Tobacco alkaloid derivatives as inhibitors of breast cancer aromatase

The inhibition of estrogen biosynthesis by the use of aromatase inhibitors is emerging as a valuable approach to breast cancer therapy. Because smoking has a profound effect on estrogen-related processes we examined the ability of tobacco constituents to suppress estrogen production by breast cancer aromatase. N-n-octanoylnornicotine and N-(4-hydroxyundecanoyl) anabasine suppressed aromatase activity in culture of two human breast cancer cell lines, MDA-MB-231 (IC50 of 310 and 20 microM, respectively) and SK-BR-3 (IC50 of 450 and approximately 2 microM, respectively). MDA-MB-231 cells induced by 250 nM dexamethasone or 1 mM (Bt)2cAMP were slightly more sensitive to both inhibitors. Kinetic analyses showed that inhibition by N-(4-hydroxyundecanoyl)anabasine is competitive with respect to androstenedione as substrate, with apparent Ki values of 0.2 microM against microsomal aromatase activity derived from both (Bt)2cAMP-induced MDA-MB-231 cells and human breast tumor tissue. The corresponding apparent Ki against human placental microsomal aromatase activity was 0.4 microM. These results indicate that acyl derivatives of nornicotine and anabasine block estrogen formation in breast tumor cells and tissue and could contribute to the decreased intra-tissue estrogen levels in women who smoke.

Catalytic efficiency of expressed aromatase following site-directed mutagenesis

Mutant aromatase cytochrome P-450s, expressed in CHO cells after transfection with cDNAs, have been characterized in terms of their catalytic efficiencies. After solubilization from microsomes, specific aromatase P-450 content of wild-type and mutants Pro308Phe, Asp309Asn, Asp309Ala and Phe406Arg was quantitated by a sandwich enzyme-linked immunosorbent assay (ELISA). Microsomal aromatase activity was determined by the 3H-water method using [1 beta-3H]androstenedione as substrate. Estimations of the actual turnover rate (catalytic efficiency) were derived from the combined data. The P-450 content in the mutants varied but was always less than that in the wild type. Hence, the decreases in the Vmax observed in the mutant enzymes did not correlate completely with reductions in catalytic effectiveness. In recent studies on the structure-function relationship of aromatase cytochrome P-450, the observed reduction of enzyme activity in terms of Vmax following site-directed mutagenesis led to the assumption that there was a corresponding loss of catalytic effectiveness. The present study reveals that a lower P-450 content can contribute significantly to decreasing catalytic activity in the mutants. In fact, in mutant Phe406Arg which exhibited virtually no catalytically active aromatase, the specific P-450 content was below the detectable level. Because of its location, the result of this latter mutation could be a major structural perturbation of the heme-binding property. Thus, interpretation of losses and reductions in aromatase activity resulting from single amino-acid replacement should take into account changes in the specific content of aromatase cytochrome P-450.

Structure-function studies of human aromatase

Site-directed mutagenesis experiments have been carried out to determine the structure-function relationship of human aromatase. By sequence comparison, the region in aromatase that corresponds to the distal helix of cytochrome P-450cam has been identified to be Gln-298 to Val-313. Eight aromatase mutants with changes in this region, i.e. C299A, E302L, P308F, D309N, D309A, T310S, T310C, and S312C, have been generated using a mammalian cell stable-expression system. The results from site-directed mutagenesis studies indicate that the region containing Gln-298 to Val-313 is indeed a very important part of the active site of aromatase. The catalytic properties of P308F, D309N, and D309A have been examined in detail and are discussed. Active site-directed labeling is also an important approach to investigate the structure-function relationship of aromatase. HPLC-linked electrospray mass spectrometry is indicated as a useful technique for the characterization of active site-directed probe-modified enzyme. The mass spectral analysis of aromatase suggests that aromatase is glycosylated.

