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Many drug targets are localized to particular subcellular compartments, yet current drug design strategies are focused on bioavailability and tissue targeting and rarely address drug delivery to specific intracellular compartments. Insights into how the cell traffics its constituents to these different cellular locations could improve drug design. In this Review, we explore the fundamentals of membrane trafficking and subcellular organization, as well as strategies used by pathogens to appropriate these mechanisms and the implications for drug design and delivery.

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Primitive streak formation in the chick embryo involves large scale highly coordinated flows of over 100.000 cells in the epiblast. These large scale tissue flows and deformations can be correlated with specific anisotropic cell behaviours in the forming mesendoderm through a combined light-sheet microscopy and computational analysis. Relevant behaviours include apical contraction, elongation along the apical-basal axis followed by ingression as well as asynchronous directional cell intercalation of small groups of mesendoderm cells. Cell intercalation is associated with sequential, directional contraction of apical junctions, the onset, localisation and direction of which correlate strongly with the appearance of active Myosin II cables in aligned apical junctions in neighbouring cells. Use of a class specific Myosin inhibitors and gene specific knockdowns show that apical contraction and intercalation are Myosin II dependent and also reveal critical roles for Myosin I and Myosin V family members in the assembly of junctional Myosin II cables.

beta-Secretase plays a critical role in beta-amyloid formation and thus provides a therapeutic target for Alzheimer's disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a beta-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active beta-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting beta-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.

Upon starvation or overcrowding, Caenorhabditis elegans interrupts its reproductive cycle and forms a specialised larva called dauer (enduring). This process is regulated by TGF-β and insulin-signalling pathways and is connected with the control of life span through the insulin pathway components DAF-2 and DAF-16. We found that replacing cholesterol with its methylated metabolite lophenol induced worms to form dauer larvae in the presence of food and low population density. Our data indicate that methylated sterols do not actively induce the dauer formation but rather that the reproductive growth requires a cholesterol-derived hormone that cannot be produced from methylated sterols. Using the effect of lophenol on growth, we have partially purified activity, named gamravali, which promotes the reproduction. In addition, the effect of lophenol allowed us to determine the role of sterols during dauer larva formation and longevity. In the absence of gamravali, the nuclear hormone receptor DAF-12 is activated and thereby initiates the dauer formation program. Active DAF-12 triggers in neurons the nuclear import of DAF-16, a forkhead domain transcription factor that contributes to dauer differentiation. This hormonal control of DAF-16 activation is, however, independent of insulin signalling and has no influence on life span.

The [221] cycloaddition of two alkynes and carbon monoxide in the presence of pentacarbonyliron represents a useful method for the construction of five-membered ring systems. [1, 2] Applications of the resulting tricarbonyl(h 4 -cyclopentadienone)iron complexes to organic synthesis are feasible by demetalation to the free cyclopentadienones. This transformation was achieved by oxidation with trimethylamine Noxide. [1,3] Recently we reported a novel method for the demetalation of tricarbonyl(diene)iron complexes by a photolytically induced exchange of the carbonyl ligands by acetonitrile. [4] Herein we describe an alternative procedure for the ligand exchange at tricarbonyl(h 4 -cyclopentadienone)iron complexes and the subsequent demetalation in the air.Tricarbonyl(h 4 -cyclopentadienone)iron complexes undergo a transformation similar to the Hieber reaction. [5] Thus, reaction of complex 1 a with aqueous NaOH in THF leads to an equilibrium of the corresponding hydrido complexes 2 a and 4 a in a ratio of about 13:1 (Scheme 1). Tricarbonyl(cyclohexa-1,3-diene)iron complexes are inert under these conditions. Addition of H 3 PO 4 affords 2 a in 94 % yield, while reaction with NaH shifts the equilibrium towards the salt 4 a Scheme 1. a) 1m NaOH/THF (1/2); b) C 5 H 11 I; c) H 3 PO 4 ; d) air, daylight, Et 2 O/THF, Na 2 S 2 O 3 , Celite, 3 h; e) NaH, Et 2 O/THF.(82 % yield). Reaction of the hydrido complex 2 a with 1-iodopentane provides the iodo complex 3 a in 98 % yield. A related transformation is reported for the hydrido complex [CpFe(CO) 2 H]. [6] The addition of 1-iodopentane after the reaction of 1 a with NaOH affords an equilibrium of the iodo complexes 3 a and 5 a that is shifted again by addition of H 3 PO 4 or NaH, respectively. Preparation of the iodo complex 3 a without isolation of the intermediate hydrido complex 2 a increases the yield (98 % based on complex 1 a).The 13 C NMR and the IR data of the hydrido complex 2 a and the iodo complex 3 a suggest an h 5 -coordinated hydroxycyclopentadienyl ligand for both compounds. [7] A characteristic structural feature of the hydrido complex 2 a is the unsymmetrical arrangement of the coligands, which is apparent from two CO signals in the 13 C NMR spectrum. This assignment was confirmed by an X-ray structure determination of complex 2 a (Figure 1), [8] which shows an h 5 -coordinated hydroxycyclopentadienyl ligand and a C1ÀO1 bond length of 1.366 . [9] A loss of C S symmetry was also found for the hydrido complex 4 a from the 13 C NMR spectrum, which exhibits the two signals for the carbonyl ligands and a peak at d 170.13 for C1. [7] Figure 1. Molecular structure of 2 a in the crystal. Selected bond lengths []: FeÀC1 2.