase activity compared to control, whereas DNA polymerase was elevated slightly.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship between DNA ploidy, glandular differentiation, and tumor spread in human prostate cancer.

DNA ploidy was evaluated by flow cytometry for 45 human prostate carcinomas (34 prostatectomy specimens and 11 biopsies). Twenty tumors (44.4%) contained a distinct aneuploid stem line. All 11 tumors confined to the prostate gland (pathological Stage B) were diploid. The frequency of aneuploidy increased with advancing stage, and most tumors with distant metastases were aneuploid. The degree of glandular differentiation was characterized by the Gleason score. One-third of tumors with a Gleason score of 5 to 6 were aneuploid, whereas over 70% of poorly differentiated tumors with a Gleason score of 9 to 10 were aneuploid. Among diploid tumors, 45.5% were localized carcinomas (Stage B), 36.4% were characterized by invasion outside the prostate (Stage C), and 18.2% formed pelvic nodal or distant metastases (Stages D1 and D2). In nearly two-thirds of patients with aneuploid tumors, pelvic nodal or distant metastases were found. When tumors were classified according to both DNA ploidy and degree of glandular differentiation, then subgroups of tumors with the highest and lowest degree of malignant potential became apparent. Only 7.1% of diploid tumors with a Gleason score of 5 to 6 formed metastases, but 80% of aneuploid tumors with a higher Gleason score (7 to 10) formed metastases. Diploid tumors with higher Gleason scores and aneuploid tumors with lower Gleason scores had intermediate frequencies of metastases. The presence of an aneuploid stem line in prostate carcinomas indicated that the tumor had spread outside the prostate gland or had metastasized. DNA ploidy may be an important prognostic factor for human prostate cancer. DNA ploidy and the degree of glandular differentiation considered together may improve prognostic evaluation of prostate carcinomas.

Apoptosis in breast carcinomas detected with monoclonal antibody to single-stranded DNA: relation to bcl-2 expression, hormone receptors, and lymph node metastases.

Precise quantitation of apoptotic cells in solid tumors is necessary to determine the role of apoptosis in cancer growth, prognosis, and treatment. In this study, the intensity of apoptotic death was determined in 91 breast carcinomas with a novel cellular marker of apoptosis based on the staining of histological sections with a monoclonal antibody (MAb) to single-stranded DNA. Staining of apoptotic cells with the MAb reflected the decreased thermal stability of DNA induced by the digestion of nuclear proteins, as demonstrated by the elimination of staining in sections reconstituted with histones before heating. The high sensitivity and specificity of apoptosis analysis with the MAb is based on the central role of protease activation in the mechanism and control of apoptosis. Apoptotic indexes (AIs) in breast carcinomas ranged between 0 and 46%. Most of the carcinomas had relatively low AIs, whereas 29 cases were classified as carcinomas with intensive apoptosis (AI >/= 10%). The high level of apoptotic cell death was associated with negative immunostaining for bcl-2 protein, the loss of estrogen and progesterone receptors, high proportion of cells in S-phase, and increased risk of lymph node metastases. There was no correlation between AI and tumor size or p53 immunostaining. Lymph node metastases were detected in 59% of patients with high levels of apoptosis in primary carcinomas and in only 21% of patients with AIs below 10% in primary carcinomas. Thus, the high sensitivity of the MAb assay made it possible to identify a subset of breast carcinomas with intensive apoptosis and markers of poor prognosis. These results demonstrate that the measurement of apoptosis in breast carcinomas provides valuable prognostic information.

Enzyme-linked immunosorbent assay (ELISA) for the specific detection of apoptotic cells and its application to rapid drug screening.

We have developed a solid-phase ELISA for the specific and sensitive detection of apoptotic cells. This method is based on the ability of a monoclonal antibody (MAb) against single-stranded DNA (ssDNA) to specifically identify apoptotic cells. The assay involves binding of cells to 96-well microtiter plates, treatment of the attached cells with formamide to denature DNA in apoptotic cells and one-step staining of the denatured DNA with a mixture of anti-ssDNA MAb and peroxidase-conjugated anti-mouse IgM. A near linear increase in signal was seen as the number of apoptotic cells increased from 500 to 5000. Untreated and necrotic cells or cells with single-stranded DNA breaks induced by H(2)O(2) did not produce signal above the background level. In leukemic cell cultures grown, treated with ID(50) concentration of etoposide, stained and analyzed in the same 96-well assay plate, intense ELISA signal was detected. The ratio of absorbance values from drug resistant and drug-sensitive cell lines treated with etoposide was in agreement with the degree of resistance determined by growth inhibition assays. These data show that this ELISA has sufficient sensitivity for use in drug screening protocols. In breast cancer cell cultures treated with cisplatin, ELISA absorbance increased only after treatment with drug concentrations 10-fold higher than concentrations inducing 95% growth inhibition. In cultures treated with staurosporine, there was a near linear relation between the ELISA absorbance values and cytotoxicity in the range of 15-92% growth inhibition. The absence of apoptotic signal in breast cancer cells treated with cytotoxic concentrations of cisplatin indicated that this drug kills cells by non-apoptotic mechanisms, whereas apoptosis was the dominant mechanism of cell death caused by staurosporine. The formamide-MAb apoptosis ELISA described here may provide a basis for high-throughput screening of drugs based on their ability to induce or suppress apoptosis.