Kinetic properties of aromatase mutants Pro308Phe, Asp309Asn, and Asp309Ala and their interactions with aromatase inhibitors

Mutant forms of aromatase cytochrome P-450 bearing modifications of amino acid residues Pro308 and Asp309 and expressed in transfected Chinese hamster ovary cells were subjected to kinetic analysis and inhibition studies. The Km for androstenedione for expressed wild type (11.0 +/- 0.3 nM SEM, n = 3) increased 4-, 25- and 31-fold for mutants Pro308Phe, Asp309Asn and Asp309Ala, respectively. There were significant differences in sensitivity among wild type and mutants to highly selective inhibitors of estrogen biosynthesis. 4-Hydroxyandrostenedione (4-OHA) a strong inhibitor of wild type aromatase activity (IC50 = 21 nM and Ki = 10 nM), was even more effective against mutant Pro308Phe (IC50 = 13 nM and Ki = 2.8 nM), but inhibition of mutants Asp309Asn and Asp309Ala was considerably less (IC50 = 345 and 330 nM and Ki = 55 and 79 nM, respectively). Expressed wild type aromatase and Pro308Phe aromatase were strongly inhibited by CGS 16949A (IC50 = 4.0 and 4.6 nM, respectively) whereas mutants Asp309Asn and Asp309Ala were markedly less sensitive (IC50 = 140 and 150 nM, respectively). CGS 18320B produced similar inhibition. Kinetic analyses produced Ki = 0.4 nM for CGS 16949A inhibition of wild type versus 1.1, 37 and 58 nM, respectively, against Pro308Phe, Asp309Asn and Asp309Ala. The results demonstrate significant changes in function resulting from single amino acid modifications of the aromatase enzyme. Our data indicate that mutation in Asp309 creates a major distortion in the substrate binding site, rendering the enzyme much less efficient for androstenedione aromatization. The substitution of Pro308 with Phe produces weaker affinity for androstenedione in the substrate pocket, but this alteration favors 4-OHA binding. Similarly, mutant Pro308Phe exhibits a slightly greater sensitivity to inhibition by CGS 18320B than does the wild type. These results indicate that residues Pro308 and Asp309 play critical roles in determining substrate specificity and catalytic capability in aromatase.

Murine monoclonal antibodies reactive with a variety of androgen independent Dunning rat prostate adenocarcinoma sublines also reactive with human prostate adenocarcinoma

Murine hybridoma-derived monoclonal antibody (MCA) to Dunning rat prostate adenocarcinoma R-3327HIS (androgen independent type) has been produced by fusing P3x63 Ag8-653 myeloma cells with splenocytes of BALB/c mice which were immunized with R-3327HIS tumor cell membranes. One monoclonal antibody designated MCA-R1 (IgG2a subtype) produced an intense immunostaining of various androgen independent Dunning rat prostate tumor sublines (HIS, HIM, HIF, AT-1, AT-2, AT-3, MAT-Lu and MAY-Ly-Lu), but did not stain other tumors of rat origin or normal rat tissues. Marginal immunostaining was detected in the androgen responsive R-3327H and R-3327G tumor subline. Although MCA-R1 antibody did not react with the regressed prostate tumor of R-3327H or R-3327G, it strongly reacted with the relapsed prostate tumor from either R-3327H or R-3327G tumor derived from rats were treated with diethyl stilbestrol (DES) or castration. MCA-R1 antibody also produced a strong cross-reaction with human prostate adenocarcinoma. Like the Dunning rat tumor, human adenocarcinoma exhibited distinct immunostaining patterns with respect to intracellular localization among well differentiated, moderately differentiated and poorly differentiated tumor. Benign prostatic hyperplasia or other normal tissues did not stain. Immunofluorescence, immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioautographic analysis revealed that the Dunning rat prostate tumor antigen recognized (m.wt. 50 and 120 Kd) by MCA-R1 antibody are localized on both cell surface and in the cytoplasm. This MCA may represent a potential reagent for the study of tumor biology and immunotherapy of prostate tumor.

