Screening Ultra-Large Encoded Compound Libraries Leads to Novel Protein-Ligand Interactions and High Selectivity

The DNA-encoded library (DEL) discovery platform has emerged as a powerful technology for hit identification in recent years. It has become one of the major parallel workstreams for small molecule drug discovery along with other strategies such as HTS and data mining. For many researchers working in the DEL field, it has become increasingly evident that many hits and leads discovered via DEL screening bind to target proteins with unique and unprecedented binding modes. This Perspective is our attempt to analyze reports of DEL screening with the purpose of providing a rigorous and useful account of the binding modes observed for DEL-derived ligands with a focus on binding mode novelty.

Diverse, Potent, and Efficacious Inhibitors That Target the EED Subunit of the Polycomb Repressive Complex 2 Methyltransferase

Aberrant activity of the histone methyltransferase polycomb repressive complex 2 (PRC2) has been linked to several cancers, with small-molecule inhibitors of the catalytic subunit of the PRC2 enhancer of zeste homologue 2 (EZH2) being recently approved for the treatment of epithelioid sarcoma (ES) and follicular lymphoma (FL). Compounds binding to the EED subunit of PRC2 have recently emerged as allosteric inhibitors of PRC2 methyltransferase activity. In contrast to orthosteric inhibitors that target EZH2, small molecules that bind to EED retain their efficacy in EZH2 inhibitor-resistant cell lines. In this paper we disclose the discovery of potent and orally bioavailable EED ligands with good solubilities. The solubility of the EED ligands was optimized through a variety of design tactics, with the resulting compounds exhibiting in vivo efficacy in EZH2-driven tumors.

Rapid Identification of Novel Allosteric PRC2 Inhibitors

Enhancer of zeste homologue 2 (EZH2), the catalytic subunit of polycomb repressive complex 2 (PRC2), regulates chromatin state and gene expression by methylating histone H3 lysine 27. EZH2 is overexpressed or mutated in various hematological malignancies and solid cancers. Our previous efforts to identify inhibitors of PRC2 methyltransferase activity by high-throughput screening (HTS) resulted in large numbers of false positives and thus a significant hit deconvolution challenge. More recently, others have reported compounds that bind to another PRC2 core subunit, EED, and allosterically inhibit EZH2 activity. This mechanism is particularly appealing as it appears to retain potency in cell lines that have acquired resistance to orthosteric EZH2 inhibition. By designing a fluorescence polarization probe based on the reported EED binding compounds, we were able to quickly and cleanly re-triage our previously challenging HTS hit list and identify novel allosteric PRC2 inhibitors.

Mapping the sugar dependency for rational generation of a DNA-RNA hybrid-guided Cas9 endonuclease

The CRISPR-Cas9 RNA-guided endonuclease system allows precise and efficient modification of complex genomes and is continuously developed to enhance specificity, alter targeting and add new functional moieties. However, one area yet to be explored is the base chemistry of the associated RNA molecules. Here we show the design and optimisation of hybrid DNA-RNA CRISPR and tracr molecules based on structure-guided approaches. Through careful mapping of the ribose requirements of Cas9, we develop hybrid versions possessing minimal RNA residues, which are sufficient to direct specific nuclease activity in vitro and in vivo with reduced off-target activity. We identify critical regions within these molecules that require ribose nucleotides and show a direct correlation between binding affinity/stability and cellular activity. This is the first demonstration of a non-RNA-guided Cas9 endonuclease and first step towards eliminating the ribose dependency of Cas9 to develop a XNA-programmable endonuclease.

X-ray Characterization and Structure-Based Optimization of Striatal-Enriched Protein Tyrosine Phosphatase Inhibitors

Excessive activity of striatal-enriched protein tyrosine phosphatase (STEP) in the brain has been detected in numerous neuropsychiatric disorders including Alzheimer's disease. Notably, knockdown of STEP in an Alzheimer mouse model effected an increase in the phosphorylation levels of downstream STEP substrates and a significant reversal in the observed cognitive and memory deficits. These data point to the promising potential of STEP as a target for drug discovery in Alzheimer's treatment. We previously reported a substrate-based approach to the development of low molecular weight STEP inhibitors with K_i values as low as 7.8 μM. Herein, we disclose the first X-ray crystal structures of inhibitors bound to STEP and the surprising finding that they occupy noncoincident binding sites. Moreover, we utilize this structural information to optimize the inhibitor structure to achieve a K_i of 110 nM, with 15-60-fold selectivity across a series of phosphatases.

Recurrent MLK4 Loss-of-Function Mutations Suppress JNK Signaling to Promote Colon Tumorigenesis

MLK4 is a member of the mixed-lineage family of kinases that regulate the JNK, p38, and ERK kinase signaling pathways. MLK4 mutations have been identified in various human cancers, including frequently in colorectal cancer, where their function and pathobiological importance have been uncertain. In this study, we assessed the functional consequences of MLK4 mutations in colon tumorigenesis. Biochemical data indicated that a majority of MLK4 mutations are loss-of-function (LOF) mutations that can exert dominant-negative effects. In seeking to understand the abrogated activity of these mutants, we elucidated a new MLK4 catalytic domain structure. To determine whether MLK4 is required to maintain tumorigenic phenotypes, we reconstituted its signaling axis in colon cancer cells harboring MLK4-inactivating mutations. We found that restoring MLK4 activity reduced cell viability, proliferation, and colony formation in vitro and delayed tumor growth in vivo. Mechanistic investigations established that restoring the function of MLK4 selectively induced the JNK pathway and its downstream targets, cJUN, ATF3, and the cyclin-dependent kinase inhibitors CDKN1A and CDKN2B. Our work indicates that MLK4 is a novel tumor-suppressing kinase harboring frequent LOF mutations that lead to diminished signaling in the JNK pathway and enhanced proliferation in colon cancer.

