OSUCCC – James clinical and basic researchers come together to improve therapy for women with triple-negative breast cancer.
BY KENDALL POWELL
Twenty years ago, oncologists treated breast cancer as if it were one disease, with some patients responding better to therapy than others. “Today, we know that breast cancer has at least four molecular subtypes, enabling us to individualize therapy based on the molecular genetic characteristics of a patient’s tumor,” says Charles Shapiro, MD, director of Breast Medical Oncology and professor of Internal Medicine.
Patients with hormone-sensitive tumors—those that test positive for estrogen (ER) and/or progesterone receptors (PR)—will likely respond to antiestrogen drugs such as tamoxifen and aromatase inhibitors. Tumors that overexpress the HER2 receptor often respond well to trastuzumab (Herceptin), an antibody that blocks HER2.
However, in 10-15 percent of breast cancer patients, the tumor lacks the ER and PR receptors and does not overexpress HER2. These so called “triple negative breast cancers” (TNBC) disproportionately affect young women who are premenopausal, especially African-American women and those who inherit a BRCA1 gene from either parent. These cancers are highly aggressive and characterized by early recurrences. Until recently, the only therapeutic option was chemotherapy. When the cancer recurred it was often resistant to chemotherapy, resulting in poor patient outcomes.
“As an oncologist you see the devastation that this type of breast cancer brings to the woman and her family,” Shapiro says. “It takes only one patient experience in which every chemotherapy regimen you try fails before you realize that we have to do better than chemotherapy alone. That’s what our work is all about. We are committed to improving therapy for this subtype of breast cancer.”
Spark of Promise
Hope for TNBC patients is emerging with a new class of agents called poly-ADP ribose polymerase (PARP) inhibitors, Shapiro says. He noted the findings of a phase II clinical trial that were reported at the 2009 American Society for Clinical Oncology meeting in Orlando. The trial investigated the use of the PARP inhibitor BSI-201 in combination with the standard chemotherapy regimen gemcitabine and carboplatin (GC) on 116 women with metastatic TNBC.
The study, led by Joyce O’Shaughnessy of US Oncology, showed that more than 60 percent of patients in the group receiving both BSI-201 and GC experienced clinical benefit, meaning their cancer either responded to the drugs or was stable for at least six months. By comparison, only 20 percent of those in the chemotherapy-alone group showed a benefit. Women receiving the PARP inhibitor had a median overall survival of 9.2 months compared to 5.7 months for women on chemotherapy alone. The addition of the PARP inhibitor also did not cause any worse side effects.
“To find a drug that improves survival is real progress, even if the improvement is only a matter of months,” says Shapiro. Although the results of the phase II trial need to be tested in a larger phase III trial, Shapiro speculates that PARP inhibitors will benefit some TNBC patients when combined with chemotherapy.
Shapiro’s optimism stems from the PARP inhibitor’s mechanism of action. There is evidence that triple negative breast cancers especially rely on PARP to repair breaks caused by DNA-damaging agents such as certain types of chemotherapy. PARP inhibitors prevent the polymerase from making that repair, causing the cells to self-destruct by apoptosis.
Shapiro is collaborating with two other OSUCCC – James researchers, Kay Huebner, PhD, and drug designer and medicinal chemist Ching-Shih Chen, PhD, to answer fundamental questions about TNBC and PARP inhibitors. For example, why is TNBC so sensitive to DNA damage, and what drugs other than chemotherapy drugs will augment the response of TNBC to PARP inhibitors?
Huebner, a specialist in the molecular genetics of cancer, notes that in the last decade, several research groups looked at the total gene expression profiles of many breast cancers and found that the patterns clustered nicely into the subsets of breast cancer—ER/PR-positive, ER/PR/HER2-positive, ER/PR-negative and HER2-positive and TNBC. She and Shapiro are dissecting the molecular profile of TNBC itself.
“If we understood the DNA damage response in TNBC, it might be possible to identify subsets of TNBC patients who are most likely to respond to PARP inhibitors or other targeted therapies,” says Huebner, professor of Molecular Virology, Immunology and Medical Genetics.
