Targeted molecular therapy
An understanding of how diseases develop down to the molecular level will enable drugs to be tailor-made with the result that therapies will become more effective. TU Delft is developing fast microscopic and spectroscopic technologies to study individual molecules and how they interact. We are using modern bioinformatics to develop algorithms that will give us an understanding of the contribution that molecules, cells and organs make to physical function – and sometimes dysfunction.
Special target-seeking molecules are being developed that will enable
radioactive substances to be targeted at tumours precisely, thus reducing or even completely avoiding damage to the surrounding tissue.
Modern image processing technologies not only provide detailed pictures of organs and how they are functioning; by quantifying anatomical structures and function, they can also reveal aberrations.
The main areas of research conducted by Bert Wolterbeek’s Radiation and Isotopes for Health team at TU Delft involve innovative approaches for the optimization of radiation and isotopes for medical imaging and therapy. These include, for example, new ways of producing radionuclides for diagnostics and the use of radionuclides in studies into their behaviour, distribution and effects. “We have a full programme, mostly aimed at where radioactivity is used in medicine,” explains Dr Wolterbeek, “such as in radiodiagnostics and radiotherapy.”
In these areas, the team collaborates with their clinical colleagues to produce the radioactivity, select the specific radionuclide and create the product with the correct dynamic stability to be administered to the patient according to the properties the clinicians require and the molecules they are targeting. An innovative way of measuring radioactivity in patients being treated for pancreatic cancer is currently being developed in collaboration with the Erasmus Medical Center. It promises both to reduce hospital employees’ exposure to radioactivity and the time patients need to spend in hospital.
We have a full programme, mostly aimed at where radioactivity is used in medicine― Prof. dr. Bert Wolterbeek
Most of the highly specific radionuclides needed for radiodiagnostics and radiotherapy are produced by only a handful of reactors. When these are down for maintenance or other reasons, hospitals can no longer obtain the supply they require. Dr. Wolterbeek’s team are developing radionuclide generators, which provide alternative production routes, removing the hospitals’ dependence on irregular production.
A ‘mother’ radionuclide is produced and sent to the hospital. The mother radionuclide decays into a daughter radionuclide, which the hospital uses for radiodiagnostics and radiotherapy. For example, the radioactive mother, molybdenum-99, is used by the hospital to generate the commonly used technetium-99. The research is producing a more elegant production process for molybdenum-99 that will allow more organizations to supply it.
“The key challenges for the role radiochemistry has in healthcare involve helping to make diagnostics more sensitive, targeted and faster and helping to make treatment as individualized and dedicated as possible. We need to continuously improve our development of very pure, highly radioactive radionuclides, without delivering a lot of chemical mass, and coupled in a very stable way to the molecules of interest for specific uses in medicine. Now we are focusing on the production of molybdenum99 to increase the number of producers.
Eventually we need to enable a shift from direct production and delivery to generators, to make hospitals less dependent on continuous production from reactors. These generators need to be robust, and produce radionuclides that meet hospitals’ clinical objectives. I’m sure within 3 to 5 years we will have the first 2 or 3 of these production routes changed into a generator production.”
Nynke Dekker and her team at TU Delft’s Kavli Institute of Nanoscience look at DNA and RNA protein interactions at the molecular level. “In the area of DNA protein interactions, we’re mostly interested in the factors concerned when proteins stop functioning. The discovery of the phenomenon of RNA interference has also meant we’ve become aware of a whole new range of RNA functions and RNA protein interactions, which is another line of our research. If you add doubled-stranded RNA to an organism, it interferes with the expressions of the genes. We look at enzymes that copy RNA, and that are also involved in the spread of the RNA interference phenomenon.”
“We also have a number of projects that look at the single molecule level, and in Bionanoscience, we look at biological material, but interface that with nanotechnology. We are studying both the replication activity (making double-stranded RNA from singlestranded RNA) and the transcription activity (making a single-stranded copy of a double-stranded RNA template) of RNA-dependent RNA polymerase using magnetic tweezers.”
In the area of DNA protein interactions, we’re mostly interested in the factors concerned when proteins stop functioning.― Prof. Dr. Nynke Dekker
Most of Nynke Dekker’s team’s work until now has involved examining molecules that have been isolated from the cell. She explains that another line of her research that is likely to present some of the most interesting and fruitful challenges for the coming few years involves widening the focus to the cellular level. “The question we now need to answer is what these molecules are doing inside the cell,” she says. “It’s also possible to follow single molecules inside the cell, to try to figure out what they’re doing there. Now that single molecule techniques have proven their utility and power, it makes sense to investigate a number of biological systems in vitro. In the case of bacteria and the lower organisms, there might only be two DNA copying machineries, so ultimately this should give us insight into pathways that could be targeted in antibiotics or therapy.”
A key research area for Dekker and her team, early findings from which have been twice published during the last five years in Nature, involves the torque dependence of DNA and DNA-protein interactions. Topoisomerases relieve the torsional strain in DNA that is built up during replication and transcription. They are vital for cell proliferation, and so are targeted by chemotherapeutic drugs such as Topotecan. Dekker and her collaborators were able to detect the binding and unbinding of an individual Topotecan molecule in real time and to quantify the druginduced trapping of topoisomerase on DNA. Dekker and her group are currently continuing to examine how Topotecan works at the molecular level. It is hoped that this will help explain why it works on certain types of cancers and not others.
Kristina Djanashvili is a researcher at the Biocatalysis and Organic Chemistry section of the department of Biotechnology. She aims to develop novel contrast agents for molecular imaging technologies. These technologies include Magnetic Resonance Imaging (MRI), Positron Emitting Tomography (PET), and Single Photon Emission Computed Tomography (SPECT).
Contrast agents are usually based on lanthanides, a group of metals with interesting magnetic properties. Gadolinium, for example, makes for a strong and clear MRI signal, but it is not without problems. “Gadolinium is highly toxic,” indicates Djanashvili. “It needs to be coated before it can be injected safely. Also, you want to get a maximum amount of contrast agent to the site of interest, so you need to add a targeting vector. During the synthetic process, the challenge is to create molecules that are stable enough for medical use, yet retain the right physical properties.”
Gadolinium makes for a strong and clear MRI signal, but it is not without problems. Gadolinium is highly toxic.― Dr. Kristina Djanashvili
Djanashvili has developed a new imaging agent that can pinpoint and visualise tumours more accurately. Besides contrast enhancing unit, it contains a targeting vector that seeks out sialic acid, the sugary substance on the surface of tumour cells. The challenge is to prevent this agent from binding to sialic acid on other cell surfaces before it reaches the tumour.
“By encapsulating the agent in thermosensitive liposomes, you can shield off the contrast agent. The liposomes will only release their active compound when they are heated to 42° Celsius. That makes the process easy to control: you locally heat the body part you want to investigate.”
Another lanthanide, holmium, offers a unique opportunity of combining imaging with radiation therapy. Holmium ‘lights up’ very well on MRI images. If holmium particles are made radioactive with a neutron beam, they can be used for imaging and treatment at the same time.
“Tumours create large networks of blood vessels,” explains Djanashvili. “The size of the radioactive holmium particles is chosen with a view to the diameter of these blood vessels. Particles equipped with special targeting groups get stuck at exactly the right place: only in cancerous tissue. There they release their radiation to destroy the cancer cells.” This form of internal radiation may be promising for the treatment of liver cancer, which is hard to combat with conventional methods. Although it will take a few years before holmium therapy becomes a reality, clinical trials are underway. This study is conducted in collaboration with Erasmus Medical Centre and Utrecht Medical Centre.