Yew and Chemotherapy drug Taxol



Certain compounds found in the bark of yew trees were discovered by Wall and Wani in 1967 to have efficacy as anti-cancer agents. The precursors of the chemotherapy drug paclitaxel (taxol) was later shown to be synthesized easily from extracts of the leaves of European yew, which is a much more renewable source than the bark of the Pacific yew (Taxus brevifolia) from which they were initially isolated. This ended a point of conflict in the early 1990s; many environmentalists, including Al Gore, had opposed the destructive harvesting of Pacific yew for paclitaxel cancer treatments. Docetaxel can then be obtained by semi-synthetic conversion from the precursors.

Paclitaxel chemotherapy drug from yew

Paclitaxel is in the taxane family of medications. (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, breast cancer, lung cancer, Kaposi sarcoma, cervical cancer and panc cancer. It works by interference with the normal function of microtubules during cell division. It is given by injection into a vein. There is also an albumin bound formulation.

Paclitaxel was first isolated in 1971 from the Pacific Yew and approved for medical use in 1993. It is on the World Health Organisation’s List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about 7.06 to 13.48 USD per 100 mg vial. This amount in the United Kingdom costs the NHS about 66.85 pounds. It is now manufactured by cell culture.

How the Scanning Electron Microscope works

Preparing samples for scanning electron microscope imaging

Blog post by Clodagh Dooley

Scanning electron microscopes (SEM) are amazing tools that allow imaging far beyond the resolution capabilities of light microscopes. SEMs work by creating a focused beam of electrons that scans over a sample; interacting with and exciting its atoms and generating signals that can be used to derive an image of the samples topography.

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Fig. 1.Sage leaf surface hairs. Images by Dr. Clodagh Dooley, AML, CRANN, TCD.

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Fig. 2. The scanning electron microscope used to image the Trinity Tree samples. The tool is based in The Advanced Microscopy Lab, CRANN, TCD. The microscope is a Zeiss Ultra FESEM with Gemini column and Quorum Cryo preparation chamber.

To avoid scattering of the electron beam, the electron source and the sample chamber are under vacuum. This causes no issue when working with a dry sample, such as a metal or ceramic, but can cause big problems when working with a sample with a high water content. Samples with a high water content, such as plant material, use the water as support for its structure, if this water is removed rapidly, as will happen when placed in a vacuum, then the sample will dehydrate and collapse.

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Fig. 3. The vacuum chamber of the SEM showing the loading stage.

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Fig. 4. The vacuum chamber of the SEM showing the loading stage.

The first step in preparing a biological sample for SEM is to preserve it using glutaraldehyde, a chemical fixative that prevents any breakdown and degradation of the structure. The next step is to deal with the water. This is usually done in one of two ways; removing the water in a slow, controlled manner with help of solvents or solidifying the water as ice and imaging a frozen sample.

In the first method the water in the sample is slowly replaced with alcohol by immersing it in deionised water/alcohol solutions with increasing alcohol concentration until it is in a 100% alcohol solution. The alcohol immersed sample is placed in the critical point dryer (CPD) chamber and the alcohol solution is very slowly replaced with liquid CO2. Once the alcohol within the chamber has been completely replaced with liquid CO2 the system is brought to what is termed as the ‘critical point’ for CO2. This is where the pressure and temperature within the CPD chamber causes the liquid CO2 in the sample to turn from a liquid to a gas. The gas can then be vented off without any distortion of the sample due to surface tension.

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Fig. 5. The Quorum Critical Point Dryer

The second method involves the use of liquid Nitrogen. The sample is plunged into liquid Nitrogen slush (-190°C) to flash freeze. It is then transferred, under vacuum, to a cold stage within the SEM imaging chamber where it is held at this temperatures throughout imaging. With this method of preparation, chemical fixation can be avoided as the flash freezing preserves the sample structure and prevents degradation.

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Fig. 6. Cryo preparation chamber on the side of SEM chamber.

The final step before we can image a biological/hydrated sample is to coat it with an electron conductive coating; commonly used coating materials include carbon, gold, palladium and platinum. Conductive coating prevents charging of the specimen, which is caused by accumulation of static electric fields and makes imaging difficult.

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Fig. 7. Cressington 208 Turbo sample coater.

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Fig. 8. Plant material coated in a 10nm layer of Gold Palladium.