Growth inhibition by diethylstilbestrol and relapse of the Noble rat prostatic tumor

The response of androgen-sensitive Noble (Nb) rat prostatic adenocarcinoma [2Pr-121D (1)] to varying doses (50 approximately 1,000 micrograms/kg body weight) of diethylstilbestrol (DES) was investigated and characterized with respect to cytosol and nuclear androgen binding profiles, histology and pattern of relapse. Inhibition of tumor growth was closely related to the dose of DES. Treatment at all but the lowest dose (50 micrograms/kg) initially caused tumor regression, whereas serum testosterone concentrations in all groups, including that receiving the lowest dose, were decreased to castrate levels. Histologically, while extensive cellular destruction was clearly evident at higher doses of DES, some active tumor cells appeared to survive. Tumors eventually relapsed when higher doses of DES were stopped or with the continued administration of low doses. The cytosol dihydrotestosterone (DHT) receptor in this tumor line, as determined by sucrose density gradient, dextran charcoal and Sephadex column methods, was negative. Nuclear binding, however, was positive. Salt-extractable and salt-resistant fractions of nuclei derived from the untreated primary tumor and relapsed tumor following DES treatment contained high affinity androgen receptor. Comparison of binding constants revealed no significant differences. Our findings, based on the Nb rat prostatic tumor model, indicate that DES acts not only by eliminating circulating testosterone, but also by a direct cytotoxic effect on malignant cells. The results also suggest the lack of an apparent relationship between the loss of hormone responsiveness associated with recurrence of prostatic tumor growth and nuclear androgen binding parameters.

Protein profiles of benign hypertrophic prostate: stroma-abundant distribution of BPH-associated nonhistone proteins

Mechanically isolated epithelium and stroma from benign hypertrophic prostates were highly pure on the basis of histochemical and biochemical criteria. By electrophoretic analyses, whole cellular and nuclear proteins were compared among whole tissues, epithelium, and stroma. The characteristic protein profiles of benign hypertrophic prostates were reflected in the electrophoretic patterns of the stroma. Two-dimensional gel electrophoretic patterns of the epithelium were different from those of the stroma with exception of about 18 major spots that were common to both fractions. Of the protein species separated, 35K/6.7 (molecular weight/pI) and 36K, which was composed of two species with pI of 4.4 and 4.6, were abundant in the epithelium and stroma, respectively. Nuclei prepared from whole tissues of benign hypertrophic prostates contained three kinds of nonhistone proteins (NHP) closely associated with benign prostatic hypertrophy (BPH); 42 K-NHP, 55 K-NHP and 190 K-NHP. Electrophoretic analysis of the nuclear proteins revealed that all the BPH-associated nonhistone proteins were abundantly distributed in the nuclei of the stroma.

Immunotherapy in a spontaneously developed murine mammary carcinoma with syngeneic monoclonal antibody

A new spontaneously arisen murine breast tumor, designated JC, has been established in immunocompetent BALB/c mice. Upon reestablishment of tumor in vitro and in vivo, the epithelial murine tumor cells retained their original papillary adenocarcinoma morphology. Various immunotherapy protocols have been performed in previously implanted and progressively growing JC tumor in syngeneic hosts with a murine monoclonal antibody (McAb), F36/22 (IgG3). Affinity of McAb binding to JC tumor cells was determined to be 6.1 x 10(7) L/M. Quantitatively 1.2 x 10(5) molecules of McAb bound to a JC tumor cell. Immunotherapeutic effectiveness in vivo on a tumor mass after its establishment is a major feature of this experimental tumor model. When four sequential administration of McAb, i.p., at a dose of 400 micrograms 4 days apart were used, McAb-treated animals showed statistically significant tumor regression and longer survival than those of control animals treated with an irrelevant McAb of the same isotype. Two temporal phases of tumoricidal activity were observed as measured by tumor volume reduction. The first phase of tumoricidal response (tumor regression) was detected within days upon the first administration of McAb. A distinct second phase followed within 3-5 weeks after the last McAb administration, which resulted in tumor necrosis even in large tumors. Histological examinations revealed heavy infiltration of inflammatory cells at the beginning of the second phase. Similar tumor regression was also obtained from animals treated with a single dose (400 micrograms) of McAb followed by injections of McAb with complete and incomplete adjuvant, respectively. These results demonstrate that this syngeneic murine mammary tumor can serve as a potential preclinical model for investigation of parameters and mechanisms associated with McAb immunotherapy.

