New tumour markers: “Spot the differences”

Pancreatic cancer (PC), the subject of this thesis, has the poorest prognosis of all cancers: the survival rate after five years with the disease is less than 5% and on average, patients who have been diagnosed with it do not live longer than six months.

The modus operandi of cells is well known: the genes (DNA) are the masterminds of the system and their role is to give orders. Those orders are transmitted in the form of messages (RNA), which ultimately become molecules that do the work (proteins). Since all cells have similar genes, they are all able to give the same range of orders. However, depending on their role and the signs and information they receive from their surroundings, each cell type sends only specific messages at any one time. While in normal cells this process is carried out following an organized pattern, this pattern of messages changes completely in cancer cells. When pancreatic cells transform into cancer cells, they abandon their usual functions and start sending abnormal messages, which encourage them to quickly divide and invade nearby tissues.

The aim of this PhD was to intercept messages sent by cancerous pancreatic cells and compare them with those sent by healthy pancreatic cells. This comparison would indicate which orders (messages) are the ones that make the cancer grow and invade and which weapons (proteins) it uses to do so. In order to carry out this work we used microarrays or DNA-chips, a technique used for multiple analyses. It allows the detection and quantification of messages sent by thousands of genes. We analysed biopsies of PC as well as samples of healthy pancreas. The RNA (thousands of messages sent by cells) from each sample was extracted and fluorescently labelled. The RNA has the ability to join complementary DNA. The organized DNA fragments contained on a microarray can detect all possible messages sent by the nearly 30,000 genes that exist in the human genome. When RNA is exposed to the microarray, each message binds to its matching DNA, producing fluorescent signal.

The next step was to compare the images obtained from tumour cells with the ones from normal cells. As we do when we solve “Spot the difference” puzzles, we try to find out what makes drawing A different from drawing B; in this case, which messages are being sent by cancerous cells but not by normal cells. However, here we do not have easy drawings with just a few lines as in a puzzle (Figure A). Instead, we compare complex images with hundreds of thousands of different intensity points. In our study we identified a total of 116 messages that were over-expressed in cancerous cells.

These findings reveal some of the orders that allow pancreatic tumours to grow quickly, feed and invade other tissues. Additionally, these messages and the proteins for which they code are potential diagnostic markers and targets to tackle when developing new anti-cancer treatments.

Finally, we generated antibodies that detect the proteins coded by some of the messages. Using a microscope and colour-labelled antibodies, we managed to dye PC cells and to distinguish them from cells of a healthy pancreas or a pancreas with chronic pancreatitis (Fig. B). These results indicate the usefulness of this marker and establish the basis for the development of a differential diagnostic system for PC.