Imidazo[5,1-f][1,2,4]triazin-2-amines as novel inhibitors of polo-like kinase 1

The synthesis and biological activities of imidazo[5,1-f][1,2,4]triazin-2-amines (imidazotriazines) as novel polo-like kinase 1 inhibitors are reported.

Protection against Chlamydia trachomatis infection in vitro and modulation of inflammatory response in vivo by membrane-bound glycosaminoglycans

Glycosaminoglycans (GAG) efficiently inhibit adherence of several strains of Chlamydia trachomatis to cell lines in vitro, but none of the GAG have been able to inhibit infections in vivo. One possible cause for failure of GAG inhibition in vivo is the inability to deliver a sustained concentration of GAG at the mucosal surface. We tested the possibility of enhancing cell protection by increasing the cell-surface concentration of GAG using membrane-anchored GAG (MAG), composed of phosphatidylethanolamine (PE)-linked GAG. These lipid conjugates were originally designed as extracellular phospholipase A2 (PLA2) inhibitors and exhibit a dual effect: the lipid moiety incorporates into the cell membrane, interfering with the action of PLA2 on cell membranes, and the anchored GAG protects the cell membrane from exogenous inflammatory mediators. We tested the ability of MAG to block chlamydia infection in vitro and in vivo. The MAG blocked infection of epithelial cells in vitro when added to the cells at the same time or before infection, but not if added after the bacteria had already invaded the host cells. One of the MAG led to the production of aberrant Chlamydia vacuoles, suggesting it may inhibit intracellular PLA2 associated with development of the vacuole. Although the MAG did not inhibit vaginal infection of mice, they decreased significantly the level of secretion of the inflammatory cytokines TNF-alpha and IFN-gamma but had no effect on secretion of the neutrophil chemokine, macrophage inflammatory protein-2 (MIP-2). Acute and chronic inflammatory cell infiltrates were not altered by MAG treatment. These findings suggest that lipid conjugation of GAG could be used as a novel approach for increasing cell-surface concentrations of GAG. The inconclusive in vivo results might be due to the physical properties of the tested MAG or an insufficient application protocol, and their improvement might provide the desired inhibitory effects.

Novel Benzophenones as Non-nucleoside Reverse Transcriptase Inhibitors of HIV-1

GW4511, GW4751, and GW3011 showed IC50 values < or =2 nM against wild type HIV-1 and <10 nM against 16 mutants. They were particularly potent against NNRTI-resistant viruses containing Y181C-, K103N-, and K103N-based double mutations, which account for a significant proportion of the clinical failure of the three currently marketed NNRTIs. The antiviral data together with the favorable pharmacokinetic data of GW4511 suggested that these benzophenones possess attributes of a new NNRTI drug candidate.

Mouse strain-dependent chemokine regulation of the genital tract T helper cell type 1 immune response

Vaginal infection with the mouse pneumonitis agent of Chlamydia trachomatis (MoPn) produces shorter courses of infection in C57BL/6 and BALB/c mice than in C3H/HeN mice, while C57BL/6 mice are more resistant to oviduct pathology. A robust Th1 response is extremely important in host defense against chlamydia. In this study we examined gamma interferon (IFN-gamma), interleukin 10 (IL-10), and the T-cell-regulatory chemokines macrophage inflammatory protein-1alpha (MIP-1alpha) and monocyte chemoattractant protein-1 (MCP-1) to determine if differences in these responses were associated with the differential courses of infection seen in these three strains of mice. Increased and prolonged IFN-gamma responses and lower IL-10 responses were observed in the C57BL/6 strain compared to BALB/c and C3H. Examination of genital tract chemokines revealed a marked predominance of MIP-1alpha over MCP-1 only in the C57 strain. Thus, a pattern of high MIP-1alpha and low MCP-1 levels during the first week of infection is associated with an increased Th1 response and a shorter, more benign chlamydial infection. Inhibition of the MCP-1 response in C3H mice increased their later T-cell production of IFN-gamma but decreased their early IFN-gamma response and had no effect on the course or outcome of infection. Inhibition of MCP-1 is not beneficial in chlamydial infection because of its pleiotropic effects.