Retardation of prostate tumor progression in the Noble rat by 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase

The effect of 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase has been evaluated on tumor growth in the Noble rat model of prostatic adenocarcinoma. The growth characteristics of the tumor line 2Pr-121D(1) were consistent with heterogeneity of cell types, composed of androgen-sensitive and androgen-insensitive malignant cells. Both sodium 4-methyl-3-oxo-4-aza-5 alpha-pregnane-20 (s)-carboxylate and 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 and 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one significantly retarded tumor progression. Each agent increased tumor volume doubling time by approximately 62%. On the basis of their similarities to female rats and male castrate group, in terms of growth rate, tumor doubling time, and histologic characteristics, the treatments with the 4-methyl-4-aza-steroids appeared to produce effects common to both castration and estrogenization (chronic administration of pharmacologic doses of estrogen). The failure of 5 alpha-reductase inhibitors to be active as antiprostatic agents in vivo has hitherto detracted from their use of therapeutic agents. Present studies demonstrate that the 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase may represent an alternative to orchiectomy and chronic estrogen therapy for the management of the hormone-dependent phase of prostate cancer.

Selective inhibition of prostatic tumor 5 alpha-reductase by a 4-methyl-4-azasteroid

The effect of sodium 4-methyl-3-oxo-4-aza-5 alpha-pregnane-20(s)-carboxylate (4-MAPC) on testosterone metabolism was investigated in rat and human prostates in organ culture. The general properties of the test system for androgen metabolism and response to inhibitors were in close agreement with in vivo observations. As an inhibitor of prostatic tumor 5 alpha-reductase, 4-MAPC was equally as effective as 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one, reported to be a potent 5 alpha-reductase inhibitor. Inhibition of 5 alpha-reductase activity by 4-MAPC, but not by 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one, was accompanied by concomitant stimulation of 17 beta-oxidation of testosterone. This differential effect was observed in explants of human prostatic carcinoma and benign prostatic hypertrophy containing a relatively high degree of glandular hyperplasia. It was also seen in explants of dorsolateral rat prostate but not in the ventral prostate. 4-MAPC exhibited low affinity for rat prostatic cytosol 8S androgen receptor. Steroid extraction of purified nuclei from inhibited rat tissues revealed substantial amounts of radioactivity derived from [3H]testosterone cochromatographed with other metabolites in addition to dihydrotestosterone. The endocrine changes produced by this inhibitor of 5 alpha-reductase are reconcilable with the responsiveness of androgen-sensitive malignant prostatic cells to hormonal therapy.

Prostatic cancer--II. Inhibitors of rat prostatic 4-ene-3-ketosteroid 5 alpha-reductase derived from 6-methylene-4-androsten-3-ones

The studied 6-methylene-4-androsten-3-ones proved to be significantly inferior to 6-methylene-4-pregnene-3,20-dione and its 17-acetoxy derivative described in Part 1 as inhibitors of 4-ene-3-ketosteroid 5 alpha-reductase [1] in vitro. Surprisingly, the 6-methylene derivative of testosterone was only weakly active until acetylated, when an effective inhibitor was obtained. Etherification of the hydroxyl-group, its replacement by a hydrocarbon chain, or introduction of a substituent at C17 or on the methylene group led to virtual loss of activity. 17 alpha-Chloro-6-methylene-4-androstene-3-one had ca 60-70% of the potency of progesterone, but was inactive as enzyme inhibitor in explants of rat prostate in tissue culture and in in vivo studies. 6-Methylenetestosterone acetate was weakly active as enzyme inhibitor in explants of human prostate in tissue culture and produced a histological picture closely resembling testosterone and differing from that of cyproterone acetate. In vivo in the rat it had 80% of the androgenic activity of testosterone propionate. The foregoing data have been used to define some structural characteristics necessary for enzyme inhibition and to draw some conclusions regarding the architecture of the androgen and progesterone receptors and of the enzyme active site.

