Issue Number:
Volume 17 - Issue 3 - March 2009
author:
John Otrompke, Contributing Editor
Mixed Melanoma Trial Results Point to Need for Tailored Studies
"Effective melanoma therapies may be inching forward, with a number of the new class of potential therapeutics in the pipeline entering Phase III trials, and researchers presenting some of the first published data on other agents at this year’s annual meeting of the American Society of Clinical Oncology (ASCO) in Chicago.
But with mixed results, some disappointing, some surprising, some researchers say clinicians and clinical trial designers must rethink development strategies, including patient selection, if some of the new class of biological therapeutics for melanoma are to make significant headway.
“The problem with melanoma is that, other than surgery, there really are no very good effective therapies. The chemotherapies that are out there are not curative but palliative treatments,” explains David Solit, MD, Elizabeth and Felix Rohatyn Chair and Assistant Attending Physician, Department of Medicine, Sloan-Kettering Cancer Center.
But medical science is progressing, says Dr. Solit, who spoke at the ASCO conference. “We actually know a lot of the genetic alterations that cause the cancer. In 2002 there was a mutation in a protein called BRAF that was identified, and the mutation is found in the tumor in 50% to 70% of patients with melanoma. Then there’s a protein called NRAS, which also gets mutated in 15% to 20% of melanoma patients. But when you have an NRAS mutation, you don’t have a BRAF mutation. In total, between 60% and 90% of patients have one of the two,” says Dr. Solit, who gave the presentation, “Genetic Predictors of RAF/MEK Dependence.”
But the news at ASCO was not all good for the new therapies.
Early Promise, Mixed Results
Some of the most important new strategies for treating advanced melanoma focus on the patient’s immune system.
“Two of the strategies use anti-CTLA 4 and anti-PD1 agents to take the brakes off the patient’s immune system. Both are receptors on a patient’s T-cells, which are part of the normal braking system, which is a good thing at most times, but not a good thing in regards to a cancer cell,” says Walter Urba, MD, PhD, Director of Cancer Research at the Earle A. Chiles Research Institute in Portland, Oregon.
“The other two strategies use antibodies 41BB or OX 40. At ASCO this year, we saw some late clinical trial results with the anti-CTLA 4 product, and the first published results with anti-41BB and anti-PD1,” says Dr. Urba, who also discussed very early results with his own institution’s investigational agent, OX 40.
A disappointing trial of a new potential therapeutic agent was a head-to-head trial of an agent called a MEK inhibitor, which was tested against temozolomide, a standard pre-existing chemotherapy for melanoma. There was no significant difference between the standard arm and the MEK inhibitor (AZD 6244 by Astra Zenaca), according to the trial results.
However, patient selection may be the problem. “Genetic differences are relevant, because the BRAF mutation found so often in melanoma patients, activates a protein called MEK. “If you have a RAF mutation, you may respond a lot better to a MEK inhibitor,” explains Dr. Solit, noting that in addition to the Astra Zenaca drug, another MEK inhibitor in research is a drug from Pfizer called PD 0325901. The Astra Zenaca drug, which encountered the disappointing result, is in Phase II trials, whereas the MEK inhibitor from Pfizer is only in Phase I.
“The problem with the Astra Zenaca trial is that they didn’t look for BRAF-mutated patients. It’s possible temozolomide is as good or better than AZD 6244 in unselected patients, but five of the six responders in the MEK inhibitor arm had BRAF mutations,” Dr. Solit says. “There is technology out there already to start looking for these mutations, and it has already become routine in lung cancer for other genes.”
There were some positive, surprising results presented as well, however. A Phase II trial of ipilimumab, an investigational immunomodulatory agent from Bristol Meyers Squibb, which is in late Phase III trials, was studied in a population of 115 patients in combination therapy with Budesonide, a currently existing therapy. “Our primary endpoint was to see whether in a randomized trial we could reduce the amount of diarrhea that occurs as a side effect of the Budesonide, and our primary endpoint was not successful, but ironically, the clinical results were outstanding. Our median survivals were over a year,” says Jeffrey Weber, MD, PhD, Director of the Donald A Adam Comprehensive Melanoma Research Center and Professor of Oncologic Sciences at the University of South Florida.