Discovery of AZ0108, an orally bioavailable phthalazinone PARP inhibitor that blocks centrosome clustering

The propensity for cancer cells to accumulate additional centrosomes relative to normal cells could be exploited for therapeutic benefit in oncology. Following literature reports that suggested TNKS1 (tankyrase 1) and PARP16 may be involved with spindle structure and function and may play a role in suppressing multi-polar spindle formation in cells with supernumerary centrosomes, we initiated a phenotypic screen to look for small molecule poly (ADP-ribose) polymerase (PARP) enzyme family inhibitors that could produce a multi-polar spindle phenotype via declustering of centrosomes. Screening of AstraZeneca's collection of phthalazinone PARP inhibitors in HeLa cells using high-content screening techniques identified several compounds that produced a multi-polar spindle phenotype at low nanomolar concentrations. Characterization of these compounds across a broad panel of PARP family enzyme assays indicated that they had activity against several PARP family enzymes, including PARP1, 2, 3, 5a, 5b, and 6. Further optimization of these initial hits for improved declustering potency, solubility, permeability, and oral bioavailability resulted in AZ0108, a PARP1, 2, 6 inhibitor that potently inhibits centrosome clustering and is suitable for in vivo efficacy and tolerability studies.

Discovery of 1-methyl-1H-imidazole derivatives as potent Jak2 inhibitors

Structure based design, synthesis, and biological evaluation of a novel series of 1-methyl-1H-imidazole, as potent Jak2 inhibitors to modulate the Jak/STAT pathway, are described. Using the C-ring fragment from our first clinical candidate AZD1480 (24), optimization of the series led to the discovery of compound 19a, a potent, orally bioavailable Jak2 inhibitor. Compound 19a displayed a high level of cellular activity in hematopoietic cell lines harboring the V617F mutation and in murine BaF3 TEL-Jak2 cells. Compound 19a demonstrated significant tumor growth inhibition in a UKE-1 xenograft model within a well-tolerated dose range.

Methyl-thiazoles: a novel mode of inhibition with the potential to develop novel inhibitors targeting InhA in Mycobacterium tuberculosis

InhA is a well validated Mycobacterium tuberculosis (Mtb) target as evidenced by the clinical success of isoniazid. Translating enzyme inhibition to bacterial cidality by targeting the fatty acid substrate site of InhA remains a daunting challenge. The recent disclosure of a methyl-thiazole series demonstrates that bacterial cidality can be achieved with potent enzyme inhibition and appropriate physicochemical properties. In this study, we report the molecular mode of action of a lead methyl-thiazole, along with analogues with improved CYP inhibition profile. We have identified a novel mechanism of InhA inhibition characterized by a hitherto unreported "Y158-out" inhibitor-bound conformation of the protein that accommodates a neutrally charged "warhead". An additional novel hydrophilic interaction with protein residue M98 allows the incorporation of favorable physicochemical properties for cellular activity. Notably, the methyl-thiazole prefers the NADH-bound form of the enzyme with a Kd of ~13.7 nM, as against the NAD(+)-bound form of the enzyme.

Emergence and recovery in children after desflurane and isoflurane anaesthesia: effect of anaesthetic duration

BACKGROUND

We hypothesized that increasing duration of inhalation anaesthesia is associated with slower emergence and recovery in children, and that this effect would be less marked with desflurane in comparison with isoflurane.

METHODS

Fifty-four infants and children assigned in groups according to age and expected length of operation were prospectively randomized to receive either isoflurane (I) or desflurane (D) for anaesthesia. After standard induction, the anaesthesia was maintained using an age-related 1.0 minimum alveolar concentration (MAC) equivalent for either agent in air and oxygen. Local analgesia was used as appropriate. End-tidal volatile agent concentration was recorded until extubation. Clinical evaluation of recovery was made by observers, blinded to group allocation.

RESULTS

For patients <4 yr of age, the median (95% CI) times in minutes to first movement [5.27 (D), 9.22 (I)], eye opening [9.42(D), 13.3(I)] and extubation [7.18 (D), 12.5 (I)] were significantly shorter (P<0.05) for desflurane. In the group >4 yr of age, the median (95% CI) times in minutes to first movement [4.42 (D), 11.6 (I)], eye opening [8.55(D), 18.0(I)] and extubation [7.08 (D), 16.7 (I)] were significantly shorter (P<0.001) for desflurane. Times to leave recovery were not significantly different for the group <4 yr of age, but were significantly shorter for desflurane in the group >4 yr of age (P<0.01). The isoflurane, but not desflurane, had a time-dependent effect on arousal. There were no significant differences in incidence of airway irritation or emergence delirium between the two agents.

CONCLUSIONS

The rate of recovery in children after exposure to desflurane was faster than those patients receiving isoflurane; recovery from desflurane, but not isoflurane, was relatively unaffected by the duration of anaesthesia.

Prospective comparison of sevoflurane and desflurane in formerly premature infants undergoing inguinal herniotomy

BACKGROUND

Formerly premature infants having inguinal herniotomy have been at a high risk of postoperative apnoea, newer less soluble anaesthetic agents may reduce this risk.

METHODS

Thirty infants, under 37 weeks gestation and under 47 weeks post-conceptional age, undergoing inguinal herniotomy had an inhalational induction with sevoflurane and were randomly allocated to sevoflurane (group S) or desflurane (group D) for maintenance. All infants received i.v. atracurium 0.5 mg kg(-1), rectal acetaminophen 20 mg kg(-1) and caudal bupivacaine 0.25% 1 ml kg(-1). Infants were monitored for apnoeas (using nasal thermistry and impedance), haemoglobin oxygen desaturations and bradycardias for 12 h before and after operation with an Alice 4 polysomnograph. Emergence timings were recorded.

