Canadian Researchers Link DICER1 Gene Mutation to Non-Epithelial Ovarian Cancers & Other Rare Tumor Types

Canadian researchers affiliated with the Ovarian Cancer Research Program of British Columbia report that recurrent, lifetime-acquired mutations affecting the DICER1 gene occur in a range of nonepithelial ovarian tumors as well as other rare cancer tumor types, and appear common in Sertoli-Leydig ovarian tumors. The study findings were published online today in the New England Journal of Medicine.

Dr. Gregg Morin, Head of Proteomics, Michael Smith Genome Sciences Centre, BC Cancer Agency; DICER 1 Mutation Ovarian Cancer Study Co-Leader

Dr. David Huntsman, Genetic Pathologist & Director of the Ovarian Cancer Research Program of British Columbia at the BC Cancer Agency & Vancouver Coastal Health Research Institute; DICER 1 Mutation Ovarian Cancer Study Co-Leader

Scientists at the British Columbia (BC) Cancer Agency, Vancouver Coastal Health Research Institute, and the University of British Columbia (UBC) are excited over a discovery made while studying rare tumor types.

Dr. David Huntsman, genetic pathologist and director of the Ovarian Cancer Program of BC (OvCaRe) at the BC Cancer Agency and Vancouver Coastal Health Research Institute, and Dr. Gregg Morin, a lead scientist from the Michael Smith Genome Sciences Centre at the BC Cancer Agency, led a research team who discovered that mutations in rare, seemingly unrelated cancers were all linked to the same gene, known as “DICER1.” The study findings were published online today in the New England Journal of Medicine. [1]

Background: RNA Interference, MicroRNAs, and DICER.

Nucleic acids are molecules that carry genetic information and include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). The DNA segments that carry genetic information are called “genes.” Together these molecules form the building blocks of life. DNA contains the genetic code or “blueprint” used in the development and functioning of all living organisms, while “messenger RNAs” or mRNAs help to translate that genetic code into proteins by acting as a messenger between the DNA instructions located in the cell nucleus and the protein synthesis which takes place in the cell cytoplasm (i.e., outside the cell nucleus, but inside the outer cell membrane). Accordingly, DNA is first “transcribed” or copied into mRNA, which, in turn, gets “translated” or synthesized into protein.

RNA interference” (RNAi) is a mechanism through which gene expression is inhibited at the translation stage, thereby disrupting the protein production within a cell. RNAi is considered one of the most important discoveries in the field of molecular biology. Andrew Fire, Ph.D., and Craig C. Mello, Ph.D. shared the 2006 Nobel Prize in Physiology or Medicine for work that led to the discovery of the RNAi mechanism. While the mechanism itself is termed “RNA interference,” there are two major types of RNA molecules that play a key role in effectuating that interference. The first type of RNA molecules consists of “microRNAs” or miRNAs, while the second type consists of “small interfering RNAs” or siRNAs.

Current thinking suggests that RNAi evolved as a cellular defense mechanism against invaders such as RNA viruses. When they replicate, RNA viruses temporarily exist in a double-stranded form. This double-stranded intermediate would trigger RNAi and inactivate the virus’ genes, thereby preventing viral infection. RNAi may also have evolved to combat the spread of genetic elements called “transposons” within a cell’s DNA. Transposons can wreak havoc by jumping from spot to spot on a genome, sometimes causing mutations that can lead to cancer or other diseases. Like RNA viruses, transposons can take on a double-stranded RNA form that would trigger RNAi to clamp down on the potentially harmful “jumping gene” activity. Also, as noted above, RNAi is important for regulating gene expression. For example, the turning down of specific genes is critical to proper embryonic development.

Of relevance to the Canadian study findings within the context of RNAi are miRNAs. MiRNAs can bind to mRNAs and either increase or decrease their activity, for example, by preventing a mRNA from producing a protein. [2] In this context, “gene silencing” can occur through mRNA degradation or prevention of mRNA translation.  MiRNAs play an integral role in numerous biological processes, including the immune response, cell-cycle control, metabolism, viral replication, stem cell differentiation and human development. MiRNA expression or function is significantly altered in many disease states, including cancer.

Because of its involvement in miRNA processing, the DICER1 gene plays an important role in maintaining health. It carries out a “factory style” function which involves chopping up miRNAs to activate them. [Ref. 2] These miRNAs, in turn, control hundreds of other genes as noted above. Based upon a study led by investigators from the University of Texas M.D. Anderson Cancer Center, the expression levels of DICER have global effects on the biogenesis of miRNA, and reduced gene expression correlates with a poor outcome in ovarian cancer. [3] In the M.D. Anderson study, two somatic (i.e., lifetime-acquired) missense DICER mutations were discovered in two epithelial ovarian cancer tumors. The M.D. Anderson investigators concluded that the DICER mutations were not associated with the alterations in DICER expression found in mRNAs. It is important to note that the type of somatic missense DICER mutations discovered in the M.D. Anderson study were not the same as those discovered in the Canadian study as discussed below.

