Parry Guilford, BSc, MSc, PhD
Cancer Genetics Laboratory
University of Otago
Dunedin, New Zealand
Parry Guilford shares an update on current research under way at the University of Otago, Dunedin, NZ
November 15, 2012
Most exciting are the implications of this research – not only for HDGC, but for non-inherited forms of diffuse gastric cancer and lobular breast cancer. Read on!
Our laboratory (the Cancer Genetics Laboratory, Dept Biochemistry) is part of a University Research Centre called the Centre for Translational Cancer Research (ctcr.otago.ac.nz).
The group has three research themes relating to HDGC:
(i) Identifying new genes that cause HDGC
(ii) Developing drugs that will prevent the development of cancer in HDGC families (chemoprevention)
(iii) Developing drugs for the treatment of advanced diffuse gastric and lobular breast cancer
1. New HDGC genes
E-cadherin (CDH1) mutations are found in roughly 40-50% of families with a high incidence of diffuse gastric cancer (DGC). It is likely that many of the remaining families will have germline (inherited) mutations in genes other than CDH1. However, we suspect that, rather than there being just one or two more genes involved, there are likely to be half a dozen or more.
To find these other genes, we are carrying out whole genome ‘exome’ sequencing of DNA from individuals from these families. Exome sequencing involves obtaining the DNA sequence of every known gene in the human genome. We started this research in mid 2012, funded by a startup grant from Illumina Ltd and have so far obtained preliminary data on nine families. We are seeing sequence variations in these families, but have a big job to determine which of these variants can actually cause cancer (the vast majority will be non-functional). Our plan is to sequence as many HDGC families (without CDH1 mutations) as we can and then follow up and validate genes that appear to be mutated in multiple families.
2. HDGC chemoprevention
In HDGC families, one copy of CDH1 (or other yet to be identified genes as described above) is mutated in every cell in the body. However, gastric cancers will only develop after the remaining normal copy of CDH1 is inactivated somewhere in the stomach. We have recent evidence suggesting that this ‘2nd hit’ can be prevented. If so, it may be possible to use drugs to prevent or delay disease development. These drugs could be used in combination with endoscopic surveillance as an alternative to total gastrectomy.
Our existing project involves examining compounds known as ‘epigenetic drugs’ to determine if they can prevent or reverse the ‘2nd hit”.
3. Drug development for HDGC
E-cadherin belongs to a class of proteins called ‘tumour suppressors’ that provide normal cells with protection against cancer development. E-cadherin achieves this by strengthening the linkages between cells, reducing the chance of cells breaking away from their neighbours and consequently eluding the normal proliferation control processes. As we all know, inactivation of the gene that encodes E-cadherin (CDH1) is the cause of HDGC.
Modern cancer drugs are designed to target proteins that are over-abundant in cancer cells compared to normal cells. The drug development process is relatively straightforward-identify a protein that is ‘turned on’ in the cancer cell and leads to tumour development, and then develop a chemical that blocks its activity. However, this process can’t be followed for tumour suppressors because, rather than being turned on in cancer, they are turned off-so there is no protein present to target with drugs.
One option is to try and keep the gene turned on – this is something we are looking at as a cancer prevention method in HDGC, but it isn’t a viable approach for the treatment of established cancers.
Instead, we propose that the loss of E-cadherin creates vulnerabilities elsewhere in the tumour cell that could be targeted with drugs. In this project we will systematically search for proteins, which, if inactivated by drugs, lead to the death of cancer cells lacking E-cadherin, but not cells with normal levels of E-cadherin. We are taking two broad approaches to achieve this goal; firstly, we have just screened 6000 known drugs against cells with and without E-cadherin. Interestingly, we have found that a small number of these known drugs did kill E-cadherin negative cells more efficiently than cells with E-cadherin. We are now in the process of confirming this observation and seeing whether the effect is strong enough for us to proceed with additional pre-clinical studies.
In the second approach, we have used a high throughput robotics facility in Melbourne, Australia, to knockout every gene in the genome (around 18,000 genes) in cells with and without E-cadherin. This large screen has just been completed and turned up around 50-100 candidates for further drug development. We are now in the process of validating these findings and choosing the best candidates to move into our drug development pipeline.
As well as a role in HDGC, we predict that these new drugs will be highly active against many common tumour types (including the non-inherited forms of diffuse gastric cancer and lobular breast cancer) and will produce fewer side effects than standard chemotherapies.