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Clinical Trial Results

Summaries of Newsworthy Clinical Trial Results
  • Posted: 12/27/2010

Trial Suggests New Treatment Option for Hodgkin Lymphoma

Adapted from the NCI Cancer Bulletin.

Intermediate results from a phase II clinical trial indicate that an investigational agent called brentuximab vedotin may be an effective alternative for some patients with Hodgkin lymphoma who have few viable treatment options. The results are promising enough that the drug’s manufacturer, Seattle Genetics, will submit the agent to the Food and Drug Administration (FDA) for approval in early 2011. The trial results were presented December 6, 2010, at the American Society of Hematology (ASH) annual meeting in Orlando, FL.

In the 102-patient clinical trial, 75 percent of patients saw their tumors shrink to at least half their original size (an objective response), and one-third of patients had complete tumor regressions (a complete response). Overall, the estimated 1-year survival rate was 88 percent.

The antitumor effect is particularly impressive, according to trial investigator Robert Chen, M.D., of City of Hope Comprehensive Cancer Center, because most of the patients in the trial were high-risk: they had never achieved a complete response to standard first- and second-line therapies such as chemotherapy or hematopoietic stem cell transplantation. Brentuximab is “very active for a single-agent therapy in this setting,” Dr. Chen said during a press briefing.

Hodgkin lymphoma most often occurs in younger patients, and trial participants’ median age was 31. The prognosis is generally poor for patients whose disease doesn’t respond to therapy or returns after an autologous hematopoietic stem cell transplant, explained Ginna Laport, M.D., of Stanford University Medical Center, during the briefing. “There is usually not much to offer them,” she said. So the results with brentuximab represent “a big breakthrough for this [patient] population.”

Although other therapies can be somewhat effective in such patients, if the FDA does approve brentuximab, it should fill an important clinical niche, said Wyndham Wilson, M.D., Ph.D., head of the Lymphoma Therapeutics Section in NCI’s Center for Cancer Research. “Certainly as a salvage regimen, it may become the first drug to turn to in the post-transplant setting,” he said.

Patients in the trial received brentuximab—also known as SGN-35—once every 3 weeks during a 30-minute infusion for as many as 16 cycles of therapy. Side effects were limited, mostly low-grade nausea, fatigue, and peripheral neuropathy. About 10 percent of patients had to halt treatment because of peripheral neuropathy, which often consists of intense tingling, burning, or pain in the extremities. But in most patients the symptoms could be managed, and many could resume treatment, Dr. Chen said.

The Technology behind the Results

Brentuximab is an antibody–drug conjugate (ADC) in which an antibody directed against the protein CD30 is chemically linked to a potent chemotherapy drug called MMAE (monomethyl auristatin E). The CD30 protein is frequently on the surface of cancer cells in Hodgkin lymphoma, but is present on less than 1 percent of healthy cells.

Unlike some other antibodies currently approved for treating cancer, the antibody component of brentuximab does not have any anticancer effect in Hodgkin lymphoma, explained the trial’s lead investigator, Anas Younes, M.D., of the University of Texas M. D. Anderson Cancer Center. Rather, Dr. Chen explained, “the antibody allows for selective delivery of the chemotherapy agent directly into Hodgkin lymphoma cells.”

The chemical that tethers the antibody to the chemotherapy drug is also extremely important, explained Helen Chen, M.D., from the Cancer Therapy Evaluation Program in NCI’s Division of Cancer Treatment and Diagnosis. “The first critical requirement is that the linker has to be very stable in the blood,” she said. “You don’t want it to release the drug before getting to the cell.”

The linker also determines whether the conjugate kills only cancer cells to which it has attached through the antibody component, or whether the drug component can be released back out of the cell to kill surrounding cancer cells (but also, potentially, healthy cells), a so-called bystander effect, Dr. Helen Chen noted. Brentuximab is designed to have a bystander effect.

In addition to the design and selection of the linker, she continued, the safety and efficacy of ADCs also depend on the chosen antibody target and the “cytotoxic payload” to which the antibody is attached.

One of the first ADCs to receive FDA approval was gemtuzumab (Mylotarg) for the treatment of acute myeloid leukemia. Gemtuzumab is composed of a CD33-targeted antibody linked to the chemotherapy drug ozogamicin. But gemtuzumab was withdrawn earlier this year after a post-approval clinical trial required by the FDA found that, in combination with chemotherapy, it was no more effective than chemotherapy alone and was associated with serious liver complications and a greater risk of death. Gemtuzumab, Dr. Helen Chen noted, used an older generation linker and a different class of chemotherapy drug than brentuximab, in addition to targeting a different cell-surface antigen, all of which may have contributed to its failure in the confirmatory trial.

A number of ADCs are under investigation. Trastuzumab-DM1, for example, an ADC that couples the HER2-targeted antibody trastuzumab (Herceptin) with the chemotherapy drug DM1, is being tested in multiple breast cancer clinical trials. And at NCI, Ira Pastan’s lab in the Center for Cancer Research has developed numerous ADCs that link an antibody to a bacterial toxin, including a conjugate called HA22, which has shown promise in patients with hairy cell leukemia and is now being developed by MedImmune.

Already Thinking Ahead

 Philip Bierman, M.D., of the University of Nebraska Medical Center called the results exciting. “There’s no question that this is an advance, and there’s no question that this is a drug that will get used,” he said. What these results mean for the future is of even more intense interest among oncologists, he continued.

“I think people are even more enthusiastic about possibly using this drug in the upfront setting,” he said, in combination with a four-drug chemotherapy regimen called ABVD that is the standard first-line therapy for Hodgkin lymphoma. The ABVD regimen has been used since the 1970s and leads to complete remissions in approximately 70 to 80 percent of patients. “So, this could become the new rituximab,” Dr. Bierman said, referring to the CD30-targeted monoclonal antibody used to treat non-Hodgkin lymphoma. (Rituximab initially showed efficacy as a third-line treatment but eventually became a first-line treatment in combination with chemotherapy.) A phase I trial of brentuximab in combination with ABVD is already underway.

“The goal in Hodgkin lymphoma is to cure,” Dr. Wilson stressed. So, testing brentuximab with chemotherapy as an initial therapy makes perfect sense, he continued, “to see if you can improve the cure rate.”

Also presented at the ASH meeting were the results from a smaller phase II clinical trial of brentuximab against a subtype of non-Hodgkin lymphoma called anaplastic large cell lymphoma. The findings were similar, with 87 percent of patients—all of whom had relapsed/refractory disease—achieving an objective response and 57 percent achieving a complete response. Seattle Genetics will also apply for FDA approval of brentuximab for use in this patient population.