Chemotherapy induces Notch1-dependent MRP1 up-regulation, inhibition of which sensitizes breast cancer cells to chemotherapy

Background Multi-drug Resistance associated Protein-1 (MRP1) can export chemotherapeutics from cancer cells and is implicated in chemoresistance, particularly as is it known to be up-regulated by chemotherapeutics. Our aims in this study were to determine whether activation of Notch signalling is responsible for chemotherapy-induced MRP1 expression Notch in breast cancers, and whether this pathway can be manipulated with an inhibitor of Notch activity. Methods MRP1 and Notch1 were investigated in 29 patients treated with neoadjuvant chemotherapy (NAC) for breast cancer, using immunohistochemistry on matched biopsy (pre-NAC) and surgical samples (post-NAC). Breast epithelial cell cultures (T47D, HB2) were treated with doxorubicin in the presence and absence of functional Notch1, and qPCR, siRNA, Western blots, ELISAs and flow-cytometry were used to establish interactions. Results In clinical samples, Notch1 was activated by neoadjuvant chemotherapy (Wilcoxon signed-rank p < 0.0001) and this correlated with induction of MRP1 expression (rho = 0.6 p = 0.0008). In breast cell lines, doxorubicin induced MRP1 expression and function (non-linear regression p < 0.004). In the breast cancer line T47D, doxorubicin activated Notch1 and, critically, inhibition of Notch1 activation with the γ-secretase inhibitor DAPT abolished the doxorubicin-induced increase in MRP1 expression and function (t-test p < 0.05), resulting in enhanced cellular retention of doxorubicin and increased doxorubicin-induced apoptosis (t-test p = 0.0002). In HB2 cells, an immortal but non-cancer derived breast cell line, Notch1-independent MRP1 induction was noted and DAPT did not enhance doxorubicin-induced apoptosis. Conclusions Notch inhibitors may have potential in sensitizing breast cancer cells to chemotherapeutics and therefore in tackling chemoresistance

Contact mechanics of filled thermoplastic and thermoset polymer systems

This study aims to relate the intrinsic mechanical response of particle-filled polymer glasses to their response in sliding friction. A previous study showed that the frictional properties of unfilled polycarbonate are quantitatively captured by finite element simulations when using a proper constitutive model, i.e. a model that captures the polymers intrinsic mechanical response quantitatively, and a rate-independent friction (stick-slip) model. Single-asperity scratch tests were successfully modeled over a range of scratch velocities and for different indenter-tip geometries.  In this thesis we extend these pioneering results to the class of practically more relevant and interesting particle-filled (thermoplastic and thermoset) polymer systems. To that end, hard- and soft-particle filled polycarbonate and epoxy systems are investigated. Starting with polycarbonate (that is over the years fully characterized) as matrix material, hard inorganic (TiO2) and soft rubber (MBS) filled model systems are designed and produced. Their intrinsic response is measured in lubricated uniaxial compression tests. To reveal local events at the interparticle level, three-dimensional representative volume elements (3D-RVEs) are constructed to model the complex microstructure of these systems. Finite element simulations of these 3D-RVEs show that the intrinsic response is captured well but, moreover, they provide insight in the critical local events that lead to global failure. The simulations provide the (homogenized) material parameters that macroscopically describe these particle-filled systems, and that are used in the simulations of their scratch response in sliding friction tests. It is confirmed that by combining a proper constitutive framework with the most simple, rate-independent, friction model, all experiments are appropriately described quantitatively by the numerical simulations. Furthermore, the onset of failure during scratching becomes accessible. The local (homogenized) strains resulting from the scratch simulations can be translated to simulations on the RVE-level that reveal the extent of critical events at the interparticle level. After the successful modeling of filled thermoplastic systems, the focus is next on thermosets. Epoxy-based composites are investigated, designed and produced, since thismatrix is more relevant for coating applications. The intrinsic mechanical response ofthe matrix material, a standard epoxy, is characterized and the material parameters usedin the constitutive model are determined. The model systems filled with either softpolysiloxane rubber particles or hard TiO2 particles are created and tested. It is shownthat the complete methodology as derived and described for polycarbonate is also validfor these thermoset systems.  The thesis ends with an onset of designing smart materials, inspired by our findingsfrom the simulations on the microstructures and the scratch tests

Global and local large-deformation response of sub-micron, soft- and hard-particle filled polycarbonate

