From Bench to Bedside and Back Again
A team of Cancer Center researchers has been on a remarkable journey of discovery for 10 years to show how a novel drug combination is showing promise for lung cancer patients.
Without the intersection between this necessary basic science and the clinic, discoveries made at the laboratory's research bench have little relevance or application for patients suffering from a disease such as cancer. Translating basic scientific findings into improved treatments for patients, and increasing our understanding of human diseases, is the core of medical research today.
For the past decade, a team of Dartmouth scientists and physicians have made the journey from the bench to the clinic and back again in translational work to find effective therapies for lung cancer, work that is showing great promise using a powerful two-drug combination.
Lung Cancer—A Deadly Disease
Worldwide, lung cancer is the most common cause of cancer-related death in men and women, and is responsible for 1.3 million deaths annually. More men and women in the United States die from lung cancer than from any other cancer type—in 2007, more than 200,000 people were diagnosed with lung cancer in this country, and nearly 160,000 people died from the disease that year. One common and deadly form of lung cancer—non-small-cell lung cancer (NSCLC)—has been a particular target for treatments. But for NSCLC, chemotherapy is toxic and its use limited, and even combined with the so-called new generation therapies targeted to the cancer, it "has led only to small improvements in overall patient survival so that improvements in treatment for this disease are needed," explains oncologist Konstantin Dragnev, MD.
Bench Studies—Early Lung Cancer Studies
Retinoids and Rexinoids. For nearly 20 years—previously at Memorial Sloan-Kettering Cancer Center, and more recently at Dartmouth Medical School and Norris Cotton Cancer Center—the research lab of Ethan Dmitrovsky, MD, has been unraveling the role that retinoids, derivatives of vitamin A, play in treating certain cancers. Retinoids regulate cell division, growth, and death, and vitamin A deficiency is linked to lung cancer formation in laboratory mice. Dmitrovsky believed that overcoming the retinoid deficiency could help prevent lung cancer. Unfortunately, clinical trials treating lung cancer patients with retinoids were unsuccessful. Dmitrovsky and his research colleagues didn't yet understand why.
But then they uncovered a biochemical pathway by which retinoids could regulate cells' cycle and death, and they also found a retinoid target gene that triggers cell death. Targeting it, Dmitrovksy thought, could restore the beneficial effects of retinoids in lung cancer cells. But, he suggests, "that receptor is repressed in lung cancers" so that retinoic acid couldn't possibly work in this disease. However, a related drug to retinoic acid—a rexinoid—would be able to activate this same destruction pathway, but could bypass the receptor. Both retinoids and rexinoids induce the destruction of cyclin D1. One rexinoid they tried was bexarotene, a drug used to treat blood cancers.
Cyclins—The Target. Cyclin D1 causes lung cancer to grow. But used alone against it, bexarotene was only modestly active against lung cancer. Dmitrovsky's team believed that combining the drug with another active drug in targeting cyclin D1 could be more effective.
For more than a decade, they focused on Cyclin D1 and Cyclin E, two proteins normally expressed in all cells that regulate cell division. A key early finding was that cyclin D1 becomes expressed abnormally during a cell's progression into becoming cancerous, causing the cells to divide uncontrollably. This was particularly true for lung cells. Thus, cyclin D1 was believed an important target for cancer therapy. To confirm this, Dmitrovsky's team engineered a mouse model of human NSCLC that overexpressed a type of cyclin protein called cyclin E, similar to human cyclin D1. In the lab, they found that inhibiting cyclin E inhibited lung cancer growth. But what agents would be best to inhibit cyclin D1 in humans?
Tarceva (Erlotinib) and KRAS. One of the targeted therapies for NSCLC is a drug called erlotinib (Tarceva®).In all normal cells, a specific protein called epidermal growth factor receptor (EGFR) signals cells to grow and multiply. The EGFR pathway is directly linked to the cell's division by controlling cyclin D1. In cancer cells, these signals are over-expressed and the cells multiply out of control. In 2004, scientists had discovered erlotinib, a targeted therapy that blocks the EGFR and cyclin D1 signals in cancer cells, causing them to stop growing and die. Whether a patient is positive or negative for a mutation in EGFR will predict how they will respond to erlotinib. EGFR-positive lung cancers in patients have an impressive 60% response rate to erlotinib. But some of these patients harbor a deadly mutation in the KRAS pathway—and patients with this mutation do not respond well to erlotinib.