RESULTS

There was no difference between pre- and postoperative incidence of apnoeas in either group, and no group difference between desflurane and sevoflurane in terms of pre- and postoperative ventilatory events or in the number of apnoeas in the postoperative period (nine patients in group D and five patients in group S had apnoeas). Median times to first movement, tracheal extubation, eye opening and first cry were all faster with group D (group D: 3.0, 10.0, 9.0 and 11.0 min and group S: 7.0, 15.1, 13.5 and 16.1 min, respectively). No infant had problems with airway irritation on emergence and no infant required airway intervention for apnoea.

CONCLUSIONS

Infants wake faster from general anaesthesia when maintained with desflurane as compared with sevoflurane, but no difference in postoperative respiratory events was demonstrated between the groups.

Structural basis for altered activity of M- and H-isozyme forms of human lactate dehydrogenase

Lactate dehydrogenase (LDH) interconverts pyruvate and lactate with concomitant interconversion of NADH and NAD(+). Although crystal structures of a variety of LDH have previously been described, a notable absence has been any of the three known human forms of this glycolytic enzyme. We have now determined the crystal structures of two isoforms of human LDH-the M form, predominantly found in muscle; and the H form, found mainly in cardiac muscle. Both structures have been crystallized as ternary complexes in the presence of the NADH cofactor and oxamate, a substrate-like inhibitor. Although each of these isoforms has different kinetic properties, the domain structure, subunit association, and active-site regions are indistinguishable between the two structures. The pK(a) that governs the K(M) for pyruvate for the two isozymes is found to differ by about 0.94 pH units, consistent with variation in pK(a) of the active-site histidine. The close similarity of these crystal structures suggests the distinctive activity of these enzyme isoforms is likely to result directly from variation of charged surface residues peripheral to the active site, a hypothesis supported by electrostatic calculations based on each structure. Proteins 2001;43:175-185.

Effector sites in the three-dimensional structure of mammalian sperm beta-acrosin

BACKGROUND

Proacrosin is a serine protease found specifically within the acrosomal vesicle of all mammalian spermatozoa. During fertilization proacrosin autoactivates to form beta-acrosin, in which there is a "light" chain cross-linked to a "heavy" chain by two disulphide bonds. beta-acrosin is thought to be multifunctional with roles in acrosomal exocytosis, as a receptor for zona pellucida proteins, and as a protease to facilitate penetration of spermatozoa into the egg.

RESULTS

The crystal structures of both ram and boar beta-acrosins have been solved in complex with p-aminobenzamidine to 2.1 A and 2.9 A resolution, respectively. Both enzymes comprise a heavy chain with structural homology to trypsin, and a light chain covalently associated in a similar manner to blood coagulation enzymes. In crystals of boar beta-acrosin, the carboxyl terminus of the heavy chain is inserted into the active site of the neighboring molecule. In both enzyme structures, there are distinctive positively charged surface "patches" close to the active site, which associate with carbohydrate from adjacent molecules and also bind sulfate ions.

CONCLUSIONS

From the three-dimensional structure of beta-acrosin, two separate effector sites are evident. First, proteolytic activity, believed to be important at various stages during fertilization, arises from the trypsin-like active site. Activity of this site may be autoregulated through intermolecular associations. Second, positively charged regions on the surface adjacent to the active site may act as receptors for binding zona pellucida glycoproteins. The spatial proximity of these two effector sites suggests there may be synergy between them.

Recognition of structurally diverse substrates by type II 3-hydroxyacyl-CoA dehydrogenase (HADH II)/amyloid-beta binding alcohol dehydrogenase (ABAD)

Human type II hydroxyacyl-CoA dehydrogenase/amyloid-beta binding alcohol dehydrogenase (HADH II/ABAD) is an oxidoreductase whose salient features include broad substrate specificity, encompassing 3-hydroxyacyl-CoA derivatives, hydroxysteroids, alcohols and beta-hydroxybutyrate, and the capacity to bind amyloid-beta peptide, leading to propagation of amyloid-induced cell stress. In this study, we examine the structure and enzymatic activity of the homologous rat HADH II/ABAD enzyme. We report the crystal structure of rat HADH II/ABAD as a binary complex with its NADH cofactor to 2.0 A resolution, as a ternary complex with NAD(+) and 3-ketobutyrate (acetoacetate) to 1.4 A resolution, and as a ternary complex with NADH and 17 beta-estradiol to 1.7 A resolution. This first crystal structure of an HADH II confirms these enzymes are closely related to the short-chain hydroxysteroid dehydrogenases and differ substantially from the classic, type I 3-hydroxyacyl-CoA dehydrogenases. Binding of the ketobutyrate substrate is accompanied by closure of the active site specificity loop, whereas the steroid substrate does not appear to require closure for binding. Despite the different chemical nature of the two bound substrates, the presentation of chemical groups within the active site of each complex is remarkably similar, allowing a general mechanism for catalytic activity to be proposed. There is a characteristic extension to the active site that is likely to accommodate the CoA moiety of 3-hydroxyacyl-CoA substrates. Rat HADH II/ABAD also binds amyloid-beta (1-40) peptide with a K(D) of 21 nM, which is similar to the interaction exhibited between this peptide and human HADH II/ABAD. These studies provide the first structural insights into HADH II/ABAD interaction with its substrates, and indicate the relevance of the rodent enzyme and associated rodent models for analysis of HADH II/ABAD's physiologic and pathophysiologic properties.

Purification, co-crystallization and preliminary X--ray analysis of the natural aspartic proteinase inhibitor IA3 complexed with saccharopepsin from Saccharomyces cerevisiae

The vacuolar aspartic proteinase from baker's yeast, saccharopepsin, has been co-crystallized with its natural inhibitor I(A)3, found in the cytosol. The I(A)3-saccharopepsin complex crystals belong to the space group P6(2)22, with unit-cell parameters a = b = 192.1, c = 59. 80 A and one molecule per asymmetric unit. The initial X-ray analysis of the complex indicates that the crystals diffract to 5.0 A, similar to native saccharopepsin crystals. This is probably a consequence in part of glycosylation of the native saccharopepsin. Full structural analysis of the complex crystal is in progress.