Flow cytometric analysis of double-stranded RNA content distributions.

A staining procedure is described for quantitative analysis of cellular RNA content distributions by flow cytometry (FCM). Cells were fixed in ethanol, treated with DNAse and stained with propidium iodide. FCM analysis showed that more than 90% of the fluorescence resulted from the double-stranded RNA (dsRNA) bound fluorochrome. The dsRNA content distributions were measured in HeLa S3 cells in culture 24-120 hr after plating, in L1210 ascitic leukemic cells 1-7 days after transplantation, and in regenerating bone marrow 3-7 days after injection of cyclophosphamide. In all three cell populations, maximal dsRNA content was observed during the period of most active cell proliferation, as determined by the S-phase index derived from the DNA histograms. In the dsRNA distributions in L1210 leukemia cell populations 1-2 days after transplantation, two separate peaks were evident, representing weakly fluorescent, presumably nontumor cells, and intensively fluorescent tumor cells. The amount of dsRNA-bound fluorochrome was significantly greater in L1210 cells than in normal and regenerating bone marrow cells and also greater in spontaneous thymic lymphoma cells than in normal thymic cells.

Identification of apoptotic cells by formamide-induced dna denaturation in condensed chromatin.

In this article we describe a novel effect of formamide on DNA of apoptotic nuclei and present a method for specific detection of apoptotic cells based on this effect. Our observations show that formamide induces DNA denaturation in apoptotic nuclei but has no such effect on DNA of non-apoptotic cells. Formamide-induced DNA denaturation combined with detection of denatured DNA with a monoclonal antibody (MAb) against single-stranded DNA made it possible to specifically identify the apoptotic cells. This procedure produced intense staining of the condensed chromatin in the apoptotic nuclei. In contrast, necrotic cells from cultures treated with sodium azide, saponin, or hyperthermia did not bind this antibody, demonstrating the specificity of the formamide-MAb assay for the apoptotic cells. However, TUNEL stained 90-100% of necrotic cells in all three models of necrosis. Because the MAb did not stain cells with single- or double-stranded DNA breaks in the absence of apoptosis, we conclude that staining of the apoptotic nuclei is not influenced by DNA breaks and is induced by specific changes in condensed chromatin, such as damage to the DNA-histone interactions. Importantly, the formamide-MAb technique identified apoptotic cells in frozen sections and in histological sections of formalin-fixed, paraffin-embedded tissues.

Synergistic induction of apoptosis in breast cancer cells by tamoxifen and calmodulin inhibitors.

Breast cancer cells are relatively resistant to the induction of apoptosis (AP) and drug regimens which readily activate apoptotic death, may enhance the antitumor effect. Rapid and intensive induction of apoptosis was observed in estrogen receptor positive and negative breast cancer cell cultures treated with tamoxifen (TMX) combined with the calmodulin antagonists trifluoperazine (TFP) or W7. TMX (1-5 microM) alone or calmodulin antagonists alone did not induce apoptosis. Importantly, intensive apoptosis was also induced by TMX and TFP in the cells obtained from primary human breast carcinomas. Inhibition of the Ca2+ calmodulin signaling pathway is an effective way to activate apoptotic death in epithelial cells. Combination of TMX with non-toxic calmodulin inhibitors may increase the preventive and therapeutic effects of TMX.

Protection from apoptotic cell death by interleukin-4 is increased in previously treated chronic lymphocytic leukemia patients.