Early local cytokine profiles in strains of mice with different outcomes from chlamydial genital tract infection

In this study, we expand on the examination of genetically determined differences in host responses that correlate with clearance of Chlamydia trachomatis from the genital tract. We infected C57BL/6, BALB/c, and C3H/HeN mice with the mouse pneumonitis agent of C. trachomatis (MoPn). C57BL/6 mice had the shortest course of infection (22 days) and the lowest incidence of severe hydrosalpinx. BALB/c mice also had a short course of infection (25 days), but all developed hydrosalpinx. C3H/HeN mice had the longest course of infection (38 days), and all developed severe hydrosalpinx. Determination of local cytokine responses by enzyme-linked immunosorbent assay (ELISA) of genital tract secretions revealed that the levels of the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) were significantly increased in the C57BL/6 and BALB/c strains compared to those in the C3H/HeN strain whereas the level of IL-6 was not different. The level of the neutrophil chemokine macrophage inflammatory protein 2 (MIP-2) was increased during the first week of infection in all three strains but was significantly higher in the BALB/c strain, the strain with the most rapid influx of neutrophils into the genital tract. Prolonged detection of MIP-2 in C3H/HeN mice was associated with a protracted presence of neutrophils in the genital tract. Early increases in the levels of the proinflammatory cytokines TNF-alpha and IL-1beta are associated with earlier eradication of infection in the C57BL/6 and BALB/c strains than in the C3H/HeN strain. Increased levels of MIP-2 and neutrophils in BALB/c and C3H/HeN mice relative to C57BL/6 mice suggest that these responses may contribute to pathology.

Does inhibition of tumor necrosis factor alpha affect chlamydial genital tract infection in mice and guinea pigs?

The role of tumor necrosis factor alpha (TNF-alpha) in host defense against chlamydial infection remains unclear. In order to further evaluate the relevance of TNF-alpha to host resistance in chlamydial genital tract infection, we examined the effect of local inhibition of the TNF-alpha response in normal C57 mice and in interferon gamma gene-deficient C57 mice infected intravaginally with the mouse pneumonitis agent of Chlamydia trachomatis. Since the guinea pig model of female genital tract infection more closely approximates the human in terms of ascending infection and development of pathology, we also examined the effect of local inhibition of the TNF-alpha response in guinea pigs infected intravaginally with the guinea pig strain of Chlamydia psittaci. We successfully blocked the early TNF-alpha response in the respective animal models. This blockade had no effect on the numbers of organisms isolated from the genital tract during the time of TNF-alpha inhibition in mice or guinea pigs. Analysis of interleukin-1beta, macrophage inflammatory protein-2, and granulocyte macrophage-colony stimulating factor in the mouse model revealed that blockade of the TNF-alpha response did not alter the release of these proinflammatory proteins. Yet, in TNF-alpha-depleted mice, increased numbers of neutrophils were detected in the genital tract, and, in TNF-alpha-depleted guinea pigs, increased numbers of neutrophils as well as infiltrating lymphocytes were seen in the endocervix. Blockade of TNF-alpha does not affect the level of infection in mice or guinea pigs, but it may decrease TNF-alpha-induced apoptosis of infiltrating inflammatory cells.

Predicting human oral bioavailability of a compound: development of a novel quantitative structure-bioavailability relationship

PURPOSE

The purpose of this investigation was to develop a quantitative structure-bioavailability relationship (QSBR) model for drug discovery and development.

METHODS

A database of drugs with human oral bioavailability was assembled in electronic form with structure in SMILES format. Using that database, a stepwise regression procedure was used to link oral bioavailability in humans and substructural fragments in drugs. The regression model was compared with Lipinski's Rule of Five.

RESULTS

The human oral bioavailability database contains 591 compounds. A regression model employing 85 descriptors was built to predict the human oral bioavailability of a compound based on its molecular structure. Compared to Lipinski's Rule of Five, the false negative predictions were reduced from 5% to 3% while the false positive predictions decreased from 78% to 53%. A set of substructural descriptors was identified to show which fragments tend to increase/decrease human oral bioavailability.

