75 research outputs found
6-(7-Nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol, a specific glutathione S-transferase inhibitor, overcomes the multidrug resistance (MDR)-associated protein 1-mediated MDR in small cell lung cancer
In the present work, we have investigated the antitumor activity of 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) on aggressive small cell lung cancer. NBDHEX not only is cytotoxic toward the parental small cell lung cancer H69 cell line (LC50 of 2.3 +/- 0.6 mu mol/L) but also overcomes the multidrug resistance of its variant, H69AR, which overexpresses the ATP-binding cassette transporter multidrug resistance-associated protein 1 (MRP1; LC50 of 4.5 +/- 0.9 mu mol/L). Drug efflux experiments, done in the presence of a specific inhibitor of MRP1, confirmed that NBDHEX is not a substrate for this export pump. Interestingly, NBDHEX triggers two different types of cell death: a caspase-dependent apoptosis in the H69AR cells and a necrotic phenotype in the parental H69 cells. The apoptotic pathway triggered by NBDHEX in H69AR cells is associated with c-Jun NH2-terminal kinase and c-Jun activation, whereas glutathione oxidation and activation of p38(MAPK) is observed in the NBDHEX-treated H69 cells. In contrast to the parental cells, the higher propensity to die through apoptosis of the H69AR cell line may be related to the lower expression of the antiapoptotic protein Bcl-2. Therefore, down-regulation of a factor crucial for cell survival makes H69AR cells more sensitive to the cytotoxic action of NBDHEX, which is not a MRP1 substrate. We have previously shown that NBDHEX is cytotoxic toward P-glycoprotein-overexpressing tumor cell lines. Therefore, NBDHEX seems a very promising compound in the search for new molecules able to overcome the ATP-binding cassette family of proteins, one of the major mechanisms of multidrug resistance in cancer cells
The Subleading Term of the Strong Coupling Expansion of the Heavy-Quark Potential in a Super Yang-Mills Plasma
Applying the AdS/CFT correspondence, the expansion of the heavy-quark
potential of the supersymmetric Yang-Mills theory at large is
carried out to the sub-leading term in the large 't Hooft coupling at nonzero
temperatures. The strong coupling corresponds to the semi-classical expansion
of the string-sigma model, the gravity dual of the Wilson loop operator, with
the sub-leading term expressed in terms of functional determinants of
fluctuations. The contributions of these determinants are evaluated
numerically.Comment: 17 pages in JHEP3, typos fixed, updated version to be published in
JHE
The Final Fate of the Rolling Tachyon
We propose an alternative interpretation of the boundary state for the
rolling tachyon, which may depict the time evolution of unstable D-branes in
string theory. Splitting the string variable in the temporal direction into the
classical part, which we may call "time" and the quantum one, we observe the
time dependent behaviour of the boundary. Using the fermion representation of
the rolling tachyon boundary state, we show that the boundary state correctly
describes the time-dependent decay process of the unstable D-brane into a
S-brane at the classical level.Comment: 9 pages, revte
Can holography reproduce the QCD Wilson line?
Recently a remarkable agreement was found between lattice simulations of long
Wilson lines and behavior of the Nambu Goto string in flat space-time. However,
the latter fails to fit the short distance behavior since it admits a tachyonic
mode for a string shorter than a critical length. In this paper we examine the
question of whether a classical holographic Wilson line can reproduce the
lattice results for Wilson lines of any length. We determine the condition on
the the gravitational background to admit a Coulombic potential at short
distances. We analyze the system using three different renormalization schemes.
We perform an explicit best fit comparison of the lattice results with the
holographic models based on near extremal D3 and D4 branes, non-critical near
extremal AdS6 model and the Klebanov Strassler model. We find that all the
holographic models examined admit after renormalization a constant term in the
potential. We argue that the curves of the lattice simulation also have such a
constant term and we discuss its physical interpretation
Exact results for static and radiative fields of a quark in N=4 super Yang-Mills
In this work (which supersedes our previous preprint arXiv:1112.2345) we
determine the expectation value of the N=4$ SU(N) SYM Lagrangian density
operator in the presence of an infinitely heavy static particle in the
symmetric representation of SU(N), by means of a D3-brane probe computation.