Chloroquine binds in the cofactor binding site of Plasmodium falciparum lactate dehydrogenase

Although the molecular mechanism by which chloroquine exerts its effects on the malarial parasite Plasmodium falciparum remains unclear, the drug has previously been found to interact specifically with the glycolytic enzyme lactate dehydrogenase from the parasite. In this study we have determined the crystal structure of the complex between chloroquine and P. falciparum lactate dehydrogenase. The bound chloroquine is clearly seen within the NADH binding pocket of the enzyme, occupying a position similar to that of the adenyl ring of the cofactor. Chloroquine hence competes with NADH for binding to the enzyme, acting as a competitive inhibitor for this critical glycolytic enzyme. Specific interactions between the drug and amino acids unique to the malarial form of the enzyme suggest this binding is selective. Inhibition studies confirm that chloroquine acts as a weak inhibitor of lactate dehydrogenase, with mild selectivity for the parasite enzyme. As chloroquine has been shown to accumulate to millimolar concentrations within the food vacuole in the gut of the parasite, even low levels of inhibition may contribute to the biological efficacy of the drug. The structure of this enzyme-inhibitor complex provides a template from which the quinoline moiety might be modified to develop more efficient inhibitors of the enzyme.

Prenatal maternal blood pressure response to stress predicts birth weight and gestational age: a preliminary study

OBJECTIVE

The objective was to test the prospective association between prenatal maternal circulatory responses to a standardized psychologic challenge and birth outcome.

STUDY DESIGN

We examined the relationship between blood pressure responses to a cognitive arithmetic stressor and birth outcome in 40 healthy primigravid women. Pregnant women between 18 and 37 years old were recruited from the University of Kentucky Prenatal Service Clinic for participation. All women performed an interactive arithmetic task while maternal heart rate and blood pressures were determined. Subsequent birth outcome parameters of birth weight and gestational age were obtained for prospective analyses.

RESULTS

Results indicated that maternal systolic and diastolic blood pressures and heart rates were significantly increased during the arithmetic task (p < or = 0.01). Regression analyses suggested that women with larger diastolic blood pressure responses during stress had infants with lower birth weights (p < 0.01) and decreased gestational age (p < 0.05).

CONCLUSIONS

This effect was specific to psychologic stress reactivity and was not related to maternal age, maternal race, baseline blood pressures, the trimester of stress testing, nor expired carbon monoxide. The relationship between maternal blood pressure response and birth outcome may reflect the transplacental impact of individual differences in systemic stress responsivity.

Risk factors for preterm delivery in a healthy cohort

To examine whether risk factors differed among subgroups of preterm (< 37 weeks of gestation) deliveries, we studied a cohort of 1,825 enlisted servicewomen who delivered from 1987 through 1990 at four U.S. Army medical centers. Preterm deliveries were classified by length of gestation (< 29 weeks, 29-32 weeks, 33-36 weeks) and clinical course [medical indication, idiopathic preterm labor, or preterm rupture of membranes (PROM)]. We abstracted medical records for information on age, race, army rank, marital status, gravidity, parity, the baby's sex, maternal prepregnancy height and weight, gestation at entry to prenatal care, alcohol drinking and smoking, time since and outcome of preceding pregnancy, surgery performed during pregnancy, anemia, and diagnoses of uterine abnormalities, sexually transmitted diseases, and urinary tract infections. We used proportional hazards analysis to evaluate associations for each subgroup of preterm delivery. The relative odds associated with a history of preterm delivery in the preceding pregnancy ranged from 3.1 for deliveries due to preterm labor or PROM to 6.2 for deliveries that occurred during 29-32 weeks; none of the other factors was consistently associated across the subgroups of preterm delivery. The paucity of associations is consistent with the conclusion of other investigators that most of the causes of preterm delivery are unknown.

Prevalence of low birth weight and preterm delivery in relation to the interval between pregnancies among white and black women

BACKGROUND

The higher mortality rate among black infants than among white infants in the United States results largely from the greater frequency of low birth weight and prematurity among black infants. Higher rates of low birth weight and preterm delivery have been associated with shorter intervals between pregnancies.

METHODS

We studied a racially mixed population of women in military families, who had access to free, high-quality health care. A total of 1992 white and black women had two consecutive, singleton pregnancies during the study period. We determined the outcome of the second of each pair of pregnancies and the length of time between the pregnancies.

RESULTS

Short interpregnancy intervals (calculated from delivery to the next conception) were more frequent among black than among white women. A total of 7.7 percent of the 298 black women and 3.2 percent of the 1628 white women delivered premature, low-birth-weight infants (P < 0.001). Among the black women, an interpregnancy interval of less than nine months was associated with a significantly greater prevalence of preterm delivery and low birth weight in the neonates (11.6 percent, vs. 4.4 percent for longer interpregnancy intervals; P = 0.020). Among the white women, only intervals of less than three months between pregnancies were associated with a greater prevalence of prematurity and low birth weight in the infants (11.8 percent vs. 2.8 percent; P < 0.001). Of the black women, 46.3 percent had interpregnancy intervals of less than nine months; 4.2 percent of the white women had interpregnancy intervals of less than three months.

CONCLUSIONS

A short interval between pregnancies is a risk factor for low birth weight and preterm delivery, and such intervals are more common among black than among white women. The relative frequency of intervals of less than nine months between pregnancies may be an important factor in the wide disparity in pregnancy outcomes between white and black women in the United States.

Antenatal hospitalization among enlisted servicewomen, 1987-1990

OBJECTIVE

To describe the prevalence of, and indications for, antenatal hospitalization among women who delivered live and stillborn infants.

