PHILADELPHIA INTERNATIONAL MEDICINE® NEWS BUREAU
Contact: Leonard N. Karp
lkarp@philadelphiamedicine.com
215-735-3989
August 26, 2004

For immediate release:

In this month's issue:

1. Vector Insertion is Viral Specific: Mapping integration sites has implications for better-engineered gene therapies and new HIV drugs
2. Molecular Therapeutics Advance Fight Against Brain Cancer
3. Children's Hospital Doctor Named Head of Gene Therapy Society
4. MossRehab Study: Ritalin Helps Individuals Recovering From Brain Injury
5. Jefferson Researcher Planning New Trial Testing Targeted Agent for High-Risk Prostate Cancer

Editors note: Research by Philadelphia International Medicine physicians and hospitals may lead to new ways to treat some of our most challenging diseases. Below are just some examples from our hospitals.

Vector Insertion is Viral Specific: Mapping integration sites has implications for better-engineered gene therapies and new HIV drugs

Philadelphia - Retroviruses are one of the most common vehicles for delivering therapeutic payloads via gene therapy in animal models of disease and human patients. Viruses integrate into host DNA to replicate, but exactly where they insert themselves has become a topic of increasing importance. This is of special concern when integration is near an oncogene that may lead to uncontrolled, cancerous cell growth.

Now, researchers at the University of Pennsylvania Medical Center have completed the first whole-genome survey of where three commonly used retroviruses integrate into human DNA. The team, led by Frederic Bushman, PhD, professor of microbiology, compared vectors derived from human immunodeficiency virus (HIV), murine leukemia virus (MLV), and avian sarcoma-leukosis virus (ASLV). They found that HIV integrated near active genes; MLV near points on the chromosome where protein translation starts (which confirms earlier work by another lab); and ASLV integrated more randomly throughout the entire genome.

That each studied virus preferred a unique integration pattern or site suggests that viruses home in on certain chromosomal features for inserting themselves within the genome. This work appeared in the August 17 issue of PLoS Biology, a new open-access journal.

"There's a picture forming of where different retroviruses integrate in human cells, and it seems to be quite different from virus to virus, which is not something anyone would have ever suspected," says Bushman. "We can only speculate as to the mechanism at present, but one attractive idea is that retroviral-integration complexes bind to cellular DNA binding proteins attached to specific locations on chromosomes." For HIV, integrating into active genes may help promote efficient viral gene expression. The reason for the choice of target is less clear in other retroviruses.

These findings are important for devising safer human gene-therapy vehicles. From studies in yeast, the researchers speculate that there is a system of biochemical recognition between proteins bound on human chromosomes and viral proteins, which helps guide integration, and that specific recognition seems to differ from virus to virus. "There's a prospect of modulating or engineering that kind of system, once we understand it better, to direct integration to different locations," comments Dr. Bushman.

These findings can also help researchers understand how HIV enters cells in order to devise drugs to block that entry. "If there's a key interaction required for growth of a virus, then that would be a target to inhibit," says Dr. Bushman. HIV needs three enzymes - reverse transcriptase, protease, and integrase - to complete a full replication cycle. AZT and protease inhibitors stop activity of the first two, respectively, and the last one left to target is integrase, the object of a new AIDS drug recently tested in rhesus monkeys. "If there is a 'targeting factor' required for efficient replication, then blocking its function might obstruct viral replication," says Bushman. "The clearest way forward is to inhibit the catalytic activity of the integrase protein and some of our future work is geared toward that."

These are still early days in harnessing knowledge about viral integration in humans to make safer and more effective gene therapies, let alone new drugs against HIV. To that end, new information on targeting integration is likely to help guide design of better therapy, say the researchers.

Other members of the research team included Penn colleagues Rick S. Mitchell, Brett F. Beitzel, and Astrid R.W. Schroder, as well as Paul P. Shinn, Huaming Chen, and Joe R. Ecker from The Salk Institute and Charles C. Berry from the University of California at San Diego School of Medicine.

Molecular Therapeutics Advance Fight Against Brain Cancer

An estimated 41,000 new cases of primary brain tumors are expected to be diagnosed in 2004, according to the American Brain Tumor Association. To further narrow the gap between diagnosis and effective therapy, physicians at the Hospital of the University of Pennsylvania now offer several promising -- and unique to the Philadelphia region -- approaches to brain tumor treatment, including novel imaging for oncologic neurosurgery and refined genetic testing for tumors to better target treatment.