CONCLUSIONS

A novel quantitative structure-bioavailability relationship (QSBR) was developed. Despite a large degree of experimental error, the model was reasonably predictive and stood up to cross-validation. When compared to Lipinski's Rule of Five, the QSBR model was able to reduce false positive predictions.

Conformation and local environment of nucleotides bound to HIV type 1 reverse transcriptase (HIV-1 RT) in the ground state

Nuclear Overhauser effect experiments were used to characterize the protein environment and conformations of dTTP, dATP and AZTTP bound to HIV-RT in the ground state. The results show the initial binding sites for the nucleotides overlap but are not completely coincident. All of the bound nucleotides assume the same anti C4'-exo conformation.

Identification and characterization of mutations in hepatitis B virus resistant to lamivudine. Lamivudine Clinical Investigation Group

Cirrhosis and hepatocellular carcinoma occur as long-term complications of chronic hepatitis B virus (HBV) infection. Antiviral therapy is potentially a successful approach for the treatment of patients with HBV infection, which includes the nucleoside analog, lamivudine [(-)2'-deoxy-3'-thiacytidine, 3TC]. Although resistance to lamivudine therapy has been reported in several HBV-infected patients, the pattern of resistance-associated mutations in HBV has not been fully characterized. We report a DNA sequence database that includes a 500-base pair region of the HBV polymerase gene from 20 patients with clinical manifestations of lamivudine resistance. Analysis of the database reveals two patterns of amino acid substitutions in the tyrosine, methionine, aspartate, aspartate (YMDD) nucleotide-binding locus of the HBV polymerase. HBV DNA from the sera of patients in Group I exhibits a substitution of valine for methionine at residue 552, accompanied by a substitution of methionine for leucine at residue 528. Patients in Group II had only an isoleucine-for-methionine substitution at position 552. Reconstruction of these mutations in an HBV replication-competent plasmid was performed in a transient transfection cell assay to determine the function/relevance of these mutations to lamivudine resistance. Both Group I and Group II mutations resulted in a substantial decrease in sensitivity to lamivudine treatment (> 10,000-fold shift in IC50 over wild-type [wt] IC50), strongly indicating that these mutations were involved in resistance to lamivudine. A hypothetical model of the HBV reverse transcriptase has been generated for further study of the role of these mutations in lamivudine resistance.

Mouse strain-dependent variation in the course and outcome of chlamydial genital tract infection is associated with differences in host response

Whether there is a pathogenic or protective outcome to chlamydial infection may be defined by the host response. We infected C57BL/6 (C57) and C3H/HeN (C3H) mice with the human biovar of Chlamydia trachomatis, serovar E, and, in select experiments, with the mouse pneumonitis agent of C. trachomatis (MoPn). We compared the courses of infection, histopathology, and host responses that resulted from these infections. The duration of infection with either chlamydial biovar was significantly increased in the C3H strain of mice. The intensity of infection was examined in mice infected with serovar E, and it was significantly increased in the C3H strain. Histopathology revealed the incidence of severe hydrosalpinx to be significantly greater in C3H mice than in C57 mice. In contrast, severe distention of the uterine horns was observed in all infected C57 mice compared to none of the C3H mice infected with serovar E and only 25% of those infected with MoPn. Acute inflammation was significantly increased in the uterine horns of C57 mice compared to that of C3H mice. Examination of antigen-specific responses revealed qualitatively similar responses in the two strains. Determination of gamma interferon- versus interleukin 4- producing cells revealed the predominance of a Th1 response in both strains. Serum enzyme-linked immunosorbent assays for immunoglobulin G1 (IgG1) and IgG2a revealed a predominance of IgG2a antibody in both strains, although the levels of antibody were significantly greater in C3H mice. Lymphocyte proliferation studies revealed increased proliferation in the iliac nodes of both strains at 1 to 3 weeks after infection. Because of the early eradication of infection observed in the C57 strain, we explored the relative production of tumor necrosis factor alpha (TNF-alpha) in the two strains. TNF-alpha levels were significantly increased in the genital tract secretions of C57 mice compared to that of C3H mice during the first week of infection. Increased TNF-alpha may be beneficial to the host by leading to earlier eradication of infection, thereby preventing infection of the oviduct and thus the major disease sequelae associated with chlamydial infection of the genital tract.