METHODS

We reviewed the records of a cohort of 1825 black and white enlisted women who delivered from 1987-1990 at the four largest Army medical centers in the United States. Women with multiple gestations and those whose pregnancies ended before 20 weeks' gestation were excluded. Records of all women with preterm deliveries and a one-third sample of women with term deliveries were abstracted.

RESULTS

Overall, 26.8 +/- 1.6% (mean +/- standard error) of the women were hospitalized antenatally. Of the estimated 702 antenatal hospitalizations, 44.0 +/- 3.4% were related to preterm labor, 10.3 +/- 1.9% to preeclampsia, 5.5 +/- 1.5% to hyperemesis, and 4.7 +/- 1.5% to urinary tract or kidney infection. The prevalence of hospitalization was lowest before 20 weeks (5.0 +/- 0.8%) and highest at 33-36 weeks (12.2 +/- 1.2%). Small and probably clinically insignificant differences between black and white women were noted in the overall prevalence of antenatal hospitalization and in the indications for hospitalization.

CONCLUSION

As measured by hospitalization, severe antenatal morbidity is common in this population of healthy enlisted women.

Preterm delivery among black and white enlisted women in the United States Army

OBJECTIVE

To examine black-white differences in preterm delivery in a healthy population who had unrestricted access to prenatal care.

METHODS

We conducted a retrospective cohort study of 842 black and 1026 white enlisted servicewomen who delivered a singleton infant of 20 or more weeks' gestation from July 1, 1987 through September 30, 1990 at four Army Medical Centers in the United States. Data were collected by reviewing maternal and newborn records. We used logistic and proportional hazards regression models to analyze outcomes defined by length of gestation, cause of preterm delivery, and jointly by length and cause.

RESULTS

Black enlisted women had a cumulative probability of preterm delivery (13.5%) that was higher than that for white enlisted women (10.5%) (hazard ratio 1.31, 95% confidence interval [CI] 1.002-1.70). However, the ratio of black-to-white hazards was not uniform. Black-white differences were small and nonsignificant from 33-36 weeks' gestation, when most preterm deliveries occur. The differences were also small and nonsignificant for deliveries related to spontaneous rupture of membranes or idiopathic preterm labor, the most common causes of preterm delivery. The black-to-white hazard ratios were greatest for all deliveries before 33 weeks' gestation and for medically indicated preterm deliveries.

CONCLUSIONS

Efforts to reduce black-white differences in preterm delivery must go beyond providing prenatal care and eliminating recreational drug use. Future studies should consider black-white differences in environments during the mother's own development and in psychosocial and physical stresses during pregnancy.

Risk of chromosomal abnormalities in patients with idiopathic polyhydramnios

This prospective investigation was designed to assess the incidence of chromosomal abnormalities in patients with idiopathic polyhydramnios. Polyhydramnios was defined as 25 cm or greater in total vertical height in all four quadrants (amniotic fluid index) in any nonreferral patient (ie, primary care population) undergoing sonographic examination with a singleton pregnancy, normal fetal anatomical survey, normal glucose screening, and negative antibody screen. During the 2-year period from May 1, 1988 through April 30, 1990, 5038 gravidas delivered at Madigan Army Hospital Center. Unexplained polyhydramnios was detected sonographically in 125 patients, an incidence of 2.5%. After obtaining informed written consent, amniocentesis was performed in all patients. Within this group (N = 125), four chromosomal abnormalities (incidence of 3.2%) were detected. There were two trisomy 18 and two trisomy 21 fetuses. None of the four patients had maternal serum alpha-fetoprotein screening performed. The incidence of aneuploidy in patients with idiopathic polyhydramnios (3.2%) is much higher than the reported incidence of major karyotype abnormalities in live births (0.59%). We conclude that fetal chromosomal analysis should be considered in all obstetric patients with sonographic evidence of idiopathic polyhydramnios.

The association of antiphospholipid antibodies with pregnancies complicated by fetal growth restriction

The association of antiphospholipid antibodies with fetal growth restriction is often cited, but the published evidence for this is based on few patients and comes primarily from patient histories, not study groups. In this prospective study, we evaluated a subgroup of our population with fetuses whose estimated weights at ultrasound were at or below the tenth percentile for gestational age. Plasma and serum testing was performed to determine the presence of antiphospholipid antibodies, specifically lupus anticoagulant and anticardiolipin antibodies, respectively. From March 1990 through March 1991, 55 women were followed for suspected fetal growth restriction. Intensive monitoring of the fetal condition and modification of the mother's activity were recommended, resulting in 100% compliance. Despite this, 37 newborns were confirmed by birth weight to be at or below the tenth percentile, and all were below the 45th percentile. Fifteen of 55 women (27%) were positive for anticardiolipin antibodies, as were nine of 37 (24%) with correctly diagnosed fetal growth restriction. Five of 15 women whose newborns had ponderal indexes below the tenth percentile tested positive for anticardiolipin antibodies. None of the women had a positive lupus anticoagulant test. The prevalence of anticardiolipin antibodies in this study group was significantly higher than in our general population. We conclude that there is a statistically significant association between the presence of circulating maternal anticardiolipin antibodies and fetal growth restriction.

A simple method of separation of Pneumocystis carinii from rat lung

Existing methods for purification of Pneumocystis carinii are unsatisfactory. Dialysis is a simple, non-stressful treatment which aided purification of organisms from rat cells. Yields were quantitated using a Petroff-Hausser chamber and nuclear staining. Following dialysis overnight, three times the yields of similar, undialysed preparations were obtained, with less than 0.2% contamination by lung cells. Overnight incubation at 4 degrees C also improved separation, but yields were only half those following dialysis. Dialysis is now used routinely in the preparation of pure Pneumocystis carinii suspensions.