Inhibitory effects of some steroidal 6-methylene derivatives on 5 alpha-reductase activity in human and rat prostate

Using a short-term organ culture assay, some 6-methylene derivatives of progesterone and testosterone have been evaluated for their effects on testosterone metabolism in rat and human prostatic tissues, and on DNA synthesis in explants from 7-day castrated rats. Comparative studies showed that the ability to inhibit 5 alpha-reductase activity was fairly specific with respect to structural requirements. Methylene substitution at the C6 position of the progesterone molecule was associated with high inhibitory activity. In explants prepared from human prostates, 6-methylene progesterone (II) had 70-85% (mean of 79% for 4 BPH tissues) of the potency of unmodified progesterone (I). Its 17 alpha-acetoxy-6-methylene analog (III), however, had only 32-73% (mean of 53% for 5 BPH specimens) of the activity of (I). The degrees of inhibition in rat and human prostatic tissues were similar. Inhibition of 5 alpha-reductase activity in cultured explants by 6-methylene progesterone (II) could not be reversed by change in media. The 6-methylene derivatives had little or no effect on DNA synthesis. Histological examination confirmed a lack of effect on basal cell proliferation. However, morphological alterations affecting epithelial cell height and secretory activity were clearly evident. These results indicate that, under our experimental conditions, the main effect of inhibition of 5 alpha-reductase activity in prostatic tissues by 6-methylene derivatives of progesterone is related to suppression of differentiated function.

A model for studies on the response of the ventral prostate to oestrogens

The effects of oestrogen administration on the weight of ventral and dorsolateral prostates were studied in castrated rats of Wistar-Furth and Copenhagen strains. Direct effect of oestradiol (Oe2) on prostatic tissue was also investigated in organ culture. Oe2-treated animals received daily injections of 50 μg for 7 days. Control animals were treated with the vehicle only (peanut oil). In 4 month old Copenhagen rats the mean weight of the ventral prostates (42.4 ± 9.4 mg/100 g body weight) was significantly higher than that in the control animals (19.9 ± 4.6 mg/100 g body weight, P < 0.0001). No such differences were observed in older Copenhagen rats (9 months old) or Wistar-Furth rats (3 and 6 months old). Thus, this effect of Oe2 on ventral prostate seems both strain specific and age specific. Similar strain and age differences in the Oe2 effect were found in the dorsolateral prostate, but to a smaller extent. Direct interaction of Oe2 with target tissue was demonstrated in culture as evidenced by the ability of the steroid to prevent regression in explants derived from prostates of Copenhagen rats.

The in vivo effects of Oe2 on the prostate weights could not be explained by differences in specific androgen or oestrogen receptor contents or in testosterone (T) metabolism. However, the prostates of younger Copenhagen rats differed from those of all other groups in three respects: 1) they contained high levels of oestramustine binding protein (OeBP), 2) they had the highest amount of uptake of radioactivity into the nuclear residue, and 3) their histological picture was characterized by diffuse stromal architecture having the appearance of oedematous tissue.

Fluid inhibition as a factor in estrogen-induced increase of prostatic weight in castrated rats

The mechanism by which estrogens inhibit castration atrophy has been investigated morphologically and biochemically utilizing ventral prostate from Copenhagen rats. The suppression of weight loss and gross edematous appearance of the prostate associated with the in vivo effect of 17 beta-estradiol (E2) could not be accounted for by DNA and protein synthesis. Increase in the fluid content in the tissues was confirmed by demonstration of significant increase in the ratio of wet/dry tissue weights. Light microscopy demonstrated that the main effects were on the stroma, characterized by large interglandular areas almost totally devoid of collagen resulting in an edematous appearance. Electron microscope studies showed an abundance of fluid localized adjacent to the capillary endothelium and some red blood cells indicating disturbances in capillary permeability. The combination of a prolactin secretion inhibiting agent with E2 alone, indicating an involvement of prolactin the estrogen effect. Differences in blood prolactin concentration between the strains of rats may influence the sensitivity of the prostate to estrogens.

Estramustine phosphate: metabolic aspects related to its action in prostatic cancer

Estramustine phosphate, a drug effective in a substantial number of patients with cancer of the prostate who had failed on other forms of therapy, has been shown to be split into its constituents, that is estradiol-17beta and the carbamate nitrogen mustard by non-cancerous and cancerous human prostatic tissues. This fact may explain, in part, the mechanism of action and efficacy of the drug in patients with cancer of the prostate. In addition to presenting results on the hydrolysis and its products accomplished by human prostatic tissues we discuss the limitations of extrapolating animal results with estramustine phosphate to the human condition and possible parameters that bear upon the insignificant toxic and estrogenic effects observed in patients given estramustine phosphate.

