A Novel Anti-Tumor Inhibitor Identified by Virtual Screen with PLK1 Structure and Zebrafish Assay

Polo-like kinase 1 (PLK1), one of the key regulators of mitosis, is a target for cancer therapy due to its abnormally high activity in several tumors. Plk1 is highly conserved and shares a nearly identical 3-D structure between zebrafish and humans. The initial 10 mitoses of zebrafish embryonic cleavages occur every∼30 minutes, and therefore provide a rapid assay to evaluate mitosis inhibitors including those targeting Plk1. To increase efficiency and specificity, we first performed a computational virtual screen of∼60000 compounds against the human Plk1 3-D structure docked to both its kinase and Polo box domain. 370 candidates with the top free-energy scores were subjected to zebrafish assay and 3 were shown to inhibit cell division. Compared to general screen for compounds inhibiting zebrafish embryonic cleavage, computation increased the efficiency by 11 folds. One of the 3 compounds, named I2, was further demonstrated to effectively inhibit multiple tumor cell proliferation in vitro and PC3 prostate cancer growth in Xenograft mouse model in vivo. Furthermore, I2 inhibited Plk1 enzyme activity in a dose dependent manner. The IC₅₀ values of I2 in these assays are compatible to those of ON-01910, a Plk1 inhibitor currently in Phase III clinic trials. Our studies demonstrate that zebrafish assays coupled with computational screening significantly improves the efficiency of identifying specific regulators of biological targets. The PLK1 inhibitor I2, and its analogs, may have potential in cancer therapeutics.     

The effect of plant growth-promoting rhizobacteria on the growth of rice (Oryza sativa L.) cropped in southern Brazilian fields

Background and Aims

Several strains of rhizobacteria may be found in the rhizospheric soil, on the root surface or in association with rice plants. These bacteria are able to colonize plant root systems and promote plant growth and crop yield through a variety of mechanisms. The objectives of this study were to isolate, identify, and characterize putative plant growth-promoting rhizobacteria (PGPR) associated with rice cropped in different areas of southern Brazil.

Methods

Bacterial strains were selectively isolated based on their growth on three selective semi-solid nitrogen-free media. Bacteria were identified at the genus level by PCR-RFLP 16S rRNA gene analysis and partial sequencing methodologies. Bacterial isolates were evaluated for their ability to produce indolic compounds and siderophores and to solubilize phosphate. In vitro biological nitrogen fixation and the ability to produce 1-aminocyclopropane-1-carboxylate deaminase were evaluated for each bacterial isolate used in the inoculation experiments.

Results

In total, 336 bacterial strains were isolated representing 31 different bacterial genera. Strains belonging to the genera Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most prominent isolates. Siderophore and indolic compounds producers were widely found among isolates, but 101 isolates were able to solubilize phosphate. Under gnotobiotic conditions, eight isolates were able to stimulate the growth of rice plants. Five of these eight isolates were also field tested in rice plants subjected to different nitrogen fertilization rates.

Conclusions

The results showed that the condition of half-fertilization plus separate inoculation with the isolates AC32 (Herbaspirillum sp.), AG15 (Burkholderia sp.), CA21 (Pseudacidovorax sp.), and UR51 (Azospirillum sp.) achieved rice growth similar to those achieved by full-fertilization without inoculation, thus highlighting the potential of these strains for formulating new bioinoculants for rice crops.     

Somatoform disorders among patients attending walk-in clinics in Trinidad: prevalence and association with depression and anxiety

Objectives Somatoform disorders are common in international primary care settings, but have been little studied in the developing world. The objective of this study was to determine the prevalence of severe undifferentiated somatoform disorder, and its relationship to depression and anxiety, among patients attending walk-in clinics in Trinidad.Methods The study participants, who were all aged 18 years or older and attending walk-in clinics at 16 randomly selected health centres, were surveyed between May and August 2007 using the PRIME-MD questionnaire.Results There were 594 participants (the response rate was 92%), of whom 72.7% were female. Their ages ranged from 18 to 93 years, and 54.5% were over 50 years of age. In total, 37.2% were married and 25.9% were single. Indo-Trinidadians represented 43.1% and Afro-Trinidadians represented 36% of the study sample; 56.5% of the participants reported that their income was less than US$ 400 per month, and 65.7% were unemployed. At walk-in clinics in Trinidad, the estimated prevalence of severe undifferentiated somatoform disorder was 10.3% (95% CI: 7.86–12.74), that of hypochondriasis was 28.5% (95% CI: 24.9–32.1), and that of body dysmorphic disorder was 15.8% (95% CI: 11.9–18.7). Severe undifferentiated somatoform disorder was statistically significantly associated with gender and ethnicity but not with age, level of education, employment status or income. Chi-square testing found significant associations between the presence of severe undifferentiated somatoform disorder and both depression and anxiety (P < 0.05), between hypochondriasis and both anxiety and depression (P < 0.05), and between body dysmorphic disorder and depression (P < 0.05) but not anxiety. Regression analysis suggested that the demographic features that predicted severe undifferentiated somatoform disorder were being female or Indo-Trinidadian.Conclusions Walk-in clinics in Trinidad that serve older patients on a lower income have a high proportion of patients with somatoform disorders as measured by the PRIME-MD scale. These patients exhibit many features of anxiety and depression. These findings have implications for medical training and service delivery.     

