From Pea Pods to Peptides In the 140 years since Gregor Mendel published his groundbreaking studies of pea plant inheritance, the field of genetics has moved on to ever smaller things.

Cancer researcher Margaret Offerman has focused much of her work since the 1994 discovery of human herpesvirus 8 on its relationship to Kaposi's sarcoma.

by Susan Riordan & Darryl Gossett

It was the best of news and the worst of news. At the beginning of this year, New Jersey resident Clare Riordan learned she had won a three-year battle with cancer. Yes, she had lost her left lung in the process and endured three depleting months of radiation, but she seemed to have beaten the odds when a follow-up examination by her surgeon, Emory thoracic specialist Joe Miller, revealed no signs of lung cancer left in her body.

Shortly before that, however, a routine mammogram back in New Jersey had detected a small lump in her right breast. While at Emory for her lung cancer follow-up, Riordan had that growth biopsied and received confirmation of breast cancer. Since this followed so soon on the heels of her previous struggle, her physicians advised against a lumpectomy and the further radiation that would entail. Instead, the 74-year-old opted for a mastectomy, successfully performed in January by William C. Wood, chair of surgery and interim director of Emory's Winship Cancer Institute. Cancer-free today, Riordan seems to have walked through the fire a second time.

The emergence of a second form of cancer, however, introduced a new dimension of fear into her struggle with health. A mother of six and grandmother of six - and well aware that heritable genetic links have been established for certain forms of cancer, including breast cancer - Riordan now wondered what the implications of her illness were for her family. Did her four daughters need to take one of the new gene tests available? What if they did and tested positive, then what?

As it turns out, none of the Riordans opted for genetic testing nor are they likely candidates. Riordan's lung cancer was most likely triggered by an environmental factor, her many years as a smoker, and not an inherited gene defect. Her age played a factor in her development of breast cancer, as, perhaps, did the radiation therapy she underwent to treat her lung cancer. However, with no other family history of breast or lung cancers, Clare Riordan's children have little or no heritable susceptibility to cancer. (To err on the side of caution, however, Riordan's daughters will be seeking more frequent and thorough mammograms.)

In any case, inheritance would be just one factor among many, says Emory cancer researcher and physician Margaret "Kenny" Offermann.

Scientists, she says, have recognized for a number of years that cancer involves multiple acquired mistakes in DNA, the genetic material that provides the master plan. These multiple mistakes allow cells to invade surrounding tissues and metastasize to distant sites, the hallmark of cancer. Environmental factors such as smoking or exposure to ultraviolet light can damage DNA, but cells have clever mechanisms to protect them from replicating damaged DNA. A frequent and early event in the development of cancer thus appears to be damage to this protective machinery.

While many cancers don't have a clear pattern of inheritance, some families do have a strong inherited tendency to develop cancer. So how does this occur? Some of the genes that lead to familial cancer have been identified. The inherited tendencies relate to inheritance of a damaged gene that increases the likelihood that additional mutations will occur during the lifetime of the host, leading to malignancy.

"This explains why some people can smoke two packs a day their entire life and never develop cancer, or not until they're very old, while other people die of exposure to secondhand smoke at age 25," says Offermann. "The second group was probably born with more strikes against them in terms of susceptibility. Their cells might be unable to repair the damage smoking has caused - or even unable to recognize that damage has taken place at all. On the other hand, the first group might have an extraordinarily efficient repair system."

Connecting the Dots

Breast cancer surgeon William Wood is Emory's principal investigator for the NCI's new Cancer Genetics Network, established to collect data to identify those at risk for heritable cancer, determine the significance of cancer predisposing genes as risk factors, and help develop therapeutic and prevention measures.

But what if the key facts in Riordan's case had been different? What if she had been shown to have an inherited predisposition to cancer? Then what?

"Then what" is a key question to be addressed by the National Cancer Institute's new Cancer Genetics Network (CGN). With $6 million in funds from the NCI, the CGN is a national alliance of eight consortiums that will support research into cancer genetics and address the psychosocial, ethical, legal, and public health issues associated with inherited susceptibility to cancer. Emory is a member of the Carolina/Georgia Consortium, which also includes Duke University and the University of North Carolina at Chapel Hill.

The network will explore several provocative areas of inquiry and the implications they raise. Is cancer more prevalent in certain populations? Do environmental factors trigger cancer genes and, if so, by what mechanism? Once more is learned about genetic links to cancer, what can be done to treat patients who test positive? With input from member institutions around the nation, researchers hope to acquire enough sheer data to begin connecting the dots in the puzzle of hereditary susceptibility to cancer.