The two have been using tissue microarrays—microscope slides with hundreds of roughly 1.0 mm cores from tumor biopsies for simultaneous study—to identify molecular markers that are unique to TNBC.
One of the team’s first tissue microarrays (TMA) had more than 400 breast cancer samples, all of which came from the Stefanie Spielman Tissue Bank, which houses tumor samples and associated clinical data from breast cancer patients treated at the OSUCCC – James. This tissue bank was made possible by the philanthropy of the late Stefanie Spielman and her husband, Chris, a former Ohio State and NFL football player.
The TMA, which included 40 TNBC samples, enabled thei nvestigators to correlate molecular differences in the samples with each patient’s age, ethnicity, response to therapy, course of disease, and ultimate outcome. The investigation confirmed that three molecular markers, a checkpoint protein, a mutated tumor-suppressor protein and a histone protein variant called gamma-H2AX were more commonly expressed in TNBC tumors. Expression of these proteins was an indication that the DNA damage response pathways were likely to provide future therapeutic targets for TNBC. To verify and extend the findings, Shapiro, Huebner and their colleagues have built another tissue microarray with nearly 200 TNBC cases that includes clinical and patient outcome data.
“This tissue array should enable us to refine the protein markers that are significant in TNBC,” Huebner says. As Shapiro explains, prognostic or predictive markers are helpful in the clinic, but they may also lead to a better understanding of TNBC biology and identification of key genes and proteins that can be targeted with new drugs.
Huebner and Shapiro are joint recipients of a $3 million grant from the National Cancer Institute (NCI) that is dedicated to further refining subtypes of TNBC by microRNA profiling and to identifying new treatment targets.
“Understanding what drives these tumors is the first step toward understanding what potential drug targets are available,” Shapiro says. Ideally, the studies with Huebner will lead to new targets that can be handed off to Chen, professor of Medicinal Chemistry and holder of the Lucius A. Wing Chair of Cancer Research and Therapy, who can then design drugs to attack those targets.
Designer drugs for TNBC Shapiro and Chen are working to learn more about PARP inhibitors. Each drug in this class has been developed by different pharmaceutical companies, and the drugs don’t all behave the same way. Chen wants to determine their mechanisms of action and whether their differences can be exploited to improve efficacy or modified to produce new therapies.
In addition, Shapiro and Chen are investigating whether combining PARP inhibitors with a second drug will make them more effective against cancer cells. This second drug, currently used to treat a neurological disorder, activates a protein called PKC-delta. This protein is part of a signaling pathway that is activated after DNA damage and directs the cell toward apoptosis.
“We hypothesize that once standard chemotherapy drugs and PARP inhibitors cause DNA damage, adding this second drug will enhance the killing of TNBC, producing a synergistic combination,” says Chen, professor of Medicinal Chemistry, Internal Medicine, and Urology.
“The beauty of this is that both the PARP inhibitors and the neurological drug are already being tested in humans,” Shapiro says. The team could therefore test this synergy hypothesis in a phase I study relatively quickly.
Finally, one of the oldest known characteristics of tumor cells may lead to an entirely new therapy for TNBC, Chen says. In the 1950s, Nobel laureate and biochemist Otto Warburg discovered that tumor cells take up glucose from the blood at a far greater rate than healthy cells. This “Warburg effect” boosts the cells’ energy production and drives their proliferation, and uncontrolled proliferation is one of the hallmarks of cancer. Chen’s laboratory has developed several potent candidate agents that block this increased glucose uptake and choke the growth of cancer cells in laboratory studies.
Eventually, he hopes to test a more fully developed drug in TNBC patients.“Doing drug discovery in academia, we have the advantage of strong interactions with our colleagues in both basic science and clinical science,” says Chen. “More importantly, we see how hard our clinicians work to save patients’ lives. We understand the urgency, and we can do things more efficiently.”
Translational Medicine at Its Best
That efficiency emerges from collaborative research and the cycle of translational medicine: Information flows from the clinic to the laboratory bench and back out again to be tested in clinical trials. Currently, the OSUCCC – James is conducting two clinical trials to test new drug regimens for TNBC (see sidebar).