The result that we obtain coincides with two previous computations of different
observables, up to kinematical factors. We argue that these agreements go
beyond the D-brane probe approximation, which leads us to propose an exact
formula for the expectation value of various operators. In particular, we
provide an expression for the total energy loss by radiation of a heavy
particle in the fundamental representation.Comment: 14 pages. This submission supersedes our previous preprint
arXiv:1112.2345. v2: numerical factors fixed, minor clarifications, added
reference
Quark--anti-quark potential in N=4 SYM
We construct a closed system of equations describing the quark--anti-quark
potential at any coupling in planar N=4 supersymmetric Yang-Mills theory. It is
based on the Quantum Spectral Curve method supplemented with a novel type of
asymptotics. We present a high precision numerical solution reproducing the
classical and one-loop string predictions very accurately. We also analytically
compute the first 7 nontrivial orders of the weak coupling expansion.
Moreover, we study analytically the generalized quark--anti-quark potential
in the limit of large imaginary twist to all orders in perturbation theory. We
demonstrate how the QSC reduces in this case to a one-dimensional Schrodinger
equation. In the process we establish a link between the Q-functions and the
solution of the Bethe-Salpeter equation.Comment: 31 pages, 1 figure; v2: minor correcton
Generalized cusp in AdS_4 x CP^3 and more one-loop results from semiclassical strings
We evaluate the exact one-loop partition function for fundamental strings
whose world-surface ends on a cusp at the boundary of AdS_4 and has a "jump" in
CP^3. This allows us to extract the stringy prediction for the ABJM generalized
cusp anomalous dimension Gamma_{cusp}^{ABJM} (phi,theta) up to NLO in
sigma-model perturbation theory. With a similar analysis, we present the exact
partition functions for folded closed string solutions moving in the AdS_3
parts of AdS_4 x CP^3 and AdS_3 x S^3 x S^3 x S^1 backgrounds. Results are
obtained applying to the string solutions relevant for the AdS_4/CFT_3 and
AdS_3/CFT_2 correspondence the tools previously developed for their AdS_5 x S^5
counterparts.Comment: 48 pages, 2 figures, version 3, corrected misprints in formulas 2.12,
B.86, C.33, added comment on verification of the light-like limi
The generalized cusp in ABJ(M) N = 6 Super Chern-Simons theories
We construct a generalized cusped Wilson loop operator in N = 6 super
Chern-Simons-matter theories which is locally invariant under half of the
supercharges. It depends on two parameters and interpolates smoothly between
the 1/2 BPS line or circle and a pair of antiparallel lines, representing a
natural generalization of the quark-antiquark potential in ABJ(M) theories. For
particular choices of the parameters we obtain 1/6 BPS configurations that,
mapped on S^2 by a conformal transformation, realize a three-dimensional
analogue of the wedge DGRT Wilson loop of N = 4. The cusp couples, in addition
to the gauge and scalar fields of the theory, also to the fermions in the
bifundamental representation of the U(N)xU(M) gauge group and its expectation
value is expressed as the holonomy of a suitable superconnection. We discuss
the definition of these observables in terms of traces and the role of the
boundary conditions of fermions along the loop. We perform a complete two-loop
analysis, obtaining an explicit result for the generalized cusp at the second
non-trivial order, from which we read off the interaction potential between
heavy 1/2 BPS particles in the ABJ(M) model. Our results open the possibility
to explore in the three-dimensional case the connection between localization
properties and integrability, recently advocated in D = 4.Comment: 53 pages, 10 figures, added references, this is the version appeared
on JHE
The quark anti-quark potential and the cusp anomalous dimension from a TBA equation
We derive a set of integral equations of the TBA type for the generalized
cusp anomalous dimension, or the quark antiquark potential on the three sphere,
as a function of the angles. We do this by considering a family of local
operators on a Wilson loop with charge L. In the large L limit the problem can
be solved in terms of a certain boundary reflection matrix. We determine this
reflection matrix by using the symmetries and the boundary crossing equation.
The cusp is introduced through a relative rotation between the two boundaries.
Then the TBA trick of exchanging space and time leads to an exact equation for
all values of L. The L=0 case corresponds to the cusped Wilson loop with no
operators inserted. We then derive a slightly simplified integral equation
which describes the small angle limit. We solve this equation up to three loops
in perturbation theory and match the results that were obtained with more
direct approaches.Comment: 63 pages, 12 figures. v2: references added, typos correcte
Semiclassical partition function for strings dual to Wilson loops with small cusps in ABJM
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