Acetylation and phosphorylation of nuclear proteins from growing or dividing rat ventral prostate cells

Acetylation and phosphorylation of nuclear histone and nonhistone proteins from rat ventral prostate cells undergoing cellular hypertrophy (growth) or cellular hyperplasia (replication) were compared in minced ventral prostate incubated for 1 h with 32PO4 and [3H]acetate.Under these conditions, phosphorylation of unfractionated prostate histones from hormone-treated animals was increased, but acetylation was not. When radioactive histones from the four experimental groups were separated by polyacrylamide gel electrophoresis, evidence for differential labelling of individual histones, especially acetylated or phosphorylated histones F1 and F2a2, was obtained. This was also true of histones labelled with radioactive amino acids. These differences were more marked with histones from replicating cells.Phosphorylation of prostate nuclear nonhistone proteins from hormone-treated rats was greater than their controls. Proteins of intermediate molecular weight (20–45 × 103) were most highly phosphorylated; nuclear extracts from replicating (C7T2) cells contained additional labelled higher molecular weight proteins and fewer lower molecular weight proteins (< 20 × 103), compared with hypertrophic (C3T3) cells. Previous treatment with testosterone propionate increased the apparent acetylation of nonhistone proteins, but its marked inhibition by puromycin and resistence to hydrolysis suggests that much of this incorporation occurred during their biosynthesis, and did not represent covalent modification of previously synthesized proteins.

Some new approaches to potential test systems for drugs against prostatic cancer

We have previously reported on test systems, based on 5alpha-reductase (5alpha-RA) and arginase activities and steroid deposition in animal prostates, potentially useful in screening drugs possibly effective in cancer of the prostate. Recently, we have concentrated on the development of other in vivo and in vitro systems which may prove of further value in testing such drugs. These systems include the following: (a) The effects of drugs on 5alpha-RA activity in human and animal non-malignant and human cancerous prostatic tissues in organ culture. The parameters necessary for the maintenance of optimal 5alpha-RA in such explants have been determined, and it has been shown that certain agents (estramustine phosphate, progesterone, estradiol-17beta) can inhibit 5alpha-RA under in vitro conditions, pointing to the potential use of such an approach in screening various cytostatic agents. In addition, 65Zn deposition, the histology, and the androgen metabolism in such tissues in organ culture are being determined as additional parameters. (b) The deposition of 65Zn in the rat dorsolateral gland, particularly as affected by prolactin and testosterone, and the effects of chemotherapeutic agents on such deposition. Methotrexate and CCNU have been shown to be potent inhibitors of 65Zn deposition in the dorsolateral gland. The parameters related to zinc metabolism in the prostate are being further investigated. (c) The demonstration of receptors for estrogens (estradiol-17beta, diethylstilbestrol) in the prostate of the baboon. The various parameters related to the specificity of such receptors have been established. The development and standardization of these approaches, some facets of which are reported in the present publication, may prove them to be more sensitive, specific, and optimal than other systems and should afford an opportunity to test various combinations of drugs potentially useful in cancer of the prostate with relative speed, efficacy, and ease of manipulation.

5alpha-Reductase as a target enzyme for anti-prostatic drugs in organ culture

Short-term organ culture of rat and human prostatic tissues has been utilized as a means of testing drlgs potentially useful in cancer of the prostate. Optimal conditions, particularly the concentration of T, have been established for organ culture of such tissues and the effects of various drugs on 5alpha-reductase activity (5alpha-RA) have been utilized as a means of ascertaining antiprostatic actions of the various compounds and drugs tested. Thus, it was shown that estracyt, estradiol-17beta, progesterone, and novel steroids and steroid-conjugates have definite effects on 5alpha-RA in this system.

Increased survival of mouse ependymoblastoma hosts previously treated with dehistonized tumor chromatin

Half of the mice treated with dehistonized chromatin (protein-DNA complex) from a transplantable mouse ependymoblastoma before subcutaneous challenge with the syngeneic tumor survived twice as long as untreated animals.