Molecular diversity in chemical databases: comparison of medicinal chemistry knowledge bases and databases of commercially available compounds

A molecular descriptor space has been developed which describes structural diversity. Large databases of molecules have been mapped into it and compared. This analysis used five chemical databases, CMC and MDDR, which represent knowledge bases containing active medicinal agents, ACD and SPECS, two databases of commercially available compounds, and finally the Wellcome Registry. Together these databases contained more than 300,000 structures. Topological indices and the free energy of solvation were computed for each compound in the databases. Factor analysis was used to reduce the dimensionality of the descriptor space. Low density observations were deleted as a way of removing outliers, which allowed a further reduction in the descriptor space of interest. The five databases could then be compared on an efficient basis using a metric developed for this purpose. A Riemann gridding scheme was used to subdivide the factor space into subhypercubes to obtain accurate comparisons. Most of the 300,000 structures were highly clustered, but unique structures were found. An analysis of overlap between the biological and commercial databases was carried out. The metric provides a useful algorithm for choosing screening sets of diverse compounds from large databases.

Sucrase-isomaltase is an independent prognostic marker for colorectal carcinoma

PURPOSE

Expression of disaccharidase sucrase-isomaltase (SI) is significantly enhanced during neoplastic transformation of colonic epithelium. Our study was designed to determine whether expression of SI within primary tumors was significantly associated with survival in patients with colorectal carcinoma (CRC).

METHODS

SI expression was analyzed by immunohistochemistry in paraffin sections from 182 Stage I to III CRC that had been resected for cure at the New England Deaconess Hospital between 1965 and 1977. Expression was scored as absent or present in 1 to 50 percent or more than 50 percent of tumor cells. Associations were explored among SI expression, other clinical or pathologic variables, and overall survival. The data set is mature, with 91 (56 percent) patients who had died of CRC at a median follow-up of 96 months.

RESULTS

Fifty-five percent of primary CRC expressed SI. When the multivariate Cox analysis was performed, nodal status, T stage, primary site, grade, and SI expression were independent covariates. SI expression was not associated with the expression of other clinicopathologic variables but increased the risk of death from colorectal carcinoma by 1.83-fold.

DISCUSSION

These results indicate that SI is a prognostic marker for CRC that is independent of stage-related variables in patients who have undergone potentially curative resections.

4-(Heteroarylthio)-2-biphenylyltetrazoles as nonpeptide angiotensin II antagonists

A series of 4-(heteroarylthio)-2-biphenylyltetrazoles was prepared, and the compounds were examined for their ability to displace [3H]AII from angiotensin II receptors. Analogues that exhibited significant receptor binding affinities at less than 10 microM were investigated further for potential antagonism of angiotensin II-mediated contraction of rabbit isolated aortic rings. Three 4-(heteroarylthio)-2-biphenylyltetrazoles were identified that exhibited sub-micromolar angiotensin II receptor binding affinities. These compounds and two reference agents, saralasin and losartan (DUP-753), exhibited concentration-dependent reversal of angiotensin II contraction in isolated aortic rings parallel to their receptor binding affinities. Molecular modeling studies were conducted to examine the conformational effects of the novel sulfide bridging unit contained in these 4-(heteroarylthio)-2-biphenylyltetrazoles. The biological effects of the sulfide bridge as well as alterations in the heteroaromatic moiety were investigated, and the resulting structure--activity relationships are discussed.

Prospective evaluation of early morphological changes in pelvic ileal pouches

BACKGROUND/AIMS

Little is known about the evolution of morphological changes in pelvic ileal-pouch mucosa. This study evaluates prospectively the sequence of early morphological, histochemical, and phenotypic features in pouch mucosal biopsy specimens.

