Innovative Treatments: Search for a Cure

To stimulate the development of more effective treatments, the CBCRP funds a variety of research approaches. These include alternative medicines, novel clinical approaches, testing promising drug and drug target leads in animal models of breast cancer, and rational drug design, which is a methodical approach based on understanding the molecule-level interactions between a potential drug and the disease process. For many of our investigators, research under this priority subject area is an extension of their research previously funded under our priority subject area of Pathogenesis.

We have divided the innovative treatment priority issue into four broad areas of research:

Research Conclusions

Immune Therapy: Mobilizing the Body's Defenses

HER2/Neu DNA Vaccines for Breast Cancer. The Her-2/neu gene is found in invasive breast tumors and also in about 50% of cases of DCIS, a pre-cancerous condition of the breast that may turn in to cancer. Michael Campbell, Ph.D., from University of California, San Francisco, explored new ways to develop a vaccine against breast cancer. Dr. Campbell's approach was to inject into mice portions of the cancer gene Her-2, in the form of DNA linked to a virus. The thinking was that the virus would infect cells in the mice and they would synthesize portions of Her-2 to generate antibodies. This approach differs from the normal method of injecting a protein produced by a gene, rather than parts of the gene itself, to stimulate the immune system. In addition, Dr. Campbell “boosted” his DNA vaccine method by incorporating proteins known to enhance the immune response. Unfortunately, the preliminary experiments showed that much more work was needed to optimize the route of administration (i.e., oral vs. injected), and there are technical problems in combining the Her-2 and the DNA into the virus. Nevertheless, the research pursued an important avenue of investigation, using Her-2 in a vaccine approach.

New Drug Design: Creative Science

Heregulin-specific Diphtheria Toxin as a Cancer Therapy. Gordon Louie, Ph.D., at the Salk Institute for Biological Studies, La Jolla, attempted to modify the diphtheria toxin into a molecule that would attack cancer cells, but not normal cells. The engineered toxin would, in theory, bind only to a protein—heregulin—found preferentially at the surface of breast cancer cells. Prior to this research, Dr. Louie and his colleagues found that diphtheria toxin would bind to a protein very similar to heregulin. The research team was able to advance the theoretical basis for engineering diphtheria toxin, but wasn't able to develop a way to test whether the modified toxin binds only to heregulin.

HER-2

HER-2, also known as HER-2-neu and ErbB2, is a protein found on the surface of breast tumor cells. It is a receptor, which means that another protein from outside the cell can combine with it like a key in a lock, and turn on other changes in the cell. If HER-2 is present in high amounts, the tumor is more likely to be fatal. About 20% of breast tumors have high levels of HER-2.

Herceptin, an immunebased drug that binds with HER-2, slows the progression of tumors. Although it doesn't stop breast cancer, Herceptin can be used to treat tumors that formerly could not even be slowed down.

Researchers are investigating HER-2 as a target for new ways to treat tumors that are resistant to other therapies.

Novel Breast Cancer Anti-Angiogenic Compounds. Breast tumors can't grow without hijacking the body's blood supply and creating a new network of blood vessels. Mai Nguyen, M.D., at the University of California, Los Angeles, investigated a variety of plant extracts for potential to be developed into a potent drug with low toxicity that could stop the growth of new blood vessels. Dr. Nguyen identified and purified compounds from a palm plant, Livistonia, that block new blood vessel growth. Water-based extracts from the seed shell and skin appear to contain the active agent(s). This extract material blocked the growth of cancer cells and also of endothelial cells (cells that line organs in the body, including the heart and blood vessels). The extract did not appear to cause any toxicities in mice. The results were published in Oncology Reports 8:1355-7 (2001).

Novel Anti-vascular Agents for Breast Cancer Therapy. Breast cancer can't grow without a network of blood vessels from normal tissue to supply oxygen and nutrients and to remove waste products. When a tumor outgrows its blood supply, it can stimulate the formation of new blood vessels to support its growth, and this process is necessary for the tumor to become malignant. However, the blood vessels the tumor creates are impaired, compared to normal blood vessels. This makes these tumor-created blood vessels attractive targets for chemotherapy. Keith Laderoute, Ph.D., from SRI International, Menlo Park, investigated a new drug compound, BTO956. It keeps tumor cells from dividing. BTO956 also suppresses the growth of human breast cancers implanted in mice, with very little toxicity to normal tissues. Dr. Laderoute and his collaborators at Duke University found, in addition, that BTO- 956 stops the growth of blood vessels that nourish tumors. This study was published in Clinical Cancer Research 7:2590 (2001).