Recurrent DICER Mutations Are Predominant In A Rare Form of Non-Epithelial Ovarian Cancer.

At the outset of the Canadian study, the OvCaRe team sequenced ovarian, uterine, and testicular tumors, expecting to find that their genomes would be distinct with specific, differing abnormalities. Much to their amazement, the researchers discovered that the same fundamental mutation in the DICER1 gene represented a common process underlying the different cancers which they examined.

Specifically, the Canadian investigators sequenced the whole transcriptomes or exomes of 14 nonepithelial ovarian tumors, which included two Sertoli–Leydig cell tumors, four juvenile (not adult) granulosa-cell tumors, and eight primitive germ-cell tumors of the yolk-sac type. The researchers identified closely clustered mutations in the region of DICER1 which encode the RNase IIIb domain in four samples. Based on these findings, the OvCaRe team sequenced the same region of DICER1 in additional ovarian tumors, and tested for the effect of the mutations on the enzymatic activity of DICER1.

Recurrent somatic (i.e., lifetime-acquired) DICER1 mutations in the RNase IIIb domain were identified in 30 of 102 nonepithelial ovarian tumors (29%), including 4 tumors which also possessed germline (i.e., inherited) DICER1 mutations. The highest frequency of somatic DICER1 mutations occurred in Sertoli–Leydig cell tumors (26 of 43, or 60%). Notably, the mutant DICER1 proteins identified in the samples possessed reduced RNase IIIb activity, but retained RNase IIIa activity.

The Canadian researchers also performed additional tumor testing and detected the DICER1 mutations in 1 of 14 nonseminomatous testicular germ-cell tumors, 2 of 5 embryonal rhabdomyosarcomas, and in 1 of 266 epithelial ovarian and endometrial carcinomas.

The groundbreaking nature of this discovery is reflected in the fact that the DICER1 “hotspot” mutations are not present in the 1000 Genomes Project data or the public data repository of The Cancer Genome Atlas consortium. To date, no recurrent DICER1 mutations have been reported in the mutation database of the Catalogue of Somatic Mutations in Cancer (COSMIC), in which 4 of 938 reported cancers possess somatic mutations but none in the RNase IIIb domain hot spots or RNase IIIa equivalents. Moreover, the Canadian researchers note that the newly-discovered DICER1 mutations were not observed in any of the more than 1000 cancer sequencing libraries which were studied.

Based upon the foregoing , the researchers concluded that somatic missense mutations affecting the RNase IIIb domain of DICER1 occur in a range of nonepithelial ovarian tumors, and possibly other cancers. Furthermore, the DICER1 mutations appear to be common in Sertoli-Leydig ovarian tumors (which are a subtype of nonepithelial, sex cord-stromal ovarian tumors). The researchers believe that the recurrent DICER1 mutations identified implicate a novel defect in miRNA processing which does not entirely destroy DICER1 functionality, but alters it.

Accordingly, the Canadian researchers suggest that the newly-discovered DICER1 mutations may represent an oncogenic event within the specific context of nonepithelial ovarian tumors, rather than a permissive event in tumor onset (as may be expected for loss of function in a tumor suppressor gene). The researchers note that DICER1 expression in tumors possessing the hotspot DICER1 somatic mutations argues against a role for DICER1 as a classic tumor suppressor gene. They further explain that the localized and focal pattern of the identified DICER1 mutations is typical of dominantly acting oncogenes, like KRAS and BRAF.

In sum, the Canadian researchers believe that the recurrent and focal nature of the DICER1 mutations and their restriction to nonepithelial ovarian tumors suggest a common oncogenic mechanism associated with a specifically altered DICER1 function that is selected during tumor development in specific cell types.

The Canadian study was supported through funding by Canadian Institutes for Health Research, Terry Fox Foundation, BC Cancer Foundation, VGH & UBC Hospital Foundation, Michael Smith Foundation for Health Research, and Genome BC.

Expert Commentary

DICER is of great interest to cancer researchers” said Dr. Huntsman, who also holds the Dr. Chew Wei Memorial Professorship in the departments of Obstetrics and Gynecology and Pathology and Laboratory Medicine at UBC. “There have been nearly 1,300 published studies about it in the last 10 years, but until now, it has not been known how the gene functions in relation to cancer.”

“This discovery shows researchers that these mutations change the function of DICER so that it participates directly in the initiation of cancer, but not in a typical ‘on-off’ fashion,” says Dr. Morin who is also assistant professor in the department of Medical Genetics at UBC. “DICER can be viewed as the conductor for an orchestra of functions critical for the development and behavior of normal cells. The mutations we discovered do not totally destroy the function of DICER rather they warp it—the orchestra is still there but the conductor is drunk.”