The dot-connecting began some 140 years ago when Austrian monk Gregor Mendel conducted his now-famous experiments breeding strains of plants with smooth peas and wrinkled peas, establishing a scientific basis for inheritance. In the years since, with the identification of genes, chromosomes, DNA, and RNA and with the introduction of genetic mapping and the Human Genome Project, the field of genetics has focused on ever smaller things.

"Genetic theory has come a long way since Mendel first published his experiments," says Wood, Emory's principal investigator for the CGN. "For the first time, we have the tools to understand the relationship between genetics and disease, particularly cancer."

One of the country's foremost breast cancer surgeons, Wood has a large patient population - some of whom have tested positive for breast cancer susceptibility genes BRCA1 or BRCA2 and others whose family history has made them consider testing.

"One of the main concerns for most people who have reason to believe they may have a genetic predisposition to cancer is how they will be treated if they test positive," Wood says. "We hope to discover which cancers are heritable, and patient participation is obviously crucial to this. The network will use all means to assure privacy while still pursuing understanding of this important cancer link."

Once stripped of identifying information, data acquired from these patients will be folded into the pool of knowledge collected by the CGN nationwide. Information from this national registry will be available to participating institutions as well as to researchers outside of the network.

The CGN's work will start with breast cancer patients but will not end there. Prostate, ovarian, lung, esophageal, renal, gastric, thyroid, and bladder cancers all have proven genetic links.

CGN investigators hope to increase their understanding of how inherited defects in oncogenes and tumor suppressor genes might lead to cancer. CGN data will also shed light on apoptosis (programmed cell death) and tumor antigens as well as new approaches aimed at correcting mutations that spur malignant growth.

The desired end result of the studies will be to find a way to identify who is genetically at high risk for heritable cancer, to determine the significance of inherited cancer-predisposing genes as cancer risk factors, and to help develop therapeutic and cancer prevention measures.

Genetics and Everything Else

Urologist John Petros and his team are working with Immunocomp Laboratories, a company in Stockbridge, Georgia, in strategies to fight prostate cancer using antigens from the patient's own tumor.

Many of the tools developed over the past decade to advance the work of the Human Genome Project have been an enormous boon to researchers in other areas of investigation, cancer perhaps more than others. With these newly developed tools, different fields of study have overlapped and become more interdependent.

"The line of distinction between genetics and everything else is getting more and more blurry," says prostate cancer researcher John Petros. "Other traditional fields of inquiry such as biochemistry or immunology used to be distinct. Now they are more connected. You don't have high-quality biochemical analysis going on that doesn't use the tools of molecular biology and genetic analysis."

The broad expanse of research under way in the urology laboratories at Emory reflects that interdependence. In one study, Petros and his team are looking at methods of genetically altering prostate tumor cells. First the researchers have created positively charged peptides that will work as a transportation device for delivering small, negatively charged, chemically synthesized pieces of DNA (oligonucleotides) through the cell membranes, allowing the synthetic DNA to interact with the cellular DNA. They use these delivery vehicles to direct the potentially therapeutic single-stranded oligonucleotides into the cytoplasm and nucleus of the cell, targeting genes such as the HER-2/neu oncogene, a breast cancer gene that also has been linked to prostate cancer. (The novel delivery peptides have been developed in collaboration with Jan Pohl, director of the cancer institute's microchemical facility; Dennis Liotta, Emory's vice president for research; and urology researcher Joan Karr.)

The hope is that the oligonucleotide - specially designed to target a specific gene or messenger RNA sequence - can affect the regulation of the cancer-causing defective gene, resulting in slower growth rates or cancer cell death.

"We have worked on five to 10 peptides and have found one that shows low toxicity, which is important for a delivery tool," says Karr, who was recruited to Emory in 1995 to work on development of novel peptides. "We have produced peptides that are highly efficient at getting the HER-2/neu oligonucleotide into prostate cancer cells in vitro." The team has applied for a patent on these newly created compounds.

Acknowledging the difficulty of perfecting a therapy that could reach all of the millions to billions of cancer cells in the body, Petros' lab is also focusing on methods to activate the body's own defenses to rid itself of the defective cells.

