Battling the big C

Laboratory News learns about the award-winning work of the Gene Function Team at the Institute of Cancer Research.

Breakthrough Breast Cancer is a unique charity that combines research, campaigning and education to remove the fear of breast cancer. Their main research goal is to increase understanding of breast cancer which will improve diagnosis, treatment, quality of life and prevention. Breakthrough funds much of the work at the Breakthrough Breast Cancer Research Centre at the Institute of Cancer Research, London. The Breakthrough Centre was the first UK research centre that is dedicated solely to breast cancer research. In total, Breakthrough Breast Cancer has awarded £55 million in research grants and £35 million of this has been used to fund the work at the Breakthrough Research Centre.

In 2009, Thermo Fisher Scientific established a grant program – the RNAi Discovery Grant – to reward life science researchers with more than $400,000 in RNA-Interference (RNAi) reagents from their industry-leading Dharmacon and Open Biosystems RNAi technology portfolios.

The RNAi Discovery Grant program was open to both academic and commercial researchers where five projects were selected based on their potential to advance science and medicine.  The recipients were chosen on the merit of their projects, their screening capabilities and the most important criteria, potential scientific and medical impact.

The winner of the miRNA Library Award was Christopher J. Lord, senior staff scientist, and Alan Ashworth, professor and director of the Breakthrough Breast Cancer Research Centre at the Institute of Cancer Research in London.

Ashworth and Lord lead the Gene Function Team in the Breakthrough Research Centre.  This group focuses on using genetics to understand the nature of breast cancer and then using this information to develop novel approaches to the treatment of the disease.  Over the years the group have focussed on a number of areas and current interests include DNA repair genes, novel drug target identification and also drug resistance. One example of their work was the identification of novel genes that cause resistance to Tamoxifen (a widely used breast cancer drug)-2.

The Gene Function Team was part of the collaborative group that identified the BRCA2 gene in 1997 – when BRCA2 is mutated it may contribute to the development of breast cancer.  As research continued, the team discovered that the BRCA2 gene is involved in DNA repair.  Both the BRCA1 and BRCA2 genes are involved in repair of double-stranded DNA breaks through a  process known as homologous recombination.  If either gene is unable to function, due to mutation for example, the cell is no longer able to repair damaged DNA, therefore increasing the patient’s risk of developing breast and other cancers. Their research on recognised genes as well as novel genes continues to increase the knowledge of breast cancer development.

In 2005, Professor Ashworth, Dr Lord and researchers at the Breakthrough Research Centre demonstrated that tumour cells lacking either the BRCA1 or BRCA2 function are very sensitive to poly (ADP-ribose) polymerase (PARP) inhibitors-3. PARP is a crucial enzyme in the base excision repair pathway that is utilised in the repair of single-strand breaks in DNA.  When either BRCA1 or BRCA2 are dysfunctional and the PARP enzyme is inhibited, chromosomal instability is created along with cell cycle arrest and therefore, apoptosis. 

The team utilised this knowledge to show in pre-clinical work that tumour size is significantly reduced when PARP inhibitors are administered in a drug format.  A new drug, Olaparib (AstraZeneca/KuDOS) inhibits the PARP enzyme in patients with inherited mutation in either BRCA1 or BRCA2. This drug is currently in phase II clinical trials. Initial clinical results suggest that when Olaparib is able to significantly repress tumour growth for prolonged periods of time without causing the damaging side effects of chemotherapy-4. Lord and his colleagues believe that there are patients with other gene mutations that may be able to benefit from PARP inhibitor therapy.

For more information on the Breakthrough Breast Cancer Charity please visit www.breakthrough.org.uk and for the Breakthrough Research Centre please visit www.breakthroughresearch.org.uk.