METHODS

Twenty-two patients with pelvic ileal pouches constructed after total colectomy for chronic ulcerative colitis had biopsies performed at the time of ileostomy closure and after 6 weeks and 6 months of pouch function and were evaluated to assess the type and degree of inflammation, villus atrophy, Paneth's cell hyperplasia, mucin histochemical changes, the mucosal proliferative activity using the murine monoclonal antibody 1 (MIB-1), and the expression of the enzyme sucrase-isomaltase.

RESULTS

Early changes (6 weeks) were characterized by neutrophilic and eosinophilic inflammation, mild villus atrophy, Paneth's cell hyperplasia, a partial transition to colonic mucin phenotype, and an increased MIB-1 proliferation index. These features remained relatively stable after 6 months, except for a greater degree of mononuclear infiltration, a progressive increase in the degree of eosinophilic inflammation and a new higher steady state level of crypt epithelial kinetics. Expression of sucrase-isomaltase remained stable.

CONCLUSIONS

Pelvic ileal pouches develop inflammatory, phenotypic, and kinetic changes early in the course of function but have only a limited potential for colonic type metaplasia. The persistence of these changes is evidence in support of an adaptive response to a new luminal environment.

Localization of tumor-associated glycoprotein DF3 in normal, inflammatory, and neoplastic lesions of the colon

BACKGROUND

The expression of DF3 was assessed by a monoclonal antibody in normal, inflammatory, and neoplastic conditions in the large bowel.

METHODS

Using immunohistochemistry, expression was examined in formalin-fixed paraffin-embedded biopsy and resection samples of 19 normal colonic mucosal specimens, 49 inflammatory lesions, 34 adenomas, and 38 primary colonic adenocarcinomas. In addition, Western blots of normal colonic mucosa and adenocarcinoma were examined.

RESULTS

DF3 expression was detected in 84% of the adenocarcinomas with coarse membrane staining, intense positivity of luminal secretions, and focal cytoplasmic and intracytoplasmic vacuole staining. Nine of 32 areas of transitional mucosa revealed reactivity along apical membranes in crypt cells. Five adenomas containing carcinoma revealed DF3 positivity in the malignant areas only, whereas the remaining 29 were negative. Staining was membrane, luminal, and intracytoplasmic. Two examples of active ulcerative colitis revealed focal reactivity along the apical membrane of crypt cells. No other areas of staining were noted, including 12 cases containing dysplasia. Four of 10 other inflammatory lesions also revealed similar membrane reactivity in crypt cells. Normal colonic mucosa was nonreactive. Examples of normal colonic mucosa were negative for DF3 by Western blot analysis, whereas two carcinoma samples that reacted immunohistochemically were positive.

CONCLUSIONS

DF3 is not detectable in normal colonic tissues. It is expressed focally and predominantly along the apical membrane of crypt cells in some inflammatory lesions and in the transitional mucosa of primary adenocarcinomas. Most adenocarcinomas of the colon and adenomas with foci of invasive carcinoma demonstrate reactivity in the cytoplasm and luminal secretions.

Decreased expression of Mac-2 (carbohydrate binding protein 35) and loss of its nuclear localization are associated with the neoplastic progression of colon carcinoma

The Mac-2 lectin (carbohydrate binding protein 35) is a soluble, 32- to 35-kDa phosphoprotein that binds galactose-containing glycoconjugates. We report here that the colonic epithelium is a major site of Mac-2 expression in vivo based on immunohistochemistry of human tissue specimens. In this epithelium, proliferating cells at the base of the crypts do not express Mac-2 but its expression increases with differentiation along the crypt-to-surface axis. Mac-2 expression is concentrated in the nuclei of these differentiated epithelial cells. The progression from normal mucosa to adenoma to carcinoma is associated with significant changes in Mac-2 nuclear localization and expression. In all adenomas (9/9) and carcinomas (13/13) examined, Mac-2 was not present in the nucleus but was localized in the cytoplasm. Sequencing of Mac-2 cDNAs from normal mucosa and carcinoma revealed no specific mutations that could account for this loss of nuclear localization. We also observed a 5- to 10-fold decrease in Mac-2 mRNA levels in cancer compared to normal mucosa as well as a significant reduction in the amount of Mac-2 protein expressed. These observations suggest that Mac-2 exclusion from the nucleus and its decreased expression may be related to the neoplastic progression of colon cancer.