Chronic lymphocytic leukemia (CLL) cells were cultured in a medium supplemented with 0.01-1 ng/ml interleukin-4 (IL-4) for 18 h, fixed and analyzed on a flow cytometer. The percentage of apoptotic (AP) cells with hypodiploid DNA content was determined from DNA histograms. IL-4 at 0.01 ng/ml protected from spontaneous apoptosis of cells from previously treated CLL patients, but had very little effect on apoptotic death in cultures of cells from untreated patients. The number of AP cells in the absence of IL-4 was similar in cultures from treated and untreated patients. The concentration of IL-4 which inhibited spontaneous apoptosis by 50% was less than 0.01 ng/ml for pretreated patients and close to 1 ng/ml for untreated patients. Stage of the disease had no effect on the level of spontaneous apoptosis and its sensitivity to IL-4. Protection from apoptosis by IL-4 was not accompanied by the upregulation of bcl-2 protein. The number of AP cells in methylprednisolone hemisuccinate (MP) treated cultures from previously treated patients was significantly lower than in cultures from untreated patients in the presence of 0.01-1.0 ng/ml IL-4. Treatment with the combination L-phenylalanine mustard (L-PAM)+ fludarabine induced synergistic apoptotic response. Apoptosis induced by this combination was relatively resistant to IL-4 in patients treated with chlorambucil and prednisone, but not in patients previously treated with fludarabine. Protection from cytotoxicity by IL-4 may be one of the mechanisms of acquired drug resistance in CLL.

Apoptosis (programmed cell death) and the evaluation of chemosensitivity in chronic lymphocytic leukemia and lymphoma.

Chronic lymphocytic leukemia and lymphoma cells were treated with antitumor drugs in vitro and analyzed by flow cytometry to measure the number of apoptotic (AP) cells and DNA damage in the cells that escaped apoptotic death. AP cells were identified by a high sensitivity of DNA to thermal denaturation, which induced binding of antibody to single-stranded DNA, and by decreased stainability of cells with the intercalating DNA dye propidium iodide. The appearance of AP cells was prevented by Zn++ and inhibited by phorbol ester. AP cells were induced by alkylating agents, antimetabolites, and anthracyclines. A linear relationship between L-phenylalanine mustard dose and the number of AP cells was observed. A synergistic interaction between drugs was detected by an increased number of AP cells and by the intensity of DNA damage in non-apoptotic cells. A most interesting example of synergism was the combination of alkylating agents with fludarabine. Linearity of dose-response curves, and the capability to detect drug synergism and to evaluate variable response of cells from different patients to single agents and combinations suggest that flow cytometry of apoptosis will provide a basis for chemosensitivity tests in leukemia and lymphoma.

Detection of apoptosis in leukemic and breast cancer cells with monoclonal antibody to single-stranded DNA.

In cultures of leukemic HL-60 and MOLT-4 cells treated with etoposide all nuclei with distinctive morphology of apoptosis (chromatin condensation at the nuclear periphery, nuclear fragmentation) were stained with monoclonal antibody F7-26 specific for single-stranded DNA. DNA in interphase and mitotic cells of control cultures and DNA in necrotic cells of cultures treated with sodium azide did not bind the antibody. In monolayer cultures of breast cancer cell line MDA-468 treated with tamoxifen for 4 hours all cells detached from substratum. These cells were apoptotic by nuclear morphology and stained with F7-26. Subset of cells without visible chromatin condensation but stained with F7-26 was detected among cells still attached to the substratum 1 hour after addition of tamoxifen. Thus, in breast cancer cells reactivity with F7-26 preceded chromatin condensation detected by fluorescence microscopy. Apoptotic cells stained with the antibody and non-apoptotic cells with background fluorescence were completely separated on two-parameter plots generated on a flow cytometer. Linear relation between percentage of apoptotic cells and ELISA reactivity with F7-26 in the cells attached to microtiter plates was demonstrated. These data show that apoptotic response can be measured by ELISA using staining with F7-26. Cells undergoing apoptosis can be detected by the procedure based on thermal denaturation of DNA in situ in the presence of Mg2+ with subsequent staining with the antibody specific for DNA in single-stranded conformation. Correlation between nuclear morphology typical of apoptosis in various cell types demonstrated that staining with monoclonal antibody F7-26 provides specific cytochemical marker for apoptotic cells.

Inhibition of DNA repair in cells treated with a combination of alkylating agents.

Aphidicolin (AP) or hydroxyurea (HU) inhibited DNA repair and enhanced cytotoxicity in human ovarian carcinoma cells A2780 treated with L-phenylalanine mustard (L-PAM) combined with cisplatin or thioTEPA, and in the cells treated with cisplatin combined with thioTEPA. In cultures treated with L-PAM or cisplatin alone post-treatment with AP or HU had no effect on DNA repair and produced only additive cytotoxicity. Post-treatment with AP + HU inhibited DNA repair and enhanced cell killing in cultures treated with L-PAM alone. The inhibitor of protein synthesis cycloheximide protected cells from the cytotoxicity of AP + HU but had no effect on synergistic cell killing produced by DNA repair inhibition. In cisplatin-resistant cells A2780/CP post-treatment with AP + HU enhanced the cytotoxicity of L-PAM, but not of cisplatin. However, in resistant cells treated with cisplatin combined with L-PAM or thioTEPA DNA repair inhibitors decreased IC90 of cisplatin. Treatment of cells with two alkylating agents enhanced the sensitivity to DNA repair inhibitors and eliminated low sensitivity to inhibitors of repair associated with drug resistance.