SXR: A Novel Target for Breast Cancer Therapeutics. Michelle M. Tabb, Ph.D., at the University of California, Irvine, is investigating the SXR gene's role in the anti-cancer effects of diverse compounds such as the drug tamoxifen, plant-derived estrogens called phytoestrogens found in soy foods, anandamide, and Vitamin A. Dr. Tabb's team has found the protein produced by the SXR gene in several breast cancer cell lines. They have also found a variant form of SXR in some cell lines that is turned on by different compounds than the normal form. When they treated the cell lines that contain the SXR protein with compounds that turn on the SXR gene, these compounds demonstrated the ability to stop the growth of breast cancer cells. The compounds that turn on the gene the most are also the best at stopping the growth of breast cancer cells. Dr. Tabb plans future research to investigate the mechanism behind the effectiveness of compounds that turn on SXR and to discover whether SXR is responsible for stopping the growth of breast cancer cells. This could provide information leading to a new anti-cancer drug, and lead to understanding of the way substances found in the diet, such as phytoestrogens, are effective in breast cancer prevention.

Receptors

Several studies in this section mention receptors. Receptors are usually proteins. They are found on or in cells. Receptors bind with another substance, such as a protein, hormone or drug that comes from outside the cell. Once the receptor has bound to the other substance, it changes chemically and triggers changes within the cell. Receptors initiate a wide variety of cell changes. In breast cells, these can include changes that make the cell produce milk, divide, or go through the normal process of cell death.

In Vitro Testing of Chinese Herbs for Breast Cancer. Debasish Tripathy, M.D., at the University of California, San Francisco, tested 71 herbs used in traditional Chinese medicine for the treatment of cancer. The team boiled each herb in water and tested whether the extract inhibited growth of four human breast cancer cell lines (SK-BR-3, MCF7, MDA-MB-23 1, and BT-474) and one mouse breast cancer cell line (MCNeuA). Nineteen of the extracts inhibited growth on three or more of the cell lines. Sixteen strongly inhibited growth on at least one cell line. Seven of the active extracts caused cancer cell death. The team began identifying the substances in the extracts that are active against breast cancer, and purified one of them. Further studies with these extracts will improve understanding of how these herbs may be acting in cancer patients and may also lead to the isolation of anti-tumor compounds.

Hormone and Chemotherapy Targets: Improving Today's Arsenal

Identifying the Breast Cancer Target for Indole-3-Carbinol. Indole-3-Carbinole (I3C), a compound found in cruciferous vegetables such as broccoli and Brussels sprouts, appears to inhibit growth of breast tumors. I3C works both on tumors that respond to estrogen (which can be treated with the drug tamoxifen) and tumors that don't respond to estrogen (which can't be treated with tamoxifen). Urmi Chatterji, Ph.D., of the University of California, Berkeley, attempted to find the protein within breast cancer cells that initially binds with I3C. She completed the first step in this process, determining that the cell nucleus contains the I3C binding protein. The study described below, from the same laboratory, also deals with I3C.

Indole Derivatives as Novel Breast Cancer Therapeutics. Gary Firestone, Ph.D., at the University of California, Berkeley, continued his investigation of potential anti-cancer compounds found in cruciferous vegetables, such as broccoli and Brussels sprouts. Previous CBCRP-funded work in Dr. Firestone's lab has shown that a compound called indole-3-carbinol (I3C) appears to inhibit the production of certain proteins cells need to produce in order to divide and form new cells. I3C, which is also the subject of the study discussed above, appears to be effective against breast cancer cells that depend on the hormone estrogen for their growth, as well as those that do not. In this project Dr. Firestone worked with a colleague, Leonard Bjeldanes, Ph.D., at the University of California, Berkeley, to develop synthetic compounds derived from I3C that might be the basis for more potent anti-breast cancer treatments. They have been able to modify the constituent indole ring in I3C to produce a molecule that can inhibit growth in human breast cancer cells at greater than 100 times the potency of the natural compound. This research was published in Biochemistry (2000) 39(5):910-8. Dr. Firestone's research may lead to cancer-inhibiting drugs that work against a wide-spectrum of breast cancers, especially estrogen receptor-negative types resistant to the chemotherapy medication Tamoxifen, and that might be used in combination with other drugs.

Pharmacogenomics

Current breast cancer drugs treat the disease, but often ignore variations in the genetics and biology of each patient.

Pharmacogenomics is a new discipline that has evolved to address this clinical uncertainty. According to the Human Genome Project: “Pharmacogenomics is the study of how an individual's genetic inheritance affects the body's response to drugs. The term comes from the words pharmacology and genomics and is thus the intersection of pharmaceuticals and genetics.