Screening for illicit drug use in a military obstetric population

The purpose of our investigation was to determine the prevalence of illicit drug use within our socioeconomically heterogeneous obstetric population, in order to assess the need for institution of universal screening. Five hundred consecutive new obstetric registrants had urine collected for routine culture. Following removal of a small aliquot of urine for culture, the samples were sent to the Armed Forces Institute of Pathology, Division of Forensic Toxicology. Each specimen was screened for the presence of alcohol, cocaine metabolites, cannabinoids, opiates, and amphetamines using fluorescent polarization immunoassay techniques. All positive screening tests were confirmed by gas chromatography mass spectrometry. Thirty samples were either lost in processing or of insufficient quantity to test. Five of the 470 samples (1.06%) tested were positive. One subject was taking prescription narcotics, so the correlated prevalence was 0.85%. Three tested positive for tetrahydrocannabinol and two for opiates. Analysis of our data demonstrates that our obstetric population has a significantly lower prevalence of illicit drug use than other populations reported previously (P less than .01). We recommend that each institution providing obstetric services determine its specific prevalence of illicit drug use.

Reproducibility of the oral glucose tolerance test in pregnancy

This prospective investigation evaluated the reproducibility of the 100 gm oral glucose tolerance test. Sixty-four obstetric patients with greater than or equal to 135 mg/dl on the 50 gm oral glucose screening test were scheduled for the 100 gm test. All patients repeated the oral glucose tolerance test in 1 to 2 weeks. Both tests included a preparatory diet, and testing conditions were identical. There were no significant differences in the mean test values at each testing interval when the entire study population was considered. Patients were then divided into four groups according to the outcome of the two tests. Forty-eight of 64 (75%) had normal results at each testing period (group 1); 11 of 64 (17%) had initially normal results and abnormal results on retest (group 2); 3 of 64 (5%) had initially abnormal results and normal results on retest (group 3); 2 of 64 (3%) had abnormal results at both testing phases (group 4). There were no significant differences between oral glucose tolerance test results within groups 1 and 4. However, significant differences occurred within groups 2 and 3 between the two tests. Group 2 patients had a greater frequency of an abnormal 1-hour value on the test than group 1 patients (p = 0.001). Overall, the reproducibility of the oral glucose tolerance test was 78% (50 of 64). We recommend the oral glucose tolerance test be repeated when the 1-hour value is abnormal or when the fasting blood sugar, 1-hour, and 2-hour values are near the upper end of the normal range.

Use of a standard preparatory diet for the oral glucose tolerance test. Is it necessary?

A prospective investigation was performed to evaluate the necessity of a diet containing greater than or equal to 150 g/d of carbohydrate for three days before the oral glucose tolerance test (OGTT). Thirty-seven obstetric patients who had a value of greater than or equal to 135 mg/dL on the one-hour, 50-g oral glucose screening test underwent a subsequent OGTT. The patients were alternately assigned to one of two groups. Nineteen of 37 (51%) were asked to precede the OGTT with a three-day diet containing greater than 150 g/d of carbohydrate. Those patients were then asked not to alter their normal dietary pattern and to repeat the OGTT in one to two weeks (group I). Eighteen of 37 (49%) followed the testing scheme in reverse order (group II). There were no significant differences in mean fasting or in one-, two- or three-hour plasma glucose values at either testing period between groups I and II. There were no significant differences between groups I and II in the number of patients who had an abnormal OGTT at the initial or repeat testing period. Dietary preparation for the OGTT is not necessary, and patients can be scheduled for the test when convenient.

Vaginal breech delivery: a five-year prospective evaluation of a protocol using computed tomographic pelvimetry

In 1983 a protocol was established at our institution that used computed tomographic pelvimetry to evaluate patients presenting with a singleton term frank breech fetus for an attempt at vaginal delivery. The criteria for a trial of labor were singleton fetus, term gestation (37 to 42 weeks' gestation from the first day of the last menstrual period), frank breech presentation, estimated fetal weight 2000 to 4000 gm, non-extended fetal head, and adequate computed tomographic pelvimetry. Two digital radiographs and a tomographic cross-section were taken of each patient, i.e., an anteroposterior view, a lateral view, and an axial section through the femoral head at the level of the fovea capitalis. Adequate pelvimetry was defined as: anteroposterior diameter of the inlet greater than or equal to 10.0 cm, transverse diameter of the inlet greater than or equal to 11.5 cm, transverse (interspinous) diameter of the midpelvis greater than or equal to 9.5 cm, and posterior sagittal diameter of the midpelvis greater than or equal to 4.0 cm. The purpose of this prospective analysis was to determine the obstetric and perinatal outcome of those breech fetuses that were evaluated with these criteria during the study period of January 1984 through July 1989. During this period the incidence of breech deliveries at our institution was 2.71% (394/14,542). Of these 394 breech deliveries, 122 patients underwent computed tomographic pelvimetry. Eighty-five patients had adequate pelvimetry, fulfilling the protocol criteria, and formed the study group. Eighty-one percent (69/85) of the study group had successful vaginal deliveries (group 1). Nineteen percent (16/85) required cesarean delivery after a trial of labor (group 2) (10 with fetal distress and six with arrested labor disorders). Of the 37 patients who had inadequate computed tomographic pelvimetry and underwent cesarean delivery without a trial of labor (group 3), 54% (20/37) had an extended fetal head, 21.6% (8/37) had an inadequate transverse diameter of the inlet, 13.5% (5/37) had an inadequate midpelvic posterior sagittal measurement, and 10.8% (4/37) had an inadequate interspinous diameter. Perinatal outcome including Apgar scores, cord gases, length of hospital stay, neonatal complications, was evaluated. No difference in infant complications was noted between the group delivered vaginally and the groups delivered abdominally. The only maternal complications in our study group were chorioamnionitis, endomyometritis, and postpartum anemia. There were no significant differences in the incidence of chorioamnionitis among the three groups of patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Reliability of fetal buttock blood sampling in assessing the acid-base balance of the breech fetus

This prospective investigation was undertaken to compare fetal buttock capillary blood pH and umbilical artery and vein pH in fetuses presenting by the breech. The study group comprised ten term patients with singleton fetuses in the frank breech presentation who met established criteria for vaginal breech delivery. All patients had a normal labor pattern. Eight fetuses had a normal fetal heart rate tracing and two had severe variable decelerations during the second stage of labor. We obtained capillary blood for pH measurement from the fetal buttock within 15 minutes of delivery. Immediately after delivery, we collected arterial and venous blood samples from the umbilical cord for measurement of pH. In all fetuses, there was a highly significant correlation between fetal buttock capillary blood pH and umbilical artery pH (r = 0.96; P less than .001) and umbilical vein pH (r = 0.88; P less than .001). We conclude that measurement of pH in capillary blood obtained from the fetal buttock provides accurate assessment of the acid-base status of the breech fetus.