This finding is the third of a series of papers published recently in the New England Journal of Medicine (NEJM) in which the OvCaRe team used new genomic technologies to unlock the molecular basis of poorly understood types of ovarian cancer. The first finding, published in the NEJM in 2009, identified mutations in the FOXL2 (forkhead box L2) gene as the molecular basis of adult granulosa cell ovarian cancer tumors. The second finding, published in the NEJM in 2010, determined that approximately one-half of clear-cell ovarian cancers and one-third of endometrioid ovarian cancers possess ARID1A  (AT rich interactive domain 1A) gene mutations.

The DICER gene mutation breakthrough discovery is particularly pivotal because it could lead to solutions for treatment of more common cancers.

“Studying rare tumors not only is important for the patients and families who suffer from them but also provides unique opportunities to make discoveries critical to more common cancers – both in terms of personalized medicine, but also in applying what we learn from how we manage rare diseases to more common and prevalent cancers,” said Dr. Huntsman “The discovery of the DICER mutation in this varied group of rare tumors is the equivalent of finding not the needle in the haystack, but rather the same needle in many haystacks.”

Dr. Phillip A. Sharp, Professor, Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology; Co-winner of the 1993 Nobel Prize in Physiology and Medicine

“This breakthrough will be of interest to both the clinical and the fundamental science communities,” says Dr. Phillip A. Sharp, Professor, Koch Institute for Integrative Cancer Research at the Massachusetts Institute of Technology, and co-winner of the 1993 Nobel Prize in Physiology or Medicine for the discovery that genes are not contiguous strings but contain introns, and that the splicing of mRNA to delete those introns can occur in different ways, thereby yielding different proteins from the same DNA sequence. “Huntsman, Morin and colleagues’ very exciting discovery of specific mutations in DICER, a factor essential for syntheses of small regulatory RNAs in ovarian and other human tumors, could lead to new approaches to treatment.”

The Canadian OvCaRe research team is now working to determine the frequency and role of DICER mutations in other types of cancers. The research team is also expanding its collaboration to discover whether mutant DICER and the pathways it controls can be modulated to treat the rare cancers in which the mutations were discovered and more common cancers.

The Michael Smith Genome Sciences Centre (Michael Smith GSC), located at the BC Cancer agency, played a key role in this discovery. By way of background, Dr. Michael Smith was a co-winner of the 1993 Nobel Prize in Chemistry for his development of oligonucleotide-based site-directed mutagenesis, a technique which allows the DNA sequence of any gene to be altered in a designated manner. His technique created a groundbreaking method for studying complex protein functions, the basis underlying a protein’s three-dimensional structure, and a protein’s interaction with other molecules inside the cell.

A decision was made more than 10 years ago, championed by Drs. Michael Smith, Victor Ling, and others to create and locate the Michael Smith GSC within the BC Cancer Agency and in close proximity to Vancouver General Hospital (VGH). The chosen location for this critical facility provided the multidisciplinary cancer research teams in Vancouver with access to state-of-the-art technologies.

“We are one of less than five places in the world doing this type of work successfully. This discovery is one of a series of recent landmark findings from Vancouver that are reshaping our understanding of many cancers,” says Dr. Huntsman. “Since my arrival in Vancouver 20 years ago I have never before sensed such a strong feeling of communal pride and excitement within our research community. Our next task is to bring the discoveries into the clinic.”

About the Ovarian Cancer Research Program of British Columbia (OvCaRe)

OvCaRe is a multidisciplinary research program involving clinicians and research scientists in gynecology, pathology, and medical oncology at VGH and BC Cancer Agency. OvCaRe is a unique collaboration between the BC Cancer Agency, Vancouver Coastal Health Research Institute, and UBC. The OvCaRe team is considered a leader in ovarian cancer research which is breaking new ground in better identifying, understanding, and treating this disease. The OvCaRe seminal paper in PLoS (Public Library of Science), which addresses ovarian cancer as a group of distinct diseases, has been embraced by the global research community who has adopted the BC approach to ovarian cancer research. To learn more, visit www.ovcare.ca.

About the Michael Smith Genome Sciences Centre

Canada’s Michael Smith Genome Sciences Centre is an internationally recognized state-of-the-art facility applying genomics and bioinformatics tools and technologies to cancer research. Led by Dr. Marco Marra, the Michael Smith GSC is one of ten leading genomic research centres in the world and the only one of its kind in the world integrated into a cancer facility. With a primary focus on cancer genomics research, its scientists have been involved in many world-class groundbreaking discoveries over the past decade. To learn more, visit www.bcgsc.ca.

About the Vancouver Coastal Health Research Institute

Vancouver Coastal Health Research Institute is the research body of Vancouver Coastal Health Authority, which includes BC’s largest academic and teaching health sciences centres: Vancouver General Hospital, UBC Hospital, and GF Strong Rehabilitation Centre. The institute is academically affiliated with the UBC Faculty of Medicine, and is one of Canada’s top-funded research centres, with $82.4 million in research funding for 2009/2010. To learn more, visit www.vchri.ca.