Pharmacogenomics holds the promise that drugs might one day be tailor-made for individuals and adapted to each person's own genetic makeup. Environment, diet, age, lifestyle, and state of health all can influence a person's response to medicines, but understanding an individual's genetic makeup is thought to be the key to creating personalized drugs with greater efficacy and safety.” In practical terms, this may prove difficult, since unrelated humans may differ in up to 100,000 single parts of their DNA. The parts of DNA where these variations occur are called SNPs (single nucleotide polymorphisms). In Impact, the UCSF Foundation's online magazine, Kathleen Giacomini, Ph.D., professor and chair of Biopharmaceutical Sciences at UCSF, has predicted, “Pharmacogenomics will take three or four forms. One will be looking at genes and their protein offspring, which are potential drug targets. That will facilitate the development of new drugs.

“Then we'll need to find out the variations that people have of that gene. There could be three forms, for example, of one gene. The next step would be to create drugs for each of those targets, or gene variations.

“Pharmacogenomics will also affect clinical trials. For example, if 3 people out of 1,000 die during a clinical trial due to a drug reaction, that drug will not make it to the market.

“The reality is that even though that drug could have worked for a majority of people, it's too dangerous to prescribe because we don't know who falls in the minority that can't tolerate it. But, by understanding the genetic qualities of the people who have these adverse reactions, we can avoid adverse reactions and a greater number of people could benefit from the drug.”

Gene Therapy and Other Treatments: New Frontiers

Tibetan Medicine for Advanced Breast Cancer. Debasish Tripathy, M.D., of the University of California, San Francisco, treated eleven women who had breast cancer with Tibetan herbal medicine. The women's cancer had spread to other body parts, they had already received conventional treatment, and at the beginning of the study, they had few or no symptoms due to cancer. Dr. Yeshi Dhonden prescribed an herbal regiment for each of the eleven women enrolled in the study, examining them every four months and changing the herbal formula as needed. The women's tumors were measured every three months; the women also received monthly examinations and safety assessments. Of 9 women whose data were evaluated for this study, one completed the study with no disease progression. Three were stable for 6-12 months. Four were stable for less than 6 months. One patient had a partial response. The patients didn't experience any significant toxic side effects. The therapy in this trial proved to be both safe and feasible. Further studies are needed to evaluate a broader range of Tibetan herbal treatments.

Breast Cancer Gene Expression Using Amplified Core Biopsies. Stefanie Jeffrey, M.D., from Stanford University, Palo Alto explored a cutting-edge technology to measure genetic variation in breast tumors. Dr. Jeffrey and collaborators are using gene chips, a technique also known as cDNA array technology that allows the research team to simultaneously measure the level of 23,000 different genes from breast tumor samples. Dr. Jeffrey's team is trying to solve a problem with current technology, which can only be used to get a gene profile from large core biopsy tissue samples. However, most women have smaller needle biopsies, which yield too little tissue. Dr. Jeffrey found that she could amplify samples from needle biopsies and get a gene profile previously possible only with larger core biopsies. In addition, her team gained information on tumor heterogeneity (different types of cells within a single tumor) and found genetic similarities between primary tumors and cells obtained from lymph nodes. This information puts them in a better position to use needle biopsies for gene chip analysis. Ultimately, they hope this new procedure will help predict whether a tumor would respond to chemotherapy.

Bispecific Antibodies for Radiotherapy of Breast Cancer. Once breast cancer has spread to other organs such as the lung and bone, current therapy options offer less than two years of survival, in most cases. However, radioimmunotherapy shows promise against cancer that has spread to other body parts. Radioimmunotherapy uses antibodies cloned in a lab (monoclonal antibodies), which attach to cancer cells. When radiation is administered later, the antibody “captures” the radioactive molecule and delivers the radiation to the cancer cell. The large size of a monoclonal antibody limits its effectiveness. To create a more effective therapy, Michelle Winthrop, Ph.D., at the University of California, Davis, developed a single-chain antibody fragment that binds to the MUC-1 antigen, a protein found on the surface of many breast tumor cells. The team created a model of the antibody's molecular structure to construct antibody fragments specific to MUC-1. This research was published in Quarterly Journal of Nuclear Medicine 2000 44:284-95. Using animal models, the team is currently testing the most promising antibody fragments for their ability to target breast tumor cells and capture a radioisotope injected later.

Research in Progress

Immune Therapy: Mobilizing the Body's Defenses

Cell-Based Immunotherapy for Breast Cancer. The human immune system protects us from illness by recognizing and attacking cells that are infected with viruses and bacteria. The immune system does not normally attack the body's own tissues. Because cancer cells are derived from the body's own tissues and don't display any foreign characteristics, the immune system does not attack them. In cancer immunotherapy the challenge is modify tumor cells in a way that the body's immune system will recognize them as dangerous and destroy them. Nabila Jabrane-Ferrat, Ph.D., at the University of California, San Francisco, is developing a method of incorporating genes involved in normal immune response into tumor cells. The strategy is to create a “danger signal” in the tumor that will activate the immune system. During the first year, the research team created tumor cells that produce one of three proteins, CIITA, IFN-gamma, or B7.1. These proteins signal the immune system to attack the tumor cells. They injected these tumor cells into mice that were genetically engineered to produce tumors. The hypothesis is that these tumor cell vaccines will stimulate the mouse immune system not only to attack the injected tumor cells, but also to attack other tumors developing in the mice.