Through enhanced magnetic resonance imaging (MRI), newer and broader information is helping to better guide tumor removal. MRI is used to measure the anatomy and metabolism of tumors. This informs surgeons pre- and post-operatively with a three-dimensional map of tumor-associated blood flow to more precisely assess the full extent of tumor growth versus conventional imaging methods. "This novel approach helps guide surgery and assessment of treatment response," says Donald M. O'Rourke, MD, associate professor of Neurosurgery. These novel imaging methods are leading to increased patient survival by allowing for greater tumor removal in a safe manner.

Neuroscientists are also ushering in a new era in which genetics will dictate treatment. In the 1990s researchers noted that a more favorable prognosis in patients with certain brain tumors, primarily oligodendrogliomas, was associated with a deletion of genes on chromosomes 1 and 19. This genetic loss translates into a significant life-expectancy gain for some patients and is therefore a robust predictor that post-surgery chemotherapy should be given to such patients.

Patients with the genetic deletion on chromosome 1 have a median survival in certain cases of about 10 years and respond particularly well to chemotherapy given immediately after surgery. Patients with the deletion have slower-growing tumors and show a better response to chemotherapy; whereas, those without the deletion have relatively faster-growing tumors and are less responsive to chemotherapy, so radiation therapy is required sooner. "Given the expected increase in the life-span of patients with this deletion, there is no need to give radiation therapy early in their treatment," explains O'Rourke.

The deletion can only be detected by genetic analysis. "Under the microscope these tumors can look identical, so there's no way of knowing the difference unless a genetic analysis is performed," explains O'Rourke.

Having the ability to provide such genetic testing to determine treatment is of benefit to patients. "The idea of using a genetic test to predict prognosis and select therapy, thereby deferring potentially deleterious treatment is tremendously attractive," says O'Rourke. "Penn's genetic testing is done in-house, so patients don't have to wait for the results." Further, there is no cost to the patient at this point since the tests are performed by the Neuro-oncology Program and supported by the Abramson Cancer Center at Penn. In addition, there is no requirement for additional blood samples, so results will be given more quickly with no need for follow-up visits.

Penn colleagues J. Carl Oberholtzer, MD, PhD, Department of Neuropathology and Myrna Rosenfeld, MD, PhD, Department of Neurology and Director of the Division of Neuro-oncology as well as Jaclyn Biegel, PhD, Director of Cytogenetics, Children's Hospital of Philadelphia, collaborated with O'Rourke on developing the genetic testing program. Dr. Biegel's laboratory performs the genetic test and has significant experience with genetic testing of brain tumors.

O'Rourke is also Director of the Human Brain Tumor Tissue Bank at Penn, a unique resource to the region and one of only a few such dedicated banks in the United States. Tissue banks allow for the direct evaluation of human tumors and are one of the best ways to advance treatment options for gliomas and other human cancers. O'Rourke's basic research interests include finding new treatments for gliomas based on genetic alterations detected in tumors. He is currently investigating a variant of the epidermal growth factor receptor that is present in many primary glioblastomas to better understand the development of malignancy in the brain and how it relates to cancer cell division, survival, and movement.

O'Rourke and colleagues are now prepared to discuss potential surgical and clinical treatments and genetic evaluation of brain tumor patients.

Children's Hospital Doctor Named Head of Gene Therapy Society

Katherine A. High, MD, a leading hematology researcher at The Children's Hospital of Philadelphia, began her term as president of the American Society of Gene Therapy (ASGT). The ASGT is the largest medical professional organization representing researchers and scientists dedicated to discovering new gene therapies.

Gene therapy, a very new field of medicine, holds the potential of treating human disease at a fundamental level by delivering therapeutic genes directly into a patient's cells.

Dr. High is internationally prominent for her studies of the molecular biology of the inherited bleeding disorder, hemophilia. Over the past decade, she has investigated a gene transfer approach to treating hemophilia B, the second most common form of hemophilia, by delivering the gene to produce the blood-clotting factor that is deficient in patients with the disease. At a recent ASGT meeting, Dr. High reported preliminary results of a clinical trial of gene therapy for hemophilia B, conducted in collaboration between The Children's Hospital of Philadelphia and Stanford University.

In addition to her position at Children's Hospital, Dr. High is a Howard Hughes Medical Institute Investigator, one of 12 physician-scientists recently selected by the Institute for major accomplishments in patient-oriented research. She also is the William H. Bennett Professor of Pediatrics at the University of Pennsylvania School of Medicine. Dr. High will serve as president of the ASGT until June 2005.