About the British Columbia Cancer Agency

The BC Cancer Agency, an agency of the Provincial Health Services Authority, is committed to reducing the incidence of cancer, reducing the mortality from cancer, and improving the quality of life of those living with cancer. It provides a comprehensive cancer control program for the people of British Columbia by working with community partners to deliver a range of oncology services, including prevention, early detection, diagnosis and treatment, research, education, supportive care, rehabilitation and palliative care. To learn more, visit www.bccancer.ca.

About the University of British Columbia

The University of British Columbia is one of North America’s largest public research and teaching institutions, and one of only two Canadian institutions consistently ranked among the world’s 40 best universities. Surrounded by the beauty of the Canadian West, it is a place that inspires bold, new ways of thinking that have helped make it a national leader in areas as diverse as community service learning, sustainability, and research commercialization. UBC offers more than 55,000 students a range of innovative programs and attracts $550 million per year in research funding from government, non-profit organizations, and industry through 7,000 grants. To learn more, visit www.ubc.ca.

References

1/Morin G, Hunstman, DG et al.  Recurrent Somatic DICER1 Mutations in Nonepithelial Ovarian CancersNEJM, published online December 21, 2011 (10.1056/NEJMoa1102903).

2/The Canadian investigators describe the operation of the RNAi pathway with respect to miRNA biogenesis as follows:

“MicroRNAs (miRNAs) are a functional class of noncoding RNA molecules that regulate translation and degradation of messenger RNA. MiRNA transcripts are processed from hairpin pre-miRNA precursors into short miRNA:  miRNA* duplexes consisting of the miRNA targeting strand and the imperfectly complementary miRNA* strand (star strand, or inert carrier strand) by Dicer, an endoribonuclease with two RNase III–like domains. The RNase IIIb domain cuts the miRNA strand, whereas the RNase IIIa domain cleaves the miRNA* strand. The resultant RNA duplex is loaded into the RNA-induced silencing complex (RISC) containing an Argonaute protein. The miRNA* strand is then removed, leaving the miRNA strand, which targets messenger RNAs (mRNAs) for degradation or interacts with the translation initiation complex to inhibit and destabilize translation of the targeted messenger RNAs.” [footnote citations omitted]

3/Merritt WM, et al. Dicer, Drosha, and outcomes in patients with ovarian cancer. N Engl J Med. 2008 Dec 18;359(25):2641-50. Erratum in: N Engl J Med. 2010 Nov 4;363(19):1877. PubMed PMID: 19092150; PubMed Central PMCID: PMC2710981.

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Clinical Conundrums: Choosing the Best Management Approaches in Patients With Ovarian Cancer

On June 16, 2010, Clinical Care Options Oncology released a Microsoft Powerpoint Presentation entitled, “Clinical Conundrums:  Choosing the Best Management Approaches in Patients With Ovarian Cancer.” The presentation provides the most recent data on managing patients with ovarian cancer in the frontline and recurrent setting and in specific clinical scenarios.

Thomas J. Herzog, M.D., Director, Division of Gynecologic Oncology, Columbia University College of Physicians and Surgeons, New York, NY

On June 16, 2010, Clinical Care Options Oncology released a Microsoft Powerpoint Presentation entitled, Clinical Conundrums:  Choosing the Best Management Approaches in Patients With Ovarian Cancer. The presentation provides the most recent data on managing patients with ovarian cancer in the frontline and recurrent setting and in specific clinical scenarios.

The presentation was created by Thomas J. Herzog, MD, Director, Division of Gynecologic Oncology Columbia University College of Physicians and Surgeons. The topics covered in the presentation include the following:

–Controversies in the Treatment of Newly Diagnosed Ovarian Cancer

–What About Alternative Taxane Therapy?

–Will Adding a Third Drug Help?

–What About Intraperitoneal (IP) Therapy?

–Will Adding a Targeted Therapy Help?

–Prognostic Factors in Ovarian Cancer.

–Does Having a BRCA Mutation Affect Ovarian Cancer Prognosis?

–Ongoing and Recently Completed Clinical Trials in Ovarian Cancer.

–Relevance of CA-125 Levels: Placing Novel Data Into Clinical Context.

–Best Management Approaches for Patients With Platinum-Sensitive Recurrent Disease.

–Who Are the Best Candidates?

–Management of Patients in Challenging Clinical Situations: Platinum Resistance and Other Clinical Scenarios.

  • PARPi Trials: Ongoing/Planned
  • Investigational Agents
  • NKTR-102: Peg-Irinotecan
  • EC145: Novel Folate Receptor Targeted Therapeutic
  • Developmental Strategies

Source: Clinical Conundrums: Choosing the Best Management Approaches in Patients With Ovarian Cancer, by Thomas J. Herzog, MD, Director, Division of Gynecologic Oncology Columbia University College of Physicians and Surgeons, Treatment Updates, Ovarian 2010, Clinical Options Oncology, June 16, 2010.