Since polymers play an increasingly important role in both structural and tribological applications, understanding their intrinsic mechanical response is key. Therefore in the last decades much effort has been devoted into the development of constitutive models that capture the polymers' intrinsic mechanical response quantitatively. An example is the Eindhoven Glassy Polymer model. In practice most polymers are filled, e.g. with hard particles or fibers, with colorants, or with soft particles that serve as impact modifiers. To characterize the influence of type and amount of filler particles on the intrinsic mechanical response, we designed model systems of polycarbonate with different volume fractions of small, order 100 nm sized, either hard or soft particles, and tested them in lubricated uniaxial compression experiments. To reveal the local effects on interparticle level, three-dimensional representative volume elements (RVEs) were constructed. The matrix material is modeled with the EGP model and the fillers with their individual mechanical properties. It is first shown that (only) 32 particles are sufficient to capture the statistical variations in these systems. Comparing the simulated response of the RVEs with the experiments demonstrates that in the small strain regime the stress is under-predicted since the polymer matrix is modeled by using only one single relaxation time. The yield- and the large strain response is captured well for the soft-particle filled systems while, for the hard-particles at increased filler loadings, the predictions are less accurate. This is likely caused by polymer-filler interactions that result in accelerated physical aging of the polymer matrix close to the surfaces. Modifying the Sa-parameter, that captures the thermodynamic state of the polymer matrix, allows to correctly predict the macroscopic response after yield. The simulations reveal that all rate-dependencies of the different filled systems originate from that of the polymer matrix. Finally, an onset is presented to predict local and global failure based on critical events on the microlevel, that are likely to cause the over-prediction in the large-strain response of the hard-particle filled systems

Sliding friction on particle filled epoxy: Developing a quantitative model for complex coatings

Epoxy resins represent an important class of thermosetting polymers that are extensively used in demanding applications like in scratch resistant coatings. Usually fillers, either hard (inorganic) or soft (rubbery), are added. Here we test hard and soft particle-filled epoxy systems in single asperity sliding friction experiments, and analyze the results with the hybrid numerical-experimental approach presented earlier. The focus is on the detailed modeling of the local deformation processes and it is confirmed that a rate-independent friction model proves appropriate to quantitatively model this complex process. The constitutive framework developed for amorphous thermoplastic polymers adequately describes also these thermoset systems. The materials response during scratching is likewise. Hard fillers decrease the penetration of the indenter into the surface, and consequently enhance scratch resistance; they cause the lateral friction force to decrease, since less material flows in front of the indenter tip. Soft fillers increase the penetration into the surface, according to expectations, but surprisingly also decrease the friction force. Simulations do not predict this, and suggest an alternative explanation. Migration of rubber particles during sample preparation to the surface could have occurred. Adding a thin rubbery layer to the surface makes the model quantitative, but SEM and TEM pictures of the cross-sections do not confirm this phase separation and instead show the presence of a large number of very small voids. Including these voids in the modeling allows to predict the penetration depth into the surface and lateral force quantitative for all sliding speeds

Finite element modeling and experimental validation of single-asperity sliding friction of diamond against reinforced and non-filled polycarbonate

Polymer composites used as protective coatings are important, tribology-critical applications. In this study, hard or soft particle-filled model systems with a polycarbonate matrix are tested in single asperity sliding friction tests against diamond tips. A numerical approach developed to simulate scratching on unfilled polycarbonate was adapted by computing the effective material parameters for the hard and soft particle filled systems using representative volume elements. Combining this proper constitutive framework with a rate-independent friction model correlated quantitatively with the results of the current scratching experiments. Polymer composites used as protective coatings are important, tribology-critical applications. In this study, hard or soft particle-filled model systems with a polycarbonate matrix are tested in single asperity sliding friction tests against diamond tips. A numerical approach developed to simulate scratching on unfilled polycarbonate was adapted by computing the effective material parameters for the hard and soft particle filled systems using representative volume elements. Combining this proper constitutive framework with a rate-independent friction model correlated quantitatively with the results of the current scratching experiments

Sliding friction on particle filled epoxy:Developing a quantitative model for complex coatings

\u3cp\u3eEpoxy resins represent an important class of thermosetting polymers that are extensively used in demanding applications like in scratch resistant coatings. Usually fillers, either hard (inorganic) or soft (rubbery), are added. Here we test hard and soft particle-filled epoxy systems in single asperity sliding friction experiments, and analyze the results with the hybrid numerical-experimental approach presented earlier. The focus is on the detailed modeling of the local deformation processes and it is confirmed that a rate-independent friction model proves appropriate to quantitatively model this complex process. The constitutive framework developed for amorphous thermoplastic polymers adequately describes also these thermoset systems. The materials response during scratching is likewise. Hard fillers decrease the penetration of the indenter into the surface, and consequently enhance scratch resistance; they cause the lateral friction force to decrease, since less material flows in front of the indenter tip. Soft fillers increase the penetration into the surface, according to expectations, but surprisingly also decrease the friction force. Simulations do not predict this, and suggest an alternative explanation. Migration of rubber particles during sample preparation to the surface could have occurred. Adding a thin rubbery layer to the surface makes the model quantitative, but SEM and TEM pictures of the cross-sections do not confirm this phase separation and instead show the presence of a large number of very small voids. Including these voids in the modeling allows to predict the penetration depth into the surface and lateral force quantitative for all sliding speeds.\u3c/p\u3