Antibody-IL-2 Fusion Proteins for Breast Cancer. T cells are part of the body's immune system. They circulate in the blood and kill infected or malignant cells. However, the body can disable T cells that have the potential to recognize cancer cells, because cancer cells are similar to other cells in the body. Joseph Lustgarten, Ph.D., at the Sidney Kimmel Cancer Center, La Jolla, is working on a way to overcome the body's disabling of T cells that have the potential to destroy breast cancer cells. His team generated two fusion proteins, anti-Her- 2/neu-IL-2 and Heregulin-IL-2. Fusion proteins are two separate proteins that have been combined to make a single new protein. In laboratory and mouse models, these two fusion proteins redirect non-specific T cells to tumors that have the Her-family receptors Her-2/neu, Her-3 and Her-4. Receptors are proteins on or in cells that combine with another substance from outside the cell, causing further changes within the cell. The Her-family receptors are found in tumors that are likely to spread or be fatal. Once at the tumor, the T cells destroy it. This immunotherapeutic approach is an alternative strategy to eliminate tumors with Her receptors (Her-positive tumors).

New Drug Design: Creative Science

Targeted Delivery of an Anti-breast Tumor Agent. Francis Markland, Jr., Ph.D., from the University of Southern California, Los Angeles is continuing work supported by the CBCRP since 1995 to develop a snake venom protein into a breast cancer treatment. The Southern copperhead snake has a venom protein, contortrostatin, (CN). CN blocks breast cancer cells from forming blood vessels, starving the tumor and preventing its growth. Dr. Markland is working with co-investigators, Nori Kasahara, M.D., Ph.D., at the University of Southern California, Los Angeles, and Gary Fuji, Ph.D., at Molecular Express, Inc., Los Angeles. The group is testing methods of drug delivery, with the aim of testing the drug in animals. The team is well on its way toward the goal of developing a method of injecting CN into the blood of patients with breast cancer, targeting the primary cancer site and any sites to which the tumor has spread. Dr. Markland has used previous funding from the CBCRP to demonstrate the biological basis for the action of the drug.

Hormone and Chemotherapy Targets: Improving Today's Arsenal

Targeted Chemotherapy to Treat Breast Cancer. Liposomes are laboratorysynthesized microscopic particles with a fatty outer layer and a water-soluble center. Liposomes can circulate in the blood for long periods and carry chemotherapy drugs, genes, or other therapeutics to selected locations. Francis Szoka, Ph.D., at the University of California, San Francisco, is working to increase the ability of drug-carrying liposomes to locate and bind to breast cancer cells, but not to normal cells. This would isolate the drug from the body until it is absorbed by breast cancer, minimizing side effects. The key to making this work for breast cancer is to target the liposomes to the cancer cells, and get them to bypass normal cells. Dr. Szoka is targeting liposomes by incorporating into them special sugar molecules that bind to a protein, CD44, found on breast cancer cells. The initial phase of this project was published in Cancer Research 61:2592-2601 (2001).

Gene Therapy and Other Treatments: New Frontiers

Can Molecular Markers Predict Response to Adjuvant Therapy. Tumorrelated markers are genes or proteins found in tumors that may provide information on the nature and severity of the disease. Shelley M. Enger, Ph.D., of Southern California Kaiser Permanente, and Michael F. Press, M.D., Ph.D., at the University of Southern California, Los Angeles, are investigating whether some of these markers—including Her-2/neu, p53 and Bcl—can be used to predict whether the patient is likely to respond to various treatments. To date, they have collected data from medical records of 1,310 breast cancer patients, about 75% of the total they wish to study. It is critical that physicians treating breast cancer have information to better match treatment with individual characteristics of tumors.

Research Initiated in 2001

Immune Therapy: Mobilizing the Body's Defenses

New Drug Design: Creative Science

Hormone and Chemotherapy Targets: Improving Today's Arsenal

Gene Therapy and Other Treatments: New Frontiers

Liposomes

Researchers are looking for ways to deliver chemotherapy directly to tumors, instead of exposing a woman's entire body to toxic drugs. One promising way is by using liposomes. Liposomes are tiny fat particles like balloons; they can be filled with a variety of substances. Research progress with liposomes is being made on several fronts.

First, putting chemotherapy drugs inside liposomes keeps the drugs circulating in the blood longer, so the tumor gets exposed to the drug more. A drug that doesn't work on its own may work if delivered inside liposomes. Second, putting antibodies on the liposome surface targets the drug specifically to cancer cells. Third, liposomes are being investigated as a way to deliver gene therapy.