Randomized comparison of oral terbutaline and ritodrine for preventing recurrent preterm labor

We compared oral ritodrine and terbutaline for the prevention of recurrent preterm labor. Women between 20 and 35 weeks' gestation who successfully completed a course of intravenous tocolysis were eligible for inclusion. One hundred two patients were randomized to oral ritodrine (20 mg every four hours) or oral terbutaline (5 mg every four hours). The groups showed no significant differences with respect to recognized risk factors for preterm labor or prognostic factors for the failure of tocolysis. Initial treatment failures occurred more frequently in the ritodrine group (nine vs. two, P = .0527). There were no statistically significant differences in the treatment results or frequency of side effects. We conclude that ritodrine appears to be less effective than terbutaline upon the initiation of oral therapy and that oral ritodrine and terbutaline are equivalent in safety and efficacy when used on a long-term basis for preventing recurrent preterm labor.

Outcome of trial of labor in patients with a single previous low transverse cesarean section for dystocia

The purpose of this prospective investigation was to evaluate the outcome of trial of labor in women with a history of a single low transverse cesarean section for dystocia in comparison with the outcome in women with a history of cesarean delivery for a reason other than dystocia. During the study period, 89 of 131 patients (68%) with a history of dystocia had a successful trial of labor, compared with 78 of 96 women (81%) who had cesarean delivery for a reason other than dystocia (P less than .025). Within the former group, 79% of women who originally had surgery while still in the latent phase of labor had a successful trial of labor, compared with 61% (.05 less than P less than .10) of patients who had an arrest of dilation in the active phase of labor and 65% (not significant) of those who had an arrest of descent. The only serious complication among study patients was a single instance of uterine scar dehiscence (0.5%). We conclude that approximately two-thirds of patients with a previous cesarean delivery for dystocia will have a successful trial of labor. Of these women, those individuals whose initial operation was performed in the latent phase of labor appear to have the best prognosis for subsequent vaginal delivery.

External cephalic version at term: is a tocolytic necessary?

This prospective investigation evaluates the benefit of a beta-mimetic tocolytic for external cephalic version. From July 1, 1984 to May 15, 1987, 58 patients who had breech presentations between 37-41 weeks' gestation were considered for external cephalic version. The patients were randomly assigned to one of two groups: tocolytic or no tocolytic. An ultrasound examination, serum alpha-fetoprotein (AFP), Kleihauer-Betke test, and nonstress test (NST) were performed before and after the attempt at version. A version was not attempted if there was evidence of intrauterine growth retardation (IUGR), oligohydramnios, or a nonreactive NST. Patients in the tocolytic group received 200 micrograms/minute of ritodrine hydrochloride for 20 minutes via continuous intravenous infusion before a version was attempted. Twenty of the 30 patients (66.7%) in the tocolytic group and 19 of the 28 patients (67.8%) in the no-tocolytic group had successful versions, a nonsignificant difference. The nine patients with unsuccessful version attempts in the group without a tocolytic then received intravenous ritodrine and underwent a second attempt. Only one of these nine attempts was successful. There were no serious maternal or fetal complications associated with the attempts at version. In our patient population, use of a tocolytic did not significantly increase the probability of a successful version.

Single-dose cefazolin versus cefonicid for antibiotic prophylaxis in cesarean delivery

The purpose of this prospective investigation was to compare a single intravenous dose of cefazolin to a single dose of cefonicid as prophylaxis for women having unscheduled cesarean delivery. In a double-blind, randomized design, 96 patients were assigned to receive a 1-g dose of cefazolin and 103 patients were designated to receive a 1-g dose of cefonicid. The antibiotics were administered after delivery of the infant. The two groups were comparable with respect to recognized risk factors for postcesarean infection. There were no statistically significant differences between the groups in the incidence of standard febrile morbidity, endomyometritis, urinary tract infection, wound infection, and bacteremia. There were also no significant differences between the groups in the fever index or the duration of hospitalization. We conclude that cefazolin and cefonicid provide a similar degree of prophylaxis against infection in patients having unscheduled cesarean delivery.

Randomized comparison of five irrigation solutions at cesarean section

A randomized double-blind study was undertaken to determine which irrigation solution might be best at cesarean section. A saline placebo was compared with ampicillin sodium and one each of three generations of cephalosporins: cephapirin sodium, cefamandole nafate, and moxalactam disodium. A total of 360 cesarean sections were studied, and comparisons made between antibiotic and control groups relative to demographics, possible risk factors, and multiple measures of postoperative morbidity. The total group was further divided into high- and low-risk labor and repeat cesarean groups. Post-cesarean endometritis was diagnosed in the following frequencies for the group as a whole: placebo (24.6%), ampicillin sodium (8.5%), cephapirin sodium (11.4%), cefamandole nafate (4.6%), and moxalactam disodium (16.4%). Cefamandole nafate consistently demonstrated significant decreases in endometritis and other morbidity measures versus placebo both in laboring patients and the group as a whole.

