New Treatments – PARP Inhibitors

microscope-webWhat new cancer treatments are scientists working on? Scientists are testing a new drug for treating some types of cancer called “PARP inhibitors”.  PARP, doesn’t sound very scientific does it?  PARP stands for Poly-ADP ribose phosphorylase  (you can see a picture of it here). PARP is a protein, we all have it inside our bodies.

Your DNA gets constantly damaged and repaired throughout your life, PARP is one protein that helps to fix damaged DNA.  This is all very good in normal cells, this is what you want. If your DNA is damaged, you want PARP to stick to the broken bit of DNA and sort it out.  What happens if you have a cancer cell though?  Current treatments to cure cancer try and damage the DNA in the cancer cells (without damaging the DNA in the normal cells), of course chemotherapy and radiotherapy damage both normal cells and cancer cells, which is why they have side effects.  Anyway, if you want to kill your cancer cell, you want to damage the DNA so much the cell dies (apoptosis), you don’t want your normal PARP binding to the DNA and trying to fix the damage.

How can we use this information to develop a new cancer treatment? There are some drugs that can stop PARP working (they are called PARP inhibitors).  The idea is that cancer cells have more DNA damage and therefore more PARP than normal cells, so if you block PARP the cancer cells are more likely to die.

Does this work? It seems to work, for SOME types of cancer, especially those types of cancer that already have errors in their DNA repair pathway (like BRCA mutations  in inherited breast, ovarian and prostate cancers). Please be aware that over 90 % of breast and ovarian cancers do NOT have BRCA mutations so this treatment doesn’t work for most of those types of cancer.

How many people have been treated with PARP inhibitors? Not many, only a few hundred worldwide and only as part of clinical trials, you can’t buy any PARP drugs yet because we’re not sure how well they work, or which people would benefit the most from taking them. Having said that, the early research looks good, about 40 % of people taking the drug had their tumours stop growing or shrink. For more information read the Questions and Answers section on Cancer Research UK’s website)

Some of this work is being carried out by Prof. Alan Ashworth, in London. This quote on the Cancer Research UK – Science Update surprised me:

Professor Ashworth is currently testing every chemotherapy drug currently in use in combination with PARP inhibitors on cancer cells grown in the lab.”

Cancer Research UK – Science Update

They are testing every chemotherapy drug in use, with PARP inhibitors, that is a LOT of work,  important work, but difficult.  Hopefully these studies, in cells in a lab, will allow the scientists to understand which combinations of cancer drugs work best. Obviously the results will need to be tested in trials in patients, but the fact that his work is going on is very encouraging.

What does this mean if you have cancer now? These new PARP drugs are at a very early and experimental stage, if you have cancer  now then it won’t affect your treatment plan, but it does give us hope that new and better treatments will be available in the future.

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