Evidence for two nonidentical drug-interaction sites in the human P-glycoprotein

Human P-glycoprotein (Pgp) confers multidrug resistance to cancer cells by ATP-dependent extrusion of a great many structurally dissimilar hydrophobic compounds. The manner in which Pgp recognizes these different substrates is unknown. The protein shows internal homology between its N- and C-terminal halves, each comprised of six putative transmembrane helices and a consensus ATP binding/utilization site. Photoactive derivatives of certain Pgp substrates specifically label two regions, one on each half of the protein. In this study, using [¹²⁵I]iodoarylazidoprazosin ([¹²⁵I]IAAP), a photoactive analog of prazosin, we have demonstrated the presence of two nonidentical drug-interaction sites within Pgp. Taking advantage of a highly susceptible trypsin cleavage site in the linker region of Pgp, we characterized the [¹²⁵I]IAAP binding to the N- and C-terminal halves. cis(Z)-Flupentixol, a modulator of Pgp function, preferentially increased the affinity of [¹²⁵I]IAAP for the C-terminal half of the protein (C-site) by reducing the K_d from 20 to 6 nM without changing the labeling or affinity (K_d = 42–46 nM) of the N-terminal half (N-site). Also, the concentration of vinblastine (Pgp substrate) and cyclosporin A (Pgp modulator) required for 50% inhibition of [¹²⁵I]IAAP binding to the C-site was increased 5- to 6-fold by cis(Z)-flupentixol without any effect on the N-site. In addition, [¹²⁵I]IAAP binding to the N-site was less susceptible than to C-site to inhibition by vanadate which blocks ATP hydrolysis and drug transport. These data demonstrate the presence of at least two nonidentical substrate interaction sites in Pgp.     

Consensus Recommendations for the Diagnosis and Management of Pancreatic Neuroendocrine Tumors: Guidelines from a Canadian National Expert Group

Annals of Surgical Oncology - Pancreatic neuroendocrine tumors (pNETs) are rare heterogeneous tumors that have been steadily increasing in both incidence and prevalence during the past few decades....     

Leishmania-induced biphasic ceramide generation in macrophages is crucial for uptake and survival of the parasite

The initial macrophage-Leishmania donovani interaction results in the formation of membrane platforms, termed lipid rafts, that help in the entry of the parasite. Therefore, it is imperative that the parasite designs a strategy to modulate its uptake and survival within the macrophages. Herein, we report Leishmania-triggered biphasic ceramide generation. In the first phase, L. donovani promastigotes induce activation of acid sphingomyelinase (ASMase), which catalyzes the formation of ceramide from sphingomyelin. Inhibition of ASMase resulted in reduced uptake and infection with the parasite. In the second phase, de novo synthesis generates ceramide that reduces the cellular cholesterol level and displaces the cholesterol from the membrane, leading to enhanced membrane fluidity, disruption of rafts, and impaired antigen-presentation to the T cells. The results reveal a novel role for ceramide in the perspective of L. donovani infection and help formulate an antileishmanial strategy that can possibly be applied to other intracellular infections as well.     

Thrombolytic Evacuation of Intracerebral and Intraventricular Hemorrhage

Intracranial hemorrhage (ICH) accounts for 10-15?% of all strokes, however it causes 30-50?% of stroke related mortality, disability and cost. The prevalence increases with age with only two cases/100,000/year for age less than 40?years to almost 350 cases/100,000/year for age more than 80?years. Several trials of open surgical evacuation of ICH have failed to show clear benefit over medical management. However, some small trials of minimal invasive hematoma evacuation in combination with thrombolytics have shown encouraging results. Based on these findings larger clinical trials are being undertaken to optimize and define therapeutic benefit of minimally invasive surgery in combination with thrombolytic clearance of hematoma. In this article we will review some of the background of minimally invasive surgery and the use of thrombolytics in the setting of ICH and intraventricular hemorrhage (IVH) and will highlight the early findings of MISTIE and CLEAR trials for these two entities respectively.     

Prognostic value of cardiovascular CT: is coronary artery calcium screening enough? The added value of CCTA

Coronary artery disease (CAD) is the primary cause of death in adults in the United States. Only 50% of patients who present with a myocardial infarction have a prior history of CAD. Non-invasive cardiac imaging tests have been developed to diagnose CAD. Current guidelines and systematic reviews have tried to determine the prognostic value of the coronary artery calcium (CAC) scoring and the coronary computed tomography angiography (CCTA) for major adverse cardiovascular events. Several studies support the roles of CCTA and CAC scoring for the diagnosis of CAD in asymptomatic patients. Further studies are needed to confirm the superior role of CCTA over CAC scoring in symptomatic patients.