Unusual Metals May Forge New Ovarian & Colon Cancer Drugs

Drugs made using unusual metals could form an effective treatment against colon and ovarian cancer, including cancerous cells that have developed immunity to other drugs, according to research at the University of Warwick and the University of Leeds.

Drugs made using unusual metals could form an effective treatment against colon and ovarian cancer, including cancerous cells that have developed immunity to other drugs, according to research at the University of Warwick and the University of Leeds.

Dr. Peter Sadler

Professor Peter Sadler of the University of Warwick. (Photo: University of Warwick)

The study, published in the Journal of Medicinal Chemistry, showed that a range of compounds containing the two transition metals Ruthenium and Osmium, which are found in the same part of the periodic table as precious metals like platinum and gold, cause significant cell death in ovarian and colon cancer cells.

The compounds were also effective against ovarian cancer cells which are resistant to the drug Cisplatin, the most successful transition metal drug, which contains the metal platinum.

Dr Patrick McGowan, one of the lead authors of the research from the School of Chemistry at the University of Leeds, explains: “Ruthenium and Osmium compounds are showing very high levels of activity against ovarian cancer, which is a significant step forward in the field of medicinal chemistry.

Sabine H. van Rijt, lead researcher in the laboratory of Professor Peter Sadler in the Department of Chemistry at the University of Warwick, said:  “Most interestingly, cancerous cells that have shown resistance to the most successful transition metal drug, Cisplatin, show a high death rate with these new compounds.”

Professor Sadler, at the University of Warwick, commented that he is “excited by the novel design features in these compounds which might enable activity to be switched on and off”.

Cisplatin was discovered in the 1970s and is one of the most effective cancer drugs on the market, with a 95% cure rate against testicular cancer.  Since the success of Cisplatin, chemists all over the world have been trying to discover whether other transition metal compounds can be used to treat cancer.

In this type of anti-cancer drug transition metal atoms bind to DNA molecules which trigger apoptosis, or programmed cell death, in the cancerous cells.

The study is a collaboration between the universities of Warwick and Leeds and was funded by the Engineering and Physical Sciences Research Council (EPSRC).

Sources:

Ovarian Cancers Detected Early May Be Less Aggressive

“The biology of ovarian cancers discovered at an early stage may render them slower growing and less likely to spread than more aggressive cancers, which typically are discovered in an advanced stage, according to a study led by investigators in the Duke Comprehensive Cancer Center.  This finding has implications for the question of whether screening for ovarian cancer could save lives. …”

“The biology of ovarian cancers discovered at an early stage may render them slower growing and less likely to spread than more aggressive cancers, which typically are discovered in an advanced stage, according to a study led by investigators in the Duke Comprehensive Cancer Center.  This finding has implications for the question of whether screening for ovarian cancer could save lives.

berchuck-andrew

Dr. Andrew Berchuck is Director of the Duke Division of Gynecologic Oncology, Duke Comprehensive Cancer Center, Durham, North Carolina

‘Our study showed that the ovarian cancers currently detected at an early stage have gene expression profiles that correlate with favorable outcome, rather than being representative of the entire spectrum of disease aggressiveness,’ said Andrew Berchuck, MD, a gynecologic oncologist at Duke and lead investigator on this study.  ‘This highlights the potential challenges of developing a screening test for this disease, because earlier detection of aggressive cases is essential if screening is to reduce ovarian cancer deaths.’

The results of this study and the implications for screening as an approach to decreasing mortality parallel the challenges seen in lung cancer and prostate cancer.  In those cancers, while screening approaches based on radiological imaging and/or blood markers detect cancers, it remains unclear whether cancer-related deaths are prevented because screening preferentially detects more benign cancers that are much less likely to be fatal, Berchuck said.

‘While these results could be seen as discouraging, it must be remembered that this information is an important piece of the ovarian cancer puzzle, and data like these that increase our understanding of the disease hopefully will eventually lead to breakthroughs in prevention, early detection and treatment of this deadly disease,’ Berchuck said.  Although there is currently no approved ovarian cancer screening test for the general population, the CA125 blood test and transvaginal ultrasound imaging currently are being evaluated in clinical trials.

The researchers looked at gene expression patterns in 166 ovarian cancer tissue samples taken from patients who were treated at Duke, H. Lee Moffitt Cancer Center, and Memorial Sloan-Kettering Cancer Center and from the Gynecologic Oncology Group Tumor Bank.  For this study, researchers examined samples of advanced ovarian cancers from patients who had experienced long-term survival — over seven years — and patients who had done extremely poorly, and died within three years of diagnosis.  The researchers used microarrays — a method for examining thousands of snippets of DNA — with about 22,000 probe sets to examine patterns of gene expression among the samples, and identified genes that were most predictive of survival.