Science Notes: Cherry Blossom Buds

SCIENCE NOTES: Autumn Cherry Blossom Bud

How much of a tree is alive, do you think? Actually only about 1%, though all of it was alive at some time or other. Wood is made up of cells, and like all living things cells will grow and multiply, and they will die. All the wood in the middle of a tree is dead. There are only two places on a tree where you find living wood. One is a thin layer just underneath the bark, and the other place is the buds. I’m talking here not about the flower buds, but the buds which are forming the new twigs and leaves. Here’s one from the autumn-flowering Cherry Blossom, seen through Clodagh’s electron microscope.

Autumn Cherry Bud fig1

In this relatively low mag picture you can appreciate the shape of the whole bud. If we zoom in a little you notice that some parts of the delicate outer leaf structures have broken, revealing several layers of living cells.

Autumn Cherry Bud fig2

The cells in a tree multiply by dividing (which sounds like a mathematical contradiction!). A tree has different types of cells to do different jobs, such as bark, roots, leaves etc. All cells start off the same, and like the stem cells in your body they differentiate into specialist types. The cells in this picture are doing the job of protecting the growing bud: quite quickly they will break up and be replaced, in fact the strange wiggly things in the picture are the remnants of earlier protective layers.

Science Notes: Lichen on Trees

We found lichen on many of the trees around the campus. And that’s very good for us, because lichens only grow where the air is clean. In the 1970’s there was almost no lichen to be found on trees in urban environments because of air pollution and acid rain.

Lichens are fascinating organisms. In fact they are not one organism at all. They are made up of a fungus and one or more algae living together in a mutually-beneficial relationship – a kind of mini-ecosystem. The fungus makes up most of what you see: it surrounds and protects the algae. In return the algae feed the fungus (which is unable to feed itself) by photosynthesis.

The beauty of lichens is not easy to see: you need at least a magnifying glass to appreciate them, but an electron microscope is even better. Here are two photos which Clodagh took of lichen on the Oregon Maples:

 Lichen fig1

In the top photo you can see the filament structure of the fungus. The small circular shapes in the bottom photo may be cells of the algae.

Lichens are great survivors. You find them all over the planet in many different environments. And it turns out that they can even survive in space! The European Space Agency arranged to take some lichen up to the International Space Station where they brought them outside, exposing them to the ultra-cold vacuum of open space, where they would be bombarded by cosmic rays and everything. No space suits for them, but they still survived the trip:



Increased Magnification reveals…


The following slideshow highlights the process by which Clodagh choose  an area of interest on the Palm Tree leaf and through increased magnification brought, in this case an individual somata, into sharp focus.

Under each palm leaf there are numerous breathing holes and these are called somata.  They are not unlike the pores on human skin.

Images start at 92 times and end at 1,600 times magnification.

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Another example of this is the seven images Clodagh took of the bark  surface from the Snake Bark Tree.  This time she started at 17 times and ended at 2,720 times magnification.  

Of interest is the pod like structure that Clodagh honed in on.  To date we have been unable to find out what it is but we plan to ask Professor Daniel L. Kelly from the Trinity College Dublin Botany Department to see if he can put a name on this structure/ organism. 

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Medicinal Garden – early artistic inspirations


clear spikes on blue fabric lo res

During recent musings on the hairy structure of the sage plant I was reminded of some early experiments I completed with transparent piped silicone.

oj & clear spiky blob on blue fabric lo res

This led me to doing another few spiky experiments (see images above).

I also decided to add some spiky silicone ‘hairs’ to an unrelated experimental piece that I have been working on.  (See the images below).

There were some interesting results from these tests so this is something that I will definitely look into further in the development of this piece.

The other thought that came to me while thinking of the work to be placed in or near the medicinal garden is that I would like to incorporate a more tactile element into this work. I hope that the piece itself or a sample of it will be accessible to the public to touch.

More artistic musing on the sage plant to follow.

Tomography – the Crab Apple and Snake Bark trees


When we were taking samples in February Clodagh attempted to image the small apple fruit from the Crab Apple Tree. She was unable to do so as it contained too much liquid. It dried out and shriveled up over the month and in March she attempted to image it again. The resultant images I think are well worth the wait.  What do you think?

When I looked at these images and those of the macro photos I took of a Snake bark lenticle (see below) they immediately reminded me of topographical images and models. Also see below for some examples.


Macro image of Snake Bark lenticle, photo Olivia Hassett

These images then inspired a further trawl through the internet to see what other works have been inspired by tomography. This really got me to thinking about the possibilites of working with stacked layers/ layers  of colour or layers of any kind…..more to follow as I progress this idea further.  

layered card? reflection in knife

Topography definition:

The arrangement of the natural and artificial physical features of an area.

The distribution of parts or features on the surface of or within an organ or organism.