Updated survival data of three Phase 2 studies of ipilimumab in patients with metastatic melanoma (Stage III or IV) who had previously been treated were presented at the European Society for Medical Oncology in Stockholm. Study results show that approximately half of patients who received ipilimumab (10 mg/kg) remained alive beyond 1 year. The results are based on follow-up of the patient population from studies 008, 022 and 007 treated with 10 mg/kg of ipilimumab (induction and maintenance) and show a consistent 1-year survival rate between 47% and 51%.
Combination Therapies of the Future, Today
Another promising strategy offering hope to advanced melanoma patients is to stimulate the patient’s immune system, by mimicking signal’s sent naturally by the body.
“We have learned from studying patients with melanoma just how powerful the immune system can be, but we need to supplement the response, and free it from some of its limitations,” says Robert H. Vonderheide, MD, Assistant Professor of Medicine at Abramson Cancer Center at the University of Pennsylvania.
The immune response in melanoma patients can be so pronounced that in rare cases, tumors even shrink in the face of it, says Dr. Vonderheide.
Dr. Urba agreed. “The immune response in melanoma is different from other cancers,” he explains. “One of the thoughts is that melanoma tumors are more immunogenic. Sometimes the response occurs after disease progression. In a couple percent of every patient population, the patient comes in and looks for all the world like they’re having tumor progression, and they end up having the tumor go away in response. The rationale is, that maybe it takes time for an immune response to build up and eliminate tumor cells following these investigational therapies,” he says, noting that these delayed responses can occur 8 or 12 weeks following therapy.
To attempt to take advantage of melanoma’s unique immunogenicity, Pfizer has developed an investigational agent that acts on an immune receptor called CD40, according to Dr. Vonderheide. “This is an antibody that binds to CD40 and mimics the signal sent to activate the immune system.”
The CD40 agonist has been tested by itself and in conjunction with standard chemotherapy drugs carboplatin and paclitaxel. The first clinical trial with the agent started about 4 years ago, and was reported 2 years ago at ASCO. Though the drug is only in Phase I trials, “taking it to Phase II is definitely warranted,” notes Dr. Vonderheide. “In the second study, we saw clinical activity: one patient has regressed, and remained in remission for years.”
In another study, the CD40 agonist will be given, along with chemotherapy, every 3 weeks, and the trial is enrolling as many as 30 patients, according to Dr. Vonderheide.
With some of the therapies, lack of experience in testing them may lead to unpredictable future results; in others, the sheer longevity of their period in trials can lead to skepticism.
“Anti-CTLA 4, an anti-inhibitory drug, has probably been in clinical trials for about 7 years, whereas anti-PD1, which is also an anti-inhibitory drug, has probably not been in trials for much more than a year,” says Dr. Urba, noting that the 41BB has also been in trials for 2 years.
For some drugs, clinical trials have enrolled hundreds of patients over the years, while other novel agents have only been tested in a few dozen humans. “The delayed response phenomenon, for example, has not been seen with other agents besides ipilimumab and tremilimumab, but with the other agents, the number of patients who have been treated is so small I’m not sure if we would have seen it,” he adds.
Still, the novel agents, whether young or old, often offer the only hope for advanced melanoma patients to hold onto.
“Nonetheless, it’s probably going to be a long series of trials to figure out which are the patients who are going to benefit. It’s a targeted therapy, and it doesn’t work for everybody. But we have insight into who it would work in, and we need to incorporate that information into our clinical trial design,” Dr. Solit says."
source: http://www.skinandaging.com/content/melanoma-update-highlights-research-presented-asco-and-update-vaccines-trials
Melanoma Update: Highlights of research presented at ASCO and an update on vaccines trials
Take care
Jimmy B
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