KRAS is a protein that acts as a molecular on/off switch for cells. Once turned on, it recruits and activates proteins necessary for the propagation of growth factor and other receptor signals. However, a mutation that knocks out normal KRAS actions destroys its vital functions, causing cells to go haywire. Oncologist Konstantin Dragnev, MD, a member of the Dmitrovsky team, says that about a third of lung cancer patients have this mutation and that treating such patients has long been a struggle because of a lack of effective options. These patients are often treated with chemotherapy, which is not highly effective. Thus, in lung cancer patients with KRAS mutations, there is a large unmet medical need.
Translating the Bench Findings—Clinical Studies
The Dartmouth team recognized that cyclin D1 levels were higher in NSCLC cells harboring EGFR mutations than in cells expressing normal EGFR and KRAS mutations. This showed a link between high cyclin D1 levels and reliance on the EGFR pathway. But other pathways could cause cyclin D1 expression. "This suggests the promise of combining EGFR inhibition with erlotinib with a rexinoid (bexarotene) that targets cyclin D1 via a separate pathway," explains Dragnev.
"We began working on a clinical trial here at Dartmouth to use the rexinoid bexarotene in conjunction with erlotinib," says Dmitrovsky. This combination of drugs was tested in two clinical trials, the results of which were just published.
In one trial, called a "window of opportunity trial," the team studied 10 patients with NSCLC, including those with KRAS mutations. Patients were enrolled for surgery to remove the tumors in their lungs, but about a week before the surgery lung samples were taken from the patients' tumors, and the patients were then treated with the erlotinib-bexarotine combination therapy until their surgery. After surgery, samples were again taken from the lungs.
Pathologist Vincent Memoli, MD, studied pre- and post-surgery lung samples to determine if the drugs had changed the tumor cells. Of the 10 patients' post-surgical lung samples, eight had lower levels of cyclin D1 and EGFR—and eight patients also showed evidence that tumor cells were dying. "Of note, these responses occurred in patients with or without EGFR or KRAS mutations," explains Dr. Memoli. The researchers also examined in the mouth (buccal) cells of patients and confirmed the lower levels of cyclin D1 from patients after treatment. In earlier trials, the team had tried this with each drug alone, but found a much lower positive response.
The research team then conducted a larger phase II trial of 40 patients with advanced NSCLC. Most patients had been heavily pretreated with EGFR inhibitors and chemotherapy but had relapsed. Normally, the survival of such patients would be about 16 weeks, but the 40 patients in the trial had a mean overall survival of 22 weeks. The combined drug treatment produced three major clinical responses with prolonged progression-free survival, an important measure of cancer treatments. Six other patients had stable lung cancer disease after treatment. While the Phase II trial did not study cyclin D1, a similar large clinical trial—the BATTLE trial—reported that the drug combination was active in mutant KRAS tumors, and cycle D1 over-expression predicted clinical response.
"This is a promising regimen," Dmitrovsky says. "It's not a cure for lung cancer, but we've taken highly resistant patients that normally would not be expected to respond, and some of them have responded for years." The encouraging study shows that this drug combination even suppresses cyclin D1 in KRAS mutant cancer cells, particularly in short-term therapy of patients with early NSCLC. Most encouraging is that this two-drug combination shows promising activity in patients with advanced NSCLC who are resistant to chemotherapy in both the Phase II trial and the larger BATTLE trial that confirmed the team's results.
"Most importantly, we did not expect to find that patients with the KRAS mutation would benefit from this combination," says Dragnev. "But this finding is particularly significant, as it shows promise in a deadly form of lung cancer for which there is a large unmet medical need."
Back to the Bench
To confirm their findings, the team investigated whether erlotinib and bexarotene suppressed the growth and expression of cyclin D1 in lung cancer cells outside the body in bench research. "This is an example of bidirectional translational research—work from the bench to the clinic and then back again," explains Dmitrovsky. The team's earlier findings were confirmed by the new bench research.
These highly significant clinical and laboratory findings are now being confirmed in a clinical trial with a much larger patient population with NSCLC with KRAS mutations. The success with this targeted therapy combination has now led the team to work with newer cyclin inhibitor drugs in NSCLC trials. Early results in the laboratory show promise and will lead to new trials in lung cancer patients. These new clinical trials offer great hope of changing the dismal prognosis of this disease.
Article by Christopher C. Dant, PhD
October 11, 2011
Subscribe to the Focus Newsletter
Receive Focus Newsletter articles in your Inbox or via RSS Feed.