MossRehab Study: Ritalin Helps Individuals Recovering From Brain Injury

Researchers at Moss Rehabilitation Research Institute (MRRI) have discovered that Ritalin (Methylphenidate), a drug commonly used for the treatment of attention-deficit hyperactivity disorder (ADHD) in children, may also help improve attention deficits in individuals recovering from a traumatic brain injury (TBI).

"We are both excited and encouraged by the findings of this study and the implications for the treatment of individuals with brain injury," said John Whyte, MD, PhD, Director, MRRI.

According to Dr. Whyte, clinicians have been experimenting with Ritalin for a number of years hoping that the drug would be effective in treating TBI, where difficulties in attention and concentration are among the most common cognitive impairments. However, most of these studies, up until now, have not produced any definite conclusions.

The randomized and controlled study at MRRI, funded by the National Institutes of Health, involved 34 individuals with moderate to severe brain injuries at least three months post injury. Each participant was given Ritalin for one week followed by a week of a placebo alternately for a total of six weeks. Throughout the trial, the participants were regularly tested in many different facets of attention ranging from clinical measures of information processing to videotape recordings of independent work in distracting environments. The results indicated significant positive effects on the speed of processing information, attentiveness during individual work tasks and caregiver ratings of the individual's attention span during a typical day.

The complete study, "Effects of Methylphenidate on Attention Deficits After Traumatic Brain Injury-A Multidimensional, Randomized, Controlled Trial," was recently published in the American Journal of Physical Medicine & Rehabilitation.

Jefferson Researcher Planning New Trial Testing Targeted Agent for High-Risk Prostate Cancer

When prostate cancer spreads to the bones, it turns deadly. Some 90 percent of deaths from prostate cancer occur in those whose disease has gone to the bones. Now, a Jefferson radiation oncologist plans to use a grant from the Department of Defense to test the potential effectiveness of a new therapy aimed at thwarting the effects of the spreading disease.

"The strategy is to use bone-targeted agents upfront in combination with standard treatment - a combination of hormones and radiation - for high-risk prostate cancer," says Richard Valicenti, MD, associate professor of radiation oncology at Jefferson Medical College of Thomas Jefferson University and Jefferson's Kimmel Cancer Center.

Many cases of prostate cancer are thought to be fed by male hormones known as androgens. One strategy against the disease, then, is to eliminate or limit androgen production. In addition, Dr. Valicenti explains that previous studies have shown evidence of an interaction between radiation and hormones; in effect, making the spreading cancer cells more sensitive to radiation. But the treatment has limited effectiveness.

Dr. Valicenti is developing a clinical trial to study individuals at increased risk for having prostate cancer spreading to the bones, but whose disease has not shown any outward clinical signs of having done so to date. "We're hypothesizing that the same sort of combination [of hormones and radiation] could be used to treat microscopic bony metastasis," he says.

He and his co-workers are using an agent that is "preferentially taken up by the bone," he explains. The idea is that the agent, called samarium-153 ethylenediaminetramethylene phosphonic acid (EDTMP), or Quadramet - which consists of a "phosphonate" attached to a radioisotope that emits radiation - will attack cancer cells that have spread from the prostate to the bone. According to Dr. Valicenti, Quadramet "seems to primarily target prostate cancer sites that harbor bony metastases." It was previously used for pain reduction.

Dr. Valicenti currently is completing a phase I trial looking at the safety and feasibility of using the strategy of a bone-targeted treatment.
"The thinking is that this will help improve a reduction in death rates from prostate cancer," says Dr. Valicenti. In 2004, an estimated 29,000 American men will die of prostate cancer, with complications from bony metastases a contributing cause in the majority of deaths. It is the second leading cause of cancer death in men in the United States.

The DOD award - one of seven initial proposals to be funded - is initially for $100,000 for one year to develop an infrastructure to carry out a two-to-three-year trial. The trial, he expects, will be at several centers and involve approximately 60 or 70 patients. It could begin next year.

Philadelphia International Medicine is an organization that provides medical and patient support services to international patients. It also provides continuing medical education and health care training and education to international physicians, administrators and other practitioners. As the international department of several Philadelphia-area hospitals, international patients gain access to physicians and hospitals rated among the best in the world through one telephone call to PIM. You can reach PIM by calling 1-215-735-3575; fax, 1-215-790-1267; or e-mail, physicians@philadelphiamedicine.com . You can find out more about PIM through its Website at www.philadelphiamedicine.com .