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A Pill Against Cancer — More than just a dream?
***A team of scientists at the Max Planck Institute for Medical Research in Heidelberg have succeeded in deciphering parts of the degenerative process of intestinal cancer. Now their efforts are being directed at methods of intervening in this process so that it can be interrupted.
As a rule cancer ts ,r,gge**d when certain, normally harmless genetic factors (genes) undergo mutation as a result of external causes. Here, for example. a *tngfe element tn the molecular chain of this gene, the DNA. ts replaced by another element. As each gene has at least hundreds, and sometimes even hundreds of thousands of such elements, this seems to be only a slight modification. Nevertheleas.
can have devastating consequences.
The reason for this la that the gene supplies the instructions for synthesizing protein molecules, and as a result this can bring about a defective protein.
Proteins are made up out of actS*0^ 20 <*l^eren* am,r’°
A mutation 1n the gene can result in an exchange of elements occurring also in the attendant proteins; valine could be Incorporated, for example. Instead of glycine. But this can have definite consequences for these proteins because they all have convoluted and Interwoven chains of molecular structures of an extremely complex naturef and ft la the structure of the respective proteins which determines their particular behavior. This Is because this structure ensures that the actual and extremely minute function complex of such chains is characteristically turned outward, thus offering access point to its reaction partner.
Thu*, if this spatial arrange ment 1* altered by the exchange of Just a single amino add, this can have fatal consequences.
It is precisely this kind of form alteration which scientists in Heidelberg have been tracing. They were able to demonstrate this on a protein called p 21 because of its low molecular weight of 21,000 unit*, -phis protein is attributed to a genetic factor, which has long been known as an oncogene : a gene whose mutation can lead to the formation of tumors. Cancer researchers have so far been able to identify about 50 of these oncongencs in human genes. In the process it has been discovered that these are very often involved tn the transmission of growth signals from the cell surface to the .cell nucleus, and tha one of them reacts with an specially energy-rich molecule, called guanosine triphospha c, better known simply a- GTP. This is p 21.
In the case of intestinal cancer It was possible lb show that defective p 21 was formed in 50 per cent of the cases, and in cancer of the pancreas the proportion was up to 90 per cent, p 21 is part of a signal chain which transmits growth instructions into the cell's interior. The trigger Is a messenger substance, which makes contact on the outer wall of the cell and attaches itself to the p 21. In this condition the protein bonds Itself with the energy-rich GTP and is now li the position to conncct Itself with a receptor molecule tn the cell's Interior.
Normally this signal is immediately interrupted again due lo Ilie fact that a part of the GTP molecule is split off. which b "a-ts the bond to the receptor molecule. However, in the case of defective p 21, the receptor molecule remains coupled and now Incessantly transmit', the growth and cell division instructions within the cell. Thus il is transformed Into an uncontrollably multiplying cancer cell : a .umor begins to proliferate.
At the Max Planck Institute in Heidelberg, scientists succeeded in making the distinction between normal and defective p 21 literally visible. It was found that two adjacent loops protrude out of the relatively co npact proteins, which have st ri ng shaped and helical structures. One of the loops is responsible for bonding the receptor molecule, while the other is Involved In the bonding of GTP. It was on the second loop where the false amino acid for defective p 21 was actually found. This tiny alteration of the characteristics of the loop prevents the splitting off and "provides the receptor molecule with a permanent parking place", as one of the scientists expressed it.
This success, which has been hailed as "pioneering", will now be pursued In two directions in Heidelberg. On the one hand, researchers are trying to discover similar disturbance mechanisms for other protein changes, which also lead to tumor developments.
On the other hand, possibilities are being sought to neutralize the fatal effect of amino acid exchange. For It Is thoroughly conceivable that there are substances which could prevent the coupling to the receptor molecule from occurring.
The problem is thai such an effect must be restricted to the defective proteins — normal p 2 1 may not be effected, so as not to interfere with the growth-of healthy cells. At present. computer simulation of the molecular processes Is being used to try to design suitable substances. If this Is successful, ft will still be many years before an appropriate medication arrives on the market.
Be that as It may: "A pill against certain types of cancer is no longer pure utopia". In the opinion of Dr Fred Wlttinghofer, one of the team leaders in Heidelberg. — GRS FEATURE
— Dietrich Zimmermann