A comparison of the conformations of the 5'-triphosphates of zidovudine (AZT) and thymidine bound to HIV-1 reverse transcriptase

Nuclear Overhauser effect experiments were performed at 500 MHz to determine the conformations of AZTTP and dTTP when bound to HIV-1 reverse transcriptase. The conformations of both ligands were found to be similar in the bound state. The orientation of the glycosidic angle is anti (chi = -120 degrees +/- 12 for AZTTP and -110 degrees +/- 12 for dTTP), gamma is +sc and the pucker of the 3'-azido-2',3'-dideoxy- and 2'-deoxyribose rings is predominantly C4' exo (P = 60 degrees +/- 10 for AZTTP and 55 degrees +/- 8 for dTTP). These results indicate that the unusual C4'endo/C3'exo pucker (P = 215 degrees) reported for the dideoxyribose ring of AZT in the solid state does not play a role in the interaction of HIV-1 reverse transcriptase with AZTTP.

Endoscopic surveillance of Barrett's esophagus. Does it help?

Patients with Barrett's esophagus are recognized as having a high risk of development of adenocarcinoma. Although endoscopic surveillance of these patients is commonly practiced, its benefits have not been proved. This study was undertaken to examine the effect of endoscopic surveillance on the stage of resected carcinoma arising in Barrett's esophagus and the effect on postoperative survival. Between 1973 and 1991, 77 patients with adenocarcinoma were seen by us, and 19 of them were under endoscopic surveillance. The 19 patients underwent endoscopic biopsies at 1-month to 4-year intervals (median 6 months). All but one patient underwent esophagogastrectomy when severe dysplasia or invasive carcinoma was detected. The stages of the resected carcinomas in the group under surveillance compared with the group not under surveillance were significantly different, 58% of the patients under surveillance having stages 0 and I disease and 21% having stage III disease compared with 17% of the patients not under surveillance having stages 0 and I disease and 47% having stage III disease (p = 0.006). The 5-year actuarial survival of patients undergoing routine surveillance was 62% and of patients not under surveillance, 20% (p = 0.007). Endoscopic surveillance of patients with benign Barrett's esophagus permits detection of carcinoma at an early stage and improves long-term survival after resection for severe dysplasia and invasive carcinoma.

Sucrase-isomaltase expression in chronic ulcerative colitis and dysplasia

Sucrase-isomaltase (SI) is a mucosal disaccharidase that is present in normal small intestine and fetal colon. It also has been noted in colonic adenomas and adenocarcinomas. We used a polyclonal antibody to human SI to investigate enzyme presence and utility in detecting dysplastic changes in chronic ulcerative colitis. Sections from 32 cases were reviewed for the presence or absence of active colitis and dysplasia. Immunostaining of these cases for SI was performed and the results were reported based on location of immunoreactivity (ie, membrane and cytoplasmic staining in superficial and crypt epithelial cells) and percentage of positivity. Of 81 sections examined, 48 were rated negative for dysplasia (23 inactive colitis, 20 active, and five probably negative) and 28 were rated positive (eight low grade and 20 high grade). Surface membrane staining of epithelial cells was noted in all 28 dysplastic slides and positive cases (sensitivity, 100%) but also in 29 of 48 negative sections (P less than .001). In contrast, cytoplasmic positivity was present in 25 of 28 dysplastic and in only two of 48 negative slides (P less than .0001). The presence of cytoplasmic staining of SI in the superficial or crypt cells revealed a sensitivity of 92% and a specificity of 94%. There were five additional sections rated as indefinite for dysplasia (probably positive or unknown); two showed staining patterns typical of negative slides and three showed positive staining patterns. Of the 18 samples of transitional mucosa next to areas of dysplasia, surface membrane staining of SI was seen in all samples and cytoplasmic staining was seen in 15. We conclude that membrane staining of SI can be detected in inflammatory, regenerative, and dysplastic mucosa in ulcerative colitis. Cytoplasmic staining, however, correlates strongly with the presence of dysplastic change and may help in its detection.