"If you have a tumor with eight, 10, or 15 different genetic abnormalities, you can transfer a piece of DNA that can make a biologic response modifier, the GMCSF-IL2 cytokine," Petros says. "That causes the immune system to kick in, to recognize that cell as foreign and eliminate it in other places in the body." Since cancer cells do not initiate apoptosis, or programmed cell death, like normal cells, this therapy may help rid the body of the malfunctioning cells.

To accomplish the task of immunologically eliminating a tumor, Petros and his team are working with a company in Stockbridge, Georgia, called Immunocomp Laboratories. Immunocomp has developed a strategy of eliminating the tumor using antigens from the patient's own tumor. The tumor antigens are mixed with the GMCSF-IL2 cytokine, and the combination is given as a vaccine in and around lymph nodes. The combination activates lymphocytes that then attack tumors. While Immunocomp has had some success with patients, Petros is taking the process back into the laboratory, changing some of the parameters in order to raise the response rate. If that response rate can be raised, Petros hopes eventually to begin clinical testing at Emory.

Viral Links to Cancer

Cancer researcher Joan Karr (right) is part of a team that has applied for a patent for peptides used as transportation devices to deliver synthetic DNA to the cell nucleus to shut down expression of an oncogene that causes breast cancer and is also implicated in prostate cancer.

Kaposi's sarcoma (KS) was considered a rare cancer prior to the early 1980s - confined almost exclusively to older Mediterranean or Jewish men - when case after case began to suddenly appear among people with AIDS. With the incidence of KS being 20,000 to 70,000 times greater among AIDS patients than other populations, it was an early and natural assumption that HIV somehow triggered the cancer.

New research, however, has shown that Kaposi's is probably caused by the recently discovered human herpesvirus 8 (HHV8). Like other herpes viruses, HHV8 may lie dormant, and as much as 20% of the population may carry it without ever being symptomatic.

Cancer researcher Kenny Offermann has focused much of her work since the 1994 discovery of HHV8 on its relationship to KS. Offermann and her team recently reported in the Journal of Virology that a gene product of HHV8 called viral interferon regulatory factor (vIRF) blocks the ability of cells to respond to interferon. Interferon, in turn, is one of the main defenses used by the body to fight viral infection and tumor development and is a therapy used in treating KS patients.

"The virus encodes about 85 genes, and one of them is vIRF," says Offermann. "We have shown that vIRF interferes with responses to interferon. We're studying the expression of that particular gene, including what turns it on and off, how it interferes with interferon response, how it leads to malignant transformation, how it affects the viral life cycle."

Offermann suspects an HIV-encoded protein may actively affect the function of HHV8, contributing to the high incidence of cancer in AIDS patients.

"There are two different scenarios by which viruses could contribute to the development of cancer. One is that host changes in response to the virus can trigger or allow multiple mutations to occur. Estimates are that you need at least five mutations in tumor suppressor genes and oncogenes to get a frank malignancy. A number of viruses can help those mutations occur," Offermann says.

The other scenario is that cancer viruses trundle in genetic material that affects the programming of the cell and allows malignancy to develop. In the case of Kaposi's sarcoma, Offermann says, it is probably a combination of both, but HHV8, like a Trojan horse, is clearly sneaking material into the cell that functions as oncogenes, or cancer-causing genes.

Results of Offermann's research are not limited to HHV8. "When we began this work, the number of viruses that were associated with human cancers were relatively limited," she says. "That number keeps going up, and recent estimates have suggested that about 30% of human cancers have some sort of viral link."

Stabilizing an Unstable Force

NCI director Richard Klausner has called cancer "a strange and remarkable disease, best described as a disease of genomic instability, itself an amazing and very daunting problem." Even with new information pouring into and out of research laboratories every day, cancer is still proving itself to be an exceedingly slippery foe. The war on cancer is still nowhere near being won.

But with the flow of information comes the promise of better understanding of how to stabilize this unstable force in the body.

"What is very exciting about tumor biology in general is the level of understanding that we've gotten in recent years on what makes a cancer a cancer," Offermann says. "We went from having this big black box to knowing many common events that occur in the genetic evolution of cancer. We know this is not just one disease, that there is not just one simple mechanism involved. But at the same time we are finding some common themes."

Susan Riordan is director of public relations at the Winship Cancer Institute. Darryl Gossett is contributing editor of Emory Medicine.


Setting Our Sights | When Abused Children Grow Up | From Peapods to Peptides

Copyright © Emory University. All Rights Reserved.
Web version by Jaime Henriquez.