‘We found that certain patterns predicted long-term survival and others predicted a poorer prognosis in advanced stage cases,’ Berchuck said. ‘Cancers that were detected at an early stage almost always shared gene expression characteristics with advanced stage cases that were long-term survivors, suggesting a shared favorable biology.’

The researchers published their results in the March 24, 2009, issue of the journal Clinical Cancer Research. The study was funded by the Gail Parkins Ovarian Cancer Research Fund and the National Institutes of Health.

Other researchers involved in this study include Edwin Iversen, Jingqin Luo, Jennifer Clarke, Hisani Horne, Angeles Secord, Jason Barnett, Susan Murphy, Holly Dressman, Jeffrey Marks of Duke; Douglas Levine and Jeff Boyd of Memorial Sloan-Kettering Cancer Center in New York City, NY; Miguel Alonso of the Universidad Autonoma de Madrid; and Johnathan Lancaster of H. Lee Moffitt Cancer Center and Research Institute.”

Primary SourceSpotlight:  Ovarian Cancers Detected Early May Be Less Aggressive, News Article, Duke Comprehensive Cancer Center, March 23, 2009.

M.D. Anderson Identifies TG2 As a Potential Target in Chemo-Resistant Ovarian Cancer

“Scientists from The University of Texas M. D. Anderson Cancer Center have found overexpression of tissue type transglutaminase (TG2) in ovarian cancer is associated with increased tumor cell growth and adhesion, resistance to chemotherapy and lower overall survival rates. When researchers targeted and silenced TG2 in animal models, cancer progression was reversed, suggesting the protein may also provide a novel therapeutic approach for late-stage ovarian cancer.”

“Scientists from The University of Texas M. D. Anderson Cancer Center have found overexpression of tissue type transglutaminase (TG2) in ovarian cancer is associated with increased tumor cell growth and adhesion, resistance to chemotherapy and lower overall survival rates. When researchers targeted and silenced TG2 in animal models, cancer progression was reversed, suggesting the protein may also provide a novel therapeutic approach for late-stage ovarian cancer.

These findings in the July 15th issue of Cancer Research by a team of researchers led by Anil K. Sood, M.D., professor in the Departments of Gynecologic Oncology and Cancer Biology, and Kapil Mehta, Ph.D., professor in the Department of Experimental Therapeutics at M. D. Anderson, are among the first to explore TG2’s functionality in ovarian cancer.

‘TG2 appears to fuel different types of cancer through multiple molecular pathways, making it an important therapeutic target,’ said Mehta, whose lab also has connected TG2 overexpression to drug-resistant and metastatic melanoma, breast cancer and pancreatic cancer.

‘Drug resistance and metastasis are major impediments to the successful treatment of ovarian cancer and until now we had little information about the role TG2 played in ovarian cancer,’ Sood said. ‘We began to see its story unfold as we translated this data from tissue samples to cell lines to animal models.’

The American Cancer Society estimates 15,000 U.S. women will die from ovarian cancer this year. Most patients present with advanced stage disease that has spread beyond the primary tumor site. More than 70 percent of ovarian cancer patients will suffer a recurrence and eventually succumb to the disease.

Higher TG2, lower survival

The study, which examined 93 ovarian cancer samples of ranging stages, found that high levels of TG2 corresponded with significantly lower patient survival than those with low levels of TG2. Sixty-nine percent of high-stage ovarian cancers overexpressed TG2 compared with 30 percent of low-stage cancers. In-depth analysis demonstrated that tumors which overexpressed the protein tended to have an increased ability to invade healthy tissue and to survive or avoid the affects of chemotherapy.

‘From this investigation it became clear that TG2 activates the survival pathway p13K/Akt in these tumors, explaining the adverse, resistant behavior we observed on a molecular level,’ said Sood. ‘We then focused on whether silencing TG2 would block these effects.’

Researchers shut off TG2 with a small interfering RNA strand (TG2 siRNA) targeted to the protein, reducing the ability of the tumor cells to invade and killing them through programmed cell death, or apoptosis. ‘When exposed to this potent targeted therapy, ovarian cancer cells greatly reduced cancer cell proliferation and blood vessel development, while increasing apoptosis,’ said Sood.

Mouse model studies of chemotherapy-sensitive and chemotherapy-resistant models showed considerable antitumor activity both with TG2 siRNA alone and in combination with docetaxel chemotherapy. The combination therapy of TG2 siRNA with docetaxel reduced tumor weight by 86 percent, proving to have the greatest efficacy compared to control groups or those without chemotherapy.

‘While it remains to be seen if these results will translate in humans, looking ahead long term, it will be an attractive option against advanced ovarian cancer,’ said co-author Gabriel Lopez-Berestein, M.D. professor in the Department of Experimental Therapeutics at M. D. Anderson.