2-[(arylmethyl) amino]-2-methyl-1,3-propanediol DNA intercalators. An examination of the effects of aromatic ring variation on antitumor activity and DNA binding

The effects of variation of aromatic ring size, shape, and side-chain position on antitumor activity and DNA binding in a series of carbocyclic 2-[(arylmethyl)amino]-2-methyl-1,3-propanediols (AMAPs) were examined. In general, the interaction of AMAPs with DNA increases as the intercalating ring system grows in area, with three distinct binding levels evident. Isomers from a specific ring system appear to bind DNA similarly. DNA binding is not the sole criterion for antitumor activity for the AMAPs studied; the magnitude of the delta Tm does not correlate with the antitumor activity observed. Significant in vivo P388 activity was seen for AMAP congeners from several tetracyclic ring systems. However, isomers from each of the specific ring systems produced a wide range of in vivo P388 activity. Thus, AMAP antitumor activity is not a function of the ring system per se, but rather appears to be related to the shape of the specific molecule. Three AMAP congeners (crisnatol (770U82, 773U82, and 502U83) are currently in clinical trials.

DNA intercalation and inhibition of topoisomerase II. Structure-activity relationships for a series of amiloride analogs

Among its many properties, amiloride is a DNA intercalator and topoisomerase II inhibitor. Previous work has indicated that the most stable conformation for amiloride is a planar, hydrogen-bonded, tricyclic structure. To determine whether the ability of amiloride to intercalate into DNA and to inhibit DNA topoisomerase II was dependent on the ability to assume a cyclized conformation, we studied the structure-activity relationship for 12 amiloride analogs. These analogs contained structural modifications which could be expected to allow or impede formation of a cyclized conformation. Empirical assays consisting of biophysical, biochemical, and cell biological approaches, as well as computational molecular modeling approaches, were used to determine conformational properties for these molecules, and to determine whether they intercalated into DNA and inhibited topoisomerase II. Specifically, we measured the ability of these compounds to 1) alter the thermal denaturation profile of DNA, 2) modify the hydrodynamic behavior of DNA, 3) inhibit the catalytic activity of purified DNA topoisomerase II in vitro, 4) promote the topoisomerase II-dependent cleavage of DNA, and 5) inhibit functions associated with DNA topoisomerase II in intact cells. Results indicated that only those analogs capable of cyclization could intercalate into DNA and inhibit topoisomerase II. Thus, the ability of amiloride and the 12 analogs studied to intercalate into DNA and to inhibit topoisomerase II appears dependent on the ability to exist in a planar, hydrogen-bonded, tricyclic conformation.

Age and growth of the American eel (Anguilla rostrata (LeSueur)) in Newfoundland waters

The age (otolith readings) and growth of American eels (Anguilla rostrata (LeSueur)) from fresh and brackish waters in Newfoundland were studied. The eels in Burnt Berry Brook grew faster than eels in the other areas. The growth of young eels in brackish water was slow. Although the growth of these eels increased in subsequent age groups, freshwater eels were consistently larger at each age.The silver eel migrates after spending 12 to 13 years in Newfoundland waters. The American eel in Newfoundland is generally larger than the European eel (Anguilla anguilla L.) at the onset of migration; however, its appearance and state of maturity parallel the condition described in the European eel.

Sex ratio of the American eel (Anguilla rostrata (LeSueur)) in Newfoundland waters

The sex ratio of the American eel in Newfoundland was estimated from studies of 354 examples from two brackish water and three freshwater habitats in Newfoundland. Sections of each gonad were cut at 10 μ, stained with haematoxylin, and counterstained with eosin. The material was divided into four classes; namely, females, immature females, males, and undifferentiated eels. Females were found in both brackish water and freshwater areas, while only one male was present in the material.The state of maturity of silver eels leaving Topsail Pond in the fall was determined from ova diameters. Ova diameters ranged from 0.109 to 0.214 mm; the average was 0.165 mm. These results agree closely with those reported by Svärdson for migrating silver eels in Europe.