Both are phase I trials under an NCI U01 contract awarded to Michael Grever, MD, professor and chair of Internal Medicine, and co-director of the OSUCCC – James Experimental Therapeutics Program.
The two trials are specific for triple negative breast cancer patients: one is led by breast cancer medical oncologist Bhuvana Ramaswamy, MD, who is evaluating the combination of carboplatin and the PARP inhibitor ABT-888 in women with metastatic TNBC who have received two or fewer prior chemotherapy regimens for treatment of metastatic disease.
The other trial is led by Ewa Mrozek, MD, also a breast cancer medical oncologist, who is evaluating two chemotherapy drugs, paclitaxel and carboplatin, in combination with a drug that inhibits the notch pathway in TNBC.
The notch pathway seems to be especially important in TNBC. Unlike the first trial, this is designed for women with localized, nonmetastatic TNBC who are receiving neoadjuvant treatment.
Both trials represent the cuttingedge of research and clinical care, which Ohio State’s Medical Center and the OSUCCC – James are dedicated to providing, Shapiro says. These trials, in turn, will provide tumor samples that may influence the next steps taken in laboratory experiments.
Shapiro and his colleagues in the Breast Program bring their clinical knowledge of how TNBC plays out in patients, and that provides the motivation to find better, targeted treatments through Huebner’s and Chen’s basic and translational science efforts.
“The pressing need right now is TNBC—that’s what is motivating all of us,” says Shapiro. “This is truly translational research that goes both ways. Clinical observations in these first trials could have an important impact on the next generation of experiments in the lab.”
Trials for Triple Negative Breast Cancer
Two phase I clinical trials are under way at the OSUCCC – James for women with triple negative breast cancer (TNBC). The trials test two targeted experimental agents in combination with standard chemotherapy. Both trials were designed by OSUCCC – James investigators and funded by the National Cancer Institute’s Cancer Therapy Evaluation Program (CTEP).
In addition to determining the maximum tolerated dose of the new agents, the trials will gather data that should give researchers new insight into the biology of these aggressive tumors.
OSU-10080 offers carboplatin and the PARP inhibitor ABT888 to patients with metastatic TNBC. Recent studies suggest that the benefit of platinum-based drugs such as carboplatin for TNBC patients may be improved when combined with a PARP inhibitor.
Breast oncologist Bhuvaneswari Ramaswamy, MD, principal investigator (PI) for the trial, notes that previous trials involving PARP inhibitors have used a three-drug cocktail, but the toxicity of the combination limited the dose of the PARP inhibitor that could be used.
Ramaswamy wants to learn if using two drugs instead of three will permit a higher PARP-inhibitor dose and greater effectiveness.
The study uses PET scans and blood tests to determine the degree of DNA damage the drug combination is producing as a surrogate marker of effectiveness. “We want to learn if we can identify tumors that respond to this regimen,” she says.
OSU-10011 is aimed at women with newly diagnosed, locally advanced TNBC (clinical stages II-III). This trial combines carboplatin and paclitaxel with the experimental notch pathway inhibitor, RO4929097. The notch pathway is overactivated in about 40 percent of all breast cancers, including a high percentage of TNBC cases.
The trial provides three drugs as neoadjuvant therapy with the goal of achieving complete pathological response, i.e., the absence of any residual tumor cells in resected breast or axillary lymph node tissue at the time of definite breast surgery. “Patients with complete pathological responses have a three-year survival rate of 95 percent,” says Ewa Mrozek, MD, PI for the trial and a breast cancer specialist in the Division of Oncology.
“Women with TNBC have an increased rate of disease recurrence and death within five years of diagnosis. We want to protect those patients in every way we can from recurrence,” Mrozek says. The best way to do that, she says, is to boost the numbers of TNBC patients who respond completely to neoadjuvant therapy. The trial opened in November: Mrozek will enroll 15 to 18 patients.
Tumor samples taken before and after therapy will be used to learn more about the regimen’s effects on tumor cells in patients. “Both of these trials include important correlative studies. They are at the cutting edge of research and will provide further insight into the biology of these cancers,” says Charles Shapiro, MD, director of Breast Medical Oncology