TG2 fuels pancreatic cancer differently

Sood and Lopez-Berestein, have developed siRNA therapy by packaging the gene-silencing strips of RNA in a fatty nanoparticle called a liposome and delivering it intravenously. TG2 is the third protein they have targeted in preclinical research. Sood and Mehta are moving TG2 siRNA toward Phase I clinical trials for ovarian and pancreatic cancers.

TG2 acts through different pathways in other types of cancer, Mehta noted. For example, TG2 overexpression causes the degradation of the tumor-suppressing protein PTEN in pancreatic cancer, Mehta and colleagues reported in Clinical Cancer Research in April. With PTEN out of the picture, pancreatic cancer is protected from a separate type of cell death called autophagy. In a separate paper, they showed that silencing TG2 with the siRNA liposome reduced tumor size, slowed metastasis and enhanced the effect of gemcitabine chemotherapy.

‘This aberrant protein is doing so many different things, you would have to develop a small-molecule drug to block each function,’ Mehta said. ‘Liposomal siRNA is exciting because it takes out TG2 completely, blocking everything that it does.’

Research was funded by grants from the National Cancer Institute, including M. D. Anderson’s Specialized Program in Research Excellence in Ovarian Cancer grant, a program project development grant from the Ovarian Cancer Research Fund, Inc., and the Zarrow Foundation.

In addition to Sood, Mehta and Lopez-Berestein, authors include Jee Young Hwang, M.D., Lingegowda S. Mangala, Ph.D., co-first authors, and Yvonne G. Lin, M.D., William M. Merritt, M.D., Whitney A. Spannuth, M.D., Alpa M. Nick, M.D., Derek J. Fiterman, M.D., and Robert L. Coleman, M.D., all of M. D. Anderson’s Department of Gynecologic Oncology; Jansina Y. Fok, also a co-first author, and Pablo E. Vivas-Mejia, Ph.D., both of the Department of Experimental Therapeutics; and Michael T. Deavers, M.D., of M. D. Anderson’s Department of Pathology. Hwang is also with the Department of Obstetrics and Gynecology, Dongguk University of College of Medicine, Kyung-ju, Korea. 07/15/08”

Quoted Source: TG2 Identified as Potential Target in Chemo-Resistant Ovarian Cancer – M. D. Anderson team silences protein with siRNA, implicates TG2 in fourth cancer, The University of Texas, M.D. Anderson Cancer Center News Release, July 15, 2008 (summarizing the findings of Clinical and biological significance of tissue transglutaminase in ovarian carcinoma; Sood, AK et. al,  Cancer Res. 2008 Jul 15;68(14):5849-58.)

Additional Information:

Clue To Prevent the Spread of Ovarian Cancer

“By inhibiting MMP-2 [matrix metalloproteinase-2] activity early in the disease course, Lengyel and colleagues were able to prevent injected ovarian cancer cells from attaching to their target tissues in the peritoneum and omentum. This reduced the growth of new tumors by 68 percent, when measured four weeks after treatment. The inhibitor nearly doubled survival time in mice that were injected with ovarian cancer cells. Those who received it survived an average of 63 days, compared to untreated mice, who survived only 36 days. Brief and early intraperitoneal treatment with an MMP inhibitor, the authors conclude, may reduce peritoneal attachment, reduce metastases and significantly prolong survival.”

“A drug that blocks production of an enzyme that enables ovarian cancer to gain a foothold in a new site can slow the spread of the disease and prolong survival in mice, according to a study by researchers from the University of Chicago Medical Center, but only if the drug is given early in the disease process.

In the April issue of the Journal of Clinical Investigation, the researchers show that an enzyme known as MMP-2 is necessary for ovarian cancer to attach itself to the sites where it tends to spread. Several drugs known as MMP inhibitors (for example, marimastat or prinomastat) inhibit the enzyme, dramatically reducing the tumor’s ability to establish itself at sites beyond the ovary. But such MMP inhibitors, which were abandoned after they failed to extend survival in earlier clinical trials, have to be given before the cancer has spread.

‘Our study suggests that MMP-2 inhibitors could have a significant impact on ovarian cancer but only if administered quite early, before the cancer has advanced beyond the ovary,’ said Ernst Lengyel, assistant professor of obstetrics and gynecology at the University of Chicago.

This approach could help women who receive surgical treatment while the disease is still limited to the ovary as well as those who have successful surgery to remove all evidence of local spread of the disease. In the earlier trial, marimastat was given to women with late-stage disease that had already spread.

The fifth leading cause of cancer death in women, ovarian cancer — unlike breast, colon or lung cancer — tends to spread within the abdominal cavity and not to distant organs. Carried by fluid, it most often spreads throughout the peritoneal cavity and to the omentum, a large fat pad draped over the small bowel.

Lengyel and colleagues wanted to understand the many steps required for ovarian cancer to dislodge from its original site and establish itself elsewhere in the peritoneal cavity. They found that one of the key steps was production of MMP-2 by cancer cells that came in contact with the cells that line the peritoneal cavity.