Effect of Photoperiods on the Behavior of Juvenile Atlantic Salmon (Salmo salar L.) in Vertical and Horizontal Light Gradients

The behavior of juvenile Atlantic salmon in vertical and horizontal light gradients was studied. Comparisons were made between the behavior of fish exposed to 16-hr photoperiods (long-photoperiod fish) and fish that had not been so conditioned (control fish). In vertical light gradients the long-photoperiod fish were very active and moved rapidly up and down the water-column. At low light intensities they tended to rise into the surface layers. Peak activity and the greatest numbers in the upper reaches of the water-column occurred at 0.04 ft-c (lowest intensity studied). The control fish, however, were relatively quiescent at all light intensities and settled to the bottom at low light intensities. Peak activity and the greatest numbers in the upper reaches of the water-column occurred at 1.0 ft-c. In horizontal light gradients the control and long-photoperiod fish remained in areas of lowest light intensities. When allowed to remain in the light gradients for a short period of time, both groups showed a stronger avoidance of light sources of higher intensity but moved into the brighter areas with low intensity light sources. With prolonged stay in the light gradients, these trends were essentially reversed due to nipping and defence of territory. The long-photoperiod fish showed a stronger avoidance reaction than the control fish with the 100-watt light source, whereas the reactions of both groups were similar with the [Formula: see text]-watt and 300-watt light sources, when these fish were allowed to remain in the gradients for a short period of time. However, with prolonged stay in the gradients, nipping and defence of territory resulted in a stronger avoidance reaction by long-photoperiod fish to all light gradients. The differences in the behavior of control and long-photoperiod fish in vertical and horizontal light gradients is believed to be a result of exposure of the latter to controlled photoperiods.

Effect of Photoperiods on the Reactions of Juvenile Atlantic Salmon (Salmo salar L.) to Light Stimuli

The reactions to light stimuli of juvenile Atlantic salmon exposed to photoperiods (light-exposed fish) and those exposed to control conditions (control fish) were compared. The light-exposed fish showed more activity and reacted more readily to stimuli than the control fish. Both the control and light-exposed fish exhibited a negative phototaxis at all light intensities except the very lowest where a slight positive phototaxis was obvious. The intensity of an intermittent light stimulus had very little effect on the intensity of the reaction in the light-exposed fish, while the control fish showed an increase in the intensity of the reaction with an increase in the intensity of the light stimulus. The control fish showed an increase in the reaction to the intermittent light stimulus the longer the stimulus was applied at the higher levels of stimulation, while the light-exposed fish showed this behavior at the lower levels of stimulation. The reactions to continuous light were similar to the reactions to intermittent light stimuli, but the light-exposed fish reacted more quickly to continuous light than the control fish. These differences in behavior are attributed to the increased activity and sensitivity of the light-exposed fish, resulting from their exposure to photoperiods.

The Biology of Arctic Char (Salvelinus alpinus L.) in Northern Labrador

Arctic char (Salvelinus alpinus L.) from the commercial sea run were sampled at five stations in northern Labrador. Otoliths were used for age determination. In the southern part of the range—Adlatok and Nain—commercial size is reached at 6 years and at places farther north in 7 years. There is also a tendency for older fish to occur as one proceeds north.Age, weight, and length frequencies as well as their relationship to one another were determined.Vertebral counts indicate little, if any, intermingling of populations between: Adlatok and Nain, Okkak Bay and Hebron, Adlatok and Ramah, Nain and Hebron. Fin ray counts conform with the vertebral results but indicate no significant difference between Adlatok and Nain or Nain and Okkak Bay fish.Variations in flesh colour from white to deep red is a distinct characteristic of Arctic char in northern Labrador; flesh colour has a distinct bearing on the market value of the fish.Principal food items included capelin, launce, young of mailed sculpin, Amphipoda, and Euphausiacea.