Changes in acidic chromatin proteins during mammary cell differentiation

Chromatin was prepared from mouse mammary epithelial cell nuclei and histones were removed by extraction with 2.0 M NaCl, pH 6.0. Electrophoresis of the residual acidic chromatin proteins in polyacrylamide gels containing sodium dodecyl sulfate revealed a heterogeneous banding pattern which was tissue specific. Six or more bands among the proteins present in differentiated, lactational cells were not detectable in undifferentiated, virginal cells.In organ culture studies insulin stimulated the incorporation of 3H-tryptophan or 3H-aspartic acid and 3H-leucine into all electrophoretic components of the mammary acidic chromatin protein. Two peak rates of synthesis, preceding and following the peak rate of DNA synthesis, were observed. Synthesis was unaffected by hydrocortisone or prolactin. Synthesis of the six bands characteristic of the lactational cells was initially undetectable in undifferentiated, virginal cells, but was induced after incubation with insulin for 42 h. These results, taken in correlation with previous studies on this system, are consistent with a proposed model in which new species of acidic chromatin proteins may participate in chromatin reconstitution during mammary cell differentiation.

Gene activation in mammary cells

Hormonal activation of gene transcription has been studied in a model system, the mouse mammary gland in organ culture. Transcriptive activity is stimulated in mammary stem cells by insulin, and in mammary alveolar cells by prolactin and insulin. Studies on the template requirement for expression of the genes for milk proteins demonstrate that DNA methylation has an obligatory dependence upon DNA synthesis, but is otherwise independent from hormonal regulation of mammary cell differentiation. Incorporation of 5-bromo-2′deoxyuridine into DNA selectively inhibits expression of the genes for specific milk proteins. Undifferentiated mammary cells activate the synthesis of specific acidic nuclear proteins when stimulated by insulin. Several of these induced acidic nuclear proteins are undetectable in unstimulated undifferentiated cells, but appear to be characteristic components of the nuclei of differentiated cells. These results indicate that mammary cell differentiation is associated with a change in acidic nuclear proteins, and they provide evidence to support the concept that acidic nuclear proteins may be involved in the regulation of gene transcription and of mammary cell differentiation.

Inhibition of DNA polymerase of E. coli by proflavine

Proflavine (3,6-diaminoacridine) inhibits the synthesis of polynucleotides in vitro by DNA polymerase of E. coli (EC 2.7.7.7). The extent of inhibition of the enzyme by proflavine was a linear function of the concentration of the dye bound to DNA up to the point of saturation of strong binding sites (1 mol proflavine for approximately five base pairs).Kinetic studies of DNA polymerase and its inhibition by proflavine were made by following the rate of loss of thymidine triphosphate. The integrated form of the Michaelis–Menten equation allowed the apparent Km to be calculated for the poly (d(A–T)) reaction = 3.6 (S.D. ± 0.6) × 10−5 for six determinations. Inhibition by proflavine was competitive with respect to polynucleotide and the apparent Ki was 7.4 × 10−7 M. The number of nucleotides involved per inhibitory dye molecule was eight, i.e. the number of base pairs involved was four.For non-rate-limiting concentrations of polynucleotide the apparent Km for deoxyribonucleoside triphosphates (one nucleotide) was 5.4 (S.D. ± 3.3) × 10−5 M (five determinations). Inhibition by proflavine was noncompetitive and the apparent Ki was 1.9 × 10−5 M.It is suggested that these findings are accounted for by the increased stability of the acridine–polynucleotide complex.

Proflavine and fidelity of DNA polymerase

With native calf thymus DNA3 as primer and DNA polymerase of E. coli, proflavine (0 × −1 × 10−4 M) inhibited the incorporation of dATP, dCTP, dGTP, and TTP about equally. Using dAT as primer there was inhibition of the rate of synthesis of polynucleotide by proflavine and no more incorporation from dGTP and dCTP than in the absence of the acridine. Nearest-neighbor analysis of the polynucleotide synthesized by DNA polymerase from dATP and TTP showed that sequences of TpT and ApA were formed in the presence of proflavine. Changed sequences were observed whether the reaction was primed with dAT or was unprimed, and the extent of change depended on the concentration of proflavine. The homopolymer dA:dT was identified as one of the products formed.