When ovarian cancer cells make contact with the cells that line this internal cavity, they produce MMP-2 (an acronym for matrix metalloproteinase-2). MMP-2 alters two proteins–vitronectin and fibronectin–found on the surface of the cells that line the cavity. These alterations change those proteins in a way that enables the cancer cells to latch on to them better. Once attached, the cancer cells can multiply rapidly and invade.

By inhibiting MMP-2 activity early in the disease course, Lengyel and colleagues were able to prevent injected ovarian cancer cells from attaching to their target tissues in the peritoneum and omentum. This reduced the growth of new tumors by 68 percent, when measured four weeks after treatment.

The inhibitor nearly doubled survival time in mice that were injected with ovarian cancer cells. Those who received it survived an average of 63 days, compared to untreated mice, who survived only 36 days.

Brief and early intraperitoneal treatment with an MMP inhibitor, the authors conclude, may reduce peritoneal attachment, reduce metastases and significantly prolong survival.

The treatment has much less impact, however, once cancerous cells have attached and formed colonies. In several earlier trials, marimastat, an oral MMP inhibitor, was given for a prolonged period of time to women with late-stage disease that had already spread.

‘MMP-inhibitors were given at the wrong time for too long, causing side effects,’ Lengyel said. Attachment is the first step for metastatic spread. MMP-2, the target of MMP inhibitors, plays a role in early cancer spread.

‘Our study examines the initial step of ovarian cancer metastasis,’ the authors note, when cancer cells meet unprepared target cells. Other steps in this process, they suggest, may also provide additional treatment targets.

The National Institutes of Health, the Department of Defense, the Ovarian Cancer Research Fund, the Gynecologic Cancer Foundation and the Illinois Department of Health funded the research. Additional authors include Hilary Kenny and Swayamjot Kaur of the University of Chicago and Lisa Coussens of the University of California San Francisco.

[Quoted Source: Clues To Prevent Spread Of Ovarian Cancer, ScienceDaily News Release dated March 18, 2008.]

Comment: The in vivo study discussed above suggests that the use of MMP inhibitors, e.g., marimastat or prinomastat, to treat an early stage ovarian cancer patient may prevent the spread of ovarian cancer outside of the peritoneal cavity.

Source Medical Article: The initial steps of ovarian cancer cell metastasis are mediated by MMP-2 cleavage of vitronectin and fibronectin, Lengyel, E., et. al., J. Clin. Invest. 118(4): 1367-1379 (2008).

2008 American Society of Clinical Oncology (ASCO) Annual Meeting Abstracts Available On-Line

The 44th Annual Meeting of the American Society of Clinical Oncology (ASCO) will be held on May 30th through June 3rd, 2008 in Chicago, Illinois. Under a new policy, ASCO publicly released clinical trial brief abstracts two weeks before the start of its 2008 Annual Meeting on May 30th, where full results will be presented before thousands of cancer doctors. The new ASCO policy was intended to avoid stock trading on non-public information that was believed to have occurred under a prior policy in which ASCO mailed out abstracts under embargo weeks before its annual meeting.

I have provided hyperlinks below to a variety of cancer topics that may be of interest to ovarian cancer survivors. Please note that with the exception of the first “ovarian cancer” category listed below, the remaining categories will contain abstracts that address various types of cancer. H*O*P*E*™ will provide one or more posts that address ovarian cancer abstract highlights after the completion of the 2008 ASCO Annual Meeting on June 3rd.

Gynecologic Cancer:

Ovarian Cancer

Developmental Therapeutics: Cytotoxic Chemotherapy:

Cytotoxic Chemotherapy
Drug Resistance
Pharmacology / Pharmacokinetics
Phase I Studies

Developmental Therapeutics: Immunotherapy:

Antibodies
Cell-Based Therapy
Cytokines
Other: developmental therapeutics: immunotherapy
Vaccines

Developmental Therapeutics: Molecular Therapeutics:

Antiangiogenic or Antimetastatic Agents
Cell Cycle Inhibitors
Chemoprevention
Epigenetic Strategies
Functional Imaging
Gene Therapy/Antisense Strategies
Other Novel Agents
Pharmacodynamics
Pharmacogenomics
Pro-Apoptotic Agents
Receptor-Targeted Antibodies/Ligands
Tyrosine Kinase Inhibitors
Vascular Targeting

Tumor Biology and Human Genetics:

Cancer Genetics
Epidemiology / Molecular Epidemiology
Immunobiology
Molecular Diagnostics and Staging
Molecular Targets
Other: Tumor Biology and Human Genetics
Prognostic Factors
Radiation Biology
Tumor and Cell Biology

Cancer Prevention:

Cancer Prevention

Patient Care:

Cancer in Older Patients
Cancer-Related Complications
End-of-Life Care
Other: patient care
Palliative Care
Quality-of-Life Management
Supportive Care

Health Services Research:

Health Services Research
Outcomes Research
Practice Management/Professional Issues