Computed tomographic pelvimetry in the evaluation of breech presentation

The purpose of this investigation was to assess computed tomographic (CT) pelvimetry in the evaluation of breech presentation for trial of labor. Thirty-two patients with singleton term breech deliveries formed the study group. Seventeen of the 32 (53.1%) patients fulfilled the criteria for attempted vaginal delivery. Fourteen of the 17 (82.4%) delivered vaginally. All infants so delivered had five-minute Apgar scores greater than or equal to 7. Three of the 17 patients required abdominal delivery: one for fetal distress and two for arrest of dilation. These results compare favorably with studies using conventional x-ray pelvimetry. The advantages of CT over conventional pelvimetry include ease of performance, ease of interpretation, and decreased radiation dose to the fetus.

Serum unconjugated estriol level as a predictor of pulmonary maturity

Lack of respiratory distress syndrome in infants delivered after the maternal serum estriol value attained greater than or equal to 15 ng/ml was investigated. In 91 cases after 34 weeks' gestation no lecithin-sphingomyelin ratio less than 2.0 was found where the serum estriol level was greater than or equal to 15 ng/ml and no respiratory distress syndrome in the patients delivered less than or equal to 3 days from amniocentesis.

Value of a screening urinalysis in pregnancy

In order to assess the value of a screening urinalysis in the detection of urinary tract infection, the results of routine urinalyses from 1,062 obstetric patients were compared to subsequent culture results. A positive urine culture was predicted by pyuria, bacteriuria and a positive nitrite test; the predictive values were 23%, 21% and 87%, respectively. If all the parameters were negative, 96% of the cultures were negative. These findings suggest that in the interest of cost effectiveness, the urine can be cultured only when the screening urinalysis shows pyuria, bacteriuria or a positive nitrite test.

The scheduling of repeat cesarean section operations: prospective management protocol experience

There are benefits to patients and a busy obstetric service if repeat cesarean section operations are performed on a scheduled basis. Optimum management avoids prematurity and reduces the need for amniocentesis. Over a period of 20 months repeat cesarean sections were performed at Tripler Army Medical Center while a protocol with the following elements was used: (1) known last menstrual period; (2) landmarks: positive urine human chorionic gonadotropin test by 6 weeks, Doppler fetal heart tone by 12 weeks, date determination by examination before 10 weeks, fetoscope fetal heart tone by 20 weeks, and date determination by size before 30 weeks; (3) date determination by midtrimester sonogram(s); (4) normal third-trimester glucose screening; (5) biparietal diameter of 9.2 or 9.5 cm before scheduling. With two or more clinical landmarks and one date by sonogram or one landmark and date by two sonograms, elective repeat cesarean section was scheduled at 39 weeks if the biparietal diameter was greater than or equal to 9.2 cm (127). If dates by sonogram were less than dates by last menstrual period but greater than 1 week or if last menstrual period was unknown, dates by sonogram and landmarks corresponding to dates by sonogram were used to electively schedule, with biparietal diameters of 9.2 or 9.5 cm respectively required (28). If protocol criteria were not met or earlier delivery was indicated (e.g., vertical scar or diabetes), amniocentesis was performed (42), except when not possible, advisable, or refused when patients either elected labor (20) or were scheduled if three or more criteria for 40+ weeks were met (18). Of 225 patients (70.5%) scheduled by protocol (173), amniocentesis (34), or medical indication (18), 188 (58.9%) were delivered without labor. In the 147 patients (46.1%) delivered electively by protocol without labor or amniocentesis, there were no cases of respiratory distress syndrome and the mean birth weight was 3517 gm. With early care and better patient compliance nearly all repeat cesarean sections can be safely delivered electively with the use of this protocol.

Significant fetal bradycardia during antepartum heart rate testing

Reviewed were 800 patients who underwent antepartum fetal heart rate testing. Significant fetal bradycardia (less than 90 beats per minute for longer than 50 seconds or a decrease of 40 beats per minute below baseline for longer than 50 seconds) was evaluated relative to its relationship to fetal outcome. Twelve fetuses exhibited significant bradycardia during monitoring. All of these babies, when delivered within a short period of time after the tracing, showed manifestations of ongoing intrauterine jeopardy. The finding of significant fetal bradycardia during antepartum testing should prompt further evaluation and consideration for delivery.

Heart rate and blood pressure in infants of pre-eclamptic mothers during the first hour of life

Neonatal heart rate (HR) and arterial blood pressure (BP) were recorded continuously for the 1st hour of life in term newborn infants of normotensive (control group) and pre-eclamptic (study group) primiparous mothers. Infants were matched for gestational age, birth weight, method of delivery, and Apgar scores. In infants of pre-eclamptic mothers, the HR was significantly lower for the 1st 50 min of life, and their mean arterial blood pressure (MAP) was significantly higher during the 1st 20 min of life.

Plasma unconjugated estriol as an indicator of fetal dysmaturity in postterm pregnancy

The role of twice-weekly plasma unconjugated estriol determinations in the prediction of fetal dysmaturity was studied in 663 patients seen at the Postdates Clinic of the Los Angeles County/University of Southern California Medical Center. The correlation between estriol and gestational age was - 0.055. According to the criteria of the Postdates Clinic protocol, sensitivity, specificity, predictive values of positive results, and those of negative results of estriol determinations in predicting fetal dysmaturity were 44.4, 80.6, 32.9, and 87.1%, respectively. The major deficiency of this test for the detection of fetal dysmaturity was in the less-than-ideal predictive value of a negative result: 13% of patients who had normal estriol values had dysmature infants. When estriol was less than 12 ng/ml and the value fell more than 20% from the previous level, the predictive value of fetal dysmaturity was 56%. In these circumstances, the termination of pregnancy is a reasonable consideration. Until a more sensitive test for fetal dysmaturity is developed, plasma unconjugated estriol determination will retain its role as a screening test in managing postterm pregnancies in a large obstetric population.