Magnetic Nanoparticles against Cancer

RST department colloquium, 11.05.15

Title: Functional magnetic nanostructures for tunable RF and biomedical applications

Speaker: Dr. Hari Srikanth (University of South-Florida, Tampa )

Author: Edgar Schönfeld

Hari Srikanth is a phycisist and works with magnetic nanoparticles. In his presentation he gave an overview over biomedical applications of magnetic nanostructures, of which some are also a subject of research in his own research group. Magnetic nanoparticles are easy to synthesize and can be manipulated non-invasively by an external magnetic field once they are within the human body. Those applications can be found in diagnosis and treatment, and encompass target drug delivery, cell sorting, MRI image enhancers, biosensors and more.

A research subject of Hari’s lab is magnetic hyperthermia treatment for cancer, which is a promising alternative to normal hyperthermia treatment or radio therapy. The idea is that magnetic particles find tumor cells and exclusively localize there. This can be achieved with an antibody tag for example. Subsequently a fluctuating external EM field is applied with frequencies around 100 kHZ.The electron magnetic moments of the nanoparticles have to realign continuously and thereby dissipate energy as heat. Raising the temperature to 42° C is often enough to kill cancer cells. The faster this heating occurs the better. An important property of such a particle is the heating efficiency that is expressed as the SAR-value (Specific Absorption Rate), as a higher SAR allows for lower radiation energies. The same is true for a higher particle density in the tissue. This is important because not heating the surrounding tissue is a big challenge and is observed in the currently running human phase 1 trials with Fe2O3 particles (Iron(III)-Oxide, the only licensed particle at the moment). A body region consisting of a complex interplay of different tissues, especially bone, has different refractive indices. This can result in local hot spots. For example, brain tumors can be treated with more power than prostate tumors [1]. The current main challenge is to engineer particles with a higher SAR value. The SAR depends on particle size R, magnetization saturation Ms and the anisotropy constant K. The objective is to fine-tune R, Ms and K. For Fe2O3 it can be shown that the peak SAR lies at a diameter of ca 17 nm. Ms depend on the material, while K also depends on the shape. Promising new techniques include for instance core-shell nanoparticles. As an example, Hari presented a particle the has an inner FeCo core and an outer Iron-Oxide shell. Ligands but also drugs can be attached to the outside. The Iron-Cobalt that is used has a 4 times higher Ms than the Fe2O3 particles. A technique from Hari’s own lab are Iron-Oxide hollow nano spheres. However, new experiments with shapes revealed that cubes have a higher SAR than spheres, and octopods have an even higher SAR than that. Then again, Fe-Co nanowires take the SAR to incredible dimensions. All in all, these advances seem very promising to me and I am sure it will cause a lot of improvement in cancer treatments.

For more theoretical insight into magnetic nanoparticles for hyperthermia (easy to understand and many coloured graphs):
1) C. Binns, “Magnetic Nanoparticle Hyperthermia Treatment of Tumours,”Berlin, Springer-Verlag, 197-215(2013)

Wnt/ß-catenin signaling controls cell reprogramming (and nucleosomes form clutches)

Bionanoscience Seminar, 08.05.2015

Speaker: Pia Cosma (Center for Genomic Regulation, Barcelona (Spain))

Author: Edgar Schönfeld

Pia Cosma’s research is focused on cell reprogramming. Her talk was divided into two major subjects that deal with cellular reprogramming: Wnt/ß-Catenin signaling and chromatin organization. Reprogramming can be achieved via nuclear transfer or direct reprogramming, which involves the introduction of the 4 pluripotency factors Oct4, Sox2, cMyc, and Klf4 into a somatic cell. A third option is reprogramming via cell fusion. Cell fusion itself is a natural process, which occurs for instance during the differentiation of muscle cells. However, cells can also be fused artificially in the lab, with the help of chemicals or electricity. If you fuse a stem cell with a somatic cell they give rise to pluripotent hybrid cell, because the pluripotent genome is dominant over the somatic one. (This process also happens in vivo and is involved in wound healing.) After such a fusion the pluripotency factor Oct4 is reactivated. In an experiment Pia tagged Oct4 with GFP to observe spontaneous cell fusions. She found out that reprogramming only occurs when the right amount of ß-Catenin is present, which is activated by the Wnt pathway.

In the last years she discovered a lot more details. She discovered that the ß-Catenin concentration fluctuates in embryonic stem cells (ESCs), which is absolutely important for the reprogramming of somatic cells via fusion with ESCs. Different levels of activity of ß-Catenin can regulate either pluripotency or differentiation. Furthermore she found out that repression of TSF3, a regulator of the Wnt pathway, can increase the reprogramming frequency several hundred times.

With that in mind, she wanted to know what happens to chromatin organization during reprogramming. As a result the textbook model of chromatin packing needs an important update! To be precise, the 3rd panel from the left in figure 1 is inaccurate. Pia discovered (using STORM) that the nucleosomes are not distributed uniformly over the genome. Instead nucleosome aggregate in small or big groups, which Pia calls ‘clutches’ (Fig.2).

biobook_dna_graphik_11
Figure 1: DNA Packaging, taken from http://www.shmoop.com/dna/dna-packaging.html

abstract_illustration_1e
Figure 2: New Model, source: http://www.cell.com/abstract/S0092-8674%2815%2900132-4

These clutches are separated by stretches of nucleosome-free DNA. Thereby the larger clutches form the silenced heterochromatin, because they contain more of the linker histone H1. RNA polymerases can still associate with the small clutches. In stem cells and during reprogramming the DNA is mostly covered with small clutches, which facilitates the docking of transcription factors and RNA polymerase. In somatic cells however, DNA is mostly packed around big silencing clutches. In an reprogramming event the cell has to switch from big dense to small loose clutches, but how is this achieved? Pia’s team hypothesized that this might occur through nucleosome sliding and removal, which is in accordance with their simulations. To summarize their findings the team created this video:

Coordination of daughter strand synthesis

Single replication machines at work:

The coordination of daughter strand synthesis

By Karl Duderstradt (van Oijen lab, University of Groningen)

One of the most important events a cell has to undergo before it will divide is DNA replication. In this event, the amount of genomic DNA is doubled by taking the two strands apart and synthesize complementary strands to them. This process is schematically shown in Figure 1:

Replication machinery

Figure 1: Figure 5-19 in Molecular Biology of the Cell (©Garland Science)

The collection of molecules involved in the replication machinery called the replisome. It is not yet entirely known how the replication machinery is assembled and what coordinates the function of it, but Karl Duderstadt works on these problems. He does this by single-molecule assays, in which single molecules are labeled with a fluorescent dye or protein, and can be followed. The power of single molecule assays is that instead of looking at what a lot of particles do together and identify averages, you can look at individual rates. This is similar to the difference between looking down from a skyscraper down to traffic and standing beside the road looking at individual cars. Every car will do very different things in both cases, but when you look down from the skyscraper you only see the average of many.

Karl uses E. Coli in his research. To be more specific, he looked at the bacteriophage T7 replisome, and was especially interested in how the enzymatic events on leading and lagging strands were coordinated. To better understand his findings, take a look at Figure 2 which shows the replication slightly more detailed. As can be seen there, the replication machinery uses two kinds of loops to synthesize the lagging-strand. These loops are called the priming loop and the trombone or replication loop. About 1% of the lagging strand DNA is synthesized in the replication loop, which are also five times less likely than the priming loops.

Trombone and priming loops

Figure 2: Priming loop and Trombone loop. Found at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2896039/figure/F4/

Kasper Spoelstra – wkspoelstra@hotmail.nl