A viral target has been discovered that paves the way for drug development aimed at destroying tumors that originate from Epstein–Barr virus (EBV). The target was discovered by researchers at the University of Wisconsin School of Medicine and Public Health (WI, USA).
The researchers have identified activity from a crucial segment of the viral protein that is essential for the tumor to remain active in the host. They also discovered that they could halt the life cycle of the virus by blocking this activity.
“We have been trying to identify specific functions of Epstein–Barr virus nuclear antigen-1 (EBNA-1) that we could target therapeutically”, researcher Bill Sugden explains. “Our goal is to develop a successful anti-viral, antitumor therapy for all EBV-positive tumors.”
The study focused on a previously discovered protein that is essential to the life cycle of Burkitt’s lymphoma, known as EBNA-1. This viral protein is unique in that it is the only one to be produced in every case of EBV-positive tumors.
“If we can identify this protein, it will be easier for us to develop assays to screen for small molecules that will compete with the protein in binding to EBNA-1”, added Sugden. “By preventing the cellular protein from binding with the segment, EBNA-1 will not be able to carry out its function and the tumor cells it sustains will die”.
Sugden and his team are optimistic that this discovery will lead to a drug that can eliminate EBV-positive tumor cells while leaving other host tissue unharmed.
Source: Alrmann M, Pich D, Ruiss R, Wang J, Sugden B, Hammerschmidt W. Transcriptional activation by EBV nuclear antigen 1 is essential for the expression of EBV’s transforming genes. Proc. Natl Acad. Sci. USA 103(38), 14188–14193 (2006).
Mechanism of action of plague bacteria identified
A new study has identified methods in which Yersinia spp., the bacteria responsible for the plague and various forms of food poisoning, exerts its adverse effects within the host. It was discovered recently by researchers at Rockefeller University (NY, USA) that the bacteria unexpectedly paralyzes the host immune system by the use of a mimicking protein.
The bacteria harbors Yersinia protein kinase A (YpkA), a multidomain protein. This protein blocks the ability of the host’s cells to move or change shape, therefore making recognition and engulfing of foreign cells by the immune system very difficult. It was already known that YpkA disrupts the eukaryotic actin cytoskeleton.
In this study, the crystal structure of the YpkA–Rac1 complex was solved and it was discovered that YpkA contains a Rac1-binding domain, which mimics the guanidine nucleotide dissociation inhibitors (GDIs) of the Rho GTPases of the host. Therefore, nucleotide exchange in Rac1 and RhoA is inhibited by YpkA. This led to the conclusion that the effects seen as a result of Yersinia are a result of its mimicking effect of the host GDI protein.
This pathogen is of particular concern with respect to biodefense and antibiotic resistance. Results were published in September’s edition of Cell.
“Yersina injects several virulence factors into its host, if we can discover which ones are critical, we might identify the pathogen’s achilles heel – an attractive target for antibacterial or antivirulence compounds”, explained researcher C Erec Stebbins of Rockefeller University. He added: “We were quite excited to see such a critical and unexpected factor in the virulence of Yersinia – a bacteria historically responsible for some of the worst diseases”.
Source: Prehna G, Ivanov MI, Bliska JB, Stebbins CE. Yersinia virulence depends on mimicry of host Rho-family nucleotide dissociation inhibitors. Cell 126, 868–880 (2006).
Proteomic fingerprinting serum used to identify tuberculosis diagnostic markers
A serum test that could be used to indicate tuberculosis (TB) infection in the developing world has been created, which with further development, is hoped to become a simple and accurate indicator of the disease. The 94% accuracy rate for the test suggests that it will be a useful tool in saving many lives in countries where TB prevails. The test recognizes unique biomarkers from serum blood samples.
Currently, microscopic analysis of sputum is used to diagnose the disease. This can have as low as a 40–60% accuracy rate in rural areas in developing countries and takes 2–6 weeks for the result to be achieved. Results from the new development were published in theLancet.
The research was conducted by scientists at the Medical Research Council National Institute for Medical Research (NIMR) and at St George’s Hospital (London, UK).
Considering that the disease is the leading cause of death, worlwide, due to infection, this tool will be valuable in helping to prevent such unnecessary deaths. Early diagnosis and treatment is important and greatly improves a patient’s chance of survival.
The team used mass spectrometric serum profiling and couple recognition methods to identify biomarkers exclusive to TB. Researchers compared active TB-infected serum samples with control samples and used following statistical analysis were able to recognize the biomarkers from TB-infected samples. The proteomic profiles were obtained using surface-enhanced laser desorption ionization time of flight mass spectrometry. The two groups were distinguished with a supervized machine-learning approach, which was based on the support vector machine (SVM).