Apoptosis in human breast and gastrointestinal carcinomas. Detection in histological sections with monoclonal antibody to single-stranded DNA.

We report application of a novel immunohistochemical procedure for the staining of apoptotic (AP) cells in paraffin sections using monoclonal antibody (MAb) to single-stranded DNA. MAb differentiated between apoptosis and necrosis and in contrast to in situ end labelling specifically stained only AP cells. AP carcinoma cells stained with the antibody were detected in 32 of 58 infiltrating human breast carcinomas and in 9 of 15 colon adenocarcinomas. Stromal cells stained with the MAb were observed in all carcinomas, including those in which no AP carcinoma cells were detected. There was a strong positive correlation between the presence of AP cells, loss of hormone receptors and a high proliferation rate in breast carcinomas. AP cells were present in 80-87% of receptor-negative carcinomas, while most of receptor-positive breast carcinomas did not contain AP cells. Apoptosis in tumor cells was detected significantly more frequently among breast carcinomas with high, than among carcinomas with low S-phase fraction. AP cells were present in 93-95% of breast carcinomas which were receptor-negative and had a high S-phase fraction. Immunostaining demonstrated a strong positive correlation between the loss of bcl-2 protein and intensive apoptosis in breast carcinomas. Association between apoptosis and markers of poor prognosis in breast cancer (loss of hormone receptors, intensive proliferation, loss of bcl-2 protein) indicates that apoptotic cell death is typical of more aggressive carcinomas.

[Mouse Lewis carcinoma cell population heterogeneity and sensitivity to cyclophosphamide]. / Geterogennost' kletochnoi populiatsii i chuvstvitel'nost' k tsiklofosfamidu kartsinomy Liuis myshi.

Cell kinetics in the large Lewis carcinoma growing in mice subcutaneously was characterized by the following parameters: at the tumor periphery -tc=11.3 hr, tG2=1.4 hr, tS=8.8hr, tG1=1.1 hr, LI=47%, Pc=61.8%; at the tumour center - 20.7 hr, 2.9 hr, 16.0 hr, 1.8 hr,31.2%, resp. Injection of cyclophosphamide induced degeneration of all the cells in slowly growing central part of the tumour, and only of part of cells on the fast proliferating tumour periphery. It is suggested that in the central part of the tumour there are no stem cells, and that this region regenerates when the transition of cells from the tumour periphery is arrested by cyclophosphamide.

[Effect of methotrexate on the leukemic cell cycle in mouse ascitic leukemia L1210]. / Vliianie metotreksata na tsikl leikoznykh kletok astsitnoi leikemii L1210 myshei

In cells of L1210 ascite leukemia cells, methotrexate inhibited H3-thymidine incorporation, blocked shortly (during 4 hours) the G1 leads to S transition, and did not affect cells in G2-phase or in the late S phase. Almost half a cell population was degenerated and cells in S- and G1-phases were affected in equal proportion. This may suggest that methotrexate is not S-phase specific for cells of leukemia L1210. A simultaneous administration of vinblastine increases the antitumour effect of methotrexate. Cells in G2-phase constitute, presumably, a significant proportion of cells recovered after methotrexate administration. A comparison of the data obtained with literature evidence shows that in the sensitive (leukemia L1210) and resistant (acute mieloid leukemia of man) forms of leukemia, methotrexate affects cells that are in S-phase, whereas cells being in G1-phase are affected only when the sensitive tumours are treated.

[Potentiation of the antitumor action of cyclophosphamide with a change in the cell population makeup and an increase in cellular permeability]. / Usilenie protivoopukholevogo deistviia tsiklofosfamida pri izmenenii sostava kletochnoi populiatsii i uvelichenii pronitsaemosti kletok

Cells of Ehrlich ascites tumor survived after cyclophosphamide injection showed no multiplication during 48 hours. As a result, vinblastine injection simultaneously with cyclophosphamide or following 24 hours produced no additional death of cells. The administration of cyclophosphamide 6 hours after vinblastine resulted in the death of cells 30 times as much as in the injection of both substances simultaneously. Synergism was due to the disappearance of cells in phase G from the population, which are resistant to cyclophosphamide. Tween 80 enhanced an antitumor effect of cyclophosphamide without increasing the toxicity.