International study to use Gribbles testing

Gribbles Molecular Science (GMS), the biotechnology and molecular diagnostic division of Healthscope (ASX:HSP), has been selected to conduct genomic testing in an international collaborative study into depression.

The study aims to determine the utility of pharmacogenomics in clinical depression and is being conducted by the International Collaborative Ethnopshycopharmacology Research Group.

Pharmacogenomics considers the way in which genetics can influence a patient's response to drugs.

"We think pharmacogenomics is going to be a big service in the coming years," said GNS general manager Dr Keith Byron. "Hopefully the data to come out of this trial that will say patients going on anti-depressant treatment should have the pharmacogenomic testing done first."

Over 2000 patients with clinical depression will be recruited for the study from seven countries in the Asia-Pacific region - Australia, Singapore, Malaysia, Korea, Taiwan, and Thailand. It is hoped that 400 of these patients will be from Australia, with Gribbles conducting the testing for participants recruited in Australia, Malaysia and Singapore.

"There's been a number of studies in the medical literature, but a lot of them have been trialled on healthy volunteers, university students or Caucasian populations," said Byron. "Not only will this [study] give information about drug selection and what dose of the drug the patient should be on, but whether there are ethnic differences between these groups."

GMS will be using a number of assays it has been developing over the past 18 months for the cytochrome P450 gene, particularly 2D6 and 2C19, as well as the serotonin transport receptor.

"Cytochrome P450s are liver enzymes, they break the drugs down and help you clear the drug," said Byron.

About 5 to 10 per cent of the population are 'poor-metabolisers', which means a drug will remain in the body longer resulting in more side effects. However, patients with several copies of these genes are called 'ultra-metabolisers' which results in drugs clearing their systems almost immediately.

Byron said that if psychiatrists can determine whether a patient is a poor-metaboliser through pharmacogenomics testing of the cytochrome P450 gene, they would give much lower doses of a drug to that patient, while ultra-metabolisers could be prescribed a different drug.

"Most psychiatrists would say it's trial and error at the moment, so they're looking for anything that will help them in their dosing regimes," said Byron.

Byron said that clinical depression is ideal for a pharmacogenomic study because treatment response is four to six weeks of daily medication with a 60 per cent positive response rate. In addition, side effects to the medication and non-compliance are common problems.

The Australian arm of the study will be based at the professorial unit of The Melbourne Clinic, which is part of the University of Melbourne's Department of Psychiatry. The principal investigator is Dr Chee Ng.

"The professorial unit educates other clinicians throughout Australia on the best practice of dosing for anti-depressant therapy," said Byron. "So to us it's great that these people will be helping sell this concept of pharmacogenomics at the end of the study when we'll start off our test throughout Australia."

While the technology behind GMS' assays is proprietary, Byron said the assays will be conducted on the MegaBase 1000 and Roche Light Cyclers.