Continuously proliferative stem germ cells partially repopulate the aged, atrophic rat testis after gonadotropin-releasing hormone agonist therapy

Aging in the male human is accompanied by testicular atrophy, although relatively little is known about the mechanisms underlying germ cell loss. Testicular atrophy in the aged Brown Norway rat, an animal model for studies of aging in the human, has been attributed to a loss of spermatogonial stem cells. However, examination of testicular cross-sections from 27-mo-old Brown Norway rats indicated that approximately 14% of type A spermatogonia were stem cells. Furthermore, using bromodeoxyuridine labeling, we found that approximately 47% of these stem cells were actively dividing, with a cell cycle time of approximately 12.6 days. Both serum and testicular interstitial fluid testosterone levels were depressed in the aged rat. Therapy with the GnRH agonist, leuprolide, which has been empirically shown to reverse testicular atrophy in other models of germ cell loss, also partially restored spermatogenesis in the aged Brown Norway rat. The extent of testicular atrophy varied considerably, not only within the control and leuprolide-treatment groups but also between the left and right testes of the same animals. No significant difference was found between the mean percentage of populated tubules in 31-mo-old control animals (16.2 +/- 28%, mean +/- SD) and 31-mo-old leuprolide-treated animals (20.9 +/- 19.8%), but categorical comparisons showed that significantly fewer leuprolide-treated animals and testes contained < or = 1% populated tubules, indicating that GnRH agonist therapy stimulates differentiation of type A spermatogonia. An increase in the ratio of soluble to membrane stem cell factor mRNA levels was present in aged rats and partially reversed following leuprolide therapy.     

Nonparametric estimation in a cure model with random cure times

Acute respiratory distress syndrome (ARDS) is a life-threatening acute condition that sometimes follows pneumonia or surgery. Patients who recover and leave the hospital are considered to have been cured at the time they leave the hospital. These data differ from typical data in which cure is a possibility: death times are not observed for patients who are cured and cure times are observed and vary among patients. Here we apply a competing risks model to these data and show it to be equivalent to a mixture model, the more common approach for cure data. Further, we derive an estimator for the variance of the cumulative incidence function from the competing risks model, and thus for the cure rate, based on elementary calculations. We compare our variance estimator to Gray's (1988, Annals of Statistics 16, 1140-1154) estimator, which is based on counting process theory. We find our estimator to be slightly more accurate in small samples. We apply these results to data from an ARDS clinical trial.     

Delayed striate cortical activation during spatial attention

Recordings of event-related potentials (ERPs) and event-related magnetic fields (ERMFs) were combined with functional magnetic resonance imaging (fMRI) to study visual cortical activity in humans during spatial attention. While subjects attended selectively to stimulus arrays in one visual field, fMRI revealed stimulus-related activations in the contralateral primary visual cortex and in multiple extrastriate areas. ERP and ERMF recordings showed that attention did not affect the initial evoked response at 60-90 ms poststimulus that was localized to primary cortex, but a similarly localized late response at 140-250 ms was enhanced to attended stimuli. These findings provide evidence that the primary visual cortex participates in the selective processing of attended stimuli by means of delayed feedback from higher visual-cortical areas.     

Analysis of failure time data with dependent interval censoring

This article develops a method for the analysis of screening data for which the chance of being screened is dependent on the event of interest (informative censoring). Because not all subjects make all screening visits, the data on the failure of interest is interval censored. We propose a model that will properly adjust for the dependence to obtain an unbiased estimate of the nonparametric failure time function, and we provide an extension for applying the method for estimation of the regression parameters from a (discrete time) proportional hazards regression model. The method is applied on a data set from an observational study of cytomegalovirus shedding in a population of HIV-infected subjects who participated in a trial conducted by the AIDS Clinical Trials Group.     

Role of Sertoli cells in injury-associated testicular germ cell apoptosis

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.