To predict if drugs like Olaparib would have the same efficacy as in BRCA mutant cells, the Gene Function Team need to identify other target biomarkers in patient sets. Utilizsing high throughput screens and Thermo Scientific Dharmacon siRNA libraries and reagents they have found that additional biomarkers of PARP inhibitor response exist5. One of these biomarkers is the PTEN mutation.  RNA interference work suggested that if a PTEN mutant cell is treated with a PARP inhibitor the same sensitisation of tumour cells occurs as with the BRCA mutation6. PTEN mutations are one of the most common types of genetic mutations that lead to cancer. Colleagues at the Royal Marsden Hospital, London, have already started clinical trials to test PARP inhibitors in patients that have PTEN mutations. As with their BRCA work, this PTEN laboratory work demonstrates how using simple and readily available genetic manipulation in the laboratory can rapidly move drugs from the bench to the bedside.

Current research has led to the idea that miRNAs are involved in determining a patient’s response to cancer therapies, including PARP inhibitors. With the awarding of the Thermo Scientific Dharmacon miRNA genome library, Lord and his colleagues will be able to perform comprehensive genome screens to identify additional clinical miRNA biomarkers of PARP inhibitor response. Lord hopes that when the screening is completed an individually tailored approach to tumour treatment will be available.  An individual patient’s tumour can be analysed for certain group of miRNAs to determine what type of drug, such as PARP inhibitors, should be used to best treat the specific type of cancer.  This tailored approach gives doctors the ability to offer patients gene specific treatment for their cancer.  It will increase patient accessibility to PARP inhibitor therapy, minimisizing the number of patients exposed to chemotherapy. 

siRNA screens have been instrumental to the Breakthrough Research Centre’s approach to investigating breast cancer.  The Gene Function Team have performed a number of siRNA screens to determine how and why current cancer drugs work on a molecular level. With this knowledge, they have a better understanding of cancer and how to develop drugs to best combat it. 

“Both the BRCA1 and BRCA2 genes are involved in repair of double-stranded DNA breaks through a process known as homologous recombination. If either gene is unable to function, due to mutation for example, the cell is no longer able to repair damaged DNA, therefore increasing the patient’s risk of developing breast and other cancers”

“It’s been clear to us for some time now that genetic screens are incredibly useful in helping us understand many of the complex issues in cancer biology and treatment,” says Lord, “miRNA screens are the next step in allowing a better understanding of cancer and cancer therapies.”

The unique set up that the Institute of Cancer Research has with it’s sister organisation, the Royal Marsden Hospital, represents a unique opportunity to move laboratory findings rapidly into the clinic. With the genetic screens Lord and Ashworth have carried out using RNAi technology, this possibility seems even greater.

References 1.     http://breakthrough.org.uk/our_work/our_research/our_unique_strategy/index.html 2.    http://www.breakthroughresearch.org.uk/breakthrough_research_centre/research_teams/gene_function/gene_function_and_regulation_subteam/index.html 3.    Farmer H, McCabe N, Lord CJ, Tutt AN, Johnson DA, Richardson TB, Santarosa M, Dillon KJ, Hickson I, Knights C, Martin NM, Jackson SP, Smith GC, Ashworth A (2005) Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy. Nature 434: 917-921 4.    Fong PC, Boss DS, Yap TA, Tutt A, Wu P, Mergui-Roelvink M, Mortimer P, Swaisland H, Lau A, O’Connor MJ, Ashworth A, Carmichael J, Kaye SB, Schellens JH, de Bono JS (2009) Inhibition of poly(ADP-ribose) polymerase in tumors from BRCA mutation carriers. N Engl J Med 361: 123-134 5.    Turner NC, Lord CJ, Lorns E, Brough R, Swift S, Elliott R, Rayter S, Tutt AN, Ashworth A (2008) A synthetic lethal siRNA screen identifying genes mediating sensitivity to a PARP inhibitor. EMBO J 27:1368-1377 6.    Mendes-Pereira AM, Lord C, Ashworth A (2009) Synthetic lethal targeting of PTEN deficient tumours with PARP inhibitors.  EMBO Molecular Medicine In the press

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