The researchers then used k-fold cross- validation and random sampling of the SVM classifier to further test the classifier. Correlational analysis and SVM, respectively, were used to select and then assess the relevant mass peaks. Peptide mass fingerprinting was used in biomarker identification and their diagnostic potential was assessed with conventional immunoassays and data-trained SVM classifiers.
Delmiro Fernandez-Reyes of NIMR was working on the method and said of the work: “Current developments in mass spectrometry together with new statistical methods for pattern discovery are allowing us to identify biomarkers of infection. Our work opens the door to further research into translating these findings to fast and reliable methods of detecting active TB infection that could have a major impact in global health. We currently apply similar approaches to malaria diagnosis”.
The classifiers distinguished between the serum of the active TB-infected and that of the sample group with high diagnostic accuracy (94%), sensitivity (93.5%) and specificity (94.9%). They also noted that results were unaffected by HIV status.
Sanjeev Krishna of St George’s Hospital added: “We are putting forward a fresh approach to an ancient problem. I think it’s going to be very exciting to make this work in clinics where a test for TB is desperately needed. The next stage will be to use the biomarkers we have identified to develop a cheap, accurate and rapid diagnostic test that can be used easily and quickly out in the field”.
Source: Agranoff D, Papadopoulos MC, Sheldon J et al. Identification of diagnostic markers for tuberculosis by proteomic fingerprinting of serum. Lancet 368, 1012–1021 (2006).
Malaria treatment failure in HIV-positive patients
HIV-1-infected patients with low CD4+ cell counts are at higher risk of recurrent parasitemia after malaria treatment compared with those with higher CD4+ cell counts. The finding appears in the October issue of the Journal of Infectious Diseases.
“HIV-1-associated immune suppression, rather than infection with HIV-1 per se, is the main determinant of malaria treatment outcome,” said the lead author of the study, Jean-Pierre Van Geertruyden of the Institute of Tropical Medicine (Belgium).
The study involved 971 Zambian adults with malaria, 33% of whom were positive for HIV-1. CD4+ cell counts were assessed and recurrent parasitemia was monitored for 45 days after malaria treatment.
Malaria treatment failure occurred in both HIV-1-negative and -positive patients. Recurrent parasitemia incidence was significantly higher in HIV-1-infected patients with fewer than 300 CD4+ cells/µl blood compared with those with higher CD4+ cell counts or HIV-1-negative malaria patients.
“Our study demonstrates that HIV-1-infected patients with suppressed immunity represent, next to children and pregnant women, an additional vulnerable group for malaria”, said Van Geertruyden.
The study raises a major concern in the effectiveness of antimalarial–antiretroviral treatment combination and the potential spread of antimalarial drug resistance. The authors suggest that malaria prevention and early diagnosis are highly important in areas where both malaria and HIV-1 infection are prevalent.
Source: Van Geertruyden J-P, Mulenga M, Mwananyanda L et al. HIV-1 immune suppression and antimalarial treatment outcome in Zambian adults with uncomplicated malaria. J. Infect. Dis. 194, 917–925 (2006).
More insight into pregnancy-associated malaria
Pregnancy-associated malaria (PAM) can be fatal to both the mother and the unborn child. Researchers at the Karolinska Institute (Sweden) have provided new understanding of the pathogenesis of PAM that can help to develop more effective PAM vaccines.
The malaria pathogen, Plasmodium falciparum, infects and lyzes the human red blood cells during one stage of its parasitic life cycle. The parasite produces proteins that cause red blood cells to attach to blood vessel wall and accumulate. Death may occur from anemia and clogging of vessels of cerebral tissues, which are most common in infants and pregnant women but this also occurs in nonimmune travelers to malaria-endemic areas. Adults in endemic areas are usually partly immune because of several infections during their life, with their immune system recognizing the parasite’s proteins.
“For some reason, women in their first pregnancy lose the semi-immunity that is normally found in adults”, said Nillofar Rasti, a research team member. “The placenta seems to be an anatomically favorable environment for a subpopulation of the parasites.”
The researchers have taken samples from pregnant Ugandan patients with malaria and studied the binding of the parasite’s variant surface antigens and placental receptors. “Most of the parasites we studied could bind to three different receptors in the placenta. This would mean that a future vaccine cannot be based on the principle of one protein–one receptor as was previously believed”, explained Rasti.
Source: Rasti N, Namusoke F, Chene A et al. Nonimmune immunoglobulin binding and multiple adhesion characterize Plasmodium falciparum-infected erythrocytes of placental origin. Proc. Natl Acad. Sci USA